bluuebunny/crossref_metadata_2025 huggingface dataset:
Ion-acoustic solitons in a plasma consisting of positive and negative ions with nonisothermal electrons
Authors: Gill Tarsem Singh , Kaur Harvinder , Saini Nareshpal Singh
Published: September 2003

In this research paper, the authors study the propagation of ion-acoustic solitons in a plasma consisting of warm positive and negative ions with different concentration of masses, charged states, and nonisothermal electrons. To account for the full nonlinearity of plasma equations, a quasipotential method is used here. The potential so obtained is characterized for solitons as a function of Mach number, positive and negative ions temperature, nonisothermal electrons, different concentration of negative and positive ions over a wide range of parameter space. Corresponding to isothermal case with β=1, coexistence of compressive and rarefactive solitons is obtained. For non-negative β≠1, only compressive solitons are observed. The prediction, that with introduction of negative ions there exists a critical ion concentration below which compressive solitons exist and above which rarefactive solitons exist, is ruled out for nonisothermal electrons.
Filamentation instability of long Alfvén waves in warm collisionless plasmas
Authors: Passot T. , Sulem P. L.
Published: September 2003

A criterion for filamentation instability of a circularly polarized Alfvén wave train propagating along a strong ambient field in a collisionless plasma is obtained from a transverse modulational analysis of a generalized kinetic derivative nonlinear Schrödinger equation. This equation, which retains Landau damping, results from the Vlasov–Maxwell equations via a long-wave reductive perturbative expansion. For bi-Maxwellian equilibrium distribution functions, it is shown that a moderate anisotropy of the electron temperature and/or a moderate ratio of the electron to ion temperatures can significantly broaden the existence range of this instability, making its occurrence possible in small-β plasmas.
High-speed transmission electron microscope
Authors: Dömer H. , Bostanjoglo O.
Published: September 2003

A high-speed transmission electron microscope was developed for probing laser-induced fast nonperiodical processes on the nanosecond time scale. 7–11 ns illuminating electron pulses—up to three—are produced by a laser pulse-driven photocathode. The electron gun can be used both for nanosecond exposure and conventional stationary operation. The introduced microscope is operated in three different modes for investigations of laser treated thin films: (1) Bright-field imaging, tracking changes of the texture and transport of neutral material; (2) dark-field imaging, mapping transient plasmas; and (3) selected area diffraction to study fast phase transitions. Presently, the space resolution is ≈200 nm.
Electron cyclotron resonance harmonics and wall material effects in a microwave discharge
Authors: Aanesland Ane , Fredriksen Åshild
Published: September 2003

In this article we investigate a 2.45 GHz microwave discharge operated at the electron cyclotron resonance (ECR) and the second harmonic, by applying a divergent magnetic field where the maximum is changed from 1400 to 500 G. The magnetic field is continuously decreased so that the ECR zone is moved axially along the chamber from about 15 cm away to very close to the microwave window. When the field is reduced to below 875 G the ECR disappears and only the second harmonic is present in the source. We observe that the second harmonic is not efficient enough for breakdown at microwave power of less than 500 W and gas pressure of 0.48 Pa, and it is shown that an overdense plasma can not be generated by use of the second harmonic (independent of gas type). It is also shown that the wall material close to the ECR zone is extremely important, probably due to an effect similar to that of the antenna material in capacitively and inductively coupled plasma sources. The possibility of measuring the thickness and location of the effective ionizing resonance zone is discussed. A calculation of the plasma density as a function of the magnetic field is performed, which takes into account the conservation of magnetic flux and the secondary emission from the wall, and excellent agreement with the measured results is obtained.
A torsional balance for the characterization of microNewton thrusters
Authors: Gamero-Castaño Manuel
Published: September 2003

We describe the performance of a torsional balance suitable for the study of microNewton thrusters. A design based on flexural pivots and electrostatic forces (for calibration and active damping) makes it possible to test thrusters with a mass of a few kilograms, and measure submicroNewton level forces with high accuracy and a resolution better than 0.03 μN. The usefulness of the balance is proved by measuring the performance of two different electric propulsion accelerators: a colloid thruster generating thrust in the 2–13 μN range, and a micropulsed plasma thruster yielding single impulse bits of 19 μN s. The low noise figure of the balance (below 0.1 μN/Hz in the 7 mHz–1 Hz bandwidth) will make it possible to measure the thrust noise requirements imposed in colloid thrusters by missions such as the Space Technology 7 and the Laser Interferometer Space Antenna.
Mechanical properties of periodic porous silica low-k films determined by the twin-transducer surface acoustic wave technique
Authors: Xiao Xia , Hata Nobuhiro , Yamada Kazuhiro , Kikkawa Takamaro
Published: September 2003

Low dielectric constant (k) materials qualified for interconnect integration of high speed devices are required in the microelectronic industry. The introduction of nanopores into the dielectrics reduces their k but also deteriorates their mechanical properties. An accurate measurement technique for determining the mechanical properties of such thin fragile low-k films is needed. We report on a designed piezoelectric twin-transducer detector for accurate and nondestructive characterization of mechanical properties for porous low-k films by the laser-generated surface acoustic wave. Experimental results of several low-k films demonstrate that influences from the fabricating processes and material treatments on Young’s elastic modulus can be sensitively detected by this technique.
A tensometer to study strain deformation and failure behavior of hydrated systems via in situ environmental scanning electron microscopy
Authors: Rizzieri R. , Baker F. S. , Donald A. M.
Published: September 2003

Large strain deformation and failure behavior of the mixed biopolymer gels have been investigated via in situ Environmental scanning electron microscopy (ESEM). ESEM has been employed to explore the changes in the structure of the material, while allowing the sample to stay hydrated as it was subjected to tensile strain. The “dog-bone” shaped samples were placed in a specially designed tensometer that fitted inside the ESEM specimen chamber. It was possible, therefore, to measure for the first time not only the mechanical properties of the hydrated material, but also to observe any morphological changes occurring as it was being stretched. By using a tensometer capable of keeping a sample moist over large strains, it was possible to observe hitherto unreported structural changes in gelatin-based systems subjected to uniaxial stretching. It was shown that bands were formed in the direction of the applied strain and that particles of maltodextrin included in the gelatin underwent deformation and fracture. Such observations have led to the conclusion that previous models were sometime inadequate due to the lack of in situ observation and novel approaches are required to describe these phenomena.
Suspended microchannel resonators for biomolecular detection
Authors: Burg T. P. , Manalis S. R.
Published: September 2003

We present a resonant mass sensor for specific biomolecular detection in a subnanoliter fluid volume. The sensing principle is based on measuring shifts in resonance frequency of a suspended microfluidic channel upon accumulation of molecules on the inside walls of the device. Confining the fluid to the inside of a hollow cantilever enables direct integration with conventional microfluidic systems, significantly increases sensitivity by eliminating high damping and viscous drag, and allows the resonator to be actuated by electrostatic forces. Fluid density measurements reveal a mass resolution of 10−17 g/μm2 in a 4 mHz–4 Hz bandwidth. To demonstrate biomolecular detection, we present real-time measurements of the specific binding between avidin and biotinylated bovine serum albumin. Based on these measurements, we expect that changes in surface mass loading on the order of 10−19 g/μm2 can be detected in an optimized system.
Enhanced magnetoresistance in the complex perovskite LaCu3Mn4O12
Authors: Alonso J. A. , Sánchez-Benı́tez J. , De Andrés A. , Martı́nez-Lope M. J. , Casais M. T. , Martı́nez J. L.
Published: September 2003

Moderate-pressure techniques (P=2 GPa) have been used to prepare the complex LaCu3Mn4O12 perovskite. It has been characterized by neutron powder diffraction, magnetic, and magnetotransport measurements. This material is ferrimagnetic below TC=361 K. The magnetoresistance (MR) is enhanced with respect to that of CaCu3Mn4O12 due to the effective electronic injection that dramatically reduces the bulk resistivity, thus promoting the grain-boundary contribution to the electrical resistance. Values of low-field MR close to 3% at room temperature are achieved for magnetic fields of 1 T.
Dynamics of liposomes gene vectors studied by anelastic spectroscopy
Authors: Castellano C. , Pozzi D. , Caracciolo G. , Cantelli R.
Published: September 2003

The anelastic spectra of synthetic liposomes interesting for gene transfection have been measured in a wide temperature range; in particular, we have studied the cationic/neutral lipid mixture di-oleoyl trimethylammonium propane/di-oleoyl phosphatidylethanolamine at different molar ratios. This technique has been applied on thin films of biological samples deposited on a solid substrate like Si 〈100〉. We have evidenced the presence of two relaxation processes around and below 200 K, likely connected with a cooperative dynamics of the water plus membrane system. In particular, the process centered at 198 K results to be clearly a favorite by the presence of two different lipidic species.
Wall material effects in stationary plasma thrusters. I. Parametric studies of an SPT-100
Authors: Gascon N. , Dudeck M. , Barral S.
Published: September 2003

The operation of a laboratory version of the flight-qualified SPT-100 stationary plasma thruster is compared for four different discharge chamber wall materials: a boron nitride–silica mixture (borosil), alumina, silicon carbide, and graphite. The discharge is found to be significantly affected by the nature of the walls: changes in operating regimes, up to 25% variations of the mean discharge current, and over 100% variations of the discharge current fluctuation amplitude are observed between materials. Thrust, however, is only moderately affected. Borosil is the only material tested that allows operating the thruster at a low mean current, low fluctuation level and high thrust efficiency regime. It is suggested that secondary electron emission under electron bombardment is the main cause of the observed differences in discharge operation, except for graphite, where the short-circuit current inside the walls is believed to play a major role. It is also suggested that the photoelectric effect, which has apparently not been given attention before in the Hall thruster literature, could increase the cross-field electron current.
Wall material effects in stationary plasma thrusters. II. Near-wall and in-wall conductivity
Authors: Barral S. , Makowski K. , Peradzyński Z. , Gascon N. , Dudeck M.
Published: September 2003

Simulations and experimental characterizations of a stationary plasma thruster are compared for four different wall materials to investigate near-wall conductivity (dielectric materials) and in-wall conductivity (conducting materials) in such a discharge. Using a one-dimensional transient fluid model that takes into account a possible electron temperature anisotropy, it is shown that electron-wall backscattering plays a crucial role by maintaining a relatively high electron temperature along the magnetic field lines which in turn drives large electron currents toward the walls. The large differences in discharge current observed experimentally for the dielectric materials are qualitatively recovered, confirming that near-wall conductivity results from the combined effects of secondary electron emission and electron backscattering. A clear correlation is found between the appearance of space charge saturation at the walls and a jump of the discharge current observed in experiments when varying the discharge voltage or the magnetic field. The anomalously high values of discharge current observed experimentally with graphite are also correctly recovered in simulations, which highlight a plasma short-circuiting effect resulting from in-wall currents.
Conductive electron heat flow along an inhomogeneous magnetic field
Authors: Held E. D. , Callen J. D. , Hegna C. C.
Published: September 2003

In this work a general closure for the conductive electron heat flux parallel to an inhomogeneous magnetic field is derived and examined. Free-streaming and collisional effects are present in the drift kinetic equation which is solved using an expansion of eigenfunctions of the bounce-averaged, pitch-angle scattering operator. For bounce times short compared to transit and collision times, the subsequent heat flow closure takes the form of an integral operator acting on electron temperature variations along magnetic field lines. The general closure agrees qualitatively with previous forms for the heat flux in homogeneous magnetic geometry and importantly, predicts a substantial reduction in the heat flow due to the trapping of particles in magnetic wells and the enhanced effect of collisions near the trapped/passing particle boundary.
Fluorinert as a pressure-transmitting medium for high-pressure diffraction studies
Authors: Varga Tamas , Wilkinson Angus P. , Angel Ross J.
Published: September 2003

Fluorinert is a liquid pressure-transmitting medium that is widely used in high-pressure diffraction work. A systematic study of five different fluorinerts was carried out using single-crystal x-ray diffraction in a diamond-anvil cell in order to determine the pressure range over which they provide a hydrostatic stress state to the sample. It was found that none of the fluorinerts studied can be considered hydrostatic above 1.2 GPa, a lower pressure than reported previously.
Design and development of an interchangeable nanomicroelectrospray source for a quadrupole mass spectrometer
Authors: Smith Douglas R. , Sagerman Gary , Wood Troy D.
Published: September 2003

An interchangeable microelectrospray and nanoelectrospray ionization source has been designed and constructed for use on a triple-quadrupole mass spectrometer. This new source is specially designed to conduct nanoelectrospray experiments utilizing pulled borosilicate glass emitters, as well as various ionization modes utilizing silica capillaries. The source design facilitates the easy exchange between a microelectrospray source and nanoelectrospray source. The microionspray assembly can be quickly replaced by the nanoelectrospray adaptation in order to conduct nanoelectrospray experiments. Furthermore, this source design allows for the coupling of low flow separation techniques, like microliquid chromatography or capillary electrophoresis.
Inelastic electron tunneling spectrometer to characterize metal–oxide–semiconductor devices with ultrathin oxides
Authors: Petit C. , Salace G.
Published: September 2003

We describe an easy to build inelastic electron tunneling spectrometer, controlled by a computer, to analyze and characterize metal–oxide–semiconductor (MOS) devices. The method, material, and circuit are also described. Typical inelastic electron tunneling spectra obtained from a MOS tunnel junction with various degrees of nonlinear conductance–voltage behavior are presented. Our results suggest that such a spectrometer has appropriate resolution (4 mV of full width half maximum) and suitable signal-to-noise ratio to clearly identify the electrode and insulator vibrational modes. Results are reported on aluminum gate 2.1 nm thick oxide devices fabricated on n-type (111) silicon substrates.
Precise measurement technology of soft-x-ray spectrum using dual transmission grating spectrometer
Authors: Yang Jiamin , Ding Yaonan , Zhang Wenghai , Zhang Jiyan , Zheng Zhijian
Published: September 2003

A novel transmission grating spectrometer, called a dual-transmission grating spectrometer, has been designed and established. This spectrometer adopts two transmission gratings to disperse x rays twice, which suppresses the overlap of the grating higher-order diffraction, cuts out the transfer of experimental errors in unfolding the measured x-ray spectrum effectively, and increases the x-ray spectrum measurement precision. It was shown by experiment that the dual-transmission grating spectrometer was applicable to precisely measure the soft-x-ray spectrum from laser-created plasmas.
Advanced research equipment for fast ultraweak luminescence analysis
Authors: Tudisco S. , Musumeci F. , Scordino A. , Privitera G.
Published: September 2003

This article describes new advanced research equipment for fast ultraweak luminescence analysis, which can detect at high sensitivity photons after ultraviolet A laser irradiation in biological probes as well as plant, animal, and human cells. The design and construction of this equipment, developed at the Southern National Laboratory of the National Nuclear Physics Institute, is described with the first experimental results and future developments. The setup, employing a photomultiplier tube working in single photon counting mode, allows accurate and reliable photoluminescence measurements with excitation wavelengths in the range 337–700 nm and the emission wavelength in the range 400–800 nm. With respect to the traditional setup, this new equipment is able to perform measurements starting at a few microseconds after the laser irradiation is switched off and with a large detection efficiency (about 10% of the total solid angle). Moreover, the adopted design assures a low background noise level. A further optimization of the system is under study, with special care for the reliability needed for the delayed luminescence for optical screening project aimed to enhance the detection of the low level photoinduced luminescence from human cells to be used as an optical biopsy technique.
Sample containment for neutron and high-energy x-ray scattering studies of hydrogen fluoride and related molecular species
Authors: Turner John F. C. , McLain Sylvia E. , Free Timothy H. , Benmore Chris J. , Herwig Kenneth W. , Siewenie Joan E.
Published: September 2003

The design of a suite of sample cells and sample preparation facilities to investigate the structure and dynamics of chemically reactive molecular fluorides, using high-energy x-ray and neutron scattering, is reported. A detailed discussion of both the neutronic and chemical considerations is provided, in support of the choice of the material of cell construction for both structural and dynamical experiments. The discussion of this suite of equipment also includes a detailed design of a hybrid high-vacuum Schlenk line for sample preparation. These cells were specifically designed to study hydrogen fluoride but may be used for other species that exhibit similar chemical reactivity. Background considerations for liquid diffraction experiments are also discussed and show that in designing cells for liquid samples, or samples that contain a large structurally amorphous fraction, crystalline sample containment affords far more tractable data analysis.
Dynamic laser alignment control for Thomson scattering on ASDEX Upgrade
Authors: Murmann H. , Jakobi M. , Kurzan B. , Schilling H. B. ,   ASDEX Upgrade Team
Published: September 2003

Thomson scattering, as a very direct diagnostic method to measure electron density ne and temperature Te of a plasma, has become a standard tool in plasma physics. Reliable Nd:YAG lasers have been developed for industrial applications, the accuracy of scattering measurements is sufficiently high to measure profile gradients of Te and ne with millimeter spatial resolution down to electron densities of 1018 m−3 with reasonable error bars. As the accuracy of the measurement increased steadily, a new category of errors has been revealed, which is not very likely to be detected when only one laser is used. Inhomogeneities of the scattered power density within the entrance slit of a polychromator cause systematic errors, thus the precise alignment of the scattering lasers is critical. Such an alignment is now continuously maintained during diagnostic operation by a new closed-loop control system implemented with a simple and effective optoelectronic balance technique.
Cross-field plasma acceleration and potential formation induced by nonlinear Landau damping of electrostatic waves in a relativistic magnetized plasma
Authors: Sugaya R.
Published: September 2003

Relativistic and nonrelativistic particle acceleration along and across a magnetic field, and the generation of an electric field transverse to the magnetic field, both induced by nonlinear Landau damping (nonlinear wave-particle scattering) of almost perpendicularly propagating electrostatic waves in a relativistic magnetized plasma, are investigated theoretically on the basis of relativistic transport equations. Two electrostatic waves interact nonlinearly with particles, satisfying the resonance condition of ωk−ωk′−(k⊥−k⊥′)vd−(k∥−k∥′)v∥=mωcs/γd2, where v∥ and vd are the parallel and perpendicular velocities of particles, respectively, γd=(1−β2)−1/2, β=vd/c and ωcs is the relativistic cyclotron frequency. The relativistic transport equations show that the electrostatic waves can accelerate particles in the k″ direction (k″=k−k′). Simultaneously, an intense cross-field electric field E0=B0×vd/c is generated via the dynamo effect owing to perpendicular particle drift to satisfy the generalized Ohm’s law, which means that this cross-field particle drift is identical to the E×B drift. The relativistic transport equations for relativistic cross-field particle acceleration are derived by Lorentz transformation of the relativistic momentum-space diffusion equation in the moving frame of reference without the electric field and the cross-field particle drift.
Two-dimensional photonic crystals with Ge/Si self-assembled islands
Authors: David S. , El kurdi M. , Boucaud P. , Chelnokov A. , Le Thanh V. , Bouchier D. , Lourtioz J.-M.
Published: September 2003

Two-dimensional photonic crystals were fabricated on silicon-on-insulator waveguides with self-assembled Ge/Si islands deposited on top of the upper silicon layer. The photonic crystals consist of triangular lattices of air holes designed to exhibit a forbidden band around 1.5 μm. Different hexagonal photonic crystals microcavities were processed whose optical properties are probed at room temperature with the Ge/Si island photoluminescence. Quality factors larger than 200 are measured for hexagonal H3 cavities. A significant enhancement of the Ge/Si island photoluminescence is achieved in the 1.3–1.55 μm spectral region using the photonic crystal microcavities. We show that the energy resonance of the defect modes can be tuned with the filling factor of the photonic crystal.
Contraction of aluminum oxide thin layers in optical heterostructures
Authors: Durand O. , Wyckzisk F. , Olivier J. , Magis M. , Galtier P. , De Rossi A. , Calligaro M. , Ortiz V. , Berger V. , Leo G. , Assanto G.
Published: September 2003

We precisely determine the contraction of AlAs in multilayer optical waveguides, associated with selective oxidation of AlAs/GaAs epitaxial heterostructures. The average thickness of each layer was determined via x-ray reflectometry before and after oxidation, yielding an induced shrinkage of 11.4%±0.7% normal to the stack. The waveguide refractive indices were evaluated via modal-index measurements in the near-infrared. The achieved accuracy is compatible with form-birefringent phase matching in AlGaAs guided-wave frequency converters.
Temperature-dependent photoluminescence of ZnSe/ZnS quantum dots fabricated under the Stranski–Krastanov mode
Authors: Kim Y. G. , Joh Y. S. , Song J. H. , Baek K. S. , Chang S. K. , Sim E. D.
Published: September 2003

Self-assembled ZnSe/ZnS quantum dots (QDs) have been grown in the Stranski–Krastanov (S–K) mode using a metalorganic chemical vapor deposition technique under the atomic-layer epitaxy mode. Atomic-force-microscopy measurements on the uncapped ZnSe/ZnS QDs reveal that lens-shaped ZnSe QDs are formed after 1–2 monolayer ZnSe is deposited. The ZnSe QDs are estimated 1–2 nm in height and 25–35 nm in radius. The temperature-dependent behavior of confined carriers in the ZnSe QDs has been investigated through photoluminescence (PL) measurements. PL spectra show a substantial PL linewidth narrowing accompanied by a large redshift of the emission peak energy with increasing temperature. This unusual temperature-dependent behavior is interpreted as the dot-to-dot carrier transfer through the wetting layer, which is common to QDs grown in the S–K mode.
Tunnel magnetoresistance in nanojunctions based on Sr2FeMoO6
Authors: Bibes M. , Bouzehouane K. , Barthélémy A. , Besse M. , Fusil S. , Bowen M. , Seneor P. , Carrey J. , Cros V. , Vaurès A. , Contour J.-P. , Fert A.
Published: September 2003

We report on the observation of magnetoresistance in a Sr2FeMoO6 (SFMO)-based tunnel junction. This result is obtained by combining a three-step process for the growth of the Sr2FeMoO6 layer by pulsed laser deposition with a technology allowing the definition of nanometer-sized junctions. A clear positive magnetoresistive signal of 50% is obtained at low temperature in a Sr2FeMoO6/SrTiO3/Co junction. Since the SrTiO3/Co interface is known to have a negative spin polarization of about 20%, this result yields a negative spin polarization of SFMO, which we find to amount to more than 85% in our film. This confirms the half-metallic character of this compound, predicted by band structure calculations.
Magnetic matching of beam optics between quasilaminar and phase-mixed states
Authors: Bliokh Yu. P. , Nusinovich G. S. , Felsteiner J. , Granatstein V. L.
Published: September 2003

Electron beams propagating in the ion focused regime (Bennett pinch) are known as phase-mixed electron beams. Such beams are of interest for various sources of coherent electromagnetic radiation (pasotrons, ion-channel lasers, ion-channel guided free-electron lasers). Typically, the transition of a beam from a quasilaminar state near the gun to a phase-mixed equilibrium state known as the Bennett pinch is accompanied by the appearance of betatron oscillations. In pasotrons these oscillations play a negative role because they often result in certain beam losses due to the interception of beam electrons oscillating with large amplitudes by the chamber walls. The betatron oscillations and the beam losses associated with them can be monitored by using a weak local external magnetic field (magnetic lens) in the transition region. This paper is devoted to the analysis of the beam dynamics in the transition region and to the study of the effect of the magnetic lens. With the use of the concept of the free energy of the ensemble of charged particles, the relation between the beam radius in the Bennett pinch and the radii at the entrance and exit from a magnetic lens is derived. The results obtained show that, by using a properly designed and positioned magnetic lens in pasotrons, a halo in the phase-mixed beam can be greatly reduced and the beam losses can be practically eliminated.
Dust grain charging and levitation in a weakly collisional sheath
Authors: Robertson S. , Gulbis A. A. S. , Colwell J. , Horányi M.
Published: September 2003

An experiment is described in which monodisperse dust grains are levitated within a dc sheath above a conducting plate in argon plasma. For plate bias voltages that are not too negative (⩾−10 electron temperatures), the observed dust levitation heights are near to values calculated from a model combining equations for the sheath with those for grain charging. When the plate is more negatively biased, the theoretical levitation heights are higher than the observed heights as a consequence of the measured sheath thickness being smaller than values obtained from the models.
Local epitaxial growth of ZrO2 on Ge (100) substrates by atomic layer epitaxy
Authors: Kim Hyoungsub , Chui Chi On , Saraswat Krishna C. , McIntyre Paul C.
Published: September 2003

High-k dielectric deposition processes for gate dielectric preparation on Si surfaces usually result in the unavoidable and uncontrolled formation of a thin interfacial oxide layer. Atomic layer deposition of ∼55-Å ZrO2 film on a Ge (100) substrate using ZrCl4 and H2O at 300 °C was found to produce local epitaxial growth [(001) Ge//(001) ZrO2 and [100] Ge//[100] ZrO2] without a distinct interfacial layer, unlike the situation observed when ZrO2 is deposited using the same method on Si. Relatively large lattice mismatch (∼10%) between ZrO2 and Ge produced a high areal density of interfacial misfit dislocations. Large hysteresis (>200 mV) and high frequency dispersion were observed in capacitance–voltage measurements due to the high density of interface states. However, a low leakage current density, comparable to values obtained on Si substrates, was observed with the same capacitance density regardless of the high defect density.
Scanning capacitance microscopy on ultranarrow doping profiles in Si
Authors: Giannazzo F. , Goghero D. , Raineri V. , Mirabella S. , Priolo F.
Published: September 2003

Scanning capacitance microscopy (SCM) has been performed both in cross-sectional and in angle-beveling configurations on ultranarrow B spikes with a full width at half-maximum smaller than the SCM probe diameter. The dependence of the SCM response on the magnification factor has been studied, demonstrating an improvement both in terms of spatial resolution and sensitivity by angle-beveling sample preparation. The range of applicability of the direct inversion approach for the quantification of SCM profiles on ultranarrow B spikes has been assessed for high doping spikes thicker than 3 nm and measured on bevel. Two-dimensional simulations allowed the reproduction of all the main features of the experimental SCM profiles.
Rigid vortices in MgB2
Authors: Jin Hao , Wen Hai-Hu , Yang Hai-Peng , Liu Zhi-Yong , Ren Zhi-An , Che Guang-Can , Zhao Zhong-Xian
Published: September 2003

Magnetic relaxation of high-pressure synthesized MgB2 bulks with different thickness is investigated. It is found that the superconducting diamagnetic moment depends on time in a logarithmic way: the flux-creep activation energy decreases linearly with the current density (as expected by Kim–Anderson model) and the activation energy increases linearly with the thickness of sample when it is thinner than about 1 mm. These features suggest that the vortices in the MgB2 are rather rigid, and the pinning and creep can be well described by Kim–Anderson model.
Liénard–Wiechert potentials in even dimensions
Authors: Gürses Metin , Sarıoğlu Özgür
Published: September 2003

The motion of point charged particles is considered in an even dimensional Minkowski space–time. The potential functions corresponding to the massless scalar and the Maxwell fields are derived algorithmically. It is shown that in all even dimensions particles lose energy due to acceleration.
Carrier loss and luminescence degradation in green-light-emitting InGaN quantum wells with micron-scale indium clusters
Authors: Cho Yong-Hoon , Lee S. K. , Kwack H. S. , Kim J. Y. , Lim K. S. , Kim H. M. , Kang T. W. , Lee S. N. , Seon M. S. , Nam O. H. , Park Y. J.
Published: September 2003

Influence of the size of indium clusters on optical properties of green-light-emitting InGaN quantum wells (QWs) was investigated by photoluminescence (PL), cathodoluminescence, PL excitation, and time-resolved PL techniques. Low luminescence efficiency was observed for green-light-emitting InGaN QWs with micron-sized indium clusters, in contrast to the case of InGaN QWs with submicron-sized small indium segregation. Both the thermal activation energy and the carrier lifetime dramatically decreased, while a large Stokes-like shift between absorption edge and PL peak energy was still observed for the InGaN QWs with micron-sized indium clusters. These facts indicate that the effective potential barrier between radiative and nonradiative channels (thus effective carrier localization) rapidly decreases due to the formation of micron-sized large indium clusters possessing a number of nonradiative centers, leading to significant luminescence degradation.
Nanorheological approach for characterization of electroluminescent polymer thin films
Authors: Gray Tomoko , Buenviaje Cynthia , Overney René M. , Jenekhe Samson A. , Zheng Lixin , Jen Alex K. Y.
Published: September 2003

Shear-modulated scanning force microscopy (SM-SFM) is introduced as a nanorheological characterization method for the determination of optoelectronic properties of semiconducting polymer thin films (<100 nm). In this letter, the photoluminescence quantum efficiency of poly(p-phenylenevinylene) (PPV) was directly correlated to the glass transition property by SM-SFM. Conformational changes and chain packing were discussed as a function of the conversion temperature of the soluble PPV precursor. Compared to the bulk, very low glass transition temperature values in the range of 65 to 85 °C were found, which imply an increased molecular mobility in thin films of conjugated polymers.
Air-coupled acoustic imaging with zero-group-velocity Lamb modes
Authors: Holland Stephen D. , Chimenti D. E.
Published: September 2003

A Lamb wave resonance has been found that allows unusually efficient transmission of airborne sound waves through plates. This occurs at the zero-group-velocity point at the frequency minimum of the first-order symmetric (S1) Lamb mode. At this frequency, plane waves with a range of incident angles can couple between the air and the Lamb mode in the solid plate, dominating the spectrum of transmitted focused sound beams by 10 dB or more. We use this frequency for C-scan imaging, and demonstrate the detection of both a 3.2-mm-diameter buried flaw and a subwavelength thickness changes of .005λ (1%).
Temperature dependence of the switching field and its distribution function in Fe-based bistable microwires
Authors: Varga R. , Garcia K. L. , Zhukov A. , Vazquez M. , Vojtanik P.
Published: September 2003

The switching field distribution for magnetization reversal in a single Barkhausen jump of a bistable Fe-based amorphous microwire as well as its temperature dependence have been investigated in the temperature range from 77 to 450 K. Two processes have been identified to be responsible for the temperature dependence of the switching field: magnetostrictive volume domain wall pinning on stresses and relaxation effects due to local structural rearrangements. While at low temperatures, pinning on the atomic level defects plays the dominant role, magnetostrictive pinning becomes more important at intermediate temperatures. A simple model is proposed considering both energy contributions that fits reasonably well with experimental data and allows us to interpret additionally the observed temperature dependence of the switching field fluctuations.
Dielectric response of relaxor ferroelectrics in the time-domain
Authors: Jang Hyun M.
Published: September 2003

Dielectric response of relaxor ferroelectrics was analyzed in the time-domain by evaluating the relaxation-time (τ) distribution of Pb(Mg1/3Nb2/3)O3-10 mol % PbTiO3 using the method of Tikhonov regularization. The distribution function g(τ) became exponentially broad and flat as temperature approached a certain critical point (∼230 K), indicating the advent of the frozen polar domains with infinitely long τ in a matrix of the thermally activated dynamic polar domains. The dielectric response of the high-temperature relaxation part was then separately estimated with the help of the two-states-polarization model. The estimated g(τ) of the relaxation part showed logarithmic Gaussian behavior, which manifested an ergodicity in the thermally activated flips of dynamic polarizations at high temperatures. In contrast to this, a resonance kernel was postulated to describe the dielectric response of the frozen polar domains at lower temperatures.
Highly-efficient backlight for liquid crystal display having no optical films
Authors: Okumura Takamitsu , Tagaya Akihiro , Koike Yasuhiro , Horiguchi Masahiro , Suzuki Hiromasa
Published: September 2003

We propose a highly-efficient backlight that requires no optical films with a polymer containing spherical particles of micron size. The developed backlight is provided with microprisms at the bottom surface, which can reflect directly the incident light into the front direction. The modeling simulation program, employing a Monte Carlo method based on Mie scattering theory, has optimized both the prismatic condition and the multiple scattering characteristics. We confirm that a uniformity of brightness can be achieved without using any optical films, resulting in a high optical efficiency of 62%.
First-principle study on GaN epitaxy on lattice-matched ZrB2 substrates
Authors: Iwata J.-I. , Shiraishi K. , Oshiyama A.
Published: September 2003

We theoretically investigate GaN epitaxy on ZrB2 substrates by clarifying the atomic and electronic structures of GaN/ZrB2 interfaces by first-principle calculations. Both the GaN epitaxial layer and the ZrB2 substrate almost maintain the bulk structures when the epitaxial growth begins with the formation of N–Zr bonds. On the other hand, a remarkable zigzag structural change, which seems to deteriorate the lattice-matched nature of ZrB2 substrates, is found in the interfacial B plane when B–N bonds are formed at the interface. These results indicate that suppression of the B–N bond formation is a key point for the effective use of ZrB2 as a substrate of GaN. We also estimate the Schottky barrier heights of these interfaces. The calculated p-type Schottky barrier height of the interface which contains three N–Zr bonds is small enough to form ohmic contacts.
High-power continuous-wave operation of a 6 μm quantum-cascade laser at room temperature
Authors: Yu J. S. , Slivken S. , Evans A. , Doris L. , Razeghi M.
Published: September 2003

We report continuous-wave (cw) operation of quantum-cascade lasers (λ=6 μm) using a thick electroplated Au top contact layer and epilayer-up bonding on a copper heat sink up to a temperature of 308 K (35 °C). The high cw optical output powers of 132 mW at 293 K and 21 mW at 308 K are achieved with threshold current densities of 2.29 and 2.91 kA/cm2, respectively, for a high-reflectivity-coated 15 μm wide and 2 mm long laser.
Low Schottky barriers on n-type silicon (001)
Authors: Tao Meng , Agarwal Shruddha , Udeshi Darshak , Basit Nasir , Maldonado Eduardo , Kirk Wiley P.
Published: September 2003

It has been reported that no metal shows a Schottky barrier of less than 0.4 eV on n-type silicon (001). This is attributed to interface states between metal and silicon (001), which pin the interface Fermi level and make the Schottky barrier more or less independent of the metal work function. We demonstrate that, by terminating dangling bonds and relaxing strained bonds on the silicon (001) surface with a monolayer of selenium, low Schottky barriers can be obtained on n-type silicon (001). Aluminum and chromium show barrier heights of 0.08 and 0.26 eV on n-type silicon (001), respectively. These results agree well with the ideal Schottky barrier heights for aluminum and chromium on n-type silicon (001), but are significantly different from the experimental barrier heights known for four decades for these metals on n-type silicon (001).
Shot noise in frustrated single-electron arrays
Authors: Kaplan Daniel M. , Sverdlov Victor A. , Likharev Konstantin K.
Published: September 2003

We have carried out numerical simulations of shot noise in two-dimensional arrays of single-electron islands with random background charges. The results show that in contrast with the one-dimensional arrays, at low currents the current noise is strongly colored, and its spectral density levels off at very low frequencies. The Fano factor F may be much larger than unity, due to the remnants of single-electron/hole avalanches. However, even very small thermal fluctuations reduce F below 1 for almost any bias.
Stress relaxation in mismatched layers due to threading dislocation inclination
Authors: Romanov A. E. , Speck J. S.
Published: September 2003

A recently observed mechanism of elastic stress relaxation in mismatched layers is discussed. The relaxation is achieved by the inclination of pure edge threading dislocation lines with respect to the layer surface normal. The relaxation is not assisted by dislocation glide but rather is caused by the “effective climb” of edge dislocations. The effective dislocation climb may result from the film growth and it is not necessarily related to bulk diffusion processes. The contribution of the dislocation inclination to strain relaxation has been formulated and the energy release due to the dislocation inclination in mismatched stressed layers has been determined. This mechanism explains recently observed relaxation of compressive stresses in the (0001) growth of AlxGa1−xN layers.
Oligomer-based organic distributed feedback lasers by room-temperature nanoimprint lithography
Authors: Pisignano Dario , Persano Luana , Visconti Paolo , Cingolani Roberto , Gigli Giuseppe , Barbarella Giovanna , Favaretto Laura
Published: September 2003

Room-temperature nanoimprint lithography in air is used in order to pattern a nonthermoplastic, low-molar-mass thiophene-based pentamer with excellent gain properties. No degradation of the luminescence efficiency of the active medium was observed after patterning. In this way, we fabricated single-mode emission distributed feedback lasers having a threshold excitation fluence of 140 μJ/cm2. The lasing line is peaked at 637 nm and exhibits a linewidth of less than 0.7 nm and a well-behaved input-output characteristic in the whole range of pump fluences. These results demonstrate room-temperature nanoimprint lithography as powerful and straightforward fabrication technique for oligomer-based nanostructured optoelectronic devices.
Liquid/liquid dynamic phase separation induced by a focused laser
Authors: Mukai Sada-Atsu , Magome Nobuyuki , Kitahata Hiroyuki , Yoshikawa Kenichi
Published: September 2003

We found that a focused laser can generate microscopic phase separation in an oil/water system. An oil droplet emerges and grows at the focus of the laser in a water-rich homogeneous medium. In contrast, in an oil-rich homogeneous phase, water droplets spring out in a successive manner from the focus of the laser, move away, and disappear in the surroundings, forming a flower-like pattern. The mechanism of this dynamic phase separation is discussed under the framework of the mean field theory.
Synthesis and field-emission properties of aligned MoO3 nanowires
Authors: Zhou Jun , Deng S. Z. , Xu N. S. , Chen Jun , She J. C.
Published: September 2003

Aligned MoO3 nanowires have been grown on silicon substrates without using any catalyst. They were prepared in a two-step process: first by thermal evaporation and then further processed by oxidation. The MoO3 nanowires are of crystalline and have an orthorhombic structure. They also have high purity. Field-emission measurement showed that, typically, their turn-on field and threshold field were about 3.5 and 7.65 MV/m, respectively. Furthermore, the spatial distribution of emission sites was studied using transparent anode technique and the emission current of the sites was relatively uniform. These may be attributed to very good uniformity in the height and diameter of the nanowires, and to the separation between nanowires. Finally, the stability of the emission current over time was found to be within 10%. These findings indicate that MoO3 nanowires as a cold cathode have a potential future.
A comparative study of GaSb (100) surface passivation by aqueous and nonaqueous solutions
Authors: Liu Z. Y. , Kuech T. F. , Saulys D. A.
Published: September 2003

We report a nonaqueous passivation regime consisting of Na2S/benzene/15-crown-5/oxidant. The use of a nonpolar, aprotic organic medium required the addition of a specific chelating agent (15-crown-5) to solubilize sodium sulfide, and organic oxidizing agents (anthraquinone, benzophenone, etc.) to act as electron acceptors. The surface optical and chemical properties of GaSb surfaces after aqueous and nonaqueous sulfide treatments were compared. Nonaqueous passivation resulted in higher photoluminescence (PL) intensity, lower oxide content, and a less amount of elemental Sb than aqueous passivation. The PL intensity from passivated surfaces was correlated with the standard reduction potentials of electron acceptors.
Study of the cross-sectional profile in selective formation of porous silicon
Authors: Kim Han-Su , Chong Kyuchul , Xie Ya-Hong
Published: September 2003

Porous Si is the semi-insulating state of Si, with low thermal expansion mismatch with bulk Si. As a result, it is an excellent material for crosstalk isolation in mixed-signal integrated circuits. We study the formation of isolated porous Si regions in p−-type and p+-type Si substrates with emphasis on the cross-sectional profile of the porous regions. Our study reveals that in addition to the primary undercut due to the isotropic nature of the anodization process, there exists a secondary undercut that is similar in shape to the bird’s beak commonly observed at the edge of field oxides in conventional Si complementary-metal-oxide-semiconductor process. The shape and the extent of the secondary undercut are dependent on the type of mask materials used during selective formation of porous Si as well as the substrate resistivity. The combined experimental and simulation studies pointed to two likely origins of secondary undercuts: the weak adhesion of some of the mask materials and current crowding in bulk Si substrates near the edge of the mask openings. Secondary undercuts result in the erosion of the precious Si chip surface area when a porous Si trench is used for rf crosstalk isolation, and should be minimized.
Pentacene thin-film transistors with Al2O3+x gate dielectric films deposited on indium-tin-oxide glass
Authors: Lee Jiyoul , Kim J. H. , Im Seongil
Published: September 2003

We report on the fabrication of pentacene thin-film transistors (TFTs) with Al2O3+x films as the gate dielectric that has been deposited on indium-tin-oxide glass by rf magnetron sputtering at room temperature. Although the Al2O3+x was expected to show lower capacitance and breakdown field than stoichiometric Al2O3, our pentacene TFTs with optimized thin Al2O3+x gate dielectric exhibited a moderately high field mobility of 0.14 cm2/V s, an outstanding subthreshold slope of 0.88 V/dec, and an on/off ratio over 106. Our work demonstrates that RT-deposited Al2O3+x is a promising gate dielectric material for organic TFTs.
Low-threshold 1317-nm InGaAsN quantum-well lasers with GaAsN barriers
Authors: Tansu Nelson , Yeh Jeng-Ya , Mawst Luke J.
Published: September 2003

Very low threshold-current-density InGaAsN quantum-well lasers with GaAsN barriers, grown using metalorganic chemical vapor deposition, have been realized with a room-temperature emission wavelength of 1317 nm. The GaAsN barriers are employed to extend the wavelength, to strain compensate the quantum well, and to improve the hole confinement inside the quantum well. RT threshold current densities of only 210–270 A/cm2 are measured for InGaAsN quantum-well lasers (Lcav=1000–2000 μm) with an emission wavelength of 1317 nm.