bluuebunny/crossref_metadata_2025 huggingface dataset:
A Theoretical Model to Predict the Vibration Response of Rolling Bearings in a Rotor Bearing System to Distributed Defects Under Radial Load
Authors: Tandon N. , Choudhury A.
Published: July 2002

A theoretical model to predict the vibration response of rolling element bearing in a rotor bearing system to distributed defects under radial load has been developed. The rotor bearing system has been considered as a three degrees of freedom model. The distributed defects considered are, the waviness of outer and inner races, and off size rolling element. The model predicts discrete spectrum with specific frequency components for each order of waviness. For outer race waviness, the spectrum has components at outer race defect frequency and its harmonics. In the case of inner race waviness, the waviness orders equal to number of rolling elements and its multiples give rise to spectral components at inner race defect frequency and its multiples. Other orders of waviness generate sidebands at multiples of shaft frequency about these peaks. The model predicts the amplitudes of the spectral components due to outer race waviness to be much higher as compared to those due to inner race waviness. In the case of an off-size rolling element, the model predicts discrete spectra having significant components at multiples of cage frequency. [S0742-4787(00)00603-2]
Passive Solar Massive Wall Systems With Fins Attached on the Heated Wall and Without Glazing
Authors: Bilgen E.
Published: July 2002

Natural convection, radiation and conduction heat transfer in passive solar massive wall systems with fins attached to the heated surface and without glazing is experimentally studied. The system was 0.78 m high, 0.40 m wide, and 0.10 m thick concrete wall with 0.025 m long, 0.004 m thick horizontal fins made as an integral part of it and placed at 0.01 m intervals. A heat source was used to impose a constant heat flux which could be varied from about 200 to 800 W/m2. Temperatures at various points and heat flux by convection at the back were measured. Using periodicity hypothesis and various assumptions, the wall with fins was also analyzed theoretically. The results indicate that for the case considered, about 35 percent of the heat flux imposed on the finned surface goes through the system and is dissipated at the back. [S0199-6231(00)00701-2]
Estimating the Probability Distribution of von Mises Stress for Structures Undergoing Random Excitation
Authors: Segalman Dan , Reese Garth , Field, Richard , Fulcher Clay
Published: July 2002

The von Mises stress is often used as the metric for evaluating design margins, particularly for structures made of ductile materials. For deterministic loads, both static and dynamic, the calculation of von Mises stress is straightforward, as is the resulting calculation of reliability. For loads modeled as random processes, the task is different; the response to such loads is itself a random process and its properties must be determined in terms of those of both the loads and the system. This has been done in the past by Monte Carlo sampling of numerical realizations that reproduce the second order statistics of the problem. Here, we present a method that provides analytic expressions for the probability distributions of von Mises stress which can be evaluated efficiently and with good numerical precision. Further, this new approach has the important advantage of providing the asymptotic properties of the probability distribution. [S0739-3717(00)00801-1]
A New Exact Approach for Analyzing Free Vibration of SDOF Systems with Nonperiodically Time Varying Parameters
Authors: Li Q. S.
Published: July 2002

A new exact approach for analyzing free vibration of single degree of freedom (SDOF) systems with nonperiodically time varying parameters is presented in this paper. The function for describing the variation of mass of a SDOF system with time is an arbitrary continuous real-valued function, and the variation of stiffness with time is expressed as a functional relation with the variation of mass and vice versa. Using appropriate functional transformation, the governing differential equations for free vibration of SDOF systems with nonperiodically time varying parameters are reduced to Bessel’s equations or ordinary differential equations with constant coefficients for several cases, and the corresponding exact analytical solutions are thus obtained. A numerical example shows that the results obtained by the derived exact approach are in good agreement with those calculated by numerical methods, illustrating that the proposed approach is an efficient and exact method. [S0739-3717(00)00902-8]
Ammonium Perchlorate, The Principal Oxidizer Used in Solid Propellants
Authors: Beard Bruce
Published: July 2002

Highly oxidized compounds are commonly used as the source of oxygen for the combustion of propellants. Determination of the early reactions and interactions of both oxidizer and fuel increases our understanding of the ignition process. Another critical aspect in propellant technology is safety: the elimination of unexpected initiation, weather combustion or explosion. The approach taken in this laboratory in the study of early reactions is to determine the nature and extent of chemical reaction in response to increasing levels of stimulus. Comparison of damaged materials (damaged below the initiation threshold) to standards permits the identification of the chemical species involved in the early reactions. To that end, control spectra of ammonium perchlorate (the most widely used oxidizer in solid propellants) have been collected from a freshly cleaved single crystal surface. The composition of ammonium perchlorate is NH4ClO4. Atomic concentrations, excluding hydrogen, are Cl 16.6%, N 16.6% and O 66.6%.
CdS by XPS
Authors: Poirier D. M. , Weaver J. H.
Published: July 2002

XPS spectra were recorded for a poly crystalline CdS sample. For comparison, a surface exposed to air for 1 h (Accession #00115) and a surface prepared by cleaving in situ (Accession #00114) were examined. The record includes Cd 4d, S 2p, Cd 3d, Cd MNN, and valence band spectra.
CuI by XPS
Authors: Vasquez Richard P.
Published: July 2002

X-ray photoemission measurements of high purity CuI are presented. XPS studies of Cu compounds in this laboratory have been motivated by the need to identify species on chemically etched high temperature superconductor surfaces [see R. P. Vasquez, M. C. Foote, and B. D. Hunt, J. Appl. Phys. 66, 4866 (1989)].
CuO by XPS
Authors: Vasquez R. P.
Published: July 2002

X-ray photoemission measurements of CuO are presented.
Analysis of Polycarbonate (PC) by XPS
Authors: Lannon John M. , Meng Qingru
Published: July 2002

We report x-ray photoemission spectra of a polycarbonate (PC) polymer. XPS spectra were acquired with a SSI model SSX-100 instrument using monochromated Al Kα x-rays. We present the survey spectrum (binding energy range of 0–1000 eV) and a narrow spectrum of the C 1s and O 1s photoelectron peaks.
Damage studies of MeV Sb-implanted Si(100) by channeling and Raman spectroscopy
Authors: Dey Soma , Pradhan Asima , Varma Shikha
Published: July 2002

The radiation damage induced in Si(100) due to 1.5 MeV Sb ions has been studied as a function of fluence using the Rutherford backscattering/channeling (RBS/C) technique and Raman spectroscopy. The damage profiles have been extracted from the RBS/C spectra and the results compared with SRIM‘97 code calculations. For a fluence of 1×1014 ions/cm2, though the position of the damage profile is in agreement with the defect profile calculated using SRIM code, theory overestimates the damage in the surface region, suggesting dynamic self-beam annealing. The total amount of damage obtained as a function of implant dose exhibits two behaviors; a small net damage and a slow rate of damage accumulation for low fluences with a crossover to faster rates beyond a dose of 1×1013 ions/cm2. At this dose, a defected-amorphized zone of a critical size can form, which may easily enlarge by further accumulation of defects at higher fluences. The total damage has been compared with the results from Raman scattering and it is observed that the net damage as detected by Raman is slightly higher at the fluences where crystalline and amorphous zones coexist. The crystalline-to-amorphous (c/a) transition in Si as a function of fluence has been investigated by RBS/C and Raman scattering. The study demonstrates that Raman scattering is more effective in probing the small concentrations of defects produced during the early stages of c/a transition.
Use of orthogonal polynomial functions for endpoint detection during plasma etching of patterned wafers
Authors: Rietman Edward A. , Layadi Nace , Downey Steve W.
Published: July 2002

We show that by using various in situ etch process signals (e.g., reflected power, induced direct current bias) as the coefficients in an orthogonal polynomial expansion we can determine endpoint for processes which heretofore have not had strong endpoint signals. The technique essentially amplifies weak signals. We have used the orthogonal expansions and the integral of the expansions to determine endpoint in, among others, via etch processes. The method is reproducible from wafer-to-wafer and can be used by inexperienced operators and simple threshold algorithms to determine endpoint in plasma processes.
Nanometer-scale Si selective epitaxial growth on Au-adsorbed Si(111) surface windows in ultrathin oxide films
Authors: Shibata Motoshi , Nitta Yoshiki , Fujita Ken , Ichikawa Masakazu
Published: July 2002

Nanometer-scale Si selective growth was performed on Au-adsorbed Si(111) windows in ultrathin (0.3 nm thick) silicon–dioxide (SiO2) films. Nanometer-scale Au-adsorbed Si(111)-5×2 terraces grew from the step edge of Si(111)-7×7 terraces. Thermal oxidation of the partially Au-adsorbed Si(111) terraces was done in an atmosphere of molecular oxygen. Selective thermal oxidation was investigated under various oxidation conditions; Si(111)-7×7 terraces were oxidized while the Au-adsorbed Si(111) terraces remained. Si crystals were selectively grown on the Au-adsorbed Si(111), while Au atoms were always on the top layer of the grown crystals. On a vicinal Si(111) surface misoriented toward the [11¯2] direction, the grown Si crystals along the step edges were 20 nm wide, 500 nm long, and 4 nm high.
Statistical considerations of the overlay error in laser driven point source x-ray lithography
Authors: Tiszauer Detlev H.
Published: July 2002

A statistical measure of the point source divergence-induced overlay error over the print field is derived. The assumptions of a wide-sense stationary distribution of gap error and the assumption of a symmetric distribution of overlay sites on the chip field give rise to simple expressions for the overlay error variance. The computations for overlay error are also expressed in the Fourier domain. From this formulation, it is found that these simple results hold for the zero frequency and high frequency limit of gap error in the Fourier domain, even without the assumptions of stationarity.
Design and implementation of optoelectronic interfaces for high-speed burst-mode transmissions
Authors: Bendé André Boyoguéno
Published: July 2002

The popularity of internet and multimedia has greatly increased the demand for high-speed transmission networks. The next generation of optical networks will likely request fast packet switching to support multimedia applications. In fact, in such applications, the amplitude and phase of the receiver can be quite different from packet to packet due to different fiber attenuation and the chromatic dispersion caused by the variation of the transmitter’s wavelength. Link performance is strongly dependent on both the sensitivity and dynamic range of the receiver circuit. Although emerging lightwave communication technologies are bringing 10 Gb/s systems into commercial use [K. Yukio, A. Yuji, N. Kiyoski, K. Hiroyuki, and Y. Imai, IEEE Trans. Microwave Theory Tech. 43, 1916 (1995)], optoelectronic interfaces are still limiting factors for better performances. In this article, we address power penalty in high-speed burst-mode operation. Architectures applicable to high-speed systems and insensitive to parasitic input loading are proposed to overcome speed limitations at the receiver’s input. A 4.7 GHz bandwidth, a transimpedance of 43 dB Ω and an average input noise current density of 9 pA/Hz have been achieved in simulations with the single-ended version.
Comparison of Cl2 and F-based dry etching for high aspect ratio Si microstructures etched with an inductively coupled plasma source
Authors: Tian W. -C. , Weigold J. W. , Pang S. W.
Published: July 2002

The differences between Cl2 and F-based dry etching are compared in this article. Inductively coupled plasma sources have been used to generate plasmas using both Cl2 and SF6/C4F8 chemistries. Trenches etched using Cl2 suffered less aspect ratio dependent etching effects because the trenches can be etched at a much lower pressure than with F-based gases. A 1.4 μm wide, 65 μm deep trench can be obtained with an aspect ratio of 46 in 12 h. The average Si etch rate was 90 nm/min and the selectivity to electroplated Ni was 23. The sidewall was vertical and smooth and the trench openings were nearly the same width before and after etching. Adjacent trenches with 0.14 μm mask opening and 2 μm line width were etched using these two etching technologies. With Cl2 etching, a wider 0.25 μm trench opening, due to the mask erosion effect, with a depth of 5.6 μm was obtained in 50 min. However, the 0.33 μm undercut increased the trench opening to 0.8 μm for 10.7 μm deep trenches after the F-based etching for 55 min. The Si etch rate in a large open area using F-based etching was 1818 nm/min, which is much faster than 201 nm/min when Cl2 etching was used. However, the Si etch rate, 112 nm/min for Cl2 and 195 nm/min for F-based gases, was similar when the trench opening was decreased to submicrometer dimensions. This shows that the Cl2 etching provides better dimension and profile control with comparable Si etch rate to F-based etching when etching submicrometer trenches. The loading effect using Cl2 chemistry is less than with F-based etching. The Si etch rate was 1.74 μm/min for ∼100% Si exposed area and 3.68 μm/min when the exposed Si area was ∼0% in F-based etching. Scalloping, which is a periodic undercut near the top of the sidewalls, disappeared when using an electroplated Ni mask. The size and period of the scalloped features decreased as the Si exposed area and etch time increased.
New very high frequency plasma source using a TM01-mode patch antenna with short pins
Authors: Okumura Tomohiro , Matsui Takuya , Suzuki Hideo , Sakiyama Kazuyuki
Published: July 2002

We evaluated the basic characteristics of a new very high frequency (VHF) plasma source using a TM01-mode patch antenna with short pins. The antenna comprises a round dielectric plate and a round metal plate which is grounded by short pins isotropically arranged. Electromagnetic field simulation has verified the isotropic distribution of both electric and magnetic fields. Ion-saturated current density measurements (Cl2=100 sccm, 1 Pa and VHF power=1000 W) by placing the antenna in a cylindrical etching chamber 450 mm in diameter and 217 mm deep have revealed that uniform plasma is generated if a circular slit is positioned properly; that higher ion density is attained with dielectric plate relative permittivity set at 20, than at 7; and that increased VHF power causes proportional increase in ion density without giving rise to mode jumping or hysteresis. Experiment has revealed that the plasma source subject to our study provides superior ignitability, being capable of starting discharge even under 0.1 Pa. Experimental etching of polycrystalline silicon using this plasma source has yielded satisfactory results that etch rate is 183.5 nm/min±3.68%, poly-Si selectivity against resist is 4.8, and that against oxide film is 280 in main etching.
Cryopumping
Authors: Hobson J. P.
Published: July 2002

A review is given of cryopumping. The flexibility, high available speed, and wide pressure range of this method of pumping are emphasized. Basic theory is presented, as well as modifications to the theory found in practical situations. Cryopumps are divided into two broad classes, cryosorption pumps and condensation pumps, depending on whether the surface coverage is less than or greater than about 5 monolayers, respectively. Five types of cryopumps, with examples, are distinguished: bare surface pumps, pumps with loose adsorbents, pumps with bonded adsorbents, pumps utilizing frozen deposits, and condensation pumps.
Clusters, chemisorption, and catalysis
Authors: Johnson K. H. , Messmer R. P.
Published: July 2002

The electronic structures of small clusters of atoms at solid interfaces and of polyatomic aggregates in supporting materials are of central importance to chemisorption and catalysis. Self-consistent field (SCF) molecular orbital theory provides a conceptually simple approach to cluster bonding, but it is of quantitative significance to chemisorption and catalysis only if accurate numerical applications to real systems are practical. A critique of the traditional Hartree-Fock molecular orbital approach to chemisorption is presented, along with a discussion of recent semiempirical “LCAO” calculations for chemisorption on graphite. The recently developed SCF-Xa “scattered-wave” method allows one to calculate highly accurate ground and excited electronic states of polyatomic clusters (as functions of cluster size, composition, geometry, and supporting environment), yet requires only moderate amounts of computer time. Current applications of this technique to chemisorption at transition-metal interfaces and to catalytically active metal aggregates are described.
Porosity in sputtered platinum films
Authors: Westwood W. D.
Published: July 2002

Platinum films have been deposited by dc sputtering in an argon discharge, using plane parallel electrodes. The system was used either for diode sputtering or, by addition of a heated filament, for triode sputtering with the same geometry. Both configurations were used to maintain constant discharge current and voltage over the pressure range 10–150 mTorr. Films were deposited over this pressure range for sputtering voltages between 1.5 and 4.0 kV. The mass deposited in a given time decreased with increasing pressure and decreasing voltage. Films up to 0.7 μ thick were deposited, and the film density decreased linearly from near the bulk value to 60% of the bulk value as the pressure increased from 10 to 150 mTorr. At the same time, the resistivity increased from twice the bulk value to ten times the bulk value while the temperature coefficient of resistance was between 30%–50% of the bulk value. For the densest films, the product of resistivity and temperature coefficient was close to the value predicted by Matthiessen's rule for platinum. Since no significant doping of the platinum was observed, the change in electrical properties is attributed to porosity in the films. The crystal structure was examined both by x-ray diffractometer and wide-film Debye-Scherrer techniques. As the resistivity increased, the crystalline orientation in the films became more random and the grain size decreased although the crystal structure of bulk platinum was maintained. It is suggested that the porosity is due to decreasing surface mobility caused by the increasing pressure and that this may be inherent in the sputtering process so that all films sputtered at pressures above approximately 20 mTorr may have some porosity.
Influence of developer and development conditions on the behavior of high molecular weight electron beam resists
Authors: Hasko D. G. , Yasin Shazia , Mumtaz A.
Published: July 2002

The nature of the developer and development conditions of high molecular weight electron beam resists is known to influence sensitivity, contrast, line edge roughness, and ultimate resolution. These resist characteristics are explained using a dissolution model based on reptation theory and predictions are compared with experimental results on high molecular weight poly(methylmethacrylate) developed in a range of solvent mixtures and conditions, including ultrasonically assisted development.
Low temperature deposition for high performance photodetector
Authors: He Lili
Published: July 2002

Thin metal films are of considerable interest for optoelectronic device fabrication. The high resistivity of thin metal films results in drawbacks of their application in the devices. The low Schottky barrier height for certain important material such as InGaAs blocks its application in optoelectronic device at long wavelength. Recent studies have been conducted in low temperature (LT) deposition of thin metal films. The LT thin films showed 4–5 orders lower resistivity compared to those formed at room temperature. The LT process also results in increased Schottky barrier height for most III–V semiconductor materials. Therefore, the LT processed thin films show superior properties for optoelectronic devices applications. In this work, computer simulation was conducted by partially implementing the LT results in device parameters. The optimum design for the high performance metal–semiconductor–metal photodetector was obtained by simulation. The results show that the LT processing is of convenient, cost-effective, and could be implemented in more optoelectronic device fabrications.
Amino-terminated self-assembled monolayer on a SiO2 surface formed by chemical vapor deposition
Authors: Hozumi Atsushi , Yokogawa Yoshiyuki , Kameyama Tetsuya , Sugimura Hiroyuki , Hayashi Kazuyuki , Shirayama Haruyuki , Takai Osamu
Published: July 2002

Well-ordered amino-terminated self-assembled monolayers (SAMs) were reproducibly prepared on Si substrates covered with native oxide in a vapor of 12.5 vol % solution of N-(6- aminohexyl)-3-aminopropyltrimethoxysilane (H2N(CH2)6NHCH2CH2CH2Si(OCH3)3,AHAPS) diluted with absolute toluene. Although aggregated AHAPS molecules were excessively adsorbed on the deposited AHAPS-SAM films, they were removed by sonication in ethanol, toluene, NaOH, and HNO3 aqueous solutions, conducted in that order. The thickness of the AHAPS-SAM as estimated by ellipsometry was 1.3±0.1 nm. The AHAPS-SAM surfaces observed by atomic force microscopy appeared very smooth with a root mean square roughness of about 0.15 nm in a several micron square area. This resulted in low hysteresis between the advancing and receding water-contact angles, which were determined to be 62±3° and 57±2°, respectively. Micropatterning of the SAM was also demonstrated on the basis of photolithography using an excimer lamp radiating vacuum ultraviolet light of 172 nm in wavelength. A microstructure composed of 5 μm×25 μm rectangular features was successfully fabricated on an AHAPS-SAM surface.
Erosion profile optimization in sputtering systems: Singular value decomposition approach
Authors: Kamali Jalil
Published: July 2002

This article is concerned with the problem of optimum magnet design in the plasma-based sputtering systems which are widely used in the thin film industry. We present a relatively simple mathematical model for the sputtering phenomena, formulate the performance optimization as a weighted least squares problem, and solve it using a singular value decomposition approach. The resulting optimum magnet has been in fact fabricated and is already in use.
Interpretation of GaAs(110) scanning tunneling microscopy image contrast by the symmetry of the surface Bloch wave functions
Authors: Jäger N. D. , Weber E. R. , Salmeron M.
Published: July 2002

A simple qualitative correlation between the corrugation anisotropy observed in scanning tunneling microscope (STM) images of GaAs(110) surfaces and the symmetry properties of the surface states is presented. We show that as a function of bias, tunneling from different electronic states near high-symmetry points of the surface Brillouin zone gives rise to a distinct corrugation along [11̄0] and [001] in STM images. Existing models of the surface band structure are used to identify these states. We show that at small bias, due to band bending effects, the same surface state near the conduction-band edge determines the image corrugation in both filled and empty states images of n-type GaAs.
Experimental model of industrial x-ray source MSX-1 with a vacuum spark for x-ray lithography
Authors: Semyonov Oleg G. , Gurey A. E. , Tikhomirov A. A.
Published: July 2002

A prototype of an industrial x-ray source based on low-inductance vacuum spark discharge was designed and tested at the P.N. Lebedev Institute of Physics in cooperation with the Institute of Precise Machinery (Zelenograd, Moscow region). The micropinch (hot-spot) formation effect in the discharge (maximum current of 120 kA, current rise time of 0.6 μs) was used to achieve the high-density (∼1022 cm−3), high-temperature (∼1 keV) metallic plasma in a local (40×200 μm) area. This plasma emits a short burst (∼3–10 ns) of x-ray line radiation corresponding to the transitions of L-shell electrons in the ionized atoms, with an efficiency ≈1% with respect to the stored bank energy (500 J). The repetition rate of the source can be set from 1 to 10 Hz. Applicability of the source to x-ray lithography is studied, and effective size of emitting area (deviation of micropinch position from shot to shot) together with x-ray yield jitter are discussed. The engineering problems of power supply and vacuum pumping, as well as x-ray source reproducibility, optimal operation mode, and operation life are also considered.
Diffusion and oxidation of plasma-enhanced chemical-vapor-deposition silicon nitride and underlying metals
Authors: Han G. C. , Luo P. , Li K. B. , Wu Y. H.
Published: July 2002

Plasma-enhanced chemical-vapor deposition (PECVD) was employed to grow silicon nitride at various temperatures to find its application in magnetic random access memory. Diffusion and oxidation of PECVD nitride (SiNx:H) and underlying metals (Ta and Cu) have been studied through Auger electron spectroscopy measurements. Oxygen content on the SiNx:H surface and characteristic sputtering time (t0), after which the oxygen signal falls below the measuring errors of the system, were used to characterize the oxidation of SiNx:H films. It is found that both oxygen content and t0 increase significantly for decreasing deposition temperature. The oxygen content is larger for SiNx:H films with lower Si/N ratios. Cu oxidation was investigated through changing sample loading methods. Strong oxidation was observed for samples loaded at higher temperatures, while almost no oxidation was detected for samples loaded at room temperature and heated to the deposition temperature after pumping the chamber to high vacuum. Strong diffusion of Si into Cu film was detected for high-temperature-deposited layers. Independent of loading methods, the Si concentration in Cu increases dramatically as the deposition temperature increases after exceeding 150 °C, whereas there is nearly no observable Si signal in Ta for the whole deposition temperature range. The Cu signal was also detected in nitride films deposited at 200 °C, while Cu cracks were observed when the deposition temperature was larger than or equal to 250 °C.
Resist hardening by fluorocarbon plasma for electron-beam and optical mix-and-match lithography
Authors: Chan Victor W. C. , Hai C. H. , Chan Philip C. H.
Published: July 2002

Electron-beam direct write for lithography is a slow process. If lithography with a small linewidth is carried out by the electron-beam direct write and the remaining pattern uses optical lithography, the throughput of masking can be increased. Electron-beam and optical lithography mix-and-match can be realized in a number of ways. In this article, we report a resist hardening process that uses low power fluorocarbon plasma. It is a simple and low-temperature process. An analysis of the process variables will be discussed. The critical dimension of the optical masking does not change significantly in our process. This method can be used to improve the electron-beam lithography throughput as well.
Integration and electrical characterization of photosensitive polyimide
Authors: Alford T. L. , Zou Y. L. , Gadre Kaustubh S. , King C. , Chen W. , Theodore N. David
Published: July 2002

A base line process of photosensitive polyimide was developed to significantly reduce cycle time in backend polyimide processes as compared to the use of conventional nonphotosensitive polyimide. A 6 μm resolution was obtained by the use of a wet etch process of photosensitive polyimide (PSPI) in aqueous tetramethylammonium hydroxide developer. The feasibility of the polyimide as a passivation stress-buffer layer and passivation-etch mask was also demonstrated. Electrical characterization was performed to measure the surface resistance and the intralevel leakage current along the interface between the polyimide and tetraethylorthosilicate. These findings suggested that reduction of the moisture content of the polymer films is critical to ensure electrical isolation during the integration of PSPI into multilevel structures.
Epitaxial ScN(001) Grown and Analyzed In situ by XPS and UPS. II. Analysis of Ar+ Sputter Etched Layers
Authors: Haasch R. T. , Lee T. -Y. , Gall D. , Greene J. E. , Petrov I.
Published: July 2002

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to characterize as-deposited epitaxial ScN(001) layers grown in situ which were Ar+ sputter etched. The films were deposited by ultrahigh vacuum reactive magnetron sputter deposition on MgO(001) at 800 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa) and shown to have a N/Sc ratio of 1.11 ± 0.03 by Rutherford backscattering spectroscopy (RBS). The films were sputter etched with 3 keV Ar+ at an angle of 40° until a constant nitrogen-to-scandium ratio was established. A Mg Kα x-ray source was used to obtain the XPS data, while the UPS data was generated by He I and He II UV radiation. The sputter etched films have a N/Sc ratio of 0.99 indicating a preferential removal of nitrogen.
Epitaxial TiN(001) Grown and Analyzed In situ by XPS and UPS. I. Analysis of As-deposited Layers
Authors: Haasch R. T. , Lee T. -Y. , Gall D. , Greene J. E. , Petrov I.
Published: July 2002

X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) were used to characterize as-deposited epitaxial TiN(001) layers grown in situ. The films were deposited by ultrahigh vacuum reactive magnetron sputtering on MgO(001) at 850 °C in pure N2 discharges maintained at a pressure of 5 mTorr (0.67 Pa). Mg Kα and monochromatic Al Kα x-ray sources were used to obtain the XPS spectra, while the UPS data was generated by He I and He II UV radiation. The spectra show that the TiN(001) surfaces are free of O and C. The films were found to be stoichiometric in agreement with Rutherford backscattering spectroscopy (RBS) results, yielding a N/Ti ratio of 1.02 ± 0.02.
Study on dark specific resistance of Au–TiO2 nanogranular films
Authors: Wang Huiyao , Xu Pei , Wang Tianmin
Published: July 2002

TiO 2 films embedding Au nanoparticles were prepared by the reactive magnetron sputtering method. Transmission electronic microscopy was used to study the structure of the films and the size of Au particles. The size and the density of Au particles had significant impact on dark specific resistance of the films. With the increasing number of Au particles, the specific resistance of the films experienced a rising phase, followed by a drop. The enhancement of photocatalytic reactivity of the films was attributed to the contact of a metal–conductor. Based on the experimental results of the photocatalytic reactivity of the films, the mechanisms of the change of dark specific resistance were studied. It was found that the increase of specific resistance with the incorporation of Au particles was ascribed to the Schottky barrier rather than to the size quantization effects of Au nanoparticles.
GaN grown by molecular beam epitaxy with antimony as surfactant
Authors: Pei C. W. , Turk B. , Héroux J. B. , Wang W. I.
Published: July 2002

In this work, we investigated the effect of Sb on the molecular beam epitaxy (MBE) growth of GaN and its optical properties. One monolayer Sb predeposition before GaN growth and different Sb beam equivalent pressures applied throughout the GaN growth were used to study the effect of Sb on GaN growth by ammonia gas-source MBE. The presence of Sb remarkably enhanced two-dimensional growth as evidenced by in situ reflected high energy electron diffraction (RHEED). RHEED patterns became streaky much more rapidly when GaN was grown in the presence of Sb than that without Sb, indicating that Sb can act as an effective surfactant to smooth the growth front of GaN and enhance the layer-by-layer growth mode for the MBE growth of GaN. The full width at half maximum of the (0004) x-ray diffraction rocking curve measured from the GaN epilayer grown with one monolayer Sb predeposited as surfactant was as narrow as 70 arcsec. In the photoluminescence measurement, besides the characteristic near band edge excitonic emissions, new transitions related to Sb-isovalent traps were observed from GaN samples grown with Sb, whose zero phonon line was located at 3.27 eV with phonon replicas on the lower energy side. Intensities of the emissions related to Sb-isovalent traps increased with Sb partial pressures applied during GaN growth.
Secondary ion mass spectrometry characterization of the diffusion properties of 17 elements implanted into silicon
Authors: Francois-Saint-Cyr H. , Anoshkina E. , Stevie F. , Chow L. , Richardson K. , Zhou D.
Published: July 2002

A systematic investigation of the diffusion of Be, B, Na, Mg, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Zn, Ge, Rb, and Mo in silicon has been carried out. The elements were implanted into silicon wafers as low dose impurities, and then postheat treatments of the ion-implanted samples were conducted at different temperatures for a specific time. Following the anneals, the depth profiles were obtained by secondary ion mass spectrometry analyses. A wide range of diffusion behavior has been observed for these elements. Based on differences in the depth profiles the diffusion mechanism was identified where possible.
Experimental and numerical analyses of electron temperature and density distributions in a magnetic neutral loop discharge plasma
Authors: Okraku-Yirenkyi Yaw , Sung Youl-Moon , Otsubo Masahisa , Honda Chikahisa , Sakoda Tatsuya
Published: July 2002

In order to study the plasma structure and its application to processing, experimental and numerical analyses of the distribution of the electron temperature (Te) and electron density (ne) in a neutral loop discharge (NLD) plasma were performed. From the experiments, NLD plasma possesses Te and ne peaks. In the cases of NL radii of RNL=80, 100, and 120 mm, the maximum values measured for Te were around the NL. However, the ne peaks of the cases mentioned were located about 30–40 mm radially inward of the NL. We calculated the electron behavior in three dimensions to analyze these measured results, taking into consideration the actual experimental conditions such as the magnetic field, antenna position, and chamber walls. We found electrons are trapped in a region that is more inward of the NL due to a mirror field that causes the peak of ne. Also it is shown that good plasma uniformity could be obtained by dynamically controlling these Te and ne peaks.
Process characterization for tapered contact etch
Authors: Celii F. G. , He Q. , Liu H.-Y. , DeBord J. R. , Sakima H.
Published: July 2002

We report the characterization of contact etch processes which give variable sidewall taper angles. Patterning at 248 nm gave contact holes at ∼0.19 μm diameter in photoresist over organic bottom anti reflection coating (BARC). The contact stack and test structures (BARC/oxide/SiN, 5–10 kÅ total stack thickness) were etched in a medium-density TEL dipole ring magnetron (DRM) system. Bottom hole diameters ranging from 0.17 down to 0.10 μm could be obtained by varying the oxide etch process, which included C4F8 or C5F8, O2, and Ar. A moderate etch selectivity of ∼8:1 (oxide: SiN etch rate ratio) was determined for the main taper process. Etched patterned wafers were characterized using top-down critical dimension scanning electron microscopy (CD-SEM), cross-section SEM, and transmission electron microscopy. Ex situ surface analysis of etched blanket wafers using x-ray photoelectron spectroscopy showed only small dependence of the surface fluorocarbon film thickness and composition on taper etch process conditions. W-filled tapered contacts showed significant improvement in contact-gate misalignment margin and in static random access memory (SRAM) yield compared to more straight-sidewall contacts.
Mg–Ga liquid metal ion source for implantation doping of GaN
Authors: Cheng J. , Steckl A. J.
Published: July 2002

A magnesium liquid metal ion source was investigated for p-type doping of GaN. The metal is an alloy composed of 33.3% Mg and 66.7% Ga. The source type is a direct heating needle source with a spring-type reservoir, which is constructed using tungsten wire and a ceramic tube. The source has been tested and characterized in a NanoFab 150 focused ion beam (FIB) system. A typical source lifetime was 250 μA h. Mg+ ion implantation of GaN thin films has been performed at different energies between 30 and 100 keV for doses ranging from 5×1013 to 1×1015 cm−2. After Mg+ FIB implantation, samples were annealed at 1100 °C in N2 ambient. Low temperature photoluminescence with a He–Cd laser of 325 nm exhibited the donor—acceptor recombination peak, which was enhanced by the activated magnesium ions.
Characterization of plasma-enhanced chemical vapor deposition carbon nanotubes by Auger electron spectroscopy
Authors: Teo K. B. K. , Chhowalla M. , Amaratunga G. A. J. , Milne W. I. , Pirio G. , Legagneux P. , Wyczisk F. , Olivier J. , Pribat D.
Published: July 2002

Plasma-enhanced chemical vapor deposition (PECVD) is a versatile technique for growing well-aligned, precisely patterned, multiwalled carbon nanotubes directly on substrates. We report on the characterization of PECVD deposited nanotubes using Auger Electron Spectroscopy (AES); we believe that this is the first comprehensive AES study of nanotubes and the effect of the deposition process on the substrate. The nanotubes contained well-crystallized graphitic carbon, in contrast to the amorphous/disordered carbon byproduct which is condensed on the substrate surface. By adjusting the deposition gas ratios, we show, using depth-profiled composition analysis, that it is possible to eliminate the unwanted amorphous carbon on the substrate surface. However, a 5 nm interfacial layer, which contained the plasma species, was always present on the substrate surface due to its exposure to the plasma. We could prevent the formation of this interfacial layer by shielding areas of the substrate from the plasma to achieve truly byproduct free deposition. This technique has allowed us to fabricate promising microelectronic field emission devices using vertically aligned carbon nanotubes.
Modified design for fabrication of metal based single electron transistors
Authors: Hofmann K. , Spangenberg B. , Kurz H.
Published: July 2002

We present a modified design for the fabrication of tunnel junctions applied in metal-based single electron transistors (SETs). The electrodes of the junction are placed on different levels which allows a significant reduction of the tunnel capacitance. The device is fabricated with relaxed 100 nm lithography requirements and shows clear SET features at an operating temperature of T=4.2 K: Coulomb blockade, pronounced staircase, and distinct oscillations. The observed experimental results are discussed in comparison with simulated data.
Comparative evaluation of protective coatings and focused ion beam chemical vapor deposition processes
Authors: Kempshall B. W. , Giannuzzi L. A. , Prenitzer B. I. , Stevie F. A. , Da S. X.
Published: July 2002

Dual-beam instruments incorporate both an electron column and an ion column into a single instrument, and therefore allow the chemical vapor deposition (CVD) process to be either ion- or electron-beam assisted. Damage has been observed in the surface layers of specimens in which ion-beam assisted CVD processes have been employed. Cross-section transmission electron microscopy (TEM) has been used to compare (100) Si substrates on which Pt metal lines have been grown by ion- and electron-beam assisted CVD processes. The micrographs show that a 30 keV Ga+ ion beam, a 5 keV ion beam, and a 3 keV electron beam imparts 50 nm, 13 nm, and 3 nm of damage to the Si substrate, respectively. In addition, Au–Pd and Cr sputter coatings were evaluated for the prevention of ion-beam induced surface damage. TEM cross-section specimens revealed that Cr sputter coatings > 30 nm in thickness are sufficient to protect the (100) Si surface from the 30 keV Ga+ ion beam while Au–Pd sputter coatings up to 70 nm in thickness may be discontinuous and, therefore, will not protect surface regions from ion beam damage.
Microscopic characterization of electron field emission
Authors: Nilsson L. , Groening O. , Kuettel O. , Groening P. , Schlapbach L.
Published: July 2002

We report on the functional capabilities of a scanning anode field emission microscope (SAFEM) which combined with a phosphor screen is used to investigate and correlate individual electron emission site characteristics of low threshold thin film electron emitters in the micrometer regime. Spatially recorded extraction voltage V(x,y) maps under constant emission current or emission current I(x,y) maps under constant anode voltage reveal spatially divergent emission properties on thin film emitters. The V(x,y) maps are used to derive the field enhancement β(x,y) maps which give a better description of the thin film emission properties as compared to electric threshold fields which depends on anode-cathode geometry. Individual emission site current stability of thin film emitters can be investigated with the SAFEM, and a high-resolution field emission microscope to investigate the environmental stability of single carbon nanotubes mounted on filaments as a function of partial gas pressures and temperature.
Ultrathin nitrided-nanolaminate (Al2O3/ZrO2/Al2O3) for metal–oxide–semiconductor gate dielectric applications
Authors: Jeon Sanghun , Yang Hyundoek , Chang Hyo Sik , Park Dae-Gyu , Hwang Hyunsang
Published: July 2002

An ultrathin nanolaminate (Al2O3/ZrO2/Al2O3) film prepared by atomic layer chemical vapor deposition was investigated for use in metal–oxide–semiconductor field effect transistor (MOSFET) gate dielectric applications. Based on transmission electron microscopy and medium-energy ion scattering spectroscopy (MEIS) analysis, an abrupt interface between stoichiometric top-layer Al2O3 and ZrO2 was found. Interfacial layers such as Zr–Al–O and Al–Si–O were also observed. An electrical equivalent oxide thickness as thin as 10.2 Å with a quantum mechanical correction was obtained. Additional plasma nitridation of nanolaminte in N2 led to a significant reduction in the interfacial oxidation of nanolaminate which was confirmed by x-ray photoelectron spectroscopy, MEIS, and capacitance–voltage (C–V) analysis. The nanolaminate film represents a promising alternative for gate dielectric applications of future sub-100 nm MOSFET.
Sub-50 nm nanopatterning of metallic layers by green pulsed laser combined with atomic force microscopy
Authors: Huang S. M. , Hong M. H. , Luk’yanchuk B. S. , Lu Y. F. , Song W. D. , Chong T. C.
Published: July 2002

Pulsed-laser assisted nanopatterning of metallic layers on silicon substrates under an atomic force microscope (AFM) tip has been investigated. A 532 nm Nd:YAG pulsed laser with a pulse duration of 7 ns was used. Boron doped silicon tips were used in contact mode. This technique enables the processing of structures with a lateral resolution down to 10 nm on gold and copper layers. Nanopatterns such as pit array and multilines with lateral dimensions between 10 and 50 nm and depths between 2.5 and 21 nm have been created. The experimental results and mechanism of the nanostructure formation are discussed. The created features were characterized by AFM, scanning electron microscope, and Auger electron spectroscopy. The apparent depth of the created pit has been studied as a function of laser intensity or laser pulse numbers. The dependence of nanoprocessing on the geometry parameters of the tip and on the optical and thermal properties of the processed sample has also been investigated. Thermal expansion of the tip, the field enhancement factor underneath the tip, and the sample surface heating were estimated. It is proposed that the field-enhancement mechanism is the dominant reason for this nanoprocessing.
Chemisorption bond lengths of chalcogen overlayers at a low coverage by convergent perturbation methods
Authors: Van Hove M. , Tong S. Y.
Published: July 2002

The bond lengths and binding locations of the p (2×2) chalcogen (O, S, Se, and Te) overlayers on Ni(001) are investigated in detail by microscopic low−energy electron diffraction (LEED) calculations. Two convergent perturbation methods are used which are as accurate as equivalent exact calculations but which minimize the use of computation core storage and time. Normal and off−normal incidences are considered and eight partial waves are used in the calculations. The results show the p (2×2) O and S bond lengths are identical to those of the c (2×2) structures determined by Demuth et al. The larger chalcogens Se and Te form slightly different bond lengths (difference less than ±0.1 Å) from those determined for the c (2×2) overlayer structures.
Angular distribution of photoelectrons from (111) silicon surface states
Authors: Traum M. M. , Rowe J. E. , Smith N. V.
Published: July 2002

Photoelectron energy spectra were obtained as a function of angle of emission from the cleaved face of lightly−doped p−type silicon using 10.2 eV normal incidence radiation. Measurements were taken in a previously described apparatus on samples prepared under conditions known to produce the 2×1 LEED pattern. A peak in the spectra due to emission from the surface state near the top of the valence bands was quite prominent between 20° and 30° from the [111] surface normal. The variation of the peak’s intensity with azimuthal angle displayed three strong lobes centered about the 〈2̄11〉 directions. Since a dangling−bond surface state of primarily pz character is almost azimuthally isotropic, we attribute the anisotropies observed either to final−state effects on the emission probabilities, or to an unexpectedly large transverse−orbital (S2) content in the initial surface state itself.
Abstract: Flash desorption activation energies: DCOOH decomposition and CO desorption from Ni(110)
Authors: Falconer J. L. , Madix R. J.
Published: July 2002

Accurate values of activation energies were measured by flash desorption methods without assumptions about preexponential factors, reaction orders, or specific reaction mechanisms. The activation energies were determined by two methods; one method employed a new relationship for the shift in peak temperature with change in heating rate, and the other utilized the change in peak amplitude with shift in peak temperature for different heating rates. Agreement between the two methods was excellent. A series of flash curves at different heating rates were obtained for the CO2 and CO products from DCOOH flash decomposition following adsorption on Ni(110) at 37°C. Adsorbed DCOOH decomposed autocatalytically with an activation energy of 26.6 kcal/mol to form CO2 and D2. Carbon monoxide formation from DCOOH decomposition, which corresponded identically to CO desorption from this surface, showed a first order activation energy of 32.7 kcal/mol; this activation energy was used to fit a series of CO flash desorption curves obtained for CO adsorption at −55°C. The preexponential factor was found to be 8.5×1015 sec−1. The desorption was first order with a coverage dependent desorption energy. The results illustrate the sensitivity of flash desorption for the determination of binding energies over a wide range of coverages.