bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanopatterning of metal-coated silicon surfaces via ion beam irradiation: Real time x-ray studies reveal the effect of silicide bonding
Authors: El-Atwani Osman , Gonderman Sean , DeMasi Alexander , Suslova Anastassiya , Fowler Justin , El-Atwani Mohamad , Ludwig Karl , Paul Allain Jean
Published: March 2013

We investigated the effect of silicide formation on ion-induced nanopatterning of silicon with various ultrathin metal coatings. Silicon substrates coated with 10 nm Ni, Fe, and Cu were irradiated with 200 eV argon ions at normal incidence. Real time grazing incidence small angle x-ray scattering (GISAXS) and x-ray fluorescence (XRF) were performed during the irradiation process and real time measurements revealed threshold conditions for nanopatterning of silicon at normal incidence irradiation. Three main stages of the nanopatterning process were identified. The real time GISAXS intensity of the correlated peaks in conjunction with XRF revealed that the nanostructures remain for a time period after the removal of the all the metal atoms from the sample depending on the binding energy of the metal silicides formed. Ex-situ XPS confirmed the removal of all metal impurities. In-situ XPS during the irradiation of Ni, Fe, and Cu coated silicon substrates at normal incidence demonstrated phase separation and the formation of different silicide phases that occur upon metal-silicon mixing. Silicide formation leads to nanostructure formation due the preferential erosion of the non-silicide regions and the weakening of the ion induced mass redistribution.
Vibrational and vibronic spectra of tryptamine conformers
Authors: Mayorkas Nitzan , Bernat Amir , Izbitski Shay , Bar Ilana
Published: March 2013

Conformation-specific ionization-detected stimulated Raman spectra, including both Raman loss and Raman gain lines, along with visible-visible-ultraviolet hole-burning spectra of tryptamine (TRA) conformers have been measured simultaneously, with the aim of obtaining new data for identifying them. The slightly different orientations of the ethylamine side chain relative to the indole lead to unique spectral signatures, pointing to the presence of seven TRA conformers in the molecular beam. Comparison of ionization-loss stimulated Raman spectra to computationally scaled harmonic Raman spectra, especially in the alkyl C–H and amine N–H stretch regions together with the retrieved information on the stabilities of the TRA conformers assisted their characterization and structural identification. The prospects and limitations of using these spectroscopic methods as potential conformational probes of flexible molecules are discussed.
On the origin of the giant isotopic effect of hydrogen on the magnetic properties of YFe2A4.2 (A = H, D): A high pressure study
Authors: Isnard O. , Paul-Boncour V. , Arnold Z.
Published: March 2013

In order to identify the origin of the giant isotope effect observed on the magnetic properties of YFe2A4.2 compounds (A = H, D) and probe the role of the cell volume difference, we have compared the effect of hydrostatic pressure up to 1.0 GPa on the ferro-antiferromagnetic transition temperatures TF-AF and spontaneous magnetization of YFe2D4.2 and YFe2H4.2. Using compressibility value of 0.013 GPa−1 and the remarkably different negative pressure slopes of TF-AF, the existence of critical volume where the ferromagnetism is suppressed at 0 K, VC = 501.7 ± 0.3 Å´3, was demonstrated. This consequently established the crucial role of volume on the huge isotope effect observed on the magnetic properties.
Mode locking in monolithic two-section InGaN blue-violet semiconductor lasers
Authors: Vasil'ev P. P. , Sergeev A. B. , Smetanin I. V. , Weig T. , Schwarz U. T. , Sulmoni L. , Dorsaz J. , Lamy J.-M. , Carlin J.-F. , Grandjean N. , Zeng X. , Stadelmann T. , Grossmann S. , Hoogerwerf A. C. , Boiko D. L.
Published: March 2013

Passive mode-locked pulses with repetition frequencies in the range 40 to 90 GHz were observed in blue-violet GaN-based quantum-well lasers without external cavities. The lasers had two-section geometry with built-in saturable absorber section. The individual pulses had durations as short as 3–5 ps at peak powers of around 320 mW.
Optical enhancement of the open-circuit voltage in high quality GaAs solar cells
Authors: Steiner M. A. , Geisz J. F. , García I. , Friedman D. J. , Duda A. , Kurtz S. R.
Published: March 2013

The self-absorption of radiated photons increases the minority carrier concentration in semiconductor optoelectronic devices such as solar cells. This so-called photon recycling leads to an increase in the external luminescent efficiency, the fraction of internally radiated photons that are able to escape through the front surface. An increased external luminescent efficiency in turn correlates with an increased open-circuit voltage and ultimately conversion efficiency. We develop a detailed ray-optical model that calculates Voc for real, non-idealized solar cells, accounting for isotropic luminescence, parasitic losses, multiple photon reflections within the cell and wavelength-dependent indices of refraction for the layers in the cell. We have fabricated high quality GaAs solar cells, systematically varying the optical properties including the back reflectance, and have demonstrated Voc = 1.101 ± 0.002 V and conversion efficiencies of (27.8 ± 0.8)% under the global solar spectrum. The trends shown by the model are in good agreement with the data.
Transient electrokinetic transport in micro/nanofluidic systems with sudden expansion and contraction cross sections
Authors: Chein Reiyu , Liao Yuchung
Published: March 2013

This study numerically investigates electrokinetic transport in a micro/nanofluidic system by solving the transient Poisson, Nernst-Planck, and Navier-Stokes equations simultaneously. The considered system is a nanochannel connected to two micro channels at its ends. Under various applied electric potential biases, the concentration polarization effect on the fluid flow, induced pressure, and electric current is examined. By comparing with the Donnan equilibrium condition and electroosmotic flow in the microscale dimension, electric body force due to non-zero charge density is the mechanism for producing vortex flow and inducing a positive pressure gradient on the anodic side of the system. The diffusive boundary layer thickness is reduced due to stirring by the generated vortex flow, resulting in over-limiting current when the applied electric potential bias is high. The steady-state current voltage curve indicates that in the Ohmic regime, higher current can be obtained when the surface charge density is large due to higher fluid velocity. In the limiting and over-limiting current regimes, higher electric current can be obtained when the nanochannel is larger with smaller surface density because more ions are available for carrying the current. The nanochannel size effect on the limiting and over-limiting current magnitudes is insignificant when the surface charge density is large.
Quantifying perpendicular magnetic anisotropy at the Fe-MgO(001) interface
Authors: Lambert C.-H. , Rajanikanth A. , Hauet T. , Mangin S. , Fullerton E. E. , Andrieu S.
Published: March 2013

We show that Fe-MgO interfaces possess strong perpendicular magnetic anisotropy of 1.0 ± 0.1 erg/cm2 in fully epitaxial MgO/V/Fe/MgO(001) and MgO/Cr/Fe/MgO(001) heterostructures. The sign and amplitude of the total anisotropy are quantified as a function of Fe thickness using magnetometry and ferromagnetic resonance. There is a transition from out-of-plane to in-plane anisotropy for 6 Fe monolayers in V/Fe/MgO and only 4 monolayers in Cr/Fe/MgO. A detailed study of the Fe magnetization and effective anisotropy in both systems explains this difference and quantifies the Fe-MgO interface anisotropy.
X-ray characterization techniques for the assessment of surface damage in crystalline wafers: A model study in AlN
Authors: Bobea M. , Tweedie J. , Bryan I. , Bryan Z. , Rice A. , Dalmau R. , Xie J. , Collazo R. , Sitar Z.
Published: March 2013

A high-resolution X-ray diffraction method with enhanced surface sensitivity has been used to investigate the effects of various polishing steps on the near-surface region of single crystal substrates. The method involves the study of a highly asymmetric reflection, observable under grazing incidence conditions. Analysis of rocking curve measurements and reciprocal space maps (RSMs) revealed subtle structural differences between the polished substrates. For aluminum nitride wafers, damage induced from diamond sawing and mechanical polishing was readily identifiable by on-axis rocking curves, but this method was unable to distinguish between sample surfaces subjected to various degrees of chemical mechanical polishing (CMP). To characterize sufficiently these surfaces, (10.3) RSMs were measured to provide both qualitative and quantitative information about the near-surface region. Two features present in the RSMs were utilized to quantitatively assess the polished wafers: the magnitude of the diffuse scatter in the omega-scans and the elongation of the crystal truncation rod. The method is able to distinguish between different degrees of CMP surface preparation and provides metrics to quantify subsurface damage after this polishing step.
Compression of scheelite-type SrMoO4 under quasi-hydrostatic conditions: Redefining the high-pressure structural sequence
Authors: Errandonea D. , Gracia L. , Lacomba-Perales R. , Polian A. , Chervin J. C.
Published: March 2013

The high-pressure behavior of tetragonal SrMoO4 was analyzed by Raman and optical-absorption measurements. Pressures up to 46.1 GPa were generated using diamond-anvil cells and Ne or N2 as quasi-hydrostatic pressure-transmitting media. A reversible phase transition is observed at 17.7 GPa. A second transition is found at 28.8 GPa and the onset of a third one at 44.2 GPa. The pressure dependence of Raman-active modes is reported for the different phases and the pressure evolution of the fundamental band-gap reported for the low-pressure phase. The observed changes in the Raman spectra contradict the structural sequence determined from previous experiments performed under higher non-hydrostaticity. This fact suggests that deviatoric stresses can influence pressure-driven transitions in scheelite-type oxides. We also report total-energy, lattice-dynamics, and band-structure calculations. They reproduce accurately the behavior of the physical properties of the low-pressure phase and predict the occurrence of phase transitions at pressures similar to experimental transition pressures. According to theory, the high-pressure phases have monoclinic and orthorhombic structures, which are much more compact than tetragonal scheelite. Theoretical results and experiments are compared with previous studies.
Charge transfer assisted nonlinear optical and photoconductive properties of CdS-AgInS2 nanocrystals grown in semiconducting polymers
Authors: Mamidala Venkatesh , Nalla Venkatram , Sankar Maiti Pradipta , Valiyaveettil Suresh , Ji Wei
Published: March 2013

Anisotropic CdS-AgInS2 nanocrystals are directly grown into benzothiadiazole-based semiconducting polymer solution. Their nonlinear optical absorption and nonlinear scattering are investigated with 7-ns laser pulses of 532-nm wavelength for optical limiting applications. Optical limiting is found to be enhanced in the polymer-CdS-AgInS2 nanocomposites, as compared to pure polymer or CdS-AgInS2 nanocrystals. The observation is explained quantitatively using a numerical model which includes one-photon-induced excited state absorption, two-photon absorption, and nonlinear scattering. Presence of charge transfer in polymer-CdS-AgInS2 nanocomposites is found from zero-biased photoconduction experiments, which plays an important role in the enhancement of nonlinear optical properties. In addition, it is also demonstrated that these nanocomposite films can be utilized for photodetection with large and fast photoconductive responses.
Improvement of the performance characteristics of deep violet InGaN multi-quantum-well laser diodes using step-graded electron blocking layers and a delta barrier
Authors: Alahyarizadeh Gh. , Hassan Z. , Yam F. K.
Published: March 2013

The performance characteristics of deep violet In0.082Ga0.918N/GaN multi-quantum-well (MQW) laser diodes (LDs) with step-graded electron blocking layers (EBLs), a new EBL structure proposed by Zhang et al. and Yang et al., were numerically investigated. The simulation results indicated that the output emission wavelength was blue-shifted because of the change in the built-in polarization and internal electric field, although the use of step-graded EBLs effectively improved LD performance. To prevent the polarization effects and consequently a blue shift in the output emission wavelength, a new MQW LD structure with step-graded EBLs and a delta barrier as a last barrier is proposed. Simulation results indicated that the proposed LD structure exhibits higher values of output power, slope efficiency, and differential quantum efficiency, as well as lower threshold current, compared with conventional LD structures. The results also showed that the use of the delta barrier reduced the changes in the built-in polarization and internal electric field, and negligible changes in the output emission wavelength were observed.
Charging and de-charging of dust particles in bulk region of a radio frequency discharge plasma
Authors: Mishra S. K. , Misra Shikha , Sodha M. S.
Published: March 2013

An analysis to investigate the effect of the dust particle size and density on the floating potential of the dust particles of uniform radius and other plasma parameters in the bulk region plasma of a RF-discharge in collisionless/collisional regime has been presented herein. For this purpose, the average charge theory based on charge balance on dust and number balance of plasma constituents has been utilized; a derivation for the accretion rate of electrons corresponding to a drifting Maxwellian energy distribution in the presence of an oscillatory RF field has been given and the resulting expression has been used to determine the floating potential of the dust grains. Further, the de-charging of the dust grains after switching off the RF field has also been discussed.
Numerical study of thermal effects in cryo-adsorptive hydrogen storage tank
Authors: Xiao Jinsheng , Yang Hao , Bénard Pierre , Chahine Richard
Published: March 2013

Hydrogen storage is an important issue in the practical application of hydrogen technology. Among various hydrogen storage technologies, the cryo-adsorptive hydrogen storage appears to have huge potential for a further research because of its high storage capacity at low pressure. In this study, a computational fluid dynamics model and a lumped parameter model are developed to simulate the cryo-adsorptive hydrogen storage processes. These two models are implemented on the fluentTM platform and matlab/simulinkTM environment, respectively. The thermodynamic behavior and thermal effect during the cryo-adsorptive hydrogen storage processes in a cryo-adsorption storage system are analyzed. Two adsorbents, activated carbon (Norit R0.8) and metal-organic-framework (Cu-BTC), have been studied. The pressure increases quickly at early stage and then keeps steady during the slow filling process. The temperature has larger gradient in the radial and smaller gradient in the axis. During the fast filling process, the release of adsorption heat leads to the temperature increasing in a short time when there is not enough time for efficient heat transfer; during the slow filling process, heat transfer becomes the main factor of temperature change. The effect of mass flow rate on temperature is more significant at the location near tank wall than the center location of the tank. A better external heat transfer condition and higher bed thermal conductivity lead to lower temperature level which will increase the adsorption capacity.
Excitation of lower hybrid waves by a gyrating ion beam in a negative ion plasma
Authors: Sharma Jyotsna , Sharma Suresh C. , Jain V. K. , Gahlot Ajay
Published: March 2013

A gyrating ion beam propagating through a magnetized plasma cylinder containing K+ positive ions, electrons, and SF6− negative ions drives electrostatic lower hybrid waves to instability via Cyclotron interaction. Numerical calculations of the unstable mode frequencies and growth rates of both the unstable positive ion and negative ion modes have been carried out for the existing negative ion plasma parameters. It is found that the unstable mode frequencies of both the modes increase, with the relative density of negative ions. In addition, the growth rates of both the unstable modes also increases with relative density of negative ions. Moreover, the growth rates of both the unstable modes scale as the one-third power of the beam density. The frequencies of both the unstable modes also increase with the magnetic fields. The real part of the unstable wave frequency increases as almost the square root of the beam energy.
Thermal effect simulation of hydrogen cryo-adsorption storage system
Authors: Xiao Jinsheng , Zhou Tingting , Bénard Pierre , Chahine Richard
Published: March 2013

One of the primary challenges to introduce hydrogen on the energy market is to improve onboard hydrogen storage and research more efficient distribution technologies to increase the amount of stored gas while lessening the storage pressure. The aim of this paper is to study hydrogen storage in an on-board hydrogen adsorption storage tank under low temperature and moderate pressures through the finite element analysis software Comsol MultiphysicsTM. The experimental study is carried out in a cylindrical tank with granular adsorbents in which the bed temperature is measured at various positions. The adsorbents we used in the experiment are activated carbon (NORIT R0.8) and metal-organic framework (Cu-BTC). Compared with the experiment results, the simulated pressure and temperature of the activated carbon (NORIT R0.8) have better agreement with experimental results than the metal-organic framework (Cu-BTC). The material properties of Cu-BTC are necessary to be identified accurately. Owing to the mass flow rate controlled comparatively accurate, the simulated mass balance have a good accordance with the experiment results. The effective thermal conductivity of the adsorbent bed and the heat transfer coefficient of the tank wall with liquid nitrogen affect significantly the heat transport during the adsorption process. The simulation results are very sensitive with the boundary type of inlet and other outer boundaries of the tank, which is valuable for further study.
Array fabrication and photoelectrochemical properties of Sn-doped vertically oriented hematite nanorods for solar cells
Authors: Liu Chunting , Dong Hongzhou , Zhang Qian , Sun Qiong , Yu Liyan , Dong Lifeng
Published: March 2013

We report on the synthesis and characterization of Sn-doped hematite nanorods as well as their implementation as the photoanode for solar cells. Hematite nanorods are prepared on fluorine-doped tin oxide (FTO) substrates by a hydrothermal method, followed by a two-step sintering in air, and Sn-doping is achieved by adding SnCl4 into the mixture solution during the hydrothermal process. In comparison to un-doped hematite, Sn-doped hematite nanorods exhibit a higher array growth density along the direction [110], which indicates that the Sn-doping can facilitate the vertically oriented growth of the hematite nanorod arrays; moreover, the Sn-doping can result in enhanced photocurrent density and photoelectrical efficiency due to the improved carrier density. These new findings will provide new information to enhance the photoelectrochemical characteristics of hematite, one of the best potential photoanode materials.
Experimental characterization of transition region in rotating-disk boundary layer
Authors: Siddiqui M. E. , Mukund V. , Scott J. , Pier B.
Published: March 2013

The three-dimensional boundary layer due to a disk rotating in otherwise still fluid is well known for its sudden transition from a laminar to a turbulent regime, the location of which closely coincides with the onset of local absolute instability. The present experimental investigation focuses on the region around transition and analyses in detail the features that lead from the unperturbed boundary layer to a fully turbulent flow. Mean velocity profiles and high-resolution spectra are obtained by constant-temperature hot-wire anemometry. By carefully analysing these measurements, regions in the flow are identified that correspond to linear, weakly nonlinear, or turbulent dynamics. The frequency that dominates the flow prior to transition is explained in terms of spatial growth rates, derived from the exact linear dispersion relation. In the weakly nonlinear region, up to six clearly identifiable harmonic peaks are found. High-resolution spectra reveal the existence of discrete frequency components that are deemed to correspond to fluctuations stationary with respect to the disk surface. These discrete components are only found in the weakly nonlinear region. By systematically acquiring low- and high-resolution spectra over a range of narrowly spaced radial and axial positions, it is shown that while the transition from laminar to turbulent regimes occurs sharply at some distance from the disk surface, a complex weakly nonlinear region of considerable radial extent continues to prevail close to the disk surface.
Spatially resolved measurements of charge carrier lifetimes in CdTe solar cells
Authors: Kraft C. , Hempel H. , Buschmann V. , Siebert T. , Heisler C. , Wesch W. , Ronning C.
Published: March 2013

The lifetime of the minority charge carriers in polycrystalline Cadmium Telluride (pc-CdTe) for solar cell applications is a crucial material parameter and has been determined by analysis of the decay curves of the luminescence signal. Both the lateral and the transversal distributions of the carrier lifetime on the surface and in the bulk of pc-CdTe material as well as the respective solar cell characteristics were measured as a function of the deposition technique, the activation treatment, and the incorporation of additional group-V elements. The results are compared to prior studies. It was found that an activation process passivates grain boundaries and increases the carrier lifetime, which is then higher at the pn-junction than at the surface. Furthermore, nitrogen and phosphorus doping of the CdTe absorber material influences the charge carrier lifetime. The results show that the spatial resolved measurement of the carrier lifetime in pc-CdTe gives an important insight to the charge carrier dynamics of the material.
Magnetic anisotropy in the boron nitride monolayer doped by 3d transitional metal substitutes at boron-site
Authors: Lu Yuan , Zuo Xu , Feng Min , Zhou Tiege
Published: March 2013

Based on density functional theory with the generalized gradient approximation, a computational study is carried out to reveal the magnetism of the hexagonal boron nitride monolayers (h-BN) doped by 3d transitional metal atoms at boron-site. The magnetic moments and magnetic anisotropy energies (MAEs) of the most stable structures are given. Among the systems investigated, the MAE of Fe doped h-BN is 1.19 meV with an easy axis in the h-BN plane, while that of Mn is 0.63 meV with an easy axis perpendicular to the plane. For Sc and Co, the doped systems are nonmagnetic. For Ti, V, Cr, Ni, Cu, and Zn, the MAEs are relatively small. Theoretical analyses by perturbation theory and molecular orbital clarify that the MAE of Fe originates from the second order spin orbit coupling, whereas the MAE of Mn is contributed by the unquenched orbital momentum.
Analysis of photonic band gap in dispersive properties of tunable three-dimensional photonic crystals doped by magnetized plasma
Authors: Zhang Hai-Feng , Liu Shao-Bin , Yang Huan , Kong Xiang-Kun
Published: March 2013

In this paper, the magnetooptical effects in dispersive properties for two types of three-dimensional magnetized plasma photonic crystals (MPPCs) containing homogeneous dielectric and magnetized plasma with diamond lattices are theoretically investigated for electromagnetic (EM) wave based on plane wave expansion (PWE) method, as incidence EM wave vector is parallel to the external magnetic field. The equations for two types of MPPCs with diamond lattices (dielectric spheres immersed in magnetized plasma background or vice versa) are theoretically deduced. The influences of dielectric constant, plasma collision frequency, filling factor, the external magnetic field, and plasma frequency on the dispersive properties for both types of structures are studied in detail, respectively, and some corresponding physical explanations are also given. From the numerical results, it has been shown that the photonic band gaps (PBGs) for both types of MPPCs can be manipulated by plasma frequency, filling factor, the external magnetic field, and the relative dielectric constant of dielectric, respectively. Especially, the external magnetic field can enlarge the PBG for type-2 structure (plasma spheres immersed in dielectric background). However, the plasma collision frequency has no effect on the dispersive properties of two types of three-dimensional MPPCs. The locations of flatbands regions for both types of structures cannot be tuned by any parameters except for plasma frequency and the external magnetic field. The analytical results may be informative and of technical use to design the MPPCs devices.
Compact prototype apparatus for reducing the circle of confusion down to 40 nm for x-ray nanotomography
Authors: Kim Jungdae , Lauer K. , Yan H. , Chu Y. S. , Nazaretski E.
Published: March 2013

We have constructed a compact prototype apparatus for active correction of circle of confusion during rotational motion. Our system combines fiber optic interferometry as a sensing element, the reference cylinder along with the nanopositioning system, and a robust correction algorithm. We demonstrate dynamic correction of run-out errors down to 40 nm; the resolution is limited by ambient environment and accuracy of correcting nanopositioners. Our approach provides a compact solution for in-vacuum scanning nanotomography x-ray experiments with a potential to reach sub-nm level of correction.
Dexterous manipulation of microparticles using Bessel-function acoustic pressure fields
Authors: Courtney Charles R. P. , Drinkwater Bruce W. , Demore Christine E. M. , Cochran Sandy , Grinenko Alon , Wilcox Paul D.
Published: March 2013

We show that Bessel-function acoustic pressure fields can be used to trap and controllably position microparticles. A circular, 16-element ultrasound array generates and manipulates an acoustic field within a chamber, trapping microparticles and agglomerates. Changes in the phase of the sinusoidal signals applied to the array elements result in the movement of the Bessel-function pressure field and hence the microparticles. This demonstrates ultrasonic manipulation analogous to holographic optical tweezers. The manipulation limits of the device are explained by the existence of unwanted resonances within the manipulation chamber.
A generalized Drude model for doped silicon at terahertz frequencies derived from microscopic transport simulation
Authors: Willis K. J. , Hagness S. C. , Knezevic I.
Published: March 2013

Unveiling the full potential of doped silicon for electronic, photonic, and plasmonic application at THz frequencies requires a thorough understanding of its high-frequency transport properties. In this letter, we present a comprehensive numerical characterization of the frequency-dependent (0–2.5 THz) complex conductivity of silicon at room temperature over a wide range of doping densities (1014−1018 cm−3). The conductivity was calculated using a multiphysics computational technique that self-consistently couples ensemble Monte Carlo (EMC) simulation of carrier transport, the finite-difference time-domain (FDTD) solution to Maxwell's equations, and molecular dynamics (MD) for the treatment of short-range Coulomb interactions. Our EMC/FDTD/MD numerical results complement the experimental data that only exist for a select few doping densities. Moreover, we show that the computed complex conductivity of Si at THz frequencies can be accurately described by a generalized Drude (GD) model with doping-dependent parameters that capture the cross-over from phonon-dominated to Coulomb-dominated electron transport as the doping density increases. The simplicity of the GD model enables one to readily compute the complex conductivity of silicon for any doping density within the range studied here.
Spherical curves design for micro-origami using intrinsic stress relaxation
Authors: Danescu A. , Chevalier C. , Grenet G. , Regreny Ph. , Letartre X. , Leclercq J. L.
Published: March 2013

Selective etching of pre-stressed multi-layered structures releases intrinsic stresses creating flexible microscopic shapes (rolls, spirals, tubes, etc.). A question of major interest is how to control design, composition, and etching process in order to obtain a prescribed macroscopic object? We report here the basic steps for (i) the mechanics of the fine curvature control, (ii) the object design and etching process, and we illustrate our approach by the design and fabrication of a three-dimensional device, two face-to-face spiral caps at optical wavelength scale.
Ultra-shallow junctions formed using microwave annealing
Authors: Xu Peng , Fu Chaochao , Hu Cheng , Wei Zhang David , Wu Dongping , Luo Jun , Zhao Chao , Zhang Zhi-Bin , Zhang Shi-Li
Published: March 2013

Microwave annealing is shown to be viable for achieving low thermal budget formation of ultra-shallow junctions. Regrowth of a 10 nm thick amorphous Si layer that is generated during a Ge amorphization process prior to BF2 or As dopant implantation proceeds at rates up to 0.53 nm/min for BF2 and up to 0.33 nm/min for As at 370 °C. The fraction of electrical activation for implanted dopants is as high as 13% for BF2 and 32% for As with negligible diffusion at 540 °C.
Thermally activated non-linearity of device in resistance-switching memory for cross-point array applications
Authors: Woo Jiyong , Kim Seonghyun , Lee Wootae , Lee Daeseok , Park Sangsu , Choi Godeuni , Cha Euijun , Hwang Hyunsang
Published: March 2013

We report a TiOx-based resistance-switching device that exhibits non-linearity in the low resistance state (LRS) under high operating current conditions for cross-point array applications. The transition of the conduction behavior in the LRS from linear to non-linear type was observed in the TiOx/TiOy bilayered structure by controlling programming currents. Our results suggest that the non-linear conduction behavior is activated in a thermally formed suboxide region due to lots of heat during the switching. By using achieved non-linearity of device, a one-resistor memory cell can be used for the suppression of sneak-path currents without the need for additional selector device.
Chemical trends of magnetic interaction in Mn-doped III-V semiconductors
Authors: Peng Haowei , Li Jingbo , Wei Su-Huai
Published: March 2013

The trends of magnetic coupling strength in Mn-doped III-V semiconductors are explained using a physically transparent band-coupling model, based on first-principles calculations. According to this model, the stability of the ferromagnetism in Mn-doped III-V semiconductors should increase with both the strength of p-d coupling and an effective coupling range parameter, α. However, these two quantities counteract to each other, i.e., increased p-d coupling strength means a decreased α value. Therefore, this competition will lead to the non-monotonic variation of ferromagnetic interaction in Mn-doped common-cation III-V semiconductors as the anion becomes heavier. Our results suggest that Mn-doped GaAs and AlAs are optimal materials for high TC spintronics, in good agreement with experimental observations.
High conductivity in Si-doped GaN wires
Authors: Tchoulfian P. , Donatini F. , Levy F. , Amstatt B. , Ferret P. , Pernot J.
Published: March 2013

Temperature-dependent resistivity measurements have been performed on single Si-doped GaN microwires grown by catalyst-free metal-organic vapour phase epitaxy. Metal-like conduction is observed from four-probe measurements without any temperature dependence between 10 K and 300 K. Radius-dependent resistivity measurements yield resistivity values as low as 0.37 mΩ cm. This is in agreement with the full width at half maximum (170 meV) of the near band edge luminescence obtained from low temperature cathodoluminescence study. Higher dopant incorporation during wire growth as compared to conventional epitaxial planar case is suggested to be responsible for the unique conductivity.
Broadband wave filtering of bioinspired hierarchical phononic crystal
Authors: Zhang Pu , To Albert C.
Published: March 2013

Broadband wave filtering effect is observed in a phononic crystal with hierarchical structure inspired by biocomposites. Through a multilayered model with hierarchical structure, it is demonstrated that the overall bandwidth covered by closely adjacent bandgaps for this structure is orders of magnitude broader in frequency than that of conventional periodic structure with single periodicity. This remarkable feature is attributed to the inherent multiscale periodicity in the microstructure, which roughly superimposes the bandgaps generated by individual periodic structures with periods corresponding to those at different hierarchies in the hierarchical structure.
Magnetoelectric coupling in solution derived 3-0 type PbZr0.52Ti0.48O3:xCoFe2O4 nanocomposite films
Authors: McDannald A. , Staruch M. , Sreenivasulu G. , Cantoni C. , Srinivasan G. , Jain M.
Published: March 2013

Magnetoelectric (ME) coupling (αE) in piezoelectric:magnetostrictive composites is mediated through mechanical strain at their interfaces. Incorporating magnetic nanoparticles (NPs) in piezoelectric matrix enhances interfacial area between the two phases and therefore large αE can be expected. Here, we present electric and ME properties of 3-0 type nanocomposite thin films with various concentrations of CoFe2O4 NPs dispersed in PbZr0.52Ti0.48O3 (PZT) matrix. Nanocomposite films show only a slight reduction in remnant electric-polarization as compared to that of PZT. A nanocomposite film with 0.1% CoFe2O4 (molar concentration) exhibited the highest transverse αE of 549 mV/cmOe at 453 Oe dc bias and 1 kHz.
Communication: A new ab initio potential energy surface for HCl–H2O, diffusion Monte Carlo calculations of D and a delocalized zero-point wavefunction
Authors: Mancini John S. , Bowman Joel M.
Published: March 2013

We report a global, full-dimensional, ab initio potential energy surface describing the HCl–H2O dimer. The potential is constructed from a permutationally invariant fit, using Morse-like variables, to over 44 000 CCSD(T)-F12b/aug-cc-pVTZ energies. The surface describes the complex and dissociated monomers with a total RMS fitting error of 24 cm−1. The normal modes of the minima, low-energy saddle point and separated monomers, the double minimum isomerization pathway and electronic dissociation energy are accurately described by the surface. Rigorous quantum mechanical diffusion Monte Carlo (DMC) calculations are performed to determine the zero-point energy and wavefunction of the complex and the separated fragments. The calculated zero-point energies together with a De value calculated from CCSD(T) with a complete basis set extrapolation gives a D0 value of 1348 ± 3 cm−1, in good agreement with the recent experimentally reported value of 1334 ± 10 cm−1 [B. E. Casterline, A. K. Mollner, L. C. Ch'ng, and H. Reisler, J. Phys. Chem. A 114, 9774 (2010)10.1021/jp102532m]. Examination of the DMC wavefunction allows for confident characterization of the zero-point geometry to be dominant at the C2v double-well saddle point and not the Cs global minimum. Additional support for the delocalized zero-point geometry is given by numerical solutions to the 1D Schrödinger equation along the imaginary-frequency out-of-plane bending mode, where the zero-point energy is calculated to be 52 cm−1 above the isomerization barrier. The D0 of the fully deuterated isotopologue is calculated to be 1476 ± 3 cm−1, which we hope will stand as a benchmark for future experimental work.
PtSi dominated Schottky barrier heights of Ni(Pt)Si contacts due to Pt segregation
Authors: Chan J. , Balakchiev M. , Thron A. M. , Chapman R. A. , Riley D. , Song S. C. , Jain A. , Blatchford J. , Shaw J. B. , van Benthem K. , Vogel E. M. , Hinkle C. L.
Published: March 2013

Temperature dependent current-voltage measurements show that the addition of only 10% Pt to NiSi causes an increase of Schottky barrier height (SBH) from 0.65 eV for NiSi to 0.78 eV for the 10% Pt alloy. Internal photoemission measurements resolve two SBHs in all alloyed samples with ≥5% Pt incorporation corresponding to NiSi and PtSi (∼0.68 eV and ∼0.80 eV), proving that each contributes independently to junction current. High angle annular dark field imaging with scanning transmission electron microscopy confirms Pt segregation to the Ni(Pt)Si/Si interface. The resulting increased SBH may therefore be detrimental to contact resistivity in future technology nodes.
Graphene-enabled tunability of optical fishnet metamaterial
Authors: Zhu Weiren , Rukhlenko Ivan D. , Si Li-Ming , Premaratne Malin
Published: March 2013

We present an effective method for actively controlling intrinsic resonances of optical metamaterials using graphene. Exploiting the Fermi level shift and associated variations in optical transitions of graphene due to voltage biasing, we attain the ability to significantly modulate the intrinsic resonance of the fishnet structure. Despite being atomically thin and having a weak optical response, graphene can be strongly coupled with the left-handed resonance of the fishnet metamaterial. We unambiguously demonstrate that the resonant transmission, absorption, and effective constitutive parameters of the graphene-coupled fishnet metamaterial can be precisely controlled by varying the bias voltage.
Real-time dual frequency comb spectroscopy in the near infrared
Authors: Zhu F. , Mohamed T. , Strohaber J. , Kolomenskii A. A. , Udem Th. , Schuessler H. A.
Published: March 2013

We use two femtosecond lasers with slightly different repetition rates to perform real-time dual frequency comb spectroscopy in the near infrared. The difference between the repetition rates is δ = 4403 Hz, yielding a minimal time interval between subsequently measured interferograms and spectra of 0.227 ms. It takes as short as 4 μs to record a single interferogram, opening the possibility of studying dynamical processes. We work with different spectral outputs from two Erbium-doped fiber lasers and employ a grating based spectral filter in a 2f-2f setup to select the common spectral region of interest, thereby increasing the signal-to-noise ratio.
Comb-assisted subkilohertz linewidth quantum cascade laser for high-precision mid-infrared spectroscopy
Authors: Galli I. , Siciliani de Cumis M. , Cappelli F. , Bartalini S. , Mazzotti D. , Borri S. , Montori A. , Akikusa N. , Yamanishi M. , Giusfredi G. , Cancio P. , De Natale P.
Published: March 2013

We report on the linewidth narrowing of a room-temperature mid-infrared quantum cascade laser by phase-locking to a difference-frequency-generated radiation referenced to an optical frequency comb synthesizer. A locking bandwidth of 250 kHz, with a residual rms phase-noise of 0.56 rad, has been achieved. The laser linewidth is narrowed by more than 2 orders of magnitude below 1 kHz, and its frequency is stabilized with an absolute traceability of 2×10−12. This source has allowed the measurement of the absolute frequency of a CO2 molecular transition with an uncertainty of about 1 kHz.
Characterization and suppression of low-frequency noise in Si/SiGe quantum point contacts and quantum dots
Authors: Takeda K. , Obata T. , Fukuoka Y. , Akhtar W. M. , Kamioka J. , Kodera T. , Oda S. , Tarucha S.
Published: March 2013

We report on the effects of a global top gate on low-frequency noise in Schottky gate-defined quantum point contacts (QPCs) and quantum dots (QDs) in a modulation-doped Si/SiGe heterostructure. For a relatively large top gate voltage, the QPC current shows frequent switching with 1/f2 Lorentzian type charge noise. As the top gate voltage is decreased, the QPC pinch-off voltage becomes less negative, and the 1/f2 noise becomes rapidly suppressed in a homogeneous background 1/f noise. We apply this top-gating technique to double QDs to stabilize the charge state for the electron number down to zero.
Collision and dynamic frictional properties of boron nitride nanotubes
Authors: Chen Xiaoming , Zheng Meng , Park Cheol , Ke Changhong
Published: March 2013

Collision and dynamic frictional properties of boron nitride nanotubes (BNNTs) are of importance to their structural applications related to impact protection. In this paper, we present an experimental study of the lateral collision between moving atomic force microscopy probe tips and individual standstill BNNTs. Our results reveal that increasing the impact velocity results in a more prominent increase of the collision force at low velocity levels. This observation is ascribed to the opposite influences of the impact velocity on the dynamic frictional force and the contact angle on the tip-tube collision contact.
Local structures of ionic liquids in the presence of gold under high pressures
Authors: Chang Hai-Chou , Hung Tzu-Chieh , Wang Hsing-Sheng , Chen Tsai-Yi
Published: March 2013

The interactions between ionic liquid ([EMI][TFS]) and gold surfaces have been investigated via the application of pressures up to ca. 2 GPa. Comparing the spectral features of [EMI][TFS]/gold with those of pure [EMI][TFS], no appreciable changes of C-H bands in the presence of gold powders were observed under ambient pressure. Nevertheless, the imidazolium C-H bands display red shifts in frequency as the [EMI][TFS] / Au mixture was compressed to the pressure above 1.4 GPa and a new alkyl C-H band at ca. 3016 cm−1 was also revealed. These spectral changes, being related to the addition of gold powders and pressure elevation, should be attributed to the local structural changes of C-H groups caused by pressure-enhanced interfacial interactions between [EMI][TFS] and Au. Gold powders tend to induce the changes in hydrogen bonding structures of imidazolium C2-H group under high pressures. The pressure-dependent spectral features in the asymmetric SO3 stretching region display band-narrowing and minor local structural changes induced by the presence of gold particles under high pressures. These observations suggest that Au powders perturb structural equilibrium of C-H groups of cations under high pressures.
Using a preclinical mouse model of high-grade astrocytoma to optimize p53 restoration therapy
Authors: Shchors Ksenya , Persson Anders I. , Rostker Fanya , Tihan Tarik , Lyubynska Natalya , Li Nan , Swigart Lamorna Brown , Berger Mitchel S. , Hanahan Douglas , Weiss William A. , Evan Gerard I.
Published: March 2013

Significance

Glioblastoma is the most common and aggressive form of brain cancer. GBM patients typically respond poorly to conventional therapies. The tumor-suppressor protein 53 pathway is disrupted in a majority of GBM cases. Using a mouse model that mimics the progression of human GBM, we evaluate and optimize the therapeutic efficacy of functional p53 restoration in gliomas. We show that the efficacy of p53 restoration therapy in the animal model as well as in human GBM cells is improved markedly by an episodic dosing regimen that circumvents the selective pressure for adaptive resistance when p53 function is chronically restored.
Dynamic scaffold of chiral binaphthol derivatives with the alkynylplatinum(II) terpyridine moiety
Authors: Leung Sammual Yu-Lut , Lam Wai Han , Yam Vivian Wing-Wah
Published: March 2013

Platinum(II)-containing complexes with inherently chiral binaphthol derivatives display a versatile scaffold between random coils and single-turn helical strands, in which the conformational transition is controlled by the Pt···Pt and π−π interactions of alkynylplatinum(II) terpyridine moiety upon solvent and temperature modulation. The bisignate Cotton effect in the circular dichroism spectra is indicative of the cooperative transformation from random coil state to a compact single-turnM- orP- helix. More importantly, as revealed by the appearance of new UV-vis absorption and emission bands during conformational change, the self-assembly of the platinum(II)-containing complex into a helical structure is assisted by the metal···metal and π−π interactions of the alkynylplatinum(II) terpyridine moieties. The folded structure with stabilization via metal···metal and π−π interactions has been supported by density functional theory calculations, which provide insights into the folded geometry of these kind of metallo-foldamers.
Phenotypic properties of transmitted founder HIV-1
Authors: Parrish Nicholas F. , Gao Feng , Li Hui , Giorgi Elena E. , Barbian Hannah J. , Parrish Erica H. , Zajic Lara , Iyer Shilpa S. , Decker Julie M. , Kumar Amit , Hora Bhavna , Berg Anna , Cai Fangping , Hopper Jennifer , Denny Thomas N. , Ding Haitao , Ochsenbauer Christina , Kappes John C. , Galimidi Rachel P. , West Anthony P. , Bjorkman Pamela J. , Wilen Craig B. , Doms Robert W. , O’Brien Meagan , Bhardwaj Nina , Borrow Persephone , Haynes Barton F. , Muldoon Mark , Theiler James P. , Korber Bette , Shaw George M. , Hahn Beatrice H.
Published: March 2013

Defining the virus–host interactions responsible for HIV-1 transmission, including the phenotypic requirements of viruses capable of establishing de novo infections, could be important for AIDS vaccine development. Previous analyses have failed to identify phenotypic properties other than chemokine receptor 5 (CCR5) and CD4+ T-cell tropism that are preferentially associated with viral transmission. However, most of these studies were limited to examining envelope (Env) function in the context of pseudoviruses. Here, we generated infectious molecular clones of transmitted founder (TF;
n
= 27) and chronic control (CC;
n
= 14) viruses of subtypes B (
n
= 18) and C (
n
= 23) and compared their phenotypic properties in assays specifically designed to probe the earliest stages of HIV-1 infection. We found that TF virions were 1.7-fold more infectious (
P
= 0.049) and contained 1.9-fold more Env per particle (
P
= 0.048) compared with CC viruses. TF viruses were also captured by monocyte-derived dendritic cells 1.7-fold more efficiently (
P
= 0.035) and more readily transferred to CD4+ T cells (
P
= 0.025). In primary CD4+ T cells, TF and CC viruses replicated with comparable kinetics; however, when propagated in the presence of IFN-α, TF viruses replicated to higher titers than CC viruses. This difference was significant for subtype B (
P
= 0.000013) but not subtype C (
P
= 0.53) viruses, possibly reflecting demographic differences of the respective patient cohorts. Together, these data indicate that TF viruses are enriched for higher Env content, enhanced cell-free infectivity, improved dendritic cell interaction, and relative IFN-α resistance. These viral properties, which likely act in concert, should be considered in the development and testing of AIDS vaccines.