bluuebunny/crossref_metadata_2025 huggingface dataset:
Anomalous effective magnetoconductivity in disordered bipolar semiconductors: Theory and experimental simulation
Authors: Chaikovsky Isaak , Alperovich Leonid , Gurvich Yuri , Melnikov Andrey , Biryukov Sergey
Published: July 2002

We present the results of measuring transverse conductivity α⊥c of bipolar heterogeneous semiconductors in classical strong magnetic fields. A stochastic distribution of current carriers (electrons and holes) was created by interband illumination through special masks. The main parameters of crystalline p-Si:B placed in liquid He were the concentrations of the main and compensating impurities, 7×1015 and 4×1012 cm−3, respectively; and the mobilities of electrons and holes, 1×106 and 5×104 cm2/V s, respectively. An anomaly in α⊥c was observed: the ratio of α⊥c for heterogeneous and homogeneous samples depended on magnetic field in a nonmonotonic way, i.e., alternation of increasing and decreasing regions of relative α⊥c for H=0–10 kGs and monotonic growth for H=10–40 kGs. To explain this effect, a theory is presented which is a development of the α⊥c theory for heterogeneous semiconductors with one kind of carrier. It is shown that the effect is due to the redistribution of roles of electrons and holes in magnetoconductivity of homogeneous semiconductors. This effect has high sensitivity to degree of disorder and can be used for detection of small irregularities and as a diagnostic of semiconductor purity.
Sensitive in situ method to measure the rate of neutral free radical production by photodeionization of negative ion beams
Authors: Hayashi Keiji , Kameko Kenji , Kawakita Seiji , Kawamura Yasunori , Konno Hiroshi , Kojima Hideki , Kanayama Takuo
Published: July 2002

Photoelectron-current measurement by low-frequency electromodulation probe (PMMP) is proposed as a sensitive method to determine the rate Gr of neutral free radical production by the photodeionization of negative ion beams (PDINIB). The PMMP method was employed to evaluate the production rate in a trial surface-processing apparatus developed in the author’s laboratory utilizing a steady-flux refined beam of neutral free radicals produced by the PDINIB procedure. A Cu−63 negative ion beam of kinetic energy Ei varied up to 15 keV was irradiated with a 514.5 nm visible light beam from a 25 W cw Ar+ ion laser. The detection limit of the production rate by the measurement setup was 6×109/s under the conditions that Ei=15 keV, the negative ion beam current Ii=4 μA, and the laser power P=6 W. Based on the results of these basic experiments, furthermore, the photodeionization efficiency defined by eGr/Ii where e is the elementary electric charge was estimated to be 27±6% under the conditions that Ei=15 keV, Ii=40 μA, and P=18 W.
1/f
noise of amorphous indium oxide
Authors: Johanson Robert E. , Kasap S. O.
Published: July 2002

The conductivity σ of amorphous In2O3−x depends sensitively on the oxygen concentration; σ increases with lower oxygen concentration (increasing x) and reversibly decreases as oxygen is added. Illumination with ultraviolet light releases oxygen and exposure to air reoxidizes causing σ to vary by many orders of magnitude. At a sufficiently large value of x, the material undergoes an insulator-metal transition. We measured the spectrum of conductance fluctuations in thin films of amorphous In2O3−x as a function of oxygen concentration. Between 5 Hz and 10 kHz, the spectra fit well to a 1/fα power law. For small x, the magnitude of the noise is unusually large, and α is near 1.0. As oxygen is removed the noise at first increases and then decreases by a factor of 500 as the material enters the metallic state. At the point where the noise begins to decrease, α jumps to about 1.12.
Interfacial roughness and carrier scattering due to misfit dislocations in In0.52Al0.48As/In0.75Ga0.25As/InP structures
Authors: Naidenkova M. , Goorsky M. S. , Sandhu R. , Hsing R. , Wojtowicz M. , Chin T. P. , Block T. R. , Streit D. C.
Published: July 2002

We demonstrate the influence of misfit dislocations on the surface morphology and transport properties of In0.52Al0.48As/In0.75Ga0.25As/InP pHEMT structures grown by molecular beam epitaxy with InGaAs channel thicknesses that range from 20–35 nm. The differences in carrier scattering along different crystallographic directions for a given sample as determined by magnetotransport Hall bar measurements correspond to the asymmetric distribution of the orthogonal 60° misfit dislocations. The misfit dislocations introduce a well-defined roughness spectrum through the introduction of surface and interface steps and this roughness can be modeled in a straightforward fashion. This highly directional interface roughness is considered to be the scattering mechanism that is responsible for differences in mobility that are observed from sample to sample along different crystallographic directions. We believe that these results have implications for structures under the initial stages of strain relaxation and for metamorphic-based structures.
Study of a field-ionization source for microprobe applications
Authors: Orloff J. H. , Swanson L. W.
Published: July 2002

Operating parameters for a field-ionization source have been measured. Sensitivities of 5×10−5 A sr−1 Torr−1 were found at 77 K. Angular distributions are uniform near ϑ=0° and show the beam to be confined to ±20°. The beam signal-to-noise ratio was found to increase with increasing current. Calculations based on parameters of lenses in use indicate a resolution of 0.1 μm at ≳10−10 A is possible.
Departure from Knudsen’s cosine law during the boat evaporation of indium
Authors: Rawat S. D.
Published: July 2002

It is shown that Knudsen’s cosine law for free molecular flow is not obeyed in the case of vacuum evaporation of indium for film deposition from Mo boats. (AIP)
Adhesion of MoS2 powder burnished on metal substrates
Authors: Stupian G. W. , Feuerstein S. , Chase A. B. , Slade R. A.
Published: July 2002

The adhesion of MoS2 powder burnished onto Ti, Cu, Cr, Al, stainless steel (types 304L and 347), and Au substrates has been studied. Scanning electron micrographs reveal substantial differences in the degree of film formation by MoS2 on these metals. The observed differences in surface coverage correlate well with the relative strengths of the substrate metal–sulfur bonds as estimated from the atomization energies of the relevant bulk compounds calculated from thermodynamic data.
Electronic surface properties of III–V semiconductors: Excitonic effects, band-bending effects, and interactions with Au and O adsorbate layers
Authors: Gudat W. , Eastman D. E.
Published: July 2002

Photoemission studies of valence bands, core levels, empty surface states, and band bending for cleaved GaAs (110) are described. These studies show that there are no intrinsic band-gap surface states for GaAs (110), and that large (approx. greater than 0.5 eV) excitronic binding energies are involved in core-level-to-empty-surface-state transitions (e.g., using yield spectroscopy or electron energy-loss spectroscopy). Studies of the effects on chemisorbed oxygen and thin Au overlayers on InAs (110) and GaAs (110) surfaces are also described. Trends and correlations in III–V semiconductor empty surface states are discussed.
Properties and use of perfluoro polyethers for vacuum applications
Authors: Caporiccio G. , Steenrod R. A.
Published: July 2002

Perfluoro polyether are fully fluorinated fluids. They are chemically inert and excellent lubricants. For vacuum use they have the added advantage that solid films are rarely deposited when the vapors are subject to electron and ion bombardment. The development of various vacuum fluids is discussed, together with physical properties such as mass range, boiling range, viscosity, vapor pressure, and chromatography measurements. Performances of the specially developed fluids in vacuum pumps are presented together with field experiences in a variety of applications.
New phenomena in Schottky barrier formation on III–V compounds
Authors: Lindau I. , Chye P. W. , Garner C. M. , Pianetta P. , Su C. Y. , Spicer W. E.
Published: July 2002

The possibility of a defect mechanism is proposed to explain the Fermi-level pinning in Schottky barriers on III–V semiconductor surfaces. This suggestion comes from the results of photoemission spectroscopy applied to the study of formation of metal–semiconductor barrier heights. Changes in the electronic structure and composition of the interface are studied. For Au metal overlayers on the (110) surfaces of GaAs, GaSb, and InP, the Fermi-level pinning occurs at 0.1 or less of a monolayer coverage. Furthermore, the pinning position is roughly independent of the choice of adatom: Cs, Al, Au, or O. The partial yield structure disappears at about monolayer coverage of Au. The Au valence band had the characteristic shape for atomiclike Au, indicating that the metal was dispersed homogeneously on the surface without the formation of thick islands. Deposition of Au onto the GaSb surface causes the compound to decompose. The antimony segregates to the surface and leaves behind a nonstoichiometric interface. The results for GaSb are compared to those for GaAs(110) and InP(110), where removal takes place of both semiconductor constituents in the interface.
Electronic structure of Al chemisorbed on GaAs(110)
Authors: Mele Eugene J. , Joannopoulos J. D.
Published: July 2002

We report results of tight binding calculation for ordered half monolayer coverages of Al on GaAs(110) in a variety of chemisorption configurations. We find that differences between the chemisorption geometries and relaxations of these configurations lead to a variety of electrical characteristics of the surfaces. The relation of this result to the barrier formed at higher coverages is discussed.
Electronic surface states on cleaved GaP(110): Initial steps of the oxygen chemisorption
Authors: Guichar G. M. , Sebenne C. A. , Thuault C. D.
Published: July 2002

Using contact potential difference measurements and photoemission yield spectroscopy, the surface state distribution in the band gap has been obtained for n- and p-type GaP(110) surfaces. All cleavages of n-type samples exhibit a band bending of approximately 0.5 eV. Correlatively, a small density of occupied surface states is found in the vicinity of the Fermi level. From comparison with calculations involving different kinds of surface reconstructions, it is thought to correspond to the tail of an intrinsic surface state band, mainly empty. Another surface state band, the shape and magnitude of which depend on the cleavage, is detected near the valence band maximum. Upon low oxygen exposure, while the band bending increases for n-type samples, the surface state distribution in the gap is modified, new states appearing close to the valence band top. Possible explanations involving surface relaxation or missing surface atoms are suggested.
Characterization of black Ge selective absorbers
Authors: Swab P. , Krishnaswamy S. V. , Messier R.
Published: July 2002

We have prepared structurally anisotropic black Ge films by rf sputtering and postdeposition etching. By careful control of various sputtering condition such as rf power, gas pressure, deposition time, and other parameters such as nature and roughness of the substrate and etching time, we can alter the morphology of these films and optimize the selective absorbing properties. Postdeposition etching in 30% H2O2 has reduced the reflectance from approximately 45% to less than 1% in the best case. This etching behavior is also observed for films immersed in water for several weeks at room temperature. This is explained on the basis of oxidation through aligned voids. The etching behavior of various films and correlation between the resulting microstructure and optical properties is discussed. Further, the various microstructures are classified and understood using the structure zone models.
Energy levels of semiconductor surface vacancies
Authors: Daw M. S. , Smith D. L.
Published: July 2002

We present calculations of the bound state energy levels of anion vacancies near the surface of a III–V semiconductor. We consider the (110) surface of GaAs, InP, and the Ga1−xAlxAs alloy system. As the vacancy is moved toward the surface, the energy levels are only slightly perturbed until the vacancy reaches the second atomic layer from the surface. At this point, the anion vacancy levels move to lower energy. We find that there is a general trend in the vacancy energy levels with semiconductor ionicity. As the material becomes more ionic, the anion vacancy levels move to higher energy. Comparing this trend with experimentally observed Schottky barrier heights, we find a strong correlation between the position of the highest occupied level in the anion vacancy and the measured Fermi level at the surface. This result suggests that the recently proposed defect model is capable of accounting for observed trends in Schottky barrier formation.
Chemisorption of Al and Ga on the GaAs (110) surface
Authors: Swarts C. A. , Barton J. J. , Goddard III W. A. , McGill T. C.
Published: July 2002

We have studied the initial stages of the chemisorption of Al and Ga on the clean GaAs (110) surface by applying quantum chemical methods to small clusters representing Al or Ga on GaAs (110). These calculations suggest that at smallest coverages Al or Ga bind to a surface Ga atom; for higher coverages Al and the surface Ga interchange positions. We have obtained the binding energy, the chemical shifts of the Ga–3d, As–3d and Al–2p states, and the microscopic dipole associated with chemisorption of Al or Ga on GaAs (110). These results are compared to experimental values and further experiments are suggested.
Photoemission investigation of the temperature effect on Si–Au interfaces
Authors: Abbati I. , Braicovich L. , Franciosi A. , Lindau I. , Skeath P. R. , Su C. Y. , Spicer W. E.
Published: July 2002

We report extensive photoemission measurements carried out with synchrotron radiation and with conventional light sources on Si(111)–Au interfaces. The coverage dependence has been studied in detail at room temperature (RT) with synchrotron radiation. We have found considerable intermixing at all coverages, and the photoemission spectrum characteristic for pure gold was not even observed at coverages of about 150 monolayers. A deeper insight into the intermixing mechanism is obtained from the te,perature dependence of the spectra, which was studied for surfaces covered with 10 monolayers. Considerable intermixing is observed for interfaces prepared and measured at liquid nitrogen temperatures (LNT). Several hours of annealing at RT are required for an interface prepared at LNT to obtain the equilibrium situation reached immediately after preparation at RT. These results indicate that the thermal energy of the sample is not the only energy responsible for intermixing during interface preparation. We propose that an important contribution comes from the condensation energy of gold. The photoemission spectra show that the intermixing increases with the temperature up to ?350°C.
AES study of tin–lead alloys: Effects of ion sputtering and oxidation on surface composition and structure
Authors: Frankenthal R. P. , Siconolfi D. J.
Published: July 2002

Using Auger electron spectroscopy, we have investigated the surface composition of a 60:40 soft solder (72a/oSn−28a/oPb), the effect of ion sputtering on the composition and structure of the surface, and the composition of the oxide film that forms during ambient and low pressure oxidation. The alloy surface is, on the average, enriched in lead. The lead-rich phase is preferentially sputtered during ion etching. Tin in the alloy surface oxidizes preferentially; however, if the conditions are such that the alloy surface layer becomes depleted in tin, lead will be oxidized.
Results from Langmuir probe measurements in PDX and PLT
Authors: Budny R.
Published: July 2002

Fits to Langmuir probe measurements made near the midplanes of the PDX and PLT tokamaks imply density and electron temperature profiles. In ohmically heated plasmas with either circular or diverted configurations, the edge densities decrease approximately with e-folding lengths of 1–4 cm. Electron temperatures are low (5–50 eV) and decrease more slowly than the density profiles in the outer edge.
Direct verification of hydrogen termination of the semiconducting diamond(111) surface
Authors: Waclawski B. J. , Pierce D. T. , Swanson N. , Celotta R. J.
Published: July 2002

Low-energy, high-resolution electron energy loss spectroscopy has been used to identify the vibrational modes of hydrogen on the semiconducting diamond surface providing the first direct evidence that the (111) 1×1 surface is terminated by hydrogen. The vibrational loss spectrum from the ’’as-polished’’ surface shows two major losses near 160 meV (CH3 deformation), a major loss at 360 meV (CH3 stretch), and two minor losses at 520 and 720 meV (combinations and overtones). All of these losses disappear from the spectrum after heating the sample to ∠1000 °C (which has been established by other experiments to be sufficient to reconstruct the surface to 2×2/2×1). The loss spectrum for the reconstructed surface is indicative of a two-dimensional metallic state of the dangling-bond surface states for clean diamond. Exposure of this reconstructed surface to atomic hydrogen results in a loss spectrum which is essentially identical to that for the as-polished surface. Further verification that the loss spectrum results from hydrogen is provided by the shift of the structure to lower loss energies when deuterium is absorbed.
Metal–GaSe and metal–InP interfaces: Schottky barrier formation and interfacial reactions
Authors: Williams R. H. , McKinley A. , Hughes G. J. , Montgomery V. , McGovern I. T.
Published: July 2002

We have studied the formation of the interface between a range of metals and the semiconductors GaSe and InP using photoelectron spectroscopy and a synchrotron source. We concentrate in particular on the reactive metal Ni and the relatively unreactive metals Au and Ag. It is shown that metals which interact only weakly with GaSe yield a Fermi-level pinning behavior close to the Schottky limit but those metals which interact strongly lead to strong pinning of the Fermi level by interfacial defects. The complex interactions at Ni–InP and Au–InP interfaces are considered and the Fermi-level pinning behavior is discussed in terms of the defect model.
Gibbsian and radiation-induced segregation in Cu–Li and Al–Li alloys
Authors: Gruen D. M. , Krauss A. R. , Susman S. , Venugopalan M. , Ron M.
Published: July 2002

Previous experiments on segregation in dilute alloys of lithium in aluminum have demonstrated rapid enrichment of lithium in the uppermost monolayer, as well as a slower buildup in the subsurface region as a result of radiation-induced segregation effects during sputtering. Surface and subsurface enrichment of lithium in copper and aluminum alloys has been observed by secondary ion mass spectroscopy (SIMS), Auger electron spectroscopy (AES), and x-ray photoemission spectroscopy (XPS). The activation energies for lithium diffusion in Cu and Al have been measured and segregation kinetics are compared for dilute alloys of Li in Cu and Al, and a high lithium content copper alloy. The results are interpreted in terms of both Gibbsian and radiation-induced segregation effects.
Auger analysis of iron–cobalt alloys
Authors: Bevolo A. J.
Published: July 2002

For the 3d transition metals in their elemental form, the ratio R of the intensity of the L23M45M45 Auger transition to that of the L23M23M23 Auger transition is proportional to N(N−1), where N is the occupancy of the 3d shell. Measurements of R should reflect changes in N due to charge transfer. Auger measurements in the Fe–Co alloy system after ion sputtering have been made. Because of overlapping transitions only iron R values were measured. It was found that R is constant within 1% across the alloy system indicating that the 3d occupancy of iron changes by less than 0.5%. This result favors the coherent potential approximation theory of the magnetism of this alloy system rather than a charge transfer model. Little preferential sputtering was found in theFe–Co alloy system with 2.5-keV Ar+ ions at near normal incidence.
Ratioed scatter diagrams. An erotetic method for phase identification on complex surfaces using scanning Auger microscopy
Authors: Browning R.
Published: July 2002

By ratioing multiple Auger intensities and plotting a two-dimensional occupational scatter diagram while digitally scanning across an area, the number and elemental association of surface phases can be determined. This can prove a useful tool in scanning Auger microscopic analysis of complex materials. The technique is illustrated by results from an anomalous region on the reaction zone of a SiC/Ti–6A1–4V metal matrix composite material. The anomalous region is shown to be a single phase associated with sulphur and phosphorus impurities. Imaging of a selected phase from the ratioed scatter diagram is possible and may be a useful technique for presenting multiple scanning Auger images.
Examination of the damage to a graphite probe cap exposed to rf heating in PLT plasmas
Authors: Manos D. , Bennett T. , Budny R. , Cohen S. , Kilpatrick S. , Timberlake J.
Published: July 2002

Visual observations, optical microscopy, and Auger spectroscopy are used to determine the effects of ion gyroradii, arcing, sputtering, and/or evaporation caused damage to a probe cap that has been exposed to 460 rf heated PLT plasmas. Arc tracks are seen on the cap, many starting on the ion side at the face of the cap extending upwards and backwards. Calculations are made to determine whether the observed quantity of material lost from the top leading edge of the cap is due to evaporation. Model calculations of the observed damage support the suggestion that the majority of effects are due to synergism between thermalized plasma and fast ions.
Surface composition of α-Cu–Al alloys
Authors: Baird R. J. , Potter T. J.
Published: July 2002

The relative Auger sensitivities for α-Cu–Al alloys were determined from in situ mechanically abraded polycrystalline surfaces. The Al-KLL to Cu-LMM relative sensitivity was unchanged on alloying. However, the Al-LVV to Cu-MVV relative sensitivity was affected by a change in the Al-LVV line shape and by an overlap of the Al-LVV and Cu-MVV Auger lines. The experimentally determined relative sensitivities were used in conjunction with a simple layer model to determine the surface compositions of thermally equilibrated (111) and (100) alloy single-crystal surfaces. The (100) surfaces exhibited weak surface segregation of Al. The (111) surfaces showed a stronger tendency toward surface segregation of Al which saturated at one-third of a monolayer of Al in the surface.
Adhesion of TiC and Ti(C,N) coatings on steel
Authors: Steinmann P. A. , Hintermann H. E.
Published: July 2002

The scratch test has been used to measure the adhesion of CVD TiC coatings on various steels by comparing the critical load factors. The critical load (Lc) of a coating–substrate interface determined by the scratch test depends not only on the adhesion but also the substrate hardness and coating thickness. For identical deposition conditions, the coating thickness depends strongly on the carbide forming elements in the steel. In this work, a careful separation of these effects has allowed us to quantify the adhesion of a given system from the critical load. Of the nine steels tested, two had improved adhesion which was shown to be caused by diffusion of substrate elements into the coating. Adhesion measurements of Ti(C,N) coatings deposited by PVD are discussed and compared to the adhesion values of CVD TiC on the same steel substrates.
Nature of defects in P- and B-doped SiO2
Authors: Offenberg M. , Maier M. , Meyer R. , Balk P.
Published: July 2002

Experimental results are presented on the diffusion at 1100 °C of B and P in SiO2 films doped with these elements using ion implantation. The diffusion behavior is dependent on the specific dopant and on the annealing ambient. Electron trapping in the films at 400 K also depends on these experimental parameters. A model is presented explaining the results in terms of oxide stoichiometry and the distribution of incomplete bonding to O between silicon and the dopant.
Design method for an electrostatic einzel lens having an asymmetric structure
Authors: Saito Kenichi , Okubo Tsuneo , Takamoto Kiichi
Published: July 2002

The guiding principle for designing an asymmetric einzel lens is obtained on the basis of an examination of the axial potential distribution in symmetric einzel lenses with lower aberrations. The asymmetric axial potential distribution resulting in lower aberrations is expressed by four quadratic curves. After the asymmetric distribution is optimized for the required optical properties, the lens structure to achieve it is determined with only a few calculation cycles. As an example, an asymmetric einzel lens is designed under the condition that the aperture angle is 5 mrad, the beam energy spread is 1×10−4, and the working distance is 10 mm. The lens has a total axial aberration as small as 0.038 μm.
The emission of atoms and molecules accompanying fracture of single-crystal MgO
Authors: Dickinson J. T. , Jensen L. C. , McKay M. R. , Freund F.
Published: July 2002

We have been investigating the emission of particles due to deformation and fracture of materials. We observe the emission of electrons (exoelectron emission), ions, neutral species, photons (triboluminescence), as well as long wavelength electromagnetic radiation; collectively we refer to these emissions as fractoemission. In this paper we describe measurements of the neutral emission accompanying the fracture of single-crystal MgO. Masses detected are tentatively assigned to the emission of H2, CH4, H2O, CO, O2, CO2, and atomic Mg. Other hydrocarbons are also observed. The time dependencies of some of these emissions relative to fracture are presented for two different loading conditions.
Epitaxial growth of CdTe on GaAs by molecular beam epitaxy
Authors: Kolodziejski L. A. , Gunshor R. L. , Otsuka N. , Choi C.
Published: July 2002

Epitaxial CdTe grown on (100)GaAs by molecular beam epitaxy can be selectively oriented with two epitaxial arrangements—(111) CdTe//(100)GaAs and (100)CdTe//(100)GaAs. Under normal conditions to initiate growth, the consistent nucleation of (111)CdTe occurs on a clean, completely oxide-desorbed (100)GaAs substrate. The nucleation of (100)CdTe occurs by deliberately providing a ‘‘disturbance’’ to the (100)GaAs surface. Various growth techniques are described which provide the ‘‘disturbance’’ required to nucleate a (100)CdTe epilayer. High resolution electron microscopy and dark field imaging have been used to investigate the CdTe–GaAs interfaces for both epitaxial orientations.
Conversion tables for pressure and leak rates
Authors: Moss Timothy A.
Published: July 2002

Two new conversion tables are presented that relate pressure and leak rates. These tables are more accurate than other than previously publishe d conversion tables. The temperature dependence of the gas leak rate must be used to convert to the temperature independent mass/time units. (AIP)
Surface structures for the O/Ni(001) system from c(2×2)O to saturated NiO
Authors: Saiki R. , Kaduwela A. , Osterwalder J. , Sagurton M. , Fadley C. S. , Brundle C. R.
Published: July 2002

The use of x-ray photoelectron diffraction (XPD) for the structural study of oxide growth on Ni(001) from c(2×2)O up to the saturated oxide of approximately two-monolayers thickness is described. Some rather unique structural information is obtained from XPD. This includes the site type and position of the c(2×2) overlayer and the geometry and lattice parameters of the saturated oxide. The XPD data are also in excellent agreement with single-scattering cluster calculations at the spherical wave level.
Metal–polymer chemistry. II. Chromium–polyimide interface reactions and related organometallic chemistry
Authors: Goldberg M. J. , Clabes J. G. , Kovac C. A.
Published: July 2002

We have studied the reactions occurring for the deposition of chromium onto pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA) polyimide for a wide range of metal coverages, using x-ray photoelectron spectroscopy as well as solution studies of model compounds. A multistep, coverage-dependent mechanism is proposed which includes an initial electron transfer from Cr to PMDA-ODA, followed by formation of Cr–O and Cr–N polymer-bound intermediates. At higher metal coverage, Cr–oxides and Cr–nitrides are formed which may activate the polymer for subsequent formation of Cr–carbide. In the course of this work we have shown that similarities exist between the chemistry of metal atoms in condensed phases and the reactions occurring between metal atoms and surfaces.
Kinetics of ordering in chemisorbed and physisorbed systems
Authors: Gunton J. D.
Published: July 2002

A review of the kinetics of adatom ordering on surfaces is presented, with an emphasis on the results of Monte Carlo studies. Topics which are covered include the nonequilibrium scattering intensity, domain growth laws and growth mechanisms, dynamical scaling, and universality classes. Monte Carlo results for lattice gas models of O/W(112), H/Fe(110), and O/Pd(110) will be discussed. It is stressed that the kinetics of adatom ordering on surfaces provides in principle an excellent example of the general subject of the kinetics of first-order phase transitions.
Microstructure of sputtered metal films grown in high- and low-pressure discharges
Authors: Kay E. , Parmigiani F. , Parrish W.
Published: July 2002

Sputtered metal films grown in different discharge environments are subject to different degrees of energetic particle bombardment during film growth, resulting in different microstructure and subsequent thin-film properties. The effect on film structure of energetic gas neutrals, backscattered from the sputtering target, together with the role of sputtered neutral metal atoms and those Penning ionized in traversing the plasma, are evaluated in different pressure regimes and under different biasing conditions. It will be shown that the film morphology, degree of texturing, and anisotropic lattice distortions change in a systematic way depending on En, the energy delivered to the growing metal film surface per arriving metal atom. En changes predictably in different discharge pressure regimes as do the resultant film structures and properties.
A precision table for ultrahigh vacuum made of aluminum alloys
Authors: Saeki H. , Ikeda J. , Ishimaru H.
Published: July 2002

Recently an ultrahigh vacuum environment has been necessary to reduce impurities in the production of high-density integrated circuits. In particular, tables permitting precise positioning with low outgassing rates have been required for thin-film processing equipment and surface analysis systems using spot beams. An X–Y–θ three-axis table made of aluminum alloys with a special surface treatment for ultrahigh vacuum environments has been developed. The stroke of the X and Y axes is 75 mm, and the rotational range of the θ axis is 360°. The X and Y axes are driven by built-in stepping motors, connected directly to aluminum alloy ballscrews. The stator of the motor is made using stainless-steel sheath cable. The screws and nuts of the ballscrews are coated with TiC, and the balls are coated with Ag. The characteristics of the table have been investigated in atmosphere before and after baking. The measured error motions for the X axis were pitch ±2.3 μm/75 mm and yaw±1.4 μm/75 mm; and for the Y axis were pitch ±0.78 μm/75 mm and yaw ±0.22 μm/75 mm. The resolution and repeatability for the X and Y axes was 15 μm ±2 μm/pulse, and for the θ axis was 1.8° ±0.09°/pulse. The mechanical characteristics were maintained after baking. The table moved in an ultrahigh vacuum environment of the order of 10−11 Torr as it had in atmosphere.
Evaporating and sputtering: Substrate heating dependence on deposition rate
Authors: Pargellis A. N.
Published: July 2002

The deposition of copper into the through holes and vias of printed wiring boards (PWB’s) has been done using vacuum processing techniques such as evaporation and sputtering. One of the most important limiting factors for any deposition process is the substrate heating. The temperature of epoxy-glass PWB’s should not exceed 180 °C (350 °F). For evaporation, there are two major contributions, the heat of condensation and radiant heating, with the heat of condensation dominating at deposition rates >2 μm/min. The radiant heating is very dependent on α ε, the product of the substrate absorptivity and the source emissivity. Sputter deposition has two main sources of substrate heating: the heat of condensation and the kinetic energy of the incident atoms and ions. The experimental apparatus used to measure the power absorbed by a PWB substrate is described. Data are presented for the power absorbed by the substrate as a function of deposition rate for sputtered copper. These data are compared with the results obtained by other investigators for evaporated aluminum and sputtered aluminum and copper. The various contributions to substrate heating are theoretically determined for both evaporation and sputtering systems. The absorbed power per unit area is calculated as a function of deposition rate and agrees very well with experimental results. It is discovered that the heating rate of a substrate is very similar for evaporation or sputtering of copper for deposition rates ≲3 μm/min. Sputtering heats the substrate more than evaporation at higher deposition rates, primarily because of heating by energetic atoms and ions.
New electrostatic dust collector for use in vacuum systems
Authors: Saeki H. , Ikeda J. , Kohzu I. , Ishimaru H.
Published: July 2002

A new active dust collector was developed for use in vacuum systems. The dust is collected using an electrostatic force only or using an electron beam. The dust collecting electrode is made from copper-clad fiberglass epoxy. The potential of the electrode can be varied from −3 to +3 kV. The current of the electron beam was 14 μA, and the vacuum pressure in the test chamber ranged from 10−6 to 10−7 Torr. The dust collecting device was tested with several conducting and nonconducting dust materials ∼60 μm in size on substrate materials of stainless steel, Al, Cu, Si wafers, and quartz. Dust removal was monitored using an optical microscope with a video camera. The results show that the new active dust collector removes 90% or more of the dust materials from most substrates.
Core-level shifts on the H2O exposed Ge(100)2×1 surface
Authors: Larsson C. U. S. , Flodström A. S. , Karlsson U. O. , Yang Y.
Published: July 2002

Core-level spectroscopy and valence-band photoelectron spectroscopy were used to study the Ge(100)2×1 surface dosed with 0.5–100 L H2O at 160 K. It is determined that H2O adsorbs molecularly at 160 K and forms ice. The H2O molecules dissociate into H and OH radicals on the Ge(100)2×1 surface when the sample is heated to 300 K. A simple adsorption model that accounts for the calculated H and OH coverages is proposed.
The molecular drag gauge as a calibration standard
Authors: Dittmann Sharrill , Lindenau Bernd E. , Tilford C. R.
Published: July 2002

The National Institute of Standards and Technology has used molecular drag gauges for six years as transfer standards in the high-vacuum range, 1×10−4 to 1×10−1 Pa. We report on the experience gained with these gauges and, in particular, on their long- and short-term calibration stability, on factors affecting accuracy, on the predictability of the effective accommodation coefficient, and on factors affecting the stability of the offset correction.
Tunneling and dark currents in HgCdTe photodiodes
Authors: Nemirovsky Y. , Rosenfeld D. , Adar R. , Kornfeld A.
Published: July 2002

The dc characteristics of front-illuminated ion-implanted n+ on bulk p-type Hg1−xCdxTe with x≊0.22, operating at 77 K, are modeled with three distinct mechanisms that dominate the dark current: In the zero- and low-bias region, diffusion current is the dominant current down to 60 K. For medium reverse bias, at 77 K, trap-assisted tunneling produces the dark current and dominates the dark current at zero bias below 50 K. For a high reverse bias, bulk band-to-band tunneling dominates. By measuring the temperature dependence of the dc characteristics in the temperature range 65–132 K, the mechanisms are studied and the validity of the modeling is confirmed. The 1/f noise phenomena measured at high reverse bias are correlated with the bulk band-to-band tunneling current. The electrical profile of the implanted junction is correlated with the origin of the p-type conductivity and with the dc characteristics.
The durability of ballscrews for ultrahigh vacuum
Authors: Saeki H. , Ikeda J. , Kohzu I. , Ishimaru H.
Published: July 2002

A test of the durability of ballscrews was carried out. Two sets of screws and nuts were used. The screws and nuts were made of stainless steel. Electrochemical buffing was performed on the surfaces of all the screws and nuts. One set, (a screw and two nuts) was further coated with TiC and Ag, while the other set was not coated. The stainless steel balls were coated with Ag. Each ballscrew was directly connected to an ultrahigh-vacuum (UHV)-compatible stepping motor. The test was carried out in an UHV environment of 10−10–10−11 Torr. The ballscrew coated with TiC and Ag was moved through more than 200 000 reciprocating cycles; the uncoated ballscrew could only be moved through 1740 cycles before failure.
Defect microchemistry in SiO2/Si structures
Authors: Rubloff G. W.
Published: July 2002

The chemical behavior of defects in SiO2/Si structures is a key to the success of Si field effect transistor (FET) technology. By exercising a high degree of control over the processing environment, it has been possible to elucidate microchemical behavior intrinsic to the SiO2/Si interface, particularly the oxide decomposition reaction Si + SiO2→2 SiO and its microstructural and electrical consequences. Initiation of this reaction is shown to occur at existing defect sites, leading to lateral growth of voids in the oxide. At earlier stages of reaction, electrically active defects are generated, following a process that can be reversed by the presence of oxygen; the detailed chemistry indicates competition between decomposition and reoxidation reactions at the defect site, i.e., the defect microchemistry emulates known macroscopic chemical reactions. These results have significance both for defect identification and control in processing. Finally, positron annihilation studies have shown strong evidence for the presence of microvoids in as-grown thermal oxide, similar to the early stages of oxide void growth under inert annealing conditions; these microvoids could be yet another manifestation of the oxide decomposition reaction, here competing with direct Si oxidation.
Effect of deposition conditions on the properties of thin permalloy film
Authors: Freeman J. D.
Published: July 2002

The saturation magnetostriction λs of thin Permalloy films, used in magnetoresistive reproduce heads, has to be strictly controlled to be negative and less than 3×10−7. The value of λs for NiFe is a strong function of film composition. [E. Klokholm and J. A. Aboaf, J. Appl. Phys. 52, 2474, (1981).] [R. M. Borzorth and J. G. Walker, Phys. Rev. 89, 624 (1951).] Since the composition of the target material could be controlled to only ±0.2% of Ni, the potential changes in λs could have been as large as 6×10−7, which exceeded the material specification. Therefore, the effect of substrate bias (0 to −60 V), sputtering pressure (2 to 20 mTorr), and target voltage (200 to 1000 V) on magnetostriction has been investigated to identify the best process control parameter. Sputtering has been performed in an argon atmosphere using a triode source. The target was vacuum cast NiFe. Thermal oxide-coated Si wafers were used as a substrate. It was found that the substrate bias has a strong effect on λs; however, the thickness uniformity becomes unacceptable. The target voltage has been found to have no effect on magnetostriction. The value of λs however, can easily be modified by varying the sputtering pressure. Varying the pressure from 4 to 10 mTorr can change λs as much as 4×10−7 without degradation of the other film magnetic properties, such as anisotropy, coercivity, and magnetoresistance. Therefore, this method has been successfully used in control of λs in our thin-film magnetoresistive heads.
Monte Carlo low pressure deposition profile simulations
Authors: Rey Juan C. , Cheng Lie-Yea , McVittie James P. , Saraswat Krishna C.
Published: July 2002

The models and algorithms used for simulation of chemical vapor deposition (CVD) profiles in Stanford profile emulator for etching and deposition in integrated circuit engineering are described. In the CVD simulation direct deposition, re-emission, and surface diffusion are considered as the mechanisms for near surface mass transport. The re-emission process is characterized by a single surface reaction coefficient (or sticking coefficient) which condenses the complex physico-chemical mechanisms (physisorption, chemisorption, desorption) in a single probability that defines the final attachment of a reactive to a surface. For desorption process, different desorption models can be selected (cosine re-emission, specular reflection). Surface diffusion is modeled with a gaussian distribution function characterized by the diffusion length. A Monte Carlo approach is used to determine the deposition rates in arbitrary topologies and a string algorithm is used for the evolution of the surface. Iteration between them allows taking into account self-shadowing effects. Comparisons of experimental versus simulation results for SiO2 trench filling, that can be characterized by direct deposition and re-emission with a pure cosine desorption law and no surface diffusion are included.
Scanning probe metrology
Authors: Griffith J. E. , Grigg D. A. , Vasile M. J. , Russell P. E. , Fitzgerald E. A.
Published: July 2002

The high resolution, three-dimensional data provided by scanning probe microscopes makes them strong candidates for use in metrology. Many technological applications, such as integrated circuit metrology, require measurement precision to better than 10 nm. To achieve this level of performance, the nonlinear behavior of the piezoceramic actuators and of the probe–sample interaction must be carefully controlled. Positioning of the actuators can be addressed in a straightforward manner. The probe–sample interaction is, on the other hand, a difficult problem, which depends on the topography being measured.
Laser ablation deposition of TiN films
Authors: Kools J. C. S. , Nillesen C. J. C. M , Brongersma S. H. , van de Riet E. , Dieleman J.
Published: July 2002

Excimer laser ablation of TiN ceramic in vacuum and of Ti metal in N2 gas environment is used to deposit thin TiN films on Si substrates. The dependence of thin film properties (stoichiometry, morphology, and crystallinity) on process parameters such as substrate temperature, background pressure, target quality, applied voltages, and laser fluence is investigated. It is shown that it is virtually impossible to grow stoichiometric TiN films by ablation of Ti in a N2 background atmosphere at a substrate temperature of 300 K. At a substrate temperature of 300 °C and a background pressure below 1 × 10−8 mbar, it is possible to grow polycrystalline TiN films with good stoichiometry from a TiN ceramic target. Comparison with other physical and chemical thin film deposition techniques shows that films of equivalent quality can be grown at a considerably lower substrate temperature (150 –250 °C lower) by this technique, a feature that opens interesting technological perspectives.
Titanium and tantalum coatings on aluminum nitride
Authors: Carter W. B. , Papageorge M. V.
Published: July 2002

Thin films of titanium and tantalum were deposited on aluminum nitride substrates by vacuum evaporation at T=573 K. Pull tests of film/substrate interfacial strengths yielded 57.57±14.41 and 67.71±9.31 MPa for Ti/AlN and Ta/AlN, respectively. The coatings have been examined by profilometry, scanning electron microscopy, x-ray diffraction, Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS). Depth profiles were performed with both AES and XPS. The data indicate that nitrogen, from either the substrates or their surfaces, diffuses into the titanium films and combines with them chemically. No clear evidence for a similar reaction between tantalum films and the AlN substrates was found.
Thermal desorption from hydrogenated and oxygenated diamond (100) surfaces
Authors: Thomas R. E. , Rudder R. A. , Markunas R. J.
Published: July 2002

Low energy electron diffraction (LEED) has been used to study the effects of atomic and molecular species of hydrogen and oxygen on the reconstructed C(100)-(2×1) surface. Thermal desorption spectroscopy was also used to study desorption products and kinetics from hydrogenated and oxygenated surfaces. Atomic hydrogen appears relatively inefficient at breaking C–C dimer bonds on the (100)-(2×1) surface. Atomic oxygen, in contrast, readily converts the surface from the 2×1 state to the 1×1 state. This process is reversible for a limited number of cycles before degradation of the surface obscures the 2×1 LEED pattern. Oxygen is thought to adsorb in one of two configurations, bridging carbon atoms on the surface, or double bonded to a single carbon atom on the surface. Thermal desorption of molecular hydrogen from hydrogenated C(100)-(2×1):H surfaces occurs at approximately 900 °C for a heating rate of 20 °C/s. Molecular hydrogen is the major desorption product and the desorption temperature appears to be coverage independent. Thus the desorption kinetics are most likely first order. Thermal desorption of carbon monoxide from oxygenated C(100)-(1×1):O surfaces occurs at approximately 600 °C for a heating rate of 20 °C/s. Carbon monoxide is the major product seen, with small quantities of carbon dioxide also observed. For increasing oxygen coverages, the desorption peak is observed to shift to lower temperatures. A peak shift to lower temperatures can be interpreted as either first order kinetics with a coverage dependent activation energy or second order kinetics. The reaction order is not known in this case, but from analysis of the peak shapes and from the fact that CO can desorb without prepairing, the data suggest that the reaction is first order.
Imaging monolayer structure by means of Auger electrons
Authors: Frank Douglas G. , Chyan Oliver M. R. , Golden Teresa , Hubbard Arthur T.
Published: July 2002

We report the complete angular distribution of 507 and 518 eV Auger electrons emitted from a monolayer of iodine atoms on single-crystal platinum, Pt(111) ((7)1/2×(7)1/2) R19.1°–I. This monolayer is of particular interest because: (i) it provides an opportunity to measure an angular distribution of relatively high kinetic energy Auger electrons emitted from a single monolayer of known structure; and (ii) the structure of the monolayer has been independently determined from scanning tunneling microscopy and low-energy electron diffraction, permitting one to unambiguously relate features in the angular distribution to the structure. The experimental angular distribution contains intensity minima along trajectories corresponding to the I–I internuclear directions and intensity maxima along trajectories corresponding to gaps between neighboring iodine atoms. A simulation of the angular distribution in which iodine atoms are treated as point-emitters and spherical blockers of Auger electrons predicts the features in the experimental angular distribution, and fits the data very closely (the correlation coefficient is >0.98). This result indicates that iodine atoms act predominantly to block Auger electrons in this energy range, producing silhouettes in the angular distribution. The locations and shapes of the silhouettes are therefore a direct consequence of the relative positions of atoms, making angular distribution Auger microscopy a useful technique for real-space imaging of surface atomic and monolayer structure.