bluuebunny/crossref_metadata_2025 huggingface dataset:
Pelvi‐ureteric junction obstruction treated with Acucise™ retrograde endopyelotomy
Authors: Gill  , Liao
Published: July 2002

Objective

 To determine the efficacy of retrograde endopyelotomy for the treatment of pelvi‐ureteric junction (PUJ) obstruction using the Acucise™ ureteric balloon cutting catheter.

Patients and methods

 Between February 1995 and July 1997, 13 consecutive patients with primary PUJ obstruction underwent Acucise™ endopyelotomy at our institution. The mean follow‐up was 17.7 months (range 7–33). The success of the procedure was based on objective patency on follow‐up diuretic isotopic renography and the subjective resolution of symptoms.

Results

 The treatment was successful by objective criteria in eight of 13 patients and by subjective criteria in nine. The mean operative duration was 33 min (range 25–45) and all 13 patients were discharged within 24 h of the procedure. There were no major complications, such as vascular injury requiring transfusion. There were no delayed failures, as all failures occurred within 3 months of the procedure. Of the four total failures, two patients have successfully undergone open pyeloplasty and one other was found to have a crossing vessel at the lower pole at the time of the operation.

Conclusion

 In this small series, Acucise™ endopyelotomy was a safe procedure that offered effective, expeditious first‐line treatment for PUJ obstruction. All failures occurred soon after treatment and did not hinder subsequent open pyeloplasty. Further studies with additional patients and a longer follow‐up are warranted to determine the long‐term efficacy of this promising new treatment.
The effects of vasodilatation and chemical sympathectomy on spermatogenesis after unilateral testicular torsion: a flow cytometric DNA analysis
Authors: Oguzkurt  , Okur  , Tanyel  , BÜYÜkpamukÇU  , HIÇSÖnmez
Published: July 2002

Objective

 To evaluate the effects of vasodilator therapies and chemical sympathectomy on ipsilateral and contralateral testicular spermatogenetic activity after unilateral testicular torsion using DNA flow cytometry and thus determine whether contralateral testicular damage occurs through a reflexively decreased blood flow.

Materials and methods

 The study comprised four groups of 20 rats each (groups 1–4) respectively receiving isotonic saline, verapamil, pentoxifylline and 6‐hydroxy dopamine hydrobromide (6‐OHD) intraperitoneally. Each group was further divided into two subgroups containing 10 rats which respectively underwent either a sham operation or 720° clockwise torsion applied to the left testis. The testes were harvested after 24 h and the relative proportions of haploid, diploid and tetraploid cells determined by DNA flow cytometry for each testis. The proportion of haploid cells was used as an estimate of spermatogenesis. The mean proportions of haploid cells in the groups were compared using a one‐way anova and paired groups were compared using Student’s t‐test.

Results

 The proportions of haploid cells in the ipsilateral testes of rats undergoing torsion were significantly lower than in their contralateral testes and in the ipsilateral testes of the control groups. In group 4 (6‐OHD) the proportion of haploid cells in the contralateral testes was significantly higher than those in the other groups after unilateral testicular torsion, but significantly lower than those in groups 1 and 4 after a sham operation. After unilateral testicular torsion the haploid cell proportions of the contralateral testes of groups 1–3 were not significantly different from each other.

Conclusions

 Because the spermatogenetic activity in the contralateral testis is depressed within 24 h of ipsilateral testicular torsion, contralateral testicular damage is an acquired effect; 6‐OHD offers some protection and thus the damage seems to result from the involvement of the sympathetic system.
Creation of deep levels in horizontal Bridgman-grown GaAs by hydrogenation
Authors: Cho Hoon Young , Kim Eun Kyu , Min Suk-Ki , Kim Jae Boong , Jang Jin
Published: July 2002

The effect of hydrogen plasma exposure on the deep levels in GaAs grown by the horizontal Bridgman method was studied. After hydrogenation at 250 °C for 3 h, the concentrations of the electron deep levels, such as the EL2 trap (Ec-0.81 eV), the EL3 trap (Ec−0.63 eV), and the EL6 trap (Ec−0.35 eV), decrease by one order of magnitude. On the other hand, three new electron traps at Ec −0.42 eV, Ec −0.54 eV, and Ec −0.94 eV are created. After rapid thermal annealing up to 550 °C for 10 s, these created traps are reduced and the deep levels decreased by hydrogenation recover nearly completely. This result reveals that the passivation and creation of deep levels by hydrogenation may be explained as the interaction of atomic hydrogen with an unsaturated bond of native defects.
Empirical photoablation rate model exemplified with the etching of polyphenylquinoxaline
Authors: Lazare Sylvain , Granier Vincent
Published: July 2002

A kinetic model of photoablation with the nanosecond pulses of an excimer laser, based on the so-called moving interface, is presented. The rate of the ablating interface is assumed to be v=k(I−It) when the intensity I exceeds the threshold intensity It. The intensity reaching the interface I attenuated by the absorption of the products is I0e−βx, where x is the position of the interface. The ablation rate constant k of the polymer and screening coefficient β of the gas products are evaluated for each polymer and wavelength, by fitting the etch curves obtained precisely with our quartz crystal microbalance technique (as well as the literature data). The etching of polyphenylquinoxaline, a thermostable polymer, at three wavelengths (193, 248, and 351 nm) is given as an example.
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u pattern formation and high quality overgrowth by gas source molecular beam epitaxy
Authors: Temkin H. , Harriott L. R. , Hamm R. A. , Weiner J. , Panish M. B.
Published: July 2002

We demonstrate a combination of focused Ga beam writing and dry etching techniques to pattern InP wafers in a common vacuum chamber. Surface steps on the order of 1000 Å can be efficiently prepared using moderate Ga ion fluences. The implanted areas exhibit a faster etch rate, even for Ga doses below ∼1014 cm−2. The implantation damage is removed by the low-energy Cl-assisted ion beam etching as shown by the high quality of p-n junctions grown on etched surfaces. GaInAs/InP heterostructures grown on in situ patterned substrates show excellent morphology and high luminescence efficiency.
Electrical response of superconducting YBa2Cu3O7−δ to light
Authors: Brocklesby W. S. , Monroe Don , Levi A. F. J. , Hong M. , Liou S. H. , Kwo J. , Rice C. E. , Mankiewich P. M. , Howard R. E.
Published: July 2002

We have studied the effect of visible and near-infrared light on the electrical properties of superconducting thin films of YBa2Cu3O7−δ. The responses we observe can all be explained in terms of light heating the film to a temperature above the superconducting transition. No evidence that the light directly affects superconductivity was found.
Three-terminal delta-doped barrier switching device with S-shaped negative differential resistance
Authors: Baillargeon J. N. , Cheng K. Y. , Laskar J. , Kolodzey J.
Published: July 2002

A molecular beam epitaxial grown GaAs three-terminal device with a delta-doped barrier and GaInAs quantum well exhibiting controllable S-shaped negative differential resistance and switching voltages has been fabricated and tested. The device has a large potential barrier between the anode and cathode regions which can be modulated via a third terminal. The modulation of the potential barrier has a substantial effect on the switching behavior of the device. For the devices having a cathode contact area of 50 μm2, a spectrum analyzer reveals unstable oscillation up to the system measurement limit of 21 GHz. The output power signal for the best device is greater than −10 dBm which is 20 dB above the noise floor at 20.8 GHz. The results show this device to be a potentially useful and promising high-frequency oscillator.
Scaling law for temporal dispersion of a short electron pulse across a diode in space-charge regime
Authors: Girardeau-Montaut C. , Girardeau-Montaut J. P. , Leboutet H.
Published: July 2002

The space-charge phenomenon in the diode of a photoinjector induces simultaneously temporal and spatial dispersions of the electrons burst in pulsed regime. They are higher when the initial pulse duration is shortened. Here, we present the results of temporal dispersion obtained by computer simulation and we give a simple scaling law accounting for it. This law can be used to compare durations of electron pulses at the cathode and anode in any well-defined operation set, in space-charge regime.
Anomalous transient diffusion of boron implanted into preamorphized Si during rapid thermal annealing
Authors: Kim Y. M. , Lo G. Q. , Kwong D. L. , Tseng H. H. , Hance R.
Published: July 2002

Diffusion of boron implanted into preamorphized silicon has been studied using secondary-ion mass spectroscopy and transmission electron microscopy. A surface preamorphized layer was created by double silicon ion implantation and the as-implanted boron profiles were confined completely within the preamorphized layer. Results show that boron diffusion during rapid thermal annealing (RTA) is anomalous in nature, and that the magnitude of the anomalous diffusion depends upon the RTA temperature. While RTA at 1150 °C shows an enhanced boron diffusion compared to that in single crystalline samples, a reduced diffusion is observed in preamorphized samples annealed at 1000 °C. Results are discussed in terms of the difference in the defect evolution during RTA.
Characterization of the KrF laser-induced plasma plume created above a BiSrCaCuO target
Authors: Girault C. , Damiani D. , Champeaux C. , Marchet P. , Mercurio J. P. , Aubreton J. , Catherinot A.
Published: July 2002

The laser-induced plasma plume created above a BiSrCaCuO superconducting target by a KrF laser beam (248 nm) is investigated by time-resolved spectroscopy. The influence of the oxygen partial pressure on the ejection velocities of the ablated species and on the relaxation of atomic and molecular excited species is particularly studied.
Superlattices of Y-Ba-Cu-O/Yy-Pr1−y-Ba-Cu-O grown by pulsed laser deposition
Authors: Wu X. D. , Xi X. X. , Li Q. , Inam A. , Dutta B. , DiDomenico L. , Weiss C. , Martinez J. A. , Wilkens B. J. , Schwarz S. A. , Barner J. B. , Chang C. C. , Nazar L. , Venkatesan T.
Published: July 2002

Superlattices of YBa2Cu3O7−x/YyPr1−yBa2Cu3O7−x(y=0.8 and 0.0) have been successfully grown in situ on MgO and LaAlO3 by using a multitarget pulsed laser deposition system. Satellite peaks have been observed in x-ray diffraction for the superlattices with modulation wavelengths from about few tens of angstroms to few hundred angstroms. The x-ray diffraction measurements also indicate that the multilayers have c axis normal to the substrates. Good crystallinity has been observed in the superlattices with He ion backscattering minimum yields of about 10%, indicating highly oriented growth. The presence of a periodic layer structure was further confirmed by the observation of composition oscillations in these structures by secondary-ion mass spectrometry.
Interdiffusion and strain relaxation in (SimGen)p superlattices
Authors: Baribeau J.-M. , Pascual R. , Saimoto S.
Published: July 2002

We report an x-ray diffraction study of interdiffusion and strain relaxation in (SimGen)p short-period superlattices. An interdiffusion coefficient Dλ was determined by monitoring, as a function of time, the decay upon annealing of the first order 000 satellite peak arising from the compositional modulation of the superlattice. Strain relaxation was obtained from the shift of the 400 superlattice peak on annealing. In the early stage of annealing the low angle satellite exhibited a rapid nonexponential decay after which a slower exponential decay was observed indicating a larger initial interdiffusion coefficient. This enhancement was correlated with the presence of strain and it disappeared upon relaxation. Diffusion was faster in structures alternating thin Si and thick Ge layers suggesting that migration of Si into Ge is the dominant diffusion process.
Submicron pattern etching of GaAs by in situ electron beam lithography using a pattern generator
Authors: Sugimoto Y. , Akita K. , Taneya M. , Hidaka H.
Published: July 2002

Pattern etching of GaAs at submicron size is carried out by in situ electron beam (EB) lithography using a computer-controlled pattern generator. GaAs oxide on the wafer surface is used as a resist film in EB-induced Cl2 etching. A 0.5 μm linewidth in a 1 μm pitch line-and-space pattern with flat top surface is obtained. Observations of the pattern edge with a scanning electron microscope show that the boundary between the etched area and the oxide mask area is abrupt and that the undulation of the pattern edge is less than about 30 nm.
Study of crystallographic orientations in the diamond film on cubic boron nitride using Raman microprobe
Authors: Yoshikawa M. , Ishida H. , Ishitani A. , Murakami T. , Koizumi S. , Inuzuka T.
Published: July 2002

We have measured Raman spectra of a diamond film prepared on the (111) surface of cubic boron nitride(c-BN) by the dc plasma chemical vapor deposition method. The polarization property of the Raman line of diamond agrees well with that of LO phonon for the (111) surface of c-BN. The agreement between the polarization property of Raman lines of diamond and c-BN indicates a possibility of the heteroepitaxial growth of the diamond film on the (111) surface of c-BN. It is found that the diamond layers on c-BN are under tensile stress of 2.2×1011 dyn/cm2. The value of the corresponding tensile strain agrees well with the lattice mismatch calculated from the lattice constants of c-BN and diamond, supporting the possibility of the heteroepitaxial growth of the diamond film. Raman spectroscopy is a powerful technique not only to estimate the stress in the diamond film but also to determine the crystallographic orientation.
p-type doping limit of carbon in organometallic vapor phase epitaxial growth of GaAs using carbon tetrachloride
Authors: Enquist P. M.
Published: July 2002

The doping limit of carbon in GaAs grown by organometallic vapor phase epitaxy (OMVPE) using carbon tetrachloride (CCl4) as a p-type dopant source has been investigated by variation of the V/III ratio, growth temperature, and CCl4 flow rate. Lower V/III ratios, lower growth temperatures, and higher CCl4 flow rates generally yielded higher hole concentrations. Hole concentrations as high as 1020 cm−3 were achieved. Attempts to achieve higher hole concentrations via higher CCl4 flow rates were limited by inhibition of growth and morphology degradation. Majority-carrier hole mobilities of carbon-doped GaAs were more than 50% greater than that of zinc-doped GaAs for comparable hole concentrations obtained in previous work. Nonalloyed contacts to this material resulted in contact resistivities of 4×10−7 Ω cm2.
Surface reconstructions of Si(001) observed using reflection-high- energy-electron diffraction during molecular-beam epitaxial growth from disilane
Authors: Mokler S. M. , Liu W. K. , Ohtani N. , Joyce B. A.
Published: July 2002

The growth of Si(001) from a gas source molecular-beam epitaxy system (Si-GSMBE) using disilane (Si2H6) was investigated. The surface reconstructions occurring between 100–775 °C were studied as a function of both substrate temperature and surface coverage. Further, we report the first observation of (2×2) and c(4×4) reconstructions during growth at substrate temperatures near 645 °C using Si2H6. All growth was found to be initiated by the formation of 3D islands which coalesce at substrate temperatures above 600 °C, following which, growth proceeds in a two-dimensional (2D) fashion. The Si surface was found to have undergone a series of reconstructions which were related to the number of hydrogen adatoms and Si dimers covering the surface.
Residual oxygen levels in AlGaAs/GaAs quantum-well laser structures: Effects of Si and Be doping and substrate misorientation
Authors: Chand Naresh , Jordan A. S. , Chu S. N. G. , Geva M.
Published: July 2002

Oxygen forms nonradiative recombination centers in GaAs and AlGaAs, and is a common contaminant in AlGaAs, irrespective of the growth technique. We find that O tends to accumulate near the GaAs active region of an AlGaAs/GaAs quantum-well laser prepared by molecular beam epitaxy. Moreover, the Be-doped Al0.6Ga0.4As cladding layer has a higher O content than its Si-doped counterpart. We present evidence that Si-doping suppresses, and Be doping favors incorporation of O in AlGaAs. In undoped and Si-doped AlGaAs, the incorporation of O is further reduced by tilting the (100) GaAs substrates towards 〈111〉A. We propose that Be forms stable Be-O complexes in AlGaAs, and thus, there is virtually no desorption of incorporated O. But in Si-doped AlGaAs, O content is reduced due to reaction between group III suboxides and Si, resulting in the formation and desorption of volatile SiO (g). The study suggests that Be doping should be avoided in the p-side of the GRIN region of a laser structure.
Visible photoluminescence of Ge microcrystals embedded in SiO2 glassy matrices
Authors: Maeda Yoshihito , Tsukamoto Nobuo , Yazawa Yoshiaki , Kanemitsu Yoshihiko , Masumoto Yasuaki
Published: July 2002

Ge microcrystals embedded in SiO2 glassy matrices were formed by a radio-frequency magnetron cosputtering technique and then annealed at 800 °C for 30 min. The average radius of the Ge microcrystals in SiO2 was determined to be about 3 nm by means of Raman spectroscopy and high resolution electron microscope. The annealed sample showed a strong room temperature luminescence with a peak at 2.18 eV. This is consistent with quantum confinement of electrons and holes.
Room-temperature CO2 laser radiation detector
Authors: Srinivas T. A. S. , Timans P. J. , Butcher R. J. , Ahmed H.
Published: July 2002

A novel microthermopile for CO2 laser radiation detection with a fast response time has been fabricated for the first time. The microthermopile is fabricated by high-resolution e-beam lithography and isotropic plasma etching of the substrate resulting in free-standing hot junctions which are thermally isolated from the substrate. The good thermal isolation and small heat capacity of the hot junctions resulted in a responsivity of 60 V/W and a time constant of 20 μs. The device operates over the entire CO2 laser wavelength range from 9.4 to 10.6 μm. Detailed measurements are presented for 10.6 μm operation.
Observation of a two-dimensional electron gas in low pressure metalorganic chemical vapor deposited GaN-AlxGa1−xN heterojunctions
Authors: Khan M. Asif , Kuznia J. N. , Van Hove J. M. , Pan N. , Carter J.
Published: July 2002

We have confirmed the presence of a two-dimensional electron gas (2DEG) in a wide band-gap GaN-AlxGa1−xN heterojunction by observing steplike features in the quantum Hall effect. The 2DEG mobility for a GaN-Al0.13Ga0.87N heterojunction was measured to be 834 cm2/V s at room temperature. It monotonically increased and saturated at a value of 2626 cm2/V s at 77 K. The 2DEG mobility remained nearly constant for temperatures ranging from 77 to 4.2 K. Using Shubnikov–de Haas (SdH) measurements the two-dimensional carrier concentration was estimated to be 1×1011 cm−2. The peak mobility for the 2DEG was found to decrease with the heterojunction aluminum compositions in excess of 13%.
In situ energy dispersive x-ray reflectivity measurements of H ion bombardment on SiO2/Si and Si
Authors: Chason E. , Mayer T. M. , Payne A. , Wu D.
Published: July 2002

We have performed in situ, energy-dispersive x-ray reflectivity measurements of damage layer formation and surface roughness of thin films of SiO2 on Si and clean Si during H ion bombardment. The reflectivity was analyzed using an optical multilayer model where the variable parameters are the number of layers, the thickness and density of the layers, and the surface roughness. Room temperature ion bombardment at doses <5×1017/cm2 results in a buried layer between the oxide and the substrate; 300 eV bombardment produces a very thin, low-density layer, while 1000 eV bombardment produces a thicker layer with the density of amorphous silicon. A damaged layer is not produced by equivalent bombardment at high temperature. Ion bombardment of clean Si surfaces at 500 °C resulted in roughening of the surface on the nanometer scale which is strongly dependent on the ion energy.
Detection of weak link effects in superconducting YBa2Cu3O7−y epitaxial thin films by magnetically modulated resistance
Authors: Kim B. F. , Moorjani K. , Adrian F. J. , Bohandy J.
Published: July 2002

Evidence of weak link effects in epitaxial thin films of YBa2Cu3O7−y with well-aligned grains is obtained from magnetically modulated resistance measurements. These results are of interest because weak links could provide a mechanism for the residual microwave loss in these types of superconductor thin films which contain predominantly low angle grain boundaries.
Shaping of wide bandwidth 20 femtosecond optical pulses
Authors: Reitze D. H. , Weiner A. M. , Leaird D. E.
Published: July 2002

We investigate the propagation of 20 fs pulses through a generalized pulse shaper/compressor and synthesize shaped waveforms with 20 fs features by linear spectral filtering using a generalized pulse shaper consisting of gratings and reflective optics. The use of reflective optics in the pulse shaper avoids cubic phase dispersion associated with lenses which significantly broaden short 20 fs pulses. As an example of our pulse-shaping capabilities, we generate pulse trains with repetition rates in excess of 12 THz using phase-only filtering.
Direct experimental observation of interactive third and fifth order nonlinearities in a time- and space-resolved four-wave mixing experiment
Authors: Wu Song , Zhang X.-C. , Fork R. L.
Published: July 2002

We have used the mechanism of Kerr lens deflection to spatially separate third and fifth order polarizations in the momentum degenerate 2k2−k1 direction for a time-resolved two pulse four-wave mixing experiment. In the far field spatially asymmetrical signals provide direct evidence of destructive interference between third and fifth order nonlinear processes. The experimental results also indicate a carrier density greater than 1016/cm3 is necessary to demonstrate exciton-exciton interaction at room temperature in GaAs bulk materials.
Diamondlike metastable carbon phases from shock-compressed C60 films
Authors: Yoo C. S. , Nellis W. J. , Sattler M. L. , Musket R. G.
Published: July 2002

Thin films of C60, 2.5-μm, have been shocked isentropically to 69 GPa, about 2200 K, and thermally quenched at rates up to 1011 K/s. The recovered specimen is transparent with a crystallographic habit, or ‘‘tilelike’’ structure, but it slowly transforms to a black highly disordered carbon at the ambient condition. The selected area electron diffraction patterns suggest that the transparent carbon phase contains an amorphous cubic diamond and n-diamond crystallites sized 50–350 Å in diameter.
Nanosecond transient electroluminescence from polymer light-emitting diodes
Authors: Braun D. , Moses D. , Zhang C. , Heeger A. J.
Published: July 2002

The transient electroluminescence from polymer light-emitting diodes is reported. When the devices are mounted on a microstrip transmission line, the temporal response is limited by the electrode geometry, with rise and fall times below 50 ns. With low duty-cycle pulses (0.5%) the electroluminescence intensity remains proportional to the current at values up to 10 A/cm2, two orders of magnitude greater than possible under direct current operation. Since the spectral blue-shift observed at high current levels (with power dissipation above 1 W/cm2) indicates significant sample heating, still higher levels should be possible with proper thermal management.
Synthesis and electrical characterization of boron-doped thin diamond films
Authors: Masood A. , Aslam M. , Tamor M. A , Potter T. J.
Published: July 2002

Patterned semiconducting polycrystalline diamond films have been synthesized by hot-filament CVD using in situ doping by pure boron powder. P-type conduction was confirmed by both Hall and Seebeck effects. The quality of deposited films, as determined by SEM and Raman spectroscopy, was unaffected by the doping. The resistivity and Hall mobility measured by the Van der Pauw method were in the range of 20–100 Ω cm and 2–32 cm2 V−1 s−1, respectively. The dopant activation energies, as computed from the resistivity versus temperature curves (up to 300 °C), were in the range of 0.38–0.30 eV corresponding to Hall concentration in the range of 9×1015–2×1017 cm−3 and boron concentration in the range of 1017–1021 cm−3. The estimated impurity concentration is consistent with SIMS results.
Growth of diamond films: General correlation between film morphology and plasma emission spectra
Authors: Balestrino G. , Marinelli M. , Milani E. , Paoletti A. , Pinter I. , Tebano A. , Paroli P.
Published: July 2002

We have studied the emission spectra from plasmas excited in several compositions of three different gas mixtures useful for the growth of diamond films, namely CH4-H2 (the classical one), CH4-CO2 and C2H2-CO2 (not previously reported by other authors). In all three cases we find the same correlation between the quality of the obtained diamond films and some spectral features: in particular, the yield of the best diamond films corresponds to the presence of the emission line at wavelength 431 nm ascribed to CH, in the absence of the emission band at 505–517 nm attributed to C2. The appearance and the progressive increase of the latter corresponds to a gradual worsening of the diamond film quality. We propose such spectral features of the plasma as a general and practical gauge of the diamond film growth conditions, for any gas mixture used.
Electron velocity distribution function in a gas in E×B fields
Authors: Shimura Naohiko , Makabe Toshiaki
Published: July 2002

We have investigated the velocity distribution function of electrons in uniform E×B fields by direct numerical analysis of the Boltzmann equation by using the finite element method. The influence of E×B fields on the distribution has been exhibited under the detailed consideration of collisions between electrons and Ar atoms in terms of the three-dimensional velocity distribution. In particular, the anisotropy of the distribution in the E×B direction is discussed in terms of swarm parameters. The onset behavior of electron trapping has been investigated as a function of B in a collision dominated swarm.
Weak link behavior of grain boundaries in Nd-, Bi-, and Tl-based cuprate superconductors
Authors: Kawasaki M. , Sarnelli E. , Chaudhari P. , Gupta A. , Kussmaul A. , Lacey J. , Lee W.
Published: July 2002

We have studied single-grain-boundary junctions in the neodymium-, bismuth-, and thallium-based cuprate superconductors and find that they behave as weak links, qualitatively similar to the YBa2Cu3O7−δ superconductor. In general, the grain boundary critical current is determined by flux flow for small misorientation angles and by Josephson junctionlike coupling for large angles. The latter is verified by the observation of voltage oscillations with an external magnetic field in superconducting quantum interference devices built using single-grain-boundary junctions of these materials. The commonality of behavior of grain boundaries in all of the high temperature cuprate superconductors suggests that the weak link is most likely associated with the structure of the grain boundary and the evidence points increasingly to dislocations, which describe the topology of the boundary.
Visible photoluminescence from nanocrystalline Ge formed by H2 reduction of Si0.6Ge0.4O2
Authors: Paine D. C. , Caragianis C. , Kim T. Y. , Shigesato Y. , Ishahara T.
Published: July 2002

Samples of nanocrystalline Ge embedded in SiO2 that display visible photoluminescence were synthesized from chemical vapor deposition-grown Si0.6Ge0.4 in a two step process of hydrothermal oxidation using steam at 25 MPa and 475 °C followed by annealing at 750 °C in flowing forming gas (80/20:N2/H2). A broad photoluminescence band, peaked at 2.14 eV (580 nm) with a full width at half maximum of 0.3 eV, was observed in samples that were annealed at 750 °C in flowing forming gas for 10, 30, and 60 min. As-oxidized (i.e., unprecipitated) samples show no photoluminescence peak when excited under identical conditions.
New dielectric material for low temperature thermometry in high magnetic fields
Authors: Maior M. M. , Molnar S. B. , Vysochanskii Yu. M. , Gurzan M. I. , van Loosdrecht P. H. M. , van der Linden P. J. E. M. , van Kempen H.
Published: July 2002

Dielectric experiments on the incommensurate solid solution (Pb0.45Sn0.55)2P2Se6 for T=1.2–200 K reveal a strong temperature dependence of the real part of the dielectric constant for T<45 K. The relative dielectric sensitivity d ln(ε′)/dT≊2–8 K−1 is found to be 2–3 times higher in comparison to widely used glass-ceramic temperature sensors. Moreover, the dielectric constant has a very good time stability and is insensitive to magnetic fields up to 20 T (dT/dB<10−4 K/T). These characteristics make this material a very promising candidate for applications in capacitive temperature sensors for low temperature thermometry in high magnetic fields.
Ge epilayer of high quality on a Si substrate by solid-phase epitaxy
Authors: Liu W. S. , Chen J. S. , Lie D. Y. C. , Nicolet M.-A.
Published: July 2002

An epitaxial Ge layer is grown by solid-phase epitaxy on an underlying Ge0.82Si0.18 seeding layer with a Ge-SiO2 matrix positioned between them. To this end, a (100)Si substrate with a Ge0.82Si0.18 epilayer is first oxidized in a wet ambient at 700 °C for 30 min to transform an upper fraction of the epilayer to amorphous Ge0.82Si0.18O2. A second annealing step (700 °C/16 h) in a 95% N2+5% H2 ambient (forming gas) reduces the GeO2 to Ge which grows epitaxially by solid-phase reaction on the remaining Ge0.82Si0.18 layer. A self-induced intermediate layer of epitaxial Ge with SiO2 inclusions restricts the propagation of dislocations, resulting in a crystalline perfection of the overlying Ge epilayer superior to that of the Ge0.82Si0.18 template.
Enhanced magneto-optic Kerr rotation in epitaxial PtFe(001) and PtCo(001) thin films
Authors: Lairson B. M. , Clemens B. M.
Published: July 2002

We observe changes in the magneto-optic Kerr rotations of Pt-Fe and Pt-Co alloys associated with the formation of the uniaxial CuAu(I) crystal structure. In particular, we report the observation of up to 60% enhancement at 2.0 eV in the magneto-optic Kerr rotation for the ordered, epitaxial PtFe intermetallic alloy over that of the random equiatomic face-centered-cubic alloy. This enhancement is wavelength dependent, with a peak in the visible at 2.0 eV. A similar enhancement, but of smaller magnitude, is observed for unoriented CuAu(I) PtFe0.5Co0.5.
Use of a three-layer quantum-well structure to achieve an absorption edge blueshift
Authors: Stavrinou P. N. , Haywood S. K. , Parry G.
Published: July 2002

Theoretical calculations are used to propose a novel structure for a quantum-well electro-optic device which gives a large blueshift of the absorption edge on application of an electric field. The structure provides spatial separation of the electron-hole pair in the ground state at zero applied field. This is achieved by use of two materials within the well which have a type II band line-up relative to each other but are type I relative to the barrier material. The combination of InAs0.4P0.6/In0.53Ga0.47As wells with InP barriers is expected to fulfill these requirements and also to operate in the 1.5 μm region.
Gas and adsorbate excitation pathways in synchrotron radiation excited Si growth using disilane
Authors: Akazawa H. , Nagase M. , Utsumi Y.
Published: July 2002

We studied reaction kinetics in synchrotron radiation excited chemical vapor deposition of Si using disilane. It was found that the growth rate depends on temperature in the irradiated region but not in the nonirradiated region. Growth in the irradiated region occurs as a result of photolysis of disilane molecules weakly trapped on the surface followed by the formation of a hydrogenated Si network. On the other hand, in the nonirradiated region, growth occurs as a result of layer-by-layer sticking and the elimination of surface hydrogen by a fragment species generated by photolysis of gas-phase disilane. The reaction model is consistent with properties of the grown Si film.
Enhancement of persistent currents in Bi2Sr2CaCu2O8 tapes with splayed columnar defects induced with 0.8 GeV protons
Authors: Krusin-Elbaum L. , Thompson J. R. , Wheeler R. , Marwick A. D. , Li C. , Patel S. , Shaw D. T. , Lisowski P. , Ullmann J.
Published: July 2002

Composite tapes of the superconductor Bi2Sr2CaCu2O8 on silver were irradiated with energetic light ions (0.8 GeV protons), creating extended splayed tracks ∼7 nm in diameter via fission of Bi nuclei. Magnetic hysteresis indicates large enhancements of persistent currents J, especially at high fields and temperatures, and substantial expansion of the irreversible regime. The technique may be suitable for large scale applications due to the long range (∼half meter) of fast protons.
Fast and slow visible luminescence bands of oxidized porous Si
Authors: Kovalev D. I. , Yaroshetzkii I. D. , Muschik T. , Petrova-Koch V. , Koch F.
Published: July 2002

The visible luminescence of porous Si is known to contain at least two spectrally distinct emission bands with widely different response times. The orange-red luminescence component (1.5–1.9 eV) decays in times being of the order of 10 μs at room temperature. The blue-green band (2.3–2.6 eV) is very much faster with response time in the 10-ns range. It is shown that with increasing degree of oxidation the fraction of the fast luminescence intensity rises from ∼1% of the total in the as-prepared porous Si to become the dominant spectral component in strongly oxidized material. For the rapid-thermal-oxidized material excited with 337-nm radiation, the intensity of the fast luminescence is comparable to that in the as-prepared state.
Mg doping of GaInP grown by chemical beam epitaxy using bis-cyclopentadienyl magnesium
Authors: Courmont S. , Maurel Ph. , Grattepain C. , Garcia J. Ch.
Published: July 2002

We have investigated the p-type doping of GaInP grown by chemical beam epitaxy using bis-cyclopentadienyl magnesium (Cp2Mg). Hole concentrations up to the 1018 cm−3 level have been achieved for substrate temperature as high as 550 °C and Mg incorporation was found to grow linearly with the Cp2Mg flow rate in this range. The doping concentration decreases as the substrate temperature increases with an activation energy of 2.15 eV (50 kcal/mol). Two other parameters are the V/III ratio and the growth rate which both enhance the Mg doping when increased.
Dimensionality of flux pinning in (Bi,Pb)2Sr2Ca2Cu3O10+δ Ag tapes with columnar defects—Crossover from two-dimensional to three-dimensional behavior
Authors: Kummeth P. , Struller C. , Neumüller H.-W. , Saemann-Ischenko G.
Published: July 2002

We introduced columnar defects into (Bi,Pb)2Sr2Ca2Cu3O10+δ Ag tapes by irradiation with 2.65 GeV 197Au ions to investigate the dimensionality of pinning for this compound. Samples were irradiated up to fluences of 3.5×1011 ions/cm2 at a temperature of 100 K. The ion beam was directed both perpendicular and under a tilt angle of −60° to the tape surface. Our samples showed homogeneous columnar line defects throughout the whole thickness of the superconducting core. As a novel result we found evidence for marked deviations from two-dimensional behavior at elevated temperatures both in magnetic and in transport measurements.
Stochastic Coulomb blockade in a double quantum dot
Authors: Kemerink M. , Molenkamp L. W.
Published: July 2002

The series resistance of two coupled quantum dots in a (Al,Ga)As heterostructure has been studied experimentally. At very low lattice temperatures conductance oscillations of irregular amplitude and spacing are observed. The irregularities decrease on raising the temperature. The observations are interpreted as resulting from the stochastic Coulomb blockade effect.
Determination of the sub-band energy in the V-shaped potential well of δ -doped GaAs by deep level transient spectroscopy
Authors: Zhu Q. S. , Zhong Z. T. , Lu L. W. , Li C. F.
Published: July 2002

Using deep level transient spectroscopy (DLTS) the conduction-subband energy levels in a V-shaped potential well induced by Si-δ doping in GaAs were determined. Self-consistent calculation gives four subbands in the well below the Fermi level. Experimentally, two DLTS peaks due to electron emission from these subbands were observed. Another two subbands with low electron concentration are believed to be merged into the adjacent DLTS peak. A good agreement between self-consistent calculation and experiment was obtained.
Development of twisted high-temperature superconductor composite conductors
Authors: Christopherson C. J. , Riley G. N.
Published: July 2002

Multifilamentary high-temperature superconductor (HTS) composite conductors have been developed for alternating current (ac) applications. A twisted HTS conductor containing the Bi-2223 phase fabricated using a modified powder-in-tube technique is reported. Transport critical current densities of 13 800 and 10 900 A/cm 2 (77 K, self-field, 1 μV/cm) have been achieved for twisted tape and wire conductors with twist pitches of 3.7 and 3.6 mm, respectively. These conductors are strongly linked and are thus suitable for use in ac applications.
Effects of chemical composition on the electrical properties of NO-nitrided SiO2
Authors: Bhat M. , Han L. K. , Wristers D. , Yan J. , Kwong D. L. , Fulford J.
Published: July 2002

The impact of nitrogen (N) concentration and distribution on the electrical and reliability properties of rapid-thermally NO-annealed oxides is studied. The use of NO-annealing of thermally grown SiO2 provides an excellent way to isolate the effects of N, since this method allows for the incorporation of varying N profiles in the oxide without a simultaneous increase in dielectric thickness. Results show that the electrical properties of the dielectric under gate and substrate Fowler–Nordheim injection are highly sensitive to the N profile in the dielectric. While interface endurance (ΔDit) is seen to improve monotonically with increasing N concentrations for both +Vg and −Vg, the same is not observed for charge-to-breakdown (QBD) properties. It is found that although QBD improves with NO nitridation under +Vg, it shows a turnaround behavior under −Vg, i.e., for a 10-s NO-annealed oxide the QBD value is improved over control oxide while further nitridation is seen to degrade QBD under −Vg. The presence of bulk N and the nonuniform N distribution in the dielectric is responsible for this behavior.
Study of amorphous germanium-nitrogen alloys through x-ray photoelectron and Auger electron spectroscopies
Authors: Zanatta A. R. , Landers R. , de Castro S. G. C. , Kleiman G. G. , Chambouleyron I. , Grilli M. L.
Published: July 2002

In this work, experimentally determined values of electron spectroscopic shifts induced by nitrogen in Ge core levels of substoichiometric amorphous germanium-nitrogen (a-GeN) alloys are discussed and presented. X-ray photoelectron spectroscopy (XPS) and x-ray excited Auger electron spectroscopy (XAES) are employed to study the behavior of the Ge 3d and LMM spectra, respectively, and combined the corresponding XPS and Auger core levels shifts to determine Δα′, the modified Auger parameter shift, which is exempt from problems inherent in the interpretation of XPS and XAES shifts. It is demonstrated how one can use Δα′ to reliably estimate ΔnGe, the change in Ge valence charge in the alloys, and how one can calibrate XPS shifts of Si and Ge based alloys in terms of approximate values of ΔnGe.
Optical diagnostics of laser-produced plasmas at UCLA (invited)
Authors: Clayton Christopher E.
Published: July 2002

This paper reviews some of the optical diagnostics employed in probing laser-produced plasmas, in conjunction with laser-plasma interaction experiments at UCLA. Experimental apparatus, techniques, and some results will be presented for the following diagnostics: (1) Collective Thomson scattering, for analyzing the space and time dependence of nonthermal (driven) waves in plasmas. Here, cylindrical focusing allows us to illuminate and thus image an interaction region of approximately 1 cm in length. This 1D image is then time resolved using either a streak camera or image dissection techniques. (2) Dark-field photography, for quantitatively probing small-scale plasmas or for probing small-scale perturbations within larger plasmas. Here, the plasma produces a phase perturbation on the probing beam’s wave front. Measurement of the exposure level on the recording film gives a measurement of the magnitude of the phase perturbation (squared) and thus of the line integrated plasma density; and (3) CO2 wavelength interferometry, for obtaining useful interferograms of plasmas of small density-length products.
Power and mode diagnostics for high-power microwave sources with over-moded output (abstract)
Authors: Bartsch R. R. , Davis H. A. , Kribel R. E.
Published: July 2002

A microwave calorimeter has been developed in the course of our work on virtual-cathode-oscillator microwave generators which may have application to gyrotrons used for plasma heating. The absorbing element uses a novel conductor array which provides a means of temperature-rise detection. Provision has been made to observe the spatial pattern of the microwave energy deposition with an infrared imaging system. The infrared image provides output mode information and a noncontacting measure of the total energy in the microwave pulse. The microwave absorption of the calorimeter has been evaluated from 8 to 40 GHz with broadband TM01 mode launchers. Mode selective directional couplers are also being developed to provide an independent measure of the mode number for the transverse magnetic (TM0n) modes which are generated by the virtual-cathode oscillator. This technique can also be utilized to discriminate other higher-order modes.1 This work was supported by the U. S. Department of Energy.
Study of impurity radiation on the PLT and TFTR tokamaks with high-resolution, time-resolving spectrometers
Authors: Wouters A. W. , Schwob J. L. , Suckewer S. , Boody F. P. , Hulse R. , Schivell J.
Published: July 2002

Soft-x-ray (5–300 Å) spectra of intrinsic impurities have been recorded with a high-resolution multichannel XUV spectrometer (SOXMOS). Measurements of line intensity ratios as a function of time are applied to the determination of the impurity contribution to the energy balance. Results from TFTR Ohmic heated plasmas, including radiation due to carbon, oxygen, iron, nickel, chromium, titanium, and zirconium, are presented. The spatial ion distribution will be directly observed by a radial scanning spectrometer (FLOPSY). This instrument, under construction, will cover the spectral range from 1500 to 7000 Å and use mirrors and lenses for fast scanning. The spatial ion distribution, deduced from forbidden and allowed lines, will be compared to both theoretical models based on impurity concentrations and transport coefficients, as well as experimental data from bolometer measurements.
Evaluation of a photon-counting detector for Doppler ion temperature measurements (abstract)
Authors: Benjamin R. D. , Nudelfuden A. , Terry J. L. , Moos H. W.
Published: July 2002

A photon-counting detector for determination of the ion temperature in magnetically confined plasmas has been developed.1 The detector is based around an image intensifier tube which is fiber optically coupled to a self-scanning linear photodiode array. The image intensifier incorporates three high strip current (∼280 μA) microchannel plates in a ‘‘Z’’ configuration. Frame times of 10 μs are possible through the use of pixel selection, resulting in a time resolution on the order of 5 ms. The detector system will be mounted on a 1-M Ebert–Fastie spectrometer and used to study the Alcator C plasma. Laboratory evaluation of the detector and associated electronics has been completed. The results of this evaluation, and progress toward integration of the detector and spectrometer systems, will be presented. This work, and additional information, will be published in greater detail in the near future.
Two-detector ellipsometer
Authors: Azzam R. M. A.
Published: July 2002

An ellipsometer with two photodetectors and no other optical elements is described. In general, each detector has a partially specularly obliquely reflecting surface and generates an electrical signal proportional to the fraction of radiation it absorbs. It is not essential (but desirable) that the two detectors absorb all of the incident radiation. The output signals of the two detectors, with parallel or nonparallel surfaces, are enough to determine the degree of linear polarization P of incident light with respect to one set of transverse orthogonal axes. If the assembly of two parallel detectors is rotated around the light beam by an angle (of 45°), a new degree of linear polarization P′ is measured. From P and P′ the (generally elliptic) polarization state of incident totally polarized light can be completely determined, except for handedness. A calibration procedure for this two-detector ellipsometer (TDE) is given.
Planar reactor plasma etching with barrel reactor power supply
Authors: Setzer C. S. , Mattauch R. J.
Published: July 2002

A very simple and inexpensive method of converting a barrel plasma etching system into a planar system is described. Details of structure and operating characteristics of the planar reaction chamber are shown.
Simple nanosecond capacitive voltage divider
Authors: Wong C. S.
Published: July 2002

The construction of a simple and inexpensive capacitive voltage probe by using coaxial cable is described. The probe has been tested to a frequency response of better than 30 MHz for sinusoidal voltage input and a rise time of <20 ns for single-pulse input. The probe is ideal for applications in small experiments involving low-energy and high-voltage capacitor discharge of nanosecond rise time.
Time-integrated x-ray measurements of the very energetic electron end loss profile in TMX-U
Authors: Osher J. E. , Fabyan J.
Published: July 2002

The time-integrated 2D profile of the thick-target bremsstrahlung produced by energetic end loss electrons has been measured during electron cyclotron resonance heating (ECRH) operation of TMX-U. Sheets of x-ray film and/or arrays of thermoluminescent dosimeters were placed on the outside of the end tank end wall to measure the relative spatial x-ray profile, with locally added filters of Pb to determine the effective mean x-ray energy. The purpose of this simple survey diagnostic was to allow deduction of the gross features of the ECRH region. The electron source functions needed to fit the x-ray data were modeled for various anchor cell radial distributions mapped along magnetic field lines to the elliptical plasma potential control plates or the Al end walls. The data are generally consistent with (1) major ECR heating in the central 25-cm-diameter core, (2) a mean ECRH electron-loss energy of 420 keV, and (3) and ECRH coupling efficiency to these hot electrons of ≥10%.