bluuebunny/crossref_metadata_2025 huggingface dataset:
Absolute calibration of small gas amounts
Authors: Winkler A.
Published: July 2002

A relatively simple but accurate calibration method for small gas amounts in the UHV region using ‘‘synthetic flash desorption spectra’’ is described. Well defined gas amounts are introduced into the vacuum chamber from a special glass vessel. The particle number in the glass vessel is obtained using a spinning rotor gas friction gauge for absolute pressure measurements. Furthermore, secondary standards can be produced and calibrated which allow a quick and easy absolute determination of the gas influx into the vacuum system. Desorption spectra obtained from calibrated tungsten filaments are used as secondary standards. As an example for the application of the methods described the saturation coverage and the initial sticking coefficient for hydrogen on various single-crystal surfaces have been determined. Further applications are the determination of the effective pumping speed in the vacuum chamber and the determination of the conductance of small tubes in the molecular flow regime. Additionally, the calibration of ionization gauges with spinning rotor gauges is discussed with respect to gas mixtures.
Stress control in reactively sputtered AlN and TiN films
Authors: Este G. , Westwood W. D.
Published: July 2002

Al and Ti planar magnetron targets have been sputtered in Ar/N2 mixtures to deposit AlN and TiN films on unheated substrates; rf and dc discharges were used for the AlN and TiN deposition, respectively. The N2 flow was always sufficient to produce a nitrided target layer and x-ray diffraction showed single-phase films of AlN and TiN1.2. In N2 discharges, the AlN film stress varied from −19 GPa (compressive) to +2.5 GPa (tensile) as the pressure increased from 0.2 to 5 Pa. Intrinsic tensile stress in reactively sputtered compound films has not previously been reported. A similar change was observed in the stress of TiN films. Zero-stress AlN and TiN films were obtained at ∼1 Pa for the sputtering conditions used. The rapid decrease in compressive stress with increasing pressure is associated with a rapid decrease in both target voltage (for constant applied power) and deposition rate. Calorimetry measurements of the power flux at the substrates show an increase with pressure. With increasing Ar content, at a constant pressure, the compressive stress decreases although the target voltage and deposition rate increase; the substrate power flux decreases. The surface coverage of N on the targets increases with increasing N2 pressure because the N+2 flux increases. The compressive stress is probably due to bombardment of the film by neutral N atoms reflected with high energy from the targets. The decrease in deposition rates and increase in substrate power density may result from increased sputtering rates of N atoms from the target with a consequent decrease in metal atom sputtering.
The electronic structure of cubic SiC grown by chemical vapor deposition on Si(100)
Authors: Hoechst Hartmut , Tang Ming , Johnson B. C. , Meese J. M. , Zajac G. W. , Fleisch T. H.
Published: July 2002

The electronic structure of chemical vapor deposition grown SiC(100) has been investigated with synchrotron radiation by angular resolved valence-band photoemission spectroscopy. SiC grown on n-type Si substrates was also n type with a Fermi level pinned at ∼2.0 eV above the Γ15 valence-band maximum. The band structure mapped along ΓX is in good agreement with theoretical predictions. A surface sensitive structure, which was nondispersive with k⊥, has been identified at ∼1.0 eV below EF. The initial reaction of Si(100) with propane at 1400 K resulted in C 2s emission at ∼7.5-eV binding energy. This emission indicates that the first reaction steps at the surface may lead to carbon bands which are typical for a ‘‘graphitic’’ material rather than a carbide. The emission of the C 2s level of SiC appears at ∼10-eV binding energy.
New partial pressure gauge for helium and deuterium using the ion backscattering principle
Authors: Akaishi K. , Uritani A. , Kubota Y. , Hori Y.
Published: July 2002

A new partial pressure gauge is proposed that is capable of measuring partial pressures of He and D2 gases in the mixture. The gauge consists of a conventional ion scattering spectrometer with a Wien filter. The influence of the residual gases CH4 and H2O on the pressure measurements of D2 and He in this gauge is discussed.
Double-beam integrated thermal vacuum sensor
Authors: van Herwaarden A. W. , Sarro P. M.
Published: July 2002

A low-offset thermal vacuum sensor, fabricated by standard bipolar integrated-circuit technology, based on the different sensitivity of two cantilever beams of unequal length is presented. After a short introduction on the working principle of the integrated thermal cantilever-beam vacuum sensor, the performance and offset of the device is calculated, and the outcome is compared to the experimental results for two different double-beam designs.
Deposition of silicon oxynitride thin films by remote plasma enhanced chemical vapor deposition
Authors: Tsu D. V. , Lucovsky G. , Mantini M. J. , Chao S. S.
Published: July 2002

We have deposited thin films of silicon oxynitride (SiO2)x(Si3N4)(1−x) by remote plasma enhanced chemical vapor deposition by infrared (IR) absorption, Auger electron spectroscopy (AES), and ellipsometry. The dominant IR stretching band feature shifts approximately linearly with frequency between the frequencies of the end member compounds and as such is a very good secondary standard for the determination of alloy composition. This behavior is also indicative of a homogeneous alloy, rather than a two-phase mixture. We have used AES to determine the O/N ratio and have combined this spectroscopy with the IR to confirm that the alloy films lie on the join line between SiO2 and Si3N4. Changes in the Si LVV line shape with alloy composition in the derivative AES spectrum make it impossible to use this feature as a measure of the relative Si composition. Finally, the ellipsometry measurements are also characteristic of a homogeneous alloy material.
Interaction of atomic hydrogen with cleaved InP. I. The adsorption stage
Authors: M’hamedi O. , Proix F. , Sébenne C. A.
Published: July 2002

The interaction of atomic hydrogen with the (110) face of InP, prepared by cleavage under ultrahigh vacuum, has been studied by Auger electron spectroscopy, electron energy-loss spectroscopy, low-energy electron diffraction, and photoemission yield spectroscopy. The interaction occurs in two stages: first, an adsorption of H, then a decomposition of the substrate. The adsorption stage is characterized by the covalent bonding of, most likely, one H atom per surface unit cell which induces a change in the surface reconstruction of the substrate, the surface unit mesh remaining 1×1. A hydrogen-induced surface state band, about 0.26 eV wide, is observed around 0.06 eV below the valence-band edge. Upon H adsorption, the Fermi level gets pinned in the gap at about 0.4 eV below the conduction-band edge on both n- and p-type samples, while the ionization energy decreases, the decrease reaching 0.35 eV at saturation.
Spectroscopic emission studies of O2/He and N2/He plasmas in remote plasma enhanced chemical vapor deposition
Authors: Tsu D. V. , Parsons G. N. , Lucovsky G.
Published: July 2002

We have analyzed He, O2 /He, and N2 /He plasmas of the remote plasma enhanced chemical vapor deposition of a-Si:H, silicon oxide, and nitride deposition by emission optical spectroscopy and by mass spectrometry. We have detected species such as atomic N and O as well as metastable He. These will be discussed relative to the deposition of silicon nitrides, oxides, and amorphous silicon.
Selectively thermalized sputtering for the deposition of magnetic films with special anisotropies
Authors: Cadieu F. J.
Published: July 2002

Special sputtering methods have been developed which allow films of rare-earth transition-metal permanent magnet systems that exhibit special magnetic anisotropies to be synthesized. Films have been synthesized that exhibit an easy direction of magnetization either out of the film plane, in the film plane, or in a particular direction within the plane of the films. Magnetic films have been applied during the sputter deposition to control the desired magnetic properties. Systems such as Nd2Fe14B have been synthesized so as to exhibit an easy axis either in or out of the film plane by varying the sputtering parameters. Films based on Sm2Co17 have been crystallized directly onto heated substrates that exhibit as sputtered in the film plane static energy products of 26 MG Oe. Films of SmCo5 have been made that exhibit coercivities >22 kOe and in-the-film-plane anisotropy constants of >10+7 erg/cm3. Recently, similar films have been made in the Sm–Ti–Fe system.
Study of metal surfaces by scanning tunneling microscopy with field ion microscopy
Authors: Kuk Y. , Silverman P. J. , Nguyen H. Q.
Published: July 2002

The reconstruction of Au and Ni surfaces has been studied by scanning tunneling microscopy (STM). The correlation between the tunneling tip geometry, observed by field ion microscopy, and the resultant STM image leads to an operational definition of STM resolution. New structural models for Ni(110)–H and Ni(110)–Au surfaces are proposed.
Heated Langmuir probe measurements of reactive direct-current magnetron plasmas
Authors: Bell Brent C. , Glocker David A.
Published: July 2002

A modified Langmuir probe has been used to study the plasma produced during dc reactive sputtering of AlN. The probe element was heated during the measurements to prevent the accumulation of an insulating layer of AlN. Ion and electron densities and electron energies have been determined as functions of cathode power, total pressure, and Ar:N2 partial pressure ratio. The electron densities increased as both cathode power and total pressure were increased, and decreased as the nitrogen content in the plasma was increased. Electron energies increased as cathode power was increased and total pressure was decreased and a strong interaction between partial pressure ratio and total pressure was observed. This interaction is understood as a result of changes in both the target voltage and the total collision cross section for electrons in the plasma as the nitrogen partial pressure increases.
The influence of heavier gases in pumping helium and hydrogen in an ion pump
Authors: Audi M. , De Simon M.
Published: July 2002

Pumping mechanisms for hydrogen and helium in an ion pump are quite different from the usual mechanisms by which other gases are pumped. Their sputtering yield is much lower and their diffusion higher than for heavier gases. Hence the pumping effect at the cathode plays an important role in pumping these two gases, being comparable with or even larger than the standard pumping at the anode. The effect of the presence of heavier gases on the pumping mechanisms for helium and hydrogen has been investigated for various pressures, concentrations, and gas species. The pumping speed for helium is shown to decrease as a function of heavier gas pressure; such a decrease is strongly dependent on helium pressure and on the amount of previously pumped gas. Pumping speed for hydrogen shows very different behavior: both considerable increases and decreases have been observed, depending on hydrogen pressure, heavier gas concentration and species, and temperature. Pumping speed for a getterable gas such as nitrogen, whose pumping mechanisms are well known, has been reported as a function of concentration of xenon for comparison. The various and sometimes contrasting phenomena responsible for these effects are analyzed, and their relative importance is pointed out.
An x-ray photoelectron spectroscopy study of Fermi level position and surface composition during formation and removal of oxides on InP
Authors: Lau W. M. , Sodhi R. N. S. , Ingrey S.
Published: July 2002

An x-ray photoelectron spectrometer coupled with an ultrahigh vacuum specimen preparation chamber was used to study the formation and removal of surface oxides on n- and p-type InP surfaces. Multiple oxide phases were formed by surface oxidation with molecular oxygen or UV/ozone. On n-type InP, the surface Fermi level initially moved down to 0.3 eV below the conduction band minimum (CBM) with low oxygen exposures but finally pinned at 0.1 eV with exposures higher than 1012 L. On p-type InP, the Fermi level moved monotonically towards the CBM and eventually pinned at 0.6 eV for an oxygen exposure higher than 1012 L. Although more indium and phosphorus oxides were formed upon prolonged air or ozone exposure, these final pinning positions were the same as for pure dry oxygen. The surface oxides could be desorbed at 458 °C resulting in a reduced surface band bending of <0.3 eV on both n- and p-type samples.
Reflection electron microscope imaging of an operating scanning tunneling microscope
Authors: Kuwabara M. , Lo W. , Spence J. C. H.
Published: July 2002

A scanning tunneling microscope (STM) has been operated inside the Philips EM 400T transmission electron microscope (TEM). The possibility of combining STM with dark-field reflection electron microscopy (REM) has been confirmed. Preliminary results using the STM for REM in a TEM indicate that this combination has the potential to be a powerful new technique for studying surfaces and for studying the basic physics of STM. The STM holder has been successfully used to obtain REM images while tunneling from the same region. The incident electron beam and the STM instrument do not appear to influence the imaging modes of each other appreciably. The tunneling gap and surface modifications due to tip contact have also been observed by REM. The calibration of the deflection of the tube type STM scanner by electron microscope images is reported. The effects of hydrocarbon contamination on STM operation in air or conventional vacuum have been studied.
Development of a two-stage light gas gun to accelerate hydrogen pellets to high speeds for plasma fueling applications
Authors: Combs S. K. , Milora S. L. , Foust C. R. , Gouge M. J. , Fehling D. T. , Sparks D. O.
Published: July 2002

The development of a two-stage light gas gun to accelerate hydrogen isotope pellets to high speeds is under way at Oak Ridge National Laboratory. High velocities (>2 km/s) are desirable for plasma fueling applications, since the faster pellets can penetrate more deeply into large, hot plasmas and deposit atoms of fuel directly in a larger fraction of the plasma volume. In the initial configuration of the two-stage device, a 2.2-1 volume (≤55 bar) provides the gas to accelerate a 25.4-mm-diam piston in a 1-m-long pump tube; a burst disk or a fast valve initiates the acceleration process in the first stage. As the piston travels the length of the pump tube, the downstream gas (initially at <1 bar) is compressed (to pressures up to 2600 bar) and thus is driven to high temperature (≊5000 K). This provides the driving force for acceleration of a 4-mm pellet in a 1-m-long gun barrel. In preliminary tests using helium as the driver in both stages, 35-mg plastic pellets have been accelerated to speeds as high as 4.0 km/s. Projectiles composed of hydrogen ice will have a mass in the range from 5 to 20 mg ( ρ≊0.087, 0.20, and 0.32 g/cm3 for frozen hydrogen isotopes). However, the use of sabots to encase and protect the cryogenic pellets from the high peak pressures will probably be required to realize speeds of ≊3 km/s or greater. The experimental plan includes acceleration of hydrogen isotopes as soon as the gun geometry and operating parameters are optimized; theoretical models are being used to aid in this process. The hardware is being designed to accommodate repetitive operation, which is the objective of this research and is required for future applications.
Reaction of Au4 and Ga(CH3)3 with GaAs(110)
Authors: Menon Madhu , Allen Roland E.
Published: July 2002

Simulations have been performed for Au4 clusters and Ga(CH3)3 molecules on the (110) surface of GaAs. Au clusters are found to disrupt the surface geometry, even though no intermixing is observed in these simulations for short times at low temperature. Ga(CH3)3 only weakly perturbs the surface, and is observed to adsorb in various symmetric configurations during the first picosecond.
Electronic surface changes induced in silicon by hydrogen, oxygen, and cesium coverages
Authors: Souzis A. E. , Seidl M. , Carr W. E. , Huang H.
Published: July 2002

The electronic surface state changes for low-energy cesium ion deposition, oxygen, and hydrogen adsorption on Si(100) are investigated. The change in surface potential (work function) is probed by electron reflection. This shift is then calibrated using photoemission onset measurements. The surface states are examined using ultraviolet photoemission spectroscopy (UPS). Results indicate that low work function surfaces attained previously by cesium and oxygen vapor deposition techniques are also attainable by ion bombardment. Results of work function and UPS measurements of atomic hydrogen adsorption are consistent with an asymmetric dimer model for the clean Si(100) surface. Atomic hydrogen adsorption on a cesiated and oxygenated surface has little effect on the work function, indicating that these surfaces may be viable in an actual dynamic negative hydrogen ion source.
Contamination reduction in vacuum processing systems
Authors: O’Hanlon John F.
Published: July 2002

Contamination is a major contributor to yield loss in a variety of vacuum processes. To produce submicron devices with high yield, it will be necessary to achieve low levels of contamination in the gas sources, the distribution systems, and use UHV processing systems. Processes such as hot wall reactors and high-pressure reactions have been shown to be more contaminating than processes which use cold wall reactors operating at low pressures. This paper reviews the state of the art in system design concepts, gas distribution systems, and new process technology.
Dry pumps operating under harsh conditions in the semiconductor industry
Authors: Troup A. P. , Turrell D.
Published: July 2002

The ability of ‘‘dry’’ primary vacuum pumps of the roots/claw configuration to handle semiconductor processes which previously could be pumped only with very frequent maintenance and great expense, has represented a quantum advance in pumping technology. A detailed knowledge of the mechanism by which dusty by-products are generated and transported through the machine, together with the characteristics of particulate deposition, is required when such pumps are serving production wafer-processing equipment. Experiments are described which detail the performance of a pump under conditions of high rates of dust loading together with techniques, by which reliability can be enhanced.
Mass flow measurement and control of low vapor pressure sources
Authors: Sullivan J. J. , Schaffer S. , Jacobs R. P.
Published: July 2002

Thermal mass flow controllers (MFC’s) have been universally accepted as the instruments of choice for the introduction and control of semiconductor process gases, and significant performance advances have been made in the technology within the past few years. However, there are many applications where standard thermal MFC’s are not the optimum choice of flow control technique. Specifically, these applications involve the accurate and repeatable delivery of low vapor pressure liquid or solid source vapors. Recent developments in pressure-based flow control have led to the successful solution of many of the liquid/solid source delivery problems, and promise to solve even more as further developments are made. A detailed discussion of these technologies will be presented.
Low-energy alkali ion scattering as a probe of resonant charge exchange on cesiated Cu(110)
Authors: Kimmel G. A. , Goodstein D. M. , Cooper B. H.
Published: July 2002

Intensities of K+ and Li+ scattered from cesium-covered Cu(110) surfaces are measured as a function of cesium-induced work function shifts ΔΦ, for ΔΦ up to ∼2 eV from the clean surface value. Various scattering geometries are used with beam energies ranging from 100 eV to 1 keV. Scattered K+ energy spectra indicate that the adsorbate-induced changes in intensity are uniform for all scattered K+ energies. Energy-integrated scattered K+ intensities are measured as a function of the work function Φ, for different beam energies and scattering geometries. The intensity decrease with decreasing Φ is attributed to an increase in the resonant electron transfer rate from the surface to the scattered particles. The work function dependence and the velocity dependence of the intensity decrease cannot be reproduced with a model of resonant charge transfer that treats the effect of the adsorbate layer as a uniform shift in the work function. To explain the observed charge transfer rates, both local and collective effects from the presence of low-coverage cesium adsorbates must be considered.
Adsorption of chlorine on clean and on oxygen preexposed Al(111)
Authors: Bermudez V. M. , Glass A. S.
Published: July 2002

The adsorption of Cl2 on clean and on O2 preexposed Al(111) has been studied using Auger and electron energy-loss spectroscopies, low-energy electron diffraction, temperature programmed desorption, and work function measurement. Near room temperature chlorine forms a disordered layer in a two-step process consisting of adsorption at surface sites, dominating at low exposure, followed by population of subsurface sites at higher exposure. Surface adsorption is characterized by a sticking coefficient of ∼0.1, an increase in work function of ∼1 eV, and a desorption peak at ∼200 °C. The subsurface phase exhibits a smaller sticking coefficient and work function change and no distinct desorption peak. Preadsorbed O blocks formation of subsurface species but not those formed in the initial adsorption step. Cl2 does not displace preadsorbed O, but O2 displaces some subsurface Cl. Chlorination is found to occur inhomogeneously rather than uniformly in a layer-by-layer mode.
Adsorption of CO, O2, and H2O on GaAs(100): Photoreflectance studies
Authors: Seebauer E. G.
Published: July 2002

Adsorption of CO, O2, and H2O on semi-insulating GaAs(100) has been examined with photoreflectance (PR). This work represents the first use of PR for quantitative adsorption measurements on semiconductors. In PR, the laser-induced change in surface reflectance is monitored as a function of wavelength. The resulting spectra are sensitive to changes in both the surface potential and the nature of surface states. Results at the E1 (3.0 eV) and E0 (1.4 eV) transitions are complementary to each other. Sticking coefficients S were obtained from E1 data for these gases, and S at low coverage was found to increase in the order CO≪O2<H2O. S decreases by at least four orders of magnitude for all the gases as saturation is approached. The results suggest that oxygen has two binding states that fill sequentially. Gas adsorption generally improves the communication between isolated surface states and the bulk.
A study of the chemical and physical interaction between copper and polyimide
Authors: Shih D-Y. , Paraszczak J. , Klymko N. , Flitsch R. , Nunes S. , Lewis J. , Yang C. , Cataldo J. , McGouey R. , Graham W. , Serino R. , Galligan E.
Published: July 2002

The interaction of pyromellitic dianhydride–oxydianiline based polyamic acid precursor with copper was investigated under various curing conditions. Two reactions were found to occur at the interphase boundary during the curing cycle: the interaction of Cu with polyamic acid, and Cu oxidation. It was found that the rates of both reactions are controlled by the oxygen level and supply of oxygen to the interface. Thus, the thickness of the polymer coating and the oxygen level in the curing ambient are found to be the rate determining factors. The presence of a high level of oxygen during curing of the polyimide film, particularly of a thin coating, was found to severely degrade the polyimide and to create an oxidized Cu film underneath. This resulted in a polyimide film having higher dielectric constant, reduced dielectric breakdown strength, a high metal-to-metal interface contact resistance, and a degraded adhesion between polyimide and the underlying Cu. The interface structure and the properties of the individual polyimide and Cu films can be improved significantly by inhibiting the interactions between Cu and polyimide and Cu oxidation during curing. This was achieved by either minimizing the oxygen content in the curing ambient or passivating the copper with a continuous chromium film. The passivation metal approach offers better tolerance to various curing conditions while still maintaining good-quality polyimide and Cu films. In addition to the Cu sheet resistance and parallel-plate capacitance measurements, the Fourier transform infrared reflection–absorption and electron spectroscopy for chemical analysis/Auger electron spectroscopy analytical techniques are used to study the imidization reactions and degradation.
Polymer surface reactivity enhancement by ultraviolet ArF laser irradiation: An x-ray photoelectron spectroscopy study of polytetrafluoroethylene and polyethyleneterepthalate ultraviolet treated surfaces
Authors: Chtaib M. , Roberfroid E. M. , Novis Y. , Pireaux J. J. , Caudano R. , Lutgen P. , Feyder G.
Published: July 2002

We have investigated by x-ray photoelectron spectroscopy (XPS) the surface of two polymers [polytetrafluoroethylene and polyethyleneterepthalate (PTFE) and (PET)] which were previously submitted to pulsed UV radiation delivered from an excimer laser (ArF: λ=193 nm). Treatments realized under different gaseous atmospheres allow us to point out mechanisms leading to several chemical transformations at the polymer surface. In the case of PTFE, the high-fluence irradiations produce defluorination with surface oxidation. The latter is mainly due to air moisture. The deposition of some ablated fragments on the surface has also been observed. For PET, the major modifications are produced below the ablation threshold. They are characterized by severe deoxidation due to the loss of CO and CO2. The irradiations under oxygen and nitrogen atmospheres show the possibility of grafting new functionalities at the polymer surface.
Polypeptide structures imaged by the scanning tunneling microscope
Authors: McMaster T. J. , Carr H. , Miles M. J. , Cairns P. , Morris V. J.
Published: July 2002

Using scanning tunneling microscopy (STM), it has been possible to image the structure of poly(γ-benzyl-L-glutamate) (PBLG) on deposition from solvent to substrate. Three forms of the molecule have been observed: a random coil conformation from dichloroacetic acid, an aggregated periodic structure from chloroform, and a periodic liquid crystalline array with strong helical character from dimethylformamide.
Observing the varying scanning tunneling microscopy image of graphite
Authors: Yao J. E. , Jiao Y. K.
Published: July 2002

Varying image of graphite was observed occasionally using a mechanically sharpened tip of Pt–Ir wire on the same sample area without any changing in bias voltage, tunneling current, scan rate. It is interesting that two images formed while the tip scanned in one frame and retraced in other frame were different. It is estimated that the end of the tip changed and the functioning part of the tip was not the same as the tip scanned and retraced.
Oxygen-induced sharpening process of W(111) tips for scanning tunneling microscope use
Authors: Wengelnik H. , Neddermeyer H.
Published: July 2002

Atomic resolution in scanning tunneling microscopy is usually obtained by a trial and error procedure for formation of the tunneling tip. The success of such attempts is particularly small when rough and contaminated surfaces have to be measured, where the macroscopic tip radius must be as small as possible in order to obtain a reasonable image of the sample. Here we report on a method by heating the tip in an oxygen atmosphere without an electric field, which routinely allows the generation of W(111) tips with an average tip radius of <2 nm. The sharpening of W tips by oxidation and annealing has already been reported by Müller [Z. Physik 108, 668 (1938)]. We have studied the mechanism of tip sharpening by scanning electron microscopy and in situ by field emission and field ion microscopy. The main effect is a preferential removal of (110)-like planes, which gives rise to strong facetting of the tip apex and the formation of sharp W microtips. The arrangement of microtips is essentially determined by the initial shape of the tip apex. In case of a very blunt tip the oxygen treatment produces several microtips. Normally, only the front microtip will contribute to the field ion microscopical images. By field desorption the outermost atomic layers were consecutively removed and the atomic structure of the microtip elucidated.
Segregation of Ca ions at the MgO(001) surface studied by neutral beam incidence ion scattering spectroscopy
Authors: Souda R. , Aizawa T. , Ishizawa Y. , Oshima C.
Published: July 2002

Low energy ion scattering with the use of a neutral He0 beam (NBISS) has been applied to analyze the structure of MgO(001) with Ca2+ impurities segregated from the bulk. The NBISS technique successfully avoids specimen charging, which is a common obstacle to analyzing the insulating surface by using ordinary ion scattering techniques. It is found that the segregated Ca2+ ions are substituted for the Mg2+ ions at the surface and are protruding from the original MgO plane by 0.4±0.1 Å.
Dynamics of the interaction of ethane with Ir(110)-(1×2)
Authors: Mullins C. B. , Weinberg W. H.
Published: July 2002

Experimentally determined values of the initial adsorption probability of ethane on Ir(110)-(1×2) are presented which probe the dynamics of the interaction. The data were obtained from supersonic molecular beam measurements with an incident kinetic energy Ei ranging between 1.2 and 24 kcal/mol, surface temperatures TS between 77 and 550 K, and incident angle θi between 0° and 45°. Experimentally determined values of the initial trapping probability ζ0 of ethane into a physically adsorbed state at TS=77 K as a function of Ei and θi and experimentally determined values of the initial probability of dissociative chemisorption S0 as a function of Ei,θi, and TS are presented. The value of ζ0 is found to decrease with increasing Ei consistent with the fact that an increasingly larger fraction of the incident kinetic energy must be dissipated in order for the molecule to physically adsorb.

The initial trapping probability has a relatively weak dependence on θi such that the value of ζ0 is found empirically to scale as Ei cos0.5 θi. Two distinct mechanisms of dissociative chemisorption on the bare surface are revealed. At low Ei a temperature-dependent trapping-mediated chemisorption mechanism dominates, while at relatively high Ei a temperature-independent direct mechanism dominates. For Ei less than 13.4 kcal/mol, the value of S0 decreases rapidly with increasing TS, consistent with a trapping-mediated mechanism. For a surface temperature of 154 K, S0 decreases with increasing Ei for 1.2≤Ei≤13.4 kcal/mol, in a manner similar to that for the molecular trapping probability. The data in the low Ei regime also support quantitatively a kinetic model consistent with a trapping-mediated chemisorption mechanism. The difference in the activation energies for desorption and chemisorption from the physically adsorbed, trapped state Ed−Ec is 2.2±0.2 kcal/mol. In the trapping-mediated chemisorption regime, the value of S0 is found to be rather insensitive to incident angle, scaling with Ei cos0.5 θi just as for trapping of molecular ethane into a physically adsorbed state. For a normal energy Ei cos2 θi greater than 8 kcal/mol, chemisorption via a direct mechanism becomes significant and increases with increasing Ei. Values of S0 in the direct chemisorption regime scale with normal energy and are independent of TS over the range from 350 to 1350 K.
Model studies of dielectric thin film growth: Chemical vapor deposition of SiO2
Authors: Crowell John E. , Tedder Laura L. , Cho Hee-Chuen , Cascarano Frank M. , Logan Mark A.
Published: July 2002

The reactive adsorption and decomposition of tetraethoxysilane is compared on Si(100) and SiO2 surfaces. The adsorption and decomposition behavior is compared to that observed for ethanol adsorption on both these surfaces. Tetraethoxysilane and ethanol both decompose to produce ethylene and hydrogen on Si(100). Ethylene desorption is also observed from decomposition of these molecules on SiO2. Ethanol adsorption on SiO2 is shown to model the chemistry of tetraethoxysilane on this surface. However, ethanol is significantly more reactive than tetraethoxysilane on the clean Si(100) surface. The decomposition is shown to be reaction limited, and distinct from that of adsorbed ethylene. The adsorbed species produced from adsorption of tetraethoxysilane on SiO2 at 450 K is shown to be a mixture of di- and triethoxysiloxanes.
CdZnTe/ZnTe and HgCdTe/CdTe quantum wells grown by molecular beam epitaxy
Authors: Feldman R. D.
Published: July 2002

The large range of band gaps and unique optical properties of II–VI semiconductors offer important opportunities for physics and device applications. Quantum wells based on Hg1−xCdxTe and Cd1−xZnxTe can give access to many of these properties, at wavelengths varying from the yellow to the long wavelength infrared region of the spectrum. High-quality quantum wells of these materials have been grown on GaAs substrates despite the large lattice mismatch. Growth, optical properties, and results of interdiffusion studies are discussed.
Plasma power dissipation at wafer surfaces measured using pulsed photoluminescence spectroscopy
Authors: Mitchell Annette , Gottscho Richard A.
Published: July 2002

A long-standing problem in plasma processing has been imprecise control and characterization of dissipated power. In particular, the partitioning of energy between gas phase and surface is not easily determined. Yet, for plasma process control and transfer from one reactor to another, it is important to monitor and control energy flux to the wafer. Using pulsed laser photoluminescence spectroscopy, we measure wafer temperatures nonintrusively as a function of time when radio frequency discharges are gated on and off. By so doing, the energy flux to the wafer surface is determined as a function of pressure, power, and frequency. This energy flux is then compared to the total power dissipated, which is calculated from measured current and voltage waveforms. We find that the fractional power dissipated at the wafer surface varies inversely with pressure regardless of applied power and frequency.
Stresses in sputter deposited thick coatings of chromium and zirconium diboride on polymeric composites
Authors: Chambers D. L. , Wan C. T. , Taylor K. A. , Susi G. T.
Published: July 2002

Moldable fiber impregnated composites are currently used to fabricate high temperature radomes, compressor vanes, and other structural parts for aerospace applications. When severe erosion and dust type environments are encountered, surface protection in the form of a hard erosion resistant coating is required. The purpose of this work is to estimate the total induced stress in chromium and zirconium diboride coatings deposited on fiber impregnated polyimide composites by magnetically enhanced direct-current (dc) sputtering. Process variables were sputtering pressure, power density, and coating thickness. Estimates of the various stress components were obtained using the bending-beam method where stress is calculated from the deflection of the composite beam formed by the combination of the substrate and coatings. The equivalent stiffness (EI) method was used to determine the relationship between the estimated stress components and the coating deposition parameters. It was observed that the coatings were in compression and the magnitude of the compressive stress was greatest in coatings deposited in an argon partial pressure of 2.0 mTorr. Compressive stress was found to increase with increased power density and coating thickness.
Angle-resolved tunneling between two atomic planes
Authors: Ezaki T. , Enomoto H. , Baba M. , Ikeda Y. , Oguro S. , Kuramochi E. , Ozaki H.
Published: July 2002

We propose a tunneling spectroscopy which observes the anisotropic nature of the Fermi surface by means of tunneling measurements between two parallel planar surfaces of crystals. In contrast to the scanning tunneling microscope, which observes the surface topography of solids, this method can observe the anisotropic nature of the Fermi surface. This method measures the tunneling current by rotating the probe surface over the sample surface. The results of the angle dependence of the tunneling current, which reflect the anisotropic nature of the Fermi surface, are calculated for 2H–TaS2. When the distance between the sample and probe surfaces is larger than the lattice constant, the anisotropic properties of the Fermi surface appear in the angle dependence of the tunneling current.
Observations of strain effects on the Si(001) surface using scanning tunneling microscopy
Authors: Swartzentruber B. S. , Mo Y. W. , Webb M. B. , Lagally M. G.
Published: July 2002

Scanning tunneling microscopy measurements of the influence of externally applied stress in Si(001) show that strain modifies the relative areas of the p(2×1) and p(1×2) domains, in agreement with low-energy electron diffraction (LEED) results. Strain produces a striped phase of majority and minority domains. The total repeat length between domains of the same type, given by the vicinal miscut of the surface, is conserved.
Scanning tunneling microscopy study of Si (001) and Si (110) surface structures resulting from different thermal cleaning treatments
Authors: Dijkkamp D. , van Loenen E. J. , Hoeven A. J. , Dieleman J.
Published: July 2002

We have studied the morphology and distribution of atomic steps on Si (001) and Si (110) with scanning tunneling microscopy. We find that native oxide removal at temperatures up to 1350 K leads to step pinning and bunching on Si (001) and to facetting on Si (110). Cleaning at temperatures in excess of 1450 K leads to regular step distributions. For both types of surfaces, the average step direction and step density reflect the macroscopic misorientation of the sample. However, locally the step edges tend to follow directions determined by surface reconstructions.
Microfabrication of integrated scanning tunneling microscope
Authors: Albrecht Thomas R. , Akamine Shinya , Zdeblick Mark J. , Quate Calvin F.
Published: July 2002

An integrated circuit-compatible process has been demonstrated for microfabricating arrays of scanning tunneling microscopes on silicon wafers. Each microfabricated scanning tunneling microscope (STM) incorporates a novel three-dimensional thin-film piezoelectric actuator which is capable of scanning the STM tip laterally over the sample surface and following surface topography. The actuator is in the form of a cantilever bimorph constructed from alternating layers of multiple metallic electrodes, dielectric films, and piezoelectric zinc oxide films. Each device is designed to scan a region 0.1×1 μm with low voltage drive, with a maximum vertical deflection of 15 μm, which simplifies sample approach. The dimensions of the device are 1000×200×8 μm. Operation of the device has been demonstrated by imaging graphite with atomic resolution. The piezoelectric actuator in this device is itself a significant contribution to the field of microactuators, with many non-STM applications.
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u measurements of film stress in AlN sputtered onto moving substrates
Authors: Bell B. C. , Glocker D. A.
Published: July 2002

An apparatus has been built, using a compact laser ranging device, which measures the in situ deflection of a cantilevered beam during thin-film deposition. The device can be transported in front of a source to study the evolution of stresses in films, analogous to those deposited in a web or in-line palletized coating process. We have measured the stress profile in direct-current reactively sputtered AlN on glass and polyimide as a function of total gas pressure and argon-to-nitrogen partial pressure ratio. We have also studied stress anisotropy by changing the beam orientation with respect to the transport direction. Typical film thicknesses were 250 nm and shielding restricted the incoming and outgoing angles of incidence to approximately 45°. Beam deflections for AlN on glass are typically linear with film thickness, revealing a constant incremental stress. However, beam deflections for the same films deposited on polyimide are highly nonlinear with thickness. For films deposited on glass at an argon-to-nitrogen ratio of  5:1, a sharp transition from neutral to a tensile stress of 11.5 Gdyn/cm2 takes place as the total gas pressure is raised from 3 to 5 mTorr. The stress in films deposited at ratio of  2:1 increases smoothly from 4.5 to 8.5 Gdyn/cm2 over the total gas pressure range of 2.5–7.5 mTorr. No significant stress anisotropy is observed. Repeated measurements give an estimate of the standard deviation for an individual stress value of  0.5 Gdyn/cm2, which includes the variability of the sputtering process as well as the error in the measurement technique.
Preparation and characterization of amorphous SiC:H thin films
Authors: Delplancke M. P. , Powers J. M. , Vandentop G. J. , Salmeron M. , Somorjai G. A.
Published: July 2002

Silicon carbide films were deposited by plasma enhanced chemical vapor deposition utilizing monomethylsilane (CH3SiH3). Silicon (100) and polycrystalline gold were used as substrates. A mass spectrometric analysis of the monomethylsilane plasma showed that the majority of the Si–C bonds were preserved in the gas phase. The composition, the density and morphology of the amorphous SiC:H (a:SiC:H) films were studied as a function of substrate temperature, composition of the ion flux bombarding the surface and the kinetic energy of these ions. The surface science techniques utilized for these investigations include x-ray photoelectron spectroscopy, Auger electron spectroscopy, scanning electron microscopy, Fourier transform infrared, and Raman spectroscopies.
Preparation and characterization of Li-doped ZnO films
Authors: Valentini A. , Quaranta F. , Rossi M. , Battaglin G.
Published: July 2002

ZnO:Li films have been prepared by radio frequency (rf) diode sputtering using a Li-doped ZnO target. The film depositions were performed in pure Ar or in 28% O2/Ar sputtering gas. For comparison undoped ZnO films were also prepared. Structural, electrical, and optical measurements have been performed on films prepared under different deposition conditions and the results related with Li content and O/Zn ratio obtained by nuclear reaction and Rutherford backscattering measurements, respectively. The Li doping has not changed the films c-axis preferential orientation typical of the undoped films, but it introduces a crystallite order change. As is expected by deposition of doped oxides the sputtering gas mixture is the main parameter controlling the dopant concentration. Moreover, the oxygen presence in gas mixture has also been found to play an important role in controlling the optical properties of the film. The change in lithium concentration does not affect the electrical resistivity if the deposition parameter values have been selected in order to produce undoped zinc oxide films with a high electrical resistivity.
Production of milliampere class mass-separated multiply charged ion beam
Authors: Amemiya K. , Tokiguchi K. , Sakudo N.
Published: July 2002

A new type of microwave ion source for a megaelectron volt ion implanter is designed to produce milliampere class multiply charged ion beams. This ion source has a single stage plasma chamber with both a mirror and an octopole magnetic field to produce milliampere class lower-charge-state ions efficiently. The extracted ion beam is mass separated, and a Kr2+ beam of 2.3 mA and an Ar2+ beam of 3.0 mA are obtained with absorbed microwave powers of 700 and 570 W, respectively. Combination of this new source with an ion accelerator should realize a milliampere class megaelectron volt ion implanter.
An x-ray photoelectron spectroscopy study of aluminum surfaces treated with fluorocarbon plasmas
Authors: Miller A. C. , McCluskey F. P. , Taylor J. Ashley
Published: July 2002

Aluminum surfaces are frequently exposed to fluorine containing plasmas during the processing of microelectronic devices. The compositions and chemistry of the films formed on the Al surfaces during exposure to fluorocarbon and fluorocarbon/oxygen plasmas have been studied by x-ray photoelectron spectroscopy. Multiple bonding states are observed in the Al 2p, O 1s, F 1s, and C 1s photoelectron lines. These were consistent with the formation of aluminum fluoride and oxyfluoride. Little, if any, fluorocarbon species were deposited on the Al surfaces. Oxygen in the plasma tended to decrease the amount of carbon on the film surfaces. The overall thickness of the passivation layer did not show large increases if the plasma contained an oxygen component.
Strain-induced surface reactivity: Low temperature Cr/W(110) nitridation
Authors: Shinn N. D. , Tsang K.-L.
Published: July 2002

Synchrotron photoelectron and Auger electron spectroscopies have been used to study the reaction of nitrogen with ultrathin chromium overlayers vapor deposited on W(110). Molecular nitrogen dissociates via a metastable π-bonded intermediate on Cr(110), the strained (1×1) Cr/W(110) monolayer and the (2×2) Cr/W(110) bilayer surfaces. However, the activation energy for dissociation of the π-bonded intermediate is lower on the strained overlayers than on Cr(110). This has been exploited to grow ultrathin CrN layers on W(110), which are spectroscopically indistinguishable from chromium nitride formed by reacting atomic Cr and N2 simultaneously on W(110) at 300 K. This demonstrates that nitridation proceeds via energetically equivalent pathways at isolated Cr adatoms on W(110) and at majority sites on the strained Cr/W(110) overlayers. In addition, an anomalous narrow band of states near the Fermi level is found for these surface nitrides and, tentatively, is attributed to unique surface or interface states of CrN:W(110). These findings suggest that strained pseudomorphic overlayers may be useful templates for low temperature nitride film growth.
Nanometer-scale instability at sliding interfaces: Tribological considerations in scanning tunneling microscopy
Authors: Jones L. A. , Thomas D. F.
Published: July 2002

We have developed a scanning tunneling microscope based upon an Inchworm(tm) motor for coarse approach control. Our aim was to fabricate an instrument from materials with matched thermal expansion coefficients to minimize thermal drift. The inchworm pushes a ceramic sled which carries the tunneling unit towards the sample until it is in range of the tube piezoscanner. When its motion is reversed (to disengage from the sled) interfacial forces at the sliding interface move the sled backwards (over distances between 100 nm and 20 μm) rather than allowing it to remain stationary. These forces vary depending upon the materials employed and we offer some recommendations regarding the choice of materials and the sled design.