bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Preparation of TEM Specimens from Hazardous or Difficult Materials
Authors: Sklad Philip S. 
Published: March 2011

ABSTRACTThe first, and often the most critical, step in any electron microscopy investigation is the preparation of an electron transparent specimen which is representative of the bulk material and in which the features of interest can be clearly observed and interpreted. However, for many materials of technological importance, specimen preparation procedures are far from routine. The application of standard, established techniques may be limited by material inhomogeneities, by physical constraints such as size or geometry, or by material constraints such as toxicity, radioactivity, or reactivity. Examples illustrating techniques for overcoming some of these difficulties will be reviewed.
Preparation Techniques For Structural Characterization of Powdered and Composite Materials
Authors: Ekmejian Evelyn M. , Bulko John B. 
Published: March 2011

ABSTRACTStandard preparation techniques such as ultramicrotomy and ion-milling are essential for obtaining accurate and detailed information about the structural and/or chemical properties of various categories of materials. The choice of a formulated matrix media has improved the preparation of thin sections of various powders ranging in degree of hardness from zinc oxide to tungsten carbide. This medium has shown superior performance when utilized in ion-milling powders and composites of high hardness such as boron carbide. This support vehicle has facilitated analysis of various geometric structures including hollow ceramic spheres. The homogeneity of chemically derived dielectric powders has been investigated by studying crystallite lattice parameter data derived from analysis of thin sections.
An Automated Jet Polishing Technique for Preparation of Transmission Electron Microscope Specimens for In-Situ Straining
Authors: Clark W. A. T. , Hardiman B. , Wagoner R. H. 
Published: March 2011

ABSTRACTThe increasing availability of intermediate and high voltage transmission electron microscopes, together with recent improvements in video recording equipment, have led to renewed interest in in situ dynamic experiments. To alleviate the problems encountered in preparing TEM specimens with the awkward geometries required for straining stages, a jet polishing technique has been developed which allows the use of a conventional twin-jet electropolishing unit, with all its attendant advantages. A pair of Teflon sheet inserts, with rectangular openings cut to a specific shape and size, are used in the conventional specimen holder. Specimens with elliptical holes close to the center of the gauge section, and with large electron transparent areas at both ends of the long axis, are produced routinely and rapidly. Samples of many annealed metals, such as brass, molybdenum, and aluminum, prepared by this method are stronger, and can be handled more easily, than those prepared by conventional methods.
Molecular-Beam Epitaxial Growth of GaAs on Si(321)
Authors: Uppal P.N. , Ahearn J.S. , Duncan S.W. 
Published: March 2011

AbstractMaterial properties of GaAs films grown on Si(321) substrates using molecular beam epitaxy (MBE) were evaluated and compared to films grown on Si(100) and Si(211). Dislocation densities in the GaAs(321) films, determined using transmission electron microscopy (TEM), were lower than those observed in GaAs(100) and GaAs(211), and the density of stacking faults in GaAs(321) also was quantitatively lower than in GaAs(211). Low-temperature (4.2 K) photoluminescence spectroscopy (PL) indicated that the tensile stress on the GaAs(321) films was greater than that on GaAs(100). These differences are attributed to changes in the strain-relaxation process caused by variations in the number of geometric arrangement of active-dislocation glide systems with different orientations. In addition, Si uptake near the GaAs/Si interface was less than 1/100 of a monolayer in GaAs(321) and 1/4 of a monolayer in GaAs(100). This difference is attributed to the presence of a non-polar (neutral) interface in the (321), whereas the (100) has a polar (charged) interface. MODFET devices with a I-)m gate length exhibited a transconductance of 180–200 ms/mm, comparable to devices on homoepitaxial GaAs(100).
Growth and Characterization of GaAs-Based Heterostructures on Si By Mocvd
Authors: Hobson W. S. , Pearton S. J. , Short K. T. , Jones K. S. , Vernon S. M. , Jacobson D. C. , Abernathy C. R. , Caruso R. 
Published: March 2011

AbstractAbstract: Several different types of GaAs-AlGaAs heterostructures were grown on Si substrates by MOCVD. The defect density in as-grown samples (~108cm−2) was similar to that of GaAs layers grown directly on Si, and the crystalline quality of the material was observed to improve slightly with post-growth annealing at 900°C. We examined the diffusion of both Si and Zn dopants during this type of annealing and found only a small amount of redistribution of both species. Laser annealing of GaAs-on-Si was also examined as a method of reducing the defect density in the material - we observed substantial improvements in surface quality, but no change in sub-surface crystalline quality.
Mbe Growth and Characterization of GaAs thin Films on SiGe Buffer Layers
Authors: Prokes S.M. , Tseng W.F. , Wilkins B.R. , Dietrich H. , Christou A. 
Published: March 2011

AbstractEpitaxial SiGe buffers have been formed by the implantation of 74Ge+ ions into Si(100)4° to <011> substrates. The implants were made at 150keV to a dose of 1×1017 /cm2 . The epitaxial layers were characterized by Rutherford backscattering, Raman spectroscopy, and electroreflectance and were found to be 300Å thick having on average a composition of Si0 . 35 Ge0.65. GaAs layers were then grown on these substrates by molecular beam epitaxy, using the standard two-step growth process. The results from Auger, Scanning Electron Microscopy, and Cross-sectional TEM indicate a lower defect production and propagation in these samples, compared to those grown directly on Si.
Characteristics of All-Omcvd Grown GaAs Mesfets on Si Substrates
Authors: Lee Jhang Woo , McCullough R. E. , Morrison R. H. 
Published: March 2011

AbstractWe present DC characteristics of all-OMCVD grown GaAs MESFET structures on Si substrates with unintentionally doped GaAs or AlGaAs buffer layers. MESFETs fabricated in two and three inch GaAs on Si wafers pinch off well and exhibit reasonably high transconductances up to 110 mS/mm for 1 µm gate devices. The reverse Schottky breakdown voltage of the MESFET gate is as high as 15 V and the forward turn on voltage is ~0.65 V. The ohmic isolation is comparable to the typical homoepitaxial layer with a leakage current of 100 nA at a I V bias. The low background doping levels of unintentionally doped GaAs buffer layers is the key factor for this successful MESFET operation.
Material Properties of GaAs-on-Si and Fabrication of Digital Integrated Circuits
Authors: Clhand N. , Ren F. , Chu S. N. G. , Sergent A. M. , Boone T. , Lang D. V. 
Published: March 2011

AbstractWe have found that the surface morphology of GaAs grown on Si by MBE is smoother at lower growth temperatures (<500° C), but that the crystalline properties improve at higher growth temperatures (575-600°C). After thermal annealing at 850°C for 15 rai the TEM plan-views indicate that the dislocation density on the surface is reduced by a factor of 4 only. However, the TEM cross-sections indicate a much larger reduction of dislocations in highly dislocated regions near the GaAs/Si interface. Dislocations which are loops or tangles tend to shrink and clean up after annealing leaving a larger volume of GaAs free from, or with fewer, dislocations. The density of electron deep levels reduces with increasing thickness. Electron traps M1, M3 and M4 are not seen when a high purity As is used. For high device performance, the GaAs buffer layer thickness should be at least 2 µm. Although the wafer warpage increases from 7 µm to 52 µm as the GaAs thickness increases from 1.2 µm to 4.2 µm on 7.5 cm wafers, the wafers are as fiat as the original Si wafers under vacuum clamping. Wafer warpage reduced significantly when GaAs was grown selectively through a Si shadow mask. For 1 µm gate MESFET's, σvT was 65 mV on a 3.5 × 3 cm2 wafer area with gmax = 153 mS/ram. A minimum propagation delay of 52 ps/stage at a power dissipation of 1.3 mW/gate was measured for the 19 stage DCFL ring oscillators with 40= yield. Conductivity of the Si substrate and GaAs buffer layer posed no problem in channel isolation. The divide-by-two circuits performed the frequency dividing operation up to 1.8 GHz. The study shows that GaAs-on-Si has a great potential for digital IC's.
The Photoluminescence and TEM Studies of Patterned GaAs films on Si Substrate Grown by Molecular Beam Epitaxy
Authors: Lee Henry P. , Huang Yi-He , Liu Xiaoming , Lin Hong , Smith John. S. , Weber Eicke R. , Yu Peter , Wang Shyh , Liliental-Weber Zuzanna 
Published: March 2011

AbstractPatterned epitaxial GaAs films have been formed on Si substrates by either growth over patterned substrate (selective -area epitaxy) or chemical etching of patterns after growth. The optical properties of these samples are studied by 77K photoluminescence (PL) and the defect structures are investigated by transmission electron microscope (TEM). The patterned substrate consisted of bare Si stripes with width ranging from 10 µm to 100 µm surrounded by Si3N4 films on both sides and a reference area of bare Si. For 1.5 µmiann d 3 µm thick films, PL intensities from the films inside the 10 µm stripe shows 140% and 75% increase over unpatterned areas while the residual tensile stress in the patterned films is very similar to that of the unpatterned area. The increase in the photoluminescence intensity is ascribed to the reduction of crystalline defects inside the the window area. In the chemically etched sample, the pattern consisted of 4 µm by 4 µm squares and 1 mm long stripes with widths ranging from 100 µm to 4 plm. From the shift of PL peaks, a monotonic decrease in the tensile stress versus stripe width is observed. In particular, when the width of the stripe is less than 7 µm. tensile stress becomes essentially uniaxial in agreement with the results obtained by Yacobi et al [16] on a GaAs on InP sample. The polarization of the luminescence spectra parallel and perpendicular to the uniaxial stress of a 4 µm wide stripe agrees well with theoretical prediction. It is also observed that tensile stress is almost completely relieved in the 4 µm by 4 muentc hed squares.
Effect of Substrate Misorientation on the Structual Strain and Defect Distribution of Mocvd Grown GaAs on Si
Authors: Hsieh K.C. , Feng M.S. , Stillman G.E. , Ito C.R. , McIntyre D.G. , Kaliski R.W. , Feng M. 
Published: March 2011

Astract:A systematic study of the structural properties and defect distribution of GaAs layers grown by metalorganic chemical vapor deposition on Si substrates misoriented 1°, 1.5°, 2°, 4°, and 6° from [100] toward [011] is reported. Double crystal x-ray rocking curves, cross-section and plan-view Transmission Electron Microscopy (TEM) are used to characterize the structural strain and defect distribution of as-grown and annealed GaAs layers. Both strain and defect density in the GaAs layers are found to be dependent of the degree of substrate misorientation as well as the direction in which measurements are made. Plan-view TEM shows an asymmetric distribution of microtwins in two perpendicular directions. There exists a correlation between the directionality of the strain and of the defect density. Furnace annealing at 850°C for 30 minutes in an arsine overpressure can reduce significantly the defects, the strain and the strain anisotropy. It is found that microtwins are of the highest density when the substrate is misoriented about 4 degrees for the as-grown samples. Though a reduction of defects after annealing occurs for all samples, the least misoriented one shows the most improvement.
The Behavior of Steps on Vicinal Si(001) and Ge(001)
Authors: Griffith J. E. , Kubby J. A. , Wierenga P. E. , Kochanski G. P. 
Published: March 2011

AbstractTunneling images of vicinal Si(001) and Ge(001) cut with a tilt about [110] are presented. Si(001) samples cut with a 4· tilt exhibit double steps with many kinks and point defects, while 2· Ge(001) samples exhibit only monoatomic steps. The behavior of the steps is essentially described by a model due to Chadi. The procedure used to clean the surface can have a strong influence on the spacing of the steps.
Defects and Interfaces in GaAs Grown on Si
Authors: McKernan S. , Zhu J. G. , Carter C. B. , Caridi E. , Schaff W. 
Published: March 2011

AbstractThe characterization of semiconductor epilayers by electron microscopy has revealed many different defects in the epilayer. Observations on three representative examples from GaAs epilayers grown on Si are presented. Double-ribbons, which are formed as a result of dislocation interactions near the heterojunction, have been used to determine the intrinsic and extrinsic stacking-fault energies in GaAs. Inverted stacking-fault pyramids have been observed which have nucleated in the epilayer and grown outward to the surface. Finally, differences in the growth rates of different twins are recorded by using AlGaAs layers to preserve the growth surface at various stages during epilayer growth.
Low-Temperature Heteroepitaxy of β-SiC on Si (111) Substrates
Authors: Eshita T. , Suzuki T. , Hara T. , Mieno F. , Furumura Y. , Maeda M. , Sugii T. , Ito T. 
Published: March 2011

AbstractWe developed a heteroepitaxial growth technique for large-area β-SiC films on Si substrates without buffer layers at 850ºC and 1000ºC. The substrates were vicinal 4-inch (111) Si wafers. The β-SiC films had smooth surfaces and were crack-free. X-ray diffraction and electron diffraction analysis revealed that the films grown at 1000ºC were single crystals. Satisfactory characteristics were obtained in aMOSFET with a β-SiC/Si02/poly-Si substrate structure. Our evaluations indicate that the β-SiC films were high-quality crystals.
Evaluation of Crystalline Quality of Zirconium Dioxide Films on Silicon by Means of Ion Beam Channeling
Authors: Nishibayashi Yoshiki , Imura Takeshi , Osaka Yukio , Fukumoto Hirofumi 
Published: March 2011

AbstractZirconium dioxide (ZrO2) films are deposited on Si(100) and Si(lll) substrates at 800ºC by vacuum evaporation. Channeling spectrum of the Rutherford backscattering shows that ZrO2 films (tetragonal(200)) are epitaxially grown on the Si(100) substrate. The fluctuation of crystallite orientation in the epitaxial layer is estimated to be 0.32º, by analyzing the angular dependence of the aligned and random backscattering spectra. Energy dependence of dechanneling factors in 0.3—2.0 MeV 4He+ indicates that the dominant defect arises from the stackingfaults.
Chemical Bonding and Lattice Mismatch in Semiconductorinsulator Heteroepitaxy: SrF2 on Si(111)
Authors: Olmstead Marjorie A. , Bringans R. D. 
Published: March 2011

AbstractThe growth of SrF2 on Si(111) is investigated using photoemission spectroscopy and compared to the growth of CaF2 on Si(l11). Both CaF2 and SrF2 have a fluorite lattice structure closely related to silicons diamond lattice structure. However, while the room temperature lattice constant of Si is only 0.6% smaller than that of CaF2, it is 6.8% smaller than that of SrF2. The photoemission results for thin films of SrF2 on Si(111) are very similar to previous measurements of the CaF2-on-Si(111) interface, reflective of strong silicon-cation bonding and the removal of fluorine from the interface. These results indicate that the chemical and electronic driving forces to dissociate the CaF2 or SrF2 molecule at the fluoride-silicon interface dominate over the structural constraints induced by the lattice mismatch.
Growth of CoSi2/Si Multilayer Structures
Authors: Ljni T. L. , Grunthaner P. J. , Schowengerdt F. D. , Fathauer R W. , Mazur J. H. , Chang K T. , Hashimoto S. , Xia Q. 
Published: March 2011

AbstractGrowth techniques for very thin CoSi2 and Si layers for multilayer applications have been studied. CoSi2 layers without observable pinholes are grown by atechnique utilizing the room-temperature codeposition of Co and Si in stoichiometric ratio with a Si cap, followed by annealing. The crystallinity of the resulting CoSI2 layers annealed at various temperatures was studied by in-situ Rutherford backscattering channeling spectroscopy. The channeling minimum yield decreases with increasing annealing temperature, and drops sharply at ~ 570ºC. Si overgrowth was studied on CoSi2 by a Si template technique, which utilizes the deposition of a thin amorphous Si layer followed by annealing prior to the growth of the bulk of the Si layer. The effect of Si thickness and annealing temperature on Islanding of the Si overlayer was studied by Auger electron spectroscopy. Critical temperatures for a numberof Si thicknesses were identified, above which islanding of these layers occurs.
Mocvd Growth of GaAs on Si
Authors: Akiyama Masahiro , Ueda Takash , Onozawa Sachiko 
Published: March 2011

AbstractThe initial stage of the growth of GaAs on Si by, MOCVD, the reduction of the residual dislocations by annealing at high temperatures and the dependence of the growth temperature on the stress in the GaAs layer were studied. The density and the size of deposited GaAs islands at the initial stage of the growth in the two-step growth sequence strongly affected the domain property of the subsequently grown layer. For reducing the residual dislocations by annealing at high temperatures, to repeat the growth and the annealing was more effective method compared with the other annealing methods we tried. The stress in the GaAs layers showed a constant value independently of the growth temperature and the value was related to the thermal expansion between room temperature and about 350°C.
Growth of Gallium Arsenide on Silicon in Masked, Etched Trenches
Authors: Adkisson J. W. , Kamins T. I. , Koch S. M. , Harris J. S. , Rosner S. J. , Nauka K. , Reid G. A. 
Published: March 2011

AbstractGaAs layers were grown in recessed silicon trenches for monolithic integration of GaAs and silicon devices. These layers were examined using cathodoluminescence (CL) and transmission electron microscopy (TEM). The CL showed no dependence on distance from the sidewall edge within its limit of resolution. Cross-sectional TEM micrographs showed the GaAs grown on the sidewall to depend on the sidewall orientation. Material grown on the near-{111} sidewalls was comparable to that grown on the well bottom, while the GaAs grown on the near-{110} sidewalls showed poorer crystal quality. A photodetector was fabricated in the recessed GaAs/Si; this device could be easily adapted to a monolithically integrated structure.
What Limits Laser Probing?
Authors: Dreyfus R. W. 
Published: March 2011

AbstractLaser-induced fluorescence, LIF, data provide a wide variety of detailed information about physical and chemical reactions and plasmas. In today's technological environment these areas commonly extend from nanosecond laser etching to ion etching (in the low gas density direction), or to combustion gases (near atmospheric pressure). In studying these dynamical processes, the laser probe is nearly ideal; note that one measures a specific species' density as a function of position, velocity, temperature and time within an unperturbed working environment (i.e. high vacuum not required). Examples are derived from our LIF probing of laser etch plumes; the surfaces included sapphire, polymers and benzene (both as a gas and frozen monolayer). LIF results distinguish between diatomic radicals due to thermal vaporization as compared to diatomics from a photochemical decomposition. Beyond the above LIF probing of a laser-etch plume, sophisticated diagnostic techniques such as CARS, multiphoton excitation and ionization, and dissociation immediately followed by optical excitation appear regularly. Enhanced information gathering by laser probing is also demonstrated by the fact that spectroscopic data can be recorded as a 2D picture of a reacting species.With respect to limitations on laser probing, consider the following: Even though plasmas and etch plumes are luminous, the pulsed nature of laser experiments discriminates heavily against background light and dark current noise. While the various techniques measure relative densities at even very low densities, establishing accurate values for absolute densities is considerably more challenging. (Spectral-linewidth uncertainties are a common culprit.) Perhaps the main limitations on laser probing relate to the patience, dedication and budget of the experimenter.
Fast-Probe Plasma Diagnostics
Authors: Manos Dennis M. , Kilpatrick Stephen J. 
Published: March 2011

AbstractWe have used a variety of electrostatic, calorimetric and sample exposure probes to diagnose the edge plasma of neutral-beam heated discharges on the tokamak fusion test reactor (TFTR).In the past, spatial profiles of electron density and temperature, and other edge parameters, were generated by repositioning probes between discharges during experiments consisting of a large number of nominally identical discharges. Recently, we have employed a probe which executes a relatively rapid stroke to generate spatial and temporal profiles during a single discharge. This has greatly enhanced our ability to perform systematic studies of the edge plasma as various operating variables are changed. In addition, this rapid radial motion permits withdrawal of the probe during portions of the discharge when the intense neutral beam heating would otherwise damage the measuring tips.Applications of such a technique to low temperature, process plasmas will be discussed.
Measurement and Modeling of Atomic Chlorine Concentrations in Plasma Processes
Authors: Nicolai Jean-Philippe , Allen Kenneth D. , Sawin Herbert H. 
Published: March 2011

AbstractSpatially resolved concentration profiles of ground-state chlorine atoms were measured in CF3 Cl/Ar RF plasmas using two-photon laser induced fluorescence. A significant Cl gradient was found between the two electrodes under conditions typical for plasma etching. This experimental observation is consistent with previous model predictions which assumed the primary loss of Cl was a second-order surface recombination on the upper electrode which is partially limited by gaseous diffusion.
Quantitative Laser-Induced Fluorescence Measurements of Reactive Species: Spectroscopy and Collision Dynamics of SiCl
Authors: Jeffries Jay B. 
Published: March 2011

AbstractLaser-induced fluorescence (LIF) is an ideal technique to determine the gas phase concentration of the chemically reactive radical species in processing plasmas. Quantitative species concentration measurements require spectroscopic and collision dynamics data. Experiments to obtain such data for the B2 and Σ+ B′2 Δ states of SiCl are described. Using LIF, the transition strengths, radiative lifetimes, and collisional removal rates are determined. Collisional transfer between the two excited electronic states, B′→B, shows a very unusual quantum state specificity for the final vibrational levels which is quite different for each of the rare gas collision partners (He, Ne, Ar). Such energy transfer makes the B′2 Δ state unsuitable for quantitative LIF diagnostics; however, the B2Σ+ state appears to be an ideal excited state for LIF diagnostic measurements in silicon etching plasmas.
Plasma Diagnostics by Laser-Induced Fluorescence
Authors: Booth J. P. , Hancock G. , Perry N. D. , Toogood M. 
Published: March 2011

AbstractRF plasmas of CFM4 have been investigated by laser-induced fluorescence (LIF). Ground state CF2 and CF radicals have been observed under a variety of experimental conditions, where LIF has enabled spatial and temporal distributions to be found. In addition, absolute concentrations have been measured and the processes of radical production and removal have been examined.