bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlates of Self‐Directed Behaviour in Wild White‐Faced Capuchins
Authors: Manson Joseph H. , Perry Susan
Published: July 2002

Elevated rates of self‐directed behaviour (SDB) such as self‐scratching and autogrooming have been widely used in recent years as an indicator of anxiety in catarrhine primates. This study presents the first examination of correlates of SDB rates in a platyrrhine primate. Subjects were 8 wild female white‐faced capuchins at Lomas Barbudal, Costa Rica, who were observed for 119 h of focal individual follows. The subjects performed significantly more self‐scratching and autogrooming while in close proximity to conspecifics than while alone, irrespective of whether the neighbour was dominant or subordinate to them. This result was attributable to elevated SDB rates during the 30 s preceding and following allogrooming bouts. Furthermore, subjects engaged in more SDB while in proximity to females (a) that were closer to them in dominance rank and (b) with whom they spent a larger proportion of their time in proximity. Self‐directed behaviour rates after conflicts did not differ from non‐postconflict rates. Nor were SDB rates above baseline levels during the 30 s before subjects descended to the ground. These results may provide support for the view that SDB rates index anxiety in this species, if grooming decisions signal individuals' current allegiances and are therefore a source of anxiety, even if being groomed is, itself, relaxing. Postconflict preparation for further aggression may mitigate against scratching and autogrooming in a fast‐moving arboreal species.
The incidence of lower‐pole nephrolithiasis — increasing or not?
Authors: Cass  , Grine  , Jenkins J.McK. , Jordan  , Mobley  , Myers
Published: July 2002

Objective

 To determine if the incidence of lower‐pole nephrolithiasis is increasing.

Methods

 A previously published meta‐analysis of trends in the location of stones in the kidney, using data from 1984 to 1992, determined the percentage of lower pole stones in 26 722 kidney stones treated by extracorporeal shockwave lithotripsy (ESWL). We performed prospective studies on all patients treated by ESWL for a single renal stone (not manipulated from the ureter) in two organizations; at Lithotripters Inc., 47 303 stones were treated with ESWL by 1000 urologists in private practice from 1989 to 1995. At the Midwest Urologic Stone Unit, 9357 stones were treated with ESWL by 200 urologists in private practice from 1987 to 1995. The distribution of stones in both samples was compared with that reported earlier.

Results

 The meta‐analysis for stone location trends from the previously published article suggested that the percentage of kidney stones in the lower pole at ESWL increased erratically from 1984 to 1989 but was then stable for 3 years. The Lithotripters Inc. sample showed an essentially constant incidence from 28% in 1990 to 30% in 1995, and the Midwest Urologic Stone Unit sample showed an essentially constant incidence from 35% in 1988 to 36% in 1995.

Conclusion

 The incidence of lower pole nephrolithiasis has remained stable from 1990.
Long‐term treatment with desmopressin in children with primary monosymptomatic nocturnal enuresis: an open multicentre study
Authors: HJÄlmÅS  , Hanson  , HellstrÖM  , Kruse  , SillÉN on behalf of the Swedish Enuresis Trial (Sweet) Group
Published: July 2002

Objective

 To study the long‐term efficacy and safety of desmopressin treatment in children with primary monosymptomatic nocturnal enuresis.

Patients and methods

 Children (aged 6–12 years) with nocturnal enuresis were recruited into an open multicentre trial. All children underwent an observation period of 4 weeks before starting a 6‐week dose‐titration period with desmopressin. If the number of wet nights decreased by more than half during medication, they began long‐term treatment on 20–40 μg desmopressin. To test for cure and avoid overtreatment, the medication was interrupted for one week every third month.

Results

 Of the 399 children forming the intention‐to‐treat cohort, 245 halved their number of wet nights and started long‐term treatment. During the periods off medication, 77 children were dry and at the end of the study another 73 (still on medication) reduced the number of wet nights to ≤10% of that during the observation period. A further 51 children halved the number of wet nights compared with the observation period. No serious adverse events occurred.

Conclusion

 Long‐term treatment with nasal desmopressin at a main dose of 40 μg is an effective and safe treatment for monosymptomatic nocturnal enuresis.
Urinary Incontinence Treatment Preferences in Long‐Term Care
Authors: Johnson Theodore M. , Ouslander Joseph G. , Uman Gwen C. , Schnelle John F.
Published: July 2002

OBJECTIVE: To elicit preferences for different urinary incontinence (UI) treatments in long‐term care (LTC) from groups likely to serve as proxy decision makers for LTC residents.

DESIGN: A descriptive, comparative study of preference for UI treatments of frail older adults, family members of nursing home (NH) residents, and LTC nursing staff. Surveys were mailed to families and self‐administered by staff. Older adults were interviewed.

SETTING: Four LTC facilities and two residential‐care facilities in Los Angeles.

PARTICIPANTS: Four hundred and three family members of incontinent NH residents were mailed surveys. Sixty‐six nursing staff caring for these incontinent residents and 79 older adult residents of care facilities (nine cognitively intact NH respondents and 70 residential care residents) answered surveys.

MEASUREMENTS: Preference rankings between seven paired combinations of five different UI treatments were measured on an 11‐point visual analog scale, with the verbal anchors “definitely prefer” this treatment, “probably prefer” this treatment, and “uncertain.” Respondents gave open‐ended comments as well.

RESULTS: Forty‐two percent of family members (171/403) returned the mailed survey. Of all respondents, 85%“definitely” or “probably” preferred diapers, and 77%“definitely” or “probably” preferred prompted voiding (PV) to indwelling catheterization. Respondent groups occasionally differed significantly in their preferences. In choosing between treatment pairs using a visual analogue scale, nurses preferred PV to diapers significantly more than did older adults or families (both of whom preferred diapers) (F (2,295) = 13.11, P < .0001). Older adults, compared with family and nurse respondents, showed a significantly stronger preference for medications over diapers (F (2,296) = 41.54, P < .0001). In open‐ended responses, older adults stated that they would choose a UI treatment based in part upon criteria of feeling dry, being natural, not causing embarrassment, being easy, and not resulting in dependence. Nurses said that they would base their choice of UI treatment upon increasing self‐esteem and avoiding infection.

CONCLUSIONS: Although there was wide variation within and between groups about preferred UI treatment, most respondents preferred noninvasive strategies (diapers and PV) to invasive strategies (indwelling catheters and electrical stimulation). Older adults preferred to a greater degree medications and electrical stimulation, therapies directed at the underlying cause of UI. Despite data documenting that diapering is a less time intensive way to manage UI and that toileting programs are difficult to maintain in LTC, nurses viewed PV as “natural” and strongly preferred it to diapering. Several family members and older adults viewed PV as “embarrassing” and “fostering dependence.” These data highlight the need to elicit preferences for UI treatment among LTC residents and their families.
Medicinal Plants of the Washambaa (Tanzania): Documentation and Ethnopharmacological Evaluation
Authors: Schlage Christina , Mabula C. , Mahunnah R. L. A. , Heinrich M.
Published: July 2002

Abstract: Medicinal plants are an important local resource for the Washambaa of the Western Usambara Mountains in Tanzania. In this study the Washambaa medicinal plants are inventoried. It is based on ethnobotanical fieldwork carried out over 15 months. This study presents for the first time an analysis of medicinal plants used in Africa with a ranking of these taxa by the frequency of their reported use. A total of 328 taxa were collected and yielded 2260 individual use reports. The most popular species are Myrica salicifolia and Toddalia asiatica. Subsequently, the use reports were arranged into 9 groups of medicinal uses based on the types of illness treated. The Factor of Informant Consensus (FIC) is used in order to evaluate the ethnobotanical importance of the plants. The largest number of plants and of use reports are in the group of gastrointestinal disorders. For the most commonly used taxa, an ethnopharmacological evaluation was performed. Studies to evaluate the Washambaa therapeutic claims as well as toxicological data are still lacking for many of the species. This study will form the basis for pharmacological and phytochemical research on selected Washambaa medicinal plants.
Quantitative theory for laser ultrasonic waves in a thin plate
Authors: Spicer J. B. , McKie A. D. W. , Wagner J. W.
Published: July 2002

Numerical inversion of the Hankel–Laplace transform has been performed for the case of ultrasonic displacements in an infinite, homogeneous, isotropic plate which is excited thermoelastically by a laser pulse. Values for the elastic moduli and the plate thickness may be extracted when the calculated displacements are compared directly to those obtained experimentally. Previous authors have demonstrated methods for determining the elastic modulus in thick plates; this letter shows that using a different method for the development of the theory allows similar modulus determinations to be made for thin as well as thick plates.
Atomic resolution images of H-terminated Si(111) surfaces in aqueous solutions
Authors: Itaya K. , Sugawara R. , Morita Y. , Tokumoto H.
Published: July 2002

The first atomic images of the hydrogen terminated Si(111) surface have been acquired in aqueous sulfuric acid solutions. The observed interatomic distance with threefold symmetry is ∼3.8 Å, indicating that the ideal Si(111):H-1×1 surface can be prepared by chemical etching in NH4F solutions. It is demonstrated that in situ scanning tunneling microscopy is an extremely important method for revealing chemical processes with atomic resolution in the chemical etching of semiconductors in solutions.
Pulsed laser deposition of high quality LiNbO3 films on sapphire substrates
Authors: Marsh A. M. , Harkness S. D. , Qian F. , Singh R. K.
Published: July 2002

High quality lithium niobate thin films were deposited onto R-cut sapphire substrates (α-Al2O3) by the pulsed laser deposition method. To stabilize single phase LiNbO3, relatively high oxygen partial pressure was required. X-ray diffraction results of these films, fabricated at an oxygen pressure of 1 Torr, showed only (012) and (024) peaks from lithium niobate. The lowering of the oxygen partial pressure or addition of argon in the ambient gas resulted in formation of intermediary phases. The substrate temperature above 650 °C did not have a significant effect on the thin-film quality. Optical measurements on the films deposited under a wide variety of chamber pressures indicated an index of refraction of 2.28, corresponding to the ideal value of bulk LiNbO3.
Oriented diamond films grown on nickel substrates
Authors: Zhu W. , Yang P. C. , Glass J. T.
Published: July 2002

A previously reported multistep hot filament chemical vapor deposition process for nucleating diamond directly on nickel substrates has been further refined to increase the nucleation density and improve the orientation of diamond films. The process employed heavy seeding of both 〈100〉 and 〈111〉 oriented single crystal Ni surfaces with diamond powders to enhance the nucleation density of diamond films. The deposition conditions were adjusted to allow for 〈100〉 and 〈111〉 orientations to grow on similarly oriented substrates to form nearly complete films with grain boundaries being eliminated. Thus, the technique holds promise for developing heteroepitaxial diamond films for microelectronics applications.
Enhancement of critical current density in direct-current-sputtered TlBa2Ca2Cu3O9±δ superconducting thin films
Authors: Juang J. Y. , Horng J. H. , Chen S. P. , Fu C. M. , Wu K. H. , Uen T. M. , Gou Y. S.
Published: July 2002

A multistep postannealing scheme has been developed for preparing nearly single phased, c-axis oriented TlBa2Ca2Cu3Ox (Tl-1223) superconducting thin films fabricated by the direct-current-sputtering process. Films obtained by the present process have shown, for the first time in this system, a critical current density (Jc) above 106 A/cm2 at 77 K with a zero-resistance transition temperature Tc0≊110 K. The order of magnitude enhancement in Jc is attributed to the improvement of film morphology which, in turn, removed most of the weak links encountered previously.
Operating experience with a GaAs photoemission electron source
Authors: Tang F. C. , Lubell M. S. , Rubin K. , Vasilakis A. , Eminyan M. , Slevin J.
Published: July 2002

We report on the development of several operating procedures that promise to make GaAs photoemission electron sources easier to construct, more reliable to operate, and more amenable to use in dynamic vacuum systems. We describe in particular a method for ‘‘ohmically’’ heating a 〈100〉 crystal of GaAs under vacuum to approximately 600 °C. We also discuss our observations of the role of oxygen in the activation of the crystal surface, the use of continuous cesiation, and of the performance of the crystal under varying vacuum conditions.
Electron beam deposition of gold nanostructures in a reactive environment
Authors: Folch Albert , Tejada Javier , Peters Christopher H. , Wrighton Mark S.
Published: July 2002

Electron beam deposition (EBD) is a maskless technique suitable for the fabrication of nanometer scale structures. Metals can be deposited from an organometallic gas, but simultaneous carbon deposition typically yields grossly impure (∼25% metal) deposits. We have found that the metal content of the deposited solid is dramatically improved by performing the whole EBD process in a reactive gaseous environment containing a source of oxygen (O2 or H2O) in addition to the organometallic gas. With simple procedures we prepared Au deposits showing significantly diminished C content (up to 50% metal) as the partial pressure of O2 (or H2O) is increased in the gas.
Wide-frequency specific heat spectrometer
Authors: Birge Norman O. , Nagel Sidney R.
Published: July 2002

We have developed a technique to measure the frequency-dependent specific heat of a liquid over a frequency range exceeding five decades, 0.01–3000 Hz. The measurement is not performed adiabatically, but rather relies on heat diffusion from a thin, planar heater immersed in the liquid sample. The spectrometer has been used to study organic liquids near the glass transition.
A novel thin film interferometer
Authors: Chim S. C. , Beck P. A. , Kino G. S.
Published: July 2002

Thin-film technology has been applied to microscope operation. Fabrication is compatible with standard silicon processing procedures enabling films and circuitry to be coproduced. A Mireau interferometer combining silicon nitride and metal films is characterized. Reflectance and transmittance curves are shown.
Frequency stabilization of a directly modulated semiconductor laser
Authors: Lee Ho Seong , Oh Cha Hwan , Yang Sung Hoon , Chung Nak Sam
Published: July 2002

A method for stabilizing the center frequency of a directly modulated semiconductor laser is described. The laser frequency is locked to a Fabry–Perot etalon by controlling both the injection current and temperature by a frequency error signal simultaneously. The square root of the Allan variance obtained here is 2.5×10−13<σy(τ)<4.0×10−13 for the sampling time 1 s<τ<1000 s.
A scheme for reducing vibration during precise positioning control
Authors: Takahashi Yoshihiko , Uchida Norio
Published: July 2002

A scheme for reducing vibration that occurs during precise positioning control is discussed. The positioning drive mechanism used in ULSI manufacturing is composed of many mechanical parts: a rotational dc motor, a ballscrew, etc. Such a mechanism causes vibration while the positioning stage approaches a desired position. Therefore, this article proposes ways to diminish this vibration. The control system currently in use utilizes the output from a tachogenerator (TG) attached to the DC motor as a damping loop. However, the TG cannot detect the positioning stage velocity but only the dc motor velocity. The vibration reduction scheme proposed in this article is to use the damping loop of the directly measured stage velocity. The stage velocity is calculated from the stage positions which are detected by a laser interferometer. A new control scheme has been designed after modeling the positioning drive mechanism and the control system currently in use. The validity of the proposed control scheme has been confirmed by computer simulations and experiments. As a result of diminishing a vibration of about 85 Hz by the proposed control scheme, the positioning time was decreased from 105 ms to 64 ms for a 20-μm positioning stroke.
Development of a high-temperature fiber-optic thermometer probe using fluorescent decay
Authors: Grattan K. T. V. , Palmer A. W. , Zhang Z.
Published: July 2002

The design and construction of a fiber-optic thermometer probe based upon the measurement of fluorescent decaytime and using gold-coated fibers to achieve such high-temperature performance are reported. The operation of the probe was monitored in the region from room temperature (and potentially below) to that of ≳500 °C and beyond, where optical pyrometry is a satisfactory technique. The calibration and characteristics of the device are discussed.
A practical pulverized coal feeder for bench-scale combustion requiring low feed rates
Authors: Burch T. E. , Conway R. B. , Chen W. Y.
Published: July 2002

A laboratory coal metering device for the entrainment of pulverized coals is described. The system uses controlled aerodynamic stripping of the powder surface by a carrier gas to effect the coal feed. This device has been used for approximately one year in bench-scale combustion studies requiring exacting feed rates with very satisfactory results.
A new sample cell for neutron scattering at high and low temperatures
Authors: Susman Sherman
Published: July 2002

We describe a simple, inexpensive sample container for neutron scattering at nonambient temperatures. The sample cell works equally well with reactive glasses, crystalline powders, or high vapor pressure liquids. Demonstrated performance has been obtained at temperatures from 10 K to 350 °C.
High-performance modular digital lock-in amplifier
Authors: Barone Fabrizio , Calloni Enrico , DiFiore Luciano , Grado Aniello , Milano Leopoldo , Russo Guido
Published: July 2002

In this paper we describe an efficient and robust digital implementation of a lock-in amplifier, based on the classic quadrature technique and on a mathematical algorithm for error signal extraction. Both the hardware and the software architecture are modular. The hardware consists of a VME-bus (IEEE 1014) standard crate, in which commercial VME boards (the CPU, the ADC and DAC) are housed. The software is written in standard C language for portability and easy integration also within complicated software architectures. The software algorithm implementing the lock-in amplifier can be particularized by the user on the basis of the needed performances and on the available hardware. Numerical and experimental tests on a lock-in amplifier prototype have shown that it performs as theoretically predicted. The limit of our prototype (50 kHz maximum sampling rate for 16 bit resolution) depends only on the hardware used, and it is not the present technological limit.
Recent progress in optical current sensing techniques
Authors: Ning Y. N. , Wang Z. P. , Palmer A. W. , Grattan K. T. V. , Jackson D. A.
Published: July 2002

This paper reviews recent developments in the field of current measurement which employ a wide range of optical and fiber optic techniques. Depending on the current sensing mechanisms involved and the sensing materials used, optical current sensors (OCSs) may be categorized into four main groups: (i) OCSs employing optical fiber as their sensing elements, (ii) OCSs using bulk glass to sense the current, (iii) OCSs using electro-optic hybrid sensing devices, and (iv) OCSs using magnetic field sensing devices. The operational modes of a variety of OCSs have been grouped and discussed, and several examples given. It can be seen that as a result of an intensive and wide ranging research effort using various approaches, substantial progress in the differing aspects of the optical current sensing techniques considered, such as the sensing material used, the configurations of sensing elements introduced, and the detection schemes adapted, has been achieved during the past years. An overall view of the field shows it to be as an active and exciting research area, highlighting several recently introduced and novel sensing materials and configurations which provide impressive results in this field of instrumentation. Examples of applications for the electric power industry are discussed more extensively.
Preparation of high-purity, high vapor pressure, complex intermetallic compounds
Authors: McDonough J. , Huxley A.
Published: July 2002

Until recently, techniques for growing intermetallic compounds with high vapor pressures at their melting points have only produced relatively low quality crystals. A new technique for growing ultra-high-purity crystals of such compounds has been developed. The sample is held in a water-cooled copper boat under 10 atm of one part per billion impurity argon while being heated by rf induction. Using this system high-purity crystals of CePb3 are grown and their resistivity compared to ones grown by a standard arc furnace technique.
Fabrication of nanostructures using atomic-force-microscope-based lithography
Authors: Sohn L. L. , Willett R. L.
Published: July 2002

We describe a novel technique for fabricating metallic nanostructures on an arbitrary substrate using an atomic force microscope (AFM). An AFM is used to plow a pattern through the top of two resist layers spun onto a substrate. The resist is then developed to create a mask through which material can be deposited. By changing the applied force, the top resist-layer thickness, or the development time, the linewidth can be varied. Continuous metallic wires ∼500 Å×400 Å×15 μm have been fabricated on bare substrates and between contact pads.
Microelectromechanical scanning probe instruments for array architectures
Authors: Miller Scott A. , Turner Kimberly L. , MacDonald Noel C.
Published: July 2002

A compact (150 μm×150 μm), electrostatic actuator for out-of-plane (z) actuation of a probe tip has been designed, fabricated, and tested. Static deflections of ±0.7 μm out of the plane of the substrate have been achieved. The device consists of a single crystal silicon tip on a torsional cantilever with out-of-plane interdigitated electrode capacitors. This cantilever and electrode design allows a wide range of stiffnesses, actuator force, and frequency response. Significant improvements in performance (larger tip displacement and increased sense capacitance) and a higher density of devices per unit area can be obtained as the minimum feature size decreases. Applications such as information storage, molecular manipulation, and nanolithography require high density, parallel arrays for reasonable throughput. To demonstrate the suitability of this device for use in such arrays, a 12×12 array of microelectromechanical probe tips with integrated actuators and capacitive sensors for scanning probe microscopy has been fabricated. The size of each array element is about 150 μm by 150 μm with a tip-to-tip spacing in the array of 200 μm. Given these dimensions, the packing density of the devices is about 2500 units/cm2.
Wide acceptance bandwidth difference frequency generation in quasi-phase-matched LiNbO3
Authors: Goldberg Lew , Burns W. K. , McElhanon R. W.
Published: July 2002

Difference frequency generation in quasi-phase-matched LiNbO3 is carried out using a Nd:YAG laser and a high power semiconductor laser. Operation at quasi-phase-matching degeneracy point results in an ultrawide 0.5 μm acceptance bandwidth. Crystal-rotation-free wavelength tuning of 4.0–4.5 μm, with 0.2 mW output power at 4.5 μm is achieved. Separately, a tuning range 3.0–5.5 μm is demonstrated with sample rotation and a Ti:Al2O3 laser.
Development of preferred orientation in polycrystalline TiN layers grown by ultrahigh vacuum reactive magnetron sputtering
Authors: Greene J. E. , Sundgren J.-E. , Hultman L. , Petrov I. , Bergstrom D. B.
Published: July 2002

The preferred orientation of polycrystalline TiN films grown by ultrahigh-vacuum reactive-magnetron sputter deposition on amorphous SiO2 at 350 °C in pure N2 discharges was controllably varied from (111) to completely (002) by varying the incident ion/metal flux ratio Ji/JTi from 1 to ≥5 with the N+2 ion energy Ei maintained constant at ≂20 eV (≂10 eV per incident accelerated N). All samples were slightly over-stoichiometric with N/Ti=1.02±0.03. Films deposited with Ji/JTi=1 initially exhibit a mixed texture with competitive columnar growth which slowly evolves into a nearly complete (111) texture at film thicknesses greater than 1 μm. However, films grown with Ji/JTi≥5 exhibit an essentially complete (002) preferred orientation from the earliest observable stages. The normalized XRD (002) intensity ratio in thick layers increased from ≂0 to 1 as Ji/JTi was varied from 1 to ≥5. Both (111) and (001) interplanar spacings remained constant as a function of film thickness yielding a lattice constant of 0.4240±0.0005 nm, equal to that of unstrained bulk TiN. Contrary to previous models, the present results establish that TiN preferred orientation can be controlled without introducing large in-plane compressive stress and/or changes in the strain energy as a function of layer thickness.
Inflatable belt for the application of electrode arrays
Authors: Sadleir R. J. , Fox R. A. , Turner V. F.
Published: July 2002

A prototype device for application of a multiple electrode array to the human abdomen is described and assessed. The device consists of a segmented pneumatic (PVC) belt that, upon inflation, presses electrodes onto the skin simultaneously and with predetermined relative spacings. A single belt can fit a wide range of subject sizes and is comfortable for subjects to wear. It may be useful under conditions where the time taken to attach electrodes is crucial—as in hospital emergency ward applications, and where the maintenance of constant relative electrode spacings is important. The noise performance of these electrodes was only slightly poorer than that obtained using adhesive ECG electrodes.
Fluorescence anisotropy sensor and its application to polymer processing and characterization
Authors: Bur Anthony J. , Roth Steven C. , Thomas Charles L.
Published: July 2002

An optical sensor containing polarizing optical components has been constructed to monitor fluorescence anisotropy during polymer processing and to carry out remote sensing of polymer products doped with fluorescent dyes. The sensor is a compact unit that is used to polarize incident excitation light as well as to analyze the polarization of generated fluorescent light. Optical fibers are used to carry light between the sensor head and the light source and detecting equipment. The anisotropy measurement yields information about the orientation of a fluorescent dye molecule that has been doped into polymer matrix. Fluorescent dyes that have geometrical asymmetry in their molecular structure are used. Experiments are described for which the sensor is positioned in line during extrusion, during specimen extension, and where the sensor is used to carry out area scans of films and sheets. Measurements were made on polyethylene, polyethylene terephthalate, and polybutadiene resins that contained a low concentration of fluorescent dye.
Phase matching of rutile single crystal
Authors: Hashimoto Tadanori , Yoko Toshinobu
Published: July 2002

Phase matching for the third-harmonic generation (THG) of rutile single crystal (110) at 1.9 μm has been investigated. THG with a visible red light (633 nm) was clearly observed, indicating that TiO2 (rutile) is one of the most promising third-order nonlinear optical materials.
A primary x-ray investigation of the turning of ferroelectric microspheres contained in electrorheological fluids under a direct current electric field
Authors: Wen Weijia , Lu Kunquan
Published: July 2002

An x-ray diffraction method is introduced to probe the turning of ferroelectric singlecrystal microspheres suspended in electrorheological (ER) fluids. The microspheres used in the experiment have their permanent dipoles polarized in the same direction. Our initial results show that the x-ray diffraction amplitude in some crystal planes will increase when a fixed dc electric field is applied to the ER fluids. We argue that the enhancement of the diffraction is due to the reorientation of the crystal planes which is caused by the turning of the permanent dipoles in the ferroelectric microspheres under an external electric field. The particle turning has not attracted much attention in the past. We propose that further work should be performed.
Giant magnetoresistance in fine particle of La0.67Ca0.33MnO3 synthesized at low temperatures
Authors: Sánchez R. D. , Rivas J. , Vázquez-Vázquez C. , López-Quintela A. , Causa M. T. , Tovar M. , Oseroff S.
Published: July 2002

Using a sol-gel method we have prepared monodispersive particles of La0.67Ca0.33MnO3 in the range from 20 to 110 nm at temperatures from 540 to 1000 °C. A magnetoresistance above 10% was obtained in a field of 1 kOe for all the particles sizes. These results may be relevant for future applications.
Excitation of a higher order transverse mode in an optically pumped In0.15Ga0.85N/In0.05Ga0.95N multiquantum well laser structure
Authors: Hofstetter Daniel , Bour David P. , Thornton Robert L. , Johnson N. M.
Published: July 2002

We report a comparison between measured and calculated far field data for an optically pumped In0.15Ga0.85N/In0.05Ga0.95N multiquantum well laser structure with AlGaN cladding layers. Optical pumping of the semiconductor device was performed with a pulsed 337 nm N2 laser, whose beam was focused to a narrow stripe. A thin upper cladding layer allowed efficient pumping of the In0.15Ga0.85N/In0.05Ga0.95N laser structure. Despite high distributed cavity losses of at least 30 cm−1, and although gain occurred in the small active region only, the seventh order transverse mode was supported in a waveguide formed by the entire 5-μm-thick epitaxial layer structure. Excellent agreement is demonstrated between measured and calculated far field patterns of the lasing mode.
Spatially resolved cathodoluminescence spectra of InGaN quantum wells
Authors: Chichibu Shigefusa , Wada Kazumi , Nakamura Shuji
Published: July 2002

Spatially resolved cathodoluminescence (CL) spectrum mapping revealed a strong exciton localization in InGaN single-quantum-wells (SQWs). Transmission electron micrographs exhibited a well-organized SQW structure having abrupt InGaN/GaN heterointerfaces. However, comparison between atomic force microscopy images for GaN-capped and uncapped SQWs indicated areas of InN-rich material, which are about 20 nm in lateral size. The CL images taken at the higher and lower energy side of the spatially integrated CL peak consisted of emissions from complementary real spaces, and the area was smaller than 60 nm in lateral size.
Ultimate limit for defect generation in ultra-thin silicon dioxide
Authors: DiMaria D. J. , Stathis J. H.
Published: July 2002

Experimental and theoretical investigations are reported for defect generation by electrical stress in silicon dioxide and for the critical number of defects necessary to trigger destructive breakdown. Experimental evidence is presented showing that the critical number of defects reaches a limit when the oxide thickness is reduced below 2.7 nm. Percolation calculations are shown to be consistent with this oxide thickness limit representing the “effective size” of one defect spanning the oxide, connecting anode and cathode together. Also, these calculations show that not all of the defects are capable of triggering a destructive breakdown event.
Influence of ambient gas on the temperature and density of laser produced carbon plasma
Authors: Harilal S. S. , Bindhu C. V. , Nampoori V. P. N. , Vallabhan C. P. G.
Published: July 2002

The effect of ambient gas on the dynamics of the plasma generated by laser ablation of a carbon target using 1.06 μm radiation from a Q-switched Nd:YAG laser has been investigated using a spectroscopic technique. The emission characteristics of the carbon plasma produced in argon, helium and air atmospheres are found to depend strongly on the nature and pressure of the surrounding gas. It has been observed that hotter and denser plasmas are formed in an argon atmosphere rather than in helium or air as an ambient.
Magnetoresistance of magnetite
Authors: Coey J. M. D. , Berkowitz A. E. , Balcells Ll. , Putris F. F. , Parker F. T.
Published: July 2002

The magnetoresistance behavior of Fe3O4 in polycrystalline thin film, powder compact, and single-crystal form are compared. Negative magnetoresistance with peaks at the coercive field, observed in thin films and powder compacts but not in the single crystal, is due to field-induced alignment of the magnetization of contiguous grains. The effect is associated with intergranular transport of spin-polarized electrons.
Laser etched gratings on polymer layers for alignment of liquid crystals
Authors: Newsome C. J. , O’Neill M. , Farley R. J. , Bryan-Brown G. P.
Published: July 2002

Liquid crystal alignment layers are prepared using a noncontact method based on laser ablation. Nonpolarized light from a KrF excimer laser at 248 nm is exposed through a phase mask to etch gratings of period 1.1 μm onto polyimide alignment layers. Twisted nematic cells were prepared using one rubbed and one grating aligned surface, and azimuthal anchoring energies were found from measurements of the twist angles as a function of grating depth. The measured anchoring energies agree with those predicted from the minimization of elastic strain energy when the liquid crystal directors at the surface are aligned parallel to the groove of the grating. This suggests that topographical rather than epitaxial alignment is achieved.
Fabrication and properties of heteroepitaxial magnetite (Fe3O4) tunnel junctions
Authors: Li X. W. , Gupta A. , Xiao Gang , Qian W. , Dravid V. P.
Published: July 2002

Micron-size magnetic tunnel junctions consisting of ferromagnetic Fe3O4 electrodes, with MgO as a barrier layer, have been fabricated on (100) MgO substrates. Reflection high-energy electron diffraction and transmission electron microscopy studies reveal that the Fe3O4/MgO/Fe3O4 trilayers grown by pulsed laser deposition are heteroepitaxial with abrupt interfaces. To achieve different coercivities for the top and bottom Fe3O4 layers, the trilayers are grown on MgO substrates with a CoCr2O4 buffer layer. The junctions exhibit nonlinear current–voltage characteristics and changes in junction resistance with applied field corresponding to the coercivities of the two magnetic layers. However, the observed magnetoresistance (∼0.5% at 300 K, ∼1.5% at 150 K) is much lower than would be expected for a highly spin-polarized system. Possible reasons for the reduced magnetoresistance are discussed.
Ultraviolet lasing in resonators formed by scattering in semiconductor polycrystalline films
Authors: Cao H. , Zhao Y. G. , Ong H. C. , Ho S. T. , Dai J. Y. , Wu J. Y. , Chang R. P. H.
Published: July 2002

A semiconductor laser whose cavities are “self-formed” due to strong optical scattering in highly disordered gain media is demonstrated. The lasers are made of zinc oxide polycrystalline films grown on amorphous fused silica substrates. Lasing occurs at an ultraviolet wavelength of ∼380 nm under optical pumping. Actual images of the microscopic laser cavities formed by multiple scattering have been captured. These results suggest the possibility of using disordered semiconductor microstructures as alternative sources of coherent light emission.
Formation of stacking-fault tetrahedra in collision cascades
Authors: Nordlund K. , Gao F.
Published: July 2002

One of the outstanding questions in radiation damage is how stacking-fault tetrahedra (SFTs) can be formed below the vacancy migration temperature. Using molecular dynamics simulations of energetic collision cascades, we now describe how a stacking-fault tetrahedron can be created directly in a collision cascade. We also show that, while the number of SFTs is small at low temperatures, at elevated temperatures the number will increase by rearrangement of complex damage clusters into the SFTs, in good agreement with experiments.
Modeling the breakdown spots in silicon dioxide films as point contacts
Authors: Suñé J. , Miranda E. , Nafría M. , Aymerich X.
Published: July 2002

Experiments and simulations are combined to demonstrate that the hard dielectric breakdown of thin SiO2 films in polycrystaline silicon/oxide/semiconductor structures leads to the formation of conduction paths with atomic-size dimensions which behave as point contacts between the silicon electrodes. Depending on the area of the breakdown spots, the conduction properties of the breakdown paths are shown to be those of a classical Sharvin point contact or of a quantum point contact.
The “nanotriode:” A nanoscale field-emission tube
Authors: Driskill-Smith A. A. G. , Hasko D. G. , Ahmed H.
Published: July 2002

A nanoscale electron tube with a field-emission cathode and a control gate (nanotriode) has been fabricated and characterized. Electrons are field emitted from metal nanopillars with radii of about 1 nm into a vacuum nanochamber, collected at the anode, and controlled by a gate electrode. The nanochamber is sealed by an integrated anode and has vertical and horizontal dimensions of 100 nm. The turn-on voltage is less than 10 V and is independent of ambient temperature. Currents of 10 nA and transconductances of up to 6 nS per device have been observed; this would yield a transconductance of 60 S cm−2 at the maximum packing density of 1010 nanotriodes cm−2 for these devices. The emission stability is better than 3% at room temperature and improves to 0.1% at 20 K.
Doped silicon single electron transistors with single island characteristics
Authors: Augke R. , Eberhardt W. , Single C. , Prins F. E. , Wharam D. A. , Kern D. P.
Published: July 2002

Uniformly doped single electron transistors nominally consisting of a single island and two silicon tunneling barriers have been fabricated on silicon–on–insulator material. Two operation regimes are found depending upon the gate voltages applied. The structure acts either as a multiple tunnel junction device or as a single electron transistor consisting of a single dot corresponding to the geometrical shape of the device. The multiple tunnel junction behavior is attributed to the formation of additional tunneling barriers, introduced into the structure by the high doping level. We demonstrate that these barriers can be removed by raising the Fermi level via the application of an appropriate gate voltage.
Ion-beam-induced spinel-to-rocksalt structural phase transformation in MgAl2O4
Authors: Ishimaru Manabu , Afanasyev-Charkin Ivan V. , Sickafus Kurt E.
Published: July 2002

An ion-beam-induced metastable phase in magnesium aluminate spinel (MgAl2O4) has been examined in detail using transmission electron microscopy. Single crystals of MgAl2O4 with (111) orientation were irradiated with 180-keV Ne+ ions at 120 K to fluences of 1016 and 1017/cm2. Selected-area electron diffraction patterns obtained from the irradiation-induced damaged layer revealed that all even hkl reflections (e.g., 222) possess strong intensity, while all odd hkl reflections (e.g., 111) are weak. The features of these diffraction patterns corresponded to those of the rocksalt (NaCl) structure, suggesting that an ordered spinel to disordered rocksalt structural phase transformation in MgAl2O4 was induced by ion beam irradiation.
Reproducible switching effect in thin oxide films for memory applications
Authors: Beck A. , Bednorz J. G. , Gerber Ch. , Rossel C. , Widmer D.
Published: July 2002

Thin oxide films with perovskite or related structures and with transition metal doping show a reproducible switching in the leakage current with a memory effect. Positive or negative voltage pulses can switch the resistance of the oxide films between a low- and a high-impedance state in times shorter than 100 ns. The ratio between these two states is typically about 20 but can exceed six orders of magnitude. Once a low-impedance state has been achieved it persists without a power connection for months, demonstrating the feasibility of nonvolatile memory elements. Even multiple levels can be addressed to store two bits in such a simple capacitor-like structure.
“Massive” vector field in de Sitter space
Authors: Gazeau J-P. , Takook M. V.
Published: July 2002

We present in this paper a covariant quantization of the “massive” vector field on de Sitter (dS) space based on analyticity in the complexified pseudo-Riemanian manifold. The correspondence between unitary irreducible representations of the de Sitter group and the field theory on de Sitter space–time is essential in our approach. We introduce the Wightman two-point function for the case of generalized free vector fields on de Sitter space. This function satisfies the conditions of (a) positiveness, (b) locality, (c) covariance, (d) normal analyticity, (e) transversality and (f) divergencelessness. The Hilbert space structure and the unsmeared field operators Kα(x) are also defined. This work is in the direct continuation of previous ones concerning the scalar and spinor cases.
Change of the magnetic properties of CoSiF6⋅6(H2O) at structural transformations under pressure. Determination of the g factor
Authors: Asadov S. K. , Zavadskiı̆ É. A. , Kamenev V. I. , Todris B. M.
Published: July 2002

The interrelationships between structural phase transformations and the magnetic characteristics of cobalt fluorosilicate hexahydrate are determined in the temperature interval 400–15 K under hydrostatic pressure up to 220 MPa. It is shown that the values of the magnetization and magnetic susceptibility in the different structural phases realized in P–T space are practically independent of the amount of compression but undergo jumps when the symmetry of the crystal lattice changes. The results obtained are used to determine the values of the g factors along two crystallographic directions for the phases studied.
GaAs/AlGaAs quantum-well photodetector for visible and middle infrared dual-band detection
Authors: Liu H. C. , Song C. Y. , Shen A. , Gao M. , Wasilewski Z. R. , Buchanan M.
Published: July 2002

We present experimental results on quantum-well photodetectors for visible and infrared dual-band detection. Large band gap top contacts were used on a standard GaAs/AlGaAs quantum-well infrared photodetector so that visible light could reach the quantum-well region and be absorbed via interband transitions. Two designs were investigated, using a high Al fraction AlGaAs and a short period GaAs/AlAs superlattice contact layer. The dual-band response spectral regions are 0.55–0.7 and 7–10 μm. Measured responsivities are about 0.7 A/W at 8.3 μm and 0.1 A/W at 0.63 μm under −6 V bias voltage.
Microstructural studies of diamond thin films grown by electron cyclotron resonance-assisted chemical vapor deposition
Authors: Gupta S. , Katiyar R. S. , Gilbert D. R. , Singh R. K. , Morell G.
Published: July 2002

A detailed investigation of the correlation among intrinsic stress (σint), nonuniform stress (σnu), and phonon lifetime (1/Γ) was performed in order to obtain a coherent and comprehensive picture of the microstructure of diamond thin films grown by the electron cyclotron resonance-assisted chemical vapor deposition (ECR-CVD) technique. It was found that the diamond growth taking place by the ECR-CVD is different to that taking place by the microwave CVD and hot-filament CVD. Point and line defects, rather than sp2 C bonds, were found to be the dominant source of both nonuniform stress and reduced phonon lifetime. The surface relaxation mechanism in these films yields sp2 C at the expense of strained sp3 C, resulting in a trade off between diamond yield and crystalline quality. The diamond precursor that spontaneously forms on the unseeded substrates yielded higher quality diamond than planted diamond seeds. The grain boundary relaxation model proposed by Hoffman accounts well for the observed behavior of the intrinsic stress, thus indicating that microstructural restructuration takes place at the grain boundaries when sufficient time and thermal energy are provided.
Infrared switching electrochromic devices based on tungsten oxide
Authors: Franke E. B. , Trimble C. L. , Hale J. S. , Schubert M. , Woollam J. A.
Published: July 2002

Different types of electrochromic devices for thermal emittance modulation were developed in the spectral region from mid- to far-infrared (2–40 μm). In all devices polycrystalline and amorphous tungsten oxide have been used as electrochromic and ion storage layer, respectively. Two types of all-solid-state devices were designed, one with a metal grid for the top and bottom electrode deposited on a highly emissive glass substrate, and another with a top metal grid electrode and a highly reflecting bottom metal electrode layer. Tantalum oxide is used as an ion conductor in both device types. The third device type consists of a polymeric ion conductor. All solid-state constituent layers were grown by either reactive or nonreactive dc or rf magnetron sputtering in a high vacuum environment. Modulation of the emittance is accomplished by reversible insertion of Li ions into polycrystalline WO3 by applying and switching a small voltage across the structure. Spectrally dependent measured reflectance modulation of the device has been used to determine the device emissivity modulation with respect to the blackbody emissivity spectra at 300 K. Best device performance was found in both solid-state devices showing an emissivity modulation of about 20%.
Rubidium clock sound velocity meter
Authors: Ho/gseth Einar , Hedwig Gavin , Ho/iland Harald
Published: July 2002

A precision sound velocity meter has been made by adding a high stability rubidium oscillator to pulsed ultrasound instrumentation, where its stability and low noise is utilized as a quality time scale and a master clock, to which major timing events such as sound excitation, scope triggering, and time measurements are synchronized. Measuring operations are computer controlled. A reproducibility of ±0.005 m s−1 has been achieved in applications in research chemistry.
Patterning of sub-50 nm dense features with space-invariant 157 nm interference lithography
Authors: Switkes M. , Bloomstein T. M. , Rothschild M.
Published: July 2002

We have implemented a space-invariant interference lithography tool for 157 nm F2 lasers, capable of creating dense line and space patterns with a spatial period of 91 nm. No gratings or curved optics are required, allowing a simple and inexpensive tool for resist and process development at 157 nm. Initial patterning of several commercial and experimental resists has resulted in high contrast features with little line edge roughness and good cross-sectional profiles, indicating that the fundamental performance of acid-catalyzed resists patterned at 157 nm may meet lithography requirements for sub-50 nm features.