bluuebunny/crossref_metadata_2025 huggingface dataset:
Donor ionization in size controlled silicon nanocrystals: The transition from defect passivation to free electron generation
Authors: Crowe I. F. , Papachristodoulou N. , Halsall M. P. , Hylton N. P. , Hulko O. , Knights A. P. , Yang P. , Gwilliam R. M. , Shah M. , Kenyon A. J.
Published: January 2013

We studied the photoluminescence spectra of silicon and phosphorus co-implanted silica thin films on (100) silicon substrates as a function of isothermal annealing time. The rapid phase segregation, formation, and growth dynamics of intrinsic silicon nanocrystals are observed, in the first 600 s of rapid thermal processing, using dark field mode X-TEM. For short annealing times, when the nanocrystal size distribution exhibits a relatively small mean diameter, formation in the presence of phosphorus yields an increase in the luminescence intensity and a blue shift in the emission peak compared with intrinsic nanocrystals. As the mean size increases with annealing time, this enhancement rapidly diminishes and the peak energy shifts further to the red than the intrinsic nanocrystals. These results indicate the existence of competing pathways for the donor electron, which depends strongly on the nanocrystal size. In samples containing a large density of relatively small nanocrystals, the tendency of phosphorus to accumulate at the nanocrystal-oxide interface means that ionization results in a passivation of dangling bond (Pb-centre) type defects, through a charge compensation mechanism. As the size distribution evolves with isothermal annealing, the density of large nanocrystals increases at the expense of smaller nanocrystals, through an Ostwald ripening mechanism, and the majority of phosphorus atoms occupy substitutional lattice sites within the nanocrystals. As a consequence of the smaller band-gap, ionization of phosphorus donors at these sites increases the free carrier concentration and opens up an efficient, non-radiative de-excitation route for photo-generated electrons via Auger recombination. This effect is exacerbated by an enhanced diffusion in phosphorus doped glasses, which accelerates silicon nanocrystal growth.
Diffusiophoretic self-propulsion of colloids driven by a surface reaction: The sub-micron particle regime for exponential and van der Waals interactions
Authors: Sharifi-Mood Nima , Koplik Joel , Maldarelli Charles
Published: January 2013

Diffusiophoresis is a mechanism for propelling colloid particles in a liquid in which the driving force for the motion derives from intermolecular interactions between solute molecules surrounding the particle and the colloid itself. When solutes are asymmetrically distributed around the particle, the solutal interactions exerted on the colloid are unbalanced, and the particle is propelled. In self-diffusiophoresis, the particle itself creates the asymmetric distribution as a means of autonomous motion (a motor). Experiments implement the asymmetric production of a solutal concentration gradient by functionalizing one side of the colloid with a catalyst, which converts a reactant solute into a product. Previous hydrodynamic models of this design have assumed the length scale L of the intermolecular interaction (typically of order 1−10 nm) to be much smaller than the colloid radius, a (order 1 μm), L/a < 1. In this limit, assuming the catalytic reaction produces a constant flux of solute, and convective effects are negligible, the self-diffusiophoretic velocity is to leading order independent of a. Anticipating future experiments on nanosized motors (a=O(10−100 nm)), numerical solutions are presented for the velocity up to order one in L/a, and an integral asymptotic approximation is constructed accurate for L/a less than 0.1. Three intermolecular interactions are examined, a hard sphere excluded volume potential, an exponential interaction and a long-range van der Waals attraction, which is computed by pairwise additivity and formulated to include the attraction of the solvent with the colloid. For each interaction, the velocity decreases as the colloid radius decreases with the interaction parameters constant. For small L/a, velocity for the exponential potential decreases with an order one correction in L/a while this correction is logarithmic for the van der Waals potential. A curve for velocity as a function of a is constructed for the van der Waals interaction in terms of the pairwise interaction parameters of the colloid with the solute and solvent.
Small angular displacement measurement based on an autocollimator and a common-path compensation principle
Authors: Li Ke , Kuang Cuifang , Liu Xu
Published: January 2013

A novel method for small angular displacement measurement based on an autocollimator and a common-path compensation principle by using single CCD detector was proposed. The principles of the angular displacement measurement and the common-path compensation were analyzed. The feasibility of measurement method was verified and the experimental results revealed that the linear correlativity between the relative displacement of the measuring beam spot and the angular displacement is 0.99996. And the measurement resolution is about 0.03 arcsec. To test the compensation's effect, a series of experiments introducing three different interferences from system and external environment were performed. The experimental results indicated that the standard deviations of the measuring beam spot's angular drift were improved by at least 25.0% to at most 80.0% in x direction while by at least 28.2% to at most 95.6% in y direction. Thus, the stability of the system and the measurement resolution were improved.
Quantum control of multi-photon dissociation of HCl+ with intense femtosecond laser pulses
Authors: Su Qianzhen , Han Yongchang , Cong Shu-lin
Published: January 2013

The multi-photon dissociation of HCl+ through three channels \documentclass[12pt]{minimal}\begin{document}$\textrm {HCl}^+\rightarrow \textrm {H}(1s|^2\textrm {S}) + \textrm {Cl}^+(^3\textrm {P})$\end{document} HCl +→H(1s|2S)+ Cl +(3P), \documentclass[12pt]{minimal}\begin{document}$\textrm { H}^+\break + \textrm {Cl}(^2\textrm {P}^0)$\end{document}H++ Cl (2P0), and \documentclass[12pt]{minimal}\begin{document}$\textrm {H}(^2\textrm {S})+\textrm {Cl}^+(^1\textrm {D})$\end{document}H(2S)+ Cl +(1D) steered by intense femtosecond laser pulses are investigated theoretically using the quantum wave packet dynamics. The numerical calculations are performed in two cases without and with the coupling between the excited states. The results show that the dissociation is sensitive to the duration τ, peak intensity I0, and the resonance of driving laser fields. In the case without the coupling, the effect of the permanent dipole moments on the dissociations dominates for τ < 15 fs, while with the increase of τ, the dissociation dynamics is mainly dominated by the transition dipole moment. In the case with the coupling, the above-threshold dissociation process is complex, and the non-resonant (λ = 400 nm) and resonant (λ = 800 and 1200 nm) laser fields lead to different variation of the branching ratios. The angle-resolved energy distribution is also discussed in detail.
Capability of charge signal conversion and transmission by water chains confined inside Y-shaped carbon nanotubes
Authors: Tu Yusong , Lu Hangjun , Zhang Yuanzhao , Huynh Tien , Zhou Ruhong
Published: January 2013

The molecular scale signal conversion, transmission, and amplification by a single external charge through a water-mediated Y-shaped nanotube have been studied using molecular dynamics simulations. Our results show that the signal converting capability is highly sensitive to the magnitude of the charge, while the signal transmitting capability is independent of the charge signal. There is a sharp two-state-like transition in the signal converting capacity for both positive and negative charges. When the charge magnitude is above a threshold (|q| ≥ ∼0.7 e), the water dipole orientations in the main tube can be effectively controlled by the signaling charge (i.e., signal conversion), and then be transmitted and amplified through the Y-junction, despite the thermal noises and interferences between branch signals. On the other hand, the signal transmitting capability, characterized by the correlation between the two water dipole orientations in the two branches, is found to be always larger than 0.6, independent of charge signals, indicating that the water-mediated Y-tube is an excellent signal transmitter. These findings may provide useful insights for the future design of molecular scale signal processing devices based on Y-shaped nanotubes.
Nanobubble stability induced by contact line pinning
Authors: Liu Yawei , Zhang Xianren
Published: January 2013

The origin of surface nanobubbles stability is a controversial topic since nanobubbles were first observed. Here, we propose a mechanism that the three-phase contact line pinning, which results from the intrinsic nanoscale physical roughness or chemical heterogeneities of substrates, leads to stable surface nanobubbles. Using the constrained lattice density functional theory (LDFT) and kinetic LDFT, we prove thermodynamically and dynamically that the state with nanobubbles is in fact a thermodynamical metastable state. The mechanism consistent with the classical nucleation theory can interpret most of experimental characteristics for nanobubbles qualitatively, and predict relationships among the gas-side nanobubble contact angle, nanobubble size, and chemical potential.
Ferrocene analogues of sandwich B12·Cr·B12: A theoretical study
Authors: Yuan Yuan , Cheng Longjiu
Published: January 2013

The bowl B12 cluster was previously reported to be analogous to benzene and predicted to be one of the best candidates to be new inorganic ligands. The structural stability and electronic properties of a new sandwich compound Cr(B12)2 (D3d) have been investigated by using density functional theory. It is found that the sandwich Cr(B12)2 (D3d) is a stable complex with large binding energy (−5.93 eV) and HOMO-LUMO gap (2.37 eV), as well as Fe(C5H5)2 and Cr(C6H6)2, following the 18-electron principle. The detailed molecular orbitals and aromaticity analyses indicate that the sandwich compound Cr(B12)2 (D3d) is electronically very stable. The natural bond orbital analysis suggests that spd-π interaction plays an important role in the sandwich compounds.
Effect of milling parameters on SmCo5 nanoflakes prepared by surfactant-assisted high energy ball milling
Authors: Pal Santosh K. , Schultz Ludwig , Gutfleisch Oliver
Published: January 2013

In this study, we discuss the effect of different milling parameters, such as the type and concentration of surfactants, milling energy, and milling time on the structural, morphological and magnetic properties of hard magnetic SmCo5 nanoflakes prepared by surfactant assisted high energy ball milling. Two kinds of surfactants, polyvinylpyrolidone (PVP) with ethanol and oleic acid (OA) with n-heptane, were used as milling media. Increase in surfactants concentration and decrease in milling energy result in the decrease of degree of amorphization and reduction in grain size with milling time. Milling at 200 rpm results in more homogeneous and thicker flakes with fewer fractions of nanoparticles as compared to milling at 800 rpm. Increase in surfactants concentration results in the increase of the aspect ratio of flakes. Due to better capping ability of OA, the degree of flaking is higher when milling in OA than that in case of PVP. A maximum coercivity of 2.3 T was obtained after milling for 1.0 and 2.0 h for 10 and 50 wt. % of OA, respectively, at 800 rpm. A maximum (BH)max of 23.8 MGOe (188.9 kJ m−3) and degree of texture of 93% were obtained for 10 wt. % OA after 10 h of milling at 200 rpm. The pronounced anisotropy and high coercivity of the nanoflakes should prove advantageous for the preparation of textured exchange spring magnets.
Runup and boundary layers on sloping beaches
Authors: Pedersen G. K. , Lindstrøm E. , Bertelsen A. F. , Jensen A. , Laskovski D. , Sælevik G.
Published: January 2013

The present study is devoted to discrepancies between experimental and theoretical runup heights on an inclined plane, which have occasionally been reported in the literature. In a new study on solitary wave-runup on moderately steep slopes, in a wave tank with 20 cm water depth, detailed observations are made for the shoreline motion and velocity profiles during runup. The waves are not breaking during runup, but they do break during the subsequent draw-down. Both capillary effects and viscous boundary layers are detected. In the investigated cases the onshore flow is close to the transitional regime between laminar and turbulent boundary layers. The flow behaviour depends on the amplitude of the incident wave and the location on the beach. Stable laminar flow, fluctuations (Tollmien-Schlichting waves), and formation of vortices are all observed. Comparison with numerical simulations showed that the experimental runup heights were markedly smaller than predictions from inviscid theory. The observed and computed runup heights are discussed in the context of preexisting theory and experiments. Similar deviations are apparent there, but have often been overlooked or given improper physical explanations. Guided by the absence of turbulence and irregular flow features in parts of the experiments we apply laminar boundary layer theory to the inundation flow. Outer flows from potential flow models are inserted in a nonlinear, numerical boundary layer model. Even though the boundary layer model is invalid near the moving the shoreline, the computed velocity profiles are found to compare well with experiments elsewhere, until instabilities are observed in the measurements. Analytical, linear boundary layer solutions are also derived both for an idealized swash zone motion and a polynomial representation of the time dependence of the outer flow. Due to lacking experimental or theoretical descriptions of the contact point dynamics no two-way coupling of the boundary layer model and the inviscid runup models is attempted. Instead, the effect of the boundary layer on the maximum runup is estimated through integrated losses of onshore volume transport and found to be consistent with the differences between inviscid theory and experiments.
Effect of interface adhesion and impurity mass on phonon transport at atomic junctions
Authors: Saltonstall Christopher B. , Polanco Carlos A. , Duda John C. , Ghosh Avik W. , Norris Pamela M. , Hopkins Patrick E.
Published: January 2013

With the characteristic lengths of electronic and thermal devices approaching the mean free paths of the pertinent energy carriers, thermal transport across these devices must be characterized and understood, especially across interfaces. Thermal interface conductance can be strongly affected by the strength of the bond between the solids comprising the interface and the presence of an impurity mass between them. In this work, we investigate the effects of impurity masses and mechanical adhesion at molecular junctions on phonon transmission via non-equilibrium Green's functions (NEGF) formalisms. Using NEGF, we derived closed form solutions to the phonon transmission across an interface with an impurity mass and variable bonding. We find that the interface spring constant that yields the maximum transmission for all frequencies is the harmonic mean of the spring constants on either side of the interface, while for a mass impurity, the arithmetic average of the masses on either side of the interface yields the maximum transmission. However, the maximum transmission for each case is not equal. For the interface mass case, the maximum transmission is the transmission predicted by a frequency dependent form of the acoustic mismatch model, which we will refer to as the phonon mismatch model (PMM), which is valid for specular phonon scattering outside the continuum limit. However, in the interface spring case, the maximum transmission can be higher or lower than the transmission predicted by the PMM.
Cascade Auger decays following Si KL23L23 Auger transitions in SiF4
Authors: Suzuki I. H. , Kono Y. , Ikeda A. , Oi M. , Ouchi T. , Ueda K. , Tamenori Y. , Takahashi O. , Nagaoka S.
Published: January 2013

Cascade Si LVV Auger decays following KL23L23 Auger transitions have been measured in SiF4 molecule using an electron spectrometer combined with monochromatized undulator radiation. Molecular cascade processes from the two 2p holes states largely generate wide band structures in the spectra due to sequential electron emission leading to multiple valence holes. However, a peak with high yield is observed for the first time at about 103 eV, an energy being considerably higher than the energies of the normal LVV Auger electron, in the instance of the resonant excitation of Si 1s electron into the vacant molecular orbital. This peak is presumed to originate from the participator decay from the state with two 2p holes and one excited electron into the state with one 2p hole and one valence hole. A similar peak with less intensity is detected in the photoexcitation of the 1s electron into a Rydberg orbital. After the normal KL23L23 Auger transition, the resultant cascade spectrum shows several peaks, e.g., 61 eV, 76 eV, and 82 eV. The former two peaks are assigned to the Auger transitions of Si atoms produced through molecular ion dissociation after cascade decays, and the latter is probably ascribed to the second step Auger decay into states having a 2p hole together with two valence holes.
Analytical second derivatives of excited-state energy within the time-dependent density functional theory coupled with a conductor-like polarizable continuum model
Authors: Liu Jie , Liang WanZhen
Published: January 2013

This work extends our previous works [J. Liu and W. Z. Liang, J. Chem. Phys. 135, 014113 (2011)10.1063/1.3605504; J. Liu and W. Z. Liang, J. Chem. Phys. 135, 184111 (2011)]10.1063/1.3659312 on analytical excited-state Hessian within the framework of time-dependent density functional theory (TDDFT) to couple with a conductor-like polarizable continuum model (CPCM). The formalism, implementation, and application of analytical first and second energy derivatives of TDDFT/CPCM excited state with respect to the nuclear and electric perturbations are presented. Their performances are demonstrated by the calculations of excitation energies, excited-state geometries, and harmonic vibrational frequencies for a number of benchmark systems. The calculated results are in good agreement with the corresponding experimental data or other theoretical calculations, indicating the reliability of the current computer implementation of the developed algorithms. Then we made some preliminary applications to calculate the resonant Raman spectrum of 4-hydroxybenzylidene-2,3-dimethyl-imidazolinone in ethanol solution and the infrared spectra of ground and excited states of 9-fluorenone in methanol solution.
Coexistence of solvated electron and benzene-centered valence anion in the negatively charged benzene-water clusters
Authors: Zhang Meng , Zhao Jing , Liu Jinxiang , Zhou Lianwen , Bu Yuxiang
Published: January 2013

We present a combined M06 functional calculation and ab initio molecular dynamics simulation study of an excess electron (EE) in a microhydrated aromatic complex (modeled by benzene (Bz)-water binary clusters, Bz(H2O)n). Calculated results illustrate that Bz ring and water clusters are indeed linked through the π⋯HO interactions in the neutral Bz(H2O)n (n = 1–8) clusters, and the size of the water cluster does not influence the nature of its interaction with the π system for the oligo-hydrated complexes. The states and the dynamics of an EE trapped in such Bz-water clusters were also determined. All of possible localized states for the EE can be roughly classified into two types: (i) single, ring-localized states (the Bz-centered valence anions) in which an EE occupies the LUMO of the complexes originating from the LUMO (π*) of the Bz ring, and the π⋯HO interactions are enhanced for increase of electron density of the Bz ring. In this mode, the carbon skeleton of the Bz part is significantly deformed due to increase of electron density and nonsymmetric distribution of electron density induced by the interacting H–O bonds; (ii) solvated states, in which an EE is trapped directly as a surface state by the dangling hydrogen atoms of water molecules or as a solvated state in a mixed cavity formed by Bz and water cluster. In the latter case, Bz may also participate in capturing an EE using its C–H bonds in the side edge of the aromatic ring as a part of the cavity. In general, a small water cluster is favorable to the Bz-centered valence anion state, while a large one prefers a solvated electron state. Fluctuations and rearrangement of water molecules can sufficiently modify the relative energies of the EE states to permit facile conversion from the Bz-centered to the water cluster-centered state. This indicates that aromatic Bz can be identified as a stepping stone in electron transfer and the weak π⋯HO interaction plays an important role as the driving force in conversion of the two states.
Current rectification in nickelocenylferrocene sandwiched between two gold electrodes
Authors: Matsuura Yukihito
Published: January 2013

I present a theoretical study of the electronic transport properties of nickelocenylferrocene sandwiched between gold electrodes. Compared with the biferrocene system, the nickelocenylferrocene system had high electrical conduction and rectification in the bias range −1 to 1 V. Furthermore, the spin-down states of the nickelocenylferrocene system exhibited perfect spin-filtering properties. From the electronic states of the nickelocenylferrocene, it was found that the rectification was caused by a difference in the bias-dependent behaviors between the Fe 3d and Ni 3d orbitals.
Temporal evolution of the re-breakdown voltage in small gaps from nanoseconds to milliseconds
Authors: Cury Basso Heitor , Qiu Xunlin , Wirges Werner , Gerhard Reimund
Published: January 2013

A detailed understanding of electric breakdown in dielectrics is of scientific and technological interest. In gaseous dielectrics, a so-called re-breakdown is sometimes observed after extinction of the previous discharge. Although time-dependent re-breakdown voltage is essentially known, its behavior immediately after the previous discharge is not precisely understood. We present an electronic circuit for accurate measurements of the time-dependent re-breakdown voltage in small gaps from tens of nanoseconds to several milliseconds after the previous spark. Results from such experiments are compared with earlier findings, and relevant physical mechanisms such as heating of the gas, decay of the plasma, and ionization of excited atoms and molecules are discussed. It is confirmed that the thermal model is not valid at times below several microseconds.
Fluorescence spectroscopy applied to study cyclic creep behaviour and internal stresses of semi-crystalline high-density polyethylene
Authors: Bouvet G. , Douminge L. , Feaugas X. , Touzain S. , Mallarino S.
Published: January 2013

Cyclic creep or ratcheting behaviour has been characterized on semi-crystalline high-density polyethylene (HDPE) at 293 K using in situ extrinsic fluorescence spectroscopy. Fluorescent probe inserted in polymer offers the opportunity to establish a relationship between fluorescence phenomena and mechanical behaviour and more specifically to internal stresses. The influence of mean stress (σm), and stress amplitude (σa), on ratcheting strain (εr) and strain amplitude (εa) was studied in term of internal stresses development. The physical base of internal stress state has been discussed.
CdSe colloidal nanocrystals monolithically integrated in a pseudomorphic semiconductor epilayer
Authors: Larramendi Erick M. , Schöps Oliver , Artemyev Mikhail V. , Schikora Detlef , Lischka Klaus , Woggon Ulrike
Published: January 2013

As optically active emitters in a semiconductor matrix, core/shell and bare CdSe colloidal nanocrystals (CNCs) were monolithically incorporated in ZnSe pseudomorphic epilayers by molecular beam epitaxy (MBE). A suspension of wet chemically synthesized CNCs was sprayed ex-situ over a pseudomorphic ZnSe/GaAs(001) heterostructure using a nebulizer. Subsequently, the matrix material growth was resumed to form a capping layer by a slow MBE growth mode. Structural investigations show high crystalline quality and pseudomorphic epitaxial character of the whole hybrid CNC-matrix structure. The core/shell CNCs remain optically active following the embedding process. Their emission is blue shifted without a significant change on the spectral shape, and shows the same temperature dependence as that of the free exciton peak energy in zinc-blende CdSe at temperatures above 80 K. Our optical characterization of the samples showed that the embedded CNCs were stable and that the structure of the host was preserved. These results are encouraging for the fabrication of more complex optoelectronic devices based on CNCs.
Friction measurement on free standing plates using atomic force microscopy
Authors: Tang X. S. , Loke Y. C. , Lu P. , Sinha Sujeet K. , O'Shea S. J.
Published: January 2013

A method is introduced to measure friction on small, free standing objects, specifically microfabricated silicon plates, based on atomic force microscopy (AFM). An AFM tip is brought into contact with the plate resting on a substrate. The substrate is displaced laterally and, provided the AFM tip does not slide over the plate, the twisting of the AFM cantilever is used to measure the friction of the underlying plate-substrate interface. The method can measure nano-Newton to micro-Newton forces (both friction and applied load) and provides a means to measure friction of macroscopic structures at low load.
Incorporation of modified dynamic inverse Jiles-Atherton model in finite volume time domain for nonlinear electromagnetic field computation
Authors: Hamimid M. , Mimoune S. M. , Feliachi M.
Published: January 2013

In this paper, a time stepping finite volume method (FVM) associated with the modified inverse Jiles-Atherton model for the nonlinear electromagnetic field computation is presented. To describe the dynamic behavior in the conducting media, the effective field is modified by adding two counter-fields associated respectively to the eddy current and excess losses. The hysteresis loss can be estimated by the integration over the obtained hysteresis loop at each frequency. To examine the validity of the proposed dynamic model coupled with FVM, the computed total losses and hysteresis loops are compared to experiments.
Radio frequency current-voltage probe for impedance and power measurements in multi-frequency unmatched loads
Authors: Lafleur T. , Delattre P. A. , Booth J. P. , Johnson E. V. , Dine S.
Published: January 2013

A broad-band, inline current-voltage probe, with a characteristic impedance of 50 Ω, is presented for the measurement of voltage and current waveforms, impedance, and power in rf systems. The probe, which uses capacitive and inductive sensors to determine the voltage and current, respectively, can be used for the measurement of single or multi-frequency signals into both matched and unmatched loads, over a frequency range of about 1–100 MHz. The probe calibration and impedance/power measurement technique are described in detail, and the calibrated probe results are compared with those obtained from a vector network analyzer and other commercial power meters. Use of the probe is demonstrated with the measurement of power into an unmatched capacitively coupled plasma excited by multi-frequency tailored voltage waveforms.
A new apparatus for study of pressure-dependent laminar premixed flames with vacuum ultraviolet photoionization mass spectrometry
Authors: Zhou Z. Y. , Wang Y. , Tang X. F. , Wu W. H. , Qi F.
Published: January 2013

We report a home-made combustion apparatus for study of pressure-dependent laminar premixed flames with tunable vacuum ultraviolet photoionization mass spectrometry. The instrument consists of a flame chamber, a photoionization chamber with a single-stage sampling system, an ion transfer/storage system, and an orthogonal-acceleration reflectron time-of-flight mass spectrometer. Preliminary results of fuel-rich C2H4/O2/Ar flames at pressures of 30, 150, and 760 Torr have been obtained with this instrument. Compared to previous instruments [T. A. Cool, A. McIlroy, F. Qi, P. R. Westmoreland, L. Poisson, D. S. Peterka, and M. Ahmed, Rev. Sci. Instrum. 76, 094102 (2005)10.1063/1.2010307; F. Qi, R. Yang, B. Yang, C. Q. Huang, L. X. Wei, J. Wang, L. S. Sheng, and Y. W. Zhang, Rev. Sci. Instrum. 77, 084101 (2006)]10.1063/1.2234855, performances of the new apparatus have higher mass resolution (∼3500 at m/z = 40), better detection limit (<1 ppm), and broader dynamic range (better than 5 order of magnitude).
Electrical properties of K0.5Na0.5NbO3 thin films grown on Nb:SrTiO3 single-crystalline substrates with different crystallographic orientations
Authors: Yu Qi , Li Jing-Feng , Sun Wei , Zhou Zhen , Xu Ying , Xie Zhen-Kun , Lai Feng-Ping , Wang Qing-Ming
Published: January 2013

To attain a deep understanding of ferroelectric and piezoelectric characteristics of K0.5Na0.5NbO3 as a promising lead-free compound, the ferroelectric and piezoelectric responses of its epitaxially grown films with three primary orientations of [001], [110], and [111] were investigated with an emphasis on the influence of crystallographic orientation. The films were prepared by sol-gel processing using Nb-doped SrTiO3 single-crystalline substrates with various cutting directions. A peak remnant polarization value (Pr) of 17.3 μC/cm2 was obtained along the [110] direction due to the coincidence between the spontaneous polarization and the film orientation, which is significantly higher than 10.5 μC/cm2 in [111]-oriented and 10.1 μC/cm2 in [001]-oriented ones. However, a better piezoelectric response was achieved in the [001]-oriented films with an average local effective piezoelectric coefficient (d33) of 50.5 pm/V, as compared with 45.1 pm/V and 39.7 pm/V in [110]- and [111]-oriented films, respectively.
Uniform, large surface-area polarization by modifying corona-electrodes geometry
Authors: Tansel T. , Ener Rusen S. , Rusen A.
Published: January 2013

We report on the uniform, large scale polarization of ferroelectric materials by a newly designed corona charging technique developing nonconventional electrodes geometry. The results of pyroelectric measurements represented the spatial homogeneity of the polarization attained through a surface area of ∼25 cm2.
Effects of cathode modification using spin-coated lithium acetate on the performances of polymer bulk-heterojunction solar cells
Authors: Jiang Liang , Li Aiyuan , Deng Xianyu , Zheng Shizhao , Wong King-Young
Published: January 2013

In this report, we show that the performances of polymer bulk-heterojunction solar cells were improved by inserting thin films of lithium acetate layers between the active layer and the cathode using a spin-coating process. Comparing with the device without the cathode modification, significant enhancements of Voc (open circuit voltage) from 0.42 V to 0.55 V and device efficiency from 1.4% to 4.1% were achieved. X-ray and ultraviolet photoelectron spectroscopic studies indicate that both the improved damage tolerance of the active layer under the thermally evaporated metal and an n-type doping at the metal/organic interface play the crucial roles in the enhanced performances.
Efficient tandem organic light-emitting device based on photovoltaic-type connector with positive cycle
Authors: Liu Huihui , Yan Fei , Wang Hua , Miao Yanqin , Du Xiaogang , Jing Shu , Gao Zhixiang , Chen Liuqing , Hao Yuying , Xu Bingshe
Published: January 2013

We designed a tandem organic light-emitting device based on an organic photovoltaic-type charge generation connector (CGC) of fullerene carbon 60/copper(II) phthalocyanine. The CGC can absorb a portion of photons radiated from emission zone and form excitons which disassociated into free charges at PN junction interface without energy barrier, leading to low driving voltage and better charge balance. The efficiency increases remarkably with increasing current density, even beyond two folds compared with single unit device under higher current density, meaning slower roll-off. The whole process is a positive cycle, and actually enhances the utilization of internal radiation and the overall performance of tandem device.
Delayed magnetic vortex core reversal
Authors: Kammerer Matthias , Sproll Markus , Stoll Hermann , Noske Matthias , Weigand Markus , Illg Christian , Fähnle Manfred , Schütz Gisela
Published: January 2013

When switching the vortex core in a magnetic disc by a short excitation with an in-plane field, there is an initial global excitation of the magnetization due to a precession of the magnetization in the spatially homogeneous field. Then an energy transport from this global excitation towards the center of the disc takes place leading to a concentration of the energy close to the vortex core which suffices to switch the core. Because this transport requires time, there is a delay between the end of the excitation and the switching. This is demonstrated for switching by in-plane rotating GHz rf-bursts.
Atomic-scale characterization of germanium isotopic multilayers by atom probe tomography
Authors: Shimizu Y. , Takamizawa H. , Kawamura Y. , Uematsu M. , Toyama T. , Inoue K. , Haller E. E. , Itoh K. M. , Nagai Y.
Published: January 2013

We report comparison of the interfacial sharpness characterization of germanium (Ge) isotopic multilayers between laser-assisted atom probe tomography (APT) and secondary ion mass spectrometry (SIMS). An alternating stack of 8-nm-thick naturally available Ge layers and 8-nm-thick isotopically enriched 70Ge layers was prepared on a Ge(100) substrate by molecular beam epitaxy. The APT mass spectra consist of clearly resolved peaks of five stable Ge isotopes (70Ge, 72Ge, 73Ge, 74Ge, and 76Ge). The degree of intermixing at the interfaces between adjacent layers was determined by APT to be around 0.8 ± 0.1 nm which was much sharper than that obtained by SIMS.
Wavelet-based multifractal analysis of large scale wind turbine main bearing
Authors: Chen Changzheng , Sun Xianming , Gu Quan , Zhou Bo , Gu Yanling
Published: January 2013

The fault vibration signals of wind turbine are non-linear and non-stationary, thus it is difficult to obtain the obvious fault features. In this study, a multifractal method based on the wavelet transform modulus maxima (WTMM) method is used to investigate the main bearing incipient fault of large scale wind turbine. The real vibration signals are analyzed using the multifractal spectrum. The spectrum of the vibration signals is quantified by spectral characteristics including its range and the Hölder exponent corresponding to the maximum dimension. We find that the range of Hölder exponent of normal bearing is narrower than that of the bearing with incipient fault. And the results also indicate that the fault features are different at various wind turbine rotational frequencies. The results demonstrate that the multifractal spectrum obtained from WTMM method is effective to extract the incipient fault features of main bearing of large scale wind turbine.
Diffusion and configuration of Li in ZnO
Authors: Knutsen K. E. , Johansen K. M. , Neuvonen P. T. , Svensson B. G. , Kuznetsov A. Yu.
Published: January 2013

Diffusion of Li into ZnO from an “infinite” surface source under oxygen-rich conditions is studied using secondary ion mass spectrometry. The Li concentration-versus-depth profiles exhibit a distinct and sharp drop, which evolves in position with temperature and time. The sharp drop is associated with an efficient conversion from highly mobile Li-interstitials (Lii) to practically immobile Li-substitutionals (LiZn) via a kick-out mechanism. The characteristic concentration level at which Li drops provides a measure of the active donor concentration in the samples at the processing temperature, and gives evidence of residual impurities being responsible for the commonly observed “native” n-type conductivity. These donors are suggested to arise from different impurities, with Al and Si as the prevailing ones in hydrothermal and melt grown material. Further, evidence of electric field effects on Li diffusion profiles is obtained, and they are considered as a main reason for the slow diffusivity obtained in this work (using O-rich conditions) relative to those previously reported in the literature (obtained under Zn-rich conditions).
A phase-cut method for multi-species kinetics: Sample application to nanoscale defect cluster evolution in alpha iron following helium ion implantation
Authors: Xu Donghua , Hu Xunxiang , Wirth Brian D.
Published: January 2013

Many kinetic processes in materials involve clustering of multiple species. Tracking concentrations of all compositions throughout the multi-species phase, space can readily become formidable when significant cluster growth occurs. Here, using nanoscale defect cluster evolution in alpha iron following helium ion implantation as an example, we demonstrate a phase-cut method that can effectively reduce this widely encountered problem. The method cuts out unnecessary compositions in the phase space and hence is much more efficient than a full-phase-space calculation. Yet, it retains the same precision in predicted experimental observables. The cutting of phase space does not require an accurate nucleation and growth path to be known a priori. The method may be applicable to other multi-species kinetic phenomena that are driven by irradiation and/or thermal annealing.
Mode recombination and alternation of surface plasmons in anisotropic mediums
Authors: Luo Rui , Gu Ying , Li Xiankuo , Wang Luojia , Khoo Iam-Choon , Gong Qihuang
Published: January 2013

Dispersion relations of surface plasmon polaritons with transverse-magnetic- and transverse-electric-polarized waves coexisting in insulator-metal-anisotropic planar waveguides are analytically derived. Aligned nematic liquid crystal, as an anisotropic medium, is employed to manipulate the mode properties. By varying its optical axis, two kinds of mode transformation are found: one is mode recombination, accompanied by dramatically extended propagation lengths at the cutoff angles, and the other is mode alternation, associated with an obvious shift of the electromagnetic energy flux from one insulator to the other. The results may have applications in actively modulated plasmon-based nanodevices and tunable surface plasmon sources.
Mid-infrared Raman sources using spontaneous Raman scattering in germanium core optical fibers
Authors: Wang Pengfei , Charlton O'Mahony Christy , Lee Timothy , Ismaeel Rand , Hawkins Thomas , Semenova Yuliya , Bo Lin , Wu Qiang , McDonagh Colette , Farrell Gerald , Ballato John , Brambilla Gilberto
Published: January 2013

Mid-infrared Raman sources based on spontaneous Raman scattering have been demonstrated in a 15-μm diameter glass-clad crystalline germanium optical fiber and in a germanium-wire. A quantum cascade laser was used as pump at a wavelength of 5.62 μm. Because of their ultra-high optical nonlinearities and extremely broad transparency window, germanium core fibers offer the possibility of fabricating compact and efficient mid-infrared sources.
Investigation of extra traps measured by charge pumping technique in high voltage zone in p-channel metal-oxide-semiconductor field-effect transistors with HfO2/metal gate stacks
Authors: Ho Szu-Han , Chang Ting-Chang , Wang Bin-Wei , Lu Ying-Shin , Lo Wen-Hung , Chen Ching-En , Tsai Jyun-Yu , Chen Hua-Mao , Liu Guan-Ru , Tseng Tseung-Yuen , Cheng Osbert , Huang Cheng-Tung , Cao Xi-Xin
Published: January 2013

This letter investigates extra traps measured by charge pumping technique in the high voltage zone in p-channel metal-oxide-semiconductor field-effect transistors with HfO2/metal gate stacks. N-Vhigh level characteristic curves with different duty ratios show that the hole discharge time (tbase  level) dominates the value of extra traps. By fitting ln (N (tbase  level = 1μs) − N (tbase  level)) − Δtbase  level at different temperatures and computing the equation t = τ0 exp (αh,SiO2dSiO2 + αh,HfO2dHfO2,trap), the results show that these extra traps measured by the charge pumping technique at high voltage zone can be attributed to high-k bulk shallow traps.
Reduction of space charge breakdown in e-beam irradiated nano/polymethyl methacrylate composites
Authors: Zheng Feihu , Dong Jianxing , Zhang Yewen , An Zhenlian , Lei Qingquan
Published: January 2013

Fast discharge of numerous space charges in dielectric materials can cause space charge breakdown. This letter reports the role of nanoparticles in affecting space charge breakdown of nano/polymethyl methacrylate composites. Space charge distributions in the composites, implanted by electron beam irradiation, were measured by pressure wave propagation method. The results show that the nanoparticles have significant effects on the isothermal charge decay and space charge breakdown in the nanocomposites. The resistance to space charge breakdown in the nanocomposites is attributed to the combined action of the introduction of deep trapping states and the scattering effect by the added nanoparticles.
Space charge suppression induced by deep traps in polyethylene/zeolite nanocomposite
Authors: Han Bai , Wang Xuan , Sun Zhi , Yang Jiaming , Lei Qingquan
Published: January 2013

NaY zeolite nanoparticles doped in low-density polyethylene (LDPE) is investigated. The zeolite nanoparticles are uniformly distributed in LDPE. Space charge distribution from pulsed electro-acoustic method and trap level from thermally stimulated current test are obtained. The results indicate that zeolite doping enormously suppresses space charge accumulation and reduces the conduction current by importing abundant deep traps. It can be explained that the zeolite nanoparticles increase the interface regions and introduce small size cavity traps from the porous surface of zeolite. The deep traps greatly weaken impurity ionization and carrier mobility, and raise potential barrier for charge injection.
Tunable conductivity at LaAlO3/SrxCa1−xTiO3 (0 ≤ x ≤ 1) heterointerfaces
Authors: Young Moon Seon , Kim Dai-Hong , Jung Chang Hye , Kwon Choi Jong , Kang Chong-Yun , Jin Choi Heon , Hong Seong-Hyeon , Baek Seung-Hyub , Kim Jin-Sang , Won Jang Ho
Published: January 2013

The two-dimensional electron gas formed at LaAlO3/SrTiO3 heterointerfaces exhibits a variety of interesting physical properties. Herein, we report on tunable conductivity at LaAlO3/SrxCa1−xTiO3 heterostructures. By changing the Sr content in the SrxCa1−xTiO3 (0 ≤ x ≤ 1) layers, the orthorhombicity of the films, which inevitably accompanies TiO6 octahedral distortions in the unit cells, could be varied. As a result, the interfacial conductivity can be tuned over 6 orders of magnitude. We suggest that the use of pseudosubstrates with chemical substitution or alloying is a promising route to finely tune conductivity at oxide heterointerfaces.
Experimental approach to the microscopic phase-sensitive surface plasmon resonance biosensor
Authors: Zhang Chonglei , Wang Rong , Min Changjun , Zhu Siwei , Yuan X.-C.
Published: January 2013

We designed and proposed a microscopic configuration of wide-dynamic-range phase-sensitive surface plasmon resonance biosensor based on differential interferometry between focused radially polarized and azimuthally polarized cylindrical vector beams recently (R. Wang et al., Opt. Lett. 37, 2091 (2012)). In this Letter, we follow the simulation results up with experimental verifications with a sensitivity of 7.385 × 10−7refractive index unit (RIU)/0.1°. It is also verified that the dynamic range of this system could be as large as 0.35 RIU in principle, which is only confined by numerical aperture of the microscopic objective lens.
Photo-assisted molecular engineering in solution-processed organic thin-film transistors with a blended semiconductor for high mobility anisotropy
Authors: Park Jaehoon , Keum Chang-Min , Kim Jae-Hyun , Lee Sin-Doo , Payne Maricia , Petty Michael , Anthony John. E. , Bae Jin-Hyuk
Published: January 2013

This paper reports a viable method for enhancing mobility anisotropy in solution-processed organic thin-film transistors (TFTs) by irradiating linearly polarized ultraviolet (LPUV) light onto a 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene)/poly (vinyl cinnamate) (PVCi) blended semiconductor film. The needle-like crystalline domains in the blended semiconductor film were aligned along the polarization direction of the LPUV light, suggesting that TIPS-pentacene molecules are oriented anisotropically due to an intermolecular interaction and aggregation with the photo-aligned PVCi molecules. The mobility anisotropy reached up to about 50, which is the highest value achieved in solution-processed organic TFTs with a polymeric insulator.
Carbon flux assisted graphene layer growth on 6H-SiC(000-1) by thermal decomposition
Authors: Liu Z. L. , Kang C. Y. , Fan L. L. , Xu P. S. , Zou C. W.
Published: January 2013

Graphene layers have been grown on C-terminated 6H-SiC (000-1) substrate by thermal decomposition with the assistance of carbon flux in a solid carbon source molecular beam epitaxy system. Results indicate that the graphene films prepared directly by the reduction of SiC in vacuum chamber are defective and disorder, while appropriate carbon flux added during the graphene growth will favor the graphene layer growth and improve the graphene layer quality. While on the other hand, too much carbon flux will affect the graphene formation and deteriorate the final graphene layer. This carbon flux assisted graphene growth behavior on SiC crystal indicates that the external carbon flux should play an important role for the graphene layer growth during the thermal reduction of SiC in vacuum condition. The mechanism of the graphene layer formed on C-face SiC and the effect of the carbon flux were discussed based on the experimental results.
Note: Switch-mode hybrid current controllers for quantum cascade lasers
Authors: Taubman Matthew S.
Published: January 2013

Chemical sensing in the mid-infrared has been revolutionized by the advent of quantum cascade lasers. Their higher current and voltage demands compared to laser diodes however, negatively impact size, weight, and power footprint for fieldable systems, particularly in hot environments. This Note presents a switch-mode/linear hybrid controller, furnishing drive currents up to 2 A at compliance voltages up to 15 V, with output noise near levels determined by shot and Johnson contributions from within the linear regulator, from frequencies below 100 Hz to the switching frequency. Current modulation from near 0 to 1.8 A is also demonstrated at frequencies up to a kilohertz.