Pierre Lucas

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• Jóvári, P., Lucas, P., Yang, Z., Bureau, B., Kaban, I., Beuneu, B., & Bednarčik, J. (2014). Short-Range Order in Ge-As-Te Glasses. Journal of the American Ceramic Society.
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  Abstract: The structure of Te-rich (75-80 at.% Te) and Te-poor (40 at.% Te) Ge-As-Te glasses has been investigated by diffraction and extended X-ray absorption fine structure (EXAFS) measurements. Large-scale structural models have been created by fitting simultaneously diffraction and EXAFS datasets by the reverse Monte Carlo simulation technique. It is found that As-As bonds improve the fit quality in the case of Te-rich glasses while no Ge-Ge bonding is necessary in these compositions. In the Te-poor glasses, Te-Te homopolar bonds are also observed while Ge binds preferentially to Te rather than to As. Ge-As and Ge-Te coordination numbers do not change significantly with increasing Ge content. © 2014 The American Ceramic Society.
• Wang, T., Gulbiten, O., Wang, R., Yang, Z., Smith, A., Luther-Davies, B., & Lucas, P. (2014). Relative contribution of stoichiometry and mean coordination to the fragility of Ge-As-Se glass forming liquids. Journal of Physical Chemistry B, 118(5), 1436-1442.
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  Abstract: The structural relaxation properties of 34 compositions of Ge-As-Se glass forming liquids are investigated by differential scanning calorimetry (DSC). The fragility index (m) and activation energies for enthalpy relaxation (E a) exhibit universal trends with respect to stoichiometry and mean coordination (〈r〉), respectively. The liquid fragility which defines the full temperature dependence of the relaxation processes shows no well defined trend with respect to 〈r〉 but instead is found to be closely determined by the excess or deficiency in selenium with respect to stoichiometry. The mean coordination on the other hand appears to be an accurate predictor of the activation energy near the glass transition where most constraints are still intact. No intermediate phase is observed in either case. These results emphasize that chemical effects rather than topological effects appear to control the wide ranging structural mobility of these glass forming liquids. The consequences of these findings in terms of the thermal stability of the corresponding glasses are discussed. It is similarly found that sub-T g relaxation is controlled by stoichiometry rather than topology. © 2014 American Chemical Society.
• Gueguen, Y., King, E. A., Keryvin, V., Sangleboeuf, J., Rouxel, T., Bureau, B., & Lucas, P. (2013). Photoinduced aging and viscosity evolution in Se-rich Ge-Se glasses. Journal of Applied Physics, 114(7).
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  Abstract: We propose here to investigate the non-equilibrium viscosity of Ge-Se glasses under and after light irradiation. Ge10Se90 and Ge20Se80 fibers have been aged in the dark and under ambient light, over months. During aging, both the relaxation of enthalpy and the viscosity have been investigated. The viscosity was measured by shear relaxation-recovery tests allowing the measurement of non-equilibrium viscosity. When Ge10Se90 glass fibers are aged under irradiation, a relatively fast fictive temperature decrease is observed. Concomitantly, during aging under irradiation, the non-equilibrium viscosity increases and reaches an equilibrium after two months of aging. This viscosity increase is also observed in Ge20Se80 fibers. Nevertheless, this equilibrium viscosity is far below the viscosity expected at the configurational equilibrium. As soon as the irradiation ceases, the viscosity increases almost instantaneously by about one order of magnitude. Then, if the fibers are kept in the dark, their viscosity slowly increases over months. The analysis of the shear relaxation functions shows that the aging is thermorheologically simple. On the other side, there is no simple relaxation between the shear relaxation functions measured under irradiation and those measured in the dark. These results clearly suggest that a very specific photoinduced aging process occurs under irradiation. This aging is due to photorelaxation. Nevertheless, the viscosity changes are not solely correlated to photoaging and photorelaxation. A scenario is proposed to explain all the observed viscosity evolutions under and after irradiation, on the basis of photoinduced transient defects. © 2013 AIP Publishing LLC.
• Gulbiten, O., Mauro, J. C., & Lucas, P. (2013). Relaxation of enthalpy fluctuations during sub-T_g annealing of glassy selenium. Journal of Chemical Physics, 138(24).
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  PMID: 23822253;Abstract: The relaxation behavior of glass is influenced by the presence of dynamical heterogeneities, which lead to an intrinsically non-monotonic decay of fluctuations in density and enthalpy during isothermal annealing. This is apparently a universal feature of fragile glass forming systems associated with localized spatial variations in relaxation time. Here we present direct experimental observation of the nonmonotonic evolution of enthalpy fluctuations in glassy selenium annealed near room temperature. The nonmonotonic change in the distribution of enthalpy fluctuations measured by heat capacity spectroscopy offers direct evidence for the presence of dynamical heterogeneity in this glass. An enthalpy landscape model of selenium is then used to simulate annealing under identical conditions. The simulation results closely follow the evolution of enthalpy fluctuations observed experimentally. The close match between model and experiment demonstrate that enthalpy and density fluctuations are sources of dynamical heterogeneities in glassy materials. © 2013 AIP Publishing LLC.
• Hubert, M., Calvez, L., Zhang, X., & Lucas, P. (2013). Enhanced luminescence in Er³⁺-doped chalcogenide glass-ceramics based on selenium. Optical Materials, 35(12), 2527-2530.
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  Abstract: Rare earth doped glass-ceramics transparent in the infrared region up to 16 μm have been prepared and studied. The enhancement of the emission of Er3+ ions at 1.54 μm with increasing crystallinity was demonstrated in a selenium-based glass-ceramic having a composition of 80GeSe2-20Ga2Se3 + 1000 ppm Er. The optical transmission, microstructure and luminescence properties of a base glass and glass-ceramics were investigated. Luminescence intensities up to 7 times greater were obtained in glass-ceramics in comparison to the base glass. These materials are promising candidates for the production of new laser sources in the mid-infrared region. © 2013 Elsevier B.V. All rights reserved.
• Lucas, P., Conseil, C., Yang, Z., Hao, Q., Cui, S., Boussard-Pledel, C., Bureau, B., Gascoin, F., Caillaud, C., Gulbiten, O., Guizouarn, T., Baruah, P., Qiang, L. i., & Lucas, J. (2013). Thermoelectric bulk glasses based on the Cu-As-Te-Se system. Journal of Materials Chemistry A, 1(31), 8917-8925.
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  Abstract: Stable bulk glasses from the quaternary system Cu-As-Te-Se are investigated for thermoelectric applications. These materials exhibit a low thermal conductivity κ ∼ 0.3 W K-1 m-1 which is appealing for raising the thermoelectric figure of merit ZT. The addition of small amounts of selenium within the telluride amorphous matrix plays two fundamental roles. First, the increased disorder associated with the size mismatch improves glass-formation and widens the glass-formation domain, and second, it increases phonon scattering and slightly decreases the thermal conductivity. Furthermore, the addition of copper up to 32% dramatically increases the electrical conductivity without notably affecting the thermal conductivity. This permits us to obtain bulk glass samples with promising thermoelectric properties, which could be manufactured through conventional low-cost glass casting methods. While addition of copper permits the increase of electrical conductivity by more than six orders of magnitude, another three orders of magnitude are required to obtain thermoelectric materials with competitive ZT. Nevertheless, predicted values of ZT > 1.2 are estimated which would constitute some of the highest reported figure of merit for a bulk solid at room temperature. The effect of glass annealing on thermoelectric properties is also discussed. © 2013 The Royal Society of Chemistry.
• Lucas, P., Gulbiten, O., Mauro, J. C., & Lucas, P. -. (2013). Relaxation of enthalpy fluctuations during sub-T(g) annealing of glassy selenium. The Journal of chemical physics, 138(24).
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  The relaxation behavior of glass is influenced by the presence of dynamical heterogeneities, which lead to an intrinsically non-monotonic decay of fluctuations in density and enthalpy during isothermal annealing. This is apparently a universal feature of fragile glass forming systems associated with localized spatial variations in relaxation time. Here we present direct experimental observation of the nonmonotonic evolution of enthalpy fluctuations in glassy selenium annealed near room temperature. The nonmonotonic change in the distribution of enthalpy fluctuations measured by heat capacity spectroscopy offers direct evidence for the presence of dynamical heterogeneity in this glass. An enthalpy landscape model of selenium is then used to simulate annealing under identical conditions. The simulation results closely follow the evolution of enthalpy fluctuations observed experimentally. The close match between model and experiment demonstrate that enthalpy and density fluctuations are sources of dynamical heterogeneities in glassy materials.
• Lucas, P., Yang, Z., Fah, M. K., Luo, T., Jiang, S., Boussard-Pledel, C., Anne, M., & Bureau, B. (2013). Telluride glasses for far infrared photonic applications. Optical Materials Express, 3(8), 1049-1058.
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  Abstract: Telluride glasses possess the widest infrared window of all amorphous materials and are key to a number of long-wavelength applications such as bio-sensing. However they are not intrinsically good glass formers and require significant materials engineering for device fabrication. Strategies for stable glass engineering are presented and the fabrication of far infrared optical fibers is described. A new type of optical sensor based on electrophoretic capture of protein is also presented. This sensor is based on a conducting telluride glass which can act as both a capture electrode and an infrared optical element for collecting vibrational signatures of target molecules such as proteins. © 2013 Optical Society of America.
• Yang, G., Gueguen, Y., Sangleboeuf, J., Rouxel, T., Boussard-Plédel, C., Troles, J., Lucas, P., & Bureau, B. (2013). Physical properties of the Ge_xSe_1-x glasses in the 0Journal of Non-Crystalline Solids, 377, 54-59.
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  Abstract: Physical properties, including mechanical, thermal and optical properties, have been investigated for chalcogenide glasses in the GexSe 1-x system, for x ranging between 0 and 0.42. In the 0
• Conseil, C., Bastien, J., Boussard-Plédel, C., Zhang, X., Lucas, P., Dai, S., Lucas, J., & Bureau, B. (2012). Te-based chalcohalide glasses for far-infrared optical fiber. Optical Materials Express, 2(11), 1470-1477.
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  Abstract: Tellurium based glasses have been studied for their optical properties in the far infrared region. New glasses, in the system Ge-Te-AgI, present a very good thermal stability. Indeed, for the first time, no obvious crystallization peak is observed in tellurium based glasses. Then, fibers have been drawn showing interesting optical losses and quite large transmission in the mid-infrared. So, these glasses are good candidates for the elaboration of single mode fibers able to detect the CO2 signature at 15μm for the ESA Darwin project. © 2012 Optical Society of America.
• Hubert, M., Calvez, L., Tessier, F., Lucas, P., & Zhang, X. (2012). Nanoporous surface of infrared transparent chalcogenide glass-ceramics by chemical etching. Materials Research Bulletin, 47(12), 4076-4081.
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  Abstract: The chemical etching of the 80GeSe 2-20Ga 2Se 3 chalcogenide glass-ceramics was performed in acidic and basic solutions. Etching in acid solution is shown to preferentially dissolve the crystalline phase while basic solutions preferentially attack the glassy phase. The selective etching of the crystals creates a porous layer with a thickness of some hundreds of nanometers composed of pores of 100 nm in size on the surface of the glass-ceramics. It is shown that the creation of the porous layer increases the infrared transmission of the materials and allows the functionalization with silane molecules. The functionalized glass-ceramics show enhanced detection sensitivity. Therefore, they represent promising materials for the design of optical elements for sensing applications in the infrared range. © 2012 Elsevier Ltd. All rights reserved.
• Lucas, P., Bureau, B., Yang, Z., Anne, M., & Jiang, S. (2012). Telluride glasses for infrared optical sensing. Advances in Optical Materials, AIOM 2012, ITh4B.1.
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  Abstract: Telluride glasses are gaining interest due to their wide transparency to infrared light and their good formability which enables the design of novel optical devices. This paper investigates the structure of novel telluride glasses and their applications for fibers and bio-sensors. © 2012 OSA.
• Yang, G., Gulbiten, O., Gueguen, Y., Bureau, B., Sangleboeuf, J., Roiland, C., King, E. A., & Lucas, P. (2012). Fragile-strong behavior in the As _xSe _1-x glass forming system in relation to structural dimensionality. Physical Review B - Condensed Matter and Materials Physics, 85(14).
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  Abstract: A series of physical properties have been measured throughout and above the glass transition for the whole As xSe 1-x system, including the activation for viscous flow E η, the activation energy for enthalpy relaxation E H, and the activation energy for structural relaxation E a obtained by specific heat spectroscopy. All properties show a double minimum at an average coordination number 〈r〉 = 2.3 and 〈r〉 = 2.5 with a local maximum at 〈r〉 = 2.4. This is in stark contrast to the physical properties previously measured on the same samples at room temperature and which instead show a single minimum centered at 〈r〉 = 2.4. The observed trend is consistent with the dimensionality of the network derived from structural data obtained by nuclear magnetic resonance. An analysis of the complex heat capacity also reveals a bimodal relaxation process in As-rich glasses, which explains why they are kinetically fragile but appear thermodynamically strong. Finally, these results demonstrate that previous observations of an "intermediate phase" in As xSe 1-x glasses near 〈r〉 = 2.3 is associated with the high temperature behavior of the glassy network and should be interpreted in terms of the temperature dependence of structural constraints rather than the number of constraints in the room-temperature glass. © 2012 American Physical Society.
• Angell, C. A., Wu, X. u., Yoshizawa-Fujita, M., Hayashi, A., Belieres, J., Lucas, P., Videa, M., Zhao, Z., Ueno, K., Ansari, Y., Thomson, J., & Gervasio, D. (2011). Physical Chemistry of Ionic Liquids: Inorganic and Organic as Well as Protic and Aprotic. Electrochemical Aspects of Ionic Liquids: Second Edition, 5-31.
• Jiang, S., Luo, T., Geng, J., Yang, Z., & Lucas, P. (2011). Single-mode low-loss optical fibers for long-wave infrared transmission. Optics InfoBase Conference Papers.
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  Abstract: We report the synthesis of single-mode fibers made of chalcogenide glasses with low-loss in the 5-12 μm range. Glasses from the Ge-As-Te-Se system were optimized to prevent nucleation and to exhibit low density of charge carriers. Single mode fibers were obtained through the rod-in-tube method by substituting 2% Te/Se between the core and cladding glasses. The resulting single mode fibers had a core diameter of 30 μm and exhibited losses of ~6dB/m at 10.6 μm and as low as 3-4 dB/m in the 6-10 μm range. © 2011 Optical Society of America.
• Lin, F., & Lucas, P. (2011). Competition between photorelaxation and photoexcitation in chalcogenide glasses and the effect of aging. Journal of Non-Crystalline Solids, 357(3), 888-892.
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  Abstract: Measurements of transient photodarkening and permanent Bragg reflector formation were performed on fragile As18S65Se17 glass and indicate that photodarkening and photorefraction can only be induced in previously aged glasses while they are prevented in freshly annealed glasses. These phenomena are associated with the photorelaxation process that is revealed to be prominent in fresh glasses and is shown to effectively anneal out the defects produced during photoexcitation thereby resulting in no net permanent changes in the structure. On the other end, aged glasses do not undergo any photorelaxation and exhibit large transient and permanent changes associated with an increase in structural enthalpy as confirmed by Differential Scanning Calorimetry. These results demonstrate that photorelaxation can be a significant problem in fragile glass compositions as it cancels out the effect of photoexcitation and impedes the photodarkening and photorefractive process. © 2010 Elsevier B.V. All rights reserved.
• Lin, F., Gulbiten, O., Yang, Z., Calvez, L., & Lucas, P. (2011). Mechanism of photostructural changes in mixed-chalcogen As-S-Se glasses investigated by Raman spectroscopy. Journal of Physics D: Applied Physics, 44(4).
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  Abstract: The structure and photosensitivity of chalcogen-rich As-S-Se glasses are investigated ex situ and in situ. The Raman spectra of these glasses exhibit three well-defined bands associated with Se-based, S-based and mixed Se-S based structural units. The deconvolutions of these bands show a coherent correlation between intensity and composition. It is then shown that the magnitude of photoexpansion and photorefraction measured ex situ increases continuously with Se content therefore indicating a central role of Se atoms in the mechanism of photostructural changes. The key role of Se is indeed directly observed and confirmed using in situ Raman characterization. It is shown that the band associated with Se-Se oscillators decays continuously during photostructural changes. Furthermore, it is shown that the kinetics of Raman decay closely matches the kinetics of photoexpansion when measured simultaneously. Overall these results demonstrate the central contribution of Se-Se fragment during sub-bandgap irradiation which is consistent with the presence of Se lone pair states at the top of the valence band. © 2011 IOP Publishing Ltd.
• Lucas, P., & Bureau, B. (2011). Advanced infrared glasses for biochemical sensing. Biointerface Characterization by Advanced IR Spectroscopy, 217-243.
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  Abstract: This chapter reviews the use of fiber evanescent wave spectroscopy (FEWS) for the characterization of biological materials. It focuses on the use of chalcogenide fibers and their application in biochemical sensing. The FEWS technique is a recent but promising analytical method for the study of biointerfaces. It makes use of infrared transparent fiber probes to guide the light source to the sample and collect the resulting signal onto a detector. This technique has recently gained much interest and has found applications in a wide range of fields, including biomedical sensing, cancer diagnosis, and in vivo monitoring of cells. It combines the advantages of Fourier transform infrared (FTIR) with the versatility of fiber sensing. This provides high selectivity of FTIR as well as the ability to probe biointerfaces in situ and in real time. Moreover, the design of appropriate sensing probes can lead to a notable increase in sensitivity and the hydrophobic nature of the glass surface promotes the signal of biomolecule versus water, making this technique a great candidate for biosensing in aqueous environments. The field of FTIR is in constant development and new improvements are regularly reported. In most cases these new advances can be directly applied to the FEWS technique and should further increase its sensitivity and detection limit in the future. © 2011 Elsevier B.V. All rights reserved.
• Lucas, P., King, E. A., Erdmann, R. G., Riley, B. J., Sundaram, S. K., & McCloy, J. S. (2011). Thermal and gamma-ray induced relaxation in As-S glasses: Modelling and experiment. Journal of Physics D: Applied Physics, 44(39).
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  Abstract: Enthalpy relaxation was measured in a series of As-S glasses irradiated with gamma rays and these samples are compared with a set of identical control samples kept in the dark. It is shown that gamma irradiation lifts the kinetic barrier for relaxation at room temperature and speeds up the enthalpy release. The measured values of thermal relaxation in the dark agree closely with modelling results obtained by fitting differential scanning calorimetry curves with the Tool-Narayanaswamy-Moynihan (TNM) equations. The measured values of activation energy for enthalpy relaxation are also in close agreement with that predicted by the TNM model, therefore lending credence to the fitting results. These measurements permit extraction of the effect of gamma irradiation on the glass structure for a series of As-S glasses with increasing structural coordination, and gamma irradiation is shown to reduce the structural relaxation time. It is also shown that lower coordination glasses exhibit greater radiation sensitivity but also greater thermal relaxation due to their lower Tg. On the other end, over-coordinated glasses show lower relaxation and almost no radiation sensitivity. This behaviour is similar to the glass response under sub-bandgap light irradiation. © 2011 IOP Publishing Ltd.
• Maurugeon, S., Bureau, B., Boussard-Plédel, C., Faber, A. J., Lucas, P., Zhang, X. H., & Lucas, J. (2011). Selenium modified GeTe₄ based glasses optical fibers for far-infrared sensing. Optical Materials, 33(4), 660-663.
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  Abstract: This study reports on the synthesis of telluride glasses that have transmission far beyond the second atmospheric window and are stable enough toward crystallisation to be drawn into optical fiber. These glasses are based on the GeTe4 initial composition which has been stabilized by the introduction of few percents of Se and a modified the Te/Ge ratio. In that domain, Ge21Se3Te76 constitute the optimum composition and some mono index optical fibers have been successfully drawn. It is shown that their optical transparencies extend from 5 to almost 16 μm in the mid-infrared, establishing a record for chalcogenide glass fibers. These fibers have been used to implement Fiber Evanescent Wave Spectroscopy experiments, permitting to detect infrared molecule signatures beyond 12 μm, infrared domain that was unreachable by now. These innovative fibers are also used to detect the broad absorption band of gaseous CO2 lying from 13 to 16 μm and therefore hold promises in the framework of the Darwin mission of the European Space Agency. Both of these results suggest that these new optical fibers will become essential in the field of infrared remote sensing. © 2010 Elsevier B.V. All rights reserved.
• Yang, Z., Fah, M. K., Reynolds, K. A., Sexton, J. D., & Lucas, P. (2011). Detection of bio-molecules using conductive chalcogenide glass sensor. 2011 Int. Quantum Electron. Conf., IQEC 2011 and Conf. Lasers and Electro-Optics, CLEO Pacific Rim 2011 Incorporating the Australasian Conf. Optics, Lasers and Spectroscopy and the Australian Conf., 2026-2028.
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  Abstract: Novel telluride glasses with high electrical conductivity, wide infrared transparency and good resistance to crystallization are used to design an opto-electrophoretic sensor for detection and identification of hazardous microorganisms. The sensor is based on an attenuated total reflectance element made of Ge-As-Te glass that serves as both an optical sensing zone and an electrode for driving the bio-molecules within the evanescent wave of the sensor. An electric field is applied between the optical element and a counter electrode in order to induce the migration of bio-molecules carrying surface charges. The effect of concentration and applied voltage is tested and the migration effect is shown to be reversible upon switching the electric field. The collected signal is of high quality and can be used to identify different bio-molecules through spectral analysis. This technique therefore provides the ability to detect hazardous microorganisms with high specificity and good sensitivity in aqueous environments. © 2011 IEEE.
• Yang, Z., Fah, M. K., Reynolds, K. A., Sexton, J. D., & Lucas, P. (2011). Detection of bio-molecules using conductive chalcogenide glass sensor. Optics InfoBase Conference Papers, 2026-2028.
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  Abstract: Novel telluride glasses with high electrical conductivity, wide infrared transparency and good resistance to crystallization are used to design an opto-electrophoretic sensor for detection and identification of hazardous microorganisms. The sensor is based on an attenuated total reflectance element made of Ge-As-Te glass that serves as both an optical sensing zone and an electrode for driving the bio-molecules within the evanescent wave of the sensor. An electric field is applied between the optical element and a counter electrode in order to induce the migration of bio-molecules carrying surface charges. The effect of concentration and applied voltage is tested and the migration effect is shown to be reversible upon switching the electric field. The collected signal is of high quality and can be used to identify different bio-molecules through spectral analysis. This technique therefore provides the ability to detect hazardous microorganisms with high specificity and good sensitivity in aqueous environments. © 2011 AOS.
• Yang, Z., Gulbiten, O., Lucas, P., Luo, T., & Jiang, S. (2011). Long-wave infrared-transmitting optical fibers. Journal of the American Ceramic Society, 94(6), 1761-1765.
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  Abstract: Tellurium-enriched high-purity chalcogenide fibers were fabricated and their infrared (IR)-transmitting properties were investigated. The thermal stability of Ge-As-Te glasses could be improved significantly by introducing a small amount of selenium into the glasses, therefore allowing the production of structurally and optically homogeneous glass fibers with minimal scattering losses. The fibers with greater electrical conductivity (σ) showed higher transmission losses than those with smaller σ because of the severer free-carrier absorption in the former, which was identified by the temperature dependence of the fibers' attenuation. In an effort to reduce σ of the glass while maintaining its outstanding transmitting property in the long-wave IR region, iodine was added to replace a quantity of tellurium in the glass. The fiber made of Ge25Te58I7Se10 glass exhibited good transmitting property in the 4-12 μm region and showed losses as low as ∼1 dB/m around 9.5 μm. © 2011 The American Ceramic Society.
• Calvez, L., Yang, Z., & Lucas, P. (2010). Composition dependence and reversibility of photoinduced refractive index changes in chalcogenide glass. Journal of Physics D: Applied Physics, 43(44).
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  Abstract: Photoinduced refractive index changes are investigated as a function of composition in Ge-As-Se chalcogenide glass by measuring the formation of Bragg reflectors photo-imprinted in polished glass discs. It is shown that the glass network connectivity has a strong effect on the photostructural changes which decrease dramatically when the rigidity percolates through the structure at coordination numbers (r) > 2.4. The Bragg reflector formation is also affected by the refractive index of the glass which varies sharply with (r) and correlates directly with the glass density. The photoinduced refractive index change is shown to reverse upon annealing near the glass transition following a non-exponential kinetic that closely matches the kinetics of structural enthalpy relaxation. The Bragg reflectors can also be reversibly erased and readjusted to a new wavelength through subsequent irradiation with a different photon energy. The composition dependence of photosensitivity is discussed in terms of structural constraints. It is suggested that over-constrained networks remain rigid despite photoexcitation of bond constraints therefore precluding photostructural rearrangements. © 2010 IOP Publishing Ltd.
• Gueguen, Y., Sangleboeuf, J. C., Keryvin, V., Lépine, E., Yang, Z., Rouxel, T., Point, C., Bureau, B., Zhang, X., & Lucas, P. (2010). Photoinduced fluidity in chalcogenide glasses at low and high intensities: A model accounting for photon efficiency. Physical Review B - Condensed Matter and Materials Physics, 82(13).
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  Abstract: Detailed measurements of photoinduced fluidity in Ge-Se glasses were performed using a novel shear relaxation test in torsion mode. It is shown that photofluidity is significant even at a very low intensity and that there is no apparent threshold for activating the photostructural processes. Instead, the mechanism of photofluidity is described as a cumulative process involving photoinduced motions of every atom within the irradiated volume. Based on this assumption, a model is proposed, which is shown to accurately predict the power and wavelength dependence of photofluidity using a single fitting parameter n. The factor n represents the photon efficiency for inducing an atomic motion. Photofluidity experiments performed on glass fibers of various mean coordination number indicate that the process is rapidly reduced in overconstrained glasses. The values of n obtained for these glasses correlate remarkably well with the mean coordination dependence of other photostructural changes (photodarkening, photoexpansion). This indicates that the model is physically sound. Moreover, the model is shown to quantitatively describe photofluidity data from other glass systems from literature, therefore suggesting that it could be universally applied to all chalcogenide glasses. © 2010 The American Physical Society.
• Jóvári, P., Kaban, I., Bureau, B., Wilhelm, A., Lucas, P., Beuneu, B., & Zajac, D. A. (2010). Structure of Te-rich Te-Ge-X (X = I, Se, Ga) glasses. Journal of Physics Condensed Matter, 22(40).
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  PMID: 21386568;Abstract: The structure of glassy Te78Ge11Ga11, Te79Ge16Ga5, Te70Ge 20Se10 and Te73Ge20I 7-promising materials for far infrared applications-was investigated by means of x-ray and neutron diffraction as well as extended x-ray absorption fine structure measurements at various edges. Experimental data sets were fitted simultaneously in the framework of the reverse Monte Carlo simulation technique. Short range order in Te85Ge15 was reinvestigated by fitting a new x-ray diffraction measurement together with available neutron diffraction and extended x-ray absorption fine structure data. It was found that Te85Ge15 consists mostly of GeTe 4 structural units linked together directly or via bridging Te atoms. Te is predominantly twofold coordinated in Te85Ge15, Te70Ge20Se10 and Te73Ge 20I7 while in Te78Ge11Ga 11 and Te79Ge16Ga5 the Te coordination number is significantly higher than 2. The Te-Te bond length is 2.80 ± 0.02 Å in Te78Ge11Ga11 while it is as short as 2.70 ± 0.02 Å and 2.73 ± 0.02 Å in Te73Ge20I7 and Te 70Ge20Se10, respectively. Our results show that the strengths of GeTe4 (GeTe3I, GeTe3Se) 'units' are very similar in all glasses investigated but the connection between these units depends on the third component. Differences in the Te coordination number suggest that unlike Se or I, Ga does not build into the Ge-Te covalent network. Instead, it forms a covalent bond with the non-bonding p electrons of Te, which results in an increase in the average Te coordination number. © 2010 IOP Publishing Ltd.
• Lepine, E., Yang, Z., Gueguen, Y., Troles, J., Zhang, X., Bureau, B., Boussard-Pledel, C., Sangleboeuf, J., & Lucas, P. (2010). Optical microfabrication of tapers in low-loss chalcogenide fibers. Journal of the Optical Society of America B: Optical Physics, 27(5), 966-971.
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  Abstract: We demonstrate the use of photoinduced fluidity in low-loss chalcogenide fibers for producing tapers with fine control of the diameter and geometry. The tapers produced this way act as sensing zones along chalcogenide glass fibers used for evanescent wave spectroscopy. The optical microfabrication method consists in irradiating the chalcogenide fiber with sub-bandgap laser light under a tensile stress. The resulting athermal photoinduced fluidity permits to produce tapers with good control over the geometry without altering the optical properties of the fiber. Gains in detection sensitivity greater than 1 order of magnitude are measured using these tapers. © 2010 Optical Society of America.
• Lucas, P., Yang, Z., Fah, M. K., Reynolds, K. A., Sexton, J. D., Riley, M. R., Anne, M., Bureau, B., & Lucas, P. -. (2010). Opto-electrophoretic detection of bio-molecules using conducting chalcogenide glass sensors. Optics express, 18(25).
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  Novel telluride glasses with high electrical conductivity, wide infrared transparency and good resistance to crystallization are used to design an opto-electrophoretic sensor for detection and identification of hazardous microorganisms. The sensor is based on an attenuated total reflectance element made of Ge-As-Te glass that serves as both an optical sensing zone and an electrode for driving the migration of bio-molecules within the evanescent wave of the sensor. An electric field is applied between the optical element and a counter electrode in order to induce the migration of bio-molecules carrying surface charges. The effect of concentration and applied voltage is tested and the migration effect is shown to be reversible upon switching the electric field. The collected signal is of high quality and can be used to identify different bacterial genus through statistical spectral analysis. This technique therefore provides the ability to detect hazardous microorganisms with high specificity and high sensitivity in aqueous environments. This has great potential for online monitoring of water quality.
• Lucas, P., Yang, Z., Luo, T., Jiang, S., Geng, J., & Lucas, P. -. (2010). Single-mode low-loss optical fibers for long-wave infrared transmission. Optics letters, 35(20).
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  In this Letter, we report single-mode fibers made of chalcogenide glasses with low loss in the 5-12μm range. Glasses from the Ge-As-Te-Se system were optimized to prevent nucleation and to exhibit low density of charge carriers. Single-mode fibers were obtained through the rod-in-tube method by substituting 2% Te/Se between the core and cladding glasses. The resulting single-mode fibers had a core diameter of 30μm and exhibited losses of ~6 dB/m at 10.6μm, and as low as 3-4dB/m in the 6-10μm range.
• Maurugeon, S., Boussard-Plédel, C., Troles, J., Faber, A. J., Lucas, P., Zhang, X. H., Lucas, J., & Bureau, B. (2010). Telluride glass step index fiber for the far infrared. Journal of Lightwave Technology, 28(23), 3358-3363.
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  Abstract: Nulling interferometry is an important technique under development for the DARWIN planet finding mission which enables the detection of the weak infrared emission lines of an orbiting planet. This technique requires the use of single mode optical fibers transmitting light as far as possible in the infrared. Tellurium based glasses transmit infrared light far beyond the second atmospheric window but are usually not stable enough toward crystallisation to be drawn into optical fiber. It was recently shown that the GeTe4 initial glass composition could be stabilized by the introduction of few percents of Se. In this paper, we report the development and the optical characterisation of far-infrared transmitting step index optical. The evolution of the refractive index of the glass versus the ratio Se/Te was measured in order to design a multi mode step index fiber. Its core diameter was 200 μm therefore permitting to easily characterise its optical properties. This multimode fiber transmitted light from 4 to about 15 μ m with losses near 20 dB.m-1. Despite these significant losses, the fiber was efficiently used to detect the broad absorption band of the CO2 located at 15 μm. These results are very promising in the context of the DARWIN mission of the European Space Agency. © 2006 IEEE.
• Yang, G., Bureau, B., Rouxel, T., Gueguen, Y., Gulbiten, O., Roiland, C., Soignard, E., Yarger, J. L., Troles, J., Sangleboeuf, J., & Lucas, P. (2010). Correlation between structure and physical properties of chalcogenide glasses in the As_xSe_1-x system. Physical Review B - Condensed Matter and Materials Physics, 82(19).
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  Abstract: Physical properties of chalcogenide glasses in the Asx Se 1-x system have been measured as a function of composition including the Young's modulus E, shear modulus G, bulk modulus K, Poisson's ratio ν, the density ρ, and the glass transition Tg. All these properties exhibit a relatively sharp extremum at the average coordination number 〈r〉 =2.4. The structural origin of this trend is investigated by Raman spectroscopy and nuclear magnetic resonance. It is shown that the reticulation of the glass structure increases continuously until x=0.4 following the "chain crossing model" and then undergoes a transition toward a lower dimension pyramidal network containing an increasing number of molecular inclusions at x>0.4. Simple theoretical estimates of the network bonding energy confirm a mismatch between the values of mechanical properties measured experimentally and the values predicted from a continuously reticulated structure, therefore corroborating the formation of a lower dimension network at high As content. The evolution of a wide range of physical properties is consistent with this sharp structural transition and suggests that there is no intermediate phase in these glasses at room temperature. © 2010 The American Physical Society.
• Yang, Z., Fah, M. K., Reynolds, K. A., Sexton, J. D., Riley, M. R., Anne, M., Bureau, B., & Lucas, P. (2010). Opto-electrophoretic detection of bio-molecules using conducting chalcogenide glass sensors. Optics Express, 18(25), 26754-26759.
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  PMID: 21165025;Abstract: Novel telluride glasses with high electrical conductivity, wide infrared transparency and good resistance to crystallization are used to design an opto-electrophoretic sensor for detection and identification of hazardous microorganisms. The sensor is based on an attenuated total reflectance element made of Ge-As-Te glass that serves as bothan optical sensing zone and an electrode for driving the migration of bio-molecules within the evanescent wave of the sensor. An electric field is applied between the optical element and a counter electrode in order to induce the migration of bio-molecules carrying surface charges. The effect of concentration and applied voltage is tested and the migration effect is shown to be reversible upon switching the electric field. The collectedsignal is of high quality and can be used to identify different bacterial genus through statistical spectral analysis. This technique therefore provides the ability to detect hazardous microorganisms with high specificity and high sensitivity in aqueous environments. This has great potential for online monitoring of water quality. © 2010 OpticalSociety of America.
• Yang, Z., Luo, T., Jiang, S., Geng, J., & Lucas, P. (2010). Single-mode low-loss optical fibers for long-wave infrared transmission. Optics Letters, 35(20), 3360-3362.
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  PMID: 20967066;Abstract: In this Letter, we report single-mode fibers made of chalcogenide glasses with low loss in the 5-12 μm range. Glasses from the Ge-As-Te-Se system were optimized to prevent nucleation and to exhibit low density of charge carriers. Single-mode fibers were obtained through the rod-in-tube method by substituting 2% Te/Se between the core and cladding glasses. The resulting single-mode fibers had a core diameter of 30 μm and exhibited losses of ∼6 dB/m at 10.6 μm, and as low as 3-4 dB/m in the 6-10 μm range. © 2010 Optical Society of America.
• Yang, Z., Wilhelm, A. A., & Lucas, P. (2010). High-conductivity tellurium-based infrared transmitting glasses and their suitability for bio-optical detection. Journal of the American Ceramic Society, 93(7), 1941-1944.
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  Abstract: Many biological molecules carry a net surface charge and have the potential to be monitored in drinking water by electrodepositing them on an optical sensing element and measuring their spectroscopic fingerprints in the infrared (IR) spectral region. In this detection scheme, glasses with high conductivity and excellent IR transmitting property are essential. Therefore, it is necessary to develop suitable materials that combine these properties. In this paper, a series of high-conductivity IR transmitting glasses in Ge-As-Te and Ge-As-Te-Cu systems are reported. The conductivity, thermal stability, IR transmitting property, as well as chemical durability are studied. Their suitability for bio-optical detection applications is also evaluated. Some glasses in these two systems have relatively high conductivities (near 10-4 (Ω·cm)-1), and exhibit superior thermal stability, excellent IR transmitting property, as well as good chemical durability. The electro-deposition and spectroscopic tests of protein molecules indicate that these glasses are promising materials for bio-optical detection applications. © 2010 The American Ceramic Society.
• Bureau, B., Boussard-Pledel, C., Lucas, P., Zhang, X., & Lucas, J. (2009). Forming glasses from Se and Te. Molecules, 14(11), 4337-4350.
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  PMID: 19924068;Abstract: Despite being close neighbors on the Periodic Table, selenium and tellurium present a totally different abilities to form glasses. Se is a very good glass former, and gives rise to numerous glass compositions which are popular for their transparency in the infrared range and their stability against crystallization. These glasses can be shaped into sophisticated optical devices such as optical fibers, planar guides or lenses. Nevertheless, their transparencies are limited at about 12 μm (depending on the thickness of the optical systems) due to the relatively small mass of the Se element. On the other hand, tellurium is heavier and its use in substitution for Se permits to shift the IR cutoff beyond 20 μm. However, the semimetallic nature of Te limits its glass formation ability and this glass family is known to be unstable and consequently has found application as phase change material in the Digital Versatile Disk (DVD) technology. In this paper, after a review of selenide glasses and their applications, it will be shown how, in a recent past, it has been possible to stabilize tellurium glasses by introducing new elements like Ga or I in their compositions.
• Calvez, L., Yang, Z., & Lucas, P. (2009). Reversible giant photocontraction in chalcogenide glass. Optics Express, 17(21), 18581-18589.
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  PMID: 20372588;Abstract: It is shown that chalcogenide glasses with suitably underconstrained network can undergo reversible giant photocontractions up to a micron depth. These effects result from the combination of two attributes particular to these glasses, (i) the high photosensitivity characteristic of low coordination floppy networks and (ii) the wide window of structural configuration characteristic of fragile glass former. Interestingly these effects are reversible and subsequent irradiation with high intensity results in giant photoexpansion in the same glass. The combination of subsequent photocontraction and photoexpansion on the same glass surface has good potential for the design of complex optical elements. ©2009 Optical Society of America.
• Delaizir, G., Sangleboeuf, J., King, E. A., Gueguen, Y., Zhang, X., Boussard-Pledel, C., Bureau, B., & Lucas, P. (2009). Influence of ageing conditions on the mechanical properties of Te-As-Se fibres. Journal of Physics D: Applied Physics, 42(9).
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  Abstract: Mechanical properties of chalcogenide glass fibres from the system Te-As-Se have been investigated as a function of environment (ageing in air, under vacuum and under static stress) through a series of tensile strength measurements. It is shown that the surface quality has a decisive effect on the tensile strength of the fibre. Surface degradation due to air oxidation induces a noticeable decrease in strength. However, a series of mechanical tests performed on fibres preserved in vacuum indicate that structural relaxation of the chalcogenide glass also plays a preponderant role in the loss of mechanical strength. Indeed the trend in mechanical properties correlates well with calorimetric characterizations performed on these glasses. Finally, it is observed that the application of a long-term static stress along the fibre induces a net increase in the tensile strength. These effects are associated with a partial alignment of the chalcogenide chains present in the glass structure. This is consistent with the observation of a longitudinal permanent deformation of these fibres under static stress. © 2009 IOP Publishing Ltd.
• Lucas, P., King, E. A., Gueguen, Y., Sangleboeuf, J., Keryvin, V., Erdmann, R. G., Delaizir, G., Boussard-Pledel, C., Bureau, B., Zhang, X., & Rouxel, T. (2009). Correlation between thermal and mechanical relaxation in chalcogenide glass fibers. Journal of the American Ceramic Society, 92(9), 1986-1992.
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  Abstract: Enthalpy relaxation processes in chalcogenide fibers at room temperature are investigated by differential scanning calorimetry and compared with bending-stress relaxation measurements obtained by rolling fibers on a mandrel and recording the viscoelastic relaxation parameters. While the kinetics of the two processes is very different, several qualitative correlations are demonstrated between the enthalpy state and the mechanical properties of chalcogenide glass fibers. It is observed that the ability to undergo stress relaxation is dependent upon the fictive temperature of the glass. Stress relaxation in a glass far from thermodynamic equilibrium is contingent upon its ability to undergo enthalpy relaxation and is minimal in glasses that have already relaxed enthalpy or in which relaxation time is overwhelmingly large. © 2009 The American Ceramic Society.
• Lucas, P., King, E. A., Gulbiten, O., Yarger, J. L., Soignard, E., & Bureau, B. (2009). Bimodal phase percolation model for the structure of Ge-Se glasses and the existence of the intermediate phase. Physical Review B - Condensed Matter and Materials Physics, 80(21).
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  Abstract: A detailed nuclear magnetic resonance and Raman study of Gex Se1-x glasses indicate that the glass structure is composed of intertwined microdomains of GeSe2 and Sen. Static nuclear magnetic resonance spectra of glasses ranging from 0≤x≤ 1 3 reveal the absence of Ge-Se-Se fragments in the structure. High temperature nuclear magnetic resonance showing considerable line narrowing confirms this observation. More importantly, the fraction of Se-Se-Se obtained by integration of nuclear magnetic resonance lines matches closely the percentage predicted for a bimodal phase model and is not consistent with the existence of Ge-Se-Se fragments. Raman spectra collected on the same glass also confirm the existence of GeSe2 domains up to high selenium concentrations. The mobility of the Sen phase observed at high temperature while the GeSe2 phase remains rigid is consistent with their respective underconstrained and overconstrained structural nature. The proposed bimodal phase percolation model is consistent with the original Phillips and Thorpe theory however it is clearly at odds with the intermediate phase model which predicts large amounts of Ge-Se-Se fragments in the structure. A calorimetric study performed over a wide range of cooling/heating rates shows a narrow composition dependence centered at r =2.4 in contrast with the wide reversibility window observed by Modulated Differential Scanning Calorimetry. This suggests that the observation of the reversibility window associated with the intermediate phase in Ge-Se glasses could be an experimental artifact resulting from the use of a single modulation frequency. © 2009 The American Physical Society.
• Tao, H., Yang, Z., & Lucas, P. (2009). Origin of photo-induced transmitting oscillations in chalcogenide glasses. Optics Express, 17(20), 18165-18170.
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  PMID: 19907606;Abstract: Light-induced oscillatory behaviors of transmission in chalcogenide glasses are investigated using a continuous wave tunable Ti- sapphire laser. It is shown that phase change, thermal fluctuation, nonlinear index change and periodic self focusing are not at the origin of light-induced oscillatory transmittance in chalcogenide glasses. Instead, results indicate that the interference of transmitting and reflecting light is at the origin of the oscillatory behaviors of transmitted light. Just like the principle of Fabry- Perot interferometer, these interferences result in a periodic change in transmission as the related interferential beams get in and out of phase. However, this transmitting oscillatory behavior can be registered by the detector only when the change of optical path length difference initiated by photo-induced effects is slower enough compared with the corresponding response time of the detector. Several photo-structural effects contribute to that phenomenon including photo-expansion, photo-darkening, and permanent self focusing. It appears that fluctuations of the light source intensity induce a wide distribution of the oscillatory periods. © 2009 Optical Society of America.
• Vargas, C. A., Wilhelm, A. A., Williams, J., Lucas, P., Reynolds, K. A., & Riley, M. R. (2009). Integrated capture and spectroscopic detection of viruses. Applied and Environmental Microbiology, 75(20), 6431-6440.
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  PMID: 19700543;PMCID: PMC2765139;Abstract: The goal of this work is to develop an online monitoring scheme for detection of viruses in flowing drinking water. The approach applies an electrodeposition process that is similar to the use of charged membrane filters previously employed for collection of viruses from aqueous samples. In the present approach, charged materials are driven onto a robust optical sensing element which has high transparency to infrared light. A spectroscopic measurement is performed using the evanescent wave that penetrates no more than 1 μm from the surface of an infrared optical element in an attenuated total reflectance measurement scheme. The infrared measurement provides quantitative information on the amount and identity of material deposited from the water. Initial studies of this sensing scheme used proteins reversibly electrodeposited onto germanium chips. The results of those studies were applied to design a method for collection of viruses onto an attenuated total reflectance crystal. Spectral signatures can be discriminated between three types of protein and two viruses. There is the potential to remove deposited material by reversing the voltage polarity. This work demonstrates a novel and practical scheme for detection of viruses in water systems with potential application to nearcontinual, automated monitoring of municipal drinking water. Copyright © 2009, American Society for Microbiology. All Rights Reserved.
• Yang, Z., & Lucas, P. (2009). Tellurium-based far-infrared transmitting glasses. Journal of the American Ceramic Society, 92(12), 2920-2923.
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  Abstract: Spectroscopic investigations of molecules having their main infrared (IR) signatures at longer wavelengths require optical elements transmitting lights as far as possible in the IR region toward 20 μm and beyond. In this paper, several far-IR transmitting glass systems including Ge-In-Te, Ge-As-Te, as well as some compositions containing gallium, CsI, KI, or iodine are reported. Their glass-forming ability, thermal stability, and IR transmitting property are investigated. The gallium-containing glasses show intrinsic absorptions in the 15-20 μm region. These absorptions disappear if gallium is replaced by indium, a heavier element, but these glasses display mediocre glass forming ability. Among the systems, Ge-As-Te glasses show superior glass-forming ability and wide IR transparency. The ΔT of glasses in this system can be as great as 145°C and most of the studied glasses exhibit excellent transparency in the 3-20 μm spectral window. These glass properties compares favorably to the state-of-the-art Ge-Te-I glasses both in terms of optical quality and thermodynamic stability. © 2009 The American Ceramic Society.
• Yang, Z., Anheier Jr., N. C., Qiao, H. A., & Lucas, P. (2009). Simultaneous microscopic measurements of photodarkening and photoexpansion in chalcogenide films. Journal of Physics D: Applied Physics, 42(13).
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  Abstract: A near-field scanning optical microscopic analysis is performed on As 2S3 film gratings in order to simultaneously collect index and topography images with sub-micrometre resolution. This technique makes it possible to unambiguously study the correlation between photodarkening and photoexpansion at the local scale. The development of a positive index change concomitantly with expansion or contraction in films of different thermal histories suggests that homopolar bonds are not a major contributor to the darkening effect. Photodarkening is instead associated with structurally stable defects that appear to be largely decoupled from the volume change mechanism. While photoexpansion and photodarkening follow the same growth kinetic during irradiation of annealed films with band-gap light, it is clearly shown that their structural origin is different. These results have relevance for grating fabrication since both the relief and the index patterns contribute to the grating efficiency, yet they appear to have distinct behaviour during processing or long-term stability. © 2009 IOP Publishing Ltd.
• Yang, Z., Anheier Jr., N. C., Qiao, H. A., & Lucas, P. (2009). Sub-wavelength imaging of photo-induced refractive index pattern in chalcogenide glass films. Optics Communications, 282(22), 4370-4373.
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  Abstract: Mapping of refractive index patterns with sub-wavelength resolution is achieved using Near-field Scanning Optical Microscopy (NSOM) in reflection mode. Imaging of index pattern is performed on surface gratings photo-imprinted in As2S3 films. The NSOM is adapted with a near infrared laser which wavelength (785 nm) is chosen to be within the transparency window of the glass film therefore allowing consistent measure of reflected light. Quantitative measurements of photo-induced index changes can then be obtained from knowledge of the initial film index. Images of gratings with a period of 0.5 micron are easily collected therefore demonstrating sub-wavelength spatial resolution. The technique permits to concurrently obtain a topographic image and index image of the gratings thereby permitting to quantify the extent of photodarkening and photoexpansion simultaneously. It is shown that relief gratings tend to vanish in films aged in air for several months however the index gratings remain. © 2009 Elsevier B.V. All rights reserved.
• Calvez, L., Yang, Z., & Lucas, P. (2008). Light-induced matrix softening of Ge-As-Se network glasses. Physical Review Letters, 101(17).
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  Abstract: Sub-band-gap irradiation of a series of bulk Ge-As-Se glass samples with a tunable laser source shows that photostructural processes in chalcogenide glasses are strongly dependent on the covalent network connectivity. The photoexcitation process is affected by the bond density as well as the network rigidity. Photostructural changes such as photodarkening and photoexpansion decrease and tend to vanish in overcoordinated glass in accordance with the rigidity percolation threshold. Also, the intensity required to achieve photofluidity is linearly dependent on the bond density. These results provide quantitative support for a description of photofluidity as a summative bond breaking process. © 2008 The American Physical Society.
• Gueguen, Y., Sangleboeuf, J., Keryvin, V., Rouxel, T., King, E. A., Robin, E., Delaizir, G., Bureau, B., Zhang, X., & Lucas, P. (2008). Sub-T_g viscoelastic behaviour of chalcogenide glasses, anomalous viscous flow and stress relaxation. Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi/Journal of the Ceramic Society of Japan, 116(1356), 890-895.
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  Abstract: Stress relaxation and viscous flow of GexSe1-x and TAS chalcogenide glasses were studied using the "bending method". Inadequacy of common models or functions to describe relaxation process of inorganic glasses were proved and the origin of an unexpected relaxation behaviour is discussed. Even if most part of the stress relaxes for short period (10 to 20 days), a significant part still remains (from 5 to 33%) after over one year. A linear viscoelastic behaviour has been demonstrated in the sense of an independence of the relaxation function to the stress level. However, the apparent viscosity seems to increase of almost one order of magnitude in only one month (from 5 1015 to 3 1016 Pa·s for TAS fibers) independently of strain or stress level, that is characteristic of glass structural changes. ©2008 The Ceramic Society of Japan. All rights reserved.
• Lucas, P., Calvez, L., Delaizir, G., & Zhang, X. (2008). The impact of glass structure on photoinduced changes in amorphous chalcogenides. Physics and Chemistry of Glasses: European Journal of Glass Science and Technology Part B, 49(5), 278-280.
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  Abstract: It is shown that the photostructural changes introduced during irradiation of chaclogenide glasses are dependent on the glass structure and composition. Photodarkening experiments performed on a series of As-S-Se glass suggest that the photostructural changes decrease as the network connectivity tends to an average coordination value of =2.4. Photorelaxation experiments perfomed on Ge-Se glasses show that contamination with oxygen does not appear to significantly affect photostrucral changes. On the contrary, the addition of CsCl in a Ge-Sb-S glass appears to suppress photostrucral effects entirely.
• Lucas, P., Calvez, L., Yang, Z., & Lucas, P. -. (2008). Light-induced matrix softening of Ge-As-Se network glasses. Physical review letters, 101(17).
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  Sub-band-gap irradiation of a series of bulk Ge-As-Se glass samples with a tunable laser source shows that photostructural processes in chalcogenide glasses are strongly dependent on the covalent network connectivity. The photoexcitation process is affected by the bond density as well as the network rigidity. Photostructural changes such as photodarkening and photoexpansion decrease and tend to vanish in overcoordinated glass in accordance with the rigidity percolation threshold. Also, the intensity required to achieve photofluidity is linearly dependent on the bond density. These results provide quantitative support for a description of photofluidity as a summative bond breaking process.
• Lucas, P., Wilhelm, A. A., Videa, M., Boussard-Plédel, C., & Bureau, B. (2008). Chemical stability of chalcogenide infrared glass fibers. Corrosion Science, 50(7), 2047-2052.
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  Abstract: Infrared fibers from the chalcogenide family are becoming increasingly prevalent for applications in optical sensing and imaging. In this work, we study the chemical stability of these fibers during long-term storage in air and medium term immersion in water comparable to normal usage conditions during optical monitoring in aqueous environments. A detailed study of surface oxidation in Te-As-Se fibers shows that the oxidation is limited to a superficial layer and progress at a rate of about 20 Å per year. While the elemental glass is insoluble in water, the oxide layer solubilizes rapidly and can lead to surface pitting after oxide removal. The dissolution process is complete after about 2 h of immersion in water. The elemental glass on the other end is chemically stable in water and no significant oxidation process can be detected by cyclic voltammetry. Finally the useful optical properties of these fibers are essentially unchanged after extended storage or immersion in water despite surface oxide or surface pitting. © 2008 Elsevier Ltd. All rights reserved.
• Wilhelm, A. A., Lucas, P., Reynolds, K., & Riley, M. R. (2008). Integrated capture and spectroscopic detection of viruses in an aqueous environment. Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 6852.
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  Abstract: A new approach to virus detection in an aqueous environment has been developed using the electrophoretic deposition of protein and viruses on a charged surface for in situ infrared characterization and identification. In this study, a potential was applied across a germanium ATR crystal, which acted as the anode, and an indium tin oxide (ITO) plate, which acted as the cathode in the electrodeposition setup. Sample aqueous solutions were placed between the germanium and the ITO with different concentrations of the protein bovine serum albumin (BSA) and the virus MS2, in tap water. The pH of the tap water was above the isoelectric point of the virus and the protein, resulting in a net negative charge for both. The negatively charged protein and virus were then driven to the surface of the positively charged germanium ATR crystal, once a potential was applied to the system. FTIR/ATR was used before and throughout electrodeposition to enable the in situ observation of the deposition with time. In this study, we evaluate the capture efficiency, compared to control experiments with no applied voltage, and the feasibility of using this approach for the collection and quantification of proteins and viruses from water samples. This technique resulted in the successful deposition of BSA, and MS2 with an applied voltage of only 1.1V. Furthermore, based on the analysis of the ATR spectra, distinct spectral features were identified for the protein and virus showing the potential for identification and characterization of biological molecules in an aqueous environment.
• Zhang, X., Bureau, B., Lucas, P., Boussard-Pledel, C., & Lucas, J. (2008). Glasses for seeing beyond visible. Chemistry - A European Journal, 14(2), 432-442.
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  PMID: 18067106;Abstract: Conventional glasses based on oxides have a transparency limited by phonon absorption in the near IR region and have a limited interest for analyzing information located far beyond the visible. The IR spectral domain is nevertheless of prime interest, since it covers fundamental wavelength ranges used for thermal imaging as well as molecular vibrational signatures. Besides spectacular advances in the field of IR detectors, the main significant progresses are related to the development of IR glass optics, such as lenses or IR optical fibres. The field of IR glasses is almost totally dominated by glasses formed from heavy atoms such as the chalcogens S, Se and Te. Their transparency extends up to 12, 16 and 28 μm for sulfide -, selenide - and the new generation of telluride-based glasses, respectively. They cover the atmospheric transparency domains, 3-5 and 8-13 μm, respectively, at which the IR radiation can propagate allowing thermal imaging and night-vision operations through thick layers of atmosphere. The development of new glass compositions will be discussed on the basis of structural consideration with the objective of moulding low-cost lenses for IR cameras used, for instance, in car-driving assistance. Additionally, multimode, single-index, optical fibres operating in the 3 to 12 μm window developed for in situ remote evanescentwave IR spectroscopy will also be mentioned. The detection of molecular IR signatures is applied to environmental monitoring for investigating the pollution of underground water with toxic molecules. The extension of this technique to the investigation of biomolecules in three different studies devoted to liver tissues analysis, bio-film formation, and cell metabolism will also be discussed. Finally we will mention the developments in the field of single-mode fibres operating around 10 μm for the Darwin space mission, which is aiming at discovering, signs of biological life in telluric earth-like exoplanets throughout the universe. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA,.
• Bernard, C., Delaizir, G., Sangleboeuf, J. -., Keryvin, V., Lucas, P., Bureau, B., Zhang, X. -., & Rouxel, T. (2007). Room temperature viscosity and delayed elasticity in infrared glass fiber. Journal of the European Ceramic Society, 27(10), 3253-3259.
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  Abstract: Infrared transparent optical fibers from the Te-As-Se system (TAS) exhibit a viscoelastic behavior at room temperature. The study of the change of the radius of curvature of fibers, once the fibers are unrolled from the mandrel onto which they were rolled just after fiber-drawing, allows the determination of constitutive laws both for the stress relaxation kinetics and for the delayed elasticity process. Whereas, a linear Burger's model provides a good modelling of the stress relaxation stage, a stretched exponential function gives a better description for the delayed elasticity behavior. The room temperature viscosity of the fibers ranges from 3 × 1016 to 2 × 1017 Pa s and the time constant of the anelastic strain recovery process is from 4 to 15 days. © 2006 Elsevier Ltd. All rights reserved.
• Calvez, L., Lucas, P., Rozé, M., Ma, H. L., Lucas, J., & Zhang, X. H. (2007). Influence of gallium and alkali halide addition on the optical and thermo-mechanical properties of GeSe₂-Ga₂Se₃ glass. Applied Physics A: Materials Science and Processing, 89(1), 183-188.
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  Abstract: A systematic compositional study of a new family of chalcogenide glasses, transparent from the visible range up to 16 μm has been performed. Numerous glass forming regions were explored in the GeSe2-Ga 2Se3-MX system (MX = alkali halide) in order to understand the role of alkali halides and the effect of Ga substitution for Sb in the glass structure. To that avail, several ternary diagrams were investigated, and optical and thermo-mechanical measurements were performed. It is shown that the introduction of an alkali halide in the GeSe2-Ga2Se 3 glasses increased the band-gap energy Eg by stabilizing electrons from the lone pairs of selenium. However, the glass hardness was lowered due to a decrease in the glass network reticulation. The chemical resistance was studied in a glass containing high CsCl content. Significant corrosion occurred when the glass was exposed to hot water for several hours. There is a great deal of interest in these glasses for use in thermal imaging devices, as they permit the alignment of infrared optical systems with visible red light. Furthermore, the low cost of raw materials and the possibility of shaping these glasses into lenses by molding could extend their utilization from defense to civilian applications. © 2007 Springer-Verlag.
• Delaizir, G., Lucas, P., Zhang, X., Hongli, M. a., Bureau, B., & Lucas, J. (2007). Infrared glass-ceramics with fine porous surfaces for optical sensor applications. Journal of the American Ceramic Society, 90(7), 2073-2077.
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  Abstract: GeS2-Sb2S3-CsCl glass-ceramics with fine porous surfaces were synthesized and tested as optical elements. The porosity is obtained through a two-step process, including controlled nucleation of CsCl nuclei in the glass matrix followed by selective etching of the nuclei with an acid solution. The porous surface is several hundred nanometers thick and results in a surface area increase of almost four orders of magnitude. The pores size is approximately 150 nm and can be tailored by controlling the nucleation process and the etching time. It is shown that the creation of the porous surface does not critically affect the optical transmission of these infrared (IR) transparent glass-ceramics. These materials can therefore be used for the design of optical elements and an attenuated total reflexion plate with porous surface was fabricated and tested as an optical IR sensor. The porous element shows higher detection sensitivity in initial experiments with an analyte sprayed at the plate surface and a coating of silane molecules. © 2007 The American Ceramic Society.
• Wilhelm, A. A., Boussard-Plédel, C., Coulombier, Q., Lucas, J., Bureau, B., & Lucas, P. (2007). Development of far-infrared-transmitting Te based glasses suitable for carbon dioxide detection and space optics. Advanced Materials, 19(22), 3796-3800.
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  Abstract: A new family of far-infrared-transmitting tellurides based glasses suitable for carbon dioxide detection and space optics and therefore enable the development of a new generation of infrared systems were developed. The metallic nature of Te was reduced by incorporating Te-Ge and Te-Ga bonds, which localized electrons in glassy network. The results show that the addition of I in the glassy network stabilizes the glass by acting as a non-bridging modifier and an addition of the tertavalent element Ge superior to 20% leads to rapid crystallization. It is also shown that the transmission of the GT17 glass extends far in the IR with a cut off beyond 20μm while the GS17 glass become opaque in the 15μm region. Glasses GT1 and GTT are shown to satisfy the spectral requirements of the telescopes used in space optics.
• Wilhelm, A. A., Lucas, P., DeRosa, D. L., & Riley, M. R. (2007). Biocompatibility of Te-As-Se glass fibers for cell-based bio-optic infrared sensors. Journal of Materials Research, 22(4), 1098-1104.
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  Abstract: The chemical stability and toxicity of Te-As-Se (TAS) infrared fibers are investigated. These fibers are used for biosensing applications that involve direct contact with live cultivated human cells. It is shown that TAS fibers exhibit a small oxidation layer after extended exposure to air. This layer is highly soluble in water and easily removed. However, the TAS glass itself is stable in water over several days. While oxidized fibers release arsenate ions, which result in toxic effects to the cells, fresh or washed fibers show no toxic effects. A good correlation is shown between surface etching and the disappearance of toxicity. © 2007 Materials Research Society.
• Wilhelm, A., Boussard-Pledel, C., Lucas, P., Riley, M. R., Bureau, B., & Lucas, J. (2007). New tellurium based glasses for use in bio-sensing applications. Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 6433.
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  Abstract: A new family of Tellurium based glasses from the Ge-Te-I ternary system has been investigated for use in bio-sensing applications. A systematic series of compositions have been synthesized in order to explore the ternary phase diagram in an attempt to optimize the glass composition for the fiber drawing process. The characteristic temperatures Tg, the glass transition temperature, and Tx, the onset crystallization temperature, were measured in order to obtain ΔT, the difference between Tg and T x, which must be maximized for optimum fiber drawing ability, The resulting glass transition temperature range lies between 139°C and 174°C, with ΔT values between 64°C and 124°C. The mechanical properties of a selected number of glass compositions were also investigated, including hardness and Young's Modulus. The Ge-Te-I glasses have an effective transmission window between 2-27 microns, encompassing the region of interest for the identification of biologically relevant species such as carbon dioxide. Furthermore, the fibering potential of the Ge-Te-I glasses makes them an interesting candidate for use in fiber evanescent wave spectroscopy (FEWS) and other bio-sensing applications.
• Lucas, P. (2006). Energy landscape and photoinduced structural changes in chalcogenide glasses. Journal of Physics Condensed Matter, 18(24), 5629-5638.
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  Abstract: It is shown that the magnitude of photostructural changes in chalcogenide glass is a function of the connectivity and fragility of the glass network. Glasses with a floppy network undergo larger photostructural changes, as shown by photorelaxation, photoexpansion and photodarkening measurements. The increasing magnitude of the changes correlates with a decrease in coordination number . The phenomenon is linked to the topography of the energy landscape and to the fragility of samples with different values. Since a high density of minima on the landscape is generally associated with a floppy network and fragile glassformers, it is suggested that photoexcitation provides a means for the system to explore these minima and that, consequently, fragile systems exhibit far larger photostructural changes, as observed. On the other hand, strong systems with optimal rigidity undergo very little structural change upon irradiation. This is attributed to the low density of configurational states on the landscape. A parallel between individual bond breaking in the bond lattice model and individual photoexcitation of bonding electrons during irradiation is made to support the use of the landscape formalism in describing photostructural changes. © 2006 IOP Publishing Ltd.
• Lucas, P., & King, E. A. (2006). Calorimetric characterization of photoinduced relaxation in GeSe ₉ glass. Journal of Applied Physics, 100(2).
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  Abstract: Enthalpy relaxation is measured during sub-band-gap irradiation of a GeSe 9 sample. The glass undergoes rapid photorelaxation and reaches a saturated state that appears to correspond to a dynamic equilibrium between photoexcitation and thermodynamically driven relaxation. The activation energy for structural relaxation is measured and found to be small enough that the glass can fully relax in a few years at room temperature. A comparison of isochronal optical and thermal treatments shows that photorelaxation is not induced by laser heating but is rather due to an optically induced softening of the glass network. The photorelaxation process is interpreted as optically lifting the kinetic impediment to relaxation at room temperature. The kinetics of optically and thermally activated relaxation both show a nonexponential response, which can be fitted with a Kohlrausch function. It is shown that the relaxation kinetics increase with higher irradiation intensity. © 2006 American Institute of Physics.
• Lucas, P., King, E. A., & Doraiswamy, A. (2006). Comparison of photostructural changes induced by continuous and pulsed laser in chalcogenide glass. Journal of Optoelectronics and Advanced Materials, 8(2), 776-779.
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  Abstract: Photorelaxation, photoexpansion and photodarkening measurements were performed during irradiation with CW and pulsed sub-bandgap light of Ge-Se glass. The kinetics and effect of irradiation appear to be mostly identical when irradiating with a CW or a low intensity, high repetition rate femtosecond laser. The entropy decrease observed during pulsed irradiation is inconsistent with the mechanism for patterning silicate glass with high intensity femtosecond lasers. Instead, the similarity between all photostructural change observed during CW and pulsed irradiation suggests that a high repetition rate femtosecond laser essentially acts as a CW laser when used at low intensity with a sub-bandgap wavelength on a chalcogenide glass. The only difference observed is due to the formation of interference fringes in the case of CW irradiation, which results in the formation of a Bragg reflector not observed with pulsed irradiation.
• Lucas, P., King, E. A., Horner, A. D., Johnson, B. R., & Sundaram, S. K. (2006). Photostructural relaxation in As-Se-S glasses: Effect of network fragility. Journal of Non-Crystalline Solids, 352(21-22), 2067-2072.
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  Abstract: The effect of photoinduced structural relaxation in As-S-Se glass is investigated during sub-bandgap irradiation. It is shown that the glass undergoes rapid optically induced structural relaxation upon photoexcitation of bonding electrons. Fragile systems exhibit larger relaxation as expected from their enthalpy profile. This suggests that the process is thermodynamically driven and that the kinetic impediment to relaxation at low temperature is lifted through photoinduced softening of the glass matrix. Activation energy for enthalpy relaxation measurement and an annealing study near Tg show that the photorelaxation effect is not a thermally activated process. The 〈r〉 dependence of photostructural changes is addressed and explained using the energy landscape formalism. © 2006 Elsevier B.V. All rights reserved.
• Lucas, P., Riley, M. R., Boussard-Plédel, C., & Bureau, B. (2006). Advances in chalcogenide fiber evanescent wave biochemical sensing. Analytical Biochemistry, 351(1), 1-10.
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  PMID: 16337139;
• Lucas, P., Solis, M. A., Coq, D. L., Juncker, C., Riley, M. R., Collier, J., Boesewetter, D. E., Boussard-Plédel, C., & Bureau, B. (2006). Infrared biosensors using hydrophobic chalcogenide fibers sensitized with live cells. Sensors and Actuators, B: Chemical, 119(2), 355-362.
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  Abstract: Chalcogenide glass fibers are used to perform remote infrared analysis in a fiber evanescent wave spectroscopy system (FEWS). Spectral analysis of a series of organic species demonstrates that the detection signal of non-polar species is enhanced by up to 60% relative to that of water. Contact angle measurements of the organic liquid/glass interaction strength shows that the spectral enhancement is the result of glass surface hydrophobicity. The greater interaction of non-polar species with the chalcogenide surface leads to a concentration gradient of the organic species at the glass surface where the evanescent wave is most intense. This results in selective detection of non-polar organic species in aqueous solution using FEWS. This behavior is beneficial for the detection of microorganism by FEWS and is used to design bio-optic sensors based on monitoring the response of live cells to toxins by detecting change in their infrared spectrum. This technique permits observation of disruption induced in living mammalian cells by at least two different types of toxicants. It is shown that it is possible to distinguish between the effect of a genotoxic agent (which damage nucleic acids) and a cytotoxic agent (which damages other cellular components) based on the cell's IR response. © 2005 Elsevier B.V. All rights reserved.
• Lucas, P., Solis, M. A., Juncker, C., Coq, D. L., Riley, M. R., Collier, J., Boesewetter, D. E., Boussard-Plédel, C., & Bureau, B. (2006). Spectroscopic properties of chalcogenide fibres for biosensor applications. Physics and Chemistry of Glasses: European Journal of Glass Science and Technology Part B, 47(2), 88-91.
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  Abstract: The spectroscopic characteristics of Te2As3Se 5 infrared optical fibres are investigated. Fibres with a diameter of approximately 400 μm are tapered to produce a sensitive sensing zone and used as both a sensor and transmission line of the infrared optical signal in evanescent wave spectroscopy experiments. The fibre surface is shown to be hydrophobic, which results in enhanced detection sensitivity for nonpolar organic species in aqueous media. The peak intensity of organic species increases systematically relative to the peak intensity of water during a comparison of fibre and transmission spectroscopy experiments. A bio-optical sensor is developed by coating the fibre with human lung cells at the surface of the sensing zone. The metabolic activity of the cell is monitored spectroscopically and it is shown that the evanescent wave can locally probe the cell membrane integrity. During exposure to Triton X-100, the cell membrane signal shows a sharp decay in response to the surfactant. The ratio of methyl and methylene vibrations from membrane lipids decreases rapidly and provides a sensitive probe of the cell membrane integrity. This experiment demonstrates the capability of these fibre based bio-optic sensors to detect micromolar amounts of environmental toxicant.
• Lucas, P., Wilhelm, A. A., Riley, M. R., Derosa, D. L., & Collier, J. M. (2006). Cell-based bio-optical sensors using chalcogenide fibers. Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 6083.
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  Abstract: An optical bio-sensor is built based on an infrared chalcogenide fiber coated with live cells. The fiber is immersed in an aqueous media appropriate for cell viability. The response of the cells to small quantities of toxicant can be monitored spectroscopically. The properties of chalcogenide fibers used for cell-based biosensors are investigated. The chemical stability of Te-As-Se fibers in aqueous media is shown to depend on the previous storage time of the fiber. Older fibers are shown to generate an oxide layer during extended exposure to air. This layer readily dissolves in aqueous solution and causes the release of As in the cell environment. The release of As during dissolution of the oxide layer is measured with ICP-MS and is shown to be complete after a couple hours. Fresh fibers do not show any detectable oxide layer and show excellent stability in aqueous solution. The surface roughness of old and fresh fibers is investigated with AFM before and after dissolution in aqueous media. Old fibers immersed in solution show sizable roughness due to the oxide surface layer dissolution. Fresh fibers do not show any detectable changes even after extended immersion in aqueous solution. The toxicity of As to various types of vertebrate cells is quantified using a colorimetric assay. Old fibers are shown to be notably toxic due to As released during dissolution. The fiber toxicity is shown to decrease when the fibers are previously washed in solution. The toxicity of the resulting wash water is then shown to increase due to the increase in As concentration.
• McMorrow, B., Chartoff, R., Lucas, P., Richardson, W., & Anderson, P. (2006). Particle surface treatment for nanocomposites containing ceramic particles. Composite Interfaces, 13(8-9), 801-817.
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  Abstract: Polymer matrix composites containing dispersed ceramic nanoparticles were formed by UV activated photopolymerization from the reactive liquid monomer hexanediol-diacrylate (HDODA). The polymer forming reaction proceeds by a free-radical mechanism. In forming polymer composites mat contain nanoparticles, dispersing the particles as discrete entities is critical for developing optimum properties. In the as-received condition, ceramic particles are aggregated. They must be dispersed in the monomer but if the particles are not surface treated and stabilized, they rapidly settle out of the suspension. Surface modification of the ceramic allows the particles to be suspended in the organic monomer and stabilizes the dispersion so that the particles will not reagglomerate. In this study silanes were employed as surface modifiers to disperse two nano-particulate ceramics in the HDODA monomer. The ceramic particles used are silicon carbide (SiC) and barium titanate (BaTiO 3). The shapes and sizes of the ceramic particles were established using transmission electron microscopy (TEM). A method for dispersing nanoparticles was developed in which silane-treated particles were stabilized so that they did not settle out of the liquid monomer. An analytical method based on atomic force microscopy (AFM) was used to characterize the particle distribution in the cured composites. Focusing on work with SiC nanoparticles in HDODA as a model system, the process for silane application was advanced so that it successfully yielded composites having no aggregates with particle sizes closely matching those of the neat ceramic particles. © VSP 2006.
• Riley, M. R., Lucas, P., Coq, D. L., Juncker, C., Boesewetter, D. E., Collier, J. L., DeRosa, D. M., Katterman, M. E., Boussard-Plédel, C., & Bureau, B. (2006). Lung cell fiber evanescent wave spectroscopic biosensing of inhalation health hazards. Biotechnology and Bioengineering, 95(4), 599-612.
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  PMID: 16900468;Abstract: Health risks associated with the inhalation of biological materials have been a topic of great concern; however, there are no rapid and automatable methods available to evaluate the potential health impact of inhaled materials. Here we describe a novel approach to evaluate the potential toxic effects of materials evaluated through cell-based spectroscopic analysis. Anchorage-dependent cells are grown on the surface of optical fibers transparent to infrared light. The probe system is composed of a single chalcogenide fiber (composed of Te, As, and Se) acting as both the sensor and transmission line for infrared optical signals. The cells are exposed to potential toxins and alterations of cellular composition are monitored through their impact on cellular spectral features. The signal is collected via evanescent wave absorption along the tapered sensing zone of the fiber through spectral changes between 3,000 and 600 cm-1 (3,333-16,666 nm). Cell physiology, composition, and function are non-invasively tracked through monitoring infrared light absorption by the cell layer. This approach is demonstrated with an immortalized lung cell culture (A549, human lung carcinoma epithelia) in response to a variety of inhalation hazards including gliotoxin (a fungal metabolite), etoposide (a genotoxin), and methyl methanse-sulfonate (MMS, an alkylating agent). Gliotoxin impacts cell metabolism, etoposide impacts nucleic acids and the cell cycle, and MMS impacts nucleic acids and induces an immune response. This spectroscopic method is sensitive, non-invasive, and provides information on a wide range of cellular damage and response mechanisms and could prove useful for cell response screening of pharmaceuticals or for toxicological evaluations. © 2006 Wiley Periodicals, Inc.
• Riley, M., Fernandez, I. M., & Lucas, P. (2006). Spectroscopic analysis of cell physiology and function. Frontiers in Drug Design and Discovery, 2(1), 259-272.
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  Abstract: Spectroscopic methods including infrared and Raman techniques have tremendous promise for providing rapid, non-invasive information on the impact of pharmaceuticals and toxicants on cells and tissues. Spectroscopy is not a new field; however these methods have only recently been applied to study the physiology and function of cells and tissue. The infrared spectrum (2,500-25,000 nm) of a cell or tissue can supply information about the fundamental vibrational modes of functional groups existing in biological molecules thus permitting quantification of material composition and in some cases can be connected to cell function. Spectroscopy permits observation of changes within the cell occurring at the molecular level and is a rapid, nondestructive, and reagent-free measurement. Infrared and Raman spectroscopy have been applied to evaluate the biochemical composition of mammalian cells or to discriminate between cancerous and healthy cells. While discriminations can be made between stages of the cell cycle due to alterations in spectral signatures of nucleic acids, only very small differences are apparent between distinct subcellular structures. Analyses of separate cell fractions, isolated by sucrose density gradient centrifugation, present the most significant spectral differences in the C-H (carbon and hydrogen) stretching region (2800-3000 cm-1), at the ester carbonyl stretching band (1737 cm-1), and in the PO2- stretching region (1089 and 1242 cm-1). This manuscript provides a critical review of these methods, including their potential use and pitfalls for drug screening applications. Significant innovations have been made over recent years in equipment, experimental approaches, and in analysis methods. All rights reserved - © 2006 Bentham Science Publishers.
• Angell, C. A., Wu, X. u., Yoshizawa, M., Hayashi, A., Belieres, J., Lucas, P., & Videa, M. (2005). Physical Chemistry of Ionic Liquids, Inorganic and Organic, Protic and Aprotic. Electrochemical Aspects of Ionic Liquids, 5-23.
• Lucas, P., Coq, D. L., Juncker, C., Collier, J., Boesewetter, D. E., Boussard-Pledel, C., Bureau, B., & Riley, M. R. (2005). Evaluation of toxic agent effects on lung cells by fiber evanescent wave spectroscopy. Applied Spectroscopy, 59(1), 1-9.
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  PMID: 15720730;Abstract: Biochemical changes in living cells are detected using a fiber probe system composed of a single chalcogenide fiber acting as both the sensor and transmission line for Infrared optical signals. The signal is collected via evanescent wave absorption along the tapered sensing zone of the fiber. We spectroscopically monitored the effects of the surfactant Triton X-100, which serves as a toxic agent simulant on a transformed human lung carcinoma type II epithelial cell line (A549). We observe spectral changes between 2800-3000 cm -1 in four absorptions bands, which are assigned to hydrocarbon vibrations of methylene and methyl groups in membrane lipids. Comparison of Ober and transmission spectra shows that the present technique allows one to locally probe the cell plasma membrane in the lipid spectral region. These optical responses are correlated with cellular metabolic activity measurements and LDH (lactate dehydrogenase) release assays that indicate a loss of cellular function and membrane integrity as would be expected in response to the membrane sohibilizing Triton. The spectroscopic technique shows a significantly greater detection resolution in time and concentration.
• Lucas, P., King, E. A., Doraiswamy, A., & Jivaganont, P. (2005). Competitive photostructural effects in Ge-Se glass. Physical Review B - Condensed Matter and Materials Physics, 71(10).
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  Abstract: A detailed calorimetric study of photostructural changes in glasses of the Ge-Se system is presented. The photomodified structure corresponds to a distinct entropy state intermediate between a fully thermally relaxed glass and a fresh glass. This intermediate photoinduced structure appears to result from the competitive effects of photorelaxation (negative entropic contribution) and photoexpansion (positive entropic contribution) whose simultaneous contribution leads to an equilibrium state after extensive irradiation. The compositional dependence of photorelaxation and photoexpansion reveals that strong glass formers are resilient to photostructural change relative to fragile glass formers. This observation can be explained by the presence of fewer minima on the energy landscape of strong glass former, therefore not allowing the structure to sample many configurational states and resulting in lesser photostructural changes. A comparison of the power dependence and kinetics of photorelaxation, photoexpansion, and photodarkening during subbandgap irradiation suggest that the three effects are individual and distinct components of the overall photosensitive process. ©2005 The American Physical Society.
• Lucas, P., Riley, M. R., Solis, M. A., Juncker, C., Collier, J., & Boesewetter, D. E. (2005). Hydrophobic chalcogenide fibers for cell-based bio-optical sensors. Progress in Biomedical Optics and Imaging - Proceedings of SPIE, 5691, 104-114.
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  Abstract: Chalcogenide fibers are shown to exhibit a hydrophobic surface behavior which results in detection enhancement for organic species in aqueous solutions. We use these fibers to monitor the infrared signature of human lung cells and detect the presence of toxic agents in the cell surrounding media. The signal is collected using a fiber evanescent wave spectroscopy set up with live human cells acting as a sensitizer for detection of minute quantities of toxicant. A monolayer of human alveolar epithelial cells form strong attachment at the surface of the fiber sensing zone and live in contact with the fiber while their IR spectra is collected remotely. Biochemical change in the living cells are detected during exposure to toxic agents. Variations in the spectroscopic features of the cells are observed in different spectral regions. Finally, the toxicity of Te2As3Se5 fibers is investigated.
• Schardt, C. R., Lucas, P., Doraiswamy, A., Jivaganont, P., & Simmons, J. H. (2005). Raman temperature measurement during photostructural changes in Ge _xSe_1-x glass. Journal of Non-Crystalline Solids, 351(19-20), 1653-1657.
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  Abstract: Direct measurement of sample temperature was performed during sub-bandgap photoinduced structural changes in bulk Ge-Se glasses. The temperature was determined by analysis of the Raman signal scattered from the microvolume of the sample undergoing photostructural change. The temperature measurement was done with 800 nm laser light at three different intensities. The sub-bandgap laser light induced photodarkening, photorelaxation, and photoexpansion in the glass samples but did not increase the temperature significantly. The temperature measurements of the irradiated microvolume represent a direct observation of the athermal nature of photoinduced structural changes in bulk Ge-Se glasses. © 2005 Elsevier B.V. All rights reserved.
• Bureau, B., Zhang, X. H., Smektala, F., Adam, J., Troles, J., Ma, H., Boussard-Plèdel, C., Lucas, J., Lucas, P., Coq, D. L., Riley, M. R., & Simmons, J. H. (2004). Recent advances in chalcogenide glasses. Journal of Non-Crystalline Solids, 345-346, 276-283.
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  Abstract: Compared to oxide-based glasses, vitreous materials involving chalcogens form a rather new family of glasses which have received attention, mainly because of their transmission in the mid-infrared. Indeed as low phonon compounds, these heavy-anion glasses allow the fabrication of molded optics for infrared cameras as well as infrared fibers operating in a large spectral range. These waveguides, when correctly tapered, allows the development of a new generation of sensitive evanescent-wave optical sensors which have been used for biomedical applications. Here we will focus on the spectral analysis of biomolecules present in human lung cells by measuring their infrared signatures. Because they contain heavy polarizable anions as well as lone-pair electrons, these glasses exhibit very large non-linear properties compared to silica and are candidates for fast optical switching and signal regeneration in telecom. Due to the technological interest in chalcogenide glasses, more information is needed on their structural organization and 77Se NMR spectroscopy appears to be a useful tool for checking the local environment of the Se atoms. © 2004 Elsevier B.V. All rights reserved.
• Lucas, J., Bureau, B., Boussard-Pledel, C., Kierse, J., Anne, M., Lucas, P., & Riley, M. (2004). Infrared evanescent wave bio-sensors. Conference Proceedings - Lasers and Electro-Optics Society Annual Meeting-LEOS, 2, 823-824.
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  Abstract: Original tapered infrared chalcogenide glass fibers have been developped in order to analyse by evanescent wave absorption the IR signatures of biomolecules in the 2 to 12μm range. In using a small contact between the fiber and the analytes, in situ measurements have been perfomed on biofilms, serum, liver and lung cells allowing the detection of metabolic anomalies.
• Lucas, P., Doraiswamy, A., & King, E. A. (2003). Photoinduced structural relaxation in chalcogenide glasses. Journal of Non-Crystalline Solids, 332(1-3), 35-42.
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  Abstract: Measurements of residual entropy were performed on irradiated chalcogenide glasses using a modulated differential scanning calorimeter. We show that glass from the GexSe1-x system can undergo extensive structural relaxation under sub-bandgap irradiation. This ability to relax is correlated with the strong/fragile character of the glass-forming system. Fragile glassformers experience larger relaxation as expected from the Kauzmann entropy plot. The temperature dependence of this photorelaxation process is also consistent with entropy relaxation. These measurements demonstrate that the glass configurational entropy decreases under irradiation. This can be regarded as a light activated aging process. © 2003 Elsevier B.V. All rights reserved.
• Lucas, P., & Petuskey, W. T. (2001). Phase Equilibria in the Lead-Magnesium-Niobium-Oxygen System at 1000°C. Journal of the American Ceramic Society, 84(9), 2150-2152.
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  Abstract: Phase equilibria in the PbO-MgO-Nb2O5 system have been determined at 1000°C and 1 atm. A solid-solution range of the cubic pyrochlore phase was observed and the extent of that domain was determined. This solid solution equilibrates with the surrounding ternary and binary compounds to form a series of diphasic areas. The compatibility relations between all phases were determined except for a small domain where at least six lead niobate phases were stable within a very short range of compositions. The formation of pyrochlore impurities during the processing of Pb(Mg1/3Nb2/3)O3 perovskite is discussed in relation to the phase diagram.
• Burgner, L. L., Lucas, P., Weinberg, M. C., Soares Jr., P. C., & Zanotto, E. D. (2000). On the persistence of metastable crystal phases in lithium disilicate glass. Journal of Non-Crystalline Solids, 274(1), 188-194.
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  Abstract: The formation of metastable crystalline phases in lithium disilicate glass has been a subject of controversy for decades. Recent experimental results mainly obtained via the use of electron microscopy have provided strong evidence for the formation of metastable phases during the early stages of crystallization in this composition, and have initiated a re-examination of this topic. Here, we discuss one aspect of this problem relating to the stability of these non-equilibrium phases when glasses are heated for extended time periods (>100 h) at temperatures in the nucleation regime. Recently, we presented experimental evidence obtained via XRD which indicated that metastable phases do not persist at long times in lithium disilicate glass. This finding is in direct contradiction to a result reported earlier which suggests that metastable crystalline phases in lithium disilicate glasses are long-lived and can be detected with the aid of XRD. Presented herein are the results of a systematic experimental investigation addressing the potential sources of this discrepancy, namely, glass preparation procedure, glass composition, and water content. Consistent with the results of our previous investigation, in no instance do we find any XRD evidence for the persistence of metastable phases.
• Lucas, P., & Angell, C. A. (2000). Synthesis and diagnostic electrochemistry of nanocrystalline Li_1+xMn_2-xO₄ powders of controlled Li content. Journal of the Electrochemical Society, 147(12), 4459-4463.
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  Abstract: Fine powders of Li1+xMn2-xO4 cathode materials were synthesized by a nitrate route based on the Lux-Flood principle. The method involves the reaction of MnSO4·H2O with an excess of nitrate from a nitrate bath. The reaction consists of three steps, dehydration, oxidation, and lithiation. Cathode powders with a grain size of approximately 100 nm were made and tested in rechargeable lithium batteries for their capacity retention and high discharge current behavior. Despite the small diffusion path offered by these nanosized grains during lithium insertion, the electrochemical performance of the cathode was not improved. The observed discharge profiles are interpreted in terms of current density-dependent mixed insertion into tetrahedral and octahedral sites. A quantitative analysis of the capacity retention data for Li-substituted Li1+xMn2-xO4 and stoichiometric LiMn2O4 cathodes suggests that Li1+xMn2-xO4 is immune to dissolution in the electrolyte. These results are interpreted as establishing that the dissolution of the cathode and the structural fatigue induced by the Jahn-Teller distortion are correlated through the formation of Li2Mn2O4 at the grain surface.
• Schardt, C. R., Simmons, J. H., Lucas, P., Neindre, L. L., & Lucas, J. (2000). Photodarkening in Ge₃Se₁₇ glass. Journal of Non-Crystalline Solids, 274(1), 23-29.
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  Abstract: In this paper, we present measurements of the kinetics of photodarkening in Ge3Se17 glass. The photodarkening is induced with sub-bandgap light and observed as transmission changes through a 1 mm thick sample of the glass. Both transient nonlinear and permanent processes are detected with these measurements. We consider the various sources that could lead to changes in sample optical properties and suggest that changes in electronic structure are the most reasonable explanation for the observed photodarkening. Comparison of the results with a model of light induced changes in amorphous selenium leads to an explanation for these effects based on the formation of dynamical bonds during illumination.
• Angell, C. A., Green, J. L., Ito, K., Lucas, P., & Richards, B. E. (1999). Glassformer fragilities and landscape excitation profiles by simple calorimetric and theoretical methods. Journal of Thermal Analysis and Calorimetry, 57(3), 717-736.
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  Abstract: In this paper we introduce two key notions related to understanding the 'glassy state' problem. One is the notion of the 'excitation profile' for an amorphous system and the other is the notion of the 'simple glassformer'. The attributes of the latter may be used, in quite different ways, to calculate and characterize the former. The excitation profile itself directly reflects the combined phonon/configuron density of states, which in turn determines the liquid fragility. In effect, we are examining the equivalent, for liquids, of the low temperature Einstein-Debye regime for solids though, in the liquid heat capacity case, there is no equivalent of the Dulong/Pettit classical limit for solids. To quantify these notions we apply simple calorimetric methods in a novel manner. First we use DTA techniques to define some glass-forming systems that are molecularly simpler than any described before, including cases which are 80 mol% CS2, or 100% S2Cl2. We then use the same data to obtain the fragility of these simple systems by a new approach, the 'reduced glass transition width' method. This method will be justified using data on a wider variety of well characterized glassformers, for which the unambiguous F 1/2 fragility measures are available. We also describe a new DTA method for obtaining F 1/2 fragilities in a single scan. We draw surprising conclusions about the fragility of the simplest molecular glassformers, the mixed LJ glasses, which have been much studied by molecular dynamics computer simulation. These ideas are then applied to a different kind of simple glass - one whose thermodynamics is dominated by breaking and making of covalent bonds - for which case the excitation profile can be straight-forwardly modeled. Comparisons with the profile obtained from computer studies of the molecularly simple glasses are made, and the differences in profiles implied for strong vs. fragile systems are discussed. The origin of fragility in the relation between the vibrational and configurational densities of states is discussed, and the conditions under which high fragility can convert to a first order liquid-liquid transition, is outlined.
• Burgner, L. L., Weinberg, M. C., Lucas, P., Soares Jr., P. C., & Zanotto, E. D. (1999). XRD investigation of metastable phase formation in Li₂O-2SiO₂ glass. Journal of Non-Crystalline Solids, 255(2), 264-268.
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  Abstract: Metastable crystal phase formation in lithium disilicate glass has been a subject of controversy for many years. However, recent evidence mainly obtained via the use of electron microscopy has provided strong evidence for formation of metastable phases during the early stages of crystallization in this composition. Very recently, however, a study has appeared which suggests that these metastable phases are long-lived and can be detected with the aid of XRD. Here, we present XRD results obtained for lithium disilicate glasses which were heated for various time periods at several temperatures in the nucleation regime. In no case do we find any evidence for metastable phase formation. Possible causes for the discrepancy between the present and previous experimental results are discussed.