bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of adsorbed Bi on the chemisorption properties of Pt(111):H2, CO, and O2
Authors: Paffett M. T. , Campbell C. T. , Taylor T. N.
Published: July 2002

The growth modes and interactions of vapor-deposited Bi on a clean Pt(111) surface and its effects on the chemisorption of H2, CO, and O2 have been monitored by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), and thermal desorption mass spectroscopy (TDMS). For submonolayer Bi coverages, LEED patterns were observed to progress with increasing coverage through p(2×2), ( 7/8 × 7/8 )R30°, p(3×3), and p(4×4) structures. The Bi TDMS and AES data are consistent with proposed structural models giving absolute coverages of 0.25, 0.33, 0.44, and 0.56, respectively. For submonolayer coverages of this s2pn-type metal, Bi adatoms are strongly repulsive and maximize their spacing subject to the constraints of the Pt(111) sites. This is to be contrasted with dnsm-type metals such as Ag, Cu, and Au on Pt(111), which show attractive interactions and coalesce into 2d islands. In chemisorption of small molecules on Pt(111), each Bi adatom blocks about two Pt surface atoms. An ensemble of two adjacent Pt sites is required for both dissociative H2 and molecular O2 adsorption versus one site for CO adsorption; therefore, uptake of the former adsorbates is much more severely attenuated as θBi increases.
Island coalescence in a chemisorbed overlayer
Authors: Pimbley J. M. , Lu T. -M. , Wang G. -C.
Published: July 2002

We have constructed and solved an overlayer island growth model in which the distribution of the islands obeys an ‘‘extended geometric distribution function.’’ This model describes quantitatively the growth of oxygen p(2×1) islands on a W(112) surface as the coverage is increased from 0 to 1. The average size of the islands is seen to increase sharply as the coverage approaches 1/2 monolayer, which is an indication of the coalescence of the overlayer islands.
Surface states and dipoles on Si(111)1×1:Na
Authors: Northrup John E.
Published: July 2002

A theoretical study of the interface formed by adsorption of one monolayer of Na on the Si(111) surface is presented. The equilibrium structure is predicted by minimizing the energy using the first principles pseudopotential method and local density approximation. The dispersion of the Na induced surface states, and the dipole resulting from charge transfer from the Na 3s orbitals into these surface states is calculated. The ionization potential of the overlayer system is predicted to be 2.1 eV.
Stress measurements on multilevel thin film dielectric layers used in Si integrated circuits
Authors: Chen Y. S. , Fatemi Homi
Published: July 2002

Thin film induced stresses on silicon substrate were measured at room temperature, using a stress gauge wafer deflection setup. The thermal oxide was in high compressive stress due to CTE mismatch between oxide and Si substrate. As deposited PSG was in tensile stress decreasing in stress level with increasing P content. After densification, stress was reversed to the compressive mode with no significant reduction in stress for 8%–10% phosphorus content. As deposited poly-Si was in the high compressive mode. However, subsequent doping reduced the stress to one-half of ‘‘as deposited’’ level and after annealing at 1000 °C the stress was further reduced. Cold sputtered aluminum metallization doped with 1% Si was found in the compressive mode, while hot sputtered copper doped Al metallization was under tension. Both films annealed at 450 °C hydrogen ambient exhibit reduced compressive and tensile levels, respectively. The CVD P-glass passivation was under low compression while plasma nitride was in high compressive stress. Most of these observations confirm previous reports. However, referenced results are confirmed and additional measurements are performed using a relatively new detection gauge system.
Control of thin film orientation by glancing angle ion bombardment during growth
Authors: Yu Lock See , Harper James M. E. , Cuomo Jerome J. , Smith David A.
Published: July 2002

Glancing angle ion bombardment during thin film deposition is shown to have a pronounced alignment effect on crystallographic orientation. Restricted fiber texture is achieved in Nb films deposited at room temperature onto amorphous silica substrates by Ar ion beam sputtering, with simultaneous bombardment by 200 eV Ar+ ions at 20° from glancing angle. The alignment direction corresponds to a channeling direction for the incident ions between (110) planes, for which a low sputtering yield is expected. The degree of alignment is measured as a function of ion/atom arrival rate ratio up to 1.3 Ar+ ions per Nb film atom, and is shown to increase monotonically with the fraction resputtered. Also, the fiber axis tilts slightly towards the incident ion beam direction, favoring the channeling direction.
Characterization of cam lobe and valve lifter antiwear films by a high-spatial-resolution Auger microprobe
Authors: Gaarenstroom Stephen W. , Caracciolo Frank
Published: July 2002

A camshaft lobe and mating valve lifter obtained from an engine-dynamometer wear study were characterized by a high-spatial-resolution Auger microprobe. The combined features of high spatial resolution and surface sensitivity in this instrument yielded substantial new information concerning the composition and distribution of engine oil-derived antiwear films formed on multiphase iron alloys. Films on the martensite phases of both parts were thicker (30 nm) than the films on the carbide phases and contained large amounts of P, S, Ca, and Zn. The carbide phases on both surfaces generally had higher surface contact load histories than the martensite phases, and the films were thinner (5–10 nm). Voids on both surfaces acted as reservoirs for engine oil constituents, including P, S, Ca, and Zn. Regions of thick, patchy films present on the lobes were identified as sulfides of Zn, Ca, and Fe.
An analytical expression for describing Auger sputter depth profile shapes of interfaces
Authors: Kirchhoff W. H. , Chambers G. P. , Fine J.
Published: July 2002

The composition versus depth distribution of a solid/solid interface as determined by Auger sputter depth profiling can be described by a logistic function of the form Y=[A+a(T−T0)]/(1+ex) +[B+b(T−T0)]/(1+e−x), where Y is a measure of the elemental surface concentration of one of the components that defines the interface. T is a measure of the sputtering depth and is usually expressed as sputtering time assuming a constant sputtering rate. A is a measure of the preinterface surface concentration for one of the elements of the interface and B is a measure of the postinterface surface concentration, where ‘‘pre’’ and ‘‘post’’ are taken in the sense of time. The empirical parameters a and b are introduced to account for additional time dependence of instrumental effects. T0 is the apparent midpoint of the interface region and x is a dimensionless, reduced time defined as (T−T0)/D. The scaling factor D is the characteristic time for sputtering through the interface region. All measures of the interface width will be proportional to D. Asymmetry in the depth profile can be accommodated by allowing D to vary with time. A least squares fitting program has been written which fits measured Auger spectral intensities to the above equation to within measurement error (approximately 1%). The statistics associated with the least squares fit allow confidence limits to be placed on the measured widths of interface regions and on the asymmetry associated with each such region.
V/Ge(111): Temperature dependent intermixing studied with high resolution photoemission and quantitative modeling
Authors: del Giudice M. , Butera R. A. , Ruckman M. W. , Joyce J. J. , Weaver J. H.
Published: July 2002

High resolution, temperature dependent core level photoemission results for the V/Ge(111) interface show the interplay between atomic diffusion and trapping in the boundary layer. Room temperature results show strong intermixing, and core level analysis allows us to identify well-defined chemical environments for Ge atoms (chemical shifts of −0.5 and −0.95 eV). Through modeling of the interface, we have determined the composition and extent of each reacted species. Studies at higher temperature showed that the extent and composition of the reacted overlayer could be varied. Indeed, by increasing the substrate temperature, we could produce an overlayer which became chemically homogeneous by 475 K. In this range, we find a diffusion activation energy of 5 kcal/mol which controls the width of the reacted layer.
Process modeling and simulation tools
Authors: Neureuther A. R.
Published: July 2002

An overview of modeling and simulation of physical processes which produce topographical effects in fabrication of integrated circuits is given. Resist characterization techniques, applications of optical aerial image simulation to lithography and inspection, and linking of layout with process, device, and circuit simulation are emphasized.
Effect of annealing on the structural and electronic properties of Au covered Si(111) surfaces
Authors: Taleb-Ibrahimi A. , Sébenne C. A. , Proix F.
Published: July 2002

Low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and photoemission yield spectroscopy (PYS) measurements are performed on a set of cleaved (111)silicon surfaces covered with a gold layer from 0 to 5 ML and vacuum annealed from 400 to 700 °C. The results show that the two dimensional Si–Au alloy which forms upon room temperature deposition transforms upon annealing into an ordered structure a few angstroms thick with the Si atoms in an outward position. This new intermixed layer covers uniformly both the crystalline Si substrate and the Au islands which form on the substrate only when gold in excess of the surface alloy composition has been deposited.
(7×7) and (5×5) superstructures of Ge-covered Si(111) surfaces studied by angle-resolved electron-energy-loss spectroscopy
Authors: Hasegawa Shigehiko , Iwasaki Hiroshi , Akizuki Makoto , Li Sung-Te , Nakamura Shogo
Published: July 2002

Using angle-resolved electron-energy-loss spectroscopy (AREELS), (7×7) and (5×5) surface structures of the ultrathin Ge films on Si(111)(7×7) surfaces are investigated. At a coverage of 1.5 monolayers (ML) of Ge, the Si(7×7)–Ge surface appears. On this surface a loss peak due to surface states of Ge dangling bonds appear at 1.15 eV (Δk∥=0 Å−1) and the one due to Si dangling bonds disappears, but the loss peaks due to the Si–Si backbonds are still observed. When the (5×5) surface structure develops at a coverage of 2 ML, the remaining loss peaks due to the Si–Si backbonds disappear and loss peaks due to Ge–Ge backbond surface states at 9 and 14 eV. We propose structural models of the Si(7×7)–Ge and Si(5×5)–Ge surfaces based on the structural models on the clean Si(7×7) surface [Takayanagi et al., J. Vac. Sci. Technol. A 3, 1502 (1985)].
The role of ammonia reagent in the surface texture and photoreactivity of thin cadmium sulfide films
Authors: Ebothé Jean , Nguyen Cong Hoan , Chartier Pierre
Published: July 2002

A smooth method of improving the surface texture of thin CdS films is presented in this work. The use of ammonia solution in this matter has been found to be safe, since no deleterious compound is released. The low rate of the process involved allows for an easy follow up of the photoreactive behavior of each of the samples treated for different immersion times. Monitoring of the change that occurred revealed that optimal conditions can be attained from either a single wet treatment of the sample or a repetitive wet treatment of the same sample in the same medium. Microstructure modification is likely to be the main factor responsible for the improvement in photoreactivity. A shiny electrochemical deposit engendered by the second method does not modify this behavior. That compound probably leads to a progressive change of the semiconductor-electrolyte junction in semiconductor insulator-electrolyte type.
Magnetron sputtering behavior in Fe–12.5 at. % Si alloy target
Authors: Ochiai Y. , Morioka Y. , Aso K.
Published: July 2002

The sputtering process in Fe–12.5 at. % Si alloy target (cbSi=12.5) of rf planar magnetron system was studied through the target surface and film concentrations by electron probe microanalyzer (EPMA) sampling depth. Si concentration of film cfSi was unchanged through total sputtering time tsp=2680 min while csSi (target surface) was constant until tsp≂500 min and decreased with further sputtering. At tsp<500 min concentrations were csSi =11.6 at. % Si and cfSi =10.7 at. % Si. The deposition rate was initially constant at 720 Å/min while at tsp≳1000 min it decreased to 610 Å/min. The anomalous behaviors in csSi were discussed and metallurgical phase change at target surface was considered but not decisive. The steady-state cfSi =cbSi was not observed even at high current density and the sputtering behaviors were interpreted as that the enhanced diffusivity could stretch the sputtering time to reach steady state.
Kinetics of surface reactions of CF3 radicals
Authors: Robertson Robert M. , Rossi Michel J. , Golden David M.
Published: July 2002

The kinetics of reactions of CF3 radicals on various substrate materials has been studied in a gold-coated, stainless-steel, very-low-pressure photolysis (VLPΦ) cell as a function of temperature and radical concentration. The substrate materials were gold, stainless steel, copper, copper oxide, and silica. The CF3 radicals were generated from CF3I by IR-multiphoton decomposition. The reaction products observed with a mass spectrometer included HF, CO, CO2, COF2, SiF4, and C2F6. Rate constants were obtained as a function of temperature. CF3 reacted most rapidly on copper oxide surfaces; the other metal surfaces were less reactive, and the silica surfaces were least reactive. Previous studies from this laboratory that had reported the reaction of CF3 on fused silica are reinterpreted as reactions of CF3 on the stainless-steel heater assembly.
Distribution of copper deposited inside holes by sputtering
Authors: Pargellis A. N.
Published: July 2002

Both cost considerations and environmental concerns have prompted the search for alternative methods to electroless copper deposition on the walls of vias (holes used for interconnecting different levels of circuitry in printed wiring boards). One attractive possibility is sputter deposition (a dry metallization process) of copper onto hole walls. This requires a knowledge of deposit thickness as a function of depth into the hole. Experimental results are presented for the variation with depth in the thickness of copper deposited onto the walls of circular holes by sputtering. For large distances into holes oriented perpendicularly to the sputter source, the thickness of the deposit decreases with depth as (D/L)3, where D is the hole diameter, L is the distance into the hole, and L/D>2. The experimental results agree with the calculated values obtained by using Lambert’s law, where the emitted flux is integrated over the magnetron area from which the sputtered copper can travel to a particular region on the hole wall. The data are used to predict the deposit thickness as a function of depth into through holes which have been subjected to sputtered copper from both sides. For a deposit thickness on the outer planar surface of 25 000 Å, and holes with aspect ratios A of 1, 2, 3, 5, and 10, the predicted deposit thickness on the hole walls at the midplane are 13 600, 8400, 4400, 1200, and 160 Å, respectively.
Inverse photoemission study of the Si(100)-(2×1) K surface
Authors: Batra Inder P. , Nicholls J. M. , Reihl B.
Published: July 2002

We report k-resolved inverse photoemission results for the unoccupied surface-state bands of the reconstructed Si(100)-(2×1) surface with potassium. The experimental results are compared to the surface-state bands obtained from geometry-optimized total-energy calculations. These self-consistent field calculations suggest an ionic type of bonding of the K atom to the Si substrate up to one-monolayer coverage. The origin of the metallization has to be attributed to the partial occupancy of the Si dangling bonds. The experimental data find the unoccupied surface bands as expected from such a picture, but their energy dispersion is not in full agreement with theory.
Radio frequency sputter deposition of SiO2 films at high rate
Authors: Logan J. S. , Jones F. , Costable J. , Lucy J. E.
Published: July 2002

SiO2 films have been deposited by rf sputtering in a conventional tuned substrate rf diode system at 40.68 MHz. Deposition rates as high as 2690 Å/min were achieved on a single 125-mm-diam silicon substrate, as compared to a typical rate of 250 Å/min for large manufacturing batch tools. Substrates were cooled using gas conduction, to limit temperatures to below 150 °C. These films were nonabsorbing and had stress and refractive indexes in the normal range for conventionally sputtered films, without the need for added oxygen to the argon gas. Temperatures were measured using a Luxtron FluoropticTM Thermometer. Deposition rates were compared to those predicted from a simple computer model of the system, using published sputter-yield data and measured electrode voltages. Good agreement was obtained using a weak plasma approximation for the sheath voltage at the system wall. Films were deposited at low and high (planarizing) resputtering conditions using simple substrate tuning adjustment.
The effect of fluorine atoms on silicon and fluorocarbon etching in reactive ion beam etching
Authors: Cheeks Teresa L. , Ruoff Arthur L.
Published: July 2002

Silicon, polymethylmethacrylate, polyvinylidenefluoride, and polytetrafluorethylene were etched with a reactive ion beam of CF4+NF3 mixtures, to simulate the effect of increasing fluorine atom concentration on polymer etching. We hypothesize that fluorocarbon deposits observed on the Si surface after beam etching are due to a lack of reactive neutrals, namely, fluorine atoms. We show that by increasing the % NF3 from 0% NF3 (F/C=4) to 50% NF3 (F/C=7) the etch rate of Si and the polymers increased. Also the polymer etch rates appear to be composition dependent. Fluorine atom intensity(7037 Å), monitored by optical emission spectroscopy, increased as NF3 was added to CF4. A comparison between reactive ion etched and reactive ion beam etching polymers was performed using electron spectroscopy for chemical analysis.
Surface roughness for metallic thin films deposited upon various dielectric coatings
Authors: Varnier F. , Mayani N. , Rasigni G. , Rasigni M. , Llebaria A.
Published: July 2002

In this paper we present some results about the dependence of the surface roughness for thin silver films deposited upon calcium and lithium fluorides. It is found out that the underlayer’s effect is not the commonly expected one.
The influence of the mica surface composition on the growth morphology of discontinuous epitaxial palladium vapor deposits
Authors: Koch R. , Poppa H.
Published: July 2002

Transmission electron microscopy (TEM) and temperature programmed desorption (TPD) have been used in a complimentary manner to characterize particulate palladium films prepared on ‘‘hydroxylated’’ and ‘‘dehydroxylated’’ mica. The state of dehydroxylation was assessed by electron energy loss spectroscopy. In both cases TEM shows almost perfect epitaxial growth of Pd with the Pd{111} parallel to the mica surface. Particle number density is increased and mean particle diameter decreased on dehydroxylated mica. TPD of CO indicates mainly Pd{100} and Pd{111} facets on hydroxylated and dehydroxylated mica, respectively. On hydroxylated mica, additional CO binding states are found on thicker deposits having energies characteristic of more open crystal faces.
Photoemission study of nitric oxide adsorption on (110) gallium arsenide
Authors: Bermudez V. M. , Williams R. T. , Long J. P. , Rife J. C. , Wilson R. M. , Tuttle A. E. , Williams G. P.
Published: July 2002

Photoemission has been used to study the effects of chemisorption of nitric oxide (NO) on the valence-band and Ga and As 3d core levels of (110)-GaAs wafers. A parallel sequence of experiments using O2 has also been carried out. For exposures of 104–107 L at 300 K, NO dissociates and reacts with the surface more slowly than does O2. This stage involves defects and shows no photoenhancement. Above 107 L oxidation occurs, at least as fast for NO as for O2, and electronic excitation of the substrate by visible/near-ultraviolet irradiation during large NO exposures is found to enhance the formation of As–O species. Little N is detected on the surface after oxidation by NO. A model for the differences in oxidation behavior of NO and O2 is proposed.
Molecular-beam scattering of O2 and Ar from Ag(111)
Authors: Spruit M. E. M. , Kuipers E. W. , Tenner M. G. , Kimman J. , Kleyn A. W.
Published: July 2002

A well-collimated supersonic beam of Ar or O2, optionally seeded in He, collides with a Ag(111) surface. The resulting momentum distribution of the scattered particles is measured using a rotatable quadrupole mass spectrometer and time-of-flight (TOF) techniques. Comparing O2 with Ar shows that O2 behaves in direct scattering from Ag(111) very much like the monoatomic Ar. Both Ar and O2 scattering can be described rather well by a hard-cube model, although the parallel momentum is not conserved. The agreement between O2 and Ar suggests the existence of a potential barrier of at least 170 meV between the physisorbed and the chemisorbed O2 state on the Ag(111) surface.
Electrode separation and convex electrode surfaces in plasma etching
Authors: Eisele Konrad M.
Published: July 2002

The interelectrode distance in a parallel-plate etch reactor has been examined as a parameter of influence on the etch rate. If this distance decreased below 12 mm the etch rate increased appreciably for both configurations, the substrate on the grounded as well as on the powered electrode. This information is applied to design a convex spherical electrode surface to equalize the etch rate over the whole wafer, which otherwise is higher at the edge than at the center for the process described. In the example given, aluminum is etched with SiCl4 at a pressure of 0.3 Torr.
Optical properties of Cs2O and Ag–Cs2O thin films
Authors: Wu Quan-De , Xue Zeng-Quan , Li Jian-Ping
Published: July 2002

The optical properties of well-activated Cs2O and Ag–Cs2O thin films have been studied. These films are important for photoemission, especially for the ultrashort laser pulse detection. The curves for the index of refraction n, extinction coefficient k, and complex dielectric constant of Cs2O with different Cs impurity content are derived as a function of wavelengths of visible and infrared lights. The variations of front reflectance RF, vacuum reflectance RV, and transmittance T of the Cs2O thin film with an amount of Ag added into it were measured. The effects of sizes and shapes of metal colloidal particles embedded in semiconductor thin film on light absorption and scattering are discussed theoretically. The values of the absorption coefficient of Ag–Cs2O are also calculated.
Electron energy-loss spectroscopy study of hydrogenated amorphous silicon
Authors: Burnham N. A. , Fisher R. F. , Asher S. E. , Kazmerski L. L.
Published: July 2002

Electron energy-loss spectroscopy is used to study hydrogenated amorphous silicon (a-Si:H). Core-level and plasma excitations were examined as a function of hydrogen content. This technique and its interpretation reveals a consistent picture of the electron excitations within this important material. The a-Si:H thin films were fabricated by rf sputtering. Their hydrogen concentrations ranged from 0% to 15%. Hydrogen content was determined by infrared spectroscopy and secondary ion mass spectroscopy. X-ray photoelectron spectroscopy and inspection of the silicon Auger-KLL peak confirmed the silicon core levels.
Thin metallic silicide films epitaxially grown on Si(111) and their role in Si–metal–Si devices
Authors: Derrien J. , d’Avitaya F. Arnaud
Published: July 2002

Recent advances in the epitaxial growth of various d-metal silicides on Si(111) are reviewed. The growth mechanisms, the structural, and electronic properties of epitaxial silicides are described. In situ surface techniques such as low-energy electron diffraction, Auger electron spectroscopy, x-ray induced photoemission spectroscopy, ultraviolet photoemission spectroscopy, extended energy-loss fine structure, electron energy-loss near edge spectroscopy, and ex situ techniques such as Rutherford backscattering, cross-section transmission electron microscopy, and deep-level transient spectroscopy have been used to study the special case of quasiperfect ultrathin films of CoSi2 on Si(111). Physical factors affecting the CoSi2 epitaxy are discussed. The role of CoSi2 film in metal base and permeable base transistors is also addressed.
The atomic structures of the Si(111)-√3×√3- and -6×6-Au surfaces studied by low-energy ion scattering
Authors: Huang Judy H. , Williams R. Stanley
Published: July 2002

Two Au-induced Si(111) reconstructions, the (3)1/2×(3)1/2 and 6×6, were studied using impact-collision ion scattering spectroscopy with a 5-keV Li+ ion beam. The nearly identical ion scattering results for the two surfaces reveal that the local atomic structures of the (3)1/2×(3)1/2 and 6×6 reconstructions are closely related. The scattered-ion angular distributions clearly show that the Au atoms are not embedded in the Si surface. A comparison of the experimental data with computer simulations gives excellent agreement for a model in which both surfaces are composed of a mixture of the honeycomb and centered hexagon structures proposed previously for these surfaces, although such a determination is not unique.
Imaging of tritium implanted into graphite
Authors: Malinowski M. E. , Causey R. A.
Published: July 2002

The extensive use of graphite in plasma-facing surfaces of tokamaks such as the Tokamak Fusion Test Reactor, which has planned tritium discharges, makes two-dimensional tritium detection techniques important in helping to determine torus tritium inventories. We have performed experiments in which highly oriented pyrolytic graphite (HOPG) samples were first tritium implanted with fluences of ∼1016 T/cm2 at energies ≲25 eV and then the near-surface implant distributions were detected in two dimensions using tritium imaging. A portion of the sample was masked off during the implant in order to produce a well-defined implant boundary. Heating of the HOPG samples to temperatures as high as 500 °C resulted in no discernible motion of tritium along the basal plane, but did show that significant desorption of the implanted tritium occurred. The current results indicate that tritium in quantities of 1012 T/cm2 in tritiated components could be readily detected by imaging at lower magnifications.
Reversible change between metastable crystalline phases by laser beam irradiation in sputtered Au–Ge alloy films
Authors: Ikegawa S. , Komatsu S. , Arai S. , Kikitsu A. , Yasuda N.
Published: July 2002

Various Au–Ge alloy thin films have been prepared by the rf magnetron cosputtering method. The β (hcp) and γ (tetragonal) metastable crystalline phases were observed in as-deposited films, depending on film composition and thickness. Films 25 nm thick with a composition of ∼50 at. % Ge, which were composed of β-phase microcrystals, showed reversible reflectance change by laser beam irradiation. The irradiated area changed to the γ phase with oriented coarse grains. When a lower power laser beam was scanned along the previously recorded bit, i.e., the changed γ phase area, the crystals returned to the β phase with a fine microstructure. This transformation between the metastable phases accompanying microstructure change causes reversible changes in the reflectance of the film, for more than 100 cycles. Laser induced crystalline-to-crystalline phase transformations in Au–Ge alloy thin films are of interest for use in reversible optical data storage.
Complex impedance versus frequency analysis of Al:SiC:Al metal–insulator–metal structures
Authors: Soukup R. J. , Tiwald T. E.
Published: July 2002

Metal–insulator–metal (MIM) structures have been fabricated by sputter depositing SiC on Al substrates, using a single SiC target, and evaporating Al contacts on the front surface. The resulting MIM structures were investigated by measuring the complex impedance of the samples as a function of frequency (5 Hz–13 MHz) under varying conditions of bias and temperature. An electrically equivalent model of the MIM structure can be developed by analyzing the plots of various parameters derived from the impedance versus frequency tests. The model consists of an RC network where each element represents a particular physical phenomenon. By fitting the test data curves to curves of the appropriate RC network, element values can be estimated and the characteristics of the film and its contact regions can be quantified. A system has been assembled that will automatically perform the tests and then allow the researcher to interactively develop models based on a curve fit to the test data. Algorithms have been developed that help determine the model configuration and estimate the element values from visual inspection of the various impedance parameter curves. The ac analysis of the films indicates that Schottky barrier contacts with depletion widths in the range of 300 to 600 Å are forming at the metal–insulator interfaces.
Quantitative reflection high-energy electron diffraction measurements of surface roughness in GaAs(100)
Authors: Heller E. J. , Savage D. E. , Lagally M. G.
Published: July 2002

Reflection high-energy electron diffraction (RHEED) measurements of the microscopic surface roughness of polished GaAs(100) wafers subjected to various surface cleaning procedures are presented. These include Br2:MeOH, HCl, and sputter etching, each followed by annealing in UHV. The results indicate that chemical etches such as Br2:MeOH and HCl produce large three-dimensional (3D) asperities that cannot be removed by annealing, while sputter etching produces less roughness. Quantitative values of the mean asperity height are presented. Measurements on GaAs(100) are compared with results from sputter-etching-induced roughness on cleaved GaAs(100), which initially has a nearly defect-free surface. Remanent roughness is always at least 2 or 3 atomic layers, with terrace widths of 100 Å or less.
Multiple initial chemisorption sites: Al on GaAs(110)
Authors: Menon Madhu , Allen Roland E.
Published: July 2002

In simulations of the initial stages of chemisorption on semiconductor surfaces, we find that atoms which are very electronegative (e.g., O) tend to bond to the cation and those which are very electropositive (e.g., Li) to the anion. However, atoms which are intermediate in electronegativity can bond to either, and we find a multiplicity of initial chemisorption sites. For example, Al has been observed to bond at six distinct initial sites.
Valence-band photoemission and electron energy-loss studies of reactive ion etched silicon dioxide
Authors: Robey S. W. , Oehrlein G. S.
Published: July 2002

Results are presented for x-ray photoemission and electron energy-loss (EELS) measurements of the valence bands and band-gap region of silicon dioxide fluorinated during reactive ion and plasma etching in CF4 based plasmas. Valence-band photoemission reveals a band of three fluorine induced features, at binding energies of ∼10.0, 11.9, and 14.4 eV. Comparisons with the SiO2 valence bands and implications for bonding are discussed. Complementary results from EELS are presented along with a discussion of transitions observed in the band gap of etched silicon dioxide. A comparison of samples etched under reactive ion etching conditions with those etched under plasma etching conditions (negligible ion bombardment) indicates that the ion bombarded surfaces exhibit a reduced level of fluorination during steady-state etching.
Scanning tunneling microscopy and atomic force microscopy of the liquid–solid interface
Authors: Schneir J. , Marti O. , Remmers G. , Gläser D. , Sonnenfeld R. , Drake B. , Hansma P. K. , Elings V.
Published: July 2002

The liquid–solid interface is important not only for science, but also for technology. Scanning tunnel microscopes (STM’s) and atomic force microscopes (AFM’s) can image and even manipulate solids covered with liquids. An image of a line 75 nm long and 5 nm wide drawn with an STM on a liquid-covered Au(111) surface demonstrates the potential for manipulating surfaces. Images of a Pt film demonstrate the ability of STM’s to find new features by zooming from large-area scans down to the atomic scale. Finally, an AFM image of a liquid-covered graphite surface demonstrates atomic resolution.
Experimental study of forces between a tunnel tip and the graphite surface
Authors: Yamada H. , Fujii T. , Nakayama K.
Published: July 2002

Forces between a scanning tunneling microscope (STM) tip and graphite surface are studied in air by use of a cantilever beam as the conducting tip holder and another tunnel tip as a detector for the deflection of the beam. The results show that the STM tip usually operates under the strong repulsive force. The measured force changes according to the topographic corrugations in the standard topographic mode: however, the change is not observed in the current-imaging mode.
Theoretical scanning tunneling microscopy and atomic force microscopy study of graphite including tip–surface interaction
Authors: Batra Inder P. , Ciraci S.
Published: July 2002

The graphite surface, due to its unusual electronic structure, offers challenges and opportunities for scanning tunneling microscopy (STM) and atomic force microscopy (AFM). To draw a measurable current at small voltages (1 nA at 50 mV) the tip has to approach close to the surface; estimated tip-to-surface distance is ∼2 Å. At such distances repulsive interatomic forces between the tip and surface set in (the basis of AFM) and it is important to consider the tip–surface interaction. Therefore, we have calculated interatomic forces and charge densities including the tip (atom) as an integral part of the system rather than treating it perturbatively. Our calculations reveal that the tip at close proximity to the surface disturbs the states near the Fermi level, and induces localized states which in turn influence the STM images. The tunneling barrier appears to collapse at small tip-to-surface distances. Some experimental evidence for this effect is cited. The repulsive force on the tip has a value in the range of 10−9 N when the tip–surface separation is ∼2.5 Å. The identification of the two inequivalent atoms by AFM is examined. It is suggested that AFM and STM are sensitive to different types of sites on the graphite surface. The effect of multiatomic tip and the tip induced relaxation on the AFM images is briefly discussed.
Kinetics of growth coalescence of In/GaAs
Authors: Adams J. B. , Hitchon W. N. G. , Holzmann L. M.
Published: July 2002

The nucleation and growth of In clusters on GaAs has been numerically modelled using a kinetic rate equation approach. The rate equations were solved using a propagator method which is more efficient than a finite-difference scheme, allowing large time steps during which clusters grow by many atoms. The rate of growth coalescence is calculated analytically. A Monte Carlo model of nucleation and growth is presented and shown to yield equivalent results to the propagator method. Both models are used to determine growth mechanisms and the diffusion rate of In atoms on GaAs, using the data of Savage and Lagally. The effect of changing the deposition rate or substrate temperature on the average island size is predicted, and shown to agree with the available data.
Optical phenomena observed in low-energy ion and electron bombardment of silica surfaces
Authors: Mogul H. C. , Haglund R. F. , Weeks R. A. , Kinser D. L. , Tolk N. H. , Wang P. W.
Published: July 2002

Optical spectroscopy has been used to characterize the interaction of ionizing radiation with glasses, including ions with energies in the 3–10 keV range, and electrons with energies ranging from 320 to 640 eV. Characteristic line emission spectra of desorbed excited atoms, as well as luminescence spectra from the near-surface bulk, were observed. A search for possible changes in desorption mechanisms as a function of radiation dose was carried out by observing the time dependence of integrated intensity and spectral linewidth for desorbed silicon and the trace element calcium. Defect formation in the near-surface bulk was monitored by spectrally resolved, time-dependent measurements of the bulk luminescence and by electron paramagnetic resonance spectroscopy. These spectroscopic observations are correlated with identifiable differences in the manufacturing processes of several silicas, and thus can be related to one particular kind of surface radiation damage, namely, ion- and electron-induced desorption.
Transmission electron microscopy study of cross-section microstructures of magnetron sputter ion-plated Al films on Ni substrate
Authors: Wan L. J. , Kuo K. H.
Published: July 2002

With cross-section samples, the microstructures of magnetron sputter ion-plated (MSIP) Al films on Ni substrates have been studied by transmission electron microscopy. The films consist of the three layers of microstructures: globular, columnar, and massive. An unknown phase in the Al–Ni system is also found at the interface between Al film and Ni substrate. By electron diffraction and energy dispersion x-ray analyses, it is identified as body-centered tetragonal with lattice constants a=b=0.588 nm, c=0.480 nm, and is rich in aluminum. Based on the observations and the character of the MSIP technique, the forming mechanism of Al films made by MSIP is discussed.
Activated metal deposition and oxide growth on semiconductors: TiO2/Si(111)-2×1
Authors: Xu F. , Hill D. M. , Benning P. J. , Weaver J. H.
Published: July 2002

We report a high-resolution x-ray photoemission study of interface formation involving 1–30 Å of TiO2 grown on p-type Si(111)-2×1 by the deposition of Ti in an activated oxygen atmosphere (5×10−6 Torr). Line-shape analysis for the Si 2p, Ti 2p, and O 1s core levels and the valence bands indicates that the Ti adatoms are in the formal 4+ oxidation state in TiO2, that a thin Si oxide interlayer also forms at the interface but is uniformly covered by TiO2, and that Ti–Si reaction is suppressed. For low TiO2 coverages, we observe a nonmonotonic movement of the semiconductor Fermi level.
Characteristics of electron cyclotron resonance plasma sources
Authors: Popov O. A.
Published: July 2002

Electron cyclotron resonance plasmas were excited at a frequency of 2.45 GHz in chambers with diameters smaller and larger than cutoff ones for fundamental TE and TM modes. Microwaves were introduced in the plasma chambers from the cw generator via a vacuum window and the microwave transmission line. It was found that microwave breakdowns at pressures 10−5–10−1 Torr (argon, nitrogen, oxygen) occurred at sites where the static magnetic field was 875 G (or close). In chambers with diameter smaller than cutoff, the breakdown occurred only near the vacuum window. A high absorption level of microwave power (>95%) was achieved in all explored chambers at microwave power P=300–1000 W. It occurred at areas where the static magnetic field was ∼875 G and the plasma density was Ncr=7.4×1010 cm−3. A high microwave power absorption level resulted in high plasma density up to Ne=1012 cm−3 at P=1000 W. No saturation in Ne=f(P) was observed. The shape and location of the high plasma density area was determined by microwave matching tuning, magnetic field and its configuration, and source chamber size.
Plasma characterization of an electron cyclotron resonance–radio-frequency hybrid plasma reactor
Authors: Lee Young H. , Heidenreich John E. , Fortuno Guadalupe
Published: July 2002

Langmuir probe measurements have been carried out for Ar, O2, and CF4 plasmas generated by an electron cyclotron resonance–radio-frequency (ECR–rf) hybrid plasma reactor. The resonance width of electron cyclotron resonance, defined at one-half of the maximum plasma density, is measured to be ∼200 G below 1 mTorr and increases with gas pressure for all three gases. No enhancement in the plasma density was observed in the ECR region at or above 70 mTorr for all three gases. The mean electron energy was measured to be 7.2 eV for a microwave power level of 700 W and the energy distribution is nearly Maxwellian. Plasma density increases with the magnetic field. The magnetic field effect becomes more prominent when rf bias is applied to the substrate electrode. The rf bias not only extracts ions from ECR-generated plasmas, but also generates a plasma more effectively due to the magnetic field.
Growth of GaAs on Si using ionized cluster beam technique
Authors: Kim K. , Sung M. Y. , Hsieh K. C. , Cowell E. W. , Feng M. S. , Cheng K. Y.
Published: July 2002

A single-crystalline epitaxial film of GaAs has been grown on Si using an ionized cluster beam technique. The native oxide layer on the silicon substrate was removed at 550 °C by use of an accelerated arsenic ion beam, instead of a high-temperature desorption. During the growth the substrate temperature was maintained at 550 °C. Transmission electron microscopy and electron diffraction data suggest that the GaAs layer is an epitaxially grown single-crystalline layer.
Surface-stoichiometry dependence of As2 desorption and As4 ‘‘reflection’’ from GaAs(001)
Authors: Tsao J. Y. , Brennan T. M. , Klem J. F. , Hammons B. E.
Published: July 2002

Using real-time reflection mass spectrometry, we have measured the temperature dependence of As2 desorption and As4 ‘‘reflection’’ from a GaAs(001) surface. The measurements agree well with the second-order flux-balance equation expected to govern surface stoichiometry, and determine its rate constant. Using that rate constant, the equation associates physically reasonable surface stoichiometries with the various well-known GaAs(001) surface reconstructions, and is strikingly consistent with measurements of the times for surface reconstruction changes in the absence of an As ambient.
Electron stimulated desorption of excited neutrals from the surface of solid rare gas
Authors: Arakawa I. , Takahashi M. , Takeuchi K.
Published: July 2002

Electron stimulated desorption from the surface of rare-gas solids (Ar, Kr, and Xe) was studied. Electronic excitations in a solid, which are produced by electron irradiation, induce the desorption of multiply charged ions, neutral molecules, and excited neutrals from the surface. The kinetic energies of the excited neutrals were determined by time-of-flight measurement: 0.6 and 0.04 eV for Ar, 0.7 eV for Kr, and 1.5–2 eV for Xe at the peak of energy distribution. These metastables, except Xe, are thought to be originated by a decay process of an ionic dimer to an excimer (R+R++e−→R+R*) before self-trapping of exciton. The authors found that H2 physisorbed on the surface of the solid Xe, enhancing the desorption of the excited neutral.
Surface photochemistry. IX. Photochemistry of small molecules on metal surfaces
Authors: Roop B. , Zhou Y. , Liu Z.-M. , Henderson M. A. , Lloyd K. G. , Campion A. , White J. M.
Published: July 2002

The chemistry of alkyl halides and ketene has been studied on Pt(111) and on thick layers of Cu on Ru(001). Using postirradiation analysis by high-resolution electron energy-loss spectroscopy and temperature programmed desorption, we have demonstrated the photodissociation of alkyl halides on these two substrates and the alteration of the decomposition channels of ketene. In this paper, we summarize previously reported work and report, for the first time, evidence for photodissociation on copper.
Surface structure determination of the cleavage faces of CdSe via low-energy positron diffraction
Authors: Duke C. B. , Lessor D. E. , Horsky T. N. , Brandes G. , Canter K. F. , Lippel P. H. , Mills A. P. , Paton A. , Wang Y. R.
Published: July 2002

Low-energy positron diffraction intensities were measured for 10 beams from CdSe(101̄0) and 14 beams from CdSe(112̄0). These were compared with calculated intensities for bond-length-conserving relaxed surface structures for both surfaces. Using an R-factor methodology the best-fit structures were obtained for these surfaces corresponding to local planar tilt angles of ω=15°±5° for CdSe(101̄0) and ω=27±7° for CdSe(112̄0). Both results are in excellent correspondence with structures predicted by tight-binding total-energy minimization calculations.
Orientational stability of silicon surfaces
Authors: Bartelt N. C. , Williams E. D. , Phaneuf R. J. , Yang Y. , Das Sarma S.
Published: July 2002

We summarize recent experimental work we have performed on the orientational stability of various Si surfaces, concentrating on the interpretation of the results in terms of the Si equilibrium crystal shape. We have found that Si surfaces misoriented by up to ∼12° from the (111) plane are stable at high temperatures. Below the ‘‘(1×1)’’-to-(7×7) reconstruction transition on Si(111) the surfaces misoriented towards the [1̄10] and [112̄] directions reversibly facet into stepped and reconstructed unstepped regions. Here we discuss in detail thermodynamical and statistical mechanical models of this faceting. Surfaces misoriented from the (111) plane in the [1̄1̄2] direction, as well as (100) and (112) surfaces are stable over the accessible temperature range. However, the introduction of small amounts of carbon causes both the (100) and (112) to facet. Calculations of the stability of Si(112) using recently proposed empirical potentials for Si are presented.
Curve fitting of photoemission spectra with physically realistic subspectra
Authors: Niemantsverdriet J. W. , Wandelt K.
Published: July 2002

A curve-fitting routine, based on nonlinear iterative least-squares optimization, for photoemission spectra is described in which theoretical or empirical relations between spectral parameters can easily be included. The advantage of the method is that the calculated fits are automatically acceptable from the viewpoint of physics, provided that the correct conditions have been formulated. The procedure is illustrated with a photoemission spectrum of xenon adsorbed on a heterogeneous surface.
Primary electron orbit calculation in a bucket-type ion source for ion milling
Authors: Ono Y. , Hakamata Y. , Sato T. , Hashimoto I.
Published: July 2002

Primary electrons in a bucket-type source for ion milling were investigated. Electron orbits were obtained using a computer program which solves the motion equation of electrons in a three-dimensional magnetic field. Calculations and experiments showed that trapped primary electron density in the source agreed well with generated plasma density. The program was used to develop a large-area ion milling machine with a 58-cm-diam bucket-type source. The machine that was developed provided a uniform ion beam and milling rate.
Sputter deposition of aluminum and other alloys at cryogenic temperatures
Authors: Chambers D. L. , Wan C. T. , Susi G. T. , Taylor K. A.
Published: July 2002

Structures of thin films deposited at ambient temperatures are similar to those of the bulk material whereas at lower temperatures films have significantly reduced grain size and may become amorphouslike. A two-stage cryorefrigerator was installed in a sputtering system to allow thin films of aluminum and aluminum–copper alloy to be deposited onto substrates cooled to cryogenic temperatures less than 30 K. Gases used for sputtering were argon, neon, and helium at pressures ranging from 0.40 to 2.0 Pa. A standard planar magnetron cathode was used. Vapor pressure–temperature data for gases show that argon will not cryocondense on substrate surfaces at temperatures greater than 40 K and neon will not cryocondense at temperatures above 11 K. Helium is considered for sputtering at substrate temperatures below 11 K. The purpose of this work is to determine the deposition rates using argon, neon, and helium and microstructure changes occurring when thin films are deposited onto cryogenically cooled substrates. Deposition rates are determined using surface profilometry and microstructure was determined by transmission electron microscopy.