bluuebunny/crossref_metadata_2025 huggingface dataset:
Approaching the theoretical strength in nanoporous Au
Authors: Volkert C. A. , Lilleodden E. T. , Kramer D. , Weissmüller J.
Published: August 2006

The mechanical properties of nanoporous Au have been investigated by uniaxial compression. Micron-sized columns were machined in the surface of nanoporous Au using a focused Ga+ beam and compressed with a flat punch in a nanoindenter. Using scaling laws for foams, the yield strength of the 15nm diameter ligaments is estimated to be 1.5GPa, close to the theoretical strength of Au. This value agrees well with extrapolations of the yield strength of submicron, fully dense gold columns and shows that in addition to foam density and structure, the absolute size of ligaments and cell walls can be used to tailor foam properties.
Optical properties of GaN and GaMnN nanowires grown on sapphire substrates
Authors: Oh Eunsoon , Choi Jung Ho , Seong Han-Kyu , Choi Heon-Jin
Published: August 2006

The authors discussed the photoluminescence (PL) spectra of GaN and GaMnN nanowires grown on sapphire substrates. Comparison of the excitonic PL peak energy with bulk GaN indicates that the strain of the nanowires is fully relaxed. For GaMnN nanowires, the redshift of the PL peak with increasing temperature was larger than that of the GaN nanowires, which was explained by redistribution of carriers into localization sites. The absence of Zeeman shift and circular polarization in GaMnN nanowires indicates that the exchange interaction between carriers and Mn2+ has to be at least one order of magnitude smaller than that in Cd0.94Mn0.06S nanowires.
Decompositions of unitary evolutions and entanglement dynamics of bipartite quantum systems
Authors: D’Alessandro Domenico , Romano Raffaele
Published: August 2006

We describe a decomposition of the Lie group of unitary evolutions for a bipartite quantum system of arbitrary dimensions. The decomposition is based on a recursive procedure that systematically uses the Cartan classification of the symmetric spaces of the Lie group SO(n). The resulting factorization of unitary evolutions clearly displays the local and entangling character of each factor.
Conformal conversion from helical hexagonal InN microtubes to In2O3 counterparts
Authors: Luo Shudong , Zhou Weiya , Zhang Zengxing , Shen Jun , Liu Lifeng , Ma Wenjun , Zhao Xiaowei , Liu Dongfang , Song Li , Xiang Yanjuan , Zhou Jianjun , Xie Sishen , Chu Weiguo
Published: August 2006

Cubic In2O3 microtubes were prepared by thermally oxidizing InN counterparts under controlled conditions. Similar to the starting InN sample, the converted In2O3 microtubes are hexagonal in cross section and exhibit helical motifs of both right-handed and left-handed architectures with helical angles of 0°–30°. InN microtubes can be retrieved by renitridation of the oxide microtubes. This work demonstrates that it is feasible to fabricate specific oxide nano-/microstructures from its corresponding nitride counterparts via controlled oxidation manner and vice versa. Temperature-dependent Raman scattering in both InN and In2O3 microtubes was measured and obvious downshifts of Raman modes were observed with increasing temperature.
Dielectric properties of c-axis oriented Zn1−xMgxO thin films grown by multimagnetron sputtering
Authors: Dhananjay  , Krupanidhi S. B.
Published: August 2006

Zn 1 − x Mg x O  (x=0.3) thin films have been fabricated on Pt∕TiO2∕SiO2∕Si substrates using multimagnetron sputtering technique. The films with wurtzite structure showed a (002) preferred orientation. Ferroelectricity in Zn1−xMgxO films was established from the temperature dependent dielectric constant and the polarization hysteresis loop. The temperature dependent study of dielectric constant at different frequencies exhibited a dielectric anomaly at 110°C. The resistivity versus temperature characteristics showed an anomalous increase in the vicinity of the dielectric transition temperature. The Zn1−xMgxO thin films exhibit well-defined polarization hysteresis loop, with a remanent polarization of 0.2μC∕cm2 and coercive field of 8kV∕cm at room temperature.
Turbid two-phase slug flow in a microtube: Simultaneous visualization of structure and velocity field
Authors: Ahn Yeh-Chan , Jung Woonggyu , Chen Zhongping
Published: August 2006

Frequency domain optical coherence tomography with phase-resolved algorithm is presented to perform high-resolution, cross-sectional imaging of turbid two-phase slug flow in a microtube. Imaging and quantifying the interfacial structure and velocity field in a turbid two-phase flow are important to understand the mechanism of bioreactions and flow dynamics in biological systems. The authors demonstrate here that optical coherence tomography can measure detailed interfacial structures, bubble velocity, and velocity field inside liquid slugs. The radial liquid velocity was quantified without refraction correction. Two toroidal vortices per liquid slug were visualized which is the essential mechanism for radial heat and mass transfers.
Growth of RuO2 nanorods in reactive sputtering
Authors: Lin Yu-Tsun , Chen Chun-Yu , Hsiung Chang-Po , Cheng Kai-Wen , Gan Jon-Yiew
Published: August 2006

The synthesis of RuO2 nanorods with reactive sputtering was demonstrated in this work. The synthesis process is very much like the metal organic chemical vapor deposition, except that RuO3 generated with reactive sputtering under high oxygen-to-argon flow ratio (>5SCCM∕15SCCM) (SCCM denotes cubic centimeter per minute at STP) and high substrate temperature (>300°C) is used in place of the metal organic precursor. RuO2 nanorods tend to grow steadily with constant aspect ratio (∼27) and the field-emission characteristics appear very sensitive to their spatial distribution.
Quasiclassical trajectory calculations of the reaction C+C2H2→l-C3H, c-C3H+H, C3+H2 using full-dimensional triplet and singlet potential energy surfaces
Authors: Park Won K. , Park Joonho , Park Seung C. , Braams Bastiaan J. , Chen Chao , Bowman Joel M.
Published: August 2006

Full-dimensional, density functional theory (B3LYP/6-311g(d,p))-based potential energy surfaces (PESs) are reported and used in quasi-classical calculations of the reaction of C with C2H2. For the triplet case, the PES spans the region of the reactants, the complex region (with numerous minima and saddle points) and the products, linear(l)-C3H+H, cyclic(c)-C3H+H and c-C33+H2. For the singlet case, the PES describes the complex region and products l-C3H+H, c-C3H+H and l-C31+H2. The PESs are invariant under permutation of like nuclei and are fit to tens of thousands of electronic energies. Energies and harmonic frequencies of the PESs agree well the DFT ones for all stationary points and for the reactant and the products. Dynamics calculations on the triplet PES find both l-C3H and c-C3H products, with l-C3H being dominant at the energies considered. Limited unimolecular reaction dynamics on the singlet PES find both products in comparable amounts as well as the C3+H2 product.
A kinetic theory of tertiary contact formation coupled to the helix-coil transition in polypeptides
Authors: Hausrath Andrew C.
Published: August 2006

The framework model and the hydrophobic collapse model represent two canonical descriptions of the protein folding process. The first places primary reliance on the short-range interactions of secondary structure and the second assigns greater importance to the long-range interactions of tertiary structure. The availability of increasingly detailed information about the folding mechanisms of diverse proteins suggests that both are important and the folding mechanism of most proteins utilizes different combinations of such interactions. A prior report described the XHC model, an extended helix-coil theory, which treats the mutual stabilization of secondary and tertiary structure in simple α-helical proteins at equilibrium. In this study, a kinetic scheme describing tertiary contact formation has been developed which relaxes to the XHC equilibrium model. The relaxation is governed by the relative stabilities of the equilibrium states and an additional factor which represents an activation energy for formation of a tertiary contact. The model can be used to simulate time-dependent properties of the ensemble of conformations during the entire folding process, and the resulting predictions are applicable to a range of experimental methods. This XHC kinetic model enables investigation of the relative influence of secondary and tertiary interactions on folding mechanisms.
Structural evidence for enhanced polarization in a commensurate short-period BaTiO3∕SrTiO3 superlattice
Authors: Tian W. , Jiang J. C. , Pan X. Q. , Haeni J. H. , Li Y. L. , Chen L. Q. , Schlom D. G. , Neaton J. B. , Rabe K. M. , Jia Q. X.
Published: August 2006

A short-period (BaTiO3)6∕(SrTiO3)5 superlattice was characterized by x-ray diffraction and transmission electron microscopy. The superlattice is epitaxially oriented with the c axes of BaTiO3 and SrTiO3 normal to the (001) surface of the SrTiO3 substrate. Despite the large in-plane lattice mismatch between BaTiO3 and SrTiO3 (∼2.2%), the superlattice interfaces were found to be nearly commensurate. The crystallographic c∕a ratio of the superlattice was measured and the results agree quantitatively with first-principles calculations and phase-field modeling. The agreement supports the validity of the enhanced spontaneous polarization predicted for short-period BaTiO3∕SrTiO3 superlattices.
Oxygen-redistribution-induced disorder and magnetotransport properties of Sm0.55Sr0.45MnO3 manganites
Authors: Egilmez M. , Chow K. H. , Jung J.
Published: August 2006

The authors studied the effects of oxygen-redistribution-induced disorder on the magnetotransport of Sm0.55Sr0.45MnO3 manganites near the metal-insulator transition. Oxygen redistribution in the sample was obtained by annealing at 325°C in vacuum. The temperature dependences of resistivity and magnetoresistance were measured as a function of the annealing time. The authors observed a dramatic increase in the magnitude of the resistivity peak at the metal-insulator transition and a reduction of its width after an initial short-time annealing, followed by a logarithmic increase of the resistivity with annealing time. The data agree qualitatively with phase-separation theories for colossal magnetoresistance manganites.
Transient spectrometer for near-IR fluorescence based on parametric frequency upconversion
Authors: Chen Xing-Hai , Han Xiao-Feng , Weng Yu-Xiang , Zhang Jing-Yuan
Published: August 2006

The authors report a unique technique for recording femtosecond time-resolved fluorescence spectra in the near IR by using idler-to-signal frequency upconversion in a 400nm pumped femtosecond noncollinear optical parametric amplifier, in which the IR fluorescence was seeded as the idler and the corresponding amplified signal branch is recorded. The spectra of the upconverted signal carry the information of the IR fluorescence and it were used in constructing the spectra of the IR dye. The transient fluorescence spectra from the upconverted signal reconstruct the spectra of the IR dye very well after deconvolution from the pump beam.
Pd-nanocrystal-based nonvolatile memory structures with asymmetric SiO2∕HfO2 tunnel barrier
Authors: Seol Kwang Soo , Choi Seong Jae , Choi Jae-Young , Jang Eun-Joo , Kim Byung-Ki , Park Sang-Jin , Cha Dea-Gil , Song In-Yong , Park Jong-Bong , Park Youngsoo , Choi Suk-Ho
Published: August 2006

Pd nanocrystals (NCs) on asymmetric tunnel barrier (ATB) composed of stacked SiO2 and HfO2 layers have been employed for nonvolatile memory devices. The Pd-NC layers are formed by electrostatic self-assembly of negatively charged colloidal Pd NCs. The presence of isolated Pd NCs of ∼5nm embedded in HfO2 is confirmed by scanning and transmission electron microscopy images. Outstanding program∕erase (P∕E) properties from C-V curves are observed with a memory window of 6V under ±17V. Extrapolation of the data up to ten years shows that the flatband voltage drops at the P∕E levels are maintained within only 1.0∕0.5V, respectively, resulting from the efficient data retention based on the ATB. These results are promising enough for the memory structure to be utilized for the multilevel charge storage.
Exciton transitions in tetrapod-shaped CdTe nanocrystals investigated by photomodulated transmittance spectroscopy
Authors: Tarì Davide , De Giorgi Milena , Pompa Pier Paolo , Carbone Luigi , Manna Liberato , Kudera Stefan , Cingolani Roberto
Published: August 2006

The excitonic nature of the optical transitions in tetrapod-shaped colloidal CdTe nanocrystals is assessed by means of photomodulated transmittance spectroscopy. The line-shape analysis of the photomodulation transmittance spectra indicates the photoinduced Stark effect as the dominant modulation mechanism, and the presence of excitonic transitions even at room temperature, with an exciton binding energy of about 25meV, larger than the bulk value.
Dopant activation in subamorphized silicon upon laser annealing
Authors: Ong K. K. , Pey K. L. , Lee P. S. , Wee A. T. S. , Wang X. C. , Chong Y. F.
Published: August 2006

In this letter, the authors study the dopant activation and dopant distribution in a Si+ subamorphized Si (SAI-Si) when subjected to laser annealing (LA). The results show an enhanced boron activation in the SAI-Si in the nonmelt regime as compared to a crystalline Si (c-Si). The enhancement is caused by a vacancy-rich surface generated by the Si+ preimplantation that promotes the incorporation of boron atoms into the substitutional sites. On the other hand, shallow-melt LA produces a similar boron activation in both SAI-Si and c-Si samples due to a melting that consumes the entire as-implanted profile and the vacancy-rich region.
Fractional diffusion models of nonlocal transport
Authors: del-Castillo-Negrete D.
Published: August 2006

A class of nonlocal models based on the use of fractional derivatives (FDs) is proposed to describe nondiffusive transport in magnetically confined plasmas. FDs are integro-differential operators that incorporate in a unified framework asymmetric non-Fickian transport, non-Markovian (“memory”) effects, and nondiffusive scaling. To overcome the limitations of fractional models in unbounded domains, we use regularized FDs that allow the incorporation of finite-size domain effects, boundary conditions, and variable diffusivities. We present an α-weighted explicit/implicit numerical integration scheme based on the Grunwald-Letnikov representation of the regularized fractional diffusion operator in flux conserving form. In sharp contrast with the standard diffusive model, the strong nonlocality of fractional diffusion leads to a linear in time response for a decaying pulse at short times. In addition, an anomalous fractional pinch is observed, accompanied by the development of an uphill transport region where the “effective” diffusivity becomes negative. The fractional flux is in general asymmetric and, for steady states, it has a negative (toward the core) component that enhances confinement and a positive component that increases toward the edge and leads to poor confinement. The model exhibits the characteristic anomalous scaling of the confinement time, τ, with the system’s size, L, τ∼Lα, of low-confinement mode plasma where 1<α<2 is the order of the FD operator. Numerical solutions of the model with an off-axis source show that the fractional inward transport gives rise to profile peaking reminiscent of what is observed in tokamak discharges with auxiliary off-axis heating. Also, cold-pulse perturbations to steady sates in the model exhibit fast, nondiffusive propagation phenomena that resemble perturbative experiments.
Dominating radiative recombination in a nanoporous silicon layer with a metal-rich Au (1−α)–SiO2 (α) cermet waveguide
Authors: Hu Xiaolong , Huang Yidong , Zhang Wei , Peng Jiangde
Published: August 2006

Aimed at improving the quantum efficiency from nanoporous silicon, a device structure with a metal-rich Au (1−α)–SiO2 (α) cermet nanowaveguide is proposed. By properly choosing the component of the cermet, the surface-plasmon-like dispersion of the nanowaveguide can be engineered so that the density of states for photon is very large at the luminescent frequencies of nanoporous silicon. Consequently, spontaneous emission is greatly enhanced and radiative recombination of the careers becomes the dominating process in a nanoporous silicon layer. The internal quantum efficiency is largely improved.
Radial interchange motions of plasma filaments
Authors: Garcia O. E. , Bian N. H. , Fundamenski W.
Published: August 2006

Radial convection of isolated filamentary structures due to interchange motions in magnetized plasmas is investigated. Following a basic discussion of vorticity generation, ballooning, and the role of sheaths, a two-field interchange model is studied by means of numerical simulations on a biperiodic domain perpendicular to the magnetic field. It is demonstrated that a blob-like plasma structure develops dipolar vorticity and electrostatic potential fields, resulting in rapid radial acceleration and formation of a steep front and a trailing wake. While the dynamical evolution strongly depends on the amount of collisional diffusion and viscosity, the structure travels a radial distance many times its initial size in all parameter regimes in the absence of sheath dissipation. In the ideal limit, there is an inertial scaling for the maximum radial velocity of isolated filaments. This velocity scales as the acoustic speed times the square root of the structure size relative to the length scale of the magnetic field. The plasma filament eventually decelerates due to mixing and collisional dissipation. Finally, the role of sheath dissipation is investigated. When included in the simulations, it significantly reduces the radial velocity of isolated filaments. The results are discussed in the context of convective transport in scrape-off layer plasmas, comprising both blob-like structures in low confinement modes and edge localized mode filaments in unstable high confinement regimes.
Effective work function of Pt, Pd, and Re on atomic layer deposited HfO2
Authors: Gu Diefeng , Dey Sandwip K. , Majhi Prashant
Published: August 2006

Platinum and Pd show a significant difference in work function on SiO2 and high-K materials (HfO2). The effective metal work functions for Pd, Pt, and Re on atomic layer deposited HfO2, which are different from the vacuum work function and important for device threshold voltage control, are measured by the C-V method. The difference is attributed to the dipoles at the metal/HfO2 interface, which is a result of charge transfer across the interface. Moreover, the extracted charge neutrality level and screening parameter are correlated with the phase development, film stoichiometry, and density of interface states at the metal/high-K interface.
High resolution dissociative electron attachment to gas phase adenine
Authors: Huber D. , Beikircher M. , Denifl S. , Zappa F. , Matejcik S. , Bacher A. , Grill V. , Märk T. D. , Scheier P.
Published: August 2006

The dissociative electron attachment to the gas phase nucleobase adenine is studied using two different experiments. A double focusing sector field mass spectrometer is utilized for measurements requiring high mass resolution, high sensitivity, and relative ion yields for all the fragment anions and a hemispherical electron monochromator instrument for high electron energy resolution. The negative ion mass spectra are discussed at two different electron energies of 2 and 6eV. In contrast to previous gas phase studies a number of new negative ions are discovered in the mass spectra. The ion efficiency curves for the negative ions of adenine are measured for the electron energy range from about 0to15eV with an electron energy resolution of about 100meV. The total anion yield derived via the summation of all measured fragment anions is compared with the total cross section for negative ion formation measured recently without mass spectrometry. For adenine the shape of the two cross section curves agrees well, taking into account the different electron energy resolutions; however, for thymine some peculiar differences are observed.
Ballistic transport in induced one-dimensional hole systems
Authors: Klochan O. , Clarke W. R. , Danneau R. , Micolich A. P. , Ho L. H. , Hamilton A. R. , Muraki K. , Hirayama Y.
Published: August 2006

The authors have fabricated and studied a ballistic one-dimensional p-type quantum wire using an undoped AlGaAs∕GaAs heterostructure. The absence of modulation doping eliminates remote ionized impurity scattering and allows high mobilities to be achieved over a wide range of hole densities and, in particular, at very low densities where carrier-carrier interactions are strongest. The device exhibits clear quantized conductance plateaus with highly stable gate characteristics. These devices provide opportunities for studying spin-orbit coupling and interaction effects in mesoscopic hole systems in the strong interaction regime where rs>10.
Exchange biased spin polarizer with an embedded nano-oxide layer for a substantially lower switching current density
Authors: Nguyen Hoang Yen Thi , Yi Hyunjung , Joo Sung-Jung , Shin Kyung-Ho , Lee Kyung-Jin , Dieny Bernard
Published: August 2006

The authors demonstrate that the spin polarizer in the form of an exchange biased ferromagnetic lead with an embedded nano-oxide layer can greatly enhance the spin transfer torque for the current induced magnetization switching. By applying it in spin valves, the switching current density (4×106A∕cm2) is one order lower and the resistance change (2.78mΩμm2) is three times higher than those gotten by using a simple spin polarizer. This spin torque enhancement is attributed to the exchange bias pinning acting on the polarizer (the fixed layer) with effective support of the nano-oxide layer, which together lead to a much higher current spin polarization.
Estimating entanglement of unknown states
Authors: Cavalcanti Daniel , Terra Cunha Marcelo O.
Published: August 2006

The experimental determination of entanglement is a major goal in the quantum information field. In general, the knowledge of the state is required in order to quantify its entanglement. Here we express a lower bound to the robustness of entanglement of a state based only on the measurement of the energy observable and on the calculation of a separability energy. This allows the estimation of entanglement dismissing the knowledge of the state in question.
Reorientation of the crystalline planes in confined single crystal nickel nanorods induced by heavy ion irradiation
Authors: Misra Abha , Tyagi Pawan K. , Rai Padmnabh , Misra D. S. , Ghatak Jay , Satyam P. V. , Avasthi D. K.
Published: August 2006

In a recent letter Tyagi et al. [Appl. Phys. Lett. 86, 253110 (2005)] have reported the special orientation of nickel planes inside multiwalled carbon nanotubes (MWCNTs) with respect to the tube axis. Heavy ion irradiation has been performed with 1.5MeV Au2+ and 100MeV Au7+ ions on these nickel filled MWCNTs at fluences ranging from 1012to1015ions∕cm2 at room temperature. Ion-induced modifications have been studied using high-resolution transmission electron microscopy. The diffraction pattern and the lattice imaging showed the presence of ion-induced planar defects on the tube walls and completely amorphized encapsulated nickel nanorods. The results are discussed in terms of thermal spike model.
The conformations of the amyloid-β (21–30) fragment can be described by three families in solution
Authors: Chen Wei , Mousseau Normand , Derreumaux Philippe
Published: August 2006

Alzheimer’s disease has been linked to the self-assembly of the amyloid-β protein of 40 and 42 residues. Although monomers are in equilibrium with higher-order species ranging from dimers to heptamers, structural knowledge of the monomeric amyloid-β (Aβ) peptides is an important issue. Recent experimental data have shown that the fragment (21–30) is protease-resistant within full-length Aβ peptides and displays two structural families in solution. Because the details of the Aβ21–30 structures found using distinct force fields and protocols differ at various degrees from those of the NMR structures, we revisit the conformational space of this peptide using the activation-relaxation technique (ART nouveau) coupled with a coarse-grained force field (OPEP v.3.0). We find that although Aβ21–30 does not have a secondary structure, it dominantly populates three structural families, with a loop spanning residues Val24-Lys28. The first two families, which differ in the nature of the electrostatic interactions, satisfy the five interproton rotating frame nuclear Overhauser effect spectroscopy (ROESY) distances and superpose well onto the NMR structures. The third family, which cannot be seen by ROESY NMR experiments, displays a more open structure. This numeric study complements the experimental results by providing a much more detailed description of the dominant structures. Moreover, it provides further evidence of the capability of ART OPEP in providing a reliable conformational picture of peptides in solution.
Photoluminescence studies of impurity transitions in AlGaN alloys
Authors: Nepal N. , Nakarmi M. L. , Lin J. Y. , Jiang H. X.
Published: August 2006

Deep ultraviolet photoluminescence (PL) spectroscopy has been employed to investigate impurity transitions in Si doped Al-rich AlGaN alloys. In addition to the previously reported donor compensating centers—isolated cation vacancy with three negative charges (VIII)3− and cation vacancy complex with two-negative charges (VIIIcomplex)2−—a group of impurity transitions with higher emission energies has been observed in AlGaN alloys grown under different conditions, which has been assigned to the recombination between shallow donors and cation vacancy complexes with one-negative charge (VIIIcomplex)−1. Similar to (VIII)3− and (VIIIcomplex)2−, the energy levels of (VIIIcomplex)1− deep acceptors in AlxGa1−xN (0⩽x⩽1) alloys are pinned to a common energy level in vacuum. A strong correlation between the resistivity and PL emission intensities of the impurity transitions associated with cation vacancies (and complexes) was found.
High responsivity 4H-SiC Schottky UV photodiodes based on the pinch-off surface effect
Authors: Sciuto Antonella , Roccaforte Fabrizio , Di Franco Salvatore , Raineri Vito , Bonanno Giovanni
Published: August 2006

In this letter, high responsivity 4H-SiC vertical Schottky UV photodiodes based on the pinch-off surface effect, obtained by means of self-aligned Ni2Si interdigit contacts, are demonstrated. The diode area was 1mm2, with a 37% directly exposed to the radiation. The dark current was about 200pA at −50V. Under a 256nm UV illumination, a current increase of more than two orders of magnitude is observed, resulting in a 78% internal quantum efficiency. The vertical photodiodes showed an ultraviolet-visible rejection ratio >7×103 and a responsivity a factor of about 1.8 higher than a conventional planar metal-semiconductor-metal structure.
Size uniformity of InAs dots on mesa-structure templates on (001) InP substrates grown by droplet metal-organic vapor phase epitaxy method
Authors: Ujihara T. , Yoshida Y. , Lee W. S. , Takeda Y.
Published: August 2006

In order to improve size uniformity of InAs quantum dots (QDs) on (001) InP substrates using droplet heteroepitaxy by metal-organic vapor phase epitaxy, the authors carried out the growth of InAs QDs on size-controlled linear mesa-structure templates fabricated by using selective-area growth technique and surrounded by facet planes. InAs QDs preferentially formed on the (001) top surface facet. The maximum size of QD was limited by the width of the top surface. On the other hand, the minimum size was defined by the practically critical size. These facts imply that the narrow width of the top surface of templates controls the dispersion of size distribution. The authors obtained the narrow photoluminescence peak from the size-controlled InAs QDs with full width at half maximum of 85meV at around 1.5μm wavelength.
Uncooled photodetectors for the 3–5μm spectral range based on III–V heterojunctions
Authors: Krier A. , Suleiman W.
Published: August 2006

The design, fabrication, and characterization of heterojunction photodiodes for room temperature operation in the mid-infrared (3–5μm) spectral range is described. Devices appropriate for carbon dioxide detection have been developed and studied. The authors report on the improvements obtained by increasing buffer layer thickness and also by using a blocking barrier to reduce leakage current.
Breakup of shearless meanders and “outer” tori in the standard nontwist map
Authors: Fuchss K. , Wurm A. , Apte A. , Morrison P. J.
Published: August 2006

The breakup of shearless invariant tori with winding number ω=(11+γ)∕(12+γ) (in continued fraction representation) of the standard nontwist map is studied numerically using Greene’s residue criterion. Tori of this winding number can assume the shape of meanders [folded-over invariant tori which are not graphs over the x axis in (x,y) phase space], whose breakup is the first point of focus here. Secondly, multiple shearless orbits of this winding number can exist, leading to a new type of breakup scenario. Results are discussed within the framework of the renormalization group for area-preserving maps. Regularity of the critical tori is also investigated.
Theoretical study of the photodesorption mechanism of nitric oxide on a Ag(111) surface: A nonequilibrium Green’s function approach to hot-electron tunneling
Authors: Nakamura Hisao , Yamashita Koichi
Published: August 2006

The photoinduced desorption of NO molecules on a Ag surface was studied theoretically using a recently developed method based on the nonequilibrium Green’s function approach combined with the density functional theory. Geometry optimizations for the stable NO dimer phase were carried out, and two structures of adsorbed dimers were identified. We calculated the reaction probabilities as a function of incident photon energy for each of the dimers and compared them with experimental action spectra. The two main features of the action spectra, (i) a long tail to the long wavelength (∼600nm) and (ii) a rapid increase at ∼350nm, were well reproduced. By theoretical analysis, we found the importance of quantum interference for the interfacial charge transfer between the metal substrate and the adsorbate, as well as the contribution of secondary electrons. Our calculations suggest that the photoactive species is dimeric and that the resonant level is single for the photodesorption of NO.
On the degeneracy of atomic states within exact-exchange (spin-) density functional theory
Authors: Pittalis S. , Kurth S. , Gross E. K. U.
Published: August 2006

The problem of degenerate ground states of open-shell atoms is investigated in spin-restricted and spin-unrestricted density functional theories using the exact-exchange energy functional. For the spin-unrestricted case, spurious energy splittings of the order of 2–3kcal∕mol are found for atoms of the second and third periods which are larger than the splittings obtained from recently proposed approximate exchange functionals depending explicitly on the current density. In remarkable contrast, for spin-restricted calculations the degeneracy of different atomic ground states is recovered to within less than 0.6kcal∕mol.
Computational studies on thermodynamic properties, effective diameters, and free volume of argon using an ab initio potential
Authors: Eskandari Nasrabad Afshin , Laghaei Rozita
Published: August 2006

A quantum mechanical derived ab initio interaction potential for the argon dimer was tested in molecular simulations to reproduce the thermophysical properties of the vapor-liquid phase equilibria using the Gibbs ensemble Monte Carlo simulations as well as the liquid and supercritical equation of state using the NVT Monte Carlo simulations. The ab initio interaction potential was taken from the literature. A recently developed theory [R. Laghaei et al., J. Chem. Phys. 124, 154502 (2006)] was used to compute the effective diameters of argon in fluid phases and the results were subsequently applied in the generic van der Waals theory to compute the free volume of argon. The calculated densities of the coexisting phases, the vapor pressure, and the equation of state show excellent agreement with experimental values. The effective diameters and free volumes of argon are given over a wide range of densities and temperatures. An empirical formula was used to fit the effective diameters as a function of density and temperature. The computed free volume will be used in future investigations to calculate the transport properties of argon.
Ring oscillator made of organic thin-film transistors produced by self-organized process on plastic substrate
Authors: Han Seung Hoon , Cho Sang Mi , Kim Jun Hee , Choi Jae Won , Jang Jin , Oh Myung Hwan
Published: August 2006

The authors studied the fabrication of a ring oscillator consisting of organic inverters showing no hysteresis in output characteristics. They designed and fabricated the ring oscillator with bootstrapping inverters made of pentacene organic thin-film transistors on plastic produced by self-organized process, exhibiting the field-effect mobility of ∼0.6cm2∕Vs, on/off current ratio of 107, and threshold voltage of −5V. The oscillation frequency of 3kHz and signal propagation delay of 15μs per stage were achieved for an 11-stage oscillator with a supply voltage of 20V.
Band structure, Wiener bounds, and coupled surface plasmons in one dimensional photonic crystals
Authors: Bergmair Michael , Huber Martin , Hingerl Kurt
Published: August 2006

Recently metallic two and three dimensional photonic crystals (PCs) have been studied with the focus on using such structures in incandescent lighting and thermal photovoltaic applications. They exhibit a metallic band gap for low frequencies as well as structural band gaps. Especially the metallic band gap allows to block the infrared transmission respectively emission. In this letter we show that also the structural simpler one dimensional (1D) system has the same features; furthermore it builds an omnidirectional band gap for the Drude dispersion relation. For the case of a polaritonic system 1D PCs are able to exhibit angle of incidence as well as frequency dependent filter characteristics. The dispersion relation of surface plasmons, extending over adjacent layers is obtained. Propagating states must lie within the Wiener bounds.
Improvement of plasma uniformity using ZnO-coated dielectric barrier discharge in open air
Authors: Choi Jai Hyuk , Lee Tae Il , Han Inho , Oh Byeong-Yun , Jeong Min-Chang , Myoung Jae-Min , Baik Hong Koo , Song Kie Moon , Lim Yong Sik
Published: August 2006

The discharge behavior in atmospheric pressure dielectric barrier discharge using ZnO-coated dielectric layer is examined. ZnO thin film on alumina using rf magnetron sputter causes about a factor of a million higher surface conductivity than bare alumina surface. Experimental result shows that discharge uniformity is improved definitely in the case of ZnO-coated dielectric barrier discharge. Increase of surface conductivity stimulates charges to spread over the dielectric surface widely. These charge spreading enhances the uniformity and the stability of atmospheric pressure discharge in open air by initiation of consecutive streamers.
Correlation between ambipolar transport and structural phase transition in diindenoperylene single crystals
Authors: Tripathi A. K. , Pflaum J.
Published: August 2006

Diindenoperylene (DIP) single crystals were grown by vapor phase sublimation growth technique, yielding crystals with preferential growth in the ab crystallographic plane. Time-of-flight (TOF) and x-ray measurements were performed over the temperature range between 300 and 405K. By TOF the mobility for electrons is found to be higher by one order of magnitude than for holes over the studied temperature range. The temperature dependent mobility behavior indicates the effect of structural phase transition in accordance with temperature dependent x-ray measurements. Observation of electron and hole transport in DIP single crystals makes this compound interesting for ambipolar organic electronics.
Experiment in lensless ghost imaging with thermal light
Authors: Basano Lorenzo , Ottonello Pasquale
Published: August 2006

According to a recent experiment in lensless ghost imaging with thermal light, the image is unblurred only when the object and the image planes are equally distant from the source of light. This result unambiguously supports the view that thermal light ghost imaging is basically a quantum effect. The authors present evidence (based on experiments as well as on simulation) that the blurring is nonexistent and no quantum explanation is necessary.
Organic-inorganic hybrid dielectrics with low leakage current for organic thin-film transistors
Authors: Jeong Sunho , Kim Dongjo , Lee Sul , Park Bong-Kyun , Moon Jooho
Published: August 2006

Using a thermally cross-linkable organosiloxane-based organic-inorganic hybrid material, a solution-processable gate dielectric layer for organic thin-film transistors has been fabricated. The hybrid dielectric was synthesized by a sol-gel process, followed by heat treatment at below 190°C. Dielectric strength of 1.4–1.65MV∕cm was measured and it was confirmed that the leakage current is governed by the Poole-Frenkel emission mechanism in which the silanol groups act as trap sites. An organic thin-film transistor utilizing the hybrid dielectric shows similar electrical performance to a transistor fabricated using surface-modified thermally grown SiO2.
Charge neutralization of dust particles in a plasma with negative ions
Authors: Merlino Robert L. , Kim Su-Hyun
Published: August 2006

Charging of dust grains in a plasma with negative ions is studied experimentally. When the relatively mobile electrons are attached to heavy negative ions, their tendency to charge the grains negatively is reduced. In a plasma in which a substantial fraction of the electrons are eliminated (positive ion/negative ion plasma), the grain charge can be reduced in magnitude nearly to zero (“decharging” or charge neutralization). If the positive ions are lighter than the negative ions, dust grains having a small net positive charge can be produced.
Adsorption of O2 on tubelike Au24 and Au24− clusters
Authors: Luo Chuanfu , Fa Wei , Dong Jinming
Published: August 2006

The nondissociative adsorptions of O2 on the neutral and anionic Au24 have been studied using the density functional theory (DFT) in the generalized gradient approximation. Their geometrical structures are optimized by using a combination of the relativistic effective core potential and all-electron potential with scalar relativistic corrections. It is found that the adsorptions of O2 on the tubelike Au24 and Au24− are more stable than it on their space-filled counterparts. Mulliken population analysis shows that the O2 adsorbed on the tubelike Au24 and Au24− got more electrons than on the amorphous ones, which may be a reason why the O2 can be adsorbed more easily on the former rather than on the latter. Compared with the previous DFT studies of O2 adsorbed on small Aun (n⩽10) clusters, we have shown that the O2 can also be adsorbed on the neutral even Au24 with an adsorption energy compatible with that on the small neutral odd gold clusters, but the adsorption energy of O2 on the anionic Au24− is lower than that on the small anionic Aun with even n. In all the optimized geometrical structures of the O2-adsorbed Au24 and Au24− clusters, including both tubelike and amorphous ones, we found that O2 prefers its two O atoms to be attached to two near gold atoms with the least coordination number rather than only one O atom to be attached to one gold atom.
Dispersion of surface plasmon polaritons on silver film with rectangular hole arrays in a square lattice
Authors: Tsai Ming-Wei , Chuang Tzu-Hung , Chang Hsu-Yu , Lee Si-Chen
Published: August 2006

Extraordinary optical transmission through a two-dimensional Ag film in the far infrared region was demonstrated. The holes were rectangular and arranged in a square lattice. When either the width or the length size of the rectangular holes was close to the half of the lattice constant a∕2, the degenerate (±1,0) Ag∕Si or (0,±1) Ag∕Si modes split into two peaks. Additionally, the surface plasmon dispersion relations of the square hole array with different aspect ratios of holes were measured. As the aspect ratio increased, the surface plasmon tended to couple strongly with the local charge dipole oscillations in a direction perpendicular to the long edges. The charge dipole oscillation parallel to the long edges gradually disappeared. This is confirmed by experiments using the polarized light. The dynamic properties of the surface plasmon dispersion relations show the interaction among localized surface plasmons and its mechanism.
Increase of blue electroluminescence from Ce-doped SiO2 layers through sensitization by Gd3+ ions
Authors: Sun J. M. , Prucnal S. , Skorupa W. , Helm M. , Rebohle L. , Gebel T.
Published: August 2006

Efficient blue electroluminescence peak at around 440nm with a maximum output power density of 34mW∕cm2 was obtained from Ce and Gd coimplanted metal-oxide-semiconductor light emitting devices. Energy transfer from Gd3+ to Ce3+ ions was observed during the excitation process, leading to a more than threefold increase of the external quantum efficiency of the blue Ce3+ luminescence up to 1.8%. This is evidenced by the increase of the excitation cross section of Ce3+ ions from 4.8×10−13to3.5×10−12cm2 and the simultaneous reduction of the decay time and the impact cross section of Gd3+ ions.
Study of domain boundary polarization in (111)-cut [Pb(Mg1∕3Nb2∕3)O3]0.7(PbTiO3)0.3 single crystal by piezoresponse force microscopy
Authors: Wong K. S. , Zhao X. , Dai J. Y. , Choy C. L. , Zhao X. Y. , Luo H. S.
Published: August 2006

Ferroelectric domain structure, especially the domain boundary polarization, in as-grown and poled (111)-cut PMN-30%PT single crystal has been studied by means of out-of-plane and in-plane piezoresponse force microscopies (PFMs). It revealed that the as-grown sample exhibits speckle-shaped microdomains, and the domain number distribution decreases exponentially as the domain size increases which can be described by the random field Ising model; in contrast, the poled sample shows stripe-shaped domains. Capacitive force-free PFM revealed a detailed domain boundary characteristic with net in-plane polarization. The presence of the in-plane polarization at the domain boundary also suggests the existence of orthorhombic phase in the rhombohedral matrix.
Residual stress minimum in nanocrystalline diamond films
Authors: Vila M. , Amaral M. , Oliveira F. J. , Silva R. F. , Fernandes A. J. S. , Soares M. R.
Published: August 2006

Nanocrystalline diamond films have been deposited on silicon nitride substrates by hot filament chemical vapor deposition. Gas mixtures of CH4–H2–Ar were used with variation of the Ar∕H2 ratio in order to study the influence of the Ar content on the formation of nondiamond phases at the grain boundaries and thus in the film residual stress assessed by x-ray diffraction techniques. By varying this ratio it is possible to optimize conditions, decreasing the film’s residual stress to a minimum of 0.09GPa.
Surface charge retention and enhanced polarization effect on ferroelectric thin films
Authors: Son J. Y. , Kyhm K. , Cho J. H.
Published: August 2006

The authors report surface charge retention and enhanced ferroelectric polarization effect on ferroelectric thin films by Kelvin probe force microscope (KFM). Since high electric field is induced at scanning probe microscope tip during domain switching and the sign of surface charge induced by this high electric field is always opposite to the sign of induced ferroelectric polarization charge, the surface potential of the KFM signal exhibits the relative potential difference between the potential of the ferroelectric polarization charge and the potential of the surface charge. After the discharge process of surface charge, the enhanced contribution from the ferroelectric polarization charge was observed. Similarly, the reduction of surface charge was observed as time passed and the surface potential indicating the ferroelectric polarization charge was enhanced due to this retention property of surface charge.
Ferromagnetic ZnO bicrystal nanobelts fabricated in low temperature
Authors: Xu Congkang , Chun Junghwan , Rho Keehan , Lee Hyo Jin , Jeong Yoon Hee , Kim Dong-Eon , Chon Bonghwan , Hong Sangsu , Joo Taiha
Published: August 2006

Zinc oxide bicrystal nanobelts were fabricated via a vapor phase transport of a powder mixture of Zn, BiI3, and MnCl2∙H2O at temperatures as low as 300°C. The bicrystal nanobelts, growing along the [011−3] direction, have the widths of 40–150nm and lengths of tens of microns. The energy dispersive x-ray spectroscopy result verifies that the bicrystal nanobelts contain higher concentration of both Bi and Mn along the grain boundary. The investigation of the growth mechanism proposes that MnBi may induce the formation of bicrystal nanobelts. Photoluminescence spectra show that the ultraviolet emission of the bicrystal nanobelts has a blueshift of 18meV as compared to Bi–ZnO nanowires at 10K. The bicrystal nanobelts also exhibit ferromagnetism at room temperature.
Enhancing memory efficiency of Si nanocrystal floating gate memories with high-κ gate oxides
Authors: Punchaipetch Prakaipetch , Uraoka Yukiharu , Fuyuki Takashi , Tomyo Atsushi , Takahashi Eiji , Hayashi Tsukasa , Sano Atsushi , Horii Sadayoshi
Published: August 2006

High-performance floating gate memory devices of Si nanocrystal (NC) dots on HfO2 gate oxide were fabricated at temperatures below 400°C. A large counterclockwise hysteresis of 5.2V, at an applied voltage of +6V, and a stored charge density of 6×1012cm−2 were observed. Moreover, the smaller band offset of the high-κ tunneling layer resulted in higher charge tunneling probabilities towards the Si NC dots than those observed with a SiO2 tunneling layer. Advantages in terms of scaling for a high-performance and stable reliability memory device are confirmed.
LnPdSb (Ln=La,Gd): Promising intermetallics with large carrier mobility for high performance p-type thermoelectric materials
Authors: Sekimoto Takeyuki , Kurosaki Ken , Muta Hiroaki , Yamanaka Shinsuke
Published: August 2006

The authors studied the thermoelectric properties of LaPdSb and GdPdSb. The values of the thermoelectric power were positive and relatively large (60–100μV∕K). The values of the electrical resistivity were on the order of 10−4Ωcm, which is unexpectedly low in view of the large values observed for the thermoelectric power. From the Hall effect measurements, the unusually low electrical resistivity was confirmed to be caused by the large carrier mobility. LaPdSb indicated a large power factor of 50μW∕K2cm at 327K and a large dimensionless figure of merit of 0.26 at around room temperature.
Electron emission from discontinuous gold-carbon compound film on etched porous aluminum oxide
Authors: Wang Zengmei , Li Dejie , Yao Baolun , Wang Jian
Published: August 2006

An electron emitter composed of discontinuous gold-carbon compound conducting film on etched porous aluminum oxide (PAO) layer is proposed in this letter. The PAO layer is located between two 30μm spaced cathode and grid electrode, and is etched in diluted phosphoric acid to introduce roughness on the soda lime glass surface and enhance discontinuity of the conducting film. Electron emission with good uniformity and stability is reproducibly obtained. The electron emission efficiency is higher than 2% at an anode voltage of 3kV.