bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison Spectra for Calcite by XPS
Authors: Baer D. R. , Marmorstein A. M. , Williford R. E. , Blanchard D. L.
Published: July 2002

Calcite is a common component of soil and a natural mineral sometimes found in the form of large high quality single crystals. The interactions of calcite with ions in ground water affects their transport in the environment. Consequently, understanding the surface chemistry of calcite is important for environmental remediation research. To establish the nature of a clean calcite surface, single-crystal rhombohedral calcite (CaCO3) was cleaved in vacuum to expose the (101¯4) plane for x-ray photoelectron spectroscopy analysis. Survey and multiplex spectra were obtained under standard operating conditions with a Perkin-Elmer Physical Electronics 550 spectrometer. An adventitious carbon peak, from a cleavage surface exposed to the environment, was used to measure surface charging and allow determination of binding energies for calcite C 1s, O 1s, and Ca 2p3/2 photopeaks. Two forms of C were observed on the vacuum cleaved specimen: a “carbonate” and a “carbide” peak.
Performance of a Modified Buried Collector Gauge
Authors: Beitel George A. , Gosselin Charles M.
Published: July 2002

The performance of a modified buried collector gauge was determined over a (helium) pressure range 10−13–10−4 Torr. Optimum operating parameters were empirically chosen. With 5.0-mA emission current and 100-V grid to filament potential, the x-ray photoelectron current of the gauge was estimated to be 5.2×10−13 A. By subtracting the measured background current, linear response was obtained between 6×10−13 and 3×10−4 Torr (He) with a gauge sensitivity of 0.015 A/Torr (He). Variations of gauge sensitivity as a function of filament geometry are discussed.
Vacuum Heat Treating Using Plasma EB
Authors: Takei H. , Yoneda Y.
Published: July 2002

This paper describes a semicontinuous heat treatment equipment with some of its operating results for metal strips or foils. Work accelerated electron flux from a hot hollow cathode discharge is used for bombarding the strip. Use of hot hollow cathod discharge for annealing of a metal strip was briefly discussed by Morley in 1963. (see Ref. 1.) Smith, Jr. and Hunt reported in 1965 (Ref. 2) the use of high-voltage high-vacuum electron beam for continuous annealing of metal strips. Homogeneous thermal history, rapid heating cycle, and a very high temperature processing are obtainable by using an electron bombardment heating for running strips. Processing of metal strips while running will also be desirable for high temperature treatment where adhesion between layers of a roll may cause defects. The high-voltage high-vacuum EB is advantageous in obtaining higher energy density than the use of hot hollow cathode EB. The latter, however, operates at a low voltage and often more economically than the former. Less evaporation of a volatile component can be another factor to be considered for some alloys. Thus refractory alloys strip rolls that require high temperature contamination free environment, minimum vaporization of volatile component, and nonsticking between layers will be suitable for the plasma EB semicontinuous or continuous processing.
Behavior of Refractory Metal Surfaces in Ultrahigh Vacuum as Observed by Low-Energy Electron Diffraction (LEED) and Auger Electron Spectroscopy
Authors: Dooley George J. , Haas T. W.
Published: July 2002

Surface phenomena of both refractory metal single crystals and polycrystalline foils in ultrahigh vacuum environments (1×10−9–2×10−11 Torr) are discussed. Some of the more common refractory metals which have been studied are Ti, V, Cr, Fe, Zr, Nb, Mo, Rh, Hf, Ta, W, Re, and Au. Surface studies are initiated once the sample has been placed in the ultrahigh vacuum chamber, and the entire system has been baked out for several hours around 250°C. The first technique employed is Auger electron spectroscopy which involves measuring the energies of certain inelastically (secondary) emitted electrons by means of any one of several available energy analyzing devices. In our case, the low-energy electron diffraction (LEED) optics of a standard Varian unit were modified to serve as the required retarding potential energy analyzers. This technique enables the composition of the sample surface to be monitored during the procedures necessary to produce the clean metal surface. Specifically, some of the cleaning procedures are high temperature anneals (to near the melting point), reaction with H or O, and Ar ion bombardment. Some of the various contaminants which segregate on several refractory metal surfaces during cleaning procedures will be identified and techniques for their removal discussed. The sample surface is considered clean when its Auger spectrum corresponds very closely to published spectra taken from surfaces thought to be clean to the limit of present detection techniques. Once clean and in the 10−10–10−11 Torr range, the surface of the sample will remain clean for extended periods of time. If the clean specimen is then exposed to somewhat higher pressures (10−6–10−8 Torr) of common gases such as O2, H2, N2, and CO, the LEED pattern will in most instances change from that characteristic of the clean surface to another pattern due to the particular structure and species of adsorbed gas. One or more coverage states may exist for the same gas being chemisorbed onto the same single crystal metal surface. In most cases, a new coverage state will give rise to a different LEED pattern. And, except for H, the particular adsorbed species can again be identified using Auger spectroscopy. Specific cases to be discussed will be the adsorption of H, O, and CO on the three most densely packed planes of Mo, namely the (110), (100), and (112) planes, the adsorption of O on the Re (0001) plane, and other selected results on W, Ta, Hf, and Zr.
A high vacuum valve with a programmed opening rate
Authors: Hablanian M. H. , Landfors A. A.
Published: July 2002

The basic mass flow capacities of a diffusion-pump–mechanical-pump combination are reviewed. Overload conditions for the diffusion pump are identified in the unstable region of inlet pressures from 3×10−4 to 3×10−3 Torr depending on pump size. Calculations show that the high vacuum vapor jet ceases to function when the ratio of numbers of pumped gas molecules to motive fluid molecules exceeds 0.2. To prevent the breakdown of diffusion pump operation at high inlet pressures a special high vacuum valve is proposed. The valve can be made to admit gas into the diffusion pump at a programmable rate not exceeding the maximum throughput of a given diffusion pump. This is accomplished by the use of coupled pneumatic and hydraulic actuators together with a cam which controls a needle valve in the hydraulic circuit. The flexibility of this arrangement for a system operation is demonstrated.
Optimization of in situ substrate surface treatment in a cathodic arc plasma: A study by TEM and plasma diagnostics
Authors: Schönjahn C. , Ehiasarian A. P. , Lewis D. B. , New R. , Münz W.-D. , Twesten R. D. , Petrov I.
Published: July 2002

Cr ions generated by a steered cathodic arc discharge are utilized to control and enhance the adhesion properties of 3.5 μm thick TixAl(1−x)N based coatings deposited on high speed steel substrates. A two-step etching procedure (negative substrate bias, US=1200 V) is suggested, operating the arc discharge initially in an Ar atmosphere (pAr=0.09 Pa, 6.75×10−4 Torr) to achieve predominantly metal removing effects (etching rate: 9 nm min−1) with a mixture of Ar and Cr ions. In the second stage at residual gas pressure level (pAr⩽0.006 Pa, 4.5×10−5 Torr, etching rate: 4 nm min−1) pure Cr ion irradiation leads to a Cr penetration as deep as 20 nm with a Cr accumulation of approximately 37 at % at the interface substrate/coating. This procedure promotes localized epitaxial growth of TixAl(1−x)N and enhances critical load values up to 85±5 N.
Cluster deposition study by molecular dynamics simulation: Al and Cu cluster
Authors: Kang Jeong Won , Choi Ki Seok , Kang Jin Cheol , Kang Eu Seok , Byun Ki Ryang , Hwang Ho Jung
Published: July 2002

The ionized cluster beam deposition of Al and Cu clusters has been investigated with a classical molecular dynamics simulation and the Metropolis Monte–Carlo simulation. The spreading of the cluster has been studied as functions of cluster size and initial cluster energy. When the local area reached the local melting spot on the surface around the impact point of an energetic cluster, during a few ps, intermixing was easily achieved and a good epitaxial film with optimum bulk density was formed. For uniform film growth using a cluster impact, it is necessary to make the local area temperature higher than melting temperature on the surface around the impact point of an energetic cluster.
Growth and characterization of InGaAsP–InP lattice-matched heterojunctions
Authors: Sankaran R. , Antypas G. A. , Moon R. L. , Escher J. S. , James L. W.
Published: July 2002

The conditions of growth of In1−xGaxAsyP1−y lattice-matched to InP by the liquid-phase epitaxy technique on (111) B-oriented substrates have been analyzed in this paper. The epilayer composition has been varied from InP to In0.53Ga0.47As. The layer quality is more sensitive to experimental variables as the composition approaches the In0.53Ga0.47As side than when growing InP-rich quaternaries. Hall measurements indicate the background doping to be in the low 1015/cm3 range if pure As and PH3 are used as the sources of the column-V elements and the melt is baked at high temperature prior to growth.
Chlorine adsorption on silver surfaces
Authors: Tu Yung-Yi , Blakely J. M.
Published: July 2002

The properties and structure of adsorbed chlorine layers on clean silver surfaces have been studied. On the Ag(111) surface, isobars over the temperature range from ∠300 to ∠900 K have been obtained using Auger electron spectroscopy. A model dependent, initial heat of adsorption of ∠50 kcal/mol was obtained. Structural observations using LEED showed that an epitaxial layer of AgCl(111) was formed. Electron impact desorption measurements give a desorption cross section for chlorine. On the Ag(110) surface a set of isotherms was obtained and the model independent isosteric initial heat of adsorption was also calculated to be ∠50 kcal/mol.
Direct-molecular-beam method for mass selective outgassing rate measurement
Authors: Komiya S. , Sugiyama Y. , Kobayashi M. , Tuzi Y.
Published: July 2002

Outgassing rates ranging from 10−1 to 10−6 Pa m3 s−1 m−2 from a small area of a solid sample can be measured by a quadrupole mass spectrometer completely isolated by a hollow cylindrical cryocollimator and a coaxial liquid nitrogen shroud from a surrounding ultrahigh vacuum chamber, except for a small solid-angle aperture where the molecular beam from the sample passes through it. The 2.4 K cryocollimator and 80 K shutter (chopper for the molecular beam) assure a clear beam shape and a well-defined signal level from the background, respectively. Outgassing rates of stainless steel 304L and polycrystalline molybdenum having a sampling area of 5 cm2 are presented for initial pumping and during baking at 500°C.
Gettering experience in ISX or titanium is good for your health
Authors: Edmonds P. H. , Mioduszewski P. , Simpkins J. E. , Wootton A. J.
Published: July 2002

Titanium gettering in the Impurity Study Experiment (ISX) vacuum vessel has allowed a significant improvement in the plasma parameters. For ohmic heating discharges, Zeff = 2.9→1.9, τE = 24→36 ms, and qψ = 3.4→2.8 ms. Most of the experiments have been carried out with titanium deposition only once or twice per day. Residual gas spectra taken between discharges show a return to the normal after only one or two plasma shots following gettering. A study of the parameters that reflect recycling and impurity content shows saturation after the first discharge following gettering. Nevertheless, the overall plasma behavior is affected by gettering for tens of discharges. Experiments continue in an attempt to evaluate more accurately the plasma effects of gettering.
Rf vs dc sputter gun copper coating of laser fusion targets
Authors: Goldstein I. S. , Varon J. , McHugh P. J.
Published: July 2002

Rf excitation of sputtering sources will be needed for deposition dielectric coatings on laser fusion targets. The current study has shown that for metals the major disadvantages of rf compared to dc excitation are lower attainable deposition rates and, for spherical substrates, rougher surface finishes at comparable deposition rates. The morphologies of rf sputtergun coated copper films on both planar substrates and molecular beam levitated hollow glass microspheres were examined and compared to previous work using the same Sloan and sputtered films (SF) sputterguns with dc power. The SF gun consistently produced smoother coatings than the Sloan gun. The SF gun produced the smoothest rf coatings on levitated microspheres at the highest argon pressure (6 μm) and lowest deposition rate (45 Å/s). The data were used to hypothesize that resputtering off these isolated spherical substrates is an important factor for surface morphology.
Bonding configurations of ligand molecules adsorbed on metal surfaces
Authors: Avery Neil R.
Published: July 2002

Recent determinations by high-resolution, electron-energy-loss spectroscopy of the bonding configurations adopted by some ligand molecules adsorbed on metal surfaces [principally Pt(111)] are reviewed. Configurations identified with (i) weak donor bonding, (ii) rehybridization of unsaturated bonds, and (iii) π bonding are discussed and compared with the corresponding inorganic molecular complexes. It is shown that whereas (i) and (iii) have close analogies in the molecular complexes, the metal surface facilitates a greater level of rehybridization than commonly seen in the (mononuclear) complexes. The need for a unified nomenclature to describe these bonding configurations is addressed, and one based on the μ-η conventions proposed by IUPAC is suggested.
Angular distributions of sputtered particles
Authors: Baxter J. P. , Schick G. A. , Singh J. , Kobrin P. H. , Winograd N.
Published: July 2002

The trajectories of neutral particles ejected from surfaces bombarded by keV projectiles have been precisely determined. The neutrals are detected with high efficiency by selective postionization of the desorbed atoms by laser initiated multiphoton resonance excitation. By employing a pulsed beam of primary Ar+ ions, the velocity of the desorbed atoms may be selected by appropriate timing between this pulse and the pulse of ionizing laser radiation. These ions are then imaged to a position-sensitive detector for angle determination. Under present conditions we can detect neutrals whose kinetic energies vary from 0.2–50 eV into a total enclosed angle of over 100° using a total dose of <1012 incident Ar+ ions/cm2. Results are illustrated for polycrystalline Rh, Rh{111}, and Rh{111} covered with adsorbed oxygen. The measurements also illustrate a number of difficiencies of theoretical treatments of the particle/solid interaction problem.
Quantitative determination of atomic concentrations by Auger electron spectroscopy
Authors: Goldstein Y. , Many A. , Millo O. , Weisz S. Z. , Resto O.
Published: July 2002

A simple mathematical analysis presented here shows that unless the ratio of the instrumental resolution width to the natural linewidth of each Auger line is less than about 0.3, the measured peak-to-peak amplitudes of the differentiated Auger signals do not represent accurately the atomic concentrations. At the same time, the analysis provides the means for overcoming this difficulty even when the linewidth ratio is considerably larger than 0.3. A universal relation is presented whereby the experimentally measured peak-to-peak amplitudes can be corrected so as to enable one to derive quite accurately the relative atomic concentrations in one’s samples; so much so, provided reliable Auger sensitivities of the elements are available. Unfortunately, however, most of the sensitivity data, especially for the high-energy Auger lines, were measured with insufficient resolution. In fact, we show that at least in some cases the published data were measured with a resolution far from satisfactory. It is our contention, therefore, that there is a need for a revision of the sensitivity data with the required resolution if they are to be used for quantification.
Radio-frequency plasma chemical vapor deposition growth of diamond
Authors: Meyer Duane E. , Dillon Rodney O. , Woollam John A.
Published: July 2002

Plasma chemical vapor deposition (CVD) at 13.56 MHz has been used to produce diamond particles in two different inductively coupled systems with a mixture of methane and hydrogen. The effect of a diamondlike carbon (DLC) overcoating on silicon, niobium, and stainless-steel substrates has been investigated and in the case of silicon has been found to enhance particle formation as compared to uncoated polished silicon. In addition the use of carbon monoxide in hydrogen has been found to produce well-defined individual faceted particles as well as polycrystalline films on quartz and DLC coated silicon substrates. Plasma CVD is a competitive approach to production of diamond films. It has the advantage over microwave systems of being easily scaled to large volume and high power.
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u spectroscopic measurements of erosion behavior of Tokamak Fusion Test Reactor redeposited carbon materials under high-flux plasma bombardment in Plasma Interactive Surface Component Experimental Station-A
Authors: Hirooka Y. , Pospieszczyk A. , Conn R. W. , Mills B. , Nygren R. E. , Ra Y.
Published: July 2002

The chemical erosion behavior of graphite materials preexposed in the Tokamak Fusion Test Reactor (TFTR) as the bumper limiter has been investigated spectroscopically under deuterium plasma bombardment in the Plasma Interactive Surface Component Experimental Station-A (PISCES-A) facility. The deuterium plasma bombardment conditions are ion bombarding energy of 300 eV, ion flux of 1.7×1018 ions s−1 cm−2, plasma density of 1.4×1012 cm−3, electron temperature of 11 eV, and neutral pressure of 3×10−4 Torr. The chemical erosion yield is measured with calibrated CD-band spectroscopy during the temperature ramp from 100 to 900 °C at an average rate of ∼5 K/s. The materials used include virgin POCO graphite and graphite tile pieces from the redeposited and eroded areas of the bumper limiter of TFTR. The deuterocarbon formation rate from TFTR redeposits maximizes at ∼500 °C. Essentially the same chemical erosion behavior is observed for TFTR-eroded and virgin graphites and is characterized by the compound peak, indicative of two erosion yield maxima at around 575 and 700 °C. The maximum erosion yield for TFTR redeposits is found to be ∼15% higher than those for TFTR-eroded and virgin POCO graphites, which is attributed to deuterium incorporated in the redeposited material. In addition, the removal behavior of redeposits by helium plasma bombardment has been studied. The removal rate is evaluated to be similar to the physical sputtering yield of carbon by helium. The surface morphology and surface composition have been analyzed with scanning electron microscopy and electron microprobe analysis along with these erosion yield measurements.
Surface density of states of TiO2(110) single crystal and adsorbed molecular observation by scanning tunneling microscopy and tunneling spectroscopy
Authors: Sakamaki K. , Itoh K. , Fujishima A. , Gohshi Y.
Published: July 2002

We present the evidence for the surface density of states (SDOS) of the hydroxylated and reduced rutile TiO2 (110) single crystal different from the bulk electronic property by tunneling spectroscopy using scanning tunneling microscopy technique (STM/TS). The surface band gap energy (SEg) was 1.6 eV as the tunneling-active free states. This experimentally obtained SEg (1.6 eV) was quite different from the bulk band gap energy (3.05 eV). The chemisorbed OH− on the Ti3+ –O vacancy state is located 1.35 eV below the EF . The observed tunneling current rectification originates in the surface electronic structure, band bending and surface coordination property. It became clear that the photo-oxidation of the chemisorbed OH− by photogenerated holes was energetically feasible through the study of SDOS using the STM/TS. Phenol molecules were adsorbed onto the hydroxylated TiO2 surface. The image of the phenol molecule was measured at a tip bias of +443 mV which is within the surface band gap and slightly larger than the vibration energy of phenol ring. The electron density of the phenol ring was apparent in the STM picture.
Quantitative aspects of secondary ion mass spectrometry analysis of pure and mixed fatty acid Langmuir–Blodgett films
Authors: Cornelio Paula A. , Gardella Joseph A.
Published: July 2002

Polycrystalline silver supported pure and mixed mono- and multilayer films of eicosanoic [CH3(CH2)18COOH] and docosanoic [CH3(CH2)20COOH] acids have been prepared by the standard Langmuir–Blodgett technique. The emission of quasimolecular ions as a function of ion dosage has been studied to infer information regarding secondary ion stability under ion bombardment. The results indicate molecular orientation and substrate dependence for (M+H)+ emission and the attenuation of (M+Ag)+ and (M−H+2Ag)+ with increased film thickness. Data are presented for studies conducted on both quadrupole mass filter and time-of-flight instrumentation. The effects of supporting substrate morphology, instrumentation, and implications for quantification of molecular static-secondary ion mass spectrometry (static-SIMS) ion emission are discussed.
Polybutadiene emulsion particles observed by scanning tunneling microscopy
Authors: Morris William G. , White Dwain M. , Gordon Janet L. , Thundat Thomas
Published: July 2002

Particles of polybutadiene were prepared by an emulsion polymerization process. We have been able to observe their size and shape in a scanning tunneling microscope. Critical to this success was the deposition of gold onto a mica substrate to give a smooth, conductive surface. A drop of methanol was then placed on this surface, and a very small amount of the polybutadiene latex (a stable emulsion of polymerized butadiene particles in water) was injected into the methanol drop. After the methanol evaporated, several areas showed isolated emulsion particles, while aggregates of particles were found in other areas. The surface of the particles was adequately conductive to get stable tunneling currents at a bias voltage of −0.1 V. The conductivity may be related to the layer of surfactant molecules on the surface. Isolated particles were typically oblate ellipsoids: 15 nm long, 10 nm wide, and 3 nm high. Individual particles of about the same size were visible in the aggregates. Because the glass transition temperature of polybutadiene is well below room temperature, the particles would be expected to be soft and deformable. The appearance of the aggregates is that of soft particles which have deformed to achieved a higher packing density.
Excitation of quasiparticles during grazing-angle ion reflection at Al surfaces
Authors: Zheng N. J. , Rau C.
Published: July 2002

We have studied ion-induced electron emission during grazing-angle scattering of 150 keV protons at clean and oxygen-covered Al surfaces. The angle-resolved energy distribution of emitted electrons reveals, in the energy range of 0–30 eV, characteristic peaks, which are directly correlated to various electron excitation mechanisms. For clean Al surfaces, these processes include single electron excitation and excitation of electrons by decay of ion-excited surface and bulk plasmons. At submonolayer oxygen coverages of the Al surfaces, we already find a drastic decrease of the electron emission peak at 6 eV, which is due to the decay of surface plasmons, and an increase of the O(2s2p2p) Auger electron emission peak located at about 5 eV.
Scanning tunneling microscopy study of the ambient oxidation of passivated GaAs(100) surfaces
Authors: Moriarty P. , Murphy B. , Hughes G.
Published: July 2002

A scanning tunneling microscope (STM) operating in air has been used to study GaAs(100) surfaces which have been passivated in aqueous P2S5/(NH4)2S and P2S5/(NH4)2Sx solutions. The growth of native oxides under ambient conditions on these passivated surfaces has been monitored by STM. A spatial analysis of the oxide growth over 3×3 μm2 areas indicates that the native oxide initiates as isolated islands across the surface which coalesce to form a uniform oxide layer. Evaluation of these surfaces in terms of peak-to-valley and root-mean-square roughness measurements indicates that surfaces treated in the P2S5/(NH4)2Sx solution oxidize at a slower rate than those treated with the P2S5/(NH4)2S solution. The repeated scanning of a particular area by the STM results in a significant increase in the local oxidation rate compared with surrounding areas which are scanned only once. The application of short high voltage pulses to the tip during an interruption in the scanning routine results in a greatly enhanced oxidation rate directly beneath the tip. Scanning tunneling spectroscopy characteristics, both I/V and (dI/dV)/(I/V), reveal considerable differences in the band bending and consequently the density of surface states, present on the passivated and unpassivated surfaces.
Extraction of inelastic mean free path data from elastic electron backscattering data
Authors: Dwyer V. M.
Published: July 2002

The possible extraction of inelastic mean free path (IMFP or λi) data from elastic backscattering experiments is analyzed within the transport approximation. It is found that the characteristic length obtained by this method is not the IMFP, λi, as previously thought, but a length Λ=[λ−1i(λ−1i+λ−1tr)]−1/2, where λtr, the transport mean free path, is the length associated with large-angle deflection. It is significant that this length Λ is also the length which characterizes the overlayer experiment for an ultrathin overlayer (thickness≪IMFP) and at an exit angle of ∼45°, and is also the length obtained using two-stream methods [V. M. Dwyer, Surf. Sci. 291, 261 (1993)].
Surface spectroscopic characterization of TiNi nearly equiatomic shape memory alloys for implants
Authors: Shabalovskaya S. A. , Anderegg J. W.
Published: July 2002

In spite of the generally good biocompatibility of TiNi revealed in numerous in vivo studies, medical applications of these shape memory alloys as implants are hindered due to the lack of knowledge on the nature of their biocompatibility. Better material characterization is necessary for understanding the chemical and physical properties which determine biocompatibility. The purpose of the present investigation is to use angle-resolved x-ray photoelectron spectroscopy to identify the differences in surface chemical state and composition between the layers formed on the surface of TiNi alloys after mechanical polishing, chemical etching, autoclaving in water and steam, and exposure to H2O2 or air. The surface chemistry drastically depends on the preparation method; the Ni surface concentration can be varied in the range 0–30 at. %. In natural conditions (air, water, and steam) TiNi surfaces revealed a tendency to be covered by TixNiyO2x oxides (where x varies in the range of 7–20 and y varies in the range of 0–5 depending on preparation procedure) with a small amount of Ni in metallic state (∼0.5 at. %). This finding is considered to be the reason for the good biocompatibility of TiNi.
Characterization of an aluminum etching process in an inductively coupled discharge using measurements of discharge impedance and current and voltage sensors
Authors: Patrick Roger , Lee Chii-Guang , Hilliker Steven E. , Moeller Ronald D.
Published: July 2002

The rf characteristics of a BCl3/Cl2 discharge used to etch aluminum films for semiconductor interconnect applications have been studied in a transformer coupled plasma™ (TCP™) etching system. The impedance (both real and imaginary parts) of the discharge was obtained as a function of process condition by studying the capacitor positions of the matching network attached to the TCP plasma source. By correcting for the contribution of the excitation coil, estimates were made of the plasma resistance and reactance as a function of generator power and chamber pressure. In addition, measurements of rf current and voltage were made using IV probes incorporated into the match as a function of TCP power measured at the generator, pressure, and total gas flow. It was found that the rf current and voltage at the input to the coil were both linearly dependent on power, inversely dependent on total pressure and virtually independent of total gas flow. The current–voltage measurements were correlated with measurements of etch rate and uniformity for both aluminum and oxide films as a function of generator power, pressure, and total gas flow.
Influence of reactor wall conditions on etch processes in inductively coupled fluorocarbon plasmas
Authors: Schaepkens M. , Bosch R. C. M. , Standaert T. E. F. M. , Oehrlein G. S. , Cook J. M.
Published: July 2002

The influence of reactor wall conditions on the characteristics of high density fluorocarbon plasma etch processes has been studied. Results obtained during the etching of oxide, nitride, and silicon in an inductively coupled plasma source fed with various feedgases, such as CHF3, C3F6, and C3F6/H2, indicate that the reactor wall temperature is an important parameter in the etch process. Adequate temperature control can increase oxide etch selectivity over nitride and silicon. The loss of fluorocarbon species from the plasma to the walls is reduced as the wall temperature increased. The fluorocarbon deposition on a cooled substrate surface increases concomitantly, resulting in a more efficient suppression of silicon and nitride etch rates, whereas oxide etch rates remain nearly constant.
Fourier-transform infrared measurements of CHF3/O2 discharges in an electron cyclotron resonance reactor
Authors: Goeckner M. J. , Goeckner N. A.
Published: July 2002

Knowledge of the neutral gas composition in a discharge is important for understanding the chemical processes involved in both etching and deposition environments. We have performed Fourier-transform infrared absorption spectrometry measurements of CHF3/O2 plasmas in an electron cyclotron etching tool. Spectral bands were observed from both gas-phase and surface-phase species (deposited on the vacuum windows). The primary gas-phase species were CF4, H2O2, and HF. Strong absorption bands due to CFx, where x=1, 2, or 3, deposition on the vacuum windows were also observed. The densities of the gas-phase species were calculated from the strength of the measured absorption. It was found for typical discharge powers that the HF density was approximately 80% of the total gas density and depended on the plasma density and neutral pressure. In addition, because HF, H2O2, and CF4 are not the feed gas, these data clearly show that recycling of the daughter species (C, CFx, Fx, etc.) on the chamber walls play an important role in determining the plasma chemistry in this high-electron density, >1011 cm−3, low neutral pressure, <10 mTorr, discharge.
Nanoscratch characterization of dual-ion-beam deposited C-doped boron nitride films
Authors: Chan K. F. , Ong C. W. , Choy C. L.
Published: July 2002

Boron nitride (BN) films with carbon (C) contents varying from 3–11.8 at. % were fabricated using dual-ion-beam deposition. Films with low C contents (⩽6.2 at. %) consist mainly of the c-BN structure. The hardness of these films is as high as 43 GPa, and the coefficient of friction μ is described by the formula μ=0.14 W0.25, where W is the normal load in millinewtons. The critical load of damage is above 50 mN. Because of the existence of high internal stresses, the films peel off readily from the substrates, and delamination occurs immediately once a scratch track is produced. When more C is added, the formation of the c-BN structure is suppressed, while a graphite-like structure becomes dominant. The hardness and critical load drop to 8.6 GPa and 6.8 mN, respectively, when the C content is 11.8 at. %. The values of μ remain unchanged. The internal stresses are partially released, thereby leading to improved film adhesion. We have found an optimum C content of 7.2 at. %, at which both the mechanical and adhesion properties are satisfactory.
Deceleration of silicon etch rate at high aspect ratios
Authors: Kiihamäki J.
Published: July 2002

The molecular-flow conductance of a high aspect ratio feature can limit the etching species arriving at the bottom of the feature and thus limit the etch rate. A simple conductance model can predict the etch rate of the time-domain multiplexed etch process with good results at moderate-aspect ratios (5–20) for trenches, but at very high aspect ratios (>20) the conductance model breaks down. Other mechanisms are needed to explain the deceleration of etch rate and almost complete etch stop. In this article the reasons for etch stop at the bottom of deep features are discussed. Measurement results of deep silicon etching are presented. Very deep holes and trenches were etched into silicon to study the effect of process parameters. At moderate aspect ratios the bottom of the hole is nearly flat and the sidewalls are vertical. At high aspect ratio the sidewalls start to bow and the feature bottom turns into a sharp spearhead. The shape of the feature can have an impact on the step coverage of the passivation layer deposition during the passivation step and on passivation removal during the etch step, leading to excessive sidewall etching and reduced etch rate at the feature bottom. The nonzero sidewall reaction probability and flow conductance of tapered tubes were studied by Monte Carlo simulation. The main reason for deceleration of etching seems to be the loss of etchant species due to sidewall reactions combined with feature closure by ion-limited passivation polymer etching.
Microreactor for studies of low surface area model catalysts made by electron-beam lithography
Authors: Johansson Stefan , Fridell Erik , Kasemo Bengt
Published: July 2002

A flow reactor for evaluation of low surface area, model catalysts has been designed. The aim is to measure catalytic activity at atmospheric pressure on nanofabricated model catalysts, primarily made by the electron-beam lithography (EBL) technique. This is a challenge because of the low attainable active surface area on such model catalysts, due to the serial processing in EBL manufacturing. The interest in using EBL-nanofabricated model catalysts derives from the high level of control over the catalyst geometry that is obtainable. In order to evaluate the performance of the reactor for such catalysts, two different sample types were studied with regard to their activity for CO oxidation, during a heating ramp. One sample was an EBL-microfabricated Pt/CeOx model catalyst with Pt disks 700 nm in diameter, arranged in ordered arrays, with a total active Pt area of about 0.4 mm2. The other sample was a Pt wire with a diameter of 0.1 mm and a length of about 1 mm. The light-off traces of these samples were measured during heating ramps for different relative CO partial pressures. Platinum bulk-like behavior for the CO–oxidation reaction was confirmed for both types of samples, indicating that the reactor is working properly and that the EBL fabrication technique is clean enough for model catalyst preparation. The total molar flow through the reactor at room temperature is typically 6×10−8 mol/s, corresponding to a volume flow of about 1.7 mm3/s.
Spin-coated As2S3: A barrier layer for high resolution trilayer resist system
Authors: Singh B. , Chern G. C. , Lauks I.
Published: July 2002

A trilayer resist process using spin-coated As2S3 film as a barrier layer was investigated and optimized for use in optical and electron beam submicron lithography. The As2S3 layer eliminates the intermixing of solvents used to deposit the organic layers. Dimensional loss due to reflection from the substrate is avoided. A high reactive ion etch differential rate of the As2S3 film compared to organic resists has been observed which allows a precise transfer of patterns. 0.4 μm wide patterns over 1 μm topography were replicated without dimensional loss. Preliminary work on a bilayer process using As2S3 planarizer shows promise.
A monodisperse Si-containing photoresist for a bilayer system
Authors: Saigo K. , Watanabe F. , Ohnishi Y.
Published: July 2002

A monodisperse negative Si-containing photoresist (MAS) has been developed for use as the top imaging layer for a bilayer system. MAS is a formulation of poly(allyldimethylsilyl-α-methylstyrene) (PMA Si) and a bisazide. PMA Si was synthesized by anionic polymerization of the monomer with n-butyl lithium in THF at −78 °C. The polymer has a high softening point (Ts=164–166 °C) and a narrow molecular weight distribution (Mw=41 400, Mw/Mn=1.05). Near-UV-exposure has been carried out using a Kasper 2001 P contact printer. The Dig of MAS (0.2 μm in thickness) is 4.5 mJ/cm2 on a Si wafer and the γ value is over 2.0. The thickness reductions of MAS and MP-1300 have been measured under various O2-RIE conditions. The etching ratio of MP-1300/MAS ranges from 3:1 to 10:1 depending on conditions and is decreased with an increase in rf power and with a decrease in chamber pressure. Under the optimized development and O2-RIE condition, 0.75 μm line and space (L/S) patterns were accurately fabricated on the Si wafer having 0.5 μm high step. It is also noteworthy that 2.0 μm L/S patterns with a steep profile were obtained even in the MP-1300 layer of 4.0 or 6.0 μm in thickness.
Conductive two-layer resist system for electron-beam lithography
Authors: Todokoro Yoshihiro , Kajiya Atsuhiro , Watanabe Hisashi
Published: July 2002

A conductive organic film, ammonium poly(p-styrene sulfonate) (AmPSS) and conductive two-layer resist systems using AmPSS are described. Conductive two-layer resist systems consist of silicon-containing negative resist (SNR) (Toyo Soda) as the top imaging layer and AmPSS as the conductive bottom layer. SNR/AmPSS two-layer resist systems eliminate the charging effects in electron beam lithography.
Surface modification by plasmas: X-ray photoemission studies
Authors: Thomas J. H.
Published: July 2002

Multilevel metallization schemes and ultra-large-scale integration of silicon devices require plasma-based pattern transfer processing. During plasma-based pattern transfer, the silicon surface is subjected to ion bombardment and can be coated with thin residue layers of species from the plasma, producing a damaged layer. The chemistry of the residue layer depends upon the plasma composition, system geometry, and substrate material. X-ray photoemission spectroscopy (XPS) has been used extensively to characterize plasma-induced residue layers. Various plasma etch and processing residues observed during silicon device pattern transfer will be discussed.
Analysis of an electrostatic gun with a Schottky cathode
Authors: Orloff J.
Published: July 2002

A two lens, electrostatic optical column for use with a point emitter has been designed which can be used with either ions or electrons. This article deals with its properties as an electron beam system using a Schottky cathode. A wave-optical analysis which can be easily done using a simplifying approximation indicates the column should be capable of 11-nm resolution at 25-kV beam energy and 25-mm working distance.
Structural control and the optimization of chlorinated styrene-based electron resists
Authors: Brambley D. R. , Jones R. G. , Matsubayashi Y. , Miller Tate P.
Published: July 2002

A large number of chlorinated styrene-based resists has been prepared, both by the copolymerization of methylstyrene with chloromethylstyrene, and by the direct chlorination of methylstyrene polymers. These resists have been characterized, and Inokuti’s equation has been applied to the lithographic data to obtain radiation chemical yields which have been related to polymer structure and composition. Inokuti’s theory has also been used to predict the dependence of lithographic performance on polymer parameters. Qualitative and quantitative agreement between these predictions and experimental observations has been demonstrated in several polymer systems, and this theory has been shown to provide useful pointers to resist optimization. A number of comparatively high sensitivity polymers have been found which do not undergo chain scission on irradiation and which accordingly exhibit high contrasts. From this range of polymers several well-suited for use as electron resists have been selected.
Silylated acid hardened resist process: A deep ultraviolet surface imaging technique
Authors: Pavelchek Edward K. , Bohland John F. , Thackeray James W. , Orsula George W. , Jones Susan K. , Dudley Bruce W. , Bobbio Stephen M. , Freeman Peter W.
Published: July 2002

A deep ultraviolet surface imaging technique using a silylated acid hardened resist (SAHR) is described. The resist, Shipley XP-8928, contains a meta, para-cresol novolak resin which has a high optical absorbance in the deep ultraviolet (DUV). This reduces complications from substrate reflections and restricts the image to the near-surface regions. The exposed regions, which become crosslinked, are less susceptible to vapor silylation by agents such as trimethylsilyldiethylamine (TMSDEA). The unexposed regions may be easily silylated. An anisotropic oxygen reactive ion etching is used to transfer the surface image through the bulk of the resist. This paper discusses the kinetics of silylation with TMSDEA, the resulting silicon distributions in the film before and after etch, and the lithographic performance of the process. Silicon distribution throughout the film is determined by Rutherford backscattering spectrometry and illustrated by stained cross sections. It is found that the film surface saturates at a Si content of 9–10 wt. %, and further silylation results in a sharp front at this concentration moving deeper into the film. The rate at which the front moves is determined by the temperature, pressure and the degree of crosslinking. The etch barrier formed at the surface of the resist has been investigated by x-ray photoelectron spectroscopy. This indicates that the surface oxidation of both carbon and silicon is increased, while the silicon concentration is unchanged from unetched samples. This process is capable of producing 0.5 μm line/space pairs when exposed by a 0.35 numerical aperture (NA) lens at 248 nm with as little as 7 mJ/cm2. These features can be produced with flat tops and steep sidewalls. Isolated lines with very high aspect ratios can be produced.
Scanning tunneling microscopy and atomic force microscopy visualization of the components of the skeletal muscle glycogenolytic complex
Authors: Edstrom Ronald D. , Miller Marcia A. , Elings Virgil B. , Yang Xiuru , Yang Rui , Lee Gil , Evans D. Fennell
Published: July 2002

The muscle glycogenolytic complex is responsible for providing access to the reserve carbohydrate energy stores in skeletal muscle during times of vigorous exercise. The complex is a set of enzymes and regulatory factors that are bound to the carbohydrate storage polymer, glycogen. These components provide the ordered synthesis and utilization of that stored form of glucose. Glycogen and the enzyme proteins, phosphorylase and phosphorylase kinase, have been imaged by atomic force microscopy (AFM) or scanning tunneling microscopy (STM). The images of all three generally correlated well with the known features of those molecules, as measured by traditional physicochemical methods. The exception for all three polymers is that the measured height by STM is in error. In each case, the molecules appear to be only about 30% of their true thickness, as measured by height above the graphite surface. It is clear that both AFM and STM will play important roles in biomedical investigation of macromolecular structures and complexes.
Scanning tunneling microscopy at high gap resistances and on chemically modified silicon surfaces
Authors: Wilson Troy E. , Murray Matthew N. , Ogletree D. Frank , Bednarski Mark D. , Cantor Charles R. , Salmeron Miquel B.
Published: July 2002

Scanning tunneling microscopy (STM) studies of organic or biological molecules are difficult to reproduce because strong tip-surface interactions can displace weakly bound material at the surface. We have studied conducting organic monolayers and nucleic acids with our STM instrument at high gap resistance values (100 GΩ to 1 TΩ). We have succeeded in imaging chemically modified silicon surfaces. It is our desire to use these chemically modified surfaces in conjunction with higher gap values in the future to reliably image DNA.
The relationship between critical dimension shift and diffusion in negative chemically amplified resist systems
Authors: Fedynyshyn Theodore H. , Cronin Michael F. , Szmanda Charles R.
Published: July 2002

Reports of latent image instability in several positive acid catalyzed resists have stimulated interest in the image stability of advanced negative resists (ANR). The critical dimension stability of the chemically amplified ANR resist SAL603 with respect to delay time between the exposure and post-exposure bake (PEB) steps was determined. Both dense and isolated 1.0 μm features were stable during a 24 h delay period and delay times from 24 h to 48 h resulted in a decrease in linewidth. The method of loss in linewidth as a function of delay time was not due to diffusion of the acid within the film. The threshold crosslink density model was introduced based on several simple assumptions concerning the effect of crosslink density (Θ) on image formation and the relationship of the crosslink density to resist acid concentrations. A method was described whereby the threshold crosslink density model can be used to determine the relative crosslink density of the resist as a function of distance along the feature edge. An analysis of the relative values of crosslink density within the resist was used to show that acid loss and not diffusion was responsible for the change in resist linewidth as a function of delay time.
Observation of a gold surface using scanning tunneling microscopy in an inert atmosphere and the effects of water adsorption
Authors: Roberts Clive J. , Hoffmann-Millack Britta , Steer William S.
Published: July 2002

The observation of an annealed gold surface in an inert argon atmosphere is described together with a controlled environment scanning tunneling microscope (STM). Surface mobility was found to be the predominant effect, with diffusion velocities ranging from 0.03 to 0.2 Å s−1 at room temperature. This is contrasted to the stability of similar surfaces previously scanned in air. Evidence of adsorbate behavior, also previously seen in air, is found to be absent. However on injecting trace amounts of either air or water vapor into the STM chamber, changes in the surface are apparent. Possible mechanisms for these effects are discussed.
Pb/GaAs(100): Band bending, adatom-induced gap states and surface dipole
Authors: Chen W. , Kahn A. , Mangat P. S. , Soukiassian P. , Florez L. T. , Harbison J. P. , Palmstrom C. J.
Published: July 2002

The work presented here shows a correlation between the position of Pb-induced gap states, responsible for the initial movement of the Fermi level (EF) at the Pb–GaAs(100) interface, and the position of the Pb 5d core level measured by photoemission spectroscopy. The difference in Pb-induced gap states is obtained by depositing submonolayer amounts of Pb on the As-rich (2×4)–C(2×8) or the Ga-rich (4×2)–C(8×2) GaAs(100) surfaces. These reconstructions are known to produce a large dipole-induced difference in the work function of the clean surface. The correlation suggests that the reconstruction-induced dipole is mostly preserved during the initial stage of Pb deposition and shifts the energy levels of the adsorbate.