bluuebunny/crossref_metadata_2025 huggingface dataset:
The interface chemistry of HgCdTe passivated with native sulfide layers grown from nonaqueous and aqueous polysulfide solutions
Authors: Ziegler John P. , Lindquist John M. , Hemminger John C.
Published: July 2002

We have grown anodic sulfide passivation layers on HgCdTe from both nonaqueous and aqueous polysulfide solutions. In both cases CdS layers are nominally obtained. The growth behavior of the sulfide layers is found to be quite different in the different electrolytes. Capacitance–voltage measurements on metal-insulator semiconductor device structures that incorporated a ZnS cap and Pd gate metal over the CdS have been used to compare the electrical properties of the interfaces produced. Preliminary evidence suggests that aqueous anodic sulfide layers may be more stable than nonaqueous ones, but contain more positive fixed charge and mobile ion charge. Auger electron spectroscopy depth profiles indicate that the aqueous anodic sulfides are oxide free, but appear to contain more Hg and Te contamination than nonaqueous anodic sulfides.
Si planar doping of GaAs
Authors: Torabi A. , Haugen R. B. , Harris H. M. , Summers C. J.
Published: July 2002

δ doping is demonstrated to be a scheme for reducing carrier profile width and increasing doping density. We have grown multilayers of planar Si doped GaAs by molecular-beam epitaxy and profiled the dopant distribution by electrochemical C–V profiling and secondary ion mass spectroscopy. It is estimated that the delta doping could be confined to approximately three atomic layers. The measured profiles appear much broader due to instrumentational broadening. Secondary ion mass spectroscopy profiles measure a full width at half-maximum (FWHM) of 6.3 nm for Si in GaAs, while C–V profiles measure FWHM of 3.1 nm.
Direct observation of bioelectrochemical processes by scanning tunneling microscopy
Authors: Thundat T. , Nagahara L. A. , Oden P. , Lindsay S. M.
Published: July 2002

We have imaged DNA deposits that have been reacted onto a gold electrode. Our scanning tunneling microscope (STM) is operated in a three electrode cell using insulated tips. Samples are deposited at a controlled potential relative to an Ag/AgCl reference electrode. Many different adsorption geometries are observed, different substrate potentials resulting in characteristic adsorption patterns. Here, we report initial results for negative electrodes. At −2.3 V (Ag/AgCl), the DNA appears to attach to the substrate end on. As the potential is lowered towards zero volts, the DNA attaches side on, forming aggregates of decreasing complexity with decreasing substrate potential. Isolated molecules are observed near −1 V (Ag/AgCl). Below this potential, coverage is much less dense. Those molecules that adsorb do so in aggregates, which may bind in alignment with the underlying atomic structure of the substrate.
Lithographic studies of an e-beam resist in a vacuum scanning tunneling microscope
Authors: Marrian C. R. K. , Dobisz E. A. , Colton R. J.
Published: July 2002

The scanning tunneling microscope (STM) provides a confined low energy electron beam which can be exploited for e-beam lithography. It offers the potential of overcoming the resolution degradation due to secondary and backscattered electrons produced by the high energy primary beam in conventional e-beam lithography systems. A polydiacetylene negative e-beam resist has been evaluated in an STM mounted in a ultrahigh vacuum (UHV) chamber. The resist can be both imaged and exposed in situ by the STM. Under e-beam irradiation raised features are formed which can be imaged directly. A minimum feature size of 20 nm has been observed which is less than third of the minimum feature size observed following exposure in a high voltage e-beam writer and development. The smallest features were written in the STM at an electron energy just above the exposure energy threshold which was measured to be about 8 eV.
X-ray photoelectron and Auger electron forward-scattering studies of lattice expansions and contractions in epitaxial films
Authors: Egelhoff W. F. , Jacob I. , Rudd J. M. , Cochran J. F. , Heinrich B.
Published: July 2002

X-ray photoelectrons and Auger electrons emitted by atoms in a lattice undergo forward scattering by neighboring atoms during their propagation through the lattice. This forward scattering produces enhancements in the emission intensity along nearest-neighbor directions. In the present work, the directions of these enhancements are used to infer lattice expansions and contractions in epitaxial films. Epitaxial films of Mn grown on Cu(100) expand outwards and on Ag(100) contract inwards, as compared to a simple extension of the face-centered-cubic substrate lattice. Thus, in both cases, the Mn lattice is body-centered-tetragonal. This expansion and contraction is reasonable since the Mn atom is intermediate in atomic volume between Cu and Ag, so that it must by compressed laterally to match the Cu(100) surface and stretched laterally to match the Ag(100) surface. However, it is of interest that the combined magnitude of these effects yield, in both cases, Mn with a larger atomic volume than that found in elemental α-Mn. Nevertheless, epitaxial Mn sandwich structures consisting of 60-ML-Cu/3-ML-Mn/Cu(100) and 60-ML-Ag/3-ML-Mn/Ag(100) were found not to be ferromagnetic even at 77 K. Experiments on the annealing of monolayer-range Mn films demonstrate that neither Cu(100) nor Ag(100) is wet by Mn. Studies of epitaxial Fe and Cu films on Ag(100) demonstrate that in both cases a vertical contraction occurs that yields a lattice quite close to body-centered-cubic.
Microcorrosion of Al–Cu and Al–Cu–Si alloys: Interaction of the metallization with subsequent aqueous photolithographic processing
Authors: Weston D. , Wilson S. R. , Kottke M.
Published: July 2002

The objective of this work was to systematically study the localized corrosion which can occur when Al–Cu and Al–Cu–Si metallizations are exposed to conventional photolithographic processing. The study includes electrical evaluations of a standard 1.6-m interdigitated serpentine and comb test pattern which was reactive ion etched to quantify the effect of surface corrosion on serpentine yield. Al–Cu and Al–Cu–Si (0.5%–1.5% Cu and Si by weight) films were sputter deposited at temperatures ranging from 305–465 °C and patterned using batch photolithographic processing. Localized surface corrosion was found on all metallizations, to varying degrees, after a standard 90-s batch development on both patterened and unpatterened metal substrates. Al–0.5%Cu–0.5%Si was found to have the least surface corrosion while Al–1.5%Cu had the most. Electrical shorting was observed in those cases where the corrosion site diameter was greater than the space between adjacent metal lines after RIE. The corrosion is correlated with theta phase precipitates which are known to induce corrosion on Al–Cu alloys by galvanic action in the appropriate electrolyte. The corrosion occurred when the wafer was exposed to the rinse water after the develop step. Postdeposition baking in the range 200–450 °C dramatically affects the concentrations of theta phase precipitates and as a result, the corrosion and yield. The addition of silicon to the Al–Cu alloy was found to improve its corrosion resistance.
Changes in surface composition and Fermi level position during thermal desorption of ultraviolet radiation/ozone formed oxides on GaAs
Authors: Lau W. M. , Sodhi R. N. S. , Jin S. , Ingrey S.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) has been used to study the native oxide structure and surface Fermi level of GaAs exposed to ultraviolet light (UV)/ozone, as well as to monitor changes that occur during thermal desorption of the surface oxide. The XPS results confirm that the surface oxide consists of a mixture of gallium and arsenic oxide phases which desorb at two different temperature ranges: desorption of arsenic oxide phases and oxygen transfer from arsenic to gallium occur at 250–500 °C; and desorption of gallium oxide phases occurs at 550–600 °C. In addition, we found that the surface Fermi level of GaAs below the UV/ozone formed oxide was always at about 0.8 eV from the valence- band maximum (VBM) for n-type substrates and 0.5 eV for p-type substrates. Similar results were found for wet chemically treated and then air exposed GaAs surfaces. However, the surface Fermi levels of both n- and p-type substrates, during the desorption of arsenic oxide in the temperature range of 250–500 °C, moved further away from VBM by as much as 0.4 eV. When the samples were heated to higher temperatures, the surface Fermi level moved back to midgap even before complete desorption of the gallium oxide phases. Fermi level pinning on samples before and after oxide desorption has also been characterized by in situ deposition of 5 nm of silicon nitride on the sample surface in the XPS system and by monitoring the surface potential of the semiconductor with XPS as a function of charging potential on the dielectric. It was found that surfaces both before and after arsenic oxide desorption were pinned within 0.1 eV with a negative voltage of about 2 V on the thin dielectric.
The effects of biasing and annealing on the optical properties of radio-frequency sputtered VO2
Authors: Razavi A. , Bobyak L. , Fallon P.
Published: July 2002

Vanadium dioxide thin films were deposited by radio-frequency (rf) reactive sputtering. An in situ anneal was found to improve stoichiometry, alter optical contrast, and increase grain size for a set of films. Biasing of a second set of substrates during deposition was found to increase the infrared (IR) transmission of films in the metallic state and degrade hysteresis characteristics.
Lateral dopant profiling on a 100 nm scale by scanning capacitance microscopy
Authors: Williams C. C. , Slinkman J. , Hough W. P. , Wickramasinghe H. K.
Published: July 2002

Measurement of dopant density in silicon with lateral resolution on the 100 nm scale has been demonstrated with a ‘‘near field’’ capacitance microscope. The technique is based upon the measurement of local capacitance between a 100 nm tip and the sample surface as the tip is scanned over the surface. The capacitive microscope used to image the dopant is capable of measuring capacitance variations of 3×10−22 F/(Hz)1/2, and previously has demonstrated a 25 nm resolution on metallic surfaces. Dopant imaging is achieved by scanning the tip under feedback control close to a silicon surface, and measuring the capacitance variations. Several types of measurements have been made on the submicrometer scale. First, direct two-dimensional visualization of the dopant in silicon has been achieved by this nondestructive, noncontacting technique. Second, capacitance versus voltage (C–V) measurements have been made with high spatial resolution, providing the means for the measurement of many of the properties of silicon and its oxide. Third, the effects of optical pumping on the local depletion capacitance signal have been observed. Finally, first-order modeling has shown reasonable agreement between theory and experiment, and should provide the means of extraction of dopant density in three dimensions at high resolution.
Modeling of sputtering and redeposition in focused-ion-beam trench milling
Authors: Ishitani Tohru , Ohnishi Tsuyoshi
Published: July 2002

Modeling is performed for focused-ion-beam (FIB) sputtering and redeposition on trench sidewalls in a steady state approximation. Calculations are carried out to demonstrate the sputtered surface profile under known parameters such as sputtering yield as a function of ion incident angle, the FIB current density profile, and the FIB scan speed. It is found that a steplike slope with a gradient angle of θ0 is formed at the FIB bombarding position. Furthermore, the redeposition flux on the sidewalls is calculated as a function of θ0 for the FIB trench milling assuming the cosine law for the angular distribution of the sputtered atom. The redeposition will be more accurately predictable and controllable when more information about these assumptions is obtained.
Cracking and delamination of coatings
Authors: Thouless M. D.
Published: July 2002

The mechanism by which a coating will fail is governed by a number of parameters. These include not only the properties of the coating, interface, and substrate, but also the distribution of stresses. If the coating is under a residual tensile stress, there are at least three possible mechanisms by which failure can occur. For example, a brittle coating may fracture by the development of cracks through the thickness of the film. Tougher coatings may fail by delamination along the interface or even by the propagation of a crack within the substrate. The failure mechanism associated with a compressive stress in the coating involves simultaneous buckling and delamination. This paper reviews these different modes of failure and discusses the conditions that determine which ones will operate.
The deposition of oxygen containing plasma polymers for use as permeation barrier coatings
Authors: Crawley R. L. , Evans J. L.
Published: July 2002

It has been found that common polymers containing oxygen have reduced hydrogen permeability. In this work we have incorporated oxygen into plasma polymer coatings as hydroxyl (OH) and carbonyl (C=O) side groups by codepositing organic vapors with H2O or H2O2. We can vary the amount of oxygen incorporated up to 25 wt% oxygen. By adjusting the amount of incorporated oxygen and the deposition parameters we can alter the hydrogen permeability of the coatings by more than three orders of magnitude. Choice of the organic precursor used has the largest effect on incorporation of OH groups into glow discharge polymerization coatings. Organics with multiple triple bonds codeposited with H2O2 produce polymer coatings with the highest oxygen content and the lowest hydrogen permeability. Organics with nitrogen such as acetonitrile codeposited with H2O2 produced plasma polymer coatings with reasonably low permeability and improved mechanical and chemical resistance. Coated membranes were exposed to radioactive tritium gas for extended periods of time and then analyzed for deterioration by remeasuring hydrogen permeability, infrared absorption, and mechanical stability.
H-isotope retention and thermal/ion-induced release in boronized films for the Tokamak Fusion Test Reactor
Authors: Walsh D. S. , Doyle B. L. , Wampler W. R. , Hays A. K.
Published: July 2002

Over the past decade, it has been clearly demonstrated that the composition of the very near surface (∼100 nm) of plasma-interactive components plays a determinant role in most processes which occur in the plasma edge of tokamaks. Two very successful techniques to effect control of the plasma-wall interaction are (1) in-situ deposition of amorphous carbon or boron-carbon films and (2) the use of He/C conditioning discharges or He glow discharge cleaning to modify the near surface of bulk graphite components. We have deposited boronized layers onto Si using plasma-assisted chemical vapor deposition (CVD) and sputter deposition. The plasma-enhanced chemical vapor deposition (PCVD) deposition conditions were as close as possible to those used in the Tokamak Fusion Test Reactor (TFTR), and some films deposited in TFTR have also been studied. Using these two deposition techniques, BxCHy films have been produced with x varying from 1/2–4, and y from ∼1 (sputtered) to ∼3 (PCVD). Most films also contained significant amounts of O. Thermal and ion-induced release of H isotopes from BC films is qualitatively similar to that measured for graphite. Implanted H saturates in these films at an H/host atom ratio of 0.7 which is considerably higher than that of graphite (∼0.4). As-deposited PCVD films are already saturated with H, while sputtered films are not. Sputtered BC films therefore possess an inherent H-pumping capability which could prove to be extremely beneficial to TFTR.
Etch mechanism in the reactive ion etching of silicon nitride
Authors: Dulak J. , Howard B. J. , Steinbrüchel Ch.
Published: July 2002

Reactive ion etching of silicon nitride with CHF3/O2 plasmas has been studied in a hexode reactor and compared to silicon dioxide etching. Measurements of etch rates as a function of gas composition and pressure were combined with Langmuir probe data for the ion flux to the substrate to give etch yields (number of substrate atoms removed per bombarding ion). At low oxygen content, the etch yields of both materials are about 2 atoms/ion and are essentially independent of pressure between 10 and 60 mTorr. At higher oxygen content, the etch yield is considerably larger for silicon nitride, and for both materials the etch yields increase with increasing pressure. From these results it can be concluded that in a CHF3/O2 plasma at low oxygen content, the etch mechanism is mostly direct reactive ion etching for both silicon nitride and silicon oxide. On the other hand, at higher oxygen content the etching is ion enhanced for both materials, but to a much greater extent in the case of silicon nitride.
Transverse Kerr nonreciprocal effects in transmission
Authors: Biricik V. Warren
Published: July 2002

Transmission magneto-optic effects are analyzed for a configuration consisting of a semitransparent magneto-optic layer bounded by two semiinfinite media. It is shown that two nonreciprocal effects manifest themselves in transmission. These are: a) a phase shift; and b) an amplitude change. Both of these effects depend upon the direction of film magnetization. These transmission nonreciprocal effects vanish for all angles of incidence when the magneto-optic layer is surrounded by identical media. In the case where the magneto-optic film is imbedded in two distinct media, the nonreciprocal effects are present, but vanish at one specific angle of incidence. At this angle of incidence, the optical impedances of the two bounding media are identical. For a light wave propagating from the exit medium toward the entrance medium, the nonreciprocal effects in transmission only change sign.
Dimerization and adsorption of Si on the Si(100) surface
Authors: Gryko J. , Allen R. E.
Published: July 2002

Electron spin density functional calculations of the dimerization of surface atoms, and the adsorption of additional Si atoms, are reported for Si(100). We find that the dimerization energy calculated in a nonlocal spin density approximation agrees rather well with the energies given by the empirical potentials of both Stillinger and Weber and Tersoff, although the range of these potentials is too short. The calculated values of the adsorption energy for Si on Si(100) are in moderately good agreement with Tersoff’s potential.
A novel deposition technique for switchable vanadium sesquioxide (V2O3) thin films
Authors: Case F. C.
Published: July 2002

V2O3 is a phase transition material, which, like other oxides of vanadium, undergoes large changes in optical and electrical properties upon switching from the semiconductor to metal state. The transition in V2O3 occurs at temperatures well below that of oxides in the same family, namely near 150–170 K, making it attractive for a number of low-temperature applications. This material has been deposited by a variety of methods, including chemical vapor transport, rf sputtering of a stoichiometric target, pyrolysis, and heat treatment of a sputtered vanadium oxide film. Thin films of this material have also been prepared by the reduction of predeposited VO2 thin films, requiring the flow of hazardous gases such as hydrogen or carbon monoxide over the sample, which is held at high temperatures in excess of 700 °C. A direct synthesis method for the deposition of high quality V2O3 thin films with low infrared absorption and resistivity change of more than six orders of magnitude is described. Optical, resistivity, and morphological characteristics of this material are discussed.
Anomalous magnetotransport in epitaxial TbSi2−x
Authors: Kaatz F. H. , Graham W. R. , Van der Spiegel J. , Joss W. , Chroboczek J. A.
Published: July 2002

Recent advances in heteroepitaxy have produced novel structures allowing the detailed investigation of material properties of the heterostructure components. We examine transport phenomena in 120 Å thick films of the rare earth silicide TbSi2−x. These films are epitaxial on Si(111) with channeling minimum yields below 10% as determined by Rutherford backscattering spectrometry. Electrical resistivity decreases linearly as the temperature is lowered to 38 K, where a rapid drop is observed due to magnetic ordering near the antiferromagnetic-paramagnetic transition. Hall constant data show that the majority carriers are electrons, with anomalies at 38 and 16 K. We measure for the first time the transverse and longitudinal magnetoresistance down to 4 K in magnetic fields up to 10 Tesla. At temperatures below 38 K the longitudinal magnetoresistance has a cusplike anomaly near 8 Tesla resulting from the magnetic field-induced suppression of the antiferromagnetic component of the structure. This anomalous behavior does not occur when the magnetic field is applied perpendicular to the c axis of the epitaxial layers, indicating that the antiferromagnetic structure is along in-plane directions.
The influence of ultrathin predeposited platinum layers on the formation of iridium silicide
Authors: Hoffman D. M. , McGinn J. T. , Gilmartin H. , Hewitt L. R. , Lanzillotto A.-M. , Szostak D. J. , Tams F. J. , Thomas J. H.
Published: July 2002

An investigation was made of Pt–Ir silicide films on (100)Si prepared by deposition of submonolayer thickness of Pt followed by 20–30 Å of Ir. Submonolayer coverages of Pt induce a crystalline texture approaching an epitaxial relationship between the normally amorphous IrSi film and the crystalline (100) Si substrate. Films were prepared using e-beam deposition, substrate temperature of 350 °C, and pressure at deposition ∼10−7 Torr. Rutherford backscattering, transmission electron microscopy, and Auger electron spectroscopy are used to characterize composition and thickness. Grain structure and crystallinity as well as film and substrate interface characteristics are functions of predeposition conditions. Simple diode measurements illustrate the effect of predeposited Pt on the emission coefficient and cutoff wavelength. Data suggests a model where the predeposited Pt acts as nucleation sites for crystal growth.
Plasma jet dry etching using different electrode configurations
Authors: Barklund A. M. , Blom H.-O. , Berg S.
Published: July 2002

Recently a high-rate dry-etching technique, the Plasma Jet, has been presented. An active gas, SF6, and a carrier gas, Ar, are passed through a cylindrical electrode ending in a nozzle. By applying rf power to the electrode a hollow cathode discharge is created inside the nozzle. The reactive gas will be effectively dissociated and a high concentration of reactive species will be formed. The formed species will be blown out at supersonic speed through the nozzle and enter the processing chamber in a jet-like manner. Thus there will be a very high concentration of reactive particles in front of the nozzle. Etch rates magnitudes larger than obtained in conventional etch systems can be achieved by exposing a silicon substrate to this high concentration of reactive species. Etch rates as high as 0.5 mm/min have been observed. Originally the Plasma Jet created a circular etch crater with a diameter of about 2–3 mm. This etched area is not satisfactory for most applications. We have investigated a number of new electrode configurations for the nozzle exhaust. Processing parameters, important for the etch rate, have been studied for these new nozzle configurations. It is shown that the flow of argon and the reactive gas SF6 drastically influences the operating conditions of the discharge. The shape of the nozzle is also very important for the performance of the plasma jet.
Unbalanced magnetrons and new sputtering systems with enhanced plasma ionization
Authors: Musil J. , Kadlec S. , Münz W.-D.
Published: July 2002

This paper presents a critical review of the present status and trends in the sputtering of thin films. A special attention is devoted to the magnetron sputtering, especially to unbalanced magnetrons (UM) and to new sputtering devices utilizing magnetic and/or electric plasma confinement. The last category of devices opens new possibilities in a production of high quality films. Sputtering systems using UM operated in the double-site-sustained discharge and in a closed multipolar magnetic field are described. The attention is also devoted to the effects of ion bombardment on the properties of the deposited films. In case of hard TiN coatings it is shown under what conditions dense compact porousless films can be created and how deposition conditions can influence stresses in films. At the end, several new systems which combine advantages of sputtering with other processes like the arc evaporation, the electron cyclotron resonance (ECR) plasma, and the laser irradiation are also briefly described.
Absorption and interaction of methylene chloride with metallized polyimide films
Authors: Matienzo L. J. , Emmi F. , VanHart D. C. , Lo J. C.
Published: July 2002

Metallized polyimide films are commonly used for the fabrication of flexible circuits for tape automated bonding (TAB) applications. Although there has been an extensive effort to understand the formation of the metal/polyimide interface, little information exists on the effects of humidity and temperature on adhesion. Further, since circuit fabrication processes involve a variety of chemicals, these materials can potentially induce adhesion degradation. Methylene chloride (MC), used for photoresist stripping, absorbs readily into Kapton-H. Residual MC levels in the polymer undergo decomposition upon heating above 100 °C to yield HCl. Optical microscopy, Rutherford backscattering spectroscopy and Auger electron spectroscopy are used to characterize the resulting interfaces on actual TAB circuit lines before and after exposures to humid and thermal environments. Thin metallized Kapton-H films were exposed to MC followed by a thermal cycle to determine the role of chloride on adhesion degradation. After a thermal cycle or additional temperature/humidity exposure, the fracture mode shifts from cohesive in the polyimide to the chromium/copper interface. This results in adhesion loss with concentration of chloride at the weaker interface.
X-ray induced reduction effects at CeO2 surfaces: An x-ray photoelectron spectroscopy study
Authors: Paparazzo E. , Ingo G. M. , Zacchetti N.
Published: July 2002

XPS techniques are used to study the effects of Al Kα x-rays on the surface chemical composition of CeO2. We find that prolonged exposures cause the formation of some Ce3+ oxidic species at the surface. We have studied the Ce 3p, Ce 3d, O 1s, Ce 4p, Ce 4d, and valence band regions in an attempt to localize the depth of damage. Consideration of published formulations for electron attenuation lengths and electron inelastic mean free paths indicates that the chemical reduction occurs mainly in the first 15–20 Å from the surface. Our results show that some of the XPS features, usually referred to as excited electronic states of ceria, are in fact induced by prolonged exposures to the x rays.
Development of an offline x-ray photoelectron spectroscopic personal computer-based data analysis system
Authors: McCaslin Paul C.
Published: July 2002

Although the majority of x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) instruments are interfaced to a computer upon which spectral analyses can be carried out, it is often convenient to be able to perform data analysis offline. This capability is especially desirable when one is faced with an outdated and/or slow analysis package associated with the XPS/AES instrument. Rather than upgrade the data system at an often considerable expense, one may choose to adopt an analysis package which is essentially instrument independent. Such a data analysis system has been developed. Its features include: spectral comparison (including addition and subtraction); several types of background signal generation; position and intensity data from cursor input; x- or y-axis expansion; calculation of FWHMs, areas, and precise peak maxima; spectral smoothing and differentiation; labelling facilities; XPS line library searches by element or cursor position; display of data collection statistics and run title; x-ray satellite line subtraction; channel intensity editing; x-axis shifting to account for charging; and a least-squares curve-fitting routine. Its ability to analyze XPS and AES spectra on a routinely available personal computer makes it an ideal package to serve as a front end for examining data files stored in a standardized format.
Polyethylene crystal lamella growth on the mica
Authors: Xue Z. Q. , Liu W. M. , Gao H. J. , Zhu C. , Ma Z. , Pang S. J.
Published: July 2002

The polyethylene thin films on the mica (001) plane have been prepared by the ionized cluster beam deposition technique and analyzed by the transmission electron microscope. We have found that the polyethylene crystal lamellar structures are obviously affected by the crystal mica substrate. We have observed the Moire fringe pattern and the overlap diffraction spot array for both crystal thin films, as well as explained that the polyethylene subunit cell grows along, the direction which rotates 60° relative to the unit cell of the mica (001) plane.
Optical study of strained quantum well wires
Authors: Tan I-Hsing , Yasuda Takashi , Mirin Richard , Lishan David , Hu Evelyn , Bowers John , Merz James , He Ming Yuan , Evans Anthony
Published: July 2002

We have investigated strain-induced lateral quantum confinement in a GaAs quantum well, as well as strain propagation along the material growth direction. The lateral confinement was generated by etching a grating pattern into a stressor of InGaAs which overlies a GaAs quantum well. For strain-induced quantum well wires formed by an In0.35Ga0.65As stressor, the excitation intensity- and temperature-dependent photoluminescence spectra show two well-resolved one-dimensional subband transitions whose splitting is 7.5±0.5 meV. We used luminescence data for multiple quantum wells, set at different distances beneath an In0.3Ga0.7As stressor, to confirm that the propagation depth of strain along the material growth direction is comparable to the width of wire stressors.
Growth characteristics of photolytic laser-induced chemical vapor deposition of tungsten from WF6
Authors: Mogyorósi Péter , Carlsson Jan-Otto
Published: July 2002

ArF laser induced chemical vapor deposition (CVD) of W onto (100)Si from a WF6/H2/Ar mixture and with the laser beam in parallel to the substrate surface was studied. The influence of substrate temperature on the deposition rate was investigated in a broad range (25–450 °C) for both focused and unfocused beam conditions and compared with thermal CVD data. Above the threshold temperature for the thermal process, 250 °C, a combined thermal and photolytic process takes place. Below 250 °C the laser induced photolytic process yields deposition with a nearly temperature independent deposition rate of about 100 Å/min when a focused beam is used. For an unfocused beam a slightly lower deposition rate was observed. The distance between the laser beam and the substrate surface had only a slight influence on the deposition rate. For the focused beam conditions the deposition rate was only reduced by roughly 10% when the distance was increased from 0 to 8 mm. For the unfocused case the deposition rate increased, without reaching the focused beam values, upon increasing the beam to substrate distance in the range 0–8 mm. The substrate temperature had a strong influence on the resistivity of the deposited films for both laser-induced and thermal processes. For obtaining a low resistivity value, 8 μΩ cm, a substrate temperature above 350 °C was required. This was mainly due to the fact that the high-resistivity β phase was formed at lower temperatures. The influence of H2 concentration on the growth rate was investigated by replacing H2 with Ar. A small amount of H2 was enough to increase the deposition rate considerably. Use of Ar diluted gas resulted also in a higher deposition rate. Finally, the deposition rate increased linearly with increased total pressure.
Structure of self-organizing organic films: A near edge x-ray absorption fine structure investigation of thiol layers adsorbed on gold
Authors: Hähner G. , Kinzler M. , Thümmler C. , Wöll Ch. , Grunze M.
Published: July 2002

Self-assembled films of thiols on polycrystalline Au substrates have been investigated with near edge x-ray absorption fine structure. From the angular dependence of two different resonances the orientation of the molecular axis of the alkyl chains with respect to the surface normal is determined and compared to results obtained by other techniques. By comparing data for thiol films and LB films of Cd and Ca arachidate it is found that thiol films are considerably better ordered.
Nondestructive determination of composition depth profiles on subnanometer scales using angle resolved Auger spectroscopy
Authors: Derry G. N. , Vanderlinde W. E.
Published: July 2002

The well-known attenuation of signal intensities for electrons escaping from a solid can be used, in conjunction with an angle resolving spectrometer, to measure compositions as a function of depth. The technique is nondestructive and can provide atomic-layer level resolution when the electron mean free paths are short. Such experiments have been traditionally done with x-ray photoelectron spectroscopy (XPS), but in this paper we employ a method for using Auger spectroscopy. The attenuation with depth is approximated as exponential, and the signal is integrated over depth for regions of constant composition (which can be as small as one atomic layer) at several different angles. The measured intensities as a function of angle are then used to find best-fit values for the desired quantities (compositions, layer depths, etc.). We have applied these methods to two interesting cases: surface segregation in a CuNi alloy and the layer thickness of SiO2 on a Si substrate. The data were obtained with a VG Scientific Microlab 310D using a modified sample holder. The analysis for a 50% CuNi alloy showed copper segregation with some C and S cosegregation; the surface layer was ∼70% copper, the second layer was slightly enriched, and beyond the third layer the composition approximated the bulk. Experiments for the SiO2/Si system were performed using both a thermally grown oxide of nominal thickness 7.5 nm and sample with an uncharacterized native oxide. The oxide layer thicknesses in these two cases were estimated to be 1.65λ and 0.17λ, respectively, where λ is the mean free path of the Auger electrons in the oxide layer. The reliability and precision of the technique are discussed, along with its applicability to various problems, restrictions on its use, and possible improvements.
Initial stage oxidation of the Ge:Si(111)-(5×5) and Ge:Si(111)-(7×7) surfaces
Authors: Cao R. , Bozso F. , Avouris Ph.
Published: July 2002

We have grown Ge:Si(111) epitaxial structures using low temperature photochemical vapor deposition. The electronic properties and initial stage oxidation of the reconstructed surfaces of these grown structures have been investigated with ultraviolet photoelectron spectroscopy, ion scattering spectroscopy, and low-energy electron diffraction. We find that the initial surface oxidation is a two-step process: formation of molecular precursors followed by dissociation into atomic species. Transition from the first step to the second step can be induced by thermal annealing or light irradiation. Surface oxidation is strongly affected by the local electronic structures. Oxygen reacts preferentially with adatoms on these reconstructed (7×7) and (5×5) surfaces, and changes in the top surface Ge/Si ratio result in drastic change in oxygen uptake rate.
Atomic force microscope imaging for process characterization in diamond film deposition
Authors: Chernoff Donald A. , Windischmann Henry
Published: July 2002

Atomic force microscope (AFM) images are presented for diamond films deposited using two processes. Films were deposited on polished Si from a CH4–H2 mixture by microwave plasma chemical vapor deposition (CVD) for CH4 concentrations in the range 0.4%–2.0%. At the lowest CH4 concentration, the film surface was rough (Rq = 80 nm) and contained many grains wider than 1 μ and taller than 0.4 μ. At the highest CH4 concentration, the growth of large grains was suppressed, producing much smoother films (Rq = 25 nm), which may be suitable as mask substrates for x-ray lithography. Filament-assisted CVD was also used; deposition was halted before a continuous film formed. The tallest grains (100–200-nm high) were clustered in intersecting linear arrays corresponding to marks made by diamond-polishing (seeding). Features a few nm high found in flat regions may be diamond nuclei on bare Si formed much later.
Study of the surface morphology and growth mode of in situ ion-beam sputter-deposited YBa2Cu3O7−δ thin films
Authors: Lichtenwalner D. J. , Auciello O. , Woolcott R. R. , Soble C. N. , Adu-Poku R. , Chapman R. , Rou S. H. , Duarte J. , Kingon A. I.
Published: July 2002

Films of YBa2Cu3O7−δ and YBa2Cu3O7−δ/MgO/YBa2Cu3O7−δ layered structures have been synthesized in situ using ion-beam sputter deposition. The surface morphology of the films has been studied by means of both scanning tunneling microscopy (STM) and scanning electron microscopy (SEM). STM analysis of films deposited at 720 and 680 °C reveals the presence of spiral growth columns, indicative of the screw-dislocation growth mode. However, the surface appears much smoother than that reported previously for YBCO films deposited by off-axis sputtering, revealing that particular film growth conditions affect the surface morphology. SEM analysis reveals the presence of copper-rich surface precipitates, the areal density and size of which are a function of the substrate temperature and the film composition, particularly the copper content. The deposition of YBCO/MgO/YBCO sandwich structures has also been investigated. A multilayer structure with an 80-Å-thick MgO layer has been successfully produced, and cross-sectional transmission electron microscopy analysis reveals that although the MgO layer is not epitaxial, c-axis oriented YBa2Cu3O7−δ grew on top. Very thin multilayered structures may be difficult to deposit on film surfaces dominated by the screw-dislocation growth mode, due to the high density of steps.
Structural stability of Zn-containing II–VI semiconductor alloys: Microhardness calculations
Authors: Ekpenuma Sylvester N. , Myles Charles W.
Published: July 2002

The lattice strengthening effects of the addition of ZnTe to HgTe, CdTe, and microstructural hardnesses of the resulting alloys HgZnTe, CdZnTe, and HgCdZnTe are calculated and compared with that of HgCdTe obtained in the same model. Good agreement with available experimental data is obtained for the hardness variation with composition for CdZnTe, HgZnTe, and HgCdTe. These calculations show that the alloys containing Zn have superior hardnesses to HgCdTe. They thus verify the experimental observation that these alloys are structurally superior to HgCdTe. The microhardness of HgCdZnTe for a fixed Cd composition of 0.2 is predicted to be slightly greater than that of HgZnTe for all Zn compositions. On the other hand, for simultaneous variation of the Cd and Zn compositions such that the band gap is constant and in the infrared regime, HgZnTe is predicted to always be harder than HgCdZnTe.
Surface damage threshold of Si and SiO2 in electron-cyclotron-resonance plasmas
Authors: Lee Young H.
Published: July 2002

Damage thresholds of Si and SiO2 during reactive ion etching (RIE) were measured in an electron cyclotron resonance plasma reactor equipped with an energy-analyzed mass spectrometer, Faraday cup, and in situ ellipsometer. Si damage was monitored by the minority-carrier lifetime measured by the noncontact microwave reflection technique. The threshold ion energy of displacement damage is very low near 20 eV but the RIE damage threshold for Si devices is found to be about 100 eV. This means that a RIE process with the bias voltage lower than 100 Vdc can fabricate Si devices with no serious damage effect as long as surface contamination by reactive radicals is carefully avoided. In a SF6 plasma, the threshold energy of SiO2 RIE is 15 (±2) eV, independent of a substrate temperature, while the physical sputtering threshold is roughly 40 eV in Ar plasmas.
Diamond deposition in a permanent magnet microwave electron cyclotron resonance discharge
Authors: Mantei T. D. , Chang J. J.
Published: July 2002

Diamond deposition has been investigated in a magnetoactive microwave discharge, in which a collisionally damped electron cyclotron resonance (ECR) is established by a Nd–Fe–B permanent magnet structure. Diamond crystals exhibiting a well defined 1333 cm−1 diamond Raman peak and a faceted crystal structure can be grown in hydrocarbon gas mixtures at total pressures 2.0–20 Torr, backside substrate temperatures 550–650  °C, and input microwave power levels 400–1000 W. The main effect of the magnetic field is to increase gas dissociation; optical emission spectroscopic measurements show much higher neutral radical line intensities compared to operation with no magnetic field.
Affecting factors on surface-wave-produced plasma
Authors: Komachi K.
Published: July 2002

Distribution of surface-wave-produced plasmas and profiles of electric field on a dielectric line under plasma production were measured using a surface-wave-plasma (SWP) applicator with a plasma area of 180×300 mm2. While the profile of the electric field in a direction of microwave propagation showed existence of a standing wave, the plasma, such as emission intensity or ion current, had a flat distribution. The electric field and the plasma had flat distribution in a direction perpendicular to the microwave propagation. Besides, they were hardly dependent on chamber pressure. Therefore, a uniform plasma is stably produced in the present SWP applicator and can be produced over a larger area.
Trajectory-dependent resonant neutralization of low energy 7Li+ scattered from clean and Na-covered Al(100)
Authors: German K. A. H. , Weare C. B. , Varekamp P. R. , Yarmoff J. A. , Andersen J. N.
Published: July 2002

Trajectory-dependent neutralization is observed for low energy (1–5 keV) 7Li+ ions scattered at large angles from Na-covered Al(100). Energy spectra and angular scans of the scattered Li+ ion yield are collected as a function of Na coverage. Li+ ions are partially neutralized upon single scattering from Al sites and completely neutralized when scattered from Na. This site-specific neutralization indicates that the surface electrostatic potential is nonuniform. The neutralization probability is also shown to be a function of the exit angle from the surface. The results are analyzed using theoretical ion fractions based on a semiclassical resonant charge exchange model.
Study of the CaF2/Si interface using x-ray photoelectron spectroscopy
Authors: Hong Y. , Dillingham T. R.
Published: July 2002

The interfacial properties of CaF2 on Si(111) under two different deposition conditions are studied using x-ray photoelectron spectroscopy (XPS). The CaF2/Si sample grown at a fixed temperature of 600 °C exhibits B-type epitaxy. For the second sample, the Si substrate was ramped from 100 to 600 °C in 5 min and then held at 600 °C until the end of the deposition. Under these conditions, the film exhibits A-type epitaxy, with very different electrical properties. The XPS analysis shows that for both samples, Si is bonded with both Ca and F at the interface. Significant differences are observed, however, for the chemical environment of Ca in the interfacial region for the two samples. In the first sample, Ca–Si bonding is relatively more pronounced, while in the second sample Ca–O bonding is observed to be predominant. In addition, for the sample grown under ramped temperature conditions, the fluorine dissociation is observed to be less and more F–Si bonds form at the interface. The results of this study help to explain the widely different electrical properties of the two films.
Adsorption and reaction of water on oxygen precovered Cu(100)
Authors: Ellis T. H. , Kruus E. J. , Wang H.
Published: July 2002

The reaction of water with a fractional (<0.5) monolayer of oxygen on Cu(100) at 120 K has been studied using high resolution electron energy loss spectroscopy (HREELS) and work function measurements (Δφ). Two major species were found. The prevalent species (γ) is formed for a wide range of oxygen precoverages and desorbs at ∼220 K. This γ species shows typical tilted OH vibrational modes in HREELS and is attributed to OH due to the dissociation of H2O. The second species (δ) is only dominant at low oxygen precoverage and desorbs between 255 and 300 K. It is characterized by at least three HREELS peaks at 420, 1170, and 3590 cm −1 and its formation is accompanied by a significant work function decrease. Its precise composition is not certain, but it is proposed to be a complex which involves molecular water.
Onset of crystal growth of bismuth on graphite: An atomic force microscopy study
Authors: Wang Hong , Jing Jing , Henriksen P. N.
Published: July 2002

The onset of epitaxial growth when Bi is thermally evaporated onto graphite at room temperature has been studied using atomic force microscopy. During initial growth, small linear, rodlike, structures are observed to grow along particular directions of the basal plane of graphite. As more Bi is deposited, these structures increase in length and eventually coalesce to form a network of acicular filaments which completely cover the surface. Most of the filaments are either parallel or intersect at angles of 60° or 120°, however, a few intersect at angles of 30°, 90°, or 150°. The most frequently observed structures are compatible with one-dimensional epitaxy with [110]B∥[120]G. The less frequently observed structures are compatible with one-dimensional epitaxy when [010]B∥[010]G. Two models of epitaxial growth are developed which are in agreement with these observations.
Magnetron-enhanced reactive ion etching of GaAs and AlGaAs using CH4/H2/Ar
Authors: McLane G. F. , Cole M. W. , Eckart D. W. , Cooke P. , Moerkirk R. , Meyyappan M.
Published: July 2002

Magnetron reactive ion etching of GaAs and AlGaAs has been investigated in CH4/H2/Ar gas mixtures. Etch rate was determined as a function of gas composition, power density (0.4–1.0 W/cm2), pressure (6–25 mTorr), and total flow rate (20–40 sccm). Scanning electron microscope measurements revealed that anisotropic etching characteristics and smooth etched surfaces can be obtained. Transmission electron microscope measurements showed that the addition of Ar to the gas mixture enhanced surface smoothness, but increased the etch-induced defect depth and density. Hydrogen passivation effects of etched and rapid thermal annealed GaAs were studied for two anneal temperatures (300, 400 °C).
Adsorption of Rb on Si(211)2×1 studied by the x-ray standing wave technique
Authors: Michel E. G. , Eteläniemi V. , Materlik G.
Published: July 2002

The Rb/Si(211)2×1 interface has been investigated by using the x-ray standing wave technique for different adsorbate coverages. The Rb adsorbate distances were determined from the [111], [110], and [211] lattice planes. The simultaneous use of three different reflections allowed the performance of a triangulation to determine the adsorption site, which corresponds at room temperature (θRb=0.7 ML) to the hollow site of eclipsed type, being every third Rb atom coherently located. After coverage reduction through annealing, changes in the adsorbate distances were observed. The new values are compatible with partial occupation of on-top sites.