bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultraviolet photoemission studies of the bonding of CO to the ZnO (101̄0) surface and its interaction with atomic hydrogen
Authors: D’Amico K. L. , McClellan M. R. , Sayers M. J. , Gay R. R. , McFeely F. R. , Solomon Edward I.
Published: July 2002

Angle integrated and angle resolved He ii photoemission spectroscopy have been used to characterize the adsorption of carbon monoxide and hydrogen on the ZnO (101̄0) surface, and to study their interaction. Hydrogen chemisorption is consistent with the formation of H+ (as (OH)−) and H− (as (ZnH)+) at high coverages due to the requirement of surface charge compensation. The primary interaction between the surface hydrogen and adsorbed CO is found to be site competition.
Design of a molecular beam surface scattering apparatus for velocity and angular distribution measurements
Authors: Ceyer S. T. , Siekhaus W. J. , Somorjai G. A.
Published: July 2002

A molecular beam surface scattering apparatus designed for the study of corrosion and catalytic surface reactions is described. The apparatus incorporates two molecular or atomic beams aimed at a surface characterized by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES), a rotatable, differentially pumped quadrupole mass spectrometer, and a versatile manipulator. Angular distributions and energy distributions as a function of angle and independent of the surface residence time can be measured. Typical data for the oxidation of deuterium to D2O on a Pt(111) crystal surface are presented.
A novel anisotropic dry etching technique
Authors: Geis M. W. , Lincoln G. A. , Efremow N. , Piacentini W. J.
Published: July 2002

We have developed a dry etching technique in which the chemically reactive species and the energetic ions are independently controlled. This technique, which we call ion beam assisted etching (IBAE), is accomplished by impinging a chemically reactive gas from a jet and an ion beam from a Kaufman ion source upon the sample. It is based upon the work of Coburn et al., 1 and differs fundamentally from reactive ion etching (RIE), which relies upon a plasma to produce both the chemically active species and the energic ions. In IBAE the partial pressure of the reactive gas can be as high as several Pa (tens of microns) at the sample surface while the chamber pressure can easily be maintained at about 1×10−2 Pa (10−4 Torr). Although a variety of reactive gases and sample materials have been characterized, the presentation will concentrate on using Cl2 as a reactive gas and an argon ion beam. The anisotropic character of this etching technique has been found to depend on the angles that the gas jet and the ion beam make with the surface of the sample. Etching rates as high as a few micrometers per minute have been obtained with GaAs and Al samples and anisotropic etching aspect ratios as large as 50 were easily obtained with GaAs. The etched surface of the GaAs was also electrically characterized in two ways: first, by fabricating Schottky diodes on it and measuring the ideality factor, and secondly, by growing VPE GaAs on the etched surface and profiling the traps at the interface between the etched surface and the VPE GaAs using deep level transient spectroscopy (DLTS). The quality of the etched surface was found to improve as the reactive gas flux varied from about 1×1017 to 5×1018 atoms cm−2 s−1. Measured ideality factors of the Schottky diodes fabricated on GaAs etched under high reactive gas flux conditions were equivalent to diodes fabricated on virgin GaAs. The density of traps at the interface between the etched GaAs and the VPE GaAs was less than 1×1015 cm−3 which is low enough for many GaAs device applications. The independent parameter control afforded by this technique has enabled us to achieve desirable anisotropic etching characteristics while producing etched GaAs surfaces with acceptable electrical quality.
A 100-kV ion probe microfabrication system with a tetrode gun
Authors: Cleaver J. R. A. , Ahmed H.
Published: July 2002

In the design of probe-forming systems incorporating liquid-metal ion sources, it is necessary to maximize the current into a probe of controlled diameter and to employ a configuration that is compatible with the incorporation of a filter for the selection of ion species. A variable-magnification two-lens system has been adopted as the basis of a microfabrication machine for direct selective ion implantation of wafers, and a 100-kV system has been designed. Its tetrode gun acts as the first lens and is followed by an einzel lens as the probe-forming objective. The system has been analyzed and operating characteristics have been computed, predicting a current of 0.1 nA in a 0.1 μm diameter probe and 10 nA into 1 μm diam.
Numerical simulation of fueling in tokamaks
Authors: Attenberger S. E. , Houlberg W. A. , Milora S. L.
Published: July 2002

We describe the numerical simulation of fueling and particle transport in both present and future tokamak plasmas. Models for pellet ablation and plasma density behavior after pellet injection are compared with experimental results in ISX and PDX plasmas and then extended to fusion reactor conditions. The role of fast ion ablation due to intense neutral beam injection and fusion alphas is examined along with pellet size and velocity considerations. In plasmas with high pumping efficiency (which may be obtained with divertor operation), pellet injection can significantly reduce fueling rates while maintaining more flexibility in control of the density profile than afforded by gas puffing. When fueling is dominated by gas puffing or high recycle from the walls or limiter, control of the fueling and density profiles is reduced and particle fluxes to the wall increase.
The reactive sputtering of tantalum oxide: Compositional uniformity, phases, and transport mechanisms
Authors: Reith T. M. , Ficalora P. J.
Published: July 2002

Reactive sputtering has been investigated by a number of workers, but no clear, generalized picture of the method or the phenomena involved has emerged. It is shown that the variation observed in the partial pressure of O2 during both reactive and nonreactive Ta depositions is a sensitive measure of reactive surface activity in the plasma. A detailed examination of the O2 behavior is made as the degree of activity of either target or substrate is systematically changed. A correlation is made between observed O2 partial pressure variations and resulting compositional variations of the collected films using Auger electron spectroscopy, Auger sputter profiling, and transmission electron microscopy. Most importantly, we describe the reactive sputtering of Ta in O2 in terms of two inverse reactions at two reactive surfaces; a dissociative reaction proceeds at the target while its inverse proceeds at the substrate. A generalized process in which a metal oxide dissociates to a less-stable suboxide at the target, transfers to the substrate as the suboxide, and recombines to form the original target compound, is suggested for the reactive sputtering of any metal oxide which exhibits preferential sputtering effects.
GeTe thin films: Amorphous and crystalline characteristics
Authors: Tran N. T. , Chang Y. C. , Faragalli D. A. , Roberts S. S. , Josefowicz J. Y. , Shing Y. H.
Published: July 2002

GeTe thin films were prepared by rf diode and magnetron sputtering techniques. Thicknesses from 0.5 to 7 μm were produced. Electron microprobe analysis indicated that the obtained composition of the films produced by the two different systems was Ge51.9Te48.1. As-deposited films were amorphous when deposition was onto a room temperature substrate during sputtering, the electrical conductivity of the amorphous films was increased by several orders of magnitude after crystallization. The amorphous crystalline transformation occurred at 230 °C over a narrow temperature interval of less than 20 °C. This transition was confirmed by measurements of Seebeck coefficient, and electrical conductivity versus temperature. Crystalline films were obtained by (i) furnace annealing, (ii) sputtering at substrate temperature beyond 250 °C, and (iii) laser annealing. The crystalline films had the rhombohedral structure and nonpreferred orientation. Crystalline films obtained by the three different annealing methods exhibited similar properties.
Negative ion sources for neutral beam systems
Authors: Ehlers K. W.
Published: July 2002

Neutral beams to heat the plasmas of controlled fusion experiments are generated by neutralizing the charge of positive ions after they have been focused and accelerated. The efficiency of this system decreases with ion velocity and for D+ the system is practical only at ion energies of less than about 150 keV,which is less than the energies expected to be required in the future. However, the use of negative ions, where neutralization is accomplished by removing, rather than by adding electrons, allows much higher ion energies to be efficiently employed. Programs to develop sources of large currents of H− and D− are therefore underway. The goal is to produce practical sources which can supply ampere beams of continuous, impurity-free, negative hydrogen ions in geometries that can be extended to even larger currents. This paper briefly describes the three main methods of producing negative ions and the advantages and disadvantages of each.
On the nature of oxides on InP surfaces
Authors: Hollinger G. , Bergignat E. , Joseph J. , Robach Y.
Published: July 2002

The chemical composition of surface oxides grown on InP is investigated using x-ray photoelectron spectroscopy. Native oxides prepared by various chemical treatments, anodic oxides, and thermal oxides are examined. Core level energies and intensities and valence band spectra are compared with data for standard compounds. In a first step we show that, depending on the preparation procedure, oxides can be classified into three groups which have properties similar to crystalline In(OH)3, InPO4, and In(PO3)3, respectively. The large variations observed in atomic compositions and the shape of valence band spectra suggest that the oxides could be amorphous nonstoichiometric phases. A description based on a mixture of well defined compounds (e.g., In2O3+P2O5 or In2O3+InPO4) seems to be inadequate. Chemical and anodic phosphorus-rich oxides are identified as Inx(PO3)y polyphosphates.
New methods for image collection and analysis in scanning Auger microscopy
Authors: Browning R.
Published: July 2002

While scanning Auger micrographs are used extensively for illustrating the stoichiometry of complex surfaces and for indicating areas of interest for fine point Auger spectroscopy, there are many problems in the quantification and analysis of Auger images. These problems include multiple contrast mechanisms and the lack of meaningful relationships with other Auger data. Collection of multielemental Auger images allows some new approaches to image analysis and presentation. Information about the distribution and quantity of elemental combinations at a surface are retrievable, and particular combinations of elements can be imaged, such as alloy phases. Results from the precipitate hardened alloy A1-2124 illustrate multispectral Auger imaging.
ZnSe– and Se–GaAs interfaces
Authors: Tu D.-W. , Kahn A.
Published: July 2002

We have studied via LEED, AES, and EELS the (110) and (100) interfaces between GaAs and ZnSe or Se deposited in UHV on sputter-annealed substrates. These interfaces are reactives. Although nearly stoichiometric (ϑ>20 Å) crystalline ZnSe films can be grown on GaAs by congruent evaporation, the ZnSe–GaAs interfaces are nonstoichiometric and include a thin intermediate (Ga, Se) compound layer due to a Se–As exchange taking place during the early stages of growth. Various phases of the (Ga, Se) compound can be obtained, depending on the availability of Se at the interface. The structure and chemical properties of the Se–GaAs interfaces are also investigated and related to the chemical reaction observed during the formation of the ZnSe–GaAs interfaces.
Scanning tunneling microscopy studies of Si(111)-2×1 surfaces
Authors: Feenstra R. M. , Thompson W. A. , Fein A. P.
Published: July 2002

We have used scanning tunneling microscopy (STM) to study cleaved Si(111) surfaces. On ordered regions of the 2×1 reconstruction we observe atomic rows with a [2̄11] corrugation amplitude of typically 0.2 Å and an [01̄1] corrugation amplitude of <0.02 Å, consistent with the π-bonded chain model for this surface. Structural disorder is most commonly observed as protrusions along the chains and between chains. A second type of surface disorder is observed in the magnitude and asymmetry of the [2̄11] corrugation amplitude, which we attribute to varying tilts and/or small translations of the π-bonded chains. This latter type of disorder is enhanced in low-voltage images, indicating that the associated defect states have energies concentrated in or near the band gap of 2×1 surface-state energies.
A simplified scanning tunneling microscope for surface science studies
Authors: Demuth J. E. , Hamers R. J. , Tromp R. M. , Welland M. E.
Published: July 2002

A compact, reliable scanning tunneling microscope (STM) is described which provides atomic scale resolution and is intended for surface science studies. The novel design features consist of a rigid contact between the sample and piezoelectric scanner, together with the use of a pivot and lever arm to achieve both coarse and fine mechanical motion. Topological images of the Si(111) 7×7 surface are presented showing some point and extended defects. The bias dependence of these topographs is demonstrated and briefly discussed.
New ternary semiconductors for infrared applications: Hg1−x MnxTe
Authors: Wall A. , Caprile C. , Franciosi A. , Reifenberger R. , Debska U.
Published: July 2002

Hg1−xMnxTe alloys have been proposed as a suitable alternate material to mercury–cadmium–telluride for infrared applications. We report synchrotron radiation photoemission studies of the electronic structure of such alloys for x≤0.15. Valence band resonant photoemission was exploited to probe the valence states, while high resolution core photoemission yielded information on bonding stability and ionicity. The results are compared with those obtained for Hg1−xCdxTe and for HgTe. The Mn bonding in Hg1−xMnxTe appears mostly due to the coupling of metal-s states with Te p-states, with limited evidence of d–p hybridization. The ionicity of the Hg–Te bond is not substantially modified in the ternary alloy relative to HgTe, while for Hg1−xCdxTe we directly observe dramatic destabilization of the Hg–Te bond. Correspondingly, Hg1−xMnxTe should exhibit lattice surface and interface stability similar to those of the binary parent compound and largely exceeding those of Hg1−xCdxTe.
Laser diagnostics of a silane plasma—SiH radicals in an a-Si:H chemical vapor deposition system
Authors: Matsumi Y. , Hayashi T. , Yoshikawa H. , Komiya S.
Published: July 2002

Using a laser-induced fluorescence technique, SiH radicals were detected in the rf glow discharge of SiH4 gas during CVD of amorphous silicon. The pressure, flow rate, and rf power dependencies of the relative concentration of SiH radicals were obtained. The spatial distribution of SiH radicals between rf and ground electrodes was also revealed. It was found that the behaviors of the concentration of SiH in the ground electronic state are different from those of SiH in the excited state. The latter was obtained from measurement of the spontaneous emission in the discharge. The rotational temperature of SiH radicals was derived from the laser excitation spectra with computer simulations. The obtained temperature reflects the translational temperature of the parent molecules (SiH4). The rotational energies of SiH radicals in the discharge are thermalized with surroundings by collisions during their lifetimes.
Point collector ionization gauge with spherical grid for measuring pressures below 10−11 Pa
Authors: Watanabe F.
Published: July 2002

A new hot-filament ionization gauge using a point collector and spherical grid has been developed to reduce the low-pressure limit. Since the development of the Bayard–Alpert gauge, a number of attempts have been made to overcome the x-ray limit. In all these attempts, however, the gauge collectors are either wires or plates, even if they are removed from the ionization region and hidden from x rays. If, however, a very small point collector could be used in an ionization gauge, without reducing sensitivity, the small surface area of the collector could yield a very low x-ray limit. Therefore, in the present design a point collector is approximated using a needle tip≂0.03 mm in diameter and ≂ 0.05 mm long projected from a thin tapered sleeve. A 26-mm-diam spherical grid is formed by joining two hemispheres made of finely woven molybdenum mesh. The collector is placed about 1.5 mm inside the pole of the spherical grid. A ring filament is stretched around the equator of the spherical grid. The x-ray limit of the new gauge, calculated theoretically from geometric considerations, is about 2.3×10−12 Pa; and its experimental result is about 2.5×10−11 Pa, with a sensitivity factor of 0.4 Pa−1 (53 Torr−1). If a short wire modulator is added near the collector, the pressure limit of the new gauge is reduced below 10−11 Pa, with a modulation factor of 0.95.
Imaging electronic surface states in real space on the Si(111) 2×1 surface
Authors: Stroscio Joseph A. , Feenstra R. M. , Fein A. P.
Published: July 2002

Scanning tunneling microscope images of the Si(111)2×1 surface are shown to reflect the spatial dependence of the bonding (π) and antibonding (π*) surface states. The surface states above and below the intrinsic gap are observed to have opposite parity, by the appearance of a 180° phase shift in the [011̄] corrugation with respect to tunneling into the π and π* states. A detailed voltage dependence of the phase of the surface charge density is obtained from spectroscopic images recorded simultaneously with the surface topograph.
Surface analysis of electrochromic displays of iron hexacyanoferrate films by x-ray photoelectron spectroscopy
Authors: Emrich R. J. , Traynor L. , Gambogi W. , Buhks E.
Published: July 2002

Electrochromic displays made from thin films of iron hexacyanoferrate (Prussian blue) deposited on tin oxide/glass substrates by electroreduction from solution are studied by x-ray photoelectron spectroscopy (XPS). It was determined by XPS that the concentration of potassium ions in the film increased as the number of electrochromic switches the film had undergone increased. This was accompanied by a decrease in the electrochromic performance of the film. The incorporation of potassium ions into the Prussian blue lattice causes a structural reorganization of the lattice with the expulsion of ferric ions from the lattice. The expulsion of ferric ions results in a degradation of the film’s electrochromic properties. This agrees qualitatively with data collected by in situ optical spectroscopy, XPS, atomic absorption spectrometry, optical microscopy, and x-ray diffraction. The rate of degradation can be reduced substantially by inclusion of an Fe(II)/Fe(III) containing solution in switching electrolyte. The role of ionic transport in the degradation mechanism is discussed.
X-ray photoemission investigations of clustering and electron emission, injection, and trapping at the gold/polyimide interface
Authors: Meyer H. M. , Anderson Steven G. , Atanasoska Lj. , Weaver J. H.
Published: July 2002

The evolution of the interface formed between clean [N-N-(p,p-oxydiphenylene) pyromellitimide] polyimide (PI) and evaporated gold was followed by high-resolution x-ray photoelectron spectroscopy (XPS). Overlayer and substrate core level emission behavior indicates the nucleation and growth of Au clusters on the PI surface. At low gold coverages (<1 Å nominal thickness), there was no observed interaction between the adatoms and the substrate. Above 1 Å we observe the growth of clusters on the PI surface and a shift of the Au 4f core levels as the clusters become metallic. Significantly, we observe further shifting of the Au 4f emission and the Fermi level at coverages greater than that expected for metallic behavior, and we see Au-cluster-induced broadening and shifting of the substrate core level spectra to lower binding energy. This unexpected behavior can be accounted for in terms of the injection and trapping of charge into the PI film from Au during the photoionization process. Angle-dependent XPS results showed increased broadening and shifting near the surface, indicating that the amount of trapped charge was greater at the interface. This injection profile was modified by an annealing cycle of the Au/PI interface, as indicated by the coalescing of dispersed Au clusters and the partial recovery of the clean PI substrate characteristics.
Control of microstructure and properties of copper films using ion-assisted deposition
Authors: Roy R. A. , Cuomo J. J. , Yee D. S.
Published: July 2002

The effect of argon ion bombardment on the structure and properties of thick copper films was studied. Primary deposition variables were ion flux, ion energy, substrate temperature, and substrate type. The effects of ion bombardment are profoundly different at high energy (600 eV) as opposed to low energy (62 eV). Trends in crystallographic texture, microhardness, crystallite size, and resistivity are significantly different at different ion energies on all substrates examined. At high energy, the substrate dependence of properties is small while a large dependence is seen at lower energy. This work demonstrates the independence of ion energy and ion flux as control parameters in property modification using ion-assisted deposition processes.
On the interpretation of current images in scanning tunneling spectroscopy of Si(111)7×7
Authors: Berghaus Th. , Brodde A. , Neddermeyer H. , Tosch St.
Published: July 2002

During scanning of Si(111)7×7 the tunneling current has been determined at every tip position as a function of bias voltage keeping the distance between tip and sample at a constant value by stabilization of the tunneling current for only a small time interval. For positive (2 V) and negative (−2 V) stabilization voltage we have obtained two sets of current images. Our results show that the hitherto neglected energy-dependent transmission probability on the tunneling current and the intimate relation between electronic and topographic properties prevent a simple determination of the local density of states.
The effect of cooling rate on the surface reconstruction of annealed silicon(111) studied by scanning tunneling microscopy and low-energy electron diffraction
Authors: Pashley M. D. , Haberern K. W. , Friday W.
Published: July 2002

We have incorporated a scanning tunneling microscope (STM) into an UHV analytical chamber containing low-energy electron diffraction (LEED), reflection high-energy electron diffraction, Auger, and scanning electron microscopy facilities. A second chamber has facilities for surface cleaning together with an entry lock for loading specimens. The STM incorporates a transfer system for both sample and tip, and fine control for the specimen to tip approach is achieved mechanically. X–Y scanning and data acquisition are fully computerized. This instrument has been used to study the effect of cooling rate after annealing on the surface reconstruction of Si(111). The silicon is cleaned by Ar ion bombardment and then annealed at 920 °C. When the specimen is cooled slowly over several minutes, a sharp 7×7 LEED pattern is obtained, and the STM images show areas of well-ordered 7×7. In this slow cooling regime, small areas of well-ordered 2×2 reconstruction have also been seen. As the silicon cooling rate is increased, the 7×7 LEED spots become less distinct. In contrast, the STM images show small areas of well-ordered 2×1 reconstruction typically a few hundred angstroms across, and very similar to the larger areas of 2×1 seen on cleaved Si(111). These results suggest that with rapid cooling (typically a few hundred degrees per minute), the high-temperature 1×1 surface is unable to form the energetically favorable 7×7 surface. The 2×1 structure is most easily formed, as is seen on cleaved surfaces. As the cooling rate decreases, the surface is more likely to attain the 7×7 structure, but may be trapped in the 2×2 structure which forms the basic building blocks of the 7×7 reconstruction. To be consistent with these results we conclude that the high-temperature 1×1 surface must be an ordered structure.
Scanning tunneling microscopy of machined surfaces
Authors: Gehrtz M. , Strecker H. , Grimm H.
Published: July 2002

While still considered mainly a scientific technique, the scanning tunneling microscope (STM) is a promising new tool for the detailed characterization of surfaces of industrial or technological interest, owing to its unique combination of very high lateral and vertical resolution. We report first on STM measurements of diamond turning mark topography details on aluminum substrates used in magnetic storage device manufacturing. The instrument used was designed specifically for industrial applications: operation in ambient air in a typical manufacturing laboratory, large scan range (20 μm lateral, 4 μm vertical) at low operating voltages (below 150 V), computerized and automated control. The problems associated with these requirements are discussed. The STM measurements reveal considerable detail of the diamond turning marks, that can be useful in quality control of the substrate or the turning process.
Roughness and porosity characterization of carbon and magnetic films through adsorption isotherm measurements
Authors: Wang C. L. , Krim J. , Toney M. F.
Published: July 2002

Hard carbon films are receiving much current attention on account of their potential use as protective overcoats. The tribological properties have an important influence on the functional performance of the films and can be probed through studies of film porosity and roughness. The technique of adsorption is particularly advantageous for this type of investigation because the area coated by an adsorbed monolayer is precisely that involved when the protective coating is exposed to the atmosphere. Adsorption studies have been carried out for both carbon and magnetic thin films which have been deposited onto the surface electrodes of quartz-crystal microbalances. These studies provide (i) an immediate determination of whether the film is rough or porous, and (ii) if porous, an indication of pore morphology.
The interaction of oxygen and platinum on W(110)
Authors: Demmin R. A. , Madey T. E.
Published: July 2002

Low-energy electron diffraction (LEED) and Auger electron spectroscopy have been used to characterize Pt overlayers coadsorbed with oxygen on W(110). Previous work has shown that multilayers of Pt alone will cluster into three-dimensional crystallites of bulk Pt when annealed, leaving a pseudomorphic monolayer of Pt covering the W(110) surface. When oxygen is present on the surface, the monolayer of Pt is no longer stable. Annealing a W(110) surface on which both Pt and oxygen are adsorbed causes nearly all of the Pt to agglomerate into clusters as the oxygen largely replaces the monolayer on the surface. The presence of the Pt clusters reduces the temperature required for desorption of oxygen, however, and the Pt spreads across the W surface as the oxygen is removed. The complex LEED patterns observed when coadsorbed oxygen and Pt are annealed and the changes in the temperature required for desorption of oxygen suggest that there is an interaction between the two adsorbates and that there is not complete phase separation; i.e., some Pt remains dispersed on the W surface within the oxygen phase.
On the electrochemical etching of tips for scanning tunneling microscopy
Authors: Ibe J. P. , Bey P. P. , Brandow S. L. , Brizzolara R. A. , Burnham N. A. , DiLella D. P. , Lee K. P. , Marrian C. R. K. , Colton R. J.
Published: July 2002

The sharpness of tips used in scanning tunneling microscopy (STM) is one factor which affects the resolution of the STM image. In this paper, we report on a direct-current (dc) drop-off electrochemical etching procedure used to sharpen tips for STM. The shape of the tip is dependent on the meniscus which surrounds the wire at the air–electrolyte interface. The sharpness of the tip is related to the tensile strength of the wire and how quickly the electrochemical reaction can be stopped once the wire breaks. We have found that the cutoff time of the etch circuit has a significant effect on the radius of curvature and cone angle of the etched tip; i.e., the faster the cutoff time, the sharper the tip. We have constructed an etching circuit with a minimum cut-off time of 500 ns which uses two fast metal–oxide semiconductor field effect transistors (MOSFET) and a high-speed comparator. The radius of curvature of the tips can be varied from approximately 20 to greater than 300 nm by increasing the cutoff time of the circuit.
Low resistivity indium–tin oxide transparent conductive films. II. Effect of sputtering voltage on electrical property of films
Authors: Ishibashi S. , Higuchi Y. , Ota Y. , Nakamura K.
Published: July 2002

A low resistivity and high transmittance Sn doped In2O3 (ITO) film was formed on a glass substrate by dc magnetron sputtering and lower sputtering voltage gave a lower resistivity film. At a sputtering voltage of −250 V, the resistivity obtained was 5.0×10−4Ω cm for room temperature substrate, 2.0×10−4Ω cm for 160 °C substrate, 1.9×10−4Ω cm for 200 °C substrate, and 1.2×10−4Ω cm for 460 °C substrate. At a sputtering voltage of −80 V, the resistivity was 1.3×10−4Ω cm for 200 °C substrate. A measurement of Hall effect shows that the decreased resistivity by lower sputtering voltage is not caused by the Hall mobility but by an increased carrier concentration.
Magneto-optical investigation of impurity and defect levels in HgCdTe alloys
Authors: Littler C. L. , Seiler D. G. , Loloee M. R.
Published: July 2002

We have observed and described magneto-optical transitions between impurity/defect levels and conduction band Landau levels for a variety of n-type HgCdTe samples with 0.2<x<0.3. The activation energies of these levels fall into two categories: (1) 10–12 meV above the valence band edge, independent of Eg and (2) two close spaced levels at ≂0.5 Eg. In addition, the spectra of several narrow gap (Eg≤100 meV) samples exhibit shallower and deeper acceptor-like levels.
A compact three-axis cryogenic ultrahigh vacuum manipulator
Authors: Dürr H. , Fauster Th. , Schneider R.
Published: July 2002

A compact UHV-compatible sample manipulator with three rotational and three translational degrees of freedom is described. The manipulator head has less than 25 mm radius and is completely manufactured from nonmagnetic materials. With liquid nitrogen as a coolant temperatures of 100 K can be achieved.
Effect of substrate surface roughness on the columnar growth of Cu films
Authors: Bai P. , McDonald J. F. , Lu T.-M. , Costa M. J.
Published: July 2002

Vapor-deposited films prepared under low adatom mobility conditions commonly exhibit columnar structures. We present the scanning electron microscopy study of Cu films with a thickness around 3.7 μm deposited on rough Al2O3 ceramic substrates and smooth SiO2 substrates. The Cu films were deposited using the partially ionized beam deposition technique under the same deposition conditions. The films deposited on the rough substrates have a typical columnar structure while those deposited on the smooth substrates are noncolumnar. The complete difference in physical structures is due to the difference in the substrate surface roughness. The results indicate that in any structure zone model for the physical structure of the film the substrate surface roughness is an important parameter and cannot be neglected. It is reasoned that the adatom surface diffusion length, which is determined by the deposition conditions, serves as a critical measure for the length scale of surface roughness. At the initial stage of the film growth, the columnar structure develops only for the roughness with a length scale longer than adatom surface diffusion length.
A fundamental feature scale model for low pressure deposition processes
Authors: Cale T. S. , Gandy T. H. , Raupp G. B.
Published: July 2002

The integro-differential equations which govern free molecular flow and low pressure chemical vapor deposition in long rectangular trenches are reviewed. The model equations are used to simulate the deposition of tungsten by hydrogen reduction of tungsten hexafluoride, with reactive sticking coefficients determined by local deposition conditions. Numerical solution of the governing equations provides film profiles and deposition rate profiles as a function of position in the trench at any time until the trench mouth closes. The impact of the operating conditions on step coverage is discussed in relation to reactive sticking factors. Calculated tungsten step coverages for three selected realistic initial trench shapes highlight the importance of establishing a consistent method for reporting step coverages. We introduce the percentage of feature fill as a measure of step coverage. To allow evaluation of the quantitative predictive ability of a model, cross-sectional scanning electron micrographs are required in general.
InGaAs quantum well wires grown on patterned GaAs substrates
Authors: Mirin Richard P. , Tan I-Hsing , Weman Helge , Leonard Marilyn , Yasuda Takashi , Bowers John E. , Hu Evelyn L.
Published: July 2002

Strained InGaAs/GaAs quantum well wires have been grown on 2300 Å period gratings etched into GaAs substrates. Both conventional molecular beam epitaxy and migration-enhanced epitaxy have been used as growth techniques. The low-temperature photoluminescence from the quantum well wires was compared to the photoluminescence from a planar quantum well sample grown simultaneously. The planar samples showed a sharp single peak, whereas the patterned samples displayed two peaks. The samples grown by conventional molecular-beam epitaxy had two fairly broad, overlapping peaks of comparable intensity. The samples grown by migration-enhanced epitaxy had two distinct peaks, with one peak an order of magnitude larger than the other. Polarization-dependent photoluminescence was performed on the migration-enhanced epitaxy grown samples. The larger of the two peaks on the patterned sample showed a 21% linear polarization dependence, while the other peak showed unpolarized emission. In addition, the quantum well grown on the unpatterned substrate exhibited unpolarized emission.
Electrical characterization of radio-frequency discharges in the Gaseous Electronics Conference Reference Cell
Authors: Sobolewski Mark A.
Published: July 2002

Measurements of the electrical characteristics of radio-frequency (rf) discharges can be subject to large errors due to limitations in the measurement instruments and the stray impedance of the discharge cell. This study reports electrical measurements of argon discharges in the GEC Reference Cell in which special care has been taken to identify and minimize these sources of error. Careful calibration of current and voltage probes was found to be essential. In addition, parasitic impedances in the cell were found to be large, sensitive to minor changes in electrical connections, and not adequately described by simple a priori models. A general technique for characterizing the stray impedance, including an analysis of the propagation of errors, is presented here. This technique assures accurate results with specified uncertainties. Error analysis demonstrated that large gains in the precision of the measurements can be obtained using an inductive shunt circuit. Together, these techniques should improve the utility of electrical measurements for gauging the reproducibility of plasma conditions among rf discharge cells, for testing theoretical results, and for monitoring plasma processing.
Thermal decomposition of ultrathin oxide layers on Si(100)
Authors: Sun Y.-K. , Bonser D. J. , Engel Thomas
Published: July 2002

Decomposition of ultrathin oxide layers on Si(100) has been studied using isothermal desorption, temperature programmed desorption and readsorption on partially desorbed layers using isotopically labeled oxygen. We find that inhomogeneous decomposition, with void formation in which clean silicon is exposed, occurs at coverages as low as 0.3 monolayers. Whereas the activation energy for SiO(g) formation is essentially independent of coverage between 10−3 and 10 monolayers, the apparent preexponential factor decreases substantially with increasing coverage. The discrepancy between the kinetic parameters measured for SiO(g) production in modulated molecular beam experiments and those measured using temperature programmed desorption is attributed to a strong decrease in the rate constant for desorption of SiO(g) with increasing coverage. Both methods give similar results at nearly identical coverages.
Interaction of hydrogen and water with diamond (100): Infrared spectroscopy
Authors: Struck Lisa M. , D’Evelyn Mark P.
Published: July 2002

We report the first investigation of the adsorption of water on diamond (100) by infrared multiple-internal-reflection spectroscopy using a natural type IIa diamond internal reflection element. The first direct evidence of the diamond surface hydride structures, obtained by deuterium substitution, is also presented. Infrared evidence was seen for both monohydride and dihydride surface structures, with one or two hydrogen atoms per surface carbon atom (δCD mode at 901 cm−1 and δCD2 mode at 1125 cm−1, respectively). Following exposure to water at elevated temperature, infrared modes were detected at 1280, 1200, 1125, 1080, and 720 cm−1, and are assigned to ether (C—O—C), hydroxyl (C—OH), and carbonyl (≥C=O) modes. The substantial observed reactivity of diamond with water suggests a potentially important role for surface hydroxyl and oxide species in the surface chemistry and morphological development of diamond films grown by chemical vapor deposition.
Do we need a new methodology for GaAs passivation?
Authors: Green A. M. , Spicer W. E.
Published: July 2002

Previous results on the GaAs:native oxide interface are reviewed and their implications to present attempts at GaAs passivation are discussed. Large band gap semiconductors and the use of sulfur and Sb termination as a means to passivate the surface are discussed. Although sulfur treatments do not lead to ideal (flatband) electrical termination, this treatment exhibits greatly reduced surface recombination. Sb gives an ideal termination which results in the surface Fermi level close to the flatband condition. Both of these treatments have failed as practical passivating processes because they have insufficient chemical stability against the atmosphere. A new methodology for passivating compound semiconductors is presented in which two overlayers are used. In this approach, the first overlayer defines the surface electrically and the second provides long term protection.
In situ spectral ellipsometry for real-time thickness measurement: Etching multilayer stacks
Authors: Henck Steven A. , Duncan Walter M. , Lowenstein Lee M. , Butler Stephanie Watts
Published: July 2002

A polarization modulated spectroscopic ellipsometer is used in situ to measure the thicknesses of films in real time during semiconductor plasma etch processing. Utilizing the speed of phase modulation multichannel detection, and digital signal processing techniques, this ellipsometer is capable of acquiring spectral data in less than 75 ms. Efficient algorithms were developed for determining layer thicknesses from the measured spectra of multilayer film stacks in real time with a typical solution time of a few seconds. The measured thicknesses and etch rates are used to anticipate interfaces in multiple layer stacks and control process end points. The ability of the spectral ellipsometer to measure multilayer stacks during etching is demonstrated by the etching of a stack consisting of silicon nitride, polycrystalline silicon, and silicon dioxide. Such stacks are commonly used as masks for field oxidation for electrical isolation in memory device fabrication. An isotropic plasma etch is used to remove this film in a single-wafer process environment.
Compact electron cyclotron resonance ion source with a permanent magnet
Authors: Shimada M. , Torii Y.
Published: July 2002

A new compact electron cyclotron resonance ion source that uses a magnetic mirror field and a divergent magnetic field to generate high-density and multicharged ions has been developed. A cylindrical permanent magnet is utilized to produce those magnetic fields. Excited electrons are effectively confined in the mirror field near the exit of the plasma chamber, making it possible to generate high-density and multicharged ions. The generated ions are transported near the center axis and a plasma stream is formed along the divergent magnetic field. A plasma chamber with a diameter 4 cm smaller than the cutoff size (7.2 cm for 2.45 GHz) and a two-layer microwave window are used to fashion the compact structure and to couple microwaves with high-density plasma. The plasma stream is highly directional (plasma stream diameter ∼1.8 cm), and high ion saturation current densities of 18 mA/cm2 (Ar gas) are achieved 12 cm downstream at a low microwave power of 200 W. Moreover, a high Ar2+/(Ar++Ar2+) ratio of above 50% is obtained.
Reaction of NH4F/HF solutions on Si (100) and Si (111) surfaces
Authors: Gräf D. , Bauer-Mayer S. , Schnegg A.
Published: July 2002

The reaction of NH4F/HF solutions on Si (100) and Si (111) surfaces was investigated by means of x-ray photoelectron spectroscopy and high-resolution electron energy loss spectroscopy (HREELS). The pH of the HF treatment was varied in the range from pH 1 to pH 8. Exactly oriented Si (111) surfaces show an overall smoothing of the surface with increasing pH as can be seen by the vanishing of the SiH2 scissor vibration in HREELS spectra. In contrast, Si (100) surfaces tend to roughen by using HF solutions with higher pH. At intermediate pH (pH 5–6) the Si (100) surface regularity gets disturbed and new Si (111) like facets are formed. At higher pH the etching speed increases and the Si (111) facets again disappear.
Electric field in surface-wave-produced plasmas
Authors: Komachi K.
Published: July 2002

Electric field in a chamber of the surface-wave-plasma applicator was measured. Standing waves existed both above and in a chamber. However, a profile in the chamber differed from that above the chamber. This is because the profile in the chamber was affected by the chamber wall and changed to the profile decided by the geometry of the chamber. A square of the electric field strength in the chamber with plasma decreased to 1/50 of that without plasma. Almost all of the microwave power was absorbed by the plasma near the microwave window.
In situ x-ray photoemission spectroscopic studies of Al/SiO2 interface formation
Authors: Tsukada Mitsuo , Ohfuji Shin-ichi
Published: July 2002

A structural model for the Al/SiO2 interface system after an oxidation–reduction reaction is proposed. Thermal dependence of the initial stages of the Al/SiO2 interface formation process is investigated by in situ x-ray photoemission spectroscopy analysis and secondary ion mass spectrometry measurements of depth profiles. An abrupt interface without any reaction is confirmed when the interface is formed at room temperature. During Al deposition on SiO2 at substrate temperatures beyond 300 °C, oxidation–reduction reaction occurs that produces Al2O3 and reduces metallic Si at the interface. The reduced Si spreads throughout the entire Al layer uniformly and the thin Al2O3 layer acts as a diffusion barrier that limits the reaction in the very vicinity of the interface. This suggests a distinct layer ordering of the reacted system, Al(Si)/Al2O3/SiO2.
Metallization of Teflon PFA. I. Interactions of evaporated Cr and Al measured by x-ray photoelectron spectroscopy
Authors: Shi M. K. , Lamontagne B. , Selmani A. , Martinu L. , Sacher E. , Wertheimer M. R. , Yelon A.
Published: July 2002

Cr and Al were evaporated onto Teflon PFA (polytetrafluoroethylene−co-perfluoroalkoxy vinyl ether) substrates by electron beam evaporation. In situ x-ray photoelectron spectroscopy revealed that Cr deposition leads to defluorination and the formation of fluoride and carbide species. The concentrations of fluoride and carbide increased with deposited Cr thickness, slowly at the initial stages of deposition but more rapidly afterwards. Al deposition was qualitatively similar to that of Cr, although the concentrations of fluoride and carbide formed were much lower. The sticking coefficients of both metals, low at the outset of metal deposition, were enhanced after initial deposition, with simultaneous increases in interfacial reactions. Oxygen contaminants in the form of metal oxides were observed, particularly in the case of Al.
Spin ordering on a NiO(100) surface measured by metastable He 2 3S scattering
Authors: Swan A. , Marynowski M. , Franzen W. , El-Batanouny M. , Martini K. M.
Published: July 2002

Diffractive scattering of metastable 2 3S He (He*) has been used for the first time to determine the long-range spin ordering on the surface of an antiferromagnetic insulator. Although the long-lived He* has a high probability of deexcitation on impact with a surface, its survival probability can be enhanced when an appropriately located electron energy gap and localized spins are present on the surface. A periodic arrangement of the orientation of the local moments on the surface then leads to a periodic modulation of the beam attenuation that is reflected in the corresponding diffraction pattern. We have measured the electron spin ordering on a NiO(100) surface and found a structure quite different from the bulk antiferromagnetic arrangement. We have developed a model of the scattering process that is based on a modified version of the eikonal approximation and uses a dissipative hard corrugated wall to include the effects of a spatially modulated attenuation of the He beam. Calculations performed with this model are in good qualitative agreement with our experimental data.
Computer simulation of the ion beam deposition of binary thin films: Carbon nitride and boron carbide
Authors: Todorov S. S. , Marton D. , Boyd K. J. , Al-Bayati A. H. , Rabalais J. W.
Published: July 2002

A dynamic trim-based computer simulation program that includes treatment of post-cascade atomic motion has been used to model the ion beam deposition of carbon nitride and boron carbide thin films at energies below 100 eV. Simulations of chemically enhanced phenomena are based on describing the motion of the atoms as a sequence of ballistic steps followed by a chemically guided step. In the case of B–C films, a satisfactory description of the experimental results is achieved by including only ballistic effects in the simulation. For C–N, agreement between experiment and simulation requires the inclusion of a mechanism of preferential nitrogen re-emission into the program. This mechanism is modeled by the formation of nitrogen-containing dimers which are considered volatile and are readily released through the surface. The probability of dimer formation depends on the local N concentration. The simulation reproduces well both as-deposited composition measurements and Auger sputter depth profiling. The model represents a possible implementation of chemical sputtering.