bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of a large diameter reactive ion beam generated by an electron cyclotron resonance microwave plasma source
Authors: Geisler St. , Brockhaus A. , Engemann J.
Published: July 2002

A new ion source with a large beam diameter generated by an electron cyclotron resonance microwave plasma source is presented. Ion beams with a beam diameter of >160 mm and a maximum argon-ion current density of 2.1 mA/cm2 are obtained. For this large two-electrode silicon-ion extraction optics are mounted into an electron cyclotron resonance microwave plasma source. With ion extraction optics installed an electron temperature up to three times higher than without optics was observed. Due to this high electron temperature (up to 12 eV) the O+ concentration as compared to the O2+ concentration is enhanced in an oxygen plasma. Therefore, a very reactive oxygen ion beam with an ion current density of 1.1 mA/cm2 can be generated. Ion energies of 1 keV corresponding to the screen grid voltage are obtained with a small energy spread of 10 eV full width at half maximum or less. The low working pressure (about 10−4 mbar) is well suited for low-pressure ion-beam processes.
Electron field emission properties of nanodiamonds synthesized by the chemical vapor deposition process
Authors: Yu Yu-Che , Huang Jin-Hua , Lin I-Nan
Published: July 2002

Nanodiamonds, doped with nitrogen, were successfully synthesized by using urea/methanol saturated solution as nitrogen source and in situ application of negative bias voltage during the growth period. Scanning electron microscope and Raman spectroscopic examinations reveal that increasing the urea/methanol ratio in the gas mixture markedly influences the field emission properties of diamond films, but insignificantly alters their structure and morphology. The diamond films thus obtained possess good electron field emission properties (E0=2.35 V/μm, Je=30.2 μA/cm−2, and effective work function φe=0.028 eV). Converting the grains of diamond films from submicrons into nanosize (∼50 nm) via the application of bias voltage in situ further improves these field emission properties. The turn-on field decreases to E0=1.88 V/μm, the field emission capacity increases to Je=118.2 μA/cm2 (at 6.5 V/μm applied field), and the effective work function decreases to φe=0.017 eV.
Reactions of acetaldehyde on UO2(111) single crystal surfaces. Evidence of benzene formation
Authors: Chong S. V. , Idriss H.
Published: July 2002

The reactions of aldehydes on metal oxide surfaces have exposed some of the most exquisite chemistry in comparison to their alcohol and carboxylic acid counterparts. Due to the intermediate oxidation state of the carbonyl carbon on an aldehyde, reactions such as the Cannizzaro disproportionation (forming alkoxides and carboxylates) and Tishchenko (forming ester) have been observed on various metal oxide surfaces, in addition to direct oxidation and reduction. Furthermore, condensation reactions have also been observed with aldehydes possessing alpha-H atom(s) over stoichiometric metal oxide surfaces, while surface defect sites are able to reductively couple two aldehyde adsorbates to yield alkene. Herein, we present the reactions of acetaldehyde over the stoichiometric, electron-irradiated, H2-reduced, and argon ion-sputtered surfaces of a UO2(111) single crystal. Temperature programmed desorption results over the four surfaces show evidence of benzene formation, and it appears that electron-irradiation slightly increases the conversion to benzene, H2 reduction doubles it, and argon ion-sputtering increases it by fourfold. Thus the amount of benzene formed from acetaldehyde over a UO2 single crystal might be a novel way to quantitatively estimate the extent of surface defects.
Electron emission from nanocrystalline diamond films
Authors: Gu Changzhi , Jiang Xin , Jin Zengsun , Wang Weibiao
Published: July 2002

The electron emission properties of nanocrystalline diamond films were described. The nanometer structured diamond films were deposited by the microwave plasma assistance chemical vapor deposition method via continuous H+ ion bombardment. The grain size of nanocrystalline diamond films can be modified by means of changing the energy of bombarded ions. Scanning electron microscopy and Raman spectroscopy indicated the nanometer structure of the films. The results suggested that low-field electron emission and high emission current can be obtained from the films consisting of nanosized diamond grains.
Preparation of highly ordered nanoporous Co membranes assembled by small quantum-sized Co particles
Authors: Lei Y. , Liang C. H. , Wu Y. C. , Zhang L. D. , Mao Y. Q.
Published: July 2002

Highly ordered nanoporous Co membranes were fabricated by a two-step replication from the honeycomb structure of porous anodic alumina. These metal membranes are confirmed to have two substructures: first, the Co membrane consists of very fine quantum-sized particles with diameters of about 2–5 nm; second, the very fine Co particles are assembled in a superstructure; i.e., fine and uniform channels 50 nm in diameter, more than 16 mm in thickness, having a pore density of about 1010 cm−2. New techniques were introduced into the two-step replication process, resulting in new features of the replicated metal membrane: high aspect ratio (more than 320:1), highly ordered pore arrays, and narrow size distributions of the pore diameters. These new techniques also lead to simplification of the fabrication process of metal membranes. Double-sided and single-sided Co membranes can be achieved simply by adjusting the electroless deposition time.
Direct correlation of x-ray photoelectron spectroscopy and Fourier transform infrared spectra and images from poly(vinyl chloride)/poly(methyl methacrylate) polymer blends
Authors: Artyushkova K. , Wall B. , Koenig J. , Fulghum J. E.
Published: July 2002

Correlative x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) studies of the complex heterogeneous structure of 50/50 poly(vinyl chloride) (PVC)/poly(methyl methacrylate) (PMMA) polymer blends are presented. The comparable lateral resolution and parallel (real-time) imaging capabilities of both techniques allow for a direct comparison of surface (XPS) and bulk (FTIR) measurements of polymer blends. To eliminate substrate influence and film-to-film differences, the same areas on the polymer films are analyzed by both methods. The effect of PMMA molecular weight on phase separation and surface segregation is evaluated using six blends with a constant PVC molecular weight and a PMMA molecular weight varying from 75 to 2132 kDa. Imaging capabilities of both methods are used for a qualitative comparison of the heterogeneous structure of the blends, while a quantitative comparison of the bulk and surface compositions of the same areas of the samples used small area spectroscopy from XPS and FTIR. Based on the small area quantitative analysis, it is concluded that surface segregation of PMMA increases with increasing molecular weight. This combination of small and large area correlative analyses in the determination of both surface and bulk properties of these heterogeneous polymer films leads to a more complete understanding of structure of complex samples.
Heat-depolymerizable polycarbonates as electron beam patternable sacrificial layers for nanofluidics
Authors: Harnett C. K. , Coates G. W. , Craighead H. G.
Published: July 2002

This research investigates a heat-depolymerizable polycarbonate (HDP) for use as a sacrificial layer in fabricating nanofluidic devices by electron beam lithography. When solid HDP films are heated to 300 °C, the monomer units separate into a nontoxic vapor. This property suggests that a patterned HDP film may be used as a temporary support for another film which is stable at the depolymerization temperature. Heating the structure removes the HDP, leaving a network of nanofluidic tubes without the use of solvents or other chemicals as required in most other sacrificial layer processes. We found that HDP films may be patterned directly by electron beam lithography, followed by immersion in isopropanol to remove HDP from the exposed areas. The patterns are then sputter coated with silicon dioxide at low temperature, provided with access holes for venting, heated to clear out HDP remaining inside the tubes, and injected with fluorescent dye for observation. Tube dimensions of 140 nm height, 1 μm width, and 1 mm length are reported, and fabrication of other structures is discussed.
High-Q photonic crystal microcavities fabricated in a thin GaAs membrane
Authors: Reese C. , Gayral B. , Gerardot B. D. , Imamoǧlu A. , Petroff P. M. , Hu E.
Published: July 2002

We report on the fabrication of photonic crystal microcavities in GaAs having H1 and H2 defects for lattice constants as small as 255 nm. In H2 microcavities, we observed resonances with Q factors as high as 4000. The degeneracy of these high-Q modes is lifted by the imperfect nature of the fabrication process.
Ion-implanted photoresist removal using water/carbon dioxide mixtures at elevated temperature and pressure
Authors: Chavez K. L. , Bakker G. L. , Hess D. W.
Published: July 2002

The ability of water and water/1% carbon dioxide mixtures to remove ion-implanted photoresist from silicon substrates was investigated. Photoresist with implant levels up to 2×1015/cm2 of boron and phosphorus were stripped effectively at a temperature of 165 °C and a pressure of 58.6 bar (850 psi) by both water and water/carbon dioxide. Removal of photoresist at low implant levels (2×1012/cm2) proceeded rapidly, while samples at higher dose levels (>2×1015/cm2) had a thin carbonized layer at the photoresist surface that inhibited the removal rate. Removal of this carbonized layer required approximately 2 min for water/carbon dioxide and approximately 8 min for water, while complete removal of the remaining photoresist film took less than 30 min for both fluids. Patterned, arsenic-implanted (1×1016/cm2) photoresist layers were removed by water/carbon dioxide at 200 °C, 850 psi, 3 ml/min flow rate, and 30 min exposure. Under all conditions investigated, water/carbon dioxide proved more effective than pure water at removing ion-implanted photoresist.
Field electron emission from carbon nanotubes grown by plasma-enhanced chemical vapor deposition
Authors: Tanemura M. , Filip V. , Iwata K. , Fujimoto Y. , Okuyama F. , Nicolaescu D. , Sugie H.
Published: July 2002

Densely distributed, aligned carbon nanotubes were grown on Co-covered W wires by dc-plasma-enhanced chemical vapor deposition with a mixture of acetylene and ammonia as precursors. Each nanotube was capped with a Co carbide particle. The diameter of the nanotubes ranged from 20 to 130 nm, and their average length was about 5 μm. Their field emission characteristics, measured in a modified ultra-high vacuum scanning electron microscope, were analyzed by a statistical field emission model developed for aligned carbon nanotube film cathodes. An indirect method was thus established to obtain the average electrical parameters of the film using only a limited amount of experimental data.
Contamination of Silicas during High-Temperature Degassing in Vycor Tubes
Authors: Low M. J. D. , Ramasubramanian N. , Ramamurthy P.
Published: July 2002

Materials heated in vacuo at 800 °C in Vycor tubes may become contaminated. An ir absorption near 3702 cm−1 was produced if Cab-O-Sil was degassed at 800 °C in a Vycor cell, and then partially hydrated. The band was not produced with specimens degassed in quartz cells. A variety of experiments lend strong although indirect support to the conclusion that the band was due to surface B—OH groups, brought about through the contamination of the silica surface by boron volatilized from the hot Vycor. Similar contamination can be expected to occur with all specimens heated at 800 °C in Vycor, but the effects of the contamination may not be readily discernible by means of ir spectra.
Effect of Oxygen on the rf-Sputtering Rate of SiO2
Authors: Jones R. E. , Winters H. F. , Maissel L. I.
Published: July 2002

The rf-sputtering rate of SiO2 decreases rapidly when comparatively small partial pressures (∼10−5 Torr) of oxygen are added to the argon-sputtering gas. The magnitude of the decrease is also dependent on the rf-input power. Both of these phenomena are explained by a model which assumes that the sputtering rate is lowered by the replacement (from the gas) of oxygen atoms which have previously been sputtered out of the SiO2 target.
Proton−induced electron emission from characterized niobium surfaces
Authors: Musket R. G.
Published: July 2002

Both the electron emission coefficient (electrons/ion) and the energy distribution of emitted electrons have been determined for bombardment of polycrystalline niobium by 30−400 keV protons. In situ characterization of the niobium surfaces was accomplished using electron−induced Auger electron spectroscopy. Emission coefficient measurements were made for protons incident along the surface normal and along the axis at 45° from the surface normal. Electron energy distributions were determined using a hemispherical retarding analyzer with the proton beam at 45° from the surface normal and at 90° from and coplanar with the axis of the analyzer. The results are discussed and interpreted with reference to electron emission theories and previous experiments.
Ion−beam analysis of corrosion films on 316 steel
Authors: Dearnaley G. , Hartley N. E. W. , Turner J. F. , Garnsey R. , Woolsey I. S.
Published: July 2002

Ion backscattering at MeV energies, coupled with nuclear reaction analysis, has been used to determine quantitatively the composition of complex corrosion films produced by the exposure of 316 stainless−steel specimens to a variety of alkaline solutions. The oxygen content as a function of depth, up to about 2 μ, and the trace heavy metal content were determined by helium backscattering at 2.9 MeV. The lithium content was measured by means of the Li7 (p,α) reaction at Ep = 3 MeV, with a calibration achieved by comparison with LiNbO3. It is shown how much more valuable such ion−beam techniques become when combined with microscopic examination using SEM, EDAX, and optical methods. In this way, for example, the variation in composition with depth has been correlated with oxide thickness. The advantages of this form of analysis for other corrosion problems will be described.
Analysis and optimization of closed loop vacuum control systems
Authors: Ferran Robert J. , Sullivan John J.
Published: July 2002

A detailed theoretical study of vacuum control systems operating below and in the transition region is presented. System performance of a servo controlled metal−sealed valve and capacitance manometer transducer system is analyzed by means of computer solutions of the nonlinear equations governing its performance. Characterization and optimization of various types of systems are discussed. System volume, throughput, and pumping system characteristics as well as the nature of the control valve are shown to be of prime consideration for control accuracy and step response.
Electrical resistance of metallized via−holes
Authors: Hall Peter M.
Published: July 2002

The resistance of a via−hole laser−drilled through an alumina substrate depends on the hole geometry, the type of probe, the deposition technique, and the properties of the film. If the walls of the hole constitute a truncated cone, the resistance is Rs/π[ln(d2/d1)]{1/4 + [h/(d2 − d1)]2}1/2, where Rs is the sheet resistance, h is the substrate thickness, and d1 and d2 are the diameters. Increasing the larger diameter helps by (a) reducing the rim−to−rim resistance, (b) reducing the ’’spreading’’ resistance, and (c) making the walls more accessible for metallization. A four−point probe, on the other hand, measures the rim−to−rim resistance as approximately (Rs/π) ln cosh (h/d), where d is an average diameter. If the hole is partially bare, the four−point reading will depend on probe orientation. A comparison of calculation and measurement indicates Rs in the hole to be between two and forty times Rs outside, depending on the thickness. Electrical probing of broken−open holes showed this to be due to thickness differences, not roughness or ledge resistance.
Abstract: Surface structure determination of the layered compounds MoS2 and NbSe2 by the dynamical LEED approach
Authors: Tong S. Y. , Van Hove M. , Mrstik B. J. , Kaplan R. , Reinecke T.
Published: July 2002

The surface structures of 2H polytypes of the layered transition metal dichalcogenides MoS2 and NbSe2 are studied by analyzing LEED intensity–energy (IV) data using the dynamical approach.1 We investigate contraction and expansion of the top interplanar and intersandwich distances and the stacking sequence at the surface of these compounds. Using a convergent layer-iteration method, LEED intensity profiles are calculated and compared to experimental data. Excellent agreement in the IV profiles is obtained between theory and experiment. From the comparison, we find that 2H–NbSe2, which has metallic properties, maintains the bulk spacing up to the surface plane. The semiconductor 2H–MoS2, on the other hand, exhibits a slight contraction of the top interplanar spacing of 5% or less. It is also found that lateral reconstructions that alter the bulk stacking sequence at the surface do not occur for these two compounds.
Study of Al with a combined Auger electron spectrometer–ellipsometer system
Authors: Allen T. H.
Published: July 2002

Auger electron spectroscopy and ellipsometry, two of the more sensitive techniques for surface studies, have been used to study, simultaneously, both the elemental chemical composition and optical properties of clean and contaminated Al surfaces under vacuum. This combined system has been used to measure the optical constants of both vapor-deposited Al films and ion-cleaned, high-purity bulk Al. The measured optical constants of the contamination-free bulk Al were n=1.566 and k=7.938 where N=n−ik. The measured extinction coefficient k agrees well with the computed value of 7.885 using the free-electron theory. Ellipsometer measurements were made at a wavelength of 6328 Å and an angle of incidence of 70°. Optical measurements made on contaminated surfaces showed that the presence of very thin oxide films can cause large errors in measuring both n and k for Al. Combined measurements showed a linear relationship between changes in the amplitudes of the Auger peaks associated with both O (513 eV) and aluminum oxide (53 eV) and the measured film thickness. This linear relationship was used to estimate the attenuation length of Al Auger electrons (67 eV) in the metal oxide film as 1.9 Å.
Abstract: Selective adsorption in atom-crystalline surface scattering
Authors: Chow H. , Thompson E. D.
Published: July 2002

Theoretical studies have been made of the elastic scattering of low-energy light atoms from a perfect crystalline surface with a square unit cell with particular emphasis on selective adsorption. The atom–solid surface potential is approximated by a corrugated hard wall with attractive well, by a modulated square well with a smooth hard wall, by a Morse potential, and by a sum of Yukawa-6 pair potentials. It is found, independent of the model potential and without invoking inelastic processes, that the (0,1) selective adsorption results in minima in the specular and maxima in the (−1,1) diffraction intensity in agreement with recent experiments.
Prediction of semiconductor heterojunction discontinuities from bulk band structures
Authors: Frensley W. R. , Kroemer H.
Published: July 2002

We present a first attempt to predict heterojunction band lineups from the bulk band structures of the participating semiconductors, without invoking free surface properties. Band structures and electrostatic potentials are calculated by a self-consistent pseudopotential. A simple electrostatic matching scheme lines up the electrostatic potentials, and through them the band structures. Predicted lineups are in good qualitative agreement with known lineups, and even in some cases [particularly GaAs– (Al,Ga)As] in good quantitative agreement.
Atom clustering and stacking formations on interfaces
Authors: Mattes Brenton L.
Published: July 2002

Atom clusters in the form of rhombic dodecahedrons are postulated to account for (110) facets (∠4 unit cells on a side) observed on growth, cleaved, and etched surfaces. In growth, these clusters form under saturated conditions at the solid interface to minimize the number of dangling bonds and to stabilize the surface. For GaAs, the atoms cluster about an As tetrahedron to form rhombic dodecahedron layers, each layer composed of (110) planes of Ga and As. By adding one dodecahedron layer upon another, a stable size is reached when all of the dangling bonds in the surface layer can be shared; and this size coincides with a minimum in the lattice cohesive energy—lower than for an infinite lattice. This size corresponds directly to a balance between tensile and compressive forces in the surface layer and in the bulk of the cluster, and in addition, stoichiometry for III–V compounds. The rhombic dodecahedron clusters as ’’building blocks’’ exhibit perfect packing and equal partitioning of energy on each rhombic facet. When the ’’blocks’’ stack together facetted macroscopic surfaces are formed. The exposed dodecahedron apexes have different completed-dangling-bond configurations that can account for the relative differences in attachement kinetics of ’’blocks’’ and impurities to different interface orientations. The atom saturation at the interface also affects the ’’block’’ stacking on the surface. The overlap of additional ’’blocks’’ on the surface appears to give atom arrangements with lower surface energy and the arrangements correspond to LEED patterns observed on growth, cleaved, and etched surfaces.
Heterojunctions in integrated optics
Authors: Scifres D. R. , Burnham R. D. , Streifer W.
Published: July 2002

In this review article we discuss the role of heterostructures in integrated optics. We consider, in sequence, the role of heterostructure waveguides, lasers, light couplers, modulators, and detectors, and describe the progress made to date in integrating these into a thin-film monolithic optical circuit. The primary emphasis is on the GaAs:GaAlAs heterostructure material system, which has emerged as one of the most promising for integrated optics.
Surface behavior under ion bombardment in a fusion device
Authors: Martel J. G. , St-Jacques R. G. , Terreault B.
Published: July 2002

First wall, divertors, and other components of the vacuum chamber of a fusion reactor will be submitted to ion bombardment from the thermonuclear plasma. The effects of this bombardment on the materials must be known in order to foresee and correct any major problem. Particular attention must be given to the erosion of the materials. The major mechanisms responsible for wall erosion in a fusion device, namely sputtering, blistering, and evaporation, are revised. The erosion rate due to sputtering is reported for different materials and bombarding energies. A review of the effects of blistering on surface morphology and erosion is made as a function of energy, ion dose, and temperature of the material. The evolution of surface temperature under various bombardment power is given and correlated to probable evaporation rates. The relative importance of these different phenomena is assessed.
Advances in deposition processes for passivation films
Authors: Kern Werner , Rosler Richard S.
Published: July 2002

A review is presented of deposition processes for forming dielectric passivation layers on silicon semiconductor devices, with emphasis on recent advances in this field. Materials of prime interest are thin-film dielectrics used as secondary passivants deposited by several types of chemical vapor deposition (CVD) processes. The fundamental principles, deposition parameters, advantages, applicability, and limitations of the various types of CVD for dielectric passivation films are described and compared. The CVD processes discussed include low- and high-temperature CVD at normal pressure, and the relatively new technologies about to emerge for large-scale applications−low-pressure CVD at low and high temperatures, and plasma-enhanced CVD.
Thermal decomposition of nickel carbide: an Auger lineshape study
Authors: Smith M. A. , Sinharoy S. , Levenson L. L.
Published: July 2002

A carbon Auger spectrum indicative of nickel carbide is detected in thin films of nickel evaporated onto graphite in ultrahigh vacuum. Isothermal heating of the films leads to an irreversible change in the carbon Auger lineshape. This change is interpreted as evidence for the decomposition of the nickel carbide. Initial and final spectra are representative of carbide and graphite, respectively. It is seen that intermediate phases in the Auger lineshape transition are closely approximated by linear combinations of carbide and graphite spectra. This approximation allows the retrieval of the relative amount of nickel carbide present in the film as a function of time during a heating period. Rate constants are calculated for a number of temperatures. An energy of activation for the decomposition process is then obtained. The results of this experiment are in good agreement with previous measurements employing bulk techniques.
Optimization of electron probe forming systems with respect to aberrations and vertical beam landing
Authors: Kern Dieter P.
Published: July 2002

A systematic presentation of aberrations in probe forming systems with rotationally invariant focusing and deflection fields is given, and the effect of these aberrations on the intensity distribution in the final sopt is investigated using wave-optical and geometrical-optical methods. The functional principle of methods for minimizing aberrations as well as their practical application to typical configurations like single post-lense deflection, double pre-lens deflection and Moving Objective Lens (MOL) is presented. Finally the trade-off between minimization of aberrations and reduction of the landing angle of the beam is shown in a configuration combining pre- and post-lens deflection.
GaAs IC’s fabricated by electron beam lithography
Authors: Krumm Charles F. , Ozdemir Faik S. , Greiling Paul T.
Published: July 2002

The use of direct writing electron beam lithography for the development of gallium arsenide integratd circuits is described.
Local field effects in photoabsorption
Authors: Zangwill A. , Soven Paul
Published: July 2002

We present the results of a calculation of the photoabsorption of xenon using a local-density-functional self-consistent-field formalism for both the ground state of the system and the time-dependent local fields induced by the external radiation field. The results are in good agreement with experiment, and are cast in such a way as to explicitly show the collective effects important in photoabsorption.
Metal contacts to clean and oxidized cadmium telluride and indium phosphide surfaces
Authors: Humphreys T. P. , Patterson M. H. , Williams R. H.
Published: July 2002

Examination of the scientific literature reveals a large variation in the Schottky barrier heights measured for metals such as silver deposited on atomically clean cadmium telluride surfaces. In the present studies we have probed the growth of gold, silver, and aluminium films on clean cleaved cadmium telluride by LEED, angle resolved UPS, by AES and by XPS. We have also probed the early formation of the Schottky barriers and established the thick film values for metals on clean and oxidised surfaces by C–V and I–V methods. The experiments indicate that in many cases the interfaces formed are not atomically abrupt and there is considerable intermixing between the metal and the CdTe. Low energy electron beams have dramatic effects on the CdTe (disordering it without altering its chemical composition), and on the interfaces formed with metals. The interfacial oxide layer, produced by cleaving in air, has a significant influence on the interfacial properties. The results of the experiments are compared to similar experiments for metal contacts to indium phosphide. The observations are discussed in terms of various theories of Schottky barrier formation and in particular we consider the defect model and its applicability to CdTe and InP.
SIMS study of Al and Cr metallizations on CdSe
Authors: Scilla G. J. , Wysocki J. J.
Published: July 2002

Secondary Ion Mass Spectrometry (SIMS) has been employed to study the diffusive behavior of combinations of Al and Cr thin films on polycrystalline CdSe. Samples were studied before and after annealing in a flowing N2 ambient at 350°C. Our results indicate that both Al and Cr will diffuse into CdSe under these conditions. However, Cr diffuses much more rapidly than Al. Also, Cr diffusion results in the uptake of oxygen by the CdSe and in a characteristic saddle-shaped profile for both Cr and oxygen. The results of this study further indicate that Al films as thin as 50 Å sandwiched between the CdSe and Cr films can act as an effective barrier to the diffusion of Cr.
Study of stability of MIS polycrystalline silicon solar cells by Auger electron spectroscopy
Authors: Lee B. W. , Kuo J. M. , Lalevic B. , Anderson W. A.
Published: July 2002

Auger electron spectroscopy and ion sputtering techniques were used to investigate the free surface composition and MIS solar cell fabricated on polycrystalline silicon. A layer of ∠20 Å of mixture of silicon oxide and chemisorpted oxygen atoms were found on the Si surface. For the Cr–Cu–Cr–SiO2–Si solar cell, the copper layer is the key factor for reducing the series resistance of the metal layers. The pure oxide layer was found to be almost nonexistant and a mixture of silicon oxygen and chromium was detected between the silicon and metal interface. Compositions of the cell were investigated as a function of temperature. The results were used to estimate the lifetime of the cell. It was found that the cell should have a very long lifetime if operated under 200°C.
Magnetron sputtering of solar coatings inside tubes
Authors: Walker S. J. , McKenzie D. R.
Published: July 2002

A small post-cathode magnetron sputtering system using a moving magnet inside the cathode is described. Unusual features in the voltage-current characteristics of the device are discussed. The system is particularly useful for coating inside cylindrical substrates, especially glass tubes for solar energy collectors.
Gallium arsenide large scale integrated circuits
Authors: Long S. I. , Welch B. M. , Zucca R. , Eden R. C.
Published: July 2002

Large scale digital integrated circuits containing over 6000 active devices (1 μm MESFETs and Schottky diodes) have recently been achieved in GaAs Schottky Diode FET Logic. The planar, ion implanted process used to fabricate these circuits results in very uniform device properties because of the excellent control of critical device interfaces. The present status of LSI GaAs ICs is reviewed, including a description of the performance of an 8×8 bit multiplier LSI circuit. VLSI circuit prospects and the applicability of new high speed GaAs active devices for VLSI application in GaAs are considered.
Conceptual problems in modeling submicron device physics
Authors: Grubin H. L. , Ferry D. K.
Published: July 2002

The study of high field transport in semiconductor devices has progressed very rapidly over the past decade, sustained in part by rapid technological advances in the solid state electronics industry. These have, however, generated important conceptual problems in modeling of high speed transport in nonlinear semiconductors. Some of these problems are discussed below.
Angular resolved UPS and XPS spectra of benzenethiol adsorbed on Cu(111) at 300 °K
Authors: Agron P. A. , Carlson T. A.
Published: July 2002

Angular resolved photoelectron spectra using Hei (21.2 eV) radiation have been obtained for benzenethiol (phenyl mercaptan) chemisorbed on Cu(111), as well as for the clean surface. The correlation with the gas-phase spectra suggests that the benzenethiol bonds to copper by way of sulfur-containing orbitals rather than carbon π ring orbitals. The angular dependence of the different bands formed in the photoelectron spectra indicates that the benzene ring is oriented perpendicular or near perpendicular to the surface. XPS analysis, with Al–Kα radiation, of the Cu 2p, C 1s, and S 2p orbitals confirms the stoichiometry as well as the surface coverage. The extent of surface coverage supports the argument against benzenethiol lying flat on the copper surface.
The element of luck in research—photocathodes 1930 to 1980
Authors: Sommer A. H.
Published: July 2002

Six photocathode materials were developed during the period from 1930 to 1963 to provide the spectral response and other characteristics needed for such applications as photometry, television, scintillation counters, and night vision devices. The history and the essential properties of these materials are reviewed and it is shown that all the cathodes resulted from lucky accidents and not from the application of scientific insight. The period of empirical innovation came to an end in the late 1960’s when negative electron affinity (NEA) materials became the first photocathodes that were developed on a strictly scientific basis.
Low energy neutral spectroscopy during pulsed discharge cleaning in PLT
Authors: Ruzic D. , Cohen S. , Denne B. , Schivell J.
Published: July 2002

The efflux of neutral hydrogen from PLT during discharge cleaning has been measured using a time-of-flight spectrometer. During high ionization pulsed discharge cleaning (PDC), the flux in the energy range of 5 to 1000 eV varies from 1014 H0/cm2⋅s to 1016 H0/cm2⋅s and the average energy from 10 to 80 eV. The energy distributions are nearly single temperature Maxwellians. Low ionization PDC (Taylor-type) produces a 1000 times lower fluence in the same energy range; however, a flux of 1016 H°/cm2⋅s at energies less than 5 eV is inferred. The detailed submillisecond time variation of these parameters with the fill gas pressure and state of cleanliness of the machine is presented. Comparisons with UV spectroscopy, bolometric measurements, and residual gas analysis are made.
Conditioning of ion sources for mass spectrometry of plasmas
Authors: Dylla H. F. , Blanchard W. R.
Published: July 2002

Mass spectrometry is a useful diagnostic technique for monitoring plasma species and plasma–surface interactions. In order to maximize the sensitivity of measurements of hydrogen-fueled fusion plasmas or hydrogen-based discharge cleaning and etching plasmas, the ion sources of mass spectrometers are operated at or near the high pressure limit of 10−4 Torr (10−2 Pa). Such high ambient pressures of hydrogen give rise to high background levels of residual gases such as H2O, CO, and CH4, due to surface reactions on the ion source electrodes. For a commonly used ion source configuration, the residual gas production is a linear function of the ambient H2 pressure. Hydrogen conditioning can reduce the absolute residual gas levels. Steady state residual gas production is observed in a conditioned ion source, which is related to a balance of diffusion and sorption on the electrode surfaces.
XPS analysis of PbTe surfaces prepared by various cleaning procedures
Authors: Okumura Hajime , Ihara Hideo , Gonda Shun-ichi
Published: July 2002

The effect of several chemical and physical treatments for PbTe(100) surface cleaning was investigated by XPS. Etching with a (NH4OH+H2O2) solution shows a remarkable contrast to etching with acid, the first one being suitable to eliminate carbon contamination. The combination of the (NH4OH+H2O2) etching, heating and light Ar+ sputtering was the best treatment to prepare clean stoichiometric PbTe surfaces free of carbon and oxygen contamination, which are necessary for epitaxial growth on these surfaces.
Epitaxial relations in alkaline earth fluoride–semiconductor systems
Authors: Phillips Julia M. , Yashinovitz C. J.
Published: July 2002

Previous studies of epitaxial fluoride–semiconductor systems have demonstrated that parameters such as substrate temperature during film growth and substrate orientation strongly affect epitaxial quality. The role of a good lattice match in these systems has not been clearly resolved, however. In this study we have performed Rutherford backscattering/channeling measurements on a variety of fluoride–semiconductor systems having a wide range of lattice mismatch. The results demonstrate that the largest misfit system [BaF2/Ge(111) with a 9.6% mismatch] supports two orientations of BaF2 crystallites with respect to the Ge substrate, whereas smaller misfit systems support only one orientation. This result is related to our previous finding of a novel incommensurate interface in this epitaxial system.
Surface vibrational properties
Authors: Wallis Richard F.
Published: July 2002

An overview is given of the principal types of surface vibrational modes that occur at a clean surface of a solid and the means whereby they can be studied experimentally. The modes that are discussed include long-wavelength surface acoustic modes (Rayleigh waves), short-wavelength surface acoustic modes, long-wavelength surface optical modes (surface polaritons), and short-wavelength surface optical modes. Typical dispersion curves illustrating the various types of modes are presented. Mention is also made of surface vibrational modes associated with adsorbed species on solid surfaces. Experimental techniques that are discussed include inelastic electron and helium atom scattering, Raman and Brillouin scattering, acoustic wave reflection, and attenuated total reflection. Other vibrational properties considered are surface specific heat and surface mean square displacements (Debye–Waller factor).
Photoabsorptance and electron lifetime measurement in HgCdTe
Authors: Doyle O. L. , Mroczkowski J. A. , Shanley J. F.
Published: July 2002

Photoinduced absorption modulation near the band gap is used for the first time to measure the excess electron lifetime and gap energy in several samples of bulk and LPE Hg0.2Cd0.8Te. The samples were primarily n-type with carrier concentrations from 3×1013 to 2×1015 cm−3. The fractional transmission change ΔI(E)/I(E) near Eg, due to a nonequilibrium Burstein–Moss shift, is described by a simple theory based on bandfilling, with empirical modifications to include broadening effects in LPE films. Lifetimes are determined by three methods: (1) ΔI/I spectra, (2) high frequency rolloff of the total ΔI signal, and (3) transient analysis of photoconductivity decay. Measured values of 100 to 800 ns are obtained, with excellent agreement between the three independent results for a given sample.
Growth and characterization of epitaxial SrF2 on InP(100)
Authors: Sinharoy S. , Hoffman R. A. , Rieger J. H. , Warner J. D. , Bhasin K. B.
Published: July 2002

Indium phosphide is an important substrate material for microwave metal–insulator–semiconductor field effect transistor (MISFET) devices; SrF2 is an attractive candidate for use as an insulating layer on it because of the relatively close lattice match (−1.2% mismatch). We have grown epitaxial SrF2 films on n-type and p-type InP(100) surfaces using a conventional UHV system. The combination of a brief ion bombardment at 350 °C using 0.5 keV argon ions and a subsequent anneal at the same temperature was found to be an effective cleaning technique for the InP(100) substrate that was chemicomechanically polished prior to insertion in the UHV chamber. The best quality epifilms were grown at 350 °C, using a slow (<1 Å/s) initial growth rate, with a postanneal at the same temperature. The substrate and the film surfaces were characterized in situ, using low-energy electron diffraction (LEED) and Auger electron spectroscopy (AES), and ex situ, using reflection high-energy electron diffraction (RHEED) and Nomarski optical microscopy. In this paper we report these results, along with the results of capacitance–voltage (C–V) measurements on these films.
The gettering theory approach to reactive scattering on surfaces
Authors: Brivio G. P. , Grimley T. B.
Published: July 2002

The quantum theory of gettering (the removal of a gas from a closed vessel by adsorbing it on a solid) has been used to compute sticking coefficients of H and D, with energies in the range 0–80 meV, on a model metal with energy loss to electron-hole pairs. Two aspects of the results are exhibited: many-body effects in the case of H and the isotope effect. Regarding the former, many-body effects are important but not crucial, and, in particular, they do not affect the sticking coefficient in the gas atom zero-energy limit. Regarding the latter, quantum effects in the motions of the gas atoms near the surface govern the isotope effect.
Durability of Ag based low-emissivity coatings
Authors: Nadel S. J.
Published: July 2002

Films of ZnO/Ag/Sn/ZnO deposited by dc magnetron sputtering are being widely used as ‘‘heat mirror’’ films in architectural applications. The long-term durability of these films has been studied through accelerated weathering and exposure to controlled atmospheres of C12, H2S, and moisture. After accelerated exposure, films were analyzed by ultraviolet–visible–near infrared and far infrared spectroscopy, Auger depth profiling, and scanning electron microscopy. No significant changes were seen in transmittance or infrared reflectivity. No interdiffusion of layers was seen in Auger profiling.
Surface analysis in fusion devices
Authors: Taglauer E. , Staudenmaier G.
Published: July 2002

Fusion devices with magnetic confinement of a hot plasma show a considerable amount of interaction of the plasma with material wall surfaces. This interaction strongly influences, for example, the plasma behavior due to recycling of the discharge gas (hydrogen isotopes) and release of impurity atoms from the wall surfaces. In order to assess the various effects caused by plasma–wall interactions, surface analysis techniques have been successfully applied. Among the problems studied are wall conditioning, erosion, and redeposition of material in the discharge vessel, erosion mechanisms such as sputtering or arcing, and measurement of particle fluxes into and out of the plasma by using surface probes. A variety of surface analysis techniques is used in these investigations: Rutherford backscattering, nuclear reaction analysis, proton- and electron-induced x rays, Auger electron spectroscopy, scanning electron microscopy, secondary ion mass spectroscopy, etc. Some achievements and problems of surface analysis in fusion devices are outlined and illustrated by a number of examples from tokamak experiments.
Interaction of Ti with fused silica and sapphire during metallization
Authors: Chaug Y. S. , Chou N. J. , Kim Y. H.
Published: July 2002

X-ray photoelectron spectroscopy has been used to investigate the chemical interaction of Ti with fused silica and sapphire by sequential evaporation of Ti onto these substrates. In both cases, the intermediate oxidation state of titanium, i.e., a TiOx-like (1≤x≤1.5) state, is formed at the interface at low Ti coverages (<1 monolayer). Chemical bonds appear to have developed between the Ti 3d electron and the 2p electron of oxygen at the interaction sites on the substrate surface. Comparison of the x-ray induced O(KVV) Auger spectra evolved at different Ti coverages on silica and sapphire suggests that both surfaces have the same chemical reactivity with titanium.
The effect of lattice mismatch on the dynamical microstructure of III–V compound surfaces
Authors: Ebner J. T. , Arthur J. R.
Published: July 2002

The growth by molecular-beam epitaxy on GaAs of InxGa1−xAs, x≤0.1, has been studied using reflection electron diffraction, Auger sputter profiling, and photoluminescence. Surface segregation of the In as a function of substrate temperature during growth has been observed. The effect of this segregation on optical properties was investigated by growing single quantum well structures and measuring the photoluminescence spectra. It was found that In segregation did not adversely affect the exciton recombination linewidth for most of the substrate temperatures examined; in fact anomalously high photoluminescence intensities were observed. This high luminescent efficiency is due to the formation of a long region of graded composition in the capping GaAs layer produced by the outdiffusion of In from the quantum well. The graded region increases the collection efficiency of the well by accelerating photogenerated electrons and holes into the well.
Post cathode magnetron sputter deposition inside a long, small-diameter closed-end tube
Authors: Peeples C. R. , Cuthrell R. E. , Mattox D. M.
Published: July 2002

We have demonstrated the possibility of depositing thick molybdenum films closed−end insulating tube using the post cathode magnetron sputter deposi tion configuration using a high sputtering gas pressure an a means for rem oving the surface charge buildup. (AIP)
Atomic force microscopy: General aspects and application to insulators
Authors: Heinzelmann H. , Meyer E. , Grütter P. , Hidber H.-R. , Rosenthaler L. , Güntherodt H.-J.
Published: July 2002

Atomic force microscopy (AFM) has been proposed to map the force of interaction between the sample and a sharp tip. For the first time atomic resolution imaging of nonconducting surfaces is possible. Our aim is to apply the atomic force microscope to a variety of materials. We have realized two designs with different approach mechanisms. The force sensing lever is prepared from a piece of metal foil which is electrochemically etched at one end to form a sharp tip. Two different modes of measurement are discussed. Lateral resolution of 2.5 Å has been obtained on noncrystalline quartz. Images of LiF and of optical lenses are presented.
Modulation of internal piezoelectric fields in strained-layer superlattices grown along the [111] orientation
Authors: Mailhiot C. , Smith D. L.
Published: July 2002

Large internal piezoelectric fields are generated when strained-layer superlattices are grown from III–V zinc-blende-structure compound semiconductors. The orientation of these internal fields depends on the components of the strain tensor and, consequently, on the growth orientation of the superlattice. In the usual case of strained-layer superlattices grown along the [001] axis, the piezoelectric fields vanish. However, the case of strained-layer superlattices grown along the [111] axis is particularly interesting because the internal piezoelectric fields are parallel to the growth axis and their magnitude typically exceeds 100 kV/cm for lattice mismatches as small as 1%. Therefore, [111]-oriented strained-layer superlattices exhibit novel physical properties and present technological opportunities not afforded by commonly grown [001]-oriented strained-layer superlattices. The internal strain-induced fields substantially modify the electronic structure and optical properties of [111]-oriented strained-layer superlattices. The presence of such large strain-induced polarization fields in [111]-oriented strained-layer superlattices is a physically interesting and technologically significant feature because of the possibility of modulating these internal fields by the application of an external field. Examples of modulating fields include (i) screening by photogenerated free carriers, (ii) external electric bias, or (iii) applied uniaxial stress. As a consequence of these modulations, large nonlinear optic, electro-optic and piezo-optic effects result. These effects are illustrated by calculations performed for Ga1−xInxAs–Al1−yIny As strained-layer superlattices grown along the [111] axis.