bluuebunny/crossref_metadata_2025 huggingface dataset:
Pellet injection in TFTR
Authors: Singer C. E. , Heifetz D. B. , Post D. E.
Published: July 2002

Maximizing the neutron production rate while minimizing neutron activation and tritium recycling is particularly important during early tritium operations in TFTR and other advanced tokamaks. Injecting a large tritium pellet just before compression of a low-density deuterium plasma could give a modest increase in the postcompression rate of neutron production in TFTR. The shorter duration of the neutron burst would result in reduced neutron activation of the vacuum vessel. Multiple injection of tritium pellets in a high current plasma could substantially reduce tritium recycling at the limiter. Although significant improvements can result from fueling with pellets during early tritium operations, considerable advance planning is required to ensure that a suitable injector is available at the start of tritium operations.
Anisotropic plasma etching of polysilicon using SF6 and CFCl3
Authors: Mieth M. , Barker A.
Published: July 2002

Undercutting of polysilicon overetched in fluorine-based plasmas has been limited to 0.1 μ per edge by adding small amounts of CFCl3 to SF6. This 0.1 μ undercut occurs during the initial etching stage and does not increase with overetch. To test possible mechanisms, these experiments were repeated with CHF3 and Cl2 used in place of CFCl3. It was found that Cl and photoresist are responsible for passivating the sidewalls of the polysilcon lines. This passivation is relatively insensitive to exact amount of CFCl3 added. Etch rate measurements were made for polysilicon, SiO2, and AZ 1470 photoresist and found to be essentially indistinguishable from those obtained in pure SF6 etching, thus the fast polysilicon etch rate and good selectivity characteristics of SF6 etching are preserved. The ability to etch polysilicon without sacrificing linewidth, selectivity, or etch rate makes CFCl3/SF6 plasma etching very useful for VLSI processing.
Modified extractor gauge
Authors: Fujii Y. , Inoue H. , Mima H. , Kanematsu F.
Published: July 2002

The design and performance of a modified extractor gauge for ultrahigh vacuum pressure measurement is described. The open end construction of the grid cage prevents the x rays from striking the ion collector directly except for those minor indirect x rays that are reflected at respective electrodes. The sensitivity factor is about 8.3×10−2 Pa−1 (11 Torr−1) at an electron current of 1 mA corresponding to the residual gases. Pressure measurements were carried out in the range of 1×10−6 to 9×10−10 Pa (1×10−8 to 7×10−12 Torr). It is confirmed that the x-ray limit of the gauge is lower than that of the nude-type B–A gauge. Description is also given of the modified design of the gauge for high vacuum pressure measurements facilitated by the cap electrode mounted on the top of the grid cage.
A UHV gasket removal tool
Authors: Waclawski B. J.
Published: July 2002

This note describes a safe, effective tool for removing copper gaskets from ultrahigh vacuum flanges. Use of the tool practically reduces to zero the chance of damaging the flange sealing surface, because all motion of the tool is away from the flange face, and force is required for gasket removal. In addition, the pliers maintain a positive grip on the gasket, keeping it from dropping onto delicate parts of any apparatus attached to the flange.
Synthesis of tungsten carbide films by rf magnetron sputtering
Authors: Srivastava P. K. , Rao T. V. , Vankar V. D. , Chopra K. L.
Published: July 2002

Thin films of tungsten carbide have been deposited by rf magnetron sputtering in the substrate temperature range of 200–500 °C. A mixture of mono-, di-, and tricarbides are formed at low temperatures but a single phase monocarbide is formed at high temperatures. The films consist of randomly shaped granular surface of grain size 400–500 Å. Fractured cross section of the films shows a columnar structure consisting of fine columns of width 300 Å. The interface formed between the film and substrate shows a gradual variation of the concentration of elements over a thickness of 250 Å in thin films. The thicker films show a large interfacial region, and is attributed to a loss in depth resolution due to sputter etching of the film.
Modulated electron beam
Authors: Anderson R. A.
Published: July 2002

An easily installed modification to an electron gun power supply allows the electron beam to be modulated with an externally applied, audio-frequency signal. Full on–off chopping is accomplished with an input amplitude of only 10 V rms. The modification does not interfere with normal operation of the electron gun.
Low energy Auger transitions of boron in several boron compounds
Authors: Hanke G. , Müller K.
Published: July 2002

As a general feature of Auger electron spectra of binary compounds the low energy core–valence–valence transition of the electropositive partner appears to be split into several lines. The particular fine structure of the multiplet is typical for each compound which is demonstrated for B4C, B2O3, and BN in comparison with pure boron. Characteristic changes in the low energy spectra depend on the additional decay channels supplied by the bonding partner for the recombination of the boron hole. The main features can be explained in terms of a molecular orbital model supported by SXS data for the same compounds. Some peaks, however, require a different interpretation suggested by ELS results. One line at the low energy side of the multiplet may be due to a double Auger transition involving a core exciton in the final state. The high energy peak may be the direct nonradiative recombination of such an exciton. It is shown that these effects depend on the chemical environment. Transition probabilities are estimated from experimental data.
Oxide formation on aluminum in the presence of keV electrons and CO2
Authors: Pitts J. R. , Bischke S. D. , Falconer J. L. , Czanderna A. W.
Published: July 2002

Oxidation of aluminum by carbon dioxide at room temperature is significantly enhanced by an electron beam, and oxide growth is spatially restricted to the beam impact region. The growth of the oxide on aluminum films and sheets was studied with AES, XPS, ISS, and SIMS using isotopically labelled C18O2. XPS indicates that the oxide is similar to Al2O3 and that very little carbon accumulates on the surface. Both SIMS and ISS confirm that 18O is incorporated into the Al from C18O2. Residual gases and oxygen from the substrate are eliminated as possible oxygen sources for the oxidation. Beam heating is not a factor in enhancing the oxidation. Oxide islands were grown for a range of beam voltages (0.5–10 keV), beam current densities (0.8 mA/cm2–7 A/cm2) and CO2 pressures (10−6–10−4 Pa). No CO2 adsorption or Al oxidation was detected on a clean Al sheet in the absence of an electron beam. In the presence of the beam (2 keV, 7 A/cm2), surface oxygen saturated after 5000 L (langmuir) CO2 exposures. The mechanism for the oxide growth involves dissociation of the CO2 into CO and O atoms in the region of electron beam impact on the surface. The oxygen atoms react with the Al to form the oxide and CO remains in the gas phase or desorbs.
Effect of ion mass and ion energy on the surface composition of two sputtered tin–lead alloys
Authors: Frankenthal R. P. , Siconolfi D. J.
Published: July 2002

The effect of ion sputtering on the surface composition of two Sn–Pb alloys (Pb0.97Sn0.03 and Sn0.998Pb0.002) has been studied by Auger electron spectroscopy as a function of the sputter ion mass, its energy, and the sputter rate. It was found that the data are consistent only with the concept that the element with the higher binding energy becomes enriched in the surface.
The edge-loaded metal flange seal—its characteristics and applications
Authors: Higgins R. W.
Published: July 2002

An edge-loaded metal ring flange seal has been developed for ultrahigh bakeable vacuum operation that requires closing forces comparable to elastomeric seal systems. Sealing is accomplished using a deformable rectangular cross-sectioned copper ring confined between stainless steel flanges in a manner that produces high radial compressive forces upon alternate edges of the ring section during flange closure. Conformation to the geometry and macrostructure of the confining elements of the flanges produces a leak-tight seal capable of ultrahigh vacuum operation with 400 °C bakeout. The seal ring deformation has been analyzed and the seal configuration has been tested for reliability and loading characteristics and found to require axial forces as low as 45 pounds per circumferential inch of seal for the system. A simplified analysis has been developed to predict loading characteristics and has been compared to loading studies made during the development of the seal system. Tests in ambient and elevated temperature environments show the seal to be as reliable as existing ultrahigh vacuum seal systems while requiring as little as 1/40 the bolt forces and 1/10 the time to accomplish closure. The flange seal has utility in radiation induced environments where human exposure time may be severely restricted, or where remote handling techniques for flange assembly and disassembly may be required.
Vacuum pumping of multimegawatt neutral beam injection lines
Authors: Kim Jinchoon
Published: July 2002

Neutral beam injection lines employed for heating large tokamak and mirror plasmas have a unique gas pumping requirement, which is to maintain a high pressure (∼10−3 Torr) in the gas cell neutralizer and a low pressure (∼10−6 Torr) downstream after the neutralizer. Large hydrogen gas inputs (a few tens of Torr l/s) needed for operating an ion source and also the packing of multiple ion sources in a single beamline indeed make the beamline pumping a technological challenge, requiring a pumping speed greater than 106 l/s. We have witnessed, as beamlines get bigger, that beamline pumping techniques have shifted from conventional to gettering, and then to cryocondensation pumping. Cryopumping techniques are now employed in almost every beamline for high speed pumping; cryopanel design varies widely since the panels are an integral part of a beamline. A brief review is given of the beamline pumping technology, covering such topics as gas loading characteristics, vacuum components, cryopumping techniques, gettering techniques, and reactor relevant implications.
Performance of Doublet III neutral beam injector cryopumping system
Authors: Langhorn A. R. , Kim J. , Tupper M. L. , Williams J. P. , Fasolo J.
Published: July 2002

The Doublet III neutral beam injector system is based on three beamlines; each beamline employs two 80 kV/80 A hydrogen ion sources. Two liquid helium (LHe) cooled cryopanel arrays were designed as an integral part of the beamline in order to provide high differential pumping of hydrogen gas along the beamline. The cryopanel arrays consist of a front (nearer to the torus) disk panel (3 m2 each side) with liquid nitrogen (LN2) cooled chevrons and a rear cylindrical panel of modified Santeler panels (8 m2) which also employs LN2 cooled surfaces shielding LHe cooled surfaces. These cryopanels are piped in series. The LHe delivery is based on a closed-loop, forced-flow scheme intended for variable panel temperatures (3.7 to 4.3 K). It uses small tubes for mechanical flexibility and thermal resiliency providing ease of economic defrosting. The cryogenic system consists of a liquefier (100 l/h), a large Dewar, a heat exchanger, and a liquid ring pump. Three beamlines are serviced simultaneously by the system. Pumping speeds measured locally at ionization gauges, were well in excess of the 1.4×106 l/s design goal.
Gettering in fusion devices
Authors: Cecchi J. L. , Knize R. J.
Published: July 2002

The use of gettering has been important for magnetic confinement fusion research. It has helped to increase the understanding of plasma material interactions and has facilitated the access to new modes of device operation. In this paper we review the characteristics of getters used in fusion research. We also present a survey of the past, present, and future applications in mirrors and tokamaks.
Unidirectional vacuum gauge by means of detecting excited neutrals
Authors: Arakawa I. , Kim M. , Tuzi Y.
Published: July 2002

The experimental analysis of anisotropy of the conditions of gas molecules in a vacuum chamber can be realized by the unidirectional vacuum gauge which detects molecules coming from a certain direction in chaotic space. The ability of the unidirectional vacuum gauge by means of detecting the excited neutrals produced by electronic collisions was examined. Two types of the gauge were made and the performance was tested. The half-width of the angular distribution curve of the signal when the gauge scanned a point gas source showed a directivity of 100 mrad. The proportional constant of the count rate to the pressure of Ar when the gauge saw a uniform space gave the sensitivity of the order 106 counts/s Pa. This gauge can also measure the velocity distribution of gas molecules. This type of gauge is believed to be very useful for the experimental study of gas–surface interactions.
The effect of hydrogen chemisorption on the conductivity of evaporated aluminum films
Authors: Shih D. Y. , Ficalora P. J.
Published: July 2002

Very thin Al films (<10 nm) were prepared by thermal evaporation on electroded glass substrates in an ultrahigh vacuum system. TEM studies revealed that the films had a discontinuous structure consisting of imperfectly touching crystallites. Since hydrogen adsorption should not decrease electron specular reflection, entirely diffuse scattering of the conduction electrons at the film surface was assumed. At room temperature, hydrogen adsorption caused a decrease in film conductivity and equilibrium was reached rapidly. At temperatures above 80 °C, hydrogen adsorption caused an increase in film conductivity with a slow (16 min at 80 °C) attainment of equilibrium. The results indicate an activated dissociative process which occurs via a precursor state at the higher temperatures. At lower temperatures, an electronegative layer is formed: electrons are withdrawn from the Al film and the conductivity decreases. These results are in agreement with the observation that adsorbates often undergo both dissociative and nondissociated chemisorption on the same metal surface with the former being favored at higher temperatures.
Radio frequency magnetron sputtering of radio frequency biased quartz on a scanning pallet
Authors: Mumtaz A. , Drapkin I. , Mathew R.
Published: July 2002

The microstructure and step coverage of silicon dioxide was studied with respect to its use as a planarization layer. The bonded 37.75×12 cm SiO2 target and the 31×31 cm pallet were independently driven by two rf amplifiers using a common exciter. A sliding rf contact was made to the pallet. Target power was fixed at 2.5 kW while rf induced dc offset voltage at the pallet was varied between 0 and 120 V negative on different runs. During each scan the dc offset voltage at the pallet was kept constant, and hence, the rf power to the pallet was increased when it came in front of the denser magnetron target plasma. The average film growth rate was 800 Å/min. The argon pressure in the system was varied between 5.3×10−1 to 2 Pa. It was observed that ion bombardment during film growth, when bias is used, eliminates the columnar morphology and nodular growth and results in SiO2 films that approach the quality of those grown thermally. Such films provide good step coverage for planarization.
Growth morphology determination in the initial stages of epitaxy by XPS
Authors: Egelhoff W. F.
Published: July 2002

It is found that for Cu(100) and Ni(100) x-ray photoelectrons and Auger electrons with energies of ∼1000 eV exhibit intensity variations versus polar angle which are dominated by forward scattering off neighboring atoms. In monitoring the epitaxial growth of Cu on Ni(100) this phenomenon is shown to yield clear and easily available structural information about the arrangement of atoms in the Cu adlayers.
Morphology and properties of sputtered HfN layers as a function of substrate temperature and sputtering atmosphere
Authors: Jehn Hermann A. , Kopacz Uwe , Hofmann Siegfried
Published: July 2002

HfN layers were prepared by reactive rf-magnetron sputtering onto polished flat high speed steel (HSS) surfaces. Rectangular samples were mounted on a special holder providing temperatures in the range of 775 to 300 K along the length of the sample. The HfN layers were deposited at various total pressures and different N2/Ar ratios. The film morphology and composition was studied by scanning electron microscopy (SEM) and Auger electron spectroscopy (AES), respectively, and correlated with mechanical properties like microhardness and adhesion. The results are discussed with respect to the sputtering conditions.
Selective deposition of tungsten—prediction of selectivity
Authors: Carlsson Jan-Otto , Boman Mats
Published: July 2002

Preferential or selective chemical vapor deposition to a substrate region is based on a difference in thermochemical stability between different substrate regions. The higher this difference is, the higher selectivity is expected. In this paper a thermodynamic analysis of selective deposition of tungsten from H2 and WF6 on silicon regions in the presence of silicon dioxide is presented. At the initial stages of growth—silicon present in the vapor—the selectivity is favored by a low temperature, a low total pressure and a high WF6 concentration in the vapor. For the continuation—growth on the deposited tungsten—a low total pressure, a low WF6 concentration in the vapor and a higher temperature than that used initially should be chosen for highest selectivity. From the analysis it is also seen that simultaneous etching and tungsten oxide/tungsten deposition may occur on the silicon dioxide. The technique used to analyze the selective tungsten deposition process seems to be a useful tool for optimizing the selectivity in a given system and for reducing or eliminating undesired side reactions.
Ion current modulation of a residual gas analyzer
Authors: Watanabe F. , Ishimaru H.
Published: July 2002

A residual gas analyzer (RGA) is described with a modified quadrupole mass filter. This change permits a separate analysis of ions created in the gas from those created by electron impact in the RGA. Electrically, the electron energies are modulated and the ion current is measured in a phase-lock loop. Experimental results on H+ and O+ indicate that the spurious electron-stimulated-ion-desorption peaks are eliminated.
Ion-implanted, electron-beam annealed TiN films as diffusion barriers for Al on Si shallow junctions
Authors: Armigliato A. , Finetti M. , Garrido J. , Guerri S. , Ostoja P. , Scorzoni A.
Published: July 2002

TiN films are prepared by N+2 implantation onto evaporated Ti films. By properly selecting the Ti thickness, implantation energy and annealing process, a TiSi2/TiN structure can be formed. In particular, in this work a postimplant rapid isothermal annealing is carried out at 800 °C for 30 s by using an electron beam. The effectiveness of these TiN films as a diffusion barrier is then evaluated when put in contact with a thick Al overlayer. Both the TiN/Al and TiSi2/TiN/Al contact structures are tested, after thermal treatments up to 600 °C, on shallow junction diodes and four terminal resistor test patterns for contact resistance measurements. The electrical performances of the TiSi2/TiN/Al contact system are found to be good, although the degradation resistance is slightly worse than the one observed on similar structures annealed in a vacuum furnace after the nitrogen implantation.
Formation of TiSi2 and TiN during nitrogen annealing of magnetron sputtered Ti films
Authors: Adams E. D. , Ahn K. Y. , Brodsky S. B.
Published: July 2002

Rutherford backscattering analysis was used to evaluate TiSi2 films which were prepared by sputtering Ti on various substrates and nitrogen annealing. The resulting properties were then compared with that of films prepared by thermal evaporation. Ti films were deposited on single crystal Si, polycrystalline Si, thermally grown SiO2, and CVD Si3N4 by dc-magnetron sputtering in an Ar plasma at a typical deposition rate of 20 Å/s. Some films were passivated with a thin amorphous film of Si to compare the reaction kinetics with the samples without passivation. The temperature dependence of the electrical resistivity is basically the same as with the evaporated films [Ref. 1: C. Y. Ting et al., in Proceedings of the First International Symposium on VLSI Science and Technology (Electrochemical Society, New York, 1982), p. 224.], and the minimum value obtained after an 800 °C anneal is similar. Typical resistivity after taking into account the presence of TiN on the surface is approximately 13.9 μΩ-cm. The presence of a thin Si passivation layer (300 Å) appears to prohibit the formation of TiN while allowing the formation of stoichiometric TiSi2 at a lower temperature, with a similar resistivity.
Computerized scanning Auger microprobe
Authors: Sommerer T. J. , Hale E. B.
Published: July 2002

An Auger spectrometer has been automated using a microcomputer. Fundamental considerations in the design and choice of the computerized system are presented and should be of general interest. The spectrometer was a Physical Electronics Ind. model 545 scanning Auger microprobe. The microcomputer chosen was a Southwest Technical Products 6809 computer system. Hardware details are discussed with emphasis on the four computer–spectrometer interface boards. These boards are (1) Auger energy control board, which sets the Auger detection energy with its 16 bit digital-to-analog converter (DAC); (2) read Auger signal board, which reads the Auger signal intensity with its 12 bit analog-to-digital converter; (3) multipurpose DAC board, which uses two pairs of 8 bit DAC’s to position the excitation beam and display the data in memory on a CRT monitor, and (4) timing and relay control board, which selects various instruments and power supplies as required during the fully automated depth profiling sputter sequences. Organizational details of the control, analysis, and output software are discussed. The operation of the main Auger control program is emphasized along with its menu driven options, which provide great versatility to the operator. Examples are shown of the various data output modes, which include displays on the CRT monitor and plots from the multicolor digital plotter.
New radio frequency technique for deposition of hard carbon films
Authors: Nyaiesh A. R. , Kirby R. E. , King F. K. , Garwin E. L.
Published: July 2002

We have developed a new technique to produce diamondlike carbon films in an rf system with water-cooled electrodes. Hydrocarbon gas is leaked into the experimental chamber through the upper electrode which is a Pyrex cylinder inside a coil forming an rf oven. The gas (CH4) undergoes ionization/dissociation in one rf field, within an axial magnetic field. A circular water-cooled electrode supports the substrate to be coated, and is powered from a second rf generator, developing a negative self-bias on the substrate. Thus dissociation and ion production at the upper electrode and ion acceleration by the lower electrode could be separately controlled to optimize the film properties. It is shown that low stress, highly dense carbon films can be deposited by this method. Information is also given on bulk and surface properties as well as modification of these properties by the deposition conditions.
Auger electron spectroscopy studies of near-interface SiO2
Authors: Sobolewski M. , Helms C. R.
Published: July 2002

The Auger electron spectra of thin (3–30 Å) thermal films of SiO2 on Si were measured. Xenon ion sputtering was also used to provide depth profiles of these films. A feature in the Si LVV Auger spectrum previously attributed to intermediate oxidation states of silicon (SiOx) within 1–2 monolayers of the interface was observed. In addition, the presence of a ‘‘near interface SiO2’’ region where the SiO2 spectra are shifted from their thick SiO2 values has been observed. During sputter profiling of 30 Å films these energies shift from positions close to their thick oxide values to values approximately 5 V higher at the interface. These shifts are observed even without sputtering: the 3 Å oxide has a Si KLL peak energy 3.2 V higher than the 30 Å sample, and O KLL peak energy 3.5 V higher, and Si LVV peak 2.0 V higher, after correcting for band bending in the substrate. These shifts can be attributed to a change in the relaxation energy of the oxide whose physical origin is not as yet understood.
Near-surface microstructural modifications in low energy hydrogen ion bombarded silicon
Authors: Panitz J. K. G. , Sharp D. J. , Hills C. R.
Published: July 2002

We have bombarded single crystal (100) and (111) silicon with a hydrogen ion beam produced by a Kaufman ion source. A range of dose rates from 0.2–2.0 mA/cm2, bulk sample temperatures from 35°–350° C, and doses of 2×1017, 2×1018, and 2×1019 ions/cm2 at maximum ion energies of 1600 eV was explored. Transmission electron microscopy and electron spin resonance measurements were used to characterize the bombarded samples. Extensive microstructural modifications occur as a result of hydrogen ion bombardment; the orientation, size, density, and distribution of the features which form vary as a function of crystal orientation, dose rate, bulk temperature, and total dose. Electron spin resonance studies indicate no detectable change in the number of occupied unpaired electron spin states occur in conjunction with this damage.
Vortex trapping in Pb-alloy Josephson junctions induced by strong sputtering of the base electrode
Authors: Wada Masato , Nakano Jun’ichi , Yanagawa Fumihiko
Published: July 2002

It is observed that strong rf sputtering of the Pb-alloy base electrodes causes the junctions to trap magnetic vortices and thus induces Josephson current (IJ) suppression. Trapping begins to occur when the rf sputtering that removes the native thermal oxide on the base electrode is carried out prior to rf plasma oxidation. Observed large IJ suppression is presumably induced by the concentration of vortices into the sputtered area upon cooling the sample below the transition temperature. This suggests a new method of the circumvention of the vortex trapping by strongly rf sputtering the areas of the electrode other than the junction areas.
Processing and characterization of LaB6-coated hairpin cathodes
Authors: Khairnar Rajendra S. , Mahajan P. W. , Joag Dilip S. , Nigavekar A. S. , Kanitkar P. L.
Published: July 2002

Lanthanum hexaboride (LaB6) was cataphoretically deposited on a filamentary hairpin support of tantalum. Such filaments were further processed to form cathodes. Various procedures involved during the processing of cathodes, such as carburization of the core tantalum wire in hairpin shape, deposition of LaB6 onto it, and sintering of such cathodes are described. These cathodes were characterized for thermionic work function measurements, life tests, and thermal shocks in a diode configuration. The ultrahigh-vacuum (UHV) sintering gives better emission stability, compact coating, low porosity, etc., as compared to high-vacuum sintering. The work function values were found to be in the range of 2.6–2.8 eV for various cathodes whereas, the pre-exponential factor seemed to vary in the range of 30–200 A cm−2K−2. These cathodes showed life in excess of 55 h of continuous operation. It was found that the life of such cathodes depends mainly on the adhesion of the LaB6 coating to the core wire instead of the evaporation rate of LaB6 at operating temperatures. The cathodes sustained a larger number of thermal shocks in UHV than in a high-vacuum environment.
Properties and applications of CdTe/sapphire epilayers grown by molecular beam epitaxy
Authors: Myers T. H. , Giles-Taylor N. C. , Yanka R. W. , Bicknell R. N. , Cook J. W. , Schetzina J. F. , Jost S. R. , Cole H. S. , Woodbury H. H.
Published: July 2002

Properties and applications of MBE-grown (111) CdTe films on (0001) sapphire substrates are discussed. From Laué diffraction studies, the epitaxial orientation relationships are (111)CdTe∥ (0001) sapphire, with [11̄0]CdTe∥[112̄0] sapphire. On the basis of these results, an atomic model of the CdTe/sapphire interface is proposed and discussed. As-grown p-type films convert to n type upon heating in a Cd atmosphere and become highly conducting. Hall mobilities greater than 1000 cm2/V s at room temperature have been obtained for Cd-annealed films. CdTe epilayers have also been successfully used as substrates for growth of HgCdTe by the close-spaced vapor transport technique. As-converted Hg0.83Cd0.17Te films exhibit intrinsic conduction down to about 150 K. These n-type layers have carrier concentrations of 8×1015/cm3 and electron mobilities greater than 2×105 cm2/V s at 77 K.
Sound velocity in amorphous films of germanium and silicon
Authors: Cox-Smith I. R. , Liang H. C. , Dillon R. O.
Published: July 2002

Sound velocities in evaporated amorphous Ge and Si films have been determined to be 81.6±1 and 76.8±3% of the corresponding directionally averaged crystalline speed, respectively. These results, combined with previous work, indicate a decrease of sound velocity through the preparation sequence of glow discharge, ion implantation, evaporation, and sputtering. The reason for this dependence is not known, but may be due to an increase in voids through the preparation sequence. The experimental technique was verified by also measuring sound velocities for crystalline films of Ge and Si. These velocities were 100.4±0.4 and 95.8±5% of the known corresponding directionally averaged crystalline speed for Ge and Si, respectively. Reasons for departure from 100% are discussed and the technique is concluded to yield sound velocities with an accuracy of a few percent.
Refractory metal silicide formation by sputtering a refractory metal on heated Si substrates
Authors: Tanielian M. , Blackstone S.
Published: July 2002

Refractory metal films of Ti were dc magnetron sputtered on heated Si wafers in the range from 25–620 °C. The kinetic energy of the deposited species increases the surface mobility and diffusivity on the substrate so that the resulting films, above 300 °C are refractory metal silicides. Only at temperatures above 550 °C, however, are the films fully reacted silicides. We found that during this reaction, the cleanliness and uniformity of the surface determine to a large extent the texture of the resulting films. In addition, during the silicide formation reaction, if Ti is in contact with SiO2, it will react and form an interfacial silicide layer. Our results on the hot-deposited runs are compared to the results of Ti deposited at ambient temperature and subsequently heated in a furnace.
Ablative photodecomposition of polymers
Authors: Garrison Barbara J. , Srinivasan R.
Published: July 2002

Recently it has been observed that far-UV (193 nm) laser radiation can cleanly etch organic polymer films. In contrast to etching of the film by lower energy radiation, which leaves the walls of the etch region uneven due to melting, far-UV radiation ablates the material with minimum damage to the remaining sample. A model has been developed to explain the photochemical etching due to 193-nm laser light. The predictions from this model are (1) the reacted material ablates without melting the remainder of the sample; (2) the average perpendicular velocity of the ejected material is ∼1000–2000 m/s; (3) the angular spread is small and peaked in the direction normal to the surface; and (4) the material ablates layer by layer. Items 1, 2, and 3 are in excellent agreement with the experimental results. A model has also been developed to simulate the ablation of solids by the thermal (in contrast to the photochemical) process. The predicted pit shape and angular distribution are quite different from those obtained from the photochemical model. The effect of impurity or solvent molecules is also discussed.
Contact metallization for producing stable bipolar microwave transistors
Authors: Packwood Donald L. , Figueredo Domingo A.
Published: July 2002

Bipolar microwave transistors with Ti/Pt/Au contact metallization show a reversible degradation in current gain (hFE) due to high temperature storage (HTS) stress at 240 °C. This is an elusive effect that occurs only in certain very small cavity, strip-line packages and only on devices with very shallow emitter-base junctions (∼1200 Å). A model for current gain in shallow-junction bipolar transistors is described. The model shows that hFE of such devices is very dependent on the properties of the metal–silicon interface at the emitter. The cause of the reversible hFE degradation was found to be hydrogen absorption and desorption in the Ti contact metallization. This causes shifts in the Schottky barrier of the Ti/Si contact with consequent changes in the surface recombination velocity at the emitter. A new contact metallization of W:10 wt. % Ti/Au was developed which is hFE drift free.
Compositional and electrical co-characterization of HgCdTe diodes by cross-sectional EBIC, AVC, and AES analysis
Authors: Massopust T. P. , Kazmerski L. L. , Whitney R. , Starr R.
Published: July 2002

Compositional and electrical characterization of Hg1−xCdxTe heterojunction devices has been performed by cross-sectional electron-beam induced conductivity (EBIC), Auger voltage contrast (AVC), and Auger electron spectroscopy (AES). Devices were fabricated from double layer LPE HgCdTe grown on CdTe and CdZnTe substrates. Cleaved diodes were wire bonded to a specimen mount and analyzed in a scanning Auger microscope at 123 K. This is the first reported Auger analysis of HgCdTe at cryogenic temperatures. EBIC analysis located the electrical junction while the contactless AVC also confirmed an electrical junction at the substrate interface. Subsequent AES compositional analysis located and determined interface widths of 1.2 μ and 1000 Å for the substrate and heterojunction interfaces, respectively. Although EBIC is a ‘‘bulk’’ phenomenon and AES and AVC are ‘‘surface’’ phenomena, results from concurrent experiments aid in relating device performance to structural composition.
Characterization of molybdenum disilicide/gallium arsenide Schottky barrier contacts at elevated temperatures
Authors: Truman J. K. , Holloway P. H.
Published: July 2002

The effects of heat treatment up to 800 °C on planar magnetron sputter-deposited MoSi2 Schottky barrier contacts to n-type GaAs were studied to determine the feasibility of using MoSi2 as the high thermal stability Schottky contact in a self-aligned-gate GaAs MESFET process. Current-voltage data for MoSi2–GaAs Schottky barrier diodes revealed a decreasing barrier height and an increasing ideality factor above 500 °C. Auger electron, Rutherford backscattering, ion microprobe, and cross-sectional TEM analyses were used to detect Ga and As out-diffusion into MoSi2 at T≥550 and 600 °C, respectively. The MoSi2–GaAs interface exhibited increasing broadening with increasing annealing temperature. The electrical degradation above 500 °C is believed to be the result of the formation of an n+ surface layer by the diffusion of Si from MoSi2 into GaAs.
Annealing of intimate Ag, Al, and Au–GaAs Schottky barriers
Authors: Newman N. , Chin K. K. , Petro W. G. , Kendelewicz T. , Williams M. D. , McCants C. E. , Spicer W. E.
Published: July 2002

Using valence-band and core-level photoemission spectroscopy (PES) and electrical device measurements, the effects of annealing Ag, Al, and Au on n-type (110)GaAs Schottky diodes fabricated in ultrahigh vacuum have been studied. PES was used to monitor the annealing-induced changes in the interface Fermi level position and the chemical nature of the metal–semiconductor interface for submonolayer and several monolayer coverages. Barrier height determinations were also performed using current–voltage (I–V) and capacitance–voltage (C–V) device measurements on annealed thick metal film metal–semiconductor junctions. The results of this study show that the annealing-induced microscopic changes in the electronic and chemical structure of the metal–semiconductor interface can be strongly correlated with the macroscopic changes in the electrical properties of thick film metal–semiconductor Schottky diodes.
Surface analysis of 1984/85 Tokamak Fusion Test Reactor limiter tiles
Authors: Pontau A. E. , Wampler W. R. , Mills B. E. , Doyle B. L. , Wright A. F. , Ulrickson M. A. , LaMarche P. H. , Dylla H. F. , Fukuda S.
Published: July 2002

Bare POCO AXF-5Q graphite tiles were installed as the plasma-facing surface of the Tokamak Fusion Test Reactor (TFTR) movable limiter for a series of ∼2700 high power discharges (600 with up to 6 MW neutral beams). During this operating phase, erosion and deposition processes modified the surface of the limiter. In the regions of the most intense plasma contact, which reached temperatures over 2400 °C, only small amounts of metallic impurities (<5×1016 atoms/cm2) are observed during subsequent beta backscattering and proton-induced x-ray emission (PIXE) analysis. Also observed in these regions are several small areas of surface crazing, and scattered droplets of metals (∼1 mm diam) presumed to originate from melted internal hardware. In regions more removed from direct plasma contact, thicker metallic deposits are observed (∼2×1018 atoms/cm2). There are more of these deposits on the side facing the electron drift direction than on the ion drift side. The metallic deposits are composed of ∼55% Ni, 25% Cr, and 20% Fe and several trace elements. Near-surface retained deuterium levels vary from 1016 to 1018/cm2 along one ion-side/electron-side pair of tiles. Deuterium from TFTR operations in the bulk of a tile may have been as much as 5 ppm. Hydrogen in the tile was ∼1 at. %. Surface roughness measured outside the intense plasma contact region is much more than the original POCO AXF-5Q graphite, whereas within the plasma contact region, tile surfaces are somewhat smoother than they were initially. Two of the tiles in high heat flux regions broke during operation. The resulting geometry change led to areas of enhanced erosion and nearby redeposition of carbon.
Influence of TiN coating and hydrogen glow discharge treatments on the conditioning of a direct current separator made of aluminum alloys
Authors: Momose Takashi , Ishimaru Hajime
Published: July 2002

The effects of hydrogen glow discharges and TiN coatings on the condit ng of a dc separator for the TRISTAN electron−positron collider were studi ed. In order to determine if high−voltage operation is possible, we teste d whether the conditioning time could be shortened if the TiN coating was applied to the separator cathode or if the entire assembly were treated in a hydrogen glow discharge. (AIP)
Impurity recycling and retention on Au and C surfaces exposed to the scrape-off layer of the TCA tokamak
Authors: Gimzewski J. K. , Vepřek S. , Hofmann F. , Hollenstein Ch. , Lister J. B. , Pochelon A. , Groner P.
Published: July 2002

In addition to impurity trapping, surfaces exposed to the boundary layer of a tokamak and other fusion devices are subjected to erosion phenomena. On local surface regions which do not experience unipolar arcing, these processes are due to the energetic fluxes of impurity and plasma particles which induce sputtering. Data are presented on collection probe experiments in the TCA tokamak which demonstrate that this erosion behavior may be evaluated from a knowledge of the shot dependence of the areal concentrations and impact energies of the trapped particles within the surface. Furthermore, a semiempirical parameter, which we call the ‘‘impurity recycling factor’’ (k), can be used to describe impurity retention and sputtering behavior for local plasma-surface interactions. Data on impurity retention and reemission are presented with respect to the impurity recycling factor as a function of the distance from the plasma edge.
Ru and Os film deposition from metal carbonyls
Authors: Berry A. D. , Brown D. J. , Kaplan R. , Cukauskas E. J.
Published: July 2002

Adherent, highly reflective films of Ru and Os have been deposited in vacuum on heated Si substrates by thermal decomposition of the pentacarbonyls Ru(CO)5 and Os(CO)5, at 150 and 200 °C, respectively. Auger analysis after ion bombardment cleaning revealed nearly O-free surfaces, with slight C contamination which grew with exposure to the primary electron beam, thus making accurate determination of C content difficult. X-ray diffraction showed the films to be polycrystalline with the expected hexagonal close-packed structure, while measured resistivities were about a factor of 3 greater than bulk values. This method of depositing Ru and Os offers the advantages of simplicity, modest temperature requirement, and metallization of heated surfaces only.
Peak resolving of complex Auger spectra by least-squares fitting with prefiltering of spectra: An application to depth profiling
Authors: Sekine T. , Ando Y. , Tokumasu H.
Published: July 2002

In Auger electron spectroscopy (AES), the filter-fit method, which was developed originally for the analysis of energy dispersive x-ray spectra, is applied to resolve overlapped peaks in the presence of continuum background, using the least-squares fitting (LSF) procedure after the prefiltering of spectra. With the filter-fit method, the background is first suppressed by filtration with a proper digital filter, and then the filtered complex Auger peaks are resolved by LSF calculation using filtered reference peaks. The analysis accuracy improves greatly over the conventional method because the disturbance by the background is minimized. A new depth compositional analysis routine providing the filter-fit procedure was successfully applied to the analysis of a thin TiN layer deposited on a glass substrate, in which both Ti and N profiles were obtained separately, though the two peaks overlapped each other.
High resolution electron energy loss spectroscopy: Explored regions and the frontier
Authors: Erskine J. L.
Published: July 2002

High-resolution electron energy loss spectroscopy (EELS) is rapidly being developed into one of the more useful techniques for probing physical and chemical phenomena at surfaces. Key elements of the technique include high surface sensitivity, the fact that it is a molecular sensitive rather than an atom sensitive spectroscopy, and the direct relationship that exists between experimental data and important surface parameters. New applications of EELS are currently being explored; these applications will be the primary focus of this paper. Recent work which combines EELS measurements with modeling of surface vibrations based on lattice dynamical calculations has shown that this approach can provide useful insight into structural parameters at surfaces. Other experiments aimed at refining our understanding of EELS scattering mechanisms and the selection rules that govern them have yielded some new and unexpected results which will be discussed. Finally, development of a new generation of EELS spectrometers should eventually produce improvements of two to three orders of magnitude in signal levels as well as more precise control of instrument response. These instruments will open up new applications of the EELS technique in areas including the study of technical surfaces and real time studies of surface reaction kinetics. The new spectrometers will also permit more precise studies of fundamental surface phenomena including electron scattering mechanisms.
Reflection anisotropy in evaporated aluminum: Consequences for telescope mirror coatings
Authors: Gee J. R. , Hodgkinson I. J. , Wilson P. W.
Published: July 2002

Aluminum coatings deposited in the presence of small quantities of oxygen onto substrates at oblique incidence are optically anisotropic, even at normal incidence. Values of the normal incidence reflection anisotropy are given for films deposited under controlled pressures and rates and for the range of angles 0°–45° which is appropriate to a circular array of sources for coating a large telescope mirror. Experimental arrangements for measuring anisotropy are described. One of these leads to a map showing the angular displacement of an incident linearly polarized beam which is reflected by a coated concave mirror.
Atomic structure of polar (111) surfaces of GaAs and ZnSe
Authors: Chadi D. J.
Published: July 2002

Considerable evidence for the presence of 1/4 of a monolayer of vacancies on the 2×2 reconstructed (111) surfaces of III–V semiconductors has accumulated during the last year. Very little is known, however, about the corresponding surfaces of II–VI semiconductors. The results of total-energy calculations on relaxed and 2×2-reconstructed Zn(111) surfaces of ZnSe presented in this paper show that vacancy formation is also energetically favorable on II–VI surfaces. The vacancy induced reconstruction transforms the surface atomic and electronic structure into those of a nonpolar (110)-type surface. All surface states are removed from the fundamental band gap as a result of vacancy reconstruction. For ZnSe the highest occupied Se-derived surface states are calculated to lie 1.0–1.5 eV below the bulk valence band maximum.
Effect of plasma exposure on the performance of indium tin oxide/InP solar cells prepared by radio-frequency and ion-beam sputtering
Authors: Naseem S. , Coutts T. J. , Aharoni H.
Published: July 2002

Previous work has shown that the performance of p-type single crystal/n-type thin film indium tin oxide (ITO) solar cells, can be enhanced by exposing the substrates (InP) to a very low power rf plasma prior to deposition of the ITO and by depositing the ITO very slowly. The mechanism underlying this enhancement is the subject of this experimental investigation. The principal variables studied were the duration of the low power plasma exposure (LPPE), the doping density of the substrate, and the methods of depositing the ITO. Comparison of the cells has been made on the basis of their current/voltage characteristics and their quantum efficiency. The analysis is consistent with there being a thin n-type layer at the interface between the InP and the ITO. For the ion-beam deposited ITO, the n-type layer is vanishingly small but for the rf deposited cells it is 70–100 Å thick; the thickness reducing with longer LPPE. The thickness of this layer appears to control the device performance; the cells with thicker layers have much larger open-circuit voltage and somewhat lower currents, whereas the reverse is true for thinner layers.
Growth and surface structure of Ge–Si alloy films on Si(111)-(7×7)
Authors: Seo J. M. , Doering D. L. , Black D. S. , Rowe J. E.
Published: July 2002

Thin epitaxial films of a Gex–Si1−x (50-50) alloy for x=0.5 have been grown in ultrahigh vacuum on a Si(111)-(7×7) surface and examined using Auger electron spectroscopy and digital LEED. The alloy films were prepared by thermal evaporation of Ge onto a Si(111) substrate. Following deposition onto a room temperature Si surface, a sequence of (1×1), (5×5), and (7×7) LEED patterns were observed with increasing annealing temperature. The (5×5) structure which forms near 500 °C is indicative of the Ge0.5Si0.5 alloy. Alloy films up to 1000 Å were then grown by Ge deposition onto the Si substrate held at 560 °C where intermixing readily occurs. For film thicknesses greater than two monolayers, the (5×5) surface periodicity of the alloy was always found. The lattice constant of the alloy was determined as a function of film thickness by digital analysis of the LEED patterns using a vidicon camera detector. Results show that for thicknesses less than 150 Å, the Ge–Si alloy grows pseudomorphically on the Si substrate, i.e., the lattice constant of the alloy matches that of the substrate. At thicknesses near 1000 Å, the lattice constant of the surface of the film relaxes to about 1.5% larger than the Si as compared to the value for the bulk Ge0.5Si0.5 alloy which is about 2% larger than Si.