bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear magneto-optical spectroscopy of Hg1−xCdxTe by two-photon absorption techniques
Authors: Seiler D. G. , Littler C. L. , Loloee M. R. , Milazzo S. A.
Published: July 2002

In this paper we present new and important results on Hg1−xCdxTe alloys using CO2 laser-based magneto-optical methods that include (i) the observation and analysis of two-photon magnetoabsorption spectra in a variety of samples from x≂0.24 to 0.30, and (ii) the observation of magneto-optical transitions of electrons from both midgap levels and shallow acceptor levels to the conduction-band Landau levels. These measurements allow the most accurate determination of the energy gap and binding energies associated with impurities and defects. In addition, analysis of the temperature dependence of two-photon spectra obtained on all samples investigated reveals a nonlinear variation of the energy gap versus temperature not previously reported. The temperature dependence of the energy gap below 100 K cannot be explained by any of the currently used empirical relationships. The laser-based magneto-optical techniques we present here for Hg1−xCdxTe are generic and can easily be applied to other semiconductor or superlattice systems by using an appropriate combination of laser sources and magnetic fields.
Target fabrication for laser fusion research in Japan
Authors: Norimatsu T. , Kato Y. , Nakai S. , Kubo U.
Published: July 2002

A review of target fabrication for laser fusion research in Japan conducted at the Institute of Laser Engineering, Osaka University, the Department of Electrical Engineering, Kinki University, and the Department of Electrical Engineering, Gifu University is presented. An emulsion technique is employed to manufacture polymer spheres. Excimer laser irradiation on polystyrene shells reduces permeation of hydrogen. Irradiation of UV radiation from a Hg lamp is revealed to be useful in making CHDT shells enhancing tritium exchange rate. A polymer coating on a levitated target is achieved by excimer-laser-induced chemical vapor deposition. A new immersing and heating technique has been developed to make a cryogenic foam target. Nondestructive fuel assay for the cryogenic foam target has been made by means of β-ray attenuation. A magnetic levitation technique for laser irradiation of a support-free target is introduced.
Chloride ion-induced large scale reconstruction on an electrochemically roughened Ag electrode
Authors: Otsuka I. , Iwasaki T.
Published: July 2002

We have studied changes in the surface morphology of an electrochemically roughened polycrystalline silver electrode at −0.20 V vs SCE in 0.1 M KCl using cyclic voltammetry, scanning electron microscopy (SEM) and scanning tunneling microscopy (STM). STM observations on a scale ranging from micrometer down to nanometer were made in air at atmospheric pressure and room temperature. Cyclic voltammograms for the roughened electrode in 0.1 M KCl before and after the relaxation treatment show that the current decreases in the double layer potential range. SEM images of the roughened Ag after the relaxation reveal the collapse and the coalescence of the nodules on the electrode surface compared to the surface morphology at the initial stage. These findings are consistent with STM results obtained from a large-scale observation. STM can resolve the fine structure of a nodule surface on the roughened electrode. This structure is observed to relax.
Surface analysis of copper, brass, and steel foils exposed to fluorine containing atmospheres
Authors: Cabrera A. L. , Karwacki E. J. , Kirner J. F.
Published: July 2002

The composition and thickness of fluoride films that form upon exposure of various metals to F2/N2 at room temperature were studied using x-ray photoelectron and Auger electron spectroscopy (AES). Depth profiles were obtained using AES with argon ion sputtering. The metals studied included low carbon steel, 302 stainless steel, copper, and brass (70% Cu/30% Zn). Samples treated in 0.12% F2/N2 display small amounts of surface fluorine, primarily in the form of fluorinated hydrocarbons rather than metal fluorides. In contrast, exposure to 25% F2 produces thicker films, consisting mainly of metal fluorides with some metal oxides. Fluorine does not seem to penetrate beyond the native oxide initially present on the metal foil surface. Iron fluorides form on low carbon steel, and copper fluorides form on copper. Surprisingly, iron fluorides preferentially form on stainless steel, and zinc fluorides preferentially form on brass. These results provide new insight about the passivation of metals by F2 and raise new questions.
Tritium processing at the Savannah River Site: Present and future
Authors: Ortman M. S. , Heung L. K. , Nobile A. , Rabun R. L.
Published: July 2002

Tritium handling equipment and methods at the Savannah River Site Tritium Facilities have been continually improved since tritium processing operations began in 1955. Several new technologies were introduced into the Tritium Facilities in the 1980’s. One of these is the use of fluidless, mechanical pumps (Normetex and Metal Bellows) to replace mercury pumps. A second is the use of metal hydride technology to store, purify, isotopically separate, pump, and compress hydrogen isotopes. Metal hydrides, such as La–Ni–Al alloys and Pd loaded on kieselguhr, offer significant flexibility and size advantages compared with conventional tritium handling technology, such as gas tanks, thermal diffusion columns, and mechanical compressors. Metal hydrides have been used in the Tritium Facilities since 1984 with the most important application of this technology being planned for the Replacement Tritium Facility, a $140 million facility scheduled for completion in 1990 and startup in 1991.
Potential applications of an electron cyclotron resonance multicusp plasma source
Authors: Tsai C. C. , Berry L. A. , Gorbatkin S. M. , Haselton H. H. , Roberto J. B. , Stirling W. L.
Published: July 2002

An electron cyclotron resonance (ECR) multicusp plasmatron has been developed by feeding a multicusp bucket arc chamber with a compact ECR plasma source. This novel source produces large (about 25 cm diam), uniform (to within ±10%), dense (>1011 cm−3) plasmas of argon, helium, hydrogen, and oxygen. It has been operated to produce an oxygen plasma for etching 12.7 cm (5 in.) positive photoresist-coated silicon wafers with uniformity within ±8%. Results and potential applications of this new ECR plasma source for plasma processing of thin films are discussed.
Effect of surface roughening on secondary ion yields and erosion rates of silicon subject to oblique oxygen bombardment
Authors: Wittmaack K.
Published: July 2002

The phenomenon of ripple formation on silicon surfaces subject to oblique bombardment with O+2 ions was studied by means of secondary ion mass spectrometry (SIMS). The measurements were performed with a versatile ion microprobe which allows the angle of beam incidence and the impact energy to be varied independently. Bombardment with 10 keV O+2 ions caused facetting of the whole bombarded area provided the impact angle θ ranged between about 32° and 58° to the surface normal. A smooth crater bottom with a few etch pits was produced at 30°. Facet formation gave rise to significant secondary ion yield changes. Rather large yield enhancement (up to a factor of 6) was observed for species like O+, SiO+, and Si2+ in which case the yields are very sensitive to the oxygen concentration at the surface. The sputtered depth at which the yield changes become noticeable decreases with increasing impact angle from about 4 μm for θ=35° to 0.4 μm for θ=55°. For as many as eight different ion species the stationary intensities relevant to secondary ion emission from smooth surfaces were measured as a function of θ (0°<θ<75°). On the basis of these ‘‘calibration curves,’’ the observed yield changes induced by facetting can be attributed in an essentially quantitative manner to the variation of the microscopic impact angles with depth of erosion. The interpretation is supported by measurements of yield changes observed upon varying the impact angle from oblique to normal, subsequent to short term or long term oblique bombardment. As a result of facetting the erosion rate of silicon was found to change appreciably.
The effects of alloying on stress induced void formation in aluminum-based metallizations
Authors: Ryan J. G. , Riendeau J. B. , Shore S. E. , Slusser G. J. , Beyar D. C. , Bouldin D. P. , Sullivan T. D.
Published: July 2002

Evaporated metallizations composed of aluminum alloys and titanium underlayers were patterned, passivated with plasma enhanced chemical vapor deposited SiNx and aged for 1000 h at 150 °C in order to observe stress-induced void formation. Metal films were analyzed using scanning electron microscopy, transmission electron microscopy, and secondary ion mass spectrometry. The addition of copper to aluminum results in fewer voids than in comparable noncopper metallizations. For Al–Cu films, fewer voids were observed in 1.5 μm lines compared to 5 μm lines, apparently due to the presence of greater stress gradients in the wide line case. Silicon appears to promote void formation by rapid grain boundary diffusion to precipitates. Oxygen incorporation in aluminum produces small grained films, thereby generating many void nucleation sites. High oxygen concentrations produce films with a few long, channel-like voids and many small voids. Titanium underlayers decrease the percent of metal volume voided for Al and AlSi films, while for AlCu films, the percentage void area and the average void size are increased. Volume reduction associated with interfacial TiAl3 formation may be responsible for the increase in void size associated with titanium underlayers.
Photoemission study of GaAs1−xPx and Ga1−xAlxP mixed crystals
Authors: Zhong Z. T.
Published: July 2002

The different kinds of mixed crystal systems for GaAs1–xPx and Ga1–xAlxP have been investigated by x-ray photoemission spectroscopy (XPS). The core level binding energies of Ga in GaAs1−xPx increase, whereas those of P in GaAs1−xAlPxP decrease with composition x, which are analyzed using Pauling’s ionicity and the ionicity scale of Kowalczyk et al. For two kinds of mixed crystals, we found that the energies of plasmon loss peaks increase, all major peaks in the valence band shift the band edge, and the top of the valence band recedes linearly with composition x. The composition variation of the energy gap for mixed crystals are caused basically by the top of the valence band receding.
The influence of ion bombardment on reactions between Ti and gaseous N2
Authors: Kant R. A. , Sartwell B. D.
Published: July 2002

Simultaneous Auger electron spectroscopy and ion bombardment were used to study the influence of ion bombardment on the amount of nitrogen accumulated on a Ti surface in a low-pressure nitrogen atmosphere. The nitrogen level was measured as a function of time, ion flux, nitrogen partial pressure, and Ti temperature both directly before and during bombardment with 150 keV Ti+ ions. As a result of the ion bombardment, the steady-state nitrogen level increased (and in some cases decreased) by an amount determined by the balance between the ion flux and the flux of nitrogen gas. The experimental results were interpreted in terms of a multiple-step process involving ion beam induced dissociative chemisorption of physisorbed molecular nitrogen. The time dependence of the nitrogen concentration at the Ti surface was modeled with a pair of differential equations that described the time rate of change of the physisorbed and chemisorbed contributions to the surface nitrogen in terms of both ion beam induced and thermally activated processes. These equations were solved numerically and the solutions agreed with the experimental behavior. In addition, the results of this study were used to explain observed variations in properties of thin film TiN grown by ion-assisted reactive deposition.
Theoretical investigation of chemical bonding at aluminum/polyimide interface
Authors: Selmani A.
Published: July 2002

A b initio local spin density method has been used to investigate chemical bonding of aluminum with polyimide surfaces. We focused in this work on the carbonyl group, which is, as demonstrated by x-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS), the active site, at least at low metal coverage. We found that the formation of a linear complex C–O–Al is favored over other positions in the vicinity of carbonyl group. The vibrational frequency corresponding to oxygen–aluminum stretching is calculated and compared with HREELS data. We also calculated core level chemical shifts. The agreement with XPS results is satisfactory. Finally, we suggest a mechanism for the adsorption of Al on polyimide surfaces.
High-temperature scanning tunneling microscope
Authors: Watanabe M. O. , Tanaka K. , Sakai A.
Published: July 2002

A novel scanning tunneling microscope that operates at high temperature has been developed. We originally designed a new type of microscope that heats only the sample and maintains the other elements at room temperature. The design uses bimorph piezoelectric drivers that are placed apart from the sample by five orthogonal arms. The sensitivity of the piezoelectric drivers is independent of the sample temperature. Atomic scale images of graphite at temperatures ranging from room temperature to 400 °C are obtained.
Application of factor analysis to Auger crater-edge profiling
Authors: Gatts C. , Losch W.
Published: July 2002

Factor analysis is applied to the Auger crater-edge profile of a palladium/hydrogenated amorphous silicon layered structure. The results show, apart of a considerable improvement in interface determination, new information not obtainable by the conventional Auger depth profiling technique, which makes this procedure extremely useful for thin film depth profiling.
Studies of adhesion of metal films to polyimide
Authors: Pappas David L. , Cuomo Jerome J. , Sachdev Krishna G.
Published: July 2002

Bonding of Cu/Cr films to several polyimides has been studied as a function of polymer surface modification by ion beam and chemical pretreatment. The effects of the metal deposition method and parameters have also been examined. The materials of interest include a low thermal expansion polyimide derived from 3,3′,4,4′-biphenyl tetracarboxylic acid dianhydride-p-phenylene diamine (BPDA-PDA) polyamic acid, and pyromellitic dianhydride-4,4′-oxydianiline (PMDA-ODA) polyimide, formed from polyamic acid or polyamide ethyl ester precursors. The metal/polyimide adhesive strength was determined by the 90° peel test, while the interfacial regions were examined using x-ray photoelectron spectroscopy and ellipsometry. It is found that for PMDA-ODA systems, exposure to low energy Ar+ and/or O+2 ions improves adhesion of the metal overlayer, while for BPDA-PDA polyimide, the role of O+2 is more significant. The fracture location is found to lie 20–300 Å within the polymer, depending upon the ion beam dose and the specific polyimide employed.
Biaxial modulus measurement of chemical vapor deposited polycrystalline diamond films
Authors: Cardinale G. F. , Tustison R. W.
Published: July 2002

The biaxial modulus of polycrystalline diamond (PCD) films deposited by microwave plasma assisted chemical vapor deposition on silicon substrates has been investigated. The amount of hydrogen incorporated in the PCD films is determined using Fourier transform infrared spectroscopy. Additional characterization of the PCD films is performed using x-ray diffraction, Raman spectroscopy, and scanning electron microscope analysis. Biaxial moduli of PCD films containing 0.9% and 0.3% hydrogen have been found to be 960 and 1177 GPa, respectively. Comparison with the biaxial modulus of 1228 GPa for a randomly oriented aggregate of bulk diamond is discussed.
Interpretation issues in force microscopy
Authors: Burnham Nancy A. , Colton Richard J. , Pollock Hubert M.
Published: July 2002

In this paper, we will discuss force microscopy (FM) and its potential for determining mechanical properties of thin films. We will introduce the basic principles of FM, and demonstrate how FM can be used to determine materials properties as well as image surface topography, both with nanonewton or sub-nanonewton force resolution and sub-nanometer position resolution. As FM is still a new field, not all of the questions concerning interpretation have been fully answered. We will elucidate four current issues that must be resolved before the full potential of FM can be realized. They are: (1) the role of water vapor and adsorbed films in imaging and force curve measurements, (2) the interpretation of force curves, (3) the influence of surface forces and loads on imaging, and (4) the nature of the imaging mechanisms.
Multiple source modulated molecular beam reactive scattering applied to hydrogen recombination and oxidation on the Rh(111) surface
Authors: Padowitz D. F. , Sibener S. J.
Published: July 2002

Surface kinetics which are nonlinear and involve multiple reactants are not amenable to standard modulated molecular beam reactive scattering techniques. To explore these complex reactions, we have developed a new three molecular beam arrangement. Two continuous, independently adjustable beams establish steady state surface concentrations, while a third weaker beam is modulated to induce small concentration perturbations around the selected steady state. This permits experimental linearization of nonlinear kinetics over a wide range of coverages, helping us to evaluate coverage dependent rate constants and to isolate individual elementary steps from complex reaction mechanisms. The technique has been applied to the oxidation of hydrogen to water on the Rh(111) surface. We have demonstrated linearization of the water reaction with isotopic substitution forming HDO. The analysis is illustrated by the simpler example of hydrogen–deuterium recombination. HD shows an activation energy of 20 kcal/mol and preexponential on the order of 10−2 cm2 s−1 for the linearized reaction in the low coverage limit.
Plasma diffusion from a low pressure radio frequency source
Authors: Charles C. , Boswell R. W. , Bouchoule A. , Laure C. , Ranson P.
Published: July 2002

Helicon sources are becoming a promising technique for providing high ion fluxes with controllable energy. It is still unclear how the plasma parameters evolve from the source to the diffusion chamber where the wafer is situated. To investigate this region electric probes have been used (Langmuir probe and energy analyzer) to measure electron temperature, plasma potential, plasma density, and ionic distribution functions along the axis of a symmetric Argon plasma diffusing freely away from a 6-cm-diam 20-cm-long, 13.56-MHz (Helicon) source operating at 10−6 bar and 300 W. The plasma density and potential are simply related by Boltzman’s relation. Although a potential difference of 37 V is measured between the source and the substrate, charge exchange collisions reduce the average energy of the ions arriving at the substrate to about 5 eV. This low energy should be advantageous in processing easily damaged thin films.
Annealing response of disordered sputter deposited vanadium pentoxide (V2O5)
Authors: Luksich John , Aita Carolyn Rubin
Published: July 2002

We report the response to isothermal, low temperature (280 °C) annealing in air for up to 60 min, in terms of changes in crystallography and optical absorption coefficient α(E) of two types of sputter deposited, disordered vanadium pentoxide; (1) an amorphous film and (2) a single 〈010〉-crystallographic orientation film in which the interlayer spacing b is slightly greater (0.03%) than b0, the ideal value. It was found that low temperature annealing does not crystallize amorphous vanadium pentoxide, and that no change occurs in α(E) in the charge transfer region E≥∼2.5 eV. The Tauc nondirect optical band gap E′=2.34 eV. However, the low energy absorption tail present in the as-grown amorphous film disappears upon annealing, attributed to the elimination of V+4 sites. On the other hand, annealing crystalline vanadium pentoxide causes crystallographic changes, the interlayer spacing expands, and concurrently, α(E) in the charge transfer region, E≥2.6 eV, increases. In agreement with a recent theoretical band calculation and single crystal data, the indirect optical band gap Ei=2.36 eV for both as-grown and annealed crystalline vanadium pentoxide.
Deceleration and ion beam optics in the regime of 10–200 eV
Authors: Foo K. K. , Lawson R. P. W. , Feng X. , Lau W. M.
Published: July 2002

A deceleration lens system for low energy ion beam transport applications in the region of 10–200 eV has been designed, constructed and experimentally characterized. In this ion beam system, the target is required to be in an almost field-free region at the exit of the lens to allow for maximum target maneuverability. The lens design was optimized using the simulation data obtained with chden, a computer program for calculating ion trajectories with space-charge included. The design chosen in this work was a five-electrode lens which can be operated in either a simplified two-electrode deceleration mode or, when the best system performance is required, in a five-electrode decelerator-focusing mode. The performance of the lens was experimentally evaluated by using a 3 keV pure argon ion beam with a beam size of about 1 mm2 and beam current of about 10μA which was generated by a modified Colutron Ion Gun Model G-2 unit. The lens decelerated the incident beam to 10–200 eV and transported it to either a Faraday cage for beam current and beam profile measurements or to a quadrupole mass spectrometer equipped with a cylindrical ion energy analyzer for beam energy and mass characterization. The results indicated that the lens could deliver an ion current density of approximately 100 μA/cm2 at ion energies higher than 50 eV. The available current density dropped with decreasing energies but remained at more than 10 μA/cm2 at 10 eV.
Surface etching and roughening in integrated processing of thermal oxides
Authors: Offenberg M. , Liehr M. , Rubloff G. W.
Published: July 2002

A multichamber ultrahigh vacuum processing and analysis system has been used to study integrated thermal oxide processing, in which the final precleaning process and the thermal oxidation process are integrated by employing transfer of the wafers through ultraclean, inert ambients (purified, dry N2 and then ultrahigh vacuum). Al-gate metal oxide semiconductor capacitors show high breakdown fields (∼12 MV/cm) when a thin oxide passivation layer is present prior to oxidation, but low breakdown fields (< 6MV/cm) when the Si surface is initially oxygen-free. This contrasting behavior is caused by the etching of Si surfaces which occurs at elevated temperature in the presence of trace concentrations (∼100 ppb) of oxygen (e.g., 2Si+O2→2SiO↑ ), leading to surface roughening and then field enhancement at asperities in the structure. Oxide surface passivation prevents etching and assures the dielectric integrity of the structure.
Relative sensitivity factors and useful yields for a microfocused gallium ion beam and time-of-flight secondary ion mass spectrometer
Authors: Bennett J. , Simons D.
Published: July 2002

Relative sensitivity factors for several elements in micrometer size glass particles, bulk glasses and glass thin films have been determined for a Ga+ liquid metal ion gun combined with a time-of-flight secondary ion mass spectrometer. The reproducibility of the values within and among glasses of various compositions is better than 20%. Reproducibility is improved by sputter cleaning the sample prior to data collection. Relative sensitivity factors have also been obtained from bulk glasses using pulsed, low-energy electrons to neutralize charge buildup on the sample. Useful yields for Mg and Ca in a thin glass film were calculated to be 3.4×10−4 and 8.0×10−4, respectively.
Surface characterization of polymers: Complementary information from x-ray photoelectron spectroscopy and static secondary ion mass spectrometry
Authors: Stickle W. F. , Moulder J. F.
Published: July 2002

Polymers have found a wide variety of applications ranging from biocompatible materials to use as insulators in microelectronic devices. For many applications the surface of the polymer plays an important role such as when surface modification of the polymer is required or has occurred during processing. Surface characterization of polymers may be accomplished by many methods such as analysis by x-ray photoelectron spectroscopy, (XPS), and static secondary ion mass spectrometry, (SSIMS). The information of each of these techniques is unique and together provide a complete picture of a polymer surface in terms of local chemistry and of long-range chemistry of the material. The application of XPS and SSIMS to several polymer systems will be discussed and the information of the analytical methods will be compared and contrasted.
Orientation and structure of monolayer →→ multilayer phthalocyanine thin films on layered semiconductor (MoS2 and SnS2) surfaces
Authors: Collins G. E. , Nebesny K. W. , England C. D. , Chau L.-K. , Lee P. A. , Parkinson B. A. , Armstrong N. R.
Published: July 2002

Thin films of both chloroindium and copper pthalocyanines have been vacuum deposited onto metal dichalcogenide surfaces such as MoS2 and SnS2, with ordering achieved for these four-fold symmetric molecules ranging from below monolayer to multilayers. Reflection high-energy electron diffraction suggests that square lattice geometries are adopted for low coverages of each phthalocyanine (Pc), but with multiple domains. Low-energy electron diffraction confirms the presence of three square lattice domains, each domain rotated by 60° with respect to the other. Basal plane defects, and especially terrace sites in the metal dichalcogenide surface, are implicated as the nucleation sites for the growth of these square lattice domains. Optical spectroscopies have been used to characterize submonolayer to multilayer deposits of chloroindium phthalocyanine on SnS2 thin films, where the packing geometries of the adjacent Pcs cause perceptible changes in the position and width of the absorbance band in the visible/near-infrared region. The optical data suggest that aggregation (dimerization) of InPc–Cl occurs at even submonolayer coverages, and that the square lattice domains seen actually consist of bilayers of InPc–Cl, arranged in a staggered square lattice configuration.
Growth conditions for sputter deposited niobium oxides
Authors: Lee R. C. , Aita C. R.
Published: July 2002

A Nb target was sputtered in radio-frequency-excited, Kr/O2 discharges and films were deposited on unheated fused silica and 〈111〉-cut Si substrates. Two independent process parameters, cathode voltage and gas O2 content, were varied. Optical emission spectrometry was used for in situ discharge diagnostics. From this data, we determined: (1) the values of the process parameters at which a complete target surface oxide layer was formed, and (2) the fractional flux of gaseous atomic Nb and molecular Nb-oxide incident on the substrate over the entire range of process parameters. Post-deposition film characterization for metallurgical phase identification included x-ray diffraction, infrared absorption, and electrical resistivity measurements. A ‘‘phase map’’ was constructed, interrelating the independent process parameters, the growth environment, and the metallurgical phases in the films. Comparison with phase maps previously developed for the Nb–O system grown in Ar/O2 and Ne/O2 discharges allowed generalizations to be made regarding the growth environment (in terms of Nb, Nb oxide, and oxygen flux to the substrate) under which different Nb-oxide phases were formed in the film.
Use of an externally applied axial magnetic field to control ion/neutral flux ratios incident at the substrate during magnetron sputter deposition
Authors: Petrov I. , Adibi F. , Greene J. E. , Sproul W. D. , Münz W.-D.
Published: July 2002

The development and characterization of an ultrahigh vacuum ‘‘unbalanced’’ dc magnetron sputter deposition system with a variable external axial magnetic field for controlling the ion-to-neutral flux ratio at the substrate during deposition with low negative substrate biases is reported. The target assembly is a planar-magnetron (PM) with a toroidal magnetic-field electron trap created using a set of permanent magnets. A pair of Helmholtz coils, located outside the vacuum chamber, produces an additional magnetic field Bext which is uniform along the axis orthogonal to both target and substrate surfaces. The value and sign of Bext has a strong effect on the plasma density near the substrate, and hence on the ion flux Ji incident at the substrate, with only a minor effect on the target-atom flux. For a Ti target sputtered in pure Ar at 20 mTorr with a target-substrate separation of 6.5 cm, changing Bext from −50 G (opposing the field of the outer PM pole) to +600 G (reinforcing the field of the outer PM pole) varied the ion-to-Ti flux ratio Ji/JTi incident at the substrate by a factor of 60 from 0.1 to 6 with the bias held constant at any desired negative value between ≂−15 V (limited by the difference between the floating Vf and plasma Vp potentials) and the highest negative values examined, −100 V. For reactive sputter deposition in N2 (where the primary ion is N2+) under the same conditions, Ji/JTi varied by a factor of 50 from 0.7 to 35. Vp was negative with Bext set to positive values and ranged from ≂0 (Bext=0) to −13 V (Bext≥+200 G) in Ar and 0 to −20 V in N2.
Three-dimensional characterization of conducting polymer arrays using secondary ion mass spectrometry
Authors: Gray K. H. , Gould S. , Leasure R. M. , Musselman I. H. , Lee J. J. , Meyer T. J. , Linton R. W.
Published: July 2002

Image depth profiling with dynamic secondary ion mass spectrometry (SIMS), using ion microscopy and digital imaging, provided high spatial resolution 3D images of patterned polymer films prepared from [Ru(Me4bpy)2(vpy)2]2+ and {Fe[(CH2Br)2bpy]3}2+. Although 3D SIMS has been widely applied to semiconductor device characterization, this study represents a first attempt to characterize conductive polymer arrays. The SIMS studies were useful in localizing the polymer domains, and the extent of polymer mixing within the film structures. Volume-rendered images and reconstructed local area depth profiles indicated that electropolymerization of the poly-Fe complex was not limited to the channels in the poly-Ru resist produced by optical lithography. Quantification of the SIMS image depth profiles required consideration of detection system nonlinearities, ion yield variations (especially transients at the film/substrate interface), and native and sputter induced roughness of the polymer films.
Borophosphosilicate glass crystal induction and suppression
Authors: Ahmed K. , Geisert C.
Published: July 2002

Grapelike crystalline cluster defects with no specific shapes were induced in borophosphosilicate glass (BPSG) deposited in a low-pressure chemical vapor deposition tube following cooling of the film to room temperature. The crystal defects were induced by exposing the film for about 3 min to high, controlled humidity (80%–90%) and a temperature of 30±2 °C. The film was then fused for 15 min in a 900 °C furnace at four different atmospheres: N2, O2, 1:1 O2/N2, or steam (3 min)/N2 (12 min). The steam/N2 treatment was the only effective ambient to eliminate BPSG crystal defects. A chemical mechanism is proposed to explain the crystal appearance in BPSG film.
Radio frequency sputtering process of a polytetrafluoroethylene target and characterization of fluorocarbon polymer films
Authors: Maréchal N. , Pauleau Y.
Published: July 2002

Fluorocarbon polymer films have been deposited on glass, silicon, and carbon substrates by radio frequency (rf) sputtering of a polytetrafluoroethylene (PTFE) target in pure argon and Ar–C3F8 mixtures using either a conventional sputtering mode or a self-sustaining glow discharge mode. The substrates could be isolated from the plasma region by a grounded grid electrode. The deposition rate of films produced on glass and silicon substrates was measured as a function of the gas composition and total pressure. The grounded grid electrode effect on the deposition rate of films was also investigated. The polymer films were characterized by x-ray diffraction, infrared spectroscopy, and Rutherford backscattering spectroscopy. The morphology of films was examined before and after annealing at 450 °C in pure argon ambient for 4–24 h. The optimum deposition conditions to produce (CFx)n polymer films with high fluorine contents and high deposition rates by rf sputtering of a PTFE target are reported and discussed in the article.
Investigation of the influence of electromagnetic excitation on electron cyclotron resonance discharge properties
Authors: Mak P. , King G. , Grotjohn T. A. , Asmussen J.
Published: July 2002

The influence of the permanent magnet configuration, electromagnetic excitation mode, and input microwave power on the operation of a multipolar electron cyclotron resonance (ECR) source is investigated. A 12.5-cm i.d. multipolar ECR plasma source was operated in argon gas at 0.77 mTorr with a flow rate of 20 sccm. The input power was varied from 240 to 750 W. The microwave coupling efficiency, the ion density and uniformity, and the ion production efficiency were determined for three different multipolar magnetic field configurations (8 pole/8 magnet, 4 pole/8 magnet, and 4 pole/4 magnet) and two electromagnetic modes (TE211 and TE311). The 4 pole/8 magnet configuration operated in the TE211 mode had the best efficiencies and uniformity. In particular, it had a microwave coupling efficiency as high as 98% and an ion production efficiency with 240 W of input power of 290 eV/ion. A numerical analysis of the ECR excitation indicated that this configuration excited with the TE211 mode also had the most uniform electromagnetic excitation of plasma by the microwave fields.
Quantitative and sensitive profiling of dopants and impurities in semiconductors using sputter-initiated resonance ionization spectroscopy
Authors: Arlinghaus H. F. , Spaar M. T. , Thonnard N. , McMahon A. W. , Tanigaki T. , Shichi H. , Holloway P. H.
Published: July 2002

Sputter-initiated resonance ionization spectroscopy (SIRIS) is an analytical technique with extremely high sensitivity, selectivity, dynamic range, and quantitation accuracy. SIRIS also provides good spatial resolution, and freedom from matrix effects on surfaces and at interfaces. In this paper we report the capability of SIRIS to quantitate, with high accuracy and high depth resolution, dopant and impurity concentrations in semiconductor devices at the 1013–1020 atoms/cm3 level. By utilizing layered GaAs/AlGaAs/GaAs samples grown by molecular beam epitaxy, a depth resolution of ∼2 nm has been demonstrated using 0.5 keV Ar+ primary ion energy. Depth profiles of boron in Si implants showed dynamic ranges up to 2×106. The correlation between B concentration and B SIRIS signal demonstrated high quantitation accuracy. The lateral imaging capability of SIRIS was demonstrated. We concluded that an optimized instrument could produce high depth-resolved quantitative measurements over a 1012–1021 atoms/cm3 concentration range.
Time-dependent helium and hydrogen pressure profiles in a long, cryogenically cooled tube, pumped at periodic intervals
Authors: Hobson J. P. , Welch K. M.
Published: July 2002

Many particle accelerators and colliders throughout the world make use of superconducting magnets to focus highly relativistic beams. These magnets are cooled to ∼4.2 K. For practical reasons, the beam pipes, encircled by the magnets, also operate at these cryogenic temperatures. This article presents a theoretical model for determining pressure profiles, in space and time, stemming from either helium or hydrogen gas leaks into the cold-bore tube with appendage pumps located at periodic intervals. It is shown that a wavelike pressure gradient propagates from the leak source at a rate which is dependent on the leak magnitude, gas species, speed and location of the appendage pumps, and the geometry and effective roughness of the cold-bore tube. Steady-state, linear pressure gradients eventually equilibrate between the appendage pumps in a magnitude commensurate with the mass flow in the beam pipe, while the approach to equilibrium is controlled primarily by the adsorption isotherm of the species. Results are given for a variety of conditions relevant to the relativistic heavy ion collider being constructed at Brookhaven, and a general procedure, with expressions, is provided for the making of similar calculations in other installations.
Moving-coil waveguide discharge for inner coating of metal tubes
Authors: Hytry R. , Möller W. , Wilhelm R. , Keudell A. v.
Published: July 2002

The moving-coil waveguide discharge is described as a technique for inner wall coating of metallic tubes. A magnetized microwave plasma, which can be shifted inside a tube by means of the surrounding magnetic coil, is employed for plasma-enhanced chemical vapor deposition of hydrogenated carbon films (C:H) from methane. Process parameter studies at varying microwave power, magnetic field, discharge pressure, and gas flow have been performed with a locally fixed magnetic coil. The deposition was found to be more efficient at a magnetic field which is lower than the electron cyclotron resonance (ECR) field. The power absorption remains nearly constant while decreasing the maximum magnetic field from ECR condition to half of that. This can be understood in terms of the microwave cutoff in the waveguide filled with a magnetized plasma. A simplified model of the plasma is suggested resulting from the power balance of a steady-state discharge. Electron temperatures and plasma densities measured in argon plasmas by means of a single Langmuir probe at varying pressure are in good agreement with the model predictions, while the averaged deposition from a methane plasma cannot be derived simply from the modeled methyl density.
X-ray photoelectron spectroscopy/Fourier transform infrared spectroscopy study of the interaction of YBa2Cu3Ox with CO, NO, and H2+CO
Authors: Lin J. , Wee A. T. S. , Huan A. C. H. , Tan K. L. , Neoh K. G.
Published: July 2002

The direct interaction of YBa2Cu3Ox (x=6–7) with CO, H2+CO, and NO is studied using x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and simultaneous thermal analysis. The CO interaction results in the release of CO2 at 400–800 K, and the formation of BaCO3, as well as the reduction of Cu(II) and Y(III), at temperatures above 800 K. The interaction between YBa2Cu3Ox and H2+CO results mainly in the formation of gaseous CO2 and H2O at temperatures below 830 K. At temperatures around 830 K, Cu(II) is reduced to Cu(I). In addition to barium carbonate, the methoxy group as well as the hydroxyl group can be identified on the YBa2Cu3Ox sample. At 1170 K carbides can be found on the sample surface. The NO interaction occurs at room temperature and above, leading to the release of N2, NO2, and N2O, as well as the formation of the nitride, nitrate, nitrite (NO−2), and nitrito (–ONO) groups. The nitride and nitrate species are mainly observed between 300 and 540 K, while at 830–920 K, barium nitrite is the predominant nitrogen-containing species on the surface. An active center (OBa⧠CuO) and mechanisms for the interaction between YBa2Cu3Ox and the gases are postulated and applied to explain the high catalytic activity of YBa2Cu3Ox.
Large oscillator strength of spatially indirect electron–hole recombination at type II heterojunctions: The InAlAs/InP case
Authors: Bimberg D. , Böhrer J. , Krost A.
Published: July 2002

Temperature-dependent investigations of continuous wave and time resolved photoluminescence of the type II heterojunction model system n-InAlAs/n-InP are presented. Surprisingly at room temperature the emission is completely dominated by extremely efficient interface transitions between two-dimensional (2D) holes in InAlAs, which are minority carriers, and electrons from a 2D gas on the InP side of the interface. The intensity decrease between 7 and 300 K is much less than what is usually observed in three-dimensional material. At temperatures larger than 50 K the carrier lifetime starts to drop up to room temperature from 3.8 ns at 6 K to 1.2 ns at 300 K. Both observations are consistently explained by an increasing occupation of higher subband levels of the interface potential well and an activation of new radiative and nonradiative recombination channels including Δn≠0 ones with increasing temperature. The decay time of the luminescence from the 1-μm-thick InAlAs layer is short (0.3 ns at T=6 K). Only a very small part of the carriers optically generated in InAlAs recombine there. The main part diffuses to and is captured by the interface potential well. The structural perfection of the interface is decisive for this highly efficient recombination. Double-crystal x-ray diffraction, Shubnikov–de Haas (SdH), capacitance–voltage, and calorimetric absorption experiments are used to assess the crystallographic and electronic properties of the interface. Observation of a large number of Pendellösung oscillations in the x-ray rocking curves, which can be perfectly modeled using dynamical diffraction theory, unambiguously demonstrate the quality and abruptness of our interfaces. A 2D electron gas at the InP side of the interface through carrier transfer from the unintentionally doped InAlAs is directly observed by angular dependence SdH experiments. The electron and hole subband structure at both sides of the interface is calculated on the basis of a self-consistent solution of the Poisson and Schrödinger equations including band-gap renormalization caused by many particle effects. Experimental confirmation of the subband structure is obtained by second derivative calorimetric absorption spectroscopy.
Production and characterization of doped mandrels for inertial-confinement fusion experiments
Authors: Cook R. , Overturf G. E. , Buckley S. R. , McEachern R.
Published: July 2002

A key feature of current inertial-confinement fusion (ICF) experiments is the incorporation of dopant atoms into the thin polymer microshell which, in a finished ICF capsule, forms its inner wall. These dopants provide a spectroscopic signal during the implosion that can be used to diagnose the degree of mix at the capsule–fuel interface. The high-Z dopants can also be used to directly image the fuel–pusher interface. The current status of doped mandrel development is reviewed, with a focus on the mandrel surface smoothness. With the development of unique surface mapping characterization tools which will be described, it has been discovered that mandrel surface smoothness is a function of the polymers used to form the mandrels. In this report it will be shown that Cl-doped mandrels produced from a blend of polystyrene and poly(p-chlorostyrene) are rough on a length scale of 10’s of microns with amplitudes of as much as a 100 nm. The origin of this roughness will be discussed, and it will be shown that this roughness can be removed by using a copolymer rather than a blend of two polymers. Also it will be shown how Cr-doped mandrels become rough with age due to ambient light exposure.
Comprehensive interpretation of the preferred orientation of vapor-phase grown polycrystalline silicon films
Authors: Kakinuma Hiroaki
Published: July 2002

A comprehensive interpretation of the preferred orientations (PO) of poly-Si films prepared from various vapor-phase methods is presented. Existing theories and models are examined by comparing a wide variety of experimental results of PO published so far. Preferential nucleation and the conventional concept of the surface free energy are found to apply only to a limited range of deposition parameters. On the other hand, a combination of two concepts, i.e., the microscopic geometry of growing surfaces and the surface kinetics, proves to be very important in interpreting the wide variation of PO. The concept of the microscopic geometry of the surface considers the minimum numbers of atoms and bonds required for nucleation, lateral growth, and etching that characterizes the growth ability of planes. In addition, interpretation of the deposition parameter dependencies of the PO requires the concept of surface kinetics including diffusion of precursors, hydrogen coverage, and the surface reaction time which depends on the substrate temperature and gas pressure. The combined concepts can account for most of the observed POs (mainly 〈100〉 and 〈110〉) which depend on feed gases and the deposition parameters. Other specific growth modes such as facet growth or microtwins are considered for the 〈111〉 PO. The POs for n- and p-type doped films are different from those of undoped films, and their origin is also discussed in terms of their growth rates.
Oxygen content of indium tin oxide films fabricated by reactive sputtering
Authors: Honda Shinichi , Tsujimoto Akira , Watamori Michio , Oura Kenjiro
Published: July 2002

Indium tin oxide (ITO) films, which are transparent conductive films, have been widely used in optoelectronic applications. A high quality film with correct stoichiometric composition is essential for its applications, such as a flat panel display. However, it is difficult to estimate the absolute oxygen concentration. There are few studies of oxygen depth profiling for ITO films. We have investigated a relationship between the oxygen content of ITO films and the electrical properties under various deposition conditions. The absolute oxygen concentration has been determined by 16O(α,α)16O resonant backscattering of a 3.045 MeV 4He2+ ion beam. It has been found that there is a correlation between the depth profile of oxygen concentration of ITO films and the film properties. In the case of the ITO film fabricated at room temperature, a large deficiency of oxygen can be seen at the surface of the film. When the film was formed at 400 °C, no deficiency of oxygen at the film surface was observed. The observed oxygen concentration will be discussed in terms of the electrical and optical properties of the films.
Methods to enhance absorption signals in infrared reflectance spectroscopy: A comparison using optical simulations
Authors: Katiyar M. , Abelson J. R.
Published: July 2002

We use optical simulations to determine the substrate and experimental geometry that should be used to enhance infrared absorption signals from thin films in a reflectance geometry. Our goal is to highlight those configurations which are suitable for the real-time study of surface and subsurface chemical bonding during growth or processing. The enhancement techniques reviewed are the use of metal substrates, multiple internal reflection (MIR), and an optical cavity substrate. For each technique, we simulate the absorption strength for Si–H vibrational modes in and on hydrogenated amorphous silicon films as a typical example. The techniques are discussed in terms of (i) the choice of the substrate and flexibility in measurement geometry; (ii) the sensitivity in both s and p polarizations; (iii) the effect of film refractive index (n) and extinction coefficient (k) on the line shape and absorption intensity; and (iv) the sensitivity as a function of film thickness. For the real-time study of high-refractive-index films, the optical cavity substrate and MIR are best suited. MIR is most applicable to study surface reactions during epitaxial chemical vapor deposition (CVD) on high-refractive-index crystals having low bulk absorption in the infrared region. The optical cavity substrate is best suited to study film growth on low-refractive-index material. Metal substrates work well for low-refractive-index materials, e.g., studies of adsorbate layers and metal CVD. These techniques are complementary to each other and provide a means of studying a wide variety of material–substrate combinations.