bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermoelectric properties of icosahedral cluster solids – Metallic-Covalent Bonding Conversion and Weakly Bonded Rigid Heavy Clusters
Authors: Kimura Kaoru , Okada Junpei Tamura , Kim Hongki , Hamamatsu Takehito , Nagata Tomohiro , Kirihara Kazuhiro
Published: April 2011

Boron- or Aluminum-rich icosahedral cluster solids (ICS) consist mainly of B12 or Al12 icosahedral clusters. In the ICS, a slight change of the structure or environment of icosahedral cluster can cause metallic-covalent bonding conversion, which can cause that the electrical conductivity σ and the Seebeck coefficient S can be as high as those of metals and semiconductors, respectively. Five-fold symmetry of the icosahedral cluster does not match with the translational symmetry of a crystal, consequently makes lower thermal conductivity with complex structure. For these reasons, ICS are promising candidates for thermoelectric materials.

Using MEM/Rietvelt method, we successfully obtained the clear image of the electron density distribution for alpha-AlReSi approximant crystal. The bond strength distributes widely from weak metallic to strong covalent bond, and the intra-cluster bonds are stronger than the inter-cluster ones. This means that alpha-AlReSi is located at the intermediate state of molecular, metallic- and covalent-bonded solids. Composition dependences of atomic density and quasi-lattice constant for AlPdRe icosahedral quasicrystals show the above situation is the same in the quasicrystals. The thermoelectric figure of merit Z and the effective mass m* of AlPdRe quasicrystals can be increased by strengthening the intra- and weakening the inter-cluster bonds. According to this scenario, Z was improved by a factor of 1.5 by substitution of Ru for Re.

In β-rhombohedral boron, several interstitial sites, which have space large enough to accommodate foreign atoms, are known. For the V doped sample, in which V atoms mainly occupy A1 site, the metallic-covalent bonding conversion may occur, σ is increased very much, S is decreased even to negative value and kappa is decreased. The maximum and n-type ZT value is obtained and is approaching to that of B4C, which is considered to have the largest and p-type ZT value in boron-rich ICS.
Thermoelectric Properties of K2Bi8Se13−xSx Solid Solutions
Authors: Kyratsi Theodora , Lal Sangeeta , Hogan Tim , Kanatzidis Mercouri G.
Published: April 2011

Derivatives of β-K2Bi8Se13 are an interesting series of materials for thermoelectric investigations due to their very low thermal conductivity and highly anisotropic electrical properties. Up to now substitutions on the Bi and alkali metal sites have been studied in order to tune the thermoelectric properties. In this work, the thermoelectric properties of the sulfur-substituted K2Bi8Se13−xSx (0<x<13) are presented with respect to Seebeck coefficient, the electrical and thermal conductivity as a function of temperature. Seebeck coefficient measurements showed the n-type character of all members while electrical conductivity shows higher values compare to the other solid solution series of the same type. The lattice thermal conductivity is affected due to the Se/S disorder. The temperature dependence of the figure-of-merit ZT shows that these materials have potential for high temperatures applications with promising thermoelectric performance.
High Temperature Thermoelectric Properies of LnPdX (Ln = lanthanide; X = Sb, Bi) Ternary Compounds
Authors: Sekimoto Takeyuki , Kurosaki Ken , Muta Hiroaki , Yamanaka Shinsuke
Published: April 2011

Ternary compounds LnPdX (Ln = lanthanide elements of La, Gd, Er; X = Sb, Bi) were prepared by a spark plasma sintering (SPS) technique. The crystal structure of LaPdSb and GdPdSb was confirmed to be a hexagonal ZrBeSi-type structure and different from the other compounds with a MgAgAs-type structure. The electrical resistivities ρ of LaPdSb and GdPdSb indicate the metallic or semimetallic characteristics, while those of ErPdSb and LnPdBi indicate semiconductor characteristics. From the ln ρ − 1/T plot, the band gap energies Eg were estimated to be 0.28, 0.053, 0.081, and 0.049 eV for ErPdSb, LaPdBi, GdPdBi, and ErPdBi, respectively. All the samples have positive thermoelectric powers S above room temperature. The largest power factor S2/ρ was obtained as 49.5 μW/K2 cm at 327 K for LaPdSb. From the Hall effect measurements on ErPdX, the carrier concentration n of ErPdSb and ErPdBi were obtained as 5.9×1018 and 3.21×1019 cm−3 at room temperature, respectively. It is considered that the difference of n at room temperature is mainly due to the magnitude of the band gap energy.
Investigation of Low Resistance Contacts to Pb-Sb-Ag-Te (LAST) Materials for Module Fabrication
Authors: D'Angelo Jonathan , Short Jarrod L , Downey Adam D. , Pajor Michael A. , Hogan Timothy P. , Chung Duck-Young , Kanatzidis Mercouri G , Timm Ed , Schock Harold
Published: April 2011

Low electrical contact resistance is essential for the fabrication of high efficiency thermoelectric generators. These contacts must be stable to high temperatures and through thermal cycling. Here we present the fabrication procedure and characterization of several contacts to Pb-Sb-Ag-Te (LAST) compounds. Contact materials investigated include tungsten, antimony, tin, nickel, and bismuth antimony based solder. The contacts were typically deposited by an electron beam evaporation method after careful preparation of the sample surface. The resistances were measured by using the transmission line model, and ohmic behavior was verified through current vs. voltage measurements. The best contact resistivities of less than 20 µΩ·cm2 have been measured for annealed antimony to n-type LAST samples. We present these procedures for fabricating low resistance contacts and the use of these procedures towards the fabrication of high efficiency thermoelectric generator modules.
Development of Thermoelectric generating modules and system
Authors: Ota Toshinori , Tokunaga Chieko , Fujita Kouichi
Published: April 2011

Ishikawajima–Harima Heavy Industries Co., Ltd. (IHI) is currently investigating applications of thermoelectric conversion systems based on the usage of radiant heat for industrial furnaces. The thermoelectric module units, which have been connected to a water-cooled jacket wall inside an electric resistance-heating-type industrial furnace, receive the heat originating from the in-furnace heat insulator by means of radiation, and collect the electric power based on the temperature difference. In this work, experimental results are presented, concerning the mechanical characteristics of a two-step cascade connection type module based on the heat transmission and thermoelectric conversion characteristic.

The module performance analytic result, which turned character of several physical properties of the thermal radiation receiver of the upper part of modules, heat transmission characteristic, and the result, which performed the foundation examination for industrial furnace application, is reported.
High-Performance of Half-Heusler MNiSn (M=Hf,Zr) Single-Phase Thermoelectric Alloys Fabricated using Optical Floating Zone Melting
Authors: Kimura Yoshisato , Kuji Tomoya , Zama Akihisa , Shibata Yasufumi , Mishima Yoshinao
Published: April 2011

We have succeeded to grow almost single-phase of Half-Heusler intermetallic compounds MNiSn, where M = (Hfx,Zr1−x) and x varies from 0 to 1, for the first time by directional solidification using optical floating zone melting (OFZ). Thermoelectric power and electrical resistivity can be dramatically improved since OFZ process effectively reduces solidification defects such as micro-cracks and cavities as well as unfavorable coexisting phases. Dimensionless thermoelectric figure of merit, ZT, of OFZ (Hf,Zr)NiSn alloys can be improved effectively by lowering the lattice thermal conductivity through the solid solution effects due to the substitution of Hf and Zr with each other. The maximum ZT value of 0.9 is achieved in (Hf0.5Zr0.5)NiSn at 963 K.
Thermoelectric Properties of Ag-Tl-Te Ternary System
Authors: Kurosaki Ken , Kosuga Atsuko , Goto Keita , Muta Hiroaki , Yamanaka Shinsuke
Published: April 2011

We have studied the thermoelectric properties of thallium compounds as novel thermoelectric materials. Especially, we focus on the Ag-Tl-Te ternary system, in which we found that Ag9TlTe5 exhibits an excellent thermoelectric figure of merit (ZT= 1.23) because of its extremely low thermal conductivity (around 0.22 Wm−1K−1). In this paper, we studied the thermal conductivity of four kinds of ternary silver thallium tellurides: AgTl3Te2, AgTlTe, Ag8Tl2Te5 and Ag9TlTe5, for which we found room temperature values of 0.39, 0.26, 0.14 and 0.21 Wm−1K−1, respectively. In order to understand the extremely low thermal conductivity, we performed an ultrasonic pulse echo measurement and evaluated some thermophysical properties.
Experimental and theoretical studies of plasma resonance and the electronic structure of binary skutterudites
Authors: Prytz Øystein , Løvvik Ole M. , Taftø Johan
Published: April 2011

We determine the plasmon energies of the skutterudites CoP3, CoAs3 and CoSb3 by electron energy loss spectroscopy, and compare with calculated values from the Drude model and density functional theory (DFT). For these compounds, whose doped versions have potential applications as thermoelectric materials, there is a relatively large discrepancy between experiment and theory based on the Drude model as well as the DFT-calculations. We also study the transitions from occupied to unoccupied states near the Fermi-level that show up at energies lower than the plasmon energies. The features observed are in general agreement with the DFT-calculations.
Incomplete Crystallization of Skutterudites
Authors: Smalley Arwyn L. E. , Johnson David C.
Published: April 2011

A series of CexCo4Sb12 samples were synthesized, with x = 0 to 2. The crystallinity of the samples was studied using quantitative Rietveld analysis, and revealed that the samples did not crystallize completely. These data correlated with changes in the lattice parameter, DSC peak temperature, and DSC peak area. The crystallinity was confirmed using electron back-scatter diffraction (EBSD), which showed crystallites with a background of an amorphous matrix. This unusual morphology may improve thermoelectric properties by decreasing thermal conductivity.
Growth and Characterization of Germanium-based type I Clathrate Thin Films Deposited by Pulsed Laser Ablation
Authors: Witanachchi Sarath , Hyde R. , Nagaraja H. S. , Beekman M. , Nolas G. S. , Mukherjee P.
Published: April 2011

Thin films of clathrate material have been grown using the laser ablation technique on a variety of substrates. Films deposited on silicon substrates exhibited a significant deficiency of Ga and Ge while the stoichiometry was preserved in films deposited on quartz, sapphire, and glass substrates. Ablation characteristics of the clathrate target for laser radiation at three different wavelengths in the UV, visible and IR were studied. The UV and IR laser wavelengths produce low ablation thresholds and high growth rates. Crystalline films were obtained above a growth temperature of 400°C. Conductivity measurements on the films at low current injection (<40 µA) showed semiconducting behavior. At high currents the films demonstrated a semiconductor-to-metal transition for temperatures lower than 150 K.
Cross-plane Thermoreflectance Imaging of Thermoelectric Elements
Authors: Mayer Peter M. , Ram Rajeev J.
Published: April 2011

This paper presents the first cross-plane thermoreflectance image of the temperature distribution in a thermoelectric (TE) element under bias. Using the technique of lock-in CCD thermoreflectance imaging, we can map the temperature distribution of an operational device with submicron spatial resolution and a temperature resolution of 10 mK. As such it offers a complete picture of the quasi-equilibrium transport within the device. The submicron resolution of the thermoreflectance image enables clear determination of localized heating due at interfaces - for example to due contact resistance - and thermal impedance mismatch within samples. The high spatial resolution is ideal for the characterization of thin-film thermoelectric materials where data from conventional techniques (such as the transient Harman method) are difficult to interpret. This paper also presents the first thermoreflectance data we are aware of for BiTe-based material systems. Identification and separation of the Peltier and Joule components of the heating are possible, and finite difference simulations of the devices are presented for comparison with experiment. In this way it is possible to simultaneously acquire information about the Seebeck coefficient, electrical conductivity, and thermal conductivity of the thermoelectric material. The measurements demonstrate the feasibility of non-contact thermal measurements at the sub-micron scale.
Thermoelectric properties of Mg2Si1−xCx crystals grown by the vertical Bridgman method
Authors: Sakuma Takashi , Higuchi Yoshinori , Akasaka Masayasu , Iida Tsutomu , Takanashi Yoshifumu
Published: April 2011

Multicrystalline Mg2Si crystals were grown using a Brigdman method combined with a die-casting growth technique. Although molten and/or vapor-phase Mg at elevated growth temperatures exhibit high chemical reactivity with the surrounding crucible materials, the use of an alumina crucible with a BN coating allowed single phase crystal growth and Mg2Si of good crystalline quality. Incorporation of carbon into the Mg2Si was observed to form Mg2Si1−xCx. For x=0.01 and 0.03, a lower thermal conductivity and higher figure of merit than those of Mg2Si were observed in the temperature range from room temperature to 773 K. The maximum figure of merit was 0.62 at 773 K for a Mg2Si0.99C0.01 sample.
High Efficiency Thermoelectric Power Conversion
Authors: Byrnes Donald F. , Heshmatpour Ben
Published: April 2011

Recent efforts at Teledyne Energy Systems, Inc. have lead to significant improvements in thermoelectric (TE) materials and power conversion devices. A number of improved formulations have been identified for standard n-type PbTe and p-type TAGS alloys. The preliminary test results appear to show nearly a 50% increase in the dimensionless figure-of-merit, ZT, for these two alloys. The new TE material formulations also exhibit a lower sublimation rate which is likely to allow use of these materials at higher heat source temperatures and thus result in higher Carnot efficiencies. The combination of higher ZT and higher Carnot efficiency allows achievement of exceptionally high thermoelectric conversion efficiencies through small changes to proven technology. For example, a thermoelectric conversion device which uses segmented BiTe/modified PbTe/modified TAGS thermoelectric couple design and operates between 300 °K and 900 °K will have a conversion efficiency of approximately 16.2%. Effort is continuing to confirm the preliminary test results and validate the materials fabrication processes. A number of improvements have also been made in the TE device fabrication processes and assembly techniques which have reduced the internal thermal and electrical losses, increased conversion efficiency, enhanced reliability and reduced manufacturing cost for the thermoelectric devices.
Raman and Electron Spin Resonance Investigations of as Prepared and Thermal Annealed Cluster Beam Deposited Carbon Thin Films
Authors: Compagnini Giuseppe , Puglisi Orazio , Chipara Mircea
Published: April 2011

Nanostructured amorphous carbon thin films deposited by a Low Energy Carbon Cluster Beam Deposition technique have been characterized by Raman spectroscopy and Electron Spin Resonance (ESR). This study focuses on the correlation between carbon cluster structure and sp2 related defects. The ESR spectrum of as prepared and thermally annealed carbon clusters is a single line located near the free electron g-factor. Resonance lines were accurately fitted by a single line symmetric and narrow Lorentzian line. The resonance line parameters (line position, line amplitude, and line width) were found to be extremely sensitive to the thermal treatment of the as deposited samples. The paramagnetic centres are randomly distributed and correlated with the nanosized nature of the investigated system. The absence of the resonance line asymmetry, typical for the ESR spectra of conducting carbaceneous materials, confirms the small size of carbon nanoclusters and indicates poor electrical contacts between them. The resonance line parameters (position, intensity, and width) are not affected by the orientation of the carbon cluster film relative to the direction of the external magnetic field. The evolution of the ESR signal upon thermal treatments is sensitive to the increase of the sp2 average domain size as revealed by Raman spectroscopy. The Raman spectrum of as obtained and thermally annealed carbon clusters, in the domain 1000 cm−1 to 2000 cm−1 shows two Lorentzian lines located at 1300 cm−1 and 1550 cm−1 representing the D and G bands. The position and amplitude of these lines were found to be affected by thermal annealing.
Effect of Nanoparticles on the Thermal Stability of Polymers
Authors: González-Irun Juan , Garcia Ana , Artiaga Ramón , Liz-Marzán Luís , Hui David , Chipara Mircea
Published: April 2011

The thermal stability of polymethylmethacrylate loaded with silica nnaoparticles is investigated. The temperature dependence of the mass has been accurately fitted with a single Boltzmann-like dependence. The effect of surface functionalization, size of silica nanoparticles, and concentration of silica nanoparticles is analyzed. A weak increase of the thermal stability of polymethylmethacrylate has been obtained by loading the polymer matrix with nanoparticles. Surface functionalization produced a modest increase in the thermal stability (compared to composites with silica nanoparticles without surface modification).
Investigations of dc electrical properties in electron-beam modified carbon nanotube films: single- and multiwalled
Authors: Gupta Sanju , Smith N. D. , Patel R. J. , Giedd R. E.
Published: April 2011

Carbon nanotubes (CNTs) in the family of nanostructured carbon materials are of great interest because of several unique physical properties. For space applications, it needs to be shown that CNTs are physically stable and structurally unaltered when subjected to irradiation becomes indispensable. The CNT films were grown by microwave Carbon nanotubes (CNTs) in the family of nanostructured carbon materials are of great interest because of several unique physical properties. For space applications, it needs to be shown that CNTs are physically stable and structurally unaltered when subjected to irradiation becomes indispensable. The CNT films were grown by microwave plasma-assisted chemical vapor deposition (MWCVD) technique using Fe as catalyst. Synthesis of both single- and multiwalled CNTs (SW and MW, respectively) were achieved by varying the thickness of the Fe catalyst layer. To investigate the influence of electron-beam irradiation, CNTs were subjected to low and/or medium energy electron-beam irradiation continuously for a few minutes to several hours. The CNT films prior to and post-irradiation were assessed in terms of their microscopic structure and physical properties to establish property-structure correlations. The characterization tools used to establish such correlations include scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS), and current versus voltage (I-V) measuring contact resistance (two-probe) and dc conductivity (four-probe) properties. Dramatic improvement in the I-V properties for single-walled (from semiconducting to quasi-metallic) and relatively small but systematic behavior for multi-walled (from metallic to more metallic) with increasing irradiation hours is discussed in terms of critical role of defects. Alternatively, contact resistance of single-walled nanotubes decreased by two orders of magnitude on prolonged E-beam exposures. Moreover, these findings provided onset of saturation and damage/degradation in terms of both the electron beam energy and exposure times. Furthermore, these studies apparently brought out a contrasting comparison between mixed semiconducting/metallic (single-walled) and metallic (multiwalled) nanotubes in terms of their structural modifications due to electron-beam irradiation.
Degradation of Assembled Silicon Nanostructured Thin Films: a Theoretical and Experimental Study
Authors: Bertani Valeria , D'Urso Luisa , Scalisi Alfio Alessandro , Compagnini Giuseppe , Puglisi Orazio
Published: April 2011

The study of the structures and properties of small elemental clusters has been an extremely active area of current research, due to the peculiar behavior of these species halfway between that of single atoms and of the bulk phase. In this work silicon nanoclusters are generated by ablation of a high purity polycrystalline rod with a pulsed laser vaporization source and then deposited on a support. Their structure is studied both in the gas phase by means of Time of Flight Mass Spectrometry and in the solid phase through in situ Raman and Infrared Spectroscopy. The spectra reveal that the as deposited clusters are hydrogenated with negligible amount of oxide. Degradation of silicon nanoclusters has been studied after gas exposure. In the gas of air a consistent modification was observed, leading to a near-infrared luminescent silicon nanoparticles. In the second part of the work, density functional theory is applied to investigate the geometrical structure of silicon clusters and their interaction, in term of structure and energy, with different gases. The calculations were performed with the Gaussian 03 program suite, adopting the B3LYP functional to calculate the exchange and correlation energy. Si8 has been chosen as model cluster to study the degradation of silicon clusters both kinetically and thermodynamically, in order to explain the experimental evidences. Experimental and calculated infrared spectra are compared.
Sintering of HAp precipitated from solutions containing ammonium nitrate and PVA
Authors: Safronova Tatiana Victorovna , Putlyaev Valery I. , Belyakov Alexey V. , Shekhirev Mikhail A.
Published: April 2011

Bioceramics based on hydroxyapatite (HAp) is known to be a prospective material for biomedical applications. However, sintering of HAp is still understudied in sense of reasonable selection of controlling parameters. In particular, the role of impurities and co-products of powder fabrication is still questionable. The data concerning the role of ammonium nitrate coming to precipitated HAp from the mother liquor, its effect on powder compaction and subsequent sintering, are not available.

Nanosized powders of HAp were fabricated via conventional wet-precipitation technique by dropwise adding of Ca(NO3)2 solution (0.25 -1.67 M) to the stock solution of (NH4)2HPO4 (0.15-1.00 M) with pre-adjusted pH at 60°C in presence of polyvinyl alcohol (PVA). PVA was added to the stock solution in order (i) to block crystal growth during synthesis , (ii) to improve stability of Hap suspension to sedimentation, (iii) to regulate an aggregation of HA nanoparticles during synthesis and in the stage of drying.

NH4NO3 – a by-product of the precipitation reaction, presented in as-precipitated powder in amount of 30%, was evaluated as an additive affecting a compaction of the powder and the initial stage of a sintering. The powder samples were tested by XRD, FTIR, light-scattering , TEM and SEM/EDX to get particle sizes, morphology and chemical composition, dilatometry. Ceramics were sintered at 700-1250°C and evaluated with SEM/EDX and density measurements.

Addition of PVA to the stock solution in the course of HAp precipitation is a promising technique to control an aggregation of HAp nanoparticles in the stages of drying and sintering. PVA acting as a surfactant in the solution and as a binder in dry powder can keep highly reactive small HAp particles within large agglomerates providing better molding of the powder and controllable densification of ceramics. The effect of PVA on microstructure of the HAp powder and their sintering behaviour is discussed in terms of self-organisation concept and synergetics.
Fast and Slow Magnetization Processes in Magnetic Recording Media
Authors: Zhou J. , Skomski R. , Michalski S. , Kirby R. D. , Sellmyer D. J.
Published: April 2011

Information loss due to thermal activation is a major concern in ultrahigh-density magnetic recording media. The usually considered mechanism is thermally activated magnetization reversal over micromagnetic energy barriers. However, micromagnetic approaches ignore local anisotropy fluctuations, which translate into a time-dependent reduction of the remanent magnetization. The effect is negligibly small in macroscopic magnets but becomes important on a scale of a few nanometers.
Size Control and Spectroscopic Characterization of Monolayer Protected Gold Nanoparticles Obtained by Laser Ablation in Liquids
Authors: Compagnini Giuseppe , Scalisi Alfio Alessandro , Puglisi Orazio
Published: April 2011

In this paper we present a study on the formation of gold colloids by laser ablation of a gold metal target in alkanes and thiol-alkane solutions. The results show a decrease of the gold particles' size up to 2 nm when thiol molecules are present in the liquid environment. In summary, we observed that laser ablation of gold targets in thiol-alkane solutions leads to the formation of stable gold clusters with size smaller than those obtained in the corresponding pure alkane. This result is a consequence of the competition between the aggregation of gold species in the plume (which allows a gold embryo to be formed and to grow) and the tendency of the dispersed thiol molecules to bond at each embryo surface stopping their growth.
Degradation of Copper-Silver Alloy Thin Films Induced by Annealing
Authors: Snyder S. T. , King Alex
Published: April 2011

Copper / silver alloy thin films form with a fine, polycrystalline, metastable crystal structure. The expected effects of annealing include grain growth, transformation into the two stable phases, coarsening of the phases, texture formation, and the formation and growth of pinholes or voids. Copper/silver alloy films were deposited on single crystal sodium chloride substrates, via pulsed laser deposition ablation of an alloy target, of the eutectic composition. Free-standing films of 20-30 nm thickness were studied as-deposited and after annealing on copper TEM grids at 100°C for various times. Although several of the expected degradation processes involve short-range diffusion – essentially single atomic jumps – these were not observed, while other, longer-range diffusion effects were clearly identifiable. In particular, void shrinkage was observed in the films at short times, and void growth occurred at longer times.
Effect of Deposition Parameters on the Microstructure and Growth Rate of CVD Mullite Environmental Barrier Coatings
Authors: Basu Soumendra , Kulkarni Tushar , Sarin Vinod
Published: April 2011

Si-based ceramics such as SiC require environmental barrier coatings to protect against hot-corrosion and recession in gas turbine applications. Dense, crystalline mullite coatings of uniform thickness have been deposited by hot-wall chemical vapor deposition (CVD) on SiC substrates, using the AlCl3-SiCl4-CO2-H2 system. The effects of the CVD deposition parameters such as temperature, total reactor pressure, and metal-chloride partial pressure on the coating microstructure and growth kinetics have been investigated, and are discussed in this paper.
Scaled Up Pulsed Deposition Technology: Carburization Resistant Ablation Coatings for Ethylene Pyrolysis Coils
Authors: Chauhan Alok , Anwar Mir , Montero Kelvin , White Henry J , Si Weidong , Bai Jianming
Published: April 2011

Products derived from ethylene have and will continue to replace metallic materials traditionally used for transportation, building materials, and products we use in our everyday lives. As the demand continues to increase, a more suitable material for the outlet coils of ethylene pyrolysis heaters will have to be identified. In this study, we discuss utilization of scaled up pulsed deposition technology to deposit adherent carburization resistant coatings on the inner diameter of ethylene pyrolysis tubing with the intent of extending tube life. Ablation target material selection was based primarily on elevated temperature properties and the ability of the coating to prevent transformation of the inherent protective chromium oxide surface film to metal carbides while in service. The near optimal settings of the processing parameters for pulsed laser deposition of ceramic SiC on heat resistant tubing traditionally used for ethylene service were investigated using a semi quantitative controlled random search methodology. Minimization of the objective function which was based on width, thickness and coverage of the thin film resulted in an optimal deposition time of 4.3 minutes and surface finish of 272 nm.
Laser-induced patterning of Co nanostructures under ambient conditions
Authors: Favazza C. , Trice Justin , Krishna Hare , Kalyanaraman Ramki
Published: April 2011

Increasing the efficiency and the relative ease of creating ordered nanostructures is essential to the advancement of nanotechnology. The practical benefits from ambient processing of nanostructures, like reduced complexity and increased efficiency, makes it an important avenue for investigation as nanomanufacturing processes. We have recently shown that pulsed laser melting of ultrathin metal films in vacuum leads to nanostructure ordering presumably due to metal dewetting. Here we show that UV pulsed laser irradiation (10 ns pulse width) of ultrathin Co films on SiO2 substrates under ambient conditions with a two-beam laser interference pattern generates Co nanoparticles with both long- and short-range order (LRO and SRO) and are qualitatively comparable to those created in vacuum. Furthermore, preferential etching of the metal shows that there is minimal interaction of the Co with the substrate. These results show that the presence of oxygen in the ambient does not substantially influence the resulting nanostructure formation. Therefore, ns pulsed laser processing under ambient conditions may be a practical way to realize ordered metal nanostructures.
Analysis and comparison of semiconductor materials processed at IR vs. UV laser wavelengths for DRAM yield enhancement applications
Authors: Hooper Andy E. , Kawasaki Allen , Kirby Paul , Hainsey Robert , Bang Jeongho , Shin Kyeongseon , Kang Ki Sang , Lee Kungu
Published: April 2011

This report demonstrates the effects of IR and UV laser energy on common semiconductor layer stack materials used for DRAM laser fuses. By moving from IR to UV wavelengths it is possible to significantly shrink the laser spot diameter from ∼1.6 μm to 0.8 μm. Effects and concerns for the absorption of UV energy by Si, SiO2, nitrides, and oxynitrides are also presented.
Hydrogen Radical Etching Effect on Carbon Nanotube Growth
Authors: Nagayoshi Hiroshi , Sato Hiroaki , Nishimura Suzuka , Terashima Kazutaka
Published: April 2011

The hydrogen microwave remote plasma CVD was introduced to fabricate carbon nanotubes(CNTs). C2H2 or CH4, used as source gas react with hydrogen radicals introduced from the cavity. In this experiment, hydrogen radical etching effect on the substrate surface could be controlled independently. We confirmed CNTs growth at 400°C under adequate hydrogen radical etching effect on the substrate surface. The result directly suggests that the etching effect of hydrogen radicals on the reaction surface contribute to the low temperature growth of CNTs. The CNT thickness did not depend on the hydrogen radical etching effect but the catalyst layer thickness.
Application of polyimide sacrificial layers for the manufacturing of uncooled double-cantilever microbolometers
Authors: Huang Shusen , Zhang Xin
Published: April 2011

In this paper, a low-temperature surface micromachining module with two sacrificial layers of polyimide is developed for the manufacturing of double-cantilever microbolometer focal plane arrays. The use of spin-on polyimide allows an all-dry final release step overcoming stiction problems often encountered in wet sacrificial etching processes. For the patterning of the polyimide, a plasma-enhanced chemical vapor deposited silicon oxide is employed as a mask layer. Anisotropic etching of both the mask film and the polyimide layer is accomplished by reactive ion etching. After patterning structural layers, sacrificial etching of the polyimide is conducted using an isotropic dry etch process in high-density oxygen plasma.
Strain compensation effect on stacked InAs self-assembled quantum dots embedded in GaNAs layers
Authors: Oshima Ryuji , Hashimoto Takayuki , Shigekawa Hidemi , Okada Yoshitaka
Published: April 2011

We have studied the effect of strain compensation in multiple stacking of InAs self-assembled quantum dots on GaAs (001) substrates grown by atomic hydrogen assisted RF-molecular beam epitaxy. The GaNxAs1−x material was used as a strain compensating spacer layer. We confirmed by high resolution x-ray diffraction measurements that a 40 nm GaN0.005As0.995 strain compensating layer provides compressive strain to compensate for tensile strain induced by 2.0 ML InAs quantum dots. Consequently, we achieved a multiple stack of InAs QDs up to 30 layers without formation of coalesced QDs, and the density of QDs exceeded 1012 cm−2.
Colloidal quantum dot active layer electroluminescence in a solid GaN matrix
Authors: Pagan Jennifer , Stokes Edward , Patel Kinnari , Burkhart Casey , Ahrens Mike
Published: April 2011

In this paper the preliminary results of incorporating a novel active layer into a GaN light emitting diode (LED) are discussed. Integration of colloidal CdSe quantum dots into a GaN LED active layer is demonstrated. The conductivity of the overgrowth was examined by circular transmission line method (CTLM). Effects on surface roughness due to the active layer incorporation are examined using atomic force microscopy (AFM). LED test devices were fabricated and electroluminescence was demonstrated, the devices exhibit higher turn-on voltages than would be expected for a CdSe active layer.
Material synthesis and infrared optical properties of transition metal doped binary and ternary II-VI semiconductors
Authors: Hömmerich Uwe , Nyein Ei Ei , Trivedi Sudhir B. , Bluiett Althea G.
Published: April 2011

We report on the material preparation and optical characterization of transition metal (Cr, Co) doped ternary cadmium chalcogenides for possible applications in mid-infrared (MIR) light source development. Cr2+ doped II-VI's (e.g. ZnSe, ZnS) have received significant attention for MIR solid-state laser development in the 2-3 μm region. Transition metal (TM) doped II-VI thin films are also currently being studied for the development of broadly tunable MIR sources pumped through electrical carrier-injection. In this paper, we present results of the material synthesis and IR spectroscopy of several Cr and Co doped cadmium chalcogenides including CdTe, CdMnTe, CdZnTe, CdMgTe, CdCaTe, and CdSrTe. Following the synthesis and purification of undoped II-VI materials, TM doping was achieved during in-situ Bridgman growth or through a thermal diffusion process. The Cr2+ doped II-VI materials were characterized by broad IR absorption bands centered at ∼1800–1900 nm and MIR emission extending from ∼2000–3500 nm. The emission lifetimes varied between 1-5 μs, depending on the Cr concentration and host composition. Co2+ doped cadmium chalcogenides exhibited several absorption bands in the infrared region and broad emission extending from ∼3-5 μm. Compared to Cr2+ doped II-VI's, the emission from Co2+ doped chalcogenides was significantly quenched at room-temperature due to the onset of non-radiative relaxations.
Quantum-well Intermixing using Ge-doped Sol-gel Derived Silica Encapsulant Layer
Authors: Djie Hery Susanto , Ooi Boon-Siew , Ho Charles Kin-Fai , Mei Ting , Pita Kantisara , Ngo Quoc-Nam
Published: April 2011

We report the intermixing enhancement using the Ge-doped sol-gel derived silica encapsulant layer in InGaAs/InGaAsP quantum-well laser structure. A bandgap shift of ∼64 nm has been observed from 16% Ge-doped silica capped sample at an annealing temperature of 630°C while the intermixing at the similar temperature can be effectively suppressed with the e-beam evaporated SiO2 encapsulant layer. Using our theoretical model, nearly identical activation energy of 1.7±0.5 eV was obtained from the intermixed sample with Ge-doped silica. Similar intermixing enhancement holds for high Ge-content cap in the intermixed GaAs/AlGaAs quantum-wells related to Ga vacancy injection. We postulate that the dissimilarity in interdiffusion behavior between 0% and 16% Ge-doped silica capped sample is only attributed to the difference in the number of beneficial vacancies that involve in the intermixing process.
Purification, material synthesis, and infrared emission from Nd doped PbBr2 and PbI2
Authors: Hömmerich Uwe , Nyein Ei Ei , Trivedi Sudhir B. , Bluiett Althea B. , Zavada John M.
Published: April 2011

We report on the material synthesis and infrared optical properties of Nd doped lead bromide (PbBr2) and lead iodide (PbI2) bulk crystals. Commercial PbBr2 and PbI2 materials were purified through repeated solidification and horizontal zone refinement. After purification, Nd doped lead halides were synthesized and grown by Bridgman technique. Under optical excitation, Nd:PbBr2 samples exhibited several near-infrared emission bands centered at 816 nm, 891 nm, 963 nm, 1069 nm, 1183 nm, 1356 nm, and 1535 nm. The emission from Nd:PbI2 samples was similar to that of from Nd:PbBr2, but slightly shifted to longer wavelengths. The observation of 1540 nm emission from Nd3+ ions is unusual and reflects on the small non-radiative decay rates in the investigated halides. Lead halides have low maximum phonon energies, which reduces non-radiative decay due to multi-phonon relaxations. In contrast to Nd:YAG, Nd:PbBr2 and Nd:PbI2 exhibited efficient emission from the 4F5/2, 2H9/2 excited states, which are located only ∼1000cm−1 above the 4F3/2 level of Nd3+. Under 808 nm diode pumping, both samples also exhibited broad mid-infrared emission bands centered at ∼5.1 μm.
Optical investigations on sputtered CuCl thin films
Authors: Natarajan Gomathi , Mitra Anirban , O'Reilly Lisa , Daniels Stephen , Cameron David C. , McNally Patrick J. , Lucas Olabanji F. , Bradley Louise
Published: April 2011

Copper (I) chloride (CuCl) is a potential candidate for ultra violet optoelectronics due to the fact that it is closely lattice matched with silicon, which makes it readily integrable with silicon device technology. The structural and optoelectronic properties of CuCl thin films deposited by RF magnetron sputtering are investigated. The crystallinity is studied using X-ray diffraction which confirms the growth of CuCl thin films with cubic zinc blende structure predominantly orientated in <111> direction. Excitonic transitions in the thin films were thoroughly investigated using optical absorbance and luminescence spectroscopies. Room temperature absorption spectroscopic analysis confirms the existence of two exciton peaks namely Z12 and Z3 at 372 and 380 nm respectively. A strong UV emission is observed at room temperature in cathodoluminescence and photoluminescence spectra due to the recombination of Z3 exciton at approximately 384 nm. In the low temperature photoluminescence spectrum, a free exciton (Z3) and a bound exciton (I1) are observed. A variation of 1.3 nm to 10 nm was observed in the Z3 exciton line width from 10 K to 300 K.
Fabrication of Nitrided Mask on GaAs surface and Its Machinability for STM lithography
Authors: Yamamoto Yo , MATSUOKA Sota , Kondo Toshiyuki , Maruyama Takahiro , Naritsuka Shigeya
Published: April 2011

A nitridation mask on a GaAs surface was prepared using RF-MBE and its machinability by STM lithography was studied. A 5.2 nm thick crystal-like layer was formed at 350°C, and was modified by STM at a sample bias of ±80V with good size reliability, which was sufficiently fine for realizing dislocation-free heteroepitaxial growth of GaAs / Si. The mask was maintained up to 620°C under As flux exposure at 1.5 × 10−4 Pa.
Crystal structure and physical properties of GaSe single crystals annealed in sulfur atmosphere
Authors: Voevodina Olga V. , Morozov Aleksandr N. , Sarkisov Sergey Yu. , Andreev Yuri M. , Fernelius Nils C. , Goldstein Jonathan T.
Published: April 2011

In spite of the progress in GaSe growing technology (high-quality crystals grown by the latest technology are characterized by low values of optical losses with the absorption coefficient values lying below 0.1 cm−1) the work continues on improving crystal properties for nonlinear optical applications. This paper presents the results of investigations on the influence of annealing in a sulfur atmosphere and in a vacuum on the properties GaSe single crystals, grown by the Bridgman method from the melt. The objective of this work was to study the possibility of intercalating GaSe with sulfur from the gas phase, and to compare the influence of doping with sulfur from melt and vapor phase on the structure and properties of GaSe crystals. Three series of annealing experiments have been conducted at temperatures 773, 923, 1073 K and the samples obtained have been studied by Hall effect, photoconductivity, optical absorption, microhardness measurements and X ray diffractometry. The results obtained are explained by assuming the intercalating of sulfur to the interlayer space and substitution of Se with S.
New Solar Cells with Novel Light Trapping via Textured Photonic Crystal Back Reflector
Authors: Zeng Lirong , Yi Yasha , Hong Ching-yin , Alamariu Bernard A. , Liu Jifeng , Duan Xiaoman , Kimerling Lionel C.
Published: April 2011

We have successfully developed a new light-trapping scheme for solar cells that can enhance the optical path length by more than 104 times using a textured photonic crystal structure as a backside reflector. Top-contacted crystalline Si solar cells integrated with the new back reflector were designed, fabricated and characterized. Both external quantum efficiency and power conversion efficiency of the cells have shown significant improvement due to the path length enhancement furnished by the new back reflector despite of the 675 um thick wafers and relatively short minority carrier diffusion length.
Evolution of the optical band gap in Titanium-based Oxy-(Hydroxy)-Fluorides series
Authors: Penin Nicolas , Viadere Nicolas , Dambournet Damien , Tressaud Alain , Demourgues Alain
Published: April 2011

The optical band gap related to the electronic structures as well as the refractive index function of the electronic polarizability of the network can be tailored by changing the nature and the number of anions into the vicinity of cations. New routes have been developed in order to prepare new divided Ti(IV)-based oxyfluorinated compounds. In these compounds, the optical absorptions appear at the UV-Vis frontier and the refractive index is always smaller than the one of equivalent oxides. The chemical bonding, the hybridation and the density of the network play key roles in the variation of the optical band gap and the refractive index. For this family of titanium-based oxyfluorides containing mixed anions, chemical compositions and structural features have been correlated to the optical band gap and the refractive index, i.e. the complex index of materials n(λ) + ik(λ). Several examples will be given in order to illustrate the potentialities of these new inorganic compounds by changing the F/Ti ratio and the cationic substitution.
Heterojunction, Vacuum-Glass Field Effect Transistors
Authors: Geis Michael W. , Deneault Sandra , Krohn Keith E. , Marchant Michael , Cooke David L. , Lyszczarz Theodore M.
Published: April 2011

This note reports on a surface field effect transistor, SFET, where the electron channel consists of the interface between vacuum and a Cs-doped glass, and an electrode on the back of the glass substrate is used as the gate. The device has a transconductance of 4×10−10 S cm−1. The transconductance is limited by the glass surface roughness, ∼ 0.4 nm RMS. A reduction of surface roughness to 0.1 nm RMS is expected to increase device transconductance.
Implantation and Activation of High Concentrations of Boron and Phosphorus in Germanium
Authors: Suh Yong Seok , Carroll Malcolm S. , Levy Roland A. , Bisognin Gabriele , Salvador Davide De , Sahiner M. Alper
Published: April 2011

The effect of increasing boron or phosphorus implant dose (i.e., 5×1013-5×1016 cm−2) and subsequent annealing (400-600°C for 3 hrs in N2) on the activation, diffusion and structure of germanium is studied in this work. The peak concentration of implant dose is ∼ 2×1021 cm−3. Secondary ion mass spectrometry (SIMS), spreading resistance profiling (SRP), high resolution X-ray diffraction (HRXRD), X-ray absorption fine structure (XAFS), Rutherford backscattering spectrometry (RBS), and nuclear reaction analysis (NRA) were used to characterize the implant and activation behavior. Boron is found to have a high solid solubility (i.e., > 2×1020 cm−3), even immediately after implant; while in contrast, phosphorus is limited to ∼ 1–2×1019 cm−3. Diffusion of phosphorus is also extremely extrinsic, while boron is practically immobile.
Silicon Surface Texturization Mechanism by Hydrogen Radicals Using Tungsten Hot Filament
Authors: Nagayoshi Hiroshi , Sato Hiroaki , Nishimura Suzuka , Terashima Kazutaka
Published: April 2011

This paper describes the surface texturing mechanism on crystalline Si using hydrogen radicals generated by a tungsten hot filament. Inverted pyramid or labyrinthV groove structure could be obtained by particle deposition before etching. Mesh like tungsten particle layer, works as an etching mask against hydrogen radical, was obtained when silicon substrate was used. On the other hand, tungstem particles were not deposited as mesh like pattern when SiO2/Si substrate was used. The results suggest that evaporation of silicon hydrides from the silicon surface by hydrogen radical etching causes the mesh like pattern deposition of tungsten particles. Increase of filament current enables short time texturing process of less than 1 minute.
Kinetically controlled superstructural phases at the Sb/Si (5 5 12) interface
Authors: Kumar Mahesh , Paliwal Vinod Kumar , Govind  , Vedeshwar A. G. , Shivaprasad S. M.
Published: April 2011

The adsorption of Sb on the high index Si (5 5 12) has been studied at higher substrate temperature (HT) (800°C), using in situ surface characterization techniques like Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED), and Electron Energy Loss Spectroscopy (EELS). The surface morphology of this high index Si (5 5 12) surface has row like trenches along (110) direction. We have performed the study of Sb adsorption and desorption on the Si (5 5 12) substrate held at different temperatures. The different pathways adopted during adsorption and desorption have suggested the dominant role of kinetics I forming various surface phases on the Si (5 5 12) substrate. The adsorption at room temperature resulted in the formation of (225) surface phase, while the adsorption at 680°C resulted in the (337) phase. The sequential thermal desorption of the room temperature and high temperature adsorbed surface resulted in the formation of (337) phases at 800°C, with anisotropic growth along one direction. While the adsorption at 800°C resulted in the formation of anisotropic (337) like phases, the further increase in the coverage formed a 2x Si (225) phase. Annealing this 2x Si (225) phase again resulted in the formation of anisotropic (337) phase. Thus formation of interface by controlling the growth kinetics can result in the formation of various tailored structures with desired properties.