bluuebunny/crossref_metadata_2025 huggingface dataset:
X-ray Elemental Mapping of Multi-Component Steels
Authors: Papworth Adam J. , Williams David B.
Published: April 2011

Steels used in steam turbine applications are susceptible to temper embrittlement if operated at temperatures above 400°C. The cause of this embrittlement is the segregation of impurity elements, mainly phosphorus, to the prior austenite grain boundaries. Molybdenum can act as an effective scavenger for phosphorus, but the scavenging effect is lost when the molybdenum is precipitated in carbides during service at these elevated temperatures. Thus, the very slow temper embrittlement is controlled by the rates of alloy carbide formation, rather than by the diffusion of phosphorus. The presence of vanadium apparently retards the embrittlement process even more by interfering with the formation of the molybdenum-rich carbides. Vanadium carbonitrides, are small, only a few nanometers in size, and difficult to see by standard TEM contrast mechanisms. Analysis of segregating elements to the grain boundaries has to be carried out on areas which are devoid of precipitates, especially small V precipitates or other precipitates that could be interpreted as segregation rather than precipitation. One method of detecting precipitates in the matrix is by X-ray mapping areas of interest. This paper describes a new method of X-ray mapping of multi-component steels that have overlapping lines. The method has been found to be effective in removing thickness effects from the maps and discriminating between real and artificial compositional components, which are created by the overlapping lines.
High Sensitivity Convergent Beam Electron Diffraction for the Determination of the Tetragonal Distortion of Epitaxial Films
Authors: Schuer C. , Leicht M. , Marek T. , Strunk H.P.
Published: April 2011

We have optimized the sensitivity of convergent beam electron diffraction (CBED) by orienting the specimen such that the central (000) diffraction disc shows a pattern of defect lines that are most sensitive to tetragonal distortion. We compare the position of these lines in the experimentally obtained patterns with results from computer simulations, which need to be based on dynamical diffraction theory. In both experimental and simulated patterns the positions of the defect lines are determined by applying a Hough transformation. As a result of this optimized approach, we can measure the tetragonal distortion of a low temperature grown GaAs layer as low as 0.04%.
Electronic Structures of Single-Walled Carbon Nanotubes Studied by NMR
Authors: Tang X.-P. , Kleinhammes A. , Shimoda H. , Fleming L. , Bennoune K. Y. , Bower C. , Zhou O. , Wu Y.
Published: April 2011

An individual single-walled carbon nanotube (SWNT) has been shown [1-4] to exhibit remarkable electronic properties which depend on its diameter and chirality. In this work, the 13C nuclear magnetic resonance technique is used to measure quantitatively the electronic density-of-state (DOS) at the Fermi level in a bulk SWNT sample. Two types of 13C nuclear spins are observed with drastically different nuclear spin-lattice relaxation time (Tl). About onethird of the 13C nuclear spins with shorter Tl, are identified to reside at the metallic SWNTs and two-thirds can be associated with the semiconducting SWNTs. For the metallic SWNTs, the DOS at the Feimi level is measured quantitatively, which is about 0.022 states/(eV·atom·spin). The measured electronic DOS at the Fermi level agrees with the theoretical prediction for metallic tubes. This study also found that the semiconducting SWNTs in bundles, in fact, possess weak metallic characters. This indicates that tube-tube interactions within SWNT bundles could change the electronic properties.
Electrostatic Measurement of Plasma Plume Characteristics in Pulse Laser Ablated Carbon
Authors: Mayo R. M. , Newman J. W. , Sharma A. , Yamagata Y. , Narayan J.
Published: April 2011

A triple Langmuir probe measurement has been implemented to investigate plasma plume character in low fluence (∼ 3.0 J/cm2) pulsed laser evaporation (PLE) discharges and has been found to be an extremely valuable tool. Absolute plasma plume density estimates are found to reside in the range 1.0 × 1013–2.0 × 1014 cm−3 for vacuum pulses. A simple heavy particle streaming model for vacuum pulses allows estimates of the plume ionization fraction of ∼ 10%. This is consistent with typical deposition inventory suggesting that high kinetic energy ions play an important role in DLC film deposition. Electron temperature is found to consistently reside in the range 0.5-3.0 eV, and appears to be uninfluenced by operating conditions and large variations in Ar and N2 fill gas pressure. Consistent with strong plume ion and neutral particle coupling to the background fill, constancy of Te suggests expulsion of background gas by the energetic plume. The leading edge ion plume speed is measured via temporal displacement of spatially separated probe signals on consecutive PLE pulses. Flow speeds as high as 5.0 × 104 m/s are observed, corresponding to ∼ 156 eV in C+. The ion flow speed is found to be a strongly decreasing function of fill pressure from an average high of ∼ 126 eV in vacuum to ∼ 0.24 eV at 600 mTorr N2. Raman scattering spectroscopy indicates DLC film quality also degrades with fill pressure suggesting the importance of high ion kinetic energy in producing good quality films. Optical emission indicates an increase in C2 molecular light intensity with fill gas pressure implying a reduced, if any, role of these species in DLC production. Ion current signal anomalies in high pressure pulses indicate the formation of high mass carbon clusters during plume evolution in the presence of background gas. Mass diffusivity estimates, based on density decay, suggest the presence of under these conditions. Demonstration and control of such cluster formation may provide method(s) for controlling novel advanced materials properties.
Direct Ion Beam Deposition of Diamond-Like Films From RF Inductively Coupled (IC) Plasma Source: Mechanical, Electrical, and Optical Properties
Authors: Druz B. , Zaritskiy I. , Williams K. , Hayes A. , Polyakov V.I. , Kchomich A.V. , Li Xiodung , Bhushan Bharat
Published: April 2011

Diamond-like carbon (DLC) films were deposited on various substrates using direct ion beam deposition from an RF IC hydrocarbon plasma source. Combinations of gases such as CH4. CH4–N2 were used to form plasma. The mechanical, electrical and optical properties of the films were examined as a function of deposition conditions and N2 content in gas mixture. A small amount of N2 (<8 sccm) did not markedly change hardness and stress, while electrical conductivity was significantly increased. In addition, a small amount of N2 improved wear performance of the films reducing amount of debris and wear track size. Introduction of high N2 flow into the system significantly deteriorates value of these parameters. It was found that N2 essentially increases absorption coefficient, and reduces optical band gap. Analysis of the experimental results shows that observed effects can be explained by incorporation of N2 into carbon-strained network that induces structural changes and. in turn, leads to an increase of sp2 fraction in the DLC films.
Raman Signature of Bonding and Disorder in Carbons
Authors: Ferrari A C , Robertson J
Published: April 2011

The factors controlling the position and intensity of the G3 and D peaks of the Raman spectra of disordered and amorphous carbons are separated in terms of a 3-stage model. The Raman spectra are shown to depend fundamentally on the degree of ordering of the sp2 sites, and only weakly or indirectly on the fraction of sp3 sites. Three factors control the G and D peaks; the perfection of graphitic order, replacing aromatic rings with olefinic chains and increasing the sp2 content. These rules allow us to state when the G3 peak position can be related reliably to sp3 content.
Fabrication and Characterization of Functionally Gradient Diamond-Like Carbon Coatings
Authors: Wei Q. , Sharma A. K. , Yamolenko S. , Sankar J. , Narayan J.
Published: April 2011

Pure diamondlike carbon thin films largely bonded by four-fold coordination suffer from a large internal compressive stress that gives rise to a serious adhesion problem. In this work, functionally gradient (FG) diamondlike carbon thin coatings were prepared by pulsed laser deposition in a high vacuum chamber as an alternative approach to address the adhesion problem of diamondlike films. Copper, silver and titanium were incorporated into the growing films with their concentration as a function of the distance from the substrate surface. The top of the thin coating is pure DLC of about 400 nm in thickness. The total thickness of the functionally graded superhard DLC coatings can exceed 1.0 μm without buckling. Visible micro-Raman spectroscopy was used to characterize the bonding structure of the layers which contain alloy atoms. High resolution transmission electron microscopy was employed to study the microstructure of the coatings. Nanoscale mechanical characterizations using Nanoindenter XPTM were carried out to study the mechanical behavior of the functionally gradient DLC films.
An Electrochemical Impedance Evaluation and Laser Irradiation Effects on the Electronic Structure of Silicon Containing Diamond-Like Carbon Coating
Authors: Fountzoulos Costas G. , Kelley Jack V. , Halada Garry P.
Published: April 2011

Hard, adherent, 2 μm thick lubricious silicon containing diamond-like carbon coatings (Si-DLC) were synthesized by 40 keV Ar+ ion beam assisted deposition (IBAD) of tetraphenyltetramethyl-trisiloxane oil on two, 5 cm by 5 cm by 0.64 cm thick 4340 steel substrates. Two different substrate surface finishes were examined, I polished and 1 600 grit finish (unpolished). The corrosion resistance of the Si-DLC coating was evaluated by Electrochemical Impedance Spectroscopy (EIS) in a 0.005N concentration sodium chloride (NaCI) solution. Low frequency impedance data from each of the coatings were compared with those of bare steel. The Si-DLC coating deposited on the polished substrate performed slightly better than the one deposited on the unpolished surface. Overall the Si-DLC coating did not appear to offer very much corrosion protection to the steel. This was mainly attributed to the presence of pinholes in the coating. Furthermore, to study the effect of radiation on the electronic structure of the Si-DLC coating, three Si-DLC coatings synthesized under the same deposition conditions on silicon substrates at various oil precursor temperatures were irradiated by a 355 nm wavelength, 0.37 Watts, pulsed YAG Laser at 35 kHz. Corrosion and irradiation results and procedures to minimize the pinhole density in the Si-DLC coating will be discussed in detail
Effect of Catalyst Supports in the Synthesis of Graphite Nanostructures
Authors: Anderson P. E. , Rodriguez N. M.
Published: April 2011

It is well established that the structural characteristics of graphite nanofibers can be controlled by several factors including, the chemical nature of the catalyst, the composition of the reactant gas mixture and temperature at which the growth process is performed. In the current investigation we have endeavored to modify the behavior of the catalyst by dispersing the active metals on different support media. We have found that the strength of the metal-support interaction exerts a significant impact not only on the average size of the nanofibers generated by such a procedure, but also results in major changes in the architecture of the carbon materials. The support imposes certain geometrical constraints on the metal particles and these features are manifested in modifications in the degree of crystalline perfection and arrangement of the graphite sheets constituting the nanofibers. In addition, there is also the possibility that the support can induce electronic perturbations in the metal particles, a feature that will be most pronounced with a conductive carrier.
Electrical and Structural Properties of Carbon-Nitrogen Films
Authors: Kurt R. , Sanjinesa R. , Karimi A.
Published: April 2011

To investigate the role of nitrogen in the structure formation and electrical properties of CNx thin films, several carbon thin films containing variable concentrations of nitrogen were deposited using a magnetron sputtering in a reactive N2/ Ar discharge. The chemical composition of the as-deposited films was investigated by means of Rutherford backscattering (RBS) and a [N]/[C] ratio up to 0.5 was obtained. TEM studies confirmed that the deposits are mainly amorphous and contain nanocrystalline CNx compounds. Additional STM investigations reveal a cluster-like microstructure of the surface showing a maximum cluster size of 10 nm in thin films deposited at a N2 / Ar pressure ratio of 30% in the plasma. The electrical resistivity ρ was studied as a function of temperature between 10 K and 320 K. All deposited films show semiconducting behaviour. The lowest ρ values were observed in films containing no nitrogen, whereas the films deposited with 30% N2in the sputter plasma reveal strongest semiconducting properties. The temperature dependence of the measured resistivity will be discussed according to Mott's law and the activation energy for the electrical transport estimated at room temperature will be given.
Bulk Synthesis of Nanotube-Like Carbon Material
Authors: Jacob Michael , Palmqvist Ulrik , Alberius-Henning Peter , Ekström Thommy
Published: April 2011

Nanoporous carbons have been synthesised through a selective etching reaction, performed by halogenisation of metal carbides. The structures obtained can be controlled by choice of starting materials and reaction parameters, and here one example, chlorination of aluminium carbide at 700 °C, is given. The produced material is nanotube-like with agglomerates of short and wide interconnected tubular structures, which are here described as nanobarrels. The synthesis process gives a pure product with high-yield, and may be scaled up to produce bulk amounts.
Recent Developments in Superplasticity
Authors: McFadden S. X. , Mishra R. S. , Mukherjee A. K.
Published: April 2011

The phenomenon of superplasticity is explored in the range of high strain rate for both nanocrystalline and microcrystalline materials. True tensile superplasticity has been demonstrated in nanocrystalline grain size range. The difference in the details of such superplasticity between nanocrystalline and microcrystalline state is emphasized.
Simulation of Microstructural Evolution during Superplastic Deformation
Authors: Kim B.-N. , Hiraga K.
Published: April 2011

Superplastic tensile deformation is simulated in 2 dimensions by incorporating grain boundary diffusion and concurrent grain growth derived from static and dynamic growth mechanisms. The following relationship is found between microstructural changes and deformation behavior for constant stress conditions. Grain boundary diffusion produces an increase in the aspect ratio of the matrix grains during deformation and the increased aspect ratio causes a change in creep rate parameters: the stress exponent is decreased from the initial value of 1.0 for equiaxed grains and the grain size exponent is increased from the initial value of 3.0. Accelerated grain growth is also found by the present simulation.
Hyperplastic Forming: Process Potential and Factors Affecting Formability
Authors: Daehn Glenn S. , Vohnout Vincent J. , Datta Subrangshu
Published: April 2011

This paper has two distinct goals. First, we argue in an extended introduction that high velocity forming, as can be implemented through electromagnetic forming, is a technology that should be developed. As a process used in conjunction with traditional stamping, it may offer dramatically improved formability, reduced wrinkling and active control of springback among other advantages. In the body of the paper we describe the important factors that lead to improved formability at high velocity. In particular, high sample velocity can inhibit neck growth. There is a sample size dependence where larger samples have better ductility than those of smaller dimensions. These aspects are at least partially described by the recent model of Freund and Shenoy. In addition to this, boundary conditions imposed by sample launch and die impact can have important effects on formability.
The Effect of Fe-Addition to Al-10Ti Alloy on Superplasticity at High-Strain Rates
Authors: Kum D. , Kim W. J.
Published: April 2011

Ultra-fine microstructure consisting of equiaxed Al-grains and aluminide particulate was produced by powder metallurgy process using gas-atomized powders of Al-10wt%Ti-2wt%Fe alloy. High strain rate superplasticity (HSRS) has been investigated at 873-923K and strain rates higher than 10−3s−1in tension, and total elongation up to 500% was observed at the strain-rate of 10−1s−1. The strain rate vs. flow stress behavior exhibits the typical aspect of HSRS such as the increase of strain-rate sensitivity exponent with increase in strain-rate and an apparent activation energy higher than that for lattice diffusion in aluminum. The concept of threshold stress has been incorporated to illustrate the HSRS behavior, where the stress exponent of 3 describes the experimental data. The determined threshold stress showed strong temperature dependency as in the case of a similarly processed Al-10wt%Ti alloy, which exhibited the stress exponent of 2 in the same testing conditions. Solute drag mechanism has been postulated for the Al-Ti-Fe alloy.
Superelastic Shape Memory Alloy For Seal Applications Produced by Low Pressure Thermal Spray Technology
Authors: Sickinger Albert , Teter Joseph P.
Published: April 2011

The objective of this development program was to demonstrate the feasibility of producing superelastic NiTi shape-memory alloy (SMA) foil material by the low pressure plasma spraying (LPPS) process for the development of robust, corrosion resistant and long life sealing technology.

A conventional LPPS facility was retooled for the use of electric wire arc spraying and the process parameters were reconfigured. Foil specimens sprayed up to 1.5mm thickness showed good ductility after consolidation heat treatment at 950'C for 1 hour. Subsequent rolling of the foil specimens to a thickness of 0.5mm exhibited superelastic behavior. The amount of superelasticity will have to be determined. In addition, thin (0.2 mm) and thick (0.76mm) wall tubes have been produced in the 12.5mm diameter range. These samples were heat treated and subjected to Hot Isostatic Pressing (HIP). Metallographic examination revealed dense, solid microstructures after heat treatment and rolling, and hot isostatic pressing respectively.

It was concluded, that this development established the feasibility to produce near net shape superelastic NiTi foil with a retooled Low Pressure Wire Arc Spraying (LPWAS) process, modified to permit substitution of NiTi-wire for NiTi-powder as feed stock.
Characteristics of Piezoelectric Ceramics at High Vibration Levels
Authors: Takahashi S. , Sasaki Y. , Umeda M. , Nakamura K. , Ueha S.
Published: April 2011

New piezoelectric power devices -such as ultrasonic motors, piezoelectric actuators and piezoelectric transformers- have been studied intensively in recent years. The piezoelectric ceramics in these devices are often subjected to a high level of vibration, and the electromechanical characteristics of piezoelectric ceramics at high vibration levels vary when changes in vibration level are accompanied by changes in temperature. The effects of temperature and of vibration level on specific electromechanical characteristics of typical piezoelectric ceramics were therefore separated by using two measurement methods: the continuous-voltage-wave method, which results in an increased temperature; and the burst-voltage-wave method, which does not. The elastic, dielectric and piezoelectric constants were found to be sensitive to temperature but comparatively insensitive to vibration level. Mechanical loss, however, was found to be a function of both temperature and vibration level.
Shape Memory Ceramics
Authors: Matsumura T. , Nakamura T. , Tetsuka M. , Takashina K. , Tajima K. , Nishi Y
Published: April 2011

Three types of shape memory ceramics were introduced. They were the irreversible shape memory silica glass, the reversible shape memory bi-ceramics glass and reversible shape memory silica and Si-C-O glassy fiber samples (the small size change) induced by thermal expansion.
Switching Current in Pb(Zn1/3Nb2/3)O3-PbTiO3 Single Crystals
Authors: Belegundu Uma , Du Xiaohong , Uchino Kenji
Published: April 2011

Switching current measurements have been carried out on relaxorferroelectric single crystal-pure PZN, and the solid solution (1-x) Pb(Zni1/3 Nb2/3)O3 - x PbTiO3 with x= 0.04, 0.09, 0.10. Measurements have been done for crystallographic directions [001] and [111] for all these compositions. Switching times versus the applied field showed the following results. Pure PZN along [111] and 0.90PZN—O. 10PT along [001], and [111] showed an exponential dependence. Along [001] the PZN showed a linear fit. For solid solution single crystals-0.96PZN -0.04PT and 0.91PZN £ 0.09PT, a linear fit was obtained for the reciprocal switch times versus applied field for both the directions. If we draw a parallel picture with the reported barium titanate data, it appears that the polarization reversal is controlled by nucleation along [111]- spontaneous direction for PZN and [001], [111]for 0.90PZN - O.10PT. The mobility of the reversed domains controls the reversal along [001] for PZN and the solid solution single crystals with rhombohedral composition along [001] and [111]. The transient current curves showed two maximum points for crystals with x = 0.04 and 0.09. This is attributed to the co-existence of the two phases in 0.96PZN -0.04PT and 0. 91PZN - 0.09PT crystals.
Development of a MEMS Xylophone Bar Magnetometer Using Optical Interferometry for Detection
Authors: Miragliotta Joseph , Osiander R. , Champion J. L. , Oursler D. A. , Kistenmacher T.J.
Published: April 2011

We report the results of an optical interferometric study, which was designed to measure the magnetic-field induced displacement of a resonating xylophone bar MEMS magnetometer. The MEMS magnetometer is a Lorentz-force sensor, which transduces an alternating current and an orthogonal directed magnetic field into an alternating displacement of the xylophone bar. The Michelson interferometer system includes optics and electronics for active stabilization of the optical path length difference between the reference and sample beams. The active stabilization results in the ability to control or detect pathlength differences as small as ∼ 0.6 ×10−3 Å. With this level of operational sensitivity, the presence of a one nano Tesla magnetic field was found to produce a detectable bar displacement on the order of ∼10−3 Å. In addition to the high sensitivity, the interferometer photodetector displayed linear behavior over six decades of optical path length differences, which corresponded to a magnetic field dynamic range that spanned nano- to milli-Tesla amplitudes.
Mechanical Property Measurement of Electroplated Gold Microstructure Using Resonance Method
Authors: Baek Chang-Wook , Kim Yong-Kweon , Ahn Yoo-Min
Published: April 2011

Mechanical properties of electroplated gold microstructures were determined by measuring resonance frequencies of microbeams. Cantilever and bridge beam structures of different lengths were fabricated by electroplating surface micromachining technique, specially designed to realize an ideal fixed-boundary anchor. Fabricated beams were electrostatically excited and their resonance frequencies were measured by optical system composed of laser displacement meter with dynamic signal analyzer. Young's modulus, residual stress were calculated from the measured frequency data.
Effect of Buffer Electrodes in Crystallization of Zinc Oxide Thin Film for Thin Film Bulk Acoustic Wave Resonator
Authors: Yosho Y. , Tsukai N. , Inoue K. , Takeuchi M. , Nomura T. , Makino T. , Arai S. , Hata T.
Published: April 2011

A thin film bulk acoustic wave resonator (TBAR) has been fabricated using a ZnO thin film on a SiO2 diaphragm by MEMs techniques. The ZnO/SiO2 structure TBAR can be designed to cancel a temperature coefficient of frequency (TCF) by the ZnO/SiO2 thickness ratio, because the TCF of ZnO is negative, and that of SiO2 is positive. The ZnO thin film on the SiO2 shows a c-axis orientation almost equivalent to that of the ZnO thin film on a glass substrate by RF sputtering. However, the crystallinity of the ZnO thin film is influenced by the surface conditions of substrates. ZnO thin films have been deposited on Au/Cr, Au/NiCr and Au/Ti. The Au/Ti/ZnO/Au/Ti/SiO2 structure TBAR shows the best resonant characteristics in this experiment. The resonant characteristics of the TBAR depend on the crystallinity of the ZnO thin film. The resonant resistance of the TBAR at 205MHz using a Au/Ti under electrode is about 10% less than that using an Au/Cr electrode. The x-ray diffraction result shows that the crystallinity of ZnO is greatly influenced by the crystallinity of the lower electrode. The buffer layer between an Au electrode and substrate has an influence on both the crystallinity of the ZnO thin film and the resonant characteristics of the TBAR through the Au electrode.
Preparation of High-Quality Ultra-Thin Gate Dielectrics by Cat-CVD and Catalytic Anneal
Authors: Satot Hidekazu , Izumit Akira , Matsumura Hideki
Published: April 2011

This paper reports a feasibility of Cat-CVD system for improvement in characteristics of ultra thin gate dielectrics. Particularly, the effects of post deposition catalytic anneal (Catanneal) by using hydrogen (H2)-decomposed species or NH3-decomposed species produced by catalytic cracking of H2 or NH3, are investigated. The C-V characteristics are measured by MIS diode for the 4.5nm-thick Cat-CVD SiNx and 8nm-thick sputtered SiO2 for comparison. The small hysteresis loop is seen in the C-V curve of both SiNx and SiO2 films as deposition. However, it is improved by the Cat-anneal using H2 or NH3, and the hysteresis loop completely disappears from the C-V curves for both films. This result demonstrates that the Cat-anneal is a powerful technique to improve quality of insulating films, such as Cat-CVD SiNx and even sputtered SiO2 films. In addition, the leakage current of SiNx, films with 2.8nm equivalent oxide thickness is decreased by several orders of magnitude than that of the conventional thermal SiO2 of similar EOT and the breakdown field is increased several MV/cm by Cat-anneal at 300°C.
Silicon Cleaning Methods Compared at Metal Concentrations Below 1E10 atoms/cm2
Authors: Ilardi Joseph , Saraswati Rajananda , Schwartzkopf George
Published: April 2011

An alkaline aqueous silicon wafer cleaner has been developed which reduces trace metal contamination levels on “p-type” unpatterned silicon wafers to below 1E10 atoms/cm2 without acidic cleaning. This patented technology uses a specially formulated buffering system consisting of an oxidation resistant chelating agent and salt of a weak acid. The aqueous cleaner maintains a stable pH of about 9.5 over a wide range of dilutions, temperatures, hydrogen peroxide concentrations and bath aging times. A single-step bath, megasonic bath or spray clean with this formulation leaves the chemical oxide on the silicon wafer surface free of particles, atomically smooth, free of organics and lower in trace metal contamination levels than similar surfaces cleaned with conventional formulations.

An analytical method was developed which allows the reliable detection of trace metals on silicon wafer surfaces down to 1E8 atoms/cm2 for aluminum, calcium, copper, iron, nickel, sodium and zinc. The procedure uses an ICP-MS with a concentric nebulizer and a desolvator. The acids used were ultrapure to keep the blanks to a very minimum and analyses were run in a class 10 clean room. The trace metals on the wafer were extracted using known amounts of ultrapure acids and were directly aspirated using a special arrangement with the concentric nebulizer. The J.T. Baker cleaner was compared to and outperformed the conventional RCA-1&2 clean and dilute RCA-1&2 chemistries using ultrapure ammonium hydroxide, hydrochloric acid and hydrogen peroxide.
Aspects of Gas Phase Chemistry During Chemical Vapor Deposition of Ti-Si-N Thin Films With Ti(NMe2)4 (TDMAT), NH3, and SiH4
Authors: Amato-Wierda Carmela , Norton Edward T. , Wierda Derk A.
Published: April 2011

Silane activation, predominantly in the gas phase, has been observed during the chemical vapor deposition of Ti-Si-N thin films using Ti(NMe2)4, tetrakis(dimethylamido)titanium, silane, and ammonia at 450°C, using molecular beam mass spectrometry. The extent of silane reactivity was dependent upon the relative amounts of Ti(NMe2)4and NH3. Additionally, each TDMAT molecule activates multiple silane molecules. Ti-Si-N thin films were deposited using similar process conditions as the molecular beam experiments, and RBS and XPS were used to determine their atomic composition. The variations of the Ti:Si ratio in the films as a function of Ti(NMe2)4 and NH3 flows were consistent with the changes in silane reactivity under similar conditions.
External Cavity Mid-Infrared Semiconductor Lasers
Authors: Le H. Q. , Lin C.-H. , Murry S. J. , Zheng J. , Pei S.-S.
Published: April 2011

Sb mid-IR laser can be used in external configuration to achieve wide wavelength tuning range. At low temperature, gain media with band-edge wavelengths between 3.3 to 4 pm have been demonstrated with wavelength tuning up to ∼9% of the center wavelength. Power output from few tens of mW to 0.2-W peak, 20-mW average was achieved. Type-II Sb laser promises the possibility of such performance at higher temperature, e. g. 200 K. However, significant trade-off must be considered between tuning range and power and efficiency. Optimization requires consideration of both basic wafer design and cavity geometry.
Photoconductive Properties of GaAs1−xNxDouble Heterostructures as a Function of Excitation Wavelength
Authors: Ahrenkiel R. K. , Mascarenhas A. , Johnston S. W. , Zhang Y , Friedman D. J. , Vernon S. M.
Published: April 2011

The ternary semiconductor GaAs1−xNxwith 0 < x < 0.3 can be grown epitaxially on GaAs and has a very large bowing coefficient. The alloy bandgap can be reduced to about 1.0 eV with about a 3% nitrogen addition. In this work, we measlired the internal spectral response and recombination lifetime of a number of alloys using the ultra-high frequency photoconductive decay (UHFPCD) method. The data shows that the photoconductive excitation spectra of the GaAs0.97N0.03alloy shows a gradual increase in response through the absorption edge near Eg. This contrasts with most direct bandgap semiconductors that show a steep onset of photoresponse at Eg. The recombination lifetimes frequently are much longer than expected from radiative recombination and often exceeded 1.0 µs. The data was analyzed in terms of a band model that includes large potential fluctuations in the conduction band due to the random distribution of nitrogen atoms in the alloy.
Infrared-Photovoltaic Responses of Ion-Beam Synthesized β-FeSi2/n-Si Heterojunctions
Authors: Maeda Yoshihito , Umezawa Kenji , Miyake Kiyoshi , Ohashi Kenya
Published: April 2011

Photoresponses of photovoltaic cells using ion-beam synthesized (IBS) polycrystalline p+-β-FeSi2/n-Si heterojunctions were examined in an infrared (IR) wavelength region. At room temperature, an evident photoresponse due to an internal photoemission from trap levels in β-FeSi2 with the threshold energy Φ=0.62 eV was observed at 0.6-0.87 eV. The pronounced increase of a photoresponse corresponding mostly to an interband transition in β-FeSi2 was observed at 0.87-1.1 eV. The maximum dominated by a surface recombination process appeared around ∼1.2 eV. The surface recombination rate of ∼104 cm/s was estimated. The quantum efficiency was ∼60 % in the 0.8-1.0 µm wavelength region and ∼14 % around the band-gap of βFeSi2.
Si1−xGex Bulk Crystals Growth and PN Junction Formation by Diffusing Phosphorus
Authors: Kato S. , Horikoshi T. , Ohkubo T. , Iida T. , Takano Y.
Published: April 2011

The bulk crystal of silicon germanium was grown by vertical Bridgman method with germanium composition, x, varying from 0.6 to 1.0. The temperature dependent variation of the mobility is indicative of alloy scattering dominantly for the bulk wafer. Phosphorus was diffused in as-grown p-type bulk wafer at 850 °C to form pn-junction, and the diffusion coefficient of phosphorus was evaluated as a function of x. The diffusion behavior of phosphorus in silicon germanium is closely correlated with the germanium self-diffusion with changing x. For specimens with lower content x, P concentration profiles indicated “kink and tail” shape, while it was not observed for higher x. For current-voltage characteristics measurement, an ideality factor was obtained.
Second-Harmonic Generation in Oriented CdSe-Nanocrystal-Doped Indium Tin Oxide Film and its Application to an Infrared Detector
Authors: Narazaki A. , Hirano T. , Sasai J. , Tanaka K. , Hirao K.
Published: April 2011

Second-harmonic generation in CdSe nanocrystals doped in indium tin oxide ( ITO ) films has been examined. The thin film samples were prepared by r.f. magnetron sputtering with ITO target on which CdSe chips were placed. The X-ray diffraction patterns of as-deposited films indicate that CdSe crystallites are precipitated in an amorphous ITO matrix, and they are preferentially oriented in the direction of (111) plane of zinc blende structure or (002) plane of wurtzite structure. The mean diameter of CdSe crystallite was estimated to be 3-5 nm using Scherrer's equation. Moreover, the CdSe crystallites grew with keeping its initial orientation when a dc voltage of 50 V/cm was applied in the direction parallel to the film surface. The application of the electric field effectively enhanced the second-harmonic intensity by two orders of magnitude compared to that of the as-deposited films. The second-order nonlinear coefficient d(2) for the electrically-treated specimen calculated on a basis of a modified Maker fringe theory is d31 = 3.0 × 10 pm/V at the wavelength of 1064 nm, which is comparable to d values reported for CdSe single crystal, d31 = 25 pm/V at 1054 nm and d33 =76 pm/V at 1064 nm.
Growth Processes of Hydrogenated Amorphous Silicon
Authors: Robertson John
Published: April 2011

The surface and subsurface processes occurring during the growth of a-Si:H are analysed to understand why dangling bond defects and weak Si-Si bonds form. We argue that hydrogen elimination to form the Si-Si network is the rate limiting process at low temperature, and this leads to the creation of weak Si-Si bonds. Dangling bonds form subsequently from weak bonds by a defect pool type process. Plasma processes, such as ion bombardment, which dehydrogenate the surface layers, can reduce the weak bond density.
Near Infrared Detectors and Solar Cells Based on Microcrystalline Silicon Germanium
Authors: Krause M. , Stiebig H. , Carius R. , Wagner H.
Published: April 2011

Microcrystalline silicon germanium alloys (ν-Si1−xGex:H) exhibit an enhanced optical absorption in the near infrared region with increasing germanium content. Therefore, the employment of this material as intrinsic absorber is a promising challenge for thin film technology in photovoltaics and sensorics. The influence of hydrogen dilution on the material and the performance of pin diodes prepared in a PECVD process with 10 % GeH4 in the gas phase is discussed. These results are compared with the characteristics of diodes prepared with higher germane content in the gas phase. With increasing germane content the solar cell parameters Voc and FF decrease and the deposition regime where good optoelectronic properties are observed is narrowed.
Negative Differential Resistance Characteristics of Silicon Nanocrystal Memory
Authors: Baik Seung Jae , Lim Koeng Su
Published: April 2011

Two-dimensional (2D) Si quantum dot array was fabricated by oxidation of microcrystalline Si film deposited by photo chemical vapor deposition (photo-CVD). Average size of Si quantum dot was estimated to be 2.4nm and dot density 7 ∼ 8 ×1011cm−2. Nanocrystal memory device with this 2D quantum dot array demonstrated negative differential resistance characteristics and single charge tunneling phenomena, which was observed as stepwise decrease of gate transconductance. Interface states at the oxidized surface of quantum dots were assumed to explain temperature dependence characteristics. This new process is adequate for functional device application of nanocrystal metal-oxide-semiconductor (MOS) memory.
40 Years Trajectory of Amorphous Semiconductor Research
Authors: Hamakawa Yoshihiro
Published: April 2011

A review is given on a research trajectory of amorphous and microcrystalline semiconductors and their device applications proceeded since 1970. A brief explanation on the motivation to start amorphous semiconductor research is given to produce a new kind of synthetic semiconductor having continuous energy gap controllability with valency electron controllability through our experience of modulation spectroscopy in semiconductors.

The first material we have challenged is Si-As-Te chalcogenide semiconductor which has a very wide vitreous region in Gibb's Triangle. A series of systematic experiments has been carried out in the terrestrial environment since 1971, and also within the TT-500A rocket experiment in 1980, and the Spacelab. J experiments FMPT (First Material Processing Test) project in 1992. The second material is hydrogenated amorphous silicon (a-Si:H) and its alloys started in 1976 just after the Garmisch Partenkirchen ICALS-6. With some basic research on the a-Si:H film deposition technology and film quality improvement, our continuous effort to improve the efficiency bore the tandem type solar cells in 1979, and also new products of a-SiC:H and a-SiGe:H in the early period of 1980s are described. These innovative device structures and materials have bloomed in the middle of 1980s in R & D phase such as a-SiC/a-Si heterojunction solar cells, a-Si/a-SiGe and also a-Si/poly-Si tandem type solar cells, and industrialized in recent few years. New kind of trials on full-color thin film light emitting devices has also been recently initiated with wide range of band gap controllability of a-SiC:H.

The third material is microcrystalline silicon (µc-Si) and their alloys which gathers a tremendous R & D effort as a promised candidate for the bottom cell of the a-Si/µc-Si tandem solar cells aimed for the all-round plasma CVD process for the next age thin film photovoltaic devices. In the final part of presentation, a brief discussion will be given on a technological evolution from “bulk crystalline age” to “multilayered thin film age” in the semiconductor optoelectronics toward 21 century.
Microstructure Characterization of Amorphous Silicon Based Alloys by Inert Gas Effusion Studies
Authors: Beyer Wolfhard , Camargo Sergio S. , Saleh Rosari
Published: April 2011

It is shown that inert gas effusion employing implanted neon and argon atoms is a useful tool for microstructure characterization of a-Si based alloys. The method measures sensitively interconnected voids and gives information about sizes of microstructure. Limitations of the method are discussed. The results show network reconstruction effects in a-Si:O:H and a-Si:C:H alloys as a function of annealing.
Effects of thermal annealing in the properties of PECVD a-SiC layers
Authors: Marsal L.F. , Pallares J. , Orpella A. , Bardés D. , Puigdollers J. , Alcubilla R.
Published: April 2011

Effects of thermal annealing in the properties of PECVD amorphous-Si0.8C0.2:H layers were studied. In order to reduce the density defects and increase the electrical conductivity, some samples were annealed: at 500 °C during 1 hour followed by 15 minutes at 800 °C. The results show that in the course of the thermal process, the hydrogen diffuse outside the film and the annealed Si0.8C0.2:H films tend to segregate in silicon clusters and, as a result, partially crystallize. Electrical dark conductivity shows an increase in more than six orders of magnitude, while the optical bandgap decreases from 1.9 eV to 1.4 eV. Annealed- Si0.8C0.2 films have been used as emitter in silicon bipolar transistors. Results indicate promising features such as low base currents and good emitter Gummel numbers.
Thermal Stabilization and Crystallization of Nanometric Particles of Si-C-N Produced by RF-Plasma Enhanced Chemical-Vapor-Deposition
Authors: Viera Gregorio , Bertran Enric , Polo Mari C. , Garcia-Caurel Enric , Farjas Jordi , Roura Pere
Published: April 2011

Nanoparticles of Si-alloys were grown at room temperature in a RF-PECVD process from mixtures of SiH4, CH4 and NH3. Quasi-monodisperse nanoparticles were produced in conditions of fast particle development. Among the different conditions for particle formation, we chose moderate low pressure (below 100Pa) and RF-power lower than 200W in all cases. The particle size was controlled through the modulation of the RF power supplied to the discharge. A post-thermal treatment at 800-900°C was used to eliminate the hydrogen of the particles and to stabilize them against environmental oxidation. To study the thermal crystallization of the particles, various thermal-treatments were used. The annealing of these particles at 1400°C for one hour under Ar or N2 led to different results depending on the composition of the samples as revealed by HRTEM and electron-diffraction analysis: SiC particles showed a marked internal crystallization; SiCN particles developed nanocrystals embedded in their amorphous matrix; Si particles crystallized in diamond-like silicon when annealed in Ar, whereas long whiskers of the α-Si3N4 phase, 50-200nm wide, grew from the particles in N2.
AFM and HREM Observation of the Pulse Laser Interference Crystallized a--Si:H/a-SiNx:H Multilayers
Authors: Wang Li , Huang Xinfan , Li Jian , Xu Jun , Yin Xiaobo , Li Qiliang , Li Wei , Zhu Jianming , Wang Mu , Liu Zhiguo , Chen Kunji , Fung Y. M. , Xu J. B.
Published: April 2011

The patterned nc-Si/a-SiNx:H superlattices were fabricated by using laser interference crystallization method and investigated with atomic force microscope (AFM), micro-Raman spectroscope, cross-section transmission electron microscope (TEM) and high resolution electron microscope (HREM). We found that after laser irradiation, self-assembled Si nanocrystallites (nc-Si) are formed within the initial a-Si:H sublayers, moreover, in the plane parallel to the surface of the films, these nc-Si orderly distribute in the certain regions with the same periodicity of 2.0 µm as phase shifting mask grating. Based on the structural analyses, the crystallization mechanism and the origin of the self-assembled phenomena are briefly discussed.
Excimer Laser Recrystallization of a-Si Employing Aluminum Masking Window
Authors: Jeon Jae-Hong , Lee Min-Cheol , Jung Sang-Hoon , Han Min-Koo
Published: April 2011

A new excimer laser recrystallization method of amorphous silicon is proposed to increase the grain size and control the grain boundary locations in polycrystalline silicon films. The proposed method is based on the lateral grain growth which occurs at the interface between molten and unmolten regions. To obtain selectively molten regions, the proposed method employs aluminum patterns on amorphous silicon. The aluminum patterns act as the beam shield during the laser irradiation as well as the lateral heat sink during the solidification period. The high reflectance of aluminum at the wavelength of XeCl excimer laser offers stable beam shielding property, and the high thermal conductivity enhances the lateral heat flow by the quick draining of laterally propagated heat. TEM observation has revealed that the well arranged large grains were successfully obtained.
Memory effects in MOS capacitors with silicon rich oxide insulators
Authors: Lombardo S. , Crupi I. , Spinella C. , Bongiorno C. , Liao Y. , Gerardi C. , Vulpio M. , Fazio B. , Privitera S.
Published: April 2011

To form crystalline Si dots embedded in SiO2, we have deposited thin films of silicon rich oxide (SRO) by plasma-enhanced chemical vapor deposition of SiH4 and O2. Then the materials wereannealed in N2 ambient at temperatures between 950 and 1100 °C. Under such processing, the supersaturation of Si in the amorphous SRO film produces the formation of crystalline Si dots embedded in SiO2. The narrow dot size distributions, analyzed by transmission electron microscopy, are characterized by average grain radii and standard deviations down to about 1 nm. The memory function of such structures has been investigated in metal-oxidesemiconductor (MOS) capacitors with a SRO film sandwiched between two thin SiO2 layers as insulator and with an n+ polycrystalline silicon gate. The operations of write and storage are clearly detected by measurements of hysteresis in capacitance-voltage characteristics and they have been studied as a function of bias.
Recombination in Tritiated Amorphous Silicon
Authors: Kosteski Tome , Gaspari Franco , Hum David , Costea Stefan , Zukotynski Stefan , Kherani Nazir P. , Shmayda Walter T.
Published: April 2011

Tritiated amorphous silicon was used for the intrinsic layer of a p-i-n hydrogenated amorphous silicon diode. Current versus voltage measurements were carried out on the diode over time under dark and illuminated conditions. There was a decrease in the forward characteristic of the diode when measured under dark conditions and there was a decrease in photovoltaic power. These changes can be explained by the creation of dangling bonds when bonded tritium atoms decay. By annealing the diode at 125 °C, most of its photovoltaic properties could be recovered. It was also found that luminescence could be recovered in tritiated amorphous silicon by thermal annealing.
Fast Deposition of Microcrystalline Silicon Films Using The High-Density Microwave Plasma Utilizing a Spokewise Antenna
Authors: Shirai H. , Sakuma Y. , Yoshino K. , Ueyama H.
Published: April 2011

The high-density and low temperature microwave plasma utilizing a spokewise antenna was successfully applied to fast deposition of highly crystallized and photconductive microcrystalline silicon (μ-Si:H) films at low temperatures. The deposition rate and film crytstallinity significantly depend on the axial distribution of the plasma parameters. Best crystallinity was obtained at the axial distance Z from the quartz glass plate, where the spread of the ion beam energy impinging to the growing surface was minimum. By optimizing the axial distance Z and total pressure, highly crystallized μ-Si:H films could be fabricated with a high deposition rate of ∼47Å/s in the SiH4 and Ar mixture plasma with no use of the H2 dilution. An intentional control of the ion beam energy is also attempted using a mesh grid electrode to suppress the ion bombardment to the growing surface.
Molecular Beam Epitaxially Deposited Amorphous Silicon
Authors: Lockwood D. J. , Baribeau J.-M. , Noël M. , Zwinkels J. C. , Fogal B. J. , O'Leary S. K.
Published: April 2011

We have deposited a novel form of amorphous silicon through molecular beam epitaxy in an ultra-high vacuum. In particular, by depositing silicon atoms onto an optical quality fused quartz substrate at room temperature we have obtained a silicon-based material that lacks the periodicity that characterizes crystalline silicon but nevertheless has 98% of the density. Spectroscopic studies reveal that there are only trace amounts of hydrogen and other impurity atoms in this novel form of amorphous silicon, this contrasting dramatically with the case of conventional amorphous silicon. The Raman and optical spectroscopic properties of this form of amorphous silicon are contrasted with those of conventional amorphous silicon and sputtered amorphous silicon, and conclusions, regarding the amount of disorder, are drawn. Finally, the device implications of this novel form of amorphous silicon are discussed.