bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhancement of electron spectroscopy for chemical analysis of surface silanol in silicon nitride through chemical derivatization
Authors: Dang Tuan A. , Gnanasekaran Ramaswamy
Published: July 2002

The surface silanol on Si3N4 can be successfully determined by reaction of the OH group with tridecafluoro–1,1,2,2–tetrahydrooctyl–1–1–trichlorosilane and subsequent electron spectroscopy for chemical analysis for F. The technique offers both specificity and very high sensitivity. It also has certain advantages over diffuse reflectance infrared Fourier transform, including more surface probing, better quantification, and a significantly lower detection limit.
Dynamical studies of the interaction of D2 with a Cu(111) surface
Authors: Rettner C. T. , Auerbach D. J. , Michelsen H. A.
Published: July 2002

We have used molecular beam techniques to study the dynamics of adsorption and desorption in the D2/Cu(111) system. We have determined the adsorption probability S0 for beams with kinetic energies Ei up to 0.85 eV, vibrational temperatures up to 2100 K, and incidence angles from 0° to 60°. At a surface temperature Ts of 120 K, S0 increases from below 10−6 to 0.34 over the range studied. A detailed analysis provides estimated adsorption functions for each vibrational state. Angular distributions for desorption with Ts in the range 370–800 K are strongly peaked and symmetric about the surface normal in every case. These distributions are well described by a cos12 θf distribution at 600 K, being slightly narrower at 400 K and slightly broader at 800 K. Calculations using the principle of detailed balance to calculate these angular distributions based on the dependence of the adsorption probability on incidence energy and angle are not in perfect agreement with observations. In fact, we find that desorption measurements made over a range of surface temperatures cannot be adequately accounted for by any single function of the sticking probability on the incidence energy and angle. Rather, it is found necessary to allow this function to vary slightly with surface temperature.
Report on plenary meeting of the International Standards Organization Technical Committee 112 on vacuum standards
Authors: Hauschulz Dana S.
Published: July 2002

The International Standards Organization Technical Committee 112 (ISO/TC 112) held a plenary meeting in Moscow, USSR 15–19 April 1991. This is the first such meeting since 1972. Delegations from China, Germany, Japan, Switzerland, United States, and the USSR were present. Dana Hauschulz served as the delegate from the United States. The function of ISO/TC 112 is standardization in the field of vacuum technology both in the area of apparatus (essential characteristics, dimensions, and materials) and in the area of definitions and methods of measurement. The five resolutions adopted at this meeting pertain to ultrahigh vacuum gauging, leak detection, vacuum materials and cleaning, and vacuum pumps. These are fully described in this report. Currently, the United States has only observer status on this committee. However, in view of a resurgence of activity by this international standards body and in recognition of movement towards a global economy, the American Vacuum Society board of directors has authorized the pursuit of an active role in this international committee. The means for securing this involvement are also explained.
Innovations in helium leak detector systems
Authors: Bergquist Lyle E. , Sasaki Y. Tito
Published: July 2002

Innovations in helium leak detection systems have made it possible to detect leaks many decades smaller than previously thought existed. Several units of ultrasensitive leak detectors are routinely detecting leaks as small as 1 × 10−15 atm cc He/s. These ultrasensitive leak detectors are proving their worth in the quality control of infrared imaging sensor Dewars and in determining ultrahigh vacuum (UHV) performance characteristics of prototype hardware. Other innovations enable measurement of both gross leaks and fine leaks of microelectronics packages. A large leak from a 0.015-in.-diam hole in a 0.25-cc device as well as fine leaks down to 1 × 10−12 atm cc He/s were measured using this system. Because only one test is required for the gross and fine leaks, the cost of evaluating the hermaticity of the device is reduced. Included in this paper are the design concepts, operational modes, calibration methods, and test results.
Surface composition determination of Pt–Sn alloys by chemical titration with carbon monoxide
Authors: Haner A. H. , Ross P. N. , Bardi U. , Atrei A.
Published: July 2002

The use of chemical titration with carbon monoxide to determine the surface composition of Pt–Sn alloys was studied using Pt3Sn single crystals of known surface composition. The surface composition of the (111) and (100) faces were determined independently by the combination of low-energy electron diffraction (LEED) crystallography and low-energy ion scattering (LEIS). CO was adsorbed on these surfaces to saturation at 250 K and thermally desorbed into a mass spectrometer. The area under the thermal desorption spectroscopy curve for the alloy surface was compared to the area under the curve for the pure Pt surface of the same orientation. The ratios were 0.5±0.05 for Pt3Sn(100) and 0.7±0.05 for Pt3Sn(111), in excellent agreement with the 50% Pt and 75% Pt surface compositions derived from LEED and LEIS. The success of the titration method in this case appears to be due to (a) selective adsorption of CO on Pt atoms and (b) the relatively weak effect of the Pt–Sn intermetallic bond on the Pt–CO bonding.
Electronic structure and relative stability of the MgO (001) and (111) surfaces
Authors: Gibson Andrew , Haydock Roger , LaFemina John P.
Published: July 2002

The relative stability and electronic structure of the MgO (001), (111)-Mg, and (111)-O surfaces have been studied with the Harris–Foulkes total energy functional. The computed energies of the (001), (111)-O, and (111)-Mg surfaces of MgO are 2.64, 12.80, and 13.02 J m−2, respectively. Our calculations exhibit a qualitative distinction between the Mg-terminated polar (111) surface, which has a nonzero density of one-electron states at the Fermi level, and the other (001) and (111)-O surfaces which retain the band gap properties of the bulk material. The projected local density of states for atoms in the bulk and at the various surfaces are presented, and used to explain the relative stability of different surfaces in terms of the properties of surface bonds.
Pd, Ni, and Cu overlayers on polycrystalline Re
Authors: Baer D. R. , Hubbard C. W. , Gordon R. L.
Published: July 2002

Work function (WF) and x-ray photoelectron spectroscopy (XPS) measurements are reported for Pd, Ni, and Cu overlayers on polycrystalline Re specimens. Small amounts of Pd or Ni cause a decrease in the Re work function, consistent with electron transfer from the overlayer to the substrate. This result is contrary to indications of bulk electronegativity, but consistent with observed changes in binding energies for the metal overlayers. For Cu on Re, the direction of change for both the WF and Cu binding energy depend upon the thermal history of the specimen.
Study of YBaCuO on W/Si by x-ray photoelectron spectroscopy
Authors: Chopra D. R. , Chourasia A. R. , Chen Li , Bensaoula A. H. , Bensaoula A.
Published: July 2002

With the advent of high temperature superconductors, attempts are made to integrate these materials with silicon so as to evaluate their potential in semiconductor technology. In order to investigate the reactivity between the superconductor and silicon through the different diffusion barriers, we have studied Y–Ba–Cu–O on W/Si samples subjected to different processing conditions by x-ray photoelectron spectroscopy. Thin films of superconductors Y–Ba–Cu–O were deposited on W/Si by molecular-beam epitaxy. The samples were then broken into two pieces. One piece was annealed at 860 °C for 3 h. We have studied the chemical reactivity of the superconductor with the substrate at the interface for both the annealed and unannealed samples. Such a comparative study minimizes problems inherent to sputtering. In particular, we have focused on Y 3d, Ba 3d, Cu 2p, O 1s, Si 2p, and W 4f regions. Emphasis was placed on the depth distribution, content and chemical state of the constituents as a function of different processing parameters. In the unannealed sample W diffuses into the superconductor and is oxidized progressively at the expense of Cu–O and Ba–O bonds. Silicon does not show any significant diffusion. In the annealed sample both W and Si diffuse extensively and the oxygen depleted from the superconductor constituents is mainly used in the formation of W and Si oxides. We, therefore, conclude that for thin film deposition processes requiring a high temperature anneal, thin superconducting films cannot be obtained on W/Si substrate due to the diffusion and oxygen depletion problems.
A study of Y–Ba–Cu–O/Si interfaces by x-ray photoelectron spectroscopy
Authors: Chourasia A. R. , Chopra D. R. , Bensaoula A. H. , Bensaoula A. , Ruzakowski P.
Published: July 2002

Thin films (∼300 Å) of the superconductor YBa2Cu3O7−y were deposited on a Si 〈100〉 substrate by molecular beam epitaxy. The sample was then cleaved in two pieces and one of these was annealed at 860 °C for 3 h. X-ray photoelectron spectroscopy in conjunction with sputter depth-profiling was utilized to study the interfaces in the unannealed and the annealed samples. Such a comparative study minimizes problems inherent to sputtering. The Y 3d, Ba 3d, Cu 2p, O 1s, and Si 2p regions were investigated. In the unannealed sample, Si diffuses into the constituents of the superconductor near the interface. Oxygen is found to be depleted from the CuO planes in the superconductor thin film with the formation of silicon suboxide. Also, the interface is narrow. In the annealed sample, Si diffuses extensively into the constituents of the superconductor. The Cu–O bonds are broken with the formation of SiO2. This SiO2 is detected on the surface of the sample. At a depth of 450 Å in the sample, Ba–O bonds are also broken partially and some Si suboxide is formed. Because of the extensive interdiffusion, the interface in this sample is broad. It is found that in both cases, Cu–O bonds are broken with oxygen used mainly in the formation of silicon oxides. The study shows that significant interdiffusion occurs at Si/superconductor interface during the high temperature anneal necessary to form the superconductor phase. It is concluded that oxidation of Si at the expense of copper and not the diffusion of Si into the superconductor is responsible for the degradation of performance of the superconductor thin film. Consequently, a suitable diffusion barrier which allows elevated temperature during deposition or annealing stages would be required in the fabrication of superconductor/Si devices.
Auger and electron energy loss spectroscopy studies of AlN and (AlN)x(Al2O3)1−x thin films
Authors: Shinar R.
Published: July 2002

Electron energy loss spectroscopy (EELS), Auger analysis and Auger line shape measurements were used to study composition and bonding in thin films of varying Al:N:O ratios grown by reactive magnetron sputter deposition. The films deposited in the presence of oxygen in addition to nitrogen or ammonia in the plasma are apparently composed of both AlN and Al2O3. There is no evidence for other bonding configurations. In accordance, the observed ionicity of the Al–N and Al–O bonds is the same as in the respective single-phase films. The AlN and Al2O3 phases are clearly distinguished by their Al(LVV) signals, but not by the respective Al(KLL) transitions. A relative sensitivity factor of Al(KLL) in the AlN thin films at a primary energy of 3 keV was obtained from analyses of both AlN and (AlN)x(Al2O3)1−x. The same sensitivity factors of Al(KLL), N(KLL), and O(KLL) are adequate for analysis of both single- and two-phase films. The EELS in the 4–40 eV range at primary energies of 135 and 185 eV contain unresolved contributions from both AlN and Al2O3. Results are compared to those of Al2O3, thin films of oxidized and nitrided Al, and NO exposed Al(100) surface. Bonding at the latter surface appears to differ from that at the two-phase films. Charging and stability effects in the films are also discussed.
Use of multilayer-monochromatized synchrotron radiation for direct pattern formation and Auger electron spectroscopy
Authors: Oshima Masaharu , Maeyama Satoshi , Takenaka Hisataka , Ishii Yoshikazu , Sugahara Hirohiko
Published: July 2002

A new technique has been developed for pattern delineation of fluoride films. Patterns are delineated through the use of strong synchrotron radiation semimonochromatized by a synthetic multilayer. The CaF2 and SrF2 etching processes are found to be very sensitive to substrate temperature, suggesting that surface reaction such as F–Ca bond dissociation or evaporation might play a key role. Simultaneously monitored synchrotron radiation (SR)-induced Auger electron spectra reveal that fluorine atoms are selectively desorbed from SR-irradiated surfaces at low temperature and desorbed stoichiometrically with Ca atoms at 400 °C.
Fabrication of deuterated–tritiated polystyrene shells for laser fusion experiments by means of an isotope exchange reaction
Authors: Takagi M. , Norimatsu T. , Yamanaka T. , Nakai S.
Published: July 2002

Deuterated–tritiated polystyrene shells with a silicon dopant for use in laser fusion experiments were fabricated by means of an isotope exchange method. In order to increase the isotope exchange rate, deuterated polystyrene shells in a tritium atmosphere were exposed by ultraviolet (UV) radiation from a mercury lamp. The specific activity of tritium in the shells were 92 Ci/g for partially deuterated polystyrene and 150 Ci/g for fully deuterated polystyrene, respectively. The isotope exchange rate with UV irradiation was 230 times as fast as that without the UV irradiation. The tritium in the shell was found to be strongly localized at the outer surface.
Interfacial reactions in the Co/Si/GaAs and Si/Co/GaAs systems
Authors: Hsu C. C. , Jin G. L. , Ho J. , Chen W. D.
Published: July 2002

The interfacial reactions between thin films of cobalt and silicon and (100)—oriented GaAs substrates in two configurations, Co/Si/GaAs and Si/Co/GaAs, were studied using a variety of techniques including Auger electron spectroscopy, x-ray diffraction, and transmission electron microscopy. The annealing conditions were 200, 300, 400, 600 °C for 30 min, and rapid thermal annealing for 15 s. It was found that Si layer in the Co/Si/GaAs system acts as a barrier at the interface between Co and GaAs when annealed up to 600 °C. The interfacial reaction between Co and Si is faster than that between Co and GaAs in the system of Si/Co/GaAs. The sequence of compound formation for the two metallizations studied (Co/Si/GaAs and Si/Co/GaAs) depends strongly on the sample configuration as well as the layer thickness of Si and Co (Co/Si atomic ratio). From our results, it is promising to utilize Co/Si/GaAs multilayer film structure to make a CoSi2/GaAs contact, and this CoSi2 may offer an alternative to the commonly used W silicides as improved gate metallurgies in self-aligned metal–semiconductor field effect transistor (MESFET) technologies.
Atomic hydrogen interactions with disordered regions in silicon
Authors: Srikanth K. , Ashok S.
Published: July 2002

This article addresses issues related to hydrogen migration and acceptor deactivation with disordered regions in crystalline Si. It is shown that upon annealing, hydrogenated disordered regions can act as a source of H within the substrate resulting in up to a four decade change in resistivity in the vicinity of the disordered region. From a simple model for this sustained deactivation, an effective diffusion coefficient of H in silicon is calculated for various substrate resistivities. Further, the method of hydrogenation is shown to play a role when migration is to occur across carrier-neutralized zones.
Magnetron etching of GaAs: Etch characteristics and surface characterization
Authors: Meyyappan M. , McLane G. F. , Cole M. W. , Laraeu R. , Namaroff M. , Sasserath J. , Sundararaman C. S.
Published: July 2002

Etching of GaAs in a magnetron reactor was investigated using two different etch gases, namely SiCl4 and freon-12 (CF2Cl2). SiCl4 etching yielded vertical sidewalls, whereas the etched profiles in the case of freon exhibited a negative undercut. Surface characterization was undertaken using Auger electron spectroscopy, x-ray photoelectron spectroscopy, and secondary ion mass spectroscopy to determine the composition and chemical bonding in the near-surface region of the etched samples. The etched surface in the case of SiCl4 was found to be free of any chlorine residue and predominantly GaAs. However, there were residues of Si on the sidewalls. GaF3 formation was observed in GaAs samples etched in freon-12; in addition a CxFy fluorocarbon layer was present at high pressures which may not have been effectively removed due to reduced ion bombardment.
Ion microtomography and particle-induced x-ray emission analysis of direct drive inertial confinement fusion targets
Authors: Antolak A. J. , Pontau A. E. , Morse D. H. , Weirup D. L. , Heikkinen D. W. , Cholewa M. , Bench G. S. , Legge G. J. F.
Published: July 2002

The complementary techniques of ion microtomography (IMT) and particle-induced x-ray emission (PIXE) are used to provide submicron-scale characterization of inertial confinement fusion (ICF) targets for density uniformity, sphericity, and trace-element spatial distributions. ICF target quality control in the laser fusion program is important to ensure that the energy deposition from the lasers results in uniform compression and minimization of Rayleigh–Taylor instabilities. We obtain 1% total electron density determinations using IMT with spatial resolution approaching 2 μm. Utilizing PIXE, we can map out dopant and impurity distributions with elemental detection sensitivities on the order of a few parts per million. We present examples of ICF target characterization by IMT and PIXE in order to demonstrate their potential impact in assessing target fabrication processes.
Simple aluminum gasket for use with both stainless steel and aluminum flanges
Authors: Langley R. A.
Published: July 2002

A technique has been developed for making aluminum wire seal gaskets of various sizes and shapes for use with both stainless steel and aluminum alloy flanges. The gasket material used is 0.9999 pure aluminum, drawn to a diameter of 3 mm. This material can be easily welded and formed into various shapes. A single gasket has been successfully used up to five times without baking. The largest gasket tested to date is 3.5 m long and was used in the shape of a parallelogram. Previous use of aluminum wire gaskets, including results for bakeout at temperatures from 20 to 550 °C, is reviewed. A search of the literature indicates that this is the first reported use of aluminum wire gaskets for aluminum alloy flanges. The technique is described in detail, and the results are summarized.
High selectivity electron cyclotron resonance etching of submicron polysilicon gate structures
Authors: Ma Diana X. , Lin Tsu-An , Chen Ching-Hwa
Published: July 2002

A submicron doped polysilicon etch using a Cl2–HBr/Cl2–HBr–O2 process in a downstream electron cyclotron resonance (ECR) etcher is described. Vertical and notchless profiles were achieved at 100%-to-300% overetches. By adjusting the radio-frequency (rf) power applied to the wafer holder and by adding a slight amount of oxygen in the overetch step, a very high polysilicon to oxide selectivity of ≳200:1 was obtained with oxide loss minimized to <20 Å. In addition, this ECR polysilicon etch offers a very large process latitude with more than 60% variation in process parameters. The effects of process parameters on etch performance were investigated. A 200-wafer repeatability test demonstrated a polysilicon etch rate repeatability of ±3.8%.
In situ characterization of thin-film defect generation using total internal reflection microscopy
Authors: Williams F. L. , Petersen G. A. , Carmiglia C. K. , Pond B. J.
Published: July 2002

Total internal reflection microscopy (TIRM) is a nondestructive characterization technique that provides an image of the defects in a surface and/or a thin film. The TIRM system in this study is installed in situ in an ultrahigh-vacuum deposition apparatus. Therefore, this experiment represents a unique opportunity to investigate in real time the generation of defects in thin films during deposition. Two types of defects have been observed in zirconia (ZrO2) thin films produced for this study: one type is associated with point-scatter sites and the other type corresponds to a nonlocalized speckle pattern. X-ray-diffraction spectrometry was used to show that the speckle patterns are due to thin-film crystallites. The rate of ZrO2 crystallite growth was seen to depend on O2 partial pressure during deposition. The point scatter observed in this study most likely originates from gross thin-film defects, such as evaporant spatter or inclusions originating at the substrate–film interface. In this investigation, the rate of point-defect accumulation in ZrO2 thin films produced by electron-beam evaporation displays a dependence on emission voltage, with greater voltages yielding lesser defect-formation rates.
Effects of space charge on ion energy in ionized cluster beam film deposition
Authors: Urban Frank K. , Feng Susan W.
Published: July 2002

In ionized cluster beam (ICB) deposition, thin films are said to be deposited from a beam of ionized, accelerated atom clusters. Unique properties have been reported for ICB films even though it is becoming apparent that the large (1000 atom) clusters reported in earlier work have not been duplicated by homogeneous nucleation with nozzle sources. Instead, recent results at a number of laboratories using different cluster measurement methods for gold, aluminum, gallium, silver, and other materials show what appears to be small clusters up to ten atoms in size and suggest that the nozzle may be unnecessary. It is not known whether these small clusters or other characteristics of the deposition technology are responsible for the deposited film qualities that have stirred interest in recent years. The subject of this presentation is a detailed electrostatic analysis of an ICB source to determine the fundamental parameters of ICB depositions and thus to elucidate other factors such as the effects of self-ion bombardment. Energy analysis of gold and background gas ion beams produced in the source shows that the ICB source can operate in two distinct modes. For low crucible and ionizer electron bombardment conditions the effect of space charge on the energy of ions incident on the substrate is negligible. Above critical bombardment conditions, space charge has a very significant effect, resulting in incident ion energy being raised as much as 50% above that expected based upon applied electrode potentials alone. Computer modeling of ICB source electrostatic characteristics is used to explain these findings.
Effect of deposition technique on the As-deposited microstructure of copper thin films
Authors: Walsh L. Harper , Feilchenfeld Natalie B. , Schwarz J. A.
Published: July 2002

Copper metallization is an ideal choice for use in semiconductor devices and packages. The metal’s desirable properties are low resistivity, good electromigration resistance, solderability, and low cost. Microstructural differences in copper deposited by four techniques commonly used in the microelectronics industry are determined. These differences were measured using optical microscopy, x-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, and secondary-ion mass spectroscopy. The results were compared to clearly define the differences in microstructure among the different copper films providing a basis for interpreting the effects of copper film deposition method on film microstructure and those physical properties influenced by microstructure. Finally the microstructural rather than chemical differences are used to predict how each copper sample will react to the same wet etchant.
Characterization of sputter deposited inconel/carbon x-ray multilayers
Authors: Aouadi M. S. , Parsons R. R. , Wong P. C. , Mitchell K. A. R.
Published: July 2002

The reflectivity of x-ray multilayers made of new pairs of materials was theoretically calculated at a wavelength of 45 Å. Carbon and inconel were then selected for ‘‘low index’’ and ‘‘high index’’ layers, respectively, in the multilayer system. Single layers, bilayers, and multilayers of carbon and inconel were characterized by grazing x-ray reflectometry (GXR), x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and spectroscopic ellipsometry (SE). From GXR data at 1.54 Å refractive indices and film thicknesses of inconel and carbon layers were obtained. From an analysis of SE data, the dielectric function and the thickness as of inconel and carbon thin films were deduced. XPS and AES measurements revealed the presence of carbides at the interface between carbon and inconel. GXR analysis was performed on ten-layer C/inconel multilayers. The GXR interference pattern was found to broaden after annealing the samples at 600 °C.
Modification of the x-ray photoemission spectrum of in situ deposited thin films of Y1Ba2Cu3O7−y for various oxygen treatments
Authors: Broussard P. R. , Cestone V. C.
Published: July 2002

We have grown thin films of the Y1Ba2Cu3O7−y superconductor onto MgO and LaGaO3 substrates by off-axis sputtering. The films were all deposited under the same conditions, but were cooled in various oxygen pressures resulting in films with superconducting transition temperatures from 85 K to nonsuperconducting. The samples have been examined by x-ray photoemission spectroscopy without exposing the samples to air. We have characterized the core levels of Y, Ba, Cu, and O and the Auger parameter of Ba, Cu, and O as a function of the oxygen pressure used during cooldown. We find that the core lines sharpen and the Auger parameter for copper reduces as the oxygen pressure is decreased. We interpret this latter result as a possible change in the valence state of copper. We also see a variation in the valence structure.
Temperature-programmed reaction of methylamine on the Ni{100} surface
Authors: Chang Che-Chen , Khong Cheng , Saiki Richard
Published: July 2002

The adsorption and temperature-programmed reaction of methylamine on the Ni{100} surface is investigated. Irreversible decomposition of methylamine predominates at very low exposures in which the C–N bond scission is favored over dehydrogenation to form ammonia. At slightly higher exposures, nondissociative adsorption takes place. A new adsorption state of methylamine, in which the chemisorbed methylamine molecule is hydrogen bonded to nitrogen residues on the surface, is found which has a binding energy of about 19 kcal/mol. Desorption of methylamine from this new state occurs at a temperature close to that from an oxygen-precovered Ni{100} surface and is dependent on the predosage of oxygen. Hydrogen bonding between the chemisorbed methylamine and the residual nitrogen present on the surface also results in an increase in the decomposition rate. A further increase in methylamine exposure results in molecular adsorption to form the first and the second chemisorption states as well as a third state thought to be due to multiple layers of weakly adsorbed methylamine. In addition, several adsorption states for ammonia produced from decomposition of methylamine on Ni{100} are also identified. More than 90% of the ammonia initially produced at very low methylamine exposures are hydrogen bonded to surface nitrogen residues. The trend of the reactivity of methylamine on transition metals across the Periodic Table is also discussed.
Energy and momentum distributions versus incident energy in the scattering of CO from Ag(111)
Authors: Hanisco Thomas F. , Yan Chun , Kummel Andrew C.
Published: July 2002

The effect of changing the incident translational energy on the exit translational energy, rotational state population distributions, and angular momentum alignment of monoenergetic, rotationally cold CO scattered from Ag(111) at normal incidence was measured. As the incident energy is raised, a dramatic increase in the fraction of energy transferred to the surface, a shift of the rotational rainbow to higher rotational energy, and a significant increase in the amount of angular momentum alignment in the scattered molecules were observed. In addition, the alignment versus J distribution exhibits positive curvature for CO at all incident energies. The results are consistent with (1) the effect of the surface phonons and/or physisorption well on the final energy of the scattered molecules being small except at the lowest incident energy; (2) the large ∂V/∂θ being the primary source of the greater rotational excitation seen for CO compared to N2 scattered from Ag(111); and (3) the corrugated attractive portion of the CO/Ag(111) potential being primarily responsible for the modest alignment of CO at low incident energy.
Electroluminescence and photoluminescence from microporous silicon p-n junctions
Authors: Kesan V. P. , Bassous E. , Munguia P. , Pesarcik S. F. , Freeman M. , Iyer S. S. , Halbout J.-M.
Published: July 2002

A novel immersion scanning technique for making microporous silicon has been successfully applied to blank and lithographically patterned Si substrates. The advantages of the method lie in its simplicity, speed of fabrication, and adaptability to large and odd-size substrates. The photoluminescence (PL) intensity of porous silicon shows a steady decrease between 200 and 2 K and this behavior is fully reversible. Thermal desorption spectroscopy on microporous Si shows a classic hydrogen desorption spectrum which coincides with a quenching of the PL intensity. Under constant excitation, a degradation of PL intensity occurs in oxygen and wet nitrogen but is only partially reversible in dry N2. Microporous Si p-n junctions exhibiting normal I–V characteristics have been successfully fabricated with standard Si very large scale integrated processes. Visible light emission under forward bias is detected which increases linearly in intensity with input current. This is the first observation of electroluminescence in the visible region from microporous Si p-n junctions.
Safety and health considerations related to vacuum gauging
Authors: Peacock R. N.
Published: July 2002

Safety or health hazards exist with some common types of vacuum gauging including mercury manometers, thermal conductivity gauges, and ionization gauges. Mercury filled manometers and McLeod gauges have been replaced by other gauging in most applications. The difficulty with thermal conductivity gauges arises because the calibration curves for various gases diverge widely at the upper end of the range, from 10 to 1000 Torr. When they are used to monitor backfilling to atmospheric pressure, dangerous over or under pressure situations may exist if the identity of the gas is not known. The greatest danger with hot cathode ionization gauge systems is electric shock from the high voltages supplied by the control unit. Especially with gauges using electron bombardment degas, proper use of grounds, cables, and connectors is necessary. A concern with many hot cathode ionization gauge sensors is the thorium oxide electron emitting coating on the cathode. Natural thorium is an alpha emitter with a half-life of 1.4×1010 years. Yttrium oxide is a safe alternate coating material now available in ionization gauges.
Boron nitride thin film deposition using electron cyclotron resonance microwave plasmas
Authors: Gorbatkin S. M. , Burgie R. F. , Oliver W. C. , Barbour J. C. , Mayer T. M. , Thomas M. L.
Published: July 2002

Electron cyclotron resonance microwave plasma deposition has been used to deposit BxN1−x thin films from borazine (B3N3H6)-based plasmas, including pure borazine and borazine mixed with either Kr or NH3. Deposited films were analyzed using enhanced cross-section backscattering spectrometry, forward elastic recoil detection, x-ray diffraction, and infrared absorption. A wide range of stoichiometries was accessible even with pure borazine plasmas, with the ratio of B/N ranging from 0.54 to 4.4. The hydrogen atomic fraction varied from ∼1% to 20% and was typically 2%–3% for stoichiometric boron nitride (BN) films. No evidence of c-BN formation was observed, and measurements of the ion energy at which no net deposition occurs indicate that the high momentum transfer rates to the surface used for recent successful experiments on c-BN deposition are much more difficult to access with a borazine-plasma-based process. The mechanical properties of the films were measured using depth sensing ultralow load indentation tests, and the hardness and modulus of the films are reported. Finally, mass spectrometric measurements of the ions incident on the substrate indicate high hydrogen ion (H+,H+2,H+3) concentrations and a relatively small fraction of the boron and nitrogen in the deposited film coming from elemental ion precursors.
Transparent and conductive GaN thin films prepared by an electron cyclotron resonance plasma metalorganic chemical vapor deposition method
Authors: Sato H. , Minami T. , Yamada E. , Takata S. , Ishii M.
Published: July 2002

Transparent and conductive GaN thin films have been prepared on glass substrates using the metalorganic chemical vapor deposition method utilizing electron cyclotron resonance plasma. A resistivity below 2×10−2 Ω cm and a carrier concentration on the order of 1020 cm−3 were obtained for oxygen-doped GaN thin films prepared at 350 °C using triethylgallium in combination with either NH3 or N2 as source gases. A sheet resistance of 160 Ω/⧠ and an averaged transmittance in the visible region of 80% were realized in a film 1100 nm thick. The thermal and chemical stability of GaN thin films are described.
Materials for superconducting electronics: In situ growth of PrGaO3 thin films by metalorganic chemical vapor deposition
Authors: Han Bin , Neumayer Deborah A. , Schulz Douglas L. , Hinds Bruce J. , Marks Tobin J.
Published: July 2002

Phase-pure thin films of the YBCO, BSCCO, TBCCO lattice-matched and low dielectric-loss perovskite insulator PrGaO3 have been grown in situ on single-crystal (110) LaAlO3 , (001) SrTiO3 , and (001) MgO substrates by metalorganic chemical vapor deposition (MOCVD). Films were grown at temperatures between 750 and 800 °C using the volatile metalorganic β-diketonate precursors M(dpm)3 (M=Pr, Ga, and dpm=dipivaloylmethanate). As assessed by x-ray diffraction, the films grow epitaxially on LaAlO3 and SrTiO3 substrates with a high degree of (001) and/or (110) plane orientation parallel to the substrate surface. The films grown on MgO substrates are polycrystalline. Scanning electron microscopy reveals that the MOCVD-derived PrGaO3 films have smooth, featureless surfaces on all three kinds of substrates.
Novel radio-frequency induction plasma processing techniques
Authors: Keller John H. , Forster John C. , Barnes Michael S.
Published: July 2002

A novel plasma source combining rf inductive drive and multipole plasma confinement has been constructed to process advanced semiconductor materials. Measurements show a linear dependence of density with input power. Ion current efficiencies of 1 A per 150–300 W of input power can be achieved in argon, with lower efficiencies in electronegative gases. Applying an rf bias to a substrate immersed in the plasma allows the sheath voltage to be controlled between 8 and 300 V. Insight into the rf induction process can be gained by a simple circuit model, which represents the induction process with a transformer. The physical quantities describing the transformer can be obtained from numerical calculation of the fields of the induction coil. This plasma source can etch thin films at rates exceeding 1 μm/min.
Auger electron angular distributions from Al(100): Resolution of an apparent contradiction
Authors: Chyan Oliver M. R. , Frank Douglas G. , Doyle Charles A. , Hubbard Arthur T.
Published: July 2002

Complete Auger electron angular distributions have been measured from an Al(100) surface for the two principal Auger transitions, 64 eV(LMM) and 1388 eV(KLL). The results are consistent with angular distributions measured for other crystalline samples: intensity minima are observed along the internuclear directions at low kinetic energies (<100 eV), while intensity maxima are observed along those same directions at higher kinetic energies (≳300 eV). The earliest reported polar profiles for the Al(100) 64 eV Auger peak appeared to contradict this trend, exhibiting intensity maxima along the surface normal. However, the present results do not confirm that aspect of the earliest measurements. Furthermore, the present results are found to be in good agreement with more recent measurements reported by other laboratories, suggesting that the apparent discrepancy is attributable to experimental factors in the earliest measurements. That is, the Auger emission from Al(100) follows the trends observed for other elements.
Design of an ultrahigh vacuum direct-drive, cryogenic sample manipulator providing two degrees of rotational freedom
Authors: Braun Robert M. , Winograd Nicholas
Published: July 2002

An ultrahigh vacuum direct-drive, cryogenic sample manipulator is described. It is fully bakeable in UHV, uses no lubricants, and does not require differentially pumped seals. It provides independent polar and azimuthal rotation of a sample, three degrees of translational freedom, electron-beam heating, as well as cooling to 100 K using liquid nitrogen.
Chemistry of S/GaAs and metal/S/GaAs systems
Authors: Sugahara Hirohiko , Oshima Masaharu , Oigawa Haruhiro , Nannichi Yasuo
Published: July 2002

Bonding states and the band bending of S/n-GaAs (001) and metal/S/n-GaAs (001) systems are studied by synchrotron radiation photoemission spectroscopy (SRPES). The difference in the surface chemistry between the (NH4)2Sx-treated GaAs and the sulfur-chemisorbed GaAs is explained well by the formation of the sulfur-rich transition layer for the (NH4)2Sx-treated GaAs. A structural model for the annealed S/GaAs (001) system is proposed, in which the surface is terminated with Ga–S bonds. The barrier height of the Al, Au, and In Schottky contacts on (NH4)2Sx-treated n-GaAs is also determined to be about 0.4, 0.7, and 0.3 eV, respectively, by SRPES for the first time, which are in fairly good agreement with I–V characteristics of the metal/S/n-GaAs Schottky diodes. It is found that the oxide-free interface with a sulfur interlayer plays an important role for the metal-dependent Schottky barrier formation.
Interface structure and adhesion of sputtered metal films on silicon: The influence of Si surface condition
Authors: Kondo Ichiharu , Yoneyama Takao , Kondo Kenji , Takenaka Osamu , Kinbara Akira
Published: July 2002

Ni(100–1000 nm)/Ti(250 nm) films were prepared by dc planar magnetron sputtering on Si(100) surfaces. Interface structures between Ti and Si and adhesion of the Ti films to Si after different surface pretreatments have been investigated. Before the film deposition, the Si substrate received an Ar ion bombardment or a chemical etching treatment. In the case of the Ar ion bombardment, we have investigated the effect of the cathodic voltage. A low cathodic voltage (50 V) resulted in high adhesion. The results by Rutherford backscattering spectroscopy showed that the amount of Ar incorporated in the Si surface during the Ar ion bombardment is increased with the cathodic voltage. The existence of Ar at the interface between the Si substrate and the Ti–Si mixed layer seems to lower the adhesion. In the case of the chemical pretreatment, we have investigated the effect of the exposure time in the atmosphere after the chemical etching treatment. A shorter exposure time (within 1 h) has been found to be preferred to a longer exposure time. The results of Auger electron spectroscopy and the peeling test showed that the exposure time is related to the oxide thickness, the Ti–Si alloy thickness, and the adhesion. It is considered that the stable SiO2 formation prevents the Ti–Si mixed layer formation and lowers the adhesion.
Geometric and electronic structures of Na/GaAs
Authors: Bai Chunli , Hashizume Tomi , Jeon Dong-Ryul , Sakurai Toshi
Published: July 2002

This article reports structural and electronic properties of sodium adsorbed on room-temperature GaAs(110) surface as observed with scanning tunneling microscopy in an ultrahigh vacuum. In the low-coverage regime, Na adatoms reside on the bridge site encompassing one Ga and two As surface atoms to form linear chains along the [11̄0] direction. The Na–Na nearest-neighbor distance in this low-density chain structure is 8 Å. When the Na coverage was increased to ∼0.09 ML (1 ML≡2 Na per substrate unit cell), the chains became slightly disordered. Some of them were packed closer to form domains with local 2×2 structure. None of high-density two-dimensional ordered structures or low-density zigzag chains was observed, in contrast to the Cs/GaAs(110) system. Additional Na adsorption resulted in the formation of three-dimensional disordered clusters. The saturation coverage of Na adsorption on the GaAs(110) surface was determined to be ∼0.1 ML. No evidence of metallic characteristics was found in the I–V curves recorded over the various Na-covered surfaces.
Etching of zinc selenide and zinc telluride epitaxial films in a secondary afterglow plasma: A statistical experimental design study
Authors: Schäfer P. , Hoffmann N. , Parthier L. , Jacobs K.
Published: July 2002

The conventional plasma etch processes are not suitable for II–VI compounds. This study describes the systematic development of a novel process for plasma etching of the II–VI compounds ZnSe and ZnTe with CH4/H2 mixtures in a secondary afterglow plasma using the response surface methodology. The etching process was optimized for obtaining submicrometer structures using thin photomasks that have been exposed to a blue holographic lithography process. Under optimum conditions the etching of such structures without optical (and probably also electrical) degradation is possible with etch rates for ZnSe in the order of 50 nm/min.
Computational model of reactive sputtering
Authors: Koss V. A. , Ioffe I. V. , Belkind A.
Published: July 2002

The model of reactive sputtering is modified to contain only measurable integral characteristics such as total current, discharge power, target erosion rate and volt–ampere characteristics for sputtering in metallic and reactive modes. Calculation results for Zn/ZnO and Zr/ZrN are in good agreement with experimental data.
Monte Carlo simulation of chevron baffle performance
Authors: Ross A. W. , Fink M. , Wellenstein H. F.
Published: July 2002

A Monte Carlo simulation of chevron type cold trap baffles was carried out and compared with experiments and other calculations in the literature. By examining a more complete angular range than has previously been reported in the literature, the optimum baffle plate angles for three different configurations were found.
In situ observations of Ge(001) and Ge/Si(001) using low-energy ion scattering
Authors: Taferner W. T. , Freundlich A. , Bensaoula A. , Ignatiev A. , Waters Kelley , Eipers-Smith Ketti , Guehenneuc Myriam , Schultz J. Albert
Published: July 2002

Low-energy ion scattering (LEIS) angular distributions were measured on Ge(001)-1×1-O and Ge(001)-2×1+1×2 surfaces. The intensity of 105° backscattered ions and neutrals from 3 keV Ar+ primary ions incident at 45° were recorded as a function of the surface azimuthal angle. The major symmetry directions of the Ge surface were observed. A 14.2 keV Na+ pulsed beam incident at 72.5° with direct recoiled atoms detected by time of flight (TOF) at an angle of 25°, was used to determine the levels of elemental contaminants on the Ge(001) surface at different stages of annealing. TOF-LEIS of backscattered 3 keV Ne+ was used to monitor, in ‘‘real time,’’ Ge deposition on Si(001) at room temperature.
Characterization of H− extraction for a multipole ion source located in the tail of the magnetic field distribution: Type III
Authors: Oka Y. , Ando A. , Kaneko O. , Takeiri Y. , Tsumori K. , Akiyama R. , Kawamoto T.
Published: July 2002

A magnetic multipole plasma source and the accelerator for H− ion source is installed in the distribution of the externally imposed magnetic field which is quasiuniform over the plasma electrode. As the magnetic field of the permanent magnets in this geometry works not only as a so-called magnetic filter for electron cooling, but also as a deflection field to the accompanied beam electrons, there is a possibility for making the fabrication of the H− source simpler/easier due to no use of small magnets in the accelerator. The characteristics of the ion source such as H− extraction, optimization in the magnetic field, the plasma parameters, etc. are investigated. The integrated magnetic flux of 230–320 G cm should be determined by the condition which optimizes the volume production in the source plasma. Achievable current density of H− is 6 mA/cm2 with 15 keV at the target. Large amounts of the electrons, however, are accelerated altogether to a full energy. They can be stopped with a retarding potential. It is rather unusual that the positive-ion saturation current profile with the probe becomes more like inhomogeneous across the magnetic field. The results (of H− and G cm) are compared with ones for the different three types of the magnet arrangement.
Molecular beam epitaxy cell optimized for organic compounds and preparation of a Cu phthalocyanine thin film
Authors: Hattori S. , Ishitani A. , Kuroda H.
Published: July 2002

We have established a dry process based on molecular beam epitaxy (MBE) of organic molecules under ultrahigh vacuum (UHV) condition on a clean and bare silicon surface. We designed a new MBE system suited to depositing organic materials based on the Monte Carlo simulation of the molecular motion. Cu phthalocyanine thin films were prepared with the system as a test. Films with high flatness and crystallinity without contamination were prepared on the substrates prepared by the UV/HF method developed earlier in our research group. The possibility of controlling the crystal structure of the deposited thin film by the surface crystallinity of the substrate is suggested based on the observation on differently prepared substrate surfaces.
Main features of electron cyclotron resonance ion source vacuum systems
Authors: Pivarc̆ J.
Published: July 2002

This article presents the main features in the design of vacuum systems for electron cyclotron resonance (ECR) ion sources. It is very interesting to consider them as a possible source of high-charge-state ions in upgrading present heavy-particle accelerators. Scaling relationships are given as a basis for understanding the vacuum configurations of ECR ion sources. The relevance of gas desorption effects to vacuum equilibrium and stability is also pointed out. Ion-induced pressure instability, a model of hydrogen diffusion, and the influence of neutral gases on the vacuum stability of ECR ion sources are discussed.