bluuebunny/crossref_metadata_2025 huggingface dataset:
Atmospheric pressure ion focusing in a high-field asymmetric waveform ion mobility spectrometer
Authors: Guevremont Roger , Purves Randy W.
Published: July 2002

The focusing of ions at atmospheric pressure and room temperature in a high-field asymmetric waveform ion mobility spectrometer (FAIMS) has been investigated. FAIMS operates with the application of a high-voltage, high-frequency asymmetric waveform across parallel plates. This establishes conditions wherein an ion migrates towards one of the plates because of a difference in the ion mobility at the low and high electric field conditions during application of the waveform. The migration can be stopped by applying a dc compensation voltage (CV) which serves to create a “balanced” condition wherein the ion experiences no net transverse motion. This method has also been called “transverse field compensation ion mobility spectrometry” and “field ion spectrometry®.” If this experiment is conducted using a device with cylindrical geometry, rather than with flat plates, an ion focusing region can exist in the annular space between the two concentric cylinders. Ion trajectory modeling showed that the behavior of the ions in the cylindrical geometry FAIMS analyzer was unlike any previously described atmospheric pressure ion optics system. The ions appeared to be trapped, or focused by being caught between two opposing forces. Requirements for establishing this focus for a given ion were identified: the applied waveform must be asymmetric, the electric field must be sufficiently high that the mobility of the ion deviates from its low-field value during the high-voltage portion of the asymmetric waveform, and finally, the electric field must be nonuniform in space (e.g., cylindrical or spherical geometry). Experimental observations with a prototype FAIMS device, which was designed to measure the radial distribution of ions in the FAIMS analyzer region, have confirmed the results of ion trajectory modeling.
An automated apparatus for measuring the tensile strength and compressibility of fine cohesive powders
Authors: Manuel Valverde José , Castellanos Antonio , Ramos Antonio , Pérez Alberto T. , Morgan Michael A. , Keith Watson P.
Published: July 2002

This paper describes an apparatus based on a novel use of a powder bed, whereby the relationship between consolidation stress, tensile strength, and free volume of fine powder is measured. The powder to be tested is first initialized to a reproducible state. The initialized powder is next consolidated either beyond its own weight or below its own weight by means of a controlled flow of gas. An ultrasonic device measures the height of the bed, thus providing an average value of the powder free volume. Next the consolidated bed of powder is subjected to a slowly increasing gas flow, so directed as to put the powder under tension. The overpressure causing the powder to break provides a measure of the tensile strength of the powder, which in turn is a function of the consolidation and free volume. The relationship between consolidation stress, tensile strength, and free volume is related to powder flowability.
Near-field direct-write ultraviolet lithography and shear force microscopic studies of the lithographic process
Authors: Smolyaninov Igor I. , Mazzoni David L. , Davis Christopher C.
Published: July 2002

Direct-write lithography on a 100 nm scale has been carried out using the near-field optical interaction between an uncoated tapered fiber tip and a layer of photoresist. This allows both lithography and shear force microscopic examination of the surface, which reveals morphological changes in the photoresist before development.
Record low surface recombination velocities on 1 Ω cm p-silicon using remote plasma silicon nitride passivation
Authors: Lauinger Thomas , Schmidt Jan , Aberle Armin G. , Hezel Rudolf
Published: July 2002

Outstanding surface passivation of low-resistivity single-crystalline p-silicon is reported using silicon nitride fabricated at low temperature (375 °C) in a remote plasma-enhanced chemical vapor deposition system. The effective surface recombination velocity Seff is determined as a function of the bulk injection level from light-biased photoconductance decay measurements. On polished as well as chemically textured silicon wafers we find that our remote plasma silicon nitride provides better surface passivation than the best high-temperature thermal oxides ever reported. For polished 1.5 and 0.7 Ω cm p-silicon wafers, record low Seff values of 4 and 20 cm/s, respectively, are presented.
Comparison of electric field emission from nitrogen-doped, type Ib diamond, and boron-doped diamond
Authors: Geis M. W. , Twichell J. C. , Efremow N. N. , Krohn K. , Lyszczarz T. M.
Published: July 2002

Field emission of electrons from boron- and nitrogen-doped diamond is compared. Emission from boron-doped diamond requires vacuum electric fields of 20–50 V μm−1, while nitrogen-doped, type Ib diamond requires fields of 0–1 V μm−1. Since boron-doped diamond is very conductive, very little voltage drop occurs in the diamond during emission. Nitrogen-doped diamond is insulating, so during emission a potential of 1–10 kV appears in the diamond. This potential is a function of the back contact metal-diamond interface. A roughened interface substantially reduces the potential in the diamond and increases emission. The electrons are often emitted from the nitrogen-doped diamond as beamlets. These beamlets leave the surface of the diamond at angles up to 45° from the substrate normal. Although the vacuum field is small, these electrons have energies of several kV. It is unknown whether the electrons are accelerated to these energies in the bulk of the diamond, or at high electric fields near the emitting surface.
Time-resolved study of intervalence band thermalization in a GaAs quantum well
Authors: Kim A. M. T. , Hunsche S. , Dekorsy T. , Kurz H. , Köhler K.
Published: July 2002

The thermalization of optically excited cold holes in a GaAs quantum well is investigated by femtosecond two-color pump–probe measurements. Clear evidence is found for scattering from heavy-holes into the lowest light-hole band due to LO-phonon absorption. We obtain firm data on scattering times which depend strongly on lattice temperature. They vary from 230 fs at room temperature to 900 fs at T=105 K. The experimental data are well reproduced by numerical calculations.
1.5 μm photoluminescence of Er3+ in YF3, LuF3, and LaF3 thin films
Authors: Buchal Ch. , Siegrist Th. , Jacobson D. C. , Poate J. M.
Published: July 2002

We have studied the photoluminescence at 1.5 μm of the 4I13/2→4I15/2 transition of the Er3+ ion, incorporated as ErF3 into polycrystalline YF3, LuF3, and LaF3 films, deposited onto SiO2 or Si wafers. We conclude that LaF3 is an exceptionally suitable host for Er3+, since it permits high Er3+ concentrations, long lifetimes of the excited level, and a strong Stark splitting. This results in a spectral shape suitable for broadband optical amplifiers with a usable optical bandwidth exceeding 8000 GHz (Δλ≂60 nm).
A method for fabricating silicon quantum wires based on SiGe/Si heterostructure
Authors: Liu J. L. , Shi Y. , Wang F. , Lu Y. , Zhang R. , Han P. , Gu S. L. , Zheng Y. D.
Published: July 2002

A method for fabricating silicon quantum wires with SiO2 boundaries is presented. It is accomplished by first growing Si/SiGe/Si heterostructure on silicon substrate with very low-pressure chemical vapor deposition, followed by lithography and reactive ion etching to form trench structures. Finally, the selective chemical etching of SiGe over silicon and subsequent thermal oxidation are carried out to generate expected silicon quantum wires. The result observed is demonstrated using scanning electron microscopy. Furthermore, the thermal oxidation characteristics of the silicon wires are investigated. The present method provides a well-controllable way to fabricate silicon quantum wires and is fully compatible with silicon microelectronic technology.
Initial, rapid light-induced changes in hydrogenated amorphous silicon materials and solar cell structures: The effects of charged defects
Authors: Jiao Lihong , Liu Hongyue , Semoushikina S. , Lee Yeeheng , Wronski C. R.
Published: July 2002

Large, rapid light induced changes are reported for photoconductivities, electron mobility-lifetime products, and forward bias currents in hydrogenated amorphous silicon (a-Si:H) films and Schottky barrier cell structures. The absence of concurrent changes in subgap absorption and quantum efficiencies are clearly inconsistent with the widely held view that the kinetics of degradation in a-Si:H materials and cells can be quantified solely in terms of neutral dangling bond defects. The self-consistent analysis of all the results was carried out for films and Schottky barrier structures by including charged defects and using a three-Gaussian distribution of donorlike and acceptorlike defect states. Such self-consistent development of ‘‘operational’’ parameters for these gap states offers a method for reliable and quantitative correlations between solar cell performance and stability with the properties of their bulk materials.
Anisotropy of hexagonal boron nitride core absorption spectra by x-ray Raman spectroscopy
Authors: Watanabe N. , Hayashi H. , Udagawa Y. , Takeshita K. , Kawata H.
Published: July 2002

B as well as N core excitation spectra of hexagonal boron nitride (h-BN) have been studied by means of x-ray Raman scattering (XRS) spectroscopy. Transitions from 1s core to σ* and π* states are completely distinguished by anisotropy measurements of XRS, thus making an unambiguous assignment to the symmetries of excited states and offering a sound basis to characterize h-BN with core absorption spectroscopy.
Intracavity spectroscopy in vertical cavity surface-emitting lasers for micro-optical-mechanical systems
Authors: Meissner K. E. , Gourley P. L. , Brennan T. M. , Hammons B. E. , McDonald A. E.
Published: July 2002

We demonstrate lasing action in a novel microcavity laser device based on vertical cavity surface-emitting laser technology. This laser can be used for intracavity spectroscopy, high contrast imaging of small (10 μm) structures, and is well suited for use in micro-optical mechanical systems for analysis of particles or fluids. Here, we investigate spectra of intracavity polystyrene spheres. Lasing threshold, single-mode operation, and multimode operation are all studied. Transverse mode separation in the multimode regime is found to be effective for sizing of the spheres.
InAsSb-based mid-infrared lasers (3.8–3.9 μm) and light-emitting diodes with AlAsSb claddings and semimetal electron injection, grown by metalorganic chemical vapor deposition
Authors: Allerman A. A. , Biefeld R. M. , Kurtz S. R.
Published: July 2002

Gain-guided, injection lasers using AlAsSb for optical confinement and a strained InAsSb/InAs multiquantum well active region were grown by metalorganic chemical vapor deposition. The semi-metal properties of a p-GaAsSb/n-InAs heterojunction are utilized as a source for injection of electrons into the active region of the laser. In pulsed mode, the laser operated up to 210 K with an emission wavelength of 3.8–3.9 μm. We also report on the two-color emission of a light-emitting diode with two different active regions to demonstrate multistage operation of these ‘‘unipolar ’’ devices.
Fabrication of n-type nickel doped B5C1+δ homojunction and heterojunction diodes
Authors: Hwang Seong-Don , Yang Ken , Dowben P. A. , Ahmad Ahmad A. , Ianno N. J. , Li J. Z. , Lin J. Y. , Jiang H. X. , McIlroy D. N.
Published: July 2002

We have successfully nickel doped a boron carbide (B5C) alloy film. The nickel doped boron-carbide (Ni-B5C1+δ) thin films were fabricated from a single source carborane cage molecule and nickelocene [Ni(C5H5)2] using plasma enhanced chemical vapor deposition. Nickel doping transforms the highly resistive undoped film from a p-type material to an n-type material. This has been verified from the characteristics of diodes constructed ofNi-B5C1+δ on both n-type silicon and p-type B5C. The homojunction diodes exhibit excellent rectifying properties over a wide range of temperatures.
Guiding and confinement of a laser produced plasma by a curved magnetic field
Authors: Tsui Y. Y. , Vick D. , Fedosejevs R.
Published: July 2002

An axial magnetic field with a maximum strength of 2.2 kG was used to confine and guide a laser produced carbon plasma around a 30 deg bend. The plasma was produced by a 25 ns KrF laser pulse at a peak intensity of 1×109 W cm−2. An array of Faraday cups positioned at the exit of the guide field was used to determine that approximately 20% of the original plasma was confined by the magnetic field and guided along a 15 cm trajectory to a 5 cm2 area.
Simulated annealing analysis of Rutherford backscattering data
Authors: Barradas N. P. , Jeynes C. , Webb R. P.
Published: July 2002

The combinatorial optimization simulated annealing algorithm is applied to the analysis of Rutherford backscattering data. The analysis is fully automatic, i.e., it does not require time-consuming human intervention. The algorithm is tested on a complex iron-cobalt silicide spectrum, and all the relevant features are successfully determined. The total analysis time using a PC 486 processor running at 100 MHz is comparable to the data collection time, which opens the way for on-line automatic analysis.
Alternating current losses in biaxially textured YBa2Cu3O7−δ films deposited on Ni tapes
Authors: Kerchner H. R. , Norton D. P. , Goyal A. , Budai J. D. , Christen D. K. , Kroeger D. M. , Specht E. D. , He Q. , Paranthaman M. , Lee D. F. , Sales B. C. , List F. A. , Feenstra R.
Published: July 2002

YBa 2 Cu 3 O 7−δ films grown on rolling-assisted biaxially textured substrates carry critical current densities 105–106 A/cm2 at 77 K and low applied magnetic fields. In the low-field and low-current regime, ac transport current studies show hysteresis energy loss (per cycle and per unit length) roughly the value expected for a superconductor of elliptic cross section. The critical current Ic was deduced from observed dc and dynamic current-voltage relations. The power loss rises sharply as I0 (the maximum current in each cycle) is raised above Ic. In the present configuration, ferromagnetic hysteresis of the Ni substrate contributes little or no loss.
Cluster models for the photoabsorption of divalent defects in silicate glasses: Basis set and cluster size dependence
Authors: Stefanov Boris B. , Raghavachari Krishnan
Published: July 2002

The two lowest singlet excited states of divalent Si defects in silicate glasses are studied by ab initio methods. Excitation energies of 5.2 and 6.8 eV are obtained. Steady convergence to these values is shown with the increase in size both of the model cluster and of the basis set employed in the calculations. The results clearly demonstrate the viability of the quantum-chemical cluster approach for the study of local excitations in glass defects.
High resolution positron-annihilation spectroscopy with a new positron microprobe
Authors: Greif H. , Haaks M. , Holzwarth U. , Männig U. , Tongbhoyai M. , Wider T. , Maier K. , Bihr J. , Huber B.
Published: July 2002

In cooperation with Zeiss/LEO GmbH, a monoenergetic positron source has been integrated in the electron optical system of a scanning electron microscope by help of a magnetic prism. The electron optics serves both to image the specimen with electrons and to form a positron microbeam that allows local positron-annihilation measurements with a resolution in the micron range. The fatigue damage profile along the cross section of a copper plate after a three-point bending test has been investigated. The obtained S-parameter profile coincides well with the expected fatigue damage distribution.
Photoconductivity and charge transporting properties of metal-containing poly(p-phenylenevinylene)s
Authors: Chan Wai Kin , Gong Xiong , Ng Wai Yue
Published: July 2002

A novel type of poly(p-phenylenevinylene)s which contain (bis(2,2′:6′,2′′-terpyridine) ruthenium (II) complexes has been developed. The absorption of the polymers at 500 nm was strongly enhanced by the metal complexes due to the presence of the metal–ligand charge transfer transition. The charge transportation is dispersive with hole carrier mobilities and activation energy of ∼7×10−5 cm2 V−1 s−1 and 0.20 eV, respectively, depending on the concentration of the metal complex. A log μ vs E1/2 plot shows that hole mobilities decrease with increasing field, which suggests the presence of off-diagonal disorder in the hopping sites.
Characterization of nonradiative traps by hot electron–hole plasma luminescence dynamics in polar semiconductors
Authors: Juršėnas S. , Tamulaitis G. , Kurilčik G. , Žukauskas A.
Published: July 2002

Luminescence intensity dependence on excitation intensity has been studied at quasi-steady-state conditions in CdS and CdSe crystals at T=294 K and interpreted, with heating of photoelectrons taken into account. The shape of the dependence indicates a reduction of carrier density due to increased effective temperature. A method for estimating the height of the barrier for centers governing the thermally activated nonradiative capture by multiphonon emission is proposed. The barrier heights of 140 and 170 meV in CdS and CdSe, respectively, have been estimated.
Current transport mechanisms in GaN-based metal–semiconductor–metal photodetectors
Authors: Carrano J. C. , Li T. , Grudowski P. A. , Eiting C. J. , Dupuis R. D. , Campbell J. C.
Published: July 2002

We report on the current transport mechanisms dominant at the Schottky interface of metal–semiconductor–metal photodetectors fabricated on single-crystal GaN, with active layers of 1.5 and 4.0 μm thickness. We have modeled transport in the 1.5 μm devices using thermionic emission theory, and in the 4.0 μm devices using thermionic field emission theory. We have obtained a good fit to the experimental data. We hypothesize that traps in the GaN are related to a combination of surface defects (possibly threading dislocations), and deep-level bulk states that are within a tunneling distance of the interface. A simple qualitative model is presented.
Thermally assisted reversal of exchange biasing in NiO and FeMn based systems
Authors: van der Heijden P. A. A. , Maas T. F. M. M. , de Jonge W. J. M. , Kools J. C. S. , Roozeboom F. , van der Zaag P. J.
Published: July 2002

The stability of the exchange bias field Heb has been studied for magnetron sputtered NiO/Ni66Co18Fe16 and Ni66Co18Fe16/FeMn bilayers. A forced antiparallel alignment of the ferromagnetic magnetization to Heb results in a gradual decrease of Heb as a function of time for NiO as well as FeMn based samples. The observed decrease of Heb increases with temperature and is interpreted as a thermally assisted reversal of magnetic domains in the antiferromagnetic layer.
Oscillatory perpendicular magnetic anisotropy and lattice plane spacing in Fe/Au superlattices
Authors: Takanashi K. , Mitani S. , Himi K. , Fujimori H.
Published: July 2002

Perpendicular magnetic anisotropy has been investigated for Fe(x ML)/Au(x ML) superlattices (ML: monatomic layer thickness) with x ranging from 1 to 4. The x-ray diffraction analyses indicate the formation of coherent layered structures both for x=integers and nonintegers. However, the perpendicular magnetic anisotropy for x=nonintegers shows different behavior from that for x=integers, and consequently, it oscillates as a function of x with a period of 1 ML. Furthermore, the out-of-plane lattice spacing also oscillates in the same manner.
Electrical properties and crystal structures of (Ba,Sr)TiO3 films and BaRuO3 bottom electrodes prepared by sputtering
Authors: Chu Chung Ming , Lin Pang
Published: July 2002

( Ba,Sr)TiO 3 (BST) films were synthesized on BaRuO3 (BRO) using radio-frequency magnetron sputter deposition. Conductive (∼1 mΩ cm) BRO layers of (110) texture were produced at a deposition temperature Td=400 °C, about 200 °C lower than that of SrRuO3. The BST (100 nm) deposited on the BRO showed a (110) preferred orientation and crystallization formation at temperatures as low as 200 °C. An interfacial layer and the local epitaxial growth of BST on BRO layers within columnar grains were confirmed by high-resolution transmission-electron microscopy studies. Uniform I–V characteristics (I<1×10−7 A/cm2) for bias voltages in the range 0.0–3.0 V of all the BST films deposited within Td=300–500 °C were observed. The dielectric constants of the BST films (e.g., εr=300 at Td=400 °C) are considerably higher than those generally achievable for the same Td by using Pt bottom electrodes. The dependence of the annealing atmosphere (N2 and O2) of the dielectric constants was studied and attributed to a diffused BST/BRO interfacial layer which is semiconductive in a reduced state and insulating in an oxidized state.
Deposition of tetrahedral hydrogenated amorphous carbon using a novel electron cyclotron wave resonance reactor
Authors: Weiler M. , Lang K. , Li E. , Robertson J.
Published: July 2002

Highly tetrahedral hydrogenated amorphous carbon (ta-C:H) is deposited with a novel, 13.6 MHz excited electron cyclotron wave resonance (ECWR) plasma source. The ion flux of an acetylene and a nitrogen plasma was investigated by mass spectrometry and retarding field measurements. The ECWR gives a dissociation degree between 15% and 80% depending on gas flow rate. Ion current densities up to 2 mA/cm2 can be achieved, corresponding to ta-C:H deposition rates of 2 nm/s. The fraction of sp3 bonded carbon atoms and mass density are strongly related to the amount of hydrogen in the ion flux. For low hydrogen ion fluxes (10%), a sp3 fraction of 70% and a mass density of 2.85 g/cm3 can be achieved. At higher hydrogen ion fluxes (40%), the sp3 fraction and the mass density fall to 55% and 2.55 gm/cm3, respectively.
Far-field emission narrowing effect of microdisk lasers
Authors: Lee T.-D. , Cheng P.-H. , Pan J.-S. , Tsai R.-S. , Lai Y. , Tai K.
Published: July 2002

Far-field intensity distribution of semiconductor microdisk lasers is experimentally measured and the emission angle is found to be much smaller than that of a planar source with the same near-field width. In fact the emission angle is determined mainly by the disk radius instead of the disk thickness. A scalar diffraction theory in the cylindrical coordinate is developed to explain such an emission-angle-narrowing phenomenon and numerical calculation based on a vectorial diffraction theory is carried out to explain the measured polarization state.
Observation of a two-dimensional electron gas in modulation-doped ZnTe/CdSe quantum wells
Authors: Smorchkova I. P. , Samarth N.
Published: July 2002

We demonstrate the formation of a two-dimensional electron gas in lattice-matched, modulation-doped ZnTe/CdSe quantum well structures. Despite the well-known difficulty in n doping the II–VI semiconductor ZnTe, we find that the unusual type-II band alignment between ZnTe and CdSe allows the efficient transfer of free carriers from n-ZnTe into a CdSe quantum well since the deep donor levels in the n-ZnTe barrier lie above the confined ground state in the CdSe well. The sizeable well depth (∼1.35 eV) enables the fabrication of two-dimensional electron gases with sheet concentrations up to ∼6×1012 cm−2, and with a low-temperature mobility up to 1.4×104 cm2/V s.
Texture control and interfacial structures of SrBi2Ta2O9 thin films on Pt
Authors: Lee Jeong Soo , Kim Hyun Ha , Kwon Hyun Ja , Jeong Young Woo
Published: July 2002

The influence of the Pt bottom electrode orientation on the growth of SrBi2Ta2O9 (SBT) films was elucidated in terms of the atomic matching at the SBT/Pt interfaces. A highly c-axis oriented SBT film was grown on the Pt (001) plane since the SBT (00l) plane conjugates well with the Pt (001) plane from a crystallographic point of view. Both the strong (105)tet and (110)tet SBT peaks were found in the x-ray diffraction profile when the SBT film was grown on the Pt (111) surface. It was found that not a single SBT plane can match with the whole Pt (111) plane due to the appreciably different atomic configurations. The cross-sectional transmission electron microscopy image revealed that the SBT/Pt interface was structurally stable after heat treatment at 750 °C.
Alloy ordering in GaInP alloys: A cross-sectional scanning tunneling microscopy study
Authors: Liu N. , Shih C. K. , Geisz J. , Mascarenhas A. , Olson J. M.
Published: July 2002

We present a cross-sectional scanning tunneling microscopy (XSTM) study of the spontaneous ordering of Ga0.48In0.52P and Ga0.52In0.48P grown on (001) GaAs substrates by molecular beam epitaxy (MBE) and organometallic vapor phase epitaxy (OMVPE), respectively. The (111)-type alloy ordering could be seen clearly in the OMVPE-grown alloy region. On the other hand, the MBE-grown region shows a very small degree of ordering as revealed by the STM. Most of the ordered region shows (InP)1(GaP)1-type ordering: alternating InP- and GaP-like (1̄11) planes. In addition to this type of ordering, we also observe another type of ordering consisting of two InP-like (1̄11) planes and one GaP-like (1̄11) plane that we call (InP)2(GaP)1-type ordering.
Noise temperature and local oscillator power requirement of NbN phonon-cooled hot electron bolometric mixers at terahertz frequencies
Authors: Yagoubov P. , Kroug M. , Merkel H. , Kollberg E. , Gol’tsman G. , Svechnikov S. , Gershenzon E.
Published: July 2002

In this letter, the noise performance of NbN-based phonon-cooled hot electron bolometric quasioptical mixers is investigated in the 0.55–1.1 THz frequency range. The best results of the double-sideband (DSB) noise temperature are: 500 K at 640 GHz, 600 K at 750 GHz, 850 K at 910 GHz, and 1250 K at 1.1 THz. The water vapor in the signal path causes significant contribution to the measured receiver noise temperature around 1.1 THz. The devices are made from 3-nm-thick NbN film on high-resistivity Si and integrated with a planar spiral antenna on the same substrate. The in-plane dimensions of the bolometer strip are typically 0.2×2 μm. The amount of local oscillator power absorbed in the bolometer is less than 100 nW.
Injection of self-interstitials during sputter depth profiling of Si at room temperature
Authors: Cardenas J. , Svensson B. G. , Ni W.-X. , Joelsson K. B. , Hansson G. V.
Published: July 2002

Samples consisting of multi B delta layers and a single Sb delta layer, grown using molecular beam epitaxy, have been sputter depth profiled using O2+ ions with incidence energy of 8.2 or 3.2 keV. The leading and the trailing edge of the B distributions show an anomalous broadening induced by the sputtering, which apparently increases with ion energy. Similar feature is not observed for the Sb distribution. Incorporation of substitutional C to concentrations ∼1019 cm−3 suppresses the broadening feature almost completely. This anomalous broadening is interpreted as a consequence of injection of Si self-interstitials from the region damaged by the ion bombardment. These interstitials may migrate far beyond the mixing depth and interact with the B dopants, which yields a mixing of the B atoms before the distribution is within the “ordinary” mixing depth.
Coulomb blockade effects at room temperature in thin-film nanoconstrictions fabricated by a novel technique
Authors: Kubatkin S. E. , Danilov A. V. , Bogdanov A. L. , Olin H. , Claeson T.
Published: July 2002

A technique was developed to fabricate and probe nanosize tunneling structures in thin metallic films. Using oblique evaporation through conventional undercut electron-beam lithographic masks, as the sample resistance was measured in situ, we defined constrictions with widths and lengths of about 10 nm in thin granular palladium films. The tunneling conductivity through a network of metallic grains was studied. Single electron tunneling transistor effects were registered. An electrostatic gate voltage at room temperature could clearly modulate Coulomb blockade offsets of the order of 0.1 V in the current–voltage curves.
Influence of dynamical scattering in crystalline poly(vinylidene fluoride-trifluoroethylene) copolymers
Authors: Borca C. N. , Choi Jaewu , Adenwalla Shireen , Ducharme Stephen , Dowben P. A. , Robertson Lee , Fridkin V. M. , Palto S. P. , Petukhova N.
Published: July 2002

The effective Debye temperature of poly(vinylidene fluoride-trifluoroethylene) copolymers was measured using photoemission and neutron diffraction techniques. An effective Debye temperature of 53±11 K is obtained from the photoemission data and 69±3.5 K from neutron diffraction measurements. This effective Debye temperature is a consequence of the temperature-dependent dynamic motions perpendicular to the surface of these crystalline polymer films.
The effect of native oxide on epitaxial SiGe from deposited amorphous Ge on Si
Authors: Wu Y. H. , Chen W. J. , Chin Albert , Tsai C.
Published: July 2002

We have investigated the effect of native oxide on the epitaxial SiGe from deposited amorphous Ge on Si. Instead of epitaxial growth by molecular beam epitaxy or ultrahigh-vacuum chemical vapor deposition, the SiGe layer is formed by this simple process followed by an annealing step. As observed by transmission electron microscopy, the suppression of native oxide plays an important role to achieve epitaxial SiGe. The SiGe quality degrades with increasing native oxide thickness and becomes polycrystalline with a ∼20 Å interfacial native oxide. On the other hand, single crystalline SiGe can be routinely formed from a HF-vapor treated Si surface.
Nonalloyed high temperature ohmic contacts on Te-doped InP
Authors: Ren F. , Antonell M. J. , Abernathy C. R. , Pearton S. J. , LaRoche J. R. , Cole M. W. , Lothian J. R. , Gedridge R. W.
Published: July 2002

We report on a thermal stability study of WSi0.79 contacts on Te-doped InP. The epitaxial InP layers were grown on Fe-doped semi-insulating InP substrates by metalorganic molecular beam epitaxy. Tri-isopropylindium-di-isopropyltellurium was used as the Te precursor and the doping level was 1.4×1020 cm−3. Contact metal, amorphous WSi0.79, was sputtered from a composite and an excellent specific contact resistance of 1×10−6 Ω cm2 was achieved. The specific contact resistivity was also measured at different temperature (25–200 °C) and it stayed fair contact. This is clear indication that the current transport through the contact dominates by tunneling. After alloying at temperatures up to 600 °C, there is no obvious change of specific contact resistance or sheet resistance. After 700 °C annealing, there was significant P out-diffusion detected and the specific contact resistance began to degrade. However, the contact metal morphology and edge definition were unaffected. After 800 °C annealing, there was evidence of In out-diffusion after and the surface morphology became rough.
Photogeneration of high pretilt angles of nematic liquid crystals by azobenzene-containing polymer films
Authors: Furumi Seiichi , Nakagawa Masaru , Morino Shin’ya , Ichimura Kunihiro , Ogasawara Hidehiko
Published: July 2002

A vertically aligned (VA) type of nematic liquid-crystal (LC) cell was explored using photoirradiated thin films of a polymethacrylate with mesogenic moieties of 4-trifluoromethoxyazobenzene as side chains. Optical anisotropy was generated by slantwise irradiation of films of the polymer with nonpolarized ultraviolet light, followed by annealing treatment to enhance the photodichroism which displayed thermal stability. The photoirradiated films brought about high pretilt angles of the LC so that a VA-type LC cell was fabricated. The cell exhibited electro-optical properties with excellent optical quality on applying voltages even after heating at 100 °C for several hours.
Ferroelectric behavior of Li-doped ZnO thin films on Si(100) by pulsed laser deposition
Authors: Joseph M. , Tabata H. , Kawai T.
Published: July 2002

Thin films of Li-doped ZnO of different compositions (Zn1−xLix)O, x=0.1, 0.17, and 0.3 have been prepared on Si(100) substrates, with no buffer layer, by the pulsed laser deposition method. Ferroelectric behavior with a memory window of 1.2 V has been observed in capacitance–voltage measurements. The peak maximum in the capacitance–temperature curve suggests that the ferroelectric phase transition occurs around 340 K.
Growth rate and critical temperatures to avoid the modulation of composition of InGaAs epitaxial layers
Authors: González D. , Aragón G. , Araújo D. , de Castro M. J. , García R.
Published: July 2002

Ternary and quaternary semiconductor alloys are usually limited in their band gap engineering by problems related to modulation of composition. In this contribution, we point out the importance of the growth rate in the evolution of a modulation profile in epitaxial films. As a consequence, a diagram of phases for the epitaxial growth is proposed where a window of homogeneous composition is evidenced at low temperatures of growth. The model provides a framework for the epitaxial growth where temperature and growth rate regulation permits the control of the composition modulation in heteroepitaxies.
Observation of magneto-optical second-harmonic generation with surface plasmon excitation in ultrathin Au/Co/Au films
Authors: Pavlov V. V. , Tessier G. , Malouin C. , Georges P. , Brun A. , Renard D. , Meyer P. , Ferré J. , Beauvillain P.
Published: July 2002

Magnetization-induced second-harmonic generation with surface plasmon excitation in an ultrathin Au/Co/Au multilayer structure has been investigated. The resonant coupling of surface plasmons with the fundamental light results in drastic changes of the second-harmonic intensity and a sign reversal of nonlinear magneto-optical effects. Model analysis of the observed phenomena is given on the basis of the multiple interference of interface nonlinear contributions calculated using the Green’s functions formalism.
Charge transport in polymer light-emitting diodes at high current density
Authors: Campbell I. H. , Smith D. L. , Neef C. J. , Ferraris J. P.
Published: July 2002

We present measured and calculated current–voltage (I–V) characteristics of diodes fabricated using a soluble poly(p-phenylene vinylene) derivative. Steady-state and pulsed electrical excitation were used to acquire the I–V characteristics for current densities from 1×10−3 to 1.3×103 A/cm2. Hole current is predominant in the diode. The I–V characteristics were fit using a device model that assumes an electric field-dependent hole mobility of the Poole–Frenkel form that is independent of the charge carrier density. The measured and calculated I–V characteristics are in good agreement over the full range of current density. The maximum electric field and carrier density is about 4×106 V/cm and 1×1018 cm−3, respectively. These results demonstrate that an electric field-dependent mobility, without carrier density dependence, provides an accurate description of hole transport in this polymer over this range of field and carrier density.
Determination of the critical layer thickness in the InGaN/GaN heterostructures
Authors: Parker C. A. , Roberts J. C. , Bedair S. M. , Reed M. J. , Liu S. X. , El-Masry N. A.
Published: July 2002

We present an approach to determine the critical layer thickness in the InxGa1−xN/GaN heterostructure based on the observed change in the photoluminescence emission as the InxGa1−xN film thickness increases. From the photoluminescence data, we identify the critical layer thickness as the thickness where a transition occurs from the strained to unstrained condition, which is accompanied by the appearance of deep level emission and a drop in band edge photoluminescence intensity. The optical data that indicate the onset of critical layer thickness, was also confirmed by the changes in InxGa1−xN surface morphology with thickness, and is consistent with x-ray diffraction measurements.
Optical and dielectric properties of quantum-confined SrBi2Ta2O9 mesocrystals
Authors: Higashijima Hirotaka , Kohiki Shigemi , Takada Syozo , Shimizu Akihiko , Yamada Kenichi
Published: July 2002

We report an increase in optical absorption peak energy from 3.9 to 5.3 eV, and a lowering of dielectric constant maximum temperature from 320 to 180 °C for SrBi2Ta2O9 mesocrystals.
High optical quality AlInGaN by metalorganic chemical vapor deposition
Authors: Aumer M. E. , LeBoeuf S. F. , McIntosh F. G. , Bedair S. M.
Published: July 2002

We report on the metalorganic chemical vapor deposition of the quaternary alloy AlInGaN. We found it desirable to grow quaternary films at temperatures greater than 855 °C in order to suppress deep level emissions in the room-temperature photoluminescence. Details of the conditions necessary to grow In0.1Ga0.9N at 875 °C are presented. Strained and relaxed AlInGaN films were grown with good optical and structural properties for AlN compositions up to 26% and InN content up to 11%. The effects of strain were observed by a difference in the band gap between thin and thick films with the same compositions. The potential impact of the use of quaternary films is discussed regarding strain engineering for the improvement of present device designs.
Indium incorporation during the growth of InGaN by molecular-beam epitaxy studied by reflection high-energy electron diffraction intensity oscillations
Authors: Adelmann C. , Langer R. , Feuillet G. , Daudin B.
Published: July 2002

The indium incorporation in hexagonal InGaN grown by plasma assisted molecular-beam epitaxy is studied by means of reflection high-energy electron diffraction (RHEED) intensity oscillations. It is demonstrated that, in addition to being incorporated in the alloy, indium acts as a surfactant, significantly changing the gallium incorporation. This surfactant effect has to be taken into account to allow for a precise in situ determination of the alloy composition. The indium concentrations determined in situ by RHEED intensity oscillations were found to be in good agreement with ex situ results of Rutherford backscattering spectroscopy. This method also allows us to directly assess the maximum In incorporation as a function of the substrate temperature.
Transmission electron microscopy study of the nitridation of the (0001) sapphire surface
Authors: Vennéguès P. , Beaumont B.
Published: July 2002

The purpose of this letter is to study, using transmission electron microscopy, the nitridation of the (0001) sapphire surface which is a key step for the fabrication of high-quality GaN materials. A nitridation conducted at 1080 °C during 7 min at atmospheric pressure with a 2 slm NH3 flow, results in the formation of a fully crystalline 10-atomic-planes-thick AlN film by the chemical transformation of the Al2O3 surface. From measurements of interplanar distances in high-resolution images, we show that this chemical transformation is incomplete, i.e., that a few Al vacancies and/or O atoms remain in the AlN structure.
Magnetocrystalline anisotropy of TbFe12−xTix single crystals
Authors: Wang Jianli , Wu Guangheng , Tang Ning , Yang Dong , Yang Fuming , de Boer F. R. , Janssen Y. , Klaasse J. C. P. , Brück E. , Buschow K. H. J.
Published: July 2002

TbFe 12−x Ti x single crystals have been investigated by means of magnetic measurements. With decreasing temperature, a spin-reorientation transition from easy axis to easy plane occurs. The rate of decrease of spin-reorientation temperature with x is about −380 K/Ti. There exists a strong magnetocrystalline anisotropy in the basal plane. The anisotropy field Ba between [100] and [110] for the compound TbFe11.15Ti0.85 is as high as 35 T which is about three times Ba in the axial direction. With increasing x, the easy magnetization direction at low temperatures in the basal plane changes from [110] for x=0.85 to [100] for x=1.0. The composition dependence of anisotropy can be understood in terms of a change of the crystal field parameters Anm due to substitution of Ti for Fe.
Intrinsic defect-related blue-violet and ultraviolet photoluminescence from Si+-implanted fused silica
Authors: Choi Suk-Ho , Elliman R. G. , Cheylan S. , Martin J. P. D.
Published: July 2002

Photoluminescence (PL) and electron-spin resonance have been used to study intrinsic defects in fused silica during ion implantation and annealing procedures designed to form and H-passivate Si crystallites. Under 250 nm (5 eV) photon excitation, the unimplanted silica has PL bands at 390 (3.2 eV) and 288 nm (4.3 eV). Implantation with 400 keV Si ions creates paramagnetic defects but reduces both the 3.2 and 4.3 eV emissions. Implantation to doses ⩾2×1017Si cm−2 produces an additional weak emission band at 466 nm (2.7 eV). Annealing at 1000 °C and hydrogenation at 500 °C affect both the absolute and relative intensities of the 390 and 288 nm emissions, and this is discussed with reference to known defects in the Si-crystallite/silica system. However, the emissions remain weak compared to those in unimplanted silica even though annealing removes the paramagnetic defects produced by implantation and the weak 466 nm emission observed for high doses. Since no other emission is evident at lower energies, it is concluded that implantation either alters or destroys the defect configurations responsible for the 390 and 288 nm emissions or that it creates diamagnetic defects which offer competing nonradiative relaxation channels.
AlGaN–GaN–AlInGaN induced base transistor
Authors: Shur M. S. , Bykhovski A. D. , Gaska R. , Khan M. A. , Yang J. W.
Published: July 2002

We have simulated an induced base transistor based on n-type GaN–AlGaN–GaN–AlInGaN heterostructure with a thin AlGaN emitter barrier and a thin GaN quantum well base. Our simulations show that such a majority carrier device should have a high collector current density, a low base resistance, a high current gain, and is expected to be a viable competitor to GaN-based heterostructure bipolar junction transistors.
Micromechanical cantilever magnetometer with an integrated two-dimensional electron system
Authors: Schwarz M. P. , Grundler D. , Meinel I. , Heyn Ch. , Heitmann D.
Published: July 2002

We have realized a micromechanical cantilever magnetometer with an integrated two-dimensional electron system (2DES) in an AlGaAs/GaAs heterostructure grown by molecular-beam epitaxy (MBE). The cantilever was defined by lithography and wet-etched selectively to a MBE-grown stop layer. We reach a sensitivity of 10−13 J/T, which enables us to study the de Haas–van Alphen effect in a 2DES of only 0.04 cm2 area. We demonstrate that, at low temperature, the oscillation amplitude at even filling factors is enhanced by a factor of up to 1.8 with respect to the single-particle value.
Artificial construction of SrO/(La, Sr)MnO3 layered perovskite superlattice by laser molecular-beam epitaxy
Authors: Tanaka Hidekazu , Kawai Tomoji
Published: July 2002

Epitaxial thin films of layered perovskite (La, Sr)3Mn2O7 have been artificially grown by atomic-layer stacking of SrO and (La, Sr)MnO3 [artificial SrO/(La, Sr)MnO3 superlattice] using laser molecular-beam epitaxy on an SrTiO3(001) substrate at low processing temperature. Reflection high-energy electron diffraction patterns indicate the flat surface of the films and the layer-by-layer growth mode. X-ray diffraction patterns confirm that c-axis-oriented Ruddlesden–Popper layered (La, Sr)3Mn2O7 thin films can be grown at a substrate temperature as low as 580 °C. The resulting film exhibited ferromagnetism with a Curie temperature of 75 K.
The vortex tube as a classic thermodynamic refrigeration cycle
Authors: Ahlborn Boye K. , Gordon Jeffrey M.
Published: July 2002

Vortex tubes are commonly used as refrigeration devices. We show that the thermal and fluid dynamics of the vortex tube bear the signature of a classic cooling cycle, and quantify its performance as a thermodynamic machine. In the process, we develop simple analytic formulas for the temperature and pressure profiles within the tube. The principal model predictions compare favorably against experimental measurements.
Excited vibrational states and potential energy function for OCS determined using generalized internal coordinates
Authors: Zúñiga José , Bastida Adolfo , Alacid Mercedes , Requena Alberto
Published: July 2002

Variational calculations of excited vibrational states for the OCS molecule, using generalized internal coordinates properly optimized, are presented. The calculations are made for two empirical and one ab initio potential energy surfaces previously reported. It is shown that the computed vibrational frequencies differ considerably from the experimental values for the three potential surfaces employed. Consequently a new and much more accurate potential surface is determined for OCS by nonlinear least-squares fitting to the observed vibrational terms. The surface is expressed as a Morse-cosine expansion in valence coordinates and its quality is checked by computing the vibrational frequencies of three isotopic species of the molecule.
Effects of Si-dose on defect-related photoluminescence in Si-implanted SiO2 layers
Authors: Kim H. B. , Kim T. G. , Son J. H. , Whang C. N. , Chae K. H. , Lee W. S. , Im S. , Song J. H.
Published: July 2002

Si ions were implanted into 100-nm-thick SiO2 layer thermally grown on crystalline Si at an energy of 55 keV with various doses ranging from 1×1014 to 1×1017 Si/cm2 at room temperature. Si ions go through the interface between SiO2 layer and Si substrate generating defects in SiO2 layer and Si substrate as well. Defect-related phenomena were characterized by photoluminescence (PL) and electron spin resonance (ESR) measurements. The PL experiment shows that there exists a dose window for a maximum intensity of luminescence related to radiative defects, while the ESR exhibits that nonradiative defects change from E′ centers to Pb centers as the dose increases. It is considered that the intensity is controlled by the density ratio of radiative to nonradiative defects induced by ion implantation.
Nanoindentation and x-ray diffraction studies of pressure-induced amorphization in C-70 fullerene
Authors: Patterson Jeremy R. , Catledge Shane A. , Vohra Yogesh K.
Published: July 2002

We have carried out high-pressure studies on a C-70 fullerene sample in a diamond anvil cell to 46 GPa at room temperature. Synchrotron energy dispersive x-ray diffraction studies were carried out to monitor the irreversible amorphization transformation followed by nanoindentation studies of the pressure-quenched samples. Micro-Raman studies indicate broad bands at 1570 and 1422 cm−1 indicative of an amorphous phase with a mixture of sp2- and sp3-bonded carbon. Nanoindentation studies on the quenched amorphous phase shows an elastic loading behavior with a hardness of 18 GPa, which is 2–3 times that of the surrounding steel gasket. Our results conclusively establish that the hard carbon phases can be produced from C-70 fullerene by application of pressure at room temperature.