bluuebunny/crossref_metadata_2025 huggingface dataset:
Radio frequency sputter deposited boron nitride films
Authors: Wiggins M. D. , Aita C. R. , Hickernell F. S.
Published: July 2002

Thin films (∼1 μm) of boron nitride were grown on water-cooled glass, silicon, and sapphire substrates by reactive sputter deposition from a BN target in Ar, Ar/N2, and N2 discharges. The effect of sputtering gas composition on film chemical and optical behavior is reported and discussed in the present paper. The following changes occurred as the gas N2 content was increased: (1) The concentration of excess boron in the films, relative to an external standard, decreased. (2) Absorption of visible and ultraviolet radiation decreased. (3) The energy band gap increased by >2 eV. Smaller band gap values were correlated with excess boron. (4) The average B–N bond strength and the ordering of B and N atoms to form B–N bonds increased. Near stoichiometric (B/N=1.1–1.4), colorless, wide band gap (5.4–5.6 eV) films were grown in gas containing from 25% to 100% N2.
Microwave plasma stream transport system for low temperature plasma oxidation
Authors: Miyake Kiyoshi , Kimura Shin’ichiro , Warabisako Terunori , Sunami Hideo , Tokuyama Takashi
Published: July 2002

A compact microwave plasma stream transport system is newly developed for low temperature plasma oxidation studies. The principle of the system is to irradiate magnetically confined oxygen plasma onto the sample to be oxidized in a clean vacuum environment while irradiating it with a pulsed-CO2 laser beam during plasma oxidation to enhance the reaction. Optical diagnosis of the microwave generated oxygen plasma shows that highly excited oxygen atoms and molecular ions are present in the plasma. The oxygen plasma is transported to the silicon substrate without serious loss and interaction with the vacuum vessel. 1 h irradiation of a silicon surface at 700 ° C substrate temperature produces a 23 nm thick, high quality SiO2 layer formation. Electrical properties of the plasma oxidized SiO2–Si interface were examined by making MOS diodes. Interface state densities of the MOS capacitors for the plasma oxidized SiO2 exhibited a value of 7×1010 cm−2 eV−1. This value is very close to the one for the thermally oxidized SiO2, and two orders smaller than that reported in conventional biased plasma anodization.
Coupled local mode vibrations in a-Si alloy films
Authors: Lucovsky G. , Chao S. S. , Yang J. , Tyler J. E. , Czubatyj W.
Published: July 2002

We report studies of local mode vibrations in hydrogenated a-Si alloy films, presenting new information obtained by comparisons with similar alloy films in which deuterium is substituted for hydrogen. We discuss three systems, a-Si:H(D), a-Si:[H(D),O], and a-Si:[H(D),N], and emphasize changes in the atomic displacements and frequencies of the local mode vibrations with deuteration.
Auger studies on rapid grain boundary diffusion of Ge through Au
Authors: Ingrey S. , MacLaurin B.
Published: July 2002

A commonly used, Ohmic electrical contact to n-type GaAs involves sequential evaporation of a 20 nm Au–Ge alloy and a 400 nm Au layer. During Auger analysis of such structures at a pressure of 2×10−8 Pa, we have observed diffusion of Ge through the Au layer at room temperature. When the Ge was removed by a short sputter clean with a 3 keV ion beam, the Ge Auger signal immediately started to increase. The intensity of the Au (69 eV) and Ge (1147 eV) transitions was monitored as a function of time and temperature. Temperatures used were low compared to the melting point of Au, 0.03Tm ≤T≤0.22Tm. The saturation values correspond to 0.5 monolayer of Ge on the Au surface. The experiment was repeated a number of times on the same sample. Auger sputter depth profiles showed that the Ge concentration was below the Auger detectability limit in the bulk of the gold films until the Ge–Au alloy was reached. Secondary ion mass spectrometry of similar samples showed a small Ge concentration throughout the Au film. The results are consistent with diffusion of Ge through grain boundaries in the Au film and subsequent surface accumulation. When the samples were exposed to air, the Ge oxidized but the amount of Ge did not increase. A further set of experiments involved exposing the sputter cleaned surface to hydrocarbon partial pressures or air for 2 h. In both experiments the surface accumulation of Ge is greatly reduced. From our results an activation energy for surface accumulation of 0.44 eV was determined.
Absolute densities of reaction products from plasma etching of quartz
Authors: van Veldhuizen E. M. , Bisschops Th. , van Vliembergen E. J. W. , van Wolput J. H. M. C.
Published: July 2002

The plasma of a CF4-quartz etching system is investigated with optical methods. The presence of CF2, CF, F, and CO is demonstrated from ultraviolet and visible emission. Using infrared absorption the absolute densities of the reaction products SiF4 and CO are found to be 2.5±0.4×1020 and 3±2×1020 m−3. CF2 radicals are not found with infrared absorption which means that their density is below 1019 m−3. The results indicate that quartz is etched through the reaction SiO2+2CF2 → SiF4+2CO.
Design considerations for simple gas dosers in surface science applications
Authors: Campbell Charles T. , Valone Steven M.
Published: July 2002

The flux distributions and enhancement factors for various gas doser designs typically used in surface science applications and chemisorption studies have been calculated and compared. The following conclusions, which will aid the experimentalist in the choice of doser design, can be made. (1) The enhancement factor expected for a given doser can easily be derived from Fig. 2. (2) The optimum doser design is a multichannel array with a radius slightly larger than that of the sample, and a distance from the sample < 10% of the sample diameter. (Complications of this design are discussed.) (3) Because of space requirements, the sample–doser distance must sometime be ≥40% of the sample diameter, in which cases it is better to use a cosine emitter. A good, very simple doser design is described that consists of a small cosine emitter with a sample–doser distance of 1/2 the sample diameter. This provides an enhancement factor >50% of the optimum theoretical enhancement, with only slight (±15%) flux gradients. (4) For a given doser distance, a needle doser provides the largest enhancement factor, but always has a very strong gradient in flux across the sample.
Tokamak Fusion Test Reactor gas injection control system design and operation
Authors: Thompson M. E. , Dylla H. F. , LaMarche P. H. , Arnold N. D. , Rauch W. A. , Mueller D. , Hawryluk R. J.
Published: July 2002

Magnetic fusion devices require fast-responding, versatile, and accurate gas injection systems in order to initiate and modulate the plasma density. We describe the gas injection control system (GICS), which regulates the gas injected into the torus of Princeton’s Tokamak Fusion Test Reactor (TFTR). Synchronized with each TFTR discharge, a PDP 11/23 microcomputer provides real-time control for one to six fast injection valves, each allocated to feedback or open loop operation. Up to four feedback sources, including torus pressure gauges and plasma density measurements, are checked once each cycle for 1000 cycles; the cycle duration can be set to any multiple of 2 ms up to 16 ms. Detection of various fault conditions can cause automatic shutdown or modification of GICS operation. Data is archived after each TFTR discharge, and subsequently used for particle fueling studies and analysis of system drifts. A steady state mode of operation is used for vacuum vessel discharge cleaning. The system also provides for valve calibration and torus pumping speed measurements.
Electric probes in plasmas
Authors: Lipschultz B. , Hutchinson I. , LaBombard B. , Wan A.
Published: July 2002

This paper provides a background for the use of Langmuir and gridded energy analyzer probes in diagnosing plasmas with varied characteristics. Theory is illustrated which governs the analysis of data from, and the design of these probes. Several probe analysis techniques and some of their typical problems are presented.
Phase transformations of the H/W(110) and H/Mo(110) surfaces
Authors: Altman M. , Chung J. W. , Estrup P. J. , Kosterlitz J. M. , Prybyla J. , Sahu D. , Ying S. C.
Published: July 2002

We present results of combined theoretical and experimental studies of the surface phases produced by hydrogen adsorption on tungsten (110) and molybdenum (110) planes. We have formulated a theoretical model which has the following ingredients: (1) a possible adsorbate-induced lateral shift reconstruction of the substrate surface; (2) two-body and three-body interactions among hydrogen atoms; and (3) a coupling of the overlayer ordering to the substrate reconstruction. This model gives good agreement with the observed phase diagram for H/W(110) which shows a (2×1) phase at low coverages and a (2×2) phase, as well as substrate reconstruction, at high coverages. In the case of H/Mo(110), for which no reconstruction is observed, the lack of a (2×1) phase suggests the presence of a strong three-body interaction among the adatoms.
Corrosion/passivation of aluminum in dilute sulfate solutions: A comparison of Pourbaix and surface behavior diagrams
Authors: Davis G. D. , Moshier W. C. , Ahearn J. S. , Hough H. F. , Cote G. O.
Published: July 2002

The composition and thickness of the oxide/hydroxide film that forms on pure Al polarized in 0.05M Na2SO4 solutions with and without the addition of 1000 ppm Cl− under acidic, near-neutral, and alkaline conditions have been determined using x-ray photoelectron spectroscopy. Changes in the films due to the ex situ nature of the measurements have also been characterized. The results were plotted on surface behavior diagrams to follow the evolution of the surface during polarization and compared with the results predicted by the Pourbaix diagram. Although Al(OH)3 is the most stable species to form in near-neutral solutions under equilibrium conditions, the composition of the film at the corrosion potential under our experimental conditions was found to be that of the oxyhydroxide AlOOH at each pH. In the pH 7 and pH 10 solutions, this film thickens during anodic polarization (up to the pitting potential for the Cl−-containing solutions), but the composition is unchanged. In contrast, the Cl−-free, pH 2 solutions, an oxide film forms at the oxyhydroxide–metal interface and rapidly thickens with increasing anodic overpotentials. The original AlOOH layer then slowly dissolves so that the film becomes entirely Al2O3. During cathodic polarization, we observed growth of the oxyhydroxide film, especially at pH 2, which we attributed to cathodic corrosion.
Surface segregation in donor and acceptor graphite intercalation compounds
Authors: Laguës M. , Marchand D. , Frétigny C.
Published: July 2002

Among the different spectroscopies applied to the study of graphite intercalation compounds (GIC), Auger electron spectroscopy (AES), and angle resolved photoemission spectroscopy show that the composition of the uppermost unit cell is different from the bulk composition. According to these measurements, donor compounds exhibit an increased intercalant concentration near the surface, while acceptor compounds at equilibrium exhibit two or three nearly pure graphite layers at the surface. We present here AES measurements for donor GIC (cesium compounds), and x-ray photoelectron spectroscopy and AES measurements for acceptor GIC (manganese chloride compounds). A simple model accounts for the observed surface concentration in both donor and acceptor compounds. The screening of a surface state involves an electrostatic energy, which depends on the Fermi level density of states in the most superficial unit cell or sandwich. The minimum of the free energy at equilibrium implies enrichment in cations and a depletion of anions near the surface of the compound.
Oxidation of a cobalt chromium alloy: An x-ray photoemission spectroscopy study
Authors: Fowler David E. , Rogozik Juergen
Published: July 2002

The oxidation of a Co86Cr14 alloy surface was studied by x-ray photoemission spectroscopy. Following ion sputtering at 25 °C, the unoxidized alloy surface composition was nearly the same as the bulk composition. Vacuum annealing of the surface caused Cr enrichment at the surface. This is discussed in the context of the expected behavior at thermodynamic equilibrium. Oxidations from 25 to 400 °C were done under controlled exposure conditions using dry oxygen at 10−7 Torr and under atmospheric conditions. A layered mixture of oxides was formed at the surface and was rich in Co oxides near the surface and either rich in Cr oxide or at the bulk Cr/Co ratio in the inner oxide layers, depending on the oxidation conditions. The observed oxide structure is proposed to be a consequence of the competition between the preference for Cr to oxidize because of its higher oxidation potential relative to Co and the relative supply of Co available for oxidation compared to the supply of Cr due to the different diffusivities of Co and Cr in the oxide structure. The results indicate that Co has a much higher mobility than Cr in this temperature range, as is the case above 800 °C. The oxide growth appears to be dominated by the high oxidation potential of Cr prior to the formation of a complete oxide layer and, subsequently, is dominated by the high Co diffusivity, under all conditions examined.
Atomic resolution with the atomic force microscope on conductors and nonconductors
Authors: Albrecht Thomas R. , Quate Calvin F.
Published: July 2002

The atomic force microscope (AFM) has achieved atomic resolution on nonconducting as well as electrically conducting surfaces, opening a new class of materials to atomically resolved surface imaging. Images of boron nitride (a nonconductor) reveal that AFM can distinguish different atomic species. AFM images of molybdenum disulfide and graphite are also presented. Graphite AFM images appear identical to images obtained by scanning tunneling microscopy (STM), although AFM and STM probably respond to different atomic sites on the graphite surface. Microfabrication procedures for constructing low-mass force-sensing cantilevers are discussed.
Capillary array dosing and angular desorption distribution measurements: A general formalism
Authors: Winkler A. , Yates J. T.
Published: July 2002

The flux of molecules from a source intercepted by a target has been calculated. The obtained formalism can be applied to capillary array dosing as well as angular distribution measurements in thermal desorption from single-crystal surfaces. A critical comparison of the theoretical results with recently obtained experimental data is presented.
Fractoemission from fused silica and sodium silicate glasses
Authors: Dickinson J. T. , Langford S. C. , Jensen L. C. , McVay G. L. , Kelso J. F. , Pantano C. G.
Published: July 2002

Fractoemission is the emission of photons and particles due to the fracture of materials. In this paper we present characteristic intensity versus time measurements of photon emission (phE), electron emission (EE), positive ion emission (PIE), and neutral emission (NE) due to the fracture of fused silica and sodium trisilicate glass. We show, for example, that the trisilicate is a copious emitter of atomic Na and both atomic and molecular oxygen. The phE, EE, and PIE from the two glasses share a number of properties.
Measurements of time varying plasma potential, temperature, and density in a 13.56 MHz radio-frequency discharge
Authors: Wilson Jeffrey L. , Caughman J. B. O. , Nguyen Phi Long , Ruzic D. N.
Published: July 2002

Argon plasma measurements were conducted in a commercial capacitively coupled etcher operating at 400 mTorr with 60-W coupled power at 13.56 MHz. Time varying floating potential was measured using a capacitively coupled probe which uses a capacitive voltage divider and a field effect transistor buffer amplifier. Average floating potential was obtained from a high-input-impedance Langmuir probe. The floating potential was found to be sinusoidal, [21 sin(wt)−4]V±1.5 V, with a maximum of 17±1.5 V and a minimum of −25±1.5 V. From these data and the use of a low-input-impedance Langmuir probe, a calibrated instantaneous I–V characteristic is used to obtain plasma potential and electron temperature. Plasma potential was found to be sinusoidal, [21 sin(wt)+30]V±1.6 V, with a maximum of 51±1.6 V and a minimum of 9±1.6 V. Electron temperatures were 6.58±0.19 eV at maximum plasma potential and 6.49±0.19 eV at minimum plasma potential. The electron density for this experiment was determined to be 1.48±0.83×1010 electrons/cm3 .
Conductance modulation method for the measurement of the pumping speed and outgassing rate of pumps in ultrahigh vacuum
Authors: Terada Keiko , Okano Tatsuo , Tuzi Yutaka
Published: July 2002

A new method, named the conductance modulation method (CM method), was developed for the measurement of pumping speeds (intrinsic and net) and outgassing rates in vacuum systems. The details of the formulation and the procedure of the CM method are described. The principle of the method lies in the measurement of the pressure modulation with the change of the conductance between a chamber and a pump. The pumping speed is obtained from the ratio of the modulated pressures and the value of the conductance without measurements of absolute pressures. This feature makes the method quite appropriate for measurements in ultrahigh vacuum. The CM method was applied to the measurement of the gas balance in a vacuum system pumped with a Ti getter pump. The intrinsic and the net speed of the Ti getter pump were measured for H2 in a wide pressure range down to ultimate pressure under various conditions of getter films and the amount of H2 sorbed. The outgassing rates from the wall of the chamber and the pump were simultaneously evaluated. These results confirmed the usefulness of the CM method for the quantitative analysis on the gas balance in vacuum systems.
Scanning tunneling microscopy investigation of a spontaneous monolayer dispersion system: HgCl2 on highly oriented pyrolitic graphite surface
Authors: Xie Y. , Xu Q. , Tang Y. , Bai C. , Dai C.
Published: July 2002

HgCl2 can disperse onto the surface of activated carbon as a monolayer to form a catalyst for making vinyl chloride from C2H2 and HCl. A monolayer dispersion capacity of 0.020 g. HgCl2/100 m2 activated carbon was determined by x-ray diffraction. In order to understand further the catalytic mechanism of this kind of catalyst, the dispersed structure of HgCl2 supported on highly oriented pyrolitic graphite (HOPG) has been studied by scanning tunneling microscopy (STM). The HgCl2–HOPG sample is obtained by putting a drop of dilute HgCl2 solution on the surface of HOPG and drying in air. The HgCl2–HOPG surface is imaged by computer controlled STM under ambient conditions and at room temperature. In constant-current mode, bright spots with regular structure over the periodic structure of HOPG has been observed in the image. The size of bright spot is about (4×9) Å which corresponds to a single HgCl2 molecule. It suggests that HgCl2 molecules form a monolayer on the surface of HOPG with a (3.6×3.6) R14.3° surface superlattice in contrast to the lattice of HOPG. The experimental result is consistent with the estimation derived from the monolayer dispersion theory.
Observation of Vickers imprints by scanning tunneling microscopy
Authors: Miyazaki Y. , Koga Y. , Hayashi H.
Published: July 2002

Scanning tunneling microscopy (STM) has achieved a rapid progress since first developed, and its application field is expanding into surface analysis including the use as a profilometer. We present observations of low load imprints of hardness tester using a STM–SEM (scanning electron microscopy) combined system.1 The samples tested were n-type silicon wafers, and the loads ranged from 2.94 to 19.6 mN. Result of STM observation showed that the imprints were more clearly observable under STM than under SEM or optical microscope and more accurate measurements of imprints were possible.
High resolution magnetic force microscopy
Authors: Grütter P. , Wadas A. , Meyer E. , Heinzelmann H. , Hidber H.-R. , Güntherodt H.-J.
Published: July 2002

The lateral resolution observed in recent MFM experiments on CoCr and FeNdB are compared and analyzed theoretically. On a Co80Cr20 thin film a stripe domain structure with a domain width of 220 nm is observed, the highest resolution of a periodic magnetic structure measured by MFM to this date, and magnetic fine structure of typically 50 nm width and more than 200 nm length by measuring magnetic forces as small as 0.1 nN. A resolution of 10 nm is obtained on rapidly quenched FeNdB, where domains with a typical size of 600–700 nm are observable. By comparing these measurements with simulations it is concluded that the lower resolution achieved on CoCr is to be expected as the domain size is similar to the typical spatial extent of the domain transition stray field.
Synthesis and structural properties of ion-beam sputtered Cu/Ni multilayers
Authors: Kim C. , Qadri S. B. , Twigg M. , Edelstein A. S.
Published: July 2002

Multilayers of Cu/Ni of equal amounts of Cu and Ni with compositionally modulated wavelengths λ between 20 and 200 Å have been grown by ion-beam sputtering. At large λ the separate component x-ray diffraction peaks of Cu and Ni are resolved. The lattice parameter of as deposited Cu films and the Cu constituent of the multilayer at large λ is in agreement with the bulk value for Cu. The lattice parameter of as deposited Ni films is 3.542 Å, which is 0.5% larger than the bulk value. The measured average lattice parameter of these multilayers shows an enhancement from 3.583 to 3.596 Å with decreasing wavelength for 25≤λ≤195 Å. This increase is in addition to the enhancement we observe in the lattice parameter of as deposited Ni films. The correlation length has been extracted from the width of the central peak of the (111) reflection. The disappearance of the satellite peaks observed in diffraction scans taken at different temperatures shows that the layer structure is no longer coherent at 510 °C.
Surface and interface characteristics of Cu films deposited by ionized cluster beam
Authors: Takaoka Gikan H. , Ishikawa Junzo , Takagi Toshinori
Published: July 2002

We have deposited Cu films on Si(111) and Si(100) substrates by ionized cluster beam (ICB) technique. The surface and interface characteristics of these films were investigated. When the deposition of ionized and accelerated Cu clusters was made on a Si(111) substrate, the (111) preferential orientation of the film increased and the x-ray line broadening decreased with increasing acceleration voltage Va. In addition, the NH4OH etching of the grain boundaries in the films was reduced with increasing Va. This was due to the enhancement of bonding strength between grain boundaries and/or decreased strain. The interdiffusion between Cu and Si atoms after annealing in vacuum was very small, and it decreased with increasing Va. The diffusion coefficient of Cu at 230 °C was 4×10−14 cm2/s for the case of Va=5 kV; it was smaller than one-tenth in comparison to films prepared by using neutral Cu clusters. When Cu films were prepared on a Si(100) substrate, the films showed the (100) preferential orientation. The interdiffusion between Cu and Si atoms after annealing became small at Va=3 kV, and the dependence of the diffusion coefficient of Cu on the Va corresponded to that of the (100) preferential orientation as well as the x-ray line broadening of the film. The diffusion coefficient obtained at 130 °C was 6.4×10−14 cm2/s for the case of Va=3 kV; it was larger by a factor of 5 than that for the case of Si(111) substrate.
Compositional difference between films and targets in sputtering of refractory metal silicides
Authors: Murakami Yoshio , Shingyoji Takayuki
Published: July 2002

Compositional differences between films and targets are investigated in the sputtering of various refractory metal silicides (MoSix, WSix, and TiSix). The composition of the prepared films vary with the position of the substrates relative to the target. During the sputtering of tungsten silicide, the composition of the prepared films are Si-deficient at all substrate positions compared to the target. Such compositional variation can be qualitatively understood by taking into account the difference in the angular distribution of ejected atoms and the difference in the sticking coefficient of constituent atoms on the substrate. For the latter mechanism, our basic hypothesis is that high energy atoms have a lower sticking coefficient.
Characterization of (Hg,Cd)Te by the photoconductive decay technique
Authors: Lopes V. C. , Wright W. H. , Syllaios A. J.
Published: July 2002

A spatially resolved characterization technique is described that can separate surface and bulk (Hg,Cd)Te material parameters. Photoconductive (PC) decay and metal–insulator semiconductor (MIS) measurements were used to characterize n-type (Hg,Cd)Te (x=0.22) material and the anodic oxide–(Hg,Cd)Te interface. By analysis of the transient PC decay waveform, the surface recombination velocity and minority carrier lifetime were determined and then correlated to (Hg,Cd)Te material parameters. These results have been used to obtain estimates of the average bulk Shockley–Read density and surface state density.
Application of scanning tunneling microscopy for imaging of CNBr-peptides of type I collagen
Authors: Snellman H. , Pelliniemi L. J. , Penttinen R. , Laiho R.
Published: July 2002

Biological macromolecules are considerably denatured when processed for conventional electron microscopy. To test the applicability of scanning tunneling microscopy for these purposes we chose fibrous protein collagen I pipetted and dried on an oriented pyrolytic graphite surface. Survey scans made over 500×500 nm2 showed separate and branching ridges of various lengths as well as regions of densely packed material. In scans over 50×50 nm2 there were structures with regular protrusions propoused to be generated at a basic interval of 9 nm. The recorded images corresponded well with biochemically measured dimensions of type I collagen cyanogen bromide peptides.
Analysis and reduction of conductor stress in magnetic bubble memory devices
Authors: Umezaki H. , Isomae S. , Sato T. , Toyooka T. , Suzuki R.
Published: July 2002

Stress from the overlay conductor patterns in ion-implanted magnetic bubble memory devices has been investigated using computer simulations (Boundary Element Method). In the case of the conventional SiO2 spacer which lays under the conductors, the concentrated stress at the edge of the conductors is transferred to the garnet directly. In order to reduce the stress, an elastically ‘‘soft’’ material, such as polyimide, was introduced as the spacer. The simulation shows that the stress under the polyimide spacer is reduced to about 1/3 of that under the SiO2 spacer. This is caused both by the internal stress relaxation in the conductors themselves and by the stress dispersion effect of polyimide. The devices with the polyimide spacer were evaluated and showed no influence of the conductor stress.
Formalism for quantitative surface analysis by electron spectroscopy
Authors: Tougaard S.
Published: July 2002

A new, simple formalism for quantitative surface analysis by electron spectroscopy is found. The formalism takes into account the in-depth concentration profile and consists in three algorithms. The simplest of the algorithms is reasonably accurate for spectra from most in-depth profiles. For narrow depth profiles centered at depths ≳1–2 λ and for spectra from a substrate with an overlayer of width ≳λ, one of the other two algorithms should be used. The formalism decides, by a simple criterion, which of the three algorithms is to be applied for a given spectrum. The total amount of material within the surface region of the solid as well as the approximate in-depth composition profile is determined by the formalism.
A graphite thermal evaporation source for aluminum
Authors: Folz Y. A. , Hickmann J. S. , Braun L. F. M. , Francke R. E.
Published: July 2002

A graphite evaporation source for aluminium is described. The procedure for holding the graphite source provides a large area for electrical contact and thermal dissipation. The quality of the film was measured through its reflectivity. (AIP)
Tunneling barrier height imaging and polycrystalline Si surface observations
Authors: Hosaka S. , Sagara K. , Hasegawa T. , Takata K. , Hosoki S.
Published: July 2002

An influence of the dopant concentration on polycrystalline Si grain structure, electronic structure and dopant segregation in 800 °C and 30 min annealing is investigated. Barrier height images and topographies of arsenic implanted polycrystalline silicon surface are obtained using tunneling barrier height imaging (TBI) and scanning tunneling microscopy (STM) with the vacuum pressure less than 5×10−7 Torr. As results, a conduction band bending caused by the arsenic ion implantation can be observed by the TBI. A comparison of the TBI image with the STM image can identify whether region is implanted or nonimplanted. In addition, dopant segregation structures at the grain boundary can be found out. With dopant concentration, 1014 cm−2 As+ implanted polycrystalline silicon grain structures of 4–80 nm size grow large.
Real-space images of noble metal (Cu, Ag, Au) thin films by scanning tunneling microscopy
Authors: Kim H. S. , Zheng Y. C. , Bryant P. J.
Published: July 2002

We present scanning tunneling microscopy (STM) images which resolve rows of close-packed metal atoms on the surfaces of Cu(111), Ag(111), Au(111), and Au(110) thin films. These samples were prepared by evaporating metallic elements onto cleaved graphite substrates in vacuum with a base pressure of 10−6 Torr. The thickness of the thin film is a few hundred angstroms. Copper, silver, and gold films deposited on the surface of pyrolytic graphite have been imaged in air using STM with low bias voltages (3–10 mV) and a tunneling current between 1 and 3 nA. An average corrugation amplitude of ≊0.3 Å was found for the Cu, Ag, and Au surfaces. The observed results are in good agreement with the structures predicted from theory. The goal of this research is the development of techniques to study the structure of a quantum well wire array(QWW) deposited on a vicinal surface.
Kinetic theory of thermal transpiration and the mechanocaloric effect: Planar flow of a rigid sphere gas with arbitrary accommodation at the surface
Authors: Loyalka S. K. , Hickey K. A.
Published: July 2002

The planar flow of a rarefied gas subject to pressure and temperature gradients is a problem of fundamental interest in vacuum science and technology. This problem is solved based on the linearized Boltzmann equation with the assumption of a rigid sphere molecular interaction and Maxwell’s gas–surface interaction operator. Comprehensive numerical results for the macroscopic flow profiles, and the integrated flow rates for arbitrary Knudsen numbers are obtained. The results are basic to study of planar flows of rarefied gases.
Fabrication of high-reflectance Mo–Si multilayer mirrors by planar-magnetron sputtering
Authors: Stearns D. G. , Rosen R. S. , Vernon S. P.
Published: July 2002

Molybdenum–silicon multilayer (ML) x-ray mirrors have been fabricated using a direct-current planar magnetron sputtering system. The ML structure has been characterized using x-ray diffraction and high-resolution electron microscopy, and the normal incidence x-ray reflectivity has been measured using synchrotron radiation. A striking dependence of the ML morphology on the sputtering gas pressure is observed, exhibiting a transition from layer growth at lower pressures to columnar growth at higher pressures. Correspondingly, the normal incidence x-ray reflectivity is found to decrease strongly with increasing gas pressure. By depositing Mo–Si ML at low sputtering gas pressures we have achieved a normal incidence reflectivity as high as 61% at 132 Å.
A novel technique to make foam shells with high sphericity and wall uniformity for cryogenic laser fusion targets
Authors: Takagi M. , Norimatsu T. , Yamanaka T. , Nakai S. , Ito H.
Published: July 2002

A new technique to make low-density, low-atomic-number foam shells was developed for use in cryogenic laser fusion targets. Shells with sphericity > 99% and wall uniformity > 97% were fabricated by a density matched emulsion method using cross-linked copolymerization in the oil phase of the emulsion. The diameter, wall thickness and density of the shells ranged in 100–1500 μm, 10–150 μm, and 90–310 mg/cm3, respectively. Some foam shells exhibited a membrane on the outer surface, which could be used as the protective layer to prevent liquid fuel from boiling off. The foam shell was transparent when it was saturated with liquid deuterium. This enables us to characterize distribution of the liquid fuel in the shell using an optical interference technique.
Effects of wall conditioning on plasma performance in the Advanced Toroidal Facility stellarator
Authors: Langley R. A. , Crume E. C. , Glowienka J. C. , Horton L. D. , Isler R. C. , Murakami M. , Simpkins J. E.
Published: July 2002

Various wall conditioning techniques have been used on the Advanced Toroidal Facility (ATF). Continued improvement in plasma parameters has been obtained. In ATF, a stellarator, wall conditioning is more important for obtaining favorable plasma parameters than it is in plasma devices with current. Discharge cleaning, baking, and gettering with both chromium and titanium have been used as conditioning techniques. Gettering with titanium has increased the pumping speed of nitrogen and oxygen by more than a factor of 10, significantly reducing impurity effects, and has allowed better control over wall recycling and thereby plasma density. This has increased the operating space for many of the plasma parameters. The effects of these conditioning techniques on plasma parameters are discussed.
Observation of helium gas discharge cleaning process for deuterium saturated graphite by A–U gauge
Authors: Akaishi K. , Watanabe S. , Kubota Y. , Funato Y.
Published: July 2002

A gas analyzer based on the principle of ion backscattering has been developed to measure both pressures of helium and deuterium and is called A–U gauge. The A–U gauge is applied to observe a detrapping process of retained deuterium in a graphite (IG-100 ) during rf-glow discharge with helium gas. The detrapping behavior of D atoms from the graphite is discussed with a simplified local mixing model.
Mass gain of thin films on exposure to air
Authors: Graper Edward B.
Published: July 2002

In support of work developing inert gas environment process technology and in the application of unsupported evaporated thin films as x-ray filters, the mass gain on first exposure to nitrogen and subsequently exposure to 5×1011 L (1 L=1×10−6 Torr sec) of air is reported for evaporated Ag, Al, Au, B, Ba, Be, Bi, C, Cd, Cr, Ge, In, Mg, Mn, Mo, Nb, Ni, Pb, Pd, S, Sc, Se, Si, Sn, Ta, Ti, V, W, Y, Zn, and Zr. Upon exposure to nitrogen, all materials except Cr, Mo, Sc, Y, and Zr show little mass gain. The mass gain and rate of mass gain on exposure to air are complex and are presented as functions of exposure and film thickness. Reaction rate functions are developed for many materials, which indicate the air reaction is not self-limiting. These results are compared with few available published high exposure measurements. The reversibility of the mass gain was measured for many materials. The mass gain observed (median 2%, maximum 15%) during exposure of only 4×1011 L (10 min) demonstrates that even short term exposure of thin films to atmosphere causes substantial changes in the films.
Structure and optical characterization of ZnxCd1−xTe thin films prepared by the close spaced vapor transport method
Authors: González-Hernández J. , Zelaya O. , Mendoza-Alverez J. G. , López-Cruz E. , Pawlik D. A. , Allred D. D.
Published: July 2002

Zinc cadmium telluride (ZnxCd1−xTe ) solid solution films with 0≤x≤0.12 were deposited by the close spaced vapor transport method and characterized using photoluminescence, x-ray diffraction, and scanning electron microscopy. The two former techniques indicate that films with high crystalline quality can be prepared with moderate substrate temperatures and low argon pressures. Under these conditions deposition rates of up to 1000 Å/s are achieved and Zn concentration in the film is the same as that of the source. The electron micrographs show grain sizes comparable to the film thickness.
Force microscopy utilizing tunnel junction control
Authors: Kim H. S. , Bryant P. J.
Published: July 2002

A new design for an atomic force microscope (AFM) has been developed which utilizes a dielectric tunnel junction to retain the high sensitivity of tunnel current control to lower force ranges. The junction material is located between the flexible lever and the backing probe, i.e., within the normal separation of those electrodes. Thus the type of tunneling is metal–insulator–metal. The closed tunnel junction is employed for signal sensing and force control. Significant features of this AFM include: subnanonewton force detection; a tunnel junction protected from contamination; and inherent vibration damping. This AFM has been successfully applied to physical and biological samples; results are presented.
Surface structural study of poly-hydroxy-aniline and aniline-(3-aminophenyl boronic acid) copolymer films
Authors: Porter T. L. , Oden P. I. , Lee C. Y. , Caple G.
Published: July 2002

The techniques of scanning tunneling microscopy (STM) and atomic force microscopy (AFM) have been used to characterize the initial nucleation and growth as well as the final surface structure of the conducting organic polymer films poly-hydroxy-aniline and aniline-(3-aminophenyl boronic acid). STM and AFM results on these films show that they are segregated into small, physically well defined nanometer scale domains or bundles in which the microscopic conduction varies from fully conducting to nonconducting. The overall macroscopic conductivity of the films thus depends upon the conductivity of the individual domains as well as on the electronic coupling between the separate domains.
Nulling optical bridge for nonintrusive temperature measurements
Authors: Guidotti Daniel , Wilman John G.
Published: July 2002

A null-point optical bridge for determining the relative power of two optical beams, derived from a common source, within the shot noise limit of the detector, independent of power fluctuations of the source has been developed. The optical bridge method can be used to measure very small changes in sample reflectivity caused by changes in sample temperature and can, therefore, be used as a nonintrusive optical thermometer for semiconductor substrates during processing. The range of application extends from very low temperatures to very high temperature where, for example, the sample may melt. For silicon and under ideal laboratory conditions, a temperature resolution of 0.2 °C has been demonstrated.
Secondary ion mass spectrometry analysis of Be doped GaAs/AlGaAs heterostructures
Authors: Hopkins L. C. , Nagle J. , Malik R. J.
Published: July 2002

Secondary ion mass spectrometry (SIMS) has been used to study the depth profiles of beryllium (Be) incorporation and diffusion in GaAs/AlGaAs heterostructures of graded index separate confinement heterostructure quantum well lasers. The epilayers were grown by molecular-beam epitaxy with a thermally cracked As2 source. The GaAs quantum well was Be-doped with Be at 2×1019 cm−3 using a substrate growth temperature of 580 °C and the Al0.4Ga0.6As confinement layers were grown at 630 °C. SIMS measurements show negligible diffusion of Be under these growth conditions. SIMS depth profiling was also used to resolve thin (2 nm) GaAs smoothing layers incorporated in Al0.4Ga0.6As confinement layers.
Kinetics of coverage loss for H2, HD, and D2 physisorbed on graphite
Authors: Liu Wei , Fain S. C.
Published: July 2002

Low-energy electron diffraction was used to study the kinetics of the coverage loss effect for H2, HD, and D2 physisorbed on graphite single crystals at 5 K. The present study shows striking isotope dependence of the rate of coverage loss: 4.1 × 1011 cm−2 s−1 for D2, 6.5 × 1011 cm−2 s−1 for HD and 2.8 × 1012 cm−2 s−1 for H2 in the incommensurate monolayer regime. Below monolayer completion, the rates of coverage loss depend upon coverage very weakly. The rates become larger in the multilayer regime. We found the coverage loss effect is qualitatively consistent with the infrared induced desorption effect that was found by others for hydrogen and isotopes on several metal and insulator surfaces at low temperature. The possibility of coverage loss induced by surface diffusion is also discussed and ruled unlikely.
Measurement of residual currents in ionization gauges and residual gas analyzers
Authors: Redhead P. A.
Published: July 2002

The residual current in a hot cathode ionization gauge, resulting from processes other than gas-phase ionization, limits the lowest measurable pressure. The following processes contribute to the residual current: a photoelectron current due to soft x rays; electron stimulated desorption (ESD) from adsorbed gas layers; and evaporation from the cathode. Four methods of measuring residual currents are examined and compared; (i) reduction of pressure to near zero, (ii) collector current versus electron energy plots, (iii) modulation methods, and (iv) collector current versus pressure measurements using a reference gauge with low residual current. The measurement of ESD currents in mass spectrometers (residual gas analyzers) is also discussed.
Characterization of ultrathin sputtered SiO films on alumina by inelastic electron tunneling spectroscopy and atomic force microscopy
Authors: Mallik R. R. , Henriksen P. N. , Butler T. , Kulnis W. J. , Confer T.
Published: July 2002

Amorphous SiO films are prepared by radio-frequency planar magnetron sputtering in a background of argon. Inelastic electron tunneling spectra are presented of the films incorporated in Al/SiO/Pb tunnel junctions with the aluminium films pre- or post-oxidized relative to the SiO deposition stage. Both the aluminium and lead junction electrodes are evaporated in a standard oil diffusion pumped, liquid nitrogen trapped vacuum system at a base pressure of 10−7 Torr; aluminium oxidation is achieved either by admitting oxygen into the vacuum chamber or by performing a low power dc oxygen glow discharge. Spectra obtained are similar, but not identical, to those obtained for evaporated SiO films. Different types of silicon hydride species are observed depending on the environment to which the SiO films are exposed after their deposition. Possible reactions of the films with water vapor are discussed which could produce the observed hydrides which are also assigned. Reverse bias tunneling spectra provide strong evidence that the SiH species reside on the SiO surface, and it is shown that they can be removed by exposure of the surface to a gaseous glow discharge. Atomic force microscopy images are presented of SiO films supported on aluminium and alumina which indicate that their topography is not noticeably modified by exposure to the glow discharge, and that they possess a relatively uniform quasi two-dimensional island structure.
Electron energy loss spectroscopy of H-terminated Si(111) and Si(100) prepared by chemical etching
Authors: Dumas P. , Chabal Y. J.
Published: July 2002

H-passivated Si(111) and Si(100) surfaces, prepared by chemical etching in a 40% ammonium fluoride solution, are investigated with high resolution electron energy loss spectroscopy. Extensive off-specular and energy dependence studies reveal that the scattering process is not dipolar, as previously thought, but rather is dominated by short-range interactions. On the atomically flat H/Si(111)-(1×1) surface, two new substrate phonons are observed in addition to the Si–H stretch (2084 cm−1), the Si–H bend (636 cm−1), and the 520-cm−1 substrate mode: a loss at 390 cm−1 assigned to a bulk phonon transition and a loss at 110 cm−1 assigned to a surface phonon resonance.
Growth sequence dependence of interdiffusion at the GaAs/In0.53Ga0.47As strained-layer heterojunction
Authors: Williams M. D. , Chang T. Y.
Published: July 2002

We report the results of a study of the growth front profile of the strained layer GaAs/In0.53Ga0.47As heterostructure as it was grown in sequential steps by migration enhanced molecular beam epitaxy. In situ reflection high energy electron diffraction indicated two dimensional growth for both the A/B and B/A interfaces. In situ ultraviolet photoemission spectroscopy, however, showed that the interfaces are not abrupt and consist of a chemically reacted intermediate layer. The thickness of this layer depends strongly on the growth sequence and results in a strong asymmetry in the In profile between the two interfaces.
Calculations of the barrier height and charge distribution of a metal–dielectric interface
Authors: Keller Robert C. , Helms C. R.
Published: July 2002

We present calculations of the barrier height (work function) and charge distribution of a metal–dielectric interface using a self-consistent density functional method. The metal was modeled by a semiinfinite jellium and the dielectric was characterized by a single dielectric constant. Results show a monotonic decrease of over 2 eV in the work function of high density simple metals such as aluminum with increasing dielectric constant. As the dielectric constant becomes large, the work function approaches a constant value. This change is much larger than the roughly 0.5 eV change found by others using a variational density functional method, which also showed the work function increasing as the dielectric constant becomes large (ε≳10). Low electron density metals display a smaller decrease in work function as the dielectric constant increases, due to the smaller electrostatic dipole layer at the interface. As a consequence, the work function difference between high and low electron density simple metals narrows from 1.1 to 0.15 eV in the limit of infinite screening. Similar work function screening effects are expected for noble metals, although the difference in work functions between noble metals may not be reduced as much as simple metals. These results are discussed in relation to current Schottky barrier theories and are compared to other models of metal–semiconductor interfaces.
Dry surface cleaning in integrated vacuum reactive ion etching processes
Authors: Yapsir Andrie S.
Published: July 2002

A study on dry cleaning in reactive ion etching (RIE) is conducted on a multichamber system consisting of several etch reactors. Particularly, the effects of a thin oxide residual layer on etch micromasking of selective silicon RIE are examined. An unintentionally grown oxide can be introduced, for example, during a resist removal process as well as an air exposure. To quantitatively evaluate surface cleanliness, a method for analyzing the formation of thin surface oxide is developed. The technique utilizes the selectivity property of a chlorine plasma to oxide. A criterion for a clean surface is defined based on the chlorine emission line intensity during a plasma exposure of a silicon surface. The effectiveness of a cleaning process, and its impact on the surface roughness following a selective silicon RIE process, are evaluated.