bluuebunny/crossref_metadata_2025 huggingface dataset:
Simultaneous determination of Lewis and Bronsted site densities on silica alumina using infrared techniques
Authors: Schwarz James A.
Published: July 2002

When a pyridine−covered surface of a silica−alumina catalyst is contacted with water, there is an inversion of the population of coordinately bound pyridine to species bound by proton exchange. We have used this fact along with a standard ’’titration’’ technique to determine in a single series of measurements on the same catalyst the number of Lewis and Bronsted sites both before and after water exposure. This modified titration technique was applied to a series of experimental silica−alumina catalysts. The total number of acid sites and the number of Lewis and Bronsted sites per unit area of catalyst were determined as a function of the silica content of the catalyst. The Bronsted−site concentrations agree excellently with previously published data by Clark and Holm (J. Catal., 1963) on the catalytic isomerization of o−xylene over similar silica−alumina catalysts.
Focusing of electron beams by laser-beam fields
Authors: Yadavalli S.
Published: July 2002

Employing the paraxial electron-trajectory equation of a cylindrical electron (beam) the theory of the focusing action of an enveloping annular laser beam is presented and discussed. Analogies between schemes employing laser-beam fields to focus electron beams and methods involving conventional ’’strong’’ and ’’quadrupole’’ focusing of electron beams are indicated. Some advantages and limitations of the suggested focusing method are pointed out. Also, some approximate numerical estimates regarding the parameters of a cylindrical electron beam and a (focusing) surrounding annular laser beam are obtained for a typical example.
Electron-beam lithographic pattern generation system
Authors: Patlach A. M. , Jaskar P. R. , Studwell T. W.
Published: July 2002

An electron-beam lithographic system has been evolving over the past few years at the IBM Research Laboratory in Yorktown Heights, New York. Several versions are now operational in the Yorktown Laboratory, and one in the IBM San Jose Laboratory. Many novel features which create a high degree of automation have been incorporated into each of these systems. This paper describes a pattern generator which was designed to allow a highly compact word syntax for transmission of stored mask information from a small computer, while the computer concurrently controls other system functions. The pattern generator is arranged to write shapes a minimum of data transfer. After initialization, only the origin and size of the first shape need be specified to begin execution. Then, if any parameters pertaining to a shape remain unchanged for the following shape, only the changes need be transmitted to cause the fill routine to operate. Predefined shapes (rectangles, parallelograms, triangles,...) are microcoded into the Generator and are directly invoked during the writing of a mask. A feature which provides still greater flexibility allows dynamic loading a microcode defining cells containing shapes whose perimeter may be irregular or curved. In addition, all these features may be written in an orientable array by giving a few machine instructions. This allows the repetition of millions of similar shapes with but a few transmitted words. The organization of the pattern generator is described, as well as integration with the remainder of the system to provide high-speed addressing of a 16K×16K array of points.
Design aspects of a scanning electron-beam-microfabrication instrument having 10×10 mm field coverage, normal substrate incidence, and high throughput
Authors: Jones G. A. C. , Owen G.
Published: July 2002

A microfabrication instrument with a field size of 10×10 mm is being developed so that masks for large devices can be exposed without having to stitch together a number of small fields. A satisfactory probe size has already been achieved using a postlens deflection system which has written 10 000 lines per field. Normal substrate incidence will be incorporated in order to eliminate positional errors due to electron optical distortion and to maintain a high writing speed despite the large scanned area. It is proposed that the positional errors be reduced by the application of a polynomial correction function containing terms corresponding to each of the possible deflection distortions. These errors may either be precorrected by a digital computer during data handling for the vector scan generator, or corrected in ’’real time’’ during exposure by suitable analogue modification of the scan currents. The fundamental writing speed of the magnetic deflection system is limited by the self-inductance and self-capacitance of the scan coils. It is shown how the number of turns wound on the coils may be optimized to obtain the maximum writing speed, subject to the constraints imposed by the output characteristics of the scan amplifiers and the allowable power dissipation in the scan coils.
Synchrotron radiation research: Recent developments
Authors: Lindau I. , Winick H.
Published: July 2002

Synchrotron radiation as a new tool within photon beam technology was described in the 13th Symposium on Electron, Ion, and Photon Beam Technology in Colorado Spings in May 1975. In this paper, we give a review of the developments since that time of the use of synchrotron radiation at SSRP (Stanford Synchrotron Radiation Project). The unique properties of synchrotron radiation have during the last two years been applied to an ever increasing number of research problems within x-ray absorption, diffraction, fluorescence, and scattering, within surface science, atomic, and molecular spectroscopy. The research capabilities at SSRP have been expanded and new instrumentation with, for instance, focusing x-ray optics has been developed. In particular, we want to discuss the current prospects and plans for expansion of the research facilities at SSRP.
Mechanism of cavity formation in unfired ceramic by electron-beam machining
Authors: Desilets Brian H.
Published: July 2002

A high-energy electron beam striking an unfired ceramic penetrates into the material to a maximum depth. Energy is given off along the path of penetration, but this energy transfer is a maximum at about 30% of the maximum penetration depth. Very shortly after the electron beam strikes the material, the organic binder vaporizes and forms a high-pressure, high-temperature gas pocket at the location of maximum-energy transfer. This gas pocket expands by melting the binder around its periphery until it penetrates the surface in an explosive action, drawing with it the solids and liquids and forming a cavity. This process continues until the beam is turned off. When the beam is turned off a heat-affected zone remains in the cavity wall. The heat dissipates into the bulk material, causing a temperature rise. This rise in temperature is calculated, and experimental results verifying the calculations are presented.
PR-30 ion implantation system
Authors: McCallum J. G. , Robertson G. I. , Rodde A. F. , Weissman B. , Williams N.
Published: July 2002

The PR-30 uses a 30-kV high throughput ion implanation system developed for the production line. It was designed to improve dose uniformity and control by replacing predeposition furnaces with acceptably fast ion implantation. The PR-30 uses rotating mechanical scan, in which 30 3-in. (7.6 cm) wafers are implanted simultaneously, to achieve high throughput at low as well as high doses. A doubly focusing magnet provides species selection and is the sole focusing element, and a high-current ion source allows short implant time. Typical ion beam currents are 1 mA of B+ and 5 mA of P+, As+, and Sb+. The pumping system gives a total batch change time of under three minutes which maintains high throughputs at low doses. Throughputs of 3-in. wafers at a dose of 1×1015/cm2 are 200/h for B+, and 450/h for the other species. The combination of a mechanical scanning mechanism, the doubly focusing magnet, and no accelerator section enables the machine to be compact. The beam line is vertical with the target at the top, and the required floor space is 6×7 ft (1.8×2.1 m) excluding instrumentation. The machine is fully automatic. A single button initiates the implant and a punched card defines the dose. All other functions and sequences are under computer control. PR-30’s have been used in production in the Western Electric manufacturing locations since 1974, and have significantly improved the yield of silicon devices.
Plasma etching—A discussion of mechanisms
Authors: Coburn J. W. , Winters Harold F.
Published: July 2002

The purpose of the present paper is to review the salient features of our understanding of phenomena which occur in plasma etching situations. The etching process is discussed in terms of three basic steps: adsorption, product formation, and product desorption. Experiments performed in well-defined (nonplasma) environments are discussed with the goal of clarifying the relative importance of these three steps in the etching process. An attempt is made to relate the resulting concepts to several phenomena generally observed in plasma situations (e.g. etching anisotropy, selective etching, the loading effect, and the role of additive gases). Moreover, the glow discharge, in addition to generating active species which initiate the chemical reactions, also causes the etched surface to be subjected to energetic particle (ions, electrons) bombardment. The role of this radiation in the etching process is emphasized. Speculative comments relating to plasma etching parameters and apparatus are also given.
Crosslinking positive resist for deep UV photolithography and its application to LSI fabrication processes
Authors: Yamashita Yoshio , Ogura Ken , Kunishi Mitsumasa , Kawazu Ryuzi , Ohno Seigo , Mizokami Yasuo
Published: July 2002

A new, crosslinking positive resist for deep-uv photolithography has been developed. This resist, a copolymer of glycidyl methacrylate and methyl methacrylate (GCM), degrades on irradiation with light from a D2 lamp and has a sensitivity of 0.25 J/cm2. Three-fourths μm line and space patterns are well resolved. It crosslinks at temperatures above 170°C in an inert atmosphere. This enables strengthening of the resist film by heat treatment after pattern delineation,greatly improving the adhesion and thermal properties of the resist. With these improvements, this resist can successfully be used for etching both SiO2 and phosphosilicate glass in a buffered HF solution. It can also be used for dry etching in CF4 plasma. It is preferable to use noncrosslinked GCM for CF4 plasma etching because the etching rate of noncrosslinked GCM is reduced to about one-third that of crosslinked GCM.
Comparative study of wet and dry oxides on polycrystalline GaAs by AES, SIMS, and XPS
Authors: Kazmerski L. L. , Ireland P. J. , Chu S. S. , Lee Y. T.
Published: July 2002

Complementary Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS), and x-ray photoelectron spectroscopy (XPS) are used to evaluate low-temperature wet and dry oxides and the oxide/semiconductor interfaces on polycrystalline GaAs. The dry oxides are found to be primarily Ga2O3 and are relatively uniform in composition. The wet oxides are less uniform and mixed, with a more abrupt transition region that the dry oxide/GaAs interface. XPS data confirm the presence of Ga2O3 in the dry oxide. In comparison, Ga2O3, As2O5 are detected in the wet oxide layer. SIMS shows higher trace impurity concentrations in the wet oxide with some buildup at the oxide/GaAs interface. The relative performance of solar cells fabricated from these structures is discussed.
Carbide formation due to Ar ion etching of Si
Authors: Kny E.
Published: July 2002

Mechanisms for carbide formation due to argon ion etching of silicon with resultant interference in auger electron spectroscopic analysis, are investigated. (AIP)
Unified defect model and beyond
Authors: Spicer W. E. , Lindau I. , Skeath P. , Su C. Y.
Published: July 2002

The unified defect model has been successful in explaining a wide variety of phenomena as oxygen or a metal is added to the III–V surface. These phenomena cover a range from a small fraction of a monolayer of adatoms to practical III–V structures with very thick overlayers. The tenets of the unified defect model are outlined, and the experimental results leading to its formulation are briefly reviewed. InP levels 0.4 and 0.1 eV and GaAs levels 0.7 and 0.9 eV below the conduction-band minimum (CBM) are associated with either missing column III or V elements. In InP, it has been found possible by a number of workers to ’’switch’’ between the two defect levels by variations in surface processing, temperature, and/or selection of the deposited atom. The need to apply the proper concepts for surface and interface chemistry and metallurgy is recognized, and the danger of using solely bulk concepts is emphasized. The reason for this is examined for certain cases on an atomic level. The need for new fundamental attacks on interface interaction is shown. The importance of semiconductor–oxide chemical stability is also recognized and, drawing on a large body of work from several laboratories, it is suggested that there will be more difficulties with ’’native’’ oxides on GaAs than on InP. It is concluded that ’’scientific engineering’’ of interfaces to give optimum performance should be a goal and test of the fundamental work described here. Specific possibilities are discussed for Schottky barriers on III–V’s.
Inversion layer transport and properties of oxides on InAs
Authors: Baglee D. A. , Ferry D. K. , Wilmsen C. W. , Wieder H. H.
Published: July 2002

Inversion layer transport in p-type InAs at 77 K using Van der Pauw samples has been investigated with anodic oxides and sputtered SiO2 as the gate insulators. It has been found that there is a correlation between the surface transport measurements, the fixed charge in the oxide, and possibly the insulating properties of the oxide. An attempt is made to develop a model to interrelate these measurements. It is found that fixed oxide charge appears to be the dominant mechanism in limiting the mobility at low surface carrier concentrations, while at higher concentrations surface roughness is the dominant mechanism.
Electron-beam direct writing of n-MOS devices and analysis of overlay and linewidth accuracies
Authors: Okazaki S. , Mulai F. , Takeda Y. , Mochiji K. , Takeda E. , Kume H. , Asai S.
Published: July 2002

Electron-beam direct writing of experimental, n-channel MOS devices is reported. This work has been done to identify the relative potential advantages and disadvantages of e-beam direct writing as one of the candidates for submicrometer lithography technology. The e-beam machine used in this work is a vector-scan system with a laser interferometry positioned stage. Both wafer registration and chip-by-chip registration schemes have been implemented in a simple, unified algorithm. Signal-to-noise ratio and process compatibility have been considered in determing the structure of alignment marks, with shallow (∠1.0 μm) grooves in the silicon wafer being adopted. Analysis of error factors, both instrumental and process related, which influence registration accuracy and linewidth control, has been carried out using a series of special experiments. It has been found that errors are rather evenly distributed over various causes. Electron beam direct writing has been found to provide excellent linewidth control and overlay accuracy, with 3 sigma limits of 0.1 and 0.5 μm, respectively.
Design of first walls and beam dumps for Tandem Mirror Experiment Upgrade
Authors: Drake R. P. , Lang D. D. , Hunt A. L. , Pickles W. L. , Simonen T. C. , Stack T. P. , Wilson K. L. , Baskes M. I. , Haggmark L. G. , Malinowski M. E.
Published: July 2002

Neutral reflux from the first walls and beam dumps of the Tandem Mirror Experiment (TMX) Upgrade could erode the neutral-beam-fueled end-cell plasma or cool the neutral-beam-heated central-cell plasma. To allow the TMX Upgrade to meet its design parameters, the neutral reflux to the plasma must be much less than the fluxes of both charge-exchange neutral products to the first walls and transmitted neutral-beam atoms to the beam dumps. To achieve this, we intend to evaporate titanium as a getter on the first wall and install vanadium-foil beam dumps. The vanadium beam dumps will be heated by the neutral beam during the shot, releasing most of the implanted hydrogen as they cool radiatively after the shot. The deposited titanium will be thick enough to retain the implanted charge-exchange neutral products. We describe our design of these components, report our estimates of their performance, and compare their performance to the needs of TMX Upgrade.
Methods for calibration of standard leaks
Authors: Iverson M. V. , Hartley J. L.
Published: July 2002

The Sandia Laboratories Standards Department is currently using the comparison, PΔV, and accumulate-dump methods to calibrate standard leaks. The comparison method may be used in the range from 10−5 to 10−8 atm cm3/s with a maximum uncertainty of 10%. The PΔV method can be used for fundamental calibration of faster leaks in the range from 10−3 to 10−5 atm cm3/s with a maximum uncertainty of 5%. Finally the accumulate-dump method can be used to fundamentally calibrate leaks in the range from 10−4 to 10−10 atm cm3/s with uncertainties ranging from 5 to 20%. The purpose of this paper is to introduce these three calibration methods with an analysis of the errors involved. These methods are reviewed and compared with other leak calibration methods.
An investigation of the interface electronics structure of Si–SiO2 junctions
Authors: Ciraci S. , Ellialtioğlu Ş. , Erkoç Ş.
Published: July 2002

To understand the physical origin of the interface states in the Si band gap, we have performed empirical tight-binding calculations for various model structures. We have shown that oxygen atoms breaking the bonds of a Si tetrahedron and forming Si–O–Si or Si–O bonds induce empty states localized at the backbonds. Energy location of these states is seen to depend on the depletion of charge from the backbonds. The role of Si and O vacancies in the vicinity of the interface is also discussed.
Simple, low cost, and highly stable Pd evaporation source for use in UHV
Authors: De Cooman B. C. , Vook R. W.
Published: July 2002

The design of a source for the thermal evaporation of Pd from a resistively heated W filament in UHV is presented. The source’s main advantages are its simplicity, low cost, long lifetime, and stability at low deposition rates.
Gas pressure in the end plug regions of the TMX-U thermal barrier experiment
Authors: Turner W. C. , Nexsen W. E. , Allen S. L. , Hooper E. B. , Hunt A. L. , Lang D. D. , Margolies D. S. , Pickles W. L. , Simonen T. C.
Published: July 2002

We consider briefly the upper bound on background pressure (0.5 to 1.0×10−6 Torr) that is required for operation of the thermal barrier end plugs of TMX-U and propose a rate equation for pressure buildup that includes terms for neutral beam injection and wall reflux. During early operation of TMX-U the background pressure exceeded this upper bound; in addition, axial end plugging of plasma losses seemed limited by the excessive pressure. Modifications to the vacuum system to decrease this pressure to the desired range are described. Furthermore, wall reflux is shown to depend linearly on pressure. We conclude with an example of the dramatic increase in time duration of axial plugging of plasma losses with the reduced background pressure.
UPS investigation of poorly crystallized MoS2
Authors: Liang K. S. , Hughes G. J. , Chianelli R. R.
Published: July 2002

We have performed photoemission studies on samples of poorly crystallized MoS2 prepared in situ by thermal decomposition of (NH4)2MoS4 in a UHV-compatible chamber under mixed H2S/H2 gas conditions. The results reveal new electronic states which are not present on crystalline MoS2. These states are observed as a band tail above the dz2 band of MoS2. These tail states are presumably ‘‘chemically active’’ as shown by reversible oxygen adsorption–desorption.
A hollow droplet generator for polymer shell production
Authors: Crawley R.
Published: July 2002

Small, spherical, polymer shells are used as fuel containers in inertial fusion experiments. These shells have traditionally been made by spray drying or more recently using droplet generators. It has proven difficult to control product size and wall thickness for thermosetting materials. In this work we describe a dual orifice droplet generator for making hollow shell preforms. The inner orifice injects bubbles of a desired gas into the polymer solution droplet stream. The stream is agitated using a piezoelectric diaphragm and produces uniformly sized hollow droplets. Shells formed from these hollow preforms have tight distributions of diameter and wall thickness.
Highly conducting ZnSe films by reactive magnetron sputtering
Authors: Nouhi A. , Stirn R. J.
Published: July 2002

This paper presents the results of an effort to deposit high conductivity ZnSe on glass and conducting SnO2-coated glass substrates by reactive magnetron sputter deposition, using pure metal sputter targets of Zn and dopants, such as In, Ga, and Al. Clear yellow ZnSe films were successfully obtained. By using substrate temperatures as low as 150 °C, cosputtered dopants, and sputter parameters and H2Se injection rates which maximize the Zn to Se ratio in the films, ZnSe bulk resistivities have been lowered by up to seven orders of magnitude, reaching values as low as 20 Ω cm. The most effective dopant to date has been In, cosputtered with Zn in amounts leading to In atomic concentrations as high as 1.4%. Atomic absorption measurements show an average 49.9/48.9 ratio of Zn to Se.
Automatic regeneration of multiple cryopumps
Authors: Finley Laurence A.
Published: July 2002

A method of automating the simultaneous regeneration of any of all of six 48 in. diam cryopumps is presented. (Cryopump regeneration is a process which involves multiple backfill/evacuation cycles.) Conventional Boolean logic gates are combined into control loops which are explained, along with the basic functioning of the computer, for this portion of the vacuum chamber operation. The proposed system optimizes use of the computer by using an endless loop search-and-scan procedure. The computer looks at the first cryopump, tests for the necessary operations, performs them, and then indexes to the next cryopump, eventually returning to the initial station. The cycle is repeated until all selected cryopumps are completely regenerated. Implementation of this package is planned for the winter of 1986 on the 17 000 ft3 thermal vacuum chamber at Rockwell International, Seal Beach, California.
Calorimetry in thin film processing
Authors: Shivashankar S. A. , Robinson B.
Published: July 2002

Thin film processes such as etching, deposition, reactive etching, and reactive deposition involve energy transfer which affects substrate temperature measurably. In plasma chemical reactors, these changes are related to ion flux and energy, rate of etching or deposition, and to the specifics of the reactions occurring at the substrate. We have adapted the method of thermal relaxation calorimetry, originally developed for low temperature measurements, to estimate the heats of reaction at the surface of substrates in low pressure plasmas. The technique may also be used to measure deposition and etch rates and for end point detection. Calorimetry can be important in plasma diagnosis and in understanding process mechanisms. This is shown by studies of the variation of the dissociation efficiency of O2 in a rf plasma due to the addition of CF4, and of the heat of oxidation of polyimide as a function of gas composition in a O2/CF4 microwave plasma downstream etcher.
Industrial materials processing experiments on board the Space Shuttle Orbiter
Authors: Debe M. K.
Published: July 2002

The Space Shuttle Orbiter in low Earth orbit provides a unique laboratory environment to study the effects of microgravity on many materials-processing phenomena. The intent may be to ultimately learn more about a system’s behavior in unit gravity or observe the process pathways when controlled totally by nongravitational forces. Fluid transport and interface phenomena may be expected to behave in a novel manner. A tabulation of the materials processing experiments performed on the Orbiter through August 1985 is presented. Current American industrial experiments, recently performed or presently planned are briefly discussed, with a more in-depth look at the microgravity vapor transport experiment for crystal and thin film growth. In particular, the 3M-sponsored Physical Vapor Transport of Organic Solids Experiment (PVTOS) which flew on STS-51I in August 1985, is reviewed. It contains nine vacuum-insulated reactor cells, designed to grow organic films on controlled substrates by diffusion through an inert buffer gas at temperatures up to 400 °C. The vacuum processing and design of the cells, finite element analysis thermal modeling, data acquisition, and material parameter aspects of the experiment are discussed.
The design, construction, and testing of the vacuum vessel for the tandem Mirror Fusion Test Facility
Authors: Gerich Jerry W.
Published: July 2002

In 1980, the U.S. Department of Energy gave the Lawrence Livermore National Laboratory approval to design and build a tandem Mirror Fusion Test Facility (MFTF-B) to support the goals of the National Mirror Program. We designed the MFTF-B vacuum vessel both to maintain the required ultrahigh vacuum environment and to structurally support the 42 superconducting magnets plus auxiliary internal and external equipment. During our design work, we made extensive use of both simple and complex computer models to arrive at a cost-effective final configuration. As part of this work, we conducted a unique dynamic analysis to study the interaction of the 32 000 tonne concrete-shielding vault with the 2850 tonne vacuum vessel system. To maintain a vacuum of 2×10−8 Torr during the physics experiments inside the vessel, we designed a vacuum pumping system of enormous capacity. The vacuum vessel (4200 m3) has been fabricated, erected, and acceptance tests have been completed at the Livermore site. The rest of the machine has been assembled, and individual systems have been successfully checked. On October 1, 1985, we began a series of integrated engineering tests to verify the operation of all components as a complete system.
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u fracture stage for x-ray photoelectron spectroscopy and Auger electron spectroscopy studies of internal surfaces in polycrystalline materials
Authors: Brüesch P. , Foditsch W. , Stucki F.
Published: July 2002

An in situ fracture state for x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy studies of internal surfaces in polycrystalline materials is described. The system offers the possibility to study both surfaces produced as a result of a fracture, allowing the comparison of physical and compositional features of one surface with those of its conjugate. The notched sample can be cooled to liquid-nitrogen temperature prior to fraction. By using an electron collimator only photoelectrons from the fractured surface but not from the notch area are observed. The method is illustrated by XPS measurements obtained from fractured surfaces of an AlMgSiPb alloy (transgranular fracture), a Bi-doped ZnO varistor (intergranular fracture), and polypropylene containing an antioxidant (interspherulitic fracture). The main motivation which led to the development of this fracture stage lies in the possibility to correlate the microstructure and microchemistry of internal surfaces with the relevant macroscopic properties of polycrystalline materials.
Image processing techniques for obtaining registration information with scanning tunneling microscopy
Authors: Wilson R. J. , Chiang S.
Published: July 2002

Scanning tunneling microscopy is a powerful tool for the study of surface structure. Information can be obtained by examining real-space structure within unit cells and by determining the registration of features relative to the positions of the bulk lattice. Techniques for image enhancement, distortion correction, and registration determination are described and illustrated for structural studies of the ((3)1/2×(3)1/2)R30° Ag/Si(111) surface.
X-ray photoelectron forward scattering studies of surface segregation in epitaxial Ni–Cu–Ni(100) sandwich structures
Authors: Egelhoff W. F.
Published: July 2002

The forward scattering of the Cu 2p3/2 core level photoelectrons by overlying Ni lattice atoms which occurs in the photoemission process has been used to follow the segregation of Cu to the surface of epitaxial Ni–Cu–Ni(100) sandwich structures. The results indicate that when 1 monolayer (ML) of Cu is covered by 1–2 ML of Ni, surface diffusion processes constitute the mechanism by which the segregation occurs, whereas if 1 ML of Cu is covered by 10 ML or more of Ni the segregation involves the usual bulk (vacancy) diffusion mechanism. Since these processes are quite general, it appears that the top few atomic layers of a binary alloy can equilibrate with respect to surface segregation at a temperature significantly lower than that which is required for bulk equilibration. This combination of x-ray photoelectron spectroscopy (XPS) forward scattering and epitaxial sandwich structures thus provides both more clear-cut data and a more specific understanding of segregation phenomena than is usually possible by conventional XPS and Auger studies on random alloys.
Molecular structure of organic compounds observed by high resolution scanning tunneling microscopy
Authors: Selci S. , Cricenti A. , Felici A. C. , Generosi R. , Gori E. , Djaczenko W. , Chiarotti G.
Published: July 2002

Uncoated DNA molecules marked with an activated tris (1-aziridinyl) phosphine oxide (TAPO) solution were deposited on gold substrates and imaged in air with the use of a high-resolution scanning tunneling microscope (STM). Constant-current and gap-modulated STM images show a clear evidence of the helicity of the DNA structure; pitch periodicity ranges from 2.5 to 3.5 nm whereas the average diameter is 2.0 nm. Molecular structure within a single helix turn was also observed. TAPO molecules have been imaged alone and appear as a crystalline structure of rows of molecules with a side-by-side spacing of 0.3 nm.
Elaboration and evaluation of tip manipulation of scanning tunneling microscopy
Authors: Tomitori Masahiko , Hirano Nobuo , Iwawaki Fumikazu , Watanabe Yuichi , Takayanagi Tetsuya , Nishikawa Osamu
Published: July 2002

A set of leaf springs, a micrometer head, a bellows coupling, a ball-bearing-type reduction gear, and a stepping motor were coupled in series to realize the quick and fine approach of a specimen surface to a scanning tunneling microscope tip. The minimum tip–surface displacement by the coupled system is in the range of 20–40 Å and the maximum approaching speed is 0.25 mm/s. At the final stage of approach a piezoelement brought the specimen to the tunneling region between the Pt–Ir tip and the specimen graphite surface. The material transfer from the specimen to the tip apex was revealed by the atom-probe mass analysis of the apex after a trial approach at the speed of 0.4 μm/s. However, no overshooting current by a tip–specimen contact was noticed throughout the trial approach. The observed mass transfer without a sign of the contact was attributed to the long response times of the current amplifier and the feedback circuit monitoring the approach. No material transfer was noticed for 0.16 μm/s.
Helium pumping by argon frosting on a 4.5 K surface
Authors: Kim Jinchoon , Schaubel K. M. , Colleraine A. P.
Published: July 2002

Pumping of helium gas by means of argon frosting on a bare copper surface cooled to ∼4.5 K has been investigated in one of the neutral beamlines of the DIII-D tokamak. The beamline is designed to handle high power hydrogen and deuterium beams and corresponding high gas feed rates. By prefrosting the cryo panels with argon in an actual beamline, multisecond helium gas pulses have been handled at a background gas pressure low enough for formation and transport of helium beams. Appreciable pumping of helium gas was observed even at an argon-to-helium ratio as low as 20.
Growth mode determinations for the epitaxial Cu/Pd(111)/mica and Pd/Cu(111)/mica thin film systems
Authors: Oral B. , Vook R. W.
Published: July 2002

The growth of Cu on epitaxially grown Pd(111)/mica and the growth of Pd on epitaxially grown Cu(111)/mica surfaces were studied with Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED) under UHV conditions. The results show that epitaxial Cu grows on Pd(111) by a layer mode of growth. However, Pd grows on Cu(111) in three-dimensional clusters on top of an initial approximately three monolayers, i.e., by a Stranski–Krastanov mode. LEED studies showed that in both cases a (1×1) pattern was observed with increasing overlayer thicknesses.
Observation of an organic superconductor [bis(ethylenedithio)tetrathiafulvalene]2[Cu(NCS)2] by scanning tunneling microscopy
Authors: Yoshimura M. , Fujita K. , Ara N. , Kageshima M. , Shioda R. , Kawazu A. , Shigekawa H. , Hyodo S.
Published: July 2002

The surface of an organic high-Tc superconductor, (BEDT-TTF)2[Cu(NCS)2] [BEDT-TTF: bis(ethylenedithio)tetrathiafulvalene, Tc=10.4 K under ambient pressure], was observed with a scanning tunneling microscope in air and at room temperature. The step height observed on its surface was 13.2 Å and was very close to the one layer thickness of the (BEDT-TTF)2[Cu(NCS)2] crystal (15.22 Å, determined by x-ray diffraction). Periodic zig-zag structures were observed along the diagonal line of the surface unit cell and agreed well with the two-dimensional BEDT–TFF molecular structure projected onto its crystal b-c plane.
Modification to thermal emissions by clusters on their own metallic surface
Authors: Biblarz Oscar
Published: July 2002

The permanent presence of clusters on their own solid surface is shown to modify particle emission. These modifications affect atom/molecule emission, electron emission, and photon emission from pure metallic surfaces at a vacuum interface. Data for refractory metals, particularly for tungsten, are scrutinized for effects from these bound clusters, or Maxwell–Boltzmann (MB) particle aggregates, which do not exhibit a crystalline structure but are nevertheless part of the surface. It is shown that the so-called work function temperature dependence can be alternatively accounted for by the presence of MB emission sites, and that the descriptions of mass evaporation and radiant heat emission are refined. In the case of photon emission, a complementary gas-like line radiation emerges when measurements and the classical free-electron theory in the near-infrared and visible range are examined in the context of our postulate. Actual observations of individual particle behavior on pure surfaces are enumerated, and a theoretical backup for the predicted area ratio of MB sites to total sites is given.
Statistical treatment on the formation of Si(100) 2×n surface
Authors: Tamura Akira
Published: July 2002

Si(100) 2×n structure observed recently by scanning tunneling microscopy (STM) is analyzed by a statistical method. It is shown that the defect formation energy should be positive and the stability of the structure is induced by configurational entropy term in the free energy not only by the internal energy term. The formation energy is estimated as to be 0.14 eV per one missing-dimer defect. It is emphasized that the real space image such as that of STM provides the dynamical quantity associated with the reconstruction of the surface.
Diffusion welding of silver interlayers coated onto base metals by planar-magnetron sputtering
Authors: Rosen R. S. , Kassner M. E.
Published: July 2002

Silver has been coated onto various base metals by planar-magnetron (PM) sputtering to provide interlayers for diffusion welding. The vacuum-coating process consisted of two stages: (1) sputter etching of the base metals to remove surface oxide layers, followed by (2) vapor deposition of high-purity silver onto the clean surfaces. The silvers surfaces were diffusion welded at elevated pressure (207 MPa) and temperatures (483–673 K). The structures of the diffusion-welded-silver interlayer and the ‘‘as-deposited’’ coatings were determined using optical metallography and electron microscopy. The as-deposited structure consists of fine columnar grains ∼0.25 μm in diameter, perpendicular to the base-metal surface with the axes of the columns oriented along the [111] crystallographic direction. These grains contain a high density of growth twins ∼15 nm thick. The diffusion-welded-silver interlayer consists mostly of large recrystallized grains (>1 mm in diameter) containing a high density of annealing twins. However, a significant amount of the interlayer has not recrystallized. Additionally, the diffusion-welded-silver (silver-silver) interface consists of a high-angle grain boundary often formed between recrystallized and nonrecrystallized regions. For various base metals, the tensile strengths of diffusion-welded-silver joints fabricated using PM sputter deposition were found to be equal to or greater than previously reported strengths for those fabricated using brazing, electroplating, or other vapor-deposition methods. Tensile properties of diffusion-welded-silver joints fabricated using PM sputter-deposition were also found to be more reproducible than properties previously reported for joints fabricated using hot-hollow cathode (HHC) evaporation. Torsion tests of the diffusion-welded-silver joints revealed that the yield stress and strain-hardening rates in the interlayer are much higher than corresponding values for high-purity annealed bulk silver, although the maximum (steady-state) stresses are nearly identical. These results may be at least partially explained by the high twin density in the recrystallized silver and also the very fine microstructure of the nonrecrystallized regions.
Polyimide etching in Ar, O2, and O2/F2 gas mixtures: Effect of ion energy
Authors: Tepermeister I. , Sawin H.
Published: July 2002

Dry etching of PMDA-ODA polyimide films (DuPont 2570D) in Ar, O2 and O2/F2 plasmas was studied in a novel reactor, which directly exposes a sample located in high vacuum to species present in the plasma and allows independent control of ion bombardment energy. This reactor configuration enabled a line-of-sight mass spectrometer to detect product distributions for the etching of polyimide films as a function of impinging ion energy and substrate temperature. The plasma was operated at 1.0 Torr pressure and 2.5–5 W/cm2 power density. The ion bombardment energy was varied between 0 and 500 eV, and the sample temperature was varied between 25 °C and 300 °C. Acetylene (C2H2) was a major product of ion bombardment in argon and pure oxygen plasmas. Ion-dependent production of acetylene showed a maximum with respect to ion energy, which decreased and shifted to lower ion energy with increasing substrate temperature. In pure oxygen plasmas, the maxima in acetylene signal appeared at higher ion energies for all temperatures. Addition of 2.5% fluorine to the oxygen plasma greatly increased the etching rate and substantially changed the product distributions. Abstraction of hydrogen from the polymer was observed, and the ion-dependent portion of acetylene production increased both with ion energy and with substrate temperature. Large fluorine addition passivated the surface, greatly decreasing product formation.
Low-temperature dry etching
Authors: Tachi Shinichi , Tsujimoto Kazunori , Arai Shin , Kure Tokuo
Published: July 2002

Low-temperature electron-cyclotron-resonance microwave plasma etching and reactive ion etching are described for ULSI device fabrication. Highly selective anisotropic etching at a high rate, which implies dry etching without tradeoffs, is performed without changing the discharge parameters. This etching is only achieved at reduced wafer temperatures. The etching mechanism and the model are discussed based on the etching yield results obtained by the mass-selected reactive ion beam etching experiments. The new etching system and the etching properties obtained for the low-temperature etching are reviewed comparing those obtained in the conventional reactive ion etching and electron-cyclotron-resonance microwave plasma etching.
Some experiments that provide direct visualization of reactive sputtering phenomena
Authors: Vossen J. L. , Krommenhoek S. , Koss V. A.
Published: July 2002

Experiments using a reactive gas inlet tube laying directly on substrates during reactive sputtering of Al, Ti, and Zn have provided several insights into the mechanism of reactive sputtering and the efficiency of various gases for producing oxides. These effects can be visualized directly on the substrates. Reactive gases explored were O2, N2 O, CO2, and mixtures of O2 and H2 O. The experiments were conducted in the metallic target mode. The oxidized regions of the substrate near the reactive gas inlet tube are directly visible on the substrate. The size and shape of the oxidized regions allows one to visualize directly various reactive sputtering phenomena. From the data obtained one can (1) visualize directly that the reactive gas flow is molecular for low flows at pressures up to ∼20 m Torr and starts the transition to viscous flow at about that pressure, (2) separate the effects of local reactive-gas concentration at the substrate and target oxidation on the efficiency of the reaction, (3) confirm directly the relation of metal oxidation efficiency and the free energy of oxide formation, and (4) rank order the efficiency of oxidation of the different gases investigated.
The reaction of oxygen with the hot W(001) surface studied by low-energy electron microscopy
Authors: Altman M. S. , Bauer E.
Published: July 2002

Low-energy electron microscopy has been used to study the irreversible W(001)–O p(5×1)–p(2×2) surface transformation during oxygen deposition at 1050 K. Chains of p(2×2) nuclei form in a self-avoiding-random-walk pattern. It is concluded that oxygen diffusion is an important step in the reaction path to incorporation into the hot surface.
Cosputtering of alloys. I. Cosputtering of oxides and nitrides using two planar magnetrons
Authors: Belkind A. , Ezell E. , Gerristead W. , Orban Z. , Rafalko P. , Dow D. , Felts J. , Laird R.
Published: July 2002

A study to explore the properties of mixed oxides and nitrides deposited using reactive cosputtering from two rectangular cathodes is reviewed. Deposition results of some mixed oxides and nitrides made using cosputtering from different pairs of elemental targets (Al, Ti, and Zr) are presented. Structure, composition, optical, and mechanical properties of the single and mixed oxides and nitrides are also presented and reviewed in this paper.
Metalorganic chemical vapor deposition growth of ZnTe on GaAs
Authors: Tompa G. S. , Summers C. J.
Published: July 2002

High quality ZnTe (100) films have been grown on GaAs (100) off 3° toward 〈110〉 orientated substrates by metalorganic chemical vapor deposition. The growths were performed at 304 Torr in a vertical reactor with a high speed, horizontal, rotating wafer carrier. Diethylzinc and diisopropyltelluride were used as reactants. Specular films have been grown with x-ray full width half-maximums of 110 arcsec. Hall and low temperature photoluminescence data indicate the films to be of high quality with the presence of zinc vacancy acceptors and shallow donor sites. Secondary ion mass spectrometry also shows the films to be pure with some Ga outdiffusion from the substrate.
Thermally and optically stimulated exoelectron emission from an electron-beam irradiated glass–ceramic material
Authors: Carroll D. L. , Doering D. L. , Blais B. S.
Published: July 2002

The exposure of insulating materials to an electron beam results in the trapping of excess charge on the surface. We have studied the thermally and optically stimulated emission of this excess charge in an electron-bombarded, fluorophlogopite mica glass–ceramic material (Macor). The total electron emission from the surface is measured either as a function of the sample temperature during heating or the photon wavelength. The emission as a function of temperature has four characteristic peaks whose relative intensity depends on the beam dose, energy, initial sample temperature, and history (accumulation of beam-induced defects). One peak occurs immediately upon heating and is related to the total surface charge. Two peaks occur at fixed temperatures of 280 and 325 °C and are associated with the discrete energy trap states. The highest temperature peak is only observed after prolonged beam exposure and is due to the annihilation of defects. Illumination in the ultraviolet is required to produce photoemission for an uncharged sample. However, after electron bombardment, electron emission is observed over a broad range of visible wavelengths. In addition, two photoemission thresholds at about 2.7 and 3.1 eV suggest electron trap states which can be associated with the thermally emitted peaks. The thermally and optically stimulated emission is a valuable tool to measure the electron state distribution in charged insulating materials.
High-resolution depth profiling of semiconductor structures: Preliminary results
Authors: Drummond I. W. , Dowsett M. G. , James D. M. , Street F. J.
Published: July 2002

The fabrication of semiconductor multilayer structures is becoming increasingly important. In this paper we shall outline an attempt to study such a sample in depth using the combination of 16O+2 ion beam bevel etching and imaging x-ray photoelectron spectroscopy (XPS) with the objective of establishing the method and examining the surface chemistry of Si:Ge material under the conditions obtained in secondary ion mass spectrometry (SIMS) analysis. The advantages and disadvantages of the method as applied to Si/Si0.75Ge0.25 structures will be discussed.
Adsorption and decomposition of TMGa on GaAs(100)
Authors: Stienstra J. , Lewis B. S. , Aarts J. F. M.
Published: July 2002

The adsorption and decomposition of trimethylgallium (TMGa) on the gallium-rich GaAs(100) surface has been studied using electron-energy-loss spectroscopy (EELS) and Auger electron spectroscopy (AES). It was found that the first layer of TMGa already decomposes at 100 K. Further dosing the surface resulted in condensation of TMGa. At room temperature only chemisorbed TMGa was found, with a saturation coverage of 0.3±0.1 monolayer gallium. We found the adsorbate species to be monomethylgallium and/or dimethylgallium. We also studied the adsorption and decomposition of iodomethane, as well as the adsorption of hydrogen. Coadsorption experiments showed that only TMGa could replace or react with the adsorbed hydrogen atoms. In the case of CH3I almost no coadsorption or reaction occurred.
Electron beam patterning of epitaxial CaF2 and Ca0.5Sr0.5F2/(100)GaAs
Authors: Hirose Y. , Horng S. , Kahn A. , Wrenn C. , Pfeffer R.
Published: July 2002

The electron beam patterning of crystalline CaF2 and Ca0.5Sr0.5F2 thin films grown by molecular-beam epitaxy is demonstrated. The mechanism leading to patterning is the removal of fluorine through high energy electron beam exposure and dissolution of the resulting metal oxide in a water-based solution. A scanning Auger microprobe and a scanning electron microscope are used as exposing tools. The development of the films is performed either in deionized water or in a weak HCl solution. The chemical analysis of the patterned features confirms the development of small windows. The feasibility of the fabrication of micrometers features is verified.