bluuebunny/crossref_metadata_2025 huggingface dataset:
Ti–N phases formed by reactive ion plating
Authors: Molarius J. M. , Korhonen A. S. , Ristolainen E. O.
Published: July 2002

Thin Ti–N films were prepared by reactive triode ion plating. The nitrogen content was varied from 17 to 50 at. % nitrogen. Two series of experiments corresponding to differing values of deposition rate and cathode current density were carried out. The nitrogen depth profiles were analyzed using the nuclear resonance broadening (NRB) technique. The performance of the coatings was evaluated in cutting tests. The films corresponding to a high deposition rate showed columnar growth morphology and consisted of metastable α-titanium and cubic titanium nitride. Dense and noncolumnar films approaching the structures predicted on the basis of the bulk phase diagram could be produced with a lower deposition rate and higher current density. The best cutting performance was obtained with substoichiometric films containing about 36 to 42 at. % N and consisting of a Ti+Ti2N structure. The lifetimes corresponding to critical crater wear in turning increased ninefold after coating with substoichiometric Ti+Ti2N film, while a threefold increase was observed after coating with stoichiometric TiN. Annealing at temperatures ranging from about 765 to 1175 K did not result in any major phase transformations, except at 40 at. % N, where transformation from α-Ti to δ-TiN was observed at 1175 K. The annealing did not greatly affect the cutting performance, which in some cases even decreased slightly after the heat treatment.
Electromigration in aluminum films prepared with a high rate magnetron sputtering cathode
Authors: Park Y. H. , Roessle P. , Majewski E. , Smith J. F.
Published: July 2002

Electromigration has been studied in pure aluminum films prepared by high rate magnetron sputtering. Deposition was performed under various bias and wafer preheat conditions, including those producing planarization of the aluminum. Film structure was determined by transmission electron microscopy (TEM) and x-ray diffraction (XRD). Films prepared with high bias power exhibited a relatively narrow grain size distribution; those prepared without bias had a bimodal grain size distribution. Annealing under normal alloying conditions led to the development of small voids in the latter, and the behavior of these during electromigration was ascertained.
Developments in ionization assisted processes
Authors: Matthews A.
Published: July 2002

Recent developments in ionization assisted vapor deposition processes are traced, with special attention being given to PVD ceramic coating systems. The relative ionization performance of the various techniques is evaluated and shortcomings in terms of coating variability and control are identified; some solutions to these problems are suggested. To date, the systems outlined have been primarily exploited for titanium nitride deposition, and information is given on these coatings. Alternatives to that material are also discussed, indicating their potential advantages and research relevant to their deposition.
Comparative study of activated oxygen uptake on HgTe, Hg0.69Cd0.31Te, and CdTe
Authors: Silberman J. A. , Laser D. , Lindau I. , Spicer W. E. , Wilson J. A.
Published: July 2002

Soft-x-ray photoemission spectroscopy was used to monitor the uptake of oxygen on the (110) faces of HgTe, Hg0.69Cd0.31Te, and CdTe during the formation of roughly two monolayers of oxide. The oxidation was activated by a hot filament in line-of-sight of the sample surface. The oxides formed contain Cd and Te; whereas, Hg is lost from the surface during the initial stages of oxide formation. The rate of oxidation for the Hg0.69Cd0.31Te sample was found to be 69% as great as that for the binary HgTe, and lower than observed for CdTe. The scaling of oxidation rate with the number of Hg–Te bonds between HgTe and the x=0.31 alloy, together with the observed release of Hg upon oxidation, suggests the importance of breaking the Hg–Te bond as a step in the oxidation process. Evidence for an unstable character of the oxide on the Hg containing compounds is also presented.
Effect of inert ion bombardment on chemisorption and etching of aluminum films in Cl2, Br2, CCl4, and CBr4
Authors: Park Seongju , Rathbun L. C. , Rhodin T. N.
Published: July 2002

The role of ion bombardment on the reaction of Cl2, Br2, CCl4, and CBr4 with thin aluminum films has been investigated. Experiments were carried out in a UHV system equipped with an evaporation source, a quartz crystal microbalance, Auger electron spectrometer and x-ray photoelectron spectrometer. Clean Al thin films etched spontaneously in both Cl2 and Br2 beams without ion bombardment at room temperature. The spontaneous etch rates were approximately proportional to the halogen molecule pressure. The surface coverage of aluminum halides on the etched surfaces was very small (about 0.1 monolayer). The spontaneous etch rates and the chemical states of aluminum halides were not affected by argon ion bombardment. These results suggest a mechanism for the spontaneous etching of aluminum. Etch rates of Al by ion bombardment were significantly reduced in the presence of CCl4 and CBr4. Both were dissociatively chemisorbed on the clean Al surface forming a ‘‘carbidelike’’ layer. Ion bombardment changed the chemical states of the chemisorbed aluminum halide species.
Fabrication of mosaic color filters by dry-etching dielectric stacks
Authors: Curtis B. J. , Gale M. T. , Lehmann H. W. , Brunner H. , Schuetz H. , Widmer R.
Published: July 2002

Mosaic color-encoding filters for single-chip, solid-state color imagers have been fabricated by dry etching uniform, dielectric color filter blanks. Although limited to certain three-color filter patterns, this approach enables higher definition patterns to be achieved than currently feasible using conventional lift-off techniques, and has the advantage of separating the patterning of the filter from the fabrication of the multilayer dielectric structure. The technique has been used to fabricate high resolution (definition better than 1 μm) green/cyan/white mosaic filter patterns from green filter blanks by dry etching with CHClF2.
Direct evidence for a thermal effect of Ar+ ion bombardment in a conventional sputtering mode
Authors: Okuyama F. , Fujimoto Y.
Published: July 2002

Evidence is presented that the Ar+ ion bombardment for sputtering in Auger electron spectroscopy can heat the target up to 2000 °C if the target has poor heat conduction. Polycrystalline microneedles of Cr exhibited spherical tips after being exposed to 3 keV Ar+ ions, proving that the needle tips were melted by impacting Ar+ ions. Microneedles of Mo ion bombarded under the same condition were bent plastically, which perhaps reflects the thermal annealing of the needles during ion bombardment.
Deposition of indium on Sb(111) single crystal: A low energy electron diffraction, Auger, and x-ray photoelectron spectroscopy interface investigation
Authors: Delrue J. P. , Sporken R. , Caudano R.
Published: July 2002

Stepwise evaporations of indium have been done at room temperature on Sb(111) single crystals in order to study the interface and the InSb formation conditions. From the Auger measurements, we suggest a Stranski–Krastanov growth mode where the first monolayer seems to contain a significant amount of InSb. The InSb formation was further studied by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) by annealing a thick indium overlayer on Sb(111). Comparison is made to our measurements on an InSb single crystal and also to results from the literature. Low energy electron diffraction (LEED) shows the first monolayer to be disordered. However, the Sb single crystal covered with an indium overlayer restores a (2×2) or (1×1) LEED pattern after annealing, and InSb is formed in this case.
Thin film growth rate effects for primary ion beam deposited diamondlike carbon films
Authors: Nir Dan , Mirtich Michael
Published: July 2002

Diamondlike carbon (DLC) films were grown by primary ion beam deposition and the growth rates were measured for various beam energies, types of hydrocarbon gases and their ratio to Ar, and substrate materials. The growth rate had a linear dependence upon hydrocarbon content in the discharge chamber, and only small dependence on other parameters. For given deposition conditions a threshold in the atomic ratio of carbon to argon gas was identified below which films did not grow on fused silica substrate, but grew on Si substrate and on existing DLC films. Ion source deposition parameters and substrate material were found to affect the deposition threshold and film growth rates.
Kinetic processes in molecular beam epitaxy of GaAs(100) and AlAs(100) examined via static and dynamic behavior of reflection high-energy electron-diffraction intensities
Authors: Lee T. C. , Yen M. Y. , Chen P. , Madhukar A.
Published: July 2002

The nature of competing surface kinetic processes and their consequences for the growth mechanism in molecular beam epitaxy (MBE) of GaAs and AlAs on GaAs(100) As(2×4) surfaces is examined via measurements of the static and dynamic behavior of the specular beam intensity in reflection high-energy electron diffraction. A consistent, albeit qualitative, understanding is provided within the configuration-dependent reactive-incorporation model of MBE growth. The existence of certain growth conditions requiring a combination of only a single As4 pressure, substrate temperature, and growth rate and optimum for the customary practice of growth of interfacial structures without growth interruption, as well as with growth interruption, is demonstrated.
Correlations in pseudobinary alloys
Authors: Sher Arden , Chen An-Ban , van Schilfgaarde Mark
Published: July 2002

Correlations between atoms of Cd and Zn in Cd1−xZnxTe and Hg and Zn in Hg1−xZnxTe are calculated within a generalized quasichemical approximation. A tetrahedron of alloy atoms is used for the microcluster unit. The statistical mechanics of the correlations is outlined for the present problem, an approximate method of solution is indicated. Microcluster energies are obtained from an approximation of a Keating model due to Martin, plus a correction due to Harrison to account for the coupling between the tetrahedral bonds. It is found that the correlations are significant at typical growth temperatures (300–600 K). Hg1−xZnxTe is predicted to undergo spinodal decomposition between 300 and 600 K.
Infrared photovoltaic detectors utilizing Hg1−xMnxTe and Hg1−x−yCdxMnyTe alloys
Authors: Becla P.
Published: July 2002

p–n junctions in ternary Hg1−xMnxTe and quaternary Hg1−x−yCdxMnyTe semimagnetic semiconducting alloys with energy band gaps from 100 to 770 meV were produced by the Hg diffusion method. Current–voltage curves, differential resistivity, and spectral characteristics were measured in the temperature range from 4.2 to 300 K. Material and technological parameters on the electric and photoelectric properties of p–n junctions were analyzed.
Nonlinear optical characterization of Hg1−xCdxTe using two-photon absorption techniques
Authors: Seiler D. G. , McClure S. W. , Justice R. J. , Loloee M. R. , Nelson D. A.
Published: July 2002

Nonlinear optical characterization of Hg1−xCdxTe using two-photon absorption (TPA) techniques with CO2 lasers has been achieved for samples with x≊0.32. Photo-Hall data have been used to determine the number of TPA photoexcited electrons at 10 K and ℏω≊133 meV. Measurement of the carrier lifetime of 7 μs then enabled a TPA coefficient of 1.5 cm/MW to be directly determined. Nonlinear TPA cutoff wavelengths or band gap energies were determined for the first time by varying (1) the photon energy and (2) the lattice temperature while monitoring the photoconductive amplitude. Analysis of the results allows the energy gap or x value to be extracted with a precision of Δx=±0.001. The temperature dependence of the photoconductive amplitudes and lifetimes are shown to give information about recombination mechanisms connected with impurity or defect levels and traps.
Epitaxial CdTe films on GaAs/Si and GaAs substrates
Authors: Bean R. C. , Zanio K. R. , Hay K. A. , Wright J. M. , Saller E. J. , Fischer R. , Morkoç H.
Published: July 2002

Epitaxial films of GaAs on (100)silicon were used as substrates for the preparation of high quality epitaxial layers of (100)CdTe, using a simple ultrahigh vacuum technique. Conditions were defined for the consistent formation of the (100)CdTe on (100)GaAs or GaAs/Si. Double crystal x-ray diffraction rocking curves for the GaAs films on Si have shown full width at half maximum as low as 20 s of arc. Both the CdTe and GaAs films are structurally stable to multiple thermal shocks between 80 K and room temperatures, and to elevated temperatures in the range of 400 to 600 °C.
Reaction and structure of Ti on Si probed by surface extended energy-loss fine structure and extended appearance potential fine structure
Authors: Idzerda Y. U. , Williams E. D. , Einstein T. L. , Park R. L.
Published: July 2002

The local structures of the low-temperature (<500 °C) phases of the Ti/Si system have been determined by surface extended energy-loss fine structure (SEELFS) and by extended appearance potential fine structure (EAPFS), two variations of the electron analog of x-ray absorption fine structure (EXAFS). The extended fine structure above the Ti L23 edge has been measured for thin layers of Ti deposited on atomically clean Si surface and annealed at 20 °C (a pure Ti overlayer), 250 °C (a Si-rich Ti overlayer), and 400 °C (a silicide phase). Data were analyzed using standard EXAFS analysis routines including Δl=+1 phase shifts, resulting in peak positions at 2.93±0.02 Å for the two unreacted phases and 2.39±0.04 Å for the silicide phase. These values are in good agreement with the known spacings of bulk Ti and TiSi, respectively. The ratio technique, which avoids phase-shift difficulties, was applied to these measurements showing that the pure Ti overlayer and the Si-rich Ti overlayer have the same Ti–Ti spacing, but the Si-rich Ti overlayer exhibits a higher degree of disorder. We find no evidence for the formation of a Ti–Si bond in the Si-rich Ti overlayer. This first application of the ratio technique to SEELFS and EAPFS demonstrates its usefulness.
Detailed characterization of TiC and TiN coatings prepared by the activated reactive evaporation process
Authors: Lin P. , Deshpandey C. , Doerr H. J. , Bunshah R. F. , Kaufherr N. , Nielsen R. , Fenske G.
Published: July 2002

The objective is to investigate the relationship between the composition, microstructure, and microhardness of TiC and TiN coatings prepared over a range of process parameters using the activated reactive evaporation process. The composition was measured by Auger electron spectroscopy. The phase relationships and preferred orientation were obtained by x-ray diffraction analysis. Microhardness and adhesion of the coatings were measured. The results show that the microhardness depends on the composition/stoichiometry, phases present, the preferred orientation, and possibly the grain size in the case of single-phase coatings.
Nitrogen sorption on titanium: Reconstruction of the subsurface composition profile using low- and high-energy Auger data
Authors: Dawson P. T. , Tzatzov K. K.
Published: July 2002

Although Auger electron spectroscopy (AES) is the most widely used technique for surface analysis, there are many problems associated with its application to TiN, a technologically important material. The N and high-energy Ti peaks overlap completely and there is no elemental N standard available at ambient temperature. TiN standards can be used and the overlap problem can be overcome by computer simulation of the high-energy spectrum. Furthermore, the computer simulation technique can also be applied to the low-energy TiNx spectrum to give quantitative analysis with increased depth resolution. A procedure is proposed for deconvolution of the low- and high-energy AES data during nitrogen sorption on titanium to determine the composition profile based on a simple adsorption–diffusion model. Nitrogen sorption at various pressures has been followed at sample temperatures in the range 300–900 K. For a given nitrogen pressure, the experimentally observed escape depth averaged N/Ti ratios x̄ increase with sample temperature, pass through a maximum at Tm, and then decrease. At Tm the diffusion coefficient attains a value such that the diffusion rate and nitrogen gas arrival rates balance. For TTm, x0 will decrease rapidly. The concentration profiles obtained by computer deconvolution of the high- and low-energy Auger data confirm this model. As would be expected, Tm increases with increasing nitrogen pressure which increases the supply rate to the surface. The diffusion coefficients determined by computer deconvolution agree well with literature values for higher temperature studies. Prebombardment of the surface with Ar+ ions greatly increases the amount of nitrogen sorbed at room temperature and reduces Tm. The effect on the concentration profile is equivalent to an increase in diffusion coefficient caused by the excess defect concentration, viz., radiation enhanced diffusion.
Ion beam effects on surface and subsurface composition of near-noble silicides
Authors: Valeri S. , Ottaviani G.
Published: July 2002

Modifications of Cr–silicide (Cr3Si and CrSi2) and Ni–silicide (NiSi2) surface and subsurface regions induced by an Ar ion beam were investigated by angle integrated Auger electron spectroscopy. The dependence of the surface modification on the ion beam energy and density was investigated between −80 and 400 °C. At room temperature (RT) Cr–silicides are metal enriched in the surface and subsurface region. Ion bombardment of a CrSi2 surface at high temperature (HT) produces Si enrichment with respect to RT, resulting in the formation of a CrSi layer. The Si enrichment occurs at a temperature lower than the temperature characteristic of purely thermal segregation. On the contrary, the Cr3Si surface composition is independent of the temperature. The NiSi2 surface is stoichiometric at RT; ion bombardment at HT produces a Si surface segregation in two distinct steps. On the basis of a careful line-shape analysis of the Si core–valence–valence Auger transitions, we attribute the first step to the formation of an ordered, ∼1.4 Å thick, Si overlayer, the second one to the growth of a thicker (∼3 Å) amorphous Si layer.
Effect of thin titanium interfacial layers on the formation of palladium silicide on silicon
Authors: Hoffman D. M. , McGinn J. T. , Tams F. J. , Thomas J. H.
Published: July 2002

Thin titanium and palladium were deposited on (100) and (111) silicon at 250 °C by an electron beam in a vacuum of 10−6 to 10−7 Torr. Analysis by transmission electron microscopy, x-ray photoelectron spectroscopy, Auger, and Rutherford backscattering spectroscopy showed that, in the range of titanium thicknesses from 2 to 11 Å, heteroepitaxial Pd2Si was formed with the TiOx moving to the surface. We propose that the Ti, which has a high heat of formation for the oxide, scavenges oxygen and water from the Si–SiOx surface promoting the formation of a uniform layer of heteroepitaxial Pd2Si grains.
Ion mixing of Al2O3 and Al films on SiO2
Authors: Galuska A. A. , Uht J. C. , Adams P. M. , Coggi J. M.
Published: July 2002

The influence of ion implantation on the interfacial chemistry, morphology, and adhesion of Al and Al2 O3 films on SiO2 was examined. The specimens were implanted with varying doses of 131 Xe+ and 84 Kr+ at different substrate temperatures (2×1016 Xe cm−2 at 130 °C, 1×1017 Kr cm−2 at 70 °C, and 1×1017 Kr cm−2 at 350 °C). These implanted specimens were compared to Al/SiO2 and Al2 O3 /SiO2 specimens vacuum annealed at 600 and 1000 °C, respectively. Unlike thermal processing, ion implantation induced substantial interfacial mixing and adhesion enhancement in both the Al2 O3 /SiO2 and Al/SiO2 specimens. Interfacial mixing and adhesion enhancement increased with ion dose. The adhesion increases (3–25×) were attributed primarily to interfacial Si–O–Al bonding. Interfacial bonding (adhesion enhancement) was promoted most extensively by implants which produced glassy interfacial mixtures. Implants that induced crystallization, resulting in phase separation, produced less extensive interfacial bonding. The 131 Xe+ and 84 Kr+ implants resulted in bubble, void, dendrite, and crack formation. Characterization was performed using Auger electron spectroscopy, x-ray photoelectron spectroscopy, scanning electron microscopy, and x-ray diffraction. Film adhesion was examined using a scratch test.
Low-energy electron diffraction analysis of the Si(111)7×7 structure
Authors: Tong S. Y. , Huang H. , Wei C. M. , Packard W. E. , Men F. K. , Glander G. , Webb M. B.
Published: July 2002

We have used the dynamical theory of low-energy electron diffraction to analyze data of the Si(111)7×7 surface and determined the atomic structure. The method includes the use of symmetrized wave functions in real and reciprocal spaces. Individual atomic coordinates for the first five atomic planes (containing 200 atoms) are determined. The low-energy electron diffraction optimized structure shows an oscillatory relaxation: atomic planes with stretched bonds followed by planes with compressed bonds. Geometric displacements from the bulk dimer–adatom–stacking fault model are presented.
A physical model for eliminating instabilities in reactive sputtering
Authors: Larsson T. , Blom H-O. , Nender C. , Berg S.
Published: July 2002

Reactive sputtering is an attractive method for preparing compound films like nitrides and oxides. However, one drawback is that the process often switches between the metal mode and the compound mode. This means that it is very difficult to obtain films with an intermediate composition. In a recently presented model for reactive sputtering we have been able to predict most observed effects including the hysteresis effect. In this paper we have investigated the effect of the pumping speed on the nonstable transition region. We have been able to show that, if the pumping speed is high enough, there is a smooth transition between the different sputtering modes. The hysteresis will also disappear. We will also present a method that can be used to calculate the limiting value for the pumping speed in order to obtain a smooth and stable transition region.
Scanning tunneling microscopy of semiconductor clusters
Authors: Sarid Dror , Henson Tammy , Bell L. Stephen , Sandroff Claude J.
Published: July 2002

Using scanning tunneling microscopy, we have obtained an atomically resolved image of an isolated fragment of a semiconductor cluster which was deposited on a graphite surface from a colloidal suspension. The image depicts ten atoms arranged as two fused six-membered rings which have a distance of 6.5±0.5 Å between centers.
Use of a scanning tunneling microscope to rectify optical frequencies and measure an operational tunneling time
Authors: Lucas A. A. , Cutler P. H. , Feuchtwang T. E. , Tsong T. T. , Sullivan T. E. , Yuk Y. , Nguyen H. , Silverman P. J.
Published: July 2002

This paper elaborates on the idea, recently advanced by the authors, of using the scanning tunneling microscope (STM) in new experiments on laser frequency synthesis and laser rectification at optical frequencies. We first introduce the subject of harmonic generation and mixing of laser beams by the related tunneling device called ‘‘point contact diode.’’ Then, we present new quasistatic current–voltage characteristics of several STM junctions, emphasizing their nonlinear and rectifying aspects. The physical origin of the observed asymmetrical I–V curves is discussed. Finally, we describe the proposed rectification experiment which should result in an operationally meaningful definition of a tunneling time for electrons crossing an STM junction and we present some very preliminary results.
Theory of tunneling in metal–superconductor devices: Supercurrents in the superconductor gap at zero temperature
Authors: García N. , Flores F. , Guinea F.
Published: July 2002

Tunneling experiments in metal-oxide superconductor have shown the existence of ‘‘leakage’’ currents for applied voltages V smaller than one-half of the superconductor gap Δ. These currents are independent of temperature T. Recently experiments with scanning tunneling microscopy (STM) and squeezable tunnel junctions have shown that the observation of the superconductor gap depends strongly on the resistance in the junction. In fact only for resistances larger than ∼106 Ω the gap is clearly observable. These experiments have been explained in terms of the perturbative Hamiltonian formalism of Bardeen. However, it may happen that this theory while applicable for very large resistances may not be so for small tunnel resistances. We present here a nonperturbative theory in all orders of the transmitivity ‖To‖2 and show the existence of supercurrents for values of V<Δ at T=0. This is done by performing a matching in the junction between the superconductor Bogolubov wave functions for Copper pairs and the electron and hole wave functions in the normal metal. Typical numerical results are presented for several values of ‖To‖2. We believe that experiments in STM and other junctions should be interpreted in the frame of this theory.
The effect of surface roughness and nonuniform metal thickness on the etching of sputter-deposited copper and chromium
Authors: Ganguli S. N. , Berk D.
Published: July 2002

Variations in metal thickness and surface roughness of sputter-deposited Cr/Cu/Cr metals on aluminum ceramics and glass slides were measured. The copper layer, which has a thickness of 75 kÅ, shows the most uniform surface, while the base chrome layer with an average thickness of 750 Å shows the least. Etch rates were determined as a function of surface roughness for chromium using a KMnO4 /NaOH etchant and for copper using a FeCl3 etchant. The results for both metals show that the rate increases 2–3 times when the surface roughness is increased.
Magnetron-plasma ion beam etching: A new dry etching technique
Authors: Chinn J. D.
Published: July 2002

A new dry etching technique called magnetron-plasma ion beam etching (MIBE) is described which allows for decoupling of the chemical etch component from the ionic (physical) component which cannot be achieved in other conventional plasma processing methods. In MIBE, a rf discharge at 10−4 Torr is sustained and confined by a magnetic field. Concurrently, a broad beam ion source is used to independently deliver an energetic physical flux of Ar+ ions with energies ranging from 400 to 1500 eV which passes through the confined plasma to the substrate with little interaction or deflection. It was observed that the MIBE etch rates of Si using SF6 as the etch gas were greater than the independent magnetically enhanced reactive ion etching (MIE) and the Ar+ ion milling rates combined. However, the structure profiles were observed to be directly related to the separately controllable etch components. Isotropic etching of silicon was obtained from the chemical MIE plasma but as the energy of the ionic flux was increased, physical ion milling characteristics were observed to dominate the etch profile.
Influence of ion beam activation on the mode of growth of Cu on Si(100)
Authors: Sartwell B. D.
Published: July 2002

The influence of simultaneous low-energy argon-ion bombardment on the initial nucleation and growth of sputter-deposited copper on Si(100) under ultrahigh vacuum conditions has been investigated using Auger electron spectroscopy. Argon-ion energies were either 500 or 1000 eV, with the ratio of ion arrival rate to copper atom arrival rate to the substrate ranging from 0.3 to 0.8. Proton-induced x-ray emission was used to measure the thickness (areal density) of the deposited copper. The intensities of the Si-LVV and Cu-LVV Auger transitions were measured as a function of film thickness and from those data it was possible to determine the mode of growth of the copper film. For the case of deposition without ion beam activation, an island growth mechanism was observed. For simultaneous bombardment with 500-eV Ar+ , a complete change to layer-by-layer growth was observed when the ion-to-atom arrival ratio was 0.8. For 1000-eV Ar+ bombardment, the results indicated an island growth mechanism for arrival rate ratios between 0.3 and 0.6, although the possibility of ion beam mixing between the overlayer and substrate, which would affect the interpretation of the data, cannot be discounted. Equilibrium sputtering yields for concurrent ion bombardment and film deposition were also measured and were found to be considerably less than those for equivalent Ar+ bombardment of bulk copper.
The first interlayer spacing of Ta(100) determined by photoelectron diffraction
Authors: Bartynski R. A. , Heskett D. , Garrison K. , Watson G. , Zehner D. M. , Mei W. N. , Tong S. Y. , Pan X.
Published: July 2002

A photoelectron diffraction study of Ta(100), employing the surface shifted 4 f core levels, has been performed to determine its first interplanar spacing. Photoemission intensities of the bulk and surface shifted 4 f core levels were measured as a function of photon energy at normal emission and near the 〈111〉 symmetry direction of the crystal. The binding energy of 21.7 eV (23.6 eV) for the bulk 4 f 7/2 (5/2) core level, and the large surface core level shift of 0.75 eV, result in well-resolved peaks in the photoemission spectra with areas that are easily measured independently. We find that the ratio of the surface to bulk core level intensities at normal emission exhibits large oscillations as a function of photon energy due to diffraction effects. Intensity modulation is also seen in the off-normal intensities, but the magnitude is much smaller. We have performed a multiple-scattering photoemission calculation for several first interlayer spacings ranging from the bulk value to a 15% contraction. The best agreement with experiment was obtained for a 10%±3% contraction of the first interlayer spacing, which is consistent with an earlier low-energy electron diffraction study.
A He and Ne diffraction study of the W(100) phase transition
Authors: Schweizer E. K. , Rettner C. T.
Published: July 2002

Thermal energy helium and neon diffraction have been used to follow the phase transition of the W(100) surface which reconstructs to a c(2×2) structure on cooling below room temperature. In the He case we have confirmed previous observations that the reconstruction-induced half-order peaks broaden and shift towards the specular peak on heating through this transition. However, the corresponding Ne diffraction peaks show no appreciable shift or broadening under identical conditions, indicating that thermal He and Ne atoms probe surface structures with different periodicities. Since we would expect that the impinging He and Ne atoms probe quite similar potentials, this result is surprising and the first report for such behavior. These findings are consistent with an anomalous He scattering structure factor or the diffraction of He from a charge-density wave.
Structural and electronic properties of Ag/Si(111) and Au/Si(111) surfaces
Authors: Markert K. , Pervan P. , Heichler W. , Wandelt K.
Published: July 2002

The structural and electronic properties of thin Ag and Au films adsorbed on a Si(111)-7×7 surface were studied using thermal desorption spectra of xenon, work function measurements, and photoemission spectra of the clean Si(111)-7×7 and the Ag/Si(111) and Au/Si(111) surfaces at 300 and 60 K. Similarities and differences with Au/Si(111) results are noted.
Band-edge properties of Hg-based superlattices
Authors: Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Schulman J. N.
Published: July 2002

Recent advances in the understanding of band-edge properties in Hg-based superlattices are discussed. A systematic consideration of the theoretical band structure as a function of superlattice parameters demonstrates that the in-plane and growth-direction dispersion relations for the uppermost valence band are extremely sensitive to whether the valence-band offset is small or large. Magnetotransport measurements have been performed on a large number of HgTe–CdTe and Hg1−xZnxTe–CdTe superlattices. Band gaps determined from the temperature dependence of the intrinsic carrier density are found to agree well with theoretical values if a large value (350 meV) is employed for the valence-band offset. Furthermore, the electron and hole mobilities display a number of distinctive features which are quite consistent with calculated band structures as long as a large valence-band offset is employed. However, the data and theory cannot be reconciled if a small offset is assumed.
Characterization of epitaxial Ge films grown by remote plasma enhanced chemical vapor deposition on Ge(111) and GaAs(111) substrates
Authors: Posthill J. B. , Rudder R. A. , Hattangady S. V. , Fountain G. G. , Vitkavage D. J. , Markunas R. J. , Parikh N. R. , Yu N.
Published: July 2002

Epitaxial Ge films have been grown on Ge(111) and GaAs(111) surfaces using remote plasma enhanced chemical vapor deposition. Prior to growth, all substrates were subjected to an in situ hydrogen plasma treatment to remove surface oxides. The effect of deposition temperature on the epitaxial quality has been studied using reflection high-energy electron diffraction, Rutherford backscattering/channeling spectrometry, and transmission electron microscopy. Reflection high-energy electron diffraction patterns show fundamental streaks on all deposited layers and fractional order streaks on layers grown between 300 and 400 °C. Rutherford backscattering/channeling analysis shows severe degradation in crystalline quality below 300 ° C. Currently, the lowest channeling yields have been for Ge/Ge(111) grown at 350 °C (χmin =4%) and Ge/GaAs(111) grown at 300 °C (χmin =8%). Transmission electron microscopy indicates that the predominant defects in these films are inclusions and microtwins, respectively. The possible origin of these defects is discussed.
The effect of thermal treatment on the thin-film reaction of La, Ce, and Nd on silicon surfaces
Authors: Hsu C. C. , Wang Y. X. , Hu J. , Ho J. , Qian J. J.
Published: July 2002

The formation of rare-earth metal (REM) silicides prepared by dual electron beam evaporating La, Ce, and Nd under UHV on Si(111) and Si(100) has been studied using Auger electron spectroscopy depth profile, Rutherford backscattering spectroscopy, x-ray diffraction and transmission electron microscopy (TEM) techniques. Each sample had an additional thin layer of either Si, Mo, or Nb deposited on top of the REM layer to protect the REM layer from oxidation. Isothermal, rapid thermal, and laser annealing have been used to react REM overlayers. With the isothermal annealing, REMs reacted and intermixed with Si at temperatures as low as 200 °C for 60 min, but the disilicide phase confirmed by the x-ray diffraction did not emerge until the annealing temperature was raised to 600 °C for 60 min. Therefore, an intermediate stage of formation existed for samples annealed at 200–600 °C before the formation of the disilicide final reaction product (REM Si2−x) occurred above 600 °C. The experimental data show that the thermal processing can influence strongly the formation of REM silicides, the interface chemical reaction and interdiffusion. Cross-sectional TEM micrographs of interfaces formed by isothermal, rapid thermal, or laser annealing clearly identify these differences. The rapid thermal annealed and laser annealed interfaces are both flat and uniform, while the isothermal annealed interface is rough and exhibits a wavelike variation in interface plane location.
Mechanisms for the deposition of nanometer-sized structures from organic fluids using the scanning tunneling microscope
Authors: Bernhardt R. H. , McGonigal G. C. , Schneider R. , Thomson D. J.
Published: July 2002

We have formed nanometer-sized structures on graphite surfaces by the application of voltage pulses to the tunneling tip of a scanning tunneling microscope. This work pursues a line of a study initiated by Foster et al. [Nature 331, 324 (1988)]. The structures we formed in this way range from 1 nm2 to at least 100 nm2 in size. We have successfully formed these structures using a variety of tip materials (W, PtIr) and methods of manufacture (etched, ion milled, mechanically formed).We have formed structures in air, and in the presence of dimethyl phthalate and decane. We have observed a 3–4 V threshold for structure formation. We have not observed any strong dependence on pulse length in the range of 200 ns to 2 μs. Monitoring the current and tip position as a function of time proved to be a useful diagnostic technique. A likely mechanism for the formation of these structures is the deposition of tip material onto the surface.
The growth of thin films with high thickness uniformity using ultrahigh vacuum molecular beam deposition
Authors: Hale C. H. , Muirhead I. T. , Fisher S. P. , Orr J. S. , Mathew J. G. H. , Prior K. A. , Walker A. C. , Smith S. D.
Published: July 2002

Micrometer thick layers of ZnSe and other dielectric materials have been grown with high thickness uniformity using the new ultrahigh vacuum (UHV) molecular beam deposition (MBD) technique. Optical techniques have been employed to demonstrate that variations in thickness down to as little as ±0.15% over 90 mm diam can be achieved.
A study of the linearity of transfer leaks and a helium leak detector
Authors: Ehrlich C. D. , Tison S. A. , Hsiao H. Y. , Ward D. B.
Published: July 2002

A study has been performed of the linearity of two types of variable-reservoir-pressure leaks and a commercial tuned magnetic sector mass-spectrometer helium leak detector. While the leaks exhibit predictable (but not always linear) behavior over a broad range, the linearity of the leak detector depends strongly on properly correcting for observed drift and random fluctuations in the measured leak rate.
An electrostatic quadrupole deflector for mass spectrometer applications
Authors: Mahaffy P. R. , Lai K.
Published: July 2002

A simple, two-dimensional, 90° electrostatic quadrupole deflector has been developed. This device allows an ion source to be located off the axis of a quadrupole mass spectrometer, or permits two or three ion sources to be interfaced to a common mass analyzer. A number of possible quadrupole deflector geometries have been studied by computer simulation of ion trajectories. The experimentally determined ion transmission and energy dispersive properties of the quadrupole deflector are described.
X-ray photoelectron diffraction study of surface disordering of Pb(110)
Authors: Breuer U. , Knauff O. , Bonzel H. P.
Published: July 2002

The forward scattering of 4f7/2 photoelectrons at 1344.7 eV kinetic energy was studied for a Pb(110) surface along the [001] and [11̄0] azimuths in the temperature range from 200 to 599.3 K. The forward scattering intensity peaks show a Debye–Waller-type decrease up to about 500 K. Above this temperature an additional strong intensity drop is observed indicative of disordering of the Pb(110) surface. The thickness of the disordered layer grows logarithmically with temperature, with a crossover in growth kinetics near 575 K. Assuming an exponential intensity attenuation for the photoelectrons within the disordered layer, the thickness of this layer was obtained up to 599.3 K, where about 8 monolayers are disordered. In addition the forward scattering peaks in the [11̄0] azimuth show a step-like decrease near 360 K suggestive of a structural change for this direction, e.g., a roughening transition. A comparison of the [001] and [11̄0] azimuths reveals an anisotropy of the disordering process, consistent with a narrow interface of 1.8 Å in the [11̄0] direction, and a wider interface (≂3.3 Å) in the [001] direction.
Properties of W–N and Mo–N films prepared by reactive sputtering
Authors: Shih K. K. , Dove D. B.
Published: July 2002

The structure and properties of W–N films up to 22 μm thick prepared by a reactive dc magnetron sputtering process are reported. It has been found that the properties of the deposited films not only depend on the nitrogen partial pressure in the argon–nitrogen gas mixtures but also on total gas pressure and input power during sputtering. The rate of deposition decreased with increase of nitrogen partial pressure, but was higher at higher total pressure and input power. The resistivity increased with nitrogen partial pressure but was lower at lower total gas pressure and higher input power. The hardness of W–N films could be varied from 600 to 3000 kg/mm2 depending on sputtering conditions. The hardness, in general, increased with nitrogen partial pressure with higher value at higher total pressure and input power. X-ray diffraction did not indicate presence of nitride phases when the content of nitrogen in the argon–nitrogen gas mixtures during sputtering was below 10%, and the total gas pressure was <40 mTorr. W2N was observed when the nitrogen content was over 30% and also when the nitrogen content was over 10% and total gas pressure was over 40 mTorr. These results are consistent with composition determined by the microprobe measurements. Similar studies on Mo–N films made by dc and rf magnetron reactive sputtering methods are reported. Hardness values for the Mo–N films of more than 2200 kg/mm2 have been observed.
Possible negative-U properties of the cation vacancy in HgCdTe
Authors: Cooper Donald E. , Harrison Walter A.
Published: July 2002

The cation vacancy in HgCdTe is commonly used for p-type doping, but the energy levels of the vacancy acceptor are not known. We propose that the vacancy is a negative-U center, with inverted energy levels. Comparison with the vacancy in silicon,which is a well-characterized negative-U defect, indicates that the HgCdTe vacancy is likely to be a negative-U center also. The minority carrier recombination rate involving gap levels of the vacancy will show a quadratic dependence on the vacancy concentration, and the deep levels of a negative-U vacancy may be particularly suitable as recombination centers due to their location near the middle of the gap.
Diffusion and hardness studies in mercury zinc telluride
Authors: Fang S. , Farthing L. J. , Tang M.-F. S. , Stevenson D. A.
Published: July 2002

We report studies of self-diffusion, interdiffusion, and hardness measurements in Hg1−xZnxTe (MZT) in order to compare relative properties of Hg1−xCdxTe (MCT) and MZT. Tracer diffusion behavior of MZT is similar to that of MCT, both in mechanism and in terms of diffusion quantities. Interdiffusion behavior in MZT is similar to that of MCT at low x values and shows a significant decrease with increasing x, but is less x dependent at high x values than in MCT. The self and interdiffusion results in MZT at low x values are related with a Nernst–Planck type of equation. The interdiffusion quantities in MZT are only marginally lower than in MCT for the conditions studied. Hardness values are determined as a function of composition in isothermal vapor phase epitaxial (ISOVPE) and horizontal liquid phase epitaxial (HLPE) MCT and MZT using a Vickers tester, a Knoop tester, and a Nanoindenter. There is a substantial increase of the hardness of MZT over that of MCT. Although hardening enhancement by alloying produces bowing in the hardness values as a function of composition in both MZT and MCT, the bowing is significantly more pronounced in the MZT system. In summary, MZT seems to have significant advantages over MCT with regard to improved hardness, but only a marginal difference in diffusion behavior.
Surface passivation and 1/f noise phenomena in HgCdTe photodiodes
Authors: Nemirovsky Y. , Rosenfeld D.
Published: July 2002

1/f noise currents have been measured in HgCdTe photodiodes and gate-controlled diodes as a function of gate bias, diode voltage, and dark (leakage) currents. The diodes are fabricated by ion implanting boron (n+) on bulk p-type material with x=0.22. Native anodic sulfide in combination with deposited ZnS is used for surface passivation. The measurements demonstrate that the dominant mechanism that produces 1/f noise in HgCdTe photodiodes is tunneling. With the gated diodes it is possible to separate bulk and surface related mechanisms responsible for the 1/f noise currents. 1/f noise currents are produced by surface-induced tunneling at pinched-off depletion regions adjacent to accumulated surfaces and by tunneling across field-induced junctions underneath inverted surfaces. Bulk trap-assisted tunneling that limits the R0A product below 50 K but is masked by diffusion at 77 K, is responsible for the 1/f noise currents at optimized surface potentials, (i.e., approximately flat-band conditions) at low bias voltages.

For nonoptimized surface potentials, the tunneling currents are either band to band or trap assisted, depending on material properties. The noise associated with band to band tunneling is modeled with In=αt(It)1/2( f )−1/2 where It is the measured tunneling current. The proportionality factor αt between the noise current and the tunneling current in gate-controlled devices is in the range αt=4×10−7√A to αt=1×10−8√A. HgCdTe photodiodes with the same passivation technology but without a gate, fabricated in higher-quality bulk material, operating at high reverse bias, yield αt values that range between αt=2×10−7√A for small area diodes (junction area equals to 6×10−5 cm2) to αt=6×10−8√A for large area diodes (with junctions area equal to 1.45×10−3 cm2). The noise associated with trap-assisted tunneling is modeled with In=αt(It)β( f )−1/2 where β is approximately 0.75. The numerical values of αt are strongly dependent upon material properties and the dimensions are (A)1−β.
Preparation of TbFe films by magnetron sputtering using multiphase target
Authors: Murakami Yoshio , Shingyoji Takayuki , Hijikata Kenichi
Published: July 2002

A new type TbFe sputtering target which is composed of multiphases (Tb metal, Fe metal, TbFe2 intermetallic compound) is developed. Using this new type target, uniformity of composition of the films over a wider area is achieved in preparation of TbFe films by magnetron sputtering. Composition of the films depend on various preparation conditions and especially dc or rf induced selfbias voltage is an important factor which affects the composition. Films prepared from this target have good magneto-optical properties for memory media.
Hydrogen terminated Si(100) surfaces studied by scanning tunneling microscopy, x-ray photon spectroscopy, and Auger electron spectroscopy
Authors: Niwa Masaaki , Iwasaki Hiroshi , Hasegawa Shigehiko
Published: July 2002

Si(100) surfaces were terminated by hydrogen atoms by means of several chemical methods: (1) Conventional dipping into hydrofluoric acid (HF) followed by immersion into several HF solutions of various concentrations diluted by ethanol (C2H5OH), and (2) hydrogenated porous silicon film anodically formed in an HF and C2H5OH solution. Quite clear STM images with atomic steps were obtained for HF-dipped surfaces during the first several hours in a dry N2 ambient. The observable time was longer for surfaces dipped into less dilute HF. Atomic steps could be observed on the anodically produced porous silicon surfaces even after ten days exposure to air. These phenomena were consistent with the initial oxidation behaviors of the surfaces studied by x-ray photon spectroscopy (XPS) and Auger electron spectroscopy (AES).
Dispersion of evanescent band gap states in Fe clusters on GaAs(110)
Authors: Stroscio Joseph A. , First P. N. , Dragoset R. A. , Whitman L. J. , Pierce D. T. , Celotta R. J.
Published: July 2002

We report scanning tunneling microscopy results on the band gap states observed in tunneling to nanometer size metallic Fe clusters on GaAs(110) surfaces. In the vicinity of the Fe clusters, a continuum of gap states is found in tunneling spectra from regions of the bare semiconductor. The state density in the gap, emanating from the clusters, is found to decay exponentially with a decay length that is dependent on the energy in the band gap. The gap state decay length varies continuously from 3.4 Å at midgap to a divergence at the valence and conduction band edges, reflecting the characteristics of the generalized Bloch states in the semiconductor gap having complex wave vector.