bluuebunny/crossref_metadata_2025 huggingface dataset:
Condensation coefficient measurements of H2O, N2O, and CO2
Authors: Bryson C. E. , Cazcarra V. , Levenson L. L.
Published: July 2002

A molecular beam was used in conjunction with quartz microbalances to measure the condensation coefficients, γ, of H2O, N2O, and CO2. This ratio, γ, was observed to be a function of the beam temperature, incident flux, and the time that the surface was exposed to the beam, as well as of the surface temperature. Problems associated with the definition of γ are discussed in attempts to explain the data. The range of γ observed was 0.5–0.995.
Vacuum microbalance investigations on heterogeneous surface reaction mechanisms
Authors: Grunze M. , Hirschwald W.
Published: July 2002

A vacuum apparatus including a microbalance and a gas-inlet system was designed. The microbalance had two symmetric reaction tubes which were heated with temperature-controlled furnaces. A cooling trap was built into the tubes above the furnaces to freeze out the reaction products. Thus, the thermodynamical equilibrium of the reaction and the reflection of the products from the tubewalls was avoided and the kinetics of the reaction could be studied. With the totally symmetric design, thermodiffusion of the reaction gas and other disturbances caused by thermal gasflow were minimized. Electrostatic effects were suppressed by a special grounding device inside the reaction tubes. The reduction of zinc oxide powder, pellets, and single crystals with carbon monoxide and hydrogen was studied in the temperature range of 450–950 °C and pressure range from 10−2 to 5 Torr.
Evidence for a mobility edge in inversion layers. II
Authors: Stern Frank
Published: July 2002

Potential fluctuations in inversion layers at semiconductor-insulator interfaces are expected to give rise to a mobility edge separating localized from delocalized states. Recent experimental and theoretical work on this subject is briefly described.
Electrical conduction studies of plasma enhanced chemical vapor deposited silicon nitride films
Authors: Bose Mohua , Basa D. K. , Bose D. N.
Published: July 2002

Current conduction mechanisms have been studied for three representative films, namely, silicon-rich, nearly stoichiometric and nitrogen-rich silicon nitride films, prepared by rf glow-discharge decomposition of silane and ammonia with nitrogen dilution. Ohmic conduction has been observed for all the films at low electric fields. The dominance of Poole–Frenkel conduction at intermediate fields and Fowler–Nordheim conduction at high fields has been observed both for the nitrogen-rich and the nearly stoichiometric films. However, for the silicon-rich films, the Poole–Frenkel conduction mechanism dominates both for the intermediate as well as the higher fields. This study indicates that the silicon-rich films have the highest density of traps and the nitrogen-rich films have the lowest, which may be ascribed to the effect of nitrogen dilution.
Investigations of surface reactions during C2F6 plasma etching of SiO2 with equipment and feature scale models
Authors: Zhang Da , Kushner Mark J.
Published: July 2002

During fluorocarbon plasma etching of SiO2, a polymer passivation layer is generally deposited on the surface of the wafer. The polymer layer regulates the etch by limiting the availability of activation energy and reactants, and providing the fuel for removal of oxygen. To investigate these processes, a surface reaction mechanism for fluorocarbon plasma etching of SiO2 has been developed. The mechanism describes the polymerization process as resulting from neutral sticking, ion sputtering, F atom etching, and low-energy ion assisted deposition. The etch mechanism is a multistep passivation process which results in consumption of both the polymer and the wafer. The surface mechanism was incorporated into an equipment scale simulator to investigate the properties of SiO2 etching in an inductively coupled C2F6 discharge, and predicts that the SiO2 etch rate saturates at high substrate biases due to the depletion of passivation. Experimental results for SiO2 etch rates and selectivity of SiO2 over Si as a function of substrate bias were well reproduced. The blanket reaction mechanism was also employed in a feature scale simulator to investigate high aspect ratio (HAR) trench topography. Results from the feature scale model showed that strong sidewall passivation leads to tapered profiles in HAR SiO2 etching. The incident ion energy and the ratio of the passivating neutral to ion fluxes largely determine the degree of the taper or bowing. Profile control can be obtained by regulating this ratio, with one such method being argon dilution.
High resolution electron energy loss spectroscopy investigation of plasma-modified polystyrene surfaces
Authors: Wild S. , Kesmodel L. L.
Published: July 2002

The plasma modification of polystyrene with low pressures of nitrogen, ammonia, and oxygen has been studied by high-resolution electron energy loss spectroscopy. The method is shown to be capable of detecting nitrogen incorporation by variations in NH stretching band intensity and oxygen incorporation by carbonyl related bands. The method is particularly sensitive to loss of aromaticity as seen by evolution of the aromatic and aliphatic CH stretching band intensities.
Corrosion resistance of chromium nitride on low alloy steels by cathodic arc deposition
Authors: Han S. , Lin J. H. , Wang D. Y. , Lu F.-H. , Shih H. C.
Published: July 2002

The electrochemical behavior of deposited chromium nitride (CrN) coatings on steel has been investigated in this study. The CrN coatings were prepared by using a reactive cathodic arc plasma deposition technology in an industrial scale. The microstructure and its crystallinity of the chromium nitride have been studied using x-ray diffraction and cross-sectional transmission electron microscopy. The CrN coatings exhibit a microcolumnar morphology. The aqueous corrosion behavior of the coatings was evaluated in a saline (3% NaCl solution) environment in terms of open-circuit potentials and polarization resistance (Rp) resulting from electrochemical impedance spectroscopy. The results indicated that the CrN coatings are nobler than the uncoated steel and the Rp of the CrN coatings is at least one order of magnitude higher than that of uncoated steel. However, the Rp of the CrN coatings tend to decrease with immersion duration, showing that the corrosion changes from charge transfer to diffusion controlled, especially when the immersion time is long enough.
Pulsed laser deposition of zinc oxide luminescent thin films
Authors: Wei Jue , Zhang Binglin , Yao Ning , Wang Xiaoping , Ma Huizhong , Wang Shiming
Published: July 2002

Zinc oxide (ZnO) luminescent thin films have been prepared on ITO-glass substrates by pulsed laser deposition with a KrF excimer laser. We investigated the luminance of the ZnO films depending on laser fluence and the effects of postannealing. We have tested the crystallinity of the samples by x-ray diffraction and analyzed the growth mechanism to explain high-quality ZnO luminescent thin-film preparation by adjusting laser fluence and postannealing treatment.
AlN-based film bulk acoustic resonator devices with W/SiO2 multilayers reflector for rf bandpass filter application
Authors: Kim Sang-Hee , Kim Jong-Heon , Park Hee-Dae , Yoon Giwan
Published: July 2002

In this article, a reactively sputtered aluminum nitride (AlN) piezoelectric film and its application for a film bulk acoustic resonator (FBAR) device are presented. The FBAR is composed of an AlN film sandwiched between top aluminum (Al) and bottom gold (Au) electrodes and an acoustic reflector block of SiO2/W stacked multilayers. Both the top and bottom electrodes are connected by a transmission line. The insertion loss (S21) and return loss (S11) were 6.1 and 37.19 dB, respectively. Using the empirical definition technique, the series resonance frequency (fs) and parallel resonance frequency (fp) were found to be 1.976 and 2.005 GHz, respectively. Based on these findings, the effective electromechanical coupling coefficient (Keff2) and the quality factor (Q) were also obtained as 3.53% and 4261, respectively.
Self-cleaning and antifogging effects of TiO2 films prepared by radio frequency magnetron sputtering
Authors: Zeman P. , Takabayashi S.
Published: July 2002

The article reports on the correlation between the structure, the surface morphology, and the photocatalytic behavior of transparent TiO2 films prepared at different total pressures and oxygen partial pressures. The reactive deposition process was conducted in a mixture of Ar and O2 on unheated glass substrate using a rf magnetron sputtering system. The film structure and the surface morphology were investigated by x-ray diffraction and scanning electron microscopy, respectively. The photocatalytic behavior was studied by the measurement of the decomposition of methylene blue and the reduction of the contact angle between water and TiO2 under ultraviolet irradiation. The experiments showed that the photocatalytic properties accompany the changes in the structure and the surface morphology. The phase conversion from the rutile to the anatase TiO2 film leads to an increase in the photocatalytic activity. The rutile films prepared at lower total pressures are characterized by a very low decomposition efficiency and a contact angle about 42° after irradiation. On the contrary, the anatase films with the best photocatalytic behavior are prepared at higher total pressures (>1.50 Pa) and characterized by a high decomposition efficiency, a contact angle about 10° after irradiation, and a good stability in darkness. Such anatase films possess the surface morphology of a lower density, a higher surface roughness, and a larger surface area. Moreover, the TiO2 films deposited in the transition sputtering mode showed a lower decomposition efficiency. The TiO2 films prepared in the reactive mode at the same total pressure exhibited the similar photocatalytic behavior with small variations only.
Low-bias, high-temperature performance of a normal-incidence InAs/GaAs vertical quantum-dot infrared photodetector with a current-blocking barrier
Authors: Stiff-Roberts A. D. , Krishna S. , Bhattacharya P. , Kennerly S.
Published: July 2002

The growth, fabrication, and characterization of a low-bias, high-temperature, InAs/GaAs vertical quantum dot infrared photodetector with a single Al0.3Ga0.7As current-blocking barrier are described and discussed. A specific detectivity ≈3×109 cm Hz1/2/W is measured at normal incidence for a detector temperature of 100 K at a bias of 0.2 V, and detector characteristics are measured for temperatures as high as 150 K. The equivalence of the activation energy and photoionization energy for thermionic emission in quantum dots is also verified. The superior low bias performance of the photodetector ensures its compatibility with commercially available silicon read-out circuits necessary for the fabrication of a focal plane array.
Reactive pulsed laser deposition of high-k silicon dioxide and silicon oxynitride thin films for gate-dielectric applications
Authors: Desbiens E. , Dolbec R. , El Khakani M. A.
Published: July 2002

We have successfully developed two reactive pulsed laser deposition (PLD) processes for the growth of high-k SiO2 and SiOxNy thin films. At a KrF laser intensity of 3×108 W/cm2, both SiO2 and SiOxNy films have been deposited by ablating a silicon target in a reactive gas atmosphere (O2 and O2/N2 mixture, respectively) on both Si (100) and Pt-coated Si substrates. Two key issues are presented here, namely (i) the effect of the deposition temperature (Td in the 20–450 °C range) and (ii) the effect of the N incorporation (in the 0.3–20 at. % concentration range) on the microstructure and electrical properties of PLD SiO2 and SiOxNy thin films, respectively. For the PLD-SiO2 films, 300 °C has been identified as the optimal deposition temperature that yields stoichiometric ([O]/[Si]≈1.9), hydrogen-free films with a low local disorder, a highly dense microstructure and a dielectric constant (k) higher than that quoted for thermally grown SiO2. On the other hand, the PLD SiOxNy films containing 20 at. % of N have exhibited a dielectric constant as high as ∼7. A rather good agreement is obtained between the k values deduced from the Poole–Frenkel emission (PFE) model and those obtained from direct impedance measurements, confirming thereby that the PFE remains the predominant conduction mechanism in the PLD SiOxNy films.
Effect of polishing pretreatment on the fabrication of ordered nanopore arrays on aluminum foils by anodization
Authors: Wu M. T. , Leu I. C. , Hon M. H.
Published: July 2002

It is reported that a pretreatment step is required for the fabrication of ordered nanopore arrays on Al by anodization. In this study, one step anodization was carried out on the Al foils with different surface features that resulted from different polishing conditions. The effect of surface morphologies on their anodization characteristics was determined. When the nonelectropolished Al substrate was anodized, only limited-sized ordered domains could be obtained. Nearly perfect hexagonal close packed ordered pore arrays with domain size of about 2–4 μm could be obtained on the electropolished Al substrate even with different surface features due to different electropolishing conditions. In addition, the differences of current density for the electropolished and nonelectropolished substrates were affected by the distinct characteristics of the oxide. The increase of the oxidation current in the later stage of anodization was caused mainly by the breakdown of the oxide on the nonelectropolished substrates on which highly ordered pore arrays cannot be obtained.
Influence of resist components on image blur in a patterned positive-tone chemically amplified photoresist
Authors: Houle F. A. , Hinsberg W. D. , Sanchez M. I. , Hoffnagle J. A.
Published: July 2002

Post-exposure bake-induced blurring of the latent image in a chemically amplified photoresist may limit the extendibility of this resist technology to printing of nanoscale features. It had been proposed that blurring is caused by thermally assisted diffusion of photogenerated acid, however our experimental and kinetic modeling investigations of coupled reaction-diffusion in a resist system consisting of a photoacid generator in p-t-butyloxycarbonyloxystyrene (PTBOCST) have shown that the very high efficiency of acidolysis chemistry at the edge of an exposed region is actually responsible for blurring. Studies of the role of added base and the impact of photoacid generator size on blur support this view. These previous studies were performed with a one-dimensional (1D) geometry. In order to test the relevance of the 1D blurring model to pattern formation, we have carried out new investigations of blurring in dense line-space patterns using the same PTBOCST resist systems as in our earlier work. Resist films were imprinted with 866 and 192 nm pitch gratings generated by interferometric lithography using 257 nm light. The extent of deprotection over a range of doses and bake times at 85 °C was measured by infrared spectroscopy and compared to results of simulations of the bake process using the experimental aerial image and kinetics determined in the previous work. Experiment and predictions are in good agreement in all cases, indicating that the one-dimensional kinetics are extendable to the two-dimensional case. This simulations permit visualization of the relationship between the acid latent image and the developable image that forms in the polymer, enabling a deeper appreciation of the influences of the resist components and of resist processing conditions on latent image transformations during post-exposure bake.
Physisorption of Xenon and Krypton on Glass and on Molybdenum Films
Authors: Endow N. , Pasternak R. A.
Published: July 2002

Physisorption of room temperature xenon and krypton at low pressures (10−9−10−4 Torr) on Pyrex® and on molybdenum films at 77 ° and 87 °K has been investigated. The initial sticking probabilities are close to unity, and the adsorbate shows high surface mobility. The steady-state data, which can be shown to differ little from equilibrium data, fit the Polyani potential theory and the Dubinin-Radushkevich isotherm. For the films, the isotherm slopes (which are related to the isosteric heats of adsorption) increase with film age; for old films, they approach the values found for physisorption of xenon and krypton on Pyrex and on zirconium films. Constancy of isotherm slopes for argon on widely different adsorbents has been noted previously. Thus, the physisorption forces in these systems appear to be unrelated to specific properties of the sorbing surfaces, except in the case of highly porous adsorbents.
Electrostatic Charge Distribution on Ultrahigh Vacuum Cleaved Silicates
Authors: Grossman J. J.
Published: July 2002

Recent measurements of relatively strong long-range electrostatic attractive forces, produced by ultrahigh vacuum cleavage of silicates, prompted the design and fabrication of a special UHV system to measure the charge distributions. The system is described in this paper, together with preliminary results from the experiment. Charge distributions found to date have varied from dipolar to octapolar shapes on the face of cylindrical samples in excess of 1 esu/cm2. A relationship appears to exist between the orientation of the multipolar distributions and the crystallographic axes. Results from the first cleavages of orthoclase (nominally, KAlSi3O8) at 10−10 Torr indicate that there are at least two discharging mechanisms: first, the charge decays to one half its initial (extrapolated to zero) value in 1.5 h due to gas adsorption; second, it then decays very slowly with a half-life of at least 76 days. Irradiation with uv light causes discharge. When the pressure in the system is raised towards atmospheric with dry nitrogen, the charge is stable (to a first order of approximation) up to pressures in the 10-μ range. Discharge in bursts, as the pressure is raised, is readily explained by the Paschen sparking potential relation for gaseous discharges.
The transient current behavior of metal/amorphous Si/p−Si diodes
Authors: Mei L. , Greene J. E.
Published: July 2002

The transient current behavior of M/aSi/p−Si diodes was examined. The aSi layer was rf sputter−deposited and was approximately 1000−Å thick. It was established that properly annealed Sb/aSi contacts are both good electron injectors and good hole injectors. Thus, the reverse bias characteristics of Sb/aSi/p−Si diodes are controlled entirely by the aSi/p−Si junction. The transient current recovery time of these diodes was found to be too fast to measure (<10 nsec). Finally, the trap release rate in aSi was found to be on the order of microseconds for both electrons and holes.
Atomic structure of the annealed Ge(111) surface
Authors: Taubenblatt Marc , So Edward , Sih Philip , Kahn Antoine , Mark Peter
Published: July 2002

A model for the atomic structure of the annealed Ge(111) 2×8 surface is proposed on the basis of intensity measurements in which the fractional order beams are attributed to a ripplelike distortion of (at least) the top two double layers in a manner consistent with charge density wave (Peierls) instabilities or compresive stress deformations derived from distributed rehybridization. The distortion is similar to that suggested for the annealed Si(111) 7×7 surface from a similar analysis. The superlattice is actually an 8×8 unit cell; the observed 2×8 reconstruction follows from selected structure factor cancellations owing to the specific topography of the distortion.
Rate at which molecules strike a surface or orifice in a vacuum system
Authors: Edwards D.
Published: July 2002

It is shown for a spherical vacuum chamber with system pressure in the molecular flow region, that the rate per unit area at which molecules strike a surface or orifice is, in general, not 1/4 nva but depends on the molecule–wall scattering function, the classical result (1/4 nva) being obtained for a cosine wall scattering function.
AES and XPS of silicon nitride films of varying refractive indices
Authors: Wittberg T. N. , Hoenigman J. R. , Moddeman W. E. , Cothern C. R. , Gulett M. R.
Published: July 2002

AES and XPS measurements of silicon nitride films with refractive indices ranging from 1.93 to 2.08 have been made. The films studied were grown on silicon (100) substrates by CVD using varying mixtures of silane and ammonia. Earlier AES studies of similar silicon nitride films have suggested that these films are microscopic mixtures of Si and Si3N4. We present XPS data which show that there is no measurable ’’free’’ silicon (i.e. the level of ’’free’’ silicon is ≲3 at. %) in the silicon nitride films with refractive indices ≲2.02. AES data show an increase in oxygen content corresponding to a decrease in refractive index of the silicon nitride films. These AES measurements agree qualitatively with measurements of the physical properties of silicon oxynitride films.
Electron-beam fabrication of submicron gates for GaAs FET’s
Authors: Blocker T. G. , Macksey H. M. , Doerbeck F. H.
Published: July 2002

High-performance GaAs FET’s with nominal gate lengths of 0.5, 0.75, and 1.0 μm have been fabricated with electron-beam-lithography techniques. A hybrid process was developed which only required e-beam definition of the critical gate level and was otherwise compatible with the fabrication process developed for conventional optically defined gates. The source–drain metallization mask was modified to include alignment marks for the gate level and the source–drain metallization was augmented to give marks after alloying with acceptable secondary electron contrast against the GaAs background: ±2000 Å registration was routinely achieved over the 80×80 mil2 field. A test pattern which could be examined optically with rapid turnaround to determine the proper exposures for the various gate lengths was employed. The pattern evaluation was confirmed by resist exposure studies in conjunction with SEM examination. Evaluation of the test pattern together with corrections for the GaAs substrate backscatter and proximity effect allowed control of the gate lengths to ±10% over the entire slice. The gates were tapered at the mesa edge to prevent constriction of the resist over the step. The resist used was polymethyl methacrylate (PMMA) with a nominal thickness of 7500 Å and the developed pattern served as the lift-off mask for 4000–5000 Å of aluminum gate metallization. The nominal slice size used for these runs was slightly greater than 1 cm2 (420×420 mil2) and up to 588 devices were patterned in a single pumpdown. The exposure time required per slice, including stage step and alignment, was six minutes. Both small signal and power GaAs FET’s have been fabricated with e-beam defined gates. Small signal devices with 0.75μm gate lengths had 2.0 dB minimum noise figures with 10 dB gain at 9 GHz. Power devices with 4800-μm total gate width and 1-μm gate length had up to 4.1 W output power at 8 GHz with 4 dB gain.
Proximity effect in beam-addressed metal-oxide semiconductor memory
Authors: Parikh M. , Heritage M.
Published: July 2002

Electron scattering in a semiconductor target of a an electron-beam-addressed MOS memory can result in proximity effects between a number of adjoining memory locations (bits). As bit spacings decrease, there can be significant unintended charge accumulation in regions unirradiated by the electron beam. This can set a limit to usable bit packing density in the memory.
Measurement of valence band Auger spectra for GaAs(110) from Ga and As C
C
V transitions.
Authors: Davis G. D. , Lagally M. G.
Published: July 2002

The line shapes of the Ga and As M1M45V and M23M45V Auger transitions in cleaved GaAs(110) have been measured. The line shapes are quite different, indicating that the Auger effect gives a measure of the density of filled states local to the atomic species with the initial core hole. Comparisons with the calculated local density of states for one model of the GaAs(110) surface and with Auger transitions derived for this model are made. A total transition density of filled states is synthesized by adding the Ga and As results and is compared with photoelectron spectroscopic measurements. The resulting good agreement indicates that hole–hole interactions are not severe in this system.
Ultrathin metal oxide layers by reactive sputtering: their controlled deposition and characterization
Authors: Reith T. M. , Ficalora P. J.
Published: July 2002

A method of controllably sputter depositing ultrathin metal oxide layers has been developed. First, a target oxidation run is performed in Ar/O2 during which an equilibrium oxide forms on the sputter target. Then the oxide material is nonreactively sputter deposited onto the substrate in pure Ar. The thickness of the target oxide, and hence the subsequently deposited films, can be varied by parametric changes in the sputter system. A correlation has been made between the formation and subsequent deposition of the target oxide and the behavior of the O2 peak as a function of time as measured by residual gas analysis (RGA). The physical presence of these layers has been inferred directly using Auger electron spectroscopy (AES) sputter profiling, and their impact on current transport at rectifying metal–silicon interfaces has been assessed by I–V characterization.
Angular-dependent ultraviolet photoemission spectroscopy of polycrystalline films: A probe of surface electronic structure
Authors: Kowalczyk S. P.
Published: July 2002

Angle-resolved ultraviolet photoemission (ARUPS) studies of polycrystalline noble metal are reported. In polycrystalline films, the electron exit angle with respect to the crystalline axes is averaged over, thus variation of the electron polar (exit) angle should result in variation of surface sensitivity. This work represents the first application of ARUPS with low-exit-angle geometries for the investigation of surface electronic structure. The main results are that Cu exhibits considerable (∠17%) d-band narrowing at the bottom of the d-band at the surface, while the effects in Ag and Au appear to be much smaller.
Cryogenic versus turbomolecular pumping in a sputtering application
Authors: Dennison R. W. , Gray G. R.
Published: July 2002

Performance comparisons were made using a quadrupole mass spectrometer between nominal 1000 l/s turbomolecular and cryogenic high vacuum pumps on a commercially available sputter deposition system. The quadrupole analyzer was mounted in a differentially ion-getter-pumped sampling chamber to allow gas analysis at sputtering pressures. The cryogenic pump without liquid nitrogen trapping showed pumpdown performance comparable to the turbomolecular pump with liquid nitrogen trapping. We were unable to get repeatable meaningful results of residual gas behavior during sputtering operations when argon was let into the ion-getter-pumped sampling chamber. We have concluded that the 20 l/s ion-getter pump should be replaced with a pump capable of stably handling argon gas loads during sputtering.
Cryogenic pumping of helium, hydrogen, and a 90% hydrogen–10% helium mixture
Authors: Dillow C. F. , Palacios J.
Published: July 2002

An experimental program to measure the pumping speed of an Excalibur CVV2008 liquid helium cryosorption pump is described. Pumping speeds are reported for helium, hydrogen, and a 90% hydrogen –10% helium mixture in the pressure range 1×10−7–1×10−4 Torr. The helium pumping speed at 2×10−7 Torr was 3.2 l/s cm2, but decreased with loading to 1.6 l/s cm2 at 6×10−5 Torr. Attempts to operate at higher helium fluxes (Q≳8×10−5 sccm/s cm2) resulted in pressure and eventually thermal instabilities. The pumping speed of hydrogen at 5×10−7 Torr was 4.9 l/s cm2 and increased with pressure to 7.7 l/s cm2 at 5.5×10−6 Torr. For a 90% hydrogen–10% helium mixture, pumping speeds were inconsistent, varying between 1.4 and 5.6 l/s cm2. Residual gas analysis provided some insight into this behavior and these results are discussed.
Residual gas analysis in the ISX-A tokamak
Authors: Simpkins J. E. , Colchin R. J. , Overbey D. R.
Published: July 2002

A computer-controlled mass analyzer was utilized to observe the residual gases in the ISX-A tokamak. This residual gas analysis (RGA) system enabled time resolved measurements of preselected m/e peak heights to be made during and after tokamak discharges. Routine mass scans were also made and displayed in the form of semilogarithmic plots of partial pressure (Torr) versus m/e. Wall conditioning of the stainless steel torus consisted of hydrogen discharge cleaning and titanium gettering, which ultimately produced gauge pressures on the order of 10−8 and 10−9 Torr, respectively. The dominant plasma impurities, carbon and oxygen, were observed by the RGA as light hydrocarbons and water vapor. Entrapment of deuterium by the walls was investigated by monitoring the residual D2 content after the working gas was changed to H2. The effective nuclear charge (Zeff) was found to be proportional to the residual contaminants measured by the RGA immediately following a discharge.
Monitoring secondary ions during ion etching
Authors: Hosaka Sumio , Sakudo Noriyuki , Hashimoto Seiya
Published: July 2002

Impurity contamination on etched surfaces and controllability of ion etching are important for the application of ion beam etching. In this paper, the feasibility of detecting and monitoring secondary ions emitted from the etched surface during ion etching are investigated. The experimental apparatus is composed of an improved mass filter of the quadrupole type together with a conventional ion beam etching system equipped with a Kaufman-type ion source. Experiments are carried out to detect secondary ions, examine impurity contamination, and monitor layer interfaces. A collimator and an energy filter are placed in front of the conventional quadrupole mass filter because of the large diameter ion beam. Consequently, redeposition of sputtered atoms on the sample surface is clearly observed, and the layer interfaces are monitored.
Modifications to PbTe surfaces and their interactions with oxygen produced by localized electron irradiation
Authors: McGlashan S. R. L. , King R. M. , Parker E. H. C.
Published: July 2002

The effects of localized electron irradiation of the (111) surface of PbTe are described. These studies show that fast surface diffusion processes considerably extend the lateral range of electron induced effects. The modifications that occurred over a relatively large surface area were compositional, in doping levels in the underlying material and in oxygen sorption mechanisms. The irradiated surface effectively passivated the underlying material against much of its normally strong interactions with oxygen which involve conduction and valence band electrons. A model is set up to account for these observations.
Contamination effects in thermally evaporated films of iron and iron oxide
Authors: Sundgren J.–E. , Nath P. , Nilsson H. T. G. , Söder S.
Published: July 2002

Iron and iron oxide have been evaporated, in an oil diffusion pump system, at a pressure of ∠5×10−6 Torr, onto substrates maintained at temperatures ranging from 200 to 700 K. The films have been characterized by Auger electron spectroscopy, transmission electron microscopy, electrom and x-ray diffraction, and measurements of the microhardness. Whereas the iron films are found to be contaminated with carbon and oxygen, the films obtained from evaporation of iron oxide are contaminated with tungsten. No change in contamination content with substrate temperature is found for any of the two systems. From the AES spectra it is seen that the carbon in the iron films is in carbide form and the tungsten in the evaported iron oxide films is oxidized. The origin of these contaminations and their effects on the microstructure and mechanical properties are discussed.
Aligned multilayer structure generation by electron microprojection
Authors: Frosien J. , Lischke B. , Anger K.
Published: July 2002

Electron microprojection allows the fast transfer of structures with high resolution. Using a projector with a 1:4 image scale, a resolution of 0.3 μm across an 8×8 mm image field is experimentally obtained. The development of a novel alignment technique assures the superposition of several mask levels with an alignment accuracy better than 0.1 μm.
Angle-resolved and variable impact energy electron vibrational excitation spectroscopy of molecules adsorbed on surfaces
Authors: Ho W. , DiNardo N. J. , Plummer E. W.
Published: July 2002

Discrete energy losses occur when a beam of low energy electrons (<30 eV) is scattered from surfaces. For a gas–solid interface, inelastic scattering can occur through excitation of molecular vibrations. Chemical identification, molecular structures and bonding sites can be inferred from the energies of the characteristic losses. The angle and impact energy dependence of the mode intensity can give additional information which in many cases further elucidates the bonding. A consistent picture of the vibrational excitation mechanisms is derived which leads to the identification of helpful selection rules. Discussion will center on the simplest chemical adsorbate of H on W(100) and Ni(111). The application of the basic ideas to diatomic and polyatomic adsorbates will be mentioned briefly.
Stability and reactivity of (5×20) and (1×1) Pt(100) surfaces
Authors: Norton P. R. , Creber D. K. , Davies J. A.
Published: July 2002

Pt(100)–(5×20) adsorbs hydrogen to significant coverages only below T∠260 K. At ∠190 K the coverage is sufficient to produce a LEED pattern with very strong integral order beam but some weak fractional order beams are visible. For the present purposes this pattern is designated (1×1). The most strongly adsorbed hydrogen species do not desorb from the (1×1) surface below ∠380–390 K. The difference in behavior between the (5×20) and (1×1) surfaces is attributed to a ∠30% decrease in the heat of adsorption of hydrogen on the (5×20) compared to the (1×1) surface. At 120 K both surfaces exhibit similar initial sticking coefficients. The absolute coverages of adsorbed D at 195 K were measured by nuclear microanalysis. Argon-ion-induced damage increases the temperature at which the (1×1) surface reconstructs such that at doses exceeding 3×1015 Ar+ cm−2 (5 keV), the surface does not reconstruct below 770 K. This appears to be the temperature at which the random step structure, indicated by the LEED data, anneals out. In the presence of adsorbed H, a dose of only 2×1014 Ar+ cm−2 (5 keV) increases the phase (1×1)→(5×20) transition temperature to ≳ 390 K (from ∠350 K for an undamaged surface), so that it is possible to desorb the hydrogen leaving a clean (1×1) surface. A sputtered surface (∠5×1014 Ar+ cm−2; 5 keV) was examined by Rutherford backscattering and less than 2×1014 Pt cm−2 were displaced from their bulk lattice positions.
Oxide and interface properties of anodic films on Hg1−xCdxTe
Authors: Sun T. S. , Buchner S. P. , Byer N. E.
Published: July 2002

The oxide and interface properties of a 1200 Å anodic film on Hg0.8Cd0.2Te were studied by means of x-ray photoelectron spectroscopy (XPS) and capacitance voltage (C–V)a measurements on a metal–insulator–semiconductor (MIS) capacitance. The XPS results showed that the elemental composition of the anodic oxide is 59% O, 24% Te, 14% Cd, and 3% Hg. With the support of other experimental evidence, the anodic oxide was assigned a heterogeneous oxide of 58% CdTeO3, 19% TeO2, and 13% HgTeO3. A depth profile of the interface region, performed with the aid of Ar+ sputtering, revealed a significant depletion of Hg in the semiconductor side. These results are inconsistent with the recent model of the same oxide/semiconductor system, proposed by Nemirovksy and Finkman. The C–V curves from MIS measurements exhibited a large hysteresis indicative of a high concentration of positive–charge traps in the oxide, and characteristics indicative of a high density of surface states in the semiconductor surface region. A tentative model of the oxide and interface properties of this system was derived by combining the results of these two analyses. In addition, effects of the electron beam and of ion sputtering on this material are discussed.
Science, technology, and the future
Authors: Alpert Daniel
Published: July 2002

A relatively small community of scientists, many in industrial laboratories, made basic contributions to vacuum science and technology in the 1950s and set the stage for the remarkably diverse and sophisticated AVS activities of today. Then as now, few scientists or engineers could predict the future with accuracy; but they had great confidence in their ability to make the future—and then to remake it if things didn’t turn out just right. The society at large shared this optimism and looked to science and technology as the keys to progress and prosperity. In contrast to the widespread confidence of the 50s and early 60s, the world of today is confused, concerned, and ambivalent about the role of science and technology in addressing human needs. There is a widespread preoccupation with the unintended negative consequences of science-based technology, typified by threats to privacy, to the environment, to the economy, and to human survival itself. Citizens are no longer persuaded that what is good for science is necessarily good for society; nor do they trust the traditional ways of making technological decisions. The modern R&D laboratory has provided the infrastructure for developing and managing science-based technology and relating it to the marketplace—to the economic process. Obviously, we have not as yet developed adequate infrastructures for relating science and technology to the political process. In recent years, however, we have been gradually developing a set of intellectual tools, broadly identified under the heading of ’’policy analysis,’’ that help policy-makers as well as the public at large to understand and deal with complex problem issues of our times. The development of equitable and informed procedures is necessarily an evolutionary process. While significant progress has been made, there is still widespread ignorance of the methodologies and their limits, the organizational structures in which policy analysis is effectively carried out, and ways of evaluating the policy development process. The process of technological choice in a democracy is a continuous one, occasioned by literally millions of economic and political decisions; and virtually every scientist and engineer in America is a part of this process. Thus the kind of future we shall have depends to an important degree on how effectively and responsibly we participate.
Effects of annealing in Hg vapor on the properties of rf-sputtered thin films of (Hg1−xCdx)Te
Authors: Cornely R. H. , Suchow L. , Mulligan M. , Chan T.-O. , Haq R. , Mehta C.
Published: July 2002

(Hg1−xCdx)Te films were prepared by rf triode-sputtering in a 1 to 2 μm Hg atmosphere on high resistivity Si and CdTe substrates with (111) surface orientation. Sputtering targets made by cold-pressing homogenized mixtures of HgTe and CdTe powders were used to obtain films with compositional parameters of x = 0.18, 0.23, and 0.25. Films deposited with 1.2–2 μm Hg on substrates at either 250° or 300°C were usually n-type with electron mobilities up to 1.4×103 cm2/V-s and carrier concentrations between 5.0×1015 and 1.2×1018cm−3 at −183°C. Mobility values at 25°C were 10% to 50% lower and carrier concentrations were in the 1–100×1016cm−3 range. The films were polycrystalline with 100% (111) orientation. Films on Si substrates were annealed in quartz ampoules in a two-zone furnace at 350°C under a Hg pressure of 17 mm. With these unoptimized annealing parameters, the mobilities at 25° and −188°C were significantly increased. The best result was an increase from 1.0×103 to 8.5×103 at 25°C and from 1.4×103 to 24×103 at −188°C with the carrier concentration decreasing from 4.0×1017 to 5.4×1016cm−3 at −188°C. Peeling caused by thermal stress was encountered and minimized by using small area films and raising the temperature slowly to the maximum annealing value.
A novel technique for metal–silicide formation
Authors: Padmanabhan K. R. , So/rensen G.
Published: July 2002

The formation of noble-metal silicides on a substrate of silicon single crystals was studied by a novel experimental technique. Halides of metals such as palladium, platinum, and rhodium were deposited as a thin film on the substrate from a liquid organic solution. The halide film was then decomposed by ionic bombardment with ion beams in the 50–500-keV energy range, yielding a surface-metal and metal–silicide layer. The composition and structure of the surface layers were investigated by means of Rutherford-backscattering and x-ray diffraction techniques. The experimental parameters of this ion-beam-plating technique will be discussed. Further, the present results will be compared with those obtained by conventional techniques for metal silicides with respect to consumption of the noble metals and adhesion to the substrate surface.
Interferometric measurements of multilayer and double-shell inertial fusion targets
Authors: Weinstein B. W. , Weir J. T. , Willenborg D. L.
Published: July 2002

Optical interference microscopy plays an important role in the measurement of targets for inertial confinement fusion experiments. We describe how these techniques are applied to the measurement of thickness and refractive index of multilayer films on both flat substrates and microsphere targets. We also discuss procedures for manipulating and examining microsphere targets to measure surface defects and wall thickness variations anywhere on the target. Finally, we describe the use of optical interferometry to measure the individual components and final assembled structure of double-shell targets. The accuracy of these measurements is from 0.03 to 0.05 μm, depending on the specific application.
Gas release studies from explosion-cladded materials
Authors: Craig J. H.
Published: July 2002

Gas release studies have been conducted on five explosion cladded materials which are of potential use in protection of fusion reactor first wall components. Both one and two layer claddings on OFHC Cu were studied at room temperature, 100 °, and 250 °C. Total outgassing rate and mass analysis experiments were conducted. For purposes of comparison, a 304 LN stainless steel sample was also analyzed. Results indicated comparable outgassing rates for the stainless steel and cladded samples at room temperature, but substantially higher outgassing rates at 250 °C for the cladded samples.
Acoustic microscopy for ICF target analysis
Authors: Bongianni W. L.
Published: July 2002

By 1982, 10 μm walled targets will require thickness and diameter tolerances of better than ±100 Å over spot dimensions of 10–100 μm. Such targets will be multishell and/or opaque which eliminates optical phase microscopy and severely limits x-ray analysis. In principal, an acoustic phase microscope can provide the necessary resolution, provided the acoustic beam can be coupled to, and focused within, the confines of the wall. In this paper, a shear wave acoustic microscope with an electronically variable focal length is described. A computer code has been used to study the ray optics and diffraction of this design and a spot size with the required dimensions has been obtained.
Electronic states of Si(111) surfaces
Authors: Houzay F. , Guichar G. M. , Pinchaux R. , Petroff Y.
Published: July 2002

The purpose of this paper is to review recent angle resolved photoemission measurements on cleaved 2×1 and 7×7 reconstructed surfaces using the polarization properties of synchrotron radiation. The similarity of the results for the two reconstructions (weak or no metallic edge, symmetry of the dangling bond surface state) will be discussed as a function of the different theoretical models.
Si(111): Ni surface studies by AES, UPS, LEED, and ion scattering
Authors: Chabal Y. J. , Culbertson R. J. , Feldman L. C. , Rowe J. E.
Published: July 2002

We have studied the Si(111) surface after various heat treatments with small amounts of Ni (?1 monolayer) present. We find that three types of reconstructions can be obtained: 7×7, ’’1×1’’ and √19×√19. Photoemission spectra show that the metallic nature of the dangling bond surface state, characteristic of the clean 7×7 surface, disappears for the ’’1×1’’ and √19×√19 surfaces. MeV ion scattering establishes that the average surface atom displacement parallel to the surface is significantly larger for the √19×√19 surface than for both the clean 7×7 and the ’’1×1’’ surfaces.
GaAs Schottky light emitters for the study of surface avalanching and electroluminescence
Authors: Adachi H. , Hartnagel H. L.
Published: July 2002

In connection with many operational aspects of surface-based GaAs devices, such as the lifetime of MESFETS,1 it is useful to explore simple possibilities of surface tests. Here, the observed light emission along the periphery of Schottky contacts on GaAs is investigated in view of such an analytical test facility. Additionally, it should be noted that one has the possibility of studying the surface effects on the two relevant phenomena responsible for this light emission: avalanching due to electrons or holes, electroluminescence due to hot charge carriers. We initially present the essential experimental data, then adopt the theory of Wolff 2 for our system of light emission, and finally present additional experimental observations and use them to suggest further efforts on this subject.
Advanced deflection concept for large area, high resolution e-beam lithography
Authors: Pfeiffer H. C. , Langner G. O.
Published: July 2002

A novel deflection system has been developed which essentially eliminates off-axis aberrations including the transverse chromatic aberrations by employing a variable axis lens (VAL) which shifts the electron optical axis in synchronism with the deflected beam. The system comprises two precision pole piece lenses to achieve telecentricity, two composite predeflection yokes, and two yokes positioned in the pole piece region of the final lens. The field of the latter yokes satisfies the condition for shifting the electron optical axis by the distance r. This condition is 1B(y)r(z) = 1/2 B(L) (z)r, where B(y)r denotes the deflection field of the yoke in the r direction, and B(L) the lens field on the geometrical lens axis. To successfully utilize this concept, higher order terms of the field expansions have been included in the field matching by designing yokes which satisfy first and third order conditions and dynamic focus correction coils whose field is proportional to B\\(L) (z). The theoretical analysis of the VAL concept will be discussed together with experimental results demonstrating proper shift of the electron optical axis through elimination of transverse chromatic aberrations and coma.
Surface analysis of severely corroded coal liquefaction vessel components and model laboratory films
Authors: Shalvoy R. B. , Davis B. H. , Freeman G. B. , Sagüés A. A.
Published: July 2002

When a high chloride content coal was run in the Wilsonville, Alabama Solvent Refined Coal (SRC) pilot plant, an unusually high rate of corrosion was observed in parts of a distillation tower. Appreciable corrosion was not observed during prior operation with lower chloride content coals. Corroded components were examined with ESCA with a goal of understanding the source and mechanism of the rapid corrosion. Process conditions were modeled in the IMMR laboratory with the goal of isolating the critical factors responsible for the severe corrosion. The addition of NH4Cl to low corrosivity SRC liquids resulted in severe corrosion of test samples. Films forming on the test samples and the surfaces of components taken from the corroded areas of the SRC vessel had similar spectra suggesting that the laboratory experiment had duplicated the conditions leading to severe corrosion in the SRC tower. The consequences of a low level of chlorine in the components and the film are discussed. Depth profiles revelaed a surface depletion of Fe and Cr in the samples. Possible corrosion mechanisms are considered.