bluuebunny/crossref_metadata_2025 huggingface dataset:
The magnetic and transport properties of high-critical-current Tl2Ba2Ca2Cu3Ox superconducting thin films
Authors: Chu M. L. , Chang H. L. , Wang C. , Juang J. Y. , Uen T. M. , Gou Y. S.
Published: July 2002

Highly c-axis-oriented Tl2Ba2Ca2Cu3Ox superconducting thin films with the critical current density as high as 1×107 A/cm2 at 87 K were obtained by single-target dc sputtering on LaAlO3(100) substrates followed by encapsulated compensate annealing. The strong linear temperature dependence of zero-field critical current at low temperatures suggests a creep-dominated behavior. Preliminary field dependence studies on the critical current density in low-field regime (<2 kOe) shows no evidence of hysteresis commonly encountered in films with higher granularity. The scaling behavior of the global pinning force density exhibits strong resemblance to conventional type-II superconductors with the pinning force density of the same order of magnitude as that in strong pinned NbN thin films.
High-T
C superconductor-normal metal-superconductor Josephson microbridges with high-resistance normal metal links
Authors: Ono R. H. , Beall J. A. , Cromar M. W. , Harvey T. E. , Johansson M. E. , Reintsema C. D. , Rudman D. A.
Published: July 2002

We have developed an in situ process for fabricating high transition temperature superconductor-normal metal-superconductor microbridges using a step edge to define the normal metal length. Critical current-normal resistance products over 1 mV have been measured at low temperature in devices with high-resistivity Ag-Au alloy bridges. Results on samples with Ag bridges are compared with the alloy data as an initial test of recent theories of SNS Josephson junctions. Josephson effects have been demonstrated in these devices at temperatures higher than 80 K. Clearly defined rf steps have been observed, with power dependence qualitatively similar to theoretical predictions.
Four-dimensional simulation of ultrashort optical shock radiation generated by guided-wave frequency doubling of a pulsed laser diode
Authors: Hayata K. , Koshiba M.
Published: July 2002

Using a guided-wave nonlinear-pulse simulator, we implement a spatiotemporal-domain calculation of the short-wavelength Cerenkov-shock radiation generated by frequency doubling of an ultrashort light pulse from a laser diode. Computed results for picosecond and subpicosecond blue pulse generations through the frequency doubling in a proton-exchanged MgO:LiNbO3 channel waveguide are shown. Effects due to polarization, temporal walk-off, and pump depletion are predicted.
Surface resistance of epitaxial YBa2Cu3O7 thin films on CeO2 diffusion barriers on sapphire
Authors: Merchant P. , Jacowitz R. D. , Tibbs K. , Taber R. C. , Laderman S. S.
Published: July 2002

Epitaxial thin films of YBa2Cu3O7 (YBCO) have been deposited by off-axis sputtering onto substrates of r-plane sapphire coated with a CeO2 diffusion barrier which had been previously deposited by metalorganic chemical vapor deposition process. The YBCO films display excellent superconducting properties, with critical current densities and microwave surface resistances comparable to state of the art YBCO films deposited directly onto LaAlO3 or MgO substrates. The volume fraction of YBCO with large-angle in-plane misalignment relative to the underlying layers is comparable to, or smaller than that obtained for YBCO directly deposited onto MgO substrates.
Improvement of peak-to-valley ratio by the incorporation of the InAs layer into the GaSb/AlSb/GaSb/AlSb/InAs double barrier resonant interband tunneling structure
Authors: Houng M. P. , Wang Y. H. , Shen C. L. , Chen J. F. , Cho A. Y.
Published: July 2002

InAs blocking layer is incorporated into the GaSb/AlSb/GaSb/AlSb/InAs double barrier resonant interband tunneling structure to improve the peak-to-valley ratios. It is found the ratio rises to 21 at room temperature and the peak current density keeps nearly constant for InAs layer reaches 30 A and then both of them decreases with the increase of InAs thickness. However, while the InAs blocking layer further increases to 240 A, the I-V characteristic shows multiple negative differential resistance behavior. These interesting phenomena can be modeled to be due to the coupling effect of InAs blocking layer and GaSb well layer.
Activity and diffusivity of oxygen in a liquid Yb1Ba2Cu3 high temperature superconducting precursor alloy
Authors: Chou H. , Chen H. S. , Fang W. C. , Thiel F. A. , Wu M. K.
Published: July 2002

The activity and diffusivity of oxygen in a liquid Yb1Ba2Cu3 high temperature superconducting precursor alloy have been measured by modified coulometric titration method in a temperature range from 913 to 957 °C. The standard Gibbs formation energies and the diffusivity of oxygen in liquid Yb1Ba2Cu3 for 1/2O2 (1 atm)→O (1 at. %) are determined to be ΔG=−655.20+0.335T(K) (±1.5) kJ/mol and D=1.8×10−2 exp(−48 100/RT) (cm2/s) where R=8.314 J/deg×mol. Despite very strong bonding of oxygen to the liquid alloys, the diffusion coefficient of oxygen is relatively high in the order of 10−4 cm2/s. The solubility of oxygen in the liquid alloy is low, of about 0.0145 and 0.017 at. % at 913 and 935 °C, respectively.
DX centers in Sn-doped AlxGa1−xAs grown by metalorganic vapor phase epitaxy at T≥850 °C
Authors: Mooney P. M. , Parker B. D. , Cardone F. , Gibart P. , Portal J. C.
Published: July 2002

It was recently inferred from low-temperature transport measurements that DX centers are not formed in Sn-doped AlGaAs grown by metalorganic vapor phase epitaxy at T≥850 °C. Deep level transient spectroscopy measurements reported here show that DX centers are present in this material. The high conductivity measured at low temperature comes from parallel conduction in the underlying GaAs due to Sn diffusion during growth at high temperature.
Near-field differential scanning optical microscope with atomic force regulation
Authors: Toledo-Crow R. , Yang P. C. , Chen Y. , Vaez-Iravani M.
Published: July 2002

We present the design and describe the operation of a scanning probe microscope which simultaneously provides the attractive mode force and near-field optical images of objects. In this technique, the force signal is used to track the topography, thus allowing the optical signal primarily to show variations in transmissivity. A number of results are presented on the application of the technique to imaging different samples.
Growth of carbon-doped p-type InxGa1−xAs (0<x≤0.53) by metalorganic chemical vapor deposition
Authors: Stockman S. A. , Hanson A. W. , Stillman G. E.
Published: July 2002

Carbon doping of InxGa1−xAs grown on GaAs and InP substrates by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) using CCl4 has been investigated for In mole fractions as high as x=0.53. P-type conduction was obtained over the entire composition range studied, with hole concentrations above 1×1020 cm−3 for x<0.12, and as high as 1×1019 cm−3 for In0.53Ga0.47As lattice-matched to InP. These high carbon concentrations were achieved by employing very low V/III ratios and low growth temperatures. The alloy composition was found to be dependent on several growth parameters, including CCl4 partial pressure, V/III ratio, and growth temperature. This may be due to surface reactions (etching) involving chlorine-containing compounds during growth. Samples grown at low temperature (∼500 °C) and lattice matched to InP exhibited an increase in hole concentration upon post-growth annealing.
Uniform β-SiC thin-film growth on Si by low pressure rapid thermal chemical vapor deposition
Authors: Steckl A. J. , Li J. P.
Published: July 2002

β-SiC thin films have been grown on Si by rapid thermal chemical deposition at reduced pressures (LP-RTCVD) as low as 5 Torr. The growth process involved the carbonization of the (100)Si surface by reaction with propane. Reducing the pressure resulted in a monotonic increase in growth rate. At a reaction temperature of 1300 °C, using 100 sccm of C3H8 (diluted to 5% in H2) and 0.9 lpm H2 carrier gas yielded a growth rate of 0.45 Å/s at 760 Torr and 18 Å/s at 5 Torr. A substantial increase in film thickness uniformity was observed at low pressure. At 5 Torr, the average thickness and standard deviation measured over the area of a 7.5 cm diam wafer were 1602 and 46 Å, respectively. This low standard deviation for LP-RTCVD, equivalent to 2.87% of the average thickness, is the result of uniform growth over the entire specimen, including the edge region. In contrast, atmospheric pressure RTCVD results in severely nonuniform growth in the vicinity of the wafer edge.
Enhancement of sp3/sp2 ratio in plasma deposited amorphous hydrogenated carbon films by the addition of ammonia
Authors: Seth Jayshree , Ward Anthony J. I. , Babu S. V.
Published: July 2002

Ammonia (NH3) and nitrogen (N2) were added to the hydrocarbon precursor 1,3 butadiene (C4H6) during rf plasma deposition of hydrogenated amorphous carbon (a:C-H) films. The effect of the additives on the film characteristics was determined by IR spectroscopy, solid state 13C cross polarization magic angle spinning nuclear magnetic resonance, and etching in an oxygen plasma. Nitrogen incorporation in the films was studied by Auger electron spectroscopy. Compared to films deposited in the presence of N2, the films deposited from a C4H6/NH3 plasma had an sp3/sp2 ratio that was 40% higher. IR spectra of the films confirm the higher sp3/sp2 ratio. Also, the films deposited from C4H6/NH3 mixtures exhibited lower etch rates in an oxygen plasma. The larger sp3/sp2 ratio is due to the higher concentration of NHx and H species in a C4H6/NH3 plasma.
Flicker (1/f) noise in biepitaxial grain boundary junctions of YBa2Cu3O7−x
Authors: Miklich A. H. , Clarke John , Colclough M. S. , Char K.
Published: July 2002

At low frequencies f the 1/f noise power in single biepitaxial junctions of YBa2Cu3 O7−x peaks sharply for bias currents just above the noise reduced critical current and increases as I2 for high bias currents I. This behavior is explained by a model in which both critical current fluctuations δI0 and resistance fluctuations δR contribute to the measured voltage noise. The magnitude of the normalized critical-current fluctuations ‖δI0/I0‖ is always much greater than that of the normalized resistance fluctuations ‖δR/R‖. Switching the bias current between positive and negative values at 2 kHz greatly reduces the magnitude of the 1/f noise from both sources, implying that the coherence of the noise generating process is not affected by the current reversal.
High power 1.017-μm strained-layer quantum well lasers grown by metalorganic chemical-vapor deposition
Authors: Ohkubo Michio , Ijichi Tetsuro , Iketani Akira , Kikuta Toshio
Published: July 2002

We have fabricated InGaAs/GaAs/InGaP strained-layer single quantum well (SLSQW) lasers emitting at 1.017 μm, which are suitable pumping sources for Pr3+-doped fluoride 1.3-μm fiber amplifiers, grown by metalorganic chemical-vapor deposition (MOCVD). A very low threshold current density of 80 A/cm2 was obtained for the broad-area lasers. This value is comparable to that of 0.98-μm SLSQW lasers. Continuous wave light output power of over 100 mW was achieved on the 2-μm-wide ridge waveguide lasers.
Minority carrier transport in carbon doped gallium arsenide
Authors: Colomb C. M. , Stockman S. A. , Varadarajan S. , Stillman G. E.
Published: July 2002

Minority carrier electron mobilities and diffusion lengths in p-type C-doped GaAs have been measured at room temperature and 77 K using the zero field time of flight (ZFTOF) technique on p+–n structures with p+ carrier concentrations of 1.1×1019, 6.0×1018, 1.8×1018 cm−3, which were grown by low-pressure metalorganic chemical vapor deposition (MOCVD) using CCl4 as the dopant. The electron mobilities obtained are higher than those reported for Be-doped MBE GaAs but lower than those reported for Ge-doped, LPE GaAs, while the diffusion lengths are similar to those found in similar concentration Be-doped samples.
Charge transfer in ZnS-type electroluminescence revisited
Authors: Bringuier E. , Geoffroy A.
Published: July 2002

Electrical characteristics of ac-driven, undoped ZnS electroluminescent layers are reported over a large temperature range. They show that, contrary to the currently assumed model of charge transfer wherein electrons are exchanged between the two ZnS interfaces, the operation involves an appreciable bulk charge evolving through capture and recombination of incident carriers. The meaning of the basic electrical observables is revisited. The results have relevance to the operation of blue emitting SrS-based electroluminescent devices.
Electrochemical capacitance-voltage profiling of n-type molecular beam epitaxy ZnSe layers
Authors: Wang S. Y. , Haran F. , Simpson J. , Stewart H. , Wallace J. M. , Prior K. A. , Cavenett B. C.
Published: July 2002

We report the use of electrochemical capacitance-voltage profiling of n-type ZnSe layers by the use of NaOH electrolyte. Samples with both uniform and staircase doping profiles have been measured with concentrations ranging over 1016–1019 cm−3. The profiling technique has revealed in some samples regions of lower carrier concentration at the surface and at the ZnSe/GaAs interface. Our results demonstrate that this powerful technique can now be used for assessing the growth parameters of wideband gap II-VI materials in the same way that is widely accepted for III-V semiconductors.
Si-GaAs(001) superlattices
Authors: Sorba L. , Bratina G. , Franciosi A. , Tapfer L. , Scamarcio G. , Spagnolo V. , Molinari E.
Published: July 2002

Si-GaAs(001) superlattices have been grown by molecular beam epitaxy. X-ray interference measurements and Raman spectroscopy studies in the acoustic range for (Si)2(GaAs)28 and (Si)3(GaAs)50 superlattice structures demonstrate that pseudomorphic growth conditions were achieved. Raman data in the optical range show large (∼50–70 cm−1) confinement- and strain-induced shifts of the Si-like optical modes.
Dependence of lifetime on surface concentration of copper and iron in silicon wafers
Authors: Zhong L. , Shimura F.
Published: July 2002

Minority-carrier lifetime after oxidation is investigated with a laser-microwave photoconductance (LM-PC) method for silicon wafers deliberately contaminated with Cu or Fe of different surface concentrations. The secondary ion mass spectroscopy (SIMS) depth profile clearly correlate the effect of those impurities on the bulk and surface components, which are obtained with a recently developed algorithm, of the effective lifetime. Copper impurities diffused from the wafer surface segregate at the SiO2/Si interface and near-interface region, and the surface component becomes dominant at high-surface contaminations. On the other hand, most of the iron segregates in the oxide layer and the residual iron diffuses into the bulk region, and therefore the bulk component dominates the effective lifetime.
Blue stimulated emission from a ZnSe p-n diode at low temperature
Authors: Wang S. Y. , Hauksson I. , Simpson J. , Stewart H. , Adams S. J. A. , Wallace J. M. , Kawakami Y. , Prior K. A. , Cavenett B. C.
Published: July 2002

Laser diode structures have been fabricated using molecular beam epitaxy with iodine from an electrochemical source for the n-type doping and nitrogen from a plasma source for the p-type doping. CV profiling using electrochemical etching shows uniform p doping of 4×1017 cm−3 and n doping of 1×1018 cm−3. Under pulsed current excitation blue emission at 470 nm is observed at room temperature which increases in intensity at liquid helium temperatures. Above a current density threshold of 50 A cm−2 stimulated emission is observed between 448–473 nm with a complicated mode structure.
Confinement and strain profiles produced by cation interdiffusion in In0.53Ga0.47As/InP quantum wells
Authors: Micallef Joseph , Li E. Herbert , Weiss Bernard L.
Published: July 2002

By considering cation interdiffusion only, we show that the confinement profile obtained after disordering a lattice-matched InGaAs/InP single quantum well differs from that of disordered AlGaAs/GaAs and InGaAs/GaAs quantum-well structures. An abrupt confinement profile is maintained even after significant interdiffusion, with a well width equal to that of the as-grown quantum well. In the early stages of disordering, a large strain buildup results. The bulk band gap of the disordered structure, together with the effects of this strain on the band gap, give rise to ‘‘miniwells’’ inside the potential wells.
Elemental marking of Si on Si(100) interfaces
Authors: Gates S. M. , Koleske D. D.
Published: July 2002

Submonolayer coverages of B, Sn, and Ge are prepared on Si(100) surfaces, and characterized using time-of-flight scattering and recoiling spectroscopy. The dopant ‘‘marks’’ the initial Si interface, and Si is grown on top of the ‘‘marked’’ surface, and is designated Si*. Attenuation of the elemental B, Sn, and Ge signals by Si* is used to evaluate Si precursors for atomic layer epitaxy, and compare the thermal stability of Si*/B/Si(100), Si*/Sn/Si(100), and Si*/Ge/Si(100) structures.
Electronic carrier transport and photogeneration in buckminsterfullerene films
Authors: Mort J. , Machonkin M. , Ziolo R. , Chen I.
Published: July 2002

Information concerning electronic carrier transport and photogeneration in films of undoped C60/70 has been obtained from photoinduced xerographic discharge curves in sublimed films up to 40 μm in thickness. The results, using strongly absorbed light, unambiguously reveal that the electron range, μτ, where μ is the electron drift mobility and τ the deep trapping lifetime, is ∼10−7 cm2/V. By contrast, a barely detectable discharge is observed to be associated with holes. The photogeneration efficiency for electrons is field dependent with a value at 4000 Å of 5×10−2 at a field of 2×105 V/cm. These results are discussed in a context where both charge photogeneration and transport in undoped C60/70 involve localized electronic states.
Oriented nickel-titanium shape memory alloy films prepared by annealing during deposition
Authors: Gisser Kathleen R. C. , Busch John D. , Johnson A. David , Ellis Arthur B.
Published: July 2002

Nickel-titanium shape memory alloy films, between 2 and 10 μm thick, were sputter deposited onto (100) silicon substrates. Films deposited onto a substrate at ambient temperature were amorphous; however, several post-deposition annealing procedures produced crystalline films exhibiting the B2-to-B19′ phase transition that gives rise to the shape memory effect. Films that were deposited onto a heated substrate, 350–460 °C, crystallized during deposition, eliminating the need for a separate annealing step. Powder x-ray diffraction indicated that these films were highly oriented, with the NiTi (110)B2 face parallel to the silicon substrate (100) face.
X-ray damage in low temperature ultrathin silicon dioxide
Authors: Lee K. H. , Campbell S. A. , Nachman R. , Reilly M. , Cerrina F.
Published: July 2002

The electrical characteristics of ultrathin oxides used in an x-ray lithography n-channel metal-oxide-silicon process grown at 700 and 950 °C were studied. The breakdown field exceeded 15 MV/cm for both low and high temperature oxides and the interface trap density of the fresh oxide was of order of 1010 cm−2 eV−1. Oxides grown at 950 °C had a lower interface trap density than 700 °C oxides, but 950 °C oxides are more sensitive to x-ray radiation damage. After 350 °C hydrogen annealing about 80% of the radiation damage in the form of interface traps was recovered.
Generation of positive charge in SiO2 thin films during electron irradiation
Authors: de Castro A. J. , Fernández M. , Sacedón J. L. , Anguita J. V.
Published: July 2002

The positive shifts in the energy position of the Si(L2,3VV) Auger peak produced by 1–3 kV electron irradiation of SiO2 thin films have been quantitatively explained as related to the electron trapped charge distribution. However, the electron beam also induces negative Auger shifts for certain experimental conditions. This result is interpreted in terms of a buildup of positive charge, associated to the bond breaking processes in the oxide bulk, with a formation cross section σf+≊10−17 cm2. The centroid of the spatial positive charge distribution depends on the primary beam energy, and it is not necessarily located at the SiO2/Si interface.
Origin of the low doping efficiency of nitrogen acceptors in ZnSe grown by metalorganic chemical vapor deposition
Authors: Kamata A. , Mitsuhashi H. , Fujita H.
Published: July 2002

The origin of nitrogen acceptor compensation in ZnSe:N has been studied by secondary ion mass spectrometry (SIMS) and infrared absorption (FTIR) measurements. Nitrogen-doped ZnSe layers were grown by atmospheric pressure metalorganic chemical vapor deposition. Ammonia gas was used as a nitrogen source. SIMS analysis has revealed that hydrogen was incorporated only into the ZnSe:N layer with the same concentration as nitrogen. FTIR measurements at 11 K strongly suggest the presence of N—H bonding at 3193 cm−1. It is concluded that hydrogen passivation is responsible for the acceptor compensation.
Surface resistance and penetration depth of YBa2Cu3O7−δ thin films on silicon at ultrahigh frequencies
Authors: Jaekel Christian , Waschke Christian , Roskos Hartmut G. , Kurz Heinrich , Prusseit Werner , Kinder Helmut
Published: July 2002

The surface resistance Rs and the absolute value of the magnetic penetration depth λ of ultrathin YBa2Cu3O7−δ films on silicon are determined by THz-pulse transmission experiments. We find a minimal value of Rs for a film thickness of about 30 nm. The increase of Rs with film thickness above 30 nm reveals an increase of the density of weak links possibly associated with the formation of microfractures even below the critical film thickness of 50–70 nm.
Switching energy limitation in all-optical switching due to group velocity dispersion of highly nonlinear optical waveguides
Authors: Asobe Masaki , Naganuma Kazunori , Kaino Toshikuni , Kanamori Terutoshi , Tomaru Satoru , Kurihara Takashi
Published: July 2002

We discuss the limitations of all-optical switching due to group velocity dispersion (GVD) in highly nonlinear optical waveguides. The lower limit of switching energy is primarily determined by a figure of merit which is the ratio of the nonlinear refractive index to the GVD. GVD values of several kinds of highly nonlinear optical materials are measured, the figure of merit for each material is estimated, and appropriate operational conditions for each material are discussed.
Doping of ZnTe by molecular beam epitaxy
Authors: Tao I. W. , Jurkovic M. , Wang W. I.
Published: July 2002

We have grown Cl-doped ZnTe under different growth conditions and N-doped ZnTe on different orientations. n-type doping was achieved for the first time by proper control of the Zn/Te beam flux. A p-type doping level of 1×1020 cm−3, which is the highest reported, was obtained by substrate tilting. These phenomena can be analyzed by the surface bonding structure analogous to the impurity concentration in the III-V compound semiconductors.
Evidence for a ‘‘brick wall’’ microstructure in epitaxial YBa2Cu3Ox films
Authors: Gao Z. X. , Heyvaert I. , Wuyts B. , Osquiguil E. , Haesendonck C. Van , Bruynseraede Y.
Published: July 2002

We have measured the in-plane (ab plane) critical current density Jc in sputtered, c-axis oriented YBa2Cu3Ox films as a function of the oxygen content x. The important reduction of Jc with decreasing x can be explained in terms of a ‘‘brick wall’’ microstructure, where the critical current density is dominated by the coupling strength (along the c axis) between the superconducting CuO2 planes. Scanning tunneling microscopy images of the film surfaces are consistent with the presence of the brick wall structure, which apparently results from the overlap between terraces belonging to adjacent spiral-shaped islands.
Novel parallel multijunction solar cell
Authors: Green Martin A. , Wenham Stuart R.
Published: July 2002

A novel parallel multijunction solar cell is described which allows fundamental radiative recombination limits upon photovoltaic cell energy conversion efficiency to be approached more closely in good quality material than possible in a single-junction device. However, the real advantage arises for poor quality material with the structure shown to be particularly tolerant of both impurity and grain boundary effects. A novel implementation approach is described for potentially high-performance, low-cost, thin-film polycrystalline silicon solar cells.
Reactive deposition epitaxial growth of β-FeSi2 film on Si(111): In situ observation by reflective high energy electron diffraction
Authors: Wang Lianwei , Lin Chenglu , Shen Qinwo , Lin Xian , Ni Rushan , Zou Shichang
Published: July 2002

Reactive deposition epitaxial growth of β-FeSi2 film on Si(111) has been studied by in situ observation of reflective high energy electron diffraction combined with ex situ Auger electron spectroscopy depth profile analysis. The direct phase formed at the top surface after iron coverage has been determined to be mixture Fe3Si and Fe5Si3, FeSi, and β-FeSi2, respectively, according to the results of different deposit temperature. Diffraction patterns as well as the depth profile for the Fe/Si ratio have been discussed.
Design considerations for single-stage and two-stage pneumatic pellet injectors
Authors: Gouge M. J. , Combs S. K. , Fisher P. W. , Milora S. L.
Published: July 2002

Performance of single-stage pneumatic pellet injectors is compared with several models for one-dimensional, compressible fluid flow. Agreement is quite good for models that reflect actual breech chamber geometry and incorporate nonideal effects such as gas friction. Several methods of improving the performance of single-stage pneumatic pellet injectors to muzzle velocities ranging from 2 to 2.25 km/s in the near term are outlined. Two-stage pneumatic injectors have the potential for much higher muzzle velocities (4–6 km/s) because of the higher gas pressures and temperatures achievable with the second-stage compression. The design and performance of two-stage pneumatic pellet injectors are discussed, and initial data from the two-stage pneumatic pellet injector test facility at Oak Ridge National Laboratory are presented. Finally, a concept for a repeating two-stage pneumatic pellet injector is described.
The influence of lateral forces in scanning force microscopy
Authors: den Boef A. J.
Published: July 2002

A scanning force microscope using interferometric detection of the cantilever deflection is described. The interferometer uses a multimode laser diode with a short coherence length. Despite the poor coherence of the laser, shot-noise-limited detection of displacements is possible, provided that the path difference between the interfering beams is sufficiently small. It will be shown that undesired bending of the cantilever occurs if a lateral force acts on the tip. The adverse influence of this force on image formation will be demonstrated. The results presented here are particularly relevant for applications where objects with steep slopes (e.g., integrated circuits) should be imaged.
Scale-up of electrospray atomization using linear arrays of Taylor cones
Authors: Rulison Aaron J. , Flagan Richard C.
Published: July 2002

Linear arrays of Taylor cones were established on capillary electrode tubes opposite a slotted flat plate counterelectrode to investigate the feasibility of increasing the liquid throughput rate in electrospray atomizers. It was found that individual Taylor cones could be established on each capillary over a wide range of the capillary radius to spacing ratio R/S. The onset potential Vs required to establish the cones varied directly with R/S, but the liquid flow rate per cone and current per cone were nearly independent of R/S for a given overpotential ratio P=V/Vs. Only six working capillaries were used, but the results per cone are applicable to larger arrays of cones since end effects were minimized.
Flow visualization in fluid mechanics
Authors: Freymuth Peter
Published: July 2002

The large field of flow visualization is briefly reviewed. Definition, purpose, and classification into subfields are outlined, and the reader is directed toward more detailed and more specialized reviews. The basic methods of flow visualization are explained and the long history of flow visualization is sketched by tracing the introduction of major methods and of discoveries made by flow visualization. Limitations and problem areas in the visual evaluation of velocity and vorticity fields are discussed, and a glimpse into the future role of flow visualization is ventured.
Vacuum arc ion sources
Authors: Brown Ian G.
Published: July 2002

The vacuum arc is a rich source of highly ionized metal plasma that can be used to make a high current metal ion source. Vacuum arc ion sources have been developed for a range of applications including ion implantation for materials surface modification, particle accelerator injection for fundamental nuclear physics research, and other fundamental and applied purposes. The beam parameters can be attractive, and the source has provided a valuable addition to the spectrum of ion sources available to the experimenter. Beams have been produced from over 50 of the solid metals of the periodic table, with mean ion energy up to several hundred keV and with beam current up to several amperes. Typically the source is repetitively pulsed with pulse length of order a millisecond and duty cycle of order 1%, and operation of a dc embodiment has been demonstrated. Here the source fundamentals and operation are reviewed, the source and beam characteristics summarized, and some applications examined.
The exactly focusing spherical grating monochromator for undulator radiation at BESSY
Authors: Peatman W. B. , Bahrdt J. , Eggenstein F. , Reichardt G. , Senf F.
Published: July 2002

The design goals and the performance data for the exactly focusing spherical grating monochromator at BESSY which is installed on a crossed field undulator for circularly polarized undulator radiation is described. By employing a variable deviation angle at the grating it is possible to exactly focus the entrance slit on the exit slit at all wavelengths. In addition, the optical aberrations are very small, leading to a high resolution over the energy range of the monochromator. The performance has been verified by analysis of the He (1s−1 np) and the Kr (3d−15/2,3/2 np) resonance series. A resolution of E/ΔE≊17 500 at 65 eV in second order has been achieved. Since commissioning, this monochromator has been used for a variety of experiments requiring both plane- and circularly polarized undulator radiation.
2D tomography with bolometry in DIII-Da)
Authors: Leonard A. W. , Meyer W. H. , Geer B. , Behne D. M. , Hill D. N.
Published: July 2002

A 48-channel platinum-foil bolometer system on DIII-D was installed to achieve better spatial and temporal resolution of the radiated power in diverted discharges. Two 24-channel arrays provide complete plasma coverage with optimized views of the divertor. The divertor radiation profile was measured for a series of radiative divertor and power balance experiments. A significant change in the magnitude and distribution of divertor radiation with heavy gas puffing was observed. Unfolding the radiation profile with only two views requires one to treat the core and divertor radiation separately. The core radiation is fitted to a function of magnetic flux and is then subtracted from the divertor viewing chords. The divertor profile is then fit to a 2D spline as a function of magnetic flux and distance from divertor floor.
An automated high pressure PVT apparatus for continuous recording of density and isothermal compressibility of fluids
Authors: Zhuang Wenhao , Kiran Erdogan
Published: July 2002

A unique instrumentation which permits real-time automated recording of volume or density as a function of pressure is described. The system consists of a variable volume view cell with an internal movable piston, a piston position sensor, a motorized pressure generator, and computerized control and data acquisition units. The position of the piston and hence the internal volume of the cell is monitored in real time with the aid of a linear-variable differential transformer while the pressure of the cell is changed in a slow, programed fashion using the automated pressure generator. The system is fully automated and can be used to generate density and compressibility information for pure fluids and fluid mixtures over a wide range of temperatures (up to 473 K) and pressures (up to 70 MPa). The continuous recording of density makes it possible to detect subtle changes in the state of the fluid(s) and offers a convenient approach for precise determination of the phase transition conditions. The capabilities of the system are demonstrated for two pure fluids, carbon dioxide and n-pentane, at near- and supercritical conditions.
Thermal aspects of resistors embedded in dielectrics
Authors: Caprari Robert S.
Published: July 2002

This note presents a formula for estimating the temperature of a distributed resistor or resistor chain that is immersed in a dielectric medium, which in turn is surrounded by a heat reservoir. An example computation from an actual instrument is included.
Automatic measurement and analysis of neonatal O2 consumption and CO2 production
Authors: Chang Jyh-Liang , Luo Ching-Hsing , Yeh Tsu-Fuh
Published: July 2002

It is difficult to estimate daily energy expenditure unless continuous O2 consumption (VO2) and CO2 production (VCO2) can be measured. This study describes a simple method for calculating daily and interim changes in O2 consumption and CO2 production for neonates, especially for premature infants. Oxygen consumption and CO2 production are measured using a flow-through technique in which the total VO2 and VCO2 over a given period of time are determined through a computerized system. This system can automatically calculate VO2 and VCO2 not only minute to minute but also over a period of time, e.g., 24 h. As a result, it provides a better indirect reflection of the accurate energy expenditure in an infant’s daily life and can be used at the bedside of infants during their ongoing nursery care.
Design, operation, and housing of an ultrastable, low temperature, ultrahigh vacuum scanning tunneling microscope
Authors: Ferris J. H. , Kushmerick J. G. , Johnson J. A. , Yoshikawa Youngquist M. G. , Kessinger R. B. , Kingsbury H. F. , Weiss P. S.
Published: July 2002

We have designed and constructed a low temperature, ultrahigh vacuum scanning tunneling microscope (STM), taking extreme measures to isolate the microscope from acoustic, vibrational, and electronic noise. We combined a 4 K STM with line-of-sight dosing to enable one to position the crystal surface in front of an impinging molecular beam as in scattering experiments. Due to the mechanical stability of the instrument and the minimal thermal drift associated with working at 4 K we are able to locate and to image repeatedly isolated adsorbates and atomic-scale structures, such as step edges, for extended periods days. The instrument has been designed for the topographic and spectroscopic characterization of atoms and molecules on metal and semiconductor surfaces, for the investigation of the mechanism by which the STM images adsorbates on surfaces, and for inelastic electron tunneling spectroscopy of single molecules.
Miniature fiber optic pressure sensor for turbomachinery applications
Authors: MacPherson William N. , Kilpatrick James M. , Barton James S. , Jones Julian D. C.
Published: July 2002

Development of pressure sensors for the instrumentation of experimental aerodynamic facilities has traditionally concentrated on electrical techniques. An improvement in the currently attainable temporal and spatial resolution in pressure measurement would be beneficial in the characterization of turbulent flows behind turbine rotor stages, for example. We present results obtained in a turbine test rig from a fiber optic pressure sensor based upon the interferometric response of an extrinsic cavity formed between the interrogation fiber and a reflective diaphragm. We discuss the design trade offs, optical interrogation and temperature sensitivity of such a configuration, and demonstrate the success of the design in small-scale shock tube experiments. We then describe the application of the sensor in a full scale turbine test facility in which pressure signals with frequency components exceeding 200 kHz were obtained.
An ultrahigh vacuum sputtering system with offset incidence magnetron sources onto a rotating substrate
Authors: Fujimoto Toshiyuki , Li Boquan , Kojima Isao , Yokoyama Syuu-ichi , Murakami Syun-ichi
Published: July 2002

An ultrahigh vacuum sputtering system with offset incidence magnetron sources has been designed and developed to deposit thin films and multilayers with excellent film thickness uniformity, precise control over layer thickness, and surface and interface roughness. The unique feature of the system is that the sputtering guns are aligned at 35° oblique incidence onto a rotating substrate with a 60 mm offset from the substrate center, which make full use of the best linearity of the plasma flux at the substrate, and therefore, deposit extremely uniform thin films. Other features include, computer-controlled deposition process, capability of heating the substrate to 1100 °C, and in situ monitoring of thin-film quality with reflection high-energy electron diffraction. The performance of the sputtering system is demonstrated, and a characterization of multilayers deposited by the system using a grazing incidence x-ray reflectivity and high resolution electron microscope is also presented.
Pulsed vacuum-arc ion source operated with a “triggerless” arc initiation method
Authors: Anders A. , Schein J. , Qi N.
Published: July 2002

Vacuum arcs can be initiated by simply applying a sufficiently high voltage (∼ 1 kV) between the anode and cathode, provided that there is a conducting path between these electrodes. Typically, the conducting path is obtained by coating the ceramic insulator. Plasma is formed explosively at the coating-cathode interface. Since neither a trigger supply nor a trigger electrode are required, the method has been dubbed “triggerless” arc initiation. Triggerless operation of a vacuum arc ion source was demonstrated for a number of cathode materials. It was found that triggerless operation is very reliable as long as the balance of deposition and erosion of the conducting material leads to a steady-state path resistance in the range from 1 Ω to 100 kΩ.
Surface activated bonding of silicon wafers at room temperature
Authors: Takagi H. , Kikuchi K. , Maeda R. , Chung T. R. , Suga T.
Published: July 2002

A method to bond silicon wafers directly at room temperature was developed. In this method, surfaces of two silicon samples are activated by argon atom beam etching and brought into contact in a vacuum. By the infrared microscope and KOH etching method, no void at the bonded interface was detected in all the specimens tested. In the tensile test, fracture occurred not at the interface but mainly in the bulk of silicon. From these results, it is concluded that the method realizes strong and tight bonding at room temperature and is promising to assemble small parts made by the silicon wafer process.
Compaction- and photoelastic-induced index changes in fiber Bragg gratings
Authors: Limberger H. G. , Fonjallaz P.-Y. , Salathé R. P. , Cochet F.
Published: July 2002

The tension on the core of single-mode fibers is strongly increased by the formation of a Bragg grating. This tension increase lowers the refractive index because of the photoelastic effect. On the other hand, the compaction of the core network results in an increased refractive index. The two contributions are evaluated from axial stress measurements, from the determined index modulation amplitude, and from the mean index change of the Bragg gratings. The total Bragg grating index modulation is smaller than the compaction-induced index modulation by 30%–35% because of the photoelastic effect.
Thermally activated carrier transfer and luminescence line shape in self-organized InAs quantum dots
Authors: Brusaferri L. , Sanguinetti S. , Grilli E. , Guzzi M. , Bignazzi A. , Bogani F. , Carraresi L. , Colocci M. , Bosacchi A. , Frigeri P. , Franchi S.
Published: July 2002

We investigated the temperature dependence (10–180 K) of the photoluminescence (PL) emission spectrum of self-organized InAs/GaAs quantum dots grown under different conditions. The temperature dependence of the PL intensity is determined by two thermally activated processes: (i) quenching due to the escape of carriers from the quantum dots and (ii) carrier transfer between dots via wetting layer states. The existence of different dot families is confirmed by the deconvolution of the spectra in gaussian components with full width half maxima of 20–30 meV. The transfer of excitation is responsible for the sigmoidal temperature dependence of the peak energies of undeconvoluted PL bands.
Electroluminescent device based on silicon nanopillars
Authors: Nassiopoulos A. G. , Grigoropoulos S. , Papadimitriou D.
Published: July 2002

Silicon nanopillars were fabricated by using deep UV lithography, highly anisotropic silicon reactive ion etching based on fluorine chemistry, and high-temperature thermal oxidation for further thinning. Pillars with a diameter below 10 nm and a height in the 0.4–0.6 μm range were obtained while lying on a very smooth bottom silicon surface. An isolating transparent polymer was then used to fill in the etched area containing the pillars and, therefore, planarize and isolate the pillars. Oxygen plasma was used in order to remove the resistance from the top of the pillars. They were then contacted by a thin contact layer (gold or indium tin oxide), evaporated on the top of them. An Ohmic contact was also formed on the back side of the wafer. The obtained device showed rectifying behavior and forward voltages exceeding 10–12 V electroluminescence was observed, visible with the naked eye.
An optically pumped GaN–AlGaN vertical cavity surface emitting laser
Authors: Redwing Joan M. , Loeber David A. S. , Anderson Neal G. , Tischler Michael A. , Flynn Jeffrey S.
Published: July 2002

An optically pumped GaN-based vertical cavity surface emitting laser (VCSEL) is demonstrated. Laser emission near 363 nm is observed at room temperature from the surface of a VCSEL structure optically pumped along a cleaved sample edge by focused light from a nitrogen laser. The VCSEL structure, which was grown on a sapphire substrate by metalorganic vapor phase epitaxy, consists of a 10 μm GaN active region sandwiched between 30-period Al0.40Ga0.60N–Al0.12Ga0.88N Bragg reflectors. At optical pump intensities above ∼2.0 MW/cm2, a narrow (<5 Å) laser mode at 363.5 nm emerges from the GaN photoluminescence spectrum. This mode becomes the dominant feature of the spectrum at higher pump powers, and additional modes appear ∼1.3 nm above and below this mode at 362.1 nm and 364.8 nm. The ∼1.3 nm mode spacing corresponds closely with the 1.1 nm spacing predicted from an electromagnetics model of the VCSEL structure.
Fabrication of 2-nm-wide silicon quantum wires through a combination of a partially-shifted resist pattern and orientation-dependent etching
Authors: Namatsu Hideo , Kurihara Kenji , Nagase Masao , Makino Takahiro
Published: July 2002

This article proposes a nanofabrication technique for fabricating quantum wires with dimensions in the sub-10 nm regime. This technique consists of partially shifted resist-pattern formation and orientation-dependent Si etching that takes advantage of the difference in the crystallographic properties of the {111} planes and the other planes. When {110} Si substrates are etched using a partially shifted pattern as a mask, the etching generates a smooth {111} side plane and eventually forms a straight Si line pattern whose width is equal to the difference between the size of the shift and the originally exposed linewidth. Therefore, line patterns smaller than the beam diameter of lithographic tools can be formed. We show the effectiveness of this technique by fabricating a 2-nm-wide Si line. The electrical conductance characteristics of the Si nanoline formed by this technique are also shown.
NbN/AlN/NbN tunnel junctions with high current density up to 54 kA/cm2
Authors: Wang Zhen , Kawakami Akira , Uzawa Yoshinori
Published: July 2002

We report on progress in the development of high current density NbN/AlN/NbN tunnel junctions for applications as submillimeter wave superconductor-insulator-superconductor mixers. A very high current density up to 54 kA/cm2, roughly an order of magnitude larger than any reported results for all-NbN tunnel junctions, was achieved in the junctions with about 1 nm thick AlN barriers. The magnetic field and temperature dependence of critical supercurrents were measured to investigate the Josephson tunneling behavior of critical supercurrents in the high-Jc junctions. The junctions showed high-quality junction characteristics with a large gap voltage of 5 mV and sharp quasiparticle current rise (ΔVg=0.1 mV). The Rsg/RN ratio was about 5 with a Vm value of 14 mV measured at 4.2 K.
Unidirectional radiation of widely tunable THz wave using a prism coupler under noncollinear phase matching condition
Authors: Kawase Kodo , Sato Manabu , Nakamura Koichiro , Taniuchi Tetsuo , Ito Hiromasa
Published: July 2002

A widely tunable THz wave has been parametrically generated and reported recently by us utilizing a LiNbO3 crystal with a monolithic grating coupler under a noncollinear phase matching condition. However, the output direction of the THz wave is strongly dependent on the generated frequency due to the nature of noncollinear phase matching, as well as the grating coupler. In this letter, a novel method for THz coupling is proposed using a low dispersion prism to eliminate almost completely the THz beam deflection for the entire tuning range. The unidirectional THz wave radiation was confirmed theoretically and experimentally for the range of 1–2 THz.
Submicron-sized spherical yttrium oxide based phosphors prepared by supercritical CO2-assisted aerosolization and pyrolysis
Authors: Xu Chongying , Watkins Barbara A. , Sievers Robert E. , Jing Xiping , Trowga Philip , Gibbons Carol S. , Vecht Aron
Published: July 2002

The synthesis of Eu(III)- and Tb(III)-doped yttrium oxide phosphor powders by supercritical CO2-assisted aerosolization and pyrolysis (at 1010 °C) from aqueous solutions of Y(NO3)3, Eu(NO3)3, and Tb(NO3)3 is presented. Dense, submicron aerosols are formed by contacting aqueous solutions of the precursor metal nitrates with supercritical CO2 at 1500 psi, and decompressing the mixture through a restrictor nozzle into a heated tube. X-ray diffraction data indicate that the powders are crystalline, and consist of a single phase. Scanning electron microscope shows that they are spherical in morphology and less than 1 μm in size with average diameters of ∼0.2 μm. The cathodoluminescence intensity of the Y1.91Eu0.09O3 powders, annealed at 1200 °C for 1 h, is more than twice greater than that of the industrial standard (P56, 3–10 μm in diameter) phosphor. The phosphors synthesized by this method are promising candidates for use in high-resolution low-voltage flat panel displays.
Imaging the irradiance distribution in the optical near field
Authors: Aizenberg J. , Rogers J. A. , Paul K. E. , Whitesides G. M.
Published: July 2002

This letter describes the use of a sensitive photoresist for direct imaging of optical intensity profiles in near-field photolithographic experiments. A comparison between experimental patterns in exposed, developed photoresist and calculated profiles of intensity shows that this procedure provides a reliable semiquantitative image of the irradiance distribution in the near field; experiment and theory correlate adequately. A potential use of the superficial diffraction contrast recorded in photoresist as the basis for a new method of the fabrication of nanostructures is discussed.