bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication of c-axis oriented ZnO/AlN thin films prepared by radio frequency reactive sputtering and development of ZnO/AlN layered structure surface acoustic wave devices
Authors: Yong Yoon-Joong , Kang Youn-Seon , Lee Paul S. , Lee Jai-Young
Published: July 2002

ZnO/AlN films have been continuously deposited on silicon wafers by rf reactive magnetron sputtering method. The c-axis preferred orientation of ZnO film with respect to the properties such as crystallinity and interface smoothness of AlN film at bottom has been examined by x-ray diffraction (XRD). The surface acoustic wave (SAW) filters with a wavelength of 52.8 μm using these ZnO/AlN bilayered structure have been fabricated for the first time and their SAW velocities and electromechanical coupling coefficients have been measured by a network analyzer. It is observed that as the thickness of AlN film increases, the average roughness of AlN film increases and the degree of the c-axis preferred orientation of ZnO film reduces. From these results, it is suggested that the factor determining the preferred orientation of top ZnO layer is the surface smoothness of bottom AlN layer. By measuring SAW characteristics of the ZnO/AlN bilayered structure, the phase velocity is calculated to be 4300 m/s and the electromechanical coupling coefficient is 3.23%, which are high enough for commercialization. It is also found that the velocity and the coefficient follow the better one of two films. The SAW filter fabricated in this work reveals good characteristics as the thickness of ZnO film increases and that of AlN film decreases.
Thermal agglomeration of single-crystalline Si layer on buried SiO2 in ultrahigh vacuum
Authors: Nuryadi Ratno , Ishikawa Yasuhiko , Ono Yukinori , Tabe Michiharu
Published: July 2002

Thermal agglomeration of an ultrathin Si layer in silicon-on-insulator structures with a thickness ranging from 1 to 15 nm has been studied by atomic force microscopy. We found that the size of Si islands formed by agglomeration depends on the initial thickness of the Si layer, i.e., the height and the lateral size of Si islands increase with increasing Si thickness. Because the critical temperature for the agglomeration, however, is lower for thinner Si, the thickness dependence of Si island features is accompanied by a temperature effect. A calculation model based on both strain energy and surface free energy qualitatively explains most of the observed agglomeration phenomena, i.e., island formation and ordering.
Strontium silicide termination and silicate epitaxy on (001) Si
Authors: Norton D. P. , Park C. , Lee Y. E. , Budai J. D.
Published: July 2002

We have investigated the epitaxial growth of (Sr,Ba)-based oxides on SrSi2-terminated (001) Si using laser-molecular beam epitaxy. Reflection high-energy electron diffraction (RHEED) confirms the formation of a commensurate submonolayer of (Ba,Sr)Si2 when strontium and barium ablation targets are used as the metal sources. Stability of the silicide RHEED peak intensity between laser ablation pulses indicates that the submonolayer SrSi2 coverage is relatively stable during formation despite the required high temperatures. While the subsequent growth of BaO via Ba metal ablation and O2 flux on the SrSi2-terminated surface is favored at low temperatures, the formation of an epitaxial silicate is observed for oxide formation at temperatures above 550 °C. X-ray diffraction confirms that the Ba2SiO4 film formed with elevated temperature oxidation is in-plane aligned. These results suggest that while epitaxial BaO can be realized on SrSi2-terminated Si, the interface may be susceptible to silicate formation upon thermal treatment. These results also demonstrate that laser-molecular beam epitaxy can be effective in achieving submonolayer surface coverage specifically for terminating silicon for oxide epitaxy.
CaWO
4
thin films synthesized by pulsed laser deposition
Authors: Tanaka Katsumi , Fukui Keihachi , Ohga Koh-ichi , Choo Cheow-Keong
Published: July 2002

Thin films of CaWO4 were synthesized by pulsed laser deposition (PLD) using targets composed of CaO and WO3 oxide mixtures. The crystallinity of CaWO4 thin films strongly depended on PLD conditions, that is, substrate temperature, ambient oxygen pressure, and laser fluence. Congruent thin films with stoichiometry were obtained at 873 K. They showed photoluminescence (PL) at room temperature. PL spectra were characteristic with excitation wavelength, peaked at 440 and 520 nm, which were excited with 340–360 and 300–330 nm, respectively. Cathodeluminescence (CL) spectra could be recorded at room temperature on the PLD thin films and were composed of the same species as observed in PL spectra. Intensity of CL spectra increased drastically after postannealing the PLD thin films at 873 K. PLD experiments were also carried out using CaWO4 targets at the same conditions. Crystalline CaWO4 thin films were obtained much easier than PLD using targets composed of CaO and WO3 oxide mixtures.
Improvement of oxide thickness uniformity by high then low O2 pressure oxidation in rapid thermal processing
Authors: Hong Chao-Chi , Chen Jenn-Long , Hwu Jenn-Gwo
Published: July 2002

This article presents the growth of thin oxides by rapid thermal processing (RTP) under different O2 pressures, indicating that high pressure oxidation tends to make oxide thickness less uniform as oxidation time increases. However, oxide under low pressure oxidation tends to saturate in thickness and a “self-compensating” phenomenon occurs. Thus in order to grow ultrathin gate oxide in a desired thickness regime with good thickness uniformity, we developed a technology called high then low pressure oxidation. The experimental results show that in thickness and electrical properties the uniformity of oxide obtained by oxidation under high then low pressure would indeed be improved.
Reduced pressure chemical vapor deposition of Si1−x−yGexCy/Si and Si1−yCy/Si heterostructures
Authors: Loup V. , Hartmann J. M. , Rolland G. , Holliger P. , Laugier F. , Vannuffel C. , Séméria M. N.
Published: July 2002

We have grown by reduced pressure chemical vapor deposition Si1−x−yGexCy/Si and Si1−yCy/Si heterostructures for electrical purposes. The incorporation of substitutional carbon atoms into Si is expected to play a double role. On the one hand, by creating a carrier confinement in the channel region of metal–oxide–semiconductor transistors, the compressive strained Si1−x−yGexCy and the tensile strained Si1−yCy layers can be used to improve transport properties. On the other hand, the addition of carbon atoms can compensate the compressive strain induced by large amounts of Ge. As far as high Ge concentration Si1−x−yGexCy layers are concerned (Ge=18 at. %), x-ray diffraction (XRD) measurements show the progressive shift of the Si1−x−yGexCy peak towards the Si substrate peak, evidencing the strain compensation due to the incorporation of carbon atoms into the substitutional sites of the SiGe matrix. Carbon incorporation results in a decrease of the growth rate, from 10 nm/min (for substitutional C=0.46 at. %) down to 9 nm/min (when substitutional C=1.26 at. %). High quality Si1−x−yGexCy layers with up to 1.26 at. % of substitutional carbon atoms were grown. Transmission electron microscopy imaging and the comparison between secondary ion mass spectrometry (SIMS) and XRD results revealed that a further increase of the SiCH6 flow leads to an increase of the carbon incorporation into interstitial sites, which translates into a rapid deterioration of the Si1−x−yGexCy layer. Slightly compressive-strained Si1−x−yGexCy layers (Ge=4 at. %) have also been grown. Through the increase of the SiCH6 flow we have managed to tailor the Si1−x−yGexCy layer strain from compressive to tensile. The Si1−x−yGexCy growth rate drops from 3.4 nm/min down to 3.0 nm/min when the substitutional carbon concentration increases from 0.4 up to 1.21 at. %. Finally, Si1−yCy/Si tensile-strained heterostructures were grown. Smaller growth rates (1.8 nm/min) for Si1−yCy than for Si1−x−yGexCy are obtained. SIMS and XRD measurements indicate that the highest carbon concentration Si1−yCy layer (substitutional C=1.12 at. %) also contains many interstitial carbon atoms (interstitial C=0.45 at. %).
High reflectivity and crack-free AlGaN/AlN ultraviolet distributed Bragg reflectors
Authors: Bhattacharyya A. , Iyer Sandeep , Iliopoulos E. , Sampath A. V. , Cabalu J. , Moustakas T. D. , Friel I.
Published: July 2002

High reflectivity and crack-free ultraviolet distributed Bragg reflectors (DBRs), based on AlGaN/AlN quarter-wave layers, have been designed and grown on (0001) sapphire by plasma-assisted molecular beam epitaxy. To minimize the tensile stress and thus prevent nucleation and propagation of cracks in the DBRs, the substrate was coated first with an AlN film, of thickness approximately equal to the total thickness of all the AlN layers in the epitaxially grown DBR structure. In such a configuration the AlN layers are stress-free, while the AlGaN layers are under compressive stress. Peak reflectivity higher than 99% was obtained in all samples. The design calculations and simulations of measured reflectivity data were performed using the transmission matrix method. The measured reflectivity spectra have a bandwidth of around 20% smaller than the simulated spectra, a result attributed to a combination of changes of the thickness and variations in the Al content in the quarter-wave layers.
Ion Gauge Calibration at Low Pressures Using a Leak Detector
Authors: Bergsnov-Hansen B. , Endow N. , Pasternak R. A.
Published: July 2002

A simple method for ion gauge calibration is presented. The flow rate of a pure gas through the calibration cell and a known conductance is measured with a leak detector (or a residual gas analyzer) on the high pressure side of the diffusion pump. From the known conductance and the measured flow rate the calibration pressure is calculated. Pumping by walls and gauge does not interfere with calibration, since it is based on the flow rate out of the calibration cell. This method is illustrated by calibrating an ion gauge for helium and deuterium using a standard helium leak detector as the flowmeter.
Vacuum Problems of Electron and Positron Storage Rings
Authors: Bernardini M. , Malter L.
Published: July 2002

The problem of gas evolution in electron-positron storage rings due to synchrotron radiation was explored. The spectral distribution of the radiation was first computed. From this and from data on quantum efficiency it was possible to determine an upper limit to the resultant photoemission from the ring walls. Measurements of the desorption efficiency from stainless steel 304 then made possible a determination of the maximum gas load which could be expected as a result of the synchrotron radiation.

This treatment was applied to a planned storage ring to be built at Frascati. From this it appeared that with modest processing the ring walls could be put into a condition such that the gas evolution would have completely acceptable values. The effects of wall temperature and of processing in hydrogen and oxygen upon the desorption efficiency were determined. On the basis of the results obtained it is concluded that optimum results would be obtained by the use of materials which are gas-free and on which tightly bound layers are formed from the ambient atmosphere.
Sticking Probability of Atomic Hydrogen on Graphite
Authors: Beitel George A.
Published: July 2002

Standard ultrahigh vacuum and flash filament techniques were used to measure the sticking probabilities of atomic and molecular hydrogen sH and sm, respectively, on graphite. Atomic hydrogen was produced by a hot tungsten filament. Graphite samples were specially fabricated ribbons which could be flashed to 2500 °K. The quantity of atomic hydrogen sorbed was found to be only dependent on the temperature of the graphite and the total number of incident hydrogen atoms. Thus it is possible to use a graphite ribbon as an atomic hydrogen detector.
Sputter gas pressure and dc substrate bias effects on thick rf-diode sputtered films of Ti oxycarbides
Authors: Carson W. W.
Published: July 2002

Films 1–10 μ thick have been prepared by rf-diode sputtering from targets of TiO0.5C0.5, TiO0.25C0.75, TiC, and TiN. These films were deposited on commercial, cobalt-bound, cemented, complex-carbide cutting-tool inserts. The inserts were sputter etched immediately prior to sputter coating. This etch was found to be essential for obtaining good bonding. The sputtered films were prepared under various conditions of argon gas pressure ranging from 3 to 56 μ and substrate bias from 0 to −200 V dc. The sputtered materials exhibited similar microstructures under the same deposition conditions. In general, it was found that higher pressures and less negative biasing gave a ’’cauliflower’’ structure. Reducing the pressure and increasing the negative substrate bias produced more columnar films with less porosity but at a reduced deposition rate for constant power input. X-ray diffraction analysis and Auger spectroscopic analysis of the TiO0.5C0.5 target and a sputter deposited film showed only a slight reduction in oxygen content of the material as a result of the sputtering process. The wear resistance of these films was evaluated by accelerated lathe cutting tests on hardened 4340 steel. The wear resistance was found comparable to good chemical-vapor-deposition (CVD) prepared coatings of TiC.
Adhesion of thin films
Authors: Weaver Charles
Published: July 2002

A discussion of the difficulties of measuring adhesion. Results obtained by various methods are critically considered in the light of theoretical and other estimates of the magnitude to be expected. New ideas on scratch testing are presented and some of the difficulties associated with this method are discussed. For measuring the adhesion of thin films, it still remains as one of the most successful methods and some of the more recent results obtained in this way are presented. In the case of metal films on polymer surfaces, there is increasing evidence of charge transfer across the interface and electrostatic bonding may make a significant contribution to the measured adhesion.
Field desorption of helium and neon
Authors: Krishnaswamy S. V. , McLane S. B. , Müller E. W.
Published: July 2002

Employing our energy-focused atom-probe FIM, providing high resolution and freedom from artifacts, we have obtained complete crystallographic distribution of helium and neon field adsorbed on W, Mo, Ta, Rh, Ir, Pt, and Re. In addition we have determined the abundance of metal–helium and metal–neon molecular ions of these metals as obtained by field evaporation. The dependence of the relative abundance of metal–helium molecule ions upon the substrate temperature and the crystallographic surface area is established. Whereas the triply charged W, Ta, Mo, and Re helides and doubly charged helides of other metals are predominant molecular ion species in pulsed field evaporation, metal–neïdes are formed with a probability of less than 10−3. We were unable to confirm with our precise instrument a high probability of IrHe+++ and IrNe++ as indirectly deduced by Panitz. We are convinced that the high abundance of IrNe++ and IrNe+++ reported by Waugh from observations with a time-gated imaging field desorption microscope must also be artifacts.
Effects of mechanical polishing damage on the ir reflectance and attenuated total reflection spectra of n-type GaAs
Authors: Holm R. T. , Palik E. D.
Published: July 2002

We have observed the effects of mechanical polishing with two different grit sizes on the infrared reflectance spectrum of high carrier density n-type GaAs. The two characteristic reflection minima observed with chemically etched and polished surfaces shift down in frequency and down in intensity as the grit size is increased from 0.3 to 1 μm. This behavior can be understood by assuming a damage layer in which the carrier density and mobility are decreased significantly. In addition, attenuated total reflection (ATR) spectra reveal the coupled surface plasmon–phonon modes associated with the bulk but shifted down due to the damage layer with optical constants different from those of the bulk.
Ultrasonic manometers for low and medium vacua under development at the National Bureau of Standards
Authors: Heydemann P. L. M. , Tilford C. R. , Hyland R. W.
Published: July 2002

The first part of this paper describes the use of ultrasonic interferometry for the measurement of the lengths of manometer columns. The major known sources of errors of manometers are then analyzed, and design criteria are developed which reduce these errors below set limits. Finally, two ultrasonic manometers now being developed at the National Bureau of Standards for measurements in the low and medium vacuum ranges are described. The ultrasonic mercury manometer, with a range of 13 kPa, has been operated with a resolution of 1.4 mPa.
Simple vacuum gauge using TaN thin films in the pressure range of 105 to 10−3 Pa
Authors: Shioyama T. , Takiguchi T. , Ogawa S.
Published: July 2002

Experiments investigating the use of TaN thin films for measurements of pressure over a wide range have proved to give good results, because the TaN thin films have large effective heat conducting areas available to increase the sensitivity, suitable resistance, and large temperatures coefficients of resistance. These experiments led to the construction of a film system consisting of a TaN thin film deposited on a miniature 7059 Corning glass substrate by reactive plasma sputtering. With this system, it is possible to measure pressure changes in the range of 105 to 10−3 Pa. A detailed description of the characteristics of the TaN film gauge as well as the calibration curves are given.
I
n s
i
t
u conditioning for proton storage ring vacuum systems
Authors: Blechschmidt D.
Published: July 2002

Average pressure and vacuum-stability limit as expected in the presence of a proton beam were measured after in situ treatments such as bakeout under various conditions, argon glow-discharge cleaning and sputter deposition of titanium. Measurements were carried out for test pipes made of stainless steel (untreated, electropolished, or cooled to 77 K), pure titanium and aluminum alloy. The measurement method used to obtain the vacuum-stability limit in the laboratory and in a prototype system is described. The results can be applied also to other systems of different geometry by use of scaling laws. In situ conditioning generally has a stronger influence on vacuum performance than a particular choice of material. Bakeout gives low average pressures and rather good vacuum stability. Glow discharges also increase the vacuum stability but have only a small effect on the static pressure. Coating the beam-pipe wall with titanium by in situ sputtering provides large linear pumping, thus a lower pressure and an extremely good vacuum stability.
Systematic transformations of the asymptotic aberration coefficients of round electrostatic lenses (1)
Authors: Kuyatt C. E.
Published: July 2002

In previous work we formulated the third-order asymptotic aberration coefficients of round (axially symmetric) electrostatic lenses in a form independent of object and aperture positions, and expressions for the six quantities which are sufficient to specify completely the aberration properties of the lenses were derived in the form of integrals involving derivatives of the axial potential through the fourth order. Because actual calculations involved numerical differentiation of the axial potentials, integrations by parts were used to transform the integrals to two new forms with axial derivatives of lower degree. Many other forms of the aberration integrals can be obtained by further integrations by parts, but the transformations are laborious and it is not easy to predict the forms which are possible nor to determine the sequence of operations which will yield a desired result. However, using a method originally developed by Seman and extended by Hawkes, a completely general formula has been derived from which all of the possible forms of the asymptotic integrals can be obtained simply. A few of these possible forms are derived and discussed.
X-ray exposure system using finely position adjusting apparatus
Authors: Yamazaki S. , Nakayama S. , Hayasaka T. , Ishihara S.
Published: July 2002

An apparatus for finely adjusting the three-dimensional position of a workpiece and the application of this apparatus to high power x-ray lithography are presented. The relative positioning apparatus has been designed, using electrodynamic transducers for the x, y, and z directions and an electrostrictive transducer for rotary direction (ϑ). Motions in each direction are supported by a resilient plate. The relative position of mask and wafer has been detected by applying a mechanical vibration to the wafer, with an accuracy of less than ±0.1 μm. The fine positioning mechanisms have displayed excellent performance with high accuracies. As a first step to constructing a working apparatus, a prototype exposure system was built using pattern replication in an atmospheric environment, comprised of a positioning system and a high-power x-ray source with a rotary Al target operated at more than 20-kW electron-beam input power. The characteristic x ray has been irradiated on a wafer through a contractile vacuum pipe. Using an exposure test, the system functions have been confirmed as a fine pattern replicating system.
Fabrication of micro- and submicron-bubble memory devices by a mask transfer technique with subsequent getter-ion etching
Authors: Funayama T. , Yanagida K. , Nakayama N. , Komeno K. , Inagaki T.
Published: July 2002

In order to fabricate magnetic bubble memory circuits of high bit density using x-ray lithography, it is necessary to form accurate gold absorber patterns for x-ray masks and accurate permalloy patterns for the bubble memory circuits. The combined processes of mask transfer technique and getter-ion etching instead of conventional ion etching in pure argon gas were used to make patterns in these metal films. Pattern width accuracies within ±0.1 μm and the angles of edge slope up to 70° were obtained by using these processes. Our new method was applied to the microfabrication of gold x-ray mask patterns and permalloy patterns of the circuits for magnetic bubbles of diameters 0.95 and 1.5 μm.
Errors due to zero uncertainties and buoyancy in the gravimetric measurements of sorption isotherms
Authors: Robens Erich , Gast Th.
Published: July 2002

Besides the influences of Knudsen forces and convection which are due to thermal gas flow, a zero shift during cooling down of the sample in vacuo may seriously affect the measurement of adsorption isotherms at low temperatures. This applies especially to the measurement of nitrogen isotherms at 77 K for surface area and pore size determination. Microporous samples present difficulties in determining the necessary buoyancy corrections for the sample itself; in addition, the buoyancy of the adsorbed layers has to be taken into account.
Diode-array-targeted CRT scan converter: Some operational limitations and failure mechanisms
Authors: Hashizume George , Moore John S. , Riley Larry D.
Published: July 2002

Some operational limitations of a high-speed, dual-gun, diode-array-targeted CRT scan converter when used as a transient signal acquisition unit and A/D converter are discussed with respect to trace blooming and target burning at slow trace velocities and/or excessive writing gun beam current. The blooming charactertistics of three target types are described. It is shown that a five times reduction in trace blooming can be obtained, but only with a resultant loss of a factor of four in writing sensitivity. Residual trace retention phenomena (burning) are analyzed. X-ray generation in the silicon by the 10-kV writing beam is shown to cause the damage and experimental data is offered to verify this effect and determine the x-ray dose.
PR-200 ion implantation system
Authors: Bird H. M. B. , Jackson J. H. , Weissman B. , Williams N.
Published: July 2002

PR-200 is a 200-kV, general-purpose, high-throughput ion-implantation system which was installed on Western Electric’s production line at Reading, PA in mid-1975. The ’’front end’’ is a commercial Lintott mass separator to which has been added a high-current version of the Lintott–Harwell hot-cathode ion source. The front end produces 11B currents of 1 mA and 31P, 75As, and 121Sb currents of 3 mA. The ’’rear end’’ is an acceleration and rotating scan target stage based upon the PR-500 technology which was developed at this laboratory. Careful matching of the front-end slit-beam ion optics to the rear-end circular-beam optics produces high currents on target, up to 1 mA of 11B and 2.5 mA or 31P, 75As, and 121Sb. These currents, combined with fast turnaround time (5–7 min) and rotating mechanical scan, permit more than 100 3-in. wafers/h to be implated with wafer nonuniformities (1 σu) less than 0.5% and a total product nonuniformity (1 σT) less than 2.0%. The target stage floats at high voltage, and is pumped through insulating columns by a vacuum system at ground potential. Additional pumping speed is obtained by a titanium sublimation pump inside the target stage. The pumpdown sequence is automated and the implant sequence is under minicomputer control, permitting operation of the system by unskilled personnel. Communication between the high-voltage target stage and ground potential is accomplished with a four-light-beam telemetry system. Two light beams are dedicated to the rotating-scan implant and dose control, and two other light beams communicate a variety of analog, digital, and status information.
Optical spectroscopy for diagnostics and process control during glow discharge etching and sputter deposition
Authors: Greene J. E.
Published: July 2002

Applications and limitations of optical spectroscopy for process control, as well as for more fundamental investigations, of glow discharge sputter deposition and emission spectroscopies allows the determination of concentrations and spatial distributions of sputtered and background gas species in ground, metastable, ionized, and excited states. Optical probing is a sensitive detection technique with good spatial resolution. It has the advantage of providing in situ real time information without disturbing the discharge. Examples of processes which may be monitored optically include: sputter etching and film deposition rates, net elemental sticking probabilities during bias sputter deposition, plasma ’’ashing’’ of photoresists, and reactive ion etching. Optical spectroscopy has also been used as a diagnostic technique for investigating preferential sputtering of alloys, reactive gas–surface interactions, and for providing quantitative chemical analysis and depth profiling information.
Specular reflectance of unprotected and protected evaporated metallic front-surface mirrors at various angles of incidence
Authors: Hass Georg
Published: July 2002

Today front-surface mirrors are used extensively in optical devices from the extreme ultraviolet to the far infrared. In this paper, methods for measuring the reflectance of mirror coatings at various wavelength regions, and techniques for preparing reflecting films of maximum reflectance, adherence, and durability will be described. Data on the ultraviolet, visible, and infrared reflectance of the most frequently used evaporated mirror coatings, Al, Au, Ag, Cu, and Rh will be presented. It will be shown that Al is the only film material that has high reflectance in all spectral regions. It also adheres better to glass and other substrates than the other reflecting coatings, does not tarnish in normal air, and is easy to evaporate. This makes it the most useful mirror coating. The application of single and multilayer protective layers for increasing the durability and increasing the reflectance of mirror coatings will be described and their effect on the reflectance at close to normal and higher angles of incidence will be treated. It will be shown that Al and Ag protected with rather thin silicon oxide or Al2O3 films (1000–2000 Å) have a normal incidence reflectance which is practically identical with that of unprotected mirrors in the infrared from 8 to 12 μm, but that their reflectances at higher angles of incidence is greatly decreased. This decrease is caused by the decrease in Rp rather than Rs, resulting in a sensitivity to polarization that makes possible a very efficient polarizer for the CO2 laser (10.6 μm) using four mirrors coated with Al+Al2O3.
ISS study of the oxidation of Au on Cu (300 Å) thin films
Authors: Nagasaka Michio , Vasofsky R. , Helbig H. F.
Published: July 2002

Using ISS techniques, composition versus depth profiles were made of Au (800 Å) on Cu (300 Å) films before and after heating in vacuum or 10.6 kPa of oxygen at 163°, 202°, and 250°C for 10, 100, and 1000 minutes. Prior to heating, small amounts of Cu were found on the surface but not in the bulk of the gold. Heating the double layer film in vacuum at 250°C for 1000 minutes resulted in a homogeneous Au–Cu film. On the other hand, heating the double layer in oxygen produced an inverted structure wherein the Au was found to lie beneath a gold-free copper oxide overlayer (324 Å).
Technique to determine the growth rate and resistivity of evaporated CdS thin films
Authors: Annamalai N. K. , Chao C. C. , Raymond D.
Published: July 2002

An in situ resistance measurement technique is described which was used to determine the resistivity and thickness of various layers of CdS films to be used in solar cell fabrication. A simple mathematical procedure was used to calculate the thickness and resistivity of the film during the growth process. This procedure was also used to monitor CdS films grown under different substrate temperatures and source powers. The variation of film characteristics with deposition parameters have been measured and the results correlate well with our activation energy measurements.
Simulation of plasma-etched lithographic structures
Authors: Viswanathan N. S.
Published: July 2002

The resist development model has been extended to simulate etched images in semiconductor processing. The model has been used to simulate under a variety of conditions varying from conventional wet etching to newer directional etching processes such as dry etching. As compared to the conventional wet etching processes the dry etch technologies erode the resist mask more intensively during processing. The model has been confirmed using a number of experimentally alterable and lithography-dependent conditions such as etch rates, resist profiles, resist thicknesses, etc. The effects of these on the final image shapes and the image sizes are predicted by simulations and aid the process definitions minimizing multivariate experiments. Isotropic etch processes such as those in the high-pressure reactors are also modellable by this approach.
Initial and final state effects in the photoionization spin–orbit branching ratio of core levels
Authors: Margaritondo G. , Cerrina F. , Williams G. P. , Lapeyre G. J.
Published: July 2002

We have investigated the ratio, R, of the photoionization cross sections of the In 4d5/2 and In 4d3/2 core levels on InSb (110) surfaces for energies within ∠9 eV of the threshold. We have separated for the first time the initial from the final state effects in R by employing different synchrotron radiation photoemission techniques. Energy distribution curves (EDC’s) and constant final energy spectra (CFS’s) demonstrate in particular that the R vs h/ω behavior is almost entirely determined by final state effects. This allows one to establish a relation between R and σ, the photoionization cross section, in an energy region where direct measurements of σ are made difficult by the secondary electron background.
Analysis of ELEED intensities from ZnTe(110)
Authors: Duke C. B. , Meyer R. J. , Paton A. , Mark P. , So E. , Yeh J.-L.
Published: July 2002

Elastic low-energy electron diffraction (ELEED) intensities were measured from ZnTe(110) surfaces at 300 and 125 K. The (01), (01̄), (10), (11), and (11̄) beams for normally incident electrons were analyzed using both kinematical and dynamical methods. Surface structures corresponding to covalent rotations and ionic contractions of the top three surface layers, as well as two minimum-energy structures were examined. The best description of the measured ELEED intensities achieved to date is associated with a model of the reconstructed surface in which the tellurium sublattice is found to be undistorted, while the top layer zinc sinks 0.4 Å and the second layer zinc rises 0.2 Å. Third layer distortions do not improve correspondence between the calculations and the data.
Heat of vaporization spectrometer
Authors: Edwards D.
Published: July 2002

Multilayer desorption measurements of various substances adsorbed on a stainless-steel substrate are found to exhibit desorption profiles consistent with a zeroth-order desorption model. The singleness of the desorption transients together with their narrow peak widths makes the technique ideally suited for a heat of vaporization spectrometer for either substance analysis or identification.
Performance of vacuum components operating at 1×10−11 Torr
Authors: Halama H. J.
Published: July 2002

The Intersecting Storage Accelerator (ISABELLE) consists of two rings having a circumference of 3.8 km each. The vacuum system uses an 8.8-cm circular chamber maintained at 1×10−11 Torr by a combination of Ti sublimation and 30-l sec−1 ion pumps placed at 5-m intervals. Several experimental setups which simulate sections of ISABELLE have been constructed to study the behavior of stainless steel, aluminum, H2–Ti system, and ion pumps at low pressures (?1×10−11 Torr). In this paper we will summarize the results of our measurements on (1) total outgassing of 304 stainless and 6061 aluminum, (2) hydrogen pumping speed, ultimate pressure, and sorbing capacity of titanium films as a function of surface coverage, H2 input flux and surface preparation, (3) hydrogen, methane, helium, and argon pumping speeds of ion pumps as a function of pressure, and (4) reemission of gases from ion pumps.
Vacuum system for national synchrotron light source
Authors: Schuchman J. C. , Godel J. B. , Jordan W. , Oversluizen T.
Published: July 2002

This paper describes the vacuum system for the National Synchrotron Light Source (NSLS) which is now under construction at Brookhaven National Laboratory (BNL). The system will consist of an electron linac, booster, vuv and x-ray storage rings, and up to 44 experimental beam lines. The pressures will range from 10−7 Torr in the linac and booster, to 10−10 Torr (without beam) in the storage rings. Stringent quality control and cleaning procedures are necessary to reduce the adverse effects of hydrocarbon contamination on optical elements which are used for beam handling. This thought is also reflected in the selection of materials, pumps, and other vacuum components, as well as in fabrication techniques. Sputter ion pumps are used throughout with distributed ion pumps and titanium sublimination pumps on the storage rings. Rough pumping is done with liquid-nitrogen-trapped turbomolecular pumps. In situ argon glow discharge conditioning is planned for the storage rings to reduce the desorption due to synchrotron radiation.
Twenty-kelvin cryopumping in magnetron sputtering systems
Authors: Visser J. , Scheer J. J.
Published: July 2002

There is a tendency to employ cryopumps based on closed-cycle cryogenerators in sputtering applications requiring hydrocarbon-free vacuum conditions. It has also been recognized that the residual gas contamination level can be lowered by using high inert gas throughputs. It will be shown that a cryopump of the K-20 type, providing ∠12 W at 20 K plus ∠50 W at 80 K, meets both of the above-mentioned specifications by offering a good (unthrottled) pumping performance at inert gas pressures up to 4×10−1 Pa with throughputs up to 3.3×103 Pa 1 s−1, without using LN2. The results, obtained with a standard available AlSi magnetron sputtering system, include pumping speed measurements for several gases and the effect of high gas loads on the pumping performance.
UHV compatibility of two possible fusion reactor materials: K-ramicR and ATJ graphite
Authors: Moore Richard
Published: July 2002

Outgassing characteristics of K-ramicR (manufactured by Kaman Nuclear) and ATJ graphite were evaluated under various treatments. For K-ramic, total outgassing rates of 2×10−9 Torr l s−1 cm−2 unbaked and 7×10−11 Torr l s−1 cm−2 baked were measured. Mass spectroscopic measurements showed H2 and CO to be the dominant residual gases. For ATJ, graphite the treatment consisted of repeated heatings in vacuo to 1250 K as well as repeated exposures to atmosphere. Residual gas analysis measured the time dependence of desorbed quantities of H2, H2O, CO2, CO, and CH4. During the initial heating, the maximum species atom to lattice atom ratios were obtained yielding values of 2.6×10−6 for H2, 3.4×10−5 for H2O, 1.6×10−5 for CO2, 7.6×10−6 for CO, and 5.2×10−6 for CH4. The toalt outgassed material from the graphite sample decreased by a factor of 103 after successive heatings.
First principles tight-binding method for investigating electronic properties of surfaces, interfaces, and bulk solids
Authors: Batra Inder P.
Published: July 2002

A brief discussion of first principles extended tight binding (ETB) (also known as linear combination of atomic orbitals, LCAO) method for studying electronic structure of solids is presented. As the name suggests, the method is nonempirical and employs a linear combination of Bloch-adapted Gaussian orbitals as its basis set. Hamiltonian and overlap matrix elements required for calculating electronic structure in solids can be obtained analytically using Gaussian functions. Various matrix elements are computed to convergence (which may involve interactions up to 10–12 neighbors), eigenvalues and eigenvectors are obtained by solving ∥H−ES∥−0. Since the tight binding wave functions are constructed from s, p, d, ... type of orbitals, the ETB method offers conceptual simplicity in understanding the nature of chemical bonds at a surface. Furthermore, the identification of surface states can be readily accomplished in terms of atomic localization, a quantity which is straightforward to calculate within the framework of this method. The method is illustrated by (i) absorbate band formation in CO monolayers and (ii) chemisorption studies of Cl on Si(111) surface. Future likely developments of the ETB method are briefly commented upon.
The interaction of tin oxide films with O2, H2, NO, and H2S
Authors: Capehart T. W. , Chang S.C.
Published: July 2002

A series of experiments was performed to investigate the observed changes in conductivity when sputtered tin oxide films maintained at 525 K are exposed to various ambient gases. X-ray photoemission spectroscopy (XPS) measurements on quenched samples monitored changes in both the chemical state and stoichiometry which occurs during exposure to O2, H2, NO, and H2S. The XPS results were correlated with in situ measurements of sample resistance. This comparison demonstrated no direct connection between the concentration of an adsorbed impurity, i. e., N or S, and conductivity. However, the bulk concentration of oxygen atoms is strongly correlated with the sample conductivity. We conclude that the predominant response mechanisms involve the oxidation/reduction of the sample with a concommitant decrease/increase in the bulk concentration of oxygen vacancies which mediates the conductivity.
Effects of surface relaxation on the electronic structure of ZnO (101̄0)
Authors: Ivanov I. , Pollmann J.
Published: July 2002

We have investigated the effect of atomic relaxation on the electronic structure of the nonpolar ZnO (101̄0) surface using the tight binding scattering theoretical method. The bulk material is described by a realistic empirical tight binding Hamiltonian and the relaxation is taken into account by a d−2 scaling of the interaction matrix elements. We find that the ionic surface resonances and the covalent surface states, which we have reported about for the unrelaxed surface previously, are affected very differently by surface relaxation. The covalent surface states strongly shift in energy upon relaxation while the ionic resonances are only marginally affected. This result can easily be interpreted by correlating the changes in the surface electronic structure with the relaxation induced changes of the local binding environment near the surface. Our theoretical results are in good agreement with UPS and EELS data.
A UHV compatible and miniaturized Knudsen cell used as a controlled evaporation source
Authors: Roulet H. , Alexandre E.
Published: July 2002

A miniaturized knudsen cell operable under ultrahigh vacuum conditions is discussed as a source of controlled evaporation. (AIP)
Techniques for electron beam testing and restructuring integrated circuits
Authors: Shaver D. C.
Published: July 2002

Techniques are presented for using an electron beam to control and sense logic states in integrated circuits and to control the state of nonvolatile switches. The electron beam techniques enhance testability and provide the ability to restructure circuit interconnections during testing.
Trajectory calculations of the extraction region of a liquid-metal ion source
Authors: Ward J. W. , Seliger R. L.
Published: July 2002

In the ion-extraction region of a liquid-metal (LM) source, several phenomena occur (e.g., electrostatic-lens action, axial and transverse space-charge interactions) that have major effects on the performance of the source. In an effort to better understand these effects, a trajectory analysis was made of the ion-extraction region. The trajectory calculations showed an appreciable increase in beam divergence at a Ga+ source current of only 5 μA.
Chemical control of recombination at grain boundaries and liquid interfaces: Electrical power and hydrogen generating photoelectrochemical cells
Authors: Heller A.
Published: July 2002

Recombination of carriers at a surface or at a grain boundary of a semiconductor is associated with the presence of chemical bonds that are weaker than those in the bulk. Upon strengthening these bonds, by reacting the interface with a strongly bound impurity, the rate of recombination is drastically reduced. For example, a 103-fold increase in EBIC charge collection efficiency for the polycrystalline p–InP/Ti Schottky junction and a corresponding increase in the efficiency of the photoelectrochemical cell polycrystalline p–InP/VCl3–VCl2–HCl/C are observed when silver is chemisorbed on the semiconductor grain boundaries. Chemical control of carrier recombination at semiconductor solution interfaces and grain boundaries results in 12 % efficient monocrystalline and 8 % efficient thin film polycrystalline solar cells, that generate either electrical power or hydrogen.
High-Z-doped laser fusion target ablation layers using metal colloids and metal-substituted-sulfonated polystyrene
Authors: Kim H. , Mason J. , Miller J. R.
Published: July 2002

Some inertial fusion target designs specify ablation layer coatings loaded with varying amounts of high atomic number elements. In this type of target, homogeneous dispersions of high-Z material in the ablation layer are extremely desirable. We have investigated two materials for fabricating the metal-loaded ablation layers. Targets have been coated by dipping in solutions of sulfonated polystyrene that were neturalized with Cs, Rb, K, Ba, and Ca. In the solid state, metal atoms in the sulfonated polystyrene do not reduce to the metallic state, but remain homogeneously dispersed in the polystyrene matrix. In the second approach, we have applied polymer-stabilized transition metal colloids that allow the fabrication of ablation layers having up to 6 at.% of a variety of transition metals. The coating surface finish in both approaches is better than a few hundred angstroms, and no structural features were observed by SEM.
Local bonding of oxygen and hydrogen in a-Si:H:O thin films
Authors: Lucovsky G. , Pollard W. B.
Published: July 2002

This paper provides a structural interpretation for the O-induced IR absorption bands in a-Si:H:O alloys. For films with C(O)∼0.1 to 5.0 at.% and C(H)∼10 at.%, there are three O-related IR features, at 2090, 980, and 780 cm−1. These are assigned to a local atomic arrangement in which the H and O atoms are bonded to a common Si site. The mode at 780 cm−1 strongly couples Si–H and Si–O–Si motions and is a unique signature of a particular local geometry. The other two vibrations are decoupled Si–H (2090 cm−1) and Si-O-Si (980 cm−1) stretching motions whose frequencies are perturbed by near-neighbor induction effects. Substitution of D or F for H changes the degree and character of the coupled mode, while substitution of Cl removes it completely.
Plasma enhanced chemical vapor deposition of thin crystalline semiconductor and conductor films
Authors: Reif Rafael
Published: July 2002

Plasma enhanced chemical vapor deposition (PECVD) is a technique widely accepted in microelectronics for the deposition of amorphous dielectric films such as silicon nitride and silicon oxide. The main advantage of PECVD stems from the introduction of plasma energy to the CVD environment which makes it possible to promote chemical reactions at relatively low temperatures. A natural extension of this is to use this plasma energy to lower the temperature required to obtain a crystalline deposit. This paper discusses the application of PECVD for the deposition of monocrystalline (epitaxy) and polycrystalline silicon, and of refractory metals and their silicides. It is emphasized that the PECVD technique can be used to deposit these semiconductor and conductor films at relatively low temperatures.
Soft x-ray appearance potential spectroscopic study of Sm–Co intermetallics
Authors: Chopra D. R. , Hatwar T. K. , Malik S. K.
Published: July 2002

Soft x-ray appearance-potential spectroscopy (SXAPS) exploits the abrupt changes in the total x-ray emission associated with the threshold for the excitation of core levels. The structures corresponding to the core level excitation are enhanced by differentiating the total x-ray yield as a function of incident electron energy. The present work is a study of the M4,5 and N4,5 levels of Sm and L2,3 levels of Co. SXAPS spectra, in the energy range 100–1200 eV, have been obtained for the pure metals and their intermetallics SmCo5 and Sm2Co17. The spectra, representing the derivatives of the self-convolution of the density of unoccupied states above the Fermi level (EF) give information regarding the chemical bonding in these intermetallics. The measured binding energy shifts in SmCo5 and Sm2Co17, relative to the pure metals, are positive for Sm and negative for Co. The Co L3 peak width decreases on alloying, indicating a partial filling of its 3d band as a result of the charge transfer from Sm to Co. These results correlate well with the reported measurements on similar rare earth–cobalt intermetallics.
A residual gas analyzer compatible with reactive and radioactive gases
Authors: von Seggern J. , Berger S. , Erdweg M. , Hofer W. O.
Published: July 2002

A conventional residual gas analyzer was equipped with an ion-electron converter as particle detector and tested in tritium-containing environments. Substantial advantages can be asserted for this setup: high dynamic range, easy regenerability by baking without detrimental effects on the multiplier, insensitivity to exposure to reactive gases, and inexpensive replacement.
Characterization of the treated surfaces of silicon alloyed pyrolytic carbon and SiC
Authors: Smith K. L. , Black K. M.
Published: July 2002

The treated surfaces of artificial heart valves made of silicon alloyed pyrolytic carbon were compared to similarly treated SiC using x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The materials were exposed to water, isopropanol, and acetone cleaning, diamond and alumina polishing, and sterilization. Three chemical states of carbon, three states of silicon, and low concentrations of polishing contaminants were identified and related to surface treatment. Characterization of the heart valve surfaces will assist in determining appropriate manufacturing processes required for assuring blood compatibility of the devices.