bluuebunny/crossref_metadata_2025 huggingface dataset:
Operational aspects of a gallium phosphide source of P2 vapor in molecular beam epitaxy
Authors: Wright S. L. , Kroemer H.
Published: July 2002

We report our operational experiences with a gallium phosphide source of P2 vapor in the MBE growth of GaP. The use of a P2 source results in much more favorable vacuum characteristics than the use of P4, as generated by an elemental phosphorus source, introducing no complications compared to the growth of arsenides. The phosphorus background pressure during growth is actually lower than the background pressure present during GaAs growth using an elemental arsenic As4 source, for comparable flux rates. The few P4 molecules that do form by association of P2 condense as white phosphorus on the cryobaffles and re-evaporate upon warmup. However, the pressure peaks at a value no higher than the background pressure during growth. Furthermore, the bakeout pressures are not significantly higher than those obtained using arsenic only. The P2 beam generated by the GaP source contains less Ga than one might expect from equilibrium vapor pressure considerations, thus greatly facilitating the independent control of Ga and P2 fluxes.
Simple rotating shutter for low coverage depositions of accurate thickness
Authors: Brooks J. S. , Meservey R. , MacNabb R. K.
Published: July 2002

A method is developed using a rotating shutter with a stepped sector disk to produce ultrathin evaporated layers of accurately known thickness. Deposition of insulating barriers for tunnel junctions was accomplished with this shutter.
The effect of substrate–epitaxial interface on the capacitance–voltage characteristics of Schottky barriers formed on sputtered films of gallium arsenide
Authors: Kulkarni A. K. , Soukup R. J.
Published: July 2002

The capacitance–voltage characteristics of Schottky diodes fabricated on sputtered GaAs do not yield straight line plots on a 1/C2 vs V curve. This anomalous behavior may be due to any one of the following mechanisms: (1) defective Schottky barrier fabrication, (2) the effect of an insulating interfacial layer, (3) nonuniform donor distribution, (4) the effect of deep traps, or (5) the effect of the substrate–epitaxial interface. Only the effect of the substrate–epitaxial interface capacitance adequately explains the anomalous behavior observed. Measurements of capacitance at 1 kHz and at 1 MHz coupled with complex impedance measurements led to a small signal linear circuit model. The temperature dependence of the circuit elements identified appropriately with physical phenomena yielded information about the Schottky barrier and the barrier formed at the epitaxial layer–substrate interface. The strong temperature dependence of the low–high junction barrier capacitance is explained using this model.
Auger C
V
V spectra as a probe of the electronic structure of metallic glasses
Authors: Bevolo A. J. , Severin C. S. , Chen C. W.
Published: July 2002

Additional data on the Auger KVV spectra of Be and B in the Fe82B18−xBex ferromagnetic metallic glass system are presented. A weak but sharp peak in the B KVV spectra of the ternary alloys is identified with a Fe–B bonding state that is also present in the binary Fe–B metallic glass system. In addition to the previously reported 14-eV shift in the Be KVV energy for x?4 a narrowing of the linewidth of this transition from 8 to 5 eV is reported for the same composition range. Several models are considered to explain the unusual Be KVV Auger results for the ternary Fe–B–Be metallic glass system.
Neutral-beam systems for magnetic fusion reactors
Authors: Fink Joel H.
Published: July 2002

Neutral beams for magnetic fusion reactors are at an early stage of development, and require considerable effort to make them into the large, reliable, and efficient systems needed for future power plants. To optimize their performance and establish specific goals for component development, systematic analysis of the beamlines is essential. Three ion source characteristics are discussed: arc-cathode life, gas efficiency, and beam divergence, and their significance in a high-energy neutral-beam system is evaluated.
Hg0.70Cd0.30Te anodic oxidation
Authors: Janousek Bruce K. , Carscallen Richard C.
Published: July 2002

It has been determined that anodic oxidation of (Hg,Cd)Te proceeds via a dissolution– precipitation mechanism. The initial film formation can be understood in terms of electrochemical parameters and, therefore, can be controlled in a rational manner. For example, stirring the anodization solution during dissolution prohibits film formation at low current densities due to an increase in the rate of diffusion of ionic species away from the anode. Increasing the solution pH makes the anodic oxide more soluble and semiconductor dissolution can be sustained at a higher current density. MOS structures fabricated incorporating this electroetch in the passivation process show a lower oxide fixed charge likely owing to the removal of the TeO2 film present on the semiconductor following a Br2/methanol etch.
Surface processes controlling MBE heterojunction formation: GaAs(100)/Ge interfaces
Authors: Bauer Robert S. , Mikkelsen J. C.
Published: July 2002

In situ LEED and synchrotron radiation photoemission spectroscopy were performed on Ge interfaces grown by MBE on GaAs(100) surfaces ranging from the As-rich c(4×4) to the Ga-rich 4×6 ordered MBE surface phases. By comparison to MBE and bulk grown c-GeAs, we find that when lattice-matched heterojunctions are grown on GaAs surfaces, GeAs forms an ordered 3×1 phase at the free surface of Ge(110) and a two-domain (2×1) phase at the free surface of Ge(100). The GeAsx two-domain (2×1) ordered Ge(100): As surface phase is obtained independent of the initial GaAs(100) surface As concentration. Further, As outdiffusion does not occur during the initial deposition of Ge; rather, we observe an As enrichment of the Ge surface at a Ge coverage corresponding to the initial surface As concentration. The As diffusion from the interface layer, while lowering the free energy of the Ge surface layers, also changes the band-gap offset.
Similarity in interactions between metal–semiconductor and metal–metal interfaces
Authors: Chang Chin-An
Published: July 2002

When a gold film is evaporated on Si and the Au/Si Schottky contact is exposed to air, outdiffusion of Si to the Au surface takes place even at room temperature. A similarly enhanced outdiffusion in Au films has been observed for GaAs and many metals at elevated temperatures in air over those in vacuum or inert ambients. We have investigated the interactions between metal and semiconductor, and between metal and metal in different ambients and found a similarity between these two systems: The observed ambient effects can be commonly correlated by the consideration of two factors—the electronegativity difference between the overcoating metal and the underlying species, and the ambient-induced surface potential change of the former which is a polycrystalline film in all the systems studied, thus enabling the ambient species to diffuse to the interface to affect the interactions there. These correlations have led to the prediction of a reduced diffusion of a less electronegative species in Au films by CO, and, more significantly, of a similarly reduced diffusion in Pt films by oxygen. We have confirmed these predicted effects for many systems including both semiconductors and metals. The application of this work to the fabrication of Schottky contacts for stable operation in air is also discussed.
Phase separation in interactions of tantalum–chromium alloy on Si
Authors: Palmström C. J. , Gyulai J. , Mayer J. W.
Published: July 2002

Bilayers and codeposited alloys of Cr and Ta on Si were studied using Rutherford backscattering and glancing angle x-ray diffraction as a function of thermal annealing up to 800 °C. The bilayers produce layered structures of TaSi2 and CrSi2. Phase separation was observed for the alloy CrxTa1−x layers on Si. The interaction produced CrSi2 next to the Si and an outer layer containing a mixture of CrSi2 and TaSi2. No ternary phase formation was detected for anneals up to 800 °C.
Direct measurement of temperature profiles induced by finely focused beams
Authors: Iranmanesh Ali A. , Pease R. F. W.
Published: July 2002

Beam processing of materials, such as recrystallization of amorphous semiconductors and annealing, is playing a major role in the advancement of electronics technology. Calculations of temperature profiles induced by different sorts of beams have already been reported. Here we describe the fabrication, calibration, and use of micron-size, thin-film thermocouples to measure steady state surface temperature profiles in silicon targets irradiated with 20- and 20-kV electron beams. Experimental temperature profiles are similar to, but somewhat sharper than, calculated profiles and the maximum measured temperatures exceed calculated values by about 15% at the center of the beam. This discrepancy may be due to errors in measuring beam radius and to inadequate representation of power dissipation in the target.
Chemical bonding and Schottky barrier formation at transition metal–silicon interfaces
Authors: Ho Paul S.
Published: July 2002

The transition metal–silicon interface is highly reactive; the reactivity induces material reactions altering the stoichiometry, atomic structure, and chemical bonding at the interface. For such an interface, it is essential to study the interfacial reaction and chemistry in order to understand the formation of Schottky barriers. This paper first reviews the present knowledge on the electronic and microstructural characteristics of the transition metal–silicon interface. The discussion focuses on the extent of atomistic details regarding these interface properties that can be extracted from existing results. This is followed by a summary of barrier height data obtained from two types of measurements. One, with thick-film (∼100 Å) coverages, demonstrates that the barrier height of a well-reacted silicide overlayer is large unaffected by changes of the material characteristics of the silicide phase. And the other, with a few monolayers of metal coverage, reveals that the barrier can be established with a few Å of metal coverage. These experiments establish the true interfacial character of the barrier height. Based on the extent of interfacial reaction, the nature of the transition metal–silicon interface can be classified to be extrinsic or intrinsic. The extrinsic interface contains various defects from processing and surface preparation, which control to a significant extent its barrier height. As the reaction proceeds to complete silicide formation, an intrinsic interface is formed where the barrier height seems to be determined primary by chemical bonding originating from metal–silicon interaction at the interface.
Process control of vacuum-deposited CdS for the fabrication of reproducible 8% efficient solar cells
Authors: Hench T. L. , Bragagnolo J. A. , Delgado J. E. , Leyman P. F. , Motta P. F.
Published: July 2002

As part of the research and development effort, a device fabrication line was established whose mission was to reproducibly fabricate large area (10 cm2) CuxS/CdS solar cells of greater than 8% average conversion efficiency. This goal was accomplished mainly by the careful monitoring and control of the CdS deposition process. Material properties which influence cell performance, such as back contact reflection, CdS resistivity, and deposition rate, were monitored and controlled via temperature control. Photoluminescence of the CdS and resistivity of CuxS layers formed on the CdS were used to electronically characterize the films prepared and served as tools in observing changes in the deposition process and cell performance. The reproducibility of the process was confirmed by a 2-month qualifying run in which an average conversion efficiency of greater than 8% was achieved and maintained.
Passivation properties and interfacial chemistry of photochemically deposited SiO2 on Hg0.70Cd0.30Te
Authors: Janousek B. K. , Carscallen R. C. , Bertrand P. A.
Published: July 2002

SiO2 deposited photochemically at a substrate temperature of 100 °C has been evaluated as a surface passivant on Hg1−xCdxTe  (x=0.30). It has been determined that the electrical properties of the (Hg, Cd)Te–SiO2 interface are dependent on the pretreatment given the semiconductor surface prior to the insulator deposition. Formation of a thin native oxide on the (Hg, Cd)Te surface during the pretreatment appears to enhance the resultant (Hg, Cd)Te–SiO2 interface properties. A significant spread in the (Hg, Cd)Te–SiO2 interface properties is observed, likely owing to the nature of how this native oxide forms and interactions between the native oxide and the SiH4 in the photochemical reactor. It is shown through neutron activation analysis that the Hg employed as a photochemical sensitizer is incorporated in the SiO2 at a concentration of 1.8 ppm.
Empirical tight binding description of Hg1−xMnxTe and Hg1−xCdxTe
Authors: Hass K. C. , Ehrenreich H.
Published: July 2002

This paper presents the first theoretical treatment of the electronic structure of Hg1−xMnxTe. As in the authors’ previous work on Hg1−xCdxTe, a semiempirical tight binding approach is employed, based in part on atomic energy levels, Harrison’s universal tight binding scheme, and existing experimental band structure information. The occupied Mn spin-polarized d bands are discussed and shown to have little effect on the states near the band edges. The s–p electron ‘‘complex band structure’’ of Hg1−xMnxTe is calculated in the CPA. Previous results for Hg1−xCdxTe are extended and used as a basis of comparison. The more rapid increase of the band gap with x in Hg1−xMnxTe is shown to result from the larger energy difference between cation s levels. This difference also gives rise to more pronounced disorder effects in Hg1−xMnxTe. These are discussed in the context of the CPA results for damping, band gap bowing, and the limiting electron mobilities.
A study on the purity and SIMS profiling of MOVPE–cadmium mercury telluride
Authors: Mullin J. B. , Irvine S. J. C. , Royle A. , Tunnicliffe J. , Blackmore G. , Holland R.
Published: July 2002

A preliminary study has been carried out on the electrical properties and chemical purity of epitaxial layers of cadmium mercury telluride (CMT) grown by metal-organic vapor phase epitaxy (MOVPE). It has been shown that the mobility of such layers grown at 410 °C are comparable with bulk CMT of equivalent carrier concentration. SIMS profile studies of trace impurities in the epitaxial layers and CdTe substrates used for epitaxial deposition revealed significant impurity concentration enhancement (ICE effect) for a number of elements (Li, Na, K, Al, Ga, In and Mn) at the CdTe/CMT interface: some of these elements (Li, Na, K, Al and In) also showed this ice effect at the subsequent CMT/CdTe interface. The magnitude of the ICE effect could be quite large (a factor of ∼ 100 for Li) but its origin was not identified although potential mechanisms for its formation are discussed.
A PH3 cracking furnace for molecular beam epitaxy
Authors: Chow Robert , Chai Young G.
Published: July 2002

A furnace was fabricated to crack phosphine in ultrahigh vacuum. Thermodynamic calculations showed that phosphine should dissociate into the phosphorus dimer to a high degree. Furnace materials were compared by construction of all-tantalum and all-quartz cartridges which slid into the furnace hot zone. Phosphine was found to react with tantalum, but not to any great extent with quartz. The effects of baffles, studied with the quartz cartridges, lowered the temperature at which the cracking efficiencies began to increase and increased cracking efficiencies. The temperature range studied was from 100 ° to 1170 °C.
Deposition of Au overlayers onto cleaved (Hg,Cd)Te surfaces
Authors: Davis G. D. , Beck W. A. , Byer N. E. , Daniels R. R. , Margaritondo G.
Published: July 2002

The interaction of evaporated Au overlayers with ultrahigh vacuum-cleaved p-type Hg0.72Cd0.28Te(110) surfaces has been studied with ultraviolet photoelectron spectroscopy (UPS) using synchrotron radiation. For all coverages of Au, a significant out-diffusion of Te occurs so that the cation-to-anion ratio [(Hg+Cd)/Te] decreases from 1.0 for the clean surface to 0.2 for 30 Å of Au and to 0.03 for 100 Å of Au. In contrast to the behavior previously observed following Al deposition, the Hg/Cd ratio remains constant at low coverages although it decreases to ∼70% of the initial value for thicker Au layers (20–50 Å). During the initial stages of deposition, the band bending changes from the inverted state present after cleavage toward flat band or accumulation. This behavior, probably due to in-diffusion of Au, is consistent with the use of Au as an Ohmic contact with p-type material.
Microdiffraction and lattice resolution studies of fivefold symmetry gold particles
Authors: Schabes-Retchkiman P. , Gómez A. , Vázquez-Polo G. , José-Yacamán M.
Published: July 2002

The structure of fivefold particles is studied using single particle diffraction in a STEM microscope and lattice images. The results show excellent agreement with the rhombohedral and body-centered orthohombic models for the particle. Theoretical calculations were carried out to study the influence of the number of atoms in the diffraction patterns.
Quantitative studies of cleaved and sputtered CuInSe2 surfaces
Authors: Massopust T. P. , Ireland P. J. , Kazmerski L. L. , Bachmann K. J.
Published: July 2002

CuInSe2 has emerged as an important photovoltaic semiconductor. The critical importance of stoichiometry changes, interfacial chemical reactions, and compositional variations on cell performance has made the acquisition of reliable quantitative data by surface analysis methods mandatory. In this study, single crystals of CuInSe2 were cleaved in UHV, exposing the (110) plane which is representative of the bulk material. Quantitative AES analysis was performed using both N(E) and dN(E)/dE data, yielding concentration results within 2 at. % of stoichiometric values. The method developed is based upon an independent evaluation of matrix effects using elemental standards and actual density considerations. The effects of Ar+ ion sputtering were investigated for beam energies 0.1<Ep<5.0 kV. Quantitative data for sputter-etched and virgin surfaces have been compared. Oxygen adsorption and In oxidation was observed during exposure to O2 and electron beam irradiation. Polycrystalline thin films of CuInSe2 were also analyzed, and quantitative results have been compared to the single-crystal values.
Atoms and electrons at surfaces: A modern scientific revolution
Authors: Duke C. B.
Published: July 2002

During the past 15 yr surface science has experienced extensive and profound changes. This historical review is devoted to the development of the theme that these changes considered collectively constitute a scientific revolution in the sense described by Thomas Kuhn. The recognition of the consequences of inelastic collisions of fast electrons played a key role in initiating the modern era in surface science. The resulting explosive development of surface characterization spectroscopies is discussed and shown to have led to a fundamental alteration in our perception of a surface or interface. Whereas in the mid-1960’s an interface was regarded merely as the boundary between two bulk media, today it is seen as an independent entity: a state of matter determined by its history and exhibiting its own unique composition, structure, and electronic properties. The review concludes with a brief indication of the role of the American Vacuum Society in promoting and facilitating the development of surface science and the diffusion of its results during this formative period.
Interfacial sharpnesses and thicknesses of layers in a GaAs0.2P0.8/GaP strained-layer superlattice measured by Auger sputter profiling
Authors: Chamberlain M. B. , Wallace W. O.
Published: July 2002

The interfacial sharpnesses and thicknesses of the layers in a strained-layer superlattice were measured using Auger sputter profiling. The 950-nm-thick SLS laminate was fabricated by organometallic chemical vapor deposition and it consisted of 24 alternating layers of GaAs0.2P0.8 and GaP. The Auger sputter profile through these layers measured the intensity of the P LMM Auger emission plotted as a function of time sputtering through the layers with a 700-eV Ar-ion beam. The average layer thickness measured was 39.6 nm with a standard deviation of 1.1 nm. The measured depth resolution was 0.7% at a sputtered depth of 950 nm, which is as good as the best values of 1%–10% reported at this depth in profiles of amorphous specimens. The superb depth resolution measured here is attributed to the following characteristics of the SLS material: a very low surface roughness; a uniform crystal structure throughout the SLS laminate even though the lattice constant changes between adjacent layers; a very pure material; and an absence of misfit dislocations near the area profiled.
A technique for the production of a thin film with a linearly varying composition
Authors: Nastasi M. , Barbour J. C. , Gyulai J. , Hung L. S. , Mayer J. W.
Published: July 2002

A technique is described for the fabrication of a single thin film sample with a controlled variation in composition. Vacuum evaporation through a thickness controlling aperture (in the shape of an Archimedes spiral) onto a rotating substrate yields a sample with alternating wedge-shaped films in which the composition varies linearly with distance. The composition gradient of these samples spans the entire range of a phase diagram thereby allowing thermal annealing and ion irradiation studies as a function of position (composition) on the film. Rutherford backscattering is used to investigate the films while on the NaCl substrate,  and energy dispersive spectroscopy and electron diffraction are used to study the self-supporting films on transmission electron microscope grids after dissolution of the substrate.
Internal stresses in wear and corrosion resistant amorphous metallic coatings of (W0.6Re0.4)76B24 and (Mo0.6Ru0.4)82B18
Authors: Thakoor A. P. , Lamb J. L. , Williams R. M. , Khanna S. K.
Published: July 2002

Hard, protective coatings of amorphous (W0.6Re0.4)76B24, (WReB) and (Mo0.6Ru0.4)82B18, (MoRuB) alloys have been deposited by magnetron sputtering onto soda lime glass, and heat treated AISI 52100 steel substrates. The amorphous nature of the as-deposited coatings was confirmed by x-ray diffraction, and their crystallization temperatures were determined by differential thermal analysis. Both WReB and MoRuB coatings showed high crystallization temperatures: 1000 and 790 °C, respectively. Internal stresses in the as-desposited films changed from compressive to tensile in nature with increasing argon deposition pressure. The compressive-to-tensile transition occurred at ∼12 mTorr-argon pressure for WReB and at ∼4 mTorr-argon pressure for MoRuB films on glass. WReB coatings on heat treated AISI 52100 bearing steel exhibited high microhardness (∼2400 HV50) and a reduction of ∼2 1/2 orders of magnitude in the unlubricated wear rate (measured by a pin-on-disk technique) over that of uncoated AISI 52100 steel. MoRuB coatings also showed high microhardness (∼1800 HV50) as well as excellent chemical corrosion resistance, exhibiting over 3 orders of magnitude improvement over pure Mo at high anodic potentials (measured under potentiostatic conditions in 1 N H2SO4). Influence of the internal stresses on the protective properties of the coatings deposited under different conditions is discussed in this paper.
An overview on defect studies in MCT
Authors: Cheung D. T.
Published: July 2002

Major advances in recent studies of defects in MCT are reviewed, including our current understanding of defect formation mechanisms, dynamics, and their electronic properties. New attempts to control the defects are also discussed. Several key technical issues are raised which should serve as guidelines for future research.
Study of mercury cadmium telluride (MCT) surfaces by automatic spectroscopic ellipsometry (ASE) and by electrolyte electroreflectance (EER)
Authors: Raccah Paul M. , Lee U. , Ugur Sevilay , Xue Da Zhong , Abels L. L. , Garland J. W.
Published: July 2002

A systematic study of line shapes obtained by electrolyte electroreflectance (EER) and by automatic spectroscopic ellipsometry (ASE) on samples of mercury cadmium telluride (MCT) with varying densities of defects has been carried out. The results show that the two techniques yield in all cases the same value for the interband transition energies Ej. Because the values of the Ej are quantitatively related to the alloy composition x, it is clear that both ASE and EER can be used to carry out studies of the alloy composition. On the other hand, the values of the linewidths Γj yielded by the two techniques often do not agree. In those cases in which the etch pit density is less than 106/cm2, the values agree approximately; otherwise, EER yields much larger values. The difference between the two techniques is, of course, the use of an electric field modulated at very low frequencies (EER). We show that the modulating electric field causes an electrostriction and polarization of the defects in MCT. These effects, which have not been taken into account in previous theories of electroreflectance, are shown to give rise to first- and second-derivative line shapes proportional to the Stark shifts ΔEj and to a shift Δσ 2 related to the overall defect scattering strength, respectively. These new line shapes dominate the usual third-derivative line shape for defective materials. A simple interpretation of our experimental results suggests that the relative Stark shifts ΔEj are associated with plasticity, long-range strains and extended defects, and that the shift Δσ2 arises from polarizable charged defects. Thus, the treatment present here, by allowing one to determine values for ΔEj and Δσ2 as well as values for Γj in agreement with ASE, give important physical information not previously available on defects in MCT. The quantitative determination of the defect-related parameters has allowed us to establish a hierarchy of quality among all the epitaxial techniques by comparison to bulk single crystal samples.
Cathodoluminescence of HgCdTe and CdTe on CdTe and sapphire
Authors: Bubulac L. O. , Tennant W. E. , Edwall D. D. , Gertner E. R. , Robinson J. C.
Published: July 2002

The imaging cathodoluminescence capability of a scanning electron microscope (SEM) was complemented by etch pit (EP) measurements and secondary ion mass spectroscopy (SIMS) to characterize structures of HgCdTe LPE grown both on CdTe and CdTe/sapphire (PACE-1) (Ref. 1: W. E. Tennant, IEDM Technical Digest 1983, 704) substrates. In addition to providing the source for luminescence, the high-power-density SEM beam was exploited to perform in situ annealing which improved the CL efficiency and aided in the analysis. Selected CL/SEM data are shown for substrates, epilayers and interfaces. CdTe Bridgman grown substrates exhibited defect structures (twins, dislocations, precipitates, subgrain structure) and substantial differences in CL efficiency and response to electron beam (EB) annealing. Cd annealing of Bridgman substrates increases CL efficiency, removes sensitivity to EB annealing, and causes impurity redistribution as measured by SIMS. PACE-1 substrates show higher defect density, an absence of subgrains, and more uniform defect distribution in contrast to CdTe Bridgman substrates. The defect characteristics of the epilayers grown on CdTe substrates were found to depend on Hg content in the epilayer. CdTe epilayers tend to reproduce CdTe substrates. Hg1−xCdxTe (x≂0.93) epilayers have no subgrains, and a much lower defect density (∼mid 104/cm2). A highly dislocated and disturbed interface was observed in Hg1−xCdxTe (x≂0.3)/CdTe (on a chemically angle etched surface) and in Hg1−xCdxTe (x≂0.93)/CdTe (cleaved cross section samples). Improvement in the CL intensity from the epilayer was seen with distance from the interface. Both termination of substrate defects and origin of epilayer defects at the interface was observed.
Surface stoichiometry changes induced by the hydrogenation of Hg0.72Cd0.28Te
Authors: Davis G. D. , Byer N. E. , Riedel R. A. , Daniels R. R. , Margaritondo G.
Published: July 2002

The reaction of the cleaved Hg0.72Cd0.28Te surface with atomic hyrogen has been studied with ultraviolet photoelectron spectra obtained using synchrotron radiation. Hydrogen exposures of 600 L or less caused no detectable difference in the photoelectron spectra. However, dramatic changes were observed upon extended hydrogenation with the mercury signal decreasing to ∼20% of its original value before the surface passivated at an exposure of l04 L with the apparent formation of hydrogen– Hg and Cd complexes. During hydrogenation, some of the freed Hg diffuses into the semiconductor to form a degenerate n-type surface layer. This process is contrasted to oxidation where no saturation of the surface was seen and the reacted surface was almost completely Hg free.
Interband optical absorption in thin semiconducting quantum well wires
Authors: Hassan Hassan H. , Spector Harold N.
Published: July 2002

We have calculated the optical absorption coefficient due to interband transitions between quantized subbands in the valence and conduction bands of a thin semiconducting quantum well wire having a direct energy band gap Eg. The model we have used in our calculations assumes electron wave functions and energy eigenvalues of the particle in a box type for the motion of the carriers in the direction perpendicular to the axis of the thin semiconducting wire. The threshold for the optical absorption due to interband transitions is shifted to shorter wavelengths as the cross-sectional area of the wire decreases. Above the threshold, the absorption is an oscillatory function of the photon energy when the transverse dimensions of the wire are fixed. For allowed transitions, the selection rules allow transitions only between those subbands in the conduction and valence bands having the same set of quantum numbers. In this case, the absorption coefficient has peaks whenever the photon energy is such that transitions can take place between new pairs of subbands in the valence and conduction bands. The absorption coefficient for such allowed transitions is directly proportional to the density of states of the carriers in the valence and conduction bands. For forbidden transitions, the threshold for the beginning of absorption is also shifted towards shorter wavelengths because of size quantization and the absorption is an oscillatory function of photon energy for fixed transverse dimensions of the wire, but the selection rules for transitions allow transitions to states where the quantum numbers of the quantized subbands can be different in the conduction and valence bands. Also, when the transitions are forbidden, the behavior of the absorption depends upon the polarization of the radiation relative to the axis of the quantum well wire.
Charged dislocations and jogs in Hg1−x CdxTe and other II–VI compounds
Authors: Hirth J. P. , Ehrenreich H.
Published: July 2002

In an ionic model for (Hg,Cd)Te, dislocation jogs are shown to be charged and to act as sources for cation vacancies. The charged cation jogs act as donors. This model is shown to be consistent with observations of p→n transitions in deformed (Hg,Cd)Te and with observations of charge transport by dislocations in II–VI compounds.
Hydrogen pumping with palladium membranes
Authors: Berkheimer G. David , Buxbaum Robert E.
Published: July 2002

The purpose of this investigation is to understand and improve palladium membrane oxidative pumping for large quantities of hydrogen gas at vacuum pressures. Oxidative pumping should be exceptionally fast, clean, and energy efficient. Hydrogen molecules are chemisorbed and dissociated on one surface of a palladium or palladium-coated membrane. Dissociated hydrogen atoms diffuse through the membrane and react with oxygen on the other side. Product water is removed by condensation at low temperatures. In this paper we analyze theory and relevant experiments concerning surface and bulk effects in hydrogen pumping with palladium membranes. Models are refined by comparison with experimental pumping data to suggest that the original pump design was limited by a low effective sticking coefficient, which apparently was caused by multiple pathways for dissociation on the palladium surface. Increased pumping speeds and increased economy should result from decreased operating temperatures, with 300 °C appearing as something of an optimum. At very low temperatures, surface oxidation, surface impedence, and low permeabilities will limit throughput. Commercial application appears limited to fusion reactors and to proton beam experiments.
Overview of microstructural defect development in interfacial regions of HgCdTe and CdTe layers grown on CdTe and alternate substrates
Authors: Woolhouse G. R. , Magee T. J. , Kawayoshi H. A. , Leung C. S. H. , Ormond R. D.
Published: July 2002

The origins of microstructural defects in HgCdTe epilayers grown on CdTe are reviewed. In particular the role played by lattice parameter misfit and interdiffusion in the generation of misfit dislocations is considered. Two approaches to the improvement of epilayers through the use of alternate substrates are described and examples illustrating the potential and current problems in growth of HgCdTe/CdTeSe, HgCdTe/ZnCdTe, and CdTe/GaAs systems are discussed.
Adhesion of titanium nitride coatings on high-speed steels
Authors: Helmersson U. , Johansson B. O. , Sundgren J.-E. , Hentzell H. T. G. , Billgren P.
Published: July 2002

The adhesion is of vital importance for the performance of tools coated with titanium nitride. In view of this, we have studied the effects of substrate temperature and pretreatment on the adhesion of TiN coatings. Since high-speed steels are among the most used substrate materials for tool applications we have chosen to deposit the films onto eight different high speed steels. The TiN coatings were deposited using reactive dc-magnetron sputtering, and the adhesion was measured using the scratch test. In order to study the film–substrate interface Auger electron spectroscopy was used in combination with ion beam depth profiling. On most of the steels, the adhesion of the films increased with substrate temperature, reaching a maximum between 400 and 500 °C. The increased adhesion is associated with changes in the oxide layer on the steel substrate. As the temperature increases, Fe2O3 and F3O4 decompose to FeO. Sputter etching of the substrate prior to deposition improves the film adhesion even though a complete removal of the oxide layer is not achieved. The use of an intermediate layer of pure titanium increases the adhesion for films deposited at temperatures below 400 °C. Above this temperature a thin TiC layer is formed in the titanium–steel interface reducing the adhesion. The composition and distribution of the carbides particles in the high-speed steels are also found to be important for the film adhesion. High adhesion is obtained when the steel contains a high density of MC (M, mainly vanadium). The results are discussed in terms of interfacial energies. A low interfacial energy and thus a high adhesion is e.g., obtained when the structural matching between the substrate and the film is good. In the case of TiN this can be achieved if a thin layer of FeO exists on the high-speed steel matrix, or if the surface density of MC carbides is high. Both FeO and MC have the same structure as TiN with only a small lattice mismatch.
Heteroepitaxial growth of ZnCdTe by molecular beam epitaxy
Authors: Dinan J. H. , Qadri S. B.
Published: July 2002

Epitaxial layers of ZnxCd1−xTe have been grown on InSb, CdTe, and HgCdTe substrates by the technique of molecular beam epitaxy (MBE). Composition has been varied over the range 0≤x≤0.9 by adjusting the temperatures of furnaces containing elemental Zn and polycrystalline CdTe. Oscillation and Weissenberg x-ray patterns indicate that layers are single phase and single crystal for low values of misfit between layer and substrate. Near band-edge emission is dominant in the photoluminescence spectrum of layers grown at substrate temperatures near 200 °C.
Characterization of rapidly annealed Mo–polycide
Authors: Ho V. Q. , Naguib H. M.
Published: July 2002

Mo-polycide structures were fabricated by sputtering 0.3 μm MoSi2 films onto a 0.3 μm phosphorus doped poly-Si layer using a cold pressed composite target. The properties of the Mo-polycide layers were investigated before and after rapid thermal annealing (RTA) in a tungsten halogen lamp system. The anneal temperatures were varied between 800 and 1200 °C and the cycle duration from 2 to 30 s. A minimum sheet resistance of 2.8 Ω/⧠ was obtained after a 10 s RTA cycle at 1100 °C. RBS analysis indicated no change in the film stoichiometry after the RTA treatment. However, rapid diffusion of phosphorus into the silicide film was observed by SIMS analysis. In addition, a sheet resistance increase was observed after RTA at 1200 °C and is attributed to the formation of voids in the silicide films.
Single crystal silicide silicon interfaces: Structures and barrier heights
Authors: Tung R. T. , Gibson J. M.
Published: July 2002

The atomic structures and the Schottky barrier heights of single crystal silicide–silicon interfaces were studied. Epitaxial NiSi2 and CoSi2 were grown under ultrahigh vacuum conditions on (111), (100), and (110) surfaces of Si. Lattice imaging by high resolution transmission electron microscopy allowed modeling of the interface atomic structures. Capacitance–voltage and current–voltage characteristics of these interfaces were studied. A dependence of barrier heights on orientation is observed which favors intrinsic mechanisms for their formation. The advantages of the present single crystal metal–semiconductor interfaces over the usual polycrystalline junctions in the study of Schottky barrier formation are demonstrated.
Electronic and atomic structure of arsenic terminated Si(100)
Authors: Uhrberg R. I. G. , Bringans R. D. , Bachrach R. Z. , Northrup John E.
Published: July 2002

A comparison between angle resolved photoemission data and ab initio pseudopotential calculations for a structural model of the As covered Si(100) surface is presented. After a coverage of one monolayer the Si(100):As surface shows a 2×1 low energy electron diffraction pattern. The arsenic acts as an effective passivating layer and the adsorption of further arsenic is highly reduced. We propose a symmetric As–As dimer model for the Si(100):As 2×1 surface derived from energy minimization calculations. The major feature of the electronic structure of this model is the occurrence of occupied π and π* surface state bands derived from bonding and antibonding combinations of the dangling hybrids on the As atoms. The calculated dispersions for the π and π* bands are found to be in very good agreement with the experimental surface state dispersions. The results discussed provide an example of how angle resolved photoemission in combination with ab initio pseudopotential calculations can lead to a conclusive determination of the electronic and atomic structure of surfaces.
Alloy surface segregation effect on the angular distribution of Ni–Fe sputtered particles
Authors: Nagai Yasuhiro , Toshima Tomoyuki
Published: July 2002

This paper reports the results of experimental investigation into the angular distribution of sputtered particles in ion beam sputtering. A Ni–Fe alloy target that includes many cones wherein the composition is several percent Fe-richer than in the matrix, is bombarded by Ar+ ions at 1 keV at various ion incident angles. As a result of this experiment, it is found that the characteristics of the Ni fraction for the collector angle become asymmetric and the maximum Ni fraction in the film approaches the Ni fraction of the alloy target as the ion incident angle increases. From a simple model analysis, these tendencies are found to be explained by the interaction between the oblique ion incidence and the surface topography including segregation.
Electronic excitations on GexSi1−x(100)(2×1)
Authors: Farrell H. H. , Broughton J. Q. , Schaefer J. A. , Bean J. C.
Published: July 2002

The presence of a reconstruction of a higher order than the nominal (2×1) superstructure has been observed for the (100) surface of Ge/Si alloys at room temperature. High-resolution electron energy loss spectroscopy (HREELS) has been used to study electronic excitation on these surfaces. Transitions were observed both between the valence band and the unoccupied surface state and between the occupied surface state and the conduction band at a variety of points in the two-dimensional Brillouin zone. Heating produced segregation of the Ge to the surface leaving a Si rich subregion. Therefore, the bulk transitions strongly resemble those from pure Si. Rather surprisingly, transitions between bulk and surface states also resemble those from pure Si and may be taken as a good indication that the Ge atoms have the same electronic and geometric structure as do the Si atoms on the pure substrate. Supportive evidence for a metallic surface state at the Γ point associated with the loss of long-range order is also presented.
A surface study of amorphous chromium films electrodeposited from chromic acid solutions. Part I
Authors: Hoflund Gar B. , Asbury Douglas A. , Babb Steven J. , Grogan Austin L. , Laitinen Herbert A. , Hoshino Shigeo
Published: July 2002

A previous study demonstrates that the addition of organic compounds containing a –CHO or –COOH group to a Cr plating bath results in a chromium deposit which has greatly improved properties. Such deposits have fewer defects than chromium layers produced by conventional methods, the hardness of these deposits increases with increasing annealing temperature in the range of 100 to 600 °C and they are more resistive to corrosion by hydrochloric acid than conventional deposits. In this study the composition and chemical interactions of a chromium layer prepared using this new method were examined with Auger electron spectroscopy (AES) and electron spectroscopy for chemical analysis (ESCA) before and after vacuum annealing at 700 °C and after argon-ion bombardment. S, C, O, Cl, N, and Ca are incorporated into the deposits from the electrolytic bath. Cr is present as oxides, sulfide, and metal. Annealing causes segregation of S to the surface and diffusion of oxygen into the bulk. This results in conversion of the surface chromium oxides into Cr2S3 and metallic Cr. C also segregates to the surface during annealing forming chromium carbide.
Electron-beam-induced fracture of Kevlar single fibers
Authors: Dickinson J. Thomas , Jensen L. C. , Klakken M. L.
Published: July 2002

We examine the unique situation involving the exposure of polymers to both electron bombardment and mechanical stress. Under certain conditions, crack formation, crack growth, and fracture can occur due to this combination of stimuli. These studies relate to the performance of a number of materials under hostile environments such as space, plasma, and propulsion systems. In this paper we present our initial measurements on the response of single Kevlar fibers loaded in tension to bombardment by 3-keV electrons. We present evidence that the resulting electron-beam-induced fracture is due to bond breaking.
The use of polytetrafluoroethylene bearings in ultrahigh vacuum
Authors: Kubiak R. A. A. , Driscoll P. , Manning V. , Houghton R.
Published: July 2002

The use of simple, static polytetrafluoroethylene (PTFE) bearings, as replacements for steel ball races in linear and rotary drive units is discussed, with particular reference to rotary drives operated continuously at high speeds (10–1000 rpm). Design features of the new bearings, including their mechanical and vacuum performance are reported.
Misfit and threading dislocations in HgCdTe epitaxy
Authors: Szilagyi Andrei , Grimbergen Michael N.
Published: July 2002

A new theory relating substrate, misfit, and threading dislocations is presented for abrupt and graded heterojunctions based on the assumption of complete local strain relief. We have for the first time been able to treat two- and three-dimensional misfit dislocation structures in a unified way and experimentally verify the distinction in epitaxial HgCdTe. We confirm earlier findings that the areal density of interfacial dislocations nA in a cross section of the interface is proportional to the lattice constant gradient. If the interface width w is narrower than a theoretically predicted critical value w0, the misfit structure becomes two-dimensional and a linear dislocation density nL applies. The maximum of nA (attained at w=w0) is equal to n2L. Another new result of the theory is that the average misfit segment length is inversely proportional to the substrate dislocation density. The threading dislocation density is predicted to be low when the average segment length is comparable to the substrate lateral dimensions. For cases of low epitaxial dislocation content, the calculated substrate densities corresponding to such segments compare favorably with measured values. Compositional profiles and misfit dislocation densities were obtained on the same angle lapped HgCdTe epilayers by visible reflection spectroscopy and preferential etching, respectively. The former monitored the E1 interband transition as a function of position with a microspectrophotometer while the latter employed a modified Polisar No. 2 etchant. Both linear and areal distributions were observed and their occurrence was correctly predicted by the theory.
Properties of Hg-based films and superlattices grown by molecular-beam epitaxy
Authors: Harris K. A. , Hwang S. , Lansari Y. , Cook J. W. , Schetzina J. F. , Chu M.
Published: July 2002

We report the electrical, optical, and structural properties of thin films of HgTe, Hg1−xCdxTe, and Hg1−xMnxTe and superlattices of HgTe–CdTe and Hg1−xMnxTe–HgTe. All of these epitaxial films were deposited by molecular-beam epitaxy. The Hg1−xCdxTe films exhibit large electron Hall mobilities, specular reflectances, and sharp optical absorption edges. The Hg1−xMnxTe films, grown with x values of 0.03 and 0.10, also exhibit excellent optical and electrical properties. The p-type HgTe–CdTe superlattices exhibit large hole mobilities. Superlattices containing alternating layers of Hg1−xMnxTe and HgTe have also been successfully prepared. The Hg1−xMnxTe–HgTe multilayers are the first superlattices containing alternating layers of a Hg-based dilute magnetic semiconductor to be grown by any thin-film technique.
Investigation of structural properties of epitaxially grown Hg0.84Zn0.16Te under application of hydrostatic pressure
Authors: Qadri S. B. , Skelton E. F. , Webb A. W. , Schaefer M. W. , Dinan J. H. , Chandra D. , Colombo L.
Published: July 2002

Energy dispersive x-ray diffraction measurements have been performed at room temperature under conditions of hydrostatic pressure to 11.0 GPa for the purpose of examining the structural properties of Hg0.84Zn0.16Te. The transition from the zinc blende to the cinnabar phase is determined to be 3.1±0.1 GPa; the diatomic equivalent of the beta-Sn phase is observed at 10.6±0.2 GPa. Comparison of volume compressibility and B3-to-B9 transition pressure of Hg0.84Zn0.16Te with those of HgTe and Hg0.8Cd0.2Te suggests that the effect of replacing Hg with Zn is to stabilize the B3 phase and to make it less compressible.