bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface roughness of silicon carbide etched in a C2F6/O2 inductively coupled plasma
Authors: Kim Byungwhan , Choi Hyun Jun , Lee Byung-Teak
Published: July 2002

Investigation of the surface roughness of etched SiC films is of great importance when attempting to improve electrical properties of SiC active devices. The roughness of SiC etched in a C2F6/O2 inductively coupled plasma has been examined as a function of process parameters. Experimental ranges of parameters that were varied include 600–900 W source power, 50–150 W bias power, 4–16 mTorr pressure, 0%–80% O2 fraction, and 6–12 cm gap between the wafer and plasma source, respectively. Surface roughness was characterized using atomic force microscopy. dc bias voltage was correlated to the roughness. At medium parameter levels the roughness was reduced with an increase in source power while the roughness was increased with increasing bias power. With variations in pressure or O2 fraction, the roughness varied nonlinearly. dc bias was strongly correlated to the roughness for variations in source power and bias power. Interestingly, the bias was inversely related to the roughness for variations in O2 fraction and gap. Although the roughness was degraded consistently with an increase in the parameters at a low level, this was no longer observed at a high level. When the wafer was placed closer to the plasma source, the roughness was the most significantly varied with a reduction in pressure. At this reduced pressure, the roughness was drastically increased with a decrease in O2 fraction. Meanwhile, the roughness was insensitive to the gap when varying process parameters from high to low levels. For the experimental ranges of concern, the mean roughness varied between 0.55 and 1.04 nm.
Interfacial mechanism studies of electroless plated Cu films on a-Ta:N layers catalyzed by PIII
Authors: Lin Jian-Hong , Lee Tzu-Li , Hsieh Wei-Jen , Lin Chien-Cheng , Kou Chwung-Shan , Shih Han C.
Published: July 2002

This study evaluated the interface reaction and crystallography of the electroless plated copper film (∼0.2 μm thick) catalyzed by plasma immersion ion implanted (PIII) Pd on the 150-Å-thick amorphous tantalum nitride (a-Ta:N) barrier layer. The copper plated specimens were annealed at various temperatures in an ambient atmosphere of 90% nitrogen + 10% hydrogen mixed gases. Sheet resistivity, Auger electron spectroscopy (AES) analyses showed that the PIII Pd atoms were diffused into the copper layer from the interface of a-Ta:N and copper layers after 500 °C annealing for 1 h. Results based on x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) showed a phase transformation from a-Ta:N into crystallized Ta2N phase at annealing. The Cu(111) texture was strengthened at 300 °C annealing for 1 h because of the relaxation of the residual stress and recovery of the copper film. The texture was reduced at the 500 °C annealing for 1 h because of the copper grain growth. The adhesion strength of copper films on a-Ta:N barrier layer was enhanced by the annealing because of the interdiffusion of copper layer, Pd clusters and a-Ta:N barrier layer. The annealing temperatures lower than 300 °C help to reduce the electric resistivity of copper film, to strengthen the Cu(111) preferred orientation, and to enhance the adhesion strength of copper films on a-Ta:N layer. However, the specimen annealed at 500 °C manifested the diffusion of Pd atoms into the copper film and resulted in a significant increase of the electric resistivity of copper film.
Initiation of Electrical Breakdown in Ultrahigh Vacuum
Authors: Alpert D. , Lee D. A. , Lyman E. M. , Tomaschke H. E.
Published: July 2002

Existing theories for the initiation of electrical breakdown are reviewed, together with the experimental observations on which they are based. Experiments here described have extended the available data on electrical breakdown between broad area electrodes under ultra-high-vacuum conditions. The results, together with those of several other experimenters, are interpreted on the basis of a single picture which explains and relates the phenomena of predischarge currents and the initiation of breakdown. Based on field emission from sharp submicroscopic points, this picture predicts breakdown when the local electric field at the cathode reaches a critical value. The local field, which for broad area electrodes may be much larger than the average field, is deduced from observations of field emission prior to breakdown. When properly analyzed, data for tungsten electrodes from this research and several others indicate a value for the electrical field at breakdown which is independent of gap spacing or geometrical configuration for voltages up to 250 kV. The critical breakdown field for tungsten is 6.5 × 107 V/cm. The above picture also gives physical insight into other phenomena associated with electrical breakdown.
Diffusion-Controlled Sorption in High-Density Discharges
Authors: Maddix H. S. , Allen M. A.
Published: July 2002

An experimental technique is described for obtaining reproducible sorption measurements in high-density discharges. Data are given for the sorption of argon, neon, and helium at the quartz walls of an electrodeless discharge for a surface temperature range of −35 ° to 750 °C. The complex dependence of sorption on temperature and discharge power is described in terms of sticking times, depth of ion penetration, diffusion coefficients, and flux rates. A theory is presented which gives good agreement with experiment. Maximum diffusion of gas into the walls occurs when the product of sticking time and ion flux is equal to the number of available trapping sites at the surface. The average depth of ion penetration in quartz was calculated from the theory and data to be in the range of 3 to 7×10−8 cm for helium, neon, and argon ions with bombarding energies of 12 to 17 eV.
Phonic Desorption
Authors: Denison Dean R.
Published: July 2002

The desorption of materials from the walls of a vacuum vessel by means of phonic energy has been observed. To study this effect and its application to improved pumpdown of nonbakeable systems, an ultrasonic transducer was attached to a small system and the desorption products observed with a quadrupole gas analyzer. Water vapor, CO, CO2, and hydrocarbons were observed to desorb. The apparatus and results are presented with a simple theory that describes the results.
Solar absorptance and emittance properties of several solar coatings
Authors: Pettit R. B. , Sowell R. R.
Published: July 2002

Solar absorptance αs and total hemispherical emittance εt,H properties of two potential solar selective coating systems are reported. The first coating system studied is a semiconductor-pigmented paint which consists of a high-temperature silicone binder mixed with small particles of Ge, Si, or PbS. Although most of the paints have αs values above 0.90, all the paints suffer from high εt,H values (∠0.70 to 0.90), which are shown to be due to the high emittance of the silicone binder itself. The second system studied is electroplated films of ’’black nickel’’ and a proprietary ’’black chrome.’’ Both αs and εt,H values have been obtained as a function of the electroplating time and the substrate surface roughness. Increasing the plating time initially increases both αs and εt,H; however, for long plating times, there is no improvement in αs, while εt,H continues to increase. By increasing the surface roughness of nickel-plated substrates, the solar absorptance can be increased while maintaining approximately the same total hemispherical emittance. The coatings show minor decreases in solar absorptance at angles of incidence up to 75° from normal (e.g., about 25% decrease at 75°).
Surface damage of molybdenum and TZM alloy under D+ impact
Authors: Das S. K. , Kaminsky M. , Dusza P.
Published: July 2002

The surface damage of polycrystalline molybdenum and TZM alloy under 40-, 60-, and 120-keV D+ impact has been investigated for irradition in both pulsed and continuous modes for total doses varying from 1.7×1017 to 2.2×1019 ions/cm2 and for target temperature varying from ambient temperature to 400° C. Analysis by scanning electron microscopy of the Mo samples held at ambient temperatures during D+ irradiations in both pulsed and continuous modes revealed surface damage due to blistering for the 40- and 60-keV irradiations for doses ranging from 8.7×1017 to 8.1×1018 ions/cm2, but no detectable damage for the 120-keV D+ irradiations for doses ranging from 4.3×1018 to 2.2×1019 ion/cm2. This observed difference in the blistering behavior is attributed to the difference in the ambient target temperature for the 120-keV irradiation and both the 40- and 60-keV irradiations. For irradiations at temperatures above 300° C, no blisters could be detected for any of the three energies. For similar irradiation conditions, TZM alloy showed a reduction in blistering as compared to molybdenum.
Preparation of thin films for solar energy utilization
Authors: Mattox D. M.
Published: July 2002

Thin film deposition techniques have made and are making a significant contribution to solar energy utilization. Commercial applications of thin films include photothermal selective absorbers formed by electroplating, chemical conversion, and vacuum processing; solar reflectors formed by vacuum processes; heat reflectors formed by vacuum processes and spray pyrolysis; and antireflection coating formed by vacuum processes and chemical leaching and the metallization of photovoltaic cells. CdS/Cu2S photovoltaics formed by vacuum processes and spray pyrolysis are also close to commercial utilization. Principal concerns in thin films applications include economics of fabrication and environmental stability of the thin film materials. At the present time, for many applications the best and most economical film deposition technology is not yet defined. One of the major problems with thin film evaluation is the lack of acceptable testing procedures particularly as related to lifetime. Research and development is continuing in the application of sophisticated thin films to photovoltaic conversion and other applications. This paper reviews the status of thin film in solar energy utilization.
Thermal desorption measurements of hydrogen–isotope retention in the Alcator-A tokamak
Authors: Razdow A. M. , Marmar E. S. , Cohen S. A. , Dylla H. F.
Published: July 2002

Results are presented for deuterium retention measurements in type 304 stainless steel exposed in the edge plasma of the Alcator-A tokamak. Stainless steel samples, at 300 K, with surface conditions characterized by Auger electron spectroscopy, were introduced into the limiter shadow region for exposure to deuterium plasmas, and then withdrawn into an appended UHV chamber for thermal desorption measurements. For unoxidized samples exposed at the vacuum vessel wall radius, 1×1015 D cm−2 was retained after exposure to high density (?e=3×1014 cm−3) discharges. Exposure to consecutive series of N discharges produced retention proportional to N1/2.
Summary Abstract: Investigation of the metal-support interaction in coprecipitated nickel on alumina methanation catalysts using x-ray photoelectron spectroscopy
Authors: Shalvoy R. B. , Reucroft P. J. , Davis B. H.
Published: July 2002

The use of x-ray photoelectron spectroscopy in the study of metal-support interaction in nickel on alumina methanation catalysts is reported. Although these interactions give thermal stability, they also make the catalysts more difficult to reduce. (AIP)
Microgravimetric and infrared study of the adsorption of 1-butene on delta alumina
Authors: Bianchi D. , Gass J. L. , Pajonk G. , Teichner S. J.
Published: July 2002

The adsorption of 1-butene has been studied gravimetrically on delta alumina which has been dehydroxylated at various temperatures, using a RH Cahn Electrobalance. For temperatures of dehydroxylation between 25° and 250°C delta alumina is inactive in the isomerization of 1-butene. Simultaneously only reversibly adsorbed on OH groups species has been detected by IR analysis, resembling to 1-butene. For higher temperatures of dehydroxylation the solid is active in isomerization and two new adsorbed species have appeared: one is reversibly adsorbed and the other is irreversibly adsorbed. The former has the structure of 1-butene whereas the latter has lost all unsaturated character. Poisoning experiments performed with NH3 demonstrate that these two species are adsorbed on Al3+ ions and the second one also on O2− ions. The irreversibly adsorbed species is responsible for the deactivation of the catalyst.
Oxidation studies with the vacuum microbalance in complex environments
Authors: Gulbransen Earl A.
Published: July 2002

Vacuum microbalance methods incorporating oxygen consumption and gas-flow measurements have expanded the usefulness of the simple weight-change methods. It will be shown that (1) the combined methods can be used to evaluate oxide film formation and oxide volatility, (2) the combined methods permit an evaluation of the transition between chemically controlled and gas-diffusion-controlled oxidation, (3) sample size can also be used to evaluate the transition between chemically controlled and gas-diffusion-controlled oxidation, (4) gas flow can be used to extend the study of rapid oxidation reactions to rates of oxidation approaching the collision rate of oxygen with the metal surface, and (5) thermochemical analysis of the condensed and volatile oxides was very useful in the analysis of high temperature oxidation processes.
Chemisorption and oxide formation on metals: Oxygen–nickel reaction
Authors: Holloway Paul H.
Published: July 2002

The reaction of oxygen with atomically clean nickel surfaces is reviewed. The reaction consists of three stages—chemisorption, oxide nucleation and lateral growth to coalescence, and thickening of coalesced oxide. Chemisorption is dissociative and nonreconstructive in general. However, a reconstructed chemisorbed phase is detected on Ni (110). NiO nucleates and grows laterally as islands displacing the chemisorbed phase, and finally coalescing to passivate the nickel surface. The conditions and rates at which the coalesced oxide thickens have not been well defined.
Simulation of plasma-assisted etching processes by ion-beam techniques
Authors: Mayer T. M. , Barker R. A.
Published: July 2002

Fundamental aspects of plasma-assisted etching processes can be investigated in a well-defined and controllable manner by ion-beam techniques. We review here our experiments aimed at simulating a plasma environment using beams to investigate the effects of a number of fundamental parameters of plasma processes, such as the chemical identity of bombarding ions, flux of ions and neutrals to a surface, and ejection of products from a surface. Enhanced ion etching due to reactions of neutral gases with surfaces is demonstrated, and product ejection mechanisms are shown to be possible rate limiting factors in reactive etching processes. A simple chemically enhanced sputtering model suffices to account for the main features of ion-induced etching. Applications of this model to bulk plasma processes, dependence of etch yield on ion angle of incidence, and surface composition modification are suggested.
The oxidation of zinc in air studied by XPS and AES
Authors: Hammer G. E. , Shemenski R. M.
Published: July 2002

The oxidation of zinc in air at 294 K has been studied for exposure times from 1 min to 150 h. The fraction of zinc in the Zn+2 valence state has been determined by high resolution Auger electron spectroscopy. Surface oxide thickness was measured by using AES with argon ion sputter etching. The adsorbed oxygen was shown by x-ray photoelectron spectroscopy to be in two states, one corresponding to O−2 in ZnO, the other being chemisorbed oxygen. The two O1s photoelectron peaks were partially resolved by means of a van Cittert-type deconvolution calculation and the relative separation was found to be 1.7 eV, in agreement with that for low level O2 adsorption of polycrystalline zinc under UHV conditions.1 The effect of temperature was also determined in the range of 294–573 K. The fraction of zinc in the Zn+2 valence state after 1 h exposure was found to increase nearly linearly with temperature, with ZnO formation complete at 573 K.
Target erosion and deposition rates in planar magnetron sputtering
Authors: Gurvitch M.
Published: July 2002

Erosion grooves are known to develop on a surface of a planar magnetron sputtering target in the course of its use, causing the rate of deposition per unit power applied to the target (rate efficiency) to decrease with progressing erosion. It is shown that for a given target material there is a reproducible empirical correspondence between the rate efficiency and the groove depth. Once established, this correspondence offers a simple way for estimating thicknesses of the films deposited onto stationary and rotating substrates.
Corrosion behavior of amorphous Ni based alloy coatings fabricated by ion beam mixing
Authors: Bhattacharya R. S. , Rai A. K. , Raffoul C. N. , Pronko P. P. , Khobaib M.
Published: July 2002

Amorphous thin films of MoNi, TiNi, MoNiCr, and TiNiCr with thicknesses in the range of 650–1500 Å were prepared by high energy (1 MeV) Au+ and Pt+ ion beam mixing. The compositions of these films were Mo50Ni50, Ti50Ni50, Mo35Ni54Cr11, and Ti40Ni50Cr10. Aqueous corrosion behavior of these amorphous films were studied in 1 N HNO3 and 0.1 N NaCl solutions by the potentiodynamic polarization method. The amorphous coatings showed significantly lower corrosion rates in both acidic and basic aqueous solutions compared with their polycrystalline counterpart which were obtained by annealing the amorphous layers at temperatures above the amorphous to crystalline transition temperature. The corrosion behavior of amorphous films was also significantly improved in comparison with pure elemental constituents.
Ellipsometric investigation of Be(0001) oxidation
Authors: Christensen T. M. , Blakely J. M.
Published: July 2002

Studies by ellipsometry of the early stages of oxidation of the Be(0001) surface in the temperature range 30–600 °C have been made in conjunction with Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). An initial decrease in the ellipsometric parameter Ψ is taken to indicate incorporation of oxygen into the beryllium surface. The magnitude of the decrease in Ψ depends on temperature and is greatest around 100 °C. It is proposed that at the minimum in Ψ the surface consists of islands of BeO in an electron depleted Be layer; an effective medium approximation, assuming nearly free electron behavior for Be, can describe the experimental results with reasonable values of the parameters. After oxide coalescence, p(2×2)-BeO and ((3)1/2x(3)1/2)R30° -BeO LEED patterns are observed. They are unstable under an electron beam, but can be regenerated by short anneals at 500 °C. The ellipsometric parameter Δ is observed to be significantly different for the surface with and without this ordered structure. This change in Δ is not directly related to changes in the degree of order, but may be caused by electron beam enhanced decomposition of adsorbed gas. Ellipsometry results for oxygen on Ni(111) have also been obtained; these assist in the interpretation of the Be data.
Analysis of carbon and oxygen in GaAs using a secondary ion mass spectrometer equipped with a 20 K-cryopanel pumping system
Authors: Homma Yoshikazu , Ishii Yoshikazu
Published: July 2002

The detection of carbon and oxygen in GaAs has been investigated by secondary ion mass spectrometry (SIMS). A reduction in carbon and oxygen background is achieved by means of a local pumping system using a 20 K-cryopanel placed around the sample. Detection limits are 4×1015 atoms/cm−3 for carbon, and 8×1015 atoms/cm−3 for oxygen.
Composite materials for high heat and particle flux components in fusion devices
Authors: Krauss A. R. , Gruen D. M. , Brooks J. N. , DeWald A. B.
Published: July 2002

We discuss the use of composite materials based on the use of self-sustaining coatings to reduce sputtering-induced erosion in magnetic confinement fusion devices while providing enhanced high-heat flux properties. One material, a copper–lithium alloy has been described previously. A second group of materials consists of porous tungsten, tungsten carbide, or tantalum, impregnated with an alkali metal alumino-silicate. These materials form an alkali metal overlayer similar to that found on the Cu–Li alloy. A third group of materials is obtained by infiltrating the porous high-Z refractory metal with an alkali-metal-bearing alloy such as Cu–Li or Al–Li. These materials combine the high thermal conductivity of the infiltrate material with the high-temperature strength and melt layer stability of tungsten or tantalum. Calculations of the sputtering properties indicate that it may be possible to use a tungsten composite limiter at plasma edge temperature up to ∼300 eV.
Calculation of pressure distribution in an electron storage ring and comparison with monitored pressure and beam lifetime
Authors: Miyahara Yoshikazu
Published: July 2002

Pressure distribution and average pressure in an electron storage ring was calculated with a matrix method obtained from an analogy to an electric circuit. By virtue of the method which divides the vacuum chamber of the ring into a series of short sections, it becomes easy to calculate the pressure distribution in such a complicated vacuum system as the storage ring including rf cavities and distributed gas desorption and pumping system. The calculation is carried out assuming the coefficients of the thermal and photoinduced gas desorption rates as variable parameters. By comparing with monitored pressure, the most probable pressure distribution, and thereby the average pressure, are obtained. The beam lifetime due to the residual gas scattering is estimated using the calculated average pressure and compared with observed lifetime.
The effect of the surface state on the permeation of hydrogen through palladium
Authors: Antoniazzi A. B. , Haasz A. A. , Stangeby P. C.
Published: July 2002

The effect of varying surface carbon coverage on the permeation of molecular and atomic hydrogen through palladium was examined. The elemental coverage on one of the Pd surfaces was observed by in situ Auger electron spectroscopy. For molecular permeation the upstream driving pressure ranged from ∼10−3 to 5×102 Pa. For atomic permeation the incident sub-eV atomic flux varied from ∼4×1017 to 3×1020 H0/m2 s. Phenomenological hydrogen transport models were used to determine relative hydrogen recombination and sticking coefficients.
Kinetics and initial stages of oxidation of aluminum nitride: Thermogravimetric analysis and x-ray photoelectron spectroscopy study
Authors: Katnani A. D. , Papathomas K. I.
Published: July 2002

The resistance of AlN powder to oxidation upon heat treatment in air is investigated using thermogravimetric analysis (TGA) and x-ray photoelectron spectroscopy (XPS). The results reveal that oxidation is initiated at temperatures above 700 °C. For temperatures between 750 and 900 °C, an intermediate oxidation state, which involves the formation of oxynitrides, is detected by XPS and only a linear increase in weight with time is observed with TGA. Oxynitride formation precedes the formation of aluminum oxide and the oxynitride layer persists forming an interfacial layer between oxide and nitride. At temperatures above 900 °C XPS indicated the formation of a thick oxide layer while TGA measurements showed a linear followed by a nonlinear increase in weight with time. These results suggest that the initial stage of oxidation is controlled by surface reactions followed by diffusion controlled oxidation. The activation energy for surface reaction and diffusion oxidation are 36 and 56 kcal/mol, respectively.
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u measurement of coating thickness during thermal spraying using an optical displacement meter
Authors: Kuroda S. , Fukushima T. , Kitahara S.
Published: July 2002

An optical diplacement meter was developed to measure and control the thickness of coatings deposited by thermal spraying. The displacement of the surface of a workpiece was monitored continuously during the spraying process by detecting the position of a bright spot made on the surface by laser illumination using a linear image sensor. A cylindrical lens was used to reduce the error due to speckle and a differential method was employed to discriminate the coating thickness from the displacement due to thermal deformation. By stopping deposition when the meter output reached a predetermined value, the thickness of plasma sprayed alumina coating could be controlled with a standard deviation of 24 μm.
Reactive and nonreactive ion mixing of Ti films on carbon substrates
Authors: Galuska A. A. , Uht J. C. , Marquez N.
Published: July 2002

The influence of nonreactive and reactive ion beam mixing on the interfacial chemistry, morphology, and adhesion of Ti films on glassy carbon, a-face pyrolytic graphite, and c-face pyrolytic graphite was examined and compared to thermal processing. Nonreactive ion beam mixing was performed with 180-keV 84Kr+ at doses of 1 to 5×1016 Kr/cm2. Reactive ion beam mixing was performed with 150-keV 28Si+ at doses of 1 to 5×1017 Si/cm2. Vacuum annealing was performed at 1000 °C for 1 h. Both 84Kr+ and 28Si+ implantation induced substantial intermixing between the Ti films and each of the carbon substrates. The 1000 °C anneal produced little interfacial reaction. Ion beam mixing produced adhesion increases of up to 1000× while no adhesion enhancement was observed following the anneal. Adhesion increases were attributed primarily to mechanical interlocking for both the 28Si+ and the 84Kr+ implantation. There were indications of ion induced film/substrate chemical bonding (Ti–C and Ti–O–Si-C), but this bonding did not appear to greatly influence the observed adhesion. Ion induced topographical changes included void and bubble formation, cracking, erosion, and carbon aggregation. Topographical modifications were at a minimum on the glassy carbon specimens and at a maximum on the c-face pyrolytic graphite specimens. Film characterization was performed using secondary ion mass spectrometry, Auger electron spectroscopy, x-ray photoelectron spectroscopy, scanning electron microscopy with energy dispersive x-ray analysis, and x-ray diffraction. Adhesion was examined using a scratch test.
Thirty years of turbomolecular pumps: A review and recent developments
Authors: Henning J.
Published: July 2002

The history of turbomolecular pumps (TMP’s) will be reviewed and the principle of the pumping action will be explained. Some of the theoretical considerations for TMP’s yield an easy check of the pumping speed data for a given TMP. After highlighting the rapid development of the technique, the actual technical status of TMP’s will be given in detail. Some of the applications (e.g., in magnetic fields, plasma etching, radioactive gases) demonstrate that the ‘‘standard’’ TMP has some shortcomings which have to be overcome by dedicated adaptation. The recent combination of a TMP with molecular pumping stages shifts the useful foreline pressure to higher values, and enables the use of smaller dry backing pumps. Future trends in the field of TMP will be mentioned.
Activation and recrystallization of ion-implanted amorphous silicon films by rapid thermal annealing
Authors: Kim Youn Tae , Yoo Hyung Joun , Jun Chi Hoon , Jang Won Ick , Kim Sang Ho
Published: July 2002

Amorphous and polycrystalline silicon (poly-Si) films were deposited on oxidized wafer surfaces by low-pressure chemical vapor deposition in the range 540–650 °C. After ion implantation, rapid thermal annealing (RTA) was carried out for 5–30 s by the infrared radiation at 1000–1150 °C. The films were characterized by measurements of resistivity, grain size, structure, and surface roughness. It is shown that the required conditions for successful activation of dopants (boron, phosphorus: 5×1015/cm2) were above 1000 °C and 10 s. This condition is similar to those used in RTA of comparably implanted single-crystal silicon. The typical resistivities of films deposited below 600 °C were in the range of 1.0×10−3 Ω cm which was 20%–30% lower than that of initially poly-Si films deposited above 600 °C. After RTA at high temperatures above 1000 °C, the films did not reveal any change in resistivity due to dopant segregation, and better electrical conductivity could be obtained by increasing the annealing time. The grain growth by RTA treatment was more salient in the case of the doped amorphous than that of initially polycrystalline. The surfaces of the amorphous films also preserved higher structural perfection and surface smoothness.
Influence of ion mixing on the depth resolution of sputter depth profiling
Authors: Cheng Yang-Tse , Dow Audrey A. , Clemens Bruce M. , Cirlin Eun-Hee
Published: July 2002

During sputter depth profiling, the bombarding ions for sputtering also produce ion mixing at interfaces. As a result, ion bombardment changes the original composition profile of the specimen, setting a limit on the depth resolution of the sputter depth profiling technique. The origin and magnitude of the effect of ion mixing on the depth resolution of sputter depth profiling have been studied using x-ray photoelectron spectroscopy, Auger electron spectroscopy, and Ar+ sputter depth profiling of Pt/Zr, Pt/Mo, Pt/Ti, and Pt/Ni interfaces. It is shown that the effect of ion mixing is an intrinsic limitation on the depth resolution; it depends on the thermodynamic properties, such as the heat of mixing and the cohesive energy, of the solids under examination. The magnitude of the effect of ion mixing is compared with that of the instrument-dependent limitations on the depth resolution of sputter depth profiling.
The characterization of an imaging time-of-flight secondary ion mass spectrometry instrument
Authors: Eccles A. J. , Vickerman J. C.
Published: July 2002

A detailed study has been made of the performance characteristics of a new imaging time-of-flight secondary ion mass spectrometer based on the Poschenrieder design and utilizing a 30-kV gallium primary beam column. In spectral mode the maximum transmission and mass resolution have been measured and the relationship between transmission and mass resolution have been determined. The influence of primary pulse length, extraction voltage, and secondary ion mass on these parameters are described. A variety of materials have been used in the study, ranging from pure molybdenum, cesium iodide to insulating polymers such as poly (methylmethacrylate) and polystyrene. The influence of sample charging is discussed. The spatial resolution of the liquid metal ion beam in continuous and pulsed mode has been assessed and the performance of the imaging time-of-flight secondary ion mass spectrometry system is described using a model metal on silicon device. The use of the system in micrometer scale depth profiling is also described.
High-rate sputter deposition of SiO2 and TiO2 films for optical applications
Authors: Nandra S. S.
Published: July 2002

This paper describes a process to produce SiO2 and TiO2 films at high rates of deposition by using chemically reactive gases (etch gases). Experiments were conducted using Cl2, CCl4, CCl3F, CClF3, and H2 mixed individually in Ar and O2 plasma in a magnetron sputtering process. Oxide films were deposited on glass and Si substrates from sputter-etching of Si, SiO2, Ti, and TiO2 targets. An attempt was made to understand the mechanism involved in the increased rate of deposition. The results showed that considerable enhancement of the rate of deposition was obtained for SiO2 and TiO2 films when sputtered from their pure elemental targets. The enhancement in the rate of deposition ranged between 5 and 30 times over that obtained in a conventional reactive sputtering process. The analysis of the process during sputtering indicated that deposition was accompanied by the formation of volatile chlorides resulting from the chemical etching of the targets. In most cases the coatings had refractive indices close to those of the bulk SiO2 and TiO2, the films were clear and had good resistance to scratching. However, at high concentrations of the etch gases, the optical and scratch properties of the films deteriorated.
The chemistry of the gadolinium–nickel interface
Authors: LaGraffe D. , Dowben P. A. , Onellion M.
Published: July 2002

Gadolinium overlayers on Ni(111) have been studied by angle resolved photoemission, angle resolved AES, LEED, and RHEED. We have observed pronounced interdiffusion of nickel with the gadolinium overlayer at temperatures as low as 150 K. This is in marked contrast with gadolinium overlayers on Cu(100) where substantial interdiffusion is not observed until 360 K, but is consistent with studies of ytterbium on nickel. [A. Nilsson, B Eriksson, N. Martenssom, J. N. Andersen, and J. Onsgaard, Phys. Rev. B 38, 10357, (1988) and I. Chorkendorff, J. Onsgaard, J. Schmidt–May and R. Nyholm, Surf. Sci. 160, 587, (1985).] There is a strong interfacial heat of interaction observed with gadolinium on both copper and nickel resulting in pronounced binding energy shifts observed in photoemission. An extremely small kinetic barrier to rare earth diffusion through nickel has been measured. The results are compared to transition metal overlayers on transition metal substrates.
Deformation in thin films by thermal strain
Authors: Murakami Masanori
Published: July 2002

Stresses and strains are always present in thin films deposited on substrates. When these strains are larger than the elastic limit, they are relaxed by various mechanisms, deform the films, and are detrimental to the stability or performance of thin-film devices. The relaxation processes are strongly affected by the film microstructure (such as grain size and film thickness), the shear modulus of the substrate, the surface oxide and misfit dislocations often observed in the layered-structural films. The strain relaxation causes large film microstructure changes. In contrast, although the strain is supported elastically, small microstructure changes are observed. Nonuniform distributions of the strain are observed in the film in directions both parallel and normal to the film surface. Different shrinkages are measured in grains with different crystal orientations due to strong anisotropy in the elastic constants of the film and the strain gradient from the top to bottom of the film is observed. In this paper, deformation of thin films caused by thermal strain is reviewed using illustrative data of Pb films deposited on Si substrates.
Clean and oxygen covered InP(110) surfaces differential reflectivity
Authors: Cricenti A. , Selci S. , Felici A. C. , Ferrari L. , Gavrilovich A. , Goletti C. , Chiarotti G.
Published: July 2002

We present surface differential reflectivity results on the polarization dependence of optical transitions and on the oxidation of InP(110) surfaces in the energy range between 2.0 and 4.0 eV. The surface dielectric function has been computed for light electric vector along [110] and [001] directions. Three well defined optical peaks have been detected at the following energies: 2.6 eV (light electric vector along [110] direction), 3.1 eV (unpolarized), and 3.5 eV (light electric vector along [001] direction). Absorption kinetics is analyzed by following the reflectivity variation between 1×102 and 2×106 L of molecular oxygen at three selected spectral energies. Several well defined steps of the oxidation process are clearly resolved and discussed in terms of disappearance of intrinsic surface states, creation of acceptor and donor defect states, growth of In2O3.
Combination of turbomolecular pumping stages and molecular drag stages
Authors: Levi G.
Published: July 2002

Conventional turbomolecular pumps consist of a succession of rotating and stationary bladed disks. In order to increase compression ratios, the open angle of the disks is decreased from the upper to the lower stages of the pump: a compression ratio of ≳ 107 can be obtained for nitrogen in nine stages. However, the maximum compression ratios are obtained only when the pump is working in free molecular flow conditions, corresponding to a foreline pressure in the range 10−3–10−2 mbar; at higher pressures the compression ratio decreases dramatically thus limiting the total efficiency of the pump. Molecular drag pumps, on the contrary, can work with high compression ratios also in the transition flow region, in the range from 10−2 to 10 mbar. Combination of turbomolecular pumping stages and drag stages have been tested. Molecular drag stages of a new design have been incorporated in a conventional turbomolecular pump without adding to its dimensions. From these tests it appears possible to have high compression ratios with the foreline pressures up to 10 mbar: the forevacuum pump could be a conventional, double-stage rotary pump or a less conventional diaphragm oil-free pump. The behavior for different gases has been analyzed and advantages of this arrangement are examined.
Application of scanning tunneling microscopy to study adatom diffusion and lateral interactions: Sulfur on Re(0001) at low coverages
Authors: Dunphy J. C. , Sautet P. , Ogletree D. F. , Salmeron M. B.
Published: July 2002

Scanning tunneling microscopy (STM) imaging was applied to study coverages of less than 0.3 monolayers of sulfur on a rhenium(0001) surface. At coverages near one quarter monolayer sulfur forms a p(2×2) ordered overlayer. Below this coverage islands of p(2×2) ordered sulfur form, indicating an attractive interaction between sulfur atoms at twice the Re lattice spacing. Between these islands the STM images appear noisy. A correlation technique was applied to these images which showed that this noise was actually due to sulfur atoms diffusing on the same time scale as the STM image was acquired. The pair interaction energy between sulfur atoms at twice the Re lattice distance was determined by fitting the results of this correlation technique to an Ising model. The mobility of sulfur on the surface was further investigated by coadsorbing CO. This was found to compress the dilute sulfur overlayer into an ordered structure usually only seen at higher coverages. The transformation was observed by both low energy electron diffraction and STM. An upper limit for the energy required to compress the overlayer was extracted from the adsorption energy of CO. The energy barrier to diffusion was estimated from the average residence time of the diffusing sulfur atoms. These energies compare well with an extended Hückel calculation.
Electrical and optical characterization of metal/n-InP interfaces formed by a cryogenic process in high vacuum
Authors: Shi Z. Q. , Anderson W. A.
Published: July 2002

We report a novel low temperature (LT=77 K) deposition process at high vacuum to make reliable, high-barrier height Schottky contacts to n-InP. The electrical and interface properties of the metal/n-InP were investigated by current–voltage (I–V) and capacitance–voltage (C–V) techniques, photoreflectance (PR), and Raman spectroscopies. For the LT diode made on Sn-doped n-InP, the leakage current density J0, and barrier height φB were found to be 1.4×10−8 A/cm2 and 0.83 eV, respectively. Undoped InP gave J0=6.7×10−11 A/cm2 and φB=0.96 eV. This indicated a reduction of more than six orders of magnitude in J0, corresponding to a 0.4–0.5 eV increase in φB compared with the metal/n-InP diodes made at room temperature (RT=300 K). The Schottky metal property was studied as a function of deposition temperature and film thickness. Very good agreement was obtained between the electrical and the optical measurements. The high barrier height and low leakage current can be attributed to the dual modification of metal and InP near the interface as well as less disruption of the InP surface.
Comparison between several new molecular drag pumps and turbomolecular pumps
Authors: Chu Ji-guo
Published: July 2002

Three prototypes of full molecular drag pump (MDP) have been discussed. The pumping speed is nearly equal to and even could be higher than that of a turbomolecular pump (TMP). Performances at higher pressure are much better than that of TMPs. Configurations of these new pumps are simple. A figure of merit G, defined as product of pumping speed and the logarithm of compression ratio, is introduced to compare the performances between the new MDPs and TMPs. It is possible that these new pumps would be developed in the near future to be viable alternatives to the present TMPs, diffusion pumps, and roots pumps.
Evaluation of different cleaning techniques for oxygen-free high-conductivity copper
Authors: Rao Vijendran P. , Friedlander Michael P.
Published: July 2002

Oxygen-free high-conductivity copper is a candidate material for future electron/positron storage rings with beam currents in the range of ampere or more. The advantages being high electrical conductivity and good x-ray absorption. However, there are problems of fabrication and lack of extensive data on easy cleaning techniques for complicated shapes. We have over the last year gained considerable experience and understanding of the same. Techniques varying from conventional chemical cleaning, high-pressure hot-water jet cleaning, and vacuum bakeout, to novel methods such as CO2 snow cleaning, and wet bead blasting have been tried. The samples were evaluated for surface cleanliness by x-ray photoelectron spectroscopy. Data along with some analysis and interpretation are being presented.
Radiation damage of epitaxial CaF2 overlayers on Si(111) studied by photon-stimulated desorption: Formation of surface F centers
Authors: Chakarian V. , Durbin T. D. , Varekamp P. R. , Yarmoff J. A.
Published: July 2002

The effects of radiation damage at the surfaces of CaF2 films grown on Si(111) substrates have been studied and the electronic transitions responsible for the formation of surface F centers have been identified by photon-stimulated desorption and soft x-ray photoelectron spectroscopy. The dominant desorption channel for F+ ions is a direct Auger-stimulated process following an electronic transition from Ca 3p to 3d-derived states above the CaF2 conduction band minimum. At the Si 2p edge, there is an indirect x-ray induced electron-stimulated desorption process that contributes only slightly to the desorption of F+. The changes in the kinetic energy distributions of the desorbing F+ ions as a function of film thickness are also discussed.
Imaging the surface state of Cu(111)
Authors: Qu Z. , Ye L. , Goonewardene A. , Mainkar N. , Subramanian K. , Karunamuni J. , Stockbauer R. L. , Kurtz R. L.
Published: July 2002

We have studied the surface state of Cu(111) using an ellipsoidal-mirror analyzer which gives two dimensional images of photoelectron intensity versus emission angle. By combining these images, we have obtained the surface-state dispersion in three dimensional E versus k space. We have also studied the bulk Fermi surface of Cu(100). Our results are in excellent agreement with previous studies and provide a new perspective on studies of surface electronic structure.
Transition from Stranski–Krastanov to quasi-layer-by-layer growth in Pb deposition on Cu(100)
Authors: Zeng Hong , Vidali G. , Biham O.
Published: July 2002

The fast, epitaxial deposition of Pb films on Cu(100) was monitored by helium atom beam scattering over the substrate temperature range of 150–400 K. A growth mode transition from Stranski–Krastanov to quasi-layer-by-layer growth was observed by decreasing the deposition temperature. From 150 to 180 K, intensity oscillations of the specularly reflected helium beam show a complex modulated pattern which is interpreted as due to the concurrent influence of transition in growth mode and structure and of quantum size effects in the overlayer electronic states. From low-energy electron diffraction observations, it was found that Pb grows along [111] direction with two domains rotated 90° with respect to each other at temperatures from 150 to 218 K.
Defect structure of GaAs(111)B (2×2) surface observed by scanning tunneling microscopy
Authors: Kim Jonggeol , Gallagher M. C. , Willis R. F. , Fu Jianming , Miller D. L.
Published: July 2002

Scanning tunneling microscopy (STM) and tunneling spectroscopic I–V measurements of n-type GaAs(111)B (2×2) surfaces are reported. The samples grown by molecular beam epitaxy and the As-capping technique were employed to allow transfer into the ultrahigh vacuum scanning tunneling microscopy (UHV–STM) system. Filled and empty state images exhibit a hexagonal array of bright maxima spaced 8 Å apart consistent with the unit cell dimensions. The images show a variety of domain boundaries resulting from surface stacking faults. The domain boundaries are oriented along [1̄01], [011̄], and [1̄10] directions. Numerous defects are observed at the point where these domain boundaries intersect. Atomic models for these defects are shown. Scanning tunneling spectroscopic data indicate that the Fermi level on this surface is pinned midgap.
Approximate method for reducing the effect of beam misalignment on low-energy electron diffraction I(E) curves at the normal incidence: The horizontal-beam method
Authors: Mizuno Seigi , Tochihara Hiroshi , Kawamura Takaaki
Published: July 2002

An approximate method is proposed for the measurement of intensity–energy [I(E)] curves of low-energy electron diffraction at the normal incident condition. In this method only two equivalent spots located in the horizontal direction are optimized to have identical I(E) curves. It is found that I(E) curves obtained by this method approximate well those at the exactly normal incident condition, as long as the total misalignment is less than 1°. The reason for the success of this method is discussed. Advantages and disadvantages of this method are presented. It is emphasized that reproducible I(E) curves can be obtained easily due to a clear guideline of this method.
Electrochemical and vacuum coadsorption of carbon monoxide and lead on Pt(111)
Authors: Borup R. L. , Sauer D. E. , Stuve E. M.
Published: July 2002

Coadsorption of CO with Pb adlayers on Pt(111) was examined by in situ electrochemical and ex situ surface science methods. CO alters the Pb surface redox reaction, reducing the potential for the Pb2+ad■Pb0ad reaction from 0.65 V for Pb in 0.1 M HClO4 to 0.52 V with coadsorbed CO. Pb adlayers do not appreciably affect the potential for CO oxidation at moderate Pb coverages. At high Pb coverages, oxidation of CO occurs over a broad potential range, of 0.3–0.6 V. The CO/Pb/Pt(111) system exhibits dynamic emersion with a constant emersion potential of about 0.5 V that is set by the Pb surface redox reaction, Pb2+ad■Pb0ad. Pb adatoms act as site blockers to CO adsorption, a monolayer of Pb completely blocking CO adsorption in vacuum. The thermal desorption behavior of CO from Pb/Pt(111) surfaces was modeled using three parameters: Ea the CO activation energy for desorption in the limit of zero CO coverage, Eb the coverage dependent CO activation energy term, and ΔE the change in Ea and Eb with respect to Pb coverage.
Structure of chemically prepared free-standing and vacuum evaporated polyaniline thin films
Authors: Porter T. L. , Caple K. , Caple G.
Published: July 2002

The techniques of scanning tunneling microscopy and atomic force microscopy were used to study the structure of both chemically prepared free-standing and vacuum evaporated polyaniline thin films. Free-standing films were found to be largely amorphous, with small regions exhibiting semicrystallinity. No major structural differences between protonated and nonprotonated films were observed. Vacuum evaporated, nonprotonated polyaniline films consisted of a large-scale terraced structure composed of small, nanometer-scale polymer bundles. The average dimension of these bundles was 1000 Å. After protonation, the terraced structure was lost, with the surface becoming homogeneously flat.