bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rhenium silicide as a new class of thermoelectric material
Authors: Inui Haruyuki 
Published: April 2011

ABSTRACTThe microstructure, defect structure and thermoelectric properties of binary and some ternary Re silicide have been investigated as a new class if thermoelectric material. Binary Re silicide is identified to contain many Si vacancies, which are arranged in an ordered manner in the underlying tetragonal C11b structure so that the silicide is formulated to be ReSi1.75 with a monoclinic unit cell and contains four differently oriented domains accompanied by the twinned microstructure. The density and arrangement of Si vacancies can be controlled by ternary alloying. When the number of valence electrons of a ternary element is smaller than that for Re, the density of Si vacancies decreases with ternary additions, whereas the density of Si vacancies increases with ternary additions when the number of valence electrons of a ternary element is larger than that for Re. For both cases, the variation of the density of Si vacancies upon ternary alloying is accompanied by the introduction of the so-called shear structure.Binary ReSi1.75 exhibits nice thermoelectric properties as exemplified by the high value of dimensionless figure of merit (ZT) of 0.70 at 800 °C when measured along [001], although the ZT value along [100] is just moderately high. The ZT value is further increased to 0.8 with a small amount (2% substitution for Re) of Mo addition, by which an incommensurate microstructure is formed as result of extensive shear operation on the nano-scale.
Thermoelectric Properties of Tl2Te-Sb2Te3 Pseudo-Binary System
Authors: Kurisaki Ken , Goto Keita , Kosuga Atsuko , Muta Hiroaki , Yamanaka Shinsuke 
Published: April 2011

ABSTRACTPolycrystalline-sintered samples of thallium based substances, (Tl2Te)100−x(Sb2Te3)x (x= 0, 1, 5, 10), were prepared by melting Tl2Te and Sb2Te3 ingots followed by annealing in sealed quartz ampoules. The thermoelectric properties were measured from room temperature to around 600 K. The values of the Seebeck coefficient of all samples are positive, indicating a p-type conduction characteristic. The maximum value of the power factor is 6.53×10−4 Wm−1K−2 at 591 K obtained for x= 10 (Tl9SbTe6), which is about one order lower than those of state-of-the-art thermoelectric materials. All samples indicate an extremely low thermal conductivity, for example that of Tl2Te is approximately 0.35 Wm−1K−1 from room temperature to around 600 K. Although the electrical performance of the samples is not so good, the ZT value is relatively high due to the extremely low thermal conductivity. The maximum ZT value is 0.42 at 591 K obtained for Tl9SbTe6.
Extremely Low Thermal Conductivity Substances as Novel Thermoelectric Materials
Authors: Yamanaka Shinsuke , Kurosaki Ken , Kosuga Atsuko , Goto Keita , Muta Hiroaki 
Published: April 2011

ABSTRACTWe have prepared polycrystalline bulk samples of various thallium compounds and measured their thermoelectric properties. The most remarkable point of the thermoelectric properties of the thallium compounds is the extremely low thermal conductivity. The state-of-the-art thermoelectric materials such as Bi2Te3 and TAGS materials indicate relatively low the thermal conductivity, around 1.5 W/m/K. However, the thermal conductivity of the thallium compounds is below 0.5 W/m/K; especially that of silver thallium tellurides is around 0.25 W/m/K at room temperature. This extremely low thermal conductivity leads a great advantage for an enhancement of the thermoelectric performance. In this paper, we report on the properties of some thallium compounds selected for study as novel thermoelectric materials. One of these compounds seems to have a thermoelectric figure of merit comparable to those of state-of-the-art materials.
Mechanism And Characterization Studies on Boron Carbides Deposited by Chemical Vapor Deposition Technique
Authors: Karaman Mustafa , Özbelge Hilmi Önder , Sezgi Naime Asli , Doğu Timur 
Published: April 2011

ABSTRACTBoron carbide was produced in an impinging jet CVD reactor from a gas mixture of BCl3, CH4 and H2. The mass transfer limitations on the reaction kinetics were minimised by the jet impingement on the substrate surface. XPS characterization of the produced deposits revealed a nearly pure boron carbide phase containing small amounts of oxy-boron and oxy-carbon species. After a detailed kinetic study, a reaction model was proposed to predict the rates of boron carbide and dichloroborane formation reactions. In this model, boron trichloride is adsorbed on the surface non-dissociatively, whereas hydrogen and methane are adsorbed dissociatively. BC is formed on the solid surface through the reaction of adsorbed boron trichloride with adsorbed methane in the form of CH3(s) (adsorbed CH3 on the surface). Produced BC is reacted in successive series reactions including adsorbed boron trichloride and adsorbed hydrogen. In the proposed mechanism, dichloroborane is produced only through the gas phase reaction between boron trichloride and hydrogen. The simultaneous fit of the experimental data to the model expression gave good fits for the boron carbide and dichloroborane formation reactions with the high correlation coefficient values.
Effects of MeV Ions on Thermal Stability of Single Walled Carbon Nanotubes
Authors: Adhikari Ananta Raj , Huang Mengbing , Ryu Chang , Ajayan Pullickel , Bakhru Hassaram 
Published: April 2011

AbstractThe properties of carbon nanotubes (CNTs) are closely dependent on their structures, and therefore may be tailored by controllably introducing defects in the nanotube systems. In this work, we have investigated the effects of energetic ions (H+ and He+) on the thermal stability of single wall nanotubes (SWNTs) against oxidation in air. SWNTs were irradiated with MeV ions to various doses in the range 1013-1016 cm−2. Thermogravimetric analysis (TGA) was used to determine the loss of CNT masses as a result of oxidation processes. As opposed to the case of pristine SWNTs for which the temperature (Tmax) corresponding to maximum oxidation rate was found to be ∼ 495 °C, ion beam processing significantly enhanced the thermal stability of nanotubes, e.g., Tmax increased by about 30 °C after H+ implantation (dosage: 1015 cm−2) and 17 °C after He+ implantation (dosage: 1013 cm−2). The activation energies for thermal oxidation under various conditions were also extracted from TGA data, with values ranging from 1.13 eV (for pristine SWNTs) to 1.37 eV, depending on ion doses and species. Raman spectroscopy was used to determine the characteristics of the G band (C-C stretching mode) and D band (disorder induced mode) in CNTs. The work suggests that the SWNTs modifies to more stable structure (may be cross-linked SWNTs) at small doses. Once the number of defects exceeds some critical value (depending on the type and dosage of bombarding ion) the bonding energy in CNTs weakens, leading to the reduced thermal stability of CNTs against oxidation.
Magnetic Aging
Authors: Skomski R. , Zhou J. , Kirby R. D. , Sellmyer D. J. 
Published: April 2011

ABSTRACTThermally activated magnetization reversal is of great importance in areas such as permanent magnetism and magnetic recording. In spite of many decades of scientific research, the phenomenon of slow magnetization dynamics has remained partially controversial. It is now well-established that the main mechanism is thermally activated magnetization reversal, as contrasted to eddy currents and structural aging, but the identification of the involved energy barriers remains a challenge for many systems. Thermally activated slow magnetization processes proceed over energy barriers whose structure is determined by the micromagnetic free energy. This restricts the range of physically meaningful energy barriers. An analysis of the underlying micromagnetic free energy yields power-law dependences with exponents of 3/2 or 2 for physically reasonable models, in contrast to arbitrary exponentsmand to 1/H-type laws.
Degradation in Sn Films due to Whisker Formation
Authors: Reinbold L. , Chason Eric , Jadhav N. , Kelly V. , Holmes P. , Shin J.W. , Chan W.L. , Kumar K.S. , Barr G. 
Published: April 2011

ABSTRACTWhisker formation in pure Sn coatings on Cu conductors is a serious impediment to the development of Pb-free electronics manufacturing. Understanding whisker formation is complicated by the fact that it is the result of multiple materials kinetic processes including interdiffusion, intermetallic formation and stress generation We report preliminary studies of whisker growth kinetics and stress evolution aimed at developing a fundamental understanding of the whisker growth process. A proposed model of point defect mediated stress generation provides a simple picture of how the different processes are connected.
A new method based on work-displacement curve to assess the toughness of coated system
Authors: Chen Jinju , Bull Steve J. 
Published: April 2011

ABSTRACTTraditional indentation models relating the toughness to applied load and the length of well-developed radial cracks were initially developed for monolithic bulk brittle materials. Their application can also be extended to coated systems if sufficiently thick, however, the use of such models to thin coatings will be influenced by other factors such as substrate deformation and it is difficult to use traditional approaches to assess sub-threshold cracking. The method of extrapolating the load-displacement curve has been widely used to assess the toughness of a coating when a step in the load-displacement curve is observed which is clearly associated with chipping. This approach completely ignores the change of other mechanical behaviour associated with the fracture event and it cannot be applied to displacement control experiments. The plot of the irreversible work vs. load for a range of applied loads can be used in this case but is time consuming. Also this method does not work well for sub-threshold cracking. Therefore, it is necessary to find a method to solve such problems if the fracture properties of very thin coatings (≤1μm) are to be assessed. In this paper, a method which is based on extrapolating the total work vs. displacement curve at a load where cracking occurs is presented to estimate the fracture toughness of the coated system.
The Influence Of Substrate On Partially Rapidly Solidified Alumina-3 wt % titania Nanocrystalline Coatings Deposited by Plasma Spray Technique
Authors: Venkataraman R. , Parmanick B. , Ravikumar B. , Pathak L. C. , Das D. K. , Venkataraman B 
Published: April 2011

ABSTRACTIn this paper an attempt was made to impose different degrees of rapid solidification by spraying on diverse substrates of varying thermal properties. Substrates such as Copper, Aluminum, Stainless steel, Low alloy steel substrates were used to alter the imposed cooling rate and thereby the amount of residual α phase. A start powder of 3 wt % Alumina-titania powder was used for spraying to a thickness of 250 μm on the different substrates specified. In all cases the rapidly solidified phases show nanocrystalline sizes with the most rapidly solidified metastable γ phase showing finer grain size of less than 25 nm. The surface roughness of the substrate and the coating were characterized by Atomic force microscopy. In contrary to the Alumina-13 wt % titania, coupons of Alumina-3 wt % titania had shown poor indentation fracture toughness with increased amount of residual α phase. Coupons of stainless steel and low alloy steel had shown the lowest fracture toughness when tested by Vickers type indentation at loads of 3 N and 5 N. In contrast to these results the interfacial toughness when measured by Rockwell indentation technique at loads of 150 N was found to be dependent on the elastic modulus of the substrate more than the coating hardness. The interfacial toughness was found to be lower for softer material such as aluminum and copper than stainless steel and low alloy steel.
In Situ Optical Tribometry Studies of Nanocomposite Coatings
Authors: Chromik Richard R. , Baker Colin C. , Voevodin Andrey A. , Wahl Kathryn J. 
Published: April 2011

ABSTRACTSix nanocomposite coatings of yttria-stabilized zirconia (YSZ), Au, diamond like carbon and MoS2 have been studied by in situ tribometry. The coatings all had a nominal MoS2 content of between 14 and 18 mol%, while the concentrations of the other components were varied. Steady state friction coefficients in both dry (0.04–0.05) and wet sliding conditions (0.06–0.08) were similar for all coatings. However, by in situ tribometry, wear mechanisms were found to differ depending on coating composition and test environment humidity. Friction spiking in high YSZ coatings was identified with local plowing and scoring of the track followed by an extrusion of transfer film material. Trends in coating hardness and modulus are correlated to composition and coating wear processes.
Reactive ion etching of TiN, TiAlN, CrN and TiCN Films in CF4/O2 and CHF3/O2 Plasmas
Authors: Leech Patrick W. , Reeves G. K. , Holland A. S. 
Published: April 2011

AbstractThe reactive ion etching of a range of hard coatings (TiN, TiCN, CrN and TiAlN) has been examined as a function of rf power, flow rate and pressure. The films were deposited by filtered arc deposition (TiN, TiAlN and CrN) or low energy electron beam (TiCN) on polished disc substrates of M2 tool steel. The flat surfaces were lithographically patterned with a grating structure (∼1 μm pitch). The TiN and TiCN layers have shown significantly higher etch rates (100-250 nm/min) than the CrN and TiAlN (∼5 nm/min) coatings. These regimes of higher and low etch rate were identified as ion-enhanced chemical etching and physical sputtering, respectively. In CF4/O2 plasma, the etch rate of the TiN and TiCN layers increased with rf power, flow rate and pressure which were parameters known to enhance the density of active fluorine species. The etch rates of TiN and TiCN layers were higher in CF4/O2 plasma than in CHF3/O2 gases in which polymer deposition was produced at pressure ≥ 35 mTorr.
Effects of Preferred Orientation on the Tribological Behavior of the TiN and CrN Films by the CAIP
Authors: Bae Sang Geun , Cho Yong Ki , Moon Kyoung Il , Kim Sang Gweon , Kim Sung Wan 
Published: April 2011

AbstractFor the better understanding of anti-wear properties of hard coating films, the effects of preferred orientation, surface roughness, and surface hardness on the tribological property of TiN and CrN films have been studied. TiN and CrN films were deposited by cathodic AIP (CAIP) with working temperatures of 350∼450°C, working pressures of 1∼5Pa, arc currents of 50∼90 A, and bias voltages of 30∼150V. The characteristics of microstructure and its effect on the friction coefficient were investigated with working conditions. The preferred orientation of the film was examined by XRD. The friction coefficient was determined using ball on disk tribometer. The preferred orientation of films was changed from (200) to (111) with decreasing working pressure and increasing bias voltage. It is reported that TiN coating with strong (111) orientation have better tribological property, but, in this study, although similar tendency was also found in TiN, the tribological property was increased with diminishing (111) orientation in CrN films. It is concluded in this study that the tribological property is not affected only by the orientation of the film, but it depends on the combined properties of surface roughness, surface hardness, and orientation of the film. The friction coefficients of TiN and CrN were 0.48∼0.52 and 0.49∼0.53, respectively.
Selective protein adsorption on highly hydrophilic surface modified with combined V–UV photon and plasma irradiation
Authors: Sato Yuji , Murahara Masataka 
Published: April 2011

ABSTRACTA highly hydrophilic surface, with a water contact angle smaller than 20 degrees, was rendered to a poly-methylmethacrylate [PMMA] by Xe2 excimer lamplight and plasma treatment. In result, the implant material that was highly biocompatible and adhesive to soft tissue was developed. The PMMA surface, which had been pretreated by ammonia plasma, was irradiated with Xe2 excimer lamplight in the presence of hydrazine as a reaction solution. In order to evaluate the wettability of the modified sample, the contact angle with water was measured. The contact angle was decreased from 83 degrees for untreated PMMA to 60 degrees when irradiated the Xe2 lamplight for 30 minutes. With the ammonia plasma pretreatment, the contact angle of the treated sample became to 7 degrees at the 1 minute Xe2 lamp irradiation.
Stress induced phase transition in a monomolecular perfluroalkylsilane film self assembled on aluminium surface
Authors: Biswas Sanjay Kumar , Devaprakasam D. 
Published: April 2011

ABSTRACTWe control the stiffnesses of two dual double cantelevers placed in series to control penetration into a perflurooctyltrichlorosilane monolayer self assembled on aluminium and silicon substrates. The top cantilever which carries the probe is displaced with respect to the bottom cantilever which carries the substrate, the difference in displacement recorded using capacitors gives penetration. We further modulate the input displacement sinusoidally to deconvolute the viscoelastic properties of the monolayer. When the intervention is limited to the terminal end of the molecule there is a strong viscous response in consonance with the ability of the molecule to dissipate energy by the generation of gauche defects freely. When the intervention reaches the backbone, at a contact mean pressure of 0.2GPa the damping disappears abruptly and the molecule registers a steep rise in elastic modulus and relaxation time constant, with increasing contact pressure. We offer a physical explanation of the process and describe this change as due to a phase transition from a liquid like to a solid like state.
Tribological Properties of Sputter-Deposited MoS2 Films Containing Titanium
Authors: Krzanowski James , Nunna Dyumani 
Published: April 2011

ABSTRACTThe tribological properties of sputter-deposited MoS2 and MoS2-Ti films were investigated in this study. The deposited films were characterized using microprobe analysis for composition and x-ray diffraction (XRD) for structure. The frictional properties of the films were examined using a pin-on-disk (POD) with counterfaces of 440C steel, aluminum, tungsten carbide and alumina. The tests were run under low (25%), medium (50%) and high (70%) humidity levels. MoS2 films without Ti were first examined under cyclic humidity conditions between 25 and 50% R/H. The results showed that for steel, WC and alumina counterfaces, the effect of the higher humidity was to increase the friction, but lower friction could be recovered when the humidity was reduced back to 25%. For films containing Ti, the best results were obtained at a concentration of 20 at. % Ti. These films performed well for steel and WC counterfaces, but poorly against aluminum. The effect of deposition temperature (up to 450oC) was examined for MoS2 and MoS2-5% Ti films. Higher temperatures yielded more crystalline films, but the addition of Ti partially countered this effect. The POD test showed that at medium humidity levels the friction decreased with temperature, but increased slightly when tested under low humidity. In all cases, the 5% Ti-containing films had a fiction coefficient of about 0.1 below that for films without Ti.
IV-VI Semiconductor Mid-IR Lasers
Authors: McCann Patrick J. , Selivanov Yurii 
Published: April 2011

ABSTRACTMid-IR lasers fabricated from narrow bandgap IV-VI semiconductors are proven devices for molecular spectroscopy applications. Wide single-mode tunability, low waste heat generation, and large spectral coverage from about 1000 cm−1 (10 µm) to about 2500 cm−1 (4 µm) have allowed development of laser absorption spectroscopy instrumentation for fast and sensitive measurement of specific gas phase molecules. For example, IV-VI mid-IR lasers with emission in the 5.2 µm spectral range have recently enabled the development of breath analysis instruments for real-time measurement of exhaled nitric oxide (eNO). Laser tunability with current ramping is sufficient for simultaneous measurement of exhaled carbon dioxide (eCO2), a capability that allows highly accurate determination of eNO concentrations in the low ppb range, a sensitivity required for assessing airway inflammation in patients with asthma. After discussing emerging medical diagnostic applications this paper reviews recent progress in the development of liquid-nitrogen-free cryogenic cooling systems for IV-VI mid-IR lasers. A description of continuing research on the development of improved IV-VI lasers, where the primary objective is to fabricate devices with continuous wave (cw) operation at room temperature is then presented. Theoretical and experimental analysis of (111)-oriented multiple quantum well (MQW) IV-VI materials show that it should be possible to reduce lasing thresholds significantly. In addition, results from transferring IV-VI materials from low thermal conductivity growth substrates to higher thermal conductivity copper show that new laser packaging methods can significantly improve active region heat dissipation. Together, these new materials and device packaging methods promise to enable the fabrication of IV-VI mid-IR lasers with cw operation at room temperature.
Wavefunction Engineering of Layered Quantum Semiconductor Structures: Recent Progress
Authors: Ram-Mohan L. R. 
Published: April 2011

ABSTRACTA Lagrangian formulation for the valence bands of bulk zinc blende and wurtzite compound semiconductors provides a direct approach to determining derivative operator ordering at layer interfaces in the multibandk·Pdescription of electronic states, in the envelope function approximation. The current continuity condition is obtained through a gauge-variation on the Lagrangian. The principle of least action together with the discretization of the action integral naturally leads into a finite element approach for the modeling and simulation of the multiband Schrödinger equations. Being a variational method, the wavefunctions and energy eigenvalues can be systematically improved with quadratic convergence. By including the Poisson Lagrangian, a self-consistent treatment of the Schrödinger-Poisson band-bending in arbitrarily doped structures is obtained. Numerical examples are presented for the valence band electronic states for quantum wells and superlattices. We have also coupled the finite element method with layer parameter optimizations to design heterostructures for lasers emitting at given wavelengths. It is in this sense that wavefunction engineering goes beyond the notion of bandgap engineering in providing the means for optimizing wavefunction localization in layers, selecting layer thicknesses, enhancing optical matrix elements, and laser gain.
Spatial Bandgap Tuning in Long Wavelength InAs Quantum Dots-in-Well Laser Structure
Authors: Wang Yang , Dimas Clara E. , Djie Hery S. , Ooi Boon S. , Dang Gerard , Chang Wayne 
Published: April 2011

ABSTRACTWe employed the postgrowth impurity-free vacancy diffusion technique to selectively tune the bandgap of the InAs/InGaAlAs dots-in-well laser structure grown on (100) InP substrate. A blueshift up to 170 nm with a significant decrease in the photoluminescence linewidth has been observed. Spatial control of the bandgap shifts has been achieved using SiO2 and SixNy layers as annealing caps. A differential wavelength shift of 76 nm has been observed after a rapid thermal annealing step at 750 °C for 30 s. In contrast to most reported results in other material systems using similar process, we observed a larger bandgap shift from the SixNy capped samples than from the SiO2 capped samples. Our theoretical calculation indicates that the unusual intermixing behavior in this material system is governed by different interdiffusion rates of group-III atoms.