bluuebunny/crossref_metadata_2025 huggingface dataset:
Low temperature organometallic gas introduction system for chemical beam epitaxy under micro gravity conditions
Authors: Zaltsberg M. , Bensaoula A. , Horton C. , Haacke R. , Freundlich A. , Mahavadi P. , Rossignol V.
Published: July 2002

Chemical beam epitaxy and organometallic beam epitaxy have become important techniques for use in the growth of III–V compound semiconductors and other materials such as the high temperature superconductors. A critical component of this technology is the delivery system for the organometallic precursors. The gas delivery system vacuum integrity, the flow transient characteristics, and flux uniformity and stability, are all important in the growth of high quality material. A low temperature gas cell and a cylinder based on a novel concept for use on the Wake Shield Facility, a platform that will be used for the growth of semiconductors in space was constructed. The cell is capable of working under micro gravity conditions. Triethylgallium is passed through a sintered stainless steel filter placed at the tip of the cell. The entire cell is made of stainless steel and costs much less than a standard quartz cell. The mechanical and electrical specifications of this new gas cell are presented herein. The transient and equilibrium pressure behavior will be described for triethylgallium delivery both with and without hydrogen carrier gas. The electrical (Hall mobility) and optical (photoluminescence) properties of GaAs epilayers grown with this new design will also be presented. All of the data gathered from these tests were compared to data gathered from a standard Riber low temperature gas cell under the same conditions. The two cells were found to be comparable in their performance. The Riber cell in general had the faster response time. The saturation pressures were in the same range for both cells and the saturation pressure was a linear function of flow rate in all cases studied.
Surface spectroscopic studies of a model silica-supported copper catalyst: Adsorption and reactions of CO, H2O, and NO
Authors: Xu Xueping , Vesecky S. M. , He J.-W. , Goodman D. W.
Published: July 2002

A model silica-supported copper catalyst has been studied with temperature programmed desorption, x-ray photoelectron spectroscopy, infrared reflection–absorption spectroscopy, and scanning tunneling microscopy. The reactions of water and nitric oxide on the Cu/SiO2 catalyst were also investigated. The model catalyst was prepared by evaporating copper onto a silica thin film (∼100 Å) which was, in turn, supported on a Mo(110) surface. Copper forms small metallic clusters on the silica surface with a small fraction being partially oxidized. Water dissociates on the Cu/SiO2 catalyst to yield dihydrogen at 400 K and surface oxygen during temperature programmed reaction. Nitric oxide reacts with the model silica-supported copper catalyst to produce nitrous oxide and surface oxygen, which does not desorb until copper evaporates at high temperatures.
Investigation of the structures of sulfur on Mo(100) by scanning tunneling microscopy
Authors: Dunphy J. C. , Sautet P. , Ogletree D. F. , Salmeron M. B.
Published: July 2002

The structures of the four ordered overlayers of sulfur on the Mo(100) surface were investigated by scanning tunneling microscopy (STM). In order of increasing sulfur coverage, the overlayers have c(2×2), | 12 11̄ |, c(4×2), and p(2×1) low energy electron diffraction (LEED) patterns. Only the c(2×2) overlayer geometry has been determined from LEED I(V) analysis. An examination of point and line defects and domain boundaries in STM images provides information beyond that known from LEED on the required symmetries of the ordered overlayers. Several proposed structures were shown to be incompatible with these symmetries and therefore discarded. Only one model of the c(4×2) structure was found to be consistent with the symmetry of the STM images. This structure contains sulfur atoms occupying exclusively fourfold hollow sites. Unexpectedly, STM images of the surface with the p(2×1) LEED pattern did not have p(2×1) symmetry, but consisted of small domains of the c(4×2) structure.
Electrode material and geometry effects on the formation and electrical properties of particle traps in a plasma etch system
Authors: Collins S. M. , O’Hanlon J. F. , Beck S. E. , Hong L.
Published: July 2002

Langmuir probe measurements of the near-sheath plasma region in a plasma etch system reveal that geometric discontinuities in the powered electrode surface lead to areas of elevated plasma potential. Particles trapped in the plasma in these regions are also observed optically using laser light scattering and video detection. Electrode material discontinuities are also shown to affect the plasma potential and particle traps. Maps of plasma potential are presented for plasmas above various electrode configurations.
Reflector atomic hydrogen source: A method for producing pure atomic hydrogen in ultrahigh vacuum
Authors: Bornscheuer K. H. , Lucas S. R. , Choyke W. J. , Partlow W. D. , Yates J. T.
Published: July 2002

A tungsten filament atomic hydrogen source placed in an effusive H2 molecular beam has been combined with a cryogenically cooled Pyrex reflector. This arrangement permits efficient production and transfer of atomic hydrogen to a sample surface by a non-line-of-sight route. The arrangement eliminates most radiation heating of the sample. With the beam source, high local H2 gas densities and atomic hydrogen production rates in the filament region may be achieved without producing excessive gas loads in an ultrahigh vacuum system. A silicon(100) crystal sample was used in this study. The indirect source protects the sample from possible metal contamination evolving from the hot tungsten filament, and efficiently delivers only atomic and molecular hydrogen species to the sample. The efficiency of this arrangement has been quantitatively compared to a line-of-sight filament source of atomic hydrogen.
Mixing effects in CeO2/TiO2 and CeO2/SiO2 systems submitted to Ar+ sputtering
Authors: González-Elipe A. R. , Fernández A. , Holgado J. P. , Caballero A. , Munuera G.
Published: July 2002

Mixing effects induced in CeO2/TiO2 and CeO2/SiO2 composite powdered materials by bombardment with Ar+ ions of 3.5 keV of kinetic energy have been studied by x-ray photoelectron spectroscopy (XPS) and the factor analysis method. Characterization of the ceria phase in the original composite samples was carried out by x-ray diffraction (XRD) temperature programmed reaction, transmission electron microscopy, and extended x-ray absorption fine structure. The CeO2/SiO2 sample is characterized by very small domains (∼25 Å in size) where the cerium has entered the Si–O lattice forming a kind of silicatelike amorphous phase. In CeO2/TiO2 the cerium is in a bimodal distribution with small particles of CeO2 (30–100 Å in size) and a cerium oxide phase formed by very small particles (d=16 Å) well dispersed on the TiO2 grains. XPS showed that either by heating in H2 or by Ar+ sputtering a Ce4+→Ce3+ reduction occurs to an extent which depends on the sample and reduction conditions. The reduction degree, determined from the XPS spectra by the factor analysis method, decreased in the sense CeO2/SiO2≳CeO2/TiO2≳ CeO2, for each sample being always higher after Ar+ sputtering than after heating in H2. Adsorption of O2 at 373 K on the reduced samples led to their partial reoxidation, to an extent which was dependent on the structure of the cerium in the samples and on the type of the previous reduction treatment. In the case of the CeO2/TiO2 sample the high reduction degree obtained by Ar+ sputtering can be explained by assuming a mixing of the cerium and titanium oxide phases induced by the ion bombardment. The use of a chemical probe such as the adsorption of O2 is proposed as a method to detect the existence of mixing phenomena in composite systems submitted to ion bombardment.
Fabrication of nanometer-scale structures using atomic force microscope with conducting probe
Authors: Hattori Takeo , Ejiri Yasunori , Saito Kenji , Yasutake Masatoshi
Published: July 2002

Nanometer-scale structures were fabricated using electric field enhanced oxidation using an atomic force microscope with a conducting probe. The dependencies of thicknesses and widths of oxide stripes on applied voltage and time during which voltage is applied, were investigated. Also, the dependencies of depths of trenches, which are fabricated on the silicon surface by removing oxide stripes, on applied voltage and time during which voltage is applied, were investigated. The oxidation mechanism is discussed based on these investigations.
Surface chemistry of diethylsilane and diethylgermane on Si(100): An atomic layer epitaxy approach
Authors: Mahajan A. , Kellerman B. K. , Russell N. M. , Banerjee S. , Campion A. , Ekerdt J. G. , Tasch A. , White J. M. , Bonser D. J.
Published: July 2002

The surface chemistry of diethylsilane (DES) and diethylgermane (DEG) on the Si(100) surface was studied using high-resolution electron-energy-loss spectroscopy and temperature programmed desorption. High-resolution electron-energy-loss spectra indicate that the precursors chemisorbed dissociatively as (C2H5)2MHx(ad) and (2−x)H(ad) [x=0,1; M=Si or Ge] groups at room temperature and that the ethyl groups remain bonded to the precursor Si or Ge. Thermal annealing of DEG covered surfaces indicated that the ethyl groups remain attached to Ge at least up to the desorption temperature. Ethyl ligands react to form ethylene via a β-hydride elimination pathway. The ethylene desorption peak temperature from DEG dosed surfaces was approximately 40 K lower than that from DES dosed surfaces (733 K). We propose that ethylene desorbs from Ge atoms rather than from Si surface atoms. The hydrogen remaining on the surface after ethylene desorption desorbs from the β1 state, with peak maxima at 810 and 780 K for DES/Si(100) and DEG/Si(100), respectively.
Piezoelectric tactile integrated circuit sensor
Authors: Kolesar Edward S. , Dyson Craig S.
Published: July 2002

A two-dimensional, electrically multiplexed tactile sensor was realized by coupling a piezoelectric polyvinylidene fluoride (PVDF) polymer film to a monolithic silicon integrated circuit (IC). The IC incorporates 64 sensor electrodes arranged in a symmetrical 8×8 matrix. Each electrode occupies a 400×400-μm square area, and they are separated from each other by 300 μm. A 40-μm-thick piezoelectric PVDF polymer film was attached to the electrode array with a nonconductive urethane adhesive. The response of the tactile sensor is linear for loads spanning 0.8–135 grams of force (gf). The time required to electrically interrogate, measure, and record the response of the sensor’s set of 64 taxels is less than 50 ms, the hysteresis level is tolerable, and, for operation in the sensor’s linear range, taxel crosstalk is negligible. The historically persistent stability and response reproducibility limitations associated with piezoelectric-based tactile sensors have been resolved by implementing a precharge voltage bias technique to establish known pre- and postload sensor responses. A rudimentary tactile object image measurement procedure has been devised to recognize the silhouette of a sharp edge, square, trapezoid, isosceles triangle, circle, toroid, slotted screw, and cross-slotted screw.
Growth modes of Pd, Ag, and Si thin films on B
Authors: Kearney Patrick A. , Slaughter J. M. , Shen Dian Hong , Falco Charles M.
Published: July 2002

We have studied the growth of Pd, Ag, and Si on amorphous B films at room temperature to determine the growth modes, the chemical sharpness of the interfaces, and the structure of the layers formed. All films were deposited in ultrahigh vacuum and studied in situ with Auger electron spectroscopy, x-ray photoelectron spectroscopy, and reflection high-energy electron diffraction. Scanning tunneling microscopy characterization and Rutherford backscattering calibrations were done ex situ. In the Pd case, we find that it reacts with the B to form a smooth, amorphous PdxB1−x layer, with x≊0.85. This reaction occurred for all Pd coverages studied, from 2.3 to 130 Å, with only small variations in x. Depositing Ag on B results in a polycrystalline layer composed of large Ag islands. We find that Si-on-B forms a sharp interface and an amorphous overlayer of pure Si. The applicability of these materials to multilayer extreme ultraviolet optics is discussed.
Quantitative depth profiling of oxygen in homoepitaxial SrTiO3 films
Authors: Watamori Michio , Oura Kenjiro , Nakamura Takao
Published: July 2002

We have investigated the quantitative depth profiling of oxygen content in SrTiO3 substrates and SrTiO3 films on SrTiO3 substrates using 16O(α,α)16O 3.045 MeV resonant backscattering spectrometry. SrTiO3 films were evaporated onto SrTiO3 substrates by molecular beam epitaxy methods with an introduction of reactive O3 gas. 16O(α,α)16O resonant backscattering was corrected and an absolute content of oxygen concentration could be accurately estimated as well as other metallic elements. For SrTiO3 substrates, one kind of SrTiO3 substrate fabricated at one company had a different composition from a chemical stoichiometry (namely, Sr:Ti:O=1:1:3) and indicated a remarkable deficiency of Sr and oxygen component, while another kind of SrTiO3 substrate fabricated at another company had the chemical stoichiometric composition. SrTiO3 film compositions were strongly affected by the compositions of SrTiO3 substrates, and nearly constant depth profilings were obtained from film surfaces to substrate surfaces in spite of O3 flux densities. Continuities of oxygen contents and other metallic components at the interface will be demonstrated for SrTiO3 films on SrTiO3 substrates.
Probing the different phases of self-assembled monolayers on metal surfaces: Temperature dependence of the C–H stretching modes
Authors: Bensebaa F. , Ellis T. H. , Badia A. , Lennox R. B.
Published: July 2002

Reflection-absorption infrared spectroscopy at near grazing incidence is used to investigate the thermal stability of self-assembled monolayers of alkyl thiols, HS–(CH2)n−1-R, adsorbed on polycrystalline metal surfaces. The spectral features of the C–H stretching region have been carefully analyzed in the temperature range from 150 to 450 K. These features are highly sensitive to chain orientation and chain conformation. On gold, the chains are found to gradually untilt but remain largely all-trans up to about 350 K. Above this temperature, a broad, irreversible transition to a liquidlike phase is observed, and which is characterized by a large number of gauche conformational defects. This overall behavior did not depend upon the chain length or terminal group for the systems studied. In contrast, significant differences were observed on a silver substrate.
Surface reaction–diffusion fronts observed with photoelectron emission microscopy during carbon deposition on Mo(310)
Authors: Garcia Adrian , Kordesch Martin E.
Published: July 2002

In situ, real-time photoelectron emission microscopy and post-deposition scanning Auger microscopy of carbon deposition on oxygen-covered Mo(310) at 950 K show that sulfur stabilizes the carbon layer on the Mo surface. Reaction diffusion fronts are observed to travel across the Mo surface. The leading edges of these fronts are divided into discrete bands. A model for the development of the bands based on the diffusion of carbon and sulfur and possibly other reactants is presented.
A novel technique for characterizing the surface coverage of thin-film chemical vapor deposition in ultra-high-aspect-ratio microstructures
Authors: Soave Robert J. , Tasker G. William , Then Alan M. , Mayer James W. , Shacham-Diamand Yosi
Published: July 2002

A simple technique is introduced for accurately characterizing the surface coverage of chemical vapor deposition (CVD) processes in microstructures with very high aspect ratios. Conventional microfabrication processes are used to produce a planar array of capillary-like silicon structures with entrance dimensions as small as 2 μm and aspect ratios ranging from 10:1 to 200:1. Dielectric or semiconductor films are then deposited on the inner and outer surfaces of the capillary by low pressure chemical vapor deposition (LPCVD). After deposition, the inner surface of the capillary is exposed and the thickness of the CVD film deposited on the interior of the capillary is measured by thin-film spectrophotometry. Thickness measurements are taken along the entire length of the capillary, thus providing a deposition profile for the CVD process under investigation. Deposition profiles were measured in these structures for LPCVD silicon nitride (SiH2Cl2/NH3 precursors), polysilicon (SiH4 precursor), and silicon dioxide (tetraethoxysilane/O3 precursors). The deposition uniformity (Uc), defined as the minimum film thickness within the capillary divided by the thickness just outside the capillary entrance, ranged from nearly 0.5 for the SiO2 process to greater than 0.9 for the polysilicon process, suggesting that these CVD processes may be applied to the fabrication of devices requiring conformal thin-film deposition over high-aspect-ratio features.
Faceting of the Mo(111) surface by ultrathin Pd and Pt films
Authors: Guan Jie , Campbell Robert A. , Madey Theodore E.
Published: July 2002

The interaction of Pd and Pt ultrathin films with a Mo(111) substrate has been investigated by means of Auger electron spectroscopy, low energy electron diffraction, and temperature programmed desorption. The deposition of greater than one physical monolayer of Pd or Pt followed by annealing to temperatures greater than 700 K induces the Mo(111) surface to reconstruct forming pyramidal facets with {211} orientation. For Pd overlayers we observe streaking in the low energy electron diffraction pattern for annealing temperatures between 700 and 1100 K which is explained by a (1×n) reconstruction on the surface. Pd and Pt are among the elements that can also induce faceting on W(111).
Auger electron diffraction pattern from MgO(001) obtained at high angular resolution
Authors: Ichinohe Y. , Ishii H. , Owari M. , Nihei Y.
Published: July 2002

We measured the two-dimensional diffraction pattern of Mg KL2,3L2,3 x-ray excited Auger electron (1182 eV) with higher angular resolution and high precision. The diffraction pattern showed very fine and complicated features including many dark lines and bright bands that have never been clearly observed before. It is shown that the diffraction pattern is the superposition of many kinds of diffraction features that were related to a specific crystallographic structure. The profile of the bands is similar to that of Kikuchi bands which have been observed in electron diffraction. Circular dark lines were also observed in the Mg KL2,3L2,3 diffraction pattern. These are considered as one-dimensional diffraction patterns along low-index axes.
Spin-specific photoelectron diffraction, photoelectron spectroscopy, and absorption using magnetic x-ray circular dichroism
Authors: Tobin J. G. , Waddill G. D. , Pappas D. P. , Tamura E. , Sterne P. A. , Guo X. , Tong S. Y.
Published: July 2002

We have helped to develop novel synchrotron-radiation-based techniques, using circularly polarized x rays. Photoelectron spectroscopy, photoelectron diffraction, and x-ray absorption variants will be discussed. From these, we are working to establish the structure–property relationships in nanoscale magnetic systems.
Br/Si(211)2x1 structure investigated by x-ray standing wave
Authors: Eteläniemi V. , Michel E. G. , Materlik G.
Published: July 2002

The Br/Si(211)2×1 interface was investigated using the x-ray standing wave technique. Three different Bragg reflections [(111), (220) and (422)] were used to determine the adsorption sites following a triangulation method. In all the interfaces prepared, Br adsorption reverted the 2×1 substrate reconstruction to 1×1. Br atoms occupy different sites depending on the preparation conditions: the conventional atop site of the [111]-like terraces of the surface, and also along the unsaturated dangling bonds of the [100]-like steps present at the surface. A partial occupation of other types of sites has also been detected.
Structure and adatom thermal vibrational amplitude for the 2×2 Ga/Si (001) surface
Authors: Qian Yonglin , Bedzyk Michael J.
Published: July 2002

Fundamental and higher-order harmonic x-ray standing wave measurements were combined to directly measure the lattice positions and thermal vibrational amplitudes of Ga adatoms on the Si (001) surface. In this room-temperature study, surface structural parameters such as ad-dimer bond lengths were also determined with much higher accuracy than previous studies.
Auger, photoemission, and thermal desorption studies of the interaction of water vapor with Ni3(Al,Ti) (100) and (111) surfaces
Authors: Chia W. J. , Chung Y. W.
Published: July 2002

The interaction of water vapor with single crystal Ni3(Al,Ti) has been studied with Auger electron spectroscopy, photoemission spectroscopy and thermal desorption. Water adsorbs molecularly onto the (111) and (100) surfaces at 140 K. When warmed up to room temperature, water remains as an intact molecule on the (111) surface, but dissociates to surface hydroxyl and atomic oxygen on the (100) surface. The latter process is accompanied by the evolution of hydrogen and oxidation of Al. It appears that Al is the active species in controlling the dissociation of water in Ni3Al.
Scanning tunneling microscopy modification of purple membranes
Authors: Tamayo Javier , Sáenz Juan José , García Ricardo
Published: July 2002

Imaging, manipulation, and modification at atomic and nanometer scales of some semiconductor and metallic surfaces are features of scanning tunneling microscopy. These properties have stimulated a variety of methods for generation of nanometer-scale structures. The poor electronic conductivity of biological molecules has prevented the extension of these methods to them. Here, it is described how a low current scanning tunneling microscope operating in the near field emission regime can perform reproducible imaging with a lateral resolution of about 20 nm and selective modification of biological membranes. Marks are generated by removing the proteins and lipids from a selected region of the membrane. The removal takes place by establishing tip–membrane mechanical contact. Structures with 40 nm lateral dimensions have been generated.
Enhancement of hydrogen pumping by injecting fluorine into the exhaust system of turbomolecular pumps
Authors: Ogure N. , Shibata A. , Ono K. , Hayasaka N. , Okano H. , Okumura K.
Published: July 2002

We propose a novel evacuation system with excited fluorine being injected into the outlet port of a turbomolecular pump to improve the existing hydrogen pressure ratio at the outlet and at the inlet. The object of this system is to convert hydrogen into a heavy weight molecule such as HF, which has high pressure ratio, by the reaction between fluorine and hydrogen in the outlet port. It was confirmed that the injection of fluorine increases the hydrogen pressure ratio up to 104–106 from 103 when the hydrogen partial pressure in the evacuated chamber is more than 10−8 Torr. We employed a relatively low-duty turbomolecular pump, whose compression ratio for hydrogen is near 1000, to demonstrate the effect of fluorine injection more explicitly.
Theoretical submonolayer adsorption isotherms for hydrogen on a heterogeneous surface
Authors: Hobson J. P.
Published: July 2002

The results of theoretical calculations of physical adsorption isotherms for hydrogen on a heterogeneous surface over a pressure range 10 exp–16<P (Torr)<104 and at temperatures of 3.0, 4.2, 6.0, 10, 15, 20, 25, 30, and 40 K are presented. The values of the relative coverage, Θ, span the range 10−11 up to unity. The form of the isotherm used was the Dubinin–Radushkevich equation: ln Θ=−B[RT ln(P/P0)]2 with B−1/2=528 cal/mol, R=1.9865 cal/mol deg, and P0=vapor pressure of hydrogen at the chosen temperature. In regions where this isotherm is not applicable the results have been rounded off to give the correct limiting values, i.e., Θ=kP (Henry’s law with k constant) for parts of the isotherms at T=30 and 40 K, and P=P0 for Θ≫1. Although the calculations predict only relative coverage, they provide a useful way of evaluating the surface roughness factor for hydrogen of an experimental surface. For a porous adsorbent the theory indicates how to convert the experimental data to relative coverage. Once this is done, experimental results can be compared directly with these calculations.
Optical waveguides on silicon chips
Authors: Yokoyama S. , Nagata T. , Kuroda Y. , Doi T. , Namba T. , Miyake K. , Miyamoto T. , Miyazaki S. , Koyanagi M. , Hirose M.
Published: July 2002

Optical waveguides consisting of a SiOxNy (0≤x,y≤1) core and SiO2 cladding layers have been fabricated using Si LSI technologies. Low-pressure chemical vapor deposition (CVD) at 750 °C and remote-plasma CVD at 300 °C have been employed for the deposition of core materials. The propagation loss of ridge type waveguides depends on the size (thickness and width), refractive index and surface roughness of the core. A minimum loss of 1.5 dB/cm has been obtained. Micromirrors made from substrate-Si, poly-Si or Al, which change the light propagation direction, have been fabricated using wet-chemical or chemical dry etching. The light bending efficiency ranges from 60% to 80% depending on the material. Simulations and measurements of the propagation losses of branched and curved waveguides have been carried out. It is shown that the simulated results are in good qualitative agreement with the experimental data for both branched and curved waveguides. Single-chip integration of light emitting diodes (LEDs), micromirrors, waveguides, and photodetectors has been accomplished and the signal transfer from the LED to the photodetector has been verified.
Sulfide-assisted reordering at the InP surface and SiNx/InP interface
Authors: Kwok R. W. M. , Jin G. , So B. K. L. , Hui K. C. , Huang L. , Lau W. M. , Hsu C. C. , Landheer D.
Published: July 2002

The structural and chemical changes induced by the annealing of InP which has been exposed to gas-phase polysulfide, a known passivation method for the reduction of surface states for InP, were investigated using in situ low-energy electron diffraction (LEED), thermal desorption spectrometry, and x-ray photoelectron spectroscopy (XPS). A diffused InP (1×1) LEED pattern was observed on InP which had been exposed to ultraviolet/O3 followed by etching with a 1:30 HF solution. The (1×1) LEED pattern became sharper after the gas-phase polysulfide exposure and the subsequent annealing. The sharpest pattern was obtained after annealing at 400 °C. Accompanying these structural changes were the desorptions of species containing H and S at 300 °C and the species containing H, S, and P at 400 °C. XPS analyses showed that during the structural changes, the multiple sulfide species on the as-exposed surface were converted to a single relatively stable In–S species as a result of appropriate annealing. Similar chemical changes of sulfide species were obtained at the SiNx/InP interface. The results suggest that sulfide assisted the reordering of the InP surface, thus leading to the reduction in interface state densities which were determined by capacitance–voltage measurements.
Molecular beam epitaxy growth and characterizations of (Zn, Mg)(S,Se) epilayers for II–VI blue/green laser diodes
Authors: Grillo D. C. , Ringle M. D. , Hua G. C. , Han J. , Gunshor R. L. , Nurmikko A. V.
Published: July 2002

We report room temperature (pulsed) lasing at 463 nm from a (Zn,Mg)(S,Se) separate confinement heterostructure laser diode. Two issues related to the development of even bluer II–VI laser diodes, namely, the ‘‘AX center’’ and compositional modulation, as suggested from electrical and microstructural characterizations of the blue laser diode, respectively, will be identified.
Nanoscale structures in III–V semiconductors using sidewall masking and high ion density dry etching
Authors: Ren F. , Pearton S. J. , Abernathy C. R. , Lothian J. R.
Published: July 2002

A simple deposition and etch-back technique to form narrow (∼300 Å) masks for subsequent pattern transfer into semiconductors is reported. High ion density (∼5×1011 cm−3) electron cyclotron resonance CH4/H2/Ar (for In-containing materials) or BCl3/Ar (for Ga-containing materials) discharges are used to give anisotropic low-damage etching. After initial resist patterning using conventional stepper lithography, conformal plasma-enhanced chemical vapor deposition or reactive sputtering of a metal (W, WSix) or a low temperature dielectric (SiNx, SiO2) is followed by an anisotropic etchback to leave a thin sidewall on the resist feature. The resist is then removed by dry etching, leaving a sidewall which can be used as a mask for pattern transfer into the semiconductor. Examples of novel quantum-wire laser structures fabricated in GaN and InP–InGaAsP systems are given. The nanolaser structures can be integrated with microdisk lasers using combined dry etching and selective wet chemical etching. Low ion energies (<100 eV) are required to avoid sputtering of the mask material and changes in the near-surface stoichiometry of the semiconductor.
Ponderomotive effects in helicon plasmas
Authors: Brown R. D. , Gilland J. H. , Hershkowitz N. , Breun R. A.
Published: July 2002

Computer modeling of Nagoya Type III and helical antennas, used to excite helicon waves, has been carried out with the code ANTENA. The code considers a cylindrical plasma with an arbitrary radial density and temperature profile and realistic antenna structures, in a uniform magnetic field. We report investigations of the role of radio frequency radial ponderomotive force in providing magnetohydrodynamic stability of the helicon plasma with emphasis on the roles of the m=+1 and m=0 azimuthal modes. Both antenna structures are shown to be ponderomotively stable with most of the stability coming from the near field.
Performance and modeling of a permanent magnet electron cyclotron resonance plasma source
Authors: Saproo A. , Mantei T. D.
Published: July 2002

A plasma etch reactor with a permanent magnet electron cyclotron resonance (ECR) source and multipolar process chamber has been characterized with plasma parameter and etch measurements. The ECR source uses a compact permanent magnet structure, rather than current-driven electromagnet coils, to establish the axial magnetic field required for ECR operation. The source is compact and requires no input electrical or cooling power. Plasma densities greater than 1011 cm−3 and ion current densities above 10 mA cm−2 are obtained; the plasma parameter uniformity is 1.2% (1σ) over 20 cm. The etch rate in undoped polysilicon is 3450 Å/min without applied bias, and the etch rate uniformity is 1.8% (1σ) over a 14 cm wafer diameter. The radial and axial plasma parameter profiles agree with the predictions of an ambipolar diffusion model.
Simultaneous deposition and lamination process in vacuum
Authors: Freeland A. W. , Germundson J. R. , Swisher R. L. , Barnes K. P. , Phipps J. A. , Wan C. T.
Published: July 2002

Laminating a protective layer onto a freshly deposited metal film on a web in a vacuum chamber is very useful in many applications where the deposited film must be protected from scratches or from reacting with the atmosphere when it is removed from the vacuum chamber. Some materials will oxidize in the atmosphere very quickly, causing undesirable changes in the film’s properties. When a laminated protective coverlay is used, the material can be protected until it is further processed or put into final use. A process combining the deposition and lamination in one pumpdown and pass through the machine involving the evaporation of highly reactive material, such as bismuth, onto a polycarbonate substrate in a roll-to-roll system is described. Immediately following the deposition, the coated substrate moves to a section of the vacuum chamber where a heat sealable coverlay film is bonded to the coated substrate and then rewound onto a take-up roll. A comparison of the film properties with and without the in situ lamination will be presented.
A vacuum technology for coating TiCN-based cermets
Authors: Konyashin I. Yu.
Published: July 2002

A new vacuum technology for deposition of wear-resistant coatings on cermets of the TiCN–Ni–Mo system has been developed and introduced in industry on a large scale. The technology is based on a discovered phenomenon of the formation of a two-layer coating on the surface of the cermets due to interaction between the TiCN-based cermets and Cr vapors in a vacuum. The coating obtained in such a way comprises a thin inner layer composed of a Cr solid solution in Ni, and an outer layer composed of a mixture of (Cr,Ni)7C3 and (Cr,Ni)23C6. Results of the study on the structure, composition, and morphology of the coating as well as performance properties of the coated TiCN-based cermets are presented. Some advantages connected with the use of the technology developed are also given.
High-resolution electron energy loss spectroscopy and infrared spectroscopy of polymer surfaces: High-resolution and orientation effects of polytetrafluoroethylene films
Authors: Akavoor P. , Menezes W. , Kesmodel L. L. , Apai G. , McKenna W. P.
Published: July 2002

The vibrational structure of oriented polytetrafluoroethylene has been studied using high-resolution electron energy loss spectroscopy (HREELS) and infrared spectroscopy. Record-high resolutions of 6–15 cm−1 in HREELS with a state-of-the-art spectrometer are reported. Selection rules and orientation effects probed by the two different spectroscopies are discussed and comparisons are made between surface and bulk structure. Resonance electron scattering in HREELS has been used to study orientation effects of an intense Raman-active ν(C–C) mode at 730 cm−1. The resonance seen in HREELS is identified as the σ*(C–C) state. HREELS results have been related to near-edge x-ray absorption fine structure results. We discuss several future improvements that need to be addressed if ultrahigh resolution EELS is to become a more applicable and powerful tool for the study of polymer surfaces.
Using diode laser spectroscopy to evaluate techniques for acceleration of etch chamber evacuation
Authors: McAndrew James J. F. , Inman Ronald S.
Published: July 2002

Acceleration of vacuum chamber pumpdown through the use of species which react with adsorbed moisture is an attractive idea which appears particularly appropriate for application to a plasma-etching chamber after wet cleaning. Infrared diode laser spectroscopy was used to evaluate this technique by measuring time-dependent moisture concentrations in a metal etch chamber during evacuation and while introducing gaseous drying agents. The main advantage of this approach is that moisture levels can be measured truly in situ, with a fast response time, and with no interfering effects even in the presence of the drying agent. None of the techniques evaluated [treatment with boron trichloride, dichloropropane (DCP) and dimethoxypropane] gives any improvement in the time required to evacuate the chamber despite previously published results showing a reduction in evacuation time for an ultrahigh vacuum chamber following DCP treatment. This finding is attributed to the nature of the anodized aluminum surface of the chamber used in the present study.
Analysis of ultrahigh vacuum isotherm data with the Brunauer–Emmett–Teller equation
Authors: Hobson J. P.
Published: July 2002

The Brunauer–Emmett–Teller (BET) isotherm equation is probably the most widely used analytic equation in the range 0.01≲P/P0≲0.3 where it provides a standard measure of microscopic surface area. Here P is the pressure above the adsorbed layer, and P0 is the vapor pressure of the adsorbate, both at the temperature of the measurement. Once two measurable constants have been obtained the BET equation permits the calculation of the entire isotherm from Henry’s law at low pressures and coverages to the vapor pressure at multilayer coverages. A critical comparison between the entire equation and experimental data requires data over a very broad range of pressure and coverage. These were essentially unavailable before the advent of ultrahigh vacuum and, even today, are rare. But experimental data published many years ago by the author for physical adsorption isotherms of argon, krypton, and xenon on an adsorbent of porous silver at T=77.4 K are suitable for a test of the whole BET equation that was not carried out at the time. The present article fulfills that omission. It is found that, while the BET equation is an adequate description of the data in the range 0.01≲P/P0≲1, serious and increasing divergencies occur as the pressure decreases further. A review of ultrahigh vacuum isotherm data for helium and nitrogen leads to the same conclusion for these gases also. The special case of hydrogen is important in predicting the base pressures in modern colliders. Here, however, the vapor pressure of hydrogen at 4.2 K is about 3.2×10−7 Torr, and magnitude some four orders in pressure below this (required for a decisive test of the BET equation) is already well into the range where quantitative hydrogen measurements are difficult. Hence conclusions about the applicability of the BET equation to hydrogen isotherm data are less certain. An analytic equation based, in part, on the Dubinin–Radushkevich isotherm at low pressures, which was proposed earlier, gives a good description of the argon, krypton, and xenon data on porous silver over the entire measured range, some thirteen orders of magnitude in pressure.
Carbon reference Auger electron spectra measured with a high-performance cylindrical mirror analyzer
Authors: Goto Keisuke , Takeichi Yoshinori
Published: July 2002

Secondary electron and Auger electron spectra for two types of carbons, graphite and soot (glassy), have been measured in an absolute manner with a novel cylindrical mirror analyzer for primary energies 1 eV through 5 keV. The Auger electron, elastically backscattered primary, energy-loss, secondary-electron, and background signals have been related. The degree of crystallization modifies the characteristics of the secondary and energy-loss spectra drastically, though the background continuum was not changed appreciably. Different Auger electron yields were obtained for graphite and soot. It has been found that both graphite and soot are promising candidates as reference materials for studying the properties of instruments.
Adsorption of CO and hydrogen on the K-modified Ir(111) surface
Authors: Schick M. , Lauterbach J. , Weinberg W. H.
Published: July 2002

Alkali metals are well known as promoters for catalytic reactions on transition metals. We have characterized coadsorbed CO and K on Ir(111) by means of temperature programmed desorption (TPD) and Fourier transform infrared reflection-absorption spectroscopy. Carbon monoxide is known to adsorb at on-top sites on Ir(111), and is characterized by a stretching frequency that varies from 2028 cm−1 in the limit of zero coverage to 2090 cm−1 at 0.7 monolayer (ML) which is saturation coverage on this surface. In the presence of K, however, several CO stretching bands with frequencies as low as 1395 cm−1 were found in the IR spectra depending on the K coverage. CO and K desorb simultaneously in a peak around 710 K with a half-width of 60 K, suggesting the formation of Kn(CO)m compounds for K coverages greater than 0.1 ML. In contrast to clean Ir(111), the adsorption of molecular hydrogen on the K precovered surface is activated. By exposing atomic hydrogen to this surface, the barrier for adsorption is overcome, and the hydrogen adatoms are stabilized by K, as shown by TPD. However, when atomic hydrogen is dosed on the K/Ir(111) surface precovered with CO, the Kn(CO)m compounds that are formed inhibit the adsorption of even atomic hydrogen.
Ethylene oxide interaction with Pd surfaces: Experimental and theoretical results
Authors: Shekhar Ratna , Barteau Mark A.
Published: July 2002

Ethylene oxide (EO) interaction with the clean Pd(110) surface was investigated under ultrahigh vacuum conditions using temperature programmed desorption/reaction. Most of the layer adsorbed at 120 K desorbs at 170–220 K, but a fraction decomposes indicating ring opening reactivity. The stoichiometric release of CO and the absence of water formation during EO decomposition on Pd(110) indicated that no more than one C–O bond was broken per molecule; subsequent C–C scission led to methane desorption at ∼325 K. Using the surface-cluster analogy, we have also applied density functional theory to assess electronic interactions involved in EO interaction with palladium surfaces. In particular, interaction with Pdn clusters (n=1,4,10) modeling the surface chemistry of EO on palladium surfaces has been investigated in this work. EO binding energies on these clusters range from 8 to 13 kcal/mol. In contrast to the experimental observation of ring opening of EO on Pd(110) and Pd(111) surfaces, theoretical results at this level do not indicate any significant perturbation of C–O and C–H bonds in adsorbed EO.
Effects of magnetic field on oxide etching characteristics in planar type radio frequency inductively coupled plasma
Authors: Lee Ho-Jun , Kim Jung-Hun , Whang Ki-Woong , Joo Jung-Hoon
Published: July 2002

We have developed a new magnetized radio frequency inductively coupled high density plasma etching reactor. The essential part of the system is the application of a weak volumic magnetic field (less than 30 gauss) to a planar-spiral antenna configuration. Efficient power transfer and reduction of charged particle loss are possible by magnetizing the low pressure plasma. Consequently, higher levels of plasma and ion current density can be obtained compared with a nonmagnetized discharge. It is found that the degree of magnetization in the plasma source is one of the most important parameters that affects the etching characteristics of SiO2 and Si. An improvement of SiO2/Si etch selectivity while maintaining a high SiO2 etch rate is obtained by applying the magnetic field to various fluorocarbon plasmas. Etch threshold ion energy and polymer film deposition rate increase with the external magnetic field for carbon-rich feed gases such as C4F8. Reactive ion etching (RIE) lag in fine holes is greatly reduced while keeping the high selectivity under modest magnetic induction level. At higher magnetic induction level the RIE lag worsens and is accompanied by a considerable decrease in the Si etch rate.
Formation of TiN films with low Cl concentration by pulsed plasma chemical vapor deposition
Authors: Hiramatsu Kenji , Ohnishi Hiroshi , Takahama Toru , Yamanishi Ken-ichiro
Published: July 2002

Polycrystalline TiN films containing less than 1 at. % of Cl contamination were formed from TiCl4 at a low temperature (200 °C) condition on a Si substrate by pulsed plasma chemical vapor deposition. The Cl suppression at low temperature was realized by a two-step process, TiCl4 decomposition and hydrogen reduction. The main objective for reducing Cl in the film was to establish a sufficient reduction period to free TiClx radicals in the gas phase. The length of the reduction period was affected by the radio frequency power, which decided the rate of TiCl4 decomposition and hydrogen reduction.
Etch rate and plasma density radial uniformity measurements in a cusped field helicon plasma etcher
Authors: Quick A. K. , Chen R. T. S. , Hershkowitz N.
Published: July 2002

Experiments on the University of Wisconsin helicon etcher were conducted to study the effects on uniformity of applying a cusped magnetic field to the etching chamber. Also a comparison was made between long and short antenna/substrate separation distances. The plasma radial density uniformities, measured using a Langmuir probe over the inner 10 cm diameter of the chamber, gave maximum density variations of ±22% with the cusp off and ±1.28% at the zero field region of the cusp. The maximum SiO2 etch rate in CF4/Ar plasmas occurred at 50% Ar concentration in the long source configuration. Etch rate uniformity of SiO 2 etching in a CF4/Ar/O2 plasma improved from ±8.1% to ±2.6% for a 82.5 mm wafer by shortening the antenna–substrate separation distance from 108 to 47 cm. Azimuthal asymmetry of the plasma produced from the Nagoya type III antenna was observed in the short source configuration in which the SiO2 etch rate uniformity varied from ±1.5% across the vertical axis of a 150-mm-diam wafer to ±12% across the horizontal axis of the wafer.
‘‘Self-thickness-limited’’ plasma polymerization of an ultrathin antiadhesive film
Authors: Gröning P. , Schneuwly A. , Schlapbach L. , Gale M. T.
Published: July 2002

Ultrathin (<5 nm) fluorinated polymer films of homogeneous thicknesses have been deposited from a CF4/H2 microwave discharge. The films have an extremely low surface energy of 4.2 mJ/m2, which is more than four times lower than that for polytetrafluoroethylene. The deposition was carried out in a type of ‘‘self-thickness-limited’’ mode, in which the thickness of the deposited polymer film is limited by the plasma parameters. The deposition can be separated into two phases, a growth and a treatment phase. During the treatment phase, the deposited film is fluorinated, which results in a dramatic decrease of the surface energy. The thickness limiting behavior of the plasma is explained by the dualism of etching and polymerization occurring in fluorocarbon discharges. The film was tested as antiadhesion film for the replication of micro-optical structures, using a Ni shim with a very fine surface relief grating (400 nm periodicity) to hot emboss (at 180 °C) polycarbonate sheed. The tests demonstrate the excellent antiadhesive property of the film with the polycarbonate and reveal a good adhesion of the film with the Ni substrate.
Sputtering of metallic walls in Ar/H2 direct current glow discharges at room temperature
Authors: Tabarés F. L. , Tafalla D.
Published: July 2002

Laser induced fluorescence of Cr atoms in their ground state have been used to characterize metallic sputtering in dc glow discharges (GDs) of hydrogen/argon admixtures in a stainless steel chamber at room temperature. A strong decrease in the sputtering signal was observed upon addition of H2 to the pure Ar GD plasma, at constant pressure and total current conditions, even at low H2 concentrations in the admixture. The plasma microscopic parameters have been determined from actinometry and Langmuir probe data. The H implantation characteristics of the studied plasmas were also determined by pump and release experiments. According to all the experimental evidence, hydrogen implantation in the metal surface is the main process responsible for the observed sputtering suppression. The results are compared to similar sputtering reduction observations previously reported in other light contaminant/metal systems.
High resolution electron energy loss spectroscopy study of vapor deposited pyromellitic dianhydride and oxydianiline films on Cu(110)
Authors: Plank R. V. , DiNardo N. J. , Vohs J. M.
Published: July 2002

The reaction of pyromellitic dianhydride (PMDA) and oxydianiline (ODA) on Cu(110) was studied using high resolution electron energy loss spectroscopy (HREELS). The interaction of the individual monomers with Cu(110) was also studied. PMDA dissociated on Cu(110) at 300 K forming a carboxylate link to the surface, releasing CO into the gas phase. ODA was also found to adsorb dissociatively on Cu(110) at 300 K via cleavage of one of the amine NH bonds. Vapor-deposited PMDA/ODA films on Cu(110) reacted at 300 K to form polyamic acid. Heating a polyamic acid film to 450 K was sufficient to induce imidization and form polyimide. HREELS results indicated that the resulting polyimide chains were both bonded to the surface and terminated with PMDA monomer units. The polyimide film was stable up to 500 K, consistent with the thermal stability of PMDA on Cu(110).