bluuebunny/crossref_metadata_2025 huggingface dataset:
IT and organizational change: an institutionalist perspective
Authors: Avgerou Chrisanthi
Published: July 2002

This article challenges the tendency of the information systems literature to subsume IT innovation in processes of organizational change, either with the role of “enabler” of organizational objectives, or as an instrument appropriated by situated organizational actors. Using institutionalist theory, the relationship between information systems development and organizational transformation is studied as the interaction of two institutionalization processes: the increasing momentum and legitimation of IT innovation; and the organizational efforts for the substitution of established structures and activities with new ones which often do not command adequate legitimacy. Such analysis suggests that IT innovation in organizations is to a large extent sustainable by its own institutional forces, irrespective of contribution to the processes of organizational change. This perspective is demonstrated with the case study of the Mexican oil company, Pemex, where IT projects have played a large part in its transformation from a state‐owned to private enterprise.
Different interface approximations in multi‐domain GDQ simulation of Czochralski bulk flows
Authors: Shu C. , Chew Y.T. , Liu Y.
Published: July 2002

The multi‐domain generalized differential quadrature method is applied in this paper to simulate the flows in Czochralski crystal growth. The effect of interface treatment on the numerical solution is studied through four types of interface approximations. The performance of those four interface approximations is validated by a benchmark problem suggested by Wheeler. It is demonstrated in this study that the multi‐domain GDQ approach is an efficient method which can obtain accurate numerical solutions by using very few grid points, and the overlapped interface approximation provides the most accurate numerical results.
Identifying user‐based criteria for Web pages
Authors: Abels Eileen G. , Domas White Marilyn , Hahn Karla
Published: July 2002

Reports on Phase I of a two‐part project to identify and implement user‐based design criteria in World Wide Web pages. The purpose of the identification phase (Phase I) is to identify the criteria that influence a particular user community’s use of the Web and to analyze these within the context of the users’ overall information‐gathering behavior. Data were gathered through a questionnaire and electronic focus group session with nine faculty from four business schools. Participants identified 49 Web page features which clustered into eight broad categories of criteria having a significant positive or negative impact on their use of WWW pages. They also identified types of information normally used in work activities; methods of finding this information within the current information service environment; likely changes in behavior if the information became available via the Web, including willingness to pay.
Mapping Africa’s initiative at building an information and communications infrastructure
Authors: Thapisa Amos P.N. , Birabwa Elizabeth
Published: July 2002

The article explores Africa’s initiative at building a regional plan for the formulation and development of a National Information and Communication Infrastructure (NICIP) in every African state. The paper also examines the challenges and opportunities confronting Africa in its bid to launch itself into the information age. The role of information, communication and knowledge in accelerating African socio‐economic development is emphasised. The paper makes a critical examination of the globalisation of economies and argues that globalisation appears to favour the rich and not so much the poor. It challenges the Organisation of African Unity (OAU) to provide funding for the project if it is to succeed. It eventually concludes by making the observation that Africa’s Information Society Initiative (AISI) should promote Africa.
‘I Don't Know What I'd Do without Our Mam’ Motherhood, Identity and Support Networks
Authors: Mitchell Wendy , Green Eileen
Published: July 2002

This paper explores the role and importance of kinship within the lives of 14 working class women as they seek to make sense of motherhood and their own self-identity as a young mother. Within late modernity, numerous discourses suggest that kin networks and the role and importance of kinship are in decline as ‘the family’ changes and adapts. Indeed, the idea of extended family support and networking is frequently viewed as a historically cozy image rather than an everyday reality as we enter the twenty-first century. However, this paper demonstrates that the situation is far from straightforward. The young mothers' discourses and everyday experiences remain firmly grounded in relations of class, gender and the locality within which they live. Hence, although many of the young women are increasingly individualised, self-reflexive actors seeking to make sense of intimate relations and kinship in an ontologically insecure world, kin networks, especially female kinship continue to play a pivotal role in their lives – practically, socially and emotionally. Indeed, female kinship is closely interwoven with their self-identity as a caring and capable mother.
Mutant mice deficient in NOS‐1 exhibit attenuated long‐term facilitation and short‐term potentiation in breathing
Authors: Kline David D. , Overholt Jeffery L. , Prabhakar Nanduri R.
Published: July 2002

The objective of the present study is to examine the potential role of nitric oxide (NO) in short‐term potentiation (STP) and long‐term facilitation (LTF) of breathing. Experiments were performed in wild‐type (WT) and mutant mice deficient in nitric oxide synthase‐1 (NOS‐1), as well as in WT mice administered the NOS‐1 inhibitor 7‐nitroindazole (7‐NI; 50 mg kg−1; i.p.). Respiratory responses following either single or recurrent episodes of hypoxia (7 % O2, balance N2) were analysed in unanaesthetised animals by body plethysmography along with rate of O2 consumption (V̇O2) and CO2 production (V̇CO2). After a single hypoxic challenge, respiration in WT mice remained elevated for 5 min, suggesting STP in ventilation. Following termination of three consecutive hypoxic challenges, respiration remained elevated during normoxia for as long as 30 min, indicating LTF in breathing under awake conditions. STP and LTF were significantly attenuated or absent in WT mice after 7‐NI. A similar attenuation or absence of STP and LTF was also seen in NOS‐1 mutant mice. Changes in V̇O2 and V̇CO2 were comparable among mice during the post‐hypoxic period, suggesting that the absence of STP and LTF was not due to alterations in body metabolism. These results suggest endogenous NO is an important physiological modulator of ventilatory STP and LTF.
Predictions of a Film Coolant Jet in Crossflow With Different Turbulence Models
Authors: Hoda Asif , Acharya Sumanta
Published: July 2002

This study investigates the performance of several existing turbulence models for the prediction of film coolant jet in a crossflow. Two-equation models employing k–ε and k–ω closures, broadly categorized as high-Reynolds-number formulations, low-Reynolds-number formulations, DNS-based formulation, and nonlinear formulations have been used to simulate the flow. In all, seven different turbulence models have been tested. Predictions with different models have been compared with experimental results of Ajersch et al. (1995) and with each other to critically evaluate model performance. The assessment of models has been done keeping in mind that all models have been formulated for wall-bounded flows and may not be well suited for the jet-in-a-crossflow situation. Close agreement with experimental results was obtained at the jet exit and far downstream of the jet injection region, but all models typically overpredicted the magnitude of the velocities in the wake region behind the jet. The present study clearly underscores the deficiencies of the current models, and demonstrates the need for improvements. [S0889-504X(00)03002-6]
Stress Relaxation Behavior at High-Tension Bolted Connections of Stainless-Steel Plates
Authors: Tendo Masayuki , Yamada Kenji , Shimura Yasumi
Published: July 2002

To clarify the influence of creep deformation of stainless-steel plates on the stress relaxation at high-tension bolted connections, the measurements of creep strain and residual stress in the bolt have been made. Annealed type 304 plates showed apparent creep strain and the stress decrease was approximately 6 percent for 700 hours. Creep strain could not be observed for the plates with higher yield strength, and less stress relaxation was measured. These experimental results have been ascertained by FEM using the creep equations. The stress relaxation behavior could be predicted except for the early stage immediately after loading.
Nonlinear Stability, Thermoelastic Contact, and the Barber Condition
Authors: Pelesko J. A.
Published: July 2002

The behavior of a one-dimensional thermoelastic rod is modeled and analyzed. The rod is held fixed and at constant temperature at one end, while at the other end it is free to separate from or make contact with a rigid wall. At this free end we impose a pressure and gap-dependent thermal boundary condition. This condition, known as the Barber condition, couples the thermal and elastic problems. Such systems have previously been shown to undergo a bifurcation from a unique linearly stable steady-state solution to multiple steady-state solutions with alternating stability. Here, the system is studied using the asymptotic matching techniques of boundary layer theory to derive short-time, long-time, and uniform expansions. In this manner, the analysis is extended into the nonlinear regime and dynamic information about the history dependence and temporal evolution of the solution is obtained.
Experimental Investigation of a Vortex-Flow Solar Chemical Reactor for the Combined ZnO-Reduction and CH4-Reforming*
Authors: Kra¨upl Stefan , Steinfeld Aldo
Published: July 2002

The co-production of Zn and synthesis gas by the combined reduction of ZnO and reforming of CH4 has been performed using a vortex-flow chemical reactor in a high-flux solar furnace. The reactor operating temperature ranged between 1221 and 1481 K for an input solar power of 2.3 to 4.6 kW and mean solar flux intensities of 810 to 1609 kW/m2. The performance of the reactor was determined by conducting a complete mass and energy balance for the chemical process. The chemical conversion ranged between 83–100 percent. The thermal efficiency, defined as the portion of input solar power absorbed as sensible and process heat, was in the range 11–28 percent. The exergy efficiency for the closed cycle, defined as the ratio of the maximum amount of work that the products leaving the reactor could produce if were re-combined to the input solar power, was in the range 0.3–3.1 percent. Major sources of energy loss are re-radiation heat transfer through the reactor aperture, conduction heat transfer through the reactor walls, and the quenching of the reaction products.
A Simple Estimating Method for Reduction of Welding Residual Stresses in Thick Welded Joint From Stress-Relief Annealing—Part IV: Applicability of the Simple Estimating Method for Stress-Relief Annealing of Thick Welded Joint
Authors: Nakacho Keiji
Published: July 2002

Stress-relief annealing (SR treatment) is often applied to relieve welding residual stresses in the fabrication process of pressure vessels, etc. This study aims at development of an efficient method as simple as hand calculation to estimate reduction of residual stresses of a very thick welded joint by SR treatment. In the first report, an estimating method was developed for relaxation tests, in uniaxial stress state, at changing and constant temperatures because the stress relaxation phenomenon may be considerably similar to that observed in the SR treatment of a joint. In the second report, the stresses relaxed by SR treatment in a very thick welded joint were analyzed accurately by the finite element method based on thermal elastic-plastic creep theory. The characteristics of the changes of the welding residual stresses in multiaxial stress state were studied in detail for further development of the estimating method to SR treatment of a very thick welded joint, of which the stress state and boundary condition are very complex. In the third report, the estimating equations in multiaxial stress states were developed for the stress relaxation phenomenon in the thick welded joints, based on the foregoing characteristics. In this report, the applicability of the simple estimating method is investigated for SR treatment of the thick welded joint, by comparing the estimated results with the accurate ones obtained by FEM.
Surface Feature Effects in Starved Circular EHL Contacts
Authors: Dumont M.-L. , Lugt P. M. , Tripp J. H.
Published: July 2002

Computation of the EHL film thickness of micro-pitted surfaces for starved elastohydrodynamic conjunctions has been performed. Transient calculations have shown that pits filled with lubricant release part of their content in the inlet zone as they enter the EHL contact. Initially, a fraction of this released oil remains in the inlet region and produces an upstream shift of the meniscus. The remainder of the oil is entrained and builds up the film thickness at the trailing edge of the pit. With time, the fraction of oil in the inlet also becomes entrained and the meniscus slowly returns to its equilibrium position. The time interval during which the film thickness is enhanced thus becomes prolonged and may persist even after the pit has left the contact. Computations carried out with several pits have shown that this process is not disturbed. The beneficial increase of film thickness is lost if the contact becomes fully flooded. Experimentally, the advantage of making small recesses in bearing surfaces has been shown before. This paper now reveals the lubrication mechanisms involved, allowing improvements in the design of surface features in EHL contacts.
Natural Convection in a Cylindrical Enclosure Filled With Heat Generating Anisotropic Porous Medium
Authors: Dhanasekaran M. R. , Das Sarit Kumar , Venkateshan S. P.
Published: July 2002

A numerical study has been made to analyze the effects of anisotropic permeability and thermal diffusivity on natural convection in a heat generating porous medium contained in a vertical cylindrical enclosure with isothermal wall and the top and bottom perfectly insulated surfaces. The results show that the anisotropies influence the flow field and heat transfer rate significantly. The non-dimensional maximum cavity temperature increases with increase in permeability ratio. For aspect ratio greater than or equal to two, the nondimensional maximum cavity temperature increases with an increase in the thermal diffusivity ratio. For aspect ratio equal to unity, there exists a critical value of thermal diffusivity ratio at which the maximum cavity temperature is a minimum. This critical value increases with an increase in the value of anisotropic permeability ratio. Based on a parametric study correlations for maximum cavity temperature and average Nusselt number are presented.
A Grammar Driven Data Translation System for Computer Integrated Manufacturing
Authors: Niebur Glen L. , Chase Thomas R.
Published: July 2002

The ability to share data among the numerous software applications used to design and analyze products is an important aspect of computer integrated manufacturing. In the past, data sharing has been implemented by direct translation of data files, through neutral data formats, and through central shared databases. This paper describes a data sharing architecture that addresses some of the limitations of these systems. It employs a database management system as a central repository for part data in an application independent format. A configurable translator, called Datatrans, is used to transfer data between the database management system and native application data files. In this way software from multiple independent vendors or legacy software can be supported, because applications need not incorporate code specific to any database management system nor have knowledge of the centralized database schema. The translator uses grammars to define and recognize the data to be translated. The grammar is augmented with commands that are passed to the front-end of the database management system or to application programs to store and retrieve data. Thus the query language and the application commands serve as a high level interface to the underlying database and application data files. Entity transformations that are beyond the scope of a grammatical description are performed by database methods, which are available to all applications. An implementation of the system demonstrates the feasibility of this approach.
Investigation of Temperature at Tool-Chip Interface in Turning Using Two-Color Pyrometer
Authors: Al Huda Mahfudz , Yamada Keiji , Hosokawa Akira , Ueda Takashi
Published: July 2002

A technique for measuring temperature at the interface between a cutting tool and a chip is developed. A two-color pyrometer with fused fiber coupler is applied to the temperature measurement of the tool-chip interface in dry and wet turning. By using this pyrometer, it is possible to measure the temperature of a very small object without emissivity affecting the results. A translucent alumina sintered under HIP is used as the cutting tool, and an annealed carbon steel AISI 1045 is used as the workpiece. Water-soluble coolant is introduced onto the rake surface of the tool. The technique developed is suitable for measuring temperature at tool-chip interface, either in dry or wet cutting conditions. The effect of coolant on the temperature is small, since temperature reduction is only about 3 percent compared with the temperature in dry cutting. The temperature distributions on the cutting tool and the work material are analyzed using the finite element method. Good agreement is obtained between the analytical results and experimental ones.
Direct Steam Generation in Parabolic Troughs: First Results of the DISS Project
Authors: Eck M. , Steinmann W.-D.
Published: July 2002

This article presents the latest experimental results of the European DISS (DIrect Solar Steam) project. The experiments are subdivided into steady state and transient tests. The goal of the steady state tests is the investigation of the thermohydraulic phenomena of the occurring two phase flow, whereas the transient tests are needed for the controller design. The experimental results are compared to simulation studies. Implications for the plant operation will be discussed.
Diagnosis of Rolling-Element Bearings Failure by Localized Electrical Current Between Track Surfaces of Races and Rolling-Elements
Authors: Prashad Har
Published: July 2002

The diagnosis and cause analysis of rolling-element bearing failure have been well studied and established in literature. Failure of bearings due to unforeseen causes were reported as: puncturing of bearings insulation; grease deterioration; grease pipe contacting the motor base frame; unshielded instrumentation cable; the bearing operating under the influence of magnetic flux, etc. These causes lead to the passage of electric current through the bearings of motors and alternators and deteriorate them in due course. But, bearing failure due to localized electrical current between track surfaces of races and rolling-elements has not been hitherto diagnosed and analyzed. This paper reports the cause of generation of localized current in presence of shaft voltage. Also, it brings out the developed theoretical model to determine the value of localized current density depending on dimensional parameters, shaft voltage, contact resistance, frequency of rotation of shaft and rolling-elements of a bearing. Furthermore, failure caused by flow of localized current has been experimentally investigated.
Hybrid Brush Pocket Damper Seals for Turbomachinery
Authors: Laos Hector E. , Vance John M. , Buchanan Steven E.
Published: July 2002

Pocket damper seals perform a dual function: both sealing the pressurized gas around a rotating shaft and providing large amounts of vibration damping. The annular cavity between the labyrinth seal teeth is subdivided into separate annular cavities around the circumference of the rotor by partitioning walls. Also, the upstream and downstream teeth have different radial clearances to the rotor. These seals have been shown to provide a remarkable amount of direct damping to attenuate vibration in turbomachinery, but they generally leak more than conventional labyrinth seals if both seals have the same minimum clearance. Conversely, brush seals allow less than half the leakage of labyrinth seals, but published test results show no significant amount of damping. They are considered to be a primary choice for the seals in new aircraft engine designs because of their low leakage. This paper will describe a recently invented hybrid brush/pocket damper seal that combines high damping with low leakage. Previous brush seal results were studied and calculations were made to select a brush seal to combine with the pocket damper design. The result is a hybrid seal with high damping and low leakage. A special design feature can also allow active vibration control as a bonus benefit. A computer code written for the original pocket damper seal was modified to include the brush element at the exit blade. Results from the computer code indicate that the hybrid seal can have less leakage than a six bladed (or 6 knives) labyrinth seal along with orders of magnitude more damping. Experimental evaluations of the damping and leakage performance of the hybrid seal are being conducted by the authors. The experimental work reported here tested the damping capability of the new hybrid brush seal by exciting the seal journal through an impedance head. A conventional six-bladed labyrinth seal of the same working dimensions was also tested. The brush hybrid pocket damper seal is found to leak less than the labyrinth seal while producing two to three times more damping than the original pocket damper seal (orders of magnitude more than the conventional labyrinth). [S0742-4795(00)01102-9]
Valence Band and Core-level Photoemission and Photoelectron Diffraction in Epitaxial Nb-Doped TiO2(110)
Authors: Chambers S. A. , Gao Y. , Kim Y. J.
Published: July 2002

Valence-band, Ti 2p, and Nb 3d photoemission spectra are reported for Nb-doped TiO2(110) grown as epitaxial films on TiO2(110) substrates at 600 °C. Core-level photoelectron diffraction is used to establish that Nb substitutes for Ti at cation sites in the rutile lattice. Valence band spectra reveal that the additional electronic density of states brought about by the substitution of Nb for Ti falls in the valence band region, rather than in the bandgap or conduction band region, as expected for parts-per-thousand dopant levels.
Core Level and Valence Band Spectra of PbO by XPS
Authors: Rondon Sonia , Sherwood Peter M. A.
Published: July 2002

Core and valence band spectra were obtained from a commercial PbO. The XPS data were collected with a VSW HA150 spectrometer equipped with a monochromatic Al Kα x-ray source and a multichannel detector. This report includes the Pb 4f, Pb 5d, Pb 4d, O 1s, C 1s, and valence band photoemission peaks. The XPS analysis showed the presence of small amounts of adventitious carbon, carbonate, adsorbed water, and significant amounts of hydroxide on the surface of the sample. When collected with achromic radiation the valence band region of PbO is overlapped by the Mg Kα3/4 satellites associated with the relatively intense Pb 5d and O 2s peaks. The use of monochromatic x-radiation allowed one to collect a high resolution valence band spectrum without the interference of these satellite features. This is of particular interest in the study of lead oxides because their XPS valence band spectra present features that can be used successfully to distinguish the different oxide forms.
Temperature Variation of the Resistivity of Epitaxial Gold Films
Authors: Jacobs J. T. , Birtcher R. C. , Peacock R. N.
Published: July 2002

Measurements of the resistivity of epitaxial gold films vacuum deposited upon mica were made over the temperature range of 4.2–300 K. A computerized data analysis scheme, in which the operator played the part of a judgment element in the feedback loop, was used to fit the Fuchs-Sondheimer theory of size effects to the experimental data. The specularity parameter could be determined from the data for a single film. The results for films thinner than 4000 Å are that the specularity, p, varied between 0.5 and 0.95 whereas the static lattice imperfection resistance, ρi, varied between 5.2 and 9.0×10−8 Ω-cm.
Surface Phonons and Magnos
Authors: Wolfram T. , DeWames R. E. , Kraut E. A.
Published: July 2002

A brief introductory survey of surface phonons and magnons is presented. Long-wavelength surface modes include optical modes in ionic crystals, magnetostatic waves in magnetic insulators, and elastic surface waves. The effects of retardation on the optical modes lead to surface polaritons. Calculations based on discrete atomic models show that additional surface modes occur in the ionic crystals due to abrupt changes in the short-range forces at the surface and that the electrodynamic modes are pseudosurface states when they exist in the bulk band. Experiments relating to these modes are reviewed briefly. Magnetostatic modes are the magnetic analog of the electrodynamic optical modes in ionic crystals. When the exchange interaction is considered the magnetostatic surface modes are converted into pseudosurface states called dipole-exchange surface modes which lie within the bulk spin-wave band. Elastic surface waves in isotropic, anisotropic, piezoelectric, and layered media are discussed briefly. Various types of elastic waves include generalized Rayleigh, pseudosurface, electroacoustic, Love, Lamb, Sezawa, and Stoneley waves. Short-wavelength surface waves include acoustic and optical phonons and acoustic and optical magnons in ferro-and antiferromagnets. Surface magnons are discussed and experiments and theory relating to surface spin dynamics are reviewed. Surface phonon characteristics are described and relevant experiments are mentioned.
Precision Determination of Surface Plasmon Dispersion on Al(111) Films via Inelastic Low-Energy Electron Diffraction
Authors: Duke C. B. , Landman U. , Porteus J. O.
Published: July 2002

A high-precision method of analyzing inelastic low-energy diffraction (ILEED) intensities is proposed for the determination of the surface plasmon dispersion relation from measured intensities. It is a refinement of a previously used procedure based on the two-step model of ILEED. The method is applied to analyze seven independent sets of ILEED intensities associated with electrons scattered in the specular beam from Al(111). All seven analyses are consistent with the surface-plasmon dispersion ħωs(p‖)=10.5+2p‖ and damping Γs(p‖)=1.85+3p‖. Energies are measured in eV and momenta in Å−1. If consistency with all seven data sets is required, all parameters in both the dispersion and damping are determined uniquely to an accuracy of 3% in the constant term and 50% in the term linear in p‖. No term quadratic in p‖ is required in either the dispersion or the damping.
Photovoltaic characteristics of BR/p-silicon heterostructures using surface photovoltage spectroscopy
Authors: Li Lin Song , Xu Tao , Zhang Yan Jie , Jin Jian , Li Tie Jin , Zou Bingsuo , Wang Jian-Ping
Published: July 2002

Purple membrane (PM) monolayers were deposited on hydrophilic or hydrophobic silicon substrates through the Langmuir–Blodgett (LB) technique. The photovoltaic features and interfacial charge separation of p-Si/PM/indium tin oxide (ITO) heterostructure were studied by surface photovoltage spectroscopy (SPS). The different photovoltaic response values were obtained due to the nonrandom orientation of PM in the LB films on the hydrophilic versus hydrophobic silicon substrates. The photovoltaic response value versus external potential of the p-Si/cytoplasmic-extracellular/ITO heterostructure showed an obviously rectifying behavior. Compared with the p-Si/ITO heterostructure, the response value of SPS increased more rapidly in the case of the positive external bias.
Zirconium Dioxide Thin Films Characterized by XPS
Authors: Barreca Davide , Battiston Giovanni A. , Gerbasi Rosalba , Tondello Eugenio , Zanella Pierino
Published: July 2002

In this work we use x-ray photoelectron spectroscopy (XPS) to analyze the principal core levels of a ZrO2 thin film deposited on glass using Zr(OPri)3(dpm) (OPri=isopropoxy; hdpm=2,2,6,6-tetramethyl-3,5-heptanedione) as precursor. Besides the general survey, charge corrected binding energies for the Zr 3d5/2, Zr 3d3/2, O 1s, and C 1s photoelectrons are reported. Deconvolution of the O 1s signal reveals the presence of –OH groups and adsorbed water, whose presence can be related to the air exposure of the film between its preparation and XPS analysis.
Radio-frequency molecular-beam-epitaxy growth of III nitrides for microsensor applications
Authors: Starikov D. , Boney C. , Berishev I. , Hernandez I. C. , Bensaoula A.
Published: July 2002

To date, GaN-based compounds have proven commercially viable for optoelectronic devices such as light-emitting diodes (LEDs), laser diodes, and UV detectors, and are also under investigation for use in high-power, high-temperature electronics. Other areas in which the III nitrides could be especially beneficial are in high-energy particle detectors and in narrow-band optical sensors for the UV/visible spectral range. In addition to the inherent thermal, mechanical, and chemical stability of III nitrides, such devices would benefit from the larger band gap, higher breakdown, and insulating properties of GaN and related alloys. The surface quality of nitride materials is generally good, and this is very important for fabrication of optical devices. The specific characteristics of the III-nitride layers can be achieved by appropriate substrate selection and precise control over the material growth process. In this article, results on radio-frequency molecular-beam-epitaxy growth of GaN, AlN, AlGaN, and InGaN layers on sapphire and silicon substrates for optoelectronic sensor development applications are presented. Growth of high-quality p-GaN layers with hole concentration of up to ∼5×1017 cm−3 were realized and used in Schottky barrier light-emitting and photodiode structures. AlGaN layers with an Al mole fraction up to 42% as measured by cathodoluminescence, and AlN layers with breakdown fields of 333 V/μm are currently being investigated for applications as insulating layers and active layers, respectively, for devices with an UV-extended spectral range such as hot-electron-based avalanche LEDs and photodiodes.
Mass determination with piezoelectric quartz crystal resonators
Authors: Lu Chih−shun
Published: July 2002

Early investigations on quartz crystal resonators indicated, that for small mass change, the frequency shift is linearly proportional to the added mass. The accuracy of mass determination was later improved somewhat by using the so−called ’’period measurement’’ technique, which assumes a linear relationship between added mass and change in period of oscillation. However, recent studies indicate that for large mass load, the elastic properties of the deposited material have to be taken into consideration. Based on the theory of one−dimensional acoustic composite resonators, an equation relating the resonant frequency of the composite system to the mass and acoustic impedance of deposited material can be derived. The equation shows that materials with different acoustic impedances will obey different mass−frequency relations. The experimental data for a number of materials with different elastic properties are shown to be in excellent agreement with the theoretical predictions to a mass load as large as 50×10−3 g/cm2. The results indicate that if the acoustic impedance of the deposited material is known, quartz crystal resonantors can be used for measuring a large deposited mass to a remarkable accuracy by using the proper formula.
Surface charge transport in PbSxSe1−x and Pb1−ySnySe epitaxial films
Authors: Jensen J. D. , Schoolar R. B.
Published: July 2002

We have measured the Hall coefficient and Hall mobility at 77 and 300 K of n- and p-type PbSxSe1−x and Pb1−ySnySe epitaxial films on (111) BaF2 as a function of thickness. Transport measurements were made after exposure to air and after vacuum annealing and overcoating with either 50 Å of indium or 3000 Å of As2S3. The variation of the Hall coefficient and Hall mobility as functions of thickness showed evidence of a highly p-type surface layer on all samples exposed to air. The p-type layer is attributed to surface states produced by adsorbed oxygen. We have used the Petritz two-layer model to fit the dependence of the 77 K Hall coefficient and Hall mobility on sample thickness. This analysis indicates the surface mobilities of the alloys are 5–10X lower than the bulk mobilities. This implies diffuse scattering at the air-exposed surface but may also be due to diffuse scattering from the semiconductor–substrate interface, or both. We have observed large size effects in n-type Pb1−ySnySe films resulting from diffuse scattering at the semiconductor–substrate surface. In contrast, the surface mobility of n-type PbSe approaches the bulk value indicating that the scattering may be specular at both surfaces in this compound. Vacuum annealing the samples at 150° C removes much of the oxygen-induced p-type surface layer. Indium overcoatings invert the surfaces of p-type samples to highly n-type. Samples overcoated with As2S3 after vacuum annealing are completely insulated from the effects of oxygen when exposed to air.
Influence of thermal radiation on the vapor pressure of condensed hydrogen (and isotopes) between 2 and 4.5 K
Authors: Benvenuti C. , Calder R. S. , Passardi G.
Published: July 2002

Hydrogen molecules, physisorbed or condensed on cryosurfaces at liquid-helium temperatures, can be desorbed by thermal radiation. The probability of the process depends on the nature of the cryosurface, the degree of H2 coverage, and the spectrum of the radiation. For a given spectrum the desorption rate is proportional to radiation intensity, and, with a few exceptions, to the absorptivity of the cryosurface. The desorption efficiency of the absorbed 300-K radiant energy is approximately 7×10−6 for most of the 20 bakeable cryosurfaces tested. A decrease of radiation temperature below 130 K causes a progressive reduction of the desorption efficiency which amounts to a factor of three at 80 K. This variation of efficiency can be fitted to a curve obtained by assuming that a threshold wavelength for desorption exists in the radiation spectrum at 45 μm. The energy carried by a photon of this threshold wavelength is about three times that required for the desorption of a condensed H2 molecule. Precondensed sublayers of heavier gas also introduce a decrease of the desorption efficiency in the following order: HD; D2; Ne; and Ar, N2, Kr. For the last three gases the desorption efficiency is practically constant and independent of the substrate and the radiation temperature. Similar observations for the H2 isotopes, HD and D2, are also reported. A physical model for the desorption process and its agreement with the results obtained here is discussed.
Oxidation of tin: An ESCA study
Authors: Lau C. L. , Wertheim G. K.
Published: July 2002

Tin exposed to dry oxygen (104–106 L) at 100°C has been studied by ESCA. The ESCA shift for the tin 3d5/2 line was 1.65 eV and the separation between this line and the oxygen 1s line was 43.90 eV. The oxide was identified by comparing its ESCA spectra with those of SnO and SnO2 samples carefully prepared in vacuum. Clean SnO samples were prepared in vacuum by decomposing SnO2 crystallites at high temperature and depositing the vapor product on a gold substrate. The resulting films were identified to be red SnO by ion back-scattering and by Mössbauer experiments. Clean SnO2 samples were prepared by diamond-filing bulk SnO2 crystals in vacuum. Both of these oxides were found to have the same separation between the oxygen 1s and the tin oxide 3d5/2 lines and hence, the same chemical shift. For this reason, the oxidized tin was identified by comparing its valence band and O/Sn ratio, rather than its chemical shift, with those of the SnO and SnO2 samples. The oxidized tin was found to consist of both SnO and SnO2.
Symmetry determination of surface states on GaAs (110) using polarization-dependent, angle-resolved photoemission
Authors: Williams G. P. , Smith R. J. , Lapeyre G. J.
Published: July 2002

New occupied surface states are observed on the (110) cleavage face of GaAs. Using the polarized character of the radiation at the Wisconsin Synchrotron Radiation Center the symmetry of the states in the mirror plane are determined. Among current calculations of the electronic structure, only that which includes bond length relaxation yields results that are consistent with the observations.
AES study of oxidation of surface and bulk sulfides of Ni
Authors: Windawi H. , Katzer J. R.
Published: July 2002

The interaction of oxygen with sulfur-covered nickel and nickel sulfide surfaces was investigated by AES. For the adsorbed sulfur the interaction appears to proceed via an intermediate step prior to the removal of sulfur; a proposed mechanism of interaction is presented. This interaction is dependent on oxygen pressure. Under certain conditions three-layer oxide can form on a buried sulfur layer and this oxide is destabilized by the presence of sulfur. Oxidation of the nickel sulfide appears to be similar to that of the adsorbed-sulfur-on-nickel system with regard to oxide buildup. The effect of temperature on these processes is discussed.
X-ray photoelectron spectroscopy applied to gold-decorated mineral standards of biological interest
Authors: Landis W. J. , Martin J. R.
Published: July 2002

Reproducible high resolution spectra of nonconducting minerals of interest in biological calcification have been obtained by x-ray photoelectron spectroscopy, utilizing a technique we call biased referencing, a combination of gold decoration and electron charge neutralization of the samples. Minerals examined were hydroxyapatite [Ca10(PO4)6(OH)2], fluorapatite [Ca10(PO4)6F2], calcium carbonate (CaCO3), octacalcium phosphate [Ca8H2(PO4)6 ⋅ 5H2O], monetite (CaHPO4), brushite (CaHPO4 ⋅ 2H2O), calcium pyrophosphate (Ca2P2O7), and an amorphous calcium phosphate synthesized at neutral pH (Ca/P=1.47). Samples were pressed into thin wafers onto which a small gold dot was affixed by vacuum deposition. Biased referencing provided calibration of sample core level ionizations (O 1s, Ca 2p, P 2p, F 1s, and C 1s) to the Fermi level of Au 4f7/2 set at a conductive value of 84.0 eV. Measured binding energies represent initial data for these gold-decorated insulators and may be used to compare data similarly generated from mineralized biological tissues.
Determining metal–semiconductor interface structure by optical second-harmonic generation
Authors: McGilp J. F.
Published: July 2002

Conventional surface science techniques provide little information about the structure of the buried metal–semiconductor interface, where many layers of metal have been deposited on the semiconductor surface. We show that optical second-harmonic generation (SHG) can be used successfully to probe this structure for metal–silicon systems. SHG studies of Si(111)–Au and Si(100)–Au have been carried out in a conventional ultrahigh vacuum system equipped with low-energy electron diffraction and Auger electron spectroscopy. A strong SHG signal is obtained which is shown to originate at the buried interface and to persist through at least 30 Å of gold.
The interaction of NF3 with Ru(0001): Order at steps
Authors: Walczak M. M. , Johnson A. L. , Thiel P. A. , Madey T. E.
Published: July 2002

As part of a larger study of small fluorinated molecules on metal and semiconductor surfaces we investigated the adsorption of NF3 on Ru(0001) using measurements of electron-stimulated desorption ion angular distribution (ESDIAD), low-energy electron diffraction (LEED), thermal desorption spectroscopy, and Auger electron spectroscopy (AES). At 100 K, NF3 adsorbs with a high sticking probability. Some molecular NF3 desorbs on heating, with a peak maximum at 200 K. All molecular desorption is complete by 400 K, but AES shows that nitrogen and fluorine remain on the surface up to 1100 K. The LEED pattern of the majority of the surface remains (1×1) at all coverages and annealing conditions. At most locations on the Ru(0001) surface (planar regions), ESDIAD is dominated by F+ emission normal to the surface over the temperature range 100–1100 K. On stepped regions of the surface (near edges and defects) highly directional and intense hexagonal patterns of F+ emission are observed (200–1100 K). The off-normal beams desorb at 67°±3° away from the normal. It appears that most ESDIAD patterns in this system are derived from F or NFx (x<3) fragments.
Reaction of water with hydrofluoric acid treated silicon(111) and (100) surfaces
Authors: Gräf D. , Grundner M. , Schulz R.
Published: July 2002

Si wafers with (100) or (111) oriented surfaces were treated in hydrofluoric acid (40% HF, 1 min) and then water rinsed for different times from 10 s to more than 50 h. Oxygen uptake and oxide formation were investigated by x-ray photoelectron spectroscopy and high-resolution electron energy-loss spectroscopy. The initial state after the HF dip is characterized by a coverage with Si–hydride and small amounts of oxygen and fluorine. The interaction with the liquid phase of water was investigated up to the monolayer range. It shows distinct features: The first step is a rapid exchange of Si–F with H2 O to form Si–OH groups followed by a slow nucleophilic attack of OH− on surface Si–H to produce Si–OH. Growth law is logarithmic and extends to 3–5 h of water contact. The surface Si–OH act as nuclei for the attack of water on the polarized Si–SiOH backbonds. Interior Si–H and Si–OH groups develop. Further attack of OH− on interior Si–H yields Si–OH. Condensation of Si–OH forms Si–O–Si bridges and SiO2−x nuclei appear. Strain and altered surface topography lead to a changed rate of the logarithmic oxide growth. The oxide formation is accompanied by a slight corrosive attack of H2 O, leading to roughening of the surface.
Scanning tunneling microscope equipped with a field ion microscope
Authors: Sakurai T. , Hashizume T. , Kamiya I. , Hasegawa Y. , Ide T. , Miyao M. , Sumita I. , Sakai A. , Hyodo S.
Published: July 2002

A combined field ion (FIM) and scanning tunneling microscope (STM), which is called ‘‘FI–STM,’’ was designed, constructed with multiple surface analytical functions. The instrument has been operated successfully by observing the detailed structures of the graphite (0001) and the Si(111)7×7 surfaces. The FI–STM is equipped with a low-energy electron diffraction/Auger electron spectroscopy system and a sputtering gun and/or heating devices for preparing and characterizing specimen surfaces. The field ion microscope is operated at room temperature to observe the geometry of the STM scanning tip in situ in the course of STM investigations.
Preparation and characterization of ZnS thin films produced by metalorganic chemical vapor deposition
Authors: Smith Patricia B.
Published: July 2002

Thin, polycrystalline films of ZnS are grown on single-crystal silicon(100) surfaces by metalorganic chemical vapor deposition. Exposure of the Si substrate to hydrogen sulfide and dimethylzinc at low temperature and low pressure produces films which grow uniformly across a 100-mm diameter. The reactant gases used in this work are not diluted in carrier gases. Reactions are carried out for the temperature range 25–125 °C. ZnS film growth rates for this temperature regime vary from 125 to 2700 Å/min. The ZnS thin films were characterized using scanning electron microscopy, x-ray diffraction, Rutherford backscattering, and x-ray photoelectron spectroscopy.
Photoluminescence studies in ZnxCd1−xTe single crystals
Authors: González-Hernández J. , López-Cruz Elías , Allred D. D. , Allred Worth P.
Published: July 2002

The crystalline quality of ZnxCd1−xTe single crystals prepared by a modified Bridgman method with 0≤x≤0.05 has been analyzed using photoluminescence. The spectrum of a typical sample is dominated by lines originating from the recombination of free and bound excitons. Lines due to free excitons in their ground and first excited states are observed in both the pure CdTe and the mixed crystals. Excitons bound to Cd vacancies are observed in the pure CdTe crystal but not in the mixed crystal. Weaker and broader features appearing at energies below the exciton emission range were associated with transitions involving free-to-bound and bound-to-bound levels. The origin of the various lines in the spectra was deduced from the detailed measurements of the dependence of the spectrum on temperature and excitation intensity.
Formation of cubic boron nitride films by arc-like plasma-enhanced ion plating method
Authors: Ikeda Tsutomu , Kawate Yoshio , Hirai Yo
Published: July 2002

Thin cubic boron nitride (cBN) films were synthesized at 350 °C on various substrates such as silicon, stainless steel, TiN-coated WC–Co and WC–Co by means of an arc-like plasma-enhanced ion plating process. In this process, polycrystalline cBN films were obtained at deposition rates of 0.004 to 0.03 μm/min. The infrared spectra showed strong absorption at 1050 cm−1, indicating cubic structure of the deposited film. The electron diffraction patterns also showed the cubic structure, with a lattice parameter of 3.63 Å. It is inferred that ion bombardment during film growth plays a important role in the formation of cBN films. The cBN films deposited in this process had a high compressive stress of 4×1010dyn/cm2, which is significantly greater than the value of hard amorphous boron nitride (iBN) films, 1.6×1010dyn/cm2. The internal stress of cBN films was greatly reduced if iBN was used as a buffer layer between cBN and substrate.
X-ray photoelectron spectroscopy and ellipsometry studies of the electrochemically controlled adsorption of benzotriazole on copper surfaces
Authors: Cohen S. L. , Brusic V. A. , Kaufman F. B. , Frankel G. S. , Motakef S. , Rush B.
Published: July 2002

Adsorption of the corrosion inhibitor benzotriazole (BTA) from solution has been studied on well-characterized electrochemically prepared Cu surfaces. In situ ellipsometry and ex situ x-ray photoelectron spectroscopy (XPS) have been used to probe both the nature of the Cu surfaces prior to BTA adsorption and to determine the stoichiometry, thickness, and chemical composition of the Cu–BTA overlayer films. The films grown on Cu2O and on Cu0 under oxidizing conditions are generally 5–40 Å thick and best described as Cu+1 BTA. Uptake of BTA is also observed on CuO and reduced Cu0 surfaces where the adsorbed film is limited at close to a monolayer. Therefore, Cu2O does not appear to be a prerequisite for uptake of BTA. The thickness of the inhibitor overlayer was calculated from the N 1s/ Cu 3p core level XPS data and was in good agreement with independent ellipsometric measurements on similar samples. Roughening of the Cu surface is observed for samples treated at low pH. Differing amounts of oxygen are found in the Cu+1 BTA films depending upon the preparation environment.
Scanning tunneling microscopy of chemical vapor deposition grown BiSrCaCuO films
Authors: Nakamura Tomoji , Kimura Takahiro , Kimura Takafumi , Ihara Masaru , Umebu Itsuo
Published: July 2002

We have studied chemical vapor deposition (CVD) grown Bi–Sr–Ca–Cu–O superconducting thin films by scanning tunneling microscopy (STM). Under positive sample-bias conditions we could obtain stable topographic images in which a high density of steps along the a or b axis were observed. The heights of some steps were mutiples of 1.5 or 1.8 nm which correspond to half of the c axis length in Bi2Sr2Ca1Cu2O8+δ (low Tc phase) and Bi2Sr2Ca2Cu3O10+δ (high Tc phase), respectively. The domain size of the high Tc phase could be estimated to be about several tens of nanometers.