bluuebunny/crossref_metadata_2025 huggingface dataset:
From heterojunctions to Schottky barriers
Authors: Niles D. W. , Tang M. , McKinley J. , Zanoni R. , Margaritondo G.
Published: July 2002

The relations between Schottky barriers and heterojunctions were explored by studying heterojunction band lineups with metal intralayers, as a function of the intralayer thickness. The results can be explained by introducing Schottky-like terms in midgap-energy models. Such terms, however, do not imply the formation of a truly metallic intralayer.
Titanium nitridation of metallic surfaces
Authors: Grieggs R. J. , Cornelius W. D.
Published: July 2002

This novel method of depositing a titanium nitride layer onto metallic surfaces was originally developed to reduce the effects of multipactoring in the Fusion Materials Irradiation Test (FMIT) accelerator. The constraints of room-temperature deposition and the large surface area of the inside of the accelerator cavity (∼106 cm2) effectively prevented using the usual sputter-source deposition of titanium nitride. The method described in this paper was developed to overcome the limitations of the sputtering methods and provide a more durable surface layer than one obtained by vacuum deposition of titanium followed by venting to a nitrogen atmosphere. The nitride layer produced by our method is flexible and very durable. Thin copper samples retain the integrity of the nitride surface even after bending of the samples to moderately small radii. Sanding of the coated surfaces is the only way to remove the coating. The nitride layer produced by this method was effective in eliminating multipactoring in the FMIT accelerator. Since that time, we have continued to improve the deposition method and have obtained good results on a wide variety of materials ranging from copper to stainless steel to glass and ceramic surfaces.
The modeling of standard gas leaks
Authors: Chamberlin J. L.
Published: July 2002

Standard leaks are being increasingly used to provide known quantities of gas for applications, such as determining a mass spectrometer’s sensitivity, where it is desirable to know their flow rates for various gas species, operating temperatures, and pressures. Characterizing a leak for such varying conditions presents a challenging task which has been simplified by a model that predicts a leak’s throughput for various operational parameters using a limited set of calibration conditions. The model is based on an integrated form of Knudsen’ s equation for the conductance of a tube in transitional flow. The integration circumvents a restriction of the Knudsen equation violated by the significant pressure drop occurring across a leak. Normalizing the resulting equation provides a model whose independent variable is a function of the operational parameters and whose coefficients depend on the leak’ s geometry, knowledge of which is not required for the model’s use. The resulting model accurately describes a leak’s flow rates into both the molecular and viscous regions even though it was developed from a transitional flow base. The model’s accuracy is commensurate with the accuracy of the calibration values used in determining its coefficients.
Pulsed ion beam investigation of the kinetics of surface reactions
Authors: Horton C. C. , Eck T. G. , Hoffman R. W.
Published: July 2002

Pulsed ion beam measurements of the kinetics of surface reactions are discussed for the case where the width of the ion pulse is comparable to the measured reaction time, but short compared to the time between successive pulses. Theoretical expressions are derived for the time dependence of the ion-induced signals for linear surface reactions. Results are presented for CO emission from surface carbon and CF emission from Teflon induced by oxygen ion bombardment. The strengths and limitations of this technique are described.
Continuous electron stimulated desorption using a ZrO2/Ag permeation membrane
Authors: Outlaw R. A. , Hoflund Gar B. , Davidson M. R.
Published: July 2002

During the development of an atomic oxygen beam generator for laboratory simulation of the atmospheric conditions in low Earth orbit, a new technique for performing electron stimulated desorption (ESD) in a continuous manner has been developed. In this technique, oxygen permeates through a Ag membrane at elevated temperature thereby providing a continuous supply of oxygen atoms to the 1000-Å ZrO2 coating at the vacuum interface. ESD then results in a large peak of neutral O2 molecules which ultimately decays into steady-state desorption. The ESD signal is linear with respect to primary beam flux (3.5×10−2 O2 molecules per electron at a primary beam energy of 1 keV) but nonlinear with respect to primary beam energy.
Infrared-induced single-phonon desorption of H2, HD, and D2 from graphite single crystals
Authors: Cui Jinhe , Fain S. C. , Liu Wei
Published: July 2002

H2, HD, and D2 gases are physisorbed on graphite single crystals at T≤12 K. The relation between the monolayer density [ρ=1 for the ((3)1/2×(3)1/2) R30 ° phase] and the gas flux impinging on the graphite was investigated as a function of temperature using low-energy electron diffraction. At ρ≤1.30, the gas flux required to produce a given incommensurate H2 monolayer density is found to be the same at T=5 and 10 K. This effect is interpreted by single-phonon desorption induced by the room-temperature infrared radiation. Desorption measurements indicate that for the H2 monolayer in our geometry this single-phonon desorption occurs at a rate of ∼0.02 monolayer per second.
Laser vaporization mass spectrometry of refractory materials: Graphite and YBa2Cu3Ox
Authors: Schenck P. K. , Bonnell D. W. , Hastie J. W.
Published: July 2002

A very high pressure sampling mass spectrometer has been used to study the thermochemistry and kinetics of laser induced plumes from graphite and YBa2Cu3Ox targets. Time resolved mass spectra of Cn (n=1–9) neutral vapor species were obtained from graphite targets under conditions of varying laser–surface interaction geometry and vapor plume-sampling geometry. Ionic species C+1, C+2, C+3, and impurities Na+ and K+ were also observed in the laser induced plume. Mass spectra obtained from superconducting YBa2Cu3Ox targets showed an abundance of species in the laser induced plumes including both neutral and ionic Y, Ba, and Cu. In addition, species such as BaO, CuO+, YO, and bimetallics (BaCu, YCu) were observed. Similar neutral and ionic metal atom species were observed using time resolved optical spectroscopy of the plume.
Analysis of ion-bombarded and laser-irradiated surfaces of ZnS and Zn via two-photon high-resolution laser-induced fluorescence spectroscopy
Authors: Arlinghaus H. F. , Calaway W. F. , Young C. E. , Pellin M. J. , Gruen D. M. , Chase L. L.
Published: July 2002

Doppler-shifted two-photon laser-induced fluorescence spectroscopy (LFS) has been used to measure the velocity distributions of Zn atoms ejected by Ar+ ion bombardment from both a Zn surface and a ZnS single crystal. Doppler-shifted spectroscopy in combination with time of flight(TOF), has also been employed to investigate Zn atoms ejected from a ZnS single crystal under irradiation by 308-nm photons (XeCl excimer laser). The absolute Zn sputtering yields from ion-bombarded and laser-irradiated ZnS samples were determined by comparison with LFS measurements of Zn atoms sputtered from pure Zn targets by Ar+ ions since the absolute sputtering yield is known. For the Zn target the velocity distributions of the ion-induced sputtered Zn atoms were in good agreement with the Sigmund–Thompson distribution based on the known binding energy of 1.35 eV. On the other hand, the velocity distribution of Zn atoms ion sputtered from ZnS showed some deviation from the Sigmund–Thompson distribution and had a lower binding energy, ∼0.9 eV. The velocity distributions of the laser-ablated Zn atoms from ZnS were Maxwell–Boltzmann in nature with characteristic temperatures increasing from 2000 to 9000 K at fluences of 20 and 80 mJ/cm2, respectively. The absolute sputtering yield (Y) of Zn sputtered from ZnS was found to be Y≂8 atoms/ion for ion sputtering and Y≂10−6 atoms/photon at a laser fluence of 30 mJ/cm2 for laser ablation. High-resolution Doppler-shift techniques have been combined with TOF techniques. This promising combination permits unambiguous detection of prompt and delayed emission of ablated atoms, as well as the observation of possible molecular or cluster fragmentation. The results obtained indicate that no delayed emission is occurring and suggest the possibility of molecule or cluster emission from ZnS.
Comparative study of dielectric formation by furnace and rapid isothermal processing
Authors: Singh R. , Radpour F. , Chou P.
Published: July 2002

An examination of our own and results available in the literature indicate that the dielectric properties of silicon dioxide and tin oxide on Si formed by rapid isothermal processing are superior compared to furnace processing. A possible explanation based on the primary difference in the radiation spectrum of the two sources of energy is presented in this paper. Certain physical and chemical processes can be prompted and/or initiated due to the presence of light in the rapid isothermal processing.
Electronic properties of Hg1−x−yCdxZnyTe
Authors: Ekpenuma Sylvester N. , Myles Charles W.
Published: July 2002

The electronic structure of Zn-containing Hg1−xCdxTe is investigated and the effects of Zn on the band gap and effective masses are estimated. In these studies, ZnTe is treated as an additional alloy constituent and the resulting quaternary alloy Hg1−x−yCdxZnyTe is modeled using both the virtual-crystal approximation and the coherent potential approximation. Numerical results are obtained by utilizing tight-binding band structures of the constituent compounds. Results are presented for the variation of the band gap and electron effective mass with Zn composition y for fixed Cd composition x, and for the dependence of the electron and hole effective masses on Zn composition for two different fixed band gaps in the infrared regime. The results show that Zn-induced alloy disorder effects can be important for determining both the band gap and the effective masses, but that for constant band-gap material the effective masses are almost independent of y.
Study of CdTe(111)B epilayers grown by molecular-beam epitaxy
Authors: Monfroy G. , Sivananthan S. , Faurie J. P. , Reno J. L.
Published: July 2002

The growth of high-quality Hg1−xCdxTe(111)B epitaxial layers involves the growth of a CdTe(111)B buffer layer, whether the growth is performed onto related or foreign substrates. CdTe(111)B layers have been investigated using the x-ray double-crystal rocking curve and the cathodoluminescence imaging techniques. The optimization of the growth conditions for CdTe(111)B layers is presented for a high-quality homoepitaxy. The heteroepitaxy of CdTe(111)B on GaAs(100) substrates is then discussed, in the case of GaAs substrates oriented (100), misoriented by 2° towards [110], and misoriented by 5° towards [111]. The results indicate that a 2° misorientation leads to CdTe(333) peaks with full width at half-maximum up to four times narrower then either of the other orientations tested. Furthermore, only threading dislocations were visible on this orientation by cathodoluminescence imaging.
Temperature dependence of contact resistance in noble metal/high-T
c superconductor systems
Authors: Huang C.-L. , Gildenblat G. Sh. , Fonash S. J.
Published: July 2002

A combination of three- and four-terminal measurements was used to study the temperature dependence of the contact resistance of Au/YBa2Cu3O7−y and Ag/YBa2Cu3O7−y contacts. Both as-deposited and oxygen annealed contacts were investigated. It is shown that not only the magnitude of the contact resistance but its temperature dependence above and below the transition point are strongly affected by the annealing process.
A new type of instrumentation designed for the study of chemical reactions on single-crystal surfaces
Authors: Yamada Taro , Misono Takashi , Tanaka Ken-ichi , Murata Yoshitada
Published: July 2002

Two new ultrahigh vacuum instruments were designed and constructed to study chemical reactions on single-crystal surfaces. These instruments allow samples to be cycled between high-pressure gas cells for treatment of the samples, and ultrahigh vacuum, for electron spectroscopies. By using newly developed ‘‘rod-through-chamber’’ devices, the ultrahigh vacuum and high pressure are completely separated, while the sample is smoothly transferred between those parts. We are utilizing them to prepare surface chemical compounds and to observe heterogeneous catalysis on solid surfaces.
Effect of hydrogen on carbon incorporation in indium antimonide layers grown by metalorganic magnetron sputtering
Authors: Rao T. Sudersena , Webb J. B. , Beaulieu Y. , Brebner J. L. , Noad J. P. , Jackman J.
Published: July 2002

Secondary ion mass spectrometry measurements revealed a high level of unintentional carbon doping in heteroepitaxial InSb layers grown by metalorganic magnetron sputtering. The addition of molecular hydrogen to the sputtering gas resulted in an order of magnitude decrease in the carbon content of the as-grown InSb layers. Mass spectrometric studies of the growth environment indicated methane as the major by-product of trimethylindium breakup. The relative abundance of methane in the growth chamber was found to increase with substrate temperature and with the addition of hydrogen and/or a plasma discharge.
Optical- and magneto-optical measurements using a variable angle of incidence spectroscopic ellipsometer: Application to DyCo multilayers
Authors: McGahan William A. , Shan Z. S. , Massengale Alan M. , Tiwald Thomas E. , Woollam John A.
Published: July 2002

We have extended the technique of variable angle spectroscopic ellipsometry to measurement of the magneto-optical effects as a function of wavelength and angle of incidence and field strength. Results on DyCo multilayers are reported.
I
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i
t
u deposition monitoring for solar film production by roll coating
Authors: Meyer Stephen F.
Published: July 2002

Real-time measurement of critical coating properties is a necessity for commercial success in large-scale roll coating. Both sheet resistance and optical measurements are used in modern sputter roll coating plants. This presentation will introduce sputter roll coating and discuss in situ film monitoring in that context. Some of the difficulties in interpreting the measurements and in relating them to product specifications will be addressed.
Plastic flow and preferred orientation in molybdenum and zirconium films
Authors: Window B.
Published: July 2002

X-ray diffraction measurements on samples of molybdenum and zirconium growth with ion assistance at low temperatures support the occurrence of plastic flow during growth, provided the level of bombardment is high enough. As the energy of the argon ions was increased, the lattice strain in the growth direction increased to a maximum before decreasing slowly. That this is a plastic flow transition is shown by the independence of the maximum strain on preparation conditions and by the changes in microstructure. In particular, the grain size in the growth direction decreased and the preferred orientation favored the usual wire drawing textures of these metals. For the zirconium films this involved a change in preferred orientation from a (00.2) to a (10.0) texture. A reduction in strain is observed at high bombardment levels.
Intrinsic resputtering—theory and experiment
Authors: Hoffman D. W.
Published: July 2002

This study examines a type of resputtering that attends the deposition of sputtered materials under elementary conditions—sputtering with a single ion beam at pressures below 0.01 Pa. Ne, Ar, Kr, and Xe were employed to sputter nine simple metals ranging in mass from Al to Au. Comparative weight gains on planar and concave substrates revealed the magnitude of resputtering, which varied from about 3.5% for light metals sputtered with heavier ions to over 20% for gold sputtered with neon. The results define a universal curve that appears constant at mass ratios less than unity but increases steeply beyond a mass ratio intercept slightly greater than unity. A theoretical analysis is developed that predicts the striking universality, relates the observed intercept to the existence of finite sputtering threshold energies, and fits the full range of experimental data with one adjustable parameter having a derived value of unity.
The use of splines to analyze scanning tunneling microscopy data
Authors: Wormeester H. , van Midden H. J. P. , Kip G. A. M. , Sasse A. G. B. M.
Published: July 2002

Scanning tunneling microscopy (STM) requires a two-dimensional (2D) image displaying technique for its interpretation. The flexibility and global approximation properties of splines, characteristic of a solid data reduction method as known from cubic spline interpolation, is called for. Splines were used to implement 2D representation, deconvolution, and Fourier transform routines with still a good performance in case of noisy measured functions. The implementation was done on a small computer system (8086/8087 processor) with a reasonable execution time. The underlying mathematics of 2D spline-based routines will be shown and tests on STM-like images will be given to show the performance. A reduction of 25–100 in memory of stored data is achieved using splines if these routines are used while scanning a surface as in STM.
Low-energy electron diffraction intensity analysis of the atomic geometry of p(1×1) monolayers of bismuth on GaAs(110)
Authors: Duke C. B. , Lessor D. L. , Guo T. , Ford W. K.
Published: July 2002

The elastic low-energy electron diffraction intensities of 18 diffracted beams associated with electrons normally incident on GaAs(110)-p(1×1)–Bi(1 ML) (monolayer) have been measured at 130 K. Analysis of these beams using a multiple scattering methodology previously applied to GaAs(110) and GaAs(110)-p(1×1)–Sb(1 ML) yields a best-fit structure characterized by a bond-length-conserving top layer rotation of chains of Bi atoms by a tilt angle of ω1 =3°±2° and a counter rotation (Ga displaced outward toward the Bi overlayer) in the underlying GaAs(110) layer of ω2=−3°±2°. A small contraction of the top-layer spacing is possible but is not mandated by the analysis. Only geometries analogous to that of GaAs(110)-p(1×1)–Sb(1 ML) were included in the structural search.
An ultrahigh vacuum application of a refrigerator-cooled cryopump
Authors: Kasuya M. , Yuyama J.
Published: July 2002

A refrigerator-cooled cryopump is applied to an ultrahigh vacuum system made of aluminum alloys. This system is easy to bakeout and to achieve a pressure around 2–6×10−9 Pa. A pressure in the 10−9 Pa range is obtained without the baking process being repeated, if only dry nitrogen gas, instead of air, is introduced into the vacuum chamber. Some different regeneration procedures are also studied.
A fiberepoxy vacuum vessel with thin walls
Authors: Ortner H.-W. , Malz D. , Müller R.
Published: July 2002

We present a technique to produce vacuum vessels with extremely thin walls. The low mass density of the wall is available for nearly the whole solid angle. The construction of the vessel is based on carbon fibers and epoxy resin. A prototype was realized for a low energy particle physics experiment on a liquid hydrogen target.
Backstreaming of a perfluorinated polyether pump oil—an x-ray photoelectron spectroscopy study
Authors: Sherman Robert , Vossen John
Published: July 2002

The backstreaming of a perfluorinated polyether mechanical pump oil was determined by using x-ray photoelectron spectroscopy to measure oil content on silicon wafer surfaces. Backstreaming test pressures ranged from 0.4 mTorr to 100 mTorr. Backstreaming was identified at most test pressures even though perfluorinated polyether pump oils have low vapor pressures. Overall, for the pressure range studied, the backstreaming decreased as the pressure increased.
Fast partial and total pressure measurements during tokamak discharges
Authors: Bourque G. , St. Germain J. P. , Terreault B. , Boucher C. , Kalnavarns J. , Lachambre J. L. , Pacher G. W. , Pacher H. D. , Zuzak W.
Published: July 2002

A system consisting of magnetically shielded ion gauges and a differentially pumped quadrupole mass spectrometer is described. It provides time-resolved measurements of the neutral gas fluxes during discharges in the Tokamak de Varennes. A response time of 15 ms for hydrogen and ≊50 ms for impurity gases was obtained by a judicious choice of distance (to avoid magnetic disturbances), conductance, and pumping speed. An interface between the spectrometer and the data acquisition system of the tokamak allows fast (ms) selection of the mass and real-time (≊10 ms) adjustment of the gain to optimize the signal-to-background ratio. The usefulness of this diagnostic is illustrated by its use in three experiments: propagation of a plasma density perturbation following pulsed (5 ms) gas puffing, exchange of the discharge gas from H2 to He, and chemical impurity (CO, CO2 ) production during discharges at the density limit and qa≊2. The correlation of low impurity fluxes with absence of disruptions in these last shots is shown.
A further study of the state of residual stress in TiN films made by physical vapor deposition methods
Authors: Perry A. J.
Published: July 2002

The residual stress and strain distribution in TiN films deposited by chemical vapor deposition onto cemented carbide and physical vapor deposition methods onto cemented carbide and stainless steel are studied. Two sets of samples were chosen for study which, respectively, have either strong (111) textures or show different textures apparently resulting from different deposition rates. The data indicate that the residual stress on different planes in all samples, as measured by standard x-ray diffraction methods, is affected by the texture of the film. Reduction in the deposition rate increases the lattice distortion, reduces the strain distribution and the tendency of the (220) plane to show shear stress effects. The data confirm that studies of planes not lying parallel to the surface of the film are needed to allow a more complete characterization and to permit the way to a fuller interpretation to be opened.
Vacuum technology issues for the Superconducting Super Collider
Authors: Jöstlein H.
Published: July 2002

The Superconducting Super Collider, to be built in Texas, will provide an energy to 40 TeV from colliding proton beams. This energy is twenty times higher than currently available from the only other cryogenic collider, the Fermilab Tevatron, and will allow experiments that can lead to a better understanding of the fundamental properties of matter. The energy scale and the size of the new machine pose intriguing challenges and opportunities for its vacuum systems. We discuss the effects of synchrotron radiation on cryogenic beam tubes, cold adsorption pumps for hydrogen, methods of leak checking large cryogenic systems, the development of cold beam valves, and radiation damage to components, especially electronics.
Temperature-dependent effects during Ag deposition on Cu(110)
Authors: Taylor T. N. , Muenchausen R. E. , Hoffbauer M. A. , Denier van der Gon A. W. , van der Veen J. F.
Published: July 2002

The composition, structure, and morphology of ultrathin films grown by Ag deposition on Cu(110) were monitored as a function of temperature using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and medium-energy ion scattering (MEIS). Aligned backscattering measurements with 150 keV He ions indicate that the Ag resides on top of the Cu and there is no measurable surface compound formation. Analysis with LEED shows that initially the Ag is in registry with the substrate troughs. Further deposition results in a split-c(2×4) LEED pattern, which is characteristic of a distorted Ag(111) monolayer template. As verified by both AES and MEIS measurements, postmonolayer deposition of Ag on Cu(110) at 300K leads to a pronounced three-dimensional clustering. Ion blocking analysis of the Ag clusters shows that the crystallites have a distorted (110) growth orientation, implying that the Ag monolayer template undergoes a rearrangement. This growth orientation is supported by LEED results at 130 K, which indicate that Ag multilayers develop from a Ag–Cu interface where the Ag is captured in the troughs. Changes observed in the film structure and morphology are consistent with a film growth mechanism that is driven by overlayer response to the substrate corrugation.
Sputtering of Ni+ from polycrystalline Ni with adsorbed hydrogen or oxygen: A secondary ion mass spectrometry study
Authors: Shenasa Mohsen , Lichtman David
Published: July 2002

A study of the emission of the secondary ions of Ni+ during the secondary ion mass spectrometry (SIMS) analysis of a polycrystalline nickel surface (at room temperature) covered with up to a few monolayers of oxygen or hydrogen was undertaken. A comparison was made between the experimental data and the calculated predictions using the electron tunneling model (ETM). The results showed that the ETM can successfully predict the change in emission of Ni+ secondary ions from a polycrystalline Ni surface covered with up to a monolayer of hydrogen or oxygen. However, ETM predictions did not fit well with the behavior of the Ni+ secondary ions beyond one monolayer coverage of hydrogen or oxygen. In this paper a modification of ETM is described that successfully explains the emission of Ni+ secondary ions from a polycrystalline Ni surface for coverages beyond one monolayer of hydrogen or oxygen.
Aluminum–samarium alloy for interconnections in integrated circuits
Authors: Joshi A. , Gardner D. , Hu H. S. , Mardinly A. J. , Nieh T. G.
Published: July 2002

Thin films of aluminum alloyed with copper, silicon, or titanium have been conventionally used as interconnection materials in integrated circuits to reduce hillock growth, electromigration, and junction spiking. The interconnection resistivity of these homogeneous alloys is, however, too high for maximum performance integrated circuits. In this work, hillock growth, resistivity, and stress were investigated for aluminum alloyed with samarium (Al-1 wt. % Sm) as an alternative interconnection material. The results indicated that Al–Sm metallization exhibits very favorable properties, namely, low resistivity and good thermal stability including hillock growth resistance, for potential integrated circuit applications. Other property measurements and process and material compatibility studies are, however, desired prior to its application.
Thermally induced changes in the resistance, microstructure, and adhesion of thin gold films on Si/SiO2 substrates
Authors: George M. A. , Bao Q. C. , Sorensen I. W. , Glaunsinger W. S. , Thundat T.
Published: July 2002

The resistance as a function of annealing temperature for thin gold films on a SiO2 layer on silicon (100) passes through a minimum near 600 °C for times at temperature ≤60 min. The structural changes associated with this electrical behavior have been investigated by scanning tunneling microscopy and scanning electron microscopy. Annealing temperatures as low as 100 °C affect the microstructure as well as reducing the resistance. Recrystallization and grain growth occur with increasing temperature, and the high surface energy of gold relative to SiO2 results in nucleation and growth of porosity above about 600 °C which contributes to an abrupt increase in resistance. The adhesion of gold to SiO2 was improved at elevated temperatures (≥600 °C).
Beam parameter effects on magnetic properties of sputtered amorphous Fe40Ni40B15Si5 and Fe40Co40B15Si5 films
Authors: Harris V. G. , Oliver S. A. , Nowak W. B. , Vittoria C.
Published: July 2002

Amorphous films were deposited onto fused quartz by ion beam sputter deposition to examine possible alternatives to existing polycrystalline microwave materials. Ion beam parameters were systematically varied to determine the dependence of film magnetic properties on beam conditions. Chemical composition of representative films were confirmed using Auger electron spectroscopy and Rutherford backscattering spectroscopy. Amorphousness was confirmed by x-ray diffraction analysis, and film thickness was determined by surface profilometer trace. Film magnetic properties were measured by vibrating sample magnetometer and ferromagnetic resonance techniques. It was found that films deposited under higher beam energies showed the lowest coercivities and anisotropy fields. Saturation magnetization values remained largely unaffected by beam parameter variation. Evidence suggests vacuum base pressure plays a significant role in film magnetic properties. Improvement of the films’ soft magnetic properties with increased beam energy may be attributed to reductions in trapped impurities resulting from increased deposition rates. The resulting films display promising properties for microwave magnetic applications.
Mechanical properties of high deposition rate SiO2 films
Authors: Macchioni C. V.
Published: July 2002

Thick overcoats of SiO2 sputtered at high deposition rates in a radio-frequency (rf) diode system are being considered as alternatives to Al2O3 and photoresist as passivation and planarization layers in the fabrication of thin film magnetic recording heads. The mechanical properties of 7-μm thick SiO2 films sputtered onto silicon substrates were examined as functions of bias voltage and O2 gas flow. A high rate of 3.69 μm/h was achieved in a production system at substrate temperatures below 40 °C. The addition of O2 decreased the deposition rate to 1.65 μm/h. The decrease in deposition rate produced an improvement in the p-etch rate, hardness and stress, but no change in the film density or morphology. The addition of a bias voltage during deposition was found to have the biggest effect on film properties. Bias sputtered films were found to be completely devoid of the columnar structure found in films deposited without bias. The addition of a small bias voltage reduced the film stress from −16×108 dyn/cm2 to −0.4×108 dyn/cm2. However, increasing the bias voltage further caused the film stress to increase to −3.6×108 dyn/cm2 at −160 V bias. This effect can be correlated with the increased Ar content of the films. The p-etch rates of bias sputtered films dropped two orders of magnitude to 10 Å/s. The Knoop hardness increased from 423 without bias to 663 with bias and the film density increased slightly.
New getter clean-up system for tritiated glove box atmosphere
Authors: Bonizzoni G. , Ghezzi F. , Nassi M. , Succi M.
Published: July 2002

This work was carried out to determine the utility of using getter materials for tritium purification in glove box atmospheres. The main goal of this experiment was to reach a residual tritium concentration lower than 1 mCi/m3, as imposed by the international safety rules. Two groups of measurements were carried out simulating tritium with deuterium; the first group was performed under static conditions, in order to find the best working temperature for the getter, relative to the pumping speed. The second one was performed under dynamic conditions, in order to find the tritium residual partial pressure. The measurements provided a residual pressure three times higher than the pressure predicted by Sieverts’ law. The selected getter consisted of a Zr–V–Fe alloy; two types of getter configurations were tested: a getter cartridge pump and a getter purifier. The results showed that the diffusion of D2 in argon limited the sorption speed. The results of static tests did not change when the getter temperature was changed. The results of dynamic tests showed the need for lower getter temperatures to achieve lower deuterium partial pressures. Starting from the experimental results, a proposal for an economical tritium purification system for a glove box atmosphere is presented.
A comparison of SiO2 planarization layers by hollow cathode enhanced direct current reactive magnetron sputtering and radio frequency magnetron sputtering
Authors: Dawson-Elli David F. , Lefkow Anthony R. , Nordman James E.
Published: July 2002

SiO2 films have been prepared by hollow cathode enhanced dc reactive magnetron sputtering [J. J. Cuomo and S. M. Rossnagel, J. Vac. Sci. Technol. A 4, 393 (1986)], and for comparison by rf magnetron sputtering from an SiO2 target. The hollow cathode arc source is used in a triode configuration with the magnetron. This configuration allows sputtering to take place at pressures as low as 5×10−4 Torr, as well as sputtering of the oxide without arcing below ∼600 V. These films were investigated as a dielectric planarization layer for Josephson (superconducting) devices. To this end, film deposition parameters (O2 flow rate, Ar partial pressure, magnetron target voltage, hollow cathode current) have been related to film deposition rate, index of refraction, measured by ellipsometry, stoichiometry, measured by x-ray photoelectron spectroscopy (XPS), and coating conformity as measured by electron microscopy. A similar set of experiments was performed for the rf sputtered films. The relationships were investigated using factorial experiment design.
Field-effect transistors in Hg1−xCdxTe grown by photoassisted molecular beam epitaxy
Authors: Dreifus D. L. , Kolbas R. M. , Han J. W. , Cook J. W. , Schetzina J. F.
Published: July 2002

The first demonstration of Hg1−xCdxTe metal–insulator-semiconductor field-effect transistors prepared using n-type layers grown by photoassisted molecular beam epitaxy is reported. These transistor structures were processed by means of a new low-temperature (<60 °C) semiconductor device processing technology developed at North Carolina State University, and differ significantly from structures previously reported in that (1) a depletion region instead of a surface inversion layer is used as the principle for device operation, (2) larger x-value Hg1−xCdxTe is employed as the active region of the device, and (3) the transistor structures are fabricated without the use of ion implantation and thermal annealing processing steps. In addition, the low-temperature processing technology is compatible with the future development of superlattice and multilayer device structures consisting of Hg-based alloys, in which mercury interdiffusion at heterointerfaces can significantly alter the material properties. Depletion and enhancement-mode operation have been observed and digital inverter circuits have been characterized at speeds of 1 MHz.
Studies of Au ‘‘ohmic’’ contacts to p-type Hg1−xCdxTe
Authors: Krishnamurthy V. , Simmons A. , Helms C. R.
Published: July 2002

Electroless Au contacts to p-type Hg1−xCdxTe in many cases exhibit ohmic behavior. Our investigation of the interfacial chemistry of such contacts suggest that this ohmic behavior is due to the presence of a Te, O, and Cl layer. To test this hypothesis, thin plasma oxide layers were then used in evaporated Au contacts. Ohmic behavior was also observed for the annealed plasma oxidized contacts. We believe this ohmic behavior is primarily a result of the low interface state density at the interfacial layer/Hg1−xCdxTe interface and in addition, a 100 °C anneal promoted a further reduction in the interface state density and thus lowered the contact resistance. In comparison, as-deposited and annealed Au contacts without a thin interfacial layer were rectifying with a large barrier height.
A scanning tunneling microscope for ultrahigh vacuum atom–surface interaction studies
Authors: Peale D. R. , Cooper B. H.
Published: July 2002

A compact, mechanically stable and thermally compensated tunneling microscope has been designed for use in an ultrahigh vacuum (UHV) surface characterization and analysis system. Very small concentric tubular scanning elements provide mechanical rigidity, thermal stability, and minimal cross coupling of the X, Y, and Z motions. The compact load-locking design provides full compatibility with the rest of the UHV analysis system without requiring that a disproportionately large fraction of the vacuum system be devoted to the microscope. Reported here is the design of the microscope and load-lock system, and the results of tests using the microscope in air to image the surfaces of graphite, gold, and platinum.
A simple means for reproducibly dosing low vapor pressure and/or reactive gases to surfaces in ultrahigh vacuum
Authors: Henn Frederic C. , Bussell Mark E. , Campbell Charles T.
Published: July 2002

Adsorbate gases which are very reactive with chamber walls or which have low vapor pressures present serious difficulties in attaining precisely reproducible exposures in surface science experiments, especially if the desired exposures are small. Design considerations and details are described for an inexpensive gas dosing system which is excellently suited for precisely reproducing exposures of low vapor pressure and/or reactive gases to surfaces in UHV. Also presented is a method for calibrating the doser, such that even tiny exposures can be very accurately determined and reproduced.
Macroscopic model for columnar growth of amorphous films by sputter deposition
Authors: Bales G. S. , Zangwill A.
Published: July 2002

We present a macroscopic model for the growth of amorphous films produced by sputter deposition under conditions of high buffer gas pressure. Consistent with the latter assumption, we assume that incident flux approaches the surface from all angles of incidence. Explicit account is taken of two important physical effects: (i) surface diffusion and (ii) the fact that some parts of the surface will be geometrically shadowed from receiving flux by other parts of the surface. The physical variables which define the problem (e.g., deposition rate, surface diffusion constant, temperature, etc.) can be combined to form a characteristic length and a characteristic time which determine the rescaling required to reduce the problem of morphological prediction to a characterization of the initial conditions. All the well-known features of columnar growth are found and a simple physical explanation for ‘‘survival of the fittest’’ columns is provided.
Influence of ion energy and substrate temperature on the structure of copper, germanium, and zinc films produced by ion plating
Authors: Fountzoulas Constantine , Nowak Welville B.
Published: July 2002

Thin films of copper, germanium, and zinc were deposited at an argon pressure of 2.7 Pa (20 mTorr) on cover glass substrates precoated with 10 nm of Au/Pd. The substrate temperatures Ts ranged from 77 to 417 K for zinc, 77 to 543 K for copper, and 77 to 490 K for germanium. The discharge voltage was varied from 900 to 1300 V. Average film thickness was ∼1.5 μm, with deposition rate ∼0.4 μm/min. Ion energies were measured by the retarding field method. Examination of the film structure with a scanning electron microscope (SEM) showed that zones I and T were missing. Structural zone transition temperatures were lower than in the models proposed by Movchan and Demchishin, and Thornton. All copper and zinc films were polycrystalline. Germanium, for the above deposition rates, showed an amorphous/poly- crystalline transition, as determined by reflection high-energy electron diffraction, for various ion energy and Ts combinations. Polycrystalline germanium is observed at room temperature for energies above 340 eV. A structural zone model showing the effect of the ion energy and substrate temperature on the film structure for ion plated films is proposed.
Outgassing measurement of finely polished stainless steel
Authors: Okamura Sigeru , Miyauchi Eizo , Hisatsugu Tokushige
Published: July 2002

We have measured the outgassing rate of finely polished stainless steel using cylindrical vacuum chambers. The electrolytic abrasively polished samples had very low outgassing rates of 3×10−13 to 6×10−13 Torr ℓ/s cm2. The rate with standard electrolytical polishing has remained around 1×10−12 Torr ℓ/s cm2. The semiultimate outgassing species turned out to be H2 and some samples still have desorbed H2O, even with the mirror-like polishing. Surface inspection of these samples by x-ray photoelectron spectroscopy (XPS) indicates that the quantities of adsorbed organic hydrogen and oxygen, and surface oxides can qualitatively explain the desorption rates and desorption species of individual samples.
Controlled ion beam sputter deposition of W/Cu/W layered films for microelectronic applications
Authors: Auciello O. , Chevacharoenkul S. , Ameen M. S. , Duarte J.
Published: July 2002

Initial results are presented and discussed in relation to a research program focused on investigating the feasibility of using ion beam sputter deposition to produce layered films for metallization of microcircuits. An automated ion beam sputter-deposition system has been used to produce W/Cu/W layered films and investigate their microstructural, morphological, and electrical characteristics. Layered films with smooth surfaces have been deposited on planar surfaces and in vias with reasonable conformality. It is demonstrated that the W layer microstructure can be tailored by controlling the deposition parameters. The control of the W layer microstructure can serve to improve its diffusion barrier properties with respect to similar films produced by other techniques. Initial measurements of the resistivity of the layered film structure yielded values close to that characteristic of bulk copper, a desirable parameter for application in microcircuit metallization.
Correlations of plasma properties and magnetic field characteristics to TiN film properties formed using a dual unbalanced magnetron system
Authors: Rohde S. L. , Sproul W. D. , Rohde J. R.
Published: July 2002

A number of single-cathode ‘‘unbalanced’’ magnetron systems have recently been developed to obtain increased ion-current densities at the film surface during hard coating deposition; however, as with most single-cathode systems, shadowing effects often limit the types of substrates that can be coated in these units. The deposition system employed in this research utilizes a unique dual-cathode unbalanced dc-magnetron arrangement to coat specimens mounted on a rotational substrate holder, thereby gaining the benefits of unbalanced magnetrons while eliminating the shadowing effects commonly associated with single-cathode systems. This paired unbalanced magnetron system can be used to create a well-confined discharge, yielding high substrate ion-current densities (>5 mA/cm2). In order to evaluate the effects of ‘‘unbalancing’’ on the depositional environment, the plasma and magnetic field characteristics are related to TiN film microstructures, properties, and crystallographic orientations. Microstructural investigations performed using scanning electron microscopy and cross-section transmission electron microscopy have demonstrated that the films possess fine columnar grain structures with no observable layering, and they are very near full density at substrate bias potentials of −85 V and less.
Particulate release from surfaces exposed to a plasma
Authors: Goree J. , Sheridan T. E.
Published: July 2002

Contamination can occur during plasma processing when micrometer-size particulates fall from vacuum vessel walls onto a wafer. In situ light-scattering measurements show how particulates are shed from walls. Using a test surface coated with micron-size particles, we find that when a plasma is turned on, particulates are released rapidly, and when it is turned off, this release stops. This proves that plasma exposure causes particulate shedding. The rate of dust shedding increases with plasma density. The inventory of dust on the surface decays exponentially in time, with a time constant ≊102 s in our experiment, for plasma densities of ≊1014 m−3. Particulates become negatively charged due to the flux of electrons and ions onto the surface and are then pulled off the surface by the electric field in the plasma sheath. An individual dust grain is shed when its charge Q becomes sufficiently negative.
Kinetic oscillations in the Pt(100)/NO+CO system: Bifurcation analysis
Authors: Fink Th. , Krischer K. , Imbihl R.
Published: July 2002

Under isothermal conditions at low pressure (10−6 mbar), the NO+CO reaction on Pt(100) exhibits oscillatory changes in the N2 and CO2 product partial pressures. A three-variable model based on the vacant-site requirement for NO dissociation has been formulated and analyzed by means of bifurcation theory. The constants used in the differential equations were all taken from experiment. The stability of the steady state and periodic solutions has been mapped out in one and two parameters. Kinetic oscillations were found to occur in two separate existence ranges: a large one above the stoichiometric ratio pNO:pCO = 1:1 and a very small one below the stoichiometric point. The results demonstrate that the gross features of the experimentally observed oscillations are well reproduced by the model. The role of the internal parameters of the model was also analyzed with bifurcation theory. It was found that the model reacts most sensitively to those parameters which control the dissociation of NO. The fact that oscillations were only found on Pt(100) but not on Pt(111) and Pt(110) can be attributed to the lower dissociation efficiency of NO on the latter two orientations.
Structure of the Ni–p(1×2)-H surface from time-of-flight scattering and recoiling spectrometry
Authors: Roux C. D. , Bu H. , Rabalais J. W.
Published: July 2002

The structure of the Ni{110}–p(1×2)-H surface in the range 310–350 K has been investigated by time-of-flight scattering and recoiling spectrometry. The surface reconstruction was probed by monitoring the scattered Ne flux resulting from a 4 keV Ne+ beam impinging on the sample as a function of the crystal azimuthal angle. These results along with marlowe simulations indicate a missing-row type of reconstruction in which every other 〈11̄0〉 first layer nickel row is missing. The hydrogen adsorption site was studied by monitoring the hydrogen recoil flux generated by 2–5 keV Ar+ and Ne+ beams. Shadow cone calculations indicate that hydrogen is localized and resides in the pseudo-threefold sites. The coordinates of this site were determined to be 1.56±0.12 Å from the 〈11̄0〉 first layer nickel rows and 0.21±0.12 Å above the surface.
Extended x-ray absorption fine structure and x-ray standing wave study of the clean InP(110) surface relaxation
Authors: Woicik J. C. , Kendelewicz T. , Miyano K. E. , Cowan P. L. , Richter M. , Karlin B. A. , Bouldin C. E. , Pianetta P. , Spicer W. E.
Published: July 2002

Through a unique combination of surface sensitive extended x-ray absorption fine structure (EXAFS) and x-ray standing waves (XSW), we have determined the pertinent structural parameters of the clean InP(110) surface reconstruction. We find a rotation angle of 27° between the P–In chains, no change of the first neighbor P–In bond length, and a small but measurable, ∼0.1 Å, expansion of the average P–P second neighbor distance. The general application of the EXAFS and XSW techniques to the study of clean surfaces will be discussed.
Wetting transition on vicinal surfaces of Si(100)
Authors: Salanon B. , Barbier L. , Lapujoulade J.
Published: July 2002

Vicinal Si(100) surfaces exhibit a reconstruction with double or single steps depending on miscut and temperature. For given miscut angles the nature of the transition is investigated using a full step–step interaction. The system is described by a one-dimensional potential and a transition of the second-order wetting type as defined by Chui and Weeks is obtained. Due to the finite size of the terraces, the transition appears smeared and a strong mixing of double and single steps is found over a wide temperature range in the critical region in agreement with experimental observations.