Supapan Seraphin

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• Mayhew, T. D., Ellis, M., & Seraphin, S. (2014). Natural yellow chalk in traditional old master drawings. Journal of the American Institute for Conservation, 53(1), 1-18.
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  Abstract: Beginning in the late 15th century, European artists added natural yellow chalk to their limited selection of natural chalks by sawing cohesive pieces of raw unprocessed yellow ocher into drawing sticks. This paper examines the history, geology, chemical composition, sources, production, and physical characteristics of natural yellow chalk as a traditional old master drawing material. Chalk nomenclature is presented to clarify the relationship of natural yellow chalk with respect to fabricated yellow chalks, including synthetic yellow chalks and artificial yellow chalks. Raw unprocessed specimens of natural yellow chalk from France and Germany were obtained and studied using optical microscopy and field emission scanning electron microscopy to observe their appearance, particle structure, and working properties when used as a drawing material. Their chemical composition was determined using x-ray diffraction (XRD) analysis and scanning electron microscopy with energy dispersive x-ray spectroscopic (SEM-EDX) microanalysis. These results were compared with the physical characteristics and chemical composition of traditionally used natural yellow chalk documented in the historical record. © American Institute for Conservation of Historic and Artistic Works 2014.
• Duong, B., Gangopadhyay, P., Brent, J., Seraphin, S., Loutfy, R. O., Peyghambarian, N., & Thomas, J. (2013). Printed sub-100 nm polymer-derived ceramic structures. ACS Applied Materials and Interfaces, 5(9), 3894-3899.
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  PMID: 23570335;Abstract: We proposed an unconventional fabrication technique called spin-on nanoprinting (SNAP) to generate and transfer sub-100 nm preceramic polymer patterns onto flexible and rigid substrates. The dimensions of printed nanostructures are almost the same as those of the mold, since the ceramic precursor used is a liquid. The printed patterns can be used as a replica for printing second-generation structures using other polymeric materials or they can be further converted to desirable ceramic structures, which are very attractive for high-temperature and harsh environment applications. SNAP is an inexpensive parallel process and requires no special equipment for operation. © 2013 American Chemical Society.
• Sang-urai, S., Worayingyong, A., Maensiri, S., Smith, M. F., & Seraphin, S. (2013). Structural characterization and photocatalytic activity of electrospun TiO₂ and Ce-doped TiO₂ nanofibers. Technical Proceedings of the 2013 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2013, 1, 475-478.
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  Abstract: Mixed phase TiO2 and Ce-doped TiO2 nanofibers with different content (0.5, 2.0, 8.0%) of cerium ions were prepared by a sol-gel electro-spinning method. Results from SEM showed no beads on the undoped-TiO2 and Ce-doped TiO2 nanofibers with diameters in the range of 77-130 nm. TEM images exhibited that the undoped TiO2 crystallite size on the fiber was bigger than those on the Ce-doped samples. XRD and Ti K-edge XANES were used to determine anatase/rutile phase ratios in pure TiO2 nanofibers, whereas only XANES was used to characterize the anatase/rutile phase ratios in the Ce-doped TiO2 samples. Ce L 3-edge XANES exhibited peak associated with Ce+3 (5727 eV.) in addition to Ce+4 (5731 and 5738 eV.). Samples with the lowest Ce content had the greatest fraction of Ce ions in the Ce+3 state. The photocatalytic activity of the prepared nanofibers was observed by degradation of Rhodamine B under visible light, and the fiber of 0.5 % Ce-doped TiO2 exhibited the highest activity.
• Duong, B., Gangopadhyay, P., Brent, J., Seraphin, S., Loutfy, R. O., & Thomas, J. (2012). Fabrication of polymer-derived ceramic nanostructures by imprint lithography. Technical Proceedings of the 2012 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2012, 761-763.
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  Abstract: The conventional technique used for manufacturing miniaturized ceramic components is the powder route which typically does not allow the fabrication of feature sizes smaller than 0.1mm. With the availability of preceramic polymers, processed by various lithographic methods, it is possible to realize feature sizes below 1μm in size on polymer derived ceramics (PDC). Recently, sub-500nm structures have been fabricated by soft lithography which uses a sacrificial mold. This method is not commercially viable for the production of sub-100nm feature devices in large numbers due to the tedious pre- and post processing steps involved. Currently, no studies are present in the direction of simply printing the nanostructures below 100nm on Si 3N 4/SiO 2 to the best of our knowledge. Here, we present an easy method of fabricating sub-100nm photonic devices in polysilazane which is a precursor for preparing Si 3N 4 and SiC.
• Duong, B., Gangopadhyay, P., Seraphin, S., & Thomas, J. (2012). Multiwall carbon nanotubes grown by thermocatalytic carbonization of polyacrylonitrile. Carbon, 50(12), 4754-4757.
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  Abstract: A method is reported for the growth of multiwall carbon nanotubes (MWCNTs) using polyacrylonitrile as a solid carbon source and nanosized SiO 2 particles as catalyst. The nanotubes were grown either on a Si substrate or as a freestanding film at temperatures as low as 800 °C. The smallest measured inner diameter of the resultant MWCNTs is about 0.6 nm and therefore this method provides a new direction to prepare MWCNTs with very small inner diameter from solid carbon source. © 2012 Elsevier Ltd. All rights reserved.
• Farmer, J., Duong, B., Seraphin, S., Shimpalee, S., Martínez-Rodríguez, M. J., & W., J. (2012). Assessing porosity of proton exchange membrane fuel cell gas diffusion layers by scanning electron microscope image analysis. Journal of Power Sources, 197, 1-11.
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  Abstract: A gas diffusion layer (GDL) in a proton exchange membrane fuel cell may consist of several, materials of different porosities, with each material serving a specific set of functions. For example, samples analyzed in this work consisted of a macro porous carbon paper substrate treated with a, hydrophobic wet proofing material in differing amounts, which was then coupled to a micro porous, layer. The porosities of four such GDLs were determined by using 2D scanning electron microscope (SEM) images to mathematically model the volumes filled by each solid in the 3D structures. Results, were then compared with mercury intrusion porosimetry (MIP) measurements to verify the accuracy, of the method. It was found that the use of SEM not only allowed for detailed porosity analysis of, separate porous materials within the GDL, but also porosity for the entire GDL could be calculated for, the seemingly complex structures with reasonable accuracy. With some basic geometric assumptions, and use of the superposition principle, the calculated results were accurate to less than a 2% absolute, difference of the porosity measured by MIP for each of the four samples analyzed. © 2011 Elsevier B.V. All rights reserved.
• Martínez-Rodríguez, M. J., Cui, T., Shimpalee, S., Seraphin, S., Duong, B., & Zee, J. V. (2012). Effect of microporous layer on MacMullin number of carbon paper gas diffusion layer. Journal of Power Sources, 207, 91-100.
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  Abstract: The effect of the microporous layer (MPL) and wet proofing on the MacMullin number has been evaluated for a custom series of Toray TGP-H-060 carbon paper gas diffusion layer (GDL). Complementary characterizations for these GDLs were performed by using scanning electron microscopy (SEM) images, pore size distribution (PSD) and fuel cell performance. The GDLs were customized by the addition of a microporous layer (MPL) and the treatment of, either or both, the substrate and MPL with 10% and 40% hydrophobic agent. SEM images correlated very well with the data shown for PSD. Distinction between the substrate layer and the MPL were clearly shown as two different slopes in the integral distribution and two different peaks in the differential distribution. The MacMullin number increased with increase in wet proofing but decreased with the addition of the MPL. The MacMullin number is a key parameter that contains the missing information for the path length in GDLs, which is generally approximated with the Bruggeman expression. The results provided an overview for the interpretation of the combined effect of the substrate and MPL properties as well as the cell operating conditions. © 2012 Elsevier B.V. All rights reserved.
• Mayhew, T. D., Ellis, M., & Seraphin, S. (2012). Steatite and calcite natural white chalks in traditional old master drawings. Journal of the American Institute for Conservation, 51(2), 175-198.
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  Abstract: This article examines the history, geology, chemical composition, sources, production, and physical characteristics of natural white chalks when used as traditional old master drawing materials. The nomenclature of white chalks is presented to clarify the relationship of natural white chalks with respect to other types of white chalks, including fabricated and artificial white chalks. Specimens of two types of natural white chalk, steatite natural white chalk and calcite natural white chalk, were obtained and studied using optical microscopy and field emission scanning electron microscopy to observe their appearance and to learn more about their working properties. Their chemical composition was determined using x-ray diffraction analysis and field emission scanning electron microscopy with energy dispersive x-ray spectroscopic microanalysis. These results were compared with the physical characteristics and chemical composition of traditionally used steatite and calcite natural white chalks documented in the historical record.
• Laokul, P., Amornkitbamrung, V., Seraphin, S., & Maensiri, S. (2011). Characterization and magnetic properties of nanocrystalline CuFe ₂O₄, NiFe₂O₄, ZnFe₂O ₄ powders prepared by the Aloe vera extract solution. Current Applied Physics, 11(1), 101-108.
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  Abstract: This study reports the simple synthesis of MFe2O4 (where M = Cu, Ni, and Zn) nanoparticles by a modified sol-gel method using high purity metal nitrates and aloe vera plant extracted solution. Using of aloe vera extract simplifies the process and provides an alternative process for a simple and economical synthesis of nanocrystalline ferrites. The obtained precursors were characterized by TG/DTA to determine the thermal decomposition and subsequently were cc at different temperatures in the range of 600-900 °C for 2 h to obtain the ferrite nanoparticles. The calcined samples were characterized by XRD, FT-IR, SEM, and TEM. All the prepared samples are polycrystalline and have spinel structure with crystallite sizes of 15-70 nm. The crystallite size increases with increasing the calcination temperature. Magnetic properties of the prepared ferrite samples were measured using Vibrating sample magnetometer (VSM). The room temperature magnetic behavior of as-prepared ferrite powders can be explained as the results of the three important factors: impurity phase of a-Fe2O3, cationic distribution in spinel structure, and the surface spin structure of nanoparticles. © 2010 Elsevier B.V. All rights reserved.
• Akpa, O. N., Shoieb, S., Thompson, T. R., Isaacs-Smith, T. F., Anderson, P., Seraphin, S., & Das, K. K. (2010). CuInSe₂/Si heterojunctions for photovoltaic applications. TMS Annual Meeting, 3, 3-8.
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  Abstract: Growth and characterization of CuInSe2 (CIS) thin films deposited on Si, for the purpose of forming heterojunctions to investigate the suitability of the material system for high efficiency solar cells, is reported here. Deposition was obtained by RF magnetron sputtering using a stoichiometric CIS target. As CIS and Si are closely lattice matched, large grain polycrystalline films were obtained. Rutherford backscattering spectroscopy (RBS) indicated that these CIS films have a composition of Cu 0.85In1.1Se1.9. Circular diodes were fabricated and the current- voltage characteristics of these diodes indicated that reasonable quality p-n junctions were obtained. The forward current of these devices increased by about three orders of magnitude, from 0.003 to 2.65 mA at a bias of 2 V when illuminated with a 75 watt halogen lamp. Large area samples 1 cm x 1 cm, were patterned with a window shaped contact and under illumination produced approximately 90 mV and 0.5 mA when measured in series with a precision multimeter and picoammeter. The strong response to illumination indicated that the material system has a high potential for use as a solar cell.
• Akpa, O. N., Shoieb, S., Thompson, T. R., Isaacs-Smith, T. F., Anderson, P., Seraphin, S., & Das, K. K. (2010). Sputter deposition of CuInSe2 and CuGaSe₂ from composite targets on (100) Si. Materials Research Society Symposium Proceedings, 1210, 241-244.
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  Abstract: Thin films of CuInSe2(CIS) and CuGaSe2(CGS) were deposited on (100) Si substrates by RF magnetron sputtering using stoichiometric targets, at various substrate temperatures. Prior to film deposition, the Si substrates were cleaned using the RCA cleaning procedure and treated in a buffered oxide etch (BOE) solution. Deposited films were characterized using Rutherford backscattering spectroscopy (RBS), transmission electron microscopy (TEM) of cross-sectional samples and Hall measurements. Rutherford backscattering analysis indicated that the CIS films had a composition of Cu0.8In1.1Se1.9, whereas CGS films were Cu-poor and Ga-rich with a composition of Cu0.3Ga1.5Se 1.5. Clean Cu-chalcopyrite/Si interfaces were obtained using BOE treated Si substrates. Transmission electron micrographs of cross-sectional samples indicated a polycrystalline film structure and that the native oxide on the Si substrate was eliminated. Energy dispersive X-ray spectroscopy (EDS) conducted in the TEM showed that contamination levels in the films were low. The Hall-mobility experiments performed the CIS film indicated that the material was of p-type conductivity with a carrier concentration of 9.6 × 10 20/cm3 and a Hall mobility of 390 cm2V -1s-1. © 2010 Materials Research Society.
• Akpa, O., Shaik, S., Thompson, T., Isaacs-Smith, T., Anderson, P., Seraphin, S., & Das, K. (2010). Sputter deposited ZnTe/ZnSe/ZnO heterojunctions for photovoltaic applications. Conference Record of the IEEE Photovoltaic Specialists Conference, 1897-1901.
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  Abstract: Films of ZnTe, ZnSe, and ZnO were deposited on (100) Si by RF magnetron sputtering from stoichiometric ZnTe, ZnSe, and ZnO targets for the purpose of fabricating a ZnTe/ZnSe heterojunction. Rutherford back scattering (RBS) analysis yielded a composition of Zn1.0Te1.0 for ZnTe, Zn1.1Se1.2 for ZnSe, and Zn1.0O0.8 for ZnO which indicates that near-stoichiometric films were obtained. Transmission electron microscopy (TEM) of cross-sectional samples established that the films were polycrystalline in nature. Heterostructures were grown on ZnO coated low resistivity n-type Si wafer. The heterojunctions consisted of a ∼65 nm layer of ZnSe, to serve as an absorber layer and ∼40 nm of ZnTe as a window layer. The heterojunction wafer was diced into 1 cm2 samples. A Pt back contact was deposited on the Si. The top surface of the junction was patterned with a contact leaving two, 0.25 cm × 0.65 cm ZnTe windows exposed. Both the top and bottom contacts were annealed at 350° C under N2 atmosphere for 5 min. Under 120 W halogen lamp illumination the junction showed a photovoltaic response. Between the top Al and back Pt, the device produced an approximate open-circuit voltage (VOC) of 600 mV as measured with a high impendence voltmeter. © 2010 IEEE.
• Akpa, O., Shoieb, S., Thompson, T., Isaacs-Smith, T., Anderson, P., Seraphin, S., & Das, K. (2010). Chalcopyrite/Si heterojunctions for photovoltaic applications. Journal of Electronic Materials, 39(11), 2462-2466.
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  Abstract: Films of CuInSe 2 (CIS) and CuGaSe 2 (CGS) were deposited on (100) Si by radiofrequency (RF) magnetron sputtering from stoichiometric CIS and CGS targets. Rutherford backscattering (RBS) analysis yielded a composition of Cu 0.8In 1.1Se 1.9 for CuInSe 2, which indicates that these films were Cu and Se poor. A composition of Cu 0.3Ga 1.5Se 2.0 for CuGaSe 2 shows Ga-rich and Cu-poor layers. Transmission electron microscopy (TEM) of cross-sectional samples established that the films were polycrystalline in nature and free of pinhole defects that normally short-circuit devices fabricated on glass with submicron absorber layers. From the electron and x-ray diffraction patterns, tetragonal chalcopyrite phases of the material were identified. Circular diodes, with a diameter between 100 μm and 400 μm, were fabricated on the grown films with a common Au back-contact. Diodes on both CIS and CGS films exhibited rectifying characteristics. From the polarity corresponding to the high and low currents, it was inferred that the grown films were p-type. These diodes exhibited photovoltaic response, and the forward-bias current increased by as much as two orders of magnitude when illuminated by a 75-W halogen lamp. The open-circuit voltages (V OC) for these devices are expected to approach the turn-on voltage of the diodes, 0.5 V and 0.7 V, for the CGS/Si and the CIS/Si heterojunctions, respectively. Shunting caused by degenerate phases present in the CGS film is believed to have resulted in the observed lower turn-on voltage for the CGS/n-Si heterojunction diode. © 2010 TMS.
• Klinkaewnarong, J., Swatsitang, E., Masingboon, C., Seraphin, S., & Maensiri, S. (2010). Synthesis and characterization of nanocrystalline HAp powders prepared by using aloe vera plant extracted solution. Current Applied Physics, 10(2), 521-525.
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  Abstract: Nanocrystalline hydroxyapatite (HAp) powders were synthesized by a simple method using aloe vera plant extracted solution. To obtain nanocrystalline HAp, the prepared precursor was calcined in air at 400-800 °C for 2 h. The phase composition of the calcined samples was studied by X-ray diffraction (XRD) technique. The XRD results confirmed the formation of HAp phase. With increasing calcination temperature, the crystallite of the HAp increased, showing the hexagonal structure of HAp with the lattice parameter, a, in a range of 0.9520-0.9536 nm and c of 0.6739-0.6928 nm. The particle sizes of the powder were obtained to be 43-171 nm. The optical properties of the calcined powders were characterized by Raman and FTIR spectroscopies. The Raman spectra showed a main peak of the phosphate vibration mode (ν1(PO4)) at ∼963 cm-1 for all the calcined samples. The peaks of the phosphate carbonate and hydroxyl vibration modes were observed in the FTIR spectra for all the calcined powders. The morphology tends to change from a spherical shape to a rod-like shape with increasing calcination temperature as revealed by TEM. © 2009 Elsevier B.V. All rights reserved.
• Mayhew, T. D., Ellis, M., & Seraphin, S. (2010). Natural black chalk in traditional old master drawings. Journal of the American Institute for Conservation, 49(2), 83-95.
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  Abstract: The history, geology, sources, production, and physical characteristics of natural black chalk as a traditional drawing medium were examined. Using field emission scanning electron microscope imaging, specimens of natural black chalk from Normandy, France, were studied in both unprocessed block form and as marks and lines drawn on paper. The physical characteristics of insolubility in water and variation in hardness with differing storage conditions were evaluated; chemical composition was determined using field emission scanning electron microscopy with energy dispersive x-ray spectroscopy microanalysis. Results were compared with the physical characteristics and chemical composition of traditional natural black chalk as documented in the historical record.
• Ananpattarachai, J., Kajitvichyanukul, P., & Seraphin, S. (2009). Visible light absorption ability and photocatalytic oxidation activity of various interstitial N-doped TiO₂ prepared from different nitrogen dopants. Journal of Hazardous Materials, 168(1), 253-261.
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  PMID: 19282105;Abstract: Nitrogen-doped TiO2 was developed to enable photocatalytic reactions using the visible range of the solar spectrum. This work reports on the synthesis, characterisation and kinetic study of interstitial N-doped TiO2 prepared by the sol-gel method using three different types of nitrogen dopants: diethanolamine, triethylamine and urea. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and UV-visible spectroscopy were used to analyse the titania. Different interstitial N-doped TiO2 properties, such as absorption ability in the UV-visible light region, redshift in adsorption edge, good crystallisation and composition ratio of titania structures (anatase and rutile) could be obtained from different nitrogen dopants. Amongst investigated nitrogen precursors, diethanolamine provided the highest visible light absorption ability of interstitial N-doped TiO2 with the smallest energy bandgap and the smallest anatase crystal size, resulting in the highest efficiency in 2-chlorophenol degradation. The photocatalytic activity of all N-doped TiO2 can be arranged in the following order: TiO2/diethanolamine > TiO2/triethylamine > TiO2/urea > un-doped TiO2. The initial rate of 2-chlorophenol degradation using the interstitial N-doped TiO2 with diethanolamine was 0.59 mg/L-min and the kinetic constant was 2.34 × 10-2 min-1 with a half-life of 98 min. In all cases, hydroquinone was detected as a major intermediate in the degradation of 2-chlorophenol. © 2009 Elsevier B.V.
• Maensiri, S., Phokha, S., Laokul, P., & Seraphin, S. (2009). Room temperature ferromagnetism in Fe-doped CeO ₂ nanoparticles. Journal of Nanoscience and Nanotechnology, 9(11), 6415-6420.
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  PMID: 19908543;Abstract: RT ferromagnetism was observed in nanoparticles of Fe-doped CeO 2 (i.e., Ce 0.97Fe 0.03O 2) synthesized by a sol-gel method. The undoped and Fe-doped CeO 2 were characterized by XRD, Raman spectroscopy, TEM, and VSM. The undoped samples and Ce 0.97Fe 0.03O 2 precursor exhibit a diamagnetic behavior. The 673 K-calcined Ce 0.97Fe 0.03O 2 sample is paramagnetic whereas 773 and 873 K-calcined Ce 0.97Fe 0.03O 2 samples are ferromagnetism having the magnetizations of 4.65 × 10 ~3 emu/g and 6.20 × 10 ~3 emu/g at 10 kOe, respectively. Our results indicate that the ferromagnetic property is intrinsic to the Fe-doped CeO 2 system and is not a result of any secondary magnetic phase or cluster formation. © 2009 American Scientific Publishers.
• Phoka, S., Laokul, P., Swatsitang, E., Promarak, V., Seraphin, S., & Maensiri, S. (2009). Synthesis, structural and optical properties of CeO₂ nanoparticles synthesized by a simple polyvinyl pyrrolidone (PVP) solution route. Materials Chemistry and Physics, 115(1), 423-428.
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  Abstract: This paper reports the synthesis and characterization of CeO2 nanoparticles by a simple polymer complex method using cerium (III)) acetate hydrate and polyvinyl pyrrolidone (PVP) as the starting chemicals. The precursor was calcined at 500 °C for 2 h to obtain CeO2 nanoparticles. The XRD, FTIR, Raman and electron diffraction analysis results indicated that the calcined CeO2 sample has the fluorite structure of CeO2. TEM revealed that the CeO2 sample consists of crystalline particles of 5-10 nm which are weakly aggregated. UV-vis spectroscopy was also performed to study the optical properties of the synthesized CeO2 sample. The sample exhibited a strong absorption below 400 nm (3.10 eV) with a well defined absorbance peak at around 285 nm (4.35 eV). The estimated band gap of the CeO2 sample was 3.44 eV and this value is higher than that of the bulk CeO2 powders (Eg = 3.19 eV) due to quantum confinement effect. The synthesized CeO2 nanoparticles also exhibited room temperature photoluminescence (PL). The spectrum of the CeO2 sample dispersed in methanol exhibits a broad-band character from 325 to 550 nm with four emission bands: a strong broad emission band at ∼406 nm (3.06 eV), a strong blue band at 420 nm (2.95 eV), blue-green band at ∼483 nm (2.57 eV), and a weak green band at 530 nm (2.34 eV). A peak centered at 406 nm for the CeO2 sample originates from the defect states existing extensively between the Ce 4f state and O 2p valence band. © 2009 Elsevier B.V. All rights reserved.
• Duong, B., Seraphin, S., Laokul, P., Masingboon, C., & Maensiri, S. (2008). Ni-Cu-Zn ferrite prepared by aloe vera plant extract or egg white. Microscopy and Microanalysis, 14(SUPPL. 2), 326-327.
• Ellis, M., Jutarosaga, T., Smith, S., Wei, Y., & Seraphin, S. (2008). Electron microscopy and raman characterization of multi-walled carbon nanotubes grown by chemical vapor deposition. Microscopy and Microanalysis, 14(SUPPL. 2), 304-305.
• Maensiri, S., Laokul, P., Klinkaewnarong, J., Phokha, S., Promarak, V., & Seraphin, S. (2008). Indium oxide (In₂O₃) nanoparticles using Aloe vera plant extract: Synthesis and optical properties. Optoelectronics and Advanced Materials, Rapid Communications, 2(3), 161-165.
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  Abstract: In2O3 nanoparticles with particle sizes of 5-50 nm were synthesized by a simple, cost effective and environmental friendly route using indium acetylacetonate and Aloe vera plant extracted solution. The precursor was characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found to be at above 350 °C. Nanoparticles are formed after calcination the dried precursor of In 2O3 in air at 400-600°C for 2 h. Structural, morphological and optical properties of the synthesized nanoparticles were characterized. XRD and TEM analysis showed that the In2O3 samples are cubic with particle sizes of 5-50 nm. The morphology and size of In2O3 materials were affected by the calcination temperature. The prepared In2O3 nanoparticles showed a strong PL emission in the UV region. The strong emissions of In 2O3 are attributed to the radioactive recombination of an electron occupying oxygen vacancies with a photo-excited hole. The present work proves that the Aloe vera plant-extracted solution synthesis is a new useful method using cheap precursors for preparation of In2O3 nanoparticles.
• Masingboon, C., Maensiri, S., Yamwong, T., Anderson, P. L., & Seraphin, S. (2008). Nanocrystalline CaCu₃Ti₄O₁₂ powders prepared by egg white solution route: Synthesis, characterization and its giant dielectric properties. Applied Physics A: Materials Science and Processing, 91(1), 87-95.
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  Abstract: Nanocrystalline CaCu3Ti4O12 powders with particle sizes of 50-90 nm were synthesized by a simple method using Ca(NO 3)2•4H2O, Cu(NO3) 2•4H2O, titanium(diisoproproxide) bis(2,4-pentanedionate) and freshly extracted egg white (ovalbumin) in aqueous medium. The synthesized precursor was characterized by TG-DTA to determine the thermal decomposition and crystallization temperature which was found to be at above 400 °C. The precursor was calcined at 700 and 800 °C in air for 8 h to obtain nanocrystalline powders of CaCu3Ti4O 12. The calcined CaCu3Ti4O12 powders were characterized by XRD, FTIR, SEM and TEM. Sintering of the powders was conducted in air at 1100 °C for 16 h. The XRD results indicated that all sintered samples have a typical perovskite CaCu3Ti4O 12 structure and a small amount of CuO, although the sintered sample of the 700 °C calcined powders contained some amount of CaTiO3. SEM micrographs showed the average grain sizes of 12.0±7.8 and 15.5±8.9 μm for the sintered CaCu3Ti4O 12 ceramics prepared using the CaCu3Ti4O 12 powders calcined at 700 and 800 °C, respectively. The sintered samples exhibit a giant dielectric constant, ε′ of ∼1.5-5×104. The dielectric behavior of both samples exhibits Debye-like relaxation, and can be explained based on a Maxwell-Wagner model. © 2007 Springer-Verlag.
• Masingboon, C., Thongbai, P., Maensiri, S., Yamwong, T., & Seraphin, S. (2008). Synthesis and giant dielectric behavior of CaCu₃Ti₄O₁₂ ceramics prepared by polymerized complex method. Materials Chemistry and Physics, 109(2-3), 262-270.
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  Abstract: Nano-sized powders of CaCu3Ti4O12 were synthesized by a polymerized complex method and calcined at 600, 700 and 800 °C in air for 8 h. The diameter of the powders ranges from 30 to 100 nm. The CaCu3Ti4O12 powders were characterized by TG-DTA, XRD, FTIR, SEM and TEM. Sintering of the powders was conducted in air at 1100 °C for 16 h. The XRD results indicated that all sintered samples have a typical perovskite CaCu3Ti4O12 structure with some amount of CaTiO3 and CuO. SEM micrographs of the sintered CaCu3Ti4O12 ceramics showed the average grain size of 10-15 μm. The samples exhibit a giant dielectric constant, ε′ of 10,000-20,000. It is found that ε is independent on the frequency and weakly dependent on temperature. The Maxwell-Wagner polarization mechanism is used to explain the high permittivity in these ceramics. It is also found that all three sintered samples have the same activation energy of grains, which is 0.116 eV. On the other hand, the activation energy of grain boundaries is found to be 0.219, 0.391 and 0.641 eV for CaCu3Ti4O12 ceramics prepared using the CaCu3Ti4O12 powders calcined at 600, 700 and 800 °C, respectively. © 2007 Elsevier B.V. All rights reserved.
• Seraphin, S., Chandler, G., Sellers, M., Bentley, D., Dorame, K., & Hernandez, S. (2008). Remote microscopy for education and outreach. Microscopy and Microanalysis, 14(SUPPL. 2), 874-875.
• Katterman, M. E., Birchard, S., Seraphin, S., & Riley, M. R. (2007). Cellular evaluation of the toxicity of combustion derived particulate matter: influence of particle grinding and washing on cellular response. Chemosphere, 66(3), 567-573.
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  PMID: 16824581;Abstract: There is increasing interest in continual monitoring of air for the presence of inhalation health hazards, such as particulate matter, produced through combustion of fossil fuels. Currently there are no means to rapidly evaluate the relative toxicity of materials or to reliably predict potential health impact due to the complexity of the composition, size, and physical properties of particulate matter. This research evaluates the feasibility of utilizing cell cultures as the biological recognition element of an inhalation health monitoring system. The response of rat lung type II epithelial (RLE-6TN) cells to a variety of combustion derived particulates and their components has been evaluated. The focus of the current work is an evaluation of how particles are delivered to a cellular sensing array and to what degree does washing or grinding of the particles impacts the cellular response. There were significant differences in the response of these lung cells to PM's of varying sources. Mechanical grinding or washing was found to alter the toxicity of some of these particulates; however these effects were strongly dependent on the fuel source. Washing reduced toxicity of oil PM's, but had little effect on those from diesel or coal. Mechanical grinding could significantly increase the toxicity of coal PM's, but not for oil or diesel. © 2006 Elsevier Ltd. All rights reserved.
• Maensiri, S., Maensiri, S., Masingboon, C., Masingboon, C., Boonchom, B., Boonchom, B., Seraphin, S., & Seraphin, S. (2007). A simple route to synthesize nickel ferrite (NiFe₂O₄) nanoparticles using egg white. Scripta Materialia, 56(9), 797-800.
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  Abstract: NiFe2O4 nanoparticles were synthesized by a simple and cost-effective method using Ni and Fe nitrates and freshly extracted egg white (ovalbumin) in an aqueous medium. The X-ray diffraction and selected-area electron diffraction results indicated that the synthesized nanoparticles have only the inverse spinel structure without the presence of any other phase impurities. Room temperature magnetization results showed a ferromagnetic behavior of the NiFe2O4 nanoparticles, with saturation-specific magnetization values in the range of 26.4-42.5 emu/g at 10 kOe. © 2006 Acta Materialia Inc.
• Maensiri, S., Masingboon, C., Laokul, P., Jareonboon, W., Promarak, V., Anderson, P. L., & Seraphin, S. (2007). Egg white synthesis and photoluminescence of platelike clusters of CeO ₂ nanoparticles. Crystal Growth and Design, 7(5), 950-955.
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  Abstract: This paper reports the synthesis of platelike CeO2 nanoparticles by a simple, cost-effective, and environmentally friendly method using cerium(III) acetate hydrate and freshly extracted egg white (ovalbumin) in an aqueous medium. A platelike structure of CeO2 nanoparticles having the particle size of 6-30 nm was obtained by calcining the precursors in air at 400, 500, and 600°C, for 2 h. Results from XRD, Raman spectroscopy, and SAED analysis indicated that the synthesized CeO2 nanoparticles have the fluorite structure of the bulk CeO2. All samples show a strong UV-vis absorption below 400 nm (3.10 eV) with a well-defined absorbance peak at around 284 nm (4.37 eV). The estimated direct band gaps are 3.61, 3.59, and 3.57 eV for the samples calcined at 400, 500, and 600°C, respectively. These band gaps are 0.42, 0.40, and 0.38 eV higher than that of bulk CeO2, indicating the quantum confinement effect of the nanosize particles. The 400 and 500°C calcined samples exhibited similar emission peaks of room-temperature photoluminescence. However, the sample calcined at 600°C exhibited the strongest UV emission band at 392 nm (3.17 eV) because of its better-defined crystallinity compared to the other two samples calcined at 400 and 500°C. © 2007 American Chemical Society.
• Maensiri, S., Masingboon, C., Promarak, V., & Seraphin, S. (2007). Synthesis and optical properties of nanocrystalline V-doped ZnO powders. Optical Materials, 29(12), 1700-1705.
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  Abstract: This paper reports the synthesis and optical properties of nanocrystalline powders of V-doped ZnO (i.e. Zn0.95V0.05O, Zn0.90V0.10O, and Zn0.85V0.15O) by a simple sol-gel method using metal acetylacetonates of Zn and V and poly(vinyl alcohol) as precursors. Structure of the prepared samples was studied by X-ray diffraction, FTIR spectroscopy, and selected-area electron diffraction (SAED) analysis. The morphology of the powders revealed by SEM and TEM was affected by the amount of V, causing the formations of both nanoparticles and nanorods in the Zn0.95V0.05O sample, nanorods in the Zn0.90V0.10O sample, and nanoparticles in the Zn0.85V0.15O sample. The optical properties of the samples were investigated by measuring the UV-VIS absorbance and photoluminescence spectra at room temperature. All the samples exhibited UV absorption at below 400 nm (3.10 eV) with a well-defined absorbance peak at around 364 nm (3.41 eV) and 288 nm (4.31 eV). The band gap of the V-doped samples shows a decrease with increasing V concentration. The photoluminescence spectra of all the samples showed a strong UV emission band at ∼2.98 eV, a weak blue band at 2.82 eV, a week blue-green band at 2.56 eV, and a weak green band at 2.34 eV, which indicated their high structural and optical quality. © 2006 Elsevier B.V. All rights reserved.
• Maensiri, S., Wongsaprom, K., Swatsitang, E., & Seraphin, S. (2007). Fe-doped La0.5 Sr0.5 Ti O3-δ nanoparticles: A diluted magnetic oxide system. Journal of Applied Physics, 102(7).
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  Abstract: We report room-temperature ferromagnetism in ∼11.4-14.6 nm nanoparticles of La0.5 Sr0.5 Ti0.985 Fe0.015 O3-δ. Nanoparticles of undoped and Fe-doped samples were synthesized by a polymerized complex method and were characterized using x-ray diffraction, transmission electron microscopy, and vibrating-sample magnetometer. The undoped samples exhibit a diamagnetic behavior, whereas the Fe-doped samples are ferromagnetic having the specific magnetizations of 0.041-0.101 emug at 10 kOe. Our results indicate that the ferromagnetic property of La0.5 Sr0.5 Ti0.985 Fe0.015 O3-δ system is intrinsic and is not a result of any secondary magnetic phase or cluster formation. The finding of room-temperature ferromagnetism in this system would stimulate further interest in the area of diluted magnetic oxides. © 2007 American Institute of Physics.
• Wongsaprom, K., Swatsitang, E., Maensiri, S., Srijaranai, S., & Seraphin, S. (2007). Room temperature ferromagnetism in Co-doped la_0.5Sr _0.5TiO_3-δ nanoparticles. Applied Physics Letters, 90(16).
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  Abstract: The authors report room temperature ferromagnetism in La 0.5Sr0.5Ti0.985Coc.015O 3-δ nanoparticles with particle sizes of ∼12-14nm. Nanoparticles of undoped and Co-doped samples were synthesized by a polymerized complex method and were characterized using x-ray diffraction and transmission electron microscopy. The magnetic properties of the nanoparticles were determined using vibrating sample magnetometry. The undoped samples exhibit a diamagnetic behavior, whereas all the Co-doped samples are ferromagnetic having the specific magnetizations of ∼0.011-0.038 emu/g at 10 kOe. The finding of room temperature ferromagnetism in the Co-doped samples would allow an enhanced flexibility for applications. © 2007 American Institute of Physics.
• Choi, S., O'Day, P. A., Rivera, N. A., Mueller, K. T., Vairavamurthy, M. A., Seraphin, S., & Chorover, J. (2006). Strontium speciation during reaction of kaolinite with simulated tank-waste leachate: Bulk and microfocused EXAFS analysis. Environmental Science and Technology, 40(8), 2608-2614.
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  PMID: 16683599;Abstract: Radioactive strontium (90Sr) is an important constituent of the complex wastes from past nuclear weapons production and has been stored in underground tanks at U.S. DOE sites (e.g., Hanford, WA). Using bulk and microfocused EXAFS spectroscopy, we examined temporal changes in solid-phase Sr speciation in kaolinite samples reacted for 1-369 d with high-pH, high ionic strength synthetic tank-waste leachate containing Sr2+ and Cs + at 10-3 mol kg-1. Analyses of bulk EXAFS spectra showed that Sr initially forms a precipitate by 7 d with a local structure similar to SrCD3-(s). At 33 d, microfocused EXAFS of individual particles in one sample revealed a mixture of hydrated and dehydrated Sr associated with neoformed sodalite-type phases. At aging times of 93 d and longer, bulk EXAFS spectra and supporting characterizations indicated nonexchangeable Sr with a local structure consistent with incorporation into increasingly crystalline aluminosilicate particles, particularly sodalite. These experimental studies suggest that irreversible trapping of radionuclides occurs if they are present during the formation and aging of feldspathoid alteration products of local Si-bearing sediment minerals. This may serve as an effective contaminant sequestration mechanism at sites such as Hanford. © 2006 American Chemical Society.
• Felicelli, S. D., Seraphin, S., & Poirier, D. R. (2006). A numerical model to simulate precipitate growth and ripening in oxygen-implanted silicon-on-insulator materials. Modelling and Simulation in Materials Science and Engineering, 14(7), 1197-1210.
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  Abstract: A finite element model was developed to simulate the production of silicon-on-insulator substrates through the technique known as SIMOX. The simulation initiates from an as-implanted distribution of SiO2 precipitates and calculates the time evolution during annealing of the number, size and shape of precipitates, until the eventual formation of the buried oxide layer under a surface-silicon layer. During the evolution, the precipitates can grow, dissolve, merge or split and they can adopt arbitrary shapes under the dynamic interaction of the oxygen concentration annealing and capillary forces. The simulations show that the model reproduces several phenomena observed during the SIMOX process, like Ostwald ripening and the formation of silicon islands. © 2006 IOP Publishing Ltd.
• Jutarosaga, T., Seraphin, S., Smith, S. M., & Wei, Y. (2006). Effect of RF-PECVD synthesis conditions on the carbon nanotube growth. Microscopy and Microanalysis, 12(SUPPL. 2), 662-663.
• Liewhiran, C., Seraphin, S., & Phanichphant, S. (2006). Synthesis of nano-sized ZnO powders by thermal decomposition of zinc acetate using Broussonetia papyrifera (L.) Vent pulp as a dispersant. Current Applied Physics, 6(3), 499-502.
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  Abstract: Nano-sized ZnO powders were synthesized by thermal decomposition of zinc acetate and Broussonetia papyrifera (L.) Vent pulp. The pulp was soaked in zinc acetate solution for 24 h. The impregnated pulp was dried at 70 °C for 48 h. The mixture was calcined for 1 h at 600, 700, 800, and 900 °C. The reaction mechanisms to form the ZnO nanoparticles were evaluated using FT-IR spectroscopy. The calcined powders were characterized by XRD, SEM, and TEM. The values of surface area were calculated from BET data. The particle sizes of ZnO in the calcined powders ranged from 10 nm to 60 nm, and the surface area was 18.93 m2/g. © 2006 Elsevier B.V. All rights reserved.
• Nuansing, W., Ninmuang, S., Jarernboon, W., Maensiri, S., & Seraphin, S. (2006). Structural characterization and morphology of electrospun TiO₂ nanofibers. Materials Science and Engineering B: Solid-State Materials for Advanced Technology, 131(1-3), 147-155.
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  Abstract: This paper reports on structural characterization and morphology of titanium dioxide (TiO2) nanofibers prepared by electrospinning using a solution that contained poly(vinyl pyrrolidone) (PVP) and titanium(diisoproproxide) bis(2,4-pentanedionate) 75 wt.% in 2-propanol. TiO2 nanofibers with diameters of 80-100 nm were successfully obtained from calcination of the as-spun TiO2/PVP composite nanofibers at above 300 °C in air for 3 h. The as-spun and calcined TiO2/PVP composite nanofibers were characterized by TG-DTA, Raman spectroscopy, XRD, SEM, AFM, and TEM. The results indicated a significant effect of calcination temperature on the crystalline phase in the form of either anatase or mixed anatase-rutile and the morphology of the nanofibers. The anatase-to-rutile transformation and the grain growth during the calcination of the electrospun TiO2/PVP composite nanofibers, as revealed by TEM, occurred simultaneously and affected each other. The rutile content was the highest (∼80%) at 800 °C, and it can be expected that the complete anatase-to-rutile transformation in the TiO2 nanofibers would be above 800 °C. © 2006 Elsevier B.V. All rights reserved.
• Seraphin, S. (2006). Review: Detection and identification of unknown substances. Microscopy and Microanalysis, 12(SUPPL. 2), 344-345.
• Choi, S., Crosson, G., Mueller, K. T., Seraphin, S., & Chorover, J. (2005). Clay mineral weathering and contaminant dynamics in a caustic aqueous system II. Mineral transformation and microscale partitioning. Geochimica et Cosmochimica Acta, 69(18), 4437-4451.
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  Abstract: Microscopic and spectroscopic studies were conducted to assess mineral transformation processes in aqueous suspensions of illite (Il), vermiculite (Vm) and montmorillonite (Mt) that were subjected to weathering in a simulated high-level radioactive tank waste leachate (0.05 M AlT, 2 M Na+, 1 M NO3-, pH ∼14, Cs+ and Sr2+ present as co-contaminants). Time series (0 to 369 d) experiments were conducted at 298 K, with initial [Cs]0 and [Sr]0 concentrations from 10-5 to 10- mol kg-. Incongruent clay dissolution resulted in an accumulation of secondary aluminosilicate precipitates identified as nitrate-sodalite, nitrate-cancrinite and zeolite X, by molecular spectroscopy and electron microscopy (XRD, IR, NMR, SEM-EDS and TEM-EDS). Contaminant fate was dependent on competing uptake to parent clays and weathering products. TEM-EDS results indicated that high Il affinity for Cs was due to adsorption at frayed edge sites. The Il system also comprised Sr-rich aluminous precipitates after 369 d reaction time. In Mt systems, Cs and Sr were co-precipitated into increasingly recalcitrant spheroidal precipitates over the course of the experiment, whereas contaminant association with montmorillonite platelets was less prevalent. In contrast, Cs and Sr were found in association with weathered Vm particles despite the formation of spheroidal aluminosilicate precipitates that were comparable to those formed from Mt. dissolution. Copyright © 2005 Elsevier Ltd.
• Jutarosaga, T., Jeoung, J. S., & Seraphin, S. (2005). Infrared spectroscopy of Si-O bonding in low-dose low-energy separation by implanted oxygen materials. Thin Solid Films, 476(2), 303-311.
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  Abstract: The effects of the processing conditions on the formation of buried oxide (BOX) layers in low-dose low-energy separation by implanted oxygen materials were investigated by using infrared spectroscopy and transmission electron microscopy. In as-implanted samples, the Si-O-Si stretching frequency increases either with increasing the oxygen dose or with decreasing implantation energy because the oxide composition becomes stoichiometric. However, the plateau frequencies were observed above a certain dose due to the compressive stress in the BOX layers. Upon ramping up to 1100 °C, the compressive stress decreases. Annealing beyond 1100 °C, the out diffusion of oxygen atoms was detected. © 2004 Elsevier B.V. All rights reserved.
• Jutarosaga, T., Manne, S., & Seraphin, S. (2005). Si-SiO₂ interface formation in low-dose low-energy separation by implanted oxygen materials. Applied Surface Science, 250(1-4), 168-181.
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  Abstract: The evolution of the Si-SiO2 interface morphology of low-dose low-energy separation by implanted oxygen materials was investigated by transmission electron microscopy and atomic force microscopy. The Si-SiO 2 interface morphology and the RMS roughness are strongly affected by the implantation conditions and the annealing process. Three main types of the domains including round, square, and pyramid shapes with the step-terrace structure were observed on the buried SiO2 surface. Round domains are observed in the early stage of the annealing process, while the square and pyramid domains are observed after the high temperature annealing. The mean RMS roughness decreases with increasing time and annealing temperature, while in the 1350 °C 4-h annealed samples, the mean RMS roughness decreases with either increasing the implantation dose or decreasing implantation energy. The scaling analysis shows that the Si-SiO2 interfaces were found to be self-affine on the short length scales with a roughness exponent above 0.50. Qualitative mechanisms of Si-SiO2 surface flattening are presented in terms of the variations of morphological features with the processing conditions. © 2005 Elsevier B.V. All rights reserved.
• Jeoung, J. S., Anderson, P., & Seraphin, S. (2003). Microstructural evolution of low-dose separation by implanted oxygen materials implanted at 65 and 100 keV. Journal of Materials Research, 18(9), 2177-2187.
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  Abstract: Thin separation by implanted oxygen substrates are attractive candidates for low-power, low-voltage electronic devices and can be obtained by low-dose, low-energy oxygen-ion implantation. We report in this study a variation of the process parameters that have never been investigated before, particularly for implantation with a high current density implanter. Characterization of the sample sets by transmission electron microscopy, secondary ion mass spectroscopy (SIMS), and Rutherford backscattering spectrometry (RBS) shows an optimum dose of 3.0 to 3.5 × 1017 O+/cm2 at 100 keV for forming a continuous buried oxide (BOX) layer compared to 2.5 × 1017 O+/cm2 at 65 keV. At this optimum condition for 100 keV, the thickness of Si top layers and BOX layers is in the range of 175-185 nm and 70-80 nm, respectively. Analysis of the breakdown voltage of small area capacitors shows a breakdown field in the range of 6.0-7.0 MV/cm, which is adequate for low-power, low-voltage devices. SIMS analysis shows that the maximum oxygen concentration of as-implanted samples is located at depths of 160 and 240 nm for the implantation energy of 65 and 100 keV, respectively. A significant redistribution of oxygen occurs at temperatures above 1300°C during the ramping process. RBS analysis showed that a high-quality crystalline Si layer was produced after annealing at 1350°C for 4 h. The defect density determined by the chemical etching method was found to be very low (
• Jutarosaga, T., Jeoung, J. S., & Seraphin, S. (2003). Buried oxide formation in low-dose low-energy SIMOX. Microscopy and Microanalysis, 9(SUPPL. 2), 504-505.
• Jeoung, J. S., Evans, R., & Seraphin, S. (2002). Microstructural evolution and defects in ultra-thin SIMOX materials during annealing. Materials Research Society Symposium - Proceedings, 716, 9-16.
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  Abstract: The microstructure of ultra-thin SIMOX depends strongly on implantation dose, energy and annealing conditions. We used TEM combined with AES and RBS to determine the microstructural evolution of SIMOX wafers subjected to various temperatures during annealing. We found that an optimum dose window to produce a continuous buried oxide layer without Si islands is 3.0-3.5×1017 O+/cm2 for 100 keV. The thickness of the silicon overlayer and BOX layer produced in this dose window was about 170 nm and 75 nm respectively. RBS analysis showed that a high quality crystalline Si layer was produced after annealing at 1350°C for 4 hrs. The defect density was very low (> 300/cm2) for all samples implanted at 100 keV.
• Johnson, B., Jeoung, J. S., Anderson, P., & Seraphin, S. (2002). Evolution of microstructure during annealing of low-dose SIMOX wafers implanted at 65 keV. Journal of Materials Science: Materials in Electronics, 13(5), 303-308.
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  Abstract: The microstructural changes that occur during annealing of ultra-thin oxygen-implanted silicon-on-insulator have been studied using transmission electron microscopy (TEM), Rutherford backscattering spectrometry (RBS), and Auger electron spectroscopy (AES). Silicon substrates were implanted at 65 kev with a dose of 4.5 × 1017 O+ cm-2, followed by annealing at various temperatures. TEM results show that the defects observed in the as-implanted material (stacking faults and {1 1 3} defects) were reduced after annealing at 900 °C for 2 h and were eliminated after annealing at 1100°C for 2 h. A continuous buried oxide (BOX) layer was formed after annealing at 1300°C for 6h. Numerous silicon islands were present in the BOX layer. The silicon islands can be traced to a precursor structure that developed at the implantation step. RBS results indicate that the crystallinity of the top Si layer is significantly restored after annealing at 1100 °C for 2 h and is completely restored after annealing at 1300°C for 6 h. It was also found through AES analysis that the redistribution of oxygen during annealing is initiated at 1100°C. © 2002 Kluwer Academic Publishers.
• Bonard, J., Seraphin, S., Wegrowe, J., Jiao, J., & Châtelain, A. (2001). Varying the size and magnetic properties of carbon-encapsulated cobalt particles. Chemical Physics Letters, 343(3-4), 251-257.
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  Abstract: Carbon-encapsulated cobalt particles were produced by a modified arc-discharge technique and subsequently purified with an acid treatment. The arc discharge was realized between a graphite cathode and a graphite crucible with a solid Co target, under partial He pressure with an additional quenching jet. The produced particles are spherical and covered by typically 3-5 graphitic carbon shells. The mean diameter could be varied between 5 and 45 nm by changing the deposition parameters (gas pressure and flow rate of the quenching jet). The magnetic properties were analyzed with a variable temperature SQUID magnetometer. The encapsulated particles showed ferromagnetic hysteresis loops with marked size-dependent properties. © 2001 Elsevier Science B.V.
• Johnson, B., Tan, Y., Anderson, P., Seraphin, S., & Anc, M. J. (2001). The Effects of Surface Capping during Annealing on the Microstructure of Ultrathin SIMOX Materials. Journal of the Electrochemical Society, 148(2), G63-G67.
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  Abstract: The effects of a protective capping layer on the microstructure of ultrathin separation by implantation of oxygen (SIMOX) materials formed by ion implantation were studied using transmission electron microscopy. A set of SIMOX wafers were implanted at 65 keV in a dose range of 1.5 to 7.0 × 1017 O+/cm2 followed by a high temperature (1350°C) annealing with and without a protective cap. The lowest dose to form a continuous buried oxide (BOX) layer without Si islands at 65 keV is 2.0 × 1017 O+/cm2 without a protective cap and 2.5 × 1017 O+/cm2 with a protective cap. Above 2.5 × 1017 O+/cm2 under both annealing conditions, the BOX layer formed continuously but with Si islands present. The uncapped samples show slightly lower density of Si islands. Oxygen from the annealing ambient can diffuse in the uncapped samples through the thin lop Si layer, which helps the BOX layer grow laterally and lower the Si island density. The density of defects in the lop Si layer is also slightly lower in the uncapped samples because of the ability of Si interstitials to incorporate into the surface and the effective annihilation of extended defects during the final annealing step. The top Si layers of the uncapped samples are thinner than those of the capped samples due to surface thermal oxidation. © 2001 The Electrochemical Society. All rights reserved.
• Tan, Y., Johnson, B., Seraphin, S., Jiao, J., Anc, M. J., & Allen, L. P. (2001). Effect of annealing conditions on the formation of low-dose SIMOX structures implanted at 190 keV. Journal of Materials Science: Materials in Electronics, 12(9), 537-542.
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  Abstract: The structure of low-dose SIMOX wafers as a function of annealing conditions has been studied using TEM. A set of samples were implanted at 190 kev with doses of 0.5, 0.83 and 1.8 × 1018 cm-2 oxygen followed by annealing treatment at different ramp rates (1 °C min-1 or 5°C min-1), temperatures (1310 °C or 1350 °C), and holding times (0 or 5 h). The results show that a higher annealing temperature (∼ 1350 °C) with a longer holding time improves the quality of the top Si layers and the smoothness of the interfaces in low-dose SIMOX wafers. A slow thermal ramp rate results in sharp interfaces but leads to a high density of Si islands in the buried oxide (BOX) layer. Chemical etching experiment performed on the top Si layer of a low-dose SIMOX shows pipeline structure indicating the inhomogeneous chemical reactivity of the top Si layer. © 2001 Kluwer Academic Publishers.
• Wang, R., Yang, J., Zheng, Z., Carducci, M. D., Jiao, J., & Seraphin, S. (2001). Dendron-controlled nucleation and growth of gold nanoparticles. Angewandte Chemie - International Edition, 40(3), 549-552.
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  Abstract: Passivation of the metal surface by dendrons bearing a focal 4-pyridone functionality (the second-generation dendron is shown; C: gray, N: blue, O: red) allows controlled nucleation and growth of gold nanoclusters. The particle size is a direct function of the generation number of the dendritic ligands, with higher generation dendron producing larger particles.
• Jiao, J., & Seraphin, S. (2000). Single-walled tubes and encapsulated nanoparticles: Comparison of structural properties of carbon nanoclusters prepared by three different methods. Journal of Physics and Chemistry of Solids, 61(7), 1055-1067.
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  Abstract: A comparative investigation of the preparation and structural properties of carbon nanoclusters was carried out by having the transition metals Fe, Co and Ni react with carbon using three different methods, with the focus on single-walled nanotubes and encapsulated nanoparticles. Carbon nanoclusters were synthesized first by the high temperature (approximately 3000 °C) and high carbon-content process of the conventional arc-discharge, secondly by the high temperature but low carbon-content process of the modified arc discharge, and finally by the relatively low temperature (approximately 500 °C) process of catalytic decomposition of carbon monoxide (CO). The samples were characterized with respect to morphology, internal structure, and related properties. The carbon nanoclusters prepared by the three different methods appear quite different on the surface, but have features in common that this report emphasizes. The same element can apparently serve different functions: (1) serving as catalyst under one set of conditions; and (2) being encapsulated into the growing cages in a different environment. The elements of the iron group (Fe, Co and Ni) were known as catalysts for growing the single-walled nanotubes and strings of spherical particles in conventional arc-discharge, but could be encapsulated into the graphitic particles in the modified arc discharge and the CO disproportion that this study demonstrates. It was found that variation of the metal to carbon ratio is required to make these elements assume the double roles of either catalyst or encapsulant.
• Jiao, J., Johnson, B., Seraphin, S., Anc, M. J., Dolan, R. P., & Cordts, B. F. (2000). Formation of Si islands in the buried oxide layers of ultra-thin SIMOX structures implanted at 65 keV. Materials Science and Engineering B: Solid-State Materials for Advanced Technology, 72(2), 150-155.
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  Abstract: The microstructures of separation by implanted oxygen (SIMOX) wafers, implanted at 65 keV with doses of 1.5-7.0 × 1017 O+/cm2 at 500°C followed by a high temperature (1350°C) annealing with and without a protective cap, were studied using transmission electron microscopy to investigate the relationship between the formation of ultra-thin SIMOX structures and a variety of different preparation parameters. The study found that there is an optimum dose range corresponding to the implantation energy used. The samples synthesized at an oxygen dose of 2 × 1017 O+/cm2 (annealed without a cap) or 2.5 × 1017 O+/cm2 (annealed with a cap) consist of a thin silicon top layer with a low threading dislocation density, and a thin continuous buried oxide (BOX) layer free of Si islands. For samples implanted below the optimum dose, the BOX layer is discontinuous. Capping or non-capping the sample surface during annealing affects the formation of the BOX layer. For samples without a cap, internal thermal oxidation happens even in an ambient of low concentration of oxygen and makes the BOX layer grow continuously and free of Si islands.
• Guangming, L. i., Jiao, J., Seraphin, S., Raghavan, S., & Jeon, J. S. (1999). Masking effect of copper during anisotropic etching of silicon in buffered hydrofluoric acid solutions. Journal of Applied Physics, 85(3), 1857-1863.
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  Abstract: The etching characteristics of silicon samples of (100) orientation in buffered hydrofluoric acid (BHF) solutions containing different levels of dissolved copper were studied systematically using atomic force microscopy, total reflection x-ray fluorescence, inductively coupled plasma mass spectroscopy and transmission electron microscopy techniques. It was found that the presence of trace amounts of copper ions in BHF solutions can cause not only metallic contamination but also very severe surface roughness. Copper deposits onto the silicon surfaces in the form of submonoatomic layer clusters which act as masks during silicon anisotropic etching in BHF solutions. Surface roughness as high as 12 nm was generated in 30 min of etching in buffered hydrofluoric acid solution containing 100 ppb Cu2+. Cross-sectional TEM micrographs showed that silicon was etched anisotropically in BHF solutions containing Cu 2+ ions. Etching rates as high as 1.0 nm/min were obtained on the (100) planes of p-type silicon in the presence of a 100 ppb Cu2+. The size of the etching structures depends on the Cu2+ concentration in solution and the etching time. © 1999 American Institute of Physics.
• Seraphin, S., Beeli, C., Bonard, J. -., Jiao, J., Stadelmann, P. A., & Châtelain, A. (1999). Magnetization of carbon-coated ferromagnetic nanoclusters determined by electron holography. Journal of Materials Research, 14(7), 2861-2870.
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  Abstract: The magnetic properties of carbon-coated Co and Ni nanoparticles aligned in chains were determined using transmission electron holography. The measurements of the phase change of the electron wave due to the magnetization of the sample were performed. The ratio of remnant magnetization to bulk saturation magnetization Mr/Ms of Co decreased from 53% to 16% and of Ni decreased from 70% to 30% as the particle diameter increased from 25 to 90 nm. It was evident that the inhomogenous magnetic configurations could diminish the stray field of the particles. After being exposed to a 2-Tesla external magnetic field, the Mr/Ms of Co increased by 45% from the original values with the same dependency on the particle size. The Mr/Ms of Ni particles, on the other hand, increased only 10%. The increased magnetization could be attributed to the merging of small domains into larger ones after the exposure to the external magnetic field. The validity of the interpretation of the holograms was established by simulation.
• Allen, L. P., Anc, M. J., Jiao, J., Guss, B., Seraphin, S., Liu, S. T., & Jenkins, W. (1998). Buried oxide densification for low power, low voltage CMOS applications. IEEE International SOI Conference, 39-40.
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  Abstract: The properties of 120 nm BOX (buried oxide) and 360 nm SIMOX (separation by implantation of oxygen) were examined as a function of anneal ramp rate and temperature. The slower ramp rate (1 °C/min) contributed to the reduction of islands within the buried oxide layer. Both the slow ramp rate and high temperature (1350 °C) of anneal decreased the interface roughness of the Si/BOX interface in both materials. Results of the `island free' thin BOX layer showed a 30 V reduction in the threshold voltage shift upon irradiation to 1 Mrad with consistent gate oxide integrity.
• Anc, M. J., Farley, M., Jiao, J., Seraphin, S., Kirchhoff, J., McMarr, P. J., & Hughes, H. L. (1998). High quality low-dose low-energy SIMOX implanted in high current oxygen implanter. IEEE International SOI Conference, 41-42.
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  Abstract: Separation by implantation of oxygen (SIMOX) structures were formed with an ion energy of 65 keV in Ibis 1000 high current oxygen implanter. The Si substrate temperature was 500 °C and beam current was 40 mA during implantation. Doses in the range of 0.15×1018 to 0.7×1018 O+/cm2 were implanted into the 〈100〉, p-type 10-20 Ohm-cm, 150 mm-diameter Si wafers. Implanted wafers were annealed at 1350 °C in Ar and the defect density of the Si layer was determined using the enhanced Secco etch technique and optical microscopy. The integrity of the buried oxide (BOX) was examined by measuring the current-voltage characteristics of the BOX capacitors.
• Jiao, J., & Seraphin, S. (1998). Carbon encapsulated nanoparticles of Ni, Co, Cu, and Ti. Journal of Applied Physics, 83(5), 2442-2448.
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  Abstract: Despite intensive research on the encapsulation of metal nanoparticles into carbon clusters deposited by arc discharge, the detailed pathways of the formation of these novel forms of materials remain unclear. The growth of a rich variety of morphologies is not well understood. Studies are reported here on the growth phenomena of different metals encapsulated into carbon cages that emphasize the effect of carbon and metal supply on the size of particles. Post-deposition annealing was introduced as a process that induces structural rearrangements, and thus enables changes in morphologies. A set of carbon encapsulated Ni, Co, Cu, and Ti particles were prepared by an arc discharge process modified in the geometry of the anode and flow pattern of helium or methane gas. The samples were then annealed under flowing argon gas. Three annealing temperatures were used (600, 900, and 1100 °C). Samples were characterized by transmission and scanning electron microscopy. Particles made under the same experimental conditions are of roughly the same size. When the supply of metal in the reactor space was increased by using a larger diameter of the metal pool, the average diameter of the particles is bigger than those of produced from the smaller metal pool. The thickness of the carbon cages of Ni and Co particles increased during the annealing. The carbon cages of Cu particles, however, did not change their thickness, while some carbon coatings of Ti particles disappeared under annealing. This suggests that the addition of layers for the Ni and Co cages results from a precipitation of carbon previously dissolved in the metal, while the much lower solubility of C in Cu prevents this possibility. The Ti of high reactivity, on the other hand, may further react with the available carbon under annealing to form TiC. It is suggested that annealing provides additional thermal energy that makes structural re-arrangement possible long after the initial deposition process was terminated. This may explain the rich variety of morphologies of deposit obtained at different locations of the reaction chamber. © 1998 American Institute of Physics.
• Jiao, J., & Seraphin, S. (1998). Tailoring carbon nanoclusters to desired morphologies. Journal of Materials Research, 13(9), 2438-2444.
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  Abstract: The preparation and structural characterization of carbon nanoclusters of different morphologies produced by three different methods and under a variety of conditions is reported. In a comparative manner, the growth phenomena and structural properties of carbon nanoclusters are investigated as synthesized by (a) the high temperature (∼3000°C) and high carbon-content process of the conventional arc-discharge, (b) the high temperature but low carbon-content process of the modified arc-discharge, and finally (c) the relatively low temperature (∼500°C) process of Ni catalytic disproportionation of carbon monoxide.
• S., M., & Seraphin, S. (1998). Heavy metal biomineralization in free-living nematodes, Panagrolaimus spp. Materials Science and Engineering C, 6(1), 47-51.
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  Abstract: Grass-inhabiting free-living nematodes, Panagrolaimus spp. were found to biomineralize lead heavy metal. Cultures of two isolates of Panagrolaimus superbus, collected from Oxford, UK and Tucson, Arizona, were exposed to 500 ppm lead for an exposure time of 20 min. Control worms were exposed to deionized water. TEM sections taken from the oesophageal region revealed the presence of metal particulates in lead exposed nematodes only. X-ray elemental analysis confirmed the presence of lead in the particulates. This is the first account of heavy metal biomineralization in nematodes. © 1998 Published by Elsevier Science S.A. All rights reserved.
• Jiao, J., & Seraphin, S. (1996). Internal structure and stability of carbon nanoclusters: Arc discharge preparation versus CO disproportionation. Chemical Physics Letters, 249(1-2), 92-100.
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  Abstract: Carbon nanoclusters prepared at high temperature by arc discharge, and at low temperature by CO disproportionation with and without hydrogen present, were compared in their morphology, internal structures, and stability. Electron microscopy shows similar external morphology in the three different sample types, with the internal structures different depending on the preparation conditions. These differences result in different stabilities. Nanotubes of cylindrical structure are stable to annealing at 1000°C in both helium and hydrogen atmosphere. Two-minute electron bombardment disordered tubes slightly. However, filaments of conical fishbon structure deposited in the presence of hydrogen, significantly deform under the same conditions.
• Jiao, J., Nolan, P. E., Seraphin, S., Cutler, A. H., & Lynch, D. C. (1996). Morphology of carbon nanoclusters prepared by catalytic disproportionation of carbon monoxide. Journal of the Electrochemical Society, 143(3), 932-935.
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  Abstract: Catalytic disproportionation of carbon monoxide has long been established as a method for producing graphitic deposits. Using this method, a set of samples was prepared under a variety of the process parameters: temperature, CO/CO2 ratio, hydrogen partial pressure, and duration of reaction. The morphology of the product has been characterized using both scanning electron microscopy and transmission electron microscopy, with similarities found between the CO disproportionation deposits, and the nanoclusters produced by arc discharge. In particular, the analysis revealed multiwalled, concentric hollow core nanotubes in which the layers are separated by 0.34 nm, the distance associated with separation between graphitic basal planes. The catalytically produced nanotubes are in general much longer than those typically produced in an arc discharge while other properties are almost identical. Their morphology depends on the choice of the process parameters, particularly the partial pressure of hydrogen. With no hydrogen present, only closed forms of carbon deposits such as multiwalled nanotubes are produced. As the partial pressure of hydrogen is increased, the filament-type carbon deposits with open edges are observed. The number of open edges increases with increasing H2 concentration. However, for a given hydrogen concentration, the number of open edges decreases as the reaction temperature is raised. Extending the reaction time creates longer nanotubes, reaching an average length of 10 μm after 48 h. Employing this low-temperature method for the production of nanotubes, one can expect ultimately to establish control of their morphology through variations of easily tunable process parameters.
• Jiao, J., Seraphin, S., Wang, X., & Withers, J. C. (1996). Preparation and properties of ferromagnetic carbon-coated Fe, Co, and Ni nanoparticles. Journal of Applied Physics, 80(1), 103-108.
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  Abstract: Carbon-coated iron, cobalt, and nickel particles were produced by an arc discharge process modified in the geometry of the anode and the flow pattern of helium gas. Field emission scanning electron microscopy shows that the resulting material consists of only carbon-coated metal particles without any nanotubes or other unwanted carbon formations present. The diameters of iron, cobalt, and nickel particles range predominantly from 32 to 81 nm, 22 to 64 nm, and 16 to 51 nm, respectively. X-ray diffraction analysis confirmed that the as-made particles are carbon-coated elements rather than metal carbides. High resolution transmission electron microscopy reveals that the as-made cobalt and nickel particles are covered by 1-2 graphitic layers, while iron particles are surrounded by amorphous carbon. When the samples were treated by annealing or immersion into nitric acid, particles completely coated by carbon resisted both postdeposition treatments. However, further graphitization of the carbon coating by either of the two treatments was observed. Particles only partially coated by carbon were not protected, but sintered by annealing or dissolved in the acid. The magnetic properties of the as-made particles were measured by a vibrating sample magnetometer. The values of the saturation magnetic moment per gram of each type of metal particle are 56.21, 114.13, and 34.9 emu/g representing 26%, 71%, and 64% of the saturation moments of the bulk ferromagnetic elements iron, cobalt, and nickel, respectively. All the metal particles were shown to be ferromagnetic with a ratio of remnant to saturation magnetization MR/MS∼0.3 at room temperature (25 °C). In this article the detailed preparation and the properties of these carbon-coated metal particles will be discussed. © 1996 American Institute of Physics.
• Seraphin, S., Zhou, D., & Jiao, J. (1996). Filling the carbon nanocages. Journal of Applied Physics, 80(4), 2097-2104.
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  Abstract: Twenty elements were codeposited with carbon in an arc discharge between graphite electrodes. The majority of them were evaporated from composite anodes that contained the elements or their oxides stuffed into central bores in the graphite rods. The deposits, found in the soot at the reactor walls or as slag at the cathode, were characterized using scanning and transmission electron microscopy, electron energy loss spectroscopy, and x-ray diffraction. The products fall into four categories: (1) elements that can be encapsulated in the form of their carbides (B, V, Cr, Mn, Y, Zr, Nb, Mo); (2) elements that are not encapsulated but tolerate the formation of graphitic carbon cages (Cu, Zn, Pd, Ag, Pt); (3) elements that form stable carbides, competing with and pre-empting the carbon supply for the graphitic cage formation (Al, Si, Ti, W); and (4) the iron-group metals (Fe, Co, Ni) that stimulate the formation of single-walled tubes and strings of nanobeads in the conventional arc discharge condition, and produce the nanometer-size carbon-coated ferromagnetic particles in a modified arc discharge in which metals are in molten form in graphite crucible anodes exposed to a helium jet stream. The criterion determining the formation according to one of the four categories is discussed on the basis of this extended study. It is apparent that the physical properties such as vapor pressure, melting and boiling points, the completeness of the electronic shells of the elements, or their heat of carbide formation are not sufficient to explain the selectivity of the encapsulation without exceptions. A hypothesis is advanced that emphasizes the existence of the carbide, interfacial compatibility with the graphitic network, as well as the transport and supply parameters in the reaction space. © 1996 American Institute of Physics.
• Withers, J. C., Guha, S., Loutfy, R., Lowe, T., Wang, X., Jiao, J., & Seraphin, S. (1996). Environmentally inert nano-crystalline materials. Materials and Manufacturing Processes, 11(6), 1013-1028.
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  Abstract: A novel process to generate environmentally-inert nano-crystalline materials is discussed here. In this process, nano-crystals of different metals such as Ni, Cu, Al, Ti etc. can be produced in a single processing step with each crystal protected by several carbon (graphite) layers. The technology is an adaptation of the arc technique utilized to produce carbon nano-crystals (Fullerenes) and can be controlled to produce nano-crystals with a variety of coatings including graphite. These nano-crystals are in the 10-50 nm diameter range (typically 30 nm) and of uniform size distribution. These nano-crystals were chemically stable in air and inert to various acids. Further, initial (unoptimized) experiments demonstrated the feasibility of consolidating these coated nano-particles using conventional processing approaches. Novel applications of these nano-crystals such as in the magnetic recording industry are also discussed here.
• Seraphin, S. (1995). Single-walled tubes and encapsulation of nanocrystals into carbon clusters. Journal of the Electrochemical Society, 142(1), 290-297.
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  Abstract: Single-walled carbon nanotubes can be prepared in an arc discharge between graphite electrodes of which the anode contains transition metals and their mixtures. Gram-quantities of single-walled tubes (SWT) can be obtained when a mixture of Fe/Ni, Fe/Co, or Ni/Co is used in the anode. Diameters of the SWT produced from Ni or Fe fall in the range of 0.70 to 1.00 nm compared to 0.85 to 1.30 nm of those produced with mixed Fe/Ni or Ni/Co. The SWT are a few microns long and capped at both ends. They do not associate directly to the metal particles. In contract, YC2 filled anode produced short SWT radiating from the YC2 particles. For B, Mg, Mn, Fe, Co, Ni, Cu, Y, Nb, Mo, and Ta, crystals of the carbides are encapsulated into the growing carbon nanoclusters. For Si, Cr, Zn, Pd, Ag, W, and Pt the nanotubes are formed but no encapsulation is observed. The presence of Ti, however, inhibits the formation of the carbon cages. The thermodynamics of the formation of the carbides is considered to set criteria and predict the encapsulation into the nanotubes. The growth of the strings of beads is discussed in conjunction with existing growth models.
• Zhou, D., & Seraphin, S. (1995). Complex branching phenomena in the growth of carbon nanotubes. Chemical Physics Letters, 238(4-6), 286-289.
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  Abstract: We report here the experimental observation of complex branching phenomena in the growth of carbon nanotubes produced under specific arc-discharge conditions. High-resolution transmission electron microscopy (HRTEM) images demonstrate that two or three carbon nanotubes can join together under specific angles in L, Y, and T patterns with saddle surfaces at the junction. Adding to the observation of negative curvature surface in straight-line tubes that change their diameters, we report here negative curved areas that support the topography of a branching structure. © 1995.
• Zhou, D., Seraphin, S., & Withers, J. C. (1995). Encapsulation of crystalline boron carbide into graphitic nanoclusters from the arc-discharge soot. Chemical Physics Letters, 234(1-3), 233-239.
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  Abstract: Boron carbide crystals were encapsulated into multiwalled graphitic carbon clusters that were prepared from a boron-containing composite anode by utilizing arc-discharge. The encapsulants are compounds of the lightest element that has yet been encapsulated, and the first of the non-metallic. The encapsulated multiwalled clusters are predominantly observed in the soot, a location where rarely graphitic multiwalled structures have ever been found before. The known tendency of boron to catalyze graphitization can possibly explain this observation. © 1995.
• Seraphin, S. (1994). Defects in oxygen implanted silicon. Solar Energy Materials and Solar Cells, 32(4), 343-349.
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  Abstract: Silicon-based devices in their various representations use ion implantation for the electronic modification of the basic material. The defects and their formation by ion beam must be identified and minimized to obtain a useful product. We report the characterization of defects formed during oxygen implantation of silicon using conventional and high-resolution transmission electron microscopy. The effect of water temperature as the parameter most influential on type and density of defects was investigated. The study revealed that microtwins and stacking faults were created in the top silicon layer during implantation from 450-550°C. From 600-700°C, numerous multiply faulted defects were observed. They are 40 to 140 nm long and consist of several discontinuous stacking faults which are randomly spaced and separated by six to twelve atomic layers. In the substrate region beneath the buried oxide layer created by implantation, the defects observed included stacking faults and {113} defects. Some parts of the {113} defects show a twinning structure across {115} planes. Some are converted into a hexagonal structure. After annealing at 1300°C for 6 hours in argon, samples implanted at 450-575°C contain dislocation densities higher than those implanted 575°C. Details of the structure and formation mechanisms of these defects will be discussed. © 1984.
• Seraphin, S., & Zhou, D. (1994). Single-walled carbon nanotubes produced at high yield by mixed catalysts. Applied Physics Letters, 64(16), 2087-2089.
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  Abstract: We report here on the high-density preparation of single-wall tubes in the presence of mixed catalysts of the types Fe/Ni and Co/Ni, in the soot as well as in the weblike deposits forming in the chamber. The yield is much higher than previously reported, and gram quantities can be obtained. Diameters cover the range from 0.9 to 3.1 nm, larger than previously reported, with the histogram showing only one peak at 1.7 nm. Evidence of an epitaxial action between C 60 and single-walled nanotubes is presented. Results from the mixed catalysts Co/Cu, Ni/Mg, and Ni/Ti are also reported.
• Seraphin, S., Wang, S., Zhou, D., & Jiao, J. (1994). Strings of spherical carbon clusters grown in a catalytic arc discharge. Chemical Physics Letters, 228(6), 506-512.
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  Abstract: Strings of near-spherical, multiwalled carbon clusters grow in a carbon arc discharge when nickel or iron is present. They consist of ten to twenty 'beads' of 10-20 nm diameter, nearly equal in the same string. They touch and deform each other in the contact areas, carrying a nickel or iron particle of approximately the bead diameter at one end. Termination by a catalyst particle is common to catalytically grown carbon nanofibers. However, the phenomenon reported here lacks continuity of fiber growth at the metal-graphitic interface, and requires a different explanation for the interrupted, repetitive sequence of near-spherical cluster growth. © 1994.
• Seraphin, S., Zhou, D., Jiao, J., Minke, M. A., Wang, S., Yadav, T., & Withers, J. C. (1994). Catalytic role of nickel, palladium, and platinum in the formation of carbon nanoclusters. Chemical Physics Letters, 217(3), 191-195.
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  Abstract: Carbon clusters were prepared by arc discharge from graphite anodes containing nickel, palladium, and platinum at conditions favoring nanotube production. All three metals led to very little encapsulation of themselves or their compounds into the carbon nanoclusters under the conditions studied. However, the characters of the samples, collected from the cathodic deposits as well as from the soot, were different for the three metal-filled rods. Nickel-filled anode stimulated the growth of single-walled nanotubes and also catalyzed the formation of strings of spherical carbon clusters. The growth mechanism of the strings of spherical clusters is proposed. Platinum-filled anode produced the highest density of nanotubes in the slag. Palladium-filled anode generates the same yield of fullerenes as pure graphite but shifts the ratio of fullerenes by enhancing the yield of C70 and higher-order fullerenes. © 1994.
• Yadav, T., Withers, J. C., Seraphin, S., Wang, S., & Zhou, D. (1994). Synthesis of single walled buckytubes. Materials Research Society Symposium - Proceedings, 349, 275-281.
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  Abstract: We report here a study of alternative methods for producing single walled buckytubes. In this study, we prepared graphite electrodes packed with different metal or metal combinations. These electrodes were arced under similar conditions and the products so formed characterized with TEM. The results demonstrate that single walled tubes can be synthesized in many ways and at high yields. The results also suggest that the use of more than a single dopant may provide significant advantages in the commercial synthesis of buckytubes.
• Zhou, D., & Seraphin, S. (1994). Imaging of carbon nanoclusters by high-resolution scanning electron microscopy. Microscopy Research and Technique, 29(1), 69-70.
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  PMID: 8000087;
• Zhou, D., & Seraphin, S. (1994). Production of silicon carbide whiskers from carbon nanoclusters. Chemical Physics Letters, 222(3), 233-238.
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  Abstract: We report on a method to produce SiC whiskers without the presence of metal catalysts by reacting carbon nanoclusters with SiO at 1700°C. The dark carbon nanotubes with hollow cores are converted to solid greenish SiC whiskers. Electron diffraction and EDX confirm that the product is SiC with a single crystalline hexagonal phase. TEM reveals the lattice image of the whisker with numerous defects. The formation of SiC whiskers produced from carbon nanotubes without using metal catalyst strongly suggests that the reactivity and atomic configuration of carbon nanotubes are crucial to the formation of whiskers. © 1994.
• Zhou, D., Seraphin, S., & Wang, S. (1994). Growth phenomena of carbon nanotubes produced by arc-discharge. Materials Research Society Symposium - Proceedings, 349, 257-262.
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  Abstract: Based on the high resolution TEM observations, we report here on the non-concentric growth phenomena of carbon nanotubes from the arc-discharge. We also report on a novel form of carbon nanoclusters - the strings of carbon nanobeads - produced by the catalytic arc-discharge with Ni as the catalyst, and on the bundles of single-walled carbon nanotubes, synthesized with YC2 as the catalyst, growing radially out from YC2 particles.
• Zhou, D., Seraphin, S., & Wang, S. (1994). Single-walled carbon nanotubes growing radially from YC₂ particles. Applied Physics Letters, 65(12), 1593-1595.
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  Abstract: In the primary soot produced by arc discharge using an yttrium carbide loaded anode, bundles of single-walled carbon nanotubes (SWT) are observed, protruding radially from YC2 particles coated with graphitic multilayers. The graphitic cages separating YC2 particle and SWT bundles fall into the narrow range of 10-20 layers. The morphology of the clusters suggests a two-step growth model: The radial SWT growth pattern is first initiated by catalytic action between the YC2 droplet and the carbon in the gas phase. Second, and upon cooling, the graphitic cage starts by segregating excess carbon from the YC2 bulk, arresting further growth of SWT.
• Zhou, D., Wang, S., & Seraphin, S. (1994). Single-walled carbon nanotubes grown from yttrium carbide particles. Proceedings - Annual Meeting, Microscopy Society of America, 772-773.
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  Abstract: The discovery of clusters of single-walled carbon nanotubes from arc-discharge experiments with yttrium carbide as catalyst is discussed. The clusters are arranged around nuclei of yttrium carbides in a radiolarian pattern and are present in large quantities in the primary soot. After the arc-discharge experiment, the black carbon soot was retrieved from the inner surface of the reaction chamber. The primary soot was dispersed ultrasonically in acetone and placed on holey carbon substrate for transmission electron microscopy. The morphology of the soot reveals that the primary soot contains substantial quantities of single crystalline yttrium carbide, and that a novel form of single-walled carbon nanotubes extends radially from these particles.
• Zhou, D., Wang, S., Seraphin, S., & Withers, J. C. (1994). High-density production of carbon nanotubes in contact arc-discharge at low helium pressure. Materials Research Society Symposium - Proceedings, 349, 337-342.
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  Abstract: We report here on the structural properties of carbon nanotubes prepared by contact arc-discharge at low helium pressure of 100 torr. In contrast to the conventional arc-discharge, the contact discharge reduces the gap between the electrodes to a minimum value while still maintaining a plasma. The resulting carbonaceous deposit on the cathode surface, with the contact discharge operating under 100 torr helium atmosphere, contains the columnar structures with high density carbon nanotubes. These columnar structures are several millimeters in length, much longer than those generated under the conventional arc-discharge. These experimental results reveal that reducing the gap adds greater stability to the arc-discharge and establishes conditions that favor high-density nanotube growth under a low helium pressure.
• Gallagher, M. J., Chen, D., Jacobsen, B. P., Sarid, D., Lamb, L. D., Tinker, F. A., Jiao, J., Huffman, D. R., Seraphin, S., & Zhou, D. (1993). Characterization of carbon nanotubes by scanning probe microscopy. Surface Science, 281(3), L335-L340.
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  Abstract: Carbon nanotubes, fabricated by the Ebbesen-Ajayan method, were imaged using scanning tunneling microscopy (STM) and atomic force microscopy (AFM) in air and were compared to images obtained with high-resolution transmission electron microscopy (HRTEM). The HRTEM images revealed an abundance of elongated structures ranging in diameter from 3.0 to 30 nm, and with lengths of up to 0.8 μm. Many of the structures possessed several graphitic shells as if the tubes were nested one in the other. Reproducible images of the tubular structures, typically 20 nm in diameter and with a large variation in length, were obtained with both STM and AFM when the nanotubes were deposited on hydrogen-terminated Si(111), confirming that the nested structures observed with HRTEM do indeed have a tubular morphology. No single-walled, bare nanotubes or spherical fullerenes (typical of the Krätschmer-Huffman process) were observed. © 1993.
• Seraphin, S., Zhou, D., & Jiao, J. (1993). Electron-beam-induced structural changes in crystalline C₆₀ and C₇₀. Journal of Materials Research, 8(8), 1895-1899.
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  Abstract: High-resolution transmission electron microscopy (HRTEM), electron diffraction, and electron energy-loss spectroscopy (EELS) were used to characterize electron-beam-induced structural transformations in crystalline samples of C60 and C70. During these transformations, the electron-diffraction patterns became progressively more diffuse, with the outer diffraction spots disappearing first, followed in succession by the disappearance of the inner spots. We interpret this course of evolution in the diffraction patterns as evidence of degradation of the crystalline structure via the destruction of individual molecules, as opposed to electron-beam-induced motion of intact fullerene molecules. EELS analyses of the data indicate that the final state of these transformations was amorphous carbon.
• Seraphin, S., Zhou, D., & Jiao, J. (1993). Insertion of yttrium carbide into carbon nanoclusters by vapor transport during growth. Proceedings - Annual Meeting, Microscopy Society of America, 758-759.
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  Abstract: Reported in this study is a method for filling carbon clusters of various shapes in situ through vapor transport from a composite anode of a graphite rode filled with yttrium oxide paste at a center hole. Electron energy-loss spectroscopy (EELS) was performed by placing the electron beam of nanometer size on the filling material inside a narrow channel of the tube.
• Seraphin, S., Zhou, D., & Jiao, J. (1993). Morphology and yield of carbon clusters in arc-discharge deposits. Carbon, 31(7), 1212-1216.
• Seraphin, S., Zhou, D., Jiao, J., Withers, J. C., & Loutfy, R. (1993). Effect of processing conditions on the morphology and yield of carbon nanotubes. Carbon, 31(5), 685-689.
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  Abstract: Morphology and fractional yield of carbon nanotubes depend strongly on the gas pressure in the reaction zone, as well as the current density driven by different potentials across the electrodes. We report results on the correlation caused by variations in the processing conditions, using transmission electron microscopy. In addition to nanotubes, we observed various shapes of graphitic particles such as tetrahedra and polyhedra. © 1993.
• Seraphin, S., Zhou, D., Jiao, J., Withers, J. C., & Loutfy, R. (1993). Selective encapsulation of the carbides of yttrium and titanium into carbon nanoclusters. Applied Physics Letters, 63(15), 2073-2075.
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  Abstract: Characterization of the arc-discharge deposits at the cathode from anodes containing yttrium oxide and titanium by transmission electron microscopy and x-ray diffraction shows different results with respect to an encapsulation of the metal carbides into carbon clusters. Yttrium carbide is encapsulated into carbon nanoclusters in a crystalline phase. The formation of titanium carbide, on the other hand, preempts the formation of the carbon - carbon bonds necessary to form the carbon cages, so that only titanium carbide clusters are observed. Thermodynamic data support the interpretation of the results.
• Seraphin, S., Zhou, D., Jiao, J., Withers, J. C., & Loutfy, R. (1993). Yttrium carbide in nanotubes [6]. Nature, 362(6420), 503-.
• Zhou, D., Seraphin, S., & Jiao, J. (1993). SEM study of structure and formation of the carbon cluster in the arc-discharge deposits. Proceedings - Annual Meeting, Microscopy Society of America, 756-757.
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  Abstract: The paper presents a scanning electron microscopy (SEM) study of the topography of the deposits at the graphite cathode, and attempts to correlate the growth behavior of nanotubes to the structural elements of the cathode surface.
• Seraphin, S., & F., B. (1992). TEM analysis of SIMOX produced by multiple implantation and annealing. 1991 IEEE International SOI Conference Proceedings, 86-87.
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  Abstract: The authors present a TEM (transmission electron microscopy) analysis of the structural evolution of SIMOX (separation by implanted oxygen) through three subsequent implantation/anneal cycles. Optimizing the process parameters on the basis of the TEM analysis resulted in a better understanding of the mechanisms of defect formation, and the reduction of defect density. The structural evolution of defects through the processing steps is described. A set of silicon (100) wafers was prepared in six steps with implantation and anneal alternating three times. The oxygen doses of the three implantation steps were 5 × 1017, 5 × 1017, and 8 × 1017 cm-2. All implantations were performed at 200 keV, 620°C, and at a current density of 1 mA/cm2. The anneals after each implant were carried out at 1300°C for 6 h in an argon atmosphere. After each implantation and anneal step the wafers were examined by TEM with a Philips 420 at 100 keV.
• Nielsen, B., Lynn, K. G., Leung, T. C., Cordts, B. F., & Seraphin, S. (1991). Defects in oxygen-implanted silicon-on-insulator structures probed with positrons. Physical Review B, 44(4), 1812-1816.
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  Abstract: Defects in a silicon-on-insulator structure formed by high-energy (200-keV) oxygen implantation has been studied utilizing a variable-energy positron beam. The positron-based probe is found to be especially sensitive to the condition of the top Si layer. Open-volume defects (cavities) are detected in the top 80-nm Si layer in the as-irradiated state. The majority of these defects are removed by high-temperature annealing (1300°C) after which the positron response correlates with the density of dislocations observed by transmission electron microscopy. Variations in dislocation density across a wafer were probed with positrons, demonstrating the potential of positrons in defect topology. © 1991 The American Physical Society.
• Seraphin, S., Krause, S. J., Roitman, P., Simons, D. S., & Cordts, B. F. (1991). Effect of annealing ambient on the removal of oxide precipitates in high-dose oxygen implanted silicon. Applied Physics Letters, 59(23), 3003-3005.
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  Abstract: The effect of annealing ambient on the precipitate removal processes in high-dose oxygen implanted silicon [separation by implantation of oxygen (SIMOX)] has been studied with transmission electron microscopy, electron energy-loss spectroscopy, and secondary ion mass spectroscopy. The rate of removal of oxide precipitates from the top silicon layer in SIMOX is higher during annealing in argon than in nitrogen. The removal is reduced in nitrogen due to the formation of an oxynitride complex at the precipitate surfaces which inhibits oxygen diffusion across the interfaces. Similar effects have been observed for oxide precipitation during nitrogen ambient annealing in bulk silicon.