bluuebunny/crossref_metadata_2025 huggingface dataset:
Mucosal morphological changes in the ileal neobladder
Authors: Kojima  , Asaka  , Ando  , Takanashi  , Kohri
Published: July 2002

Objective

 To determine the ultrastructural changes in the mucosa of intestinal segments used as a neobladder.

Materials and methods

 Biopsy specimens from the ileal neobladders of eight men (mean age 62 years, range 52–68) who had undergone radical cystectomy were assessed by light and electron microscopy from 1 month to 5 years after operation. The morphology was compared with that in control specimens obtained from three patients of similar age during construction of an ileal neobladder after radical cystectomy.

Results

 Light microscopy showed shorter mucosal villi and fewer goblet cells. Marked oedema was found in all ileal neobladder walls. Electron microscopy revealed fewer and shorter microvilli and fewer filamentous core rootlets; cell borders were irregular, there were few senile cells in the tip of the villi and more desmosomes.

Conclusions

 The absorptive and secretory function of the intestinal mucosa was probably decreased; the oedema of transferred ileal mucosa seemed to be associated with an inflammatory cell reaction. The cellular dynamics of the mucosa of the ileal neobladder changed with time, thus the ileal mucosa in the substitute bladder apparently adapted well to the new environment, i.e. urine retention, and neobladder expansion and contraction.
Infections in Residents of Long‐Term Care Facilities: An Agenda for Research. Report of an Expert Panel
Authors: Richards Chesley
Published: July 2002

The number of frail, older residents of long‐term care facilities (LTCFs) will increase dramatically over the next 30 years. Improving the quality of health care provided in LTCFs is an important national and international priority. Improving the prevention and management of infections in LTCFs is a critical component of efforts to improve quality of care and poses unique challenges. This report summarizes the presentations and discussions of participants in an invitational conference to propose a research agenda for prevention and management of infections in LTCFs. The conference was held in March 2001 in Atlanta, Georgia. The discussants identified key research questions to better understand general issues involving the overall burden of infections in LTCFs, prevention and control interventions, and antimicrobial use and resistance. The participants also discussed research questions involving specific infections, including pneumonia and urinary tract, skin, and soft tissue infections. Recommendations for research were discussed and are presented in summary form in this report. Improving the prevention and management of infections in LTCF residents should be a priority if quality of care in these facilities is to be improved. Many unanswered questions remain in this field, and the research agenda outlined in this report will require resources and focus. The benefit of such efforts to LTCF residents and their caregivers is likely to be substantial.
Schottky barrier instabilities due to contamination
Authors: Newman N. , Liliental-Weber Z. , Weber E. R. , Washburn J. , Spicer W. E.
Published: July 2002

We reported here a systematic study of the annealing-induced changes in the barrier height of Schottky barrier diodes fabricated on atomically clean and contaminated surfaces. Al, Ag, Au, and Cr/GaAs(110) diodes were fabricated by in situ deposition on clean n-type GaAs(110) surfaces prepared by cleavage in ultrahigh vacuum and on contaminated surfaces prepared by cleavage and exposure to the atmosphere for ∼1–2 h. This study demonstrates that the as-deposited barrier height and the annealing-induced changes in the barrier height of diodes formed with an interfacial layer of contamination are distinctly different from the characteristics of diodes formed on clean semiconductor surfaces. The presence of an interfacial layer of contamination is found to significantly degrade the stability of the diode’s barrier height to annealing.
Heteroepitaxial Pb1−xSnxSe on Si infrared sensor array with 12 μm cutoff wavelength
Authors: Zogg H. , Maissen C. , Masek J. , Blunier S. , Lambrecht A. , Tacke M.
Published: July 2002

An array of photovoltaic infrared sensors with 12 μm cutoff wavelength has been fabricated for the first time in a narrow-gap semiconductor layer grown heteroepitaxially on Si. Heteroepitaxy is achieved using intermediate stacked epitaxial CaF2-SrF2-BaF2 buffer layers to overcome the large lattice as well as thermal expansion mismatch between narrow-gap Pb1−xSnxSe and Si. The IR sensors exhibit resistance-area products up to 0.3 Ω cm2 at 77 K. This corresponds to sensitivities which are above the 300 K background noise limit and only 2–5 times lower than those of state of the art Hg1−xCdxTe sensors on CdZnTe substrates with the same cutoff wavelengths.
Evidence for a real-space transfer of hot holes in strained GeSi/Si heterostructures
Authors: Mensz Piotr M. , Luryi Serge , Bean John C. , Buescher Conor J.
Published: July 2002

A negative differential resistance is observed in p-type Ge0.2Si0.8 strained layers grown by molecular beam epitaxy on a Si (100) substrate. The peak to valley ratio is nearly 2 at T=77 K. This effect is accompanied by an increase of the hole current into the Si substrate.
Dynamics of excimer laser ablation of superconductors in an oxygen environment
Authors: Dyer P. E. , Issa A. , Key P. H.
Published: July 2002

The plume dynamics for excimer laser ablation of Y-Ba-Cu-O in an O2 atmosphere have been studied using streak photography and spectroscopy. At pressures ≳1 mbar the expansion resembles a blast wave driven by the ablation products with mixing and reaction at the contact surface. A simple model for the plume range is developed which shows agreement with experiments.
Transparent conductive metal-oxide contacts in vertical-injection top-emitting quantum well lasers
Authors: Tu Li-Wei , Schubert E. Fred , O’Bryan Hank M. , Wang Yeong-Her , Weir Bonnie E. , Zydzik George J. , Cho Alfred Y.
Published: July 2002

Optically transparent and electrically conductive cadmium tin oxide is employed in vertical cavity surface-emitting lasers for vertical current injection. Continuous wave lasing at room temperature is achieved in GaAs/AlGaAs quantum well lasers. Devices with a 10 μm optical window, which also serves as a vertical current injection inlet, give lasing threshold currents as low as 3.8 mA. The differential series resistance is 350–450 Ω with a diode voltage of 5.1–5.6 V at lasing threshold. Far-field pattern of the laser emission is Gaussian-like with a full width at half maximum of 7°.
Massive thinning of diamond films by a diffusion process
Authors: Jin S. , Graebner J. E. , Kammlott G. W. , Tiefel T. H. , Kosinski S. G. , Chen L. H. , Fastnacht R. A.
Published: July 2002

Substantial thinning or polishing of diamond films is a nontrivial problem because of the extraordinary hardness of diamond. In this letter, we report the observation of massive thinning of CVD diamond film (from ∼220 to ∼120 μm thickness) by simple diffusional transfer of carbon from diamond to iron foil at 900 °C. The thinning process also creates relatively smooth surfaces by eliminating much of the roughness from the top faceted surface of the film. A very sharp Raman peak at 1332 cm−1 indicates that the high quality of the diamond bonding is not compromised by the thinning heat treatment. This technique may be useful for conveniently removing the undesirable part of the diamond films, such as the rough growth facets or the fine-grained bottom layer with inferior thermal properties.
Preparation and magnetic properties of epitaxial barium ferrite thin films on sapphire with in-plane, uniaxial anisotropy
Authors: Hylton T. L. , Parker M. A. , Howard J. K.
Published: July 2002

For the first time, epitaxial barium-ferrite thin films, predominantly of the magnetoplumbite structure, with an easy axis of magnetization in-plane have been prepared on single-crystal sapphire substrates by reactive sputtering and post-deposition annealing. Lattice images by high resolution transmission electron microscopy reveal the probable origin of the magnetic anisotropy to be epitaxy between the Ba-ferrite and sapphire, causing the c-axis of the Ba-ferrite to lie nearly in-plane. Coercivities of more than 9 kOe have been achieved in the easy-axis direction in Al substituted films with magnetization reduced to approximately 25% of the value for unsubstituted films.
Laminated polarization splitter with a large split angle
Authors: Sato T. , Shiraishi K. , Tsuchida K. , Kawakami S.
Published: July 2002

A new spatial walk-off polarizer with a large polarization-splitting angle is fabricated. The polarizer, which utilizes artificial anisotropic dielectrics, is composed of layers of periodically laminated a-Si:H/SiO2 thin films. The thickness of each layer is 67 nm, while the total number of the layers amounts to 1440. The measured polarization-splitting angle is 15.5° at λ=1.55 μm, which is 2.7 times larger than that of existing polarizers.
White light-emitting organic electroluminescent devices using the poly(N-vinylcarbazole) emitter layer doped with three fluorescent dyes
Authors: Kido J. , Hongawa K. , Okuyama K. , Nagai K.
Published: July 2002

White light-emitting electroluminescent devices were fabricated using poly(N-vinylcarbazole) (PVK) as a hole-transporting emitter layer and a double layer of 1,2,4-triazole derivative (TAZ) and tris(8-quinolinolato)aluminum(III) complex (Alq) as an electron transport layer. The PVK layer was doped with fluorescent dyes such as blue-emitting 1,1,4,4-tetraphenyl-1,3-butadiene, green-emitting coumarin 6, and orange-emitting DCM 1. A cell structure of glass substrate/indium-tin-oxide/doped PVK/TAZ/Alq/Mg:Ag was employed. White emission covering a wide range of the visible region and a high luminance of 3400 cd/m2 were obtained at a drive voltage of 14 V.
Apertureless near-field optical microscope
Authors: Zenhausern F. , O’Boyle M. P. , Wickramasinghe H. K.
Published: July 2002

We demonstrate a new method whereby near-field optical microscope resolution can be extended to the nanometer regime. The technique is based on measuring the modulation of the scattered electric field from the end of a sharp silicon tip as it is stabilized and scanned in close proximity to a sample surface. Our initial results demonstrate resolution in the 3 nm range—comparable to what can be achieved with typical attractive mode atomic force microscopes. Theoretical considerations predict that the ultimate resolution achievable with this approach could be close to the atomic level.
Dimensional limitations of silicon nanolines resulting from pattern distortion due to surface tension of rinse water
Authors: Namatsu Hideo , Kurihara Kenji , Nagase Masao , Iwadate Kazumi , Murase Katsumi
Published: July 2002

In a nanometer-scale regime, high-aspect-ratio Si lines running in parallel bend plastically toward each other during the drying process after being rinsed in water. Pattern distortion occurs when the line distance is smaller than the product of the squared aspect ratio and a constant k dependent on the condition of the Si surface, i.e., (distance)<k×(aspect ratio)2. This relationship can be derived theoretically on the assumption that water remains between lines and the water pressure is reduced due to the surface tension of water.
Measurement of the energy content of the JET tokamak plasma with a diamagnetic loop
Authors: Tonetti G. , Christiansen J. P. , de Kock L.
Published: July 2002

An accurate and reliable measurement of poloidal β is essential to assess the performances of Joint European Torus (JET). The diamagnetic loop can measure β values as low as 0.1 in JET discharges with a plasma current larger than 2×106 A. The instrumentation used includes a flux loop rigidly fitted on a toroidal field (TF) coil, a large Rogowski coil measuring the TF busbar current, and a displacement gauge measuring the TF coil expansion. The fluxes to be compensated originate, in order of importance, from the TF current, the eddy current in the vessel, the TF coil expansion, and the stray coupling with the poloidal fields. The TF and eddy currents must be particularly well compensated on JET since the plasma current starts before the toroidal field has reached its plateau value. Comparison between the diamagnetic and other evaluations of β shows a good agreement.
JET polari-interferometer
Authors: Braithwaite G. , Gottardi N. , Magyar G. , O’Rourke J. , Ryan J. , Véron D.
Published: July 2002

A multichannel far-infrared interferometer used on the Joint European Torus (JET) is described. The light source is a 195-μm DCN laser. The instrument is of the Mach–Zehnder type, with a heterodyne detection system. The modulation frequency (100 kHz) is produced by diffraction from a rotating grating. There are six vertical and two oblique channels. The latter rely on retroreflection from mirrors mounted on the vessel wall. Their vibration is compensated by a second wavelength interferometer at 118.8 μm. The various subsystems are described, with emphasis on features necessitated by (a) large path lengths, (b) remote handling requirements, (c) fluctuations in atmospheric humidity, and (d) unmanned automatic operation. Typical measurements, along with real-time and off-line data analysis, are presented. The phase-shift measurement is made with an accuracy of (1)/(20) of a fringe, corresponding to a line-integrated electron density of 5×1017 m−2. Comparison with other electron density diagnostics are shown. The introduction of additional optics allows measurements of the Faraday effect and a determination of the poloidal magnetic field distribution. The signal processing and data analysis are described. Errors introduced by the calibration procedure, birefringence of the probing beams, toroidal field pickup, the flux geometry, and the density profile are considered. The Faraday angle is measured with an accuracy of 5% and a time resolution of 1–10 ms. The poloidal magnetic field is deduced with an accuracy of ±15%.
Neutral beam emission spectroscopy diagnostic for measurement of density fluctuations on the TFTR tokamak
Authors: Paul S. F. , Fonck R. J.
Published: July 2002

A multichannel diagnostic for measuring low amplitude, long wavelength (k⊥ρi<0.5) density fluctuations along the outer half of the plasma has been installed on TFTR. It is based on observing fluctuations in the Hα fluorescence of a neutral heating beam due to collisional excitation from the plasma and impurity ions. Both radial and poloidal correlation lengths as short as 2–3 cm can be determined, with the spatial resolution limited primarily by the width and geometry of the three neutral beam sources. Optical fibers transmit the light from a 20-cm-diam vacuum window, reentrant mirror, and lens assembly to 16 interference filter/photomultiplier combinations located outside the radiation area. Initially, the fibers comprise a fixed 55-channel radial array and readily movable 10-channel vertical arrays which can be positioned at 27 radial locations. The filters are designed to accept the Doppler-shifted Hα emission from primary energy component of the neutral beam, and reject background lines and unshifted edge Hα. The measurable fluctuation amplitude (@ S/N=1) is limited to 0.5% over a 100 kHz bandwidth by the photon noise associated with the dc level of the beam emission. The contribution of impurity collisions to the total beam fluorescence will be determined directly by measuring impurity density fluctuations using charge-exchange recombination emission from the n=8–7 CVI line at 5292 Å.
Dispersion interferometer for controlled fusion devices
Authors: Drachev V. P. , Krasnikov Yu. I. , Bagryansky P. A.
Published: July 2002

A dispersion interferometer for measurements of line plasma density has been developed with a sensitivity 〈ne l〉min = 1013 cm−2 and a temporal resolution of 10 μs. The main advantages of the interferometer are compactness and minimal sensitivity to vibrations. The interferometer does not require specific vibration isolation structure and can be mounted directly on the working chamber of the plasma device. The use of short-wave radiation (λ=1.06 μm) eliminates the influence of refraction and enables one to use quartz windows, which are the most resistant to neutron and gamma radiation. The above-mentioned advantages have been successfully demonstrated in a gas-dynamic trap experiment. These properties make the dispersion interferometer a very attractive diagnostic tool for large tokamaks.
Impedance-matching anode for fast timing signals
Authors: Wurz Peter , Gubler Lukas
Published: July 2002

In this article a novel design for signal anodes for ultrafast microchannel plate detectors is introduced. A detector assembly was designed and built with an impedance-matched transition line (50 Ω line resistance) from anode to cable connector which is considerably smaller than other, commercially available, solutions and at the same time has about four times the active area with no limitations for up scaling to even larger active areas. Theoretical proof is given that the impedance matching can be achieved over the entire transition line. The design makes use of a bipolar geometry and is flexible to accommodate differing experimental needs. The design was chosen to optimize for small overall size with good temporal response at the same time. The detector was tested with an alpha particle source and an excellent time response was obtained. Although the design was driven by special needs for space application the detector can be applied wherever short timing pulses are needed.
Development of 180 GHz heterodyne radiometer for electron cyclotron emission measurements in JT-60U
Authors: Isei N. , Sato M. , Ishida S. , Uchino K. , Nagashima A. , Matoba T. , Oyevaar T.
Published: July 2002

A 12-channel heterodyne radiometer system has been developed to obtain electron temperature with high time and spatial resolution from the electron cyclotron emission (ECE) in JT-60U. Resolutions of a single-sideband-type receiver are (1) Δt∼1 μs and (2) Δf=0.5 GHz. The second harmonic extraordinary mode of ECE is utilized for this system and the frequency band is 176–188 GHz. The noise level of the system is determined by unavoidable photon fluctuations, and the signal-to-noise ratio was measured to be about 50 with a video bandwidth of 100 kHz for a signal temperature above ∼200 eV. Details of the design, the obtained performance, and typical measurements are described.
Contrast and resolution in imaging with a microfocus x-ray source
Authors: Pogany A. , Gao D. , Wilkins S. W.
Published: July 2002

A simple general treatment of x-ray image formation by Fresnel diffraction is presented; the image can alternatively be considered as an in-line hologram. Particular consideration is given to phase-contrast microscopy and imaging using hard x rays. The theory makes use of the optical transfer function in a similar way to that used in the theory of electron microscope imaging. Resolution and contrast are the criteria used to specify the visibility of an image. Resolution in turn depends primarily on the spatial coherence of the illumination, with chromatic coherence of lesser importance. Thus broadband microfocus sources can give useful phase-contrast images. Both plane- and spherical-wave conditions are explicitly considered as limiting cases appropriate to macroscopic imaging and microscopy, respectively, while intermediate cases may also be of practical interest. Some results are presented for x-ray images showing phase contrast.
Raman spectroscopy combined with small angle x-ray scattering and wide angle x-ray scattering as a tool for the study of phase transitions in polymers
Authors: Bryant G. K. , Gleeson H. F. , Ryan A. J. , Fairclough J. P. A. , Bogg D. , Goossens J. G. P. , Bras W.
Published: July 2002

A novel combination of simultaneous experimental techniques has been developed as a tool for the study of phase transitions in polymers. Based upon a small angle x-ray scattering (SAXS) synchrotron radiation beamline it has been shown to be feasible to collect, in addition to the time-resolved SAXS data, wide angle x-ray scattering and Raman spectroscopy data with a time resolution of a few seconds.
Construction and operation of parallel electric and magnetic field spectrometers for mass/energy resolved multi-ion charge exchange diagnostics on the Tokamak Fusion Test Reactor
Authors: Medley S. S. , Roquemore A. L.
Published: July 2002

A novel charge exchange spectrometer using a dee-shaped region of parallel electric and magnetic fields was developed at the Princeton Plasma Physics Laboratory for neutral particle diagnostics on the Tokamak Fusion Test Reactor (TFTR). The E∥B spectrometer has an energy range of 0.5⩽A (amu)E (keV)⩽600 and provides mass-resolved energy spectra of H+, D+, and T+ (or 3He+) ion species simultaneously during a single discharge. The detector plane exhibits parallel rows of analyzed ions, each row containing the energy dispersed ions of a given mass-to-charge ratio. The detector consists of a large area microchannel plate (MCP) which is provided with three rectangular, semicontinuous active area strips, one coinciding with each of the mass rows for detection of H+, D+, and T+ (or 3He+) and each mass row has 75 energy channels. To suppress spurious signals attending operation of the plate in the magnetic fringe field of the spectrometer, the MCP was housed in a double-walled iron shield with a wire mesh ion entrance window. Using an accelerator neutron generator, the MCP neutron detection efficiency was measured to be 1.7×10−3 and 6.4×10−3 counts/neutron/cm2 for 2.5 MeV-DD and 14 MeV-DT neutrons, respectively. The design and calibration of the spectrometer are described in detail, including the effect of MCP exposure to tritium, and results obtained during high performance D–D operation on TFTR are presented to illustrate the performance of the E∥B spectrometer. The spectrometers were not used during D–T plasma operation due to the cost of providing the required radiation shielding.
Exponential analysis in physical phenomena
Authors: Istratov Andrei A. , Vyvenko Oleg F.
Published: July 2002

Many physical phenomena are described by first-order differential equations whose solution is an exponential decay. Determining the time constants and amplitudes of exponential decays from the experimental data is a common task in semiconductor physics (deep level transient spectroscopy), biophysics (fluorescence decay analysis), nuclear physics and chemistry (radioactive decays, nuclear magnetic resonance), chemistry and electrochemistry (reaction kinetics) and medical imaging. This review article discusses the fundamental mathematical limitations of exponential analysis, outlines the critical aspects of acquisition of exponential transients for subsequent analysis, and gives a comprehensive overview of numerical algorithms used in exponential analysis. In the first part of the article the resolution of exponential analysis as a function of noise in input decays is discussed. It is shown that two exponential decays can be resolved in a transient only if the ratio of their time constants is greater than the resolution limit, which can be explicitly calculated from the signal-to-noise ratio in the transient. Although the signal-to-noise ratio is generally limited by the sensitivity of the equipment, it is shown that digitalization of the decays may be a major source of noise. The requirements for type of analog-to-digital converter, number of digitized data points and duration of digitized transients, which must be met to obtain the theoretical resolution limit and to improve stability of the exponential analysis, are formulated. The second part of the review article gives an overview and comparison of major numerical techniques of exponential analysis, such as the nonlinear least squares fit, the Prony method, the method of modulating functions, the method of moments, the Laplace–Padé approximation, the Tikhonov regularization method, the Gardner transformation, the method of maximum entropy and others.
Use of Langmuir probes in non-Maxwellian space plasmas
Authors: Hoegy Walter R. , Brace Larry H.
Published: July 2002

Disturbance of the Maxwellian plasma may occur in the vicinity of a spacecraft due to photoemission, interactions between the spacecraft and thermospheric gases, or electron emissions from other devices on the spacecraft. Significant non-Maxwellian plasma distributions may also occur in nature as a mixture of ionospheric and magnetospheric plasmas or secondaries produced by photoionization in the thermosphere or auroral precipitation. The general formulas for current collection (volt–ampere curves) by planar, cylindrical, and spherical Langmuir probes in isotropic and anisotropic non-Maxwellian plasmas are examined. Examples are given of how one may identify and remove the non-Maxwellian components in the Langmuir probe current to permit the ionospheric parameters to be determined. Theoretical volt–ampere curves presented for typical examples of non-Maxwellian distributions include: two-temperature plasmas and a thermal plasma with an energetic electron beam. If the nonionospheric electrons are Maxwellian at a temperature distinct from that of the ionosphere electrons, the volt–ampere curves can be fitted directly to obtain the temperatures and densities of both electron components without resorting to techniques that attempt to derive the plasma distribution from the current by taking derivatives. For an arbitrary isotropic distribution, the current for retarded particles is shown to be identical for the three geometries. For anisotropic distributions, the three probe geometries are not equally suited for measuring the ionospheric electron temperature and density or for determining the distribution function in the presence of non-Maxwellian background electrons.
Pulsed laser deposition of BaTiO3 thin films and their optical properties
Authors: Kim D. H. , Kwok H. S.
Published: July 2002

Highly oriented a-axis BaTiO3 thin films were grown by pulsed laser deposition on (001) MgO substrates. The full width at half-maximum of the (200) BaTiO3 rocking curve was as narrow as 0.6°. A large hysteretic quadratic electro-optic effect was observed in a transverse geometry at 6328 Å. A birefringence shift up to 3×10−3 was measured at an applied dc electric field of 1 kV/mm. It was found that laser repetition rate plays an important role on the surface morphology of the deposited films.
Thermoelectric figure of merit of quantum wire superlattices
Authors: Broido D. A. , Reinecke T. L.
Published: July 2002

The electrical conductivity, the thermoelectric power, and the electrical contribution to the thermal conductivity of quantum wire superlattices have been studied. The effects of tunneling through the barriers due to finite potential off-sets and of the thermal currents through the barrier layers are shown to be essential to describe properly the thermoelectric figure of merit of realistic quantum wire superlattices. The figure of merit exhibits a maximum as a function of superlattice period which, for large barrier off-sets, is found to be substantially enhanced over that for the bulk material and also larger than that for quantum well superlattices.
Study of a backgated metal-semiconductor-metal photodetector
Authors: Vickers A. J. , Hassan M. A. , Mashakekhi H. R. , Griguoli A. , Hopkinson M.
Published: July 2002

In this letter we outline our results on a new type of high-speed photodetector [E. Gregor et al., Appl. Phys. Lett. 65, 2223 (1994)]. The device is based on the hybridization of a metal-semiconductor-metal photodetector and a p-i-n photodiode. The advantage of the device, which operates in the transit-time limited regime, is that it removes the hole current from the high-speed circuit through a third contact, and hence, increases the response speed of the device. In contrast to the previously published work [E. Gregor et al., Appl. Phys. Lett. 65, 2223 (1994)] we have used an excitation pulse that is much faster than the device response in order to fully investigate the effect of the third contact. We observe significantly more effect on the response once the third contact is connected with a subsequent increase of device response speed with increasing application of bias to this third contact.
Dielectric, pyroelectric, and electro-optic monitoring of the cross-linking process and photoinduced poling of Red Acid Magly
Authors: Yilmaz S. , Wirges W. , Bauer-Gogonea S. , Bauer S. , Gerhard-Multhaupt R. , Michelotti F. , Toussaere E. , Levenson R. , Liang J. , Zyss J.
Published: July 2002

Crosslinking of polymers with dipoles can be followed by means of dielectric, pyroelectric, and in situ electro-optic measurements. All three techniques provide similar insights as to the cross-linking process. In addition, electro-optic measurements allow for the determination of the resulting optical nonlinearity. After crosslinking is completed the polymer behaves like a side-chain polymer. In addition, photoinduced poling of an already cross-linked dipolar polymer network is demonstrated.
X-ray photoelectron spectroscopy and x-ray diffraction study of the thermal oxide on gallium nitride
Authors: Wolter S. D. , Luther B. P. , Waltemyer D. L. , Önneby C. , Mohney S. E. , Molnar R. J.
Published: July 2002

The oxidation of single crystal gallium nitride in dry air has been investigated. X-ray photoelectron spectroscopy (XPS) revealed minimal oxide growth at 450 and 750 °C for up to 25 h. However, at 900 °C the growth of an oxide approximately 5000 Å thick was observed after 25 h. This oxide was determined to be the monoclinic β-Ga2O3 using glancing angle x-ray diffraction. XPS spectra of the Ga 3d and Ga 2p core levels indicated peak shifts of 1.2 and 1.3 eV, respectively, from Ga–O to Ga–N bonding. The Ga L3M45M45 core level binding energy was also investigated and β-Ga2O3 and GaN each presented a characteristic peak shape.
Growth and characterization of InSbBi for long wavelength infrared photodetectors
Authors: Lee J. J. , Kim J. D. , Razeghi M.
Published: July 2002

The epitaxial growth of InSbBi ternary alloys by low-pressure metalorganic chemical vapor deposition is reported on. X-ray diffraction spectra showed well resolved peaks of InSbBi and InSb films. Bi incorporation was confirmed by energy dispersive x-ray analysis. Photoresponse spectrum up to 9.3 μm which corresponds to 0.13 eV energy band gap has been measured in a sample with Bi composition of 5.8 at.% at 77 K. Electron mobility at room temperature ranges from 44 100 to 4910 cm2/Vs as Bi composition increases.
Electromechanical properties of SrBi2Ta2O9 thin films
Authors: Kholkin A. L. , Brooks K. G. , Setter N.
Published: July 2002

Weak field piezoelectric coefficient and strain were investigated in ferroelectric SrBi2Ta2O9 (SBT) thin films by means of optical interferometry. Though the maximum polarization and dielectric constant were small enough (7 μC/cm2 and 150, respectively), the piezoelectric coefficient attained 17 pm/V under the dc electric field. This value is comparable with the piezoelectric coefficients reported previously on poled SBT ceramics. Electrically induced strain of 5⋅10−4 was observed using bipolar driving field of 300 kV/cm. No piezoelectric fatigue was found until 109 switching pulses, in agreement with polarization data. The piezoelectric properties and strains were successfully described by using a simple electrostriction equation with the effective electrostriction coefficient of 0.1 m4/C2. The electromechanical behavior of SBT films suggested no or weak contribution of non-180° domain walls to the strain response.
Electroluminescence and electron transport in a perylene dye
Authors: Ranke P. , Bleyl I. , Simmerer J. , Haarer D. , Bacher A. , Schmidt H. W.
Published: July 2002

Charge carrier transport in vapor-deposited films of 1,6,7,12-tetraphenoxy-N,N′-bis-(2,6-diisopropylphenyl)-perylene-3,4,9,10-bis(dicarboximide) was investigated using two different methods, the time-of-flight (TOF) technique and time-resolved electroluminescence. Electron mobilities of 10−5 cm2/V s were measured in the bulk using a time-of-flight technique. Hole transport was found to be dispersive and, thus, a transit time for holes could not be obtained. The above dye was also used to fabricate single layer light emitting diodes showing clearly visible red electroluminescence under ambient conditions. Our experiments on transit electroluminescence confirmed the measured electron mobility and ruled out the possibility that the transit time of holes is shorter than the time range investigated in our time-of-flight experiments.
Cavitation and acoustic emission around laser-heated microparticles
Authors: Lin Charles P. , Kelly Michael W.
Published: July 2002

We studied transient cavitation bubble formation and acoustic emission around individual laser-heated microparticles using subnanosecond time-resolved microscopy. Microcavitation bubbles were observed as early as 0.5 ns after the particles were heated by a 30 ps laser pulse. The bubbles expanded to a few micrometers in size and collapsed on the time scale of 0.1–1 μsec. We discuss microcavitation as the origin of anomalously large photoacoustic effects and nonlinear optical responses observed in laser-heated colloidal suspensions, as well as a mechanism for cellular damage in biologic tissue containing pigment particles.
Photoinduced and thermal stress in silicon microcantilevers
Authors: Datskos Panos G. , Rajic Slobodan , Datskou Irene
Published: July 2002

The photogeneration of free charge carriers in a semiconductor gives rise to mechanical strain. We measured the deflection of silicon microcantilevers resulting from photoinduced stress. The excess charge carriers responsible for the photoinduced stress, were produced via photon irradiation from a diode laser with wavelength λ=780 nm. For Si microcantilevers, the photoinduced stress is of opposite direction and about four times larger than the stress resulting from only thermal excitation. In this letter we report on our study of the photoinduced stress in silicon microcantilevers and discuss their temporal and photometric response.
Nonlinear absorption of Cr4+:YAG studied with lasers of different pulsewidths
Authors: Yim Sang-Hoon , Lee Dong-Ryeol , Rhee Bum Ku , Kim Doseok
Published: July 2002

A saturable absorber Cr4+:YAG, used for a passive Q switching of Nd:YAG laser was studied in order to understand the physical mechanism of nonlinear absorption (photobleaching). An optical bleaching experiment was carried out using the two pulsed lasers with duration of pico- and nanoseconds at 1.064 μm wavelength. Experimental results were compared with numerical analysis of theoretical rate equations with all relevant energy levels. The inclusion of intersystem crossing between singlet- and triplet-excited states with reasonable rate of transition kisc was necessary to explain the difference in the saturation behaviors for nanosecond and picosecond laser pulses.
Effect of initial plasma geometry and temperature on dynamic plume expansion in dual-laser ablation
Authors: Mukherjee Pritish , Chen Shudong , Witanachchi Sarath
Published: July 2002

Recent experiments have revealed the capability of large-area, uniform film growth using dual-laser ablation. The mechanism of this dynamic plume expansion is investigated in this letter. We report the critical role played by the initial geometry and temperature of the plasma in the subsequent expansion under dual-laser ablation. Initial plasma dimensions in the dual-laser ablation of ZnO are quantified by gated intensified charge-coupled detector-array imaging and combined with a hydrodynamic theoretical expansion model to yield radial thickness profiles for the deposited films. Comparisons with ellipsometric film thickness profiles indicate that the primary factors responsible for increased expansion of the dual-laser ablated plume are an extension of the initial plasma dimension in the axial direction as well as enhanced plasma temperature.
Reflection spectroscopy on the photoinduced local metallic phase of Pr0.7Ca0.3MnO3
Authors: Fiebig M. , Miyano K. , Tomioka Y. , Tokura Y.
Published: July 2002

Optical spectroscopy and topography techniques were used to study the local photoinduced insulator-metal transition (IMT) in a Pr0.7Ca0.3MnO3 crystal. Although the change of reflectivity due to the transition exhibits features which are characteristic for the IMT, the spectrum reveals strong modifications as compared to the magnetic-field induced bulk IMT. The different nature of the photoinduced IMT is attributed to the competition of the ferromagnetic metallic region with its antiferromagnetic insulating surrounding, which possibly leads to a filamentary metallic phase. Modifications also include a pronounced broadband electrochromism in the >1.8 eV spectral range.
Towards background-limited, room-temperature, infrared photon detectors in the 3–13 μm wavelength range
Authors: Elliott C. T. , Gordon N. T. , White A. M.
Published: July 2002

We have analyzed the various noise processes occurring in photon infrared detectors operating at room temperature and show that background-limited performance for photon detectors is potentially achievable at room temperature over the 3–13 μm band even in restricted fields of view. We discuss practical embodiments in which this might be realized and give quantitative estimates of the material properties required to achieve this performance. A critical feature to achieve the highest performance is that devices within an array should not be radiatively coupled to each other.
The effect of stress on the dielectric properties of barium strontium titanate thin films
Authors: Shaw T. M. , Suo Z. , Huang M. , Liniger E. , Laibowitz R. B. , Baniecki J. D.
Published: July 2002

Barium strontium titanate thin films are being developed as capacitors in dynamic random access memories. These films, grown on silicon substrates, are under tensile residual stress. By a converse electrostrictive effect, the in-plane tensile stress reduces the capacitance in the thickness direction of the film. We measured the substrate curvature change upon the removal of the film, and found the magnitude of the residual stress to be 610 MPa. In a separate experiment, we applied a force to vary the stress in a film on a substrate, and simultaneously recorded the capacitance change of the film. The measurements quantify the effect of stress on thin film capacitance. The stress free capacitance was found to be 23% higher than the capacitance under residual stress.
Photonic crystals as optical components
Authors: Halevi P. , Krokhin A. A. , Arriaga J.
Published: July 2002

Photonic crystals (PCs) have already found numerous applications associated with the photonic band gap. We point out that PCs could be also employed as custom-made optical components in the linear region well below the photonic gap. As an example, we discuss a birefringent PC lens that acts as a polarizing beam splitter. This idea is supported by a precise method of calculation of the optical constants of a transparent two-dimensional (2D) PC. Such a process of homogenization is performed for hexagonal arrays of polymer-based PCs and also for the mammalian cornea. Finally, 2D PCs are classified as optically uniaxial or biaxial.
Formation of crystalline Ba-ferrite phase from α-Fe2O3 phase in amorphous precursor
Authors: Cho Tae Sik , Je Jung Ho , Noh Do Young
Published: July 2002

The formation of crystalline Ba-ferrite/sapphire(001) films in an amorphous precursor during annealing was studied in a real-time synchrotron x-ray scattering experiment. From the x-ray integrated intensity and the surface morphology, we found that the crystalline Ba-ferrite phase was formed by solid phase transformation of the intermediate crystalline α-Fe2O3 phase, not by direct crystallization of the amorphous precursor. The solid phase transformation occurred at temperature above 500 °C. The high crystallization temperature of the Ba-ferrite phase was attributed to the activation barrier for the diffusion of Ba ions into the α-Fe2O3 phase.
Pressure-induced crossover from long-to-short-range order in [Pb(Zn1/3Nb2/3)O3]0.905(PbTiO3)0.095 single crystal
Authors: Samara G. A. , Venturini E. L. , Schmidt V. Hugo
Published: July 2002

A pressure-induced crossover from normal ferroelectric–to–relaxor behavior has been observed in single crystal [Pb(Zn1/3Nb2/3)O3]0.905(PbTiO3)0.095, or PZN-9.5% PT. Analogy with similar observations for other perovskites indicates that this crossover is a general feature of compositionally disordered soft mode ferroelectrics. The pressure-temperature phase diagram has been also determined.
GaAs/InGaAs quantum well infrared photodetector with a cutoff wavelength at 35 μm
Authors: Perera A. G. U. , Matsik S. G. , Liu H. C. , Gao M. , Buchanan M. , Schaff W. J. , Yeo W.
Published: July 2002

GaAs/InGaAs far-infrared quantum well photodetectors based on a bound-to-continuum intersubband transition with a (zero response) cutoff wavelength of 35 μm are reported. A peak responsivity of 0.45 A/W and detectivity of 6.0×109 cmHz/W at a wavelength of 31 μm and a temperature of 4.2 K have been experimentally achieved. Infrared response was observed at temperatures up to 18 K. A calculated responsivity spectrum using a bound-to-continuum line shape corrected for phonon absorption is fitted to the experimental response. The calculated line shape without absorption gives a cutoff wavelength of 38 μm with a peak responsivity of 0.50 A/W and a detectivity of 6.6×109 cmHz/W at 32 μm.
Fast-convergent resummation algorithm and critical exponents of φ4-theory in three dimensions
Authors: Jasch Florian , Kleinert Hagen
Published: July 2002

We develop an efficient algorithm for evaluating divergent perturbation expansions of field theories in the bare coupling constant gB for which we possess a finite number L of expansion coefficients plus two more information: the knowledge of the large-order behavior proportional to (−α)kk!kβgBk, with a known growth parameter α, and the knowledge of the approach to scaling of the type c+c′/gBω, with constants c,c′ and a critical exponent of approach ω. The latter information leads to an increase in the speed of convergence and a high accuracy of the results. The algorithm is applied to the six- and seven-loop expansions for the critical exponents of O(N)-symmetric φ4-theories, and the result for the critical exponent α is compared with a recent satellite experiment.
A broadly tunable extreme ultraviolet laser source with a 0.008 cm−1 bandwidth
Authors: Hollenstein U. , Palm H. , Merkt F.
Published: July 2002

A new coherent narrow bandwidth extreme ultraviolet (XUV) laser source has been developed that is broadly tunable in the range 10–17 eV with a bandwidth of 0.008 cm−1 and intensities of 108 photons/pulse at 20 Hz. The source is based on two-photon resonance-enhanced sum-frequency mixing in rare gases. To demonstrate its properties, high-resolution photoionization and photoelectron spectra of argon have been recorded in the vicinity of the second, spin-orbit excited ionization threshold (Ar+2P1/2). From the analysis of the autoionization line shapes of the ns′[1/2](J=1) and nd′[3/2](J=1) resonances, reduced linewidths Γr,l=Γl×n*3 of 499.3(46) cm−1 and 28.76(89)×103 cm−1 have been determined for the s′ and d′ series, respectively. The results for the ns′[1/2](J=1) series confirm the conclusion reached by Klar et al. [Z. Phys. D 23, 101 (1992)] that earlier single-photon XUV investigations have overestimated the width of these sharp resonances. The narrow bandwidth of the source is also used to accurately determine the range of principal quantum number of the high Rydberg states that are probed by selected electric field ionization sequences in pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy.
Reverse Monte Carlo analysis of extended x-ray absorption fine structure spectra of monoclinic and amorphous zirconia
Authors: Winterer Markus
Published: July 2002

Extended x-ray absorption fine structure spectra of monoclinic zirconia (m-ZrO2) and of amorphous zirconia (a-ZrO2) in form of a thin film are analyzed by reverse Monte Carlo simulations. Partial pair distribution functions (PDF, gZr–O and gZr–Zr) are extracted. Coordination numbers and distances determined for m-ZrO2 are identical to results of structural analysis by diffraction. The local structure of a-ZrO2 consists of a widely spread Zr–O shell (from 1.9 to 3.3 Å) corresponding to an eightfold oxygen coordination around zirconium ions. The first peak consists of four nearest oxygen neighbors at 2.15 Å. The Zr–Zr PDF of a-ZrO2 displays a broad peak between 3.2 and 5.2 Å consisting of twelve zirconium next nearest neighbors at an average distance of about 4 Å and weak density fluctuations at larger coordination distances.
Structural and electrical anisotropy of (001)-, (116)-, and (103)-oriented epitaxial SrBi2Ta2O9 thin films on SrTiO3 substrates grown by pulsed laser deposition
Authors: Lee Ho Nyung , Visinoiu Alina , Senz Stephan , Harnagea Catalin , Pignolet Alain , Hesse Dietrich , Gösele Ulrich
Published: July 2002

Epitaxial SrBi2Ta2O9 (SBT) thin films with well-defined (001), (116), and (103) orientations have been grown by pulsed laser deposition on (001)-, (011)-, and (111)-oriented Nb-doped SrTiO3 substrates. X-ray diffraction pole figure and φ-scan measurements revealed that the three-dimensional epitaxial orientation relation SBT(001)‖SrTiO3(001), and SBT[11̄0]‖SrTiO3[100] is valid for all cases of SBT thin films on SrTiO3 substrates, irrespective of their orientations. Atomic force microscopy images of the c-axis-oriented SBT revealed polyhedron-shaped grains showing spiral growth around screw dislocations. The terrace steps of the c-axis-oriented SBT films were integral multiples of a quarter of the lattice parameter c of SBT (∼0.6 nm). The grains of (103)-oriented SBT films were arranged in a triple-domain configuration consistent with the symmetry of the SrTiO3(111) substrate. The measured remanent polarization (2Pr) and coercive field (2Ec) of (116)-oriented SBT films were 9.6 μC/cm2 and 168 kV/cm, respectively, for a maximum applied electric field of 320 kV/cm. Higher remanent polarization (2Pr=10.4 μC/cm2) and lower coercive field (2Ec=104 kV/cm) than those of SBT(116) films were observed in (103)-oriented SBT thin films, and (001)-oriented SBT revealed no ferroelectricity along the [001] axis. The dielectric constants of (001)-, (116)-, and (103)-oriented SBT were 133, 155, and 189, respectively.
Lift-up growth of aligned carbon nanotube patterns
Authors: Wei Bingqing , Zhang Z. J. , Ramanath G. , Ajayan P. M.
Published: July 2002

The fabrication of three-dimensional networks of carbon nanotubes with controlled orientation will be essential for building large-scale functional devices integrated with microelectronics circuits. We describe here our recent work on the controlled synthesis of vertically aligned carbon-nanotube patterns, grown under patterned metal layers on Si substrates by combining chemical-vapor deposition and conventional lithography. We show that metal patterns are lifted up by vertically aligned nanotubes during growth. This lift-up growth links the thin-film metal patterns and the Si substrate via nanotube assemblies, giving the possibility of creating nanotube architectures in three dimensions. The possible scenarios of the growth of aligned nanotube films leading to the lift up of the metal films are discussed.
Measurements of the absolute value of the penetration depth in high-Tc superconductors using a low-Tc superconductive coating
Authors: Prozorov R. , Giannetta R. W. , Carrington A. , Fournier P. , Greene R. L. , Guptasarma P. , Hinks D. G. , Banks A. R.
Published: July 2002

A method is presented to measure the absolute value of the London penetration depth, λ(T=0), from the frequency shift of a resonator. The technique involves coating a high-Tc superconductor with film of low-Tc material of known thickness and penetration depth. The method is applied to obtain λ(YBa2Cu3O7−δ)≈1460±150 Å, λ(Bi2Sr2CaCu2O8+δ)≈2690±150 Å and λ(Pr1.85Ce0.15CuO4−δ)≈2790±150 Å. λ(YBa2Cu3O7−δ) from this method is very close to that obtained by several other techniques. For both Bi2Sr2CaCu2O8+δ and Pr1.85Ce0.15CuO4−δ the values exceed those obtained by other methods.