bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-assembled quantum dot transformations via anion exchange
Authors: Shen Jeng-Jung , Brown April S. , Wang Yongqian , Wang Zhong L.
Published: July 2002

We report the effect of dissimilar anion anneals on the properties of layered quantum dot structures exhibiting vertical self-organization. Such anneals may provide an additional means of controlling dot properties, such as composition, size, and position. In addition, the modification of surface strain is critical to the subsequent nucleation of dots after the initial seed layer. Anion exchange may modify the strain at the semiconductor surface. We find that the effects of P2 and As4 anneals on InAs quantum dot size distributions are different. P2 anneals at relatively high temperatures (350 °C) can cause the loss of the three-dimensional morphology due to surface exchange. P2 anneals at lower temperatures (300 °C) appear to improve the uniformity of the dot size distribution. This behavior is not observed for anneals under As4. The dot size uniformity decreases by annealing dots under As4 at 300 °C.
Electron traps at interfaces between Si(100) and noncrystalline Al2O3, Ta2O5, and (Ta2O5)x(Al2O3)1−x alloys
Authors: Johnson R. S. , Hong J. G. , Lucovsky G.
Published: July 2002

The physical and electrical properties of noncrystalline Al2O3, Ta2O5, and their alloys, (Ta2O5)x(Al2O3)1−x, are investigated. Characterization by Auger electron spectroscopy and Fourier transformation infrared spectroscopy confirm these alloys are homogeneous with pseudobinary in character, and display increased thermal stability. Capacitance–voltage and current density–voltage data as a function of temperature demonstrate that the Ta d states of the alloys act as localized electron traps, and are at an energy approximately equal to the conduction band offset of Ta2O5 with respect to Si.
Emission-uniformity improvement and work-function reduction of Si emitter tips by ethylene gas exposure
Authors: Matsukawa Takashi , Kanemaru Seigo , Nagao Masayoshi , Yokoyama Hiroshi , Itoh Junji
Published: July 2002

Emission uniformity improvement of a silicon field emitter array (FEA) by ethylene (C2H4) gas exposure has been investigated in detail especially about its origin. Scanning Maxwell-stress microscopy has been utilized to evaluate the surface potential at the Si tip apex in the FEA before and after the improvement. Careful consideration to eliminate the influence of the surrounding gate has been made in order to estimate work function at the tip apex. It has been found that the work function at the tip apex decreased upon C2H4 exposure. It has been clarified that the uniformity improvement by C2H4 exposure is mainly due to the reduction in the tip work function.
Deposition of amorphous and microcrystalline silicon using a graphite filament in the hot wire chemical vapor deposition technique
Authors: Morrison Scott , Madan Arun
Published: July 2002

The use of a graphite filament in the “hot wire” chemical vapor deposition technique is demonstrated to produce “state-of-the-art” intrinsic and doped (p- and n-) amorphous silicon (a-Si:H) material and microcrystalline silicon (μc-Si) materials. Preliminary p-i-n type solar cells have led to a conversion efficiency of >8.5%. The filament is found to be rugged and remains intact even after deposition of ∼500 μm in thickness. This is in contrast to the use of conventional filament materials, such as W or Ta, whose longevity is limited to less than a few microns of deposition. Unlike the case of a Ta filament, the deposition rate remains constant with the use of a graphite filament.
Photolithographic patterning of proteins with photoresists processable under biocompatible conditions
Authors: Douvas Antonios , Argitis Panagiotis , Diakoumakos Constantinos D. , Misiakos Konstantinos , Dimotikali Dimitra , Kakabakos Sotirios E.
Published: July 2002

The microlithographic patterning of proteins on solid substrates using photoresists, which can be processed in the presence of biomolecules without affecting their bioactivity, is reported. Chemically amplified resist materials based on poly(t-butyl acrylate) and a newly synthesized copolymer of t-butyl methacrylate, 2-hydroxyethyl methacrylate, isobornyl methacrylate, and acrylic acid designed for this application, are evaluated regarding capabilities for processing under biocompatible conditions (processing temperatures at about 50 °C or lower and development with dilute aqueous base developers). The photoresist formulations based on the newly synthesized (meth)acrylate copolymer had higher sensitivity and contrast allowing lithographic processing even without postexposure bake. Patterns down to 3.75 μm lines/spaces of two different protein molecules, rabbit Immunoglobulin G and bovine serum albumin, on aminosilane-treated silicon surfaces, were obtained with a photoresist formulation based on the new copolymer and an onium salt photoacid generator under biocompatible processing conditions.
High sensitivity actinic detection of native defects on extreme ultraviolet lithography mask blanks
Authors: Yi Moonsuk , Haga Tsuneyuki , Walton Chris , Bokor Jeffrey
Published: July 2002

We present recent experimental results of actinic extreme ultraviolet lithography mask blank defect inspection. The detection sensitivity of the current actinic inspection system is predicted to be able to reach approximately 30 nm in cross correlation experiments done with commercial visible-light, scanning electron microscopy (SEM), and atomic force microscopy (AFM) inspection tools. Random, native defects identified using the visible-light tool were scanned by the actinic tool and the scattering characteristics were compared. SEM and AFM characterization of selected defects were also performed for physical measurement. We found a defect whose size was as small as 60 nm and AFM analysis showed that this defect was a 3 nm high substrate defect that was smoothed-out by the multilayer coating.
Effect of resist sensitivity ratio on T-gate fabrication
Authors: Chen Y. , Macintyre D. S. , Thoms S.
Published: July 2002

The need for short length T gates with good process control is demanding because pattern resolution is required in the lower level of resist. This article considers different resist systems and uses the resist sensitivity ratio between the head and foot defining layers to build two models. These are useful for determining the optimum parameters for T-gate fabrication and associated gate feeds. We show that the optimum resist sensitivity ratio is about 6 at 50 kV where bloating is negligible and good footwidth control is obtained. We also show that further improvements can be obtained by moving to 100 kV where a sensitivity ratio of 14 can be used. Sensitivity ratios between 6 and 14 can be achieved using either the poly(methylmethacrylate)/UVIII or ZEP520/UVIII bilayers since in both cases the sensitivity ratio can be varied by changing the development times and the bake temperatures.
Characteristics of sputtered Ti1−xAlxN films for storage node electrode barriers
Authors: Park Dae-Gyu , Cha Tae-Ho , Lee Sang-Hyeob , Yeo In-Seok , Park Jin Won , Kim Sam-Dong
Published: July 2002

We report on the characteristics of sputter-deposited Ti1−xAlxN (TiAlN) thin films for storage node electrode barriers of Pt/(BaSr)TiO3(BST)/Pt metal–insulator–metal (MIM) capacitors with a comparative study of TiN films. The substrate temperature (Ts) was found to be one of the key factors affecting the properties of TiAlN thin films, i.e., the resistivity of TiAlN is ∼350 μΩ cm for high Ts deposition (∼450 °C) and ∼1100 μΩ cm for low Ts (∼100 °C). The lower resistivity of TiAlN films deposited at high Ts (450 °C) is attributed to the (200) texture with larger grain size and smaller oxygen concentration compared to those prepared at low Ts. The electrical characteristics of Pt/BST/Pt MIM capacitors on TiAlN were superior to those on the TiN barrier in terms of smaller equivalent oxide thickness (tox), lower tangent δ, and lower leakage current. Better oxidation resistance of TiAlN over TiN appears to be responsible for the better electrical results, especially with the (111) or (200) texture. We also discuss a BST bulge and local thinning due to the Pt deformation on TiAlN over an anneal of 600 °C in O2, resulting in leakage current degradation of the BST MIM capacitor.
Investigation of macroscopic uniformity during CH4/H2 reactive ion etching of InP and its improvement by use of a guard ring
Authors: Janiak K. , Niggebrügge U.
Published: July 2002

We investigated the wafer uniformity of the etch attack obtained by reactive ion etching of InP in a CH4/H2 plasma. We found that this process inherently tends to produce a rather nonuniform distribution of etch rates across InP wafers with the fastest etching occuring at the wafer edge. Nonuniformities of up to 35% are observed. We propose a simple model, which explains the observation by reactants, which originate from nonetched regions, diffuse parallel to the wafer surface, and locally enhance the etch rate. The nonuniformity can be efficiently counteracted by a proper choice of the process pressure or even completely avoided by the introduction of a guard ring. In addition we also found that the arrangement of the masked areas on the wafer influences the etch rate profile.
Fabrication of mesoscopic superconducting Nb wires using conventional electron-beam lithographic techniques
Authors: Kim Nam , Hansen Klavs , Toppari Jussi , Suppula Tarmo , Pekola Jukka
Published: July 2002

Conventional electron-beam lithography has been used to fabricate mesoscopic Nb wires. Nb was deposited in an ultrahigh vacuum evaporation chamber using electron gun heating. The typical linewidth and the thickness were 200 and 50 nm, respectively. The transition temperatures were above 7 K. They increased with thickness and linewidth. To demonstrate the feasibility of two angle evaporation techniques, we also fabricated Nb/(Al–)AlOx/Nb tunnel junctions showing superconducting single-electron transistor characteristics.
Depth distribution and diffusion behavior of implanted Bi+ ions into KTiOPO4
Authors: Wang Ke-Ming , Hu Hui , Lu Fei , Chen Feng , Zhang Jian-Hua , Liu Xiang-Dong , Liu Ji-Tian , Liu Yao-Gang
Published: July 2002

KTiOPO 4 samples were implanted by Bi+ ions with energies from 100 to 350 keV in increments of 50 keV. The depth distribution and diffusion behavior of implanted Bi+ into KTiOPO4 were investigated by normal and oblique incidence Rutherford backscattering. The results show that the maximum difference between experimental and calculated values of the mean projected range is less than 22%; the experimental range straggling somewhat deviates from the prediction by TRIM'98. After annealing, the redistributions of implanted Bi+ ions in KTiOPO4 do not obey Fick’s law, and there is a segregation process to the surface for 700 °C annealing. After 800 °C annealing for 30 min, most of the segregated Bi+ ions had evaporated, and the distribution of the remaining Bi+ ions became flat.
Ion energy distribution functions and Langmuir probe measurements in low pressure argon discharges
Authors: Kaeppelin V. , Carrère M. , Layet J-M.
Published: July 2002

Using an energy selective mass spectrometer, ion energy distribution functions (IEDFs) in a low pressure radio frequency (rf) argon discharge have been measured. This experiment has been done in the diffusion chamber of a helicon source. Two kinds of IEDF have been observed depending on the gas pressure: classical “one-peak” spectra at high pressure (>1 μbar) and “two-peak” spectra at low pressure (<1 μbar). These results have been correlated with the plasma potential and density profiles along the axis of the reactor obtained with a Langmuir probe and the IEDF have been fitted using a simple analytical model. In this way, noncollisional diffusion of energetic ions from the source chamber to the diffusion chamber has been shown.
Growth and characterization of ferromagnetic Ga1−xMnxAs epilayers on (001) ZnSe
Authors: Chun S. H. , Ku K. C. , Potashnik S. J. , Schiffer P. , Samarth N.
Published: July 2002

We describe the fabrication of ferromagnetic Ga1−xMnxAs (x=0.03 and 0.04) epilayers on (001) ZnSe using a recrystallized GaAs template. The magnetic properties are comparable to those of Ga1−xMnxAs epilayers grown directly on GaAs. For instance, as-grown samples have a Curie temperature TC=65 K that can be increased to 80 K after postgrowth annealing in a N2 atmosphere. The temperature dependence of the sample resistivity changes from insulating to metallic at the transition temperature. The n doping of ZnSe with Cl does not affect the ferromagnetism of Ga1−xMnxAs, hence providing a way to possible applications with Ga1−xMnxAs/ZnSe heterostructures.
Material properties of ion beam deposited oxides for the optoelectronic industry
Authors: Devasahayam Adrian J. , Agatic Ivo , Druz Boris , Hegde Hari , Zaritsky Isaac , Das Suhit R. , Boudreau Marcel , Yin Tao , Mallard Robert , LaFramboise Sylvain
Published: July 2002

High quality, dense films of SiO2, Al2O3, Ta2O5, and TiO2 were deposited with an ion beam deposition system (IBD). IBD has significant advantages over other techniques in terms of directionality, stress control, repeatability, thermal stability, and film uniformity [J. J. Cuomo, J. M. E. Harper, C. R. Guarnieri, D. S. Yee, L. J. Atanasio, J. Angilello, C. T. Wu, and R. H. Hammond, J. Vac. Sci. Technol. 20, 349 (1982)]. To decrease the surface damage induced by ion bombardment, a multi-energy process was developed. This is especially important for laser facet coatings. The oxide films were optimized for the desired refractive index and zero absorption. Stress values of −0.2 to −0.5 GPa (compressive) and extremely good uniformity (<0.2%) of film thickness and refractive index were obtained. The impact of the IBD deposition angle on film stress was also investigated. These films showed excellent thermal stability with virtually no degradation of optical properties after three 1 h anneals at 350 °C (Δn<0.0124). With the exception of TiO2, all films remained in compressive stress after annealing. TiO2 turned tensile. With the variety of oxide materials developed, designing an anti-reflective or highly reflective stack, which satisfies requirements of stress, uniformity, deposition rate, and reflectance, becomes a matter of choosing the appropriate material set.
In situ probing of surface hydrides on hydrogenated amorphous silicon using attenuated total reflection infrared spectroscopy
Authors: Kessels W. M. M. , Marra Denise C. , van de Sanden M. C. M. , Aydil Eray S.
Published: July 2002

An in situ method based on attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) is presented for detecting surface silicon hydrides on plasma deposited hydrogenated amorphous silicon (a-Si:H) films and for determining their surface concentrations. Surface silicon hydrides are desorbed by exposing the a-Si:H films to low energy ions from a low density Ar plasma and by comparing the infrared spectrum before and after this low energy ion bombardment, the absorptions by surface hydrides can sensitively be separated from absorptions by bulk hydrides incorporated into the film. An experimental comparison with other methods that utilize isotope exchange of the surface hydrogen with deuterium showed good agreement and the advantages and disadvantages of the different methods are discussed. Furthermore, the determination of the composition of the surface hydrogen bondings on the basis of the literature data on hydrogenated crystalline silicon surfaces is presented, and quantification of the hydrogen surface coverage is discussed.
Characterization of methyl-doped silicon oxide film deposited using Flowfill™ chemical vapor deposition technology
Authors: Lu Hongqiang , Cui Hao , Bhat Ishwara , Murarka Shyam , Lanford Williams , Hsia Wei-Jen , Li Weidan
Published: July 2002

In this article, methyl-doped silicon oxide films deposited using Flowfill™ chemical vapor deposition (CVD) technology have been chracterized for use in inter-layer dielectrics application. Films with different methyl concentrations were deposited and characterized in order to study the effect of methyl concentration on film properties. Material properties including chemical composition and bonding structure, density, dielectric constant (κ), refractive index, thermal stability, resistance to moisture absorption, leakage current, and hardness were investigated. The films have a κ as low as 2.7 and were found to be thermally stable up to 550 °C. They show excellent resistance to moisture absorption. Low-leakage current and breakdown voltage higher than 3 MV/cm were obtained. Their hardness is lower than silicon oxide deposited using plasma-enhanced CVD but is higher than most polymer and nanoporous low-dielectric constant (low-κ) materials. The chemical mechanical polishing (CMP) characteristics of these films and their stability under plasma treatments were also studied. Film’s CMP removal rate decreases as the methyl concentration in film increases. An atomically smooth surface with root mean square surface roughness <1 nm over a 10×10 μm area was obtained after CMP. This film remains stable under nitrogen (N2) and hydrogen (H2) plasma but is damaged by oxygen (O2) plasma.
Feasibility of thin film microfabricated hydrogen ion sources
Authors: Reuss Robert H. , Chalamala Babu R.
Published: July 2002

A thin film hydrogen ion source integrating field emission cathode arrays with metal hydride thin film technology is demonstrated. A prototype broad area hydrogen ion source was fabricated using Mo field emitter arrays to induce electron stimulated desorption and ionization of hydrogen from titanium hydride thin films on the gate electrodes. The hydrogen ion generation characteristics of the device were measured. In addition, these ion sources provide for the easy operation in pulsed mode by the direct modulation of gate voltage.
Vacuum Vapor Deposition of Plutonium onto Aluminum
Authors: Coffey D. L. , Tucker P. A.
Published: July 2002

A technique was developed for depositing plutonium-239 coatings up to 100 μ thick on aluminum sheet. The deposition system was an electron beam vacuum evaporator. Of several crucible materials evaluated, tantalum–0.1% tungsten was the most satisfactory material for containing the plutonium vapor source. The essential feature of the deposition process was a controlled sequence of substrate temperatures and evaporation rates. The average experimental rates of evaporation of plutonium agreed well with theoretical values, but wetting of the crucible resulted in scattering of the data. The aluminum–plutonium bond area was examined metallographically to determine the factors which influenced the adherence of the deposit. Insufficient reaction as well as excessive reaction between the substrate and the coating resulted in poor adherence.
An Analysis of Physical Adsorption Isotherms in Ultrahigh-Vacuum Range
Authors: Huang A. B.
Published: July 2002

The detailed mechanism of physical adsorption was studied by use of the statistical theory of imperfect gases. The Kirkwood—Muller potential was used for the gas–solid interaction. Adsorption isotherms computed from both the classical method (high-temperature case) and the quantum-mechanical method (very low-temperature case) are given. In the case of the quantum-mechanical method of solution, the important portion of the Kirkwood–Muller potential is approximated by a linear potential, the Schrödinger equation is solved in terms of Bessel functions, and the eigenvalues of the energy are obtained. Comparisons of present results with Hobson's measurements (He on Pyrex glass at 4.2 °K and N2 on Pyrex glass from 63.3 ° to 90.2 °K) show that the present theories are adequate in the ultrahigh-vacuum range and suggest that physical adsorption of helium on Pyrex glass at 4.2 °K is completely quantized.
X-Ray Diffraction Study of Vacuum-Evaporated Silver Films
Authors: Light T. B. , Wagner C. N. J.
Published: July 2002

Silver films were prepared by evaporation onto glass substrates held near 130 °C at different residual gas pressures (10−4 to 10−7Torr). Powder-pattern peaks of these films (thicknesses 2000 Å and 6000 Å) were measured with Cu Kα radiation at room temperature, and the profiles subjected to a Fourier analysis to determine particle size, strains, and faulting. Films prepared in poorer vacuum (10−4–10−6Torr) show small particle sizes (∼500Å), very small root-mean-squared strains (∼0.0005) and evidence for deformation stacking faults and micro-twinning. Lattice parameter measurements indicate the presence of internal strains in films heated to 250 °C for 2 h and measured at room temperature.
Interaction of Gases with a Condensed Phase
Authors: Yu J. S. , Soo S. L.
Published: July 2002

By use of a classical model, the phenomenon of trapping of a gas particle at the surface of a cold solid is investigated. The equation of motion is solved by the adoption of a semirepulsive potential of interaction and the equations determining the critical kinetic energy for trapping which is essential for the evaluation of the capture coefficient are obtained. These equations are simplified for the case that a gas particle collides on its own crystalline phase on account of the long “regression time” and the critical kinetic energy is thereby obtained. The regression time is the total time during which an initially free gas particle becomes trapped by the crystal surface before it is reevaporated again. It is long as compared to the period of lattice vibration.

The cryopumping of condensable nonpolar gases is investigated. The existence of an adsorbed, mobile phase is taken into account in the derivation. The capture coefficients obtained for N2 and CO2 based on the geometric area of the cryosurface are quite satisfactory as compared with those derived from experimental data. Pressures as functions of flow rates were measured for CO2 at a cryosurface temperature of 77.4 °K. The results are in good agreement with that calculated from the present simple theory.
Characterization of Backstreaming Fluids in High-Vacuum Systems by Gas Chromatography
Authors: O’Neill H. J. , Langdon W. M. , Frerichs J. , Somora A.
Published: July 2002

Backstreaming of both diffusion-pump and mechanical-pump fluids has been a constant problem with respect to their safe and efficient operation in high-vacuum systems. In most instances, the exact nature of the backstreaming oil is unknown. This study describes a gas-chromatographic procedure that was used to characterize the composition of backstreamed samples when a polyphenyl ether, Convalex-10, was used as the diffusion-pump fluid. The backstreamed fluid used for analysis was collected and removed from specially designed collection plates mounted within the diffusion pumps, which were maintained at −75 °F. The oil samples removed from the plates were further characterized by ir, uv, and gravimetric techniques.
Kinetics of N2 Desorption from the Surfaces of Iron–Nitrogen Solid Solutions
Authors: Podgurski H. H. , Davis F. N. , Smith R. P.
Published: July 2002

The kinetics of nitrogen desorption from iron surfaces was studied between 400 ° and 550 °C. The nitrogen desorbed isothermally into the gas phase was made available to the surface by diffusion from within the iron at the desorption temperature. The method of rate measurement involved the collection and volumetric measurement of gas samples at low pressures from specimens only a few square centimeters in area. Specimens were prepared by nitrogenizing zone-refined iron with NH3–H2 mixtures having a range of N2 fugacity between 10 and 3000 atm. The surfaces were then cleaned by ion bombardment in a bakeable high-vacuum system.

The kinetics of nitrogen desorption from iron was observed to be a surface-controlled process, which showed first-order dependence upon the nitrogen concentration in the iron when conventional ion-bombardment cleaning procedures were employed. However, it was discovered that carbon monoxide is generated in glass systems during ion bombardment and can contaminate the iron surface. When this contamination was reduced, the nitrogen-desorption process was observed to be diffusion controlled at temperatures as low as 400 °C.
Experimental Apparatus and Procedures for Evaluating Parameters Affecting the Pumping Efficiency of a Cryogenically Cooled Plane
Authors: Mullen L. O. , Hiza M. J.
Published: July 2002

The collection efficiency of a plane acting as a pump in a vacuum system can be determined by measuring the rate at which molecules of a given species strike and the rate at which they return from that plane. This paper discusses an experimental vacuum system incorporating a movable partial-pressure analyzer capable of making such measurements. The experimental procedure discussed here provides a means for evaluating parameters affecting the pumping efficiency. Efficiency values obtained by the present approach are compared with values obtained from kinetic theory and from speed-factor measurements. The experimental data show that much of the deviation of reported pumping efficiencies can be explained by fragmentation of the test-gas molecules and by a pressure anisotropy in the test dome. A means of calibrating the analyzer with vapor-pressure data is also discussed.
Differentially Pumped, Ultrahigh-Vacuum System Bakeable to 900 °C
Authors: Blahnik C. E.
Published: July 2002

A differentially-pumped, ultrahigh-vacuum (uhv) system has been developed that is capable of 900 °C bakeout and can attain pressures below 10−10 Torr in as little as one hour, depending upon the thermal mass of the enclosed apparatus. This paper describes a two-part uhv system and some of the design and materials considerations for mechanical, electrical, and optical couplings through the vacuum walls. Suitable solutions to these and related problems are discussed.
Glass Orbitron Pump of 5-cm Diameter
Authors: Naik Pramod K. , Herb R. G.
Published: July 2002

A glass, orbitron pump of 5-cm diam was constructed and its performance was studied. A stainless-steel mesh is used around the inside wall of the glass body to avoid difficulties due to peeling of titanium. Average pumping-speed values are 11.6 liters/sec for nitrogen, 5.6 liters/sec for air, and 0.1 liters/sec for argon in the range of pressures between 10−10 Torr and 10−5 Torr.
Pressure Dependence of the Axial Ion Current in a Penning Discharge
Authors: Young J. R.
Published: July 2002

Measurements have been made of the ion current which passes through a small axial hole in the cathode of a Penning discharge cell. As the pressure decreases from 10−4 to 10−10, the ratio of the axial current to the total current increases and is almost 10 times higher at 10−10 Torr than at 10−4 Torr. These results do not support the hypothesis that the ion current in a Penning discharge at pressures below 10−8 Torr is predominantly confined to a thin annular ring near the outer diameter of the cathode. Further, these results indicate the ion current is focussed more into a smaller area in the center of the cathode as the pressure is reduced from 10−4 to 10−10 Torr.
Striking Characteristics and Time Lags of the Magnetron Gauge in Helium from 1.9×10−7 Torr to 7×10−10 Torr
Authors: Lassiter William S.
Published: July 2002

The striking characteristics, or lower limits of operation, of the magnetron ionization gauge in helium were experimentally measured over the pressure range of 1.9×10−7 Torr to 7×10−10 Torr. The dependence of the striking voltage on the striking magnetic field on the upper branches of the striking characteristic curves deviates slightly from the parabolic dependence predicted by theory. On the lower branches of the striking characteristic curves, the results show that below 10−8 Torr, the minimum striking voltage decreases with a decrease in pressure instead of increasing, as predicted by theory. Striking time lags are measured below 10−8 Torr. The time lags increase with a decrease in pressure and are shown to contribute no significant error in the measurements of the striking characteristics.
New Developments in Getter—Ion Pumps in the U.S.S.R.
Authors: Kuznetsov M. V. , Nasarov A. S. , Ivanovsky G. F.
Published: July 2002

A series of sublimation titanium getter-ion pumps with directly heated titanium evaporators has been described by the authors in earlier publications. The pumps have pumping speed capability of 500–5000 liter/sec. The pumps find an application in thin-film technology, in the manufacture of vacuum electron tubes, in the metallurgy of extra-pure metals, and in particle accelerators. The present work reports results of the development of sublimation pumps which offer higher capacity and can operate under more rigid temperature conditions.
Performance of a Large Vacuum Chamber During a Continuous 10 000-h, 2200 °F Materials Test
Authors: Cunningham C. W.
Published: July 2002

A 4-ft-diam by 12-ft vertical vacuum chamber was operated at 1–5×10−8 Torr to contain a 10 000-h, 2200 °F boiling-potassium refractory metal test. This test required what is believed to be a record 11 000 h of continuous operation of a large size sublimation and getter-ion pumped chamber containing high-temperature test equipment. Sublimation pumping capacity of 20 000 liters/sec and ion pumping capacity of 2400 liters/sec were provided. An unexpected exponential increase in ion pump current from 0.35 to 35.0 mA in 8500 h was experienced before “hi-potting” and alternate operation of the two ion pumps was used to reduce the current increase. This test unexpectedly demonstrated that during long term operation, excessive ion pump currents may force early pump maintenance or cause premature test termination. Argon, nitrogen, and hydrogen remained the principal gases throughout the test period. Lesser amounts of methane and carbon dioxide were present. Other organic compounds and water remained at, or decreased to, very low concentrations.
Adsorption of Nitrogen on a Pyrex Glass Surface at Very Low Pressures
Authors: Tuzi Y. , Saito T.
Published: July 2002

The adsorption of nitrogen on a Pyrex glass surface has been studied in the region of 77 ° to 120 °K by using a dynamic method. The relation among the amount of adsorption (109∼1013 molecules/cm2), the temperature, and the pressure are well expressed by the Dubinin-Radushkevich equation. Analysis of desorption curves gives the activation energy of desorption Ed as a function of the amount of adsorption, and sτ as a function of temperature, where s and τ are the condensation coefficient and the mean adsorption time of nitrogen molecules, respectively. For example, Ed is ca. 6 kcal/mole at the amount of adsorption of 1×1010 molecules/cm2 and sτ is ca. 0.1 sec at 90 °K.
Anisotropic Film Growth and Pseudomorphism of Silver on a Germanium (110) Surface
Authors: Wübbenhorst R. , Hartig K. , Niedermayer R.
Published: July 2002

Ag films were evaporated under clean conditions onto a Ge (110) surface, in order to investigate the growth of a film of high misfit on an anisotropic surface. The structure of the resulting films was analyzed with LEED. The films grew in the form of three-dimensional islands in parallel orientation to the substrate. They showed up to 20% distortion in the [001] direction and no distortion in the [110] direction. At the same time the islands were narrow in [001̄] and elongated in [1̄10]. This connection of unidirectional pseudomorphism and anisotropic islands form is in qualitative agreement with previous theoretical considerations.
Some Physical Properties of Si–Si3N4 Interfaces and Silicon Nitride Thin Films Prepared by Reactive Sputtering in Nitrogen
Authors: C̆ervenák J. , Aleksandrov L. N. , Lovjagin R. N. , Krivorotov E. A.
Published: July 2002

In this work the influence of the surface layers (amorphous, polycrystalline) on single-crystalline Si substrates upon the form and frequency dependence of the C-U characteristics is experimentally investigated. Measurements have been made with Al–Si3N4–Si structures in which Si3N4, thin layers have been prepared by reactive cathodic sputtering in nitrogen. The breakdown voltage of Si3N4 layers has been found in the region (2–7)×106 V/cm, with a dielectric constant of 6–7 and a refraction index of 2.
Practical Application of Leak Detection Methods
Authors: McKinney H. F.
Published: July 2002

The 12 major leak detection methods that are commonly used are analyzed and discussed in this paper. Problem areas that are encountered when using these leak detection methods are also discussed. A brief discussion of the four main categories of system leakages is presented. Details of several representative leak detection programs are also presented and include both quantitative and qualitative analyses. Experimental experience is generalized in this paper in order to develop standardized application of various leak detection methods.
Ultrahigh vacuum system for metering gas flow (leaks) and computing flow rate (U)
Authors: Fultz C. R. , Carver D. W.
Published: July 2002

An instrument is described which is used as a multimass leak detector for quantitative gas-flow-rate (leak-rate) measurements. The system utilizes a residual gas analyser (RGA) (quadrupole-type mass spectrometer) which is calibrated to provide a gas-flow-rate measurement capability in the range of 10−9–10−14 mole/s for hydrogen, hydrogen–deuterium, helium, neon, nitrogen, oxygen, argon, and carbon dioxide. An automatic controller for the system is provided by a minicomputer interfaced to the other system components. All arithmetic, logic, and system-control operations are performed by the computer.
Outlook for Si photovoltaic devices for terrestrial solar-energy utilization
Authors: Wolf M.
Published: July 2002

The feasibility of silicon solar cells for large scale energy conversion is examined. In this context the availability of silicon and the cost of fabrication of devices are discussed. It is proposed that a complete rethinking of solar array processing is necessary to achieve large reduction in production costs. (AIP)
Abstract: Analysis of a temperature-field electron gun
Authors: El-Kareh A. B.
Published: July 2002

The temperature-field (TF) gun described by J. E. Wolfe and L. Swanson was analyzed using a high-speed digital computer. The field is approximately 107 V/cm and the temperature 1800 K. From scanning electron microscope micrographs of needles used in TF guns (where tungsten needles are chemically etched), it was found that the profile is very close to an ellipsoid. The potential distribution in the gun region and around the needle was obtained by a relaxation technique. Due to the high field strength in the vicinity of the cathode, the mesh size had to be extremely small, of the order of 1 Å. In order to decrease the storage and computer time requirements, the entire gun was initially analyzed with a mesh size of 4 μm. This size was systematically cut by factors of 2 together with the area of the gun being analyzed. The potential distribution for each region and mesh size was stored for the trajectory calculation. Starting from the cathode, or needle tip, a family of trajectories with initial conditions consisting of various slopes, heights, and thermal velocities were calculated until they emerged from the gun or reached a field-free region beyond the anode. From their heights and slopes in that region, the disk of minimum confusion was calculated by projecting back all the trajectories and searching for the narrowest constriction. It was found that, for an anode voltage of 5000 V and a temperature of 1800 K, the disk of minimum confusion is approximately 120 Å in diameter.
Abstract: Electromask generator
Authors: Beasley J. P. , Squire D. G.
Published: July 2002

An electron-beam pattern generator has been made for mask fabrication, either for conventional photolithography or more specifically for making electromasks for use in an image projection system. The maskmaker draws the pattern required at the final size in electron-sensitive resist which in turn defines the pattern in an opaque metal film on a transparent substrate. A 50-mm -square mask covered with detail down to at least 1 μm can be made in less than three hours. To achieve this speed of working two stages of beam deflection are used together with mechanical movement of the substrate. The high-speed deflection system runs at a 10-MHz stepping rate over a maximum amplitude of 32 μm. The slow-speed system covers an area of 2×2 mm.

An array of markers predefined over the substrate is used to obtain a pattern accuracy of ±1/8 μm relative to these markers. They are also used to check and, if necessary, correct the beam focus after each mechanical movement of the table. The pattern drawing, positioning, and beam focusing are entirely automatic.

An integrated-circuit mask-generation program is used on a larger computer to prepare the data for the patterns to be drawn. Magnetic tape is used to transfer this data to the maskmaker’s small computer.
Molecular parameters and lithographic performance of poly(glycidyl methacrylate-co-ethyl acrylate): A negative electron resist
Authors: Thompson L. F. , Ballantyne J. P. , Feit E. D.
Published: July 2002

To facilitate the production of a polymeric electron resist of consistent quality we must know how molecular parameters are related to lithographic performance. Previous work has indicated that for negative resists in general, sensitivity and contrast increase with increasing molecular weight and decreasing polydispersivity, respectively. We describe experiments on eight batches of a particular resist, poly(glycidyl methacrylate-co-ethyl acrylate) [P(GMA-co-EA)], which compare lithographic performance, in terms of sensitivity, contrast, and edge sharpness, with molecular weight (Mw), molecular content (%GMA), and polydispersivity (Mw/Mn). The earlier conclusions are borne out. To achieve a sensitivity of 4×10−7 C cm−2 at 10 kV and a contrast of about 1.0 (the latter being needed for lithography for chromium photomask production), the required values for this resist of Mw, %GMA, and Mw/Mn are, respectively, ?1.6×105, 70±2, and ?3.0.
Microfabrication using laser-beam interferometric technique coupled with simultaneous exposure and development method
Authors: Tsang Won-Tien , Wang Shyh
Published: July 2002

We have demonstrated the fabrication of two-dimensional periodic arrays of shaped openings with uniform submicrometer to micrometer size and spacing over large areas in photoresist films coated on top of glass substrates using laser-beam interferometric technique in conjunction with a simultaneous exposure and development (SED) method. The shapes of the openings obtained experimentally were compared with the theoretically calculated constant-energy contours and found to be in good agreement. The two-dimensional grating masks generated this way were shown to be comparable in quality with those generated by using computer-controlled scanning-electron-beam (CCSEB) technique. Furthermore, the shape and size of the openings and the grid pattern can be conveniently varied. Most important of all is the fact that this technique is able to eliminate most of the disadvantages of the CCSEB technique.
Laser technique for the divestment of a lost Leonardo da Vinci mural
Authors: Asmus J. F. , Westlake D. L. , Newton H. T.
Published: July 2002

On 4 May 1504 Leonardo da Vinci was commissioned to paint a wall mural for the recently constructed Sala del Gran Consiglio adjacent to the Palazzo Vecchio of Florence. Several reports during the first half of the 16th century lauded this fresco (The Battle of Anghiari) as the most important sight in the city, and art historians suggest that it may have been Leonardo’s most significant work. Surprisingly, the mural was never again seen after the room was renovated in 1565. Recent investigative work has yielded evidence suggesting that the lost masterpiece may be intact somewhere on the large east wall of the present Salone dei Cinquecento, but walled-in by substructures of the more modern Visari frescos. The probable delicate nature of the mural indicates that the removal of the final plaster covering without damaging the artwork may be exceedingly challenging. Consequently, we have been exploring a pulsed-laser radiation technique that will accomplish selective vaporization of the plaster to reveal the surface of the Leonardo mural.
Energy straggling of 4He ions below 2.0 MeV in Al, Ni, Pt, and Au
Authors: Harris J. M. , Nicolet M.−A.
Published: July 2002

In recent years, backscattering spectrometry has become an important tool in the analysis of thin films. An inherent limitation, though, is the loss of depth resolution due to energy straggling of the beam. To investigate this, energy straggling of 4He ions has been measured in thin films of Ni, Al, and Au. Straggling is roughly proportional to square root of thickness and appears to have a slight energy dependence. The results are compared with predictions of Bohr’s theory and with previous measurements made in Pt. While Ni measurements are in fair agreement with theory, Al measurements are 30% above and Au measurements are 40% below predicted values. The Au and Pt measurements are consistent with one another.
The optical properties and stoichiometry of evaporated bismuth oxide thin films
Authors: Medernach J. W. , Martin R. C.
Published: July 2002

The optical properties of bismuth oxide thin films were measured for samples prepared by direct evaporation of Bi2O3. The as−evaporated low−rate (1−5 Å/sec) films are microcrystalline, bismuth rich (relative to Bi2O3), and their optical absorption edge broadens and shifts to lower energies. High−rate (15−25 Å/sec) films are amorphous and oxygen−rich with an absorption edge shifted to higher energies. Thermal decomposition of the Bi2O3 during evaporation causes these variations in film stoichiometry. We show that shifts in the absorption edge may be correlated directly with departures from stoichiometry. The refractive index and absorption edge change with thermal treatment in oxygen; the former varies linearly with the partial oxygen pressure over the range of pressures observed during evaporation in this study. The refractive index and extinction coefficient are compared with published data on Bi2O3 thin films. Using the Lorenz−Lorentz equation, the dependence of the refractive index on the bismuth/oxygen ratio is derived. Application to as−evaporated films shows a good correlation with our data.
Structure and property relationships of Ni−20Cr produced by high−rate physical vapor deposition
Authors: Agarwal N. , Kane N. , Bunshah R. F.
Published: July 2002

In high−rate physical vapor deposition (HRPVD) processes, a change in substrate temperature produces a marked change in microstructure, mechanical properties, and hardness of the deposits. By varying this parameter, the relationship between microstructure and mechanical properties of vapor−deposited Ni−20Cr sheets was investigated. These sheets were characterized by grain size, grain morphology, density, tensile properties, bend ductility, and hardness. The grain morphology of deposited sheets at different substrate temperatures was in agreement with the morphology zone model suggested by Movchan and Demchishin. Samples of wrought (cast, rolled, and annealed) sheets from the same material were characterized by the same procedures to form a basis of comparison for deposited sheets. The investigation of mechanical properties and Hall−Petch relationship showed that deposited material was very similar to rolled and annealed material and constitutes a true engineering material.
Thin−gate valves for vacuum applications
Authors: Brink Gilbert O.
Published: July 2002

Two thin−gate valves are described which are useful in separating differentially pumped chambers in vacuum systems. They are easy to construct from readily available components and allow a small separation between the chambers.
Evaporator facility for deposition of multielement thin-film patterns
Authors: Meray L. H.
Published: July 2002

A versatile mask changer and evaporator is described for use in fabricating experimental thin-film circuits. Its operation is demonstrated for two examples: the preparation of the integrated sensor (512×512 units, each containing active and passive elements) and the optical three-color-stripe filter having each color 3–40 layers spaced within 8 μ side-by-side, up to 2 in. sq area (approx 25 cm2).
Structures of GaAs and GaP thin films formed by rf ion-beam epitaxy
Authors: Murayama Yoichi
Published: July 2002

Structures of GaAs and GaP, prepared by an ion-beam-epitaxy system having two ion sources and a rf coil, have been studied. GaAs and GaP films were deposited onto the cleavage surfaces of rock salt (001) and silicon (111) surfaces by the ion-beam-deposition system. Film structures have been studied under the electron microscope. Good epitaxy was found and the epitaxial temperature was lower than that found in ordinary deposition. These effects seem to have resulted from the ionized portion in the vapor beam.
Infrared properties and morphology of ThF4 films
Authors: Mar Henry Y. B. , Bernal G. Enrique
Published: July 2002

Thorium-fluoride films, approximately 2.5 μm thick, were vacuum evaporated onto substrates of potassium chloride. The ThF4 was evaporated by electron-beam and resistance-heating techniques. The effect on film properties of substrate temperature and a background pressure of sulfur hexafluoride (SF6) during deposition were observed. Transmission and reflection spectra were measured from 2 to 200 μm and a CO2 laser calorimeter was used to measure film absorption at 10.6 μm. Film microstructure was observed by scanning electron microscopy. The SF6 caused high film absorption and severe cracking. Severe cracking was also caused by low substrate temperature. Electron-beam-evaporated films had lowest absorption.
Epitaxial growth of Ag deposited by ion deposition on NaCl
Authors: Namba Yoshikatsu , Mōri Toshio
Published: July 2002

Epitaxial growth caused by ion deposition in the Ag/NaCl and Ag/Ag systems at room temperature has been studied and compared with conventional vacuum evaporation. It is shown that ionized atoms play an important role in the early (heteroepitaxial) stages of growth (Ag/NaCl), while its effect is very small in the succeeding (homoepitaxial) stage of growth (Ag/Ag). This latter stage of epitaxial growth proceeds even for zero ionization rate. Similar results were also observed for Au and Cu. The following contributions to the mechanism of epitaxial growth by ion deposition are discussed: (i) the temperature rise of film surface caused by ion deposition; (ii) influence of various defects produced by ion impact during ion deposition; and (iii) additional effect such as entropy decrease of deposited atoms on the substrate surface.
Three-stage Roots high vacuum pump
Authors: Fukutome R. , Aikawa J. , Hayashi C.
Published: July 2002

A three-stage Roots pump which has geometrical displacements of 305, 100, and 33 l/s is designed to extend the operating pressure region from 10 to 10−4 Pa. Mechanical features of the Roots pump are coaxial three-stage design with minimum clearance seals for intermediate sealing between the first, second, and third stages without a lubricant; and computer designed flat-waist-cocoon shape rotors which enable more precise machining and narrower rotating clearances. To meet the requirement of hydrocarbon-free pumping for many modern applications, especially sputtering, ion plating, and high intensity ion sources, a high throughput for different gases must be achieved occasionally at a higher pressure beyond the operating range of turbomolecular or diffusion pumps. The subject Roots pump has pumping speed of 220 and 260 l/s for nitrogen and helium, respectively, at 4100 rpm in the range of 1.3×10−3 to 4.0 Pa at the intake. The compression ratio is 104 for hydrogen, helium, and nitrogen, and an ultimate pressure is 1.3×10−4 Pa without bakeout.