bluuebunny/crossref_metadata_2025 huggingface dataset:
Factors influencing haematological recovery after allogeneic haemopoietic stem cell transplants: graft‐versus‐host disease, donor type, cytomegalovirus infections and cell dose
Authors: Dominietto Alida , Raiola Anna Maria , Van Lint Maria Teresa , Lamparelli Teresa , Gualandi Francesca , Berisso Giovanni , Bregante Stefania , Frassoni Francesco , Casarino Lucia , Verdiani Simonetta , Bacigalupo Andrea
Published: July 2002

Platelet recovery after allogeneic haemopoietic stem cell transplant (HSCT) and predictive factors were analysed in 342 patients with haematological malignancies. All patients were prepared with cyclophosphamide plus total body irradiation, and received an unmanipulated HSCT from an HLA‐identical sibling (n = 270), a matched unrelated donor (n = 67) or an identical twin (n = 5). The source of stem cells was peripheral blood (n = 15) or bone marrow (n = 327). Graft‐vs.‐host disease (GvHD) prophylaxis consisted of cyclosporin A with or without methotrexate. The proportion of patients with < 50 × 109/l platelets on d +50, d +100, d +200 and d +365 after HSCT was 26%, 27%, 14% and 11% respectively. Thrombocytopenia was independent of the degree of complete donor chimaerism. Four variables were predictive of platelet recovery: donor type, acute GvHD, cytomegalovirus (CMV) infection and number of cells infused at transplant. Recipients of an unrelated graft had lower platelet counts (49 × 109/l) on d +50 than identical sibling grafts (108 × 109/l) (P < 0·001) and twin grafts (149 × 109/l) (P < 0·001). Patients with GvHD grades 0, I, II, III and IV had significantly different platelet counts on d +50 (153 × 109/l, 102 × 109/l, 85 × 109/l, 32 × 109/l and 22 × 109/l; P < 0·001) and thereafter. Thrombocytopenia was more frequent in patients with high‐level CMV antigenaemia (> four positive cells/2 × 105) (P < 0·0001) and in patients who received a low cell dose at transplant (≤ 4·1 × 108/kg) (P = 0·009). Platelet counts predicted transplant‐related mortality (TRM) and were higher at all time intervals in patients surviving the transplant. Patients with grade II GvHD and > 50 × 109/l platelets had a lower TRM than patients with grade II GvHD and ≤ 50 × 109/l platelets (14% vs. 40%, P < 0·0001).

In conclusion, (i) a significant proportion of allogeneic HSCT recipients are thrombocytopenic long‐term, irrespective of complete donor chimaerism, (ii) thrombocytopenia identifies patients at greater risk of lethal complications, and (iii) platelet recovery is influenced by GvHD, donor type, CMV infections and cell dose, not by stem cell source or other patient–disease‐related variables.
Microvessel overexpression of aquaporin 1 parallels bone marrow angiogenesis in patients with active multiple myeloma
Authors: Vacca Angelo , Frigeri Antonio , Ribatti Domenico , Nicchia Grazia Paola , Nico Beatrice , Ria Roberto , Svelto Maria , Dammacco Franco
Published: July 2002

The erythrocyte water channel aquaporin 1 (AQP1) is expressed in multiple absorptive and secretory epithelia including the capillary endothelia. Immunoblot analysis showed that bone marrow biopsies of patients with active multiple myeloma (MM) display significantly higher levels of AQP1 than those from patients with non‐active MM, whose values are higher, but to a lesser extent, than those of patients with monoclonal gammopathies of undetermined significance (MGUS). Values of MGUS overlapped those of patients with anaemia as a result of iron or vitamin B12 deficiencies (called ‘benign anaemias’). Immunohistochemistry and computerized image analysis of AQP1 highlighted bone marrow microvessels whose area per microscopic field was significantly greater in patients with active MM, and always larger than and closely correlated with the microvessel area when assessed with factor VIII‐related antigen/von Willebrand's factor (FVIII–VWF). The intensity of AQP1 expression by microvessels evaluated using image analysis was significantly greater in active than non‐active MM and in the latter over MGUS or benign anaemias. It is suggested that, among plasma cell tumours, AQP1 expression is preferentially associated with microvessels of MM and that the highest degree of expression occurs in active MM in step with enhanced angiogenesis, in which AQP1 recognizes more immature neovessels than FVIII–VWF. It may, perhaps, favour angiogenesis in a positive loop and, hence, MM progression, and thus be applied for therapeutic vascular targeting.
CD14‐Dependent and Independent Pathways in Lipopolysaccharide‐Induced Activation of a Murine B‐Cell Line, CH12.LX
Authors: Kimura S. , Tamamura T. , Nakagawa I. , Koga T. , Fujiwara T. , Hamada S.
Published: July 2002

Using a lipopolysaccharide (LPS)‐responsive murine B‐cell line, CH12.LX, we assessed the possible role of CD14 in LPS‐induced activation of B cells. Flow cytometric analysis indicated that CH12.LX cells expressed the CD14 molecule with a lower intensity than did the macrophage cell line J774.1. A reverse transcription‐polymerase chain reaction and Northern blot analysis revealed low, but significant, levels of CD14 mRNA in CH12.LX cells, whose cDNA was identical to that of the mouse macrophage CD14 gene. After stimulation with LPS, CH12.LX cells proliferated, accompanied by up‐regulations of CD14, transforming growth factor (TGF)‐β and interleukin (IL)‐6 mRNA, and increased IgM and IgA secretion. In the absence of serum or with the addition of anti‐CD14 monoclonal antibodies, however, LPS‐stimulation induced neither the up‐regulation of CD14 and TGF‐β mRNA nor an increase in IgA secretion. These findings indicate that CD14 expression is not restricted to myeloid cells, but is involved in some cellular activation events of murine B cells elicited by LPS. Furthermore, a CD14‐independent pathway may also exist in the LPS‐induced activation of B cells that leads to proliferation, IL‐6 production and the enhancement of IgM (but not IgA) secretion.
Three‐dimensional organisation of mitochondrial clusters in regenerating dorsal root ganglion (DRG) neurons from neonatal rats: evidence for mobile mitochondrial pools
Authors: Dedov Vadim N. , Armati Patricia J. , Roufogalis Basil D.
Published: July 2002

Abstract  We report for the first time the rearrangement of mitochondrial arrays in developing dorsal root ganglion (DRG) neurons isolated from neonatal rats in culture. Neurons were loaded with the mitochondria‐specific fluorescent dye JC‐1, and three‐dimensional (3D) reconstruction of mitochondrial fluorescence was performed by confocal laser sectioning in fresh neurons and neurons kept in culture up to a week. We found that after 24 hours the mitochondria become reorganised to form clusters in the axonal hillocks. Axonal extension and neuronal network formation coincided with a redistribution of the mitochondrial clusters. In the extended axons the mitochondria become spaced along the axonal length; however, they formed clusters in the branch points and growth cones. We conclude that the initial clusters of mitochondria may be storage pools of mobile mitochondria able to be mobilised to provide energy for axonal transport during neuronal regeneration and neuronal outgrowth. These findings may have relevance to the rate of axonal regeneration and axonal transport in adult DRG neurons, and neuronal polarisation and axonal outgrowth regulation in developing DRG neurons.
Boron doping of diamond thin films
Authors: Mort J. , Kuhman D. , Machonkin M. , Morgan M. , Jansen F. , Okumura K. , LeGrice Y. M. , Nemanich R. J.
Published: July 2002

The electrical conductivity of diamond thin films produced by the hot-filament technique is found to increase when diborane is incorporated in the precursor gas mixture. The combination of well-defined bulk conductivity measurements with quantitative secondary-ion mass spectrometry and Raman spectroscopy shows that the conductivity increase is associated with atomic boron doping and rules out any significant role for a graphitic-type component.
Distortion of excitonic emission bands due to self-absorption in ZnSe epilayers
Authors: Shahzad Khalid , Cammack David A.
Published: July 2002

In this letter we investigate the influence of self-absorption on the excitonic emission spectra of ZnSe epitaxial layers grown by molecular beam epitaxy on GaAs substrates. We observe that, very often, samples grown under identical conditions show a widely ranging ratio of neutral donor-bound-exciton to free-exciton intensities in photoluminescence (PL). We present experimental evidence to show that these differences can arise from the variations in the epilayer thickness and detailed PL experimental conditions and do not necessarily represent the layer-to-layer purity fluctuations, as the spectral line shapes may suggest.
Growth of large, defect-free pure C60 single crystals
Authors: Meng R. L. , Ramirez D. , Jiang X. , Chow P. C. , Diaz C. , Matsuishi K. , Moss S. C. , Hor P. H. , Chu C. W.
Published: July 2002

Millimeter-sized single crystals of C60 were grown by sublimation of C60 powder in a vacuum for 6–24 h. The crystals had excellent facets, were free of C70 or solvent, and showed face-centered cubic symmetry with a very small mosaic spread down to 0.01°.
Mechanism of pulsed laser-induced amorphization of silicon films
Authors: Sameshima T. , Usui S.
Published: July 2002

Amorphization and crystallization were studied through homogeneous solidification of molten silicon layers on quartz substrates induced by irradiation with a 30 ns XeCl excimer laser. The crystalline nucleation rate was obtained to be 8×1030 m−3 s−1. Silicon films were completely amorphized for films thinner than 18 nm due to the fact that grain growth is reduced as film thickness decreases. It was also experimentally determined that recalescence caused by latent heat released at solidification can cause grain growth.
Vapor pressure of Buckminsterfullerene
Authors: Abrefah J. , Olander D. R. , Balooch M. , Siekhaus W. J.
Published: July 2002

The vapor pressures of the fullerenes C60 and C70 have been measured over the temperature range 400–600 °C by the Knudsen-effusion thermogravimetric technique. For C60, a heat of sublimation of 38±1 kcal/mol is obtained, and the value for C70 is 45±1 kcal/mol. The vapor pressure of C60 ranges from 1.8×10−5 and 1.4×10−2 Torr and that of C70 is between 1.4×10−5 and 8.7×10−3 Torr over the temperature range investigated. At 500 °C, the vapor pressure of C60 is about 1035 that of graphite. The entropy of vaporization of C60 obeys Trouton’s rule.
Effect of Al doping on low-temperature epitaxy of 3C-SiC/Si by chemical vapor deposition using hexamethyldisilane as a source material
Authors: Takahashi Koji , Nishino Shigehiro , Saraie Junji
Published: July 2002

Low-temperature growth of 3C-SiC by atmospheric-pressure chemical vapor deposition was carried out using hexamethyldisilane (Si2(CH3)6) as a source material. Single-crystal undoped SiC was grown on Si(111) without employing a carbonized buffer layer and on Si(100) with a buffer layer. In the case of adding Al(CH3)3 to the source gas, the Al-doped initial layer works as a buffer layer which controls the initial nucleation. The Al doping lowers the expitaxial temperature of this gas system down to 1000 °C.
Denuded zone formation in carbon-implanted silicon and its application to device quality silicon-on-insulator preparation
Authors: Tong Q.-Y. , You H.-M. , Cha G. , Gösele U.
Published: July 2002

For producing ultrathin (<0.1 μm) device quality silicon-on-insulator (SOI) films, commercially available 4-in. diameter (100) SOI wafers with single-crystal layer thickness of 1.5±0.5 μm were carbon-implanted (190 keV and 3×1016 cm−2) followed by bonding to oxidized Si wafers. The buried oxide in the SOI wafers was used as the first etch stop and the second etch was stopped at the implanted carbon peak. The formation of a carbon denuded zone allowed us to obtain ≤900±50 Å SOI films free of carbon precipitation. Since precision polishing to thin one wafer of a bonded pair down to ±0.5 μm in thickness variation is available in industry, it should be possible to start the described SOI process with a bulk Si wafer, rather than an expensive SOI wafer, and obtain similar results.
Transient velocity overshoot dynamics in GaAs for electric fields ≤ 200 kV/cm
Authors: Son J. , Sha W. , Kim J. , Norris T. B. , Whitaker J. F. , Mourou G. A.
Published: July 2002

We have experimentally studied the transient velocity overshoot dynamics of photoexcited carriers in GaAs for electric fields as great as 200 kV/cm. Time domain waveforms proportional to the velocity and the acceleration of carriers have been acquired, respectively, from guided and free-space radiating signals which contain terahertz frequency components. The measurements demonstrated that the degree of overshoot was maximized for an electric field on the GaAs between 40 and 50 kV/cm when 1.44-eV photons in an 80-fs laser pulse excited the sample. For carriers excited with higher initial energy (1.55 eV), the degree of overshoot decreased and the maximum degree of overshoot occurred at a higher electric field.
Variable density high mobility two-dimensional electron and hole gases in a gated GaAs/AlxGa1−xAs heterostructure
Authors: Kane B. E. , Pfeiffer L. N. , West K. W. , Harnett C. K.
Published: July 2002

We have fabricated undoped GaAs/AlxGa1−xAs heterojunctions in which an electric field produced by a top gate confines carriers to the interface, and where contact is made to carriers at the interface using a novel self-aligned contacting process. Densities for both electrons and holes ranging from n2D < 1010/cm2 to n2D ≳ 5 × 1011/cm2 are obtainable with mobilities comparable to those measured in high quality modulation-doped heterojunctions.
Laser heating and photoluminescence in GaAs and AlxGa1−xAs
Authors: Dobal P. S. , Bist H. D. , Mehta S. K. , Jain R. K.
Published: July 2002

Low-temperature band-to-band photoluminescence of GaAs and AlGaAs excited by the 514.5 nm line of an argon ion laser beam was used as a probe to measure the temperature at the focused laser spot. A combined study of the dependence of band-gap energy on increasing laser power density and temperature was undertaken. The band-gap variation with temperature has been correlated with laser induced temperature at the focused laser spot as a function of laser power density. The induced temperature is lower than anticipated from the theories for cw laser heating. This disagreement can be explained by the contribution of photoexcited carriers to the thermal conductivity, which is not considered by theories available for laser heating in semiconductors.
Schottky-based band lineups for refractory semiconductors
Authors: Wang M. W. , McCaldin J. O. , Swenberg J. F. , McGill T. C. , Hauenstein R. J.
Published: July 2002

An overview is presented of band alignments for small-lattice parameter, refractory semiconductors. The band alignments are estimated empirically through the use of available Schottky barrier height data, and are compared to theoretically predicted values. Results for tetrahedrally bonded semiconductors with lattice constant values in the range from C through ZnSe are presented. Based on the estimated band alignments and the recently demonstrated p-type dopability of GaN, we propose three novel heterojunction schemes which seek to address inherent difficulties in doping or electrical contact to wide-gap semiconductors such as ZnO, ZnSe, and ZnS.
Microwave mixing and noise in the two-dimensional electron gas medium at low temperatures
Authors: Yang J. X. , Li J. , Musante C. F. , Yngvesson K. S.
Published: July 2002

Microwave mixing and noise measurement techniques have been used to characterize energy relaxation and noise phenomena for the two-dimensional electron gas (2DEG) medium in single AlGaAs/GaAs modulation-doped quantum wells. Mixing experiments at 94 GHz yield the energy relaxation time directly, in good agreement with optical methods previously reported. The noise output power at low microwave frequencies (1.5–3.5 GHz), is shown to have one term due to Nyquist noise at the electron temperature, and a second frequency-dependent term caused by fluctuations in the electron temperature.
Transformation of C60 fullerenes into a superhard form of carbon at moderate pressure
Authors: Kozlov M. E. , Hirabayashi M. , Nozaki K. , Tokumoto M. , Ihara H.
Published: July 2002

A very hard and conducting form of carbon has been obtained from pure C60 fullerenes, as well as its mixture with aluminium at nonhydrostatic pressures of 2.6–3 GPa and a temperature of 700 °C. The hardness of the material is more than 4000 kg/mm2. Its electrical conductivity is about 100 Ω−1 cm−1 and is weakly dependent on temperature in the range 4.2–300 K. X-ray diffraction and Raman measurements show lack of the long-range crystalline order in the transformed material.
A parabolic mirror time-of-flight electron energy analyzer
Authors: Trevor D. J. , Van Woerkom L. D. , Freeman R. R.
Published: July 2002

We have designed and built a high-efficiency time-of-flight electron spectrometer which has the potential to record accurately the angular distribution of the photoemitted electrons. This analyzer uses an electrostatic analog of an optical parabolic mirror to collimate, in an isochronic fashion, half of the electrons emitted from an isotropic point source and measure each electron’s energy by time-of-flight. Results are presented which demonstrate that the spectrometer operates near its design collection efficiency and energy resolution.
Aerodynamic device for generating mono-disperse fuel droplets
Authors: Green G. J. , Takahashi F. , Walsh D. E. , Dryer F. L.
Published: July 2002

A device has been developed for generating well-defined, one-dimensional streams of small (200–1000 μm), mono-sized droplets of a variety of fuels. The droplets produced are well separated (>30 droplet diameters), making this technique well suited to experimental combustion studies of unsupported, isolated droplets. This method has been used successfully to generate droplets of light and mid-distillate petroleum fuels, heavy oils, boron/JP-10 slurries, and coke/oil slurries, for a range of combustion studies. The principle of operation of the device is the aerodynamic stripping of incompletely formed droplets emerging from the tip of a capillary/fine wire which resides in the throat of a venturi or convergent nozzle. By varying the fuel flow rate through the capillary, the gas flow rate through the nozzle, and the diameter of the capillary, precise control of the initial droplet size, spacing, frequency, and velocity can be achieved. Design criteria, exemplary results, and a brief survey of other droplet generating schemes are presented, along with a description of the integration of this device into a laboratory combustion apparatus.
Effect of contact size and placement, and of resistive inhomogeneities on van der Pauw measurements
Authors: Koon Daniel W.
Published: July 2002

The measurement errors of resistivity and Hall coefficient in the van der Pauw technique due to contact lead size or lead placement errors is calculated for square and cloverleaf-shaped samples, and compared to the results for a simple circular disk. Both the square and the cloverleaf greatly reduce these errors, compared to the circular sample shape. Another source of measurement error, sample inhomogeneity, is also analyzed, and it is shown that the error introduced by inhomogeneities is proportional to E2 in the region of the inhomogeneity. Consequences of these results are discussed.
Improved pulsed laser vaporization source for production of intense beams of neutral and ionized clusters
Authors: Milani Paolo , deHeer Walt A.
Published: July 2002

We describe an improved laser vaporization source for production of intense and stable cluster beams. Intensity and stability are notably improved compared with standard sources by the introduction of a cavity in which the vaporization takes place before expansion. This source has been successfully used for electric deflection studies of highly collimated cluster beams.
Diaphragm magnetometer for dc measurements in high magnetic fields
Authors: Swanson A. G. , Ma Y. P. , Brooks J. S. , Markiewicz R. M. , Miura N.
Published: July 2002

We describe the design and operation of a force magnetometer with high sensitivity which can be easily used between room and sub-kelvin temperatures. The device can accommodate a large range of sample masses (10–0.001 g) with a relative resolution of 10−5 emu. The maximum sample size is only restricted by the geometry of the cryogenic and magnetic environment. The design is particularly suited for high magnetic field measurements or where no gradient coil is available.
High-resolution time of-flight mass spectrometers. Part II. Cross beam ion optics
Authors: Bergmann T. , Goehlich H. , Martin T. P. , Schaber H. , Malegiannakis G.
Published: July 2002

Injecting neutral species at right angles to the direction of acceleration and using quadrupole ion optics allows for highest resolution and good sensitivity in time-of-flight mass spectrometers. We have designed such ion optics using a finite element field calculation. Imaging and timing errors have been compensated. With an acceleration voltage of 6.5 kV it accepts neutral species having energies up to 500 eV.
Simple two-dimensional piezoelectric micropositioner for a scanning tunneling microscope
Authors: Blackford B. L. , Jericho M. H.
Published: July 2002

A simple piezoelectric tube device is described which allows remote micropositioning in two dimensions with step sizes from ∼50 to ∼3000 nm. Speeds up to 0.1 mm/s have been achieved. It uses the principle of inertial sliding of a mass on an accelerated support. The design is a modification of a one-dimensional device which was recently reported in the literature. The device is compact, rigid, and has low thermal drift.
A double/triple time-of-flight mass spectrometer for the study of photoprocesses in clusters, or how to produce cluster ions with different temperatures
Authors: Haberland Hellmut , Kornmeier Hans , Ludewigt Christoph , Risch Andreas , Schmidt Martin
Published: July 2002

An apparatus is described for the measurement of photo processes in mass-selected cluster ions. A gridless reflectron type of time-of-flight (TOF) mass spectrometer is used to select an ion of known mass. The selected ion is photoexcited with a pulsed dye laser. The charged fragments are mass separated in a second linear TOF. A new combination of reflectron and linear TOF is described, which allows one to measure the complete photofragment mass distribution over an arbitrary large mass range for each laser shot, which was not possible earlier. It is discussed how clusters with different temperatures can be prepared. The first measurement of a temperature-dependent effect for mass-selected free cluster ions is presented.
Simultaneous void fraction measurement, bubble velocity, and size estimate using a single optical probe in gas–liquid two-phase flows
Authors: Cartellier Alain
Published: July 2002

Optical probes are now commonly used in industrial conditions as well as in laboratory experiments. Although they have been primarily devoted to void fraction measurements, additional information could be extracted from the raw signals they deliver. For a stretched optical probe, it is shown that the modulus of the ensemble velocity of a bubble ‖V0‖ could be inferred from the rise time Tu associated with the liquid/gas transition. These two parameters are correlated thanks to piercing experiments in which the interface curvature R and the angle β between the probe and the normal to the interface are controlled. While the influence of R is negligible, the rise time is very sensitive to β. A one-to-one relation between Tu and ‖V0‖ is ensured for quasiperpendicular impactions which must be accordingly distinguished among the bubble signatures. The software which includes the adequate signal processing criteria is described. It gives access to void fraction and to the chord-velocity joint distribution which provides a guide to determine the flow regime. The void fraction is shown to be weakly sensitive to the criteria. Besides, velocity and chords estimates are in rather good agreement with those deduced from direct visualization, both in a bubble and a slug flow. Such extensions of the measuring capabilities of optical probes are expected to be also applicable to other phase detection probes.
Neutron measurements from the preliminary tritium experiment at JET (invited)
Authors: Jarvis O. N.
Published: July 2002

A comprehensive range of neutron diagnostics has been installed on the Joint European Torus (JET) for studying deuterium plasma discharges; measurements are made for the 2.5-MeV neutrons emitted from d–d fusion reactions and for the 14-MeV neutrons from t–d burn-up reactions undergone by the 1.0-MeV tritons emitted in the d–d reactions. The time-resolved 2.5-MeV neutron emission is recorded with fission chambers, while the very low intensity 14-MeV neutron emission is recorded with silicon diodes. Absolute calibrations of these measurements are obtained by application of activation techniques. A 19-channel neutron profile monitor provides emissivity profiles for both 2.5- and 14-MeV neutrons independently. Finally, 2.5-MeV neutron energy spectra are recorded with a time-of-flight spectrometer. The recently performed preliminary tritium experiment (PTE) has provided a unique opportunity to test the performance of these neutron diagnostics with deuterium–tritium plasmas, although the time scale from proposal to completion was too short to permit the installation of dedicated instrumentation for the highly intense 14-MeV neutron fluxes. Such instrumentation will be provided for the final, active, phase of JET operation. This presentation will concentrate on the performance of the existing diagnostics during the PTE and will indicate some of the lessons that have been learned regarding neutron measurements for future deuterium–tritium discharges.
A convenient method for removing surface oxides from tungsten STM tips
Authors: Hockett Lisa A. , Creager Stephen E.
Published: July 2002

A convenient treatment that can be applied to tungsten scanning tunneling microscope tips prepared by electrochemical etching in aqueous base is described. The treatment removes the majority of the tungsten oxide layer present after etching and produces a very stable tunnel junction and a high success rate in preparing tips for atomic-resolution imaging.
A SQUID-based ac susceptometer
Authors: Hibbs A. D. , Sager R. E. , Kumar S. , McArthur J. E. , Singsaas A. L. , Jensen K. G. , Steindorf M. A. , Aukerman T. A. , Schneider H. M.
Published: July 2002

We have developed a high-resolution ac susceptometer that uses a rf superconducting quantum interference device to directly measure the flux coupled into a superconducting detection coil from a sample’s changing magnetic moment in an applied ac field. The system operates in a frequency range from 0.01 to 1500 Hz and an applied ac field range of 0.1–400 μT with a sensitivity of about 5×10−12 A m2 for magnetic moment measurement, and at a reduced sensitivity down to 0.001 Hz. The instrument is based on an existing dc magnetometer system and uses that system’s temperature control and dc superconducting magnet to allow operation over a temperature range from 2 to 400 K and in applied dc fields of ±5.0 T. During a measurement all operations are controlled automatically by computer from a menu-driven software system, with user input required only on initiation of a measurement sequence. Both real and imaginary components of the ac susceptibility can be determined.
Characterization of carbon material as a scanning tunneling microscopy tip for in situ electrochemical studies
Authors: Ohmori T. , Nagahara L. A. , Hashimoto K. , Fujishima A.
Published: July 2002

We have studied the feasibility of using carbon as a scanning tunneling microscopy tip material for experiments conducted under electrochemical environments. The tips were found to be stable and durable in acidic or alkaline solution for several hours. The fabricated carbon tips were capable of resolving graphite atoms in electrolyte solution under potentiostatic condition as well as in air.
Trace gas detection with cavity ring down spectroscopy
Authors: Jongma Rienk T. , Boogaarts Maarten G. H. , Holleman Iwan , Meijer Gerard
Published: July 2002

Trace gas detection of small molecules has been performed with cavity ring down (CRD) absorption spectroscopy in the near UV part of the spectrum. The absolute concentration of the OH radical present in trace amounts in heated plain air due to thermal dissociation of H2O has been calibrated as a function of temperature in the 720–1125 °C range. Detection of NH3 at the 10 ppb level is demonstrated in calibrated NH3/air flows. Detection of the background Hg concentration in plain air is performed with a current detection limit below 1 ppt. The effect of the laser linewidth in relation to the width of the absorption line is discussed in detail. Basic considerations regarding the use of CRD for trace gas detection are given and it is concluded that CRD spectroscopy holds great promise for sensitive [(sub)-ppb] and fast (kHz) detection of many small molecules.
Interference of fluorescence x rays and coherent excitation of core levels
Authors: Ma Yanjun , Blume M.
Published: July 2002

The question of coherence in inelastic x-ray absorption and fluorescence processes among identical interacting atoms is studied using a simple diatomic model. Conditions for the coherence are discussed in terms of energy scales, such as the core hole lifetime, instrument energy resolutions, and the splitting of the electronic levels. As in the classical Young double-slit experiment, the primary requirement is that it be impossible to determine which atom has undergone the excitation-decay process. In contrast to the elastic scattering of x rays, noninteracting atoms do not contribute coherently to the inelastic scattering cross section.
High density polarized hydrogen gas target for storage rings
Authors: Zapfe K. , Braun B. , Gaul H.-G. , Grieser M. , Povh B. , Rall M. , Steffens E. , Stock F. , Tonhäuser J. , Montag C. , Rathmann F. , Fick D. , Haeberli W.
Published: July 2002

A target of gaseous polarized hydrogen was formed by injecting polarized hydrogen atoms (produced by Stern–Gerlach spin separation) into a storage cell consisting of a cylindrical tube open at both ends. The target was placed in a storage ring to study the target characteristics (nuclear polarization, target thickness, radiation resistance). A weak transverse guide field (5 G) was applied to define the polarization direction. When atoms in a single hyperfine state were selected, the nuclear polarization of the target was measured to be 0.80±0.02. The areal density of the target under these conditions was (5.5±0.2)×1013 H/cm2, while for two spin states (applicable to experiments in high energy rings where a strong magnetic field can be applied to the target) the target thickness was found to be (8.2±0.3)×1013 H/cm2. The target polarization was unaffected by prolonged exposure of the target to beams up to 1 mA.
A picosecond optical pulse generator to calibrate the optical streak camera
Authors: Rai V. N. , Shukla M. , Khardekar R. K. , Pant H. C.
Published: July 2002

A simple pulser circuit to drive a single heterojunction GaAs laser diode which provides a single short duration (∼120 ps) optical pulse is described. However, study of emission characteristics of the diode laser shows many equally time spaced optical pulses when injection current in the diode is increased beyond the threshold of lasing. This phenomenon of diode laser emission is used to calibrate the picosecond time resolution optical streak camera, which provided sweep speed of ∼15 mm/1ns and nonlinearity in the sweep of ∼10%.
New results on core excited N2O obtained by electron–ion coincidence spectroscopya)
Authors: Ferrand-Tanaka Laurence , Simon Marc , Thissen Roland , Lavollée Michel , Morin Paul
Published: July 2002

In this paper we show and discuss new results on the dissociation of N2O after core (N 1s) excitation and ionization. We have developed an experimental setup combining an electrostatic electron analyzer with a time-of-flight mass spectrometer without angular discrimination, operated with a strong pulsed extraction field. Taking advantage of the pulsed character of the synchrotron radiation light, we have been able to efficiently remove fortuitous coincidences, without perturbing the electron energy analysis. We relate in detail the experimental setup and show new results obtained on 14N15NO. A selective fragmentation is shown depending on the excited site (central or terminal nitrogen) and the influence of the electronic excited state of the ion on the fragmentation pattern is pointed out.
Elevated ion charge states in vacuum arc plasmas in a magnetic field
Authors: Oks E. M. , Brown I. G. , Dickinson M. R. , MacGill R. A. , Emig H. , Spädtke P. , Wolf B. H.
Published: July 2002

We report on measurements of the charge state distributions of ions formed in a vacuum arc plasma in a magnetic field. A vacuum arc ion source was used for plasma formation and ion beam extraction, and the charge state spectra were investigated using both magnetic and time-of-flight charge state diagnostics. We find that the charge states of all of the metal species investigated are significantly increased by a magnetic field of up to 6 kG. New high ion charge states are created, and the mean of the charge state distribution is increased by about 30% at 3.75 kG and 50% at 6 kG. The results are important fundamentally as well as being of relevance to vacuum arc ion source applications such as ion implantation and accelerator injection.
Capacitance measurements of the volume fraction and velocity of dielectric solids near a grounded wall
Authors: Louge Michel , Tuccio Mark , Lander Eduardo , Connors Patrick
Published: July 2002

We describe capacitance probes that infer the volume fraction of solids near a grounded wall from a measurement of the effective dielectric constant of the suspension. The probes consist of three conductors, namely the sensor, guard, and ground surfaces. The instrument records capacitance between the sensor and ground by supplying an oscillating current of constant amplitude to the sensor. A control circuit maintains the guard and sensor voltages equal without affecting the sensor circuit. Because it surrounds the sensor conductor everywhere except at the probe surface, the guard eliminates stray and cable capacitances. By locating the ground at the periphery of the probe, this configuration renders the new instrument particularly useful in metallic vessels. Cross-correlation of the signals from two adjacent capacitance probes also permits measurements of the velocity of dielectric solids.
Falling capillary tube viscometer suitable for liquids at high pressure
Authors: Kumagai Akibumi , Kawase Yasuo , Yokoyama Chiaki
Published: July 2002

A new high pressure viscometer based on a falling capillary tube was developed for the study of liquids and solutions. The viscometer was used to determine the viscosity of water containing 4.8 wt % CO2 at pressures up to 40 MPa and over the temperature range from 273.15 to 323.15 K. Measurements of methanol at 0.1 MPa and water at pressures up to 40 MPa and over the temperature range from 273 to 333 K were used to confirm the accuracy of the new viscometer. For the methanol and water, agreement to within 1.8% of the literature values was found. The new viscometer should be applicable up to 200 MPa as judged by the current apparatus and materials of construction.
Spectroscopic ellipsometry determination of the refractive index of strained Si1−xGex layers in the near-infrared wavelength range (0.9–1.7 μm)
Authors: de Sande J. C. G. , Rodríguez A. , Rodríguez T.
Published: July 2002

The refractive index of fully strained Si1−xGex layers, with compositions x=0.20, 0.25, 0.30, and 0.33, has been measured using spectroscopic ellipsometry as a function of the wavelength in the 0.9–1.7 μm range. The dependence of the refractive index on the wavelength, for these compositions, is similar to that of crystalline Si. Its value for any wavelength is lower than that of relaxed Si1−xGex of the same composition. The experimental values of the refractive index of the fully strained Si1−xGex were fitted to the expression nSiGe(x,λ)=nSi(λ)+(1.16–0.26 λ)x2. This expression is applicable for wavelengths from 0.9 to 1.7 μm and compositions x≤0.33.
Mass spectrometric characterization of a high-field asymmetric waveform ion mobility spectrometer
Authors: Purves Randy W. , Guevremont Roger , Day Stephen , Pipich Charles W. , Matyjaszczyk Matthew S.
Published: July 2002

Ion mobility spectrometry (IMS) has become an important method for the detection of many compounds because of its high sensitivity and amenability to miniaturization for field-portable monitoring; applications include detection of narcotics, explosives, and chemical warfare agents. High-field asymmetric waveform ion mobility spectrometry (FAIMS) differs from IMS in that the electric fields are applied using a high-frequency periodic asymmetric waveform, rather than a dc voltage. Furthermore, in FAIMS the compounds are separated by the difference in the mobility of ions at high electric field relative to low field, rather than by compound to compound differences in mobility at low electric field (IMS). We report here the first cylindrical-geometry-FAIMS interface with mass spectrometry (FAIMS-MS) and the MS identification of the peaks observed in a FAIMS compensation voltage (CV) spectrum. Using both an electrometer-based-FAIMS (FAIMS-E) and FAIMS-MS, several variables that affect the sensitivity of ion detection were examined for two (polarity reversed) asymmetric waveforms (modes 1 and 2) each of which yields a unique spectrum. An increase in the dispersion voltage (DV) was found to improve the sensitivity and separation observed in the FAIMS CV spectrum. This increase in sensitivity and the unexpected dissimilarity in modes 1 and 2 suggest that atmospheric pressure ion focusing is occurring in the FAIMS analyzer. The sensitivity and peak locations in the CV spectra were affected by temperature, gas flow rates, operating pressure, and analyte concentration.
Simulation of ion extraction and beam transport (invited)
Authors: Spädtke P. , Mühle C.
Published: July 2002

The three dimensional code KOBRA3 has been used to simulate nonsymmetric extraction systems such as from an electron cyclotron resonance (ECR) ion source and a Penning ion source (PIG). For the ECR case the particle distribution is nonsymmetric due to the hexapole magnet. The PIG source extraction is usually a slit in magnetic field direction. The extracted ion beams usually cannot be transported without space charge compensation. The creation and behavior of the compensating particles and the resulting beam transport has been simulated with KOBRA3 as well. The applied model in the simulation describing this compensation is similar to the model used for space charge compensation in the plasma for extraction problems. Good agreement of the simulations with the experimental results has been obtained.
Behavior of Ni in carbon nanotube nucleation
Authors: Yudasaka Masako , Kikuchi Rie , Ohki Yoshimasa , Ota Etsuro , Yoshimura Susumu
Published: July 2002

A nucleation model was proposed for a carbon nanotube enclosing a Ni bar which was grown by chemical vapor deposition (CVD) at 700 °C using round Ni particles. At an early stage of CVD, each round Ni particle with a diameter of about 30 nm is covered with graphite layers. The graphite-covered Ni particle is considered to be unstable because the graphite layers have a large curvature. This instability is thought to make the graphite-covered Ni particles transform into a Ni bar enclosed within a carbon nanotube. In order to verify this nucleation model, we show that the size of the round Ni particle is a decisive condition for carbon nanotube formation by CVD, and that an intermediate state of the transformation of the graphite-covered Ni particles to the carbon-nanotube-enclosed Ni bar was observed by transmission electron microscopy.
Femtosecond studies of carrier dynamics in InGaN
Authors: Sun C.-K. , Vallée F. , Keller S. , Bowers J. E. , DenBaars S. P.
Published: July 2002

Ultrafast carrier dynamics in In0.16Ga0.84N were investigated using femtosecond transient transmission measurements. We observed a fast initial carrier cooling on a time scale of 500 fs followed by a slow relaxation process which persisted longer than 5 ps due to a hot phonon effect. Band gap renormalization induced transient absorption was observed using a probe photon energy 300 meV above the band edge. These results were compared to a model based on the numerical resolution of the carrier Boltzmann equations.
Dual Hall effects in inhomogeneous doubly connected GaAs/AlGaAs heterostructure devices
Authors: Mani R. G.
Published: July 2002

Transport measurements of partially gated doubly connected 2D GaAs/AlGaAs heterostructure devices which include striplike bimodal electron density distribution are used to demonstrate that the Hall resistance determined from a fixed set of voltage contacts can be quite sensitive to connectivity between source and drain. Some experimental results investigating the effect of exchanging current and voltage leads are also presented.
GaN and AlxGa1−xN molecular beam epitaxy monitored by reflection high-energy electron diffraction
Authors: Grandjean N. , Massies J.
Published: July 2002

GaN and AlxGa1−xN alloys were grown by gas source molecular beam epitaxy using NH3. High quality GaN layers with smooth surfaces being obtained, reflection high-energy electron diffraction (RHEED) can be used to monitor the growth. The oscillations of the specular beam intensity indicate a layer-by-layer growth which allows one to precisely measure the deposition rate and the composition of AlxGa1−xN alloys. The transition from two dimensional nucleation to step flow growth mode when increasing the substrate temperature is also evidenced. Finally, RHEED is used to investigate the relaxation processes which take place during the growth of AlN on GaN and GaN on AlN.
Effects of rapid thermal annealing on GaInP/AlGaInP lasers grown by all-solid-source molecular beam epitaxy
Authors: Jalonen Marko , Toivonen Mika , Savolainen Pekka , Köngäs Jukka , Pessa Markus
Published: July 2002

We have examined the influence of rapid thermal annealing on the performance characteristics of GaInP/AlGaInP quantum well lasers which were grown by all-solid-source molecular beam epitaxy. It was found that when the laser structures were annealed the threshold current densities of the lasers decreased significantly. This improvement in lasing performance could be associated with the possibility that annealing removed nonradiative recombination centers from the quantum wells. The emission wavelength, differential quantum efficiency, and characteristic temperature were not affected to any remarkable extent, indicating that the interdiffusion of group-III elements did not damage the structures.
Epitaxial SrRuO3 thin films on (001) SrTiO3
Authors: Chen C. L. , Cao Y. , Huang Z. J. , Jiang Q. D. , Zhang Z. , Sun Y. Y. , Kang W. N. , Dezaneti L. M. , Chu W. K. , Chu C. W.
Published: July 2002

Highly conductive metallic oxide thin films of SrRuO3 with single crystalline quality have been grown on (001) SrTiO3 by using pulsed laser deposition. The films have a [00l] orientation with an in-plane relationship of [110]SrRuO3 // [100]SrTiO3. They have excellent metallic behavior with room temperature resistivity of ∼310 μΩ cm and a residual resistance ratio of about 7 at 4.2 K, the largest reported to date. A clear ferromagnetic transition at ∼147 K was detected by resistivity and magnetic measurements. However, the transition becomes blurred as the density-of-point defects increases in the films following a 400 keV proton irradiation with an accumulative dose up to ∼6.0×1016 ions/cm2.
Thermally bonded planar waveguide lasers
Authors: Brown C. T. A. , Bonner C. L. , Warburton T. J. , Shepherd D. P. , Tropper A. C. , Hanna D. C. , Meissner H. E.
Published: July 2002

A new technique for fabricating active planar waveguide devices is reported. This process, based on the thermal bonding of precision finished crystal or glass components, allows waveguides to be assembled from very dissimilar materials and could be applied to a wide range of solid state laser or other optical media. The waveguide propagation losses, inferred from the laser performance, are found to be 0.7 dB/cm for Nd:Y3Al5O12 bonded to Y3Al5O12, Nd:Y3Al5O12 bonded to glass, and 0.4 dB/cm for Nd:Gd3Ga5O12 bonded to Y3Al5O12 devices.
CdSe/ZnSe quantum structures grown by migration enhanced epitaxy: Structural and optical investigations
Authors: Leonardi K. , Heinke H. , Ohkawa K. , Hommel D. , Selke H. , Gindele F. , Woggon U.
Published: July 2002

Migration enhanced epitaxy has been applied to induce the change from two-dimensional growth to formation of self-assembling islands in the growth of CdSe on ZnSe. Transmission electron microscopy images from samples with a ZnSe caplayer show a transition from a flat quantum well to an interrupted layer with pronounced thickness fluctuations when the CdSe exceeds its critical thickness. These results are confirmed by high resolution x-ray diffraction measurements, as only for the former sample the 004 rocking curve can be simulated assuming a flat quantum well with abrupt interfaces. Compared to bulk CdSe, the photoluminescence peak is blueshifted by about 0.5 eV. PL excitation experiments indicate that the interrupted layer consists of CdSe islands embedded in Zn1−xCdxSe with a composition gradient. Atomic force microscopy images of uncapped samples show spherical islands with a height of 20 nm and a diameter-to-height ratio of 4:1.
Relationship of background carrier concentration and defects in GaN grown by metalorganic vapor phase epitaxy
Authors: Zhang G. Y. , Tong Y. Z. , Yang Z. J. , Jin S. X. , Li J. , Gan Z. Z.
Published: July 2002

Experimental results show that the background carrier concentrations in GaN films grown by metalorganic vapor phase epitaxy are related to defects. A thermal equilibrium method was used to calculate the background carrier concentration related to intrinsic defects in an ideal GaN crystal. The results show that the N vacancy concentration does not exceed 2×1017 cm−3 in GaN grown at temperatures ranging from 800 to 1500 K. It can be concluded that the N vacancy is one of the major sources of carriers when the carrier concentration n<2×1017 cm−3, but the main sources should be other defects when n>2×1017 cm−3; this conclusion may lead to ways for further improving the quality of GaN films.
Nanocrystalline-silicon superlattice produced by controlled recrystallization
Authors: Tsybeskov L. , Hirschman K. D. , Duttagupta S. P. , Zacharias M. , Fauchet P. M. , McCaffrey J. P. , Lockwood D. J.
Published: July 2002

Nanocrystalline-silicon superlattices are produced by controlled recrystallization of amorphous-Si/SiO2 multilayers. The recrystallization is performed by a two-step procedure: rapid thermal annealing at 600–1000 °C, and furnace annealing at 1050 °C. Transmission electron microscopy, Raman scattering, x-ray and electron diffraction, and photoluminescence spectroscopy show an ordered structure with Si nanocrystals confined between SiO2 layers. The size of the Si nanocrystals is limited by the thickness of the a-Si layer, the shape is nearly spherical, and the orientation is random. The luminescence from the nc-Si superlattices is demonstrated and studied.
The activation of Mg in GaN by annealing with minority-carrier injection
Authors: Miyachi Mamoru , Tanaka Toshiyuki , Kimura Yoshinori , Ota Hiroyuki
Published: July 2002

The activation of a Mg acceptor in GaN, by means of annealing under minority-carrier injection, is observed at a temperature above 300 °C. This activation is carried on with hydrogen left in the layer. The p-type GaN layers activated by this treatment are repassivated by additional annealing in an open-circuit configuration even in inert gas, and then reactivated by annealing under minority-carrier injection. Hydrogen remaining in the layer seems to play a major role in this reversible phenomenon.