bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved differential heterodyne interferometer for atomic force microscopy
Authors: Sasaki Minoru , Hane Kazuhiro , Okuma Shigeru , Hino Motohito , Bessho Yoshinori
Published: July 2002

A highly sensitive displacement sensor for atomic force microscopy is described which enables one to measure the relative displacement of the tip from a sample surface. The sensor is based on the differential heterodyne interferometer formed between the reflections from the microscope cantilever backside and the sample surface. As a result of using an optical common-path construction, the sensor is essentially insensitive to the mechanical vibration, and achieves high stability at low frequencies, even though there are certain restrictions imposed by the reflection from the examined surface and the variable deflection mode. Images are presented demonstrating the atomic resolution of mica and graphite.
Infrared absorption in GexSi1−x quantum wells
Authors: Misra R. , Greve D. W. , Schlesinger T. E.
Published: July 2002

The absorption characteristics of GexSi1−x quantum well infrared photodetector (QWIP) structures have been studied in samples over a range of germanium compositions and doping levels. In all these samples, quantum well intersubband transitions are either very weak or nonexistent for normally incident light. However, free carrier absorption in GexSi1−x quantum wells is a strong absorbing mechanism in the long wavelength infrared regime, and has been found to be stronger than in silicon for similar doping levels. Therefore, detectors relying upon free carrier absorption in GexSi1−x quantum wells may offer superior responsivity and quantum efficiency.
Practical nitric oxide measurement employing a nitric oxide-selective electrode
Authors: Ichimori K. , Ishida H. , Fukahori M. , Nakazawa H. , Murakami E.
Published: July 2002

An NO-selective electrode was developed as an easily applicable tool for a real-time nitric oxide (NO) measurement. The working electrode (0.2 mm diam) was made from Pt/Ir alloy coated with a three-layered membrane. The counterelectrode was made from a carbon fiber. When a stable NO donor, S-nitroso-N-acetyl-dl-penicillamine, was applied, the electrode current increased in a dose-dependent fashion. The current and calculated NO concentration showed a linear relationship in the range from 0.2 nM (S/N=1) to 1 μM of NO. The response of the electrode was 1.14±0.09 s. The effects of temperature, pH, and chemicals other than NO on the electrode current were also evaluated. Electrodes which were placed in the luminal side of rat aortic rings exhibited 30 pA of current due to NO generation induced by the addition of 10−6 M of acetylcholine. The current was eliminated in the presence of 50 μM NG-monomethyl-L-arginine, an inhibitor of NO synthase. Thus, this NO-selective electrode is applicable to real-time NO assay in biological systems.
Generation of picosecond pulses at millimeter wavelengths
Authors: Jones C. R. , Kosai H. , Dutta J. M. , Peters M. J. , Guo W. , De Lucia F. C. , Benson S. V. , Madey J. M J. , Swartz J. C. , Guenther B. D.
Published: July 2002

We report here on an experiment in which picosecond electron pulses, produced by a compact radiation frequency (rf) electron gun, were used to excite a rectangular waveguide, generating 5 ps pulses of radiation with a bandwidth of ∼200 GHz. The interaction of the electron pulses with the waveguide can be modeled quite simply by performing a harmonic expansion of the pulse train produced by the electron gun and employing Poynting’s theorem to compute the power coupled into the modes of the waveguide by each harmonic. The resulting model for the distribution of spectral power yields good agreement with the observed spectrum.
Single-stage 5 GHz ECR-multicharged ion source with high magnetic mirror ratio and biased disk
Authors: Leitner M. , Wutte D. , Brandstötter J. , Aumayr F. , Winter HP.
Published: July 2002

A low-cost, single-stage 5 GHz electron cyclotron resonance (ECR) multicharged ion source (MCIS) has been constructed for various atomic collision experiments. It features an axial magnetic field with a mirror ratio of up to five, and a magnetic hexapole field produced by a simple Nd–Fe–B permanent-magnet assembly. A disk probe axially mounted near the ECR resonance zone opposite to the ion extraction, and negatively biased with respect to the ECR plasma potential, permits reduction of the appropriate neutral feeding gas pressure by an order of magnitude, resulting in greatly improved ion charge state distributions, as normally offered by two-stage ECR–MCIS only. We present performance data for multicharged ion production from Ar and N2, including measured ion current emittances.
Flicker noise in  YBa2Cu3O7−δ  bicrystal grain boundary junctions in weak magnetic fields
Authors: Surya Charles , Israeloff N. E. , Widom A. , Seed R. , Vittoria C.
Published: July 2002

Flicker noise in c-axis oriented long YBCO bicrystal grain boundary junctions was characterized as a function of temperature, biasing conditions, and magnetic field applied perpendicular to the a–b plane over a wide range of temperatures from 15 K to over 70 K. Aperiodic variations, as a function of magnetic field, were observed in both the junction voltages, VJ, and the flicker noise magnitude under constant current bias as the magnetic field was scanned from 0 to 8 G. The noise magnitudes were found to peak at the minima of VJ. Analyses of the field dependencies of the magnitudes and the functional form of the voltage noise power spectra show that the noise did not arise from thermally activated flux motion. Based on the dependencies of the noise power spectra on the bias current and the dynamic resistance of the junction, we conclude that the noise originates from the fluctuations of the critical current of the devices most likely due to trapping of carriers or defect motion within the grain boundary.
Time-resolved study of carrier capture and recombination in monolayer Be δ-doped GaAs
Authors: Damen T. C. , Fritze M. , Kastalsky A. , Cunningham J. E. , Pathak R. N. , Wang H. , Shah J.
Published: July 2002

The first measurements of subpicosecond dynamics of carrier capture and decay in Be δ-doped GaAs structures with p-doping density ranging from 6×1012 to 2×1014 cm−2 and spatial distribution on monolayer scale show that photoexcited carriers are captured in the δ-doped layer in <1 ps. Luminescence decay rates show a strong dependence on energy of the hole in the two-dimensional Fermi gas. We attribute this to a change in the spatial electron-hole overlap resulting from band-mixing effects. We show that Be density fluctuations lead to strong carrier localization.
Damping of the oscillations of a permanent magnet levitating between high-T
c superconductors
Authors: Grosser R. , Jäger J. , Betz J. , Schoepe W.
Published: July 2002

A permanent magnet (spherical shape, radius 100 μm) is levitating inside a superconducting parallel plate capacitor made of YBCO. Translational oscillations of the magnet at its resonance frequency (∼150 Hz) can be excited and detected. The damping of the oscillations is investigated as a function of temperature and oscillation amplitude. Close to Tc we observe a steep minimum of the damping. The data can be described by a linear frictional force which decreases near Tc, and a quadratic one which diverges at Tc. These frictional forces are attributed to flux flow phenomena in the high-Tc superconductor.
Self-organized light-induced scattering in periodically poled lithium niobate
Authors: Pruneri V. , Kazansky P. G. , Webjörn J. , Russell P. St. J. , Hanna D. C.
Published: July 2002

A new species of self-organized light-induced scattering, appearing only in bulk periodically poled lithium niobate, is reported. Clearly defined diffracted beams develop on exposure to 532 nm light from a frequency-doubled, Q-switched, and mode-locked Nd:YAG laser. The structure thus created also diffracts light at 1064 nm. The effect is strongly dependent on temperature, the polarization state of the light, and the period of domain reversal. It exhibits a sharply defined nonlinear threshold at which the far-field pattern of the diffracted light evolves rapidly.
Single-lobed far-field radiation pattern from surface-emitting complex-coupled distributed-feedback diode lasers
Authors: Kasraian Masoud , Botez Dan
Published: July 2002

Theoretical analysis of surface-emitting complex-coupled distributed-feedback (SE-CC-DFB) lasers with a second-order grating reveals that operation in a single-lobed, orthonormal beam can be fundamentally favored. This happens when the modal-gain difference between symmetric and antisymmetric modes due to the optical-field (longitudinal) overlap with the gain/loss grating overcomes the modal-gain difference based on radiation losses. The analysis is performed for a simple three-layer structure with gain placed in the high-index regions (i.e., in-phase, second-order CC-DFB). Lasing at or near the Bragg frequency provides essentially uniform near-field patterns, thus immunizing the device to gain spatial hole burning. The results and their implications are discussed.
Performance limitations of niobium-based submillimeter-wave quasiparticle mixers operating near the gap frequency
Authors: Febvre P. , Salez M. , McGrath W. R. , Bumble B. , LeDuc H. G.
Published: July 2002

We have measured the noise temperature of heterodyne receivers employing Nb/AlOx/Nb tunnel junction mixers at frequencies ranging from 70% to 93% of the gap frequency of niobium (∼700 GHz). The sensitivity of the receiver is decreased by the overlap of the n=1 and n=2 photon steps of opposite sign. At bias voltages where these photon steps overlap, there is an increase in receiver noise up to 50%. Theoretical calculations using the Tucker theory agree well with the observed mixer performance. This overlap already affects the receiver operation for best performance at frequencies well below 700 GHz.
64 meV measured energy dispersion from cold field emission nanotips
Authors: Purcell S. T. , Binh Vu Thien , Garcia N.
Published: July 2002

In this letter, we report on the extremely narrow energy distributions that can be obtained in field emission from W and Pt nanotips. For example, the measured full width at half-maximum for a Pt nanotip can be as low as 64 meV at 80 K and 100 meV at room temperature. Moreover, these emitted beams are autocollimated to a 4° opening and have hours of stability for a current of ∼1 nA due to the fact that the emission comes from one atom.
Observation of the anomalous current–voltage characteristics of GaAs/n+-InGaAs/GaAs doped-channel structure
Authors: Liu Wen-Chau , Laih Lih-Wen , Tsai Jung-Hui , Hsu Wei-Chou , Wu Cheng-Zu , Thei Kong-Beng , Lour Wen-Shiung
Published: July 2002

A GaAs/n+-In0.2Ga0.8As/GaAs doped-channel field-effect transistor structure has been fabricated and studied. A typical transistor performance with a threshold voltage of about −3.0 V and transconductance of up to 160 mS/mm is obtained in the lower gate-source voltage (VGS <−1.0 V) regime. However, for some devices, the three-terminal-controlled N-shaped negative-differential-resistance (NDR) behavior is observed at the saturation regime of current–voltage characteristics under higher gate-source bias (VGS≥−1.0 V) condition. The interesting NDR phenomenon is believed to be attributed to the real-space transfer and deep-level electron trapping effect.
Spectrum analyzer for low magnetic field
Authors: Aroca C. , Prieto J. L. , Sánchez P. , López E. , Sánchez M. C.
Published: July 2002

A device to obtain an estimate of the spectrum of a time-variable magnetic field has been developed. The amplitude of each spectral component of the magnetic field series is obtained by analyzing with a double demodulation technique the signal generated from a flux-gate-like detector operating in open loop configuration. This device shows a sensitivity of about 1 mV/nT in the range from 0 to 300 Hz. For frequencies higher than 300 Hz the sensitivity decreases, and a correction factor that depends on the transfer function of the electronic device must be applied. The present device can be applied to environmental measurements, industrial applications, traffic control, and scientific research.
Intensity dependent mode competition in second harmonic generation in multimode waveguides
Authors: Treviño-Palacios C. G. , Stegeman G. I. , De Micheli M. P. , Baldi P. , Nouh S. , Ostrowsky D. B. , Delacourt D. , Papuchon M.
Published: July 2002

Second harmonic generation (SHG) in waveguides which are multimode at the second harmonic exhibit an intensity dependence in both the phase-match wavelength and relative conversion efficiency of the different SHG modes because they are coupled to the same fundamental.
Variation of composition of sputtered TiN films as a function of target nitridation, thermal anneal, and substrate topography
Authors: Tsai W. , Hodul D. , Sheng T. , Dew S. , Robbie K. , Brett M. J. , Smy T.
Published: July 2002

The chemical composition of reactively sputtered TiN was measured with RBS and AES for aspect ratio 2 topography as a function of Ti target nitridation. The bottom of the aspect ratio 2 topography was nitrogen depleted (Ti:N=1.78:1) as compared to the field (Ti:N=1.01:1) for films sputtered with a non-nitrided target at 20 kW and 400 °C. No such depletion effect was observed for TiN films sputtered with a nitrided target. Thermal annealing of the depleted TiN films at 450 °C in N2 restored the composition to near-stoichiometric. SIMBAD simulation with a saturation-dependent nitrogen sticking coefficient was used to understand the nature of the nitrogen depletion.
Gigahertz bandwidth ultrahigh vacuum 50 Ω coaxial high-voltage coupling capacitor for photoelectron spectroscopy
Authors: Stolow Albert
Published: July 2002

A bakeable (200 °C) ultrahigh vacuum 50 Ω coaxial coupling capacitor is described. The capacitor is compatible with the General Radio G874 coaxial standard, has a large capacitance (6 nF) allowing for efficient transmission of both fast pulses and long analog waveforms, can hold off dc voltages of up to 5 kV, and has a bandwidth greater than 2 GHz, allowing coupling of very fast rise-time signals from cathode ground microchannel-plate detectors, often used in photoelectron spectroscopy. The capacitor design also provides a convenient bias tee for applying high voltage to the detector anode.
Integrated multilayer sputter-induced 45° YBa2Cu3O7−x grain boundary junctions
Authors: Vuchic B. V. , Merkle K. L. , Dean K. A. , Buchholz D. B. , Chang R. P. H. , Marks L. D.
Published: July 2002

A versatile multilayer technique has been developed to form 45° YBa2Cu3O7−x [001] tilt grain boundary junctions on LaAlO3 substrates. An epitaxial MgO layer is initially deposited on a (100) LaAlO3substrate using pulsed organometallic beam epitaxy (POMBE). After a pregrowth sputter treatment, an YBa2Cu3O7−x thin film is then grown using POMBE. The resultant film is c-axis oriented with a cube-on-cube orientation over the unsputtered portion of the MgO, and rotated by 45° about the [001] axis on the sputtered region of the substrate. The resulting grain boundary junction shows weak-link behavior. The advantage of this technique is the ability to place the grain boundary anywhere on the substrate in any configuration, and the potential to use any substrate upon which MgO can be epitaxially grown.
Effect of methane concentrations on surface morphologies and surface structures of (001) homoepitaxial diamond thin films
Authors: Lee Naesung , Badzian Andrzej
Published: July 2002

Homoepitaxial diamond films were grown on misoriented (001) substrates with CH4 concentrations of 1%, 2%, and 6% in H2. Reflection high-energy electron diffraction was used to characterize the surface structure. At 1% CH4, step-flow growth occurred with the surface close to the single-domain structure. This growth mode is expected to produce films with fewer crystal defects. On the other hand, when grown with 2% and 6% CH4, growth hillocks and random growth morphology were observed with the double-domain surface structure, respectively. The surface morphologies and surface structures are considered to change due to lower mobility and shorter diffusion lengths of adsorbates at higher CH4 concentrations.
PdGeTiPt Ohmic contacts to p+-AlxGa1−xAs
Authors: Han W. Y. , Cole M. W. , Casas L. M. , Jones K. A. , Lee H. S. , Wade M. , DeAnni A. , Lapore A. , Lu Y. , Yang L. W.
Published: July 2002

Ohmic contacts to heavily C-doped AlGaAs were made using PdGeTiPt that had specific contact resistances Rc, as low as 1.7×10−6 Ω cm2 when annealed at 600 °C. The less heavily doped samples annealed at temperatures between 350 and 500 °C were non-Ohmic, and Rc decreased with increasing annealing temperature between 500 and 600 °C. For the more heavily doped samples, Rc decreased with increasing annealing temperature. Rc increased for all samples at annealing temperatures above 600 °C. Rc rose quickly by 102 when the samples were reannealed at 300 °C for 20 h, but remained unchanged with further reannealing for up to 100 h. This behavior is consistent with partial compensation generated by the rapid out-diffusion of Ga at low annealing temperatures and the subsequent in-diffusion of Ge into the Ga vacancies left behind. The lower Rc obtained with the 600 °C anneal can be explained by an increased As out-diffusion and the subsequent in-diffusion of Ge into the As vacancies at the higher annealing temperatures. Interfacial reactions and elemental diffusion of the contacts investigated via transmission electron microscopy and elemental depth profiles obtained by Auger electron spectroscopy are also consistent with this mode.
Two types of local oxide/substrate defects in very thin silicon dioxide films on silicon
Authors: Lau W. S. , Sane V. , Pey K. S. , Cronquist B.
Published: July 2002

The local oxide defects observed in thin silicon dioxide films on p-type Si were studied with the electron beam induced current/tunneling current microscopy technique. Excluding pinholes, all the local defects observed are local oxide/substrate defects, i.e., local oxide defects propagated from defects in the Si substrate into the SiO2. It was observed that local oxide/substrate defects can be further differentiated into two different types by studying the transition from the true oxide electron beam induced current contrast to the tunneling current microscopy contrast.
Enhanced superparamagnetism in two-dimensional arrays of nanometer-sized Fe islands
Authors: Heim K. R. , Hembree G. G. , Schmidt K. E. , Scheinfein M. R.
Published: July 2002

Iron grown on room-temperature CaF2/Si(111) substrates form two-dimensional arrays of nanometer-sized superparamagnetic islands. Deposition of Ag on the Fe/CaF2/Si(111) produced a superparamagnetic response where the effective moment was proportional to the number of Fe islands covered by an average-sized Ag island. The nonmagnetic Ag overlayer mediates a long-range exchange between neighboring Fe islands within an individual Ag island. Monte Carlo methods are used to examine ordering in two dimensions and to set minimum interisland coupling strengths.
Silicon-based surface plasmon resonance combined with surface-enhanced Raman scattering for chemical sensing
Authors: Nikitin P. I. , Beloglazov A. A. , Valeiko M. V. , Creighton J. A. , Wright J. D.
Published: July 2002

A Si-based surface plasmon resonance (SPR) technique has been successfully applied to NO2 sensing at ppm level, with estimated detectability at less than 100 ppb. Surface-enhanced Raman scattering (SERS) has been used in this scheme as an inherent additional data acquisition channel capable of providing spectroscopic selectivity and amplified sensitivity. The behavior of both the SERS spectrum and the SPR-induced photosignal produced by Au-on-Si grating structures coated with thin 18-crown-6 metal-free phthalocyanine films was simultaneously recorded for exposure of the films to 10 ppm of NO2 in air and its reversal in clean air. Both responses have been found to be reversible. The combination of Si-based SPR and SERS looks promising for thin-film and surface explorations, both in fundamental and sensor applications.
Enhancement of room-temperature photoluminescence in thin-film polycrystalline silicon produced by low power laser annealing
Authors: Ostapenko S. , Savchuk A. U. , Nowak G. , Lagowski J. , Hoff A. M.
Published: July 2002

We have found that seconds of 100 mW Ar laser exposure produces more than 100 times an increase in infrared photoluminescence (PL) intensity in thin-film polycrystalline silicon (poly-Si). The change of PL intensity on laser exposed film areas (minimum spot size of 20 μm) and the variation in film surface morphology measured by atomic force microscope are compared. The effect of PL enhancement strongly correlates to two distinctive processes: (a) the increase of a grain size due to poly-Si recrystallization, and (b) the oxygen incorporation into the film from glass or quartz substrates or/and from ambient gas.
Carrier collection losses in amorphous silicon and amorphous silicon–germanium alloy solar cells
Authors: Banerjee A. , Xu X. , Yang J. , Guha S.
Published: July 2002

The carrier collection losses in amorphous silicon (a-Si) and amorphous silicon–germanium (a-SiGe) alloy single-junction nip cells have been experimentally investigated by measuring the biased quantum efficiency and color (blue and red) fill factor values. The study has identified losses near the p/i junction and the bulk of the i layer. The extent of the losses have been found to be dependent on the quality and thickness of the i layer and the nature of the n-layer surface. The results suggest a broad interrelationship between the initial film properties and deposition conditions and an inhomogeneity in the direction of film growth.
A critical look at surface force measurement using a commercial atomic force microscope in the noncontact mode
Authors: Fontaine P. , Guenoun P. , Daillant J.
Published: July 2002

The use of commercial atomic force microscopes (AFM) operating in the noncontact mode for surface force measurements is critically reviewed. Approach curves (i.e., vibration amplitude versus tip–surface distance) using standard microfabricated tips are discussed with respect to the basic theory of an equivalent harmonic oscillator. Different artifacts are addressed. In particular, we show theoretically and experimentally that the force exerted by the layer of air confined between the cantilever and the surface is a major contribution to the force on the cantilever. However, by carefully choosing the parameters (essentially the vibration amplitude) for the measurement of the approach curve, and by taking into account the damping within the confined air layer, we succeeded in measuring reliable surface force profiles with commercial AFM in the air and in describing them quantitatively by dispersion force interactions.
An ac microcalorimeter employing a diode laser as a heater
Authors: Marone M. J. , Payne J. E.
Published: July 2002

We have built an ac microcalorimeter which uses a diode laser as the heater. The absence of a contact heater reduces the total addendum. This method has several advantages over the typical quartz lamp and mechanical chopper wheel configuration. The laser is modulated by a lock-in amplifier which provides a wider choice of operating frequencies, typically from 0.2 to 50 Hz. The microcalorimeter has been used from near room temperature to 5 K. Single-crystal samples of YBCO with a mass as small as 4 μg have been measured. The device is particularly useful in the study of whiskers and other very small samples.
Self-restoration of p-n junctions in (Hg,Cd)Te
Authors: Lyubomirsky Igor , Lyakhovitskaya Vera , Triboulet Robert , Cahen David
Published: July 2002

While a p-n junction is a stable situation for electronic carriers, it represents an unstable one for the very dopants that create the junction, i.e., the junction is only kinetically stabilized against equilibration of the dopant concentrations in the chemical and electrical potential gradients in the junction region. However, when a dopant migrates with a charge opposite to the effective one that it has as a dopant, the electrical potential gradient, instead of destabilizing, can now help to stabilize the junction. Ag, which acts as an acceptor in (Hg,Cd)Te, is an example of such a dopant. We show here that in Cd-rich n-(Hg,Cd)Te, Ag creates a p-n junction that is capable of restoring itself after being smeared out by small perturbations. This behavior is inconsistent with pure kinetic stabilization of the junction and indicates that Ag dissolution in (Hg,Cd)Te strongly deviates from ideal behavior. Reasons for this nonideality are suggested.
Controlling opacity and gain coefficients of soft x-ray transitions by ion dilution
Authors: Ozaki Tsuneyuki , Kuroda Hiroto
Published: July 2002

Experimental and numerical results with He-like C ions are presented which show that soft x-ray gain coefficients can be controlled and optimized by changing the composition of the lasing atomic species in a slab target. It is shown that under optically thick conditions, gain coefficients are drastically increased by using composite materials as targets, thus reducing undesirable reabsorption effects.
Formula for the asymmetric diffraction peak profiles based on double Soller slit geometry
Authors: Ida Takashi
Published: July 2002

The asymmetric diffraction peak profiles and peak shift of conventional powder diffractometry systems caused by the angular divergence along the vertical axis are reproduced by asymmetrized peak profile functions. The asymmetrization is achieved by convoluting the angular dispersions of both incident and scattered beams along the vertical axis. A general method for mapping vertical window functions to the horizontal direction is proposed, and the formulas of two types of horizontal window functions mapped from symmetric double vertical Bartlett (triangular) and Gaussian window functions are presented. Both formulas incorporate a single asymmetry parameter connected with the open width of the Soller slits along the vertical direction. When experimental diffraction peak profiles are fitted by asymmetrized pseudo-Voigt functions, the asymmetry parameter gives good coincidence with the Soller slit angle, which is clearly specified in a given diffractometer.
Pulsed terahertz-beam spectroscopy as a probe of the thermal and quantum response of YBa2Cu3O7−δ superfluid
Authors: Liu Yongqian , Whitaker John F. , Uher Ctirad , Hou S. Y. , Phillips J. M.
Published: July 2002

Pulsed terahertz spectroscopy is used to determine the superfluid response of a YBa2Cu3O7−δ film under both thermal and optical stimulation. The coherent, time-domain technique is used in a novel configuration to directly measure the complex conductivity of the film versus temperature and continuous-wave laser illumination. At 0.6 Tc, the superfluid shows an identical response regardless of whether the stimulus is thermal or optical. This contrasts with the behavior of the superfluid at 0.26 Tc, where dramatic differences are observed depending on whether the sample is heated or subjected to optical illumination. It is suggested that these differences arise from an enhanced contribution due to quantum effects, and thus also from a strong temperature dependence of the quasiparticle recombination time at low temperatures.
Synthesis of aluminum oxide thin films: Use of aluminum tris-dipivaloylmethanate as a new low pressure metal organic chemical vapor deposition precursor
Authors: Ciliberto E. , Fragalà I. , Rizza R. , Spoto G. , Allen G. C.
Published: July 2002

Amorphous aluminum oxide thin films have been produced with low pressure metal organic chemical vapor deposition technique using the aluminum tris-dipivaloylmethanate volatile precursor. Different carrier gases were used for the depositions. The surfaces of the films were analyzed using x-ray photoelectron spectroscopy and secondary ion mass spectrometry. A very low content of carbon was verified when oxygen and water vapor saturated argon were used as carrier gases. A higher hydration percentage of the deposited material was verified when water vapor was present during the deposition process.
Germanium- and tellurium-doped GaAs for non-alloyed p-type and n-type ohmic contacts
Authors: Park Joongseo , Barnes Peter A. , Lovejoy Michael L.
Published: July 2002

Epitaxial ohmic contacts to GaAs were grown by liquid phase epitaxy. Heavily Ge-doped GaAs was grown to prepare ohmic contacts to p-GaAs while Te was used for the n-type contacts. Hall measurements were carried out for the samples grown from melts in which the mole fraction of Ge was varied between 1.55 atomic % and 52.2 atomic %, while the Te mole fractions varied between 0.03% and 0.5%. Specific contact resistance, rc, as low as rcp=2.9×10−6 ohm-cm 2 for Ge doping of p=(Na−Nd)=6.0×1019 holes/cm3 was measured for p-contacts and rcn=9.6×10−5 ohm-cm2 was measured for Te doping of n=(Nd−Na)=8.9×1018 electrons/cm3 for GaAs metallized with non-alloyed contacts of Ti/Al.
Effect of residual ion damage on the minority carrier lifetime in molecular beam epitaxy grown silicon doped by low-energy ion implantation
Authors: Peters C. J. , Noël J. P. , Xu D. X. , Buchanan M. , Du J. , Tarr N. G.
Published: July 2002

The residual ion damage due to low-energy ion implantation during molecular beam epitaxy growth was investigated by measuring the minority carrier lifetime in the base of a silicon bipolar transistor. The base was doped with As+ ions at 200 eV to a concentration of 1019 cm−3. Three samples were grown at temperatures of 500, 650, and 800 °C. The 500 °C sample had a minority carrier lifetime in the base ∼1/6 that of the samples grown at the higher temperatures. On annealing at 650 °C the lifetimes of all samples were essentially equal. The results indicate that at this dopant concentration the collision cascades caused by ion bombardment do not overlap.
Low-temperature B doping of Si by synchrotron radiation irradiation of disilane/decaborane during gas-source molecular beam epitaxy
Authors: Utsumi Yuichi
Published: July 2002

Very low-temperature doping of B achieved by synchrotron radiation (SR) irradiation has been performed using disilane molecular beam epitaxy (MBE). It was observed that B incorporation can be significantly enhanced by SR irradiation during Si epitaxy and B concentration had linear dependence on the decaborane partial pressure. Furthermore, doped epitaxial film can be attained by SR excitation of source molecules even at 80 °C, where the conventional gas-source MBE method can not so far achieve Si growth.
Epitaxial planarization of patterned yttria-stabilized zirconia substrates for multilayer structures
Authors: Chang Bertha P. , Sonnenberg Neville , Cima Michael J. , Sun Jonathan Z. , Yu-Jahnes Lock See
Published: July 2002

In situ planarization of epitaxial films has been demonstrated. This is a critical technology for the processing of any epitaxial multilayer device. Ion beam assisted deposition (IBAD) has been used to planarize patterned yttria-stabilized ZrO2 (YSZ)(001) substrates using YSZ films. X-ray diffraction measurements have shown that the IBAD YSZ grows homoepitaxially. The IBAD planarization mechanism has similarities to those previously observed for rf bias sputtering. Critical current densities of up to 7×105 A/cm2 at 77 K have been measured for Ba2YCu3O7−x (BYC) films deposited on planarized patterned YSZ substrates using pulsed laser deposition. In contrast, BYC deposited on unplanarized patterned YSZ substrates did not become fully superconducting for measurements down to 25 K.
Second harmonic generation and atomic-force microscopy studies of porous silicon
Authors: Aktsipetrov O. A. , Melnikov A. V. , Moiseev Yu. N. , Murzina T. V. , van Hasselt C. W. , Rasing Th. , Rikken G.
Published: July 2002

Structural properties of porous silicon were studied with atomic-force microscopy (AFM) and optical second harmonic generation (SHG). Depending on etching conditions, the SHG response was observed to be either anisotropic, showing C2v symmetry, or isotropic. This correlated with AFM observations of quasi ordered structures in the first case. The Si etching process was studied by in situ SHG measurements.
Carbon doping of Ga0.47In0.53As using carbontetrabromide by metalorganic molecular beam epitaxy for InP-based heterostructure bipolar transistor devices
Authors: Hamm R. A. , Malik R. , Humphrey D. , Ryan R. , Chandrasekhar S. , Lunardi L. , Geva M.
Published: July 2002

Metalorganic molecular beam epitaxy of carbon-doped heterostructures and InP/Ga0.47In0.53As heterostructure bipolar transistors using carbontetrabromide (CBr4) as the dopant source is reported. Secondary ion mass spectrometry show H incorporation associated with the carbon doping. Hall data for as-grown and postgrowth annealed samples showed a clear increase in doping only for samples grown at the lowest temperature, 450 °C, and higher doping levels. An increase in the mobility, however, was measured for nearly all samples after annealing, indicating that the neutral C–H complexes most likely contribute to majority carrier scattering. The gain variation for various devices with base thickness, WB, and base doping, p, was found to be nearly proportional to 1/(WB×p)2 consistent with diffusive base transport and Auger dominated recombination in the heavily doped base region. It was also observed that in devices where the C-doped base was grown at temperatures ≳500 °C, the gain was shifted to much lower values possibly indicating a reduced electron carrier lifetime.
Effect of pressure on the crystallization of amorphous Fe–Mo–Si–B alloy with diffusion reaction at its surface
Authors: Yao Bin , Ding Bingzhe , Wang Aimin , Hu Zhuangqi
Published: July 2002

The amorphous (Fe0.99,Mo0.01)78Si9B13 alloy with diffusion reaction with Al at its surface transformed into α-Fe(Al) solid solution under 4 GPa and α-Fe(Mo,Si) and (Fe,Mo)3B or Fe2B under other pressures at a temperature range of 783–933 K. A thermodynamic mechanism was suggested by discussing the changes of the chemical potentials with pressure.
Electroplating of poly(tetrafluoroethylene) using plasma enhanced chemical vapor deposited titanium nitride as an interlayer
Authors: Weber A. , Dietz A. , Pöckelmann R. , Klages C.-P.
Published: July 2002

A low-temperature process for titanium nitride (TiN) deposition by means of an electron cyclotron resonance (ECR) plasma enhanced chemical vapor deposition process was applied to poly(tetrafluoroethylene) (PTFE). Tetrakis(dimethylamido)titanium introduced into the downstream region of a nitrogen ECR plasma was used as a precursor for TiN deposition at 100 °C. The thin TiN films (thickness 15–30 nm) act as interlayers to activate the electroless deposition of copper followed by an electroplating process. Prior to the deposition of the interlayer, the samples were treated on a biased susceptor with argon ions to enhance the adhesion of the TiN interlayer. This metallization procedure avoids the use of toxic and pollutive etching agents and yields adherent copper layers on PTFE. Films were characterized by four-point probe resistivity measurements, atomic force microscopy, and secondary ion mass spectrometry.
Magneto-optical absorption spectra and self-similarity of GaAs–(Ga,Al)As quasiperiodic Fibonacci superlattices under in-plane magnetic fields
Authors: Bruno-Alfonso A. , Oliveira L. E. , de Dios-Leyva M.
Published: July 2002

A theoretical study of the effects of in-plane magnetic fields on the interband optical absorption spectra of quasiperiodic GaAs–(Ga,Al)As Fibonacci superlattices is presented within the effective-mass approximation. The electron-envelope wave functions and magnetic subbands are obtained by an expansion in harmonic-oscillator wave functions. The theoretical optical absorption spectra are calculated for magnetic fields related by integer powers of the golden mean τ=(1+√5)/2. It is unambiguously shown that, for magnetic-field values scaled by τ2n, the corresponding optical absorption spectra essentially exhibit a self-similar behavior, with the width of the peaks increasing linearly with the field, in agreement with the experimental results by D. Toet, M. Potemski, Y. Y. Wang, J. C. Maan, L. Tapter, and K. Ploog [Phys. Rev. Lett. 66, 2128 (1991)].
Effect of silver in Bi1.7Pb0.3Sr2−xAgxCa2Cu3Oy
Authors: Yu Y. , Jin X. , Ding S. Y. , Zhen Z. Y. , Yao X. X. , Shen G. J.
Published: July 2002

The oxide superconductor Bi1.7Pb0.3Sr2−xAgxCa2Cu3Oy has been synthesized under the ordinary pressure. The x-ray diffraction spectra of these specimens show the presence of only 2212 phase when x<0.4, and the transition temperature achieved 99 K. With the x increase, the structure of sample transfers to 2223 phase. The investigation indicates that substitution of Sr2+ by Ag1+ increases the distance between layers. This may respond to Tc increase in 2212 phase and 2223 phase form at a relatively low temperature.
All-optical light modulation in bacteriorhodopsin films
Authors: Aranda F. J. , Garimella R. , McCarthy N. F. , Narayana Rao D. , Rao D. V. G. L. N. , Chen Z. , Akkara J. A. , Kaplan D. L. , Roach J. F.
Published: July 2002

We report a convenient method to obtain all-optical light modulation in bacteriorhodopsin films using a degenerate four-wave mixing geometry. Chemically stabilized films of bacteriorhodopsin in a polymer matrix for which the lifetime of the excited M state is tens of seconds were used to demonstrate all-optical light intensity modulation. The films are observed to be stable over a period of 4 years. Due to the sensitivity of the films, small intensities of order microwatt/ cm2 are required in the modulation experiments. Furthermore the fast photochemical transition from M to B permit reasonably fast modulation speeds independent of the slow thermal M and B relaxation time. The experimental system also acts as an all-optical switch where a low power blue pulse turns on a signal red beam.
Generalized formula for the surface stiffness of fluid-saturated porous media containing parallel pore channels
Authors: Nagy Peter B. , Nayfeh Adnan H.
Published: July 2002

The surface stiffness of a fluid-saturated porous solid is defined as the ratio between a small change in capillary pressure and the average displacement of the boundary due to the resulting rise or fall of the fluid level in the pore channels. When the surface pores are structurally open, the surface stiffness is entirely due to the stiffness of the microscopic fluid membranes extended by capillary forces over the surface pores. Due to interfacial tension between the immiscible wetting fluid in the pores and nonwetting fluid (air) above the surface, essentially closed-pore boundary conditions can prevail at the interface. It has recently been shown that the surface stiffness of a porous material containing cylindrical pores can be calculated simply as the surface tension of the saturating fluid divided by the static permeability of the porous solid [P. B. Nagy, Appl. Phys. Lett. 60, 2735 (1992)]. In this letter, we show that the same simple relationship can be generalized for the surface stiffness of fluid-saturated porous media containing parallel prismatic pore channels of any number, size, or shape.
Electrical properties and microstructures of Au/Pt/Ti/Ni ohmic contacts to p-type ZnTe
Authors: Mochizuki Kazuhiro , Terano Akihisa , Momose Masayuki , Taike Akira , Kawata Masahiko , Gotoh Jun , Nakatsuka Shin-ichi
Published: July 2002

Electrical properties and microstructures of Au/Pt/Ti/Ni ohmic contacts to p-type ZnTe were investigated using the transmission line model method and cross-sectional transmission electron microscopy. The specific contact resistance decreases when the annealing temperature is increased and reaches a minimum at 300 °C. The formation of NiTe2 from the reaction between Ni and ZnTe plays an important role in lowering the contact resistance. A contact stability test performed at 102 °C suggests that these ohmic contacts are stable even under high-current injection.
Low 1/f normal-state resistance noise in high-resistivity YBa2Cu3Oy films
Authors: Chen N. Y. , Jonker R. , Matijasevic V. C. , Jaeger H. M. , Mooij J. E.
Published: July 2002

We have measured 1/f resistance noise at room temperature in laser-ablated YBa2Cu3Oy (YBCO) thin films over a wide range of normal-state resistivities. Surprisingly, the high resistivity films exhibit lower normalized noise powers than the low resistivity films. The lowest normalized noise power is 100 times lower than any previously reported values for single crystals of YBCO and is comparable to the lowest noise levels found in other cuprates. Upon oxygen reduction, the noise power in the high resistivity films increases monotonically whereas it decreases in the low resistivity films. We conclude that the high noise level in YBCO is most likely intrinsic to the structure and due to conduction along the Cu-O chains. Therefore, the low noise power in high resistivity films appears to indicate a degraded chain conductivity.
A high-current-gain, high-speed P-n-p AlGaAs/InGaAs/GaAs collector-up heterojunction bipolar transistor
Authors: Tseng H. C. , Hsieh R. C. , Hwang K. C. , Ballingall J. M.
Published: July 2002

A P-n-p AlGaAs/InGaAs/GaAs collector-up heterojunction bipolar transistor (C-up HBT), grown by three-stage molecular beam epitaxy, has been fabricated, and its dc and high-frequency performances have been evaluated. The use of a graded InxGa1−xAs (x=0.0–0.09) is shown to improve the common-emitter current gain (β) and to greatly reduce the base transit time (τb) for the P-n-p C-up HBTs. A maximum current gain (β) of 150 was measured for a 16×17 μm2 device. From S-parameter measurements, a best unity-gain cutoff frequency fT=43 GHz at a collector current of −10 mA was achieved using a 5×10 μm2 collector area. The results show that the P-n-p C-up HBTs may be useful for future planar integrated circuit applications.
Investigation of nondegenerate four wave mixing in semiconductor optical amplifier through bias current modulation
Authors: Soto H. , Erasme D.
Published: July 2002

An experimental study of the combination of four-wave mixing and current modulation in a semiconductor optical amplifier is presented. The measurement of the small signal chirp parameter for the conjugate signal is performed giving results between 0 and −1 for all detuning below 1.5 THz. Its value is much smaller than that of the directly modulated amplifier and furthermore is negative. A conjugate pulse traveling along a standard fiber exhibits no noticeable broadening. The results are in very good agreement with the theory developed in the literature.
Effect of BF2 implantation on ultrathin gate oxide reliability
Authors: Lin Chuan , Chou Anthony I. , Kumar Kiran , Choudhury Prasenjit , Lee Jack C.
Published: July 2002

BF2 implantation is widely used to form P wells, adjust channel threshold voltage, and reduce short channel effects. In this letter, we study effect of BF2 implantation on ultrathin gate oxide reliability. It has been found that BF2 implantation into Si substrate causes degradation of gate oxide reliability in the ultrathin oxide thickness regime. N2O oxide can be used to reduce degradation caused by the implantation and improve gate oxide reliability.
High energy resolution x-ray detection based on a coupled Fiske cavity and Josephson junction oscillator
Authors: Song S. N. , Maglic S. R. , Thomas C. D. , Ulmer M. P. , Ketterson J. B.
Published: July 2002

We describe the use of a miniature microwave Fiske cavity coupled to a Josephson junction oscillator to monitor the dynamic quasiparticle population created in the surrounding superconductor by incident x rays. An expression is obtained for the phase velocities of the TM modes supported by this structure. The design has the advantage of being inherently thick—sufficient to completely absorb low energy x rays and is potentially scalable to a pixilated device with a pixel size 50 μm in linear dimension. The device represents an alternative strategy to implement the dynamic microwave absorption approach suggested by Gulian and Van Vechten and subsequent variations.
Lomer–Cottrell misfit dislocations in [001] In0.2Ga0.8As/GaAs single heterostructures
Authors: Zou J. , Cockayne D. J. H.
Published: July 2002

Lomer–Cottrell misfit dislocations in [001] In0.2Ga0.8As/GaAs single heterostructures are observed using high resolution electron microscopy. They result from the interaction of two parallel 60° dissociated misfit dislocations lying on intersecting {111} planes. Elasticity calculation is carried out to estimate the geometrical conditions in which the interaction can occur.
Evolution of implanted carbon in silicon upon pulsed excimer laser annealing
Authors: Kántor Z. , Fogarassy E. , Grob A. , Grob J. J. , Muller D. , Prévot B. , Stuck R.
Published: July 2002

Formation of epitaxial Si1−yCy substitutional alloy layers on monocrystalline silicon surfaces with y≊1 at. % is reported. The preparation method was carbon ion implantation, followed by KrF excimer laser annealing. Results of Rutherford backscattering (RBS), secondary ion mass spectrometry (SIMS) and infrared absorption analyses are compared. The authors concluded that, up to ∼1 at. % carbon content, the dominant process is nonequilibrium trapping of carbon in substitutional lattice sites upon fast resolidification. Above this concentration the complex carbon redistribution processes are influenced by silicon carbide precipitation in the melt and segregation effects in the near-surface region.
Photoluminescence of copper-doped porous silicon
Authors: Huang Y. M.
Published: July 2002

In this letter, we report the results of copper-doped porous silicon. In the photoluminescence spectrum of porous silicon without Cu doping, only one red luminescence band appears with a peak at 676.5 nm; while in the photoluminescence spectrum of Cu-doped porous silicon, red and near infrared luminescence bands appear with peaks at 660.6 and 802.2 nm, respectively. Energy dispersive x-ray spectroscopy and Fourier transform infrared spectroscopy indicate the near infrared luminescence band is related to copper impurity in porous silicon. We assign the red luminescence band to band-to-band emission, and the near infrared luminescence band to band-to-acceptor emission.
Degradation phenomena of multilayer ZnO–glass varistors studied by deep level transient spectroscopy
Authors: Wang Yin-Pin , Lee Wei-I. , Tseng Tseung-Yuen
Published: July 2002

The degradation of non-Ohmic electrical characteristics of ZnO–glass chip varistors due to high-intensity impulse currents was correlated with the deep trap levels investigated by means of deep level transient spectroscopy. Three electron traps located at 0.11, 0.27, and 0.94 eV below the conduction band were observed for chip varistors before current impulse testing. These trap energy depths of the chip varistors after current impulse testing were found to be almost unchanged, but their trap densities and capture cross sections both decreased. The concentration of the trap at 0.94 eV was decreased and ascribed to oxygen vacancies existing at the grain boundaries of the varistor. The electrical degradation phenomenon of the chip varistors is closely related to the reaction between the trap at 0.94 eV and adsorbed oxygen ions at the grain boundaries.
The influence of demixing on the properties of a free-burning arc
Authors: Murphy A. B.
Published: July 2002

Demixing in an atmospheric-pressure free-burning welding arc was investigated using a two-dimensional numerical model. Simulations of arcs in argon–nitrogen and argon–helium mixtures demonstrated that demixing can have a major influence on the composition of the arc in both the central and edge regions. Convection suppressed the change in composition in the central 0.5 mm of the argon–nitrogen arc only. Furthermore, demixing was found to have only a relatively minor effect on temperature and axial velocity, but it significantly altered thermal transport in the argon–nitrogen mixture. It is concluded that demixing can be important in both chemical and thermal applications of mixed-gas arcs.