bluuebunny/crossref_metadata_2025 huggingface dataset:
Semiclassical theories and quantum hardwall calculation of atom surface scattering
Authors: Masel R. I. , Merrill R. P. , Miller W. H.
Published: July 2002

A semiclassical formalism for atom and electron scattering from solid surfaces is presented and compared to exact quantum calculations for scattering from a sinusoidal hardwall and to experimental scattering distributions for thermal helium and neon beams scattered from W〈112〉. The helium results are well represented by elastic calculations, but large inelastic effects are evident in the neon scattering. The semiclassical calculations for the hardwall are in agreement with the exact quantum results to within a few percent. Qualitatively, either a specularly dominated distribution or a rainbow pattern is predicted, depending on the k vector and the amplitude of the surface periodicity. A preliminary attempt to apply this formalism to low-energy electron scattering from Ni(100) is also presented. The results, while not in exact agreement with more conventional dynamic LEED calculations, do reproduce absolute peak positions to within 7 V.
Self-consistent proximity effect correction technique for resist exposure (SPECTRE)
Authors: Parikh Mihir
Published: July 2002

Submicron electron-beam lithography for the direct exposure of wafers and for the fabrication of masks cannot be successful until the incident electron exposure can be properly adjusted to compensate the proximity effects. A self-consistent proximity effect correction technique for resist exposure (SPECTRE) has been developed to compute, for any given pattern, the corrections to the incident electron exposure which must be applied in order to obtain ’’uniform’’ absorbed (incident plus backscattered) exposure in the resist. Mathematically, the solution is unique for any given proximity function. SPECTRE has been successfully implemented on practical pattern data. Experimentally, simultaneous delineation of pattern geometries from 1/4 to 2 μm has been achieved by an automatic application of SPECTRE.
On the geometrical structure of cleaved Si (111) surfaces
Authors: Mönch W. , Auer P. P.
Published: July 2002

LEED intensity-versus-energy curves have been measured with clean, cleaved, and subsequently annealed Si (111) surfaces between 30 and 250 eV. After cleavage the surfaces exhibited single-domain 2×1 LEED patterns. The analysis of the observed peak energies in the double-diffraction picture confirms Haneman’s model of the 2×1 structure and gives: (1) The first layer is uniformly displaced inward by 0.08 Å and is buckled by 0.47 Å, (2) the spacing between second and third layer is relaxed by 0.22 Å. After anneals at approximately 300°C an apparent ′′1×1′′ structure is observed. The analysis of the measured I–V spectra reveals for this structure: The spacing between the first two layers is enlarged by 0.04 Å, while the distance between second and third layer is nearly unchanged. The I–V spectra of the final 7×7 structure, which are observed after anneals above the conversion temperature, are very similar to those of the ′′1×1′′ structure.
Application of Auger electron spectroscopy to studies of the silicon/silicide interface
Authors: Roth John A. , Crowell C. R.
Published: July 2002

We discuss the use of Auger electron spectroscopy to obtain chemical state information about the transition-metal/Si and silicide/Si interfaces. Characteristic Si L2,3VV Auger spectra for silicides of nine different transition metals are presented and analyzed in terms of chemical bonding in the compounds. The use of Auger peak shape analysis to obtain depth profiles of chemical state is illustrated by the detection of thin silicide layers at the metal/Si interface in as-deposited samples. The possibility of chemical state changes induced by inert gas ion bombardment is discussed and this effect is proposed to explain almost identical Si LVV peak shapes observed for different silicides of a particular transition metal. Pd2Si is shown to be stable against bombardment-induced bonding changes, and for this system sequential deposition studies of Pd on Si yield basically the same information as does sputter profiling.
Scale-up problems in electron-beam evaporation and sputtering
Authors: Hughes John L.
Published: July 2002

A variety of problems are encountered in the scale-up of electron-beam evaporation and sputtering processes from bell jar experiments to production processes. These problems include greatly altered outgassing characteristics, the effects of substrate motion, residual gas pressure and deposition rates. The overall efficiencies with which substrates can collect condensing vapor and the energy efficiency of electron beam and sputtering vaporization processes are also significant with respect to reliable production coater designs. Specific considerations and problems are examined with respect to actual processes which have been scaled-up, both successfully and unsuccessfully.
Adlayer-induced LEED beams near order–disorder transitions
Authors: Roelofs L. D. , Park Robert L. , Einstein T. L.
Published: July 2002

We present a Monte Carlo study of the adlayer-induced LEED beams in a representative order–disorder transition. Calculations of the widths of fractional order beams indicate that, as seen in recent experimental work on the O/Ni(111) system, these widths rise sharply and suddenly above Tc. Furthermore the slope of this rise provides a sensitive probe of the adatom-adatom interactions. The increase in the width results from the existence of ordered domains above Tc, and has not been previously discussed since prior calculations have concentrated on beam intensities. We further derive a functional relation between the window approach used in simulations of order–disorder transitions and the instrument response function approach of the experimentalist, to detail the effect of the LEED apparatus on the profile of the extra beams.
Enhanced photoexcitation from the surface of aluminum
Authors: Levinson Harry J. , Plummer E. W. , Feibelman P.
Published: July 2002

The enhancement of photoionization cross sections due to the spacially varying photon field at the surface of a metal has been observed by measuring the cross section for the surface state and Fermi level on Al(001) for photon energies between 9 and 23 eV. The data are in excellent agreement with the results of a self-consistent jellium calculation which takes into account the induced short wavelength longitudinal fields at the surface of the metal. These fields are much more effective than the transverse fields in providing the momentum necessary for photoexcitation and this mechanism dominates all others, including direct vertical transitions, in the energy range considered. The implications of this effect on photoemission studies of surface and bulk properties will be discussed.
Influence of spherical and chromatic aberrations on the half-radius of an electron beam
Authors: Slówko W.
Published: July 2002

Root mean square deviation and half-radius (containing a half of the beam current) of an axially symmetric beam from a point source, as a function of the beam crossover plane position, were solved analytically. Current density distributions and values of the half-radius of a beam generated from a source with a Gaussian current density distribution were numerically calculated. The spherochromatic aberration with electron energy dispersion (Maxwell and rectangular energy distributions) and without it (focusing deviation) were taken into account. The quadratic (geometric) way of aberration mixing has been confirmed, with the mixed quantities defined.
Two-dimensional electron transport in semiconductor layers II: Screening
Authors: Price P. J.
Published: July 2002

The theory of the screening of scattering fields by the carrier space charge for a semiconductor heterolayer (in which the electrons are confined in one direction, with discrete quantum levels, and mobile in the perpendicular plane), is developed on a general basis. The layer geometry makes the screening depend on functions of the normal-direction wave functions and the perpendicular Fourier wave vector. Applications, in particular for Ga–Al–As heterostructures, are made to the scattering between the two-dimensional Bloch states due to phonons and due to ions. For the phonons, moderate effects of screening on the mobility, in practical conditions, are found. For optical-mode phonons the plasma resonance at the lattice frequency can appreciably modify the scattering. For the ions, strong screening and correspondingly enhanced mobility is possible, in particular for modulation doping; the result for the mobility in the latter case is applied to recent experimental data. The ’’secondary screening’’ effects due to the polarizability of the normal-direction quantum states are analyzed and are found to be normally small.
Design of an electrostatic ion optical system for microfabrication with 100 Å resolution
Authors: Ohiwa H. , Blackwell R. J. , Siegel B. M.
Published: July 2002

A computer-aided design program (CAD) has been developed to provide rapid, interactive design of electron and ion optical systems. The CAD program simulates the focusing and deflection properties of systems consisting of cylinder electrodes and octupole deflectors. Ion optical systems for use with an H2+ gaseous field ion source were designed using the CAD program. The design goals were to produce a 100-Å-diam probe capable of scanning a 0.2-mm-square field with an expected energy spread in the source of ΔE/E = 1/30 000. A system of five cylindrical electrodes (6-mm-diam bore) with the middle electrode containing double octupole deflectors would produce a 100-Å-diam probe using an acceptance half-angle of 4 mrad when dynamic correction is used. Another sytem was calculated using cylinders with bores of 8-mm diam and somewhat larger lens elements to produce a 100-Å-diam probe without dynamic corrections if a 2 mrad acceptance half-angle is used.
Study of the stepwise oxidation and nitridation of Si(111) by electron stimulated desorption and Auger spectroscopy
Authors: Knotek M. L. , Houston J. E.
Published: July 2002

Electron stimulated desorption (ESD) and Auger electron spectroscopy (AES) measurements are reported for the electron-activated stepwise oxidation and nitridation of the Si(111) surface. In ESD it is found that appreciable levels of surface hydrogen are present which can lead to hydroxyl formation upon oxidation. The hydroxyl-rich films are unstable in an electron beam, while surfaces oxidized with activated O2, where no OH is formed, are much more stable. On the OH-free oxide, ESD shows two chemically distinct O species, one thought to be SiO2 and the other either adsorbed O2 or a chemical intermediate. The Auger spectra for both oxide and nitride films, which show a continual change from Si to Si-compound nature, suggests that in the earliest stages of reaction the reacted film is made up mainly of low coordination intermediates which gradually evolve to the full compound as the coordination increases.
Laser quenched and impurity induced metastable Si(111)1×1 surfaces
Authors: Chabal Y. J. , Rowe J. E. , Christman S. B.
Published: July 2002

Metastable rearrangements of the surface atoms yielding a 1×1 LEED pattern can be obtained on Si (111) either by quenching from high temperatures or/and by impurity stabilization. In particular, laser annealing produces clean 1×1 structures with no LEED evidence for long-range reconstruction. We have investigated by UV photoemission and LEED laser-annealed flat and vicinal Si (111) surfaces. We find that, for 10-ns pulses (0.4 J/cm2) at λ = 0.53 μ, the surface is mostly disordered (<16 Å domains) with possibly a local buckling reconstruction. For 15-ns pulses (2 J/cm2) at λ = 0.69 μ, the surface is still disordered with a 7×7-like reconstruction. Since different laser parameters can alter the regrowth velocity by over a factor of two, kinetic parameters were determined from LEED studies of vicinal surfaces. There is evidence that different amounts of long-range order can be obtained by varying regrowth velocities in the range 2 to 7 m/s. Impurity stabilized 1×1 surfaces also involve a certain amount of disorder. The relevance of the study of 1×1 surfaces to the understanding of the stable reconstruction on Si (111) is discussed.
Interaction of oxygen with silicon d-metal interfaces: A photoemission investigation
Authors: Abbati I. , Rossi G. , Calliari L. , Braicovich L. , Lindau I. , Spicer W. E.
Published: July 2002

We have carried out synchrotron radiation measurements both from valence states and core levels from Si(111)–Cu, Si(111)–Ag, Si(111)–Au, Si(111)–Pd interfaces before and after exposure at room temperature to 30×106 L of oxygen and we compare the results with those for the oxidation of Si(111). In all cases the oxygen interacts with Si and not with the metal, and the Si reaction rate is strongly increased with respect to that of Si(111). The strongest oxidation enhancement is obtained with Cu and Pd. In the noble metal case the interaction with oxygen produces the overgrowth of a SiO2-like phase having a Si 2 p chemical shift of ∠3.8 eV as opposite to Si(111) which cannot be oxidized to SiO2 in these conditions. Moreover, in the Si–Pd case the oxidation number is lower and the chemical shift is ∠2.3 eV. We discuss the relevance of the results both in terms of the structure of the interface and of the nature of the chemical interaction between Si and d metals.
Factors determining the compound phases formed by oxygen or nitrogen implantation in metals
Authors: Kelly Roger
Published: July 2002

Oxygen or nitrogen implantation in a metal is well known to lead to oxides or nitrides, often in the form of precipitates. In some cases the phase formed is unambiguous in that there is either no phase stable with respect to O or N loss (e.g., Ag) or only one (e.g., Al). In other cases (e.g., Ti), however, two or more phases are possible in the sense of being stable with respect to O or N loss. We present a model based on the postulate that implanted O or N leads to precipitates which tend to be in qualified thermodynamic equilibrium with the metal. The qualifications are that a phase will fail to appear if subject to amorphization, O or N loss, or (for a phase the cations of which are crystallographically like the metal) randomization.
Permeation, diffusion, and solution of hydrogen isotopes, methane, and inert gases in/through tetrafluoroethylene and polyethylene
Authors: Miyake Hitoshi , Matsuyama Masao , Ashida Kan , Watanabe Kuniaki
Published: July 2002

Permeation of three hydrogen isotopes, methane, and inert gases were measured for a tetrafluoroethylene (TFE) and a polyethylene (PE) film at room temperature by means of the time-lag method in order to establish physicochemical properties which determine the solubility and the diffusivity of these gases. It was observed that the diffusion constant of the inert gases changed exponentially with the heat of vaporization, and their solubility constant was an exponential function of the Lennard-Jones force constant of the gases for both films. On the other hand, hydrogen isotopes and methane deviated from these relations. It is concluded that the dispersive force plays an important role for the solution and the diffusion of the inert gases, whereas chemical interactions between the solute and the solvent play an important role.
Carbon monoxide oxidation on the kinked Pt(321) surface
Authors: Gland John L. , McClellan Michael R. , McFeely F. Read
Published: July 2002

Carbon monoxide oxidation has been studied using high resolution electron energy loss spectroscopy, temperature-programmed reaction (TPR), and titration of adsorbed atomic oxygen on a kinked Pt(321) surface characterized using Auger electron spectroscopy and low energy electron diffraction. Two previous papers detail adsorption and dissociation of oxygen and adsorption of carbon monoxide on the Pt(321) surface. Vibrational spectra taken during interrupted reaction experiments clearly indicate that atomic oxygen adsorbed on terraces reacts with CO more rapidly than atomic oxygen adsorbed near the kinked step sites. Reaction between coadsorbed atomic oxygen and carbon monoxide begins just above 100 K and persists above 400 K on a (321) surface saturated with both atomic oxygen and carbon monoxide. The multiple-reaction-limited CO2 peaks observed in the 100 to 400 K region can be rationalized by proposing that the activation energy for reaction of terrace and step CO with terrace and step atomic oxygen is sufficiently different to cause discernible CO2 peaks as the various species are sequentially depleted by reaction during the TPR experiment.
Rf sputtering–voltage division between two electrodes
Authors: Horwitz Chris M.
Published: July 2002

In a dc sputtering system only the cathode is bombarded by positive ions. However, in a two-electrode rf sputtering system, both electrodes are bombarded. In both sputter deposition and sputter etching this bombardment must be controlled for control of contamination and film properties. The ratio of ion bombardment energies at the two electrodes has been studied here by an indirect method using measurements of the rf and induced dc voltages between the electrodes. The behavior of this voltage ratio, and of the corresponding ion energy ratio, has been studied as a function of the electrode area ratio (varied between 0.3 and 1), the electrode material (SiO2 and stainless steel), the rf voltage on the electrodes (varied from 300 to 2000 Vpp), the gas (He, Ne, Ar, Xe, and CF4), and its pressure (from 0.1 to 100 Pa). The results show that while it is easy to obtain roughly equal ion bombardment of the rf electrodes, large ion bombardment energy ratios are difficult to obtain and require careful system design. In particular the dependence of the ion bombardment ratio on the fourth power of the electrode area ratio, which has been widely assumed in the past, has not been confirmed. The analysis also describes the effect of the dc bias voltage and the rf peak-to-peak voltage on target etch rates.
Theoretical studies of metal clusters and of chemisorption on metals
Authors: Messmer R. P.
Published: July 2002

The results of different theoretical methods are compared in the analysis of three illustrative problems. The methods involved are: local density functional (LDF), Xα, Hartree–Fock, generalized valence bond (GVB), and configuration interaction (CI). The three problems considered are: (1) the bonding of Mo2 and Cr2, (2) the photoelectron spectra of Cu clusters, and (3) the chemisorption of N2 on Ni. The comparisons provide new insights both into these problems and into the physical content of the methods per se. In the case of the comparison of studies on Cu clusters, one is led to reinterpret the nature of photoemission from narrow d bands and its relationship to conventional band theory.
Interfacial reaction during metallization of cured polyimide: An XPS study
Authors: Chou N. J. , Tang C. H.
Published: July 2002

To characterize the intrinsic adhesion properties of various metal–polyimide systems we have used x-ray photoelectron spectroscopy (XPS) to monitor interfacial reactions during metallization of cured polyimide at room temperature. In situ measurements were made in a UHV system when monolayers and submonolayers of Cr, Ni, Cu, or Ag film were successively deposited on a freshly cured PI substrate. Examination of the changes in various core electron spectra associated with the substrate and overlayer and their comparison with expected escape length effect indicate that while Cr and Ni react with the pendent oxygen in the substrate, Cu and Ag do not. A simple thermodynamic calculation shows that limiting values can be derived for the effective partial molar free energy of the pendent oxygen in PI, which may be used to predict whether a given metal will form chemical bonds with PI during metallization at room temperature.
Long-term changes in the sensitivity of quadrupole mass spectrometers
Authors: Blanchard W. R. , McCarthy P. J. , Dylla H. F. , LaMarche P. H. , Simpkins J. E.
Published: July 2002

We routinely use quadrupole mass spectrometers (QMS) to monitor vacuum conditions, gas purity, and plasma–wall interactions in the Tokamak Fusion Test Reactor (TFTR) at Princeton. Two QMS systems have been operating on TFTR continuously for a 2 year period. Both QMS systems are absolutely calibrated at weekly intervals using a six-part standard gas mixture. The calibration procedure is based on the use of transfer standards (ion gauge and capacitance manometer) that are calibrated against a primary standard (spinning rotor gauge) on an external vacuum system. We have identified variations in the efficiency of the QMS ionizer and drifts in the sensitivity of the electron multiplier ion detector to be the major reasons for the observed changes in overall QMS sensitivity. Weekly variations in sensitivity greater than 100% have been observed following system bakeout at 150 °C and with the use of rhenium filaments which were initially in the QMS ionizer. Operation of the QMS system with tungsten filaments and at constant temperature has yielded more stable operation with weekly sensitivity changes generally being less than 10%.
Alloying effect on the activation processes of Zr-alloy getters
Authors: Ichimura Kenji , Matsuyama Masao , Watanabe Kuniaki
Published: July 2002

Gettering materials, most of which are alloys, have wide applicability to tritium processing functions in fusion and fission reactors such as storage, supply, recovery, separation, and so on. However, required getter properties differ depending on unit process conditions. To develop suitable getters for each unit process, it is important to investigate fundamentals of alloying effects on their properties. Therefore, we studied the activation processes of three Zr-alloy getters (Zr–Al, Zr–Ni, and Zr–V–Fe) by means of x-ray photoelectron spectroscopy–secondary ion mass spectrometry and thermal desorption spectroscopy. It was observed that the formation of a metallic Zr surface is the principal process for activation, by which the getters show pumping action for various gases. A considerable alloying effect was observed on the activation processes of the three getters. The activation temperature varied with alloying elements: 800 °C for Zr–Al, 700 °C for Zr–Ni, and 400 °C for Zr–V–Fe. It was concluded that the activation temperature is determined by the balance between the stability of corresponding oxides and carbides present on the surface and the diffusivity of oxygen and carbon from the surface into the bulk.
Oxidation of microcrystalline Si:H:Cl films
Authors: Grossman E. , Grill A. , Polak M.
Published: July 2002

The oxidation of microcrystalline (mc-) silicon films, deposited from silicon tetrachloride by an rf glow discharge, was studied using x-ray photoelectron spectroscopy (XPS). The mc-Si films containing between 1% and 3% Cl, were exposed to 200-Torr oxygen, or water vapors, for 50 h and their oxidation was compared to that of single-crystal Si(100), under identical conditions. The Si 2p spectra, changing with depth, contained contributions from all oxidation states (+4, +3, +2, +1, 0), with composition depending on the reacting gas and the crystallinity of the Si substrate. Exposure to water vapors leads to heavier oxidation (higher oxidation states and thicker oxides), as compared to oxygen exposure. In both cases, the oxidation resulted in some chlorine depletion mainly in the SiO2-rich external surface of the mc-Si films. As to the role of the microcrystalline structure, the most pronounced effects involved enhancement of oxidation to the Si1+ and Si3+ states across the thicker SiO2–Si interface.
Kinetics of high-temperature thermal decomposition of SiO2 on Si(100)
Authors: Liehr M. , Lewis J. E. , Rubloff G. W.
Published: July 2002

The decomposition of oxide films of 50 to 500 Å on Si(100) during ultrahigh vacuum anneal has been studied in a scanning Auger microscope. The decomposition of the oxide occurs locally, in that voids form in the oxide and grow laterally with time and temperature, leaving the oxide areas in between unperturbed. Void growth kinetics data are derived from in situ absorbed current and secondary electron imaging during vacuum anneal. The growth of the void diameter is found to be linear in time with an activation energy of 2.0±0.25 eV. This implies that oxide decomposition rates after the void nucleation phase are dominated by chemical reactions and/or diffusion processes near the circumference, not by the nature of the defect which nucleated the void.
Adsorption kinetics of H2/Ni and its dependence on surface structure, surface impurities, gas temperature, and angle of incidence
Authors: Rendulic K. D. , Winkler A. , Karner H.
Published: July 2002

We have for the first time determined the change in the angular distribution function of the adsorption probability with beam temperature. This change is an extremely sensitive indicator for the particular adsorption dynamics at work; it is used to determine the physical effects of surface impurities and surface defects as well as surface structure in the adsorption of hydrogen on nickel. On all single-crystal surfaces investigated there seems to be activated adsorption with a parallel channel of nonactivated adsorption through a precursor. Defects and oxygen impurities generate additional adsorption sites for nonactivated adsorption. These sites are predominantly active at low temperatures.
Design and performance of a reflectron based time-of-flight secondary ion mass spectrometer with electrodynamic primary ion mass separation
Authors: Niehuis E. , Heller T. , Feld H. , Benninghoven A.
Published: July 2002

In many secondary ion mass spectrometry (SIMS) investigations, the total number of generated secondary ions is limited by the amount of sample material available. This is the case in surface reaction studies as well as in organic and inorganic trace analysis or imaging SIMS. In such cases a time-of-flight mass spectrometer has some considerable advantages: quasisimultaneous detection of all masses, unlimited mass range, and very high transmission. We have developed a high-resolution reflectron based time-of-flight secondary ion mass spectrometer with a new electrodynamic mass separation and beam chopping technique based on a pulsed 90° deflection of the primary ion beam. A primary ion pulse width of less than 1.5 ns has been obtained. Second-order energy focusing in the flight path of the secondary ions is achieved by a two-stage reflectron. A mass resolution m/Δm=13 000 and a dynamic range of five orders of magnitude have been obtained with this instrument.
Deposition of vanadium oxide films by direct-current magnetron reactive sputtering
Authors: Kusano E. , Theil J. A. , Thornton John A.
Published: July 2002

Vanadium dioxide is well known for the semiconductor–metal phase transition at 67 °C which has yielded resistivity changes as high as 105 in single crystals. Our objective is to demonstrate that thin films with high transition resistivity ratios can be deposited at modest substrate temperatures by dc reative sputtering from a vanadium target in an O2–Ar working gas using a planar magnetron source, because of the capabilities of this method for depositing large-area thermal control surfaces. We have obtained resistivity ratios of ∼5×103, between a semiconductor phase with a resistivity of ∼5 Ω cm, and a metallic phase with a resistivity of ∼10−3 Ω cm for films deposited onto borosilicate glass substrates at ∼400 °C. X-ray diffraction showed the films to be single-phase VO2 with a monoclinic structure. The VO2 films are obtained for a narrow range of O2 injection rates which correspond to conditions where cathode poisoning is just starting to occur, i.e., where the sputtered flux of vanadium, as measured by in situ optical emission spectroscopy, is decreasing and the oxygen partial pressure is increasing. Higher or lower injection rates, for a given discharge current, give films with unfavorable stoichiometry and/or structure and lower resistivity ratios during the transition.
Growth of cubic phase gallium nitride by modified molecular-beam epitaxy
Authors: Paisley M. J. , Sitar Z. , Posthill J. B. , Davis R. F.
Published: July 2002

Gallium nitride is a compound semiconductor with a wide direct band gap (3.45 eV) and a large saturated electron drift velocity. Nearly all single-crystal thin films grown to date have been wurtzite (hexagonal) structure. Cubic GaN has the potential for higher saturated electron drift velocity and somewhat lower band gap. These properties could increase its applicability for high-frequency devices (such as impact ionization avalanche transit time diodes) as well as short-wavelength light emitting diodes and semiconductor lasers. This paper reports the growth of cubic phase single-crystal thin-film GaN using a modified molecular-beam epitaxy technique. A standard effusion cell was used for gallium, but to activate nitrogen gas prior to deposition, a microwave glow discharge was used. Auger electron spectroscopy showed a nominally stoichiometric GaN film. Transmission electron microscopy with selected area diffraction indicated the crystal structure to be zinc blende.
A scanning tunneling microscopy/current imaging tunneling spectroscopy investigation of an organic molecule: 4-cyano-4′-n-heptylbiphenyl
Authors: Okumura A. , Miyamura K. , Gohshi Y.
Published: July 2002

A current imaging tunneling spectroscopy (CITS) technique was applied to a scanning tunneling microscopy (STM) investigation of a liquid crystal: 4-cyano-4′-n-heptylbiphenyl adsorbed on cleaved surfaces of graphite under ambient conditions. Although STM images were highly variable, a molecular image of 7CB was observed. Current images showed contrast variation over the molecule and were dependent on the bias voltage. This result indicates that the CITS technique is effective for the investigation of local electronic properties of adsorbed molecules.
Surface imaging in air with a force microscope
Authors: Ishizaka T. , Morita S. , Sugawara Y. , Okada T. , Mishima S. , Imai S. , Mikoshiba N.
Published: July 2002

Using force microscopy (FM), we investigated the surface conductivities of various metals in air. In the case of the Ag surface, current began to flow only under a strong repulsive force of ∼10−6 N in contrast to the Au surface, so that the Ag surface seemed to be oxidized weakly. In the case of the Ni surface, current was not observed even under a strong repulsive force of ∼2×10−6 N, so that the Ni surface seemed to be oxidized thick enough to sustain the strong repulsive force of ∼2×10−6 N.
New scanning tunneling microscopy tip for measuring surface topography
Authors: Akama Y. , Nishimura E. , Sakai A. , Murakami H.
Published: July 2002

Electron-beam deposition inside scanning electron microscope (SEM) is used to prepare a new scanning tunneling microscope (STM) tip [electron-beam deposited (EBD) tip] which has a submicron diameter and a long straight sidewall. An EBD tip as small as less than 0.1 μm in diameter can be formed with careful beam focusing. This EBD tip is formed to be capable of providing a low-distortion STM image of deep grooves, and is quite useful in topographic measurements of microfabricated patterns.
Photoemission investigation of silver/poly(ethylene terephthalate) interfacial chemistry: The effect of oxygen-plasma treatment
Authors: Gerenser L. J.
Published: July 2002

High resolution x-ray photoelectron spectroscopy (XPS) has been used to study the interfacial chemistry between vacuum-deposited silver and poly(ethylene terephthalate) (PET) surfaces. The initial stages of metallization in the subatomic layer regime (∼0.1–1.0 atomic layer of Ag) were monitored. For the untreated PET, the XPS results suggest charge transfer between silver and the carbonyl oxygen in PET in the early stages of metallization. The effect on the untreated PET is small with only about 7% of the PET surface atoms providing reaction sites. Plasma modification with oxygen introduces specific reaction sites resulting in additional chemical bond formation between the vacuum-deposited silver and the PET surface. The XPS results suggest the primary reaction sites are the plasma-induced acid groups. The resultant structure is similar to that of a silver carboxylate species. The number of reaction sites is estimated at 3–4 times greater compared to untreated PET. These results are consistent with the significant improvement in adhesion observed for plasma treatment with oxygen.
Growth of TaC thin films by reactive direct current magnetron sputtering: Composition and structure
Authors: Håkansson G. , Petrov I. , Sundgren J.-E.
Published: July 2002

Single-phase TaC films were grown by reactive dc magnetron sputtering onto high speed steel substrates kept at 650 °C (0.22 Tm ). The films were grown in both Ar/CH4 and Xe/CH4 mixtures using target-to-substrate distances, dts, of 6 and 15 cm. For all growth conditions, plasma-probe measurements were carried out. As-deposited films were analyzed using Auger electron spectroscopy (AES), x-ray diffraction (XRD), and transmission electron microscopy (TEM). The C content of the films, as measured with AES, was found to increase linearly with increasing CH4 partial pressure in all cases. However, both the slope of these curves and the CH4 pressure needed in order to obtain a certain C content in the films were different depending on both dts and the sputtering gas. These results are explained with arguments based on cracking of the CH4 molecules into more reactive CHn radicals in the plasma and a different gas scattering of these radicals compared to the sputtered Ta atoms. Also, the structure of the deposited films was depending on the sputtering gas and all films grown in Ar/CH4 showed a considerably higher strain level compared to films grown in Xe/CH4 discharges. This higher strain level is due to the generation of defects in the films induced by a large flux of backscattered energetic neutral Ar atoms that imping on the growing film. In the Xe case, the energy of the backscattered neutrals is not sufficient to generate defects in the films. The structure of the films was also found to depend on the C content. For over-stoichiometric films, TEM analyses showed that the grain size was only a few nanometers and that there are low density regions surrounding the grains suggesting a precipitation of the excess C. When this precipitation occurred, the preferred orientation of the films changed from (200) to (111).
Analysis of iridium–aluminum thin films by x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy
Authors: Anderson D. R. , Lampert J. K. , Mishra A. , Wu H. Z. , Unruh K.
Published: July 2002

Thin films consisting of individual iridium and aluminum layers were sputter deposited onto various substrates. These films were then heat treated in air or in vacuo at temperatures ranging from 300 to 850 °C. We have demonstrated by x-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy (RBS) analyses of air-treated films that unusual oxidation behavior occurs. Oxygen diffuses through the iridium layers and forms discrete layers of alumina in the film’s interior. Aluminum diffuses outward and reacts with oxygen at the alumina-iridium interface.
Scanning tunneling microscopy of the phosphatidylcholine bilayers
Authors: Luo Changhong , Zhu Chuanfeng , Ruan Like , Huang Guizhen , Dai Changchun , Cheng Zhengbo , Bai Chunli , Su Yaxian , Xu Sanduo , Lin Kechun , Baldeschwieler John D.
Published: July 2002

The bare surface of the egg-PC bilayers after being dried at room temperature was observed by the STM and images with angstrom resolution were obtained. Results indicate that the lipid heads form islands of an average of 210 Å in diameter and 40 Å in separation on the bilayers and that each island contains about 170 lipid heads of 7.5 Å in diameter. The size of the lipid heads is correspondent with that calculated from the standard bond distances and the bond angles. The ordered distribution of the lipid heads in some areas may correspond to the ordered arrangement of the lipid heads on the egg-PC bilayers before being dried. The STM results also show that there exists the ripple phase in the egg-PC bilayers below its phase transition temperature.
The surface structure of artificial and natural membranes as studied by scanning tunneling microscopy
Authors: Ya-Xian Su , Yue-Kan Jiao , San-Duo Xu , Jun-En Yao , Ke-Chun Lin
Published: July 2002

The surface structures of noncoated biological membranes were studied by the scanning tunneling microscopy, including the surfaces of egg PC(phosphatidylcholine) liposomes, soybean PE(phosphatidylethanolamine) nonbilayer lipid tubes and the membranes of liver ascites cells.
High Φ values in scanning tunneling microscopy: Field emission and tunnel regimes
Authors: Gómez-Herrero J. , Gómez-Rodríguez J. M. , García Ricardo , Baró A. M.
Published: July 2002

Local barrier height (Φ) images on a Ni (110) sample in ultrahigh vacuum (UHV) conditions show the coexistence of small regions (50 Å) with low and high Φ values. Thus, we measured I–s and s–V plots at a fixed point and several tip–sample voltages in order to understand the behavior of the barrier height with different gap distances. A good fitting of these plots with theoretical expressions is obtained for high Φ values, and we evaluate the contribution of the image potential to the tunnel barrier. Anomalously low Φ values in the tunnel regime correspond to quite high values in field emission. The data are consistent with the suggestion that apparently low barrier heights in tunneling are due to forces between tip and sample, resulting in changes of the real gap distance.
Surface electronic properties on BiO plane of Bi2Sr2CaCu2O8 single crystal measured by scanning tunneling microscopy
Authors: Tanaka M. , Yamazaki S. , Fujinami M. , Takahashi T. , Katayama-Yoshida H. , Mizutani W. , Kajimura K. , Ono M.
Published: July 2002

Scanning tunneling microscope (STM) and tunneling spectroscopy were used to study the surface electronic states of a Bi2Sr2CaCu2O8 single crystal. We obtained an STM image of the BiO plane which showed a series of rows spaced by 2.6 nm. The density of electronic states of the BiO plane obtained from the tunneling spectra showed a depression around zero-bias voltage. From the present experimental results, it is concluded that the BiO plane is almost nonmetallic and therefore Bi2Sr2CaCu2O8 crystal is composed of an alternating stacking of metallic (CuO2 ) and nonmetallic (BiO) planes.
Oxidation kinetics of diamond, graphite, and chemical vapor deposited diamond films by thermal gravimetry
Authors: Joshi A. , Nimmagadda R. , Herrington J.
Published: July 2002

Oxidation kinetics of diamond films synthesized by plasma-assisted chemical vapor deposition (CVD) in flowing oxygen were evaluated using thermal gravimetric analysis. The oxidation rates of diamond films, measured in the 500 to 750 °C range, were significantly lower than natural diamond, which was lower than grafoil and pyrolytic forms of graphite. The mechanisms of oxidation in the CVD diamond films and natural diamond were explored by scanning electron microscopy and Auger electron spectroscopic examination of localized regions. In CVD films, oxidation occurred preferentially at grain boundaries, local defects, and diamond-like carbon containing regions during the early stages of oxidation process. The results suggest that preferred orientation of diamond crystallites in the CVD film plays a major role on its oxidation behavior.
A warning concerning the use of glass capillary arrays in gas dosing: Potential chemical reactions
Authors: Leavitt P. K. , Thiel P. A.
Published: July 2002

We have encountered complications using a glass, capillary-array gas doser in our laboratory. In this note, we discuss the possibility that chemical reactions occur on the glass surface.
Electron interferometry using a coherent beam from point electron source
Authors: Tonomura Akira
Published: July 2002

Using the electron holography principle, a coherent field-emission electron beam is employed to quantitatively measure to a precision of 2π/100 the phase distribution of an electron wave function transmitted through or reflected from a sample. This technique opens up the possibility of previously impossible high-precision measurements such as the quantitative measurement of magnetic lines of force in a microscopic region, and thickness measurement in atomic dimensions.
Au-induced reconstructions of the Si(111) surface
Authors: Hasegawa T. , Takata K. , Hosaka S. , Hosoki S.
Published: July 2002

Au-adsorbed structures (∼1 ML) on the Si(111) surface are studied using a scanning tunneling microscope. In the initial stage of deposition, locally Au atoms are adsorbed onto the Si(111) surface with a 5×5 periodicity. At lower coverage, images showing a 5×2 periodicity are recorded, in which there are a dark line and two atomic rows running in the [1̄01] direction in a five times period. In each atomic row, atoms are arranged in a two times period along the row. At higher coverage, images showing a (3)1/2×(3)1/2 structure are also recorded. In these images, in addition to the (3)1/2 ×(3)1/2 periodicity, there is an undulation which is explained as a phase shift of the (3)1/2 ×(3)1/2 structure.
Superstructures of sulfur on stepped copper surfaces observed by scanning tunneling microscopy
Authors: Rousset S. , Gauthier S. , Siboulet O. , Sacks W. , Belin M. , Klein J.
Published: July 2002

We have obtained atomically resolved scanning tunneling microscopy images of sulfur adsorbed on two copper surfaces. These surfaces, the Cu(11,1,1) face and the Cu(8,1,0) face, which are both vicinal from the (100) plane, differ essentially by the atomic structure of their step edges. Two sulfur superstructures are resolved on both surfaces, a p(2×2) and a c(4×2). On S/Cu(11,1,1), a two-dimensional faceting of the step edges, induced by the sulfur adsorbate, is observed. In contrast, such a phenomenon does not appear on S/Cu(8,1,0). This behavior of the two surfaces is interpreted as a consequence of the different structure of the initial step edges.
Field emission from hafnium carbide
Authors: Mackie William A. , Morrissey Jennifer L. , Hinrichs Clarence H. , Davis Paul R.
Published: July 2002

We report on experiments to determine the feasibility of using refractory transition metal carbides as stable field emission cathodes. Applications of such cathodes could include radiation immune microcircuitry, radio frequency (rf) vacuum microelectronic amplifiers, flat panel displays, e-beam lithography, and other uses where the need is for very high density, small spot size electron sources. Hafnium carbide (HfC) single crystal specimens were prepared by arc floating zone refinement from sintered stock. Field emission patterns from heated HfC emitters were observed, and emission stability measurements were made. Ordering of the work functions of low-index crystal planes was determined through field emission microscopy and comparisons were made with thermionic projection microscopy. An effective thermionic work function of φ{100}=3.34 eV was obtained for a clean surface. The ability of heated HfC field emitters to operate at pressures above those commonly found for field emission cathodes is demonstrated. Current versus time plots are shown on heated emitters having stable dc currents of 0.5 mA and lifetimes ≳2400 h. Pulsed field emission measurements on room-temperature HfC emitters are also reported.
Secondary ion mass spectrometry test structures for analyses of semiconductor product wafers
Authors: Harris W. C. , Smith H. E. , Pelillo A. J. , Beagle J. L.
Published: July 2002

As semiconductor device dimensions continue to shrink, the demands placed on secondary ion mass spectrometry (SIMS) measurements on these devices increase. The small lateral dimensions of the features of interest result in lost sensitivity due to the reduced number of atoms within the analyzed area. Superimposed upon this fundamental limitation are instrumental or sample specific effects, which degrade performance with decreased probe size or analysis area. Further complications arise when the layer of interest is buried under several overlying layers of differing compositions. This article discusses the use of specially constructed SIMS test structures in unused areas of product wafers to circumvent these problems, thereby achieving a true on-chip analytical capability.
Low resistivity body-centered cubic tantalum thin films as diffusion barriers between copper and silicon
Authors: Catania Philip , Doyle James P. , Cuomo Jerome J.
Published: July 2002

Both bcc and β-Ta thin films (50 nm) have been deposited onto (100) Si by dc magnetron sputtering at pressures between 4 and 7×10−2 Pa. Ta nucleates in the bcc structure when the substrate is at ground potential. However, when a negative bias voltage is applied, a mixture of bcc and β phases is formed. Below −100 V bias, only the β structure is observed. We conclude that ion bombardment during the deposition process plays an important role in the growth of the Ta films. We also compare the effectiveness of thin bcc and β-Ta layers as diffusion barriers to copper penetration into Si. Ta films (bcc and β) were sputtered onto Si wafers (100) and overcoated with 150 nm of copper. Diffusion and reaction were monitored as function of temperature and time (up to 60 min) by four point resistance measurements and by Rutherford backscattering spectrometry. It has been observed that bcc Ta films exhibited no copper–silicon interdiffusion up to 650 °C, indicating that this Ta structure is a potential candidate for use as diffusion barrier. We also point out the dramatic effect of the microstructure of the Ta barrier on the breakdown temperature.
Deposition and properties of polycrystalline TiN/NbN superlattice coatings
Authors: Chu X. , Wong M. S. , Sproul W. D. , Rohde S. L. , Barnett S. A.
Published: July 2002

Polycrystalline TiN/NbN superlattice coatings were deposited on M2 tool steel substrates using an opposed dual-cathode unbalanced magnetron sputtering system. Superlattice deposition was achieved by placing the substrates on a cylindrical holder that rotated on an axis equidistant between, and parallel to, the faces of opposed Ti and Nb targets. Cross contamination of the targets and the alternating superlattice layers was minimized using a baffle or an extra-large cylindrical substrate holder. The superlattice period was determined by the substrate holder rotation speed. Analytical techniques including x-ray diffraction, energy-dispersive spectroscopy and transmission electron microscopy were used to characterize the structure of the superlattice coatings. Microhardness values for the superlattice coatings as high as 5200 kg/mm2 Hv0.05 have been achieved, comparable to the reported highest hardness values of single crystal TiN/VN, TiN/V0.6Nb0.4N and TiN/NbN superlattice coatings. The results indicate that the hardness of the polycrystalline TiN/NbN superlattice coatings is affected not only by superlattice period, but also by nitrogen partial pressure and ion bombardment during deposition.