bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective reactive ion etching of GaAs/AlAs in BCl3/SF6 for gate recess
Authors: Lee Y.-S. , Upadhyaya K. , Nordheden K. J. , Kao M.-Y.
Published: July 2002

A selective reactive ion etch process for GaAs high electron mobility transistor gate recess has been developed using BCl3/SF6 gas mixtures. The influence of gas flow ratio, pressure, and radio-frequency (rf) power on the selectivity was examined. An optimum selective etching process using a Plasma Therm 790 reactive ion etching system was determined to be 50 W rf power, gas flow ratio of BCl3/SF6=2.5 sccm/7.5 sccm, and chamber pressure of 50 mTorr. Excellent etch uniformity was achieved by using an HCl/ethanol solution to remove native oxide prior to plasma etching.
On the structure of Ni–Cr–B–Si hardfacing alloys and their bonding reactions
Authors: Knotek O. , Lugscheider E.
Published: July 2002

Silicon is dissolved in the nickel-rich mixed crystal of Ni–Cr–B–Si alloys which are used for hardfacing. Boron forms several different borides due to the small solubility in the mixed crystals. There is a wide liquidus range during solidification of these alloys caused by the metastable solidification of the Ni–Ni2B eutectic instead of the stable solidification of the Ni–Ni3B eutectic. This wide liquidus range facilitates the hardfacing process which can be conveniently done by fusing the alloyed powders in a furnace. The hot hardness of nickel-based hard alloys is higher, up to 900 °C. The boron diffusion into the base metal is of the volume diffusion type; no grain boundary diffusion was observed with type 316 stainless steel.
Surface Photovoltage Spectroscopy—A New Approach to the Study of High-Gap Semiconductor Surfaces
Authors: Gatos Harry C. , Lagowski Jacek
Published: July 2002

Surface photovoltage spectroscopy is based on the photostimulated depopulation and population of surface states brought about by sub-bandgap monochromatic illumination, while the over-all number of bulk free carriers remains essentially unchanged. Such transitions and their transients (as determined by changes is the contact potential difference) allow the direct determination of the energy positions and the dynamic parameters of the surface states. Surface photovoltage spectroscopy was successfully applied to the surfaces of CdS, ZnO, and GaAs. A model was developed which accounts for the processes involved in surface photovoltage spectroscopy.
Comparative study of sputtered and spin-coatable aluminum oxide electron beam resists
Authors: Saifullah M. S. M. , Kurihara K. , Humphreys C. J.
Published: July 2002

The electron beam exposure characteristics of sputtered AlOx and spin-coatable Al2O3 resists are compared and contrasted. When exposed to an electron beam, sputtered AlOx resists on a silicon substrate undergo an intense mass loss. However, electron energy loss spectroscopy shows that even after a prolonged exposure some aluminum and oxygen remains on the silicon surface. Spin-coatable Al2O3 resist was prepared by reacting aluminum tri-sec-butoxide, Al(OBus)3, with acetylacetone (AcAc) in isopropyl alcohol. These are negative tone resists and they are >106 times more sensitive to an electron beam than the sputtered AlOx, bringing its sensitivity very close to high resolution organic resists such as calixarene. The exposure properties of spin-coatable and sputtered aluminum oxide resists are discussed together with their sensitivity, damage mechanisms, line edge roughness, and etching characteristics. A brief note on the change of methodology of resist design is added when inorganic resists are to be used in high resolution electron beam nanolithography.
Microstructure and secondary phases in coevaporated CuInS2 films: Dependence on growth temperature and chemical composition
Authors: Álvarez-Garcı́a J. , Pérez-Rodrı́guez A. , Romano-Rodrı́guez A. , Morante J. R. , Calvo-Barrio L. , Scheer R. , Klenk R.
Published: July 2002

The microstructure of CuInS2 (CIS2) polycrystalline films deposited onto Mo-coated glass has been analyzed by Raman scattering, Auger electron spectroscopy (AES), transmission electron microscopy, and x-ray diffraction techniques. Samples were obtained by a coevaporation procedure that allows different Cu-to-In composition ratios (from Cu-rich to Cu-poor films). Films were grown at different temperatures between 370 and 520 °C. The combination of micro-Raman and AES techniques onto Ar+-sputtered samples has allowed us to identify the main secondary phases from Cu-poor films such as CuIn5S8 (at the central region of the layer) and MoS2 (at the CIS2/Mo interface). For Cu-rich films, secondary phases are CuS at the surface of as-grown layers and MoS2 at the CIS2/Mo interface. The lower intensity of the MoS2 modes from the Raman spectra measured at these samples suggests excess Cu to inhibit MoS2 interface formation. Decreasing the temperature of deposition to 420 °C leads to an inhibition in observing these secondary phases. This inhibition is also accompanied by a significant broadening and blueshift of the main A1 Raman mode from CIS2, as well as by an increase in the contribution of an additional mode at about 305 cm−1. The experimental data suggest that these effects are related to a decrease in structural quality of the CIS2 films obtained under low-temperature deposition conditions, which are likely connected to the inhibition in the measured spectra of secondary-phase vibrational modes.
Fundamental study of ion-irradiation effects on the columnar growth of chromium films prepared by ion-beam and vapor deposition
Authors: Kuratani Naoto , Ebe Akinori , Ogata Kiyoshi , Shimizu Ippei , Setsuhara Yuichi , Miyake Shoji
Published: July 2002

The effects of ion irradiation during deposition on columnar growth of Cr thin films prepared by ion-beam-assisted deposition were studied. Cr films were prepared by evaporation of Cr metal and simultaneous irradiation of Ar ions onto Si 〈100〉 wafers. The energies of Ar ions were varied over the range of 0.5–20.0 keV, and the transport ratios of irradiating Ar ions to depositing Cr atoms, TR(Ar/Cr), to the substrates were also varied between 0.01 and 0.20. Vaporized Cr atoms were deposited onto substrates at an angle of 45° from the substrate normal and Ar ions were irradiated perpendicular to the substrate surface. Si substrates were not rotated and were kept at low temperature during deposition by a water-cooling system. The experimental results showed that every Cr film had a columnar structure regardless of ion-irradiation conditions. The column size became larger with increasing ion energy and TR(Ar/Cr). The growth direction of the column tilted considerably with increasing ion energy and TR(Ar/Cr) in the cases where the Ar-ion energy was 10.0 keV or less. On the other hand, the column growth direction became perpendicular to the substrate with increasing TR(Ar/Cr) in the case where the ion energy was 20.0 keV. The difference of column growth direction due to ion irradiation conditions could be understood by considering the preferential adatom movements as well as the shadowing effect.
Synthesis and characterization of transparent conducting oxide cobalt–nickel spinel films
Authors: Windisch Charles F. , Ferris Kim F. , Exarhos Gregory J.
Published: July 2002

Cobalt–nickel oxide films of nominal 100 nm thickness, and resistivity on the order of 10−2 Ω cm have been deposited by spin casting from both aqueous and organic precursor solutions followed by annealing at 450 °C in air. Films deposited on sapphire substrates exhibit a refractive index of about 1.7 and are relatively transparent in the wavelength region from 0.6 to 10.0 μm. They are also magnetic. The electrical and spectroscopic properties of the oxides have been studied as a function of the x=Co/(Co+Ni) ratio. An increase in film resistivity was found upon substitution of other cations (Zn2+, Al3+,…) for Ni in the spinel structure. However, some improvement in the mechanical properties of the films resulted. A combination of x-ray diffraction, x-ray photoelectron spectroscopy, UV/Vis, and Raman spectroscopy indicated that NiCo2O4 is the primary conducting component and that the conductivity reaches a maximum at this stoichiometry. When x<0.67, NiO forms leading to an increase in resistivity; when x>0.67, the oxide was all spinel but the increased Co content lowered the conductivity. The influence of cation charge state and site occupancy in the spinel structure markedly affects calculated electron band structures and likely influences an anomalous switch of p-type conductivity to n-type conductivity seen at x=0.67. Electronic structure modeling studies also suggest the important role of the Ni3+ cation in the conductivity mechanism. Finally, Raman spectra of the films were relatively easy to obtain and therefore were useful as a routine tool for identifying composition and optimizing conductivity.
Epitaxial VN(001) Grown and Analyzed In situ by AES After (1) Deposition and (2) Ar+ Sputter Etching
Authors: Finnegan N. , Lee T.-Y. , Haasch R. T. , Greene J. E. , Petrov I.
Published: July 2002

In situ Auger electron spectroscopy (AES) spectra were obtained on single-crystal VN(001) layers grown on MgO(001)1 × 1 in a multichamber ultrahigh vacuum (UHV) system. A turbomolecular-pumped magnetron sputter deposition chamber was attached to a Physical Electronics model 660 scanning Auger system to allow spectra to be collected on the as-deposited film without exposure to air. The spectra show that the film surfaces are free of O and C. Spectra are also presented following sputter etching with a 3 keV Ar+ beam at an incident current density of 0.3 mA cm−2. The film was sputtered until the N/V peak height ratio reached equilibrium, then spectra were acquired for the after sputter condition. AES spectra were collected for both the as-deposited and Ar+ sputter etched films using primary beam energies of 3, 5, 10, and 20 keV. The as-deposited bulk film composition was analyzed by Rutherford backscattering spectroscopy (RBS) and found to be stoichiometric with a N/V ratio of 1.04 ± 0.02.
Epitaxial CrN(001) Grown and Analyzed In situ by AES After (1) Deposition and (2) Ar+ Sputter Etching
Authors: Finnegan N. , Lee T.-Y. , Haasch R. T. , Greene J. E. , Petrov I.
Published: July 2002

In situ Auger electron spectroscopy (AES) spectra were obtained on single-crystal CrN(001) layers grown on MgO(001)1 × 1 in a multichamber ultrahigh vacuum (UHV) system. A turbomolecular-pumped magnetron sputter deposition chamber was attached to a Physical Electronics model 660 scanning Auger system to allow spectra to be collected on the as-deposited film without exposure to air. The spectra show that the film surfaces are free of O and C. Spectra are also presented following sputter etching with a 3 keV Ar+ beam at an incident current density of 0.3 mA cm−2. The film was sputtered until the N/Cr peak height ratio reached equilibrium, then spectra were acquired for the after sputter condition. AES spectra were collected for both the as-deposited and the Ar+ sputter etched films using primary beam energies of 3, 5, 10, and 20 keV. The as-deposited bulk film composition was analyzed by Rutherford backscattering spectroscopy (RBS) and found to be stoichiometric with a N/Cr ratio of 1.02 ± 0.02.
Triple-junction issues in field emission displays
Authors: Ma Xianyun , Sudarshan T. S.
Published: July 2002

This article addresses triple-junction issues related to vacuum insulation in field emission displays (FEDs), both from a theoretical and practical point of view. A technique to inhibit the triple-junction initiated breakdown in dielectric spacer insulation has been demonstrated. In order to simulate the vacuum insulation structure in a FED, thin-film electrodes bridged by a thin-wall-structured spacer were used. Using the developed technique, the breakdown voltage was improved from ∼10 to ∼21 kV for the first run and ∼13 to 24 kV for the conditioned regime. The mechanism of breakdown of the solid insulator is discussed.
Process development of methane–hydrogen–argon-based deep dry etching of InP for high aspect-ratio structures with vertical facet-quality sidewalls
Authors: Grover Rohit , Hryniewicz John Vetold , King Oliver Simon , Van Vien
Published: July 2002

We examine methane–hydrogen–argon-based deep dry etching of InP for facet-quality sidewalls by reactive ion etching. A process is developed for etch depths as high as 5.8 μm. Masks studied include Ni, NiCr, Ti, SiO2, and Ti–SiO2. Sidewall roughness was estimated to be a few nm (based on high resolution scanning electron micrographs). This may be useful for fabrication of optical microelectromechanical systems, photonic wires, and photonic crystals in the InP material system.
Patterning nonflat substrates with a low pressure, room temperature, imprint lithography process
Authors: Colburn Matthew , Grot Annette , Choi Byung Jin , Amistoso Marie , Bailey Todd , Sreenivasan S. V. , Ekerdt John G. , Grant Willson C.
Published: July 2002

Step and flash imprint lithography (SFIL) is a technique that has the potential to replace photolithography for patterning resist with sub-100 nm features. SFIL is a low cost, high throughput alternative to conventional photolithography for high-resolution patterning. It is a molding process in which the topography of a template defines the patterns created on a substrate. The ultimate resolution of replication by imprint lithography is unknown but, to date, it has only been limited by the size of the structures that can be created on the template. It is entirely possible to faithfully replicate structures with minimum features of a few hundred angströms. SFIL utilizes a low-viscosity, photosensitive silylated solution that exhibits high etch contrast with respect to organic films in O2 reactive ion etching. In this article we describe the SFIL process, the development of a multilayer etch scheme that produces 6:1 aspect ratio features with 60 nm linewidths, a method for patterning high-aspect-ratio features over topography, and a metal lift-off process. A micropolarizer array consisting of orthogonal 100 nm titanium lines and spaces fabricated using this metal lift-off technique is reported.
Optical and structural studies in InGaN quantum well structure laser diodes
Authors: Chichibu Shigefusa F. , Azuhata Takashi , Sugiyama Mutsumi , Kitamura Toshio , Ishida Yuuki , Okumura Hajime , Nakanishi Hisayuki , Sota Takayuki , Mukai Takashi
Published: July 2002

An InGaN multiple-quantum-well laser diode wafer that lased at around 400 nm was shown to have the InN mole fraction, x, of only 6% in the wells. Nanometer-probe compositional analysis showed that the fluctuation of x was as small as 1% or less, which is the resolution limit. However, the wells exhibited a Stokes-like shift (SS) of 49 meV at 300 K, which was approximately 65% of the luminescence linewidth, and effective localization depth, E0, was estimated to be 35 meV at 300 K. Since the effective electric field due to polarization in the wells was estimated to be as small as 300 kV/cm, SS was considered to originate from effective band-gap inhomogeneity. Because the well thickness fluctuation was insufficient to reproduce SS or E0 and bulk cubic In0.02Ga0.98N that does not suffer any polarization field or thickness fluctuation effect exhibited a SS of 140 meV at 77 K, the exciton localization is considered to be an intrinsic phenomenon in InGaN, which is due to the large band-gap bowing and In clustering in InGaN material. The spontaneous emission from the InGaN wells was thus assigned as being due to the recombination of excitons localized at the exponential tail-type potential minima in the density of states. The upper bound of the lateral localization size has been estimated to be 50 nm. Such shallow and low density localized states are leveled by injecting high density carriers under the lasing conditions.
Characterization and simulation of surface and line-edge roughness in photoresists
Authors: Constantoudis V. , Gogolides E. , Patsis G. P. , Tserepi A. , Valamontes E. S.
Published: July 2002

The problem of surface and line-edge roughness characterization and prediction is discussed. Different roughness parameters, such as the root mean square deviation (rms or σ), the fractal dimension, and the Fourier spectrum, are presented and compared. These roughness parameters for three negative tone resists (wet and plasma developed) are analyzed versus exposure dose, photoacid generator concentration, and plasma development conditions. Finally, a molecular type simulator is used to predict the experimental roughness behavior.
Low-voltage electron emission from mineral films
Authors: Rech J. , Grauby O. , Morin R.
Published: July 2002

Electron emission from mineral films deposited on carbon membranes is observed for applied fields between 1 and 10 V/μm. A field emission process is demonstrated by current versus voltage characteristic measurements. These characteristics are approximately linear on a Fowler–Nordheim plot after the effects of a Mohm resistor (for an emitting film area of 3 mm2) are accounted for. The shapes and density of the microcrystals of the different films are characterized by scanning electron microscopy and a correlation between flat crystal shapes and field emission is observed. A tendency to destroy the emission from these insulating materials is induced by a gold layer deposition. The relevance of an insulator character and of a high secondary electron coefficient is discussed.
High-density etching plasma excitation by slot type and coaxial line type of microwave antennas
Authors: Yamauchi T. , Sugai H.
Published: July 2002

Microwave radiation by slot antennas is used to generate large-diameter high-density plasmas where transverse magnetic (TM) mode of surface waves is excited along the plasma–quartz interface. When fluorine-rich etching plasma is produced in CF4/O2 at 40 Pa, anomalous erosion (many deep microholes) of quartz surface is observed after 40 h. This serious erosion limits the throughput of etching process. In order to overcome this problem, a coaxial line antenna is newly introduced and its performance is compared with the slot antenna excitation. In the same discharge conditions, the coaxial line antenna does not give rise to anomalous erosion of quartz surface. This different result is explained by simplified analysis of cylindrical transmission electron microscope mode and planar TM mode. In addition, the coaxial line antenna has a great advantage of no need of large-area thick quartz window, no density jump, higher power efficiency, and better density uniformity.
Calculation of Deposition Uniformity in rf Sputtering
Authors: Brodie I.
Published: July 2002

Assuming a uniform flux of ions upon the target, a cosine distribution of sputtered material, unity sticking coefficient on the substrate, no surface mobility and no gas collisions, deposition uniformities are calculated for several device configurations. These include: (1) the “peak” configuration of adjacent rectangular targets, (2) the disk type, and (3) coaxial cylindrical targets and substrate holders. Areas over which the deposition uniformities are predicted to be within ±1% to ±10% were computed and these results compared with available experimental results obtained from rf sputtering devices. The good agreement obtained shows that the method does give a practical approach to estimating deposition uniformities for rf sputtering systems where the assumptions are reasonably well obeyed. The peak configuration is examined in some detail and it is found that there is an optimum position for the substrate table at which the largest, area of uniform deposition is obtained.
Physisorption of Nitrogen on 304 Stainless Steel at Very Low Pressures
Authors: Troy M. , Wightman J. P.
Published: July 2002

Physisorption isotherms have been measured for nitrogen on 304 stainless steel in the temperature range 77–90 K and in the pressure range 10−9−10−4 Torr. A static technique was used to obtain the isotherms whereby the pressure change of nitrogen in a constant volume system was measured on immersion of the test surface in different cryogenic baths. The Dubinin-Radushkevich equation provided a good correlation of the data and the extrapolated value for monolayer coverage of 6.6×1014molecules/cm2 indicated a roughness factor near unity for stainless steel. The isosteric heat of adsorption of nitrogen on stainless steel remained constant at about 4.4 kcal/mole in the range of surface coverages from 0.02–0.08.
Design and optimization of magnetic lenses and deflection systems for electron beams
Authors: Munro E.
Published: July 2002

Methods are described for computing the optical properties of any combination of magnetic lenses and deflection yokes, including the most general case in which the lens and deflector fields may be physically superimposed. These techniques can handle either toroidal or saddle deflection yokes, wound on either nonmangetic of ferromagnetic formers, and can handle cases where the magnetic materials of the lenses directly influence the deflection fields. The basic program for calculating the properties of any given lens and deflection system has been combined with an optimization program, which systematically searches (subject to given physical constraints) for the arrangement which minimizes the deflection aberrations for any specified field size and aperture angle. Illustrative computed results are presented. It appears that conventional postlens single-deflection systems can have better properties than conventional prelens double-deflection systems. However, the performance of double-deflection systems can be improved dramatically by placing the second yoke inside the lens and rotating it relative to the first yoke. An arrangement has been found, which, at the corners of a 5×5-mm deflection field with 0.005-rad aperture and 1 in 104 beam voltage ripple, produces a total aberration disk of 0.45 μm before dynamic corrections, or 0.15 μm after dynamic corrections. The properties of in-lens single-deflection systems have also been investigated. Such systems offer the possibility, for the same operating conditions as quoted above, of producing a total aberration disk of less than 0.2 μm after dynamic corrections. By introducing a ’’predeflection coil’’ before the main deflection coil, this value can be reduced to less than 0.1 μm.
Thin-film deposition using low-energy ion beams (3) Mg+ ion-beam deposition and analysis of deposits
Authors: Amano J. , Lawson R. P. W.
Published: July 2002

The energy dependence of the growth characteristics of Mg thin films on C substrates deposited by retarding a 4-keV mass-analyzed ion beam of Mg+ ions to a range of energies between 24 and 500 eV has been studied by Rutherford backscattering analysis and scanning electron microscopy. An incident Mg+ beam energy of about 100 eV produced the optimum film in the shortest time when space-charge spreading of the beam at low energies is compared with self-sputtering of the deposit at the higher energies. The adhesion of the films is energy dependent and improves at higher energies. This is thought to be due to deeper penetration of the Mg+ ions into the C substrates above 100 eV.
Influence of the free surface on the electrical behavior of metal contacts to p-InAs
Authors: Millea M. F. , Silver A. H.
Published: July 2002

The study of electrical (evaporated gold) contacts to p-InAs has been extended down to an acceptor doping of 2×1016 cm−3. The steady-state current–voltage characteristic is independent of the free surface, except for a reverse-breakdown effect which appears to be surface dependent. A space-charge generation-recombination mechanism is proposed to explain the carrier flow for contacts on low-doped p-InAs. The free surface is found to strongly influence both the capacitance and photoresponse of gold contacts evaporated on low-doped p-InAs. A novel technique employing combined photocurrent and capacitance measurement has been employed to investigate the electrical characteristic of the free surface. With this technique we can easily determine both the spatial and temporal variation of the surface sheet resistance. For a freshly etched surface the surface electron concentration is small and spatially variable; with time the surface electron concentration increases. This indicates that although the conduction band minimum at the surface is below the Fermi level, the lowest quantized surface electron level is above the Fermi level.
Low work function electron emitter hexaborides
Authors: Schmidt P. H. , Joy D. C.
Published: July 2002

Desirable properties of potential electron emitter materials include a high melting point, low vapor pressure and compound stability at elevated temperatures, in addition to a favorable work function φ and Richardson number. The rare-earth hexaborides combine many of these properties. We have evaluated and intercompared these properties in an attempt to establish groups of materials desirable for useful thermionic electron emitters. We find that La, Pr, and Nd hexaborides exhibit the most desirable combination of the above properties. Compounds of Pr or NdB6 with 10%–30% additions of LaB6 appear most promising as future emitter materials.
High voltage CdSe thin film transistor
Authors: Luo F. C.
Published: July 2002

This paper describes the design, fabrication, and characteristics of a high voltage, high gain CdSe thin film transistor (TFT). The main features of the TFT are the use of In–Cu for the source and drain contact electrodes, a very thin layer of In above or under a CdSe layer as the conducting channel, and Al2O3 as the insulator. It has been found that In–Cu source–drain contacts stand much higher voltage than Al or In–Au contacts. A trace of In deposited above or under the CdSe layer enhances the transconductance and improves the stability of the TFT. The reported TFT can stand up to 400 V and achieve ON–OFF ratios up to 40 000.
Dependence of F atom density on pressure and flow rate in CF4 glow discharges as determined by emission spectroscopy
Authors: Coburn J. W. , Chen M.
Published: July 2002

The dependence of the density of atomic fluorine as a function of pressure and flow rate in CF4 glow discharges has been measured using emission spectroscopy. The emission intensity of the 7037 Å line of atomic fluorine and of the 7504 Å line of argon, which is added to the CF4 discharge in small quantities (1%–2%), is used to deduce the F atom density. It is found that the pressure dependence of the F atom emission intensity alone is a poor indicator of the relative F atom concentration because the excitation efficiency of the CF4 discharge decreases rapidly with increasing pressure. The F atom density decreases with increasing flow rate as is to be expected if the lifetime of the F atom is determined largely by the vacuum pump. However, at low flow rates the F atom density is determined primarily by contaminant gases, in this case CO and CO2, through several mechanisms which are discussed.
Refractory metal contacts to GaAs: Interface chemistry and Schottky-barrier formation
Authors: Waldrop J. R. , Kowalczyk S. P. , Grant R. W.
Published: July 2002

A survey of the interface chemistry of the refractory metals W, Ta, Re, Ir, and Mo during room- temperature Schottky-barrier contact formation to GaAs by using x-ray photoemission spectroscopy (XPS) is reported. The metals were deposited onto clean n-type GaAs (100) surfaces within the XPS system by two methods: Evaporation and plasma sputtering. For each metal a distinct interfacial reaction which produced GaAs dissociation and formation of a new metal arsenide is observed. Refractory metals are in general not chemically inert in contact to GaAs and nonabrupt interfaces ∠10 Å in width are formed. XPS was also used to correlate interface chemistry with measurement of Schottky-barrier height during contact formation. XPS measured barrier heights ranged from 0.9–0.7 eV, in the order W, Ir, Mo, Ta, and Re.
A simple procedure for rejuvenating Cu/Be electron multipliers using an O2 plasma
Authors: Frick K.
Published: July 2002

The gain of an electron multiplier can be restored by a plasma treatment lasting 45 min. (AIP)
Stress relief of basal orientation zinc oxide thin films by isothermal annealing
Authors: Gawlak C. J. , Aita C. R.
Published: July 2002

The effect of isothermal annealing on residual strain in the lattice of as-deposited basal crystallographic orientation zinc oxide was studied. Films were prepared by rf diode sputter deposition from a zinc oxide target and annealed in air for 5 to 1995 min at 300 or 500 °C. The change in crystallography as a result of annealing was determined by x-ray diffraction. The results show that as-deposited films have a residual tensile strain along the c axis with an average value of +0.62%. Strain relaxation begins to occur after 5 min at 300 °C. The small activation energy, ∼0.2 eV, suggests that interstitial diffusion assisted by local plastic strain may be the process by which strain relaxation initiates. Annealing at 500 °C for longer than 5 min causes a compressive strain to develop along the c axis upon cooling. This effect is attributed to the difference in the coefficient of thermal expansion of zinc oxide and silicon. Comparison with other annealing studies suggest that the magnitude of this effect is likely to be dependent upon the structure of the film–substrate interface.
Sample carousel transfer mechanism
Authors: Fearon D. H. , Helbig H. F. , Steward S. A. , Uribe F. S.
Published: July 2002

A carousel transfer system for a UHV surface analysis chamber has been designed and built. (AIP)
Real-time x-ray topography: Applications to bulk HgCdTe materials
Authors: Rosemeier R. G.
Published: July 2002

Commercially available portable image x-ray intensifiers have found their usefulness with all existing x-ray topographic techniques. Real-time x-ray topography can be employed to align the diffraction images rapidly before recording them on high resolution film. As a quality control procedure, real-time Berg–Barrett x-ray topography can be used to assess macrostructural quality of HgCdTe with approximately 100 μm spatial resolution. As a x-ray screening technique prepared samples of HgCdTe can be assessed in real time before undergoing unnecessary costly processing on poor material. The advantages and disadvantages of the three basic types of x-ray topographic system will be discussed. The usefulness of real-time x-ray intensification as a support tool to Berg–Barrett, Lang, and ACT topography techniques is evaluated. Also, instrument characteristics of the x-ray intensifiers which are useful in real-time x-ray topography applications will be presented.
Depressurization as a means of leak checking large vacuum vessels
Authors: Callis R. W. , Langhorn A. , Petersen P. I. , Ward C. , Wesley J.
Published: July 2002

A common problem associated with large vacuum vessels used in magnetic confinement fusion experiments is that leak checking is hampered by the inaccessibility to most of the vacuum vessel surface. This inaccessibility is caused by the close proximity of magnetic coils, diagnostics and, for those vessels that are baked, the need to completely surround the vessel with a thermal insulation blanket. These obstructions reduce the effectiveness of the standard leak checking method of using a mass spectrometer and spraying a search gas such as helium on the vessel exterior. Even when the presence of helium is detected, its entry point into the vessel cannot always be pinpointed. This paper will describe a method of overcoming this problem. By slightly depressurizing the vessel, an influx of helium through the leak is created. The leak site can then be identified by personnel within the vessel using standard sniffing procedures. There are two conditions which make this method of leak checking practical. First, the vessel need only be depressurized 2 psi, thus allowing personnel inside to perform the sniffing operation. Second, the sniffing probe used (Leybold–Heraus ‘‘Quick Test’’) could detect a change in helium concentration as small as 100 ppb, which allows for faster scanning of the vessel inferior. Use of this technique to find an elusive 10−3 Torr⋅l/s leak in the Doublet III tokamak vacuum vessel will be presented.
Thin films of a-Si1−xGex:H alloys by dual magnetron sputtering in a UHV chamber
Authors: Rudder R. A. , Cook J. W. , Lucovsky G.
Published: July 2002

This paper discusses the bonding of H atoms in a-Si1−xGex: H alloys that are deposited in a dual magnetron sputtering system. The relative numbers of SiH and GeH bonds, as a function of the Ge content are found to be qualitatively different than in films (a) grown by the glow discharge (GD) decomposition of germane, silane mixtures, or (b) deposited in diode sputtering (DS) systems with Ge/Si targets. The intrinsic films deposited by magnetron sputtering display higher concentrations of bonded H in monohydride arrangements and higher majority carrier photoconductivities than either the GD or DS alloy films. These differences are explained in terms of a model for H atom incorporation which emphasizes the relative importance of surface and plasma phase chemical interactions. In the magnetron films, H atom bonding is primarily determined by surface reactions, whereas in the other two techniques plasma phase chemistry is the dominant factor which favors precursors with SiH rather than GeH bonds.
Pumping of methane by a low power hot-cathode ion pump/gage
Authors: Chapman R. , Hobson J. P.
Published: July 2002

Sealed-off devices, such as evacuated solar absorbers, with long life spans (about 25 years) frequently require a means of holding down the pressure of gases like methane which are not easily pumped by getters. Required pumping speeds are not high because leak-up rates are low, but simplicity, low power consumption, together with a means of monitoring the pressure are desirable features. To meet these requirements we have constructed a small hot-cathode ion pump/gage similar to a small Bayard–Alpert gage and we have subjected it to accelerated life tests in methane. The device consumed less than 1 W of power in operation. After 7×10−2 Torr l of methane had been pumped and with 1 mA of emission current the pumping speed was 2×10−4 l s−1, the equilibrium pressure was 3×10−4 Torr, and the reemission of pumped gas was 6×10−8 Torr l s−1, all quantities being slowly varying functions of the quantity of methane pumped. The sensitivity factor throughout the experiment was 3.3 Torr−1.
Metallurgy of Ti–W/Au/Cu system for TAB assembly
Authors: Meyer D. , Kohli A. , Firth H. , Reis H.
Published: July 2002

Tape automated bonding or TAB has been an I/C assembly method for over 15 years, but only recently has it gained such wide attention. One reason is that technology and equipment exist today to reliably and economically passivate I/C chips and electroplate bumps on chip bonding pads. Both are a prerequisite for TAB. One very successful metallization system for obtaining bumped wafers is that of Ti–W/Au. By using a load lock magnetron sputtering system for deposition of a Ti–W barrier layer, it is possible to both passivate the entire chip by sealing the pad and prevent interaction of the aluminum bonding pad with the gold bump which is required for automatically attaching the chip to a beamed tape. This barrier capability was tested by submitting 64 pin TAB bonded circuits to 1000 h bake at 200 °C in nitrogen. No degradation of the bump to pad interface was observed.
Migration of beryllium in the Impurity Study Experiment-B tokamak during the Beryllium Limiter Experiment
Authors: Langley R. A. , Zuhr R. A. , Lewis M. B.
Published: July 2002

A beryllium limiter was installed in the Impurity Study Experiment-B (ISX-B) tokamak to test the applicability of beryllium as a plasma-side component for possible use in the Joint European Torus (JET). This test was a collaborative effort involving both ORNL and JET personnel. The ISX-B tokamak was operated for more than 3000 high power neutral beam injected discharges using the beryllium limiter as the main confining aperture. In order to access the migration of beryllium in the tokamak and attached diagnostics, both stainless steel and silicon samples were placed at various strategic positions and used as catcher plates. Nuclear reaction analysis was used to measure the beryllium deposited on the plates and provided a measure of the beryllium migration. Both particulates and a thin film were found. The toroidal distribution of these two migration components is presented as well as a discussion of the analysis technique for the deposited beryllium. Analysis was made of the distribution of beryllium particulate matter deposited on the inside of the vessel wall. Both a size distribution and spatial distribution are presented.
Carbon monoxide production in low energy oxygen ion bombardment of pyrolytic graphite and Kapton surfaces
Authors: Horton C. C. , Eck T. G. , Hoffman R. W.
Published: July 2002

We report the results of an investigation of the interaction of low energy oxygen ions with pyrolytic graphite and Kapton surfaces. CO molecules emitted from the surface as a result of the ion bombardment were detected by a mass spectrometer. Because the ion-induced signals were small compared to that arising from the CO background pressure in our vacuum system, the ion beam was modulated and the modulated component of the CO signal measured with a lock-in amplifier. The quantum yield (CO molecules emitted per incident oxygen ion) for graphite rose from 1.9 at 4.5 eV ion energy to 6.6 at 465 eV. Comparable yields were obtained for Kapton. The large size of our yields suggests contributions to the reaction process from the background O2 molecules in our vacuum system.
Diamondlike carbon films on semiconductors for insulated-gate technology
Authors: Kapoor Vik J. , Mirtich Michael J. , Banks Bruce A.
Published: July 2002

Carbon dielectric films with diamondlike properties were investigated as a new electronic material in a metal–insulator(carbon)–semiconductor (MIS) device configuration for solid state power devices for space applications. Films were directly deposited on the InP, GaAs, and Si substrates by ionizing a 25 vol % mixture of methane in argon using both single and dual ion beam systems. Electrical measurements at various frequencies of metal–carbon–InP devices showed a turn on voltage of −1.6 V with 0.2 V hysteresis, a fixed charge number density of 8×1010/cm2, and an interface state density of 3.0×1012 cm−2 eV−1. The capacitance–voltage (C–V) characteristics for carbon on GaAs were stretched out with 1.1 V hysteresis and indicated a fixed charge number density of 1×1012/cm2 and an interface state density of 1×1013 cm−2 eV−1. The MIS device performance improved significantly due to in situ ion beam treatment of the semiconductor surfaces prior to the film deposition. This was determined to be related to oxygen at the film–semiconductor interface as determined by scanning Auger electron spectroscopy.
Electronic structure of Laves-type uranium intermetallics studied with synchrotron radiation
Authors: Höchst H. , Tan K. , Hillebrecht U.
Published: July 2002

Synchrotron radiation photoemission spectroscopy in the photon energy range hν=22–130 eV has been used to study the electronic structure of intermetallic Laves-type compounds UMe2, with Me=Mn, Fe, Co, and Ni. With increasing 3d occupation, the 3d states show a much smaller shift away from EF than expected from theory. Satellite emission at ∼7.5 eV binding energy, which resonates at the 3p threshold, indicates that the 3d bands are not completely filled in UNi2. Resonant valence band photoemission around the U 5d threshold has been used to investigate the U 5f valence band DOS. These 5f states are located at EF in UNi2 with a FWHM that is much narrower than the experimental resolution ΔE=0.6 eV. In UMn2, 5f states are energetically less localized with a FWHM of ∼1.6 eV below EF.
A secondary ion mass spectrometry study of the catalytic oxidation of methanol on Cu(110)
Authors: Karwacki E. J. , Winograd N.
Published: July 2002

Formaldehyde formation via the oxidation of methanol has been studied on a Cu(110) surface by static secondary ion mass spectrometry (SIMS). Previous work by temperature programmed thermal desorption (TPTD or TPD) suggests enhanced methanol adsorption at 180 K after preadsorption of oxygen and the formation of a methoxide intermediate (CH3O) species. Upon heating, this intermediate decomposes and formaldehyde is desorbed above 365 K. Using isotopically labeled oxygen-18 and deuterated methanol (CH3OD), SIMS analysis suggests the presence of D218O, CH3OD, CH2O, and H by observation of their Cu cations (CuD218O+, CuCH3OD+, CuCH2O+, and Cu2H+) after methanol adsorption at 178 K. By the use of SIMS and thermal desorption SIMS (TDSIMS), methanol is observed to initially react at oxygenated sites to form water by reaction of its hydroxyl hydrogen and surface oxygen. The methoxide intermediate then reorients itself into a transition state which, during the collision process, breaks apart to form surface hydrogen and formaldehyde. These results suggest SIMS may be capable of assuming a limited role in fundamental catalysis studies. However, its dependence on molecular cations as the means to observe surface species will limit its use to systems that can efficiently produce such clusters.
Anomalous sputtering of gallium–antimonide under cesium-ion bombardment
Authors: Homma Yoshikazu
Published: July 2002

A large distortion in the secondary ion mass spectrometry depth profile in GaSb is found under cesium-ion bombardment. The result is interpreted in terms of a nonuniform sputter removal near the initial surface. On the cesium-ion-bombarded GaSb surface, microcrystalline GaSb growth takes place to upheave the bombarded region up to 0.1 μm from the initial surface in the very early stage of cesium-ion bombardment. Above a cesium-ion dose of 1×1017 ions cm−2, the normal sputtering rate versus ion dose was obtained. This phenomenon is thought to be the cesium induced microcrystal growth specific to the stoichiometric GaSb surface.
Surface imaging by carbon monoxide field desorption
Authors: Panitz J. A. , Hren J. J.
Published: July 2002

The morphology of a field-emitter tip has been visualized in atomic resolution for the first time at a field strength below 15 V/nm. Images are generated by continuous field desorption of a physisorbed carbon monoxide monolayer. The monolayer is replenished at 25 K by CO adsorption from the gas phase. High-contrast images are obtained by time gating for CO+ (the dominant field-desorbing species) in the imaging atom probe. Images integrated over several hundred field-desorption events show morphology at the center of large (thermally annealed) flat, crystal planes, and document the decrease in spatial resolution that accompanies pulsed-laser imaging of surface adsorbates. CO desorption images demonstrate that high-field imaging is no longer restricted to edge, kink site, and protruding atoms on the surface of a field-emitter tip.
Vibration isolation for scanning tunneling microscopy
Authors: Okano M. , Kajimura K. , Wakiyama S. , Sakai F. , Mizutani W. , Ono M.
Published: July 2002

Vibration isolation technology for scanning tunneling microscopy (STM) to suppress the external mechanical perturbation down to a subatomic scale is described. The system is simplified into two subsystems, a tunneling assembly and a supporting table. Each of them has its own mechanical eigenfrequency. The principle of the isolation exists in making the two eigenfrequencies very different from each other. A theory of isolation developed is based on a model of multiply coupled oscillators with damping. Experimental results of the isolation characteristics for the two types of isolators constructed, one consisting of two-stage coil springs and the other of multiply stacked metal plates with rubber pieces among them, are well explained by the theory. STM images of graphite are obtained by using these isolators combined with various tunneling assemblies. Thereby the basis for design of the isolators is clarified.
The large electron positron storage ring preinjector vacuum systems: Design and performance
Authors: Bourgeois M. , Brouet M. , Godot J. C. , Malthouse F. , Poncet A. , Roch M.
Published: July 2002

The large electron positron storage ring (LEP) preinjector will provide the particles to be stored in the LEP. It is composed of a high-intensity linear accelerator (linac) providing 200-MeV electrons for the production of positrons, a low-intensity linac (LIL) for the acceleration of electrons and positrons to 600 MeV (LIL), and an electron positron accumulator (EPA) ring to collect dense bunches of electrons and positrons at 600 MeV (EPA). The LIL rf accelerating cavities and waveguides are typical of severely conductance limited vacuum systems with high rf induced gas loads, in which a low hydrocarbon free residual pressure has to be maintained (5×10−8 mbar). For the EPA ring, subjected to synchrotron radiation induced gas desorption, considerations of beam lifetime require a base pressure in the 10−9 mbar range, achievable without in situ bakeout in the shortest possible time. The design features with particular emphasis on conceptual choices, cleanliness and special treatments, new hardware, low outgassing achievements, as well as cost and initial performances of these vacuum systems are presented.
The vacuum system for a British long baseline gravitational wave detector
Authors: Bennett J. R. J.
Published: July 2002

A description is given of the vacuum system for a 1×1 km long optical interferometric gravitational wave detector. The vacuum chamber consists of two tubes, 900-mm diameter, 1 km long, joined together in the shape of an L. End tanks ∼3-m diameter ∼3 m long contain the optical equipment. The tubes will be heated to 150 °C to reach outgassing rates of ∼10−12 Torr l/s/cm2 and pumped by turbomolecular pumps at 500-m intervals to obtain a pressure of ∼10−8 Torr. A significant cost saving is achieved by using thin-walled corrugated stainless-steel tube. The sensitivity of the detector is governed, among other things, by fluctuation in the vacuum pressure. Some discussion of the possible causes of these fluctuations is given.
Measurement of the hydrogen recombination coefficient for ZrAl
Authors: Knize R. J. , Emerson L. C. , Cecchi J. L.
Published: July 2002

The hydrogen recombination coefficient for ZrAl was measured over a temperature range of 450 to 650 °C. The measured values were found to be in good agreement with the values calculated using a previously described theory, along with other measurements. This present measurement technique for determination of the hydrogen recombination coefficient can also be applied to other materials.
Hollow cathode etching and deposition
Authors: Horwitz Chris M. , Boronkay S. , Gross M. , Davies K.
Published: July 2002

The hollow cathode has yielded high-rate low-pressure operation, with good etch selectivity and etched angle control. This paper shows that high SiO2 etch selectivity is most easily obtained at low pressure in the CF4/H2 process. The etched angle is controlled by metal film deposition which can be independent of the etch selectivity. A combined (metal+polymer) deposition and SiO2 etch process has been tested on commercial complementary metal–oxide semiconductor wafers with excellent yield and reliability results. This multiple deposition and etch process is best done in a new trielectrode hollow cathode chamber which exhibits 1 μm/min SiO2 etch rate with better than ±1% etch uniformity, an etched angle of ∼75°, and SiO2/Si selectivities of 50 (wafer edge) and 150 (wafer center). In addition, polymer deposition on surfaces near the wafer has been eliminated. The voltage and pressure dependence of Si deposition from SiH4 is described, and the hollow cathode ion bombardment is shown to give best planarization at low pressures (2 Pa) and low deposition rates (0.2 μm/min). A planarized SiO2 film is also shown.