bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of surface anion antisite defects in (110) surfaces of III–V semiconductors
Authors: Ebert Ph. , Quadbeck P. , Urban K. , Henninger B. , Horn K. , Schwarz G. , Neugebauer J. , Scheffler M.
Published: July 2002

We identify surface anion antisite defects in (110) surfaces of GaAs, GaP, and InP using scanning tunneling microscopy combined with density-functional theory calculations. In contrast to subsurface arsenic antisite defects, surface antisite defects are electrically inactive and have a very localized defect state which gives rise to a distinct feature in scanning tunneling microscopy images.
Structural phase transition as a mechanism for broadband, low-threshold reflectivity switching in gallium
Authors: MacDonald K. F. , Fedotov V. A. , Zheludev N. I. , Zhdanov B. V. , Knize R. J.
Published: July 2002

We report that a nanoscale laser-induced structural phase transition involving just a few nanometers of gallium at an interface with silica can drive reversible changes in the optical properties of the interface in a very broad spectral range from 440 to 680 nm and beyond. At temperatures up to 15° below the melting point of gallium (30 °C) 3 ns excitation pulses, with fluences of just a few mJ/cm2, are sufficient to induce reflectivity increases of up to 40%.
Localized variations in electronic structure of AlGaN/GaN heterostructures grown by molecular-beam epitaxy
Authors: Smith K. V. , Yu E. T. , Elsass C. R. , Heying B. , Speck J. S.
Published: July 2002

Local electronic properties in a molecular-beam-epitaxy-grown AlxGa1−xN/GaN heterostructure field-effect transistor epitaxial layer structure are probed using depth-resolved scanning capacitance microscopy. Theoretical analysis of contrast observed in scanning capacitance images acquired over a range of bias voltages is used to assess the possible structural origins of local inhomogeneities in electronic structure, which are shown to be concentrated in areas where Ga droplets had formed on the surface during growth. Within these regions, there are significant variations in the local electronic structure that are attributed to variations in both AlxGa1−xN layer thickness and Al composition. Increased charge trapping is also observed in these regions.
Selective growth of GaN on a SiC substrate patterned with an AlN seed layer by ammonia molecular-beam epitaxy
Authors: Tang H. , Bardwell J. A. , Webb J. B. , Moisa S. , Fraser J. , Rolfe S.
Published: July 2002

Highly selective growth of GaN on 4H–SiC using the SiC substrate as a pseudomask has been demonstrated using the ammonia molecular-beam-epitaxy technique. A total lack of nucleation on the bare SiC surface was observed under typical GaN growth conditions. The nucleation of the GaN layer occurred preferentially from a patterned thin (300 Å) AlN seed layer, which had been predeposited on the SiC surface using the magnetron-sputter-epitaxy technique and patterned into parallel stripes by photolithography and chemically assisted ion-beam etching. Evidence of lateral overgrowth was observed by scanning electron microscopy and x-ray diffraction studies. The GaN stripes grown show extremely smooth side facets due to the lateral growth.
Scanning-nonlinear-dielectric-microscopy study on periodically poled LiNbO3 for a high-performance quasi-phase matching device
Authors: Cho Yasuo , Kazuta Satoshi , Ito Hiromasa
Published: July 2002

Studies of the domain distribution of periodically poled LiNbO3 (PPLN) using scanning nonlinear dielectric microscopy (SNDM) were performed for high-quality quasi-phase matching (QPM) devices and some very important results were obtained. First, a single domain surface layer formed on PPLN was found and second, the SNDM studies also revealed that a very strong residual stress or an internal electric field remained in PPLN fabricated using the application of a high voltage due to the pinning effect in single crystal LiNbO3. This stress or internal field substantially reduced the nonlinear dielectric constant of LiNbO3. By annealing to release this stress, it was confirmed that the LiNbO3 recovered from the reduced nonlinear dielectric constant. In the optical region, this constant is equivalent to the second harmonic generation constant, therefore, it is proposed that annealing is an effective method for obtaining a highly efficient high-performance QPM device.
Effect of microgravity on Ca mineral crystallization and implications for osteoporosis in space
Authors: Liu Xiang Yang
Published: July 2002

A study of the effect of microgravity on biomineralization/remineralization by considering Ca mineral nucleation under gravity and microgravity is presented. The structure of human bone is determined to a large extent by the turnover of the bone, which included nucleation of biominerals adjacent to biosubstrates. Heterogeneous nucleation will promote a compact bone structure, whereas homogeaneous nucleation will lead to a porous bone structure. Our experimental results show that microgravity will suppress convection, and consequently promote homogeneous-like nucleation during biomineralization/remineralization. This may explain the formation of the porous bone structure under microgavity condition.
Conducting tip atomic force microscopy analysis of aluminum oxide barrier defects decorated by electrodeposition
Authors: Carrey J. , Bouzehouane K. , George J.-M. , Ceneray C. , Fert A. , Vaurès A. , Kenane S. , Piraux L.
Published: July 2002

We show that the electrodeposition of Ni80Fe20 on top of a thin aluminum oxide barrier leads to particle growth occurring on preferential nucleation centers. The particle sites are attributed to local defects in the aluminum oxide barrier. As a function of the thickness of the barrier, different growth modes can occur. For thinner barriers, new nucleation centers are created during electrodeposition. The resistance of the defects, characterized by conducting atomic force microscopy, ranges from less than 104 to greater than 1012 Ω. Various I(V) characteristics were also obtained, depending on the resistance of the defect. These results suggest that this experimental technique could be a very interesting one with which to fabricate nanoconstrictions dedicated to ballistic magnetoresistance studies.
Interpretation of photoluminescence spectra obtained for spark-processed Si
Authors: Hummel R. E. , Shepherd N. , Burton D.
Published: July 2002

Absorption spectra obtained from spark-processed Si (sp-Si) utilizing differential reflectometry yield a series of closely spaced energy levels, as expected for amorphous materials, which reside between 1.7 and 2.8 eV. Further, a broad absorption band is observed between about 3.2 and about 6.2 eV. A HeCd laser pumps electrons from the ground state into this absorption band. The blue and green photoluminescence peaks of sp-Si are interpreted as originating from emission energy levels at 3.22 and 2.36 eV into which the electrons revert from the just mentioned absorption band by nonradiative transitions. In contrast, pumping with an argon ion laser provides only enough energy to excite the electrons from the ground state into the above mentioned, closely spaced, lower absorption bands and thus causes only a 1.9 eV (red) radiation.
Bulk stress due to surface damage of crystalline silicon and germanium
Authors: Fisher P. , Vickers R. E. M.
Published: July 2002

It is found that abrading two opposing surfaces of either crystalline Si or Ge samples results in homogeneous, uniaxial stress throughout the bulk perpendicular to the damaged surfaces. The latter are chosen to coincide with simple crystallographic planes. This conclusion is reached by analyzing the splittings, intensities, and polarizations of the absorption lines of the Lyman series of bulk shallow impurities in the abraded semiconductors. This effect has been observed for samples which range in thickness, t, from 1 to 3 mm, the internal stress being proportional to t−1.
Chemical role of oxygen plasma in wafer bonding using borosilicate glasses
Authors: Hansen D. M. , Albaugh C. E. , Moran P. D. , Kuech T. F.
Published: July 2002

Plasma-treated oxide layers are commonly used in wafer bonding applications. Borosilicate glass (BSG) layers deposited by low-pressure chemical vapor deposition treated with an O2 plasma in reactive ion etching mode for 5 min at 0.6 W/cm2 and rinsed with DI H2O readily bond to GaAs and Si. The chemical role of this prebonding treatment was investigated using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The peak intensities for both the Si–O and B–O absorbance bands decreased in intensity as a result of the plasma treatment is consistent with the uniform sputtering of 9.8 nm±0.8 nm of BSG. Polarization dependent ATR-FTIR revealed that the H2O/OH absorbance bands decreased in peak intensity with the OH groups being preferentially oriented perpendicular to the sample surface after the plasma treatment. The subsequent DI H2O rinse restores the water to the surface while removing B2O3 from the BSG layer. This prebonding treatment, therefore, results in a hydrophilic bond, but alters the composition of the BSG film at the bonded interface.
Electrical properties of magnetron sputtered amorphous carbon films with sequential sp3-rich/sp2-rich layered structure
Authors: Hastas N. A. , Dimitriadis C. A. , Tassis D. H. , Panayiotatos Y. , Logothetidis S. , Papadimitriou D.
Published: July 2002

The electrical properties of thick amorphous carbon (a-C) films with sequential sp3-rich/sp2-rich layered structure, grown by magnetron sputtering on Si substrates at room temperature, were investigated. At low electric fields, the conduction is due to the variable range hopping mechanism. At high electric fields, thermally assisted band-to-band indirect tunneling is the dominant conduction mechanism, while the Arrhenius plots of the current show a deviation from straight lines in the form of continuous bending satisfying the Meyer–Nelder rule. Comparative studies of low-frequency noise in sp2-rich single layer and sp3-rich/sp2-rich layered a-C films indicate that the noise in the a-C layered originates from traps located mainly at the interfaces of the sp3-rich/sp2-rich bilayers.
Generation of high energy femtosecond pulses from a side-pumped Yb-doped double-clad fiber laser
Authors: Hideur A. , Chartier T. , Brunel M. , Louis S. , Özkul C. , Sanchez F.
Published: July 2002

We present a passively mode-locked side-pumped Yb-doped double-clad fiber laser, emitting around 1.05 μm. Polarization additive-pulse mode-locking technique is used. Mode locking is self-starting and produces 670 fs pulses after compression with a grating pair inserted in the cavity. The energy per pulse is 24 nJ.
Distorted surface and interface structures of catalytic gold nanoparticles observed by spherical aberration-free phase electron microscopy
Authors: Kawasaki Tadahiro , Takai Yoshizo , Shimizu Ryuichi
Published: July 2002

The surface and interface atomic structure of catalytic gold nanoparticles was studied by analyzing a spherical aberration-free phase image. Typically, a catalytic gold particle forms a single crystal having a cuboctahedral shape. The atomic structure of the surface and interface is largely deformed from the bulk structure by stress produced by the atom missing row structure, the reconstructed surface structure, and strong interaction with the substrate. In addition, the structure inside the particle is also deformed by distortion of the surface and the interface.
Single-electron transistor based on a silicon-on-insulator quantum wire fabricated by a side-wall patterning method
Authors: Kim D. H. , Sung S.-K. , Sim J. S. , Kim K. R. , Lee J. D. , Park B.-G. , Choi B. H. , Hwang S. W. , Ahn D.
Published: July 2002

We propose and implement a promising fabrication technology for geometrically well-defined single-electron transistors based on a silicon-on-insulator quantum wire and side-wall depletion gates. The 30-nm-wide silicon quantum wire is defined by a combination of conventional photolithography and process technology, called a side-wall patterning method, and depletion gates for two tunnel junctions are formed by the doped polycrystalline silicon sidewall. The good uniformity of the wire suppresses unexpected potential barriers. The fabricated device shows clear single-electron tunneling phenomena by an electrostatically defined single island at liquid nitrogen temperature and insensitivity of the Coulomb oscillation period to gate bias conditions.
Fabrication of silicon thin films with defects below detection limit of electron spin resonance for solar cells by high-speed zone-melting crystallization of amorphous silicon
Authors: Ihara Manabu , Yokoyama Shuhei , Yokoyama Chiaki , Izumi Koichi , Komiyama Hiroshi
Published: July 2002

Silicon (Si) thin films with very-low defect density for solar cells were fabricated by using high-speed (0.7–4.5 mm/s) zone-melting crystallization (ZMC) of amorphous-silicon (a-Si) thin films, resulting in films that had defects below the detection limit of electron spin resonance (ESR). In this letter, poly-crystalline silicon (poly-Si) films for zone-melting recrystallization (ZMR) and a-Si films for ZMC were each sandwiched between two SiO2 films. The Si films were 0.3–2.0 μm thick, the top SiO2 films were 0.35–1.5 μm thick, and the bottom SiO2 films were 0.18–1.2 μm thick. The a-Si ZMC films had higher crystal quality than did the poly-Si ZMR films. Over 90% of the grains in the a-Si ZMC films had preferred (100) orientation when the films were formed at scan speeds 0.7–4.5 mm/s. Transmission electron microscopy (TEM) revealed that neither distinct grain boundaries nor defects were visible in the a-Si ZMC films within the 9-μm-diam observation field. The a-Si ZMC films fabricated from the a-Si films with the thickness smaller than 1 μm had no voids. Such a low defect density indicates that silicon thin-film solar cells with high efficiency can be fabricated by using such very-low defect density silicon thin films.
Domain structure of the antiferromagnetic insulating state in Nd0.5Sr0.5MnO3
Authors: Shklyarevskiy I. O. , Shvedun M. Yu. , Gnatchenko S. L. , van Bentum P. J. M. , Cristianen P. C. M. , Maan J. C. , Kamenev K. V. , Balakrishnan G. , Paul D. McK
Published: July 2002

Optical reflectivity studies of the ferromagnetic metal (FMM) to antiferromagnetic insulator (AFI) phase transition are performed on Nd0.5Sr0.5MnO3 manganite in a wide temperature and magnetic field range. The formation of a domain structure in the AFI state during the FMM−AFI phase transition is observed. It is shown that the two types of domains observed are energetically equivalent states. On the basis of the experimental results and symmetry analysis we conclude that these domains are crystal twins. The twin domain structure of the AFI state in the Nd0.5Sr0.5MnO3 is visible in reflected unpolarized light due to a different tilting of the surface in the domains. The two-phase domain structure FMM+AFI formed in the vicinity of the phase transition is also studied. It is found that a thermodynamically equilibrium two-phase stripe domain structure does not develop. The absence of the magnetic intermediate state is due to the large energy of the interphase wall, which results in the stripe structure period being much larger than the size of the sample.
Temperature increase and charging current in polyethylene film during application of high voltage
Authors: Zhang Chao , Kaneko Kazue , Mizutani Teruyoshi
Published: July 2002

Temperature increase in a low density polyethylene film during the application of high dc voltage was estimated by measuring the sound velocity with a pulsed electroacoustic method. The temperature shows no change under the electric field of 50 MVm−1 at ambient temperature of 30 °C. However, the temperature increases with time, and rises to 63.7 °C in 90 min of the voltage application at ambient temperature of 60 °C. The temperature increase was caused by Joule heating and it resulted in the increase of charging current during the application of high dc voltage. The increase in charging current calculated from the temperature increase agreed well with the experimental one.
Dependence of electromigration-induced failure lifetimes on NiFe thin-film thickness in giant magnetoresistive spin-valve read heads
Authors: Bae Seongtae , Judy Jack H. , Tsu I-Fei , Davis Marshall , Murdock Edward S.
Published: July 2002

The physical mechanisms responsible for the dependence of electromigration-induced failure lifetimes on NiFe thin film thickness in giant magnetoresistive spin-valve read heads have been studied to determine the maximum allowable current density. Based on measured median-times-to-failure, a maximum current density of about 1–2×108 A/cm2 was found to be safely used in 3–5 nm thick NiFe films. Grain size analyses using a transmission electron microscopy suggests that the longer lifetimes of thinner films are mainly due to the smaller number of grain boundaries and fewer triple points which result in less atomic flux divergence.
Towards Si1−xGex quantum-well resonant-state terahertz laser
Authors: Altukhov I. V. , Chirkova E. G. , Sinis V. P. , Kagan M. S. , Gousev Yu. P. , Thomas S. G. , Wang K. L. , Odnoblyudov M. A. , Yassievich I. N.
Published: July 2002

We report on the experimental evidence for terahertz (THz) lasing of boron-doped strained Si1−xGex quantum-well structures. The lasing arises under strong electric fields (300–1500 V/cm) applied parallel to interfaces. The spectrum of THz stimulated emission is presented showing the lasing wavelength near 100 μm and the modal structure caused by a resonator. The mechanism of population inversion is based on the formation of resonant acceptor states in strained SiGe layer.
Individually injected current pulses with conducting-tip, tapping-mode atomic force microscopy
Authors: Fein Asa , Zhao Yanming , Peterson Charles A. , Jabbour Ghassan E. , Sarid Dror
Published: July 2002

Individually injected current pulses during the operation of a conducting-tip tapping-mode atomic force microscope have been measured under a range of experimental conditions. The bias pulses, applied during the tip-sample contact time, did not perturb the tapping operations, and eliminated artifacts associated with displacement currents. The reproducible injection of current density pulses on the order of 10 μA/nm2 per tap can be applied to spreading resistance measurements and to storage applications employing, for example, phase change by Joule heating and magnetic switching by spin-polarized current.
WS
2
nanotubes containing single-walled carbon nanotube bundles
Authors: Whitby R. L. D. , Hsu W. K. , Watts P. C. P. , Kroto H. W. , Walton D. R. M. , Boothroyd C. B.
Published: July 2002

Single-walled carbon nanotubes (SWCNs) encapsulated in multiwalled WS2 nanotubes are produced by pyrolyzing a mixture of WO3−x and SWCNs in N2/H2S atmosphere.
GaInSb/InAs/AlGaAsSb “W” quantum-well light-emitting diodes
Authors: Gevaux D. G. , Green A. M. , Phillips C. C. , Vurgaftman I. , Bewley W. W. , Felix C. L. , Meyer J. R. , Lee H. , Martinelli R. U.
Published: July 2002

We report on the characterization of molecular-beam epitaxy-grown Ga0.75In0.25Sb/InAs/Al0.15Ga0.85As0.05Sb0.95 “W” quantum-well light-emitting diodes (LED). The devices demonstrated room-temperature emission with a peak wavelength of 3.3 μm. A pulsed current output power of 55 μW with a slope efficiency of 98 μW/A was measured and the 300 K internal efficiency was estimated to be 2.5%. Comparative power analysis suggests that LED and laser diode efficiencies are limited by the same thermally activated nonradiative mechanism, probably Auger recombination.
Response of superconducting Y–Ba–Cu–O films to millimeter wave radiation
Authors: Repšas K. , Laurinavičius A. , Vaškevičius A. R. , Anisimovas F.
Published: July 2002

The origin of temperature and radiation power response dependencies to millimeter wave radiation is analyzed for Y–Ba–Cu–O thin films. These dependencies were both experimentally measured and described by an empirical formula. The results which were obtained indicate that the peak shape of temperature dependence for the nonbolometric response is determined by the temperature of the thermostat and is less inertial than for τ=1/f (f=35 GHz).
Lattice parameters of wurtzite Al1−xSixN ternary alloys
Authors: Taniyasu Yoshitaka , Kasu Makoto , Kobayashi Naoki
Published: July 2002

Lattice constants and bond lengths of wurtzite Al1−xSixN ternary alloys (0⩽x⩽0.08) were determined by reciprocal lattice maps around Al1−xSixN (0002) and (11–24) reflections. The measured lattice constants obtained directly from as-grown Al1−xSixN layers were scattered because they include the factor of residual strain. Therefore, the lattice constants in the strain-free case were calculated from the measured lattice constants taking the residual strain into account. We found that the a-axis and c-axis lattice constants of the strain-free Al1−xSixN linearly decreased with the Si content as a0=3.1113−0.1412x (Å) and c0=4.9814−0.2299x (Å). Further, we obtained the bond length as d0=1.86818−0.0862x (Å). The bond length is nearly equal to the interpolation between the Al–N bond and the Si–N bond.
Measurement of interstitial oxygen concentration in silicon below 1015 atoms/cm3
Authors: Sassella A.
Published: July 2002

The absorption coefficient of silicon at 1118 cm−1 due to the multiphonon contribution related to the combination of two transverse optical and one transverse acoustical phonons is measured at the liquid He temperature. The precise knowledge of this contribution, usually hidden by the absorption band of the unavoidable oxygen impurities, permits the quantitative measurement of interstitial oxygen concentration down to 3×1014 atoms/cm3.
ac transport in ferromagnetic tunnel junctions
Authors: Chui S. T. , Hu Liangbin
Published: July 2002

To study possible capacitive effects, we incorporate the effect of electron interaction on the ac spin-polarized tunnelling. Under steady-state nonequilibrium conditions, the voltage-induced charge accumulated at the interface is a sum of two terms, decaying with length scales of the order of the screening length and the spin diffusion length. As a result, the effective width of the capacitor is changed by an additional term. This additional term is a function of the magnetic configurations on opposite sides of the junction and a magnetocapacitance is introduced.
Lateral redistribution of excitons in CdSe/ZnSe quantum dots
Authors: Strassburg M. , Dworzak M. , Born H. , Heitz R. , Hoffmann A. , Bartels M. , Lischka K. , Schikora D. , Christen J.
Published: July 2002

Lateral redistribution processes of excitons localized in CdSe/ZnSe quantum dot structures are investigated by time-integrated and time-resolved spectroscopy. The photoluminescence properties are governed by lateral energy transfer within a dense ensemble of quantum dots. The quantum dots differ in size and Cd concentration and provide a complex potential landscape with localization sites for excitons. At low temperatures, lateral transfer by tunneling leads to a redshift with increasing delay after pulsed excitation. The mobility edge was determined to 2.561 eV. Above 100 K, thermally activated escape and recapture of excitons cause a strong redshift of the PL maximum in the first 500 ps.
Why does an external electrical field stimulate formation of new phase nuclei in dielectrics?
Authors: Vorob’ev V. S. , Malyshenko S. P.
Published: July 2002

Contrary to many previous theoretical considerations, we show that both uniform and nonuniform electrical fields facilitates formation of vapor bubbles in superheated liquid and liquid drop in supersaturated gas. In the latter case, the field must exceed some threshold value, which becomes smaller in nonuniform field. Such conclusions are based on adequate expression for nucleus work formation in the presence of electrical field which we use in our consideration and are in agreement with experimental observations.
Influence of the barrier height on carrier recombination and transparency density in GaN-based laser structures
Authors: Vehse M. , Michler P. , Gösling I. , Röwe M. , Gutowski J. , Bader S. , Lell A. , Brüderl G. , Härle V.
Published: July 2002

Using temperature-dependent and gain measurements, we have examined the laser threshold density of (In,Ga)N/GaN/(Al,Ga)N laser structures with various well widths and different In contents in the active layer. Thermal activation energies, obtained by temperature-dependent photoluminescence measurements at low excitation densities, yield information on the nonradiative recombination channels and demonstrate the existence of two different activation processes. One of them may be related to thermal activation of localized carriers into quasifree states and subsequent nonradiative recombination. The other is attributed to thermal emission of carriers into the barriers. The influence of the barrier height is also reflected by the dependence of the threshold densities required on the temperature.
Analysis of photoexcited charge carrier density profiles in Si wafers by using an infrared camera
Authors: Brendel Rolf , Bail Michael , Bodmann Benno , Kentsch Jörg , Schulz Max
Published: July 2002

We demonstrate the mapping of lateral photoexcited charge carrier density profiles in a Si wafer that is illuminated in a spot by strongly absorbed light, using an infrared camera. The radial decay measured for the charge carrier density yields information on the effective carrier lifetime. The lifetime is extracted from the infrared camera image by modeling the transport. The carrier lifetime determined with the infrared camera technique is in accord with results obtained by conventional transient microwave reflectance measurements.
InAs/GaAs quantum dot lasers with InGaP cladding layer grown by solid-source molecular-beam epitaxy
Authors: Yeh Nien-Tze , Liu Wei-Sheng , Chen Shu-Han , Chiu Pe-Chin , Chyi Jen-Inn
Published: July 2002

This letter presents the lasing properties of InAs/GaAs quantum dot lasers with InGaP cladding layers grown by solid-source molecular-beam epitaxy. These Al-free lasers exhibit a threshold current density of 138 A/cm2, an internal loss of 1.35 cm−1, and an internal quantum efficiency of 31% at room temperature. At a low temperature, a very high characteristic temperature of 425 K and very low threshold current density of 30 A/cm2 are measured.
Magnetic coupling and magnetoresistance in Fe/Si1−xAgx multilayers
Authors: Wang Hai , Tang Yunjun , Li Xiang , Chen Xi , Wang Yinjun , Zhu Tao , Zhao Hongwu , Zhan Wenshan
Published: July 2002

In this letter, we present a study on the magnetic coupling and magnetoresistance (MR) properties in Fe/Si1−xAgx multilayers (MLs) with a granular Si1−xAgx spacer layer. We found that with increasing silver content (x) in a silicon matrix, the magnetic state of MLs varies from a nonmagnetic-coupling state to a weak-antiferromagnetic state around the percolation point of the ∼24-Å-thick granular spacer Si1−xAgx. The MR measurements also reveal an abrupt increase of MR near the same percolation point. These variations are ascribed to the formation of the percolation path in the granular spacer.
Photoluminescence degradation in organic light-emitting devices
Authors: Ke Lin , Chen Peng , Chua Soo Jin
Published: July 2002

Polymer degradation under electrical stress was studied using the device structure indium tin oxide/poly(p-phenylene vinylene)/Ca/Ag. The devices that were used in this study do not show any significant decrease in electroluminescent intensity for up to several thousand hours of operation. However for devices that were electrically stressed and then exposed to normal ambient, there was a significant decrease in the photoluminescence. Those that were not electrically stressed but exposed to normal ambient or were electrically stressed but not exposed to normal ambient, there was no significant degradation in the photoluminescence. These results showed that both conditions of electrical stress and photo-oxidation are necessary for a significant decrease of the photoluminescence intensity. Degradation is accompanied by an increase in the x-ray crystallization peak. We interpret that the photoluminescence intensity degradation is due to the change in polymer crystallinity caused by electrical stress followed by photo-oxidation.
Sputtering of Si with decaborane cluster ions
Authors: Sosnowski Marek , Albano Maria A. , Li Cheng , Gossmann Hans-Joachim L. , Jacobson Dale C.
Published: July 2002

Decaborane cluster ions (B10Hx+) may play an important role in the manufacturing of future semiconductor devices, as they facilitate a very shallow implantation of B with a relatively high beam energy, due to its partition among the constituent atoms. While the formation of B-doped shallow junctions in Si has been demonstrated, little is known about other effects of these complex ions on a solid. We have measured the sputtering yield of Si with decaborane cluster ions at 12 keV and demonstrated that their impacts smooth rather than roughen the surface, similarly to much larger Ar cluster ions. The results have implications for the understanding of low-energy atomic impacts in terms of collective motion of many surface atoms and of the behavior of solids far from equilibrium.
Noise properties of an individual and two crossing multiwalled carbon nanotubes
Authors: Ouacha H. , Willander M. , Yu H. Y. , Park Y. W. , Kabir M. S. , Persson S. H. Magnus , Kish L. B. , Ouacha A.
Published: July 2002

The noise properties at room temperature of multiwalled carbon nanotubes under forward bias, for frequencies between 10 Hz–10 kHz, have been investigated. The noise measurements were made for one individual multiwalled carbon nanotube (1 MW) and two crossing multiwalled carbon nanotubes (2 CMW). The excess noise found in 1 MW is consistently 1/f-like. However, 2 CMW shows higher noise level, and the noise spectrum has an unusual dependence on the current. The main origin of noise in 2 CMW was attributed to the diffusion noise.
Shapiro steps observed in a dc superconducting quantum interference device with multiple junctions in each arm
Authors: Chen L. , Chen P. , Ong C. K.
Published: July 2002

A high-Tc dc superconducting quantum interference device (SQUID) with three Josephson junctions (JJs) in series in each of its arms has been fabricated. Its Shapiro steps were studied using microwave (rf) radiation of 10 GHz and weak magnetic fields. The appearance of giant Shapiro steps and of some of half-integer steps was observed. Separation between the adjacent Shapiro steps could be tuned by rf magnetic fields and small external dc magnetic fields. This phenomenon was analyzed by phase locking the JJs in the SQUID.
T-junction tuning system for large-area surface-wave plasma sources
Authors: Kudela Jozef , Terebessy Tibor , Odrobina Igor , Kando Masashi
Published: July 2002

A tuning system for large-area surface-wave plasma source is proposed. The system is based on T-junction tuning elements applied directly on the plasma-dielectric resonator and it provides remarkable control of microwave discharges sustained on large areas. Along with the control of matching, it enables also the control of discharge diameter and, most importantly, control of the radial plasma density profile. Considering its principle of operation, the system is applicable to any large-area guided-wave plasma source, magnetized or unmagnetized.
Guided microfluidics by electromagnetic capillary focusing
Authors: Zabow G. , Assi F. , Jenks R. , Prentiss M.
Published: July 2002

As fluid channel sizes are reduced, nonspecific binding to channel walls and particle clogging of microchannels present key obstacles thus far limiting the application of microfluidic lab-on-a-chip technologies. Here we show how combining applied electric or magnetic fields with the increasing surface tension effects inherent in channel miniaturization can guide particle flow and prevent adhesion to channel walls. We demonstrate effective two-dimensional particle focusing within arbitrary channel geometries that prevents adhesion, allowing accurate control of Poiseuille flow effects, and acts as either a robust particle accumulator or a separator.
Laser-induced pressure pulse as a tool to determine surface charges in inhomogeneous (solid/gas) dielectric
Authors: Malec D. , Lebey Th.
Published: July 2002

Most of the reliability problems of system involving solid dielectric materials are supposed to be due to both space-charge existence and material inhomogeneities (such as cavities, voids, etc.). A method allowing the measurement of internal surface charges in the surrounding of the walls of these flaws is presented. Theoretical basis of the calculation necessary to perform these measurements using the laser-induced pressure pulse method are given.
Heat flux distribution on a substrate in capacitively coupled radio-frequency discharges
Authors: Takaki K. , Koseki D. , Fujiwara T.
Published: July 2002

This letter investigates the heat flux distribution on a substrate in capacitively coupled radio-frequency argon glow discharges. The heat fluxes were determined from substrate temperature distributions measured by a high-sensitivity laser interferometer method with a LiNbO3 birefringent substrate. This method is based on monitoring the variation of refractive index with temperature. The distribution was obtained by sliding the 1-cm long LiNbO3 substrate between two semicircular glass substrates placed on a disk electrode, 12 cm in diameter. The gap length was fixed at 2 cm and gas pressure was 100 mTorr. For the substrate placed on the powered electrode, the heat flux increases radically from the glow center to the radial electrode edge from 40 to 58 mW/cm2. The heat flux toward the grounded electrode increases radically from 15 to 21 mW/cm2. The total measured heat flux to the electrode is in good agreement with electrical power consumption determined from voltage and current measurements. The radial electron density profile in the discharge chamber was measured using a Langmuir probe. The results show that the maximum electron density observed at the electrode edge coincides with the maximum heat flux.
Effect of N2O plasma treatment on the stabilization of water absorption in fluorinated silicon-oxide thin films fabricated by electron-cyclotron-resonance plasma-enhanced chemical-vapor deposition
Authors: Kim S. P. , Choi S. K. , Park Youngsoo , Chung Ilsub
Published: July 2002

The variation of residual stress with the water absorption was reduced drastically by the N2O plasma treatment for fluorinated silicon-oxide thin films. Fourier transformed infrared spectroscopy analysis showed that the film was oxidized by the plasma treatment. It was also determined that the oxidation occurred on the film surface from the P-etch rate and x-ray photoelectron spectroscopy analysis. The experimental results show that the stabilization results from the oxidation of the surface by the N2O plasma treatment.
Transition from negative magnetoresistance behavior to positive behavior in Co20(Cu1−xGex)80 ribbons
Authors: He J. , Zhang Z. D. , Liu J. P. , Sellmyer D. J.
Published: July 2002

We report a transition of the giant magnetoresistance (GMR) behavior in nanocrystalline Co20(Cu1−xGex)80 ribbons from negative to positive, as the semiconductor Ge substitutes for the Cu matrix. The growth of the hexagonal Co3Ge2 compound leads to a change of the physical origin of the GMR. The normal spin-dependent transport behavior in the CoCu granular system evolves into Coulomb blockade behavior of electronic tunneling in ribbons with a Co/Co3Ge2/Co junctionlike configuration.
Magnetic behavior of epitaxial SrRuO3 thin films under pressure up to 23 GPa
Authors: Le Marrec F. , Demuer A. , Jaccard D. , Triscone J.-M. , Lee M. K. , Eom C. B.
Published: July 2002

We report on measurements of electrical resistivity and determination of the Curie temperature of single-crystal epitaxial ferromagnetic SrRuO3 thin films under hydrostatic pressures up to 23 GPa. The SrRuO3 thin film was grown on vicinal (001) SrTiO3 substrate using 90° off-axis magnetron sputtering. At atmospheric pressure, the thin-film Curie temperature is about 150 K. To generate the high pressure, the Bridgman anvil technique was used. Up to 13 GPa, a linear decrease of the Curie temperature was observed at a rate of 5.9 K GPa−1. Above 13 GPa, a striking saturation of the magnetic transition temperature at 77 K was observed.
Improved designs of tunable ferroelectric capacities for microwave applications
Authors: Ott Roland , Wördenweber Roger
Published: July 2002

Epitaxial SrTiO3 films are deposited by on-axis magnetron sputtering on CeO2-buffered r-cut sapphire. The ferroelectric films possess low losses (e.g., tan δ≈0.001–0.004 at 300 K) and a large tunability at small electric fields. Different complex designs for ferroelectric capacities are prepared via dry etching ranging from standard designs to those in which the ferroelectric material is restricted to the gap of the capacity. The resulting capacity data can be explained in terms of an analytic model for parallel capacities. Due to modifications and optimization of the design, the quality factors for an improved capacity design exceeds the requirement for most applications K>45 already for extremely small voltages U≈18 V, which demonstrates the good properties of the design in combination with the quality of our ferroelectric films.
Low readout field magnetic resonance imaging of hyperpolarized xenon and water in a single system
Authors: Shao Wenjin , Wang Guodong , Fuzesy Raymond , Hughes Emlyn W. , Chronik Blaine A. , Scott Greig C. , Conolly Steven M. , Macovski Albert
Published: July 2002

Using a low-field magnetic resonance scanner, we have obtained images of gaseous polarized Xe129 and water cells at room temperature. This potentially low-cost imaging technique offers the possibility of high-resolution imaging using both polarized noble gas and proton magnetic resonance imaging of tissues in the same scanner.
Tunneling magnetoresistance in fully epitaxial MnAs/AlAs/MnAs ferromagnetic tunnel junctions grown on vicinal GaAs(111)B substrates
Authors: Sugahara Satoshi , Tanaka Masaaki
Published: July 2002

We have fabricated fully epitaxial single-crystal MnAs/AlAs/MnAs magnetic tunnel junctions (MTJs) grown by molecular-beam epitaxy on vicinal GaAs(111)B substrates. After the bottom MnAs layer was grown at 250 °C, the successive AlAs tunnel barrier and the top MnAs layer were grown at a lower temperature of 200 °C in order to suppress the surface segregation of Mn atoms. High-resolution transmission electron microscopy revealed that a monocrystalline MnAs/AlAs/MnAs trilayer heterostructure with atomically flat and chemically abrupt interfaces was realized. Tunneling magnetoresistance (TMR) was clearly observed in fully epitaxal MTJs made up of this trilayer heterostructure. The TMR ratio was 1.4% at 10 K and it decreased with increasing the bias voltage and with increasing temperature, but the TMR effect still remained at room temperature.
Ultrafast optical nonlinearity of low-temperature-grown GaInAs/AlInAs quantum wells at wavelengths around 1.55 μm
Authors: Biermann K. , Nickel D. , Reimann K. , Woerner M. , Elsaesser T. , Künzel H.
Published: July 2002

The ultrafast optical response of low-temperature-grown GaInAs/AlInAs multiple quantum wells is studied in pump-probe experiments with a femtosecond Er:fiber laser. As-grown samples doped with beryllium (concentration of 8×1017 cm−3) display a nonlinear transmission change, which decays by carrier trapping with a time constant of 230 fs. Experiments with pairs of ultrashort pulses separated by 1.5 ps demonstrate a fast modulation of transmission and very small accumulation effects, making this material highly promising for all-optical switching. Substantially longer recovery times are found in annealed, Be-doped samples and in undoped samples.
Local vibrational modes of carbon in GaSb and GaAsSb
Authors: Chen X. K. , Wiersma R. , Wang C. X. , Pitts O. J. , Dale C. , Bolognesi C. R. , Watkins S. P.
Published: July 2002

We have measured the Raman spectra of heavily carbon doped (p>1019 cm−3) GaSb and GaAsSb. A local vibrational mode (LVM) due to carbon residing on group-V lattice sites was observed at 540 cm−1 for GaSb and 568 cm−1 for GaAs0.44Sb0.56. A gap mode at 164 cm−1 was observed for GaSb. The frequency of the LVM as well as the gap mode is in quantitative agreement with recent theoretical predictions.
Heteroepitaxial growth of CdTe on a p-Si(111) substrate by pulsed-light-assisted electrodeposition
Authors: Takahashi Makoto , Todorobaru Makoto , Wakita Koichi , Uosaki Kohei
Published: July 2002

Highly oriented CdTe(111) films of high-crystalline quality were grown on a Si(111) substrate by pulsed-light-assisted electrodeposition at room temperature. Strong photoluminescence peaks due to the bound exciton recombination were observed for the electrodeposited CdTe films, confirming the high quality of the films prepared by the present method. Atomic-force microscopy measurements showed an atomically ordered arrangement and demonstrated the epitaxial growth of the CdTe films.
Metallized pyramidal silicon probe with extremely high throughput and resolution capability for optical near-field technology
Authors: Yatsui T. , Itsumi K. , Kourogi M. , Ohtsu M.
Published: July 2002

An optical near-field probe with extremely high throughput and resolution capability was fabricated with a metallized pyramidal silicon structure. Using a finite-difference time-domain method, we found the tip parameters that are required for localized surface plasmon resonance at the probe tip. The optical near-field energy distribution on the metallized pyramidal silicon probe was observed by scanning a fiber probe that had an aperture diameter of 50 nm. The spatial distribution profile observed was in good agreement with the numerical results. The throughput and spot size were determined to be 2.3% and 85 nm, respectively.
Delayed nucleation during molecular-beam epitaxial growth of GaN observed by line-of-sight quadrupole mass spectrometry
Authors: Koblmüller G. , Pongratz P. , Averbeck R. , Riechert H.
Published: July 2002

We present a nucleation study for molecular-beam epitaxial growth of GaN on 6H-SiC and sapphire using Rutherford backscattering, atomic force microscopy, and in situ line-of-sight quadrupole mass spectrometry. Film thickness measurements by Rutherford backscattering reveal a strong deviation from thickness calculations assuming steady-state growth. We differentiate two regimes of growth, initially a highly nonlinear growth mode during island formation and later a linear growth mode after coalescence of islands. The mechanisms leading to the nonlinear behavior are attributed to energy barriers that supress immediate nucleation and provide for a substantial desorption of Ga and N atoms. Employing line-of-sight quadrupole mass spectrometry, we developed a quantitative in situ method to determine the amount of desorbing Ga atoms during the entire GaN growth procedure. The amount of initial GaN desorption in heteroepitaxy is independent of the substrate material and is as high as 8±1.5 nm.
Local electrostatic potential and process-induced boron redistribution in patterned Si/SiGe/Si heterostructures
Authors: Orchowski A. , Rau W.-D. , Rücker H. , Heinemann B. , Schwander P. , Tillack B. , Ourmazd A.
Published: July 2002

We present microscopic maps of the electrostatic potential in Si/SiGe/Si patterned structures of the type used in heterostructure bipolar transistors. By obtaining such maps before and after anneals typically used in device processing, we directly reveal the “vertical” and “lateral” redistribution of boron during device fabrication. Such data can be compared with the results of process simulation to extract the fundamental parameters for dopant diffusion in complex device structures.
Interface-controlled gate of GaAs metal–semiconductor field-effect transistor
Authors: Kang Min-Gu , Park Hyung-Ho , Kim Haecheon
Published: July 2002

A two-step passivation using sulfidation and hydrogenation has been reported to improve the gate leakage current and breakdown voltage of the GaAs metal–semiconductor field-effect transistor (MESFET). The combination of S passivation and interfacial hydrogenation was applied to the gate line in the MESFET; leakage current was reduced over an order and breakdown voltage was improved to a maximum level of 14 V from 10 V. It was revealed that the improvement of device properties after this two-step treatment resulted from the suppression of defective states such as oxides and excess As at the interface of the gate junction. The evolution of their bonding states through the treatment was found to have a close relationship with the device parameters.
Conceptual design of nanostructures for efficient photoinduced phase transitions
Authors: Kawamoto Tohru , Abe Shuji
Published: July 2002

By means of Monte Carlo simulations on a kinetic model, we demonstrate that the efficiency of a photoinduced phase change can in general be enhanced drastically by using a superstructure of an appropriate combination of two components. This is due to the accelerated nucleation of converted domains in the structural blocks relatively close to local instability. The present mechanism provides a general guideline on the design of photocontrollable materials with potential applications for memory and storage devices.
Determining the profile of textured membranes by the alpha particle energy loss method
Authors: Kaiser C. , Levy Y. , Tiedje T. , Young Jeff F. , Kelson I.
Published: July 2002

Alpha particle energy loss (AEL) spectroscopy was used to characterize a 5 μm pitch grating of silicon bars on a silicon dioxide membrane. Comparison of the data with simulated spectra shows that the angle of nonvertical grating sidewalls are readily quantified by AEL. The potential of AEL for distinguishing undercut and overcut etch profiles is assessed.
Giant magnetoimpedance in FeAg granular alloys
Authors: Soares J. M. , de Araújo J. H. , Cabral F. A. O. , Dumelow T. , Machado F. L. A. , de Araújo A. E. P.
Published: July 2002

We have observed giant magnetoimpedance (GMI) in an FeAg granular alloy. Impedance and transverse susceptibility (TS) measurements as a function of the external dc magnetic field were made at room temperature. The variation of the magnetoimpedance ratio with magnetic field has been related to a corresponding TS ratio change as a function of the magnetic field. The peaks in the GMI and TS curves are in the same position and have been associated in both cases to effective anisotropy fields.
Features of the magnetic behavior of Mn2−xCrxSb alloys in the low-temperature state
Authors: Val’kov V. I. , Kamenev V. I. , Buzhinsky S. A. , Romanova N. A.
Published: July 2002

The spontaneous and magnetic-field-induced first-order magnetic phase transitions in single-crystal samples of the alloy system Mn2−xCrxSb (symmetry space group P4/nmm) are investigated in samples with x=0.06 and x=0.12. It is found that the spontaneous first-order transitions from the high-temperature to the low-temperature phase are not accompanied by complete vanishing of the magnetization. At the induced transitions the magnetization before and after the transition is an increasing linear function of field. It is concluded on the basis of the results that the ground state in these alloys cannot be one of collinear antiferromagnetism, as had been thought previously. Other possibilities for interpreting the ground state and the mechanisms of order–disorder transitions inherent to magnets with itinerant carriers of magnetism are examined. It is conjectured that the local magnetic moment has a ferromagnetic and a periodic component which are formed by itinerant d electrons and coexist in low- and high-temperature phases.