bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron energy-loss spectroscopy of molybdenum disilicide
Authors: Rastogi R. S. , Vankar V. D. , Bhatanagar M. C. , Chopra K. L.
Published: July 2002

Thin films of molybdenum disilicide prepared by solid-state diffusion of Mo/Si(111) have been investigated by electron energy-loss spectroscopy for their valence level and core level electron excitations. In the valence band, interband transitions around 2.2, 3.9, and 5.3 eV have been observed. These transitions have been interpreted as electron excitations of the metal d band and Mo(4d)–Si(3p) levels. These transitions are in excellent agreement with the available experimental and theoretical data on MoSi2 electronic band structure. In the core levels, the electron excitations corresponding to the Si(2p) core level are shifted towards higher energy while that of the Mo(3d) are shifted towards lower energy. These shifts indicate a change in the bonding nature of Mo–Si during silicidation.
Hydrogen pumping and release by graphite under high-flux plasma bombardment
Authors: Hirooka Y. , Leung W. K. , Conn R. W. , Goebel D. M. , Labombard B. , Nygren R. , Wilson K. L.
Published: July 2002

Inert gas (helium or argon) plasma bombardment has been found to increase the surface gas adsorptivity of isotropic graphite (POCO-graphite), which can then getter residual gases in a high-vacuum system. The inert gas plasma bombardment was carried out at a flux ≊1×1018 ions s−1 cm−2 to a fluence of the order of 1021 ions/cm2 and at temperatures around 800 °C. The plasma bombarding energy was varied between 100 and 200 eV. The gettering speed of the activated graphite surface is estimated to be as large as 25 l s−1 cm−2 at total pressures between 10−6 and 10−7 Torr. The gettering capacity estimated is 0.025 Torr l/cm2 at room temperature. The gettering capability of graphite can be easily recovered by repeating inert gas plasma bombardment. The activated graphite surface exhibits a smooth, spongelike morphology with significantly increased pore openings, which correlates with the observed increase in the surface gas adsorptivity. The activated graphite surface has been observed to pump hydrogen plasma particles as well. From calibrated H-alpha measurements, the dynamic hydrogen retention capacity is evaluated to be as large as 2×1018 H/cm2 at temperatures below 100 °C and at a plasma bombarding energy of 300 eV. The graphite temperature was varied between 15 and 480 °C.

Due to the plasma particle pumping capability, hydrogen recycling from the activated graphite surface is significantly reduced, relative to that from a presaturated surface. A presaturated surface was also observed to reproducibly pump a hydrogen plasma to a concentration of 9.5×1017 H/cm2. The hydrogen retention capacity of graphite is found to decrease with increasing temperature. At temperatures between 450 and 480 °C, the hydrogen retention estimated for the activated surface and presaturated surface is 7.9×1017 and 2.7×1017 H/cm2, respectively. A transient pumping mechanism associated with the spongelike surface morphology is conjectured to explain the large hydrogen retention capacity. Hydrogen release behavior under helium and argon plasma bombardment was also investigated, and the result indicated the possibility of some in-pore retrapping effect. The effective plasma impact desorption cross sections are evaluated in the plasma bombarding energy range from 15 to 300 eV. A significant fraction (70%–80%) of preimplanted hydrogen was observed to release under inert gas plasma bombardment to a fluence of 6×1019 ions/cm2. The graphite surface, once saturated, can be reactivated via plasma-impact hydrogen desorption, regardless of the helium and argon bombarding energy in the range examined here.
A new method for the simultaneous condensation of complete ternary alloy systems under ultrahigh vacuum conditions
Authors: Mehrtens A. , Moske M. , Samwer K.
Published: July 2002

An ultrahigh vacuum apparatus is described for the simultaneous condensation of complete ternary alloy systems. Three singly controlled electron beam evaporation sources provide a constant evaporation rate of the different elements. A specially designed rotating mask guarantees a concentration gradient on the substrate according to a ternary phase diagram. The conversion of the actual concentration profile into a standard ternary phase diagram is done by simple computer calculations. They involve corrections for the beam characteristics of the evaporation sources and for the rotating mask. As an example, measurements for the Zr–Cu–Co system are given. The concentration range for the amorphous phase is compared with thermodynamic predictions using Miedema’s parameter.
A method of determining hydrogen in aluminum by removing surface gases with ion beam etching
Authors: Kato Y. , Kitamura T. , Isoyama E. , Hasegawa M. , Momose T. , Ishimaru H.
Published: July 2002

A method of determining gases after ion beam etching on aluminum surface has been tried to improve the present lower limit of determining hydrogen in aluminum. The present lower limit of determining internal hydrogen is 0.05 cm3/100 g Al STP. To improve the present lower limit, it is necessary to remove surface gases on aluminum. Carbon compounds and oxide film on aluminum were removed by neon ion beam etching on the dose of 2.8×1017 ions/cm2 or more. On the etched surface, no carbon and oxygen were observed using Auger electron spectroscopy. Determined hydrogen was 0.0055 cm3/100 g Al, about one-tenth of the lower limit by the traditional method.
Pthalimide on copper: A model system to address certain site-specific interactions at the polyimide–copper interface
Authors: Salaneck W. R. , Stafström S. , Brédas J.-L. , Andersson S. , Bodö P. , Kowalczyk S. P. , Ritsko J. J.
Published: July 2002

As a model molecule for a specific part of a polyimide, pthalimide has been studied adsorbed upon copper substrates at low temperatures using angle-dependent x-ray photoelectron spectroscopy. A stable adsorbate is found to exist in the approximate range −30 °C≤T≤−5 °C. The pthalimide molecule lies approximately flat upon the polycrystalline copper surface. Charge transfer from the copper to the adsorbate is observed. The present results are in contrast with those obtained when copper is vapor deposited upon a polyimide, as reported in the literature.
Issues in molecular-beam epitaxy kinetics of compound semiconductor based heterostructures
Authors: Singh Jasprit , Bajaj K. K.
Published: July 2002

We present a conceptual picture of the molecular-beam epitaxy growth of compound semiconductors and describe an atomistic computer simulation model developed to study growth. Key kinetics and thermodynamic parameters controlling growth quality and interface abruptness are discussed. The quality of the heterostructure is controlled by an intricate interplay of growth kinetics (growth rate, atomic evaporation, and most importantly atomic surface migration) and thermodynamics (bond strengths). This can lead to difficulty in growth of high-quality heterostructures from very dissimilar semiconductors. Potential role of novel growth approaches such as growth interruption, substrate temperature pulses, and laser enhanced kinetics in overcoming these difficulties will be discussed. Issues in nonlattice matched growth will be also examined and potential role of computer simulations in understanding dislocation formation during growth will be discussed.
Laser diagnostic techniques for reactive ion etching: Plasma understanding to process control
Authors: Selwyn Gary S.
Published: July 2002

Reactive ion etching is the current process of choice for production of high-speed integrated circuits; yet the development and use of this technology has evolved largely through empirical efforts. Beam/surface studies have proven instrumental in examining fundamental issues in etching; however, extension of these results to process plasmas requires considerable extrapolation. Laser diagnostic measurements may be used as a bridge between UHV measurements and the process plasma, a role which is possible due to the high specificity and sensitivity of these techniques. Spatially resolved laser studies provide three-dimensional in situ measurement of concentration gradients for reactive etchants and ions in the plasma. Key plasma etchants such as O and Cl may be studied using two-photon excitation processes. Finally, the emerging use of lasers for process control applications is discussed and compared with conventional approaches, such as optical emission end-point detection.
Automated system for measuring leak standards
Authors: Ball John M.
Published: July 2002

An inexpensive, automatic measurement system for standard leaks has been developed and tested. The principal of operation is pressure rise in a measurement chamber held at a low pressure. This design minimizes temperature effects, considerably improving performance over what would be achievable using a similar technique at atmospheric pressure. Provision is made for determining working measurement volume by expansion from a calibrated reference volume incorporated in the piping. Demonstrated operating range is ∼10−8–10−4 atm cm3/s (10−13–10−9 mol/s) regardless of the gas being used. The sensing element is an industrial grade capacitance diaphragm manometer. A very inexpensive home computer performs all control and calculations. The accuracy and performance of this system have been verified through comparison to other leak calibrators.
Space–time resolved kinetics of mixed rare-gas-attaching gas plasmas
Authors: Gottscho Richard A. , Scheller Geoffrey R. , Intrator Thomas , Graves David B.
Published: July 2002

Because plasma processing recipes are usually determined empirically, it is desirable to develop methods for isolating kinetic mechanisms in discharges through gas mixtures. In this manuscript, we show how space–time resolved measurements of plasma-induced emission and laser-induced fluorescence intensities are used to distinguish between electronic, ionic, and neutral mechanisms for excited-state production in radio frequency discharges containing Ar and BCl3. Although it was expected that the Ar metastable state would affect the degree of BCl3 dissociation, the mechanism uncovered using in situ diagnostics had not been considered previously: superelastic collisions between Ar metastables and electrons produce hot electrons capable of dissociating BCl3 more efficiently. By contrast, direct dissociative energy transfer from Ar metastables to BCl3 is unimportant. This mechanism leads to a narrow concentration range over which the dissociative excitation of BCl3 is increased tenfold relative to the pure BCl3 discharge.
Experimental and theoretical investigation of hydrogen diffusion on a metal surface
Authors: Felter T. E. , Stulen R. H. , Koszykowski M. L. , Gdowski G. E. , Garrett B.
Published: July 2002

We describe experimental and theoretical studies of hydrogen diffusion on metal surfaces. The experimental system is H/Pd(111) and we describe the utilization of low-energy electron diffraction in combination with electron stimulation of the surface by the incident beam to investigate surface diffusion. Electron stimulated desorption, as well as disordering are discussed with regard to the interpretation of the experiments. To study surface diffusion theoretically, variational transition state theory is employed. The system studied by this technique is H/Ni(111) and comparison to experiment is given.
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u spectroscopic erosion yield measurement with applications to sputtering and surface morphology alterations
Authors: Leung W. K. , Hirooka Y. , Conn R. W. , Goebel D. M. , Labombard B. , Nygren R.
Published: July 2002

An in situ spectroscopic erosion yield measurement is developed and used to monitor material surface erosion during bombardment by a plasma. The experiments are performed in a plasma that has the characteristics of a fusion tokamak boundary plasma but the technique is applicable to many processes where plasma erosion is important. Erosion yield of materials bombarded in a high flux (up to 1018 ion/cm2 s) plasma environment has been previously studied using weight loss measurements. In the present study, the sputtered flux from a material is monitored by the line emission intensities of atoms eroded from the surface. The line intensities can be used to infer erosion yields after proper calibration. The method agrees well with results from weight loss measurements. Earlier work established that the material surface structure can substantially influence the erosion yield. When a change of surface morphology (e.g., cone formation) occurs, weight loss methods cannot be used to determine the erosion yield. However, the in situ erosion measurement is suitable and is used to investigate the relation between the onset of morphology changes and alternations in erosion yield during plasma bombardment. Experiments are reported for copper, as an example of a pure material, and stainless steel, as an example of an alloy system. The formation of surface cones is observed only when both the sample temperature is above a critical value and surface impurities exist. If the source of impurities is removed, or the sample temperature is lowered below the critical value, a surface rough with cones will be returned to a smooth state.
Effects of Pt and Zr on the oxidation behavior of FeTbCo magneto-optic films: X-ray photoelectron spectroscopy
Authors: Majumdar Debasis , Hatwar T. K.
Published: July 2002

We report the effects of Pt and Zr on the oxidation behavior of FeTbCo magneto-optic films. The addition of 10 at. % Pt or Zr increased environmental stability without significantly affecting the magneto-optic properties. X-ray photoelectron spectroscopy was used to study in situ oxidation of clean FeTbCoPt and FeTbCoZr films under 5×10−7 Torr of oxygen at room temperature. Pt and Zr played different roles in increasing the oxidation resistance of the alloy. In the FeTbCoPt alloy, Pt reduced the oxygen uptake and retarded the oxidation kinetics of Fe. No oxidation of Pt was observed. In the FeTbCoZr alloy, Zr oxidized readily and segregated to the surface to form a protective layer. The Tb/Fe ratio at the surface increased with oxygen exposure in both alloys but at a faster rate in the FeTbCoPt alloy than in the FeTbCoZr alloy.
Buildup of ion implantation damage in Hg1−x CdxTe for various x values
Authors: Uzan-Saguy C. , Comedi D. , Richter V. , Kalish R. , Triboulet R.
Published: July 2002

The buildup of damage induced by In ion implantation into Hg1−x Cdx Te for various composition (x=0, x=0.24, x=0.4, x=0.7, and x=1) was measured by means of channeling Rutherford backscattering spectroscopy (RBS). Damage profiles were extracted from the spectra using a model based on Quere’s dechanneling treatment. Despite the large difference in bond nature and the related physical properties between the different compositions, the general trends in damage formation were found similar for all x values studied, though displaced by about two orders of magnitude in dose, HgTe damaging much easier than CdTe. For all compositions, different types of damage seem to be created at different stages during the implantation. The results can be understood if agglomeration of point defects to extended defects followed by a redistribution of the defects to deeper lying clusters with increasing dose is assumed.
Effects of thin interlayers on Ag/(HgCd)Te interface behavior
Authors: Davis G. D. , Beck W. A. , Kilday D. G. , McKinley J. T. , Margaritondo G.
Published: July 2002

The interactions between cleaved (HgCd)Te substrates and Ag overlayers with and without monolayer interlayers of Sb, Al, and Ti (unreactive, reactive, and ultrareactive metals, respectively) have been investigated with photoelectron spectroscopy using synchrotron radition. The Sb interlayer reduces, but does not eliminate, the indiffusion of Ag observed with no interlayer. In addition, a synergism between the Sb and the Ag allows a partial exchange reaction with the HgTe component to occur. Although the Al interlayer prevents Ag indiffusion in the very initial stages of deposition (0.2–0.5 nm), neither it nor the Ti interlayer reduces the indiffusion at higher coverages and little Ag accumulates at the surface.
Understanding of surface chemistry of III–V metalorganic chemical vapor deposition reactants
Authors: Lüth Hans
Published: July 2002

Beside molecular-beam epitaxy, metalorganic chemical vapor deposition (MOCVD) and metalorganic MBE (MOMBE) have developed into promising deposition techniques for the epitaxial growth of III–V semiconductor layer structures. In the latter two methods the layers are grown from gaseous starting materials, usually metal alkyls such as Ga(CH3)3, Ga(C2H5)3, etc., and hydrids such as AsH3, PH3, etc. The growth process on the wafer surface is determined by complex surface reactions, e.g., decomposition of the metalorganic, addition of hydrogen to an alkyl radical, etc. In the present paper results from growth studies in the MOMBE system as well as results from surface spectroscopic investigations on the adsorption behavior of MOCVD reactants are discussed with respect to a deeper understanding of the surface chemistry involved in MOMBE and MOCVD.
Temperature control of morphology and barrier formation at the In/GaAs(110) interface
Authors: Miyano K. E. , Cao R. , Kendelewicz T. , Lindau I. , Spicer W. E.
Published: July 2002

A photoemission spectroscopy study has been performed to investigate the 80 K low temperature (LT) to room temperature (RT) transition at the In/GaAs(110) interface. In/GaAs interfaces prepared at LT were slowly brought to RT while changes in overlayer morphology and band bending were observed via the Ga 3d and In 4d core level spectra. When several monolayers of In were deposited on LT p-GaAs and this interface was subsequently warmed to RT, the band bending increased from the high-coverage value of 0.5 eV to the 0.8 eV ‘‘overshoot’’ value that is seen at submonolayer coverages. From examination of the In 4d spectra, the In overlayer was found to cluster strongly upon warming, but In chemisorbed to the substrate remained between the clusters. The return of the overshoot that accompanies this In clustering may be explained by attributing the overshoot to states provided by the chemisorbed In. This reovershoot upon clustering further implies that the high-coverage pinning of the In/LT p-GaAs is due directly to the presence of the In overlayer rather than deposition-induced defects in the GaAs.
Angle-resolved photoelectron spectroscopy studies of surface alloying in Au/Cu(001)
Authors: Hansen J. C. , Tobin J. G.
Published: July 2002

We have performed an extensive angle-resolved photoelectron spectroscopy investigation of the surface-alloying phenomena in the system Au/Cu(001), utilizing resonance lamp emission and synchrotron radiation. The alloy surface state, near M̄ in the Cu(001) surface Brillouin zone, and the Au 4 f core levels exhibit significant binding-energy shifts as a function of adsorbate coverage and substrate temperature. These and other changes are indicative of the formation and subsequent elimination of the surface-alloy structure. Our new results will allow the consolidation of a vast body of previous results, including low-energy electron diffraction, Auger electron spectroscopy, and photoemission measurements of Au/Cu(001), bulk Cu1−x Aux alloys, Cu3 Au(001), and Au(111).
Epitaxial silicide interfaces: Fabrication and properties
Authors: Tung R. T.
Published: July 2002

The growth of single-crystal NiSi2 and CoSi2 thin films on silicon is briefly reviewed. Recent results concerning the growth of epitaxial CoSi2 on Si(111) are also included. Various growth models to explain the observed epitaxial orientations based on reaction kinetics and interface energetics are examined. Present experimental data of the Schottky barrier heights and atomic structures of epitaxial silicide interfaces will be discussed and compared with results from recent calculations.
Photon-stimulated desorption as a measure of surface electronic structure
Authors: Yarmoff J. A. , Joyce S. A.
Published: July 2002

The yield of ions desorbed via excitation of the Si 2p and F 1s levels was measured for fluorine adsorbed on Si(111). These photon-stimulated desorption (PSD) spectra were compared with the absorption measured via secondary or Auger electrons. It was seen that the PSD is dominated by direct excitations, and that the PSD spectra are sensitive to the final-state density at the local atomic site associated with the initial excitation. At the Si 2p edge, the PSD is sensitive to the oxidation state of the bonding silicon atom. At the F 1s edge, it is sensitive to the correspondence between the polarization vector of the incident light and the bond direction. Measurements of the kinetic energies of the desorbed ions were used to ascertain details of the desorption mechanism.
Metal/Al/Si contacts formed by eutectic rapid thermal melting
Authors: Katz A. , Komem Y.
Published: July 2002

Rapid thermal processing (RTP) of Ni(30 nm)/Al(10 nm)/Sin〈100〉 and Ti(30 nm)/Al(10 nm)/Sip〈100〉 at temperatures between 580 and 900 °C for 2 s resulted in the formation of unique contact structure due to an eutectic melting reaction initiated at the Al–Si interface. These contacts are in general composed Al compound layers on a metal silicide layer on the Si substrate and have a fairly smooth interface between the layers and the silicon. In the Ti/Al/Si system, the silicide layer of TiSi2 (45 nm thick) grew epitaxially. In both the Ni/Al/Si and Ti/Al/Si systems the Schottky barrier height and the sheet resistance of the layered structure were strongly affected by the eutectic melting due to the RTP at temperatures higher than 580 °C compared to RTP at temperatures lower than 580 °C, where solid-state reactions took place.
Photoemission and glancing-angle extended x-ray absorption fine-structure studies of vacuum-deposited Al/Cu bilayers
Authors: Di Marzio D. , Chen H. , Ruckman M. W. , Heald S. M.
Published: July 2002

The effects of oxygen exposure and substrate temperature on the structure and chemical composition of vacuum-deposited Al/Cu and Al/O2/Cu bilayers are studied using photoemission and glancing-angle extended x-ray absorption fine-structure (EXAFS) measurements. Use of these complementary techniques permits detailed atomic-level characterization of thin-film structure and chemical composition during thin-film deposition in vacuum or thin-film modification by heat treatment in air. In absence of oxygen contamination, photoemission indicates significant interfacial reaction at room temperature at the Al/Cu interface. Glancing-angle EXAFS shows that an Al-rich Cu–Al alloy forms at the interface at room temperature. Heat treatment promotes alloy formation and CuAl2 forms at temperatures from 120 to 150 °C. For interfaces formed after substrate oxygen exposure significant alloying is still observed and Al reduces the Cu–O substrate leading to the formation of Cu–Al and Al2O3 compounds at room temperature. Annealing the oxygen exposed interface leads to the formation of a CuAl2 phase but at higher temperatures than was observed for samples produced in ultrahigh vacuum.
CdTe/GaAs/Si substrates for HgCdTe photovoltaic detectors
Authors: Bean R. , Zanio K. , Ziegler J.
Published: July 2002

CdTe epitaxial films have been grown on GaAs on (100) silicon by congruent evaporation on CdTe in ultrahigh vacuum. The (100)CdTe orientation is strongly preferred in growth on (100)GaAs/Si, in contrast with the (111)CdTe preference on (100)GaAs substrates. Growth of the (111) orientation requires special processing. The (100)GaAs epilayer grows on misoriented (100)Si with a lattice tilt of ∼0.04° (back toward normal) for each degree of silicon misorientation. A similar lattice tilt in CdTe growth, in combination with the variable misorientation of the three-dimensional as-grown GaAs epilayer, is probably responsible for a mosaic structure in CdTe epilayers on GaAs/Si. In (111)CdTe layers, rotational twinning can occur on unpolished GaAs/Si. With increasing GaAs/Si misorientations, increasing numbers of (100) twin inclusions can also be found. Chemical polishing prior to CdTe growth eliminates the mosaic and twinning problems in most cases.
Pulsed laser induced effects on the HgCdTe surface
Authors: Afonso C. N. , Alonso M. , Neira J. L. H. , Sequeira A. D. , da Silva M. F. , Soares J. C.
Published: July 2002

Laser annealing of mercury cadmium telluride (MCT) is interesting from both physical and practical perspectives. We have investigated the behavior of nominal Hg1−xCdxTe(x=0.2) wafers under pulsed laser irradiation and analyzed the role of some of the laser beam parameters. Rutherford backscattering spectroscopy (RBS), auger sputter depth profiling (SDP), and scanning electron microscopy (SEM) have been used to achieve a general picture of the process and to characterize the compositional, morphological, and order–disorder changes produced by the laser irradiation. We report the first depth profiles of laser treated MCT by both RBS and Auger SDP techniques. Significant differences are found when compared with results for other annealing methods. A Te-rich layer is observed at the surface. The Hg deficient region is found a few tens of monolayers below the top of the surface with the maximum depletion at 18–30 nm. At this depth, small increases of Hg concentration are detected in the surrounding nonirradiated areas. Thermal and compositional changes are discussed taking into account that laser irradiation produces the melting of surface and near-surface regions and a consequent liquid phase epitaxial regrowth.
Cross-sectional transmission electron microscopy/electron beam induced current investigations on as-grown and hydrogen-passivated, gas-assisted solidified polycrystalline silicon
Authors: Chu C. H. , Sun C. Y. , Hwang H. L.
Published: July 2002

Gas-assisted-solidified (GAS) polycrystalline silicon was developed for low-cost solar cells. The as-grown and hydrogen-passivated samples were investigated by the electron beam induced current (EBIC) technique and cross-sectional transmission electron microscopy (XTEM). The shallow penetrated EBIC line profiles across the grain boundaries were used to monitor the effects of hydrogen passivation, and the results were correlated with those revealed by the XTEM. All the samples after hydrogen passivation have reduced EBIC line profile contrast and grain boundary recombination velocities. But the thickness of the damaged layer observed from XTEM is 100 and 200 nm for 10 and 60 min passivation, respectively. Dislocations, defect clusters, thin amorphous layers, planar cracks, and bubbles were observed in the hydrogen-passivated samples. The near surface damaged areas were investigated by the 15 keV electron beam and resulted in the reduction of minority carrier diffusion length.
Scanning tunneling microscopy of the intergrowth tungsten bronze Rb0.05WO3
Authors: Norton Michael L. , Mantovani J. G. , Warmack R. J.
Published: July 2002

The surface structure of the intergrowth tungsten bronze, Rb0.05 WO3 was imaged at nanometer scale resolution using a scanning tunneling microscope in air. The images are explained within the context of the crystallographic properties of the material.
Intercomparison of vacuum standards between the Physikalisch Technische Bundesanstalt (Germany) and the National Physical Laboratory (India) using two spinning rotor gauges
Authors: Sharma J. K. N. , Mohan Pardeep , Jitschin W. , Röhl P.
Published: July 2002

The paper describes the results of a comparison of low-pressure standards maintained at the National Physical Laboratory (NPL, India) and the Physikalisch Technische Bundesanstalt (PTB, FRG) over the range 10−3–2 Pa. The intercomparison was carried out by employing spinning rotor gauges shipped with a novel transport device. Both the laboratories, i.e., NPL and PTB, use static expansion systems for pressure generation. The gauge coefficients σ0,eff of the two gauges for Ar agree within ±0.5% for the two laboratories. This result proves agreement of the respective national standards in the above range of pressures. The small deviation of −0.4% between calibrations over a period of one year before and after air-parcel transportation from Berlin to New Delhi and back is indicative of a careful handling of the rotors during operation and a good performance of the employed transport device.
Hydrogen pressure measurement using the intensity of the light emitted from a Penning discharge
Authors: Ogiwara N. , Maeno M.
Published: July 2002

This paper describes a new method for using a Penning gauge to measure pressure in high magnetic fields. The intensity of the Hα and Hβ Balmer lines emitted from a Penning discharge is a function only of the discharge ion current and is independent of anode voltage and magnetic field from 0.1 to 2.0 T. The light intensity is proportional to the ion current below ∼0.1 Pa. The ratio of the light intensity to the ion current increases by 40% for pressures above ∼0.1 Pa because of a change in the type of discharge. The higher pressure discharge probably has a lower electron temperature.
Single-board computer low-energy electron diffraction intensity measuring apparatus
Authors: Shan Ye-liang , Liu Qing-hua , Lu Jia-ho , Cai Si-min
Published: July 2002

A very simple printed circuit board attached to a single-board microcomputer for low-energy electron diffraction (LEED) intensity measurement is developed. The principle and the block diagram are given. Some preliminary experimental results of I–E curves of Si(111)-(7×7) and V(100)-(2×2) are given. The angular profiles of the integral spot of Si(111)-(7×7) under different primary electron energies are given, from which the instrument response of our LEED gun is calculated.
Thermal annealing studies on boron-implanted HgCdTe diodes
Authors: Syz J. , Beck J. D. , Orent T. W. , Schaake H. F.
Published: July 2002

Junction profiles of B+-implanted Hg1−xCdxTe are examined using reverse bias capacitance–voltage measurements. All devices are fabricated on residual copper-doped, low vacancy concentration, p-type bulk material with a net doping of 1.5×1015 cm−3. The junction profiles showed the as-implanted junctions to be abrupt with one side of the junction doped in the low- to mid-1014 cm−3 range. These data and related circumstantial evidence are consistent with an n−/p junction after implantation. Type conversion in the immediate vicinity of the junction is postulated to result from indiffusion of interstitial Hg that is created by implant damage, the annihilation of group-II site vacancies by the Hg, and the associated movement of the highly mobile copper acceptor away from the low vacancy concentration region via an interstitial gettering mechanism. An immobile background donor concentration produces the n− region in the copper denuded region. During thermal anneal treatments, grading of the junction and improvement of the reverse-recovery lifetime was observed. The junction grading due to some anneals accounts for the markedly lower tunnel-limited leakage currents. Secondary ion mass spectrometry profiles show no movement of the boron away from the implant region. With previous information showing the damage region to be n+, it is concluded that the overall structure of the as-implanted and annealed junctions is n+/n−/p with the important junction properties determined by the n−/p region.
Interdiffusion, interfacial state formation, and band bending at metal/CdTe interfaces
Authors: Shaw J. L. , Viturro R. E. , Brillson L. J. , LaGraffe D.
Published: July 2002

We report the results of several complementary measurements which relate the Fermi-level position at metal/CdTe interfaces to bulk crystal quality, interdiffusion, and directly observed interface states. Defect states form at the Au/CdTe interface and move thousands of angstroms into the semiconductor. The presence of deep levels in the bulk correlates with the Au Schottky barrier heights measured for different CdTe crystals. We demonstrate control of interdiffusion, interfacial state formation, and band bending with a reactive interlayer.
Optical emission and mass spectroscopic studies of the gas phase during the deposition of SiO2 and a-Si:H by remote plasma-enhanced chemical vapor deposition
Authors: Tsu D. V. , Parsons G. N. , Lucovsky G. , Watkins M. W.
Published: July 2002

This paper will present mass spectrometric and optical emission spectroscopic studies of the deposition process of amorphous hydrogenated silicon (a-Si:H) and silicon dioxide (SiO2) by remote plasma-enhanced chemical vapor deposition (remote PECVD). We have established that the silane reactant, which is not directly exposed to a rf plasma in either of the deposition processes, is not fragmented or chemically combined in the gas phase. Specifically there is no evidence for the formation of disilane, Si2H6, or siloxanes or silanols in the gas phase, as in the direct PECVD process. In the case of the a-Si:H depositions, the silane is excited in the gas phase and the excited species, SiH*4 , is the deposition precursor. In the case of the SiO2 depositions, the active species promoting deposition is an O2 metastable neutral molecule. The by-products of the respective reactions are H2 and H2O.
Precursors for the deposition of amorphous silicon–hydrogen alloys by remote plasma enhanced chemical vapor deposition
Authors: Parsons G. N. , Tsu D. V. , Wang C. , Lucovsky G.
Published: July 2002

We have grown thin films of intrinsic and doped a-Si:H alloys by remote plasma enhanced chemical vapor deposition (remote PECVD) and studied their optical, electrical, and infrared vibrational properties. The electronic properties of remote PECVD films deposited at Ts =240 °C are similar to glow discharge (GD) films produced at the same Ts . Remote PECVD a-Si:H films deposited at Ts =100 °C show predominantly monohydride bonding in the infrared absorbance spectrum, and have electrical properties that are markedly improved over GD films deposited at this same relatively low Ts. We have studied the deposition process by mass spectrometry and optical emission spectroscopy and find that the concentration of silane fragments (SiHx, x=0–3) and higher silanes (e.g., disilane, Si2H6) in the gas phase is below our detection limit of 1%. Bias experiments and a comparison of the a-Si:H deposition rate with the known concentration of silane in the gas phase suggest that in remote PECVD, electrons from the He plasma produce vibrationally excited silane molecules (as opposed to silane fragments) in the gas phase or on the deposition surface which then act as the precursors for the a-Si:H thin-film deposition reactions.
A modified technique for the production of Al2O3 by direct current reactive magnetron sputtering
Authors: Pang T. M. , Scherer M. , Heinz B. , Williams C. , Chaput G. N.
Published: July 2002

Current technology permits the deposition of Al2O3 films up to a few tens of microns thick at low temperature, only after several hours. To this end, a modified technique for the production of films by dc reactive magnetron sputtering is presented focused on a combined hard and software approach using the principle of separation of the reactive gas feed from the target gas region. Results obtained from this are reported in the context of the hysteresis effect associated with such deposition processes. The applicability of this approach is extended to the deposition of other nonconducting materials. Film properties such as adhesion, optical absorption, hardness, and composition are presented and compared to those for Al2O3 produced by rf diode and rf magnetron sputtering. Deposition rate and process performance are also given for all techniques. The suitability of the material to magnetic head applications is also discussed.
Monte Carlo simulations of phase separation during growth of semiconductor alloys
Authors: Kaspi R. , Barnett S. A.
Published: July 2002

Monte Carlo simulations have been used to study the vapor phase growth of semiconductor alloys characterized by solid-phase miscibility gaps. Alloy phase separation occurred by a surface spinodal decomposition mechanism resulting in composition modulations in the plane of the film with a period of 2 to 5 nm. Decomposition was observed mainly within the spinodal region, but composition fluctuations persisted outside the spinodal. The amplitude of the composition modulations increased with increasing alloy interaction parameter but was kinetically limited over most of the parameter space investigated. This was indicated by the increased decomposition observed upon increasing the growth temperature T or decreasing the growth rate R. A strong dependence of decomposition on the surface reconstruction of the growing alloy films was also observed. In particular, stable surface dimers acted as traps for diffusing surface atoms, reducing the diffusion length and strongly limiting decomposition. Methods for minimizing decomposition are discussed.
Crystal structures and optical properties of ZnO films prepared by sputtering-type electron cyclotron resonance microwave plasma
Authors: Matsuoka Morito , Ono Ken’ichi
Published: July 2002

This paper describes the crystal structure and photochromism of Zn oxide films fabricated by sputtering-type electron cyclotron resonance microwave plasma. C-plane preferential orientation and (101) plane preferential orientation are achieved in Zn oxide films deposited on glass substrates below 200 °C. These films have strong crystallite orientation. Films with (101) plane orientation exhibit typical photochromic characteristics induced by x-ray irradiation. Photochromism is probably caused by a color center, that is, the oxygen vacancy in Zn oxide films. The absorption center exists in an energy range of 1.5 to 4 eV. The activation energy in the fading process is ∼0.03 eV.
Ion beam milling of pyroelectric ceramics for advanced thermal detector arrays
Authors: Bache R. A. C. , O’Hara C. , Parsons A. D. , Shorrocks N. M. , Pedder D. J.
Published: July 2002

Imaging thermal detector arrays are currently being developed with large pixel counts at fine pitch. One major cause of image degradation in such arrays is by lateral thermal spread within the pyroelectric ceramic wafer on which the sensing array is defined. This paper discusses the use of ion beam milling to create thermal breaks between adjacent elements, significantly improving the modulation transfer function of the array. Masking techniques, etch rates, and pattern transfer characteristics are described. The effects of the ion milling conditions upon the chemical composition and electric resistivity of pyroelectric ceramic surfaces are described and discussed in the context of thermal detector array applications. The use of broad-beam ion milling to thin pyroelectric ceramic wafers with minimal surface damage is also briefly described.
Some aspects of adsorption, diffusion, and thermal desorption properties of a La–Mo system
Authors: Sreenivasa Rao G. , Dharmadhikari C. V. , Nigavekar A. S.
Published: July 2002

Thin films of lanthanum on polycrystalline molybdenum surfaces have been investigated using a variety of techniques such as the Auger electron spectroscopy (AES)–Ar+ sputtering combination, quadrupole mass spectrometry (QMS), neutron activation analysis (NAA), small-angle x-ray diffraction (SAXRD), field emission microscopy (FEM), and scanning electron microscopy (SEM) with a view of understanding the interaction in a La–Mo system. The experiments with AES consisted of evaporating La from a LaB6 source onto polycrystalline Mo and heating it at different temperatures. The variation of adsorbate (substrate) signal as a function of surface coverage suggests that the growth at room temperature takes place in the form of clusters. FEM and SEM investigations of these films suggest cluster sizes of 35- to 100-Å diameter with average spacings of the same order. Annealing of thick (∼35 Å) films at 400 K for 30 s results in redistribution leading to uniform thickness of La. Further heating of the same at higher temperatures caused considerable penetration of La into Mo. The detailed analysis of depth profiles in the temperature range 800–1300 K indicated that this could be attributed to both bulk and grain boundary diffusion. The temperature dependence of diffusion coefficients in this temperature range could be expressed by the following equations: Db=1.9×10−8 exp(−1.7/kBT) and Dgb=1.2×10−6 exp(−1.07/kBT), where Db,Dgb correspond to the bulk and grain boundary diffusion coefficients and kB, the Boltzmann constant. Further heating of these films at still higher temperatures resulted in depletion of La. Isothermal desorption studies in the temperature range 1673–1913 K yielded values of 3.8 eV and 109 s−1 for the activation energy of desorption and the prefactor, respectively. The low value of prefactor suggested a complex desorption mechanism involving a surface precursor molecule with a very low degree of freedom as compared to a single atom adsorbed on the

surface. The diffusion and desorption are compared with available relevant information by other techniques. The evaporation kinetics of the blue colored LaB6 compound which constituted La source in our work has also been investigated and existing controversy in this field has been critically but briefly reviewed. The results are believed to be important in the context of development of La–Mo cathodes.
Growth of PbTe/Pb1−xMnxTe quantum well structures by molecular-beam epitaxy
Authors: Clemens H. , Weilguni P. C. , Stromberger U. , Bauer G.
Published: July 2002

PbTe/Pb1−xMnxTe (x≤0.03) structures were grown from PbTe, Te, and Mn sources with in situ control of the growth mode using reflection high energy electron diffraction. As a substrate material cleaved (111) oriented BaF2 was used. The period of multiquantum well structures was determined by high–angle x-ray diffraction patterns. Mobilities in excess of 2×104 cm2/Vs were observed at temperatures T>30 K.
Thermally stimulated exoelectron emission from glass deposited on metal by argon plasma treatment
Authors: Momose Y. , Takahashi H.
Published: July 2002

Argon plasma treatment of gold metal in a glass reactor deposited silicon oxide originating from the reactor on the metal surface. The deposited silicon oxide was nonstoichiometric and had a strong exoelectron emission activity. The chemical and structural nature of the emitting centers has been investigated. The thermally stimulated exoelectron emission (TSEE) glow curves for the surfaces exhibited one strong emission peak at ∼170 °C (in a few cases, three peaks at ∼120, 190, and 240 °C ) with increasing temperature. The intensity of the TSEE peak appearing at 170–190 °C varied in parallel to the atomic ratio of Si2p/O1s obtained by x-ray photoelectron spectroscopy as a function of operational parameters in the plasma treatment. The TSEE peak intensity increased with an increase in the ratio of Si2p/O1s. The emitting centers for the TSEE peak can be related to electron trapping sites located in the neighborhood of the oxygen-deficient silicon atoms deposited on the metal surface.
Spontaneous decomposition of dimethyl gold hexafluoroacetylacetonate on ion bombarded surfaces
Authors: Kirch S. J. , Wagner A.
Published: July 2002

Aluminum and gold coated quartz crystal oscillators were bombarded by 7 keV Ga+ and then exposed to fairly low pressures (∼1 mTorr) of dimethyl gold hexafluoroacetylacetonate [denoted Me2Au(hfac) ] at room temperature for several hours. While unirradiated crystals exhibit a mass increase corresponding to approximately one monolayer of Me2Au(hfac), irradiated crystals accumulate significantly more mass. Typically, the accumulated mass on the irradiated surfaces corresponds to a film of gold several hundred angstroms thick. Thus, simple condensation of the organometallic molecules cannot explain the large mass increase. Rather it suggests that spontaneous decomposition of the Me2Au(hfac) is occurring on the irradiated surface. X-ray photoelectron spectroscopy indicates that the deposited mass is essentially pure gold. Rutherford backscattering spectroscopy indicates that as many as 20 Au atoms are deposited for each implanted Ga atom. Surfaces irradiated with Au ions show much less mass accumulation, but some growth still occurs. These results indicate that two processes contribute to film growth during ion induced deposition: ion decomposition plus the spontaneous decomposition described here.
A model for simultaneous reactive sputtering, etching, and chemical vapor deposition
Authors: Koss V. A. , Vossen J. L.
Published: July 2002

The model of reactive sputtering of Berg [T. Larsson, C. Nender, and H.-O. Blom, J. Appl. Phys. 63, 887 (1988)] was extended to include chemical reactions on target and substrate due to an additional reactive gas (etchant). The model explains both the increased deposition rate of the oxides under some conditions and decreased deposition rate under others.
A 20–350 K variable-temperature sample holder with sample interchangeability
Authors: Vitomirov I. M. , Aldao C. M. , Waddill G. D. , Weaver J. H.
Published: July 2002

A simple design is presented for an ultrahigh-vacuum-compatible sample holder capable of maintaining temperatures between 20 K and ∼350 K. The design involves a copper sample holder (tank) mounted on a closed-cycle He refrigerator. Mechanical, thermal, and electrical contact between the sample and the tank is obtained by melting and resolidifying Ga in a recess in the tank. Temperature regulation is achieved through simultaneous action of the cold stage and a filament heater attached to the tank. This allows in situ sample exchange without compromise of ultimate vacuum or temperature.
Optical properties of electron-beam evaporated TiO2 films deposited in an ionized oxygen medium
Authors: Rao K. Narashimha , Mohan S.
Published: July 2002

Optical absorption in TiO2 films depends upon starting material and deposition conditions. The influence of the combined effect of substrate temperature and ionized oxygen on the optical properties of TiO2 films deposited by reactive electron beam evaporation of TiO is presented. The ionized oxygen medium reduced the absorption in films considerably. The substrate temperature has only marginal influence on the extinction coefficient of these films. The influence of film thickness on the optical properties of TiO2 films is also studied. The variation in optical properties of TiO2 films has been explained on the basis of enhanced reactivity of oxygen and the decrease of the condensation coefficient of reacting species at elevated substrate temperature.