bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular-Beam Epitaxial Growth of GaAs on Si(321)
Authors: Uppal P.N. , Ahearn J.S. , Duncan S.W.
Published: March 2011

Material 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

Abstract: 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

Epitaxial 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

We 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

We 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

Patterned 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

Tunneling 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

The 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

We 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

Zirconium 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

The 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

Growth 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

The 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

GaAs 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

Laser-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

We 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

Spatially 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

Laser-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

RF 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.
Laser Diagnostics of Microelectronics Fabrication Processes
Authors: Wormhoudt J. , McCurdy K. , Freedman A.
Published: March 2011

Laser diagnostics, including long path infrared diode laser absorption and dye laser induced fluorescence, are able to provide microscopic information on the gas phase of such important semiconductor fabrication processes as plasma etching and plasma enhanced deposition. It is possible to measure temperatures, concentration profiles, and absolute concentrations if independent laboratory measurements of quantitative spectroscopic parameters have been made. Infrared band strength measurements on several molecular radicals important in semiconductor processing systems are described. We also describe a new apparatus which allows multipass absorption and laser induced fluorescence diagnostics of a large volume of plasma.
Irradiation Effects on the Interfacial Adhesion Between Ti Films and SiO2 Substrate
Authors: Cheng Guoan , Liu Baixin , Li Hengde
Published: March 2011

The interfacial adhesion of Ti films on SiO2 substrate was studied by room temperature argon ion irradiation. Range of ion energy was chosen from 100 to 300 keV. Adhesive strength was measured by scratching test. For Ti/SiO2 pair irradiated by 100 keV argon ions, the adhesion was easier to enhance and much greater strength was obtained than that irradiated by 300 keV argon ions. The threshold dose also increased with the increasing of ion energy. The adhesive strength and the threshold dose increased when the metallizing temperatures were higher. Rutherford backscattering spectra(RBS) showed that a transition layer of about 10 nm thick was formed in Ti/SiO2 interface region after irradiation to a dose of 5X1016 Ar/cm2, indicating some chemical reaction has probably taken place. The experimental results are discussed in terms of thermodynamics of solids.
Improved Adhesion for SiO2 Particles on Silica Substrates using Helium-Ion Irradiation
Authors: Musket R. G. , Thomas I. M.
Published: March 2011

We have examined the effects of irradiation with 200 keV helium ions on the adhesion and optical transmission properties of 220 nm thick antireflective, optical coatings that consisted of layers of spherical, 20 nm diameter silica particles. In the as-deposited state these sol-gel coatings have very low adhesion to the fused silica subtrates. Results for adhesion and optical transmission have been obtained for doses of 1013–1017 He/cm2. Significant improvement in adhesion was found for doses exceeding about 2×1014 He/cm2. Optical transmission measurements for wavelengths of 200–1200 nm showed increasing absorption with dose. We have evidence that the helium ions decompose various contaminants in the coating into two types of degradation products. One is volatile and the other remains in the coating as optically absorbing species. UV/oxidative-gas treatment effectively removes the absorbing species.
Residual Stress, Fracture, and Adhesion in Sputter-Deposited Molybdenum Films
Authors: Mattox D. M. , Cuthrell R. E.
Published: March 2011

Atomistically deposited films may form with high residual stresses which may be either tensile or compressive in nature. These film stresses represent stored strain energy which may affect the adhesion of the film-substrate couple and in the limit may cause spontaneous fracture at or near the film-substrate interface (loss of adhesion). In the post cathode magnetron sputter deposition of molybdenum films, we have found that the intrinsic film stresses are generally anisotropic and may easily exceed the fracture or adhesive strength of the film-substrate couple. The residual stress anisotropy in the film is dependent on the orientation with respect to the post cathode and the magnitude and nature of the stresses are very dependent on the deposition conditions, particularly gas pressure during sputtering. By using a pressure-cycling technique, we have deposited thick (5 microns) films of molybdenum which have little residual stress or stress anisotropy.
Quantitative Study of Al/W Interaction In Si/SiO2/W-Ti/Al Thin Film System
Authors: Liu Hung-Yu , Chang Peng-Heng , Bohlman Jim , Tsai Hun-Lian
Published: March 2011

The interaction of Al and W in the Si/SiO2/W-Ti/Al thin film system is studied quantitatively by glancing angle x-ray diffraction. The formation of Al-W compounds due to annealing is monitored by the variation of the integrated intensity from a few x-ray diffraction peaks of the corresponding compounds. The annealing was conducted at 400°C, 450°C and 500°C from 1 hour to 300 hours. The kinetics of compound formation is determined using x-ray diffraction data and verified by TEM observations. We will also show the correlation of the compound formation to the change of the electrical properties of these films.
Metal-Ceramic Interfacial Reactions: The Copper-Cordierite and Titanium-Cordierite Systems.
Authors: Bortz M. , Ohuchi F. S.
Published: March 2011

Interfacial reactions between either copper or titanium and cordierite-based (2MgO.2Al2O3.5SiO2) ceramic substrates are probed using X-ray Photoelectron Spectroscopy (XPS). Room temperature reactions are found to be strongly dependent on interfacial chemistry; while copper reacts weakly with the cordierite surface, titanium strongly reduces the Si-O and Al-O substrate bonds. Behavior during subsequent “in situ” annealing is dependent on substrate morphology. On amorphous cordierite films copper remains nonreactive while titanium dissociates remaining Si-O and Al-O bonds, forming a low valency Ti1+ oxide. On crystalline cordierite substrates copper diffuses rapidly upon annealing while titanium reduces substrate bonds forming a high valency Ti3+ oxide. Furthermore, thin 5Å Ti interlayers prevent copper diffusion at temperatures below 650°C. This study represents the first comprehensive treatment of the interfacial reactions in metal-multicomponent ceramic systems.
Quantitative Studies of the Effect of Adhesion on the Mechanical and Physical Properties of Polymer Composites
Authors: Williams J. W. , Shang S. W. , Sacks M. D.
Published: March 2011

Young's modulus, tensile strength and the storage shear modulus experiments were performed on silica-filled ethylene-vinyl acetate composites and the results were correlated with polymer-filler interaction energy. The polymer-filler interaction energy was determined by wetting and infrared spectroscopy experiments. The interaction energy was characterized by the work of adhesion. The results indicate there is a strong correlation between modulus and tensile strength and the work of adhesion. There was an exponential relationship of modulus and tensile strength with the reciprocal of the work of adhesion.
Ion-Implantation of Reactive Elements in Improving the Adhesion of Thermally Grown Cr2O3 Sales
Authors: Hou P. Y. , Stringer J.
Published: March 2011

The high temperature oxidation behavior of Al, Y and Hf ion-implantation in Ni-25wtCr alloy with dosages ranging from 1015-1017 ions/cm2 has been studied. Results are compared with the unimplanted alloy, a Xe-implanted alloy and alloys with 0.2wt% Y or lwt% Al additions. Oxidation tests were carried out at 1000°C and 1100°C in 1 atm. O2. It is found that the ion-implantation of Y and Hf greatly reduced oxidation rate and improved scale adherence after a critical implantation dosage, ∼ l×1016 ions/cm2, has been reached. The improved scale adhesion is attributed to both a reduction in growth stress and a strengthened scale/alloy interface, which all developed as a result of a modified scale growth process.
The Adherence of Nickel Oxide on Nickel During High-Temperature Oxidation
Authors: Liu Yung Y. , Natesan K.
Published: March 2011

A combined experimental/analytical study is being conducted to investigate the fundamental nature of adherence of oxide scales formed on metals during high-temperature oxidation. Isothermal oxidation experiments were conducted on high-purity nickel (Ni 270) specimens in air at temperatures of up to 1200°C. None of the experiments resulted in physical separation of nickel oxide scales from the nickel substrate, even though substantial amounts of porosity were found in scales close to the scale/matal interfaces. The results of numerical and analytical calculations of stresses in the NiO/Ni system suggest that metal and oxide plasticities play a role in the experimental observations.
Enhancing Mechanical Properties of Polymer Composites by Modification of Surface Acidity or Basicity of Fillers
Authors: Fowkes F. M. , Dwight D. W. , Manson J. A. , Lloyd T. B. , Tischler D. O. , Shah B. A.
Published: March 2011

The surface of a powdered glass has been treated to optimize its performance as a filler in polymer composites cast from solution. The aim has been to enhance acid-base interactions between the functional sites of polymers and the surface sites of the glass particles so as to insure complete coverage of the glass particles by adsorbed polymer molecules, and to thereby enhance both the adhesion and dispersion of the filler. The glass chosen for this study is a magnesium aluminum silicate of very low alkali metal content, and its surface sites have negligible basicity and only moderate acidity, as evidenced by weak adsorption of polymethylmethacrylate and negligible adsorption of chlorinated polyvinylchloride from solution in methylene chloride. Because of the negligible surface basicity of the filler, acidic polymers such as polyvinylbutyral and polyvinyl chloride are not adsorbed sufficiently to promote adhesion or dispersibility, and brittle or weak composites result.

Surface treatments to enhance surface acidity or basicity of the glass particles were evaluated by electrophoresis in organic solvents, in which acidic particles had negative zeta-potentials and basic particles had positive zeta-potentials; untreated glass particles had zero zetapotentials. The most effective treatments were done with silane coupling agents; amino-silanes provided strong negative zeta-potentials and methacryloxy-silanes provided strong positive zeta-potentials. Angleresolved ESCA spectra showed that the adsorbed amino-silanes averaged about a monolayer in thickness and that half of the nitrogens bonded to the surface as ammonium groups and half were in the outer surface as basic amine groups; the carbonyl oxygens of the methacryloxy-silanes appeared to be bonded to the surface.

Heavily-loaded polymer composites were made with the silane-treated and with untreated glass powders, using two acidic binders and a basic binder. The acidic binders were a polyvinylbutyral (PVB) binder cast from solution in a methanol-MIBK mixture, and a post-chlorinated polyvinylchloride (CPVC) binder cast from solution in a mixture of cyclohexane and tetrahydrofuran (THF): the glass transition temperature (Tg) for CPVC is about 140 C, but for PVB it is only about 35 C. The basic polymer (PEHM, polyethyl-hexylmethacrylate) has a Tg well below room temperature. Thus the extension to break in tensile tests was about 1% for CPVC, 10% for PVB, and 20 % for PEHM. About ten stress-strain Instron tests were made on each composite, and the composites with appreciable acid-base interactions between the matrix polymer and the surface sites of the treated glass fillers were in all cases much tougher than those without such acid-base interactions. The brittleness of the polyvinylbutyral composites filled with untreated glass powders was not observed at all on silane-treated glass powders.
On the Modifiection of Polyethyleneterephtplgte Surfaces to Improve Pohesion
Authors: Occhiello E. , Gprbassi F. , Morini G.
Published: March 2011

The adhesive properties of PET have been enhanced by treatments with alkaline solutions and CF4/02 plasmas. Alkaline solution induce hydrolysis of the polyester and etching, with consequent strong roughening of the surface. Adhesion siemed more related to etching than to surface chemistry modifications, suggesting a prominent role of mechanical interlocking.

CF4/02 plasmas did not induce significant etching, but the surface chemistry was strongly altered. Ester bridges were effectively removed by the plasma, high oxygen mixtures destroyed aromatic rings and introduced oxygen by the
hydroperoxide mechanism. Adhesion was worsened by the introduction of fluorocarbon radicals by Low oxygen discharges. The most effective enhancement was obtained with the 30 % discharge, where the aromatic rings are still quite intact, while ester bridges are removed with formation of phenolic end groups.
Mechanism of Adhesion Between Polyolefins and Steel as Studied by XPS and Static Sims
Authors: Ooij Wim J. Van , Rangarajan V.
Published: March 2011

XPS and static SIMS have been used to characterize the interfaces between squalene or cis-polyisoprene and steel in an attempt to elucidate the mechanism of bonding.
Polylmide Adhesion as a Function of Substrate Structure
Authors: Mil Jan Van , Helms Aubrey
Published: March 2011

We have investigated the effect of different inorganic substrates on the adhesion of polymer films. We have used crystalline surfaces in an effort to “map” the adhesive interactions that take place through the interface between substrate and polyimide (-arnic acid). Significant differences were found in the adhesion of polyimide films (as measured by peel tests) on substrates varying only in crystalline orientation. Detailed analytical investigations are reported of the interfaces of these substrates after peeling of the film, using angular dependent ESCA. A correlation was found between the chemical nature of the substrate and the adhesion quality. This correlation involves the crystalline matrix of the substrate surface.
Characterization of Plasma-Fluorinated Polypropylene and Polystyrene Surfaces by Static Sims
Authors: Van Ooij W. J. , Michael R. S.
Published: March 2011

Static SIMS was used to characterize polypropylene and polystyrene films following exposure to SF 6 and C2F 6 plasmas. The predominant species which are incorporated into the polymer surfaces are fluorine atoms and CF 2 /CF 3 radicals, respectively.
Electron Microscope Observations of Mechanisms of thin Film Delamination from Substrates
Authors: Goyal D. , King A. H.
Published: March 2011

Transmission electron microscope techniques have been applied to the problem of thin film delamination from substrates during film formation. Model systems involving metal films on single crystal silicon substrates have been used and it is found that delamination of the films is initiated by the formation of damage in the substrate. This understanding removes some of the fundamental problems regarding delamination.
Mechanics of the Peel Test for Thin Film Adhesion
Authors: Kim K-S.
Published: March 2011

The mechanics aspects of the peel test are analyzed. In this analysis, the limitation and applicability of the peel test for thin film adhesion have been investigated. Firstly, the effect of plasticity in the peel test of thin metallic films is analyzed. The analysis has given a closed form solution for the partitioning of peel strength between the energy expenditure rate for the decohesion process and the internal work expenditure rate caused by plastic deformation (bending) of the film. The results predicted the variation of peel strength as a function of the film thickness, the film yield stress and the compliance of the substrate. This analysis shows that the peel strength is very sensitive to the thickness of the film and the yield stress of the film. As observed in the experiment, the peel strength has a peak value at a certain thickness of the film. This is explained for both L and T peel tests. Unlike the L peel test, the peak phenomenon in the T peel test (of metallic films) is due to the hardening of the adhered film. Secondly, the effect of plasticity and viscoelasticity in the peel test of thin polymer films is analyzed. Unlike the peel test of metallic films, tension and shear effect of the film deformation is very important in the analysis of the polymer peel test. An integral equation is formulated for the viscoelastic models of the adhered film. The solution of the integral equation reveals the important parameters in polymer peeling and their contribution to the peel force as well as to the viscoelastic dissipation. In addition, the meaning of the interface toughness is reexamined and the interface toughness is evaluated by the peel test. Based on these analyses, a Universal Peel Diagram has been constructed, which accounts for the hardening behavior of the film. On this diagram, objective interfacial decohesion toughness can be readily obtained using very simple peel tests. The analysis includes not only the 900° peel test but also the general angle peel test. Comparison between the theory and experiment has been made with the experimental data provided by J. Kim of IBM. The comparison shows good agreement.
Mechanical Properties Of Cu-Based Composites with in Situ Formed Ultrafine Filaments
Authors: Bevk J. , Sunder W. A. , Dublon G. , Cohen David E.
Published: March 2011

Elastic and plastic properties of in situ Cu-based composites with Nb, V, and Fe filaments are reviewed. The evidence is presented for a pronounced size dependence of both the ultimate tensile strength and the Young's moduli. In composites with the smallest filaments (d∼50–200Å) and filament densities as high as 1010/cm2 dislocation density reaches values of 1013 cm/cm3. The yield stress of these samples increases dramatically over the predictions based on the “rule of mixtures” and their ultimate tensile strength approaches the estimated theoretical strength of the material (∼2.7GPa). The observed decrease of Young's modulus as a function of inverse wire diameter in the as-drawn composites is attributed to lattice softening due to high density of extended lattice defects. Upon annealing, Young's modulus increases by as much as 100% and exceeds the maximum values calculated from bulk elastic constants. Possible mechanisms leading to modulus enhancement and to related changes in magnetic and superconducting behavior of in situ composites are discussed.
Solidification And Strength Characteristics Of Ni-Cr-Ti And CO-CR-MO Eutectics
Authors: Thomas M. K.
Published: March 2011

The results of an exploratory study of eutectics based on Ni-25Cr–15Ti (wt %)and Co-10Cr-32Mo compositions will be presented. These alloys were selected from a total of ten different eutectic systems, all having melting points above 1200°C, a specific gravity less than 9,000 kg/m3, and a parabolic oxidation rate below 10−7 g2 · cm−4 · s−1 at 1150°C as reported by Haour, Mollard, Lux, and Wright on work done at Battelle-Geneva Research Centre. The Ni-25Cr-15Ti eutectic appeared to have a high volume fraction of ductile chromium fibers in a brittle Ni3Ti matrix. This alloy although the strongest of the six alloys that have been tested from the group reported by Battelle is still not competitive with advanced superalloys. Its tensile strength at 1093°C was 227 MPa2 and its elongation was 14%. The Co-10Cr-32Mo eutectic had the highest melting point (1340°C) of the alloys screened by Battelle. It appeared to solidify in a basically bladelike or lamellar structure, consisting of the intermetallic μ phase in a metallic Co (Cr) matrix. The strongest of the Co-Cr-Mo eutectics tested had a tensile strength of 164 Mpa and an elongation of 15% at 1093°C. The correlation observed between the strengths of the Ni-Cr-Ti and Co-Cr-Mo alloys, compositional variations, and their microstructures will be discussed.
The Growth of Submicron Eutectic Thin Film Structures
Authors: Cline Harvey E.
Published: March 2011

As the minimum dimension of electronic circuits is reduced below one micron, there has been increased interest in developing techniques for fabricating submicron structures. Pb-Sn, Cd-Pb and Al-Al 2Cu eutectic thin films were directionally solidified at rates between .0015 cm/sec and .15 cm/sec with both a lamp and a laser heat source to fabricate fault free submicron periodic structures. A transition from lamellar to cellular structures with increasing solidification rate was observed with a thermal gradient of 200°C/cm applied with the lamp heat source. Cells did not form with the increased thermal gradient produced by the laser heat source, 8000° C/cm. Spacings as fine as .1 micron were observed in the Cd-Pb eutectic. A maximum theoretical growth rate was estimated which corresponds to a spacing of 80A.
In Situ Electron Microscopy : Solidification of Eutectic Alloys.
Authors: Lemaignan Clément , Pélissier Joseph
Published: March 2011

A heating stage and an advanced video recording system were used in the 1 MeV electron microscope of CEN Grenoble. This allowed us to observe various aspects of eutectic solidification. These observations include regular lamellar solidification with faceted or non faceted solid-liquid interfaces, change of lamellar spacing with solidification rate, non reciprocal heterogeneous nucleation of eutectic solidification.

We discuss them with respect to the classical theories and introduce a new eutectic nucleation mechanism based on surface dendrites.
Mechanical And Superconducting Properties Of Cu-Nb3Sn In Situ Produced Composite Wires
Authors: Kolb-Telieps A. , Mordike B.L. , Mrowiec M.
Published: March 2011

Cu-Nb composite wires were produced from powder, electrolytically coated with tin and annealed to convert the Nb fibres to Nb 3Sn. The content was varied between 10 wt % and 40 wt %. The superconducting properties of the wires were determined. The mechanical properties, tensile strength, yield strength and ductility were measured as a function of volume fraction and deformation over a wide temperature range. The results are compared with those for wires produced by different techniques.
Fatigue Crack Growth in Co and Ni Base Directionally Solidified Eutectic Composites
Authors: Hoffmann C. , Bhowal P. , Mcevily A. J.
Published: March 2011

A study of fatigue crack growth behavior in four directionally solidified eutectic composites has been carried out in air at room temperature and at 870°C (1600 °F). The alloys investigated included two cobalt-base alloys, CoTaC and CoTaC+Cr, and two nickel base alloys, γ′-Mo and γ/γ′-δ. Fatigue crack growth was studied in directions parallel and perpendicular to the solidification direction. It was found that the addition of chromium to the CoTaC alloy strengthened the interface and promoted trans-fiber crack growth. In addition, the effect of interlamellar spacing on the rate of fatigue crack growth was examined for the γ/γ′-δ alloy. A reduction in interlamellar spacing reduced the crack growth rate. The growth rates are related to the corresponding stress intensity factors and are discussed in the light of prior investigations reported in the literature.
Microstructural Effects on Ductile Phase Toughening of Nb-Nb Silicide Composites
Authors: Lewandowski J. J. , Dimiduk D. , Kerr W. , Mendiratta M. G.
Published: March 2011

In the Nb-Si system, the terminal Nb5 Si3 phase and the Nb Si phase are virtually immiscible up to approximately 2033K. This system offers the potential of producing composites consisting of a ductile refractory metal phase and a strong intermetallic phase. In-situ composites containing different volume fractions of the ductile Nb phase were produced via vacuum arc-casting. Microhardness testing as well as smooth bend bar testing was conducted at temperatures ranging from 298K to 1673K in an attempt to determine microstructural effects on the yield strength and smooth bar fracture strength. Notched bend specimens were similarly tested to determine the effects of the ductile phase (i.e. Nb) on enhancing the notched bend toughness. It is shown that the Nb phase often behaves in a ductile manner during testing, thereby toughening the in-situ composite. The mechanism of toughening appears to be due to crack bridging.
Fracture behavior of 3-d Braided Nicalon/Silicon Carbide Composite
Authors: Yang J.-M. , Chou J.-C. , Burkland C. V.
Published: March 2011

The fracture behavior of a 3-D braided Nicalon fiber-reinforced SiC matrix composite processed by chemical vapor infiltration (CVI) has been investigated. The fracture toughness and thermal shock resistance under various thermomechanical loadings have been characterized. The results obtained indicate that a tough and durable structural ceramic composite can be achieved through the combination of 3-D fiber architecture and the low temperature CVI processing.
Suspension Processing of SiC Whisker-Reinforced Composites
Authors: Sacks Michael D. , Lee Hae-Weon , Rojas Oswaldo E.
Published: March 2011

Suspension processing was used to prepare Al2O3 /SiC whisker and Al2O3/ZrO2 /SiC whisker compacts with high green density, fine pore sizes, and homogeneous microstructure. Procedures for optimizing particle/whisker co-dispersion and subsequent consolidation by slip casting are reviewed. Compacts prepared by slip casting showed significantly higher sintered densities compared to dry-pressed samples.
Pyroeiec1ric and Dielectric Properties of Polymer-Ceramic Composites
Authors: Das-Gupta D. K. , Abdullah M. J.
Published: March 2011

Ferroelectricity in well-poled polyvinylidene fluoride (PVDF) is a phenomenon which is now well supported. However, the piezo- and pyroelectric responses in this polymer are significantly weaker than those of ceramic oxides. It would be attractive to design composite materials which will have the mechanical properties of polymers with the electro-active properties of ceramics. Such materials will be useful for diverse sensor applications, viz, acoustic emission detection, hydrophones, biomedical applications, thin film capacitors etc. One of the chief requirements of a capacitor is that a large capacitance to volume ratio is desirable. A high ratio requires a thin film, a high dielectric constant and an acceptable electrical breakdown strength. Such a material may be designed by a judicious incorporation of fine grain ceramics in a suitable polymer matrix.
The Mechanical Properties at High Temperatures of SiC Whisker-Reinforced Alumina
Authors: Xia Kenong , Langdon Terence G.
Published: March 2011

Creep tests were conducted at temperatures from 1673 to 1823 K on samples of Al2O3 containing 9.3, 18 and 30 vol % SiC whiskers. The results show that the strains to failure tend to decrease and the stress exponents for the steady-state creep rates tend to increase with increasing volume percentages of SiC whiskers.
Fracture Mechanisms in SiC-Whisker Reinforced Alumina
Authors: Boulanger Christophe H. , Chiang Yih-Cherng , Majidi Azar P. , Chou Tsu-Wei
Published: March 2011

The fracture mechanisms involved in the toughening of alumina by whisker reinforcement are studied at room temperature. The fracture toughness of a hot pressed SiC-whisker/alumina composite is measured and good agreement is found between the experimental data and a model that takes into account the effects of crack deflection and whisker pullout mechanisms. From the model, it is seen that the role of whisker pullout is negligible compared to that of crack deflection.