bluuebunny/crossref_metadata_2025 huggingface dataset:
High resolution photoemission investigation: The oxidation of W
Authors: Morar J. F. , Himpsel F. J. , Hughes G. , Jordan J. L. , McFeely F. R. , Hollinger Guy
Published: July 2002

Surface-sensitive core-level photoelectron spectra excited by synchrotron radiation are presented for surface oxide phases of W in the monolayer range. Discrete chemically shifted core levels are observed and are shown to be associated with specific formal oxidation states by comparison with bulk reference compounds. Slight increases in the value of the core-level shift for each oxidation state as the surface oxygen content increases are attributed to changes in the screening response of the system. Decomposition of the spectra into the separate contributions from each oxidation state provides specific and quantitative chemical information about the surface oxides. This and similar studies should be particularly useful for characterizing the disordered systems typical in applied surface physics where clarity of interpretation is very important.
Erratum: Hydrogen pumping with palladium membranes [J. Vac. Sci. Technol. A 3, 412 (1985)]
Authors: Berkheimer G. D. , Buxbaum R. E.
Published: July 2002

The reaction rate constant for oxidation on the surface of palladium, Eq. (6), has a sign error in its activation energy, and has an error in its units. The equation and its subsequent sentence should read k(molecules cm2/atom2 s)=4×10−8 exp (−7000/RT), (6) where R=1.987 cal/mol K. There are approximately 4×1014 available sites per cm2 of palladium. It is interesting to note that, since the enthalpy of H ⋅ adsorption is greater than the activation enthalpy of H ⋅ reaction, the per-area reaction rate should increase with decreasing temperature (at constant pressure) until a saturation maximum is reached.
An updated review of getters and gettering
Authors: Giorgi T. A. , Ferrario B. , Storey B.
Published: July 2002

A brief review of present day getter materials is made with reference to the two principal families, i.e., evaporable and nonevaporable getters. The main physicochemical processes involved in the gettering process are reviewed in order to establish the concept of gettering-selective chemical pumping. Examples of practical getter devices are described in connection with a brief overview of some of the most common applications. However, most emphasis will be placed in describing some of the most advanced and more unusual applications of getters which may not always be in widespread use but which indicate the versatility of gettering in widely differing fields.
Transfer leak studies and comparisons of primary leak standards at the National Bureau of Standards and Sandia National Laboratories
Authors: Hyland Richard W. , Ehrlich Charles D. , Tilford Charles R. , Thornberg Steve
Published: July 2002

Primary leak standards are being developed at the National Bureau of Standards (NBS), and a cooperative NBS–Sandia National Laboratories (SNL) program is underway to compare their different primary standards and investigate the properties of transfer leaks. Initial results of comparisons of the primary standards at the two laboratories, accomplished via sintered metal transfer leaks in the range 5×10−12 to 5×10−9 mol/s, show that the calibration methods used in the two laboratories agree to within a few percent for nitrogen, argon, and helium. Significant instabilities with time have been observed for one of the two leaks used in the comparison. Temperature coefficient data for helium diffusion leaks are presented which illustrate the possibility of significant errors when a linear temperature dependence is assumed over too wide a temperature range.
Synthesis of aromatic polyimide film by vacuum deposition polymerization
Authors: Takahashi Y. , Iijima M. , Inagawa K. , Itoh A.
Published: July 2002

A new method for preparing the polymer films directly in the reduced atmosphere has been developed. In this process the polymerization can be carried out through depositing the component monomer vapors. Both pyromellitic dianhydride and 4,4′-diaminodiphenyl ether (oxydianiline) were evaporated at a molar ratio in terms of stoichiometry by controlling the heating power for each evaporation source. From the infrared absorption spectrum observation, it was found that the as-deposited film was the mixture of the polyamic acid and both nonreacted monomers. After having been heated to 200 °C for 60 min, the deposited film was finally transformed into the polyimide film through the condensation reaction. The obtained polyimide film had good adhesion to the glass and metal substrate and showed excellent chemical resistance, heat resistance, and electrical insulation characteristics. By selecting the appropriate combination of monomers, other polymer films could be obtained through the vacuum deposition polymerization process.
Study of the enhanced oxidative degradation of polymer films at polymer/copper (oxide) interfaces using depth profile and inert marker techniques
Authors: Burrell Michael C. , Fontana Julie , Chera John J.
Published: July 2002

The degradation of poly(ester imide) films on metal substrates was monitored by determining the changes in polymer film thickness using x-ray photoelectron spectroscopy combined with ion sputter depth profiling. Thin films (1000–7000 Å) of poly(ester imide) wire enamel were spin coated onto metal substrates and aged in air at 200 °C for several hours. For films on copper substrates, thermal oxidative degradation of the polymer led to thinning of the film (2.5–3 Å/min), whereas films on aluminum substrates did not exhibit a decrease in thickness. The catalytic effect of copper upon the degradation of the polymer occurs primarily at the copper (oxide)/polymer interface, as revealed by the location of an inert gold marker layer within the polymer film before and after aging.
Photoyield spectromicroscopy of silicon surfaces using monochromatic synchrotron radiation
Authors: Tonner B. P. , Harp G. R.
Published: July 2002

A photoemission electron microscope has been used to generate spatial maps of silicon surfaces, along with chemical spectroscopy of the silicon core levels at micron-scale spatial resolution. The electron optics permits scanned photon energy imaging of the sample surface, with image capture at video rates in a 512×512 pixel buffer memory. The image is generated primarily by low-energy secondary electrons produced by photoabsorption. Near-edge structure in the image photoyield as a function of photon energy is used to determine the oxidation state of microscopic regions of the surface of a single-crystal Si(111) sample. These measurements show that spectroscopic imaging with 100-nm resolution will be possible using undulator generated synchrotron radiation.
Determination of valence states in Fe3O4 by resonant photoemission
Authors: Lad Robert J. , Henrich Victor E.
Published: July 2002

We report resonant photoemission measurements across the Fe 3p→3d photoabsorption threshold from the (110) surface of cleaved single-crystal Fe3O4 using synchrotron radiation. The resonant enhancement effect is used to distinguish the Fe 3d-derived states from the overlapping O 2p states in the valence band. The Fe 3d-derived states are found to extend about 18 eV below the Fermi level. Constant-initial-state spectroscopy across the Fe 3p excitation threshold reveals that this large valence bandwidth is due to a significant amount of cation–ligand hybridization; this result is in accord with recent configuration interaction cluster calculations of the photoemission final states in iron oxides reported by Fujimori et al. The electronic levels that are primarily associated with the different Fe2+ and Fe3+ cation environments in Fe3O4 are identified based on a comparison with photoemission spectra measured from cleaved FexO (x≂0.945) and α-Fe2O3 single crystals. Upon O2 adsorption, the Fe3O4(110) surface is rapidly oxidized, as evidenced by a decrease in the photoemission features associated with the Fe2+ valence state.
Effect of some elements and temperature on the surface segregation of boron nitride
Authors: Minami Y. , Tohyama A. , Yamada T.
Published: July 2002

Effect of alloying elements, impurities, and temperature on the surface segregation of boron nitride (BN) was studied using Auger electron spectroscopy (AES) and scanning Auger microscopy. Type 316L stainless steels, which have various levels of contents of B, N, P, and S, were prepared in the laboratory. During heating in a vacuum of 10−7 Pa, the change of the surface composition of the specimen was continuously analyzed using AES. The precipitation of BN was observed for heating at 700 and 800 °C. Enrichment of Cr and N was observed for heating at 600 °C, and Sn and P segregated at 900 °C. Increase in the B content suppressed the precipitation of BN through the reduction of soluble nitrogen. The precipitation of BN was not observed for the steels with <0.1 wt. % N. The elimination of P and S and the addition of Ca accelerated the precipitation of BN. X-ray diffraction analysis revealed that the precipitated BN was hexagonal type.
Topography and microstructure of Al films formed under various deposition conditions
Authors: Chang C. Y. , Vook R. W.
Published: July 2002

Al films were vapor deposited in high vacuum onto SiO2/Si substrates at various substrate temperatures (T) and deposition rates (R) which ranged, respectively, from 24 to 250 °C and from 2 to 90 Å/s. The films were examined by scanning electron microscopy (SEM) and showed systematic variations in topography. Hillock formation occurred only on films deposited at low substrate temperatures and low deposition rates. Films which were deposited at high substrate temperatures and low deposition rates had rough surfaces. The high deposition rate films were smooth. Transmission electron microscopy (TEM) showed that the average grain size and the widths of the grain size distributions increased as the substrate temperature increased. The topographical and microstructural results are plotted on ln R versus 1/T graphs which thus show in a convenient format how these film properties depend upon supersaturation.
Structure, chemistry, and band bending at the epitaxial NiAl/p-GaAs(001) interface
Authors: Chambers S. A. , Loebs V. A.
Published: July 2002

We have investigated interface formation between epitaxial, intermetallic NiAl and As-stabilized, molecular-beam epitaxy (MBE)-grown, p-GaAs(001)-c(2×8)/(2×4). The epitaxial films were prepared by MBE growth of Ni and Al onto substrates at a temperature of ∼100 °C. The growth was interrupted every few monolayers in order to obtain measurements aimed at deducing interface structure, chemistry, and band bending as a function of coverage. High-energy resolution x-ray photoemission was used to measure chemistry of interface formation and band bending, and low-energy electron diffraction and x-ray photoelectron diffraction were used to follow surface and interface structure. Epitaxial growth at 100 °C was found to be essentially laminar, with no measurable indiffusion of Ni. The first NiAl bilayer bonds with the Ni layer down (i.e., in direct contact with the substrate) and the Al layer up. Ga disruption was observed at ∼1.4 monolayers, the lowest coverage grown, while As disruption was not observed until a coverage of ∼4.2 monolayers. Reacted Ga appears to remain trapped at the interface, possibly in the form of NiAlxGa1−x, whereas liberated As segregates at the surface. The Schottky barrier height goes from a free-surface value of 0.33±0.04 to 0.47±0.04 eV after growth of ∼1.4 monolayers, and then converges to a final value of 0.33±0.04 eV by a coverage of ∼6 monolayers, which persists at higher coverages. When added to the value determined previously for MBE-grown n-GaAs(001) with the same doping density in the buffer layer, this value sums to the band gap of GaAs, within experimental error. This fact establishes that the Fermi level is indeed pinned by NiAl deep in the forbidden gap of GaAs, rather than being unpinned.
Composition and growth mode of MoSx sputtered films
Authors: Moser J. , Lévy F. , Bussy F.
Published: July 2002

MoSx lubricating thin films were deposited by nonreactive, reactive, and low energy ion-assisted radio-frequency (rf) magnetron sputtering from a MoS2 target. Depending on the total and reactive gas pressures, the film composition ranges between MoS0.7 and MoS2.8. A low working pressure was found to have effects similar to those of low-energy ion irradiation. Films deposited at high pressure have (002) planes preferentially perpendicular to the substrate, whereas films deposited at low pressure or under low-energy ion irradiation have (002) mainly parallel to it. Parallel films are sulfur deficient (MoS1.2−1.4). Their growth is explained in terms of an increased reactivity of the basal surfaces, itself a consequence of the creation of surface defects due to ion irradiation. The films exhibit a lubricating character for all compositions above MoS1.2. The longest lifetime in ball-on-disk wear test was found for MoS1.5.
Calculation of the figure of merit for indium tin oxide films based on basic theory
Authors: Knickerbocker S. A. , Kulkarni A. K.
Published: July 2002

Indium tin oxide (ITO) exhibits some of the most impressive properties such as high electrical conductivity and high optical transparency. These qualities have competing mechanisms which give rise to the need for a compromise between the transmission and conductivity. In order to optimize the conductivity and the transmission as a function of doping, it is necessary to determine the figure of merit as a function of the carrier concentration. We have compared different figures of merit as a function of carrier concentration on the basis of basic theoretical concepts instead of experimental values of conductivity and transmission. Estimates of the refractive index (n) and the extinction coefficient (k) are made and used to predict the optical transmission as a function of the carrier concentration in the films. It appears there is an optimum value of doping in ITO thin films.
Chemical reactions of triethylantimony on GaAs(100)
Authors: Heitzinger John M. , Ekerdt J. G.
Published: July 2002

The surface chemistry of triethylantimony was studied on GaAs(100) using thermal desorption spectroscopy, static secondary ion mass spectroscopy, and x-ray photoelectron spectroscopy. Triethylantimony is reversibly adsorbed following exposures at 160 K. The saturation coverage at 160 K is approximately 0.3 monolayers. Following triethylantimony exposure at 330 K, ethylene, the major hydrocarbon reaction product, desorbs from the GaAs(100) surface during thermal desorption spectroscopy experiments with a peak temperature of 569 K. This indicates a β-hydride elimination reaction is responsible for the elimination of ethyl groups from the surface. Additionally, a small amount of ethyl radicals desorb from the surface. Our results indicate that ethyl groups migrate to Ga sites and then undergo a β-hydride elimination reaction at these sites. For saturation coverage (0.3 monolayers), 90% of the triethylantimony is irreversibly adsorbed. Exposures at 675 K led to adsorbed Sb atoms as well as GaSb formation. The reactive sticking coefficient of triethylantimony is low, 4×10−4, and decreases as the surface becomes Sb rich. Eventually, adsorption of triethylantimony ceases at 675 K, indicating self-limiting adsorption.
Scanning force microscopy and polymerization studies on cast thin films of hectorite and montmorillonite
Authors: Porter Timothy L. , Eastman Michael P. , Hagerman Michael E. , Attuso Jennifer L. , Bain Edlin D.
Published: July 2002

Thin films of the smectite clays Na+ exchanged montmorillonite, Ca2+ exchanged montmorillonite, Na2+ and Cu2+ exchanged hectorite, Cu2+ exchanged sintered hectorite, and Cu2+ and Na2+ exchanged hectorite exposed to benzene, aniline, and thiophene were studied using the techniques of scanning force microscopy (SFM), electron spin resonance (ESR), and x-ray diffraction. The microstructure of the two montmorillonite clays was markedly different, with the Ca-montmorillonite exhibiting a sturdy, close packed array of crystallites of average dimension 0.4 μm. The Na-montmorillonite clays consisted of smaller (0.1 μm), more poorly defined crystallites with an overall cauliflowerlike appearance. The pure Na-hectorite and Cu-hectorite clays exhibited large flat regions composed on interlocking platelets. Heat sintering as well as exposure to benzene resulted in measurable shifts in the platelets perpendicular to the surface for the Cu-hectorite. It is proposed that in the sintered case these shifts are due to interlayer water loss accompanied by Cu reactions, while in the benzene case interlayer benzene polymerization causes inhomogeneous vertical expansion of the clay. Exposure of Cu-hectorite films to both aniline and thiophene results in large-scale polymerization of these monomers. The microstructure of both of these polymers is similar to that observed in electrochemically prepared films on Pt substrates. Na-hectorite samples did not exhibit surface polymerization upon thiophene, aniline, or benzene exposure.
Relative sensitivity factors of B related to SiGe alloy composition on secondary ion mass spectrometry with an oxygen primary ion beam
Authors: Fujinaga Kiyohisa
Published: July 2002

This paper describes the useful yields of positive 11B, 28Si, and 70Ge ions produced from the surface of B-doped Si1−xGex alloys when the surface is irradiated by an 8 keV positive O2 ion beam. Boron doping into alloys was done by implanting 11B ions with an energy of 30 keV at a dose of 1×1015 cm−2. The reactive sensitivity factors (RSFs) of 11B to the matrix isotopes of 28Si or 70Ge are determined using the useful yields, and the relationships between the RSFs and the alloy compositions are shown. Also described are the RSFs of 11B estimated from the local thermal equilibrium model with two internal standard elements of Si and Ge. The theoretical RSFs were a factor of 3–4 greater than the experimental RSFs.
Synthesis of epitaxial films of Fe3O4 and α-Fe2O3 with various low-index orientations by oxygen-plasma-assisted molecular beam epitaxy
Authors: Gao Y. , Kim Y. J. , Chambers S. A. , Bai G.
Published: July 2002

Epitaxial thin films of pure-phase Fe3O4(110), Fe3O4(111), α-Fe2O3(112̄0), and α-Fe2O3(11̄02) have been grown on MgO(110), α-Al2O3(0001), α-Al2O3(112̄0), and α-Al2O3(11̄02) substrates, respectively, by molecular beam epitaxy using an elemental Fe source and an electron cyclotron resonance oxygen plasma source. Characterization of the crystal structures, chemical states, and epitaxial relationships was carried out using a variety of techniques, including in situ reflection high-energy electron diffraction (RHEED), low-energy electron diffraction, x-ray photoelectron spectroscopy/diffraction, and ex situ x-ray reflectivity and diffraction. Real-time RHEED reveals that Fe3O4 growth on MgO appears in a step-flow fashion, whereas the growth of Fe3O4(111) on α-Al2O3(0001) occurs initially by island formation, and then island coalescence. However, the growth of α-Fe2O3 on α-Al2O3 appears to follow an intermediate growth mode. The formation of pure-phase films is controlled largely by oxygen partial pressure, plasma power, and growth rate, but appears to be independent of growth temperature, at least from 250 to 550 °C. The present study demonstrates that selective growth of pure-phase iron oxides with various low-index orientations can be achieved by controlling the growth conditions and selecting suitable substrates.
Vacuum requirements for next wafer size physical vapor deposition system
Authors: Hashim I. , Raaijmakers I. J. , Park S.-E. , Kim K.-B.
Published: July 2002

The major sources of impurities in sputtered Al alloy films for interconnects prepared by physical vapor deposition (PVD) include those originating from the target material, residual gases present in the vacuum system, and those introduced through the gas delivery system. In this study, we report the effect of impurities incorporated from residual gases present in vacuum systems on the properties of Al–Cu interconnects, in particular, electromigration performance of 0.6-μm-wide Al–1% Cu lines. Controlled leaks of isotope gases H2O18, N215, O218, and C13H4, in the 10−6–10−9 Torr range, were introduced into a PVD tool during the sputtering process. Using these isotope gases, the impurities originating from residual gases were distinguished from those originating from other sources of impurities. The sputtering target was found to be the major source of H and O impurities in the film, whereas N atoms are introduced in the film mainly through the gas phase. The microstructural properties of blanket Al–Cu films deposited with intentionally introduced residual gas phase contaminants were also investigated using transmission electron microscopy, x-ray diffraction, and secondary ion mass spectroscopy. Controlled leaks of N2 during the sputtering process were found to affect the distribution of Cu in the blanket Al–Cu films as well as the electromigration behavior of the patterned structures to a larger extent than O2, CH4, and H2O. On the other hand, upon controlled exposures of the above mentioned residual gases to blanket Al–Cu films, N2 was found to have the lowest sticking coefficient to a clean Al–Cu surface.
Secondary ion mass spectrometry of a copper polyimide thin film packaging technology
Authors: Parks Christopher C.
Published: July 2002

Secondary ion mass spectrometry (SIMS) supported the development of a polyimide and chromium-clad copper thin film packaging technology. The unique usage of SIMS was to analyze buried defects using extremely deep (10–40 μm) elemental profiles. An example of a delamination is given in which SIMS is able to verify the presence of and to quantify an aminosilane adhesion promotor in the monolayer-coverage range under 13 μm of polyimide. Several defects are described in which wiring layer species (Cr or Cu) are found in the polyimide together with traces of chlorine. These examples motivated a more detailed investigation of chlorine at CuCr to polyimide interfaces. Quantification aspects of SIMS are developed using a Cl ion implant through a CuCr to polyimide interface. Yield saturation, in which the ion yield of Cl− approaches unity for SIMS using a Cs+ primary beam, is evaluated as a simplifying quantification concept. The CuCr interface is demonstrated to actively getter chlorine during curing of intentionally chlorine-contaminated polyimide.
Anisotropy in the lateral momentum of CO chemisorbed on Cu(110) studied by time-of-flight electron simulated desorption ion angular distribution
Authors: Ahner Joachim , Mocuta Dan , Ramsier R. D. , Yates John T.
Published: July 2002

While it is well appreciated that electron simulated desorption ion angular distribution (ESDIAD) measurements contain information about chemical bond directions at surfaces, it is also known that the lateral momentum of the adsorbate must influence the ESDIAD patterns. We present, for the first time, energy resolved ESDIAD patterns which allow one to measure the anisotropy in the lateral momentum of the chemisorbed species. Using a new method, momentum-resolved ESDIAD patterns are acquired in narrow kinetic energy windows by time-of-flight selection. For CO chemisorbed on Cu(110), the excited neutral CO* species exhibits an elliptical pattern at low kinetic energies with the major axis of the ellipse in the 〈11̄0〉 azimuthal directions. For increasing CO* kinetic energies, the ellipticity decreases, and at very high kinetic energies, the ellipticity changes to the 〈100〉 azimuth. These observations, together with the temperature dependence of the pattern shape over the range 32–180 K, yield information about the frustrated translational energy of the adsorbed molecule, and permit a qualitative assessment of the shape of the potential energy well governing the adsorbate’s librational motion.
Vapor deposition polymerization of polyimide for microelectronic applications
Authors: Malba Vincent , Liberman Vladimir , Bernhardt Anthony F.
Published: July 2002

We report the high-throughput vapor deposition polymerization (VDP) of smooth, uniform polyimide films for microelectronic applications. Using infrared (IR) spectroscopy, waveguiding refractive index measurements, atomic force microscopy, and matrix assisted laser desorption ionization, we have characterized both cured and uncured films. Uncured VDP films consist of oligomers (up to tetramers) and unreacted monomeric species. Cured VDP films are chemically identical to commercially available spin cast polyimides. Both IR and refractive index anisotropy are used to determine the extent of cure, and the stoichiometry of the cured film. Integration of the VDP films into a multichip module process is presented, and the application of VDP films in ultra-large-scale integrated circuit manufacturing is discussed. Finally, the vapor deposition of 3,3′,4,4′-biphenyltetracarboxylic dianhydride and p-phenylenediamine, a high performance polyimide system, is presented.
Determination of the emission characteristics of evaporation sources and of the thickness and composition of mixed layers
Authors: Podolesheva I. , Gushterova P. , Platikanova V. , Konstantinov I.
Published: July 2002

Methods are developed for determining the emission characteristics of enclosed evaporation sources with small apertures and for calculating the composition and thickness of mixed layers by controlling the condensation rates with quartz crystal monitors. For describing the emission characteristics of the sources the cosn law is used and a method for determining n is presented. A procedure for calculating the composition and thickness of mixed layers at each point of stationary substrates by measuring the condensation rates is described and the calculated characteristics of the layers are experimentally confirmed by means of analytical, electron dispersive spectroscopy and profilometrical analyses. The procedure is quite simple and does not require knowing the temperature dependence of the vapor pressure of the evaporated substances. It can be used for characterizing all layers obtained by evaporation from one or more sources as well as for selecting the experimental conditions for obtaining layers of desired composition and thickness.
Deposition of SiO2 films from novel alkoxysilane/O2 plasmas
Authors: Bogart K. H. A. , Ramirez S. K. , Gonzales L. A. , Bogart G. R. , Fisher Ellen R.
Published: July 2002

The deposition of SiO2 films from novel alkoxysilane/O2 rf plasmas has been investigated using tetraethoxysilane and the novel alkoxysilanes, triethoxysilane, tetramethoxysilane, and trimethoxysilane. We have demonstrated that high quality SiO2 films can be deposited from each of these alkoxysilanes under similar conditions. For all precursors, film deposition rates decrease with the addition of O2. Using 20:80 alkoxysilane/O2 plasmas, film deposition rate decreases with increasing substrate temperature and plasma power, while the SiO2 film quality increases, as determined by Fourier transform infrared spectroscopy, ellipsometry, and wet etch rates. Substrate temperature appears to be the most influential deposition parameter, significantly affecting both composition and properties of the deposited SiO2 films. Measured apparent activation energies for SiO2 deposition from alkoxysilane/O2 plasmas are negative for all precursors. This suggests an adsorption/desorption-limited deposition mechanism controls film formation in all systems. Additional data for SiO2 films deposited from the halogenated alkoxysilanes triethoxyfluorosilane and triethoxychlorosilane are also presented.
Material characteristics and thermal stability of cosputtered Ta–Ru thin films
Authors: Wuu D. S. , Chan C. C. , Horng R. H.
Published: July 2002

Ta–Ru alloy films were studied for use as a heater material in thermal ink-jet printheads. Thin films with different Ta/Ru compositions were deposited on oxidized Si substrates by cosputtering. The Ru/Ta ratio in the alloy was found to strongly affect the structure, resistivity, stress, and thermal stability. From x-ray and transmission electron microscopy examinations, the Ta1Ru1 phase has formed and dominated in the compositions exceeding 54 at. % Ru. With increasing the Ru content above 13 at. %, the resistivities of the Ta–Ru thin films begin to rise and can reach a maximum of ∼320 μΩ cm in the composition range between 35 and 54 at. % Ru. It is found that the films with small Ru ratios (⩽22%) exhibit poor thermal stability and the compressive stress increases after each thermal cycle (from 25 to 450 °C) in air, while the films with larger Ru atomic ratios show good stability. The measured stress-temperature behavior was investigated by Auger depth profiling analysis and x-ray photoelectron spectroscopy. The oxygen content of samples after repeated thermal cycling is largely related to the alloy composition. The observed preferential oxidation of Ta in the Ta–Ru samples can be further interpreted by thermodynamic calculations. The Ta-rich surface oxide is believed to be responsible for the oxidation resistance of the Ru atom at high temperatures. This results in the Ru of the metallic state though the oxidation of Ta occurs. Finally, an open pool test environment is arranged such that the liquid pool can be regarded as an infinite reservoir for the heater, from the standpoint of both momentum and energy transport. A lifetime over 1×107 driving pulses can be obtained for the Ta–Ru thin-film heater with 54 at. % Ru content.
Effective potentials for kinetic processes on semiconductor surfaces
Authors: Ying S. C. , Reinecke T. L.
Published: July 2002

The effective potentials for atomic motion on semiconductor surfaces are given in terms of the displacement–displacement correlation functions of the substrate by a Langevin equation approach. The method is illustrated by detailed calculations of the surface dynamics of the unreconstructed Si(100) surface for which several interesting new features are obtained. It is shown that the total effective potential for atomic diffusion on the surface differs substantially from the adatom-rigid substrate interaction as a result of coupling to the dynamic substrate vibrations.
Secondary ion mass spectrometry study of Pd-based ohmic contacts to GaAs and AlGaAs/GaAs
Authors: Chen C. L. , Hollis M. A. , Mahoney L. J. , Goodhue W. D. , Manfra M. J. , Murphy R. A.
Published: July 2002

Secondary ion mass spectrometry (SIMS) has been used to study nonalloyed Zn/Pd/Au (p-type) and Ge/Pd/Au (n-type) ohmic contacts to GaAs. Both contacts have very low contact resistances and smooth surface morphologies. It appears that Pd, a fast diffuser in GaAs, helps the diffusion of Zn into GaAs in the Zn/Pd/Au contact. On the other hand, it was found that Pd and Ge diffused together during the heat treatment of the Pd/Ge/Au contact. SIMS profiles of a Pd/Ge/Au ohmic contact fabricated upon a high-electron mobility transistor (HEMT) structure provide two possible explanations for its significantly higher contact resistance than a conventional Ni/Ge/Au alloyed contact. The SIMS data indicates that Pd may have caused Al and Ga interdiffusion at the AlGaAs/GaAs interface and that the metallization failed to make contact to the electron gas because of the interdiffusion.
Fabrication and optical characterization of quantum wires from semiconductor materials with varying In content
Authors: Maile B. E. , Forchel A. , Germann R. , Grützmacher D. , Meier H. P. , Reithmaier J.-P.
Published: July 2002

We have fabricated semiconductor wires from materials with varying In content and measured the quantum efficiency as a function of lateral wire width and temperature. The intensity decay observed for narrow wires can be explained by surface recombination at the wire sidewalls and the existence of an optically inactive layer. Sidewall recombination velocity as well as the width of the inactive layer are found to systematically depend on the In content.
Use of Raman spectroscopy to characterize strain in III–V epilayers: Application to InAs on GaAs(001) grown by molecular-beam epitaxy
Authors: Diebold Alain C. , Steinhauser S. W. , Mariella R. P.
Published: July 2002

Strain in thin layers of molecular-beam epitaxy (MBE) grown InAs on GaAs(001) was characterized by both Raman spectroscopy and double crystal x-ray diffraction (DCD). The goal of this study was to evaluate the use of Raman spectroscopy as a method of strain determination and compare it to DCD. Recent results of Burns et al., for InxGa1−xAs proved that Raman spectroscopy could be an important in situ analysis method for MBE [G. Burns, C. R. Wie, F. H. Dacol, G. D. Pettit, Appl. Phys. Lett. 51, 1919 (1987)]. We find that Raman spectroscopy has several advantages over DCD. Raman data samples the stress in a much thinner volume than DCD, allowing one to determine when a surface layer of the thin film is no longer under stress. Films that are highly lattice mismatched with the substrate have a large number of defects at the substrate/epilayer interface. Raman analysis determines straain in a more defect free layer of these films when the layer thickness is greater than tc, the critical thickness. DCD samples an average strain over the entire thickness of most semiconductor films. There are several disadvantages in the use of Raman spectroscopy as a strain analysis method. We found that the materials parameters of InAs required to calculate the strain from the shift in the optical phonon energy of the epilayer were not accurately known. Quantitative strain determination by Raman spectroscopy depends on accurate values of the phonon deformation potentials of InAs and other III–V compounds of interest. Also, DCD is capable of determining much smaller strains than Raman spectroscopy.
A scanning tunneling microscopy study of an insect lipoprotein ice nucleator
Authors: Yeung King Lun , Wolf Eduardo E. , Duman John G.
Published: July 2002

A scanning tunneling microscopy (STM) study of the lipoprotein ice nucleator (LPIN) from hemolymph of the cranefly, Tipula trivittata, showed strong organization of the individual LPINs into chain structures. Each strand of the chain is two lipoproteins wide with the lipoproteins arranged in aligned conformation. The size of the spherical LPINs within the strands (diameter of 90–120 Å) agrees with the value of 135±29 Å obtained from transmission electron microscopy (TEM). A non-ice-nucleating lipoprotein from Manduca sexta was used as a control. The Manduca lipoprotein does not exhibit any organizational tendency, but sometimes forms large aggregates. The two apolipoproteins of the LPIN, Apo-I (MW=265 000) and Apo-II (MW=82 000) were also imaged. The apolipoproteins exist as isolated individuals with platelike morphology, indicating the possibility of protein unfolding.
Comparative study between gas- and liquid-phase silylation for the diffusion-enhanced silylated resist process
Authors: Baik Ki-Ho , Van den hove L. , Roland B.
Published: July 2002

Surface imaging in combination with dry development has been suggested as a means of overcoming the inherent limitations present in conventional wet develop lithography. The diffusion-enhanced silylated resist process has been demonstrated as one such solution. Silylation is one of the more critical steps in the process, with hexamethyldisilazane being typically used as silylating agent. Alternative gas-phase silylating agents, such as dimethylsilyldimethyl-amine, 1,1,3,3-tetramethyl disilazane and N,N-dimethylamino trimethylsilane, have additionally been studied [Ki-Ho Baik et al., J. Vac. Sci. Technol. B 8, 1481 (1990)]. Liquid-phase silylation holds promise for simplifying the hardware requirements as well as improving silylation properties. Several mono-functional and polyfunctional silylating agents have been investigated. Bis(dimethylamino)dimethylsilane has been found to be promising. N-methyl-2-pyrrolidone was used as diffusion promoter and xylene as the solvent. The influence of solvent composition on the silylation kinetics has been studied. An in-depth study of the silylation process has been performed using both Rutherford backscattering spectroscopy (RBS) and Infrared spectroscopy. Si profiles are measured for liquid- and gas-phase silylation using RBS. A possible mechanism is suggested for liquid silylation. Newly formulated resists as well as the influence of a presilylation bake have been studied.
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u scanning tunneling microscopy of inhibited Cu and Cu–Au electrodissolution in aqueous media
Authors: Pickering H. W. , Wu Y. C. , Gregory D. S. , Geh S. , Sakurai T.
Published: July 2002

I n situ scanning tunneling microscopy (STM) of copper dissolution in the Tafel region, shows that the initial mechanically polished surface (0.05-μm Al2O3 ) roughens by forming large scale (μm) plateaus that appear to consist of low index hkl facets, while the plateaus, themselves, become smoother (<100 nm scale) than the as-prepared surface. The tendencies for both plateau development and smoothing of the plateaus are slowed by the addition of inhibitor to the solution and this inhibiting effect is particularly strong in some regions suggesting the preferential adsorption of the inhibitor on the surface. Real-time STM of the profuse surface roughening (10–102 nm scale) that occurs during selective dissolution of Cu from the Cu–Au alloy is illustrated. As in post (ex situ) STM examination, the scale of the roughness in the plane of the surface is found to be in good agreement with scanning electron microscopy results, but the depth of the roughness (pits) is severely underestimated except at the very initial stages of surface roughening.
Scanning tunneling microscopy studies of conducting molybdenum oxide bronzes
Authors: Rudd G. , Novak D. , Saulys D. , Bartynski R. A. , Garofalini S. , Ramanujachary K. V. , Greenblatt M. , Garfunkel E.
Published: July 2002

Compounds of the formula AxMozOy, known as molybdenum bronzes, display interesting quasi-low-dimensional electronic properties such as anisotropic conduction, superconductivity, and charge-density waves (CDW). Scanning tunneling microscopy studies have been performed on Na0.9Mo6O17, a purple bronze, and Rb0.3MoO3, a blue bronze, demonstrating that they can be imaged in air with near atomic resolution. Surface defects can be created on these bronzes exhibiting varied in-air stabilities. The interpretation of images is discussed with reference to the structures, CDWs, defect creation techniques, and relative defect stabilities.
Free-standing gratings and lenses for atom optics
Authors: Keith David W. , Soave Robert J. , Rooks Michael J.
Published: July 2002

A fabrication process has been developed for making free-standing gratings of silicon nitride. These structures are critical components of an atom interferometer, which uses four gratings as coherent beam splitters of atom waves. The quality of gratings necessary for an interferometer is considerably higher than is needed to demonstrate the diffraction of atoms. In particular, the gratings must be phase coherent over their entire area. This implies that the grating lines must be straight to the order of their linewidth over the full extent of the grating. In addition, the open fraction of the grating structure is more critical for an interferometer. In this paper the development of new fabrication techniques that were used to make free-standing gratings with periods as small as 100 nm and support structure open fractions as high as 0.8 were reported on. To achieve depth-to-linewidth ratios greater than 4:1 with grating periods as small as 100 nm a selective, highly directional reactive ion etching (RIE) process has been developed.
Atomic force microscope and Auger electron microscopy studies of thin film ultrasmooth Au–Cr films on mica
Authors: Carmi Y. , Dahm A. J. , Eppell S. J. , Jennings W. , Marchant R. E. , Michal G. M.
Published: July 2002

Atomic force microscope (AFM) and Auger electron spectroscopy (AES) studies were made of thin (3.5<t<8.5 nm) Au–Cr alloy films thermally deposited on cleaved mica. The root mean square roughness measured by the AFM ranged between 0.25 and 0.6 nm on 10×10 μm2 areas. AES mapping showed very uniform lateral distribution of the two metals and a pronounced diffusion of Cr atoms toward the surface.
Binary AlAs/GaAs versus ternary GaAlAs/GaAs interfaces: A dramatic difference of perfection
Authors: Bimberg D. , Heinrichsdorff F. , Bauer R. K. , Gerthsen D. , Stenkamp D. , Mars D. E. , Miller J. N.
Published: July 2002

Large differences between the structural and chemical modifications binary AlAs and ternary Al0.4Ga0.6As barriers of GaAs quantum wells (QWs) upon undergoing growth interruption are found in an investigation of luminescence of type I and type II QWs. There are no increased trap incorporation but rapid smoothing and formation of interface islands larger than the diameter of type I excitons but smaller than the diameter of type II excitons is observed on the AlAs surface. Chemical lattice images obtained by high-resolution transmission electron microscopy visualize directly the structure of the interfaces. Areas without monoatomic steps in the interface plane extending more than 0.1 μm are observed at the top surface. The bottom interfaces show structure on the scale of the exciton diameter in agreement with the luminescence results. Superimposed to the in-plane variations of the interface positions is a grading extending over 2–4 monolayers in growth direction.
GaSb-oxide removal and surface passivation using an electron cyclotron resonance hydrogen source
Authors: Lu Z. , Jiang Y. , Wang W. I. , Teich M. C. , Osgood R. M.
Published: July 2002

We describe the use of a low-temperature technique, which is based on H atoms from a microwave electron cyclotron resonance (ECR) H2 plasma, to remove surface oxides and carbon from a single-crystal GaSb surface. Our experiments indicate that oxide removal occurs at a temperature of ∼250 °C, much lower than that for thermal evaporation of the oxide. In addition, we have found that subsequent exposure to N atoms from a N2 plasma leaves a thin nitride layer, which prevents degradation of the H-cleaned surface. To demonstrate this technique, we have applied it to the processing of an AlGaSb PIN photodiode, which is fabricated with molecular-beam epitaxy material. Our electrical measurements show that the leakage current, after surface Sb-oxide removal, is significantly reduced from that before the ECR-H treatment.
Performance tradeoffs in AlInAs/GaInAs single- and double-heterojunction NpN heterojunction bipolar transistors
Authors: Farley C. W. , Higgins J. A. , Ho W.-J. , McDermott B. T. , Chang M. F.
Published: July 2002

This article reports on the speed-power tradeoffs between single- and double-heterojunction AlInAs/GaInAs heterojunction bipolar transitor devices. Single-heterojunction devices with ft=100 GHz and fmax=112 GHz have been demonstrated with a breakdown voltage BVceo=2.5 V. AlInAs collectors produce higher breakdown voltages, but reduced current gain bandwidth (e.g., ft=30 GHz/BVceo=7.5 V), which results in a limited ft-BVceo product. Simulations of transient electron transport in the collector confirm that the low saturated velocity of AlInAs leads to long collector transit times. A significant improvement in the ft-BVceo product can be made by using an InP collector (ft=70 GHz and BVceo=7 V).
Lithographic patterning of self-assembled films
Authors: Calvert Jeffrey M.
Published: July 2002

This article discusses a new, general approach for fabricating surfaces with precise positional control of chemical functionalities utilizing direct patterning of self-assembled (SA) or- ganosilane monolayer films with lithographic exposure tools, including deep ultraviolet, x-ray, and e-beam sources. Lithographically patterned one- and two-component SA films have been used to selectively deposit or attach a wide variety of materials to surfaces, including catalysts, electroless metal films, proteins, cells, and organic moieties. Selectively metallized, patterned SA films have been employed to fabricate functioning Si metal–oxide–semiconductor field effect transistor test structures. The utility of patterned SA films for microelectronics, sensors, and other applications is discussed.
Sample preparation for scanning tunneling microscopy imaging of proteins: Characterization of gold surfaces chemically modified with a disulfide reagent
Authors: Cricenti A. , Scarselli M. A. , Paleari R. , Mosca A.
Published: July 2002

A protocol for sample preparation that may offer a good tool for the study of proteins with the scanning tunneling microscope is described. Gold surfaces have been mechanically polished and then incubated overnight with 4,4′-dipyridyl disulfide (DPDS) dissolved in ethanol. This mixed disulfide is able to produce an ordered hydrophilic monolayer above the gold surface, with the pyridine group exposed to the outer surface. Furthermore, the treatment with DPDS significantly improves the wettability of the gold substrates, as seen by taking measurements of the solid/liquid contact angles. Human liver ferritin (HLF) molecules have successively been deposited. Samples have also been characterized under ultrahigh vacuum conditions by means of Auger and photoemission spectroscopy. With regard to the untreated gold surfaces, we found the usual structures of the valence band of gold, as well as almost contaminant free outer layers. Samples treated with DPDS and later with the HLF showed their fingerprints in the ‘‘new’’ valence band together with a good stability under the Auger beam.
Ion-beam-induced densification of sol-gel ceramic thin films
Authors: Levine Timothy E. , Revesz Peter , Giannelis Emmanuel P. , Mayer James W.
Published: July 2002

Ion-beam-induced densification of sol-gel zirconia thin films is examined here. Ion irradiation of sol-gel zirconia films leads to microstructural and chemical changes (densification) in the films. Ion beam analysis indicates the loss of carbon, hydrogen, and oxygen as a result of implantation. Oxygen:zirconium ratios less than that predicted for stoichiometric ZrO2 for the higher dose implanted films were observed. The chemical and microstructural modifications were attributed to both electronic interactions and nuclear collisions between the energetic ions and the target atoms. Densification of only a near-surface region of a sol-gel zirconia thin film proved that the effects of beam heating on the observed densification are minimal.
Coulomb effects in retarding field lenses
Authors: Brodie Alan D.
Published: July 2002

The purpose of this article is to investigate the Coulomb interaction aberration and its impact on retarding field lens design. Discussion of Coulomb effects in electron beam systems have mainly been limited to analysis methods, accuracy of assumptions in analytical models, and optimization of computational analysis. Here, a basic column design is considered and analyzed to give some design rules. A practical system, KLA’s SEMSpec, based on these design rules is analyzed and performance given.
Development of a scanning atom probe
Authors: Nishikawa Osamu , Kimoto Masahiro , Iwatsuki Masashi , Ishikawa Yuuichi
Published: July 2002

In order to extend the applicability of the conventional atom probe (AP), a new AP named ‘‘scanning atom probe (SAP)’’ is proposed. The SAP has a microextraction electrode which scans over a flat specimen surface with many microcusps. Then the electrode and a cusp forms a minute field ion microscope. Calculation of field distribution in the confined small space between the cusp apex and the electrode indicates that the field can be high enough to field evaporate the apex atoms and that the atom-by-atom mass analysis by the SAP is highly feasible. Accordingly, a trial SAP is under construction modifying a low-temperature UHV scanning tunneling microscope.