bluuebunny/crossref_metadata_2025 huggingface dataset:
Core level excitation of simple gases
Authors: Zhang Andong , Morar John F. , Park Robert L.
Published: July 2002

The ionization of simple gases by electron bombardment exhibits distinct resonances at electron energies slightly below the core level binding energies of the atomic constituents of the gas. A vacancy in an inner shell of the atom may recombine by a radiationless Auger process, thus leaving the molecule in a singly or higher ionized state. These ions are easily collected and the threshold resonances for excitation are evident in the second derivative of the ion yield plotted as a function of the energy of the electron beam. By using a mixture of gases, such as CO and CO2, it is possible to measure relative chemical shifts of the C and O 1s thresholds. In this case the C 1s threshold is 3.9 eV lower in CO than in CO2, and the O 1s threshold is 2.7 eV lower in CO than in CO2. We will discuss the feasibility of constructing a simple analyzer based on this technique to supplement conventional mass spectrometer analysis of gas composition.
Recent progress on LADA growth of HgCdTe and CdTe epitaxial layers
Authors: Cheung J. T. , Magee T.
Published: July 2002

Laser assisted deposition (LADA) has been used to deposit epitaxial Hg0.7Cd0.3Te layers on CdTe substrates and CdTe layers on GaAs substrates. As- grown Hg0.7Cd0.3Te layers are n-type and can be converted to p-type by annealing. Implanted n+/p photodiodes have been demonstrated. Heteroepitaxial (111)CdTe/(100) GaAs layers were characterized by x-ray diffraction, UV reflectance, photoluminescence, and transmission electron microscopy (TEM). Results indicate good crystallinity with 105 cm−2 dislocation densities beyond a few microns from the CdTe/GaAs interface.
Explosive recrystallization during pulsed laser irradiation
Authors: Narayan J. , Pennycook S. J. , Fathy D. , Holland O. W.
Published: July 2002

The phenomenon of explosive recrystallization has been studied in Si+ and Cu+ implanted amorphous silicon layers by electron microscopy and Rutherford backscattering techniques (RBS). Cross-section and plan-view electron microscopy techniques (TEM) have been used to obtain a detailed characterization of microstructures associated with the explosive mode of recrystallization. RBS and analytical TEM studies on segregation of copper provided information on the mechanism of explosive recrystallization involving a thin liquid film interposed between crystallized and uncrystallized regions.
Highly photoconducting O2-doped CdS films deposited by spray pyrolysis
Authors: Richards D. , El-Korashy A. M. , Stirn R. J. , Karulkar P. C.
Published: July 2002

CdS films have been prepared by spraying in air solutions of thiourea with either cadmium chloride or cadmium acetate with varying mole ratio and substrate temperature, and subsequently heat treating in oxygen. Substrates included both bare glass or sapphire and transparent conducting oxide-coated sapphire for electrical measurements lateral and transverse to the CdS plane, respectively. Dark resistances of over 1014 Ω and light-to-dark conductivities of up to 107 were obtained using uncoated substrates. The use of Cd(C2H3O2)2 in place of CdCl2 greatly increased the speed of response although with some sacrifice in photoconductivity. Deposition of CdS on ITO-coated surfaces led to greatly reduced dark resistances for the case of CdCl2, but not Cd(C2H3O2)2, presumably due to HCl reaction with the ITO coating in the course of spraying with the former. Ion microprobe analysis detected indium within the CdS films exhibiting low dark resistance. Measurements of the dark and light conductivities at temperatures down to 77 K are given as are the response times for unetched and HCl-etched surfaces.
Resistance of tantalum and columbium coatings to propellant gas erosion
Authors: Grabatin H. , Schlett V. , Stuke H. , Weiss H.
Published: July 2002

Alloy steel tubes of 70 mm length and 20 mm bore diameter were coated with tantalum or niobium by the wire explosion technique. This process uses the energy of an electric current pulse to melt or vaporize the coating material which is in the form of a wire in the center of the tube, and to deposit it on the bore surface. For testing, these tubes were mounted as outlet nozzles on a vented vessel and subjected to propellant gas pulses of 30 ms duration and 2500 K. The pressure buildup inside the vessel was 1000 bar. After each pulse the erosive wear of the test pieces was determined and after testing the reaction zone of the coatings was sputtered to a depth of 2 μm and analyzed by AES and SIMS during the process. Both coating materials showed excellent adhesion and their erosion resistance proved superior to the unprotected alloy steel. Tantalum, however, exhibited a much better performance than niobium. This was due to the different properties of the gas/metal reaction layers formed. In both cases the bore surface was covered with propellant gas residue of 1 μm thickness, that was built up and carried out with each pulse. Underneath, a layer consisting of Ta2O5 or Nb2O5 was formed. While Ta2O5 was mechanically stable and therefore, built up to a considerable thickness providing good protection, the Nb2O5 layer was formed and removed continuously with every round. This pattern exposed the unprotected Nb to the next pulse and caused a much faster wear rate.
Correction of a vacuum design fault in leak detectors
Authors: Langley R. A.
Published: July 2002

A design fault in the vacuum system of the MS 170 Leak Detector has been corrected by reorienting the vent valve. Other type of leak detectors, most notable the Leybold−Heraeus Model F, have had similar faults that can probably be corrected with a simialar type of modification. (AIP)
Effects influencing the structural integrity of semiconductors and their alloys
Authors: Sher Arden , Chen An-Ban , Spicer W. E. , Shih C-K
Published: July 2002

The bond length and energy changes of the constituents of alloys relative to their pure crystal values are calculated from an extension of Harrison’s method. It is demonstrated that the already weak HgTe bonds are destabilized by adjacent CdTe, HgS, or HgSe, but are stabilized by ZnTe. It is also argued that dislocation energies and the hardness of semiconductors vary as a high inverse power of the bond length of the constituents. Hence, the shorter ZnTe bond as an additive should improve the structural properties of HgTe and CdTe. Experiments that support these predictions are noted. The electronic transport properties of 0.1 eV band gap HgZnTe are about the same as those of HgCdTe, and the structural properties of the Zn compound are superior; thus, we conclude that HgZnTe is likely to be the better material for IR devices.
The reactive Cr/InP and Mn/InP interfaces
Authors: List R. S. , Kendelewicz T. , Williams M. D. , Lindau I. , Spicer W. E.
Published: July 2002

Soft x-ray photoemission spectroscopy studies were performed in ultrahigh vacuum on cleaved n-InP(110) with sequential room-temperature Cr and Mn depositions of up to 30 Å. The In 4d, P 2p, and Cr 3p or Mn 3p core levels were monitored as a function of coverage. Both systems exhibited strong metallic In-phase separation and surface segregation, formation of a metallic phosphide, and no evidence of island formation. Fermi level-pinning positions of 0.6 and 0.3 V below the CBM were estimated for the Cr and Mn systems, respectively, by deconvoluting the substrate from the interfacial components of the In core lines. These results are discussed in the context of different models of Schottky barrier formation.
Secondary ion mass spectrometry/digital imaging for the three-dimensional chemical characterization of solid state devices
Authors: Bryan S. R. , Woodward W. S. , Linton R. W. , Griffis D. P.
Published: July 2002

The use of a microcomputer based digital imaging system for automated acquisition of secondary ion image depth profiles is demonstrated. By combining the ion microscope’s capabilities of elemental imaging and depth profiling, image depth profiling provides information on the three-dimensional distribution of elements within microvolumes of the near surface region of solids. The technique is used for the three-dimensional multielement characterization of a solid state device (a npn bipolar transistor). Several methods for processing and displaying the multidimensional data are presented.
Microscopic electronic structure and growth mode of Sn/InSb(111) interfaces
Authors: Höchst Harmut , Calderón Isaac Hernández
Published: July 2002

The electronic properties and growth mode of Sn/InSb(111) interfaces have been investigated by angular resolved photoemission spectroscopy (ARUPS), high energy electron diffraction (RHEED), and work function measurements. For Sn coverages of ∼1 ML the Fermi level is pinned at the bottom of the conduction band. The interfacial growth is heteroepitaxial and extends to a thickness of ∼5 ML of Sn. This is followed by the formation of diamond structured α-Sn up to ∼40 ML. Beyond this thickness three dimensional island growth starts and the films are a mixture of semiconducting α-Sn and metallic β-Sn. Above ∼120 ML Sn, the surface region consists of pure β-Sn while due to a strong substrate stabilization effect the interface region still consists of the α-Sn phase.
Transmission channeling study of the Au/Si(100) interface
Authors: Jin H. S. , Ito T. , Gibson W. M.
Published: July 2002

The Au/Si (100) interface has been studied by the transmission channeling technique. The results show that at the very beginning the deposited Au atoms are partially registered with the 〈100〉 axis in the substrate crystal and are partially randomly distributed across the 〈100〉 channel. In addition to the Au–Si atom interaction, the Au–Au interaction already plays an important role in the submonolayer region, which causes the Au atoms to be more and more randomly distributed as monolayer coverage is approached. Cluster formation is a possible mechanism for the interface growth in this region. Through the transmission Si surface peak, evidence has been found that room-temperature intermixing takes place at ∼4 ML Au coverage. The observed initiation threshold appears to favor an electron screening model over a diffusion model to explain room-temperature Au–Si intermixing.
Reflection high energy electron diffraction studies of epitaxial growth on semiconductor surfaces
Authors: Cohen P. I. , Pukite P. R. , Van Hove J. M. , Lent C. S.
Published: July 2002

Reflection high-energy electron diffraction (RHEED) is so well suited to studies of epitaxial growth that it has become the standard in situ technique for monitoring the growth of III–V semiconductors during molecular beam epitaxy. The characteristic diffraction pattern for a smooth surface is a family of parallel streaks. The intensity along the length of these streaks is shown to be due primarily to the distribution of atomic steps over the surface. These steps are readily observable because RHEED is able to resolve order over long distances. During epitaxial growth synchronous oscillations in the intensity and width of the diffracted beams are observed. These are due to the competition between cluster nucleation and step propagation. The period of the oscillations is the time required to deposit a monolayer.
Gas injection system in the Tara central cell
Authors: Brau K. , Goodrich P. , Post R. S. , Sevillano E.
Published: July 2002

The gas injection system in the Tara central cell has been redesigned to overcome problems associated with fueling in the high field region at the ends of the central cell. Previous experimental studies indicated that plasma ions created in the region between the gas injection point and an ICRH antenna were lost radially before passing to the downstream side of the antenna. In the new system gas is injected at two diametrically opposite ports into a cylinder (‘‘gas box’’) located near the midplane, between the two double half turn antennas. A maximum in the magnetic field at the midplane divides the central cell into two R=2 mirrors. Ions trapped in one of these mirrors must scatter into the loss cone before passing into the fueling region, where the loss rate due to charge exchange is highest. This configuration produces separate regions for ionization (at the gas box) and for heating (near the magnetic field minimum). Pumping of neutral gas by the central cell plasma reduces the amount of neutral gas flux into the axicell to acceptable levels. Gas utilization efficiencies are roughly twice as high as in the original configuration.
Thermally stimulated discharge currents in polyacrylic acid polymer films
Authors: Rao V. V. R. Narasimha , Das N. Narsing
Published: July 2002

Polyacrylic acid polymer films of thickness 15 μm were grown by the solution growth technique. Thermally stimulated discharge currents (TSDC) were studied on these polymer films as a function of polarizing field strength and polarizing temperature at a constant heating rate of 0.08 K s−1. In all these studies, one TSDC peak was observed and the temperature corresponding to this peak was found to shift to higher temperatures as the polarizing temperature increases. But for a given polarizing temperature, the temperature corresponding to the peak was independent of the polarizing field strength. The activation energies and relaxation parameters were evaluated. The origin of TSDC was attributed to the dipolar orientation process.
Large scale microwave plasma polymerization: A study on hydrogenated carbon films
Authors: Kieser J. , Sellschopp M.
Published: July 2002

A systematic investigation of the pressure changes in low pressure microwave discharges of C2H2, C2H4, and C2H6, respectively, with Ar as a carrier gas, is presented as a function of plasma power and admixture of nitrogen. The results are discussed in terms of the generation of clusters of active species in the plasma volume. Properties of plasma polymerized layers from these monomers with and without the admixture of nitrogen are investigated with respect to their anticorrosion behavior as well as their wear resistance.
Erosion profile of a radio frequency planar magnetron sputtering target with aperture shield
Authors: Holdeman L. B. , Morell N.
Published: July 2002

We have measured the erosion profile of a fully utilized, 8 in. diam gold target from an rf planar magnetron system that has an aperture shield between the sputter target and the substrate carrier. The depth of erosion was not cylindrically symmetric with respect to the center of this planar disk target.
Adsorption characteristics of H2 on the porous layers of condensed Xe, Kr, and CO2
Authors: Arakawa I.
Published: July 2002

Equilibrium pressures of H2 adsorbed on porous layers of condensed Xe, Kr, and CO2 were measured in the temperature range from 5 to 18 K and in the pressure range from 10−4 to 10−7 Pa. Vertical rises in adsorption isotherms, suggesting two-dimensional condensation of the adsorbed layer, were found at pressures ∼10−6 Pa and at temperatures below 10 K. A plateau was found in the adsorption isostere which has not been observed in the case of 2D condensation of rare gases on graphite. This behavior seems to be related to some change of the adsorption state of H2. The experimental result of electron stimulated desorption on the same system shows that the change of ESD yield of H2 corresponds to that of adsorption condition expected from the adsorption isostere.
High resolution electron energy loss study of AlxGa1−xAs mixed crystals
Authors: Thiry P. A. , Liehr M. , Pireaux J. J. , Caudano R. , Kuech T.
Published: July 2002

The surface optical phonon spectra of AlxGa1−xAs mixed crystals have been measured by high resolution electron energy loss spectroscopy (HREELS). Two modes (Al–As and Ga–As types, respectively) were observed whose frequencies shifted almost linearly with aluminum concentration. The relative intensities of these modes are analyzed. Comparison is made with Raman scattering measurements and theoretical calculations.
Schottky barrier height measurements of type-A and type-B NiSi2 epilayers on Si
Authors: Hauenstein R. J. , Schlesinger T. E. , McGill T. C. , Hunt B. D. , Schowalter L. J.
Published: July 2002

Schottky barrier heights of single-crystal type-A and type-B NiSi2 epilayers on nondegenerate n-(111) Si have been measured by photoresponse and forward I–V methods. High-quality molecular beam epitaxy grown NiSi2 layers of thicknesses ranging from 70 to 600 Å on sputter-cleaned, P-doped Si subtrates (∼1.5×1015 cm−3) were studied. The type-A and type-B orientations consistently yield photoresponse barrier heights which differ by greater than 0.1 eV. We observe the value φBn=0.62±0.01 eV for all type-A structures from both photoresponse and I–V measurements. However, we obtain a discrepancy between barrier heights measured by I–V (φBn=0.69±0.01 eV) and photoresponse (φBn=0.77±0.05 eV) methods, and in addition consistently observe an unusual bowing of the type-B photoresponse curves at low photon energies. We show that both the detailed shape of the type-B photoresponse curves and the discrepancy between I–V and photoresponse-measured barrier heights can be accounted for by modeling the type-B barrier as a mixture of high and low barrier regions. Quantitative agreement with experiment is obtained for the values φhi =0.81±0.01 eV and φlo 0.64±0.01 eV, with effective fractional area coverages of 91% and 9% for high- and low-barrier regions, respectively.
Incorporation of chlorine during chlorine reactive ion beam etching of aluminum–copper alloys
Authors: Whetten Timothy J. , Ruoff Arthur L.
Published: July 2002

Reactive ion etching of aluminum–copper thin films, used for interconnects on semiconductor devices, is complicated by implantation of reactive gases in the film during etching. Incorporation of chlorine in aluminum–copper thin films during reactive ion beam etching with chlorine ions was studied. Unannealed thin films of aluminum-4% copper alloys were etched with 500 and 1000 eV chlorine ions at current densities that ranged from 0.01 to 0.5 mA/cm2. Copper, oxygen, and chlorine concentrations as a function of position were determined using Auger sputter depth profiling, scanning electron microscopy with x-ray fluorescence spectroscopy and Rutherford backscattering spectroscopy. The amount of chlorine incorporated in the film was measured as a function of ion energy, current density, and angle of incidence. If chlorine was not removed from the near surface layer before exposure to air, numerous mounds formed on about 30% of the surface; these were composed primarily of aluminum, oxygen, and chlorine. The chlorine was observed to be completely confined to these mounds and the oxide layer that forms on the surface of the film after etching and upon contact to air. Implications for developing reactive ion etching techniques in which no chlorine remains in the near surface layer will be discussed.
Properties of Hg1−xZnxTe grown by liquid-phase epitaxy
Authors: Sher Ariel , Eger D. , Zemel A. , Feldstein H. , Raizman A.
Published: July 2002

Epilayers of Hg1−xZnxTe 0.16≤x≤0.26, were grown by liquid-phase epitaxy on CdTe and nearly lattice matched Cd0.76Zn0.2Te substrates. The crystalline, electrical, and optical properties of the epilayers are described. Significant improvement of the epilayer surface morphology and crystallinity was achieved by lattice matching with the substrate. The temperature and composition dependence of the energy band gap in the spectral range relevant to IR photodetection was determined.
Electronic structure of cesium adsorbed on Al(111)
Authors: Hohlfeld A. , Sunjic M. , Horn K.
Published: July 2002

The electronic structure of Cs adsorbed on Al(111) was studied in order to provide experimental data for a comparison with density-functional calculations using the jellium model. The work function change data show excellent agreement with the theoretical predictions. Photoemission results give direct evidence for a coverage-dependent charge transfer between adsorbate and substrate. Electron energy loss spectra exhibit loss features which are close to atomic excitations, in disagreement with theoretical predictions.
Friction measurement of coated surfaces with a vibrated diamond stylus
Authors: Baba S. , Kikuchi A. , Kinbara A.
Published: July 2002

A new apparatus which can measure frictional properties of surfaces microscopically is applied to various coatings on glass substrates. The coefficient of friction is determined through the measurement of the phase difference between the external force and the motion of the contact stylus. The motional signal is picked up by a phonograph cartridge. The principle and technique of the measurement is described first, and then results on the coatings of MgO, ZnO, and C are presented. Some ceramic coatings showed a nonuniformity of friction coefficient over the surface which is apparently flat.
On angle resolved x-ray photoelectron spectroscopy of oxides, serrations, and protusions at interfaces
Authors: Darlinski A. , Halbritter J.
Published: July 2002

Oxidized surfaces show smeared out x-ray photoelectron spectroscopy (XPS) lines which cannot be fitted by bulk compounds and by lateral growth. By simultaneously fitting XPS spectra obtained for takeoff angles between 5° and 80° not only is the resolution enhanced, but also a new dimension is gained. Thus, small amounts (<0.5 nm) of interface oxides are identified in level shift, stoichiometry, and spatial distribution, i.e., serration and protrusion of interfaces are revealed. The angle resolved x-ray photoelectron spectroscopy analysis of oxidized (<100 °C) NbN, NbC, and Nb, shows that the metal surface is serrated by metallic (≂1 nm) and dielectric (≊1 nm) interface oxides, where Nb2O5 forms the outermost layer. The serration is deeper for Nb than for NbN, because Nb is weaker and dissolves more O. In contrast, in high-temperature oxidation (900 °C) of Si(100), the interface shows no serration and less interface oxides (<1 nm) but Si clusters at the outer SiO2 surface exist as remnants from low (≪300 °C) temperature oxidation.
Thermal stability among HgTe/CdTe, Hg1−xCdxTe/CdTe, and Hg1−xMnxTe/CdTe superlattices
Authors: Staudenmann J.-L. , Knox R. D. , Faurie J.-P.
Published: July 2002

I n situ interdiffusion measurements on X-alloyed Hg1−xXxTe/CdTe superlattices reveal that superlattices with x>0 are more stable than HgTe/CdTe superlattices (X=Cd and Mn for the present study). These alloyed superlattices have, therefore, a better chemical stability and hence, longer device lifetime than the nonalloyed ones, allowing for technological developments to proceed. It is hypothesized that the differences between Fourier components of the diffusion coefficients D(T) are due to Cd and Mn substitutions which presumably slow down interstitial and vacancy motions.
Crystalline intermediate phases in the formation of epitaxial NiSi2 on Si(111)
Authors: Bennett P. A. , Halawith B. N. , Johnson A. P.
Published: July 2002

We have studied the structure and formation of nickel overlayers on Si(111) using Auger and reflection high-energy electron diffraction microanalysis in a custom-built UHV scanning electron microscope. A novel technique of generating a continuous range of coverages in a single deposition is described. Two crystalline phases were found as intermediate stages in the growth of epitaxial NiSi2: Ni2Si delta phase forms for a substrate temperature of 185 °C and coverage of 13 Å in the orientation Ni2Si (020)∥Si(111), and Ni2Si(002)∥Si(220). Also, nickel crystallites form for a substrate temperature of 185 °C and coverage of 28 Å in the orientation Ni(220)∥Si(111) and Ni(002)∥Si(220). The nickel crystallites are small and highly strained. The possible role of these two phases as precursors in the formation of NiSi2 is discussed.
High-speed input/output device for controlled atmospheres
Authors: Mantilla O. A. , McLain H. A.
Published: July 2002

A continuous feed, high-speed input/output device for controlled atmospheres has been developed and built for an electron-beam tester. This device permits a throughput of 12 substrates per minute (36-mm metallized ceramic) through a high-vacuum (5.0×10−7 Torr) chamber. This paper describes the input/output apparatus, its operation, and its performance. Furthermore, special emphasis is given to the unique high-vacuum, gas-bearing valves used in this application.
Cooling rate dependence of the morphology of Hg0.80Cd0.20Te liquid phase epitaxial layer
Authors: Suh S. H. , Stevenson D. A.
Published: July 2002

Hg0.80Cd0.20Te liquid phase epitaxial layers were grown at 502 °C on CdTe substrates. The cooling rate was varied from 0.15 to 1.32 °C/min, and the terrace surface morphologies were evaluated for all the liquid phase epitaxial (LPE) layers. The width of terraces was inversely proportional to the cooling rate. This result is explained by the increase in constitutional supercooling with increasing cooling rate. Composition of the LPE layer was uniform up to the surface except at the interface region. The composition profile did not depend on the cooling rate.
Simple resistance model fit to the oxidation of a vanadium film into VO2
Authors: Case F. C.
Published: July 2002

A simple resistance model is used to describe the in situ resistance changes which occur during the oxidation of a thin vanadium film to VO2. Separation of the resistance characteristics into two regions proves useful in the interpretation of experimental data. The time dependence of the vanadium dioxide thickness follows a tn behavior where 1.5<n<3, depending on the oxidation conditions of pressure and temperature.
Optimization of the sputter-deposition process for preparing smooth coatings of beryllium on microspherical substrates
Authors: Chen C. W. , Alford C. S.
Published: July 2002

The process of physical vapor deposition of beryllium by magnetron sputtering is studied in broad terms of major operational parameters. Optimal conditions are established for the preparation of Be coatings on glass microspheres. The coatings prepared in both dc and rf modes displayed 200–300 Å surface finish. Such superior surface finish is made possible by the application of a modest, negative bias voltage to the substrate that suppresses columnar growth and promotes nucleation as a result of resputtering.
Magnetoreflectivity study of excitons in molecular-beam epitaxially grown Zn1−xFexSe crystals
Authors: Liu X. , Petrou A. , Jonker B. T. , Prinz G. A. , Krebs J. J. , Warnock J.
Published: July 2002

Single-crystal films of (001) Zn1−xFexSe(x=0.017, 0.027, and 0.043) grown by molecular-beam epitaxy on (001) GaAs have been studied by magnetoreflectivity over the temperature range 4–77 K in magnetic fields up to 8 T in the spectral region near the band gap of 2.8 eV. The excitonic transitions were observed in both Faraday and Voigt geometries, permitting the determination of the Zeeman splitting of the exciton states in both the conduction and valence bands, and showed the Zeeman splitting precisely reflects the magnetization obtained earlier in bulk crystals. Combined with that magnetization data, these splittings yielded the electron/Fe2+ exchange energy for both bands. The Fe-concentration dependence of the data showed the Fe2+–Fe2+ antiferromagnetic exchange clustering becomes evident for x>0.02. The temperature dependence of the spectra confirm that this system is a Van Vleck paramagnet and the spin-orbit splitting of the lowest Fe2+ crystal-field states is 2.2 meV.
An x-ray photoemission spectroscopy study of chemical interactions at silver/plasma modified polyethylene interfaces: Correlations with adhesion
Authors: Gerenser L. J.
Published: July 2002

Plasma treatment is a convenient way to modify the surface (∼25–50 Å) of a polymer for improved adhesion of vacuum deposited metals. X-ray photoemission analysis of plasma modified polyethylene (PE) indicates no detectable chemical effects for argon plasmas, whereas oxygen and nitrogen plasmas create new chemical species which alter the chemical reactivity of the PE surface for vacuum deposited Ag. The adhesion strength of vacuum deposited Ag on PE is shown to increase in the following order: untreated<argon plasma<oxygen plasma<nitrogen plasma treated PE. Changes in chemical bonding and nucleation of submonolayer vacuum deposited Ag on plasma treated PE correlate with Ag/PE adhesion. Changes in the PE core levels after submonolayer deposition of Ag are interpreted as due to the formation of Ag–O–C and Ag–N–C species on oxygen and nitrogen plasma treated PE, respectively. In contrast, no chemical bonding effects are observed on untreated or argon plasma treated PE. The Ag valence-band structure suggests that the plasma induced species act as nucleation and chemical bonding sites resulting in a much smaller average cluster size for vacuum deposited Ag. Interfacial analysis of peeled thin films of vacuum deposited Ag on PE suggests the locus of failure changes from interfacial adhesive failure for untreated and argon plasma treated PE to cohesive failure of the PE for oxygen and nitrogen plasma treated PE.
Thin-film thermocouple gauge
Authors: Kuo T. C. , Flattery J. , Ghosh P. K. , Kornreich P. G.
Published: July 2002

The importance of the thermocouple gauge in vacuum technology is well established. In this paper we present the fabrication and the calibration of a miniature thermocouple gauge using Cu–Cr thin films. The thermocouple gauge consists of a thin-film Cr heater and a thin-film Cu–Cr differential thermocouple on a glass substrate. The thin-film Cu–Cr thermocouple was calibrated using a standard K-type thermocouple. At constant temperature the change in the input power is a monotonic function of the change in the pressure. The measurement was repeated for several gases at a constant heater temperature of 100 °C. Experimental results show that our device can be used for a wide range of measurements. Owing to its small size, fabrication simplicity, and compatability with the existing thin-film processing it is rather easy to incorporate our device with other integrated circuits.
Chemical cleaning of metal surfaces in vacuum systems by exposure to reactive gases
Authors: Grunze M. , Ruppender H. , Elshazly O.
Published: July 2002

Chemical surface cleaning procedures for metals using oxidation/reduction cycles by exposure to oxidizing (O2, NO) and reducing (H2, NH3 ) gases are summarized and an update of the original compilation for chemical cleaning procedures published by Musket et al. [Appl. Surf. Sci. 10, 143 (1982)] is given. Examples discussed in this paper are cleaning procedures for iron, nickel, palladium, copper, and silver surfaces. We also present data on the reduction of gaseous contaminants in a stainless-steel UHV system by flowing nitric oxide through the system during bakeout.
A thermal desorption and x-ray photoelectron spectroscopy study of the surface chemistry of iron pentacarbonyl
Authors: Zaera Francisco
Published: July 2002

We have studied the surface chemistry of iron pentacarbonyl by using thermal programmed desorption and x-ray photoelectron spectroscopy (XPS). Thermal desorption is mostly molecular and takes place in two stages. At low coverages a peak at 195 K was detected. For exposures above 4 L a second peak due to multilayer growth is seen with maximum below 180 K. A small fraction of the chemisorbed carbonyl decomposes as seen by XPS. The iron pentacarbonyl fragmentation takes place between 170 and 240 K and results in the deposition of metallic iron and chemisorbed carbon monoxide. Metal film growth is inhibited by coadsorbed CO. The samples need to be flashed to above 600 K in order to desorb this CO and allow further iron deposition. However, we found that films can be grown in a steady-state condition by exposing the sample to Fe(CO)5 at 300 K. Displacement of CO by either the incoming molecules of by new CO product of the decomposition may explain the lack of poisoning at these low temperatures.
Thermocouple gauge for partial pressure measurements
Authors: Wang Chi-Luen , Ghosh Prasanta K. , Kornreich Philipp
Published: July 2002

We here present the design and testing of a thermocouple gauge with unique properties. Operating the gauge at different temperatures allows one to measure the partial pressure of different gases in a vacuum system. The gauge system consists of two parts, the detector and the control circuitry. The detector consists of a filament and a heat shield. A differential thermocouple measures the temperature difference between the filament and the heat shield. The control part consists of circuitry that keeps the temperature difference between the filament and heat shield constant by controlling the filament power. The gauge has been calibrated with a Mcleod gauge and with various gases, such as He, Ar, N2, and CO2 gas. This gauge measures pressure without ionizing the gases. Experimental results show that the gauge is very sensitive down to 10−4 Torr.
The angular dependence of preferential sputtering and composition in aluminum–copper thin films
Authors: Rudeck P. J. , Harper J. M. E. , Fryer P. M.
Published: July 2002

The copper concentration in aluminum–copper alloys can be altered by ion bombardment during film deposition. We have measured the sputtering yields of aluminum and copper in Al–Cu alloys as a function of the Cu concentration (5–13 at. %) and the angle of ion incidence (0–40° from normal). During deposition, the films were partially resputtered by 500-eV Ar+ ion bombardment from a Kaufman ion source. We found that the Cu sputtering yield decreases by up to a factor of 10 in the alloy, relative to elemental Cu. The Al sputtering yield remains close to the elemental value. The net effect is a strong preferential sputtering of Al relative to Cu, which enhances the Cu concentration in an ion bombarded film. The Al/Cu sputtering yield ratio for normal incidence ion bombardment ranges from 3 to 5 as a function of Cu concentration. This ratio decreases with increasing angle of incidence to as low as 2 for 40° incident ions. However, since a higher fraction of the film is resputtered from a sloping surface, a higher Cu concentration is found on a sloping surface relative to a flat surface. These results show that in multicomponent film deposition under ion bombardment, the film composition will vary as a function of the surface topography. We will also show how the level of argon left trapped in the films varies inversely with respect to the ion flux.
High-rate deposition of Al2O3 films using modified cathodic arc plasma deposition processes
Authors: Randhawa H.
Published: July 2002

Aluminum oxide films have been deposited using a modified cathodic arc plasma deposition process. The aluminum and aluminum oxide films have been characterized using x-ray photoelectron spectroscopy, scanning electron microscopy, x-ray diffraction, and optical analysis. The film deposition is compared to rf sputtered aluminum oxide films in order to investigate the advantages, if any, of the cathodic arc process. The cathodic arc deposited films were found to have correct stoichiometry, high density, and good mechanical properties. Further, the cathodic arc deposition process yielded aluminum oxide films with deposition rates almost three times that of rf sputtered films.
Corrosion-resistant ion-plated Al–Zn films
Authors: Nowak W. B. , Burns L. E. , Harris V. G.
Published: July 2002

Microcrystalline, thin, passivated, metal films can surpass similar bulk material in corrosion resistance. If these films form a spinel oxide in situ, corrosion protection might be further enhanced over simple oxides. We extend our previous work on Al–Mg and Al–Cu films to Al1−xZnx, 0<x<1. We deposited Al–Zn films, 1–2 μm thick, onto liquid-nitrogen-cooled substrates at ∼0.1 μm/min by dc ion plating. Films were smooth, fine grained, and columnar. Potentiodynamic data were taken at 20 mV/min in aerated 3.5% NaCl solutions at room temperature. Corrosion (rest) potentials were ∼−1.05 V (saturated calomel electrode) for all x. Anodically scanned specimens had a short passive region, then one to three active–passive peaks followed by a long passive region that ended in transpassive behavior due to crevice corrosion. The total protection range (rest to transpassive potential) was ∼2.2 V for all x. Galvalume (55Al–Zn) and Galfan (5Al–Zn), commercial hot-dipped alloys, have ranges of 0.4 V. Thus, ion-plated Al–Zn alloys seem markedly superior to hot-dipped coatings. Auger electron analysis of corroded films indicated the presence of aluminum and oxygen with only small amounts of zinc. No evidence of spinel oxide was found by reflection electron diffraction (RED). RED results best fit aluminum oxides. The role of zinc is unclear. It may have formed a very thin spinel layer, or it may have facilitated the formation of the aluminum oxides that are good barriers.
Surface melting of Pb(110): A compilation of experimental results
Authors: Frenken J. W. M.
Published: July 2002

Recently, the first direct experimental observations have been made of a depression in melting point at the surface of a three-dimensional crystal. Since then, numerous experiments with various techniques have been devoted to surface melting. The most intensively studied surface in this respect, so far, is Pb(110). This paper attempts to compare and combine the experimental information which is presently available for this surface. A detailed picture of surface melting of Pb(110) emerges.
Energy transfer and photochemistry on a metal surface: Mo(CO)6 on Rh(100)
Authors: Germer Thomas A. , Ho W.
Published: July 2002

The occurrence of photoinduced reactions on solid surfaces depends on the relative rates between the excited-state decomposition and the energy transfer to the surface. In this study, the photodecomposition of Mo(CO)6 on Rh(100) at 90 K by 325-nm UV irradiation has been studied as a function of coverage and surface preparation using thermal desorption spectroscopy, electron energy-loss spectroscopy, and photoinduced desorption spectroscopy. It is found that Mo(CO)6 adsorbs dissociatively on Rh(100) into carbonyl fragments and CO in the first monolayer and molecularly in multilayers. Photoinduced desorption of CO is observed for the multilayers adsorbed onto the dissociated first layer via a nonthermal electronic excitation of adsorbed metal carbonyls. The presence of the metal surface prevents complete decarbonylation as in the gas phase; deexcitation of electronically excited carbonyls is not sufficiently fast to quench all the observed photochemistry. It is also found that Mo(CO)6 adsorbs molecularly on a presaturated CO ordered overlayer on Rh(100) and undergoes photodissociation to a greater degree than on the dissociated and disordered surface of carbonyl fragments. The ordered CO layer effectively screens the interaction between the molecular carbonyls and the Rh(100) layer surface.
Texturing of polyimide films during O2/CF4 sputter etching
Authors: Dunn D. S. , Grant J. L. , McClure D. J.
Published: July 2002

Texturing of polyimide films during rf sputter etching in O2 /CF4 mixtures was studied as a function of mixture composition. The size of the observed features was dependent on the O2 /CF4 ratio. The deepest textures were observed after sputtering in gas mixtures containing 30%–70% CF4. These features are larger and have greater aspect ratios than features induced by texturing with pure Ar, O2, or CF4 under otherwise identical conditions. Analyses of spin-cast polyimide films after etching indicated no C–F bond formation at CF4 sputter gas concentrations <30%, moderate surface fluorination for 30%–70% CF4, and significant surface fluorination for CF4 percentages exceeding 70%. Polyimide etch rates, observed chemical modification effects, and properties of O2 /CF4 process plasmas were used to describe the observed texturing trends and to suggest possible texturing mechanisms. The influence of etch gas composition on extent of chemical modification and on etch rates is also described.
TiSi2 formation by rapid thermal processing in a diffusion furnace
Authors: Kumar P. K. Ashwini , Kumar Vijay , Sarkar S. K.
Published: July 2002

Rapid thermal processing (RTP) for the synthesis of refractory metal silicides has been in use recently. The techniques used in RTP for heating the samples include the use of a graphite strip heater and quartz halogen lamps. In the present case we have synthesized titanium disilicide (TiSi2) by RTP by using a conventional diffusion furnace. The annealing times were 90 and 180 s while the temperature of the hot zone was 800 °C (±0.5 °C) in which the sample was introduced for annealing. Auger electron spectroscopy studies of the samples indicated that there is a thin top layer of oxide of titanium with the titanium silicide buried underneath. Scanning and transmission electron microscopies were also done of the samples to ascertain surface and bulk microstructure. Measured sheet resistance of the samples is ∼1.2 Ω/sq. The present investigations thus suggest an alternative RTP technique for synthesis of silicide.
An Auger investigation of the effects of rapid thermal annealing of GaAs on Si with or without intermediate Ge layers
Authors: Opila R. L. , Awal M. A. , Lee E.-H. , Lum R. M.
Published: July 2002

Scanning Auger analyses have been performed on angle lapped GaAs/Ge, Ge/Si, GaAs/Si, and GaAs/Ge/Si structures grown by vacuum evaporation and metalorganic chemical vapor deposition techniques. Elemental Auger line scans are shown to have an inherent spatial resolution of 60 Å as a result of the angle of lapping, electron beam diameter, and Auger electron escape depth. To minimize the effects of artifacts such as residual lapping and Ar+ sputtering damage and electron backscattering, the interfacial width Wi for each species i, is defined by the difference (in Å) between the point where the Auger intensity is 75% of the full intensity in that layer (Ii=0.75Ii0) and the point where the Auger intensity is 25% of the full intensity in that layer (Ii=0.25Ii0). These structures have interfaces that are 60–150 Å wide. The GaAs/Si and GaAs/Ge interfaces are broadened due to As depletion near the interface, resulting in a total interface width larger than the interface width of any individual species. Rapid thermal annealing at 900 °C for 5 s, resulted in narrower interfaces and specifically reduced the As depletion.
A low-cost high performance low-energy electron diffraction intensity measuring apparatus with video data acquisition rate
Authors: Zhang Zhi-yuan , Lu Jia-ho , Chai Si-min
Published: July 2002

In order to get the low-energy electron diffraction (LEED) I–E curves of a time-varying surface structure, we developed a well-designed multichannel programmable data acquisition system. By using a 2 μs (ADC) chip and some other hardwares the video data acquisition rate is realized. Up to 20 beams could be acquired. The tracking of spots is accomplished by the computation of the spots’ position. The size of the sampling window is slectable in the range of (4×4) to (16×16) pixels according to the size of the spot. Considering the inertia of the camera tube and the LEED gun supply, a pause of one-half to several tens of frames may be assigned after the control of energy is setup. In this paper, I–E curves of diffraction spots of Si (111)-(7×7) structure, including that of individual fractional spots, are demonstrated. This system can also measure the intensity distribution pattern of diffraction, the spot intensity variation of time I–t curve, and may be used for reflection high-energy electron diffraction (RHEED) as well.
Vitreous ice as a cryoprotectant for imaging atom-probe studies of adsorption phenomena at a solid–liquid interface
Authors: Panitz J. A.
Published: July 2002

A novel approach is outlined for studying adsoption phenomena at a solid–liquid interface in the imaging atom-probe mass spectrometer. An interface is preserved for analysis by embedding it within a thin, conducting layer of vitreous ice formed from its native environment. The ice is controllably sublimed at 20 K using a high electric field to dissect the layer, and to map the distribution of species within the layer as a function of depth from its surface. Procedures are described for creating a layer of ice believed to be vitreous in nature, and for transporting an interface embedded within the ice layer into high vacuum without damage (and without contamination from laboratory ambient). Field-ion imaging suggests these procedures are effective for preserving the surface structure of a solid on a subnanometer scale.
CdTe and ZnTe metal interface formation and Fermi-level pinning
Authors: Wahi A. K. , Carey G. P. , Chiang T. T. , Lindau I. , Spicer W. E.
Published: July 2002

Interfacial morphology and Fermi-level pinning behavior at the interfaces of Al, Ag, and Pt with UHV-cleaved CdTe and ZnTe have been studied using x-ray photoelectron and ultraviolet photoemission spectroscopies. Results are compared to metal/HgCdTe interface formation, where the weak Hg–Te bond and consequent ease of Hg loss strongly influence semiconductor disruption and metal–semiconductor intermixing. For Al/CdTe, we observe a case where the strong Al–Te reaction yields a significantly more extensive Al–Te reacted region than has been observed for HgCdTe. The Al/ZnTe interface is observed to be more abrupt than Al/CdTe. The final Fermi-level pinning positions Efi=Ef−Evbm for Al, Ag, and Pt on p-type CdTe and p-ZnTe have been determined. Efi is found to be roughly the same for both CdTe and ZnTe, with the value for ZnTe lying ∼0.2 eV closer to the valence-band maximum for all three metals. From these results, one would expect Schottky barriers of about the same height for these metals on p-CdTe and p-ZnTe; and also that, in principle, metal interfaces with the two alloys HgCdTe and HgZnTe would have the same properties. Comparisons and implications for electrical behavior of metal contacts to the alloys are discussed.
Measurement of hydrogen permeation through bilayer copper–iron membranes
Authors: Haasz A. A. , Andrew P. L. , Antoniazzi A. B.
Published: July 2002

The rate of hydrogen permeation through copper–iron composite membranes was measured for incident hydrogen molecules and atoms for membrane temperatures of 570 to 780 K. Incident fluxes ranged from 2.7×1022 to 7.3×1025 H2/m2 s for molecules and 6×1015 to 1.2×1019 H0/m2 s for atoms. From the diffusion-limited permeation data for H2 the H permeability for Cu was measured to be (DS)Cu≂2.0×1016 exp(−0.64 eV/kT) H/m s Pa1/2. Hydrogen recombination coefficients for Cu were derived from both the surface-limited molecular hydrogen permeation data and the diffusion-limited atomic permeation data. The two methods yielded consistent results. An effective recombination coefficient of ∼8×10−27 H2 m4/H2 s, nearly independent of temperature over the range 570–780 K, was obtained for a Cu surface whose impurity coverage was measured in situ by Auger electron spectroscopy.
Deuterium pumping speed measurements on 77 K cryopanels and implications for deuterium–tritium retention in neutral beam systems
Authors: Dylla H. F.
Published: July 2002

An upper limit for the pumping speed of deuterium (D) on 77 K surfaces has been determined by in situ pressure measurements in a (TFTR) neutral beam line pumped by 423 m2 of liquid-nitrogen-cooled cryopanels. The measurement has importance for estimating the tritium (T) retention in the beam line following operation of the ion sources with tritium. No D2 pumping was observed. An upper limit for D2 pumping on 77 K surfaces of ≤2.4×10−7 l/s cm2 was determined, corresponding to a D2 sticking coefficient of ≤1.5×10−8. Based on the upper limit a D–T retention factor, equal to the ratio of retained D–T to D–T input, has been determined to be ≤5×10−3. This upper limit for D–T retention bounds the tritium inventory within the beam line to a small fraction of the tritium throughput. Comparably small upper limits for hydrogenic sticking coefficients, of the order of 10−6 to 10−10, have been determined from a review of H2O cryotrapping measurements at 77 K and from the physical adsorption studies of H2 on H2O at 4 K.