bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlled crystal growth of layered-perovskite thin films as an approach to study their basic properties
Authors: Watanabe Takayuki , Funakubo Hiroshi
Published: September 2006

This article describes the current progress in thin bismuth layer-structured ferroelectric films (BLSFs) including SrBi2Ta2O9 and (Bi,La)4Ti3O12, particularly those developed in the last ten years. BLSF thin films can be applied to ferroelectric random access memories because of their durable fatigue-free properties and lead-free composition. We will briefly introduce epitaxial thin films grown on a variety of substrates. Because of the difficulty in growing single crystals of sufficient size to characterize the ferroelectric behavior in specific crystal growth directions, we will characterize epitaxially grown thin films to obtain basic information about the anisotropic switching behavior, which is important for evaluating the performance of emerging materials. We will then discuss the fiber-textured growth on the (111)Pt-covered Si substrates of SrBi2Ta2O9 and Bi4Ti3O12 thin films. Because we expect that the spread crystal orientation will affect the bit-to-bit errors, we believe that the fiber-textured growth and the characterization technique for the deposited film orientation are interesting from a practical standpoint. Another specific challenge of thin film growth is the growth of a-axis-(polar axis)-oriented films. a-∕b-axis-oriented films are characterized both crystallographically and by electric hysteresis loop. The hysteresis performance was in accordance with the volume fraction of the a∕b domains; however, no evidence for 90° switching of the b domain by an external electric field was obtained. The control of film orientation also allows systematic studies on the effects of a structural modification and relation between spontaneous polarization and Curie temperature, examples of which are given in this paper. After a short description of the piezoelectric properties, we will conclude with a summary and the future prospects of BLSF thin films for research and applications.
Thermally stimulated currents in amorphous barium titanate thin films deposited by rf magnetron sputtering
Authors: El Kamel F. , Gonon P. , Jomni F. , Yangui B.
Published: September 2006

Thermally stimulated currents (TSCs) are measured in amorphous barium titanate thin films deposited by the rf sputtering technique. The TSC global curve is composed of three overlapping peaks in the 0–200°C temperature range. At 50°C, a first TSC peak is observed that can be related to a shallow-trap level. A second peak due to a dipolar polarization process is observed at 95°C. Finally, a third peak appears at 140°C that is ascribed to the oxygen vacancy motion and their accumulation at electrodes. The different peaks constituting the global TSC spectrum are separately studied by the fractional polarization technique in order to analyze their fine structures and to determine their activation energies.
Crystal structure, electrical properties, and mechanical response of (100)-/(001)-oriented epitaxial Pb(Mg1∕3Nb2∕3)O3–PbTiO3 films grown on (100)cSrRuO3‖(100)SrTiO3 substrates by metal-organic chemical vapor deposition
Authors: Yokoyama Shintaro , Okamoto Satoshi , Funakubo Hiroshi , Iijima Takashi , Saito Keisuke , Okino Hirotake , Yamamoto Takashi , Nishida Ken , Katoda Takashi , Sakai Joe
Published: September 2006

Relaxor-type ferroelectric (1−x)Pb(Mg1∕3Nb2∕3)O3–xPbTiO3 (PMN-PT) films, 2–3μm in thickness, with a PbTiO3 content (x) ranging from 0 to 1 were grown on (100)cSrRuO3‖(100)SrTiO3 substrates at 650°C by metal-organic chemical vapor deposition. The effects the x value had on the crystal structure, dielectric and ferroelectric properties, and mechanical response of these films were systematically investigated. Epitaxial growth having (100)∕(001) orientation irrespective of x and the constituent phase change with x were ascertained from both x-ray diffraction reciprocal space mapping analysis and Raman spectroscopy. The constituent phase changed from a rhombohedral (pseudocubic) single phase, a mixture phase of rhombohedral (pseudocubic) and tetragonal phases, and a tetragonal single phase, with increasing x. The mixed phase region was found to exist at x=0.40–0.55, which was different from that reported for single crystals (x=0.31–0.35). The dependencies of relative dielectric constant and remanent polarization on x showed a similar trend in the case of a PMN-PT sintered body; however, the magnitudes of these values were relatively low. The effective longitudinal piezoelectric coefficient (d33,f) and the transverse coefficient (e31,f) of 100–120pm∕V and ∼−11.0C∕m2 were, respectively, calculated for a film with x=0.39, which corresponds to a larger x edge for the rhombohedral (pseudocubic) region following the engineered domain concept proposed for PMN-PT single crystals.
Structure and thermoelectric properties of boron doped nanocrystalline Si0.8Ge0.2 thin film
Authors: Takashiri M. , Borca-Tasciuc T. , Jacquot A. , Miyazaki K. , Chen G.
Published: September 2006

The structure and thermoelectric properties of boron doped nanocrystalline Si0.8Ge0.2 thin films are investigated for potential application in microthermoelectric devices. Nanocrystalline Si0.8Ge0.2 thin films are grown by low-pressure chemical vapor deposition on a sandwich of Si3N4∕SiO2∕Si3N4 films deposited on a Si (100) substrate. The Si0.8Ge0.2 film is doped with boron by ion implantation. The structure of the thin film is studied by means of atomic force microscopy, x-ray diffraction, and transmission electron microscopy. It is found that the film has column-shaped crystal grains ∼100nm in diameter oriented along the thickness of the film. The electrical conductivity and Seebeck coefficient are measured in the temperature range between 80–300 and 130–300K, respectively. The thermal conductivity is measured at room temperature by a 3ω method. As compared with bulk silicon-germanium and microcrystalline film alloys of nearly the same Si∕Ge ratio and doping concentrations, the Si0.8Ge0.2 nanocrystalline film exhibits a twofold reduction in the thermal conductivitity, an enhancement in the Seebeck coefficient, and a reduction in the electrical conductivity. Enhanced heat carrier scattering due to the nanocrystalline structure of the films and a combined effect of boron segregation and carrier trapping at grain boundaries are believed to be responsible for the measured reductions in the thermal and electrical conductivities, respectively.
Negative magnetoresistance in metal/oxide/InMnAs tunnel junctions
Authors: May S. J. , Phillips P. J. , Wessels B. W.
Published: September 2006

The electronic and magnetoresistive properties of metal/oxide/p-InMnAs magnetic tunnel junctions have been characterized. Ni and Al were each used as the metal electrode, while Al2O3 and SiO2 layers were utilized as tunnel barriers. A conductance well, with a width ∼100meV less than the band gap of InMnAs, is observed for all samples, consistent with tunneling between a metal and p-type degenerate semiconductor. At temperatures up to 150K, a negative magnetoresistance is measured in the tunnel junctions. The absence of the normal tunnel magnetoresistance effect in the Ni-based junctions is attributed to strong interlayer coupling between the ferromagnetic Ni and InMnAs layers.
Coupling of Fe thin films through a granular magnetic layer
Authors: Gómez J. , Weston J. L. , Butera A.
Published: September 2006

We have studied the magnetic coupling between two continuous Fe layers of fixed thickness separated by a granular Fe–SiO2 spacer of varying thickness (1.1nm<t<18nm) and composition (0.45<x<0.95). We have analyzed the magnetic response with dc magnetization and ferromagnetic resonance (FMR). Depending on the characteristics of the Fe–SiO2 layer the hysteresis loops can have a continuous or a two step process reversal. FMR data show one or two absorption lines, depending on the microwave excitation frequency. From these data we were able to determine that the Fe∕Fe interlayer coupling is ferromagnetic with an exchange field in the range of 0.5kOe<HE<3.5kOe. The largest coupling occurs for thin spacers and large Fe concentrations. Fe∕Fe–SiO2 layers are also coupled ferromagnetically with an exchange coupling constant that is larger than the Fe∕Fe interlayer interaction.
On the validity of Avrami formalism in primary crystallization
Authors: Bruna Pere , Crespo Daniel , González-Cinca Ricard , Pineda Eloi
Published: September 2006

Calorimetric data of primary crystallization is usually interpreted in the framework of the Kolmogorov [Dokl. Akad. Nauk SSSR 1, 355 (1937)], Johnson and Mehl [Trans. AIME 135, 416 (1939)], and Avrami [J. Chem. Phys. 7, 1103 (1939); 8, 212 (1940); 9, 177 (1941)] (KJMA) theory. However, while the KJMA theory assumes random nucleation and exhaustion of space by direct impingement, primary crystallization is usually driven by diffusion-controlled growth with soft impingement between the growing crystallites. This results in a stop of the growth before the space is fully crystallized and induces nonrandom nucleation. In this work, phase-field simulations are used to check the validity of different kinetic models for describing primary crystallization kinetics. The results show that KJMA theory provides a good approximation to the soft-impingement and nonrandom nucleation effects. Moreover, these effects are not responsible of the slowing down of the kinetics found experimentally in the primary crystallization of glasses.
Nitrogen-doped p-type ZnO films prepared from nitrogen gas radio-frequency magnetron sputtering
Authors: Tu Ming-Lung , Su Yan-Kuin , Ma Chun-Yang
Published: September 2006

Wide band gap nitrogen-doped p-type ZnO films are prepared by radio-frequency magnetron sputtering from a 99.99% purity ZnO target. The sputtering gas is Ar mixed with various flow rates of nitrogen gas. Hole concentrations increase from 1.89×1015to2.11×1019cm−3 as the N2 flow rate decreases from 15to6SCCM (SCCM denotes cubic centimeter per minute at STP), i.e., increasing N2 flow rate above 6SCCM decreases the p-type carrier concentration. Microphotoluminescence (PL) spectra peaks are in the near-UV range and change from 384nm(3.23eV)to374nm(3.32eV) with increasing N2 flow rate. The PL peaks agree with the band gap of bulk ZnO, which comes from the recombination of free excitons. Raman spectra show six peaks: 436 (E2 high-frequency phonon mode for undoped ZnO film), 581 [A1 (LO) mode in ZnO:N film], 275, 508, 640, and 854cm−1 (local vibrational modes of Raman features in N-doped ZnO film).
Carrier spin dynamics in modulation-doped InAs∕GaAs quantum dots
Authors: Marcinkevičius S. , Siegert J. , Zhao Q. X.
Published: September 2006

Photoexcited electron and hole spin relaxation was studied in modulation-doped and undoped InAs∕GaAs quantum dots by means of time-resolved photoluminescence. After excitation into the barriers or the wetting layer, the electron spin polarization is preserved during the capture and relaxation in the dots, especially in the p-doped structures, and decays with a characteristic time of about 100ps. Spin state admixture in combination with electron interaction with acoustic phonons is suggested as the spin relaxation mechanism. Rapid spin polarization decay during carrier relaxation in undoped quantum dots is attributed to electron-optical phonon interaction. For carrier excitation directly into the dots, no significant spin polarization was observed, which points to the mixed nature of hole levels in quantum dots. The hole spin polarization randomizes on a much shorter time scale and is not detected in the experiment.
Transmission electron microscopy study of CoFe films with high saturation magnetization
Authors: Craig B. R. , McVitie S. , Chapman J. N. , Johnston A. B. , O’Donnell D. O.
Published: September 2006

Transmission electron microscopy (TEM) has been used to study magnetization processes in four high moment CoFe films. While all films were of similar total thickness, 50nm, the differences between them were the inclusion or otherwise of a seed layer and the introduction of nonmagnetic spacers to form laminated films. The detailed reversal mechanism for easy and hard axis reversals of each film was investigated. As expected cross-tie walls were observed in the films with thicker CoFe layers and wall displacements between layers were seen with the introduction of one or more spacer layers. Magnetization dispersion was reduced as multilayering was introduced. In the laminated film with three spacer layers, defect areas where the local magnetization distribution differed markedly from the surrounding film were observed. Cross-sectional TEM showed that layer roughness increased through the stack and this was the probable cause of the localized magnetic anomalies.
Surface expansion of channel waveguides formed by ion exchange in glass
Authors: Oven R.
Published: September 2006

The surface expansion profiles of Cu+–Na+ ion exchanged channel waveguides in glass are measured and compared with the lateral refractive index distribution. It is shown that the surface profile extends laterally further than the index profile and that the maximum height of the surface profile depends on the channel width as well as the quantity of ions exchanged. The surface profiles are compared with a two dimensional analytical model based on elastic theory with which reasonable agreement is obtained. Some consequences for the accurate modeling of ion exchanged waveguides are discussed.
X-ray photoelectron spectroscopic and secondary ion mass spectroscopic examinations of metallic-lithium-activated donor doping process on La0.56Li0.33TiO3 surface at room temperature
Authors: Yang Kai-Yun , Fung Kuan-Zong , Wang Moo-Chin
Published: September 2006

The donor doping process at the interface between the cation-deficient La0.56Li0.33TiO3 and lithium was elucidated by x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS). XPS revealed a chemical shift (∼1.48eV) from the main peak of Ti4+ 2p3∕2 toward the low energy side, due to the conversion of 12% Ti4+ to Ti3+. The SIMS analysis indicates that a local electric field was responsible for the insertion of oxidized Li+6 isotope ions. The doping with Ti3+ donors, accompanying the insertion of Li+ ions into cation vacancies of La0.56Li0.33TiO3, yields the n-type semiconducting characteristics at room temperature.
Multigrating quasi-phase-matched optical parametric oscillation in periodically poled MgO:LiNbO3 device
Authors: Su Hong , Ruan Shuang-Chen , Qin Yi-Qiang , Guo Hong-Chen , Tang Sing-Hai
Published: September 2006

A widely tunable middle-infrared quasi-phase-matched optical parametric oscillation that uses a periodically poled magnesium-oxide-doped lithium niobate with a multigrating structure is reported. The optical parametric oscillation device is tuned by translating the crystal through the resonator and the pump beam, with no realignment needed. The results show that the idler range lies in 3.6–4.1μm in 0.1μm increment as the pump wavelength is fixed at 1.064μm. The grating periods on the crystal and the threshold pump energy in this experiment are verified, respectively.
Heavily Sn-doped GaAs with abrupt doping profiles grown by migration-enhanced epitaxy at low temperatures
Authors: Chavanapranee Tosaporn , Horikoshi Yoshiji
Published: September 2006

The characteristics of heavily Sn-doped GaAs samples grown at 300°C by a migration-enhanced epitaxy (MEE) technique are investigated in comparison with those of the samples grown by a conventional molecular-beam epitaxy (MBE) at 580°C. While no discernible difference is observed in the low doping regime, the difference in doping characteristics between the MBE- and MEE-grown samples becomes apparent when the doping concentration exceeds 1×1019cm−3. Sn atoms as high as 4×1021cm−3 can be incorporated into MEE-grown GaAs films, unlike the MBE-grown samples that have a maximum doping level limited around 1×1019cm−3. Due to an effective suppression of Sn segregation in the MEE growth case, high quality GaAs films with abrupt high-concentration Sn-doping profiles are achieved with the doping concentrations of up to 2×1021cm−3. It has been shown that even though a high concentration of Sn atoms is incorporated into the GaAs film, the electron concentration saturates at 6×1019cm−3 and then gradually decreases with Sn concentration. The uniform doping limitation, as well as the electron concentration saturation, is discussed by means of Hall-effect measurement, x-ray diffraction, and Raman scattering spectroscopy.
Numerical study for ballistic switching of magnetization in single domain particle triggered by a ferromagnetic resonance within a relaxation time limit
Authors: Nozaki Y. , Matsuyama K.
Published: September 2006

Magnetization reversal via successive ballistic rotation caused by an application of alternative field temporally varying within a relaxation time limit has been numerically investigated. As the Gilbert damping constant is smaller than 0.03, a pronounced beat appears in the temporal evolution of rotating angle of magnetization. The amplitude of the rotating angle at the first peak of the beat is larger than that achieved in the stable ferromagnetic resonance, so that the magnetization reversal occurred at the first peak of the beat. Consequently, subnanosecond switching of magnetization is realized even though a ferromagnetic resonant phenomenon is utilized to enhance the rotating angle of magnetization. In such a switching scheme, it is most important to optimize the frequency of the alternating field to ensure a practical margin of the operation current creating the switching field.
Spectral dependence of third order nonlinear optical susceptibility of zinc phthalocyanine
Authors: Santhi A. , Namboodiri Vinu V. , Radhakrishnan P. , Nampoori V. P. N.
Published: September 2006

Wavelength dependence of saturable absorption (SA) and reverse saturable absorption (RSA) of zinc phthalocyanine was studied using 10Hz, 8ns pulses from a tunable laser, in the wavelength range of 520–686nm, which includes the rising edge of the Q band in the electronic absorption spectrum. The nonlinear response is wavelength dependent and switching from RSA to SA has been observed as the excitation wavelength changes from the low absorption window region to higher absorption regime near the Q band. The SA again changes back to RSA when we further move over to the infrared region. Values of the imaginary part of third order susceptibility are calculated for various wavelengths in this range. This study is important in identifying the spectral range over which the nonlinear material acts as RSA based optical limiter.
Determination of the d31 piezoelectric coefficient of PbZrxTi1−xO3 thin films using multilayer buckled micromembranes
Authors: Ayela C. , Nicu L. , Soyer C. , Cattan E. , Bergaud C.
Published: September 2006

The aim of this paper consists in the determination of the piezoelectric transverse coefficient d31 of PbZrxTi1−xO3 (PZT) thin films integrated in dedicated multilayer silicon-based micromembranes exhibiting an initial buckled profile. An analytical model specific to this configuration was built and used for the calculation of d31 starting with the static profiles of the microfabricated devices determined by means of a double-beam interferometer. The influence of dc voltage and buckling effects on the d31 piezoelectric coefficient at the microscale were investigated, and high values were obtained, from 30to75pm∕V, within a hysteresyslike cycle. These results demonstrated the good electrical behavior of PZT thin films at the microscale with a low influence of buckling effects and determined optimal operation conditions for high values of d31.
Ostwald ripening of interstitial-type dislocation loops in 4H-silicon carbide
Authors: Persson P. O. Å. , Hultman L. , Janson M. S. , Hallén A.
Published: September 2006

The annealing behavior of interstitial-type basal plane dislocation loops in Al ion implanted 4H-SiC is investigated. It is shown that the loops undergo a dynamical ripening process. For annealing below 1700°C the total area of dislocation loops increases, indicating that point defects are still available for accumulation, but for annealing times longer than 100min at this temperature the value of the total loop area saturates. For longer annealing times, or higher temperatures, the dislocation loops are subjected to a conservative coarsening process, also known as Ostwald ripening. In this process the mean loop radius increases with increasing annealing time and temperature while the number of loops decreases. Meanwhile the summarized area of the loops stays constant. The observed ripening is suggested to occur by a mechanism, which involves coarsening by direct loop coalescence. Through this mechanism, loops on the same basal plane move towards each other until they coalesce into one, but loops on neighboring basal planes can only move until their loop edges meet (in a basal plane projection) where they remain. Climb along the c axis is not favorable as shown by experimental results and is suggested to be caused by the atomic configuration of the loop. Upon continuous annealing, this results in a situation where the loops are confined in clusters.
Two-dimensional quantum propagation using wavelets in space and time
Authors: Sparks Douglas K. , Johnson Bruce R.
Published: September 2006

A recent method for solving the time-dependent Schrödinger equation has been developed using expansions in compact-support wavelet bases in both space and time [H. Wang et al., J. Chem. Phys. 121, 7647 (2004)]. This method represents an exact quantum mixed time-frequency approach, with special initial temporal wavelets used to solve the initial value problem. The present work is a first extension of the method to multiple spatial dimensions applied to a simple two-dimensional (2D) coupled anharmonic oscillator problem. A wavelet-discretized version of norm preservation for time-independent Hamiltonians discovered in the earlier one-dimensional investigation is verified to hold as well in 2D and, by implication, in higher numbers of spatial dimensions. The wavelet bases are not restricted to rectangular domains, a fact which is exploited here in a 2D adaptive version of the algorithm.
Dispersion of the electro-optic properties of cerium-doped Sr0.61Ba0.39Nb2O6
Authors: Imlau Mirco , Bastwöste Kathrin , Möller Stefan , Voelker Uwe , Goulkov Mikhail
Published: September 2006

The product of the linear electro-optic coefficient with the electron-hole competition factor r33ζ is determined as a function of the wavelength together with the photorefractive trap density Neff in cerium-doped strontium barium niobate. The photorefractive method of photoinduced light scattering is applied. A pronounced increase of r33 by more than a factor of 2 is self-evident in the blue-green spectral range, which is described by a theoretical approach based on the combination of the Sellmeier formulation and the polarization tensor concept. By this further important material parameters are estimated, such as the strength and frequency of the average dipole oscillator characterizing the optical interband transfer.
Fabrication and characterization of silicon nanowires with triangular cross section
Authors: Pennelli Giovanni , Piotto Massimo
Published: September 2006

Fabrication processes for silicon nanowires with triangular cross section are presented. Processes based on high resolution electron beam lithography and anisotropic etching have been developed on silicon on insulator substrates. As shown by numerical simulations, the triangular shape of the wire allows strong reduction of the dimensions by successive oxidation steps. Moreover, it is easy to define a gate on top of the wire that wraps the device and, with the back gate silicon substrate, allows the biasing of the structure on all sides. The conduction through the wire, as a function of the gate bias and for different temperatures, is reported and discussed.
Study on synthesis and blue emission mechanism of ZnO tetrapodlike nanostructures
Authors: Cheng Wende , Wu Ping , Zou Xingquan , Xiao Tan
Published: September 2006

Zinc oxide (ZnO) tetrapodlike nanostructures were synthesized by thermal evaporation of Zn powder at different flow rates of argon. Scanning electron microscopy, x-ray diffraction, transmission electron microscopy, and photoluminescence were employed to study the structural features and optical properties of the product. Results show that the flow rate of argon gas has a comparative great influence on the morphology of ZnO nanostructures. As the flow rate increases, nano-ZnO morphology changes from an initial mixture of tetrapod, nanowire, nanosheet, and nanodendritic forms to a uniform tetrapodlike morphology. The fact that the ultraviolet emission weakens and the blue emission strengthens with increase of the argon flow rate suggests that the oxygen vacancy is most likely responsible for the blue emission. This was confirmed by the experimental results: the blue light emission disappears after the products are oxidized in air at 700°C, and then reappears after the oxidized products are deoxidized in H2 at 700°C. The growth mechanism of the ZnO tetrapods is also discussed.
Effect of reactive species on surface crosslinking of plasma-treated polymers investigated by surface force microscopy
Authors: Tajima S. , Komvopoulos K.
Published: September 2006

Polymer surface modification by ions, uncharged particles, and photons of inductively coupled Ar plasma was investigated with a surface force microscope. Optical windows consisting of crystals with different cutoff wavelengths and a metal shield were used to deconvolute the effects of the various plasma species on the modification of the surface nanomechanical properties of polyethylene. The extent of surface crosslinking was related to the frictional energy dissipated during nanoscratching. It is shown that surface crosslinking is primarily due to the simultaneous effects of uncharged particles and vacuum ultraviolet photons, while the ion bombardment effect is secondary.
Scheme for a quantum random number generator
Authors: Wang P. X. , Long G. L. , Li Y. S.
Published: September 2006

A scheme for a random number generator based on the intrinsic randomness of quantum mechanics is proposed. A Fresnel multiple prism which can act as a perfect 50∕50 beam splitter is used to realize the random events by choosing single photons from a polarized laser beam. A procedure to get rid of the bias of the raw sequences is discussed in detail together with the random number generation efficiency per light pulse.
Laser isotope separation of lithium by two-step photoionization
Authors: Saleem M. , Hussain Shahid , Rafiq M. , Baig M. A.
Published: September 2006

Lithium isotope separation has been achieved employing the two-step photoionization technique along with a narrow band dye laser in conjunction with a time of flight mass spectrometer. The demonstrated method yields a high degree of selectivity by tuning the dye laser at the resonance levels of Li6 and Li7. It is inferred that the concentration of the natural abundance of the Li6 isotope gets enhanced up to over 47% as the exciter dye laser is tuned to the P1∕22 of Li6 even if the linewidth of the exciter laser is not sufficiently narrow to excite the isotopic level. It is also noticed that the much higher energy density of the exciter laser limits the resolution of the fine structure levels of the lithium isotopes that leads to a loss in the enrichment of Li6 due to the power-broadening effect. Measurements of the photoionization cross section of the lithium isotopes from the 2pP1∕2,3∕22, excited states for Li6 and Li7 and the corresponding number densities are reported.
Transmission electron microscopy studies of GaAs nanostructures in InGaAs∕InP matrix grown by molecular beam epitaxy
Authors: Lin S. D. , Lin Z. C. , Lee C. P.
Published: September 2006

Self-assembled GaAs nanostructures in In0.53Ga0.47As matrix on (100) InP substrate have been investigated using atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM). In measured AFM images, dotlike and wirelike GaAs nanostructures were obtained with different deposition thicknesses. The XTEM images clearly showed composition modulation in the overgrown InGaAs matrix. The reason for this composition modulation is explained by strain field compensation and surface energy minimization.
Rigorous carrier dynamic model of electroluminescent metal-oxide-semiconductor silicon tunneling diodes
Authors: Liang Eih-Zhe , Su Ting-Wei , Lin Ching-Fuh
Published: September 2006

The carrier dynamics of electroluminescent metal-oxide-semiconductor silicon tunneling diodes is rigorously modeled in this study. Various tunneling and recombination current densities are formulated without using the Maxwell-Boltzmann approximation for the carrier concentrations. This model satisfactorily explains the current-voltage characteristics in strong accumulation using a self-consistent formulation. It also relates light emission efficiency to the interface-state density and the bulk-trap density in a straightforward manner. The internal radiative recombination efficiency in the bulk Si substrate is estimated to be in tens of percents. The model also explains clearly the strongly influenced small-signal light-current response time with respect to the injection current density. It enables the small-signal method to be useful in extracting the parameters of the interface-state density and the bulk-trap density.
Raman scattering investigation on structural and chemical disorder generated by laser ablation and mechanical microindentations of InSb single crystal
Authors: Joya M. R. , Pizani P. S. , Jasinevicius R. G. , Samad R. E. , de Rossi W. , Vieira N. D.
Published: September 2006

This paper reports on a topographic and tomographic Raman scattering study of the structural and chemical disorders generated by microindentations in indium antimonide. Two different microindentation mechanisms were investigated: mechanical and laser ablations. In the mechanical indentation, three main effects were observed: amorphization, structural pressure induced phase transition from zinc blende to wurtzite structure, and the presence of both compressive and tensile residual strains. On the other hand, an intense irreversible chemical disorder in the laser ablation was observed, the main effect being the segregation of crystalline antimony up to the surface of the indentation mark.
On the semiclassical initial value calculation of thermal rate coefficients for the N+N2 reaction
Authors: Lago N. Faginas , Laganá A. , Gargano R. , Barreto P. R. P.
Published: September 2006

In this paper we compare semiclassical initial value representation, conventional transition state theory with Wigner and Eckart tunneling correction, quantum reduced dimensionality, and quasiclassical thermal rate coefficients for N+N2 exchange reaction.
Lengthening of the photoluminescence decay time of InAs quantum dots coupled to InGaAs∕GaAs quantum well
Authors: Mazur Yu. I. , Liang B. L. , Wang Zh. M. , Tarasov G. G. , Guzun D. , Salamo G. J. , Mishima T. D. , Johnson M. B.
Published: September 2006

Time-resolved photoluminescence measurements are carried out for InAs quantum dots (QDs) coupled through a GaAs barrier to an In0.3Ga0.7As quantum well (QW). It is found that decay time of photoluminescence response from the QW is significantly shortened when compared to a reference sample only containing a QW with similar parameters while the decay time of photoluminescence response for the QD layer is significantly lengthened compared to reference sample only containing a QD layer. A rate equation model is developed to describe the observed behavior via carrier capture from QW to QD states in the QD:QW structure.
Magnetic properties of Co–Al–Ni melt-spun ribbon
Authors: Saito Tetsuji
Published: September 2006

Co–Al–Ni alloys were produced by melt-spinning followed by heat treatment. X-ray and thermomagnetic studies revealed that the rapidly solidified melt-spun ribbons consisted of a nonequilibrium bcc-(Co,Ni)Al-type structure. The Curie temperature was closely dependent on the Ni content of the Co–Al–Ni alloy. Although the Co–Al–Ni melt-spun ribbons had low coercivity, annealing of the ribbons at 823K for 1h resulted in an increase in the coercivity. The coercivity of the annealed Co–Ni–Al melt-spun ribbon was also dependent on the Ni content. The Curie temperature of the β-(Co,Ni)Al phase in the annealed Co–Ni–Al melt-spun ribbon decreased as its Ni content increased. Annealed Co30Al30Ni40 melt-spun ribbon with hcp-(Co,Ni) and β-(Co,Ni)Al phases exhibited the highest coercivity of 2.0kOe. The origin of the high coercivity in the annealed Co–Al–Ni melt-spun ribbon was found to be the formation of the hcp-(Co,Ni) phase. It was found that annealing at 1173K for 1h resulted in the formation of the fcc-(Co,Ni) and β-(Co,Ni)Al phases and led to a drastic decrease in the coercivity.
Fatigue behavior of heterostructured Pb(Zr,Ti)O3∕(Bi,Nd)4Ti3O12 ferroelectric thin films
Authors: Sim C. H. , Soon H. P. , Zhou Z. H. , Wang J.
Published: September 2006

Heterolayered Pb(Zr0.52Ti0.48)O3∕(Bi3.15Nd0.85)Ti3O12 (PZT/BNT) thin films were synthesized via a route of combining sol-gel and rf sputtering. A fatigue anomaly is observed for the heterolayered PZT/BNT thin films, where a switchable polarization peak, which is more than five times higher than that of the virgin state, occurs upon polarization switching for 108–109cycles. Interestingly it shifts towards smaller numbers of switching cycles at elevated temperatures. Both the aging and dielectric behavior suggest that the fatigue anomaly is related to the defects accumulated at the interfaces in the heterolayers.
Germanium diffusion during HfO2 growth on Ge by molecular beam epitaxy
Authors: Ferrari S. , Spiga S. , Wiemer C. , Fanciulli M. , Dimoulas A.
Published: September 2006

The authors study the Ge diffusion during HfO2 growth by molecular beam epitaxy on differently in situ prepared germanium substrates and at different growth temperatures. While HfO2 layers grown directly on Ge do not show any germanium contamination, oxygen rich interfacial layers such as GeOx or GeOxNy partly dissolve into the HfO2 layer, giving rise to high Ge contamination (from 1% to 10%). The use of nitridated interfacial layers does not prevent Ge diffusion into the HfO2 during the growth process because of the high oxygen content present in the nitridated germanium layer.
Array-compatible transition-edge sensor microcalorimeter γ-ray detector with 42eV energy resolution at 103keV
Authors: Zink B. L. , Ullom J. N. , Beall J. A. , Irwin K. D. , Doriese W. B. , Duncan W. D. , Ferreira L. , Hilton G. C. , Horansky R. D. , Reintsema C. D. , Vale L. R.
Published: September 2006

The authors describe a microcalorimeter γ-ray detector with measured energy resolution of 42eV full width at half maximum for 103keV photons. This detector consists of a thermally isolated superconducting transition-edge thermometer and a superconducting bulk tin photon absorber. The absorber is attached with a technique compatible with producing arrays of high-resolution γ-ray detectors. The results of a detailed characterization of the detector, which includes measurements of the complex impedance, detector noise, and time-domain pulse response, suggest that a deeper understanding and optimization of the thermal transport between the absorber and thermometer could significantly improve the energy resolution of future detectors.
Radical SBr: A challenge to spectroscopists?
Authors: Ornellas Fernando R.
Published: September 2006

A theoretical description of the electronic states of the SBr radical at a high level of correlation effects treatment is presented for the first time. Most of its potential energy curves have a repulsive nature, but a set of bound Π2 states should provide a means for the experimental characterization of this species. The ground state can support over 40 vibrational states, but transitions from the 2Π2 state, with a very shallow well (four levels), should have intensities spread over a maximum around v″=10; lower vibrational levels can only be accessed for transitions from two high-lying Rydberg states. A whole set of spectroscopic constants, including vibrationally averaged spin-orbit coupling constants, and radiative transition probabilities and lifetimes quantify the theoretical description, thus supplying reliable results to guide the experimental investigation of this species.
Spin transport across a quantum dot doped with a magnetic ion
Authors: Qu F. , Vasilopoulos P.
Published: September 2006

A quantum theory of spin-dependent electronic transport through a single Mn2+-ion-doped II-VI quantum dot weakly coupled to ferromagnetic (FM) leads is presented. The electron-Mn-ion exchange interaction in the quantum dot strongly enhances the spin polarization of the current and the tunneling magnetoresistance (TMR) and yields a highly spin-polarized current even when the FM source is not 100% polarized. Both the spin polarization and the TMR depend strongly on the bias voltage VSD. In the presence of an external magnetic field, the TMR oscillates with VSD. The results open the way to voltage-controlled spin filters and magnetic sensors.
Enhanced transmission through Penrose subwavelength hole arrays
Authors: Przybilla F. , Genet C. , Ebbesen T. W.
Published: September 2006

Transmission through Penrose subwavelength hole arrays is studied in the optical regime. The loss of strict periodicity does not prevent surface plasmon modes from being excited. The authors study the spectral evolutions of these modes by increasing both the spacings between the holes in a commensurate way and the size of the array. When compared to the situation of a periodic array, their measurements show a reduction of the propagation length of the surface modes, most likely related to the influence of multiple scattering, which lowers the contribution of long-range interactions in the transmission spectra.
Ab initio potential energy surface, infrared spectra, and dynamics of the ion-molecule complexes between Br− and H2, D2, and HD
Authors: Grinev T. A. , Buchachenko A. A. , Kłos J. , Bieske E. J.
Published: September 2006

A three-dimensional potential energy surface (PES) for the Br−–H2 complex is computed using the ab initio CCSD(T) method and an extended basis set. The PES has two equivalent minima at the linear geometries (equilibrium interfragment distance Re=3.34Å and interaction energy De=670cm−1) separated by the barrier at the T-shaped configuration (interfragment distance Re=4.03Å and barrier height of 610cm−1). Ab initio points are fitted to a flexible analytical form and used in the variational rovibrational energy level calculations. Simulated infrared spectra of the Br−–H2 and Br−–D2 complexes in the monomer stretching excitation region are in good agreement with the measured ones. Nonstatistical intensity ratios of the complexes of para- and ortho-monomers are qualitatively explained by monomer ligand exchange reactions. Predissociation of the complexes containing vibrationally excited monomers is analyzed and shown to proceed through the near-resonant vibration-to-rotation energy transfer. For complexes involving Br− and the HD monomer, two energetically low-lying states are predicted, corresponding predominately to the Br−–DH and Br−–HD isomeric forms. The results demonstrate the close similarity of the bromide containing complexes to their analogs containing the chloride anion.
Generation of over 5MeV carbon ions from a fibrous polytetrafluoroethylene film irradiated with a 2.4TW, 50fs tabletop laser
Authors: Okihara Shin-Ichiro , Fujimoto Masatoshi , Takahashi Hironori , Matsukado Koji , Ohsuka Shinji , Aoshima Shin-Ichiro , Okazaki Shigetoshi , Ito Toshiaki , Tsuchiya Yutaka
Published: September 2006

The authors generated energetic carbon ions C4+ above 5MeV by focusing 2.4TW, 50fs, 10Hz laser pulses onto a fibrous polytetrafluoroethylene (PTFE) film. The PTFE film is composed only of carbon and fluorine and has microporous structure. A laser target made of this film is useful in generating carbon ions. A polyethyleneterephthalate film was also used as an alternative target for comparison. The results show that the number of carbon ions emitted from the PTFE target was approximately two orders of magnitude greater than that from a polyethyleneterephthalate target.
Mid-infrared luminescence of an InNAsSb∕InAs single quantum well grown by molecular beam epitaxy
Authors: Yuen Homan B. , Kim Seongsin M. , Hatami Fariba , Harris James S. , Chin Alan H.
Published: September 2006

The authors report the growth and characterization of a dilute nitride, InNAsSb∕InAs, by solid source molecular beam epitaxy. Optimizing growth conditions for nitrogen incorporation has resulted in high-quality InNAsSb epilayers without any structural degradation, as confirmed by high-resolution x-ray diffraction. Optical properties were investigated by temperature dependent and excitation power dependent photoluminescence. The authors obtained mid-infrared luminescence around 4μm at low temperature, which reveals strong carrier localization behavior at low temperature, induced by nitrogen and antimony interaction. The band alignment of InNAsSb∕InAs can be type I instead of the conventional type II found for InAsSb∕InAs. A conduction band offset, Ec, of ∼102meV was obtained.
Water-soluble multiwall-carbon-nanotube-polythiophene composite for bilayer photovoltaics
Authors: Miller Anthony J. , Hatton Ross A. , Silva S. Ravi P.
Published: September 2006

A water-soluble acid oxidized multiwall carbon nanotube (o-MWCNTs)-polythiophene composite for bilayer photovoltaics is reported. Discrete heterojunction photovoltaic cells utilizing this nanocomposite material as the donor layer exhibit a ∼20% increase in fill factor and commensurate increase in power conversion efficiency as compared to cells without o-MWCNTs. Crucially o-MWCNTs are incorporated into the cell structure using an environmentally compatible solvent without complicating the process of device fabrication.
Current-driven resistance oscillation in exchange-biased spin valves with a low aspect ratio
Authors: Jiang Y. , Tezuka N. , Inomata K.
Published: September 2006

The authors report on current-induced magnetization switching (CIMS) in current-perpendicular-to-plane exchange-biased spin-valve nanopillars with a low aspect ratio of 1. Due to the complex domain structure of the nanopillars, an intermediate resistance state has been clearly observed in the CIMS curve. A distinctive current-driven resistance oscillation and a very low critical current density of 6×105A∕cm2 have been demonstrated and explained to result from the competition between magnetic field, spin torque, and thermal activation.
Polarization rotation enhancement and scattering mechanisms in waveguide magnetophotonic crystals
Authors: Levy Miguel , Li Rong
Published: September 2006

Intermodal coupling in photonic band gap optical channels in magnetic garnet films is found to leverage the nonreciprocal polarization rotation. Forward fundamental-mode to high-order mode backscattering yields the largest rotations. The underlying mechanism is traced to the dependence of the grating-coupling constant on the modal refractive index and profile of the propagating beam. Large changes in polarization near the band edges are observed in first and second orders. Extreme sensitivity to linear birefringence exists in second order.
Engineering broad root-knot resistance in transgenic plants by RNAi silencing of a conserved and essential root-knot nematode parasitism gene
Authors: Huang Guozhong , Allen Rex , Davis Eric L. , Baum Thomas J. , Hussey Richard S.
Published: September 2006

Secreted parasitism proteins encoded by parasitism genes expressed in esophageal gland cells mediate infection and parasitism of plants by root-knot nematodes (RKN). Parasitism gene
16D10
encodes a conserved RKN secretory peptide that stimulates root growth and functions as a ligand for a putative plant transcription factor. We used
in vitro
and
in vivo
RNA interference approaches to silence this parasitism gene in RKN and validate that the parasitism gene has an essential function in RKN parasitism of plants. Ingestion of
16D10
dsRNA
in vitro
silenced the target parasitism gene in RKN and resulted in reduced nematode infectivity.
In vivo
expression of 16D10 dsRNA in
Arabidopsis
resulted in resistance effective against the four major RKN species. Because no known natural resistance gene has this wide effective range of RKN resistance, bioengineering crops expressing dsRNA that silence target RKN parasitism genes to disrupt the parasitic process represents a viable and flexible means of developing novel durable RKN-resistant crops and could provide crops with unprecedented broad resistance to RKN.
Characterization of brain neurons that express enzymes mediating neurosteroid biosynthesis
Authors: Agís-Balboa Roberto C. , Pinna Graziano , Zhubi Adrian , Maloku Ekrem , Veldic Marin , Costa Erminio , Guidotti Alessandro
Published: September 2006

Allopregnanolone (ALLO) and tetrahydrodeoxycorticosterone (THDOC) are potent positive allosteric modulators of GABA action at GABAAreceptors. ALLO and THDOC are synthesized in the brain from progesterone or deoxycorticosterone, respectively, by the sequential action of two enzymes: 5α-reductase (5α-R) type I and 3α-hydroxysteroid dehydrogenase (3α-HSD). This study evaluates 5α-R type I and 3α-HSD mRNA expression level in mouse brain by usingin situhybridization combined with glutamic acid decarboxylase 67/65, vesicular glutamate transporter 2, glial fibrillary acidic protein, and S100β immunohistochemistry. We demonstrate that 5α-R type I and 3α-HSD colocalize in cortical, hippocampal, and olfactory bulb glutamatergic principal neurons and in some output neurons of the amygdala and thalamus. Neither 5α-R type I nor 3α-HSD mRNAs are expressed in S100β- or glial fibrillary acidic protein-positive glial cells. Using glutamic acid decarboxylase 67/65 antibodies to mark GABAergic neurons, we failed to detect 5α-R type I and 3α-HSD in cortical and hippocampal GABAergic interneurons. However, 5α-R type I and 3α-HSD are significantly expressed in principal GABAergic output neurons, such as striatal medium spiny, reticular thalamic nucleus, and cerebellar Purkinje neurons. A similar distribution and cellular location of neurosteroidogenic enzymes was observed in rat brain. Taken together, these data suggest that ALLO and THDOC, which can be synthesized in principal output neurons, modulate GABA action at GABAAreceptors, either with an autocrine or a paracrine mechanism or by reaching GABAAreceptor intracellular sites through lateral membrane diffusion.
Intranuclear Binding Kinetics and Mobility of Single Native U1 snRNP Particles in Living Cells
Authors: Grünwald David , Spottke Beatrice , Buschmann Volker , Kubitscheck Ulrich
Published: September 2006

Uridine-rich small nuclear ribonucleoproteins (U snRNPs) are splicing factors, which are diffusely distributed in the nucleoplasm and also concentrated in nuclear speckles. Fluorescently labeled, native U1 snRNPs were microinjected into the cytoplasm of living HeLa cells. After nuclear import single U1 snRNPs could be visualized and tracked at a spatial precision of 30 nm at a frame rate of 200 Hz employing a custom-built microscope with single-molecule sensitivity. The single-particle tracks revealed that most U1 snRNPs were bound to specific intranuclear sites, many of those presumably representing pre-mRNA splicing sites. The dissociation kinetics from these sites showed a multiexponential decay behavior on time scales ranging from milliseconds to seconds, reflecting the involvement of U1 snRNPs in numerous distinct interactions. The average dwell times for U1 snRNPs bound at sites within the nucleoplasm did not differ significantly from those in speckles, indicating that similar processes occur in both compartments. Mobile U1 snRNPs moved with diffusion constants in the range from 0.5 to 8 μm2/s. These values were consistent with uncomplexed U1 snRNPs diffusing at a viscosity of 5 cPoise and U1 snRNPs moving in a largely restricted manner, and U1 snRNPs contained in large supramolecular assemblies such as spliceosomes or supraspliceosomes.