bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygen monitors for aluminum and Al–O thin films
Authors: Faith T. J. , Irven R. S. , O’Neill J. J. , Tams F. J.
Published: July 2002

Methods for detecting increases in oxygen concentration in aluminum-based integrated-circuit (IC) metallizations through increases in monitor-film resistivity have been developed. Since the resistivity of the IC film is itself not sensitive to small changes in oxygen concentration, monitor configurations were designed such that the ratio of oxygen-species to aluminum-atom flux on the monitor substrate was many times higher than that on the IC substrates. This resulted in a higher oxygen concentration in the monitor films and a stronger dependence of film resistivity on system oxygen concentration. Monitors were tested in an E-beam evaporator and in an S-Gun magnetron sputtering system during the deposition of aluminum films in a residual-gas environment, and during the deposition of Al–O films deposited with oxygen inputs to the system. Enhancement of the oxygen to aluminum flux ratio was accomplished by shuttering or canting the monitor substrate to decrease the aluminum flux, or by placing it close to the oxygen inlet (in Al–O depositions) to increase the oxygen flux. Monitor resistivity vs flux ratio curves from Al–O depositions have demonstrated the reproducibility of Al–O films and of the oxygen input process. Corresponding curves from residual-gas-only depositions have detected differences in film oxygen concentrations which could not have been detected from pressure measurements.
Mismatch dislocation dangling bond distributions at zinc blende and wurtzite interfaces
Authors: Jones K. A.
Published: July 2002

The dangling bond structures for the ideal mismatch dislocations in zinc blende films growing on (001), (110), and (111) and wurtzite films growing on (0001), (112̄0), and (101̄0) oriented substrates are described. Where possible, the ideal dislocation structure is compared to the experimentally observed structure. The crystallographic structure of the (1/6)[1̄21̄](111) and (1/6)[2̄11](111) partial dislocations which together form the (1/2)[1̄10](111) 60 ° dislocation, and the wurtzite–zinc blende interface across the (001)/(3̄034), (110)/(303̄8), and (111)/(0001) interfaces are described. It is suggested that deciphering the electronic properties of the (1/2)[1̄10](111)≡(1/3)[1̄21̄0](0001) 60 ° dislocation dangling bonds would be more straightforward in wurtzite films since there are no intersecting slip planes, and the dislocation does not decompose into partials. Also, a number of experiments are described which could help in the understanding of the different electronic effects produced by the different types of dangling bond configurations.
Scanning microbeam using a liquid metal ion source
Authors: Ishitani T. , Tamura H. , Todokoro H.
Published: July 2002

A scanning ion microprobe system using a liquid-Ga ion source and a voltage-asymmetric three-electrode lens is developed. It produces 2–20 keV Ga+ beams of 0.1–5 μm diameter with 20 pA–8 nA current. Beam sizes are directly measured by a combined sharp-edge and Faraday cup mehtod. This optical system is well suited for variable energy microprobe applications.
SAM studies on high-temperature annealing of vanadium thin films on oxidized silicon wafers
Authors: Chen Jiann-Ruey , Sung Chia-Pin , Yeh Fon-Shan , Liu Yuen-Chung , Wang Chikuang C.
Published: July 2002

Vanadium thin films were deposited on oxidized silicon wafers. Their solid-state reactions were studied by scanning Auger microscopy (SAM). It was found that when annealing at temperatures above 1000 °C, concentric ring structures were observed on the surface. These ring structures consist of circular grooves with shallow depth all the way to the substrate Si. Between the circular grooves, vanadium silicides composed mostly of VSi2 were formed from the reactions between the V thin film and the oxidized Si substrate.
Unique design of Doublet and Big Dee vacuum vessels
Authors: Miller J. E.
Published: July 2002

The Doublet III tokamak now in its fourth year of operation at General Atomic Company, has its plasma contained in a kidney-shaped toroidal vacuum vessel, a configuration that presented unique design challenges. Most tokamak vacuum vessels are constructed of solid walled sections separated by either thin walled bellows (to increase the toroidal resistance) or by poloidal insulation breaks. Such control of the toroidal resistance is crucial in minimizing magnetic error fields in the plasma region caused by currents induced in the vessel by the changing fields. The Doublet III vessel is unique in its all-welded construction consisting of thin skins over a corrugated center. Such a construction results in a low cross sectional area of material to increase the toroidal resistance, while maintaining adequate strength. The design process for such a vessel is reviewed with a description of its design. In order to more closely address the design issues of next generation devices, plans are being formulated to modify Doublet III to a large Dee-shaped plasma facility. This would be accomplished by disassembling the device and replacing the Doublet vessel with a large Dee vessel. The design approach for the new vessel will be similar to that of the present vessel, but because of different operating requirements and experience gained in the operation of Doublet III and other large tokamaks, the specific design criteria are different. These differences and their implications are reviewed.
Hydrogen–deuterium changeover experiments in a plasma-wall interaction simulator
Authors: Clausing R. E. , Heatherly L. , Emerson L. C.
Published: July 2002

Hydrogen recycling from walls and limiters of tokamaks constitutes the major source of plasma particles after the initial few milliseconds of a plasma pulse. The physical processes involved in recycling are thus very important to the control of plasma density and composition. Isotope changeover experiments in the laboratory show that thermally activated processes such as recombination and diffusion play significant roles in recycling. These processes are important not only during the plasma pulse but also continue after the plasma pulse ends, thus the length of time between pulses, the wall temperature, and the vacuum pumping rate all influence changeover dynamics. This paper shows that for type 304 stainless steel walls changeover can range from ≳95% to <50% complete in one 200 ms pulse depending upon these parameters. The initial part of changeover during a plasma pulse is very rapid and involves equilibrating the isotopic compositions of the plasma reservoir and the near-surface wall hydrogen reservoir involved in recycling. The rate limiting step then seems to become vacuum pump-out rates. Because one of the steps in gas evolution during and after the pulse is the recombination process, which is dependent on the square of the surface hydrogenic concentration, changeover can be accelerated if the hydrogenic concentration at the surface is kept high by repeated plasma pulses in the new isotope. The old isotope is evolved as HD.
High rate deposition of uniformly thick wear-resistant films onto spherical surfaces
Authors: Schlossman G.
Published: July 2002

A method for depositing thin wear-resistant films onto spherical substrates is explained. Development of the technique is summarized including description of a special wear test on flats which simulates the spherical closed tribosystem. A unique sputtering machine designed to achieve uniform coatings on spheres and spherical cavities is also discussed.
CdS–Cu interface formation: A microscopic study of the interdiffusion and chemical processes
Authors: Stoffel N. G. , Daniels R. R. , Margaritondo G. , Brucker C. F. , Brillson L. J.
Published: July 2002

The interdiffusion and chemical processes during the in situ (pressure in the 10−10 Torr range) deposition of Cu on cleaved CdS (112̄0) were investigated by soft-x-ray photoemission spectroscopy. The extreme surface sensitivity of this technique enabled us to improve the understanding of the interface structure with respect to previous investigations. The Cu overlayer attenuated the Cd 4d and S 2p core-level intensity at a rate incompatible with the formation of a sharp interface. The measured Cd 4d/S 2p intensity ratio was consistent with stoichiometry changes not in excess of 10% during Cu deposition. The Cd 4d peak, however, gradually shifted from its bound-Cd energy position to a free-Cd position. These data point to the formation of the interface in two distinct chemical stages, a first stage in which a Cu-S compound is formed which involves the appearance of an increasing proportion of dissociated Cd and a second stage in which islands of metallic Cu begin to form. S 2p partial-yield data support this interpretation. This extended interface exhibits dielectric properties significantly different from those of CdS and therefore it can play a central role in the Schottky barrier formation.
Planar channeling of ions in compound semiconductor superlattices
Authors: Barrett John H.
Published: July 2002

Computer simulations have been done to show how planar channeling of high-energy ions in compound semiconductor superlattices offers a further means of studying structure at the interfaces in these materials. Such a technique will supplement earlier work with axial channeling concerning offsets at the interfaces in rows of atoms inclined to the surface normal. The method involves having the interface at a depth of 10–20 nm and adjusting the ion energy so that the ions travel about one quarter wavelength in reaching the interface. The tilt angle of the beam relative to the planar channel can be varied to sweep the beam across the channel and make a precise determination of the offset position. This procedure can provide a confirmation of the offset and a more accurate determination of its size.
Valence band and core lines investigation on the Ge–Au system by photoelectron spectroscopy with synchrotron radiation
Authors: Perfetti P. , Katnani A. D. , Zhao Te-Xiu , Margaritondo G. , Bisi O. , Calandra C.
Published: July 2002

Core level and valence band photoemission experiments coupled to theoretical calculations reveal the formation of a stoichiometric Ge–Au phase during gold deposition onto Ge(111) at room temperature. This result is significantly different with respect to that found for the Si–Au system.
Thermal removal of surface carbon from GaAs substrate used in molecular beam epitaxy
Authors: Chang Chin-An
Published: July 2002

Chemical etching of GaAs substrates followed by deionized-water rinsing and loading to a molecular beam epitaxy chamber always leaves carbon contamination on the substrate surface. Auger analysis shows that an extensive exposure of the substrate to the Auger beam, especially during the initial substrate heating process below ∠350 °C, strengthens the bonding between surface carbon and the substrate which makes subsequent thermal removal of surface carbon above ∠350 °C very difficult. The effect of substrate surface cleanliness on the initial growth of GaAs is also studied using high-energy electron diffraction.
First phase nickel silicide nucleation and interface structure at Si(100) surfaces
Authors: Chang Yu-Jeng , Erskine J. L.
Published: July 2002

Photoemission and work function measurements are used to investigate the formation and structure of Ni–Si(100) interfaces at 300 K. For Ni coverages θ≲0.5 Å (4.6×1014/cm2) a chemisorbed phase of Ni surface atoms forms. This chemisorbed phase persists to coverages θ≂2 Å; but also in this coverage range, a diffusion layer forms in the Si lattice. At θ≊1.5 Å the surface composition closely resembles NiSi. Addition of more Ni atoms (θ≥1.5 Å) initiates nucleation of Ni2Si. The growth of this phase continues up to θ≊1.5 Å where silicide formation stops. Additional Ni atoms deposit as a pure Ni overlayer. These results yield a model for Ni–Si interfaces formed at room temperature which consists of a shallow diffusion layer of Ni atoms in the Si lattice, a very thin (1.5-Å thick) interface having NiSi chemical characteristics, a Ni2Si phase (15-Å thick) of relatively uniform stoichiometry followed by a Ni layer.
Plasma edge studies using carbon resistance probes
Authors: Wampler W. R. , Manos D. M.
Published: July 2002

A new experimental technique, the resistance probe, was used to study the plasma edge in the PLT and PDX tokamaks. This technique involves measuring the change in resistance of a thin carbon film due to bombardment by energetic particles escaping the plasma. The probes have been calibrated by measuring the resistance change caused by implantation of various ions at different energies. A model has been developed which can be used to determine the flux and energy of the incident particles from the measured resistance changes. For probes exposed in PDX and PLT near the wall, resistance changes were observed due to charge exchange neutrals. Larger changes were observed in the ion scrape-off region closer to the plasma. In PLT the effect of ions at the plasma edge begins to dominate the neutral flux near the radius of the ring limiter. The energy of ions at the plasma edge was estimated to be low (≲100 eV) in PDX during neutral beam-heated discharges, but higher (≳300 eV) in PLT during ion cyclotron resonance heating.
The far UV emission spectrum of H2
Authors: Terry J. L.
Published: July 2002

A detailed, quantitative model is constructed to describe excitation of the B 1Σ+u and a 3Σ+g states in molecular hydrogen by thermal electrons with 1 eV<Te<10eV and densities <1015 cm−3. The resulting radiative decay is also quantitatively modeled, and synthetic far UV spectra are produced. These synthetic spectra are compared with measured laboratory spectra from three sources, one of which is the high temperature discharge of the Alcator C tokamak. The agreement is quite good. A cross section of 1×10−18 (Eth/E)2 cm2 is deduced for electron excitation from X 1Σ+g to a 3Σ+g.
Perturbation of tokamak edge plasma by laser blow-off impurity injection
Authors: Budny R. , Cavallo A. , Cohen S. , Daughney C. , Efthimion P. , Fonck R. , Hulse R. , Hwang D. , Manos D. , Pecquet A-L. , Ruzic D. , Schivell J. , Smith B. , Yelle R.
Published: July 2002

We describe measurements of tokamak edge plasma perturbations caused by rapid injection of impurities such as Sc, Fe, and Mo into Ohmically heated PLT discharges. The temporal evolution of the radiated power, convected power, charge-exchange neutral flux, electron temperature, density, and floating potentials were monitored using recently developed fast bolometers, directional calorimeters, and other diagnostics. The central radiated power can be doubled without plasma disruptions. Radiation from the edge then increases tenfold for ∼2 ms. Neutral efflux at the limiter decreases up to two orders of magnitude for approximately 20 ms after injection. The electrical potential of the limiters increases, approaching the potential of the vacuum vessel. MHD activity in the m=1 (sawtooth) mode tends to increase while that in the m=2 and m=3 modes decreases. The power flowing along field lines in the limiter shadow region sometimes increases or sometimes decreases by more than a factor of 4. The density and electron temperature in the limiter shadow region, generally, does not change more than 50%.
Structural properties of titanium dioxide films deposited in an rf glow discharge
Authors: Williams L. M. , Hess D. W.
Published: July 2002

An rf glow discharge has been used to promote the reaction between titanium tetrachloride and oxygen in order to deposit thin films of titanium dioxide at low temperatures. Structural properties of the films have been studied as functions of deposition temperature (25 to 700 °C) and of substrate material (Si, sapphire, glass, NaCl, and Ti). Films deposited onto glass substrates were amorphous at temperatures less than 300 °C, anatase at 300 and 400 °C, a mixture of anatase and rutile at 500 °C, and only rutile at 600 °C and above. Films deposited on the other substrates showed similar behavior but the temperatures for specific crystalline forms differed for each substrate material. Deposition at low power densities and 400 °C resulted in large (∼5 μm) anatase crystallites in 1–2 μm films.
Photodesorption studies of CO2 from an oxygen-saturated silicon(100) surface
Authors: Van Hieu Nguyen , Lichtman David
Published: July 2002

Photodesorption from an oxygen-saturated silicon(100) surface was studied with photons of wavelength 250–1100 nm. The desorbing species were monitored with a mass spectrometer over the mass range of 2 (H2) to 44 (CO2). Only CO2 was observed to desorb with a threshold value of ∼2.76 eV, and the desorbing signal was linearly dependent on the incident photon intensity. Perhaps most important, the photodesorption activity decreases markedly with the controlled decrease of surface impurity carbon content.
Core electron energy loss spectroscopy of cerium: Surface oxidation
Authors: Strasser Gregor , Netzer Falko P.
Published: July 2002

Core electron excitations of clean Ce and of Ce exposed to varying amounts of oxygen and H2O have been studied by electron energy loss spectroscopy (ELS) in reflection geometry. The valence change of Ce atoms during surface oxidation with oxygen is well reflected in ELS of core levels. 4d→4f excitations provide the best spectral fingerprint of the valence state, but 3d→4f and 4p→5d excitations also show spectral modifications which can be correlated to the change in f count. The spectral profiles of core level excitations of a CeO2-like oxide phase are discussed in terms of screening effects on the core hole–excited electron final states.
Vacuum double crystal x-ray monochromator for synchrotron and related uses
Authors: Crider C. A.
Published: July 2002

A full featured, versatile double crystal x-ray monochromator using the Golovchenko–Levesque–Cowan1 scheme has been developed to operate in near UHV conditions. The vacuum requirements arise from the use of the monochromator at low x-ray energies in synchrotron beamline applications. The feedback stabilized instrument can scan Bragg angles from 6° to 68° [2.13 to 16.3 keV using Si(111) crystals]; the scan can be effected without losing lock. The instrument’s features include an incremental encoder with absolute indexing, four stepping motor driven alignment adjustments, cooled crystal holders, and a piezo pusher, all operating in vacuum. The complete instrument achieves 6×10−8 Torr after a mild 100 °C bakeout. This vacuum x-ray monochromator will be useful in other areas such as plasma diagnostics and x-ray laser studies. The in-vacuum stepper motors developed for the monochromator can solve a wide variety of motion in vacuum problems; the effects of operating parameters on mechanical and vacuum performance have been investigated and guidelines for sensible driving electronics have been developed. Optical test data taken with the monochromator will be presented.
Micromechanical investigations of amorphous hydrogenated carbon films on silicon
Authors: Pethica J. B. , Koidl P. , Gobrecht J. , Schüler C.
Published: July 2002

Amorphous hydrogen containing carbon films (α-C:H) can be obtained on various substrates by exposure to an rf-glow discharge in a low pressure hydrocarbon atmosphere. The films show interesting optical and mechanical properties and are thus attractive candidates for hard and wear resistant coatings. In this paper results of microhardness measurements on thin (0.8 μm) α-C:H films are presented which were taken with a specially designed microhardness tester which allows indentation depth as low as 50 nm. In this way the influence of the substrate on the hardness results can be minimized. A large influence of the film deposition parameters was found. The hardness of films deposited under high dc bias voltage (>1000 V) is comparable to or better than that of bulk silicon. Heat treatment of the films above 350 °C decreases the hardness significantly. The elastic properties of α-C:H may be estimated using the elastic relaxation of the indents.
Energy and material dependence of the inelastic mean free path of low-energy electrons in solids
Authors: Powell C. J.
Published: July 2002

Calculations have been made of the inelastic mean free paths (IMFP’s) of 100–2000-eV electrons in C, Mg, Al, Al2O3, Cu, Ag, Au, and Bi. These calculations have been based on experimental optical data and on theory. The optical data gives the dependence of the differential inelastic scattering cross section at zero momentum transfer on electron energy loss; the data used here satisfy optical sum rules closely. Theory is needed to specify the dependence of the differential inelastic scattering cross section on momentum transfer; results for free-electron-like solids were assumed to be applicable to the present materials. The calculated IMFP’s show significant deviations from the dependencies on electron energy and material expected from the formulas of Seah and Dench, Szajman et al., and Ashley.
Plasma modeling of MFTF-B and the sensitivity to vacuum conditions
Authors: Porter G. D , Rensink M.
Published: July 2002

The tandem mirror machine, MFTF-B, is scheduled to begin operation early in 1987. We have developed a time-dependent plasma-modeling code to examine the expected operating parameters. Using this code, we studied the effect of vacuum conditions on the plasma in each region of the machine. In particular, this study specified the vacuum requirements to which the machine is being designed. We will present the details of our study together with the current design of the vacuum system.
THM, a breakthrough in Hg1−xCdxTe bulk metallurgy
Authors: Triboulet R. , Duy T. Nguyen , Durand A.
Published: July 2002

After a short review of the different methods of Hg1−xCdxTe bulk crystal growth, the travelling heater method (THM) is presented as a method which allows reaching a steady state, charge purification, and growing oriented crystals. Ingots of 30 mm diam and 80 mm in length are currently produced with a longitudinal homogeneity better than ±0.02 mol and a radial homogeneity better than ±0.002 mol for different x. Electron concentrations of 2×1014 cm−3 with mobilities of 160 000 cm2/Vs at 77 K, for crystals with x=0.21, among other typical characteristics, as well as significant characteristics of photoconductor and photovoltaic detectors, such as R0A products of 16 Ω×cm2 at 77 K for λ=10.5 μm, and 105 Ω×cm2 at 300 K for λ=1.4 μm, attest to the high quality of the grown crystals.
Planarization by radio-frequency bias sputtering of aluminum as studied experimentally and by computer simulation
Authors: Bader H. P. , Lardon M. A.
Published: July 2002

Aluminum was deposited on silicon grooves with an aspect ratio (depth/width) of 0.27 ⋅ ⋅ ⋅ 0.5 by rf sputtering with substrate bias leading to the planarization of the silicon structure. This process was also studied by computer simulation. Excellent agreement between experimental and simulated profiles was achieved. The simulation makes it possible to study the influence of single parameters (redeposition and ion energy) on profile evolution separately, which cannot be done experimentally.
Microcellular foams via phase separation
Authors: Young Ainslie T.
Published: July 2002

A study of wide variety of processes for making plastic foams shows that phase separation processes for polymers from solutions offer the most viable methods for obtaining rigid plastic foams which meet the physical requirements for fusion target designs. Four general phase separation methods have been shown to give polymer foams with densities less than 0.1 g/cm3 and cell sizes of 30 μm or less. These methods involve the utilization of nonsolvent, chemical or thermal cooling processes to achieve a controlled phase separation. Two distinct phases are obtained where either the polymer phase is a continuous phase or two bicontinuous phases are obtained where both the polymer and solvent are interpenetrating, continuous, labyrinthine phases. Subsequent removal of the solvent gives the final foam structure.
Bias-induced stress transitions in sputtered TiN films
Authors: Kattelus H. P. , Tandon J. L. , Sala C. , Nicolet M.-A.
Published: July 2002

We report on intrinsic stress properties of magnetron sputtered titanium nitride films deposited under different conditions. By proper selection of processing parameters, films with low stress can be obtained. Unstressed film formation is favored by low substrate bias voltage, high pressure, or use of heavy sputtering gases. Stress relief is, however, accompanied by an increase in resistivity and a decrease in film density. As a result of these changes the effectiveness of such titanium nitride films as diffusion barriers between silicon and aluminum is minimal.
Recent advances in sputter depth profiling
Authors: Wittmaack K.
Published: July 2002

This paper summarizes some of the advances recently made with respect to beam-induced broadening effects in sputter depth profiling. It is shown that research carried out by different groups has led to a significantly improved understanding of the relevance of the various experimental parameters, i.e., the energy of the probing beam, the angle of incidence, the crystalline structure, and the temperature of the sample, as well as the chemistry of the near-surface region.
Surface differential reflectivity spectroscopy of semiconductor surfaces
Authors: Selci S. , Ciccacci F. , Chiarotti G. , Chiaradia P. , Cricenti A.
Published: July 2002

An overview of the method of surface differential reflectivity (SDR) for the study of semiconductor surfaces is presented. This includes the principles of the technique, the experimental apparatus, and some theoretical considerations concerning the connection of SDR data with the microscopic properties of the surface. Experimental results are also presented as an example of the application of this spectroscopy to the study of semiconductor surfaces.
An evaluation of outgassing from titanium–molybdenum alloy wire
Authors: Hu Y. Z.
Published: July 2002

Outgassing of 85% Ti–15% Mo wire has been studied by a quadrupole mass spectrometer in a continuously pumped vacuum system. The mass spectral analysis of residual gases during degassing was investigated in the range of 500–1500 °C. The experiments showed that the dominant measured gases were different and separable into approximately three types in the temperature range. In measuring outgassing rates of hydrogen from the wire at various temperatures, the diffusion constants of H2 have been derived and fitted by D=5.2×10−4 exp(−10 900/RT) cm2/s. The present work showed that the outgassing of wires greatly depends on the surrounding atmosphere in which the process is carried out. To determine a proper vacuum condition for thermal treatment of the wires, the effect of H2 pressure (from 5×10−4 to 10−7 Torr) on the treatment of the wires has been observed. Storage of the wires in the laboratory atmosphere for 1 to 35 days showed that the evolution of H2 or total gases was not changed markedly.
Molybdenum and tungsten–10% titanium deposition characterization
Authors: Dawson R.
Published: July 2002

Refractory metal interconnects are of interest for very large scale integration to obtain reliable electromigration resistant conductors. GE has developed and characterized deposition processes for these films in a Varian 3180 cassette-to-cassette sputtering system. The base metal is tungsten containing 10 wt. % titanium. The bulk resistivity varies slightly (7%) with deposition pressure. The bulk resistivity minimum value has a deposition rate dependence as well. The functional form of RB seems to be independent of deposition temperature, while the absolute value depends very strongly on temperature. Bulk resistivity is a monotonically decreasing function with increasing temperature. All RB values were taken in the as-deposited condition and remeasured after a 400 °C forming gas anneal. Step coverage appears to be independent of deposition conditions in the range of operating parameters accessible to the 3180. Contact resistance is also a function of deposition temperature, roughly tracking the bulk resistivity. Stress in the TiW was in the mid 109 dyn/cm2 range, and was compressive in all cases. Stress versus deposition rate and temperature was measured. The stress appears to be independent of deposition pressure. Molybdenum deposition has been characterized as a function of deposition temperature. The bulk resistivity decreases strongly with increasing temperature, but shows almost no variation with pressure outside the measurement uncertainty. Stress increases with increasing deposition pressure. The bulk resistivity is apparently not a function of deposition rate. Step coverage of moly is equal to or slightly worse than aluminum step coverage. The optimum deposition window for aluminum step coverage is much narrower than that for moly. Any deposition condition we had access to in the 3180 had no effect on moly step coverage.
Rapid thermal annealing of indium phosphide compound semiconductors
Authors: Biedenbender Michael D. , Kapoor Vik J. , Williams W. D.
Published: July 2002

Rapid thermal annealing of ion implanted indium phosphide has been investigated. X-ray photoelectron spectroscopy was used to determine surface conditions of InP substrates cleaned with a degreasing procedure and subsequent treatment with either an iodic acid etch or an HF solution. The HF clean was found to remove the most oxygen from the surface. The indium phosphide substrates were implanted with Si at 100, 150, and 500 keV with doses of 5×1012, 1×1012, and 2×1013 cm−2, respectively. These implants were activated using rapid thermal annealing from 700 to 900 °C for 10–60 s in nitrogen or hydrogen ambients. Indium phosphide surfaces were protected during annealing by proximity contact with silicon wafers or by encapsulation with silicon nitride. Proximity contact was found to provide inadequate protection. Silicon was detected on the annealed InP surfaces and indium and phosphorus were detected on the silicon contact wafers. Indium phosphide substrates implanted with silicon at 100 keV with a dose of 5×1012 cm−2 showed a peak atomic concentration of 2×1017 cm−3 at a depth of 0.13 μm using secondary ion mass spectroscopy after encapsulation with silicon nitride and rapid thermal annealing at 700 °C for 30 s.
Measurements of weakly bound hydrogen on Pd(111) between 5 and 80 K
Authors: Stulen Richard H. , Kubiak Glenn D.
Published: July 2002

The adsorption of hydrogen and deuterium onto a low-temperature surface of Pd(111) has been studied experimentally using electron-stimulated desorption (ESD) and temperature programmed desorption spectrometry (TPD). At a surface temperature TS=7.5±1 K, exposure to D2 leads to multilayer formation which is reflected in the desorption of deuterium ion clusters D+n by ESD (Ee−=100 eV). Cluster sizes up to n=21 have been observed which, except for n=2, consist exclusively of odd numbers of atoms. The temperature dependence of the ESD signal following exposure at TS=7.5±1 K suggests that by 9.5±1 K the multilayer desorbs leaving a diatomic molecular species which, in the high-coverage limit, is stable up to ∼20 K. Exposure to hydrogen at these low temperatures gives rise to two TPD peaks: the β (chemisorption) peak and a new TPD peak denoted γ (near 60 K at low coverage) which is assigned to desorption of a surface molecular hydrogen species. Mixed isotope experiments show that there is no mixing in the γ state consistent with this assignment. With increasing exposure, the γ peak grows in intensity and shifts rapidly towards lower temperature. TPD peak shape analysis gives a binding energy for the molecular state at low coverage of ∼0.020±0.010 eV and a corresponding preexponential of approximately 102 s−1.
Lattice location of chemisorbed bromine on Si(111) thin crystal by mega-electron-volt 4He+ transmission channeling
Authors: Cheng H.-S. , Luo Li , Okamoto Masako , Thundat T. , Hashimoto Shin , Gibson W. M.
Published: July 2002

Experimental x-ray standing-wave and theoretical studies of Br adsorbed on Si(111) surface have indicated the a-top position as the most probable adsorption site. Transmission channeling through a thin crystal provides a direct and precise method to determine the position of adsorbate atoms on a crystal surface with respect to the surface crystal lattice. We have carried out such a study of Br adsorbed on chemically cleaned Si(111) surface in order to examine the adsorbate bonding site. The observed Br adsorption site was confirmed to be the expected a-top position. In addition, possible effects of the concentration of B on the Br adsorption site are discussed.
Ultrahigh vacuum pressure measurements: Limiting processes
Authors: Redhead P. A.
Published: July 2002

The processes limiting the accuracy or range of total pressure measurements in the UHV range by ionization gauges are examined. These processes include x-ray induced photoemission, ion currents resulting from electron stimulated desorption, Kingdon orbits of the ions in Bayard–Alpert gauges, variations in electron yield by ion impact at electrode surfaces, and the effects of variations in electrode geometry. The various methods and designs of UHV ionization gauges that have been developed to reduce or eliminate these limiting processes are critically reviewed.
Use of native oxide and multiple-step anneals to activate boron implanted Hg1−xCdxTe
Authors: Kao T.-M. , Sigmon T. W. , Bubulac L. O.
Published: July 2002

Channeling-in–grazing-angle-out ion beam analysis techniques have been used for the evaluation of encapsulated Hg1−xCdxTe epilayers following thermal processing. Neither spun on SiO2 nor rf sputtered ZnS prohibit Hg loss from the epilayers during rapid thermal annealing above 300 °C without Hg overpressure. However, the Hg1−xCdxTe native oxide is found to be a successful encapsulant and has been used for studying the annealing behavior and activation of boron implanted Hg1−xCdxTe . Based on our electrical measurements, we suggest that for a 77 K boron implant the most suitable implantation doses are between 1013 and 1014 cm−2 with native oxide encapsulation, multistep postimplant anneals. The mesa diodes fabricated in this work show excellent I–V characteristics.
Optical coatings deposited using ion assisted deposition
Authors: McNally James J. , Jungling K. C. , Williams F. L. , McNeil J. R.
Published: July 2002

The properties of Ta2O5 and Al2O3 optical coatings deposited using oxygen-ion assisted deposition (IAD) were investigated. Previously,1 we reported preliminary results for Ta2O5 and Al2O3 coatings deposited using IAD. In this paper, we present results illustrating the effects of oxygen-ion bombardment on film optical constants, environmental durability, and laser damage resistance. The coatings were bombarded with 200-, 300-, 500-, and 1000-eV oxygen ions during deposition. Increased values of refractive index were obtained for coatings deposited with simultaneous O+2 bombardment. Antireflection coatings deposited using IAD did not exhibit increased laser damage thresholds at λ=351 nm.
Low-energy neutral/ion backscattering at As/Si(001)
Authors: Niehus H. , Mann K. , Eldridge B. N. , Yu M. L.
Published: July 2002

The surface crystallography of arsenic covered Si(001) has been analyzed by low-energy neutral impact collision ion scattering spectroscopy (NICISS). The 170° backscattered He neutrals and ions have been detected by a time-of-flight technique. The measured data show two well-time-resolved lines for He scattered at Si and As atoms, respectively. Hence NICISS angular pattern for Si and As could be measured simultaneously. Adsorption of arsenic lifts the original 1×2 reconstruction of the Si(001) substrate and forms itself a 1×2 As overlayer. The As overlayer is well described by a dimer arrangement with an interatomic distance of 2.55 Å of the As dimers. From the ion scattering experiment considerable thermal vibrations of the As atoms in the overlayer have been concluded. Best agreement with Monte Carlo trajectory calculations is obtained for a Debye temperature of 120 K.
Mechanical property and structure relationships in hard coatings for cutting tools
Authors: Quinto Dennis T.
Published: July 2002

The trends in the use of hard protective coatings in WC–Co metal cutting inserts are reviewed in light of recent evaluations of mechanical and structure-sensitive properties such as elevated temperature microhardness, microfracture toughness, and internal stress. A better understanding of the role of hard coatings has evolved due to development of reliable methods to measure mechanical properties of thin coatings (of the order of 5 μ thick). There are intrinsic differences in the microstructure and residual stress state of chemical and physical vapor deposited (CVD and PVD) hard coatings. High compressive residual stress and fine grain size in PVD coatings contribute to increased microhardness and microfracture toughness. However, these benefits are reduced at high temperatures. Certain well-known structure/property concepts in bulk materials are shown to be applicable to hard coatings, which aid in interpretations of metal cutting wear behavior.
Scanning tunneling microscopy imaging of biological structures
Authors: Dahn D. C. , Watanabe M. O. , Blackford B. L. , Jericho M. H. , Beveridge T. J.
Published: July 2002

We report scanning tunneling microscope (STM) images of the outer sheath of the cell wall of the archaebacterium Methanospirillum hungatei. The 120-Å-thick sheath forms a cylinder that, according to extensive electron microscope studies, is known to contain a two-dimensional crystalline lattice on its outer surface with p2 symmetry and with a=56.6 Å and b=28.1 Å. The sheath tends to fragment perpendicular to the cylinder axis to give rings or hoops but is otherwise mechanically rigid and therefore well suited for STM studies. Our STM results show extended corrugations with a strong indication that their width is a random multiple of an ∼30-Å minimum period. The p2 symmetry of the surface lattice was, however, not seen in the STM images. We also report results on the imaging of sheath material under water.
Temporal evolution of collisionless sheaths
Authors: Cho M. H. , Hershkowitz N. , Intrator T.
Published: July 2002

We have performed experimental measurements to determine the temporal evolution of Langmuir sheaths near an electrode to which a negative step bias is applied in a collisionless argon plasma. The plasma was produced by a hot-filament discharge in a multidipole device. Plasma potential data were obtained using emissive probes with two different techniques: time resolved sampling and time averaged techniques. The sheath is found to initially form close to the electrode, to extend to a maximum separation, and to contract to a steady-state value. The time scale required to reach a steady state is close to the time scale of the presheath relaxation. Characteristics of sheaths in rf plasmas are also measured using a parallel-plate plasma capacitor. It is observed that the plasma potential profile has significant variation with frequency, even for frequencies as low as 1 kHz which are far below the ion plasma frequency (∼1 MHz).
Photoemission study of the band bending and chemistry of sodium sulfide on GaAs(100)
Authors: Spindt C. J. , Besser R. S. , Cao R. , Miyano K. , Helms C. R. , Spicer W. E.
Published: July 2002

Recently, there has been a great deal of interest in Na2S⋅9H2O as a passivating chemical treatment for GaAs surfaces. It has been shown that it reduces the high surface recombination velocity characteristic of GaAs surfaces, and may offer hope for ‘‘unpinning’’ the surface Fermi level. We have used photoemission spectroscopy to study the band bending and chemistry of these overlayers on n-type GaAs(100). Identically prepared samples show the characteristic increase in photoluminescence signal, and have also been characterized using surface conductivity measurements. We find using photoemission that the surface Fermi level of the treated wafer is still near midgap. We also observe the chemistry at the interface, and offer a possible explanation of the photoluminescence and surface conductivity data in terms of it and the advanced unified defect model.
Stress in Y2O3 thin films deposited by radio-frequency magnetron and ion beam sputtering
Authors: Tustison R. W. , Varitimos T. E. , Montanari D. G. , Wahl J. M.
Published: July 2002

Thin films of yttrium oxide have been deposited onto substrates of zinc sulfide by rf magnetron and ion beam sputtering. The measured magnitude and the sign of the stresses in these films (interferometric Newton rings method) vary between 7 and 21×109 dyn/cm2 and are found to be compressive. The relationship of the measured stress to various deposition parameters is explored. It is proposed that these compressive film stresses increase the flexural strength and apparent indentation fracture toughness of the ZnS substrates.
Metal cluster formation on GaAs(110): A temperature dependence study
Authors: Cao Renyu , Miyano Ken , Lindau Ingolf , Spicer William E.
Published: July 2002

The temperature effects on the cluster formation of column III and noble metals on GaAs(110) surfaces have been studied using surface sensitive photoelectron spectroscopy. At room temperature, these metal atoms tend to form three-dimensional islands, whereas at 80 K low temperature, a Stranski–Krastanov growth mode appears because of slow surface mobility. A simple model is established to estimate the cluster size and cluster distribution density. The electronic structures of the metal clusters have been simultaneously studied and correlated with the cluster size. This study shows the evolution from isolated atoms to bulk materials. The criteria of the establishment of the overlayer metallicity are discussed.
Time-of-flight secondary ion mass spectrometry of polymer materials
Authors: van Leyen D. , Hagenhoff B. , Niehuis E. , Benninghoven A. , Bletss I. V. , Hercules D. M.
Published: July 2002

Secondary ion formation from polystyrene standards with well-defined molecular weight distributions between 103 and 106 amu has systematically been investigated. Maximum yields of cationized fragments and oligomers are obtained from silver substrates covered by about one monolayer of polymer material. Intact oligomers of polystyrene are detected in the mass range up to 10 000 amu. Disappearance cross sections of sputtered molecules are correlated to the size of the desorbed species and increase almost linearly with mass. Transformation probabilities of cationized oligomers decrease by about three orders of magnitude between 1000 and 10 000 amu. Number and weight average molecular weights (Mn , Mw ) determined from peak intensities of intact polymer molecules compare well with data from gel permeation chromatography. A correction of Mn and Mw for decreasing transformation probabilities is necessary for broad molecular weight distributions. The formation of high molecular weight fragment ions can be explained by a statistical main chain scission. For polystyrenes with Mn >10 000 amu the emission of fragment ions in the mass range between 500 and 5000 amu seems to be independent of the chain length of the original polymer.
Scanning tunneling microscopy study of low-temperature epitaxial growth of silicon on Si(111)-(7×7)
Authors: Köhler U. , Demuth J. E. , Hamers R. J.
Published: July 2002

Scanning tunneling microscopy is used to investigate nucleation and growth phenomena in the molecular-beam epitaxial (MBE) growth of silicon on Si(111)-(7×7) from the submonolayer range up to a few monolayers. At room temperature small amorphous clusters form which grow in locally ordered arrays on the (7×7) lattice. Deposition at a higher substrate temperature produces triangular islands of epitaxial silicon which have preferred step propagation in the [1̄1̄2] direction. Preferred nucleation of Si islands is found to occur along boundaries between (7×7) superstructure translational domains of the substrate. The preferred nucleation which arises from defects in the epilayer accounts for the formation of a second epitaxial layer long before the first layer is completed. A variety of metastable reconstructions which differ from (7×7) are also found in the epitaxial islands and are discussed.
Macroscopic modeling of radio-frequency plasma discharges
Authors: Misium G. R. , Lichtenberg A. J. , Lieberman M. A.
Published: July 2002

We describe a self-consistent model of a symmetric plane parallel rf discharge. The model is built upon basic laws such as conservation of particles and energy, and is capable of predicting rapidly the important discharge parameters from a processing point of view, such as the ion energy and flux to the electrodes. The following physics is incorporated into the model: energy-dependent electron–neutral ionization, excitation and elastic scattering; nonuniform, self-consistent collisionless and collisional rf sheaths; electron Ohmic heating by elastic scattering in the sheaths and bulk plasma stochastic heating by the oscillating fields in the sheaths; electron energy losses to neutrals through collisions and to the electrodes; ambipolar ion diffusion; and total rf power balance. A set of equations describing this dynamics has been obtained and used in a code to simulate different discharges. The model has proven to be useful in comparing the effect of varying parameters on the discharge. Comparisons with experimental results show a good agreement between predicted and measured parameters.
Preparation of superconducting Y–Ba–Cu–O thin films
Authors: Leskelä M. , Truman J. K. , Mueller C. H. , Holloway P. H.
Published: July 2002

The preparation of YBa2 Cu3 07−x high critical temperature superconducting thin films is reviewed. Thin films have been grown by many techniques, including sputtering, electron beam evaporation, laser ablation, spray pyrolysis, molecular-beam and epitaxy (MBE). Stoichiometric films with high Tc and Jc have been obtained using each of these methods. The choice of substrate significantly affects the superconducting properties, and among the numerous substrates studied MgO, ZrO,2 and SrTiO3 yield best results. This review outlines the various deposition techniques, the effect of postdeposition annealing and the subsequent film–substrate interactions.
Vacuum microtriode characteristics
Authors: Carr W. N. , Wang H. J. , Chin K. K. , Marcus R. B.
Published: July 2002

Pentode-like I–V characteristics are simulated for lateral vacuum microelectronic devices with wedge-shaped field emission cathodes. A single grid provides electrostatic isolation between the cathode and anode for a large equivalent anode series resistance. Device characteristics are presented for a structure with a field emission cathode, one control grid, an anode, and two trajectory deflection electrodes. The cathode-to-control grid separation for trajectory simulation is a nominal 1 μm and the emission tip radii are 0.01 and 0.05 μm. The device length including deflectors is 18 μm. Device characteristics are modelled over an anode potential range of 10–200 V. At 50 V anode potential, a transconductance of 4 μ S/mm and 0.1 S/mm is calculated based on 0.05 and 0.01 μm wedge radii, respectively.
Indirect band gap in α-ZrO2
Authors: Kwok Chee-Kin , Aita Carolyn Rubin
Published: July 2002

Measurements of the absorption coefficient on the fundamental optical absorption edge of α-ZrO2 show that an indirect interband transition at 4.70 eV precedes two previously reported direct transitions. This result is in agreement with recent theoretical calculations of the α-ZrO2 band structure.