bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional Tissue Engineering of Articular Cartilage Through Dynamic Loading of Chondrocyte-Seeded Agarose Gels
Authors: Mauck Robert L. , Soltz Michael A. , Wang Christopher C. B. , Wong Dennis D. , Chao Pen-Hsiu Grace , Valhmu Wilmot B. , Hung Clark T. , Ateshian Gerard A.
Published: July 2002

Due to its avascular nature, articular cartilage exhibits a very limited capacity to regenerate and to repair. Although much of the tissue-engineered cartilage in existence has been successful in mimicking the morphological and biochemical appearance of hyaline cartilage, it is generally mechanically inferior to the natural tissue. In this study, we tested the hypothesis that the application of dynamic deformational loading at physiological strain levels enhances chondrocyte matrix elaboration in cell-seeded agarose scaffolds to produce a more functional engineered tissue construct than in free swelling controls. A custom-designed bioreactor was used to load cell-seeded agarose disks dynamically in unconfined compression with a peak-to-peak compressive strain amplitude of 10 percent, at a frequency of 1 Hz, 3× (1 hour on, 1 hour off)/day, 5 days/week for 4 weeks. Results demonstrated that dynamically loaded disks yielded a sixfold increase in the equilibrium aggregate modulus over free swelling controls after 28 days of loading (100±16 kPa versus 15±8 kPa,p<0.0001). This represented a 21-fold increase over the equilibrium modulus of day 0 4.8±2.3 kPa. Sulfated glycosaminoglycan content and hydroxyproline content was also found to be greater in dynamically loaded disks compared to free swelling controls at day 21 (p<0.0001 and p=0.002, respectively). [S0148-0731(00)00703-2]
Mechanical Properties of a Biodegradable Bone Regeneration Scaffold
Authors: Porter, B. D. , Oldham, J. B. , He, and S.-L. , Zobitz M. E. , Payne R. G. , An and K. N. , Currier B. L. , Mikos and A. G. , Yaszemski M. J.
Published: July 2002

Poly (Propylene Fumarate) (PPF), a novel, bulk erosion, biodegradable polymer, has been shown to have osteoconductive effects in vivo when used as a bone regeneration scaffold (Peter, S. J., Suggs, L. J., Yaszemski, M. J., Engel, P. S., and Mikos, A. J., 1999, J. Biomater. Sci. Polym. Ed., 10, pp. 363–373). The material properties of the polymer allow it to be injected into irregularly shaped voids in vivo and provide mechanical stability as well as function as a bone regeneration scaffold. We fabricated a series of biomaterial composites, comprised of varying quantities of PPF, NaCl and β-tricalcium phosphate (β-TCP), into the shape of right circular cylinders and tested the mechanical properties in four-point bending and compression. The mean modulus of elasticity in compression Ec was 1204.2 MPa (SD 32.2) and the mean modulus of elasticity in bending Eb was 1274.7 MPa (SD 125.7). All of the moduli were on the order of magnitude of trabecular bone. Changing the level of NaCl from 20 to 40 percent, by mass, did not decrease Ec and Eb significantly, but did decrease bending and compressive strength significantly. Increasing the β-TCP from 0.25 g/g PPF to 0.5 g/g PPF increased all of the measured mechanical properties of PPF/NVP composites. These results indicate that this biodegradable polymer composite is an attractive candidate for use as a replacement scaffold for trabecular bone. [S0148-0731(00)01203-6]
Suppression of Micro Stick-Slip Vibrations in Hydraulic Servo-System
Authors: Hayase Toshiyuki , Hayashi Satoru , Kojima Kazunori , Iimura Ikuro
Published: July 2002

This paper deals with suppression of two kinds of micro stick-slip vibrations occurring in a typical computer-controlled hydraulic servo-system. The relevant system consists of a single-rod hydraulic cylinder, an electrohydraulic servo-valve and a personal computer. The discontinuous control signal from a D/A converter causes a stick-slip vibration of micron order of magnitude over a wide range of the feedback gain. Increasing the feedback gain results in the other stick-slip vibration of nearly ten times larger amplitude due to the nonlinear pressure-flow characteristic of the servo-valve. The numerical simulation revealed the latter micro stick-slip vibration could be efficiently suppressed with the feedback linearization technique to compensate the nonlinearity of the servo-valve, while the former one reduced by improving the resolution of the D/A converter. Validities of both the methods were also confirmed with experiment. [S0022-0434(00)00102-7]
Thermomechanical Behavior and Modeling Between 350°C and 400°C of Zircaloy-4 Cladding Tubes From an Unirradiated State to High Fluence (0 to 85s˙1024 nm−2,E>1 MeV)
Authors: Scha¨ffler I. , Geyer P. , Bouffioux P. , Delobelle P.
Published: July 2002

This paper first describes the effect of neutron irradiation on the thermomechanical behavior of stress-relieved Zircaloy-4 fuel tubes that have been analyzed after exposure to five different fluences ranging from nonirradiated material to high burnup. In the second part, a viscoplastic model is proposed to simulate, for different isotherms, 350°C<T<400°C, out-of-flux anisotropic mechanical behavior of the cladding tubes over the fluence range 0<ϕ<100s˙1024 nm−2E>1 MeV. The model, identified for tests conducted at 350°C, has been validated from tests made at 380°C and 400°C. The model is capable of simulating strain hardening under internal pressure followed by a stress relaxation period, the loading producing an interaction between the pellet and cladding. Introduction of a state variable characterizing the damage caused by a bombardment with neutrons into the model has allowed us to simulate the irradiation-induced hardening and creep rate decrease, as well as the saturation noticed after two cycles of irradiation ≅45s˙1024 nm−2E>1 MeV in a pressurized water reactor (PWR). Finally, the numerical simulations show the model is able to reproduce the totality of the thermomechanical experiments. [S0094-4289(00)00202-4]
1997 Soichiro Honda Lecture: Pathways to Achieving a New Generation of Engines for Personal Transportation
Authors: Borman Gary L.
Published: July 2002

As we move into the twenty-first century the spread of affluence to a greater portion of an ever growing world population, coupled with dwindling reserves of crude oil, will make it imperative that we simultaneously protect our environment and enhance the fuel efficiency of transportation vehicles. Although reduced vehicle weight is the major contributor to conservation, it is argued that safety considerations limit vehicle size reduction. The engine thus remains an important component in meeting the needs of the new century; it is the primary subject of this lecture. The lecture first specifies those areas of engine design which provide the best opportunities for changes that will meet the needs of fuel economy and reduced emissions at an affordable cost. The discussion then concentrates on defining the pathways to achieving such goals. In particular, the tools available to perform the needed studies are discussed. The lecture ends with a discussion of the types of programs and methods of technical interchange required to produce a new generation of engines. [S0742-4795(00)00202-7]
Influence of Thermal and Elastic Deformations on Connecting-Rod Big End Bearing Lubrication Under Dynamic Loading
Authors: Piffeteau S. , Souchet D. , Bonneau D.
Published: July 2002

A numerical procedure is developed for the analysis of transient thermoelastohydrodynamic (TEHD) behavior of connecting-rod bearings under dynamic loading. The Reynolds and energy equations in the film and heat transfer equation in the solids are all solved using the Newton-Raphson method and the finite element formulation. The finite element meshes of the three domains are interconnected, and so the heat flux continuity conditions become implicit. As a consequence, the study of complicated structures, such as actual connecting-rod bearings, can be handled and boundary conditions can easily be changed. [S0742-4787(00)02301-8]
Experimental and Numerical Investigation of the Flow in a Centrifugal Compressor Volute
Authors: Hagelstein D. , Hillewaert K. , Van den Braembussche R. A. , Engeda A. , Keiper R. , Rautenberg M.
Published: July 2002

This paper presents the experimental and numerical investigation of an outward volute of rectangular cross section. The investigation is carried out at the level of stage performance, volute performance, and detailed flow field study at selected peripheral positions for various operating points. The objective of the investigation was to gain further knowledge about the flow structure and loss mechanism in the volute. Simultaneously with the experimental investigation, a numerical simulation of the flow in the volute was carried out. A three-dimensional Euler code was used in which a wall friction term and a tuned artificial dissipation term account for viscous effects. A reasonable agreement between the experimental and numerical results is observed. As a result a good and detailed knowledge about the pressure recovery and loss mechanism in the volute is obtained. [S0889-504X(00)00301-9]
Heat Transfer and Flow on the First-Stage Blade Tip of a Power Generation Gas Turbine: Part 2—Simulation Results
Authors: Ameri A. A. , Bunker R. S.
Published: July 2002

A combined experimental and computational study has been performed to investigate the detailed distribution of convective heat transfer coefficients on the first-stage blade tip surface for a geometry typical of large power generation turbines (>100 MW). This paper is concerned with the numerical prediction of the tip surface heat transfer. Good comparison with the experimental measured distribution was achieved through accurate modeling of the most important features of the blade passage and heating arrangement as well as the details of experimental rig likely to affect the tip heat transfer. A sharp edge and a radiused edge tip was considered. The results using the radiused edge tip agreed better with the experimental data. This improved agreement was attributed to the absence of edge separation on the tip of the radiused edge blade. [S0889-504X(00)01802-X]
PVRC Task Group on Increased Allowable Stresses
Authors: Karcher Guido G.
Published: July 2002

[S0094-9930(00)02201-0]
Optical Properties of Plasma-Sprayed ZrO2-Y2O3 at High Temperature for Solar Applications
Authors: Ferriere A. , Lestrade L. , Robert J-F.
Published: July 2002

Experimental determinations of the absorptivity and of the total hemispherical emissivity of plasma-sprayed ZrO2-7wt%Y2O3 layers were performed in the range of temperature 1000 K–2300 K. For this purpose, solar facilities of CNRS-IMP laboratory were used. The experimental set-up is described and the obtained results are presented and discussed. The spectral absorptivity at 0.65 μm ranges from 0.10 below 1000 K to 0.75 at 2300 K, and the total hemispherical emissivity increases from 0.25 at 1300 K up to 0.60 at 2200 K. [S0199-6231(00)00301-4]
Energetic Materials. I. Pure Single Crystal Cyclo-1,3,5-Trinitramine-2,4,6-Trimethylene, RDX by XPS
Authors: Beard Bruce C.
Published: July 2002

Cyclo-1,3,5-trinitramine-2,4,6-trimethylene (RDX) is a principal energetic component in many high performance military explosives. [R. Meyer, Explosives, 2nd ed. (Chemie, Weinheim, 1981), p. 74. Encyclopedia of Explosives and Related Items, PATR 2700, edited by S. M. Kaye and H. L. Herman (Picatinny Arsenal, Dover, NJ, 1966), p. C611]. Optical quality single crystal RDX has been obtained and examined by x-ray photoelectron spectroscopy prior to the input of shock damage as a control experiment. The effect of localized crystalline disruption, as generated by a hardness impression, on the shock energy threshold for the creation of chemical decomposition is to be assessed. The data reported here are from the undamaged material.
Fresh Cleaved Single Crystal NaCl, XPS Spectra, Al Source
Authors: Beard Bruce C.
Published: July 2002

High quality single crystal NaCl has been analyzed as one in the series of Na salts (chloride to perchlorate) with the Cl anions. The spectra include survey and high resolution scans over the major photopeaks, the Na Auger transitions and the valence band of the compound. Spectra were collected with an Al monochromator. A companion submission shows spectra collected with a Mg source.
Nanobubbles on solid surface imaged by atomic force microscopy
Authors: Lou Shi-Tao , Ouyang Zhen-Qian , Zhang Yi , Li Xiao-Jun , Hu Jun , Li Min-Qian , Yang Fu-Jia
Published: July 2002

Gas bubbles of nanometer size were produced on atomically flat solid surfaces and imaged by atomic force microscopy (AFM) in tapping mode in water. In AFM images, nanobubbles appeared like bright spheres. Some of the bubbles remained stable for hours during the experiments. The bubbles were disturbed under high load during AFM imaging. A related mechanism is discussed.
Effect of the first antimony layer on AuZn ohmic contacts to p-type InP
Authors: Yamaguchi Akira , Asamizu Hirokuni , Okada Takeshi , Iguchi Yasuhiro , Saitoh Tadashi , Koide Yasuo , Murakami Masanori
Published: July 2002

The electrical properties of the Sb/Zn/Au/Nb ohmic contacts to p-type InP were investigated, where a slash (/) indicates the deposition sequence. The first Sb layer improved the contact resistivity and reduced the optimum annealing temperature, compared with the Au/Zn/Au/Nb contacts whose first layer was Au. The minimum contact resistivity of 4×10−5 Ω cm2 was obtained from the Sb(3 nm)/Zn(5 nm)/Au(10 nm)/Nb(50 nm) contacts annealed at 325 °C for 2 min. The interfacial microstructure was studied using the cross-sectional transmission electron microscope. It was considered that the deposited Sb deoxidized and removed the native oxides of the InP surface and that facilitated the upper Au and Zn diffusion into InP.
Effects of deposition parameters on properties of rf sputtered molybdenum films
Authors: Nowicki R. S. , Buckley W. D. , Mackintosh W. D. , Mitchell I. V.
Published: July 2002

We report a preliminary survey of the effects of dc substrate bias and residual gas contamination on the average composition, internal stress, electrical conductivity, and crystal structure of molybdenum films deposited by rf sputtering. We find strong interrelations among all these parameters. Thus films sputtered in residual pressure approximately 10−5 Torr exhibit stress changing from tensile to compressive with increasingly negative bias, passing through neutrality at about −15 V. Quantitative analysis, however, reveals that stress relief is attained only at the expense of the incorporation of large (30 at.%) amounts of oxygen and nitrogen. This in turn substantiates the attribution of the fcc structure observed in such films to a MoNx phase rather than a new polytype of Mo. Deposition at lower residual pressure with floating bias results in bcc structure, negligible gas incorporation, closer approach to bulk conductivity, but compressive stress. These results suggest the necessity for compromise in the choice of deposition parameters for practical applications.
Plasma deposition of optical films and coatings: A review
Authors: Martinu Ludvik , Poitras Daniel
Published: July 2002

Plasma enhanced chemical vapor deposition (PECVD) is being increasingly used for the fabrication of transparent dielectric optical films and coatings. This involves single-layer, multilayer, graded index, and nanocomposite optical thin film systems for applications such as optical filters, antireflective coatings, optical waveguides, and others. Beside their basic optical properties (refractive index, extinction coefficient, optical loss), these systems very frequently offer other desirable “functional” characteristics. These include hardness, scratch, abrasion, and erosion resistance, improved adhesion to various technologically important substrate materials such as polymers, hydrophobicity or hydrophilicity, long-term chemical, thermal, and environmental stability, gas and vapor impermeability, and others. In the present article, we critically review the advances in the development of plasma processes and plasma systems for the synthesis of thin film high and low index optical materials, and in the control of plasma–surface interactions leading to desired film microstructures. We particularly underline those specificities of PECVD, which distinguish it from other conventional techniques for producing optical films (mainly physical vapor deposition), such as fabrication of graded index (inhomogeneous) layers, control of interfaces, high deposition rate at low temperature, enhanced mechanical and other functional characteristics, and industrial scaleup. Advances in this field are illustrated by selected examples of PECVD of antireflective coatings, rugate filters, integrated optical devices, and others.
Temperature and Thickness Distribution on the Substrate during High-Rate Physical Vapor Deposition of Materials
Authors: Nimmagadda Rao , Bunshah R. F.
Published: July 2002

In high-rate physical-vapor-deposition processes, the thickness of the deposit and the temperature vary along the substrate. The deposition temperature has a strong effect on grain size and density of the deposit. The deposition rate, thickness variation, and temperature variation depend on the 15 experimental variables, viz., evaporation temperature, source to substrate distance, source diameter, etc. This paper illustrates a method of calculating the temperature and thickness distribution of the deposit. The deposition of yttrium and yttria are used as examples to illustrate the actual range of experimental conditions to be explored. An estimate of probable errors in calculated temperatures due to errors in the emittance data used is made. Radiation from the evaporating source, condensation of vapors, and the reaction of the elements are the sources of heat input to the substrate and the relative contributions of these are calculated for various experimental conditions.
Enhancement of Superconductivity and Softening of Phonons in Superconducting Semiconductors
Authors: Benyon A. , Grassie A. D. C.
Published: July 2002

Following experiments on inhomogeneously doped semiconductors which exhibited an elevation of the superconducting transition temperature due to the softening of phonons associated with a phase transition, the phonon spectrum in these alloys of PbTe, SnTe, and GeTe has been computed and has been found to imply an elevation of Tc in the homogeneous alloys.
Nanoimprint lithography at the 6 in. wafer scale
Authors: Heidari Babak , Maximov Ivan , Montelius Lars
Published: July 2002

We demonstrate the nanoimprint lithography (NIL) technique with sub 100 nm resolution, on 6 in. Si substrates. The pattern transfer is performed using a specially designed NIL machine optimized to achieve a very high degree of parallelism between stamp and substrate. The stamp is made with the help of electron beam lithography and Ni electroplating achieving features below 100 nm in size. The nanoimprint process is done in a single layer as well as in a multilayer resist scheme with subsequent O2-plasma etching and metal lift-off.
Reliable Ti/Al and Ti/Al/Ni/Au ohmic contacts to n-type GaN formed by vacuum annealing
Authors: Papanicolaou N. A. , Rao M. V. , Mittereder J. , Anderson W. T.
Published: July 2002

In this work, we investigated Ti/Al and Ti/Al/Ni/Au ohmic contact metallizations to n-GaN which were formed by a vacuum annealing method. Our effort was focused on minimizing the oxidation of the Al, which limits the performance of the Al-based contacts. We have also investigated the effect of the Ni/Au overlayers on the performance and morphological characteristics of the contacts. Vacuum annealing was found to require temperatures similar to those used in halogen lamp rapid thermal annealing for forming ohmic contacts on n-type GaN, but with minimal oxidation of the Al surface. It was found that the Ni/Au overlayer on the Ti/Al reduces the specific contact resistivity values slightly and at the same time causes an upward shift, by ∼200 °C, in the contact formation temperature. For the Ti/Al and Ti/Al/Ni/Au on n-GaN doped at 1.1×1018 cm−3, a minimum specific contact resistivity of 1.2×10−5 Ω cm2 was achieved after 950 and 1100 °C anneals, respectively. Auger electron spectroscopic studies revealed that obtaining optimum ohmic contact resistance requires the penetration of Al through the Ti layer to reach the GaN surface in addition to N outdiffusing from the GaN surface and into the metal layers. Atomic force microscopy investigations indicated that the introduction of the Ni/Au overlayer on the Ti/Al had the effect of increasing the surface roughness after annealing.
Solution and Diffusion of Hydrogen in Tungsten
Authors: Frauenfelder R.
Published: July 2002

Using mass spectroscopic and ultrahigh vacuum techniques, solution and diffusion of hydrogen in tungsten was investigated for pressures between 600 and 10−8 Torr and temperatures between 1100 and 2400 K. Solubility and diffusion constants are derived from degassing rates of a solid cylinder which was pre-loaded with hydrogen at ≈600 Torr. The solubility constant, S=2.9×10−1×exp (−24000/RT) Torr liter/cm3Torr1/2, and the diffusion constant, D=4.1×10−3×exp (−9000/RT) cm2/sec, are obtained, which in conjunction with literature values for the permeation constant P are consistent with the equation P=SD. Comparison to theory indicates that the solubility and diffusion constants are characteristic of interstitially dissolved hydrogen. Expressions are derived for the concentration of interstitial hydrogen as a function of pressure and temperature. Semiquantitative values for the total hydrogen concentration at low pressures are derived from H2 pressure changes which result when a sample is flashed between selected, high temperatures. Below 10−4 Torr, the total hydrogen concentration appears to be several orders of magnitude higher than the concentration of interstitial hydrogen, indicating that hydrogen is held in, and diffuses via both interstitial sites and a second kind of site of unknown nature. A semiquantitative analysis of diffusion is given for the case of the diffusing species held in, and diffusing via, two different kinds of sites.
Photoemission studies of surface and interface states on III–V compounds
Authors: Spicer W. E. , Chye P.W. , Gregory P. E. , Sukegawa T. , Babalola I. A.
Published: July 2002

The GSCH model for surface states on (110) GaAs proposed by Gregory et al. appears (based on a wide range of results) to be well established and to apply to all faces of all III–V semiconductors. In this model, the filled and empty surface states are associated with and localized on the column V and III atoms, respectively, and a band gap (greater than 1 eV) separates the filled and empty surface states. For example, detailed studies of GaAs and InP locate the bottom of the empty states at 0.7 and 0.25 eV, respectively, below the conduction band minimum (CBM), whereas in GaSb it lies above the CBM. The filled states in all three cases are located well below the valence band maximum (VBM). In the context of the GSCH model, the details of the first steps in oxidation and formation of Schottky barrier with Cs have been examined experimentally. It is concluded from studies of Ga and As chemical shifts by Pianetta et al. that, in the first step of oxidation, the oxygen gains electrons from As but not the Ga surface atoms. The formation of a Schottky barrier with Cs has been studied from very low coverage to completion of the first Cs layer (at which coverage good correlation is found with the literature for thick metallic layers). For GaAs and InP, good correlation is found between the final Fermi-level pinning position and the bottom of the intrinsic empty surface states. For GaSb, where the empty intrinsic surface state do not lie in the band gap, no such correlation is found.
Theoretical study of the GaAs (100) surface
Authors: Appelbaum Joel A. , Baraff G. A. , Hamann D. R.
Published: July 2002

We present the results of self-consistent calculations of the potential, wave functions, spectrum, and charge density of the Ga (100) surface of GaAs. The spectrum contains two bands of gap surface staes whose spatial form is similar to those of (100) silicon. In contrast to Si, these bands are separated by a 1/2-V energy gap, a gap which is caused by the heteopolar potential. The lower energy band is 3/4 full, a situation which is predicted by a simple quantum-mechanical counting argument and which leads to a conclusion that back bonds are very similar to bulk bonds. Its Fermi surface lies in a region of high state density and has an almost perfect diamond shape. By studying the change in ionization potential with position of the surface plane, we have calculated an effective charge of 0.2 electrons for surface Ga atoms.
Correlation of short-range order and sputter dose in GaAs(110) using a vidicon-based LEED system
Authors: Welkie D. G. , Lagally M. G.
Published: July 2002

The change in short-range order with sputter dose and annealing of a GaAs (110) surface is followed by measuring the angular profiles of diffraction spots in low-energy electron diffraction from the surface. In particular, step densities and the step height are determined. Evidence for structural damage beyond the creation of steps can be interpreted in terms of coherent domains of limited size.
Oxygen interaction with GaAs surfaces: An XPS/UPS study
Authors: Brundle C. R. , Seybold D.
Published: July 2002

The interaction of unexcited oxygen with vacuum-cleaved GaAs(110) surfaces has been studied by XPS (hν=1253 eV) and UPS (hν=21.2, 40.8, and 48.4 eV) over the exposure range 105 to 1014L. The corresponding coverage range is estimated as ϑ∠0.2 to ϑ∠0.8 monolayers (where ϑ=1 corresponds to an oxygen atom for each surface atom). From the UPS and O 1s XPS results it is concluded that the adsorption is dissociative over this entire range. From a study of the Ga and As 3d core levels; and the Ga and As L3MM x-ray-induced Auger lines it is shown that chemical shifts associated with both As and Ga levels occur over the entire adsorption range. These shifts are appropriate to those for Ga2O3 and As2O3, as is the stoichiometry of the reacted layer. There is no direct evidence for a stable chemisorption state preceeding oxidation in the 105 to 1015 L exposure regime. It is suggested that reaction with molecular oxygen takes place by dissociation at defect sites leading to growth of Ga and As oxides.
Survey of ion plating sources
Authors: Spalvins Talivaldis
Published: July 2002

Ion plating is a plasma deposition technique where ions of the gas and the evaporant have a decisive role in the formation of a coating in terms of adherence, coherence, and morphological growth. The range of materials that can be ion plated is predominantly determined by the selection of the evaporation source. Based on the type of evaporation source, gaseous media, and mode of transport, the following will be discussed: resistance, electron beam, reactive ion beam evaporation, and sputtering. Ionization efficiencies and evaporant energies in the glow discharge determine the percentage of atoms which are ionized under typical ion plating conditions. The plating flux consists of a small number of energetic ions and a large number of energetic neutrals. The plating flux energy distribution ranges from thermal energies up to the voltage applied to the discharge. The various reaction mechanisms which contribute to the exceptionally strong adherence—formation of a graded substrate/coating interface are not fully understood; however, the controlling factors are evaluated. The influence of process variables on the nucleation and growth characteristic are illustrated in terms of morphological changes which for example affect the mechanical and tribological properties of a coating.
Column III and V elements on GaAs (110): Bonding and adatom-adatom interaction
Authors: Skeath P. , Su C. Y. , Lindau I. , Spicer W. E.
Published: July 2002

Column V elements adsorbed on GaAs (110) exhibit strikingly different behavior than adsorbed column III elements in terms of the overlayers bonding to the semiconductor, the effect on the semiconductor surface lattice, and long-range order. A strong interaction between adatoms is found with submonolayer coverings of column III metals which leads to the formation of flat raftlike metallic patches. Unlike the column III metals, Sb adsorption produces large changes in the electronic states and atomic arrangement of the semiconductor surface lattice. An elementary view of the factors responsible for the different characteristics and effects of these overlayers on GaAs (110) is given, but its extension to other adatoms is shown to be limited. These results have strong relevance to current theoretical models of Al and Ga overlayers on GaAs (110), as well as to molecular beam epitaxy and Schottky barrier formation.
Surface analysis of Cu–Be dynode
Authors: Fujii Y. , Kanematsu F. , Koshikawa T. , Sugata E.
Published: July 2002

Surfaces of Cu–Be (2%) dynodes activated at various conditions were studied. The mechanism of formation of the BeO layer was studied by means of surface analysis with ESCA, SEM, and AES. Peaks of oxidized Be, O, and a little C were detected but Cu was not found at all in the ESCA and AES spectra of surface products produced at various conditions, i.e., at activation temperatures between 750 ° and 870 °C in oxygen at a pressure of about 5×10−3 Torr (7×10−1 Pa). The BeO layers activated at low temperature were thin and smooth on the surface, indicating uniform growth of BeO grains, while those activated at high temperature had a rather roughened surface with fissures and apparent coarse uneveness in the form of grains. The maximum yield of the secondary electrons was around 5.2 at approximately 700 eV and about 4.7 at 600 eV, at activation temperatures of 780° and 870°C. It is concluded that transition in the formation mechanism of the growth of the BeO layer takes place between an activation temperature of approximately 800° and 870°C.
Influence of ion bombardment and intermediate layers on the adherence of gold to oxide substrates
Authors: Salem J. , Sequeda F.
Published: July 2002

The noble metals generally demonstrate minimal adhesion to oxide and halide surfaces. The film adherence has been shown to be often significantly improved by specific substrate treatments prior to deposition. In this work, we report on the effect on gold adhesion due to two surface treatment processes: argon or oxygen ion bombardment of the substrate surface and the deposition of an intermediate oxide or halide layer, immediately prior to the gold deposition. The results will be shown to be consistent with an adhesion model based on charge transfer at the metal–nonmetal interface and the resultant electrostatic stress and field enhanced diffusion.
Internal stresses in amorphous silicon films depositied by cylindrical magnetron sputtering using Ne, Ar, Kr, Xe, and Ar+H2
Authors: Thornton J. A. , Hoffman D. W.
Published: July 2002

Previous investigations of the thin metal films deposited using cylindrical-post magnetron sputtering sources have identified working gas transition pressures below which the internal stresses are compressive and above which they are tensile. The transition pressures increase with the atomic mass of the target material (Mt) relative to that of the working gas (Mg). This paper reports the occurrence of stress transitions in amorphous silicon films formed by dc cylindrical magnetron sputtering from a P-doped Si target using Ne, Ar, Kr, Xe, and Ar+H2 as working gases. The compressive stresses were comparable to those seen in metal films (∠1 GN/m2). However, the transition pressures and entrapped gas contents were greater than for metal films with comparable Mt/Mg. Experiments with special shields were conducted to investigate the mechanism of gas entrapment. The occurrence of large compressive stresses and entrapped gas concentrations for films such as these, where Mt/Mg<1, suggests that mechanisms different from simple target ion reflection, proposed in the earlier metallic film studies, are operative.
Structure study of Au–Si interface by MeV ion scattering
Authors: Narusawa T. , Kinoshita K. , Gibson W. M. , Hiraki A.
Published: July 2002

An application of the MeV ion backscattering/channeling technique to the Au–Si interface problem is described in this report. It is directly shown that at room temperature both Si(100) and Si(111) surfaces interact with deposited Au atoms abruptly if the Au film thickness exceeds a critical value of ∠4 monolayer (ML). The interface structure is similar in both cases and consists of ∠2 ML of strained Si and ∠10 ML of disordered (amorphous) silicide layer. When the substrate temperature is kept at 550°C during Au-film deposition, the interfacial reaction occurs if the average Au-film thickness reaches 1 ML in the Au–Si(111) system and ∠2 ML in the Au–Si(100) system. This is a suggestion of interaction between Si dangling bonds and the first few monolayers of Au-film.
Differential sputtering and surface segregation: The role of enhanced diffusion
Authors: Swartzfager D. G. , Ziemecki S. B. , Kelley M. J.
Published: July 2002

Composition measurements of Cu–Ni and Au–Pd alloy surfaces annealed at 600 °C and under steady-state bombardment conditions are reported. A unique procedure for studying the effects of enhanced diffusion is employed. The ion-bombardment-induced alteration of the composition of the near surface region of a Cu–Ni, Ag–Au, and Au–Pd alloy has been studied between 200 ° and 550 °C. The results have been extrapolated to lower temperatures and used to explain conflicting reports of differential sputtering in these alloys.
Resonant contributions to the cross section for electron stimulated desorption of neutral particles from adsorbates
Authors: Rubio J. , López-Sancho J. M. , López-Sancho M. P.
Published: July 2002

The total ESD cross section from an α layer of carbon monoxide adsorbed on the (110) face of tungsten has been measured as a function of the electron bombarding energy. A clear peak at 9 eV, which should also appear in electron energy loss spectroscopy (ELS), is here reported for the first time. An attempt is made at correlating this peak with the electronic structure of the adsorbed molecule, concluding that it stems from 5σ→2π* transitions.
Size dependence of ’’effective’’ barrier heights of mixed-phase contacts
Authors: Freeouf J. L. , Jackson T. N. , Laux S. E. , Woodall J. M.
Published: July 2002

The literature currently abounds with experimental studies of Schottky barrier heights of various metals upon many semiconductors. Unfortunately, these studies present some puzzling aspects: (1) Commonly, barriers determined by C–V studies are larger than barriers determined by I–V studies, and (2) Results obtained by different workers under apparently identical conditions are not always similar. A possible explanation for such effects is simply that many/most contacts experimentally achieved are in fact multiphase; these different barrier-height regions could result from variations in the metallurgical reactions assumed by many current models of Schottky barrier energetics. The different barrier heights measured by different techniques follow directly from the functional form of the relevant probes (e.g., I–V would more heavily weight a low-barrier region). The lack of reproducibility would follow from kinetic aspects of the relevant metallurgical interactions. A recent publication discusses the functional form for I–V and C–V ’’effective’’ barrier heights from mixed-phase contacts isolated from one another. These results apply directly to mixed-phase contacts only if the linear dimensions of all contact regions are large compared to the Debye length of the substrate (≊0.1 μ for 1015 silicon). In this paper, we examine the effects of contact dimensions upon equilibrium potentials (e.g., band bending) as well as transport studies to infer ’’effective’’ barrier heights for truly mixed-phase contacts of varying dimensions but fixed area ratios.
Crystallographic relationships and interfacial properties of Ag on GaAs(100) surfaces
Authors: Ludeke R. , Chiang T.-C. , Eastman D. E.
Published: July 2002

The crystallographic relationships, growth morphology, chemical activity, and electronic properties of Ag deposited at room temperature on GaAs(100) c(2×8) and (4×6) surfaces were investigated. Ag(110) growth was observed independent of growth rates. The growth is three- dimensional (nucleated) and the interfaces are abrupt. Stabilization of the Fermi level occurs beyond Ag coverages of 10 Å, is uncorrelated with the appearance of the metallic Ag phase at ∠0.5 Å and appears to be dependent on the formation of atomiclike interfacial states near the bottom of the bandgap. Schottky barrier heights of 0.83 and 0.97 eV were determined for Ag on the c(2×8) and (4×6) surfaces, respectively. The results are at variance with current Schottky barrier models.
X-ray photoelectron and Auger electron spectroscopic study of the CdTe surface resulting from various surface pretreatments: Correlation of photoelectrochemical and capacitance-potential behavior with surface chemical composition
Authors: Ricco Antonio J. , White Henry S. , Wrighton Mark S.
Published: July 2002

The surface chemistry and stoichiometry of p- and n-type CdTe photoelectrodes treated with oxidizing and reducing etches have been characterized by x-ray photoelectron and Auger electron spectroscopies. The results of surface analysis have been correlated with the photoelectrochemical and capacitance–potential behavior of the photoelectrodes. ‘‘Oxidized’’ surfaces are covered by a thin Te0/TeO2 layer (or a thicker Te0 layer, if the etching procedure is slightly altered), resulting in Fermi level pinning: a constant photovoltage is found for a wide range of redox potentials and potential-independent space charge layer capacitance obtains. ‘‘Reduced’’ surfaces closely resemble ion sputtered CdTe in chemical state and stoichiometry, resulting in more nearly ‘‘ideal’’ behavior: the semiconductor/electrolyte interface is rectifying in the dark; capacitance–potential behavior follows the Mott–Schottky equation near flat band conditions; and photovoltage varies with redox potential, from 0 to ∼0.7 V for p-CdTe.
Decreases in deuterium pumping by St707 getter alloy caused by carbon dioxide preexposure
Authors: Malinowski M. E.
Published: July 2002

Intentional passivation of the deuterium pumping of the solid getter alloy St707 has been attempted by exposing samples of St707 to carbon dioxide at different pressures, temperatures and exposure times relevant for application to the getter modules in the ALT-I pump limiter. It was found that one of the most effective treatments examined was a 30 min, 1 Torr exposure at approximately 100 °C. This preexposure kept the getter pumping speed less than 0.001 of its rated value for about 3 min when exposed to deuterium at 1 Torr and 30 °C. After this ‘‘incubation’’ period, the getter speed increases to values greater than ∼1% of fully activated values. If left under high deuterium pressure, the getter eventually flakes off the substrate. Video observations of the flaking process indicate that individual particles leave the constantan getter substrate at velocities of 1 m/s. Attempts at passivating the getter using oxygen and carbon monoxide were found to be no more effective than using carbon dioxide, suggesting that there is no way to completely passivate the getter with these gases at pressures low enough for application to in situ getter arrays used in tokamaks.
Structure-related optical properties of thin films
Authors: Macleod H. Angus
Published: July 2002

Vacuum-deposited thin films have a columnar structure that includes appreciable void volume. This structure is responsible for many differences between the properties of materials in the form of thin films and in bulk. Refractive index is usually reduced and is a sensitive function of preparation conditions. Films also exhibit considerable inhomogeneity and form birefringence. Theoretical predictions of the refractive index of columnar thin films are finding confirmation in recent measurements. Moisture adsorption over the internal surface of the films and in the voids leads to instability of optical properties and a dependence on environmental conditions greatly exceeding that of bulk materials.
Pyroelectric calorimeter for photothermal studies of thin films and adsorbates
Authors: Coufal Hans J. , Grygier Robert K. , Horne Donald E. , Fromm Jacob E.
Published: July 2002

A pyroelectric calorimeter for studies of radiation induced thermal transients in thin films and at surfaces is described. The signal generation and detection process, as well as design criteria are briefly reviewed. Detailed data are presented whereby our design, which has found extensive utility, can be fabricated. This device is compatible with standard Inficon quartz microbalance hardware and provides a sensitivity of several nanojoules at a time resolution of <100 ns over a wide temperature and pressure range.
Precision, accuracy, and uncertainty in quantitative surface analyses by Auger-electron spectroscopy and x-ray photoelectron spectroscopy
Authors: Powell C. J. , Seah M. P.
Published: July 2002

A quantitative surface analysis by Auger-electron spectroscopy (AES) or x-ray photoelectron spectroscopy (XPS) requires a series of operations that typically includes instrument setup, specimen positioning, data acquisition, data manipulation, and data analysis. These operations involve a sequence of measurements which are combined and/or compared with other data to yield an analysis. The final result has an estimated uncertainty that reflects the sum of the separate random and systematic errors in the various measurements and sources of data. We identify the major steps in typical analyses and comment on the major sources of error leading to estimates of uncertainty. Systematic errors generally exceed those of a random nature and are associated with the complex morphology of typical specimens, with parameters of instrument performance, and with limitations of current methodology and data. We review general measurement principles for surface analysis, the development of a suitable analytical strategy, and identify and discuss many of the sources of error. The discussion is specific to AES and XPS but many of the issues are relevant to other techniques of surface analysis. Finally, two examples are presented to illustrate the sources and magnitudes of some of the errors and the final uncertainties in some common examples of surface analyses.
p-type arsenic doping of CdTe and HgTe/CdTe superlattices grown by photoassisted and conventional molecular-beam epitaxy
Authors: Arias J. M. , Shin S. H. , Cooper D. E. , Zandian M. , Pasko J. G. , Gertner E. R. , DeWames R. E. , Singh J.
Published: July 2002

In this paper we report on p-type arsenic doping of CdTe and HgTe/CdTe superlattices by photoassisted and conventional molecular-beam epitaxy (MBE). We also report on some of the problems involved in doping and growing the HgTe/CdTe superlattice system by theoretically examining two key aspects of its growth: (i) growth of CdTe at low temperatures under Cd-stabilized conditions, and (ii) effect of laser excitation on the growing CdTe surface. p-Type arsenic-doped CdTe and HgTe/CdTe superlattice epilayers were grown on (100) CdTe and CdZnTe substrates at low temperatures under cation-stabilized conditions obtained either with excess Cd, or excess Hg fluxes. As-grown arsenic-doped CdTe layers had room temperature carrier concentrations in the 1014–1016 cm−3 range, and hole mobilities of about 35–65 cm2/V s. Low-temperature photoluminescence spectra of arsenic-doped CdTe epilayers grown by photoassisted MBE showed an emission peak at 1.51 eV, which is associated to the AsTe acceptor (arsenic occupying a Te site) with a 92 meV ionization energy. CdTe epilayers grown at low temperatures with photoassisted MBE have superior structural, optical, and electrical properties than those grown by conventional MBE. Arsenic doping of the HgTe/CdTe superlattice structure has resulted in in situ growth of p-type modulation-doped superlattices with enhanced mobilities. Undoped superlattices grown under the same conditions are n-type. These results represent a significant step towards the in situ fabrication of photodiodes and other advanced devices based on HgTe/CdTe doped superlattice structures.
Uses of ultraviolet/ozone for hydrocarbon removal: Applications to surfaces of complex composition or geometry
Authors: McIntyre N. S. , Davidson R. D. , Walzak T. L. , Williston R. , Westcott M. , Pekarsky A.
Published: July 2002

The use of ultraviolet (UV)/ozone treatment for the removal of hydrocarbon contamination is discussed for a number of substrates involving complex composition or geometries. Treatment of gold and silicon dioxide surfaces in a reactor attached on line to an x-ray photoelectron spectrometer showed that the chemistry of oxidized hydrocarbon on SiO2 differs from that on gold and the removal rate of hydrocarbon bonded to SiO2 is much faster than that on gold. Treatments of thin film transistor surfaces consisting of field oxides and metallurgical strips showed that considerably longer reaction times are required to clean the field oxide regions compared to treatment of a single component surface. Cross-contamination of specimen surfaces can occur if labile contaminants such as fluoride are present anywhere on the structure. UV/ozone treatment has also been investigated for obscured surfaces not directly irradiated by UV. Effective cleaning is still directly possible using ozone alone as a reactant, although the reaction time is longer.
Improving the interpretation of x-ray photoelectron and Auger electron spectra using numerical methods
Authors: Stickle W. F. , Watson D. G.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) have long been used for sputter depth profiling for the determination of sample chemical composition as a function of depth. Often in XPS and AES, peak overlap or a subtle change in chemistry makes the chemical analysis of the elements in a material difficult. By using a variety of numerical methods, such as linear least squares fitting and target factor analysis, it is possible to improve the analysis and interpretation of depth profiles. The use of numerical methods can aid in the interpretation of chemical state information and in most cases significantly improves the detection limits of specific elements. An XPS sputter depth profile of tantalum silicide on silicon and an AES profile of a multilayer structure of gold, tantalum, and silicon carbide are shown as examples of the improvements offered by applying numerical methods.
X-ray photoelectron spectroscopy study of x-ray irradiated metal/fluoropolymer interfaces
Authors: Shi Ming-Kun , Lamontagne Boris , Selmani Amine , Martinu Ludvik
Published: July 2002

Interaction of Cr, Ti, Al, Ag, Au, and Cu with Teflon PFA (polytetrafluoroethylene- co-perfluoroalkoxy vinyl ether) and FEP (fluoroethylene propylene), and the effect of x-ray irradiation on the metal/polymer interfaces, were studied using in situ x-ray photoelectron spectroscopy (XPS) and mass spectrometry. Cr, Ti, and Al were found to react with both PFA and FEP, leading to polymer surface graphitization and formation of carbide and fluoride species, which are enhanced at higher metal thicknesses. On the other hand, evaporation of Au, Ag and Cu causes only a slight loss of fluorine, but no chemical interaction occurs. Post-deposition x-ray irradiation does not promote metal–polymer interactions, but it leads, in the case of reactive metals, to a pronounced increase of the C–CFn peak intensity, which rises with the metal thickness. A mechanism based on radical recombination reaction and accumulation of the small fragments, inside the metal film and/or near the metal/polymer interface, is proposed to explain this behavior. The metal XPS signal decreases upon x-ray exposure, which is interpreted by diffusion of metals into the polymer matrix. The relative change in XPS signal is enhanced at longer x-ray irradiations, but decreases at a higher metal thickness. This effect is most pronounced for Cu, Cr, and FEP.