bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic steps on Si(100) surfaces
Authors: Martin J. A. , Aumann C. E. , Savage D. E. , Tringides M. C. , Lagally M. G. , Moritz W. , Kretschmar F.
Published: July 2002

It is demonstrated that surface-sensitive electron diffraction measurements of steps on singular, but rough Si(100) surfaces are subject to a multiple-scattering effect that can be misinterpreted as double-atomic-height steps. It is shown that only single-height steps are present. This phenomenon can occur in any surface in which adjacent terraces have different terrace structure factors. Determination of terrace sizes can be influenced; however, they can be accurately made if the diffraction geometry is chosen appropriately. Possible terrace shape effects may also be inherent in the diffraction data.
Salt smoke: The formation of submicron sized RbCl particles by thermal evaporation in 0.5–100 Torr of argon and helium
Authors: Panitz J. K. G. , Mattox D. M. , Carr M. J.
Published: July 2002

We have shown that it is possible to form submicron-sized particles of a highly ionic compound RbCl by thermally evaporating the reagent salt in 0.5–100 Torr of inert gas. By collecting the particles on a surface and then carefully removing them, bulk powder can be collected. The ambient gas species, pressure, system geometry, and evaporation temperature profile affect the size and geometry of the particles which form. Evidence indicates that if strong convection currents are present during evaporation, the number of individual primary particles in the powder is increased and the number of sintered strings of primary particles is reduced. The primary particle size depends on the geometry of the evaporation source used and is independent of the ambient pressure. In argon, the size of the particles collected is independent of the distance between the collection plates and the source. In helium, the size of the primary particles collected from a single run can vary from ∼10 to 1000 nm; the particle size collected is strongly dependent on the distance of the collection plates from the evaporation source.
CO adsorption and dissociation on Rh(111)
Authors: de Koster A. , van Santen R. A.
Published: July 2002

Using the atom superposition and electron delocalization molecular orbital method, we studied the adsorption of C, O, and CO on different sites of Rh(111) represented by a small cluster of 29 Rh atoms. By calculating the activation energy of several possible reaction paths, the most probable mechanism of CO dissociation can be found. A stepped Rh(111) is simulated by a ridge of six extra Rh atoms. The influence of this ridge on both CO adsorption and dissociation will be discussed.
Evidence for two pinning mechanisms with noble metals on InP(110)
Authors: Cao Renyu , Miyano K. , Lindau I. , Spicer W. E.
Published: July 2002

Interfacial chemistry and Fermi-level movement for interfaces of noble metals on InP(110) prepared at room temperature (RT) and 80 K low temperature (LT) have been examined using photoelectron spectroscopy. An interfacial reaction is detected for all the RT interfaces as well as the LT Cu/InP interface, and the Fermi levels are pinned at 0.95 eV above the valence-band maximum (VBM). However, for LT Au/InP and Ag/InP, no reaction is seen, and the Fermi level is pinned around 0.7 eV above the VBM. The 0.7-eV pinning position at the near ideal LT Au/InP and Ag/InP interface is associated with metal induced gap states (MIGS), whereas, that at 0.95 eV is associated with defects formed during the interfacial reaction. These results indicate that both MIGS and defects can be important in the Fermi-level pinning and that the former is dominant only when the defect density is sufficiently low.
Mechanisms for success or failure of diffusion barriers between aluminum and silicon
Authors: Harper J. M. E. , Hörnström S. E. , Thomas O. , Charai A. , Krusin-Elbaum L.
Published: July 2002

Diffusion barrier layers with improved stability are needed in very large scale integrated (VLSI) devices to prevent aluminum from interacting with silicon, under the demanding constraints of shallow junctions and processing heat cycles. We present a comparison of the mechanisms controlling the integrity or failure of diffusion barriers at temperatures above 500 °C. Three classes of high-temperature barrier materials are discussed: amorphous metal alloys, conducting nitrides, and conducting oxides. The advantage of an amorphous barrier is shown to be minimal. Amorphous refractory metal alloys (W–Re) fail by intermetallic reaction with Al at ∼525 °C, well below their crystallization temperature, to form Al12(W,Re). This performance is only slightly better than a polycrystalline film of the same composition, and offers little improvement over pure W. Conducting nitrides (TiN, W–N) have been shown to be effective barriers up to 600 °C or higher, but only if exposed to air prior to Al metallization. In this case, we show evidence for the formation of interfacial aluminum oxide, which prevents further Al reaction. When not exposed to air, these nitrides fail as Al barriers at much lower temperature (450–500 °C) through the formation of Al3Ti and Al12W. Conducting oxides (RuO2, Mo–O) also prevent Al penetration up to 600 °C. Here, the growth of interfacial aluminum oxide is even more pronounced, and reduction of the barrier layers occurs. We conclude that the presence of an interfacial aluminum oxide layer is responsible for the high-temperature (600 °C) stability of diffusion barriers between Al and Si.
A surface analytical study of GaAs(100) cleaning procedures
Authors: Lu Z. H. , Lagarde C. , Sacher E. , Currie J. F. , Yelon A.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) have been used to examine the chemical composition of GaAs(100) surfaces after different standard cleaning sequences, using aqueous H2 SO4 :H2 O2/ HCl and H3 PO4 :H2 O2/ HCl solutions. XPS measurements show that the oxides, Ga2 O3 and As2 O3 , which remain at a relative concentration of 1.7:1 after H3 PO4 :H2 O2 :H2 O etch, are totally removed by the subsequent aqueous HCl solution. These same oxides, which have a relative concentration of 2.5:1 after H2 SO4 :H2 O2 : H2 O etch, are then not totally removed by HCl. Elemental arsenic was found to increase in concentration as the surface oxides decreased. The surface, initially gallium rich (Ga/As ratio 1.11), became arsenic rich (Ga/As ratio 0.93) after cleaning in HCl. The excess elemental As can be removed by subsequent treatment in NH4 OH. LEED patterns could be obtained only for H3 PO4 :H2 O2 /HCl cleaned surfaces. Au/Ti/GaAs Schottky diodes were made on both types of samples after cleaning. I–V measurements show that the diodes on the H3 PO4 :H2 O2/HCl cleaned surfaces have a better ideality factor (ranging from 1.15 to 1.20), than those on H2SO4 :H2 O2/HCl cleaned surfaces (ranging from 1.20 to 1.25), while the barrier heights are about the same for both (∼0.74 eV).
Studies of individual nanometer-sized metallic clusters using scanning tunneling microscopy, field emission, and field ion microscopy
Authors: Castro T. , Li Y. Z. , Reifenberger R. , Choi E. , Park S. B. , Andres R. P.
Published: July 2002

Individual clusters of gold, grown in a gas aggregation reactor and deposited on a variety of different substrates, have been studied using a combination of scanning tunneling microscopy, field emission techniques, and field ion microscopy. The scanning tunneling microscope studies show that by proper choice of substrate, individual nanometer-sized clusters can be reproducibly imaged and studied. The field emission and field ion microscope studies yield information about the work function and melting temperature of individual supported clusters.
Ta as a barrier for the Cu/PtSi, Cu/Si, and Al/PtSi structures
Authors: Chang Chin-An
Published: July 2002

The effect of Ta as a barrier is studied for the Cu–PtSi, Cu–Si, and Al–PtSi reactions. Using Cu/Ta/PtSi structure, an extensive mixing among Cu, Ta, and PtSi is observed around 300 °C, with both an increase in the sheet resistance and detection of Cu silicides. Comparison with the reactions of Cu/Ta/Si and Al/Ta/PtSi structures helps in understanding the mechanisms involved. The Cu/Ta/Si structure also shows mixing at 300 °C, and the Al/Ta/PtSi at 450 °C. The work indicates that, for the Cu/Ta/PtSi structures with and without barriers, Cu penetrates through the Ta layer to react with PtSi and Si, forming Cu silicides, releasing Pt for outdiffusion, and diluting the unreacted PtSi. The high affinity of Cu toward Si is suggested to play a major role in such reactions, which is consistent with the work using other barrier materials for the Cu/PtSi/Si structures, including amorphous carbon.
Laser-induced and room temperature etching of copper films by chlorine with analysis by Raman spectroscopy
Authors: Tang Hua , Herman Irving P.
Published: July 2002

The reactions of copper films on glass with chlorine are studied at room temperature with and without a focused laser (4880 Å) present for localized heating. Raman scattering is used to follow the transformation of the copper film in situ to the copper chlorides, CuCl and CuCl2. At room temperature, a thin film forms on top of partially passivated copper with chlorine present, which is identified to be CuCl by Raman spectroscopy at 77 K. This copper chloride film is locally desorbed by laser heating in vacuum. Deposition-like features are produced on passivated Cu films and CuCl-on-Cu films by laser heating with Cl2 present. Raman spectroscopy shows that these features are CuCl2, with CuCl sometimes also present. After the copper chloride is removed, ∼4 μm wide etched features remain in the copper film. The Raman spectrum of anhydrous CuCl2 presented here is apparently the first such measurement.
Radio frequency sputtering of tungsten/tungsten nitride multilayers on GaAs
Authors: Boher Pierre , Houdy Philippe , Kaïkati Pierre , Van Ijzendoorn L. J.
Published: July 2002

Thick tungsten nitride films have been deposited on GaAs substrates using a reactive rf-sputtering system. The optical indexes of the WNx films (determined by in situ kinetic ellipsometry) and their nitrogen contents (determined by Rutherford backscattering), have been determined versus the pressure ratio PN2/Ptot. Using reactive sputtering conditions which provide highly nitrogenated films, W/WNx twenty period multilayers with nanometric layer thicknesses have been deposited. The experiment has also been monitored in situ by kinetic ellipsometry at 1.96 eV and the multilayer has been analyzed ex situ by grazing x-ray reflection measurements at 1.54 Å. The composition of the different layers has been determined precisely by Rutherford backscattering analysis. Both W–WNx and WNx–W interfaces in the multilayer appear very sharp by kinetic ellipsometry. This is confirmed by the occurrence of well defined Bragg peaks on the grazing x-ray reflectivity curves in spite of the low density contrast between W and WNx layers.
Reusable quartz crystals for thickness monitoring in thin film deposition
Authors: Chao W. K. , Wong H. K.
Published: July 2002

Substantial savings on quartz thickness sensors can be made by using a thin buffer layer of photoresist. Any additional coating on the buffered sensor can be washed away easily by acetone, without damaging the sensor electrodes. Therefore, the sensor can be reused many times.
Scanning tunneling microscopy studies of substituted polyaniline thin films
Authors: Porter T. L. , Lee C. Y. , Wheeler B. L. , Caple G.
Published: July 2002

The technique of scanning tunneling microscopy was used to obtain images of structures present on the surface of chemically prepared and electrochemically prepared poly-hydroxy-aniline thin films. In both cases, amorphous island-like structures were present along with long polymer strands. These polymer strands had an average diameter of 20±5 Å and a periodicity along the strands of about 30 Å. These dimensions suggest a coil or simple helical conformation for the polymer strands.
Oxidation and corrosion studies by valence band photoemission
Authors: Sherwood P. M. A.
Published: July 2002

A combination of valence band x-ray photoelectron spectroscopy (VXPS) interpreted by Xα calculations, and x-ray diffraction is discussed as a means of understanding the surface chemistry associated with oxidation and its prevention. The cluster models used to interpret VXPS for oxide systems are discussed, and the spectrum of cuprous oxide is examined in detail. It can be seen that good agreement can be obtained with the valence band spectra of oxidation films and corrosion inhibitor films. Examples are given that show how VXPS can reveal chemical features that cannot be obtained from core x-ray photoelectron spectroscopy.
Ultralow density plume measurements using a helium mass spectrometer
Authors: Jafry Y. , Vanden Beukel J.
Published: July 2002

Gravity Probe-B and the Satellite Test of the Equivalence Principle are two proposed experiments in basic physics which will utilize drag-free satellites equipped with proportional helium thrusters. In order to calibrate the thrust systems for precise aeronomic measurements, it is necessary to model the effects of thruster plume impingement. Conventional plume models are invalid, owing to the high degree of rarefaction in the nozzles (Kn=0.01–1.1). An experiment was devised to measure the plume angular mass flux distribution using a helium mass spectrometer. The results suggest that the plume shapes are unchanged with mass flows around the nominal, and are generally wider than for conventional spacecraft control jets. A narrowing effect was observed at very low mass flows, in qualitative agreement with Monte Carlo results from the literature. The continuum model for the plume was found to be surprisingly accurate at nominal mass flows, and the inverse-square law was demonstrated to be a valid description of the far-field radial density profile.
Comparison of two filtered cathodic arc sources
Authors: Falabella S. , Sanders D. M.
Published: July 2002

Cathodic arcs produce a highly ionized metal vapor which has proven useful in the production of dense, adherent coatings. For many applications, the macroparticles normally produced by the cathodic arc are unacceptable and must be filtered out. We have developed two filtered cathodic arc sources which have distinctly different operational characteristics. One of these makes use of so-called ‘‘steered arc’’ magnetic control of the arc trajectory, while the other employs a different form of arc control. The ion transmission efficiencies of these sources were improved by carrying a portion of the arc electron current through the filter.
Photoreflectance study of the surface Fermi level at (001) n- and p-type GaAs surfaces
Authors: Yin X. , Chen H-M. , Pollak F. H. , Chan Y. , Montano P. A. , Kirchner P. D. , Pettit G. D. , Woodall J. M.
Published: July 2002

We report a photoreflectance study of Fermi level pinning (VF) on (001) n- and p-type GaAs with large, uniform electric fields. Surface photovoltage (Vs) effects were evaluated as a function of temperature (77 K<T<450 K), pump beam wavelength (633 and 407 nm) and W–metal coverage (in situ). The dependence of the measured barrier height, Vb (=VF−Vs), on T can be explained by a modification of the theory of M. Hecht [Phys. Rev. B 41, 7918 (1990)] yielding values of VF =0.77±0.02 V and VF =0.75±0.02 V for n- and p-type GaAs, respectively, at 300 K. In addition, by introducing the ratio (r) of the area of the surface states to the illuminated area into the theory of Hecht we have been able to estimate the density of surface states on the GaAs surface. The effect of metal coverage is to increase r and reduce the influence of Vs.
Electrical and dielectric properties of thin film BaTiO3 capacitors deposited by radio frequency magnetron sputtering
Authors: Shi Z. Q. , Jia Q. X. , Anderson W. A.
Published: July 2002

Thin film BaTiO3 capacitors were deposited by rf magnetron sputtering. The dielectric constant, dielectric loss, conductivity, and breakdown strength of the capacitor were investigated as a function of the sputtering condition and the capacitor design. Films deposited at low substrate temperature were amorphous whereas those deposited at a high substrate temperature were polycrystal. Amorphous films had a low conductivity (7.7 × 10−11/Ω cm), a high breakdown voltage up to 2.5 × 106 V/cm, and a small dielectric constant of around 16. Polycrystal films yielded a high dielectric constant up to 330. However, they also lead to large conductivity. With double layer or graded design, i.e., amorphous layer on the top of polycrystal layer or graded layer, the conductivity could been reduced to the same order as in the amorphous films. The dielectric constant and breakdown voltage of the capacitor with double layer structure were found to be as high as 210 and 1.2 × 106 V/cm, respectively. The dielectric properties of the capacitors were measured over a wide range of frequency (12 Hz–100 kHz). The frequency dependence of the dielectric constant and dielectric loss were explained by polarity, leakage, and interface dissipation mechanism, respectively.
Surface roughness development during sputtering of GaAs and InP: Evidence for the role of surface diffusion in ripple formation and sputter cone development
Authors: MacLaren S. W. , Baker J. E. , Finnegan N. L. , Loxton C. M.
Published: July 2002

Surface diffusion is shown to be the important factor in sputter–induced ripple and cone development on GaAs and InP surfaces for conditions typical of depth profiling when using surface analysis techniques. Ripple formation has been observed on both GaAs and InP when sputtered using Cs+ and O+2 ion beams. For GaAs, the ripple ‘‘wavelength’’ increases with sample temperature in the range from 45 to 100 °C, in qualitative agreement with the surface diffusion model of Bradley and Harper. No ripple formation is observed when the GaAs sample is cooled to −30 °C where surface diffusion is limited, or heated above 100 °C, where a proposed surface phase change may alter the diffusion rate. Ripple development also occurs on InP, but it is impossible to observe at 100 °C due to extensive cone formation. At this elevated temperature, Ar+ sputtering of InP leads to a surface enrichment of indium that is accompanied by a change in the In M4,5N4,5N4,5 Auger line shape toward that for indium metal. This result, together with the observation that cone formation is eliminated for sputtering at −20 °C, supports the intrinsic model where sputtering causes indium enrichment and surface diffusion that results in the agglomeration of indium metal into clusters. These clusters produce cone formation, possibly through the difference in sputter rates of indium and InP.
Initial boronization of the DIII–D tokamak
Authors: Phillips J. , Hodapp T. , Holtrop K. , Jackson G. L. , Moyer R. , Watkins J. , Winter J.
Published: July 2002

A system has been installed to deposit a thin film of elemental boron on the walls of the DIII–D tokamak, in order to reduce the influx of impurities during plasma discharges. Subsequently new regimes of substantially improved tokamak energy confinement were obtained. The deposition of the boron layer is achieved during a glow-discharge session using a helium-diborane gas mixture and a film of ≊100 nm is deposited. The boronization system includes special storage and handling precautions for the diborane, a delivery and metering system for the glow discharge, modifications to the tokamak’s residual gas analyzer system, and a dedicated system for handling and neutralizing the exhaust gas from the tokamak. Tokamak discharges with similar parameters before and after boronization are used to characterize the effects of the boron film. Nickel has been reduced by a factor of 30, while impurities such as oxygen and carbon are reduced fivefold. A system of pulsing the glow discharge has been developed in order to improve the uniformity of the film applied
Ion and neutral energies in a multipolar electron cyclotron resonance plasma source
Authors: King G. , Sze F. C. , Mak P. , Grotjohn T. A. , Asmussen J.
Published: July 2002

Discharge species energies have been measured in a multipolar electron cyclotron resonance (ECR) plasma source excited in the TE211 mode at 2.45 GHz. Diagnostic measurements were performed in argon gas discharge with a 12.5-cm-diam multipolar ECR reactor operating in the 0.5–7-mTorr pressure regime. The experimental diagnostic techniques of (1) laser induced fluorescence, (2) emission spectroscopy, (3) Langmuir probes, and (4) multigrid energy analyzer measurements were employed. The ion and neutral energies versus pressure, input power, and position were measured for two static magnetic field configurations: (1) 8 pole/8 magnet and (2) 4 pole/8 magnet. In both configurations the ion energies are (1) low (<30 eV) and relatively monoenergetic, and (2) decrease with increasing pressure, and (3) increase slightly with increasing power. The 4 pole/8 magnet configuration exhibits the lowest average ion energy, approximately 11 eV, and has less neutral gas heating (<0.07 eV) as the input power is increased to 700 W.
Structural and optical studies in oxygenated amorphous CdTe films
Authors: Espinoza-Beltran F. J. , Zelaya O. , Sanchez-Sinencio F. , Mendoza-Alvarez J. G. , Farias M. H. , Baños L.
Published: July 2002

Amorphous oxygenated CdTe films (a-CdTe:O) were grown by the radio-frequency sputtering deposition technique in an Ar–N–O atmosphere; by increasing the nitrogen partial pressure in the growth chamber we are able to increase the amount of oxygen in the films in the range: 0–66 at. %. Auger analysis indicated that only Cd, Te, and O were present in the different samples. X-ray diffraction patterns showed that the incorporation of oxygen leads to the amorphization of the zinc blende lattice. The optical absorption spectra for each sample was measured from optical transmission and photoacoustic techniques, and using the Tauc model for amorphous materials the band gap energy was obtained. From the analysis of the structural and optical measurements we propose that the a-CdTe:O films are ternary semiconductors described by the formula: [CdTe]1−xOx, and that they do not show evidence of any phase mixture and/or precipitates.
Bias voltage diagnostics during oxide etch in Drytek 384T
Authors: McNevin S. C. , Vitkavage D. J. , Bredbenner C. N.
Published: July 2002

This article will report the results of voltage measurements across a matching network capacitor in a commercial rf etch machine during oxide etching. It will be demonstrated that this ‘‘bias voltage’’ is an accurate way to measure endpoint, especially for patterned wafers with small open oxide areas which are difficult to measure with optical emission endpoint. It will also be shown that the impedance between the wafer and the wafer platen can have a strong effect on this bias voltage. The presence of an intervening layer of insulating oxide, either from back side wafer oxide or from platen anodization, can reduce the magnitude of the bias voltage. When the bias voltage is changed by changing the rf power, there is a linear change in the oxide etch rate. When the bias voltage is changed by changing the layer of intervening oxide, there is no corresponding change in the oxide etch rate. One interpretation is that the change in the bias voltage due to the voltage drop across the intervening layer of oxide does not affect the voltage difference between the wafer and the plasma, which is the critical voltage difference in terms of etching.
Experimental modeling of inductive discharges
Authors: Chevalier Gaétan , Chen Francis F.
Published: July 2002

The density profile and efficiency of inductively excited helicon wave discharges are found to be sensitive to parameters not usually considered in theoretical treatments. A diverging magnetic field in the antenna region increases the central density by a factor of five and the total plasma production by a factor of two. A carbon or boron nitride aperture limiter also increases the density, but only if placed under a particular part of the antenna. Theoretical modeling can be carried out only after the important variables are found by exploratory measurements such as these.
Comparative study of the crystal structure of synthesized CuGa1−yInyTe2 compounds
Authors: León M. , Merino J. M. , Martin De Vidales J. L.
Published: July 2002

The Rietveld method for structure refinement has been used to study the synthesized CuGaTe2, CuGa0.8In0.2Te2, CuGa0.5In0.5Te2, CuGa0.2In0.8Te2, CuInTe2 compounds. The discrepancy index are under 0.0806 for Rp, 0.1043 for Rwp, 0.0842 for RB, and 0.1460 for RF. The derived structural parameters at 26.5 °C follows linear regression laws: a=(0.602 22+0.016 25y) nm and c=(1.194 95+0.045 06y) nm, where y is the In contents. Both the ratio between lattice parameters η=c/2a and the anion displacements x[Te] diminish with the increase of In contents. Introducing In in CuGaTe2 produces an interchange in the geometrical behavior (bond distances) between Cu and Ga atoms. The distortion of Te tetrahedra increases with the In contents.
Mo–Si multilayer as soft x-ray mirrors for the wavelengths around 20 nm region
Authors: Kim D. , Lee H. W. , Lee J. J. , Je J. H. , Sakurai M. , Watanabe M.
Published: July 2002

Molybdenum–silicon multilayer soft x-ray mirrors have been fabricated using a magnetron sputtering system. Their structures have been characterized by x-ray diffraction and reflectivities at normal incidence have been measured by using monochromatized synchrotron radiation in the 18–24 nm region. A normal incidence reflectivity as high as 40% at 20.8 nm was achieved.
Model for the growth and reactivity of metal films on oxide surfaces: Cu on ZnO(0001̄)–O
Authors: Campbell C. T. , Ludviksson A.
Published: July 2002

In the many studies of vapor deposition of late transition metals on single-crystal oxide surfaces, never has a low-energy electron diffraction superstructure been observed in the first layer. Although layer-by-layer behavior is often reported at ≤300 K, annealing the films generally leads to irreversible clustering into thick islands that cover a tiny part of the oxide. We discuss here a growth model that explains these general observations and is also consistent with the expected energetics for metal atom diffusion over oxide and metal terraces and up and down over the edges of metal islands. We briefly review our recent studies which led to this model, in which the structural, electronic, and chemical properties of Cu films on the oxygen-terminated ZnO(0001̄)–O surface were examined. At coverages beyond a few percent, vapor-deposited Cu adatoms become nearly neutral. Their chemical behavior indicates that they form two-dimensional (2D) islands with metal-like Cu–Cu distances, much shorter than the substrate lattice parameter. Further deposition of Cu leads to spreading of these 2D islands without forming thicker layers, until about 55% of the surface is covered. Thereafter, these Cu islands grow thicker without filling the voids between islands, except at a rate much slower than the rate at which Cu vapor strikes in these voids. Our new model shows that a large fraction of an oxide surface will first be covered by 2D islands during metal deposition at low temperatures due to a kinetic effect.

This occurs even when the metal’s adsorption energy on itself significantly exceeds its adsorption energy on the oxide (i.e., when 3D clustering is thermodynamically favored), provided the difference in these energies does not exceed the energy of 2D evaporation from island edges onto terraces. As soon as islands nucleate in the second layer, 2D spreading ceases and energetic pathways open that allow metal atoms to migrate up from the oxide terrace into this new layer. This can lead to thick, flat-topped islands. Atom-thin (2D) Cu islands on ZnO(0001̄)–O react with CO, O2, H2O, HCOOH, and CH3OH very much like Cu(110), although there are some differences: The transiently adsorbed H and CO2 products of HCOOH dissociation migrate off or under the Cu islands and interact strongly with ZnO sites, and Oa is not as good a Bro/nsted base as on Cu(110). Annealed 3D islands behave much like Cu(111). We present here new results for methyl iodide adsorption and methyl dissociation on these Cu islands which further support this general picture.
Development of a high-resolution quadrupole mass spectrometer capable of detecting 3He and 4He in a hydrogen isotope atmosphere
Authors: Hiroki S. , Abe T. , Murakami Y. , Yanagishita K. , Nakamura S.
Published: July 2002

A high-resolution quadrupole mass spectrometer (QMS) which can detect 3He in HD and 4He in D2 has been developed. The QMS is equipped with two resolving powers, i.e., a high-resolution mode and a normal one, and voltages for realizing the two modes are supplied by a common circuit. The high-resolution mode adopts a condition of the second stability zone (zone II) in the Mathieu diagram and can analyze a range of 1–9 amu. The detectable peak ratios of 3He/HD and 4He/D2 were obtained at roughly 0.1 and 10−4, respectively. The normal mode adopts the first stability zone (zone I) and has an analyzable range of 1–60 amu.
Residual current of the modified Lafferty gauge
Authors: Gotoh Nobuaki , Momose Takashi , Ishimaru Hajime , Paitich Ron
Published: July 2002

For extreme high vacuum pressure measurements a modified gauge of the type described by Lafferty was fabricated [J. M. Lafferty, J. Appl. Phys. 32, 424 (1961)]. To determine the limit of low pressure measurement, its residual current was experimentally estimated. Residual current consists of x-ray-produced photoelectron current and electron stimulated desorption (ESD) ion current. Residual current was studied using the Bayard–Alpert method [R. T. Bayard and D. Alpert, Rev. Sci. Instrum. 21, 571 (1950)]. The linear relationship between emission current and residual current was obtained. The ratio of x-ray-produced photoelectron current to emission current was on the order of 10−7; the ratio of ESD ion current to emission current was on the order of 10−8; both ratios were obtained using a cleaned stainless steel anode. In order to investigate the upper limit of ESD ion current, the anode was exposed to oxygen gas at a fixed pressure and ESD ion currents were measured as a function of exposure. The upper limit of the ratio of ESD ion current to emission current was on the order of 10−5; residual current was on the order of 10−16 A with an emission current of 10−9 A. Sensitivity obtained was 4×10−3 A/Pa with an emission current of 10−9 A. Therefore, the predicted low pressure limit for the modified Lafferty gauge was on the order of 10−13 Pa.
High resolution photoemission and Auger parameter studies of electronic structure of tin oxides
Authors: Kövér L. , Moretti G. , Kovács Zs. , Sanjinés R. , Cserny I. , Margaritondo G. , Pálinkás J. , Adachi H.
Published: July 2002

The electronic structure of metallic Sn, polycrystalline Sn oxides, and (110) natural single crystal SnO2 (cassiterite) was studied by high resolution measurements of core and valence photoemission, photoinduced Auger spectra, and energy loss spectra. The advantage of in vacuo scraping in obtaining SnO surfaces is shown in comparison with surface cleaning by ion sputtering. Valence band x-ray photoemission spectroscopy spectra are interpreted by a cluster-type discrete variational Xα molecular orbital model, revealing the change in the electronic structure which leads to an increased conductivity. The use of the Auger parameter approach in gaining information on the initial and final state effects, ligand polarizability, and final state hole–hole repulsion energies are demonstrated for the case of tin oxides.
Effects of nitrogen pressure and ion flux on the properties of direct current reactive magnetron sputtered Zr–N films
Authors: Inoue Shozo , Tominaga Kikuo , Howson Ronald P. , Kusaka Kazuya
Published: July 2002

Zr–N films have been deposited by direct current reactive magnetron sputtering using a plasma emission monitoring (PEM) control system, where a signal proportional to the light emitted by the sputtered Zr in the plasma created by the electrical discharge was used to control the admission of the reactive nitrogen into the system. The Zr line set point for PEM control, φ, was used as a parameter; as the partial pressure of nitrogen rises the Zr line emission falls due to target poisoning. The influence of the nitrogen partial pressure on the Zr–N film structure, reflectivity, resistivity, and internal stress was investigated. The effect of ion flux during film deposition on the film properties was also investigated. The Zr–N films deposited at the Zr line set point φ=60%–70% revealed the minimum resistivity and goldlike reflectivity spectra. These films showed a ZrN single phase. The internal stress of the films showed a maximum at φ=60%–70%, which corresponds to the condition for depositing minimum resistivity films. The external magnetic field scarcely affected the optical and the electrical properties of the deposited Zr–N films. The internal stress of the films deposited at the lower φ (higher nitrogen partial pressure) was only dependent on the ion flux.
Outgassing reduction of type 304 stainless steel by surface oxidation in air
Authors: Odaka Kenji , Ueda Shinjiro
Published: July 2002

The effects of surface oxidation in air on the outgassing reduction from stainless steel are investigated. The outgassing measurement system of a throughput method is fabricated from a type 304 commercial-grade stainless steel. It is mirror-finished with buff- and electropolishing before the prebaking at 450 °C for 30 h. An evacuation cycle including 18-h baking at 200 °C is repeated four times to bring the chamber into the thoroughly degassed state before oxidizing in the atmosphere at 200 °C for 3 h. Then, four evacuation cycles including 200 °C baking are conducted. An outgassing rate of 6.1×10−11 Pa m3/s m2 is obtained at the thoroughly degassed state. The lowest value of 1.6×10−11 Pa m3/s m2 is attained in the first evacuation after the oxidation in air. A hydrogen peak is significantly reduced to be lower than a carbon monoxide peak. In the following three evacuations, the outgassing rate is maintained below 3×10−11 Pa m3/s m2, half of that in the thoroughly degassed state. These results confirm that the effect of the oxidation in air on the outgassing reduction is significant and is maintained during many evacuation cycles. The outgassing reduction is caused by the reduction of hydrogen. This may be due to the strengthening of a barrier function of an oxide layer on the stainless steel surface that prevents hydrogen from diffusing out of the metal and escaping into the vacuum.
Origin of stresses in sputtered elemental and alloy thin films
Authors: Hudson C. , Somekh R. E.
Published: July 2002

The properties of a sputtered film are strongly influenced by the deposition conditions. In this article we try to develop an understanding of the way in which the many parameters associated with sputtering process combine together to give only a few parameters which ultimately determine the film properties. In particular we consider the stresses in films and consider the conditions required to produce films with neutral stress, a state often required in films made in routine production. It is apparent that the product of the sputtering gas pressure and the substrate–target distance is a major factor in controlling the film stress, but also of relevance are the sputtering voltage and the substrate temperature. Many elemental and alloy films have been investigated, using variable argon pressures and substrate–target distances, at a low power and therefore a deposition temperature of approximately 20–40 °C. Detailed analyses have shown that a model of the total energy flux of particles bombarding the film is required to explain the results fully. In this article, the origin of film stress is ascribed to the total energy flux to the substrate per deposited atom, which in sputtering comes from both the arriving film atoms and the reflected neutrals.
Crystallographic tilting in high-misfit (100) semiconductor heteroepitaxial systems
Authors: Riesz Ferenc
Published: July 2002

A model is presented for the formation of crystallographic tilting (misorientation) in highly mismatched (100) oriented zinc-blende semiconductor heteroepitaxial layers grown on vicinal substrates. The model is based on the asymmetric generation of 60° misfit dislocations upon island coalescence in the initial growth process and the asymmetric strain release at substrate steps, and predicts a correlation between tilt angle and initial growth planarity. Good agreement is found between model and experimental data on the GaAs/Si and other systems. It is also shown that, if the net tilt is small, an azimuthal rotation of the tilt axis may occur, even if the system symmetry would hinder it. The influence of thermal annealing and thermal mismatch on the tilt is discussed as well.
Effect of supplied substrate bias frequency in ultrahigh-frequency plasma discharge for precise etching processes
Authors: Samukawa Seiji , Ohtake Hiroto , Tsukada Tsutomu
Published: July 2002

The characteristics of silicon etching using radio-frequency (rf) substrate biased ultrahigh-frequency (UHF) plasma determined by using a Cl2 etchant were investigated. The silicon etching rate and the etching profile were improved by decreasing the substrate bias frequency to less than 600 kHz. It is suggested that a large number of negative chlorine ions is generated in the high-density, low-pressure UHF plasma because of the extremely low electron temperature. The low-frequency substrate bias accelerates the negative and positive ions alternately to the substrate surface. As a result, the low-frequency biased UHF plasma can be used to achieve high-rate, highly anisotropic, and microloading-free silicon etching with a 600 kHz rf substrate bias.
Electron-induced surface chemistry: Production and characterization of NH2 and NH species on Pt(111)
Authors: Sun Y.-M. , Sloan D. , Ihm H. , White J. M.
Published: July 2002

Irradiating molecularly adsorbed NH3 with controlled fluences of 50 eV electrons on Pt(111) at 100 K leads to NH2, NH, and H species. Temperature programmed desorption shows dihydrogen desorption, confirming electron induced decomposition of ammonia, and a new NH3 desorption peak (210 K) attributed to hydrogenation of NH2. High resolution electron energy loss spectroscopy identifies NH2 through two vibrational features at 830 and 1392 cm−1 that are assigned to rocking and wagging modes, and NH through a single strong stretching feature at 3280 cm−1. NH was stable up to 400 K where it dehydrogenated, leaving N on the surface, which was stable up to 700 K. In x-ray photoelectron spectroscopy a N(1s) peak, shifted to lower binding energy, appears after electron irradiation.
Initial stages of Cu growth on ordered Al2O3 ultrathin films
Authors: Wu Yutong , Garfunkel E. , Madey T. E.
Published: July 2002

The initial stages of Cu growth (up to 20 Å) on ordered Al2O3 ultrathin films (∼20 Å thick) synthesized on a Re(0001) substrate are studied by low-energy ion scattering (LEIS) and x-ray photoelectron spectroscopy (XPS). LEIS results indicate that Cu grows as three-dimensional clusters on the Al2O3 films at both 80 and 300 K. XPS results show decreases in the Cu 2p3/2 binding energy and increases in the Cu L3M4,5M4,5 kinetic energy as a function of coverage. Analysis of these results indicates that Cu is not oxidized at the interface. For the coverage-dependent shifts in the Cu 2p3/2 peaks, the initial-state and final-state contributions and their relation to Cu cluster size are discussed.
Electrical characterization of Pt/SrBi2Ta2O9/Pt capacitors fabricated by the pulsed laser ablated deposition technique
Authors: Lee Jeon-Kook , Jung Hyung-Jin , Auciello O. , Kingon A. I.
Published: July 2002

Pulsed laser ablation deposition was used to synthesize polycrystalline SrBi2Ta2O9 layered ferroelectric thin films on the platinized silicon substrate. The surface roughness of the deposited film was an average of 4 nm. The titanium element was diffused to the SrBi2Ta2O9 layer through the platinum layer. P-E hysteresis loop for the Pt/SrBi2Ta2O9/Pt/Ti capacitor was well saturated and symmetric (Pr=3 μC/cm2, Ec=25 kV/cm).
Photochemical routes to silicon epitaxy
Authors: Dippel O. , Wright S. , Hasselbrink E.
Published: July 2002

The photochemistry of Si2H6 adsorbed on a hydrogen terminated silicon surface and the subsequent reactions of the photolysis products were investigated using high resolution electron energy loss spectroscopy and by measuring time-of-flight distributions with a mass spectrometer. The cracking pattern of the products ejected directly into the gas phase without colliding with either the surface or other molecules indicates that the primary photolysis channels yield mostly fragments that contain one silicon atom. It is likely that silicon is added to the surface by insertion of SiH2 radicals into Si–H bonds at the surface but there is little evidence for reactions that remove excess hydrogen from the surface at 110 K.
Some effects of boron and phosphorus doping on the properties of SiC:H films prepared using electron cyclotron resonance-chemical vapor deposition
Authors: Yoon S. F. , Ji R. , Ahn J. , Milne W. I.
Published: July 2002

Hydrogenated silicon carbide films (SiC:H) were deposited using the electron cyclotron resonance chemical vapor deposition method from a mixture of methane, silane, and hydrogen, and using diborane and phosphine as doping gases. The effects of changes in the diborane and phosphine levels on the deposition rate, optical band gap and conductivity were investigated. In the case of boron-doped films, there is evidence from Raman scattering analysis to show that films deposited at a low microwave power of 150 W were all amorphous and the band gap decreases as the diborane level is increased, whereas films deposited at a high microwave power of 800 W at low diborane levels are highly conductive and contain the silicon microcrystalline phase. These films become amorphous as the diborane level is increased, while the optical band gap remains relatively unaffected throughout the entire range of diborane levels investigated. In the case of phosphorus-doped films, Raman scattering analysis showed that the deposition conditions strongly influence the structural, optical, and electrical properties of the SiC:H films. Unlike boron doping, doping with phosphorus can have the effect of increasing the silicon microcrystalline phase in the SiC:H films, which were prepared at low (150 W) and high (600 W) microwave powers. Films prepared at high microwave power showed only small variations in the optical band gap, suggesting that good phosphorus doping efficiency can be achieved in films that contain the silicon microcrystalline phase (mc-SiC:H).
Properties of vanadium oxide thin films for ethanol sensor
Authors: Micocci G. , Serra A. , Tepore A. , Capone S. , Rella R. , Siciliano P.
Published: July 2002

Thin films of vanadium oxides for ethanol sensor applications were been prepared by means of rf reactive sputtering from a vanadium pentoxide target in an Ar–O2 atmosphere. Films with the best sensitivity and selectivity were obtained with 15% oxygen at a working temperature between 280 and 300 °C. These films show a very low sensitivity to CO, CO2, and CH4 and total insensivity to NH3.
Investigation of framework and cation substitutions in Keggin-type heteropoly acids probed by scanning tunneling microscopy and tunneling spectroscopy
Authors: Kaba M. S. , Song I. K. , Barteau M. A.
Published: July 2002

Scanning tunneling microscopy (STM) and spatially resolved tunneling spectroscopy were used to characterize surface arrays of heteropoly acids (HPAs) of the Keggin structural class. STM images revealed that these discrete oxide anions formed single, ordered monolayers on inert graphite surfaces, with lattice spacings of ∼11 Å, which is the characteristic dimension of the Keggin anion. However, increases in the lattice constants were observed in the STM images upon the substitution of the protons in H3PMo12O40 with larger counter cations such as Cs and K. This finding is consistent with those observed for bulk crystals of these salts. Substitution of metal ions in the Keggin ion framework (such as the replacement of Mo with W, or vice versa), led to insignificant variations in the lattice constants of the surface arrays. Tunneling spectroscopy measurements on discrete polyanions in the STM images revealed that the HPAs (both cation-exchanged and framework-substituted) exhibited current peaks in their respective current-voltage spectra, but at different applied potentials. The location of the current peak, or negative differential resistance (NDR) feature, was characteristic of the reducibility of the Keggin-type HPA in each case—the more reducible the HPA, the smaller the magnitude of the NDR peak voltage.
Preparation and characterization of superhard CNx/ZrN multilayers
Authors: Wu Mei-Ling , Lin Xi-Wei , Dravid Vinayak P. , Chung Yip-Wah , Wong Ming-Show , Sproul William D.
Published: July 2002

A dual-cathode, unbalanced dc magnetron sputtering system was used to grow CNx/ZrN multilayers on Si and polished M1 steel substrates at ambient temperature. Nanoindentation results showed that, under apprepriate conditions, it is possible to get CNx/ZrN multilayer coatings with hardness in the 50 GPa regime and modulus up to 410 GPa. X-ray diffraction studies revealed a strong correlation between hardness and the occurrence of (111) texture of ZrN. Cross-sectional transmission electron microscopy showed a high degree of crystallinity throughout the coating without obvious voids. These multilayers are crystalline only at small bilayer thicknesses on the order of 2 nm.
Reflection adsorption infrared spectroscopy of the oxidation of thin films of boron and hafnium diboride grown on Hf(0001)
Authors: Belyansky Michael , Trenary Michael
Published: July 2002

The oxidation of thin films of boron and hafnium diboride grown on a Hf(0001) single crystal surface was studied with reflection absorption infrared spectroscopy (RAIRS). For both the boron and hafnium diboride films an intense broad band near 1500 cm−1 as well as features near 750 and 1250 cm−1 were detected. These vibrational features are characteristic of solid B2O3. The formation of B2O3 is also indicated by x-ray photoelectron spectroscopy (XPS) by the appearance of a chemically shifted B(1s) peak at a binding energy of 193.1 eV. However, the sensitivity for detecting surface oxide formation is considerably higher for RAIRS than for XPS.
Optimized time-of-flight secondary ion mass spectroscopy depth profiling with a dual beam technique
Authors: Iltgen K. , Bendel C. , Benninghoven A. , Niehuis E.
Published: July 2002

High resolution depth profiling has been performed in a time-of-flight secondary ion mass spectroscopy (TOF-SIMS) instrument equipped with independent ion sources for sputtering (crater formation) and for SIMS analysis. In this dual beam mode a low energy sputter gun (Cs or any gas ion) allows a free selection of optimum sputter conditions with regard to depth resolution and matrix optimization. For secondary ion generation an independent high energy ion beam, optimized with regard to focussing and secondary ion yield (Ga or gas ion source) is applied. For different sputter gases (Ar, Xe, O2, and SF6), energies (0.3–2 keV) and angles of incidence a systematic investigation of B layers in Si and GaAlAs multilayers has been carried out. Decay lengths of 0.53 nm were achieved for low energy sputtering of B layers in Si with 0.6 keV SF5+. In this dual beam mode the depth profiling performance of TOF-SIMS exceeds that of state of the art quadrupole and magnetic sector field instruments in several fields of application, important in particular in microelectronics.