bluuebunny/crossref_metadata_2025 huggingface dataset:
Anticipated performance of achromatic quadrupole focusing systems when used with liquid metal ion sources
Authors: Harriott L. R. , Brown W. L. , Barr D. L.
Published: July 2002

Current focusing systems for producing finely focused ion beams from liquid metal ion sources (LMIS) using axially symmetric electrostatic lenses are limited by chromatic aberration due to the relatively high (∼10 eV) energy spread inherent in LMIS. The highest current densities achievable are in the range of 1–5 A/cm2 at energies above 20 keV. In this paper, we discuss the use of achromatic quadrupole lenses to overcome the limitation due to energy spread. These lenses require both magnetic and electrostatic focusing elements. Lens acceptance angles are limited by the electrode positions and by the necessary magnetic gradients. The coefficients relating image distance to lens excitation of some of the elements in the quadrupole multiplet are found to be much larger than in electrostatic systems. These factors combine to require excitation stabilities as high as 1 part per million in order to achieve current densities more than 10 A/cm2, although such performance can be expected at beam energies of 5 keV or below.
Surface-defect formation in graphite targets during magnetron sputtering
Authors: Chen C. W. , Makowiecki D. M. , Alford C. S. , McKernan M. A. , Ramsey P. B.
Published: July 2002

Magnetron sputtering of graphite targets is frequently marred by the formation of topographic defects. The defects are either soft with a furry appearance or hard with a stalagmite appearance. The soft defects are often found on top of the hard ones, implying a close connection in formation sequence between the two types of defects. The formation mechanism of the hard defects is related to the presence on the surface of low sputtering-yield impurities or other types of lattice imperfections, which suppress the erosion induced locally by sputtering, and to porosity-induced asperities. The emergence of the soft defects is ascribed to a growth phenomenon involving redeposition of carbon from debris and possibly generated in a chemical vapor deposition (CVD) process. The gradual coverage of the target surface by defects causes a steady decrease of the sputtering rate of carbon. Also, the breakup of the soft defects promotes nodular defects in the subsequent growth of the carbon film, thus severely degrading the film quality. Remedial measures are devised for limiting the onset of defect formation.
Growth of CoSi2 on Si(001): Structure, defects, and resistivity
Authors: Jimenez J. R. , Schowalter L. J. , Hsiung L. M. , Rajan K. , Hashimoto Shin , Thompson R. D. , Iyer S. S.
Published: July 2002

Epitaxial films of CoSi2 on Si(001) have been grown by molecular-beam epitaxy, and their electrical and structural properties studied by resistivity and Schottky barrier height measurements, by Rutherford backscattering spectroscopy (RBS), and by transmission electron microscopy (TEM). Most growth conditions successful on Si (111) have been found to result in misoriented grains when applied to Si(001). However, single-orientation (001) CoSi2 films, with low resistivities (16 μΩ cm) and low ion channeling minimum yields (χmin=5%) have been obtained by direct codeposition of Co and Si at ∼500 °C at Co-rich stoichiometries. Single orientation (001) CoSi2 films have also been obtained by using a template method on epitaxially grown Si buffer layers, but the resistivities of these films have not been as good. A Schottky barrier height of 0.71 eV has been measured for single-orientation CoSi2(001)/Si(001). This is significantly higher than the barrier height of 0.64 eV for CoSi2(111)/Si(111).
Ellipsometric studies of low-temperature metalorganic chemical vapor deposited ZnS thin films
Authors: Strong Roger L. , Smith Patricia B.
Published: July 2002

The most common techniques used for the determination of thin film thickness are profilometry, spectrophotometry, and ellipsometry. Spectrophotometers require the refractive index of the film (generally assumed to be transparent) as an input parameter. Profilometers yield nonreproducible and often inaccurate film thickness measurements when the films exhibit rough surface structure. Ellipsometric analyses of polycrystalline metalorganic chemical vapor deposition (MOCVD) ZnS films which assume that the thin films are single, uniform, transparent layers do not produce reliable or self-consistent optical parameters or thickness values for the films. We employed multiple wavelength ellipsometry to analyze thin, polycrystalline MOCVD ZnS films. A two-layer model incorporating absorption and surface roughness was used to determine the thicknesses of the two layers self-consistently at wavelengths of 4050, 5461, and 6328 Å. The optical constants of the two layers are related through the Bruggeman effective medium approximation. The outer layer represents surface roughness and is characterized by a volume void fraction. The thickness of the rough outer layer was assumed proportional to the total film thickness based on scanning electron micrographs of the films. Results for MOCVD ZnS films deposited on HgCdTe and Si substrates indicate that the nucleation period differs for the two materials.
Effect of deposition parameters on properties of films deposited on fibers by hollow cathode magnetron sputtering
Authors: Ihsan M. , Pourrezaei K.
Published: July 2002

Thin films of Al and TiN were deposited on SiC monofilaments using a hollow cathode magnetron sputtering system. The deposition rate was 1100 Å/min in the case of Al films deposited at 45.75 W direct current power and 5 mTorr sputtering pressure and 257 Å/min for TiN films deposited at 6 mTorr sputtering pressure, 6% N2, and 48 W applied direct current power. The effects of deposition parameters such as the direct current power, sputtering pressure, and substrate bias on the film microstructure were studied. The substrate temperature varied from 67.7 to 168 °C, which corresponds to a T/Tm value of 0.1 to 0.25. The Al films consisted of a voided columnar structure with domed tops. The width of the grains increased with increase in temperature over a T/Tm range of 0.1–0.22. When the pressure was increased, while keeping the power constant, the size of the columnar grains and voids decreased. The TiN films deposited at 6 mTorr exhibited zone 1 type structure with voids whereas for the films deposited at higher pressures, that is, 10 and 15 mTorr, the same effect of pressure as in the case of Al films was seen. When a bias is applied to the substrate, the voided structure is clearly suppressed. Preliminary studies show that bias sputtered films show better diffusion barrier properties against both Si and Al, after being annealed at 650 °C for 6 h, as compared to the films deposited without bias.
Anomalous copper diffusion through samarium
Authors: Wieliczka David M. , Olson Clifford G.
Published: July 2002

We report the observation of enhanced diffusion of Cu through thick films of Sm at temperatures of 250–300 K. The rate of diffusion of Cu to the surface is found to be independent of temperature. The time dependence of the intensities of the Sm divalent and trivalent features indicate the Cu occupies interstitial sites below the divalent Sm surface layer and above the trivalent Sm bulk. The measured binding energies of the divalent and trivalent Sm show no shift with respect to pure Sm, indicating the Cu does not react with the Sm. The spectral features associated with Cu indicate it is in an atomic-like configuration. An examination of these intensities also provide evidence for heterogeneous mixed valence in Sm.
Scanning tunneling microscopy of cytoskeletal proteins: Microtubules and intermediate filaments
Authors: Hameroff Stuart , Simic-Krstic Yovana , Vernetti Lawrence , Lee Y. C. , Sarid Dror , Wiedmann Jerome , Elings Virgil , Kjoller Kevin , McCuskey Robert
Published: July 2002

Direct STM observation of native biomolecules has proven feasible. In this study we have used STM to image two filamentous protein components of the intracellular cytoskeleton: microtubules (MT) and intermediate filaments (IF). MT are 25 nm diameter cylinders comprised of 13 ‘‘protofilaments’’ which are linear chains of 8 nm × 4 nm × 4 nm ‘‘dimer’’ subunits. More variable than MT, IF are 10 nm diameter coils comprised of from 4 to 8 ‘‘subfilaments’’ which are chains of ‘‘tetramer’’ subunits. MT were isolated from porcine brain and IF from cell culture by standard techniques. Preparation/stabilization factors included magnesium buffer, 0.8 molar glycerol, and 0.1% glutaraldehyde. Samples were scanned on graphite in a Nanoscope I or II STM (Digital Instruments, Santa Barbara, California). STM images of MT demonstrated flattened 25 nm diameter structures composed of 4 nm wide protofilaments. Processed inverted images showed rows of 8 nm × 4 nm subunits. STM images of IF showed flattened, parallel 10 nm filaments comprised of coiled chains of 6–12 nm tetramer subunits. Thus STM demonstrated internal structure of two different classes of cytoskeletal proteins. STM and related techniques have an important future in biomolecular studies.
Surface science studies on the Ni/Al2O3 interface
Authors: Zhong Q. , Ohuchi F. S.
Published: July 2002

The Ni/Al2O3 system has been studied using surface sensitive techniques in an attempt to achieve fundamental understanding of metal matrix composite interfaces. Interfaces were prepared in situ in ultrahigh vacuum (UHV) systems designed for metal/ceramic interface studies. Dynamic processes of the interface formation were characterized. X-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) were used to elucidate the conditions controlling the different types of interfacial reactions, which were identified as Ni–Al intermetallic formation in the absence of oxygen, and NiAl2O4 formation in the presence of oxygen, each at elevated temperatures. The role of oxygen in the reactions was examined. Furthermore, reflection high-energy electron diffraction (RHEED) has been used to study the interfacial structure and growth mechanisms as well as different degrees of mismatch between each component under various conditions. Preliminary results confirmed epitaxial growth. Such knowledge is expected to provide insight into fabrication techniques and properties of composite materials.
Gallium growth and reconstruction on the Si(100) surface
Authors: Baski A. A. , Nogami J. , Quate C. F.
Published: July 2002

The behavior of gallium on the Si(100) 2×1 surface has been studied using scanning tunneling microscopy (STM) for metal coverages below one monolayer (ML). Below 0.5 ML, the Ga atoms form dimers that bond to the Si dimers, with the Ga dimers forming rows perpendicular to the underlying Si dimer rows. The Ga dimer rows form areas of 2×3 order for coverages below 0.3 ML and 2×2 order at 0.5 ML, in agreement with reflection high-energy electron diffraction (RHEED) and low-energy electron diffraction (LEED) data. Ga growth is anisotropic at low coverages, forming areas covered by long 2×3 islands oriented parallel to the Ga dimer rows. When the surface exhibits mixed 2×3 and 2×2 ordering between 0.3 and 0.5 ML, the Ga dimers are strongly correlated along the rows, but the rows themselves are randomly spaced every two or three unit cells apart. Since all surface dangling bonds are saturated at 0.5 ML (2×2), a different bonding behavior is expected above 0.5 ML. For such coverages, STM results give evidence for Ga growth on the 2×2 Ga terminated surface with an (n×8) ordering, where n usually equals 4 or 5. The detailed nature of this reconstruction is not yet known, but does not appear to involve Ga dimers.
Scanning tunneling microscope combined with optical microscope for large sample measurement
Authors: Yasutake M. , Miyata C.
Published: July 2002

A new scanning tunneling microscope (STM) which can easily search the sample area of interest and can observe the whole area of the sample up to 150 mm diameter has been developed. Its key design feature is the built-in piezo driver tube, which scans up to 12 μm and is nearly the same size as the objective lens. This tube is located in the revolver of the optical microscope (OM), which has a rotation position reproducibility of better than 1 μm. Tip position can be easily found for comparing the STM and OM images by scanning the standard patterns before measurement. Tip position accuracy of better than 2 μm has been obtained. The whole system, which has a minimum resonance frequency Rf of around 400 Hz, is built on an air damping table (Rf=1.5 Hz) to isolate it from vibrations. However, care must be taken with larger samples because their low resonant frequencies pick up acoustic vibrations more easily. Thermal drift is another problem, as the lengths of the frame holding the piezo driver and the sample stage are quite long (≂50 cm). Symmetric design is adopted to reduce the surface drift (<2 nm/min) and materials have been chosen to compensate for the vertical drift.
Deposition of (100) Au, Ag, Pd, Pt, and Fe on (100) Si using different metal seed layers
Authors: Chang Chin-An
Published: July 2002

Deposition near room temperatures by evaporation of several face-centered cubic (fcc) metals, and the body-centered cubic iron, all 1000 Å thick, in the (100) orientation is described. Using the (100) Cu film epitaxially grown on (100) Si as the seed layer, (100) Pd is obtained. The Pd layer is then used as a seed to provide an improved lattice match for the (100) growth of Au, Ag, Pt, and Fe. The (100) growth of Fe is also found using seed layers of Au, Ag, and Pt. Direct deposition of these layers on Cu, except for Pd, fails to give the (100) oriented metals due to the large lattice mismatch present. For the (100) Fe on (100) fcc metals, a 45° rotation between the two lattices around the (001) axis is suggested and confirmed, which allows an exact line-up of the bonds with the needed lattice match. Two major factors are suggested to be involved in the growth: an initial heteroepitaxy at the interface, followed by a subsequent self-epitaxy of the metals grown.
The effects of oxidation and air exposure on RbxBa1−xBiO3 superconducting thin films
Authors: Sobolewski M. A. , Semancik S. , Hellman E. S. , Hartford E. H.
Published: July 2002

Using x-ray photoelectron spectroscopy (XPS), we have investigated the effects of oxidation on RbxBa1−xBiO3, the degradation of its surface on exposure to air, and the feasibility of cleaning techniques to reverse this degradation. The sample was a superconducting thin film grown on MgO by molecular-beam epitaxy. XPS spectra of the initial, air-exposed surface show two O 1s peaks. The main O 1s peak increases in intensity upon oxidation at 300 °C for 10 min in 100 Torr O2, and decreases upon air exposure. Also, this peak shifts, together with the Ba and Bi peaks, to lower binding energy upon oxidation. These shifts to lower binding energy upon gain of oxygen (and to higher binding energy upon oxygen loss) can be explained by a rise in the conductivity of the film with rising oxygen content. Carbon and chlorine are observed on the initial air-exposed surface. Higher binding energy contributions in the Rb XPS peaks indicate that impurity compounds containing Rb are also present. Air-exposed surfaces do not show any XPS features at the Fermi level. However, removal of C and Cl by Ar+ sputtering at 1 kV, followed by oxidation, results in the appearance of intensity at the Fermi level. Hence sputter/oxidation treatments may prove useful in restoring the surfaces of films exposed to air (during patterning, for example) prior to overlayer deposition.
Three-dimensional finite element analysis of thin-film stresses using algor personal-computer-based software
Authors: Krus D. , Mearini G. , Chaffee K. , Hoffman R. W.
Published: July 2002

algor, a commercially available, personal computer-based, finite element software package was used to study three-dimensional stress–strain relations in both free standing and adherent thin films. The accuracy of the analyses was verified by comparison to tensile tests and analytical calculations of radius of curvature. The results also agree with earlier two-dimensional calculations. The program was used to simulate tensile testing in order to establish limits on film dimensions to yield Young’s modulus upon the application of a uniaxial stress approximation. Stress contours and deflections arising from submicroscopic elastic Poisson effects (necking) were determined for different film dimensions. In addition, the effect of using adhesives in sample mounting for tensile testing was studied, and the three dimensional models and results are compared to similar two-dimensional calculations.
A solution for pressure variations in vacuum process tools due to pressure regulator fluctuations
Authors: Fournier Jeffrey P. , Passow Michael L. , Cotler Tina J. , Elta Michael E.
Published: July 2002

We have observed plasma variations which were found to be due to gas pressure regulator fluctuations.1 The fluctuations in pressure may not be noticeable when operating in a normal process configuration since changes in flow, and hence pressure, are generally compensated for by an automatic downstream pressure controller. Although chamber pressure is maintained to ±0.5 mTorr of the pressure setpoint, other important parameters, i.e. plasma chemistry, may be out of control as we will further discuss. These effects can be apparent when, for example, attempting etch stops utilizing plasma emission.
Chemical etching of Si(111)-(7×7) and Al/Si(111) by atomic hydrogen
Authors: Kao Chi-Tzu , Dubois Lawrence H. , Nuzzo Ralph G.
Published: July 2002

We have observed an etching reaction on the Al/Si(111) surface (θAl≥1) induced by the chemisorption of atomic hydrogen at low temperature (T=250–400 K). The major silicon containing product detected by temperature programmed desorption (TPD) is silane (SiH4). An approximate sixfold increase in silane production is observed in the presence of aluminum, with a decrease in the TPD peak temperature from 645 K on Si(111) to 335 K on Al/Si(111). A kinetic model is presented to explain this catalyzed etching reaction.
Reactive N+2 ion bombardment of GaAs{110}: A method for GaN thin film growth
Authors: DeLouise Lisa A.
Published: July 2002

We have measured using x-ray photoelectron spectroscopy the surface composition, chemical state, and band bending of a GaAs{110} surface exposed to medium energy (0.5 and 3.0 keV) reactive N+2 ion bombardment at room temperature as a function of ion dose. Thermally stable, thin GaN films are formed at a rate is limited by ion-induced physical desorption of the surface layer. After annealing the sample, a small band bending shift toward higher kinetic energy (0.15 eV) is observed which results from the ion-induced formation of midgap charge acceptor states. The implication of these results on the use of GaN thin films for surface passivation of GaAs in device applications is described.
Adsorption kinetics of n-alkyl thiols on gold studied by second harmonic generation and x-ray photoelectron spectroscopy
Authors: Buck M. , Grunze M. , Eisert F. , Fischer J. , Träger F.
Published: July 2002

Optical second harmonic generation (SHG) was used to study the adsorption kinetics of self-organizing n-alkyl thiol films on polycrystalline gold substrates in situ and in real time. Thiols with carbon chains ranging from 1 to 22 were studied. SHG results showed that the average thiol coverage is constant for thiols longer than hexanethiol. The relation between the SHG signal change and the degree of thiol coverage was established by comparison with ex situ x-ray photoelectron spectroscopy measurements. The temporal dependence of the adsorption is well described by Langmuir adsorption kinetics and the source of the SHG signal is found to be linearly related to the nonlinear susceptibility of the adsorbate–substrate interaction allowing a straightforward in situ determination of the coverage.
X-ray photoelectron microscopy applied to metal/epoxy laminates
Authors: Kinzler M. , Grunze M. , Blank N. , Schenkel H. , Scheffler I.
Published: July 2002

In this article we describe the application of x-ray photoelectron microscopy to an industrial epoxy laminate. Cold rolled steel and galvanized steel bonds of an epoxy/dicyandiamide adhesive were studied by lap-shear strength measurements; the fracture surfaces of the sheared coupons were subsequently examined by x-ray photoelectron microscopy and x-ray photoelectron spectroscopy. X-ray photoelectron microscopy allows one to identify the lateral distribution of chemical elements and to distinguish between particulates (silicate filler), adhesively failed regions, and bulk epoxy material with a resolution of 10 μm. Areas selected in the microscopy mode were then analyzed by x-ray photoelectron spectroscopy to get information on the local interfacial composition. We find that a reaction between dicyandiamide and the zinc-oxide surface leads to diffusion of molecular zinc complexes into the polymer matrix when the bonds are aged for 14 days in a saturated water vapor environment at 70 °C. No significant decrease in bond strength is induced by the aging process.
Microscopic aspects of the initial growth of metastable fcc iron on Au(111)
Authors: Stroscio Joseph A. , Pierce D. T. , Dragoset R. A. , First P. N.
Published: July 2002

We report on the microscopic aspects of the growth of Fe on the Au(111) surface observed with scanning tunneling microscopy (STM). Nucleation of triangular Fe islands is observed to occur at the corners of the herringbone reconstruction of the Au(111) surface, which are imaged with atomic resolution. STM measurements show the existence of a metastable close-packed face-centered-cubic (fcc) phase of Fe with a 0.288±0.01-nm in-plane nearest neighbor distance. Initial fcc film growth proceeds in a nonideal layer-by-layer growth mode in which new layers start before preceding layers are complete.
Infrared optical properties of dielectric/metal layer structures of relevance to reflection absorption spectroscopy
Authors: Bermudez V. M.
Published: July 2002

The reflection of mid-infrared (IR) radiation from a non-absorbing (dielectric) layer of varying thickness on a semiinfinite metallic substrate is modeled using the classical Fresnel relations. Reflectance, phase shift, and field intensity are calculated as functions of polarization and angle of incidence. An ultrathin layer of an IR-absorbing molecule is then included in the model and the magnitude of the reflection absorption band calculated. The results provide insight into the design of experiments in which a metal layer buried beneath the surface of a dielectric material is used to enhance sensitivity to adsorbates in external-reflection IR reflection absorption spectroscopy.
Plasma particulate contamination control. II. Self-cleaning tool design
Authors: Selwyn Gary S. , Patterson Edward F.
Published: July 2002

Macroscopic particles are often observed in etching, sputtering, and deposition plasmas, in laboratory and manufacturing tools, in concentrations far exceeding ambient cleanroom conditions and acceptable process specifications. Controlling particle contamination is an important goal in modern fabrication lines. Controlling plasma-generated particulates is especially important as these tools and processes are a major source of wafer contamination. Plasma particles acquire negative charge by electron attachment and are influenced by electric fields and plasma inhomogeneities. Improper tool design exacerbates tool contamination problems by trapping particles near wafers or other sensitive surfaces. Conversely, proper tool and electrode design can provide greatly improved contamination results. The concept of a self-cleaning plasma tool is presented for the first time, along with evidence of the effectiveness and usefulness of this approach in laboratory and manufacturing studies. The method does not reduce the generation of particles, but limits the number deposited on the wafer. The self-cleaning plasma tool uses a topographically designed electrode to intentionally trap particles in designated regions of the plasma. Feed gas drag forces carry the trapped particles along a groove or series of grooves in the electrode away from the wafer and into the pump port. Manufacturing tools fitted with this electrode design have shown particle reductions ranging from 20% to 70%, depending on the tool condition, percentage of plasma-generated particles, and competition from other particle traps formed by the tooling or wafers. No influence on other aspects of the process quality is noted.
Characterization of a large volume electron cyclotron resonance plasma for etching and deposition of materials
Authors: Ghanbari A. , Ameen M. S. , Heinrich R. S.
Published: July 2002

A novel microwave electron cyclotron resonance plasma source capable of producing a large volume high density plasma for wafer processing has been designed and constructed. The source utilizes an unique eight-loop antenna microwave coupling and a magnetic single/multicusp magnetic field configuration to generate a radially uniform plasma. Various single and multicusp magnet geometries were investigated. Depending on the magnetic field configuration, ion density ranges from 3.50 × 1010 to 8.00 × 1010 cm−3, the electron temperature ranges from 3.50 to 5.50 eV and the plasma potential varies between 13 and 20 V for 200–600 W of microwave power. For this range of parameters, the physical sputter etch rate of SiO2 with argon is about 120 Å/min with ±5% etch uniformity over a 150 mm wafer.
X-ray photoelectron spectroscopic study of the interaction of low energy carbon ions with GaAs and InP
Authors: Meharg P. F. A. , Ogryzlo E. A. , Bello I. , Lau W. M.
Published: July 2002

To simulate the low energy ion bombardment that occurs in reactive ion etching (RIE) using alkanes, GaAs and InP were exposed to 20, 100, and 500 eV carbon ions, using a mass-separated carbon ion beam in an ultrahigh vacuum chamber. The InP sample structure consisted of a 40 Å ultrathin, epitaxial InP layer on InGaAs. The changes induced by ion bombardment and the effects of subsequent damage-removal treatments were determined by in situ polar-angle dependent x-ray photoelectron spectroscopy. Initially, carbon ion irradiation caused minor sputtering of the semiconductors and preferential removal of the group V constituents, with concurrent formation of carbon-semiconductor phases. The depth of these phases and the extent of the damage increased with increasing bombardment energy. An amorphous carbon residue formed after further bombardment. Several damage removal techniques were applied to the carbon bombarded surfaces. It was found that heating was ineffective in annealing the damage, although surface Fermi level movements were observed. Ozone oxidation did not remove the residual carbon efficiently, yet the underlying semiconductor components were readily oxidized. Hydrogen ion bombardment was effective in removing the carbon bombardment induced damage. The implications of these results for alkane based RIE processes are discussed.
Conversion electron Mössbauer characterization of Fe–Ti and Fe–TiN interfaces in dependence on pretreatments and bias voltage in physical vapor depositiona)
Authors: Hanžel Darko , Meisel W. , Hanžel D. , Griesbach P. , Navinšek B. , Panjan P. , Gütlich P.
Published: July 2002

Conversion electron Mössbauer (CEMS) and Auger electron spectroscopies (AES) were used to investigate the interfaces of Ti and TiN coatings on iron. The microstructure of the interface has been studied regarding the dependence on physical vapor deposition (PVD) parameters. In particular, the substrate temperature and the negative voltage (bias) applied during the PVD process were considered. An amorphous FexTi1−x phase has been identified at the interface of Fe/Ti. Its portion increases with increasing bias used during the deposition process. Mössbauer spectra also reveal a small amount of a magnetically ordered Fe–C phase in the FeTi interface. Its formation can be explained by a reaction of the residual gas in the PVD preparation chamber with iron. However, Fe/TiN interfaces show mainly iron carbide and/or nitride phases. Iron oxides always appear in the interfaces between the substrate and the deposited Ti or TiN thin films and their contribution increases when cleaning procedures in acetone and isopropyl alcohol were applied previous to the PVD deposition. They occur mostly in the form of magnetically ordered magnetite or/and in the form of small superparamagnetic particles, depending on the deposition conditions. Samples of Fe/Ti and Fe/TiN were annealed in vacuum at 773 K for 1 h, and CEMS spectra as well as AES depth profiles by argon ion sputtering were recorded. For the Fe/Ti interface, only minor changes were found. Fe/TiN interfaces, however, were found to be destabilized at an elevated temperature by an oxidative decomposition of TiN combined with reactions of the interface components with the substrate material.
Imaging entire genetically functional DNA molecules with the scanning tunneling microscope
Authors: Allison D. P. , Thundat T. , Jacobson K. Bruce , Bottomley L. A. , Warmack R. J.
Published: July 2002

Deoxyribonucleic acid (DNA) can be immobilized on epitaxial gold surfaces treated with 2-dimethylaminoethanethiol preventing removal of the molecules due to forces exerted by the scanning tunneling microscope probe tip. We present reproducible images of entire plasmid molecules on these surfaces and discuss differences in image contrast that we have observed.
Transport in strain relaxed In0.15Al0.85As/In0.17Ga0.83As heterojunctions
Authors: Fernández J. M. , Chen Jianhui , Wieder H. H.
Published: July 2002

The electrical and galvanomagnetic properties of the two-dimensional electron gas (2DEG) in δ-doped and modulation doped strain–relaxed In0.15Al0.85As/In0.17Ga0.83As heterojunctions have been determined, as a function of sheet carrier density, by temperature dependent resistivity Hall and 1.6 K Shubnikov de Haas (SdH) oscillatory magnetoresistance measurements. The structures were grown by molecular-beam epitaxy on misoriented (001) GaAs substrates; strain relaxation, confirmed by double crystal x-ray diffraction, was obtained by means of step graded InxGa1−xAs buffer layers with x=0.10, and x=0.15 steps of 0.3 μm in thickness. Low temperature (1.6 K) SdH measurements confirm the presence of well behaved 2DEG layers with negligible parallel conduction, and single band occupancy for sheet carrier densities ranging from 7.4×1011 cm−2 to 1.0×1012 cm−2, and respective mobilities of 7.5×104 cm2/V s and 6.1×104 cm2/V s. Low field resistivity and Hall measurements suggest a transition, at a sheet carrier density of approximately 1012 cm−2, from an alloy scattering dominated mobility, to a mobility limited by ionized impurity scattering. The excellent transport properties of the 2DEG channels suggests the use of strain relaxation by means of appropriate buffer layers for heterostructure devices grown on gallium arsenide substrates.
Phase formation in sputter deposited metal (V, Nb, Zr, Y) oxides: Relationship to metal, metal–oxygen, and oxygen flux
Authors: Aita Carolyn Rubin
Published: July 2002

It is well documented that an oxide is formed on the surface of a metal target sputtered in an O2-bearing discharge. The sputtered flux will, in general, consist of metal atoms (M) and metal–oxygen molecules (M–O). In this study, a series of metal (M=V, Nb, Y, Zr) targets were sputtered in rare gas–O2 discharges. Films were grown on substrates at low temperatures (70–325 °C). Optical emission spectrometry was used to index the growth environment in terms of (a) the fractional flux of M and M–O species to the growth interface, and (b) the availability of oxygen for reaction at the growth interface. The interrelation of process parameters, phase formation, and the growth environment indices was presented in the form of phase maps. Common features in the phase maps of all systems were identified.
Sputter deposition of yttrium–oxides
Authors: Jankowski A. F. , Schrawyer L. R. , Hayes J. P.
Published: July 2002

The yttrium–oxide phase diagram contains only one equilibrium compound, a Y2O3 cubic structure. The process of reactive sputter deposition is used to synthesize previously unreported, yttrium-rich oxide compounds. A planar magnetron is operated in the direct–current mode using a working gas mixture of argon–20% oxygen. For low sputter gas pressure and flow conditions, the yttrium content of the coating is directly controlled as a function of the applied target power, i.e., the deposition rate. The composition and structure of the coatings are characterized using Auger depth profiling and x-ray diffraction. A continuous series of compounds are formed with an orthorhombic crystal structure for concentrations ranging from 40 to 75 at. % yttrium.
Variational principle of thin film adhesion
Authors: Jeong Hyo-Soo , White Robert C.
Published: July 2002

The interfacial fracture energy between a thin polyimide film and a rigid Si substrate was measured via the blister test. A dynamic debonding mechanism was used instead of a static debonding mechanism. A nonlinear analytical method was developed based on local energy balance for the dynamic debonding process of the blister test. The main advantages of this method are that (1) the dissipated energies which accompany the debonding processes can be measured and (2) the mechanical properties of thin films do not enter into the calculation of adhesion strength. A minimum value for adhesion energy can be obtained which compares favorably with estimated values of adhesion.
Monte Carlo simulations of textured planar magnetron targets
Authors: Bouchard F. , Dittmar M. B. , Manring B.
Published: July 2002

The effect of sputtering target crystallographic texture and grain size on film uniformity has been studied for advanced planar sputtering equipment. A grid of polygons over the target area was created by a computer program. Each polygon of the grid represented an individual grain, with a discrete crystal orientation. Crystallographic orientation distribution function (ODF) files were obtained for a number of polycrystalline targets through pole figure x-ray analysis and harmonic texture analysis. The ODF files were used to assign a crystal orientation to each polygon. The program then simulated the sputtering process by randomly choosing a location on the target, calculating the sputtering probability from the depth profile of a used target, and, finally, calculating the sputtered atom emission angles from the crystal orientation of that grain. An angular thermal correction was added to the emission angles. Each sputtered atom trajectory and arrival position on the substrate was then calculated. After 50 million events, film uniformity was calculated from all arrival positions for a 200 mm substrate. We found that for a full erosion planar magnetron sputtering target, at a 4.5 cm target–substrate separation, film uniformity was directly proportional to grain size. For full erosion sputtering cathodes, at 4.5 cm separation, no effect of target crystal orientation was observed. When the target–substrate separation was increased from 4.5 to 12 cm, the effect of grain size was decreased and crystal orientation played a more important role. Experimental sputtering data from a full erosion round planar cathode qualitatively confirmed the trend in the simulation results. It was also found that for sputtering systems in general, there is an absolute limit on film uniformity standard deviation. This limit was associated with the presence of an erosion profile on the sputtering target.
Metallization of Teflon PFA. II. Interactions of Ti, Ag, and Au measured by x-ray photoelectron spectroscopy
Authors: Shi M. K. , Lamontagne B. , Selmani A. , Martinu L. , Sacher E. , Wertheimer M. R. , Yelon A.
Published: July 2002

Ti, Ag, and Au were evaporated onto Teflon PFA (polytetrafluoroethylene-co-perfluoroalkoxy vinyl ether) surfaces by electron beam evaporation. Au was also sputtered onto PFA, in order to examine the effect of the kinetic energy of the depositing metal atoms on the metal/polymer interaction. The evolution of metal/polymer interfacial structures with increasing deposited metal thickness was followed using x-ray photoelectron spectroscopy. It was found that Ti deposition leads to defluorination and the formation of fluoride and carbide species. The reactions increased with deposited Ti thickness, slowly in the initial stages of deposition but more rapidly afterwards. The effects of evaporated Ag and Au were very similar, both resulting in slight losses of fluorine: No formation of new species was detected. Compared to evaporated Au, sputtered Au increased polymer surface modification, indicated by the formation of –CF3, –CF–, and –C– species; an enhanced chemical reactivity was manifested by the appearance of Au fluorides. After deposition of the first several Å of metal, the rate of deposition onto the PFA was enhanced for evaporation but decreased for sputtering, due to the action of subsequently sputtered species.
Purity of atomic oxygen production from heated iridium surfaces
Authors: Smentkowski V. S. , Yates J. T.
Published: July 2002

Hot iridium filaments for the production of atomic oxygen have been characterized by two complementary techniques—gas phase line-of-sight mass spectrometry and surface trapping experiments using a gold substrate. It is demonstrated by both techniques that Ir is detected as a subliming species prior to detectable atomic oxygen production. This calls into question previous studies which have employed iridium as a thermal source of pure atomic oxygen for research purposes.
Pb preadsorption facilitates island formation during Ge growth on Si(111)
Authors: Hibino H. , Shimizu N. , Sumitomo K. , Shinoda Y. , Nishioka T. , Ogino T.
Published: July 2002

On a clean Si(111)-7×7 surface, Ge grows in the Stranski–Krastanov mode. At 300–450 °C, relaxed islands begin to form when the Ge growth is 6 monolayers (ML) thick. When Ge is grown on a Pb/Si(111)-√3×√3 surface, Pb segregates on the surface and agglomerates into two-dimensional islands. And the critical thickness for the formation of relaxed island becomes 4 ML. This change in critical thickness is explained by Pb reducing the surface energy or by an improved crystallinity of Ge layers (due to a simplified substrate surface reconstruction), or by both.
Examination of wax on surface of extruded Pellethane by scanning electron microscopy attenuated total reflection-infrared and x-ray photoelectron spectroscopy and its importance in blood compatibility
Authors: Sawyer Anita , Bandekar Jagdeesh , Li Hong
Published: July 2002

Many types of polymers have been used for medical devices for blood contacting application. Polyurethanes have been determined to be one of the more blood-compatible. However, there is variability within types of polyurethanes and even within the same type of polyurethane as far as hemocompatibility. This variability stems in part from differences in processing aids, including waxes, which manufacturers add. An understanding of the surface chemical properties is essential for the determination of the hemocompatibility of polyurethanes. For this presentation, we describe analysis of the wax component of the surface of a polyurethane commonly used for extruded medical devices, Pellethane 2363 (Dow), by Fourier-transform infrared-attenuated total reflection (FTIR-ATR) and x-ray photoelectron spectroscopy (XPS), and the effect of its presence on the hemocompatibility of Pellethane. Solvent cleaned samples, demonstrating reduced amide processing wax component by the two techniques, are also evaluated for blood–surface interactions. Tubing samples are evaluated for hemocompatibility by exposure to human platelet/plasma solutions followed by analysis using scanning electron microscopy. There is a direct correlation between the amount of amide processing wax in Pellethane as determined by FTIR-ATR and XPS and the in-vitro hemocompatibility.
Model of lead loss in Pb(MgxNb1−x)Oz ion beam sputtered thin films
Authors: Pignolet A. , Roy R. A. , Doyle J. P. , Cuomo J. J.
Published: July 2002

Thin films of Pb(MgxNb1−x)Oz (hereafter called PMN) have been deposited on carbon substrate by reactive ion beam sputtering, from a mixed oxide–metal multicomponent target composed of magnesium oxide, and metallic niobium and lead. The substrate temperature and sputtering gas composition (oxygen pressure during deposition) were varied and their effects on the film composition and compositional uniformity were investigated. The major effect seen was the systematic variation in Pb content with changes in temperature and gas composition. We also observed a spatial variation in Pb composition across the substrate and believe this to be caused by film bombardment by argon ions specularly reflected by the target surface. This was supported by results showing a systematic reduction in Pb content in films subjected to secondary ion bombardment during film growth. The selective Pb depletion in PMN films is discussed in terms of various mechanisms found in reactive sputtering environments.
In situ pulsed laser-induced thermal desorption studies of the silicon chloride surface layer during silicon etching in high density plasmas of Cl2 and Cl2/O2 mixtures
Authors: Cheng C. C. , Guinn K. V. , Donnelly V. M. , Herman I. P.
Published: July 2002

We have used laser-induced thermal desorption, combined with laser-induced fluorescence of SiCl(g) to study, in real time, the Si-chloride (SiClx(ads)) layer that is present on the surface during Si etching in a high-plasma density, low pressure Cl2 helical resonator plasma. The SiClx(ads) layer that builds up during etching contains about twice as much Cl as the saturated layer that forms when Si is exposed to Cl2 gas. By varying the laser repetition rate we determined that the surface is chlorinated with an apparent first-order time constant of ∼6 ms at 1.0 mTorr, and 20 ms at 0.3 mTorr. Therefore in the plasma at pressures above ∼0.5 mTorr, the SiClx(ads) layer reaches saturated coverage on a time scale that is short compared to the time required to etch one monolayer (40 ms). From the weak dependence of the SiClx(ads) layer coverage on discharge power (0.2–1 W/cm3), substrate bias voltage (from 0 to −50 V dc), and pressure (0.5–10 mTorr), we conclude that ion flux, and not neutral etchant flux (i.e., Cl and Cl2), limits the etch rate, even in a low pressure, high-charge-density plasma. The chemically enhanced Cl+2 sputtering yield is 0.38 at an ion energy of 50 eV and 0.60 at 125 eV. Because of the relatively low neutral-to-ion flux ratios (∼2:1 at the lowest pressures) compared to reactive ion etching conditions, a substantial portion of the chlorine needed to form volatile products can be provided by the impinging ions. The SiClx(ads) layer does not change appreciably (<10% decrease in Cl coverage) after the plasma is extinguished and the gas is pumped away. Consequently, post-etching surface analysis measurements on samples that are transferred under ultrahigh vacuum to an analysis chamber provide information on the surface as it was during etching. The SiClx(ads) coverage and etch rate decreases with increasing addition of O2 to Cl2, due to the competition for adsorption sites by O.
Ion beam induced chemical vapor deposition procedure for the preparation of oxide thin films. I. Preparation and characterization of TiO2 thin films
Authors: Leinen D. , Espinós J. P. , Fernández A. , González-Elipe A. R.
Published: July 2002

A new method of preparation of oxide thin films is presented in this paper. The method consists of the bombardment of a substrate with accelerated O+2species while a flow of a volatile organometallic precursor is directed on its surface. This ion beam induced chemical vapor deposition procedure (IBICVD) has been used to prepare TiO2 thin films from Ti(CH3CH2O)4 as a precursor. Also, for comparison, TiO2 thin films have been grown by a plasma assisted chemical vapor deposition (CVD) method. A study of the growing process has been carried out by x-ray photoelectron spectroscopy (XPS), while the films have been characterized by XPS, scanning electron microscopy, transmission electron spectroscopy, and UV-visible (UV-vis) spectroscopy. Values of the refraction index of the TiO2 films prepared by IBICVD are similar to those of other TiO2 prepared by ion beam assisted methods as given in the literature, but superior to those of the films grown in the present study by plasma assisted CVD.
Chemical properties of Zn on Ru(001): Coadsorption with Cs, O, Cu, and Au
Authors: Rodriguez José A. , Hrbek Jan
Published: July 2002

The coadsorption of Zn with Cs (an electropositive species) or O (an electronegative species) on Ru(001) does not induce significant changes in the thermal stability of the Ru–Zn bond. On the other hand, two-dimensional CuZn (or AuZn) alloys in contact with Ru(001) show Ru–Zn and Zn–noble metal bonds more stable than the corresponding bonds in Zn/Ru(001) and thick CuZn (or AuZn) alloys. This phenomenon is caused by synergistic interactions in three-center metal–metal bonding. Photoemission studies indicate that at submonolayer coverages of Zn and O there is no lateral bonding between these species on Ru(001). The formation of ZnOx films on Ru(001) occurs when the Zn and O coverages are higher than 1 ML. On Zn films supported on Ru(001), the initial adsorption probability of O2 is extremely low, and O2 exposures in the range of 103–104 L are necessary to produce a significant transformation of metallic Zn into ZnO. The presence of Cs enhances the oxidation rate of Zn by 2–3 orders of magnitude. In the Cs/Zn/Ru(001) systems, the alkali adatoms adsorb and dissociate O2 molecules, producing a reservoir of oxygen species that react with Zn.
Two-step, oxygen-free route to higher hydrocarbons from methane over ruthenium catalysts
Authors: Wu Ming-Cheng , Lenz-Solomun Petra , Goodman D. Wayne
Published: July 2002

Methane coupling on single-crystal ruthenium catalysts has been studied utilizing combined elevated-pressure kinetic measurements/surface science studies. The reaction consists of the activation of methane on Ru(0001) and Ru(112̄0) surfaces to produce carbonaceous deposits at temperatures (TCH4) between 350 and 700 K and rehydrogenation of these species to ethane and propane at TH2≂ 370 K. It is found that under reaction conditions employed, the maximum yield in ethane/propane production occurs at TCH4≂ 500 K on both the surfaces. High-resolution electron energy-loss spectroscopy (HREELS) has been used to identify various forms of hydrocarbonaceous intermediates following methane decomposition. The HREELS data reveal that methane decomposes on both the surfaces to produce methylidyne (CH) and vinylidene (CCH2) intermediates. A correlation between the hydrocarbon intermediates identified by HREELS and the gas phase products observed in the elevated pressure experiments has been found. The results show that the surface vinylidene species is likely to be the key intermediate responsible for the C2 production.
Photodesorption dynamics of ammonia from Ni(111) and NiO/Ni(111)
Authors: Mackay R. Scott , Junker K. H. , White J. M.
Published: July 2002

The photodesorption dynamics of ammonia, adsorbed on Ni(111), both clean and oxidized, was studied using 193 and 248 nm pulsed laser excitation. Time-of-flight and angular distributions were measured. The angular distributions for both surfaces peak along the surface normal; there is a second maximum located 20° off-normal for the oxidized surface. The desorption cross section depends on wavelength (1×10−18 and <1×10−20 cm2 at 193 and 248 nm, respectively), and on the surface used (higher for Ni) than oxidized Ni at 193 nm. The time-of-flight spectra are adequately fit using two characteristic energies, which do not depend on the wavelength (300 and 35 meV for Ni, 225 and 35 meV for oxidized Ni).