bluuebunny/crossref_metadata_2025 huggingface dataset:
The Relationship Between Quality of Life, Binge‐Eating Disorder, and Obesity Status in an Ethnically Diverse Sample
Authors: Perez Marisol , Warren Cortney S.
Published: April 2011

This study examined the relationship between obesity status, binge‐eating disorder (BED), and quality of life (QOL) in a large, ethnically diverse community sample of adult men and women. Using data from the Collaborative Psychiatric Epidemiological Surveys (N = 20,013), individuals were categorized into four groups: nonobese with BED (n = 142), nonobese without BED (n = 14,301), obese with BED (n = 136), and obese without BED (n = 4,863). Results indicated obese individuals with BED consistently reported the poorest QOL. Findings suggested that obesity status was more strongly related to physical health‐related QOL variables (e.g., number of physical conditions, mobility impairment) whereas diagnostic status was more predictive of mental health and social functioning QOL variables (e.g., cognitive impairment, social interaction impairment, time out of role). The degree to which lifetime BED diagnosis was associated with impairment in social interaction differed across ethnic groups. For black individuals, the number of physical health conditions was associated with BED presence moreso than weight status.
Energy transfer rates and population inversion investigation of 1G4 and 1D2 excited states of Tm3+ in Yb:Tm:Nd:KY3F10 crystals
Authors: Marconi da Silva M. D. Linhares Horácio , Felipe Henriques Librantz André , Gomes Laércio , Coronato Courrol Lilia , Lícia Baldochi Sonia , Marcia Ranieri Izilda
Published: April 2011

In this work we present the spectroscopic properties of KY3F10 (KY3F) single crystals activated with thulium and co-doped with ytterbium and neodymium ions. The most important processes that lead to the thulium up-conversion emissions in the blue and ultraviolet regions were identified. A time-resolved luminescence spectroscopy technique was employed to measure the luminescence decays and to determine the most important mechanisms involved in the up-conversion process that populates 1G4 and 1D2 (Tm3+) excited states. Analysis of the energy-transfer processes dynamics using selective pulsed-laser excitations in Yb:Tm:Nd, Tm:Nd, and Tm:Yb KY3F crystals show that the energy transfer from Nd3+ to Yb3+ ions is the mechanism responsible for the enhancement of the blue up-conversion efficiency in the Yb:Tm:Nd:KY3F when compared with the Yb:Tm system. A study of the energy transfer processes in Yb:Tm:Nd:KY3F crystal showed that the 1G4 excited level is mainly populated by a sequence of two nonradiative energy transfers that starts well after the Nd3+ and Tm3+ excitation at 797 nm according to: Nd3+ (4F3/2) → Yb3+ (2F7/2) followed by Yb3+ (2F5/2) → Tm (3H4) → Tm3+ (1G4). Results of numerical simulation of the rate equations system showed that a population inversion for 483.1 nm laser emission line is attained for a pumping rate threshold of 98 s−1, which is equivalent to an intensity of 3.3 KW cm−2 for a continuous laser pumping at 797 nm for Yb(30 mol%):Tm(0.5 mol%):Nd(1 mol%):KY3F. Nevertheless, best Yb3+ concentration for the laser emission near 483.1 nm was estimated to be within 40 and 50 mol%. On the other hand, a population inversion was not observed for the case of 960 nm (Yb3+) pumping.
Dipolar alignment and consequent enhanced charge transport in poly (9, 9′ di octyl fluorene)-2, 7-ylene ethylnylene
Authors: Bajpai Manisha , Srivastava Ritu , Kamalasanan M. N. , Tiwari R. S. , Chand Suresh
Published: April 2011

Current density–voltage characteristics of poly (9, 9′ di octyl fluorene)-2,7-ylene ethylnylene thin films (∼120 nm) have been studied in hole only device configuration at different temperatures (290–100 K) in unpolarized and polarized samples. The hole mobility has been found to be enhanced as a result of dipolar alignment by exposure to a dc electric field via cooling at all elevated temperatures. At higher field, current density has been found to be governed by trapped charge limited currents (TCLC) with hole mobility strongly dependent on electric field and their respective charge transport parameters have been obtained for both samples. The density of trap states has been found to be decreased on polarization from 1.1 × 1018 to 7.6 × 1017 cm−3 and trap energy has correspondingly decreased from 43 to 35 meV. The TCLC model with Poole–Frenkel-type field-dependent mobility has been fitted into the data and found to be in excellent agreement. Temperature dependence of zero field mobility (µ0) and disorder parameter (σ) also has been estimated. We conclude that the relatively higher hole mobilities may be due to the orientational ordering of polar molecules and displacement of excess charges.
Atomic structure of Sr-induced reconstructions on the Si(100) surface
Authors: He Jiehui , Zhang Guanhua , Guo Jiandong , Guo Qinlin , Wu Kehui
Published: April 2011

The Sr-induced reconstructions on Si(100) at elevated temperature were studied using scanning tunneling microscopy and reflection high energy electron diffraction. With the Sr coverage increasing from 0 to 0.5 monolayer, the surface exhibits phase transitions from 2×1-Sr to 2×3-Sr and then to 1×2-Sr. The bias-dependent, high resolution STM images unambiguously support a dimer-vacancy structural model for the 2×3-Sr phase. Furthermore, the coverage-dependent evolution of the surface from 2×3-Sr to 1×2-Sr can also be nicely explained by extending the 2×3-Sr model to the 1×2-Sr.
Modeling of interface thermal conductance in longitudinally connected carbon nanotube junctions
Authors: Varshney Vikas , Lee Jonghoon , Roy Ajit K. , Farmer Barry L.
Published: April 2011

This article explores the behavior of interface thermal conductance of longitudinally connected (6,6) nanotubes—connected through CH2 linkages—using nonequilibrium molecular dynamics (NEMD) and wave packet simulations. Here, we study the effect of connected linkers on the interface thermal conductance and thermal energy transmission coefficients for several phonon modes. Our simulation results suggest that interface thermal conductance between nanotubes strongly depends on the number of CH2 linkers. The more the number of CH2 linkers, the higher the conductance. Further insights into phonon energy transmission are provided from wave packet simulations. Here, we find that the behavior of transmission for various studied acoustic and optical phonon modes is complex in nature, where the thermal transmission coefficients do not always correlate with number of CH2 linkages. However, when the contributions from all the modes are added together, the overall interface thermal conductance agrees well with NEMD simulations.
Ultra-low-noise MoCu transition edge sensors for space applications
Authors: Goldie D. J. , Velichko A. V. , Glowacka D. M. , Withington S.
Published: April 2011

A study of ultra-low-noise MoCu transition edge sensors (TESs) has been performed in the context of realizing the highly sensitive far infrared imaging arrays needed for the next generation of space telescopes. More than 50 TESs, on four different chips, cut out of two different wafers were characterized. The TESs were in the form of 16-element arrays and were read out using superconducting quantum interference device (SQUID) time division multiplexing. The devices were fabricated on 200-nm-thick silicon nitride membranes, with leg widths and lengths covering the ranges of 1–4 μm and 160–960 μm, respectively. The apparent critical temperatures varied over 110–127 mK, but it is shown that much of the variation was due to differential loading by stray light, amounting to 2 ± 2 fW across the array. The measured thermal conductances to the heat bath spanned the range 0.12–1.1 pW/K, with the lowest values being typical of those needed for ultra-low-noise operation. We also studied the inherent variation in the conductances of 15 nominally identical TESs on the same chip and found a value of ±10%, which is higher than that seen on our high-conductance devices designed for ground-based operation. We measured and modeled the electrical input impedance of a subset of these TESs, and studied their step responses. The models, based on previously determined material parameters, are in excellent agreement with the measurements. Dark noise spectra were recorded and compared with the same electrothermal models using the same parameters as the dynamical simulations. The measured noise is reasonably well described by the sum of the contributions from phonon noise in the legs, Johnson noise in the bilayer, and SQUID readout noise. Dark noise equivalent powers as low as 4.2 × 10−19 W/Hz were measured. The NEP was higher than the theoretical limit by a factor of about 1.6.
Efficient nonradiative energy transfer from InGaN/GaN nanopillars to CdSe/ZnS core/shell nanocrystals
Authors: Nizamoglu Sedat , Guzelturk Burak , Jeon Dae-Woo , Lee In-Hwan , Demir Hilmi Volkan
Published: April 2011

In this study, we propose and demonstrate efficient electron-hole pair injection from InGaN/GaN multiple quantum well nanopillars (MQW-NPs) to CdSe/ZnS core/shell nanocrystal quantum dots (NQDs) via Förster-type nonradiative energy transfer. For that we hybridize blue-emitting MQW-NPs with red-emitting NQDs and the resultant exciton transfer reaches a maximum rate of (0.192 ns)−1 and a maximum efficiency of 83.0%. By varying the effective bandgap of core/shell NQDs, we conveniently control and tune the excitonic energy transfer rate for these NQD integrated hybrids, and our measured and computed exciton transfer rates are found to be in good agreement for all hybrid cases.
H2/N2 plasma damage on porous dielectric SiOCH film evaluated by in situ film characterization and plasma diagnostics
Authors: Yamamoto Hiroshi , Takeda Keigo , Ishikawa Kenji , Ito Masafumi , Sekine Makoto , Hori Masaru , Kaminatsui Takeshi , Hayashi Hisataka , Sakai Itsuko , Ohiwa Tokuhisa
Published: April 2011

This study investigates the mechanism of H2/N2 plasma ashing damage of porous SiOCH films. Porous SiOCH films were treated by a H2/N2 plasma using a 100-MHz capacitively coupled plasma etcher. The impact of ions, radicals, and vacuum ultraviolet radiation on the porous SiOCH films was investigated using in situ bulk analysis techniques such as spectroscopic ellipsometry and Fourier-transform infrared spectroscopy and ex situ film characterization techniques such as dynamic secondary ion mass spectrometry and x-ray photoelectron spectroscopy. In addition, plasma analysis including vacuum ultraviolet absorption spectroscopy was performed. The film characterization and plasma analysis show that the extraction of methyl by H radicals was enhanced by light while N radicals were responsible for inhibit the extraction of Si-CH3 bonds by forming nitride layer. The H2/N2 plasma damage mechanism is discussed based on characterization of the film and plasma diagnostics.
Hole injection in tri-arylamine containing polyfluorene co-polymer devices with molybdenum oxide contacts
Authors: Buckley Alastair , Pickup David , Yates Chris , Zhao Yi , Lidzey David
Published: April 2011

We report spectroscopic and electrical measurements to explore hole injection and conduction in devices comprising a molybdenum sub-oxide (MoOx) hole injection layers and poly[(9,9-dioctylfluorenyl-2, 7-diyl)-co-(4,4’(N-(4-sec-butylphenyl))) diphenylamine](TFB) hole transporting polymer. We report improvements in device conductivity over benchmark structures incorporating an ITO electrode and polyethylenedioxythiophene polystyrene sulfonate (PEDOT:PSS) hole injection layers and furthermore achieve injection from MoOx to TFB that is efficient even with an underlying low workfunction Al electrode. XPS spectroscopy has been used to investigate the electronic structure of the interfaces and we find discrete energy alignment regimes consistent with recent surface science studies by Tengstedt et al. [Appl. Phys. Lett. 88, 053502 (2006)], corresponding to Fermi level pinning for MoOx/TFB and vacuum level pinning in the case of Al/TFB. While the energetic alignment regime is measured to be independent of MoOx thickness, the device conductivity continuously varies with MoOx thickness; an observation that can be qualitatively explained by considering two independent charge injection mechanisms from molybdenum oxide sites having different stoicheometry.
Nonorthodox heterodyne electro-optic detection for terahertz optical systems
Authors: Darmo J. , Dietze D. , Martl M. , Unterrainer K.
Published: April 2011

An electro-optic detector of terahertz electromagnetic waves with boosted performance is presented. The detector utilizes a heterodyne detection technique to achieve orders of magnitude better responsivity compared to a standard detector setup. We prove theoretically as well as demonstrate experimentally the feasibility of this technique for electro-optic detection.
Analysis of periodic metallic nano-slits for efficient interaction of terahertz and optical waves at nano-scale dimensions
Authors: Hsieh Bing-Yu , Jarrahi Mona
Published: April 2011

We analyze the unique property of periodic arrays of subwavelength metallic slits to allow extraordinary electromagnetic transmission at multiple frequency bands. The diffraction limit in periodic arrays of subwavelength metallic slits is mitigated by excitation of surface waves which assist efficient coupling of a transverse magnetic–polarized incident electromagnetic wave into the TEM waveguide modes of the subwavelength slab waveguides formed by metallic slits. By investigating the geometry dependence of the electromagnetic guided modes supported by periodic arrays of subwavelength metallic slits, we present the design of a periodic array of metallic nanoslits which enables efficient interaction of terahertz and optical waves at nanoscale dimensions.
Influence of crystal polarity on crystal defects in GaP grown on exact Si (001)
Authors: Beyer Andreas , Németh Igor , Liebich Sven , Ohlmann Jens , Stolz Wolfgang , Volz Kerstin
Published: April 2011

For the implementation of optoelectronic devices on silicon, which could be realized by a combination of Si and direct-bandgap III/V semiconductors, a defect free nucleation layer of GaP on Si is essential. This paper summarizes the results of structural investigations carried out by transmission electron microscopy on defects, which can be observed in GaP films grown by metal organic vapor phase epitaxy on exactly oriented (001) Si substrates. Under optimized growth conditions the anti phase domains (APDs), which arise in the III/V semiconductor at the monoatomic steps on the silicon surface, show a specific typical shape. They self-annihilate on {112} planes in the GaP and can be observed in [110] cross-section, looking perpendicular to the steps on the Si surface. In contrast to that, the anti phase boundaries (APBs) lie on {110} GaP planes in the [−110] direction, parallel to the steps on the Si surface. From convergent beam electron diffraction one can show, that the GaP has Ga-polarity in the [110] direction, viewing perpendicular to the steps on the Si-surface. With the knowledge of the polarity and the shape of the APDs, we suggest a model for chemical composition of their boundaries. According to this model the APBs, which lie on {110} and {112} planes, consist of an equal amount of Ga-Ga and P-P bonds. Furthermore, when stacking faults and twins are observed, they only occur in the Ga-polar [110] GaP direction, and consequently lie on {111}A planes. With the knowledge of the structure of the defects that arise at the GaP/Si interface we suggest growth conditions and an optimum Si surface structure, which guarantee a defect-free GaP overgrowth layer after several 10 nms of III/V material, even on exact Si substrates.
The half-metallic properties and geometrical structures of cubic BaMnO3 and BaTiO3/BaMnO3 superlattice
Authors: Li N. , Yao K. L. , Sun Z. Y. , Zhu L. , Gao G. Y.
Published: April 2011

The electronic structure and electrical transport properties of the cubic perovskite (E21) oxide barium manganese (BaMnO3) and the BaMnO3/BaTiO3 superlattice are investigated by the density-functional theory in this report. The results show that the cubic BaMnO3 exhibits half-metallic properties with an integral magnetic moment of 3.000 μB per unit cell in its metastable state, while the BaTiO3/BaMnO3 superlattice also shows a stable half-metallic ground state with an integral magnetic moment of 12.000 μB per unit cell. In conclusion, we show that the construction of a BaMnO3/BaTiO3 superlattice could stabilize the cubic metastable phase of the BaMnO3 and provide a stable half-metallic material for potential applications in spintronic devices.
Tunable lens by spatially varying liquid crystal pretilt angles
Authors: Tseng Man-Chun , Fan Fan , Lee Chung-Yung , Murauski Anatoli , Chigrinov Vladimir , Kwok Hoi-Sing
Published: April 2011

We report a method of obtaining controllable spatially varying liquid crystal pretilt angles using a stacked alignment layer. The stacked alignment layer consists of nano-domains of horizontal and vertical alignment materials. The pretilt angle is controlled by varying the domain ratio of the two layers. By using photoalignment material as the top layer, the pretilt angle can be controlled by varying the UV light dosage. A spatially variable UV light beam can be used to control the pretilt angle spatially. An electrically tunable-focus liquid crystal lens is obtained using this method.
Simulations of domain evolution in morphotropic ferroelectric ceramics under electromechanical loading using an optimization-based model
Authors: Zhou X. L. , Li F. X.
Published: April 2011

In this paper, an optimization-based computational model is proposed to study the nonlinear performance and domain texture evolution in morphotropic ferroelectric ceramics composed of numerous random oriented grains, each of which contains fourteen types of domains (six are tetragonal and eight are rhombohedral). Field induced phase transformations between the tetragonal and rhombohedral domains are permissible; thus, both the in-phase and inter-phase domain switching can occur in this model. The charge screening effect in real ceramics is taken into account and thus the electric depolarization field caused by incompatible polarization vanishes. The mechanical constraint from the neighboring grains, however, cannot be neglected and is considered using the Eshelby inclusion approach. Under any prescribed electromechanical loading, the volume fraction of each domain in a grain is obtained by minimizing the sum of the potential energy and switching the related dissipation energy of the whole grain using the sequential quadratic programming optimization algorithm. Similar to the phase field model, this model also does not require the imposition of any a priori domain-switching criterion. The computational efficiency of this model is fairly high and it is feasible to study 3-D cases using numerous grains. The domain texture evolution process can also be calculated step by step and shown using the pole figures of the polar axis. Simulation results on the morphotropic lead titanate zirconate ceramics under uniaxial electromechanical loading show that with the increase of the uniaxial compression, both the D-E hysteresis loops and the butterfly curves becomes more flat and the electric coercive field becomes less distinct, which is in good agreement with existing experimental results. The calculated domain-texture evolution process indicates that when the compression is large enough, the domains have been constrained with their polar axis aligned in those planes nearly perpendicular to the compressive direction and almost cannot switch under moderate electric loading, thus leading to the more flat D-E hysteresis loops and butterfly curves.
Photoluminescence studies of (Mg, Zn)O epilayers via metalorganic vapor phase epitaxy on m-plane ZnO substrates
Authors: Liu K. , Pierce J. M. , Ali Y. S. , Krahnert A. , Adekore B. T.
Published: April 2011

Hexagonal wurtzite MgxZn1−xO intrinsic and gallium-doped epilayers were deposited on m-plane ZnO substrates by metalorganic vapor phase epitaxy. We demonstrate a linear dependence in the energy gap with increasing Mg concentration for n-type alloys 0.10 ≤ x ≤ 0.30 and for intrinsic alloys 0.20 ≤ x ≤ 0.50. We show a comparison of m-plane and c-plane MgxZn1−xO indicating a dependence of the electronic activity of Mg with crystallographic orientation. Further, we demonstrate an increase in exciton localization associated with the strong enhancement of photoluminescence intensity and reduction in the near band-edge full-width at half–maximum with increasing Mg concentration. Additionally, the thermal activation energy corresponding to the localization is considered.
Ink-jet printed thin-film transistors with carbon nanotube channels shaped in long strips
Authors: Li Jiantong , Unander Tomas , López Cabezas Ana , Shao Botao , Liu Zhiying , Feng Yi , Bernales Forsberg Esteban , Zhang Zhi-Bin , Jõgi Indrek , Gao Xindong , Boman Mats , Zheng Li-Rong , Östling Mikael , Nilsson Hans-Erik , Zhang Shi-Li
Published: April 2011

The present work reports on the development of a class of sophisticated thin-film transistors (TFTs) based on ink-jet printing of pristine single-walled carbon nanotubes (SWCNTs) for the channel formation. The transistors are manufactured on oxidized silicon wafers and flexible plastic substrates at ambient conditions. For this purpose, ink-jet printing techniques are developed with the aim of high-throughput production of SWCNT thin-film channels shaped in long strips. Stable SWCNT inks with proper fluidic characteristics are formulated by polymer addition. The present work unveils, through Monte Carlo simulations and in light of heterogeneous percolation, the underlying physics of the superiority of long-strip channels for SWCNT TFTs. It further predicts the compatibility of such a channel structure with ink-jet printing, taking into account the minimum dimensions achievable by commercially available printers. The printed devices exhibit improved electrical performance and scalability as compared to previously reported ink-jet printed SWCNT TFTs. The present work demonstrates that ink-jet printed SWCNT TFTs of long-strip channels are promising building blocks for flexible electronics.
Enhanced effect of Ce3+ ions on 2 μm emission and energy transfer properties in Yb3+/Ho3+ doped fluorophosphate glasses
Authors: Tian Ying , Xu Rongrong , Zhang Liyan , Hu Lili , Zhang Junjie
Published: April 2011

Effect of Ce3+ ions introduction on 2 μm emission properties and energy transfer mechanism in Yb3+/Ho3+-doped fluorophosphate glass has been investigated. From the measured fluorescence spectra, strong emission near 2 μm is demonstrated due to the sensitization of Yb3+ and Ce3+. Based on the absorption spectra, the Judd-Ofelt parameters and radiative properties were calculated and compared with those of other glass hosts. In addition, the energy transfer coefficient from Yb3+ to Ho3+ is 9.52 × 10−40 cm6/s in Yb3+/Ho3+/Ce3+ triply doped sample and is three times larger than that in undoped Ce3+ sample. These results suggest that this Yb3+/Ho3+/Ce3+ fluorophosphate glass with excellent thermal stability and efficient energy transfer from Yb3+ to Ho3+ is a good candidate for 2 μm laser.
Equation of state of the NaCl-B2 phase up to 304 GPa
Authors: Sakai Takeshi , Ohtani Eiji , Hirao Naohisa , Ohishi Yasuo
Published: April 2011

We compressed NaCl-B2 to 304 GPa and presented a pressure scale based on the Birch–Murnaghan and Vinet equations of state for this phase. The pressure difference between the two formulations of the equation of state was less than 2.0% within the pressure range of 50–364 GPa. The present data indicates that the uniaxial stress of the platinum used in the sample is 2.4 GPa and comparable with that of runs using a helium pressure medium. The compression curve of NaCl-B2 was expressed by the Birch–Murnaghan equation of state with fixed volume at ambient pressure, where V0 = 37.73(4.05) Å3, K = 47.00(46) GPa and K′ = 4.10(2) based upon Matsui et al.’s platinum scale.
Imaging of subsurface structures using atomic force acoustic microscopy at GHz frequencies
Authors: Hu Shuiqing , Su Chanmin , Arnold Walter
Published: April 2011

We describe a technique to image subsurface structures using atomic force acoustic microscopy operated at 1 GHz. The devices to be imaged are insonified with 1 GHz ultrasonic waves which are amplitude-modulated at a fraction or multiple frequency of cantilever contact resonance. The transmitted signals are demodulated by the nonlinear tip–surface interaction, enabling one to image defects in the device based on their ultrasonic scattering power which is determined by the ultrasonic frequency, the acoustic mismatch between the elastic properties of the host material and the defects, by their geometry, and by diffraction effects.
Microstructure and magnetic viscosity of bulk amorphous Nd60Fe20Al5Co10B5 alloy
Authors: Tan X. H. , Xu H. , Man H. , Tang Y. J. , Yang L. P. , Bai Q.
Published: April 2011

The microstructure and magnetic viscosity of bulk amorphous Nd60Fe20Al5Co10B5,prepared by suction casting the molten alloy into a copper mold under an argon atmosphere, have been investigated. The results show that clusters with size 3–5 nm are found to be embedded in the amorphous matrix of as-cast bulk amorphous Nd60Fe20Al5Co10B5 alloy. The Nd60Fe20Al5Co10B5 alloy shows hard magnetic behavior at room temperature, with an intrinsic coercivity of 360 kA/m and a remanence of 69.39 mT. The magnetic viscosity of bulk amorphous Nd60Fe20Al5Co10B5 has been investigated on the major hysteresis loop, and simple logarithmic time dependence is observed. A value for the fluctuation field of 8.24 kA/m is obtained. Analysis based on a Henkel plot is used to confirm the existence of magnetic interaction among clusters. The coercivity mechanism responsible for the hard magnetic behavior of bulk amorphous Nd60Fe20Al5Co10B5 alloy is also discussed.
Two-probe study of hot carriers in reduced graphene oxide
Authors: Ruzicka Brian A. , Kumar Nardeep , Wang Shuai , Ping Loh Kian , Zhao Hui
Published: April 2011

The energy relaxation of carriers in reduced graphene oxide thin films is studied using optical pump-probe spectroscopy with two probes of different colors. We measure the time difference between peaks of the carrier density at each probing energy by measuring a time-resolved differential transmission and find that the carrier density at the lower probing energy peaks later than that at the higher probing energy. Also, we find that the peak time for the lower probing energy shifts from about 92 to 37 fs after the higher probing energy peak as the carrier density is increased from 1.5×1012 to 3×1013/cm2, while no noticeable shift is observed in that for the higher probing energy. Assuming the carriers rapidly thermalize after excitation, this indicates that the optical phonon emission time decreases from about 50 to about 20 fs and the energy relaxation rate increases from 4 to 10 meV/fs. The observed density dependence is inconsistent with the phonon bottleneck effect.
Engineering of nitrogen-vacancy color centers in high purity diamond by ion implantation and annealing
Authors: Orwa J. O. , Santori C. , Fu K. M. C. , Gibson B. , Simpson D. , Aharonovich I. , Stacey A. , Cimmino A. , Balog P. , Markham M. , Twitchen D. , Greentree A. D. , Beausoleil R. G. , Prawer S.
Published: April 2011

The negatively-charged nitrogen-vacancy (NV) center is the most studied optical center in diamond and is very important for applications in quantum information science. Many proposals for integrating NV centers in quantum and sensing applications rely on their tailored fabrication in ultra pure host material. In this study, we use ion implantation to controllably introduce nitrogen into high purity, low nitrogen chemical vapor deposition diamond samples. The properties of the resulting NV centers are studied as a function of implantation temperature, annealing temperature, and implantation fluence. We compare the implanted NV centers with native NV centers present deep in the bulk of the as-grown samples. The results for implanted NV centers are promising but indicate, at this stage, that the deep native NV centers possess overall superior optical properties. In particular, the implanted NV centers obtained after annealing at 2000 °C under a stabilizing pressure of 8 GPa showed an ensemble linewidth of 0.17 nm compared to 0.61 nm after annealing at 1000 °C. Over the same temperature range, the ensemble NV−/NV0 ratio increased by a factor of ∼5, although this was accompanied by an overall decrease in the NV count.
Influence of the alignment of ZnO nanorod arrays on light extraction enhancement of GaN-based light-emitting diodes
Authors: Dai Kehui , Soh Chew Beng , Chua Soo Jin , Wang Lianshan , Huang Dexiu
Published: April 2011

ZnO nanorod arrays (ZNAs) were hydrothermally synthesized on the surface of patterned indium-doped tin oxide p-type contact (PIPC) of GaN-based light-emitting diodes (GaN-LEDs) for enhancing the light extraction efficiency (LEE). It was found that the alignment of the ZnO nanorod arrays in the grooves of the PIPC was poorer than these grown on the ridges of the PIPC. By comparing the light output of the GaN-LEDs with and without ZNAs grown in the grooves of PIPC, the influence of the alignment of ZNAs on the LEE of GaN-LEDs was revealed and investigated. Numerical analysis based on the finite difference of time domain (FDTD) method suggested that the poorer alignment of ZNAs grown on GaN-LEDs resulted in more energy reflected back into GaN-LEDs and lower light extraction efficiency.
Internal structure of laser supported detonation waves by two-wavelength Mach–Zehnder interferometer
Authors: Shimamura Kohei , Hatai Keigo , Kawamura Koichi , Fukui Akihiro , Fukuda Akio , Wang Bin , Yamaguchi Toshikazu , Komurasaki Kimiya , Arakawa Yoshihiro
Published: April 2011

Characteristics of the internal structure of the laser supported detonation (LSD) waves, such as the electron density ne and the electron temperature Te profiles behind the shock wave were measured using a two-wavelength Mach–Zehnder interferometer along with emission spectroscopy. A TEA CO2 laser with energy of 10 J/pulse produced explosive laser heating in atmospheric air. Results show that the peak values of ne and Te were, respectively, about 2 × 1024 m−3 and 30 000 K, during the LSD regime. The temporal variation of the laser absorption coefficient profile estimated from the measured properties reveals that the laser energy was absorbed perfectly in a thin layer behind the shock wave during the LSD regime, as predicted by Raizer’s LSD model. However, the absorption layer was much thinner than a plasma layer, the situation of which was not considered in Raizer’s model. The measured ne at the shock front was not zero while the LSD was supported, which implies that the precursor electrons exist ahead of the shock wave.
Resonance effects in photoemission from TiO2-capped Mo/Si multilayer mirrors for extreme ultraviolet applications
Authors: Faradzhev Nadir S. , Yakshinskiy Boris V. , Starodub Elena , Madey Theodore E. , Hill Shannon B. , Grantham Steven , Lucatorto Thomas B. , Yulin Sergiy , Vescovo Elio , Keister Jeffrey W.
Published: April 2011

In the unbaked vacuum systems of extreme ultraviolet (EUV) lithography steppers, oxide formation and carbon growth on Mo/Si multilayer mirrors (MLMs) are competing processes leading to reflectivity loss. A major contribution to this mirror degradation is a series of surface reactions that are thought to be driven in large part by photoemitted electrons. In this paper, we focus on the resonance effects in photoemission from Mo/Si MLMs protected by thin TiO2 cap layers. In the vicinity of the resonant energy of the mirror, the energy flux of the EUV radiation forming standing wave oscillates throughout the multilayer stack. As a result, light absorption followed by the emission of photoelectrons becomes a complex process that varies rapidly with depth and photon energy. The electron emission is characterized as a function of the EUV photon energy, the angle of incidence, and the position of the standing wave with respect to the solid/vacuum interface. In our experiments, the position of the standing wave was controlled both by deliberately varying the thickness of the Si terminating layer (of the Mo/Si stack) and by depositing C films of various thicknesses on the TiO2. The experimental data are compared with model simulations to examine the changes in photoemission yield due to the presence of carbon and to the changes in the position of the standing wave. We find that carbon deposition can have a dramatic impact on the yield and, therefore, on the rates of electron mediated reactions at the surface.
Nature of interface traps in Ge metal-insulator-semiconductor structures with GeO2 interfacial layers
Authors: Taoka Noriyuki , Mizubayashi Wataru , Morita Yukinori , Migita Shinji , Ota Hiroyuki , Takagi Shinichi
Published: April 2011

The nature of interface traps in Ge metal-insulator-semiconductor (MIS) structures with GeO2 interfacial layers have been systematically investigated at various temperatures by C-V method and the conductance method including surface potential fluctuations. The nature of interface traps was found to depend on the oxidation temperature. Furthermore, the charged center density evaluated from the magnitude of the surface potential fluctuations (which includes charged interface traps, charged slow traps, and fixed oxide charges) increases from the valence bandedge (VBE) to the conduction bandedge (CBE) of Ge in the case of high-temperature oxidation when the Fermi level moves from the VBE to the CBE. This indicates that acceptorlike traps are distributed across the Ge bandgap.
Origin of the threshold voltage shift of organic thin-film transistors under light illumination
Authors: Wasapinyokul Kamol , Milne W. I. , Chu D. P.
Published: April 2011

The apparent shift of threshold voltage of organic thin-film transistors under light illumination has been explained as a result of the superposition of a photo-generated current on the dark current overall biases. Our model has been confirmed by demonstrating that the apparent threshold voltages calculated under different illumination intensities matched perfectly with the experimental values, for two devices with different channel widths. Our model indicates that (1) there is a photo-current associated with the photo-excitation process in organic thin-film transistors and (2) the apparent threshold voltage under illumination is not the intrinsic threshold voltage of a device as measured in the dark; instead, it is monotonically shifted from the intrinsic value due to the increase in photo-current under normal laboratory conditions.
Size effect of Ruderman–Kittel–Kasuya–Yosida interaction mediated by electrons in nanoribbons
Authors: Mi Shuo , Yuan Shuo-Hong , Lyu Pin
Published: April 2011

We calculated the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction between the magnetic impurities mediated by electrons in nanoribbons. It was shown that the RKKY interaction is strongly dependent on the width of the nanoribbon and the transverse positions of the impurities. The transverse confinement of electrons is responsible for the above size effect of the RKKY interaction. It provides a potential way to control the RKKY interaction by changing nanostructure geometry.
A generalized fractional trace identity and Hamiltonian structure of the fractional soliton equation hierarchy
Authors: Yu Fajun
Published: April 2011

A generalized fractional trace identity and Hamiltonian structure of the fractional soliton equation hierarchy are presented by using the modified Riemann–Liouville derivative and exterior derivatives of fractional orders. Example of the fractional Kaup Newell (KN) soliton equation hierarchy and Hamiltonian system are considered, which is a new integrable hierarchy and possesses Hamiltonian structure.
Carbon nanotube-induced macroscopic helical twist in an achiral nematic liquid crystal
Authors: Basu Rajratan , Chen Chia-Ling , Rosenblatt Charles
Published: April 2011

An achiral nematic liquid crystal was doped with a small quantity of carbon nanotubes having a net chirality, and the mixture was found to exhibit an average mechanical twist over macroscopic dimensions. The nanotube-induced chiral pitch length P was determined as a function of the average nanotube concentration by measuring the radii of curvature of reverse twist disclination lines in 90° nematic twist cells. The results suggest that the nanotubes’ spatial concentration can vary significantly across the cell and that at high average concentration, the nanotubes undergo aggregation, resulting in an apparent saturation of P−1 at high concentrations. The macroscopic helical twisting power of the nanotubes has been estimated from the results.
Decisive role of oxygen vacancy in ferroelectric versus ferromagnetic Mn-doped BaTiO3 thin films
Authors: Shuai Yao , Zhou Shengqiang , Bürger Danilo , Reuther Helfried , Skorupa Ilona , John Varun , Helm Manfred , Schmidt Heidemarie
Published: April 2011

Single-phase perovskite 5 at. % Mn-doped and undoped polycrystalline BaTiO3 thin films have been grown under different oxygen partial pressures by pulsed laser deposition on platinum-coated sapphire substrates. Ferroelectricity is only observed for the Mn-doped and undoped BaTiO3 thin films grown under relatively high oxygen partial pressure. Compared to undoped BaTiO3, Mn-doped BaTiO3 reveals a low leakage current, increased dielectric loss, and a decreased dielectric constant. Ferromagnetism is seen on Mn-doped BaTiO3 thin films prepared under low oxygen partial pressure and is attributed to the formation of bound magnetic polarons (BMPs). This BMP formation is enhanced by oxygen vacancies. The present work confirms a theoretical work from C. Ederer and N. Spaldin on ferroelectric perovskites [Nature Mat. 3, 849 (2004)] that shows that the existence of ferroelectricity is incompatible with the existence of a spontaneous magnetization in Mn-doped BaTiO3 thin films.
High-field Overhauser dynamic nuclear polarization in silicon below the metal–insulator transition
Authors: Dementyev Anatoly E. , Cory David G. , Ramanathan Chandrasekhar
Published: April 2011

Single crystal silicon is an excellent system to explore dynamic nuclear polarization (DNP), as it exhibits a continuum of properties from metallic to insulating as a function of doping concentration and temperature. At low doping concentrations DNP has been observed to occur via the solid effect, while at very high-doping concentrations an Overhauser mechanism is responsible. Here we report the hyperpolarization of 29Si in n-doped silicon crystals, with doping concentrations in the range of (1–3) × 1017 cm−3. In this regime exchange interactions between donors become extremely important. The sign of the enhancement in our experiments and its frequency dependence suggest that the 29Si spins are directly polarized by donor electrons via an Overhauser mechanism within exchange-coupled donor clusters. The exchange interaction between donors only needs to be larger than the silicon hyperfine interaction (typically much smaller than the donor hyperfine coupling) to enable this Overhauser mechanism. Nuclear polarization enhancement is observed for a range of donor clusters in which the exchange energy is comparable to the donor hyperfine interaction. The DNP dynamics are characterized by a single exponential time constant that depends on the microwave power, indicating that the Overhauser mechanism is a rate-limiting step. Since only about 2% of the silicon nuclei are located within 1 Bohr radius of the donor electron, nuclear spin diffusion is important in transferring the polarization to all the spins. However, the spin-diffusion time is much shorter than the Overhauser time due to the relatively weak silicon hyperfine coupling strength. In a 2.35 T magnetic field at 1.1 K, we observed a DNP enhancement of 244 ± 84 resulting in a silicon polarization of 10.4 ± 3.4% following 2 h of microwave irradiation.
Pulsatile flow past an oscillating cylinder
Authors: Qamar Adnan , Seda Robinson , Bull Joseph L.
Published: April 2011

A fundamental study to characterize the flow around an oscillating cylinder in a pulsatile flow environment is investigated. This work is motivated by a new proposed design of the total artificial lung (TAL), which is envisioned to provide better gas exchange. The Navier–Stokes computations in a moving frame of reference were performed to compute the dynamic flow field surrounding the cylinder. Cylinder oscillations and pulsatile free-stream velocity were represented by two sinusoidal waves with amplitudes A and B and frequencies ωc and ω, respectively. The Keulegan–Carpenter number (Kc=Uo/Dωc) was used to describe the frequency of the oscillating cylinder while the pulsatile free-stream velocity was fixed by imposing ω/Kc=1 for all cases investigated. The parameters of interest and their values were amplitude (0.5D<A<D), the Keulegan–Carpenter number (0.33<Kc<1), and the Reynolds number (5<Re<20) corresponding to operating conditions of the TAL. It was observed that an increase in amplitude and a decrease in Kc are associated with an increase in vorticity (up to 246%) for every Re suggesting that mixing could be enhanced by the proposed TAL design. The drag coefficient was found to decrease for higher amplitudes and lower Kc for all cases investigated. In some cases the drag coefficient values were found to be lower than the stationary cylinder values (A=0.5, Kc=0.3, and Re=10 and 20). A lock-in phenomenon (cylinder oscillating frequency matched the vortex shedding frequency) was found when Kc=1 for all cases. This lock-in condition was attributed to be the cause of the rise in drag observed in that operating regime. For optimal performance of the modified TAL design it is recommended to operate the device at higher fiber oscillation amplitudes and lower Kc (avoiding the lock-in regime).
Alfvén cascades with downward frequency sweeping
Authors: Marchenko V. S. , Reznik S. N.
Published: April 2011

It is suggested that relatively rare, but challenging for the existing theory Alfvén cascades with downward frequency sweeping are actually the infernal Alfvén eigenmodes (IAEs). Such modes exist in discharges with flat or weakly reversed q-profile in the broad central region, when the value of the safety factor in this region is slightly above the integer or low-order rational. Similar to the toroidal Alfvén eigenmode, but in contrast to the “conventional” Alfvén cascade with upward frequency sweeping, the spectrum of IAE is almost degenerate with respect to the mode numbers. Both features mentioned above are consistent with experimental observations.
Numerical study on the shape oscillation of an encapsulated microbubble in ultrasound field
Authors: Liu Yunqiao , Sugiyama Kazuyasu , Takagi Shu , Matsumoto Yoichiro
Published: April 2011

The shape oscillation of an encapsulated microbubble in an ultrasound field is numerically investigated. To predict the nonlinear process, the continuity equation and the Navier–Stokes equation are directly solved by means of a boundary-fitted finite-volume method on an orthogonal curvilinear coordinate system. The mechanics of neo-Hookean membrane is incorporated into the dynamic equilibrium at the bubble surface. The numerical results show that the membrane raises the natural frequency of an encapsulated bubble especially for small bubble, whereas this effect is attenuated as the initial bubble size grows. For a small encapsulated bubble of which the natural frequency is sufficiently higher than the driving frequency, the oscillation is stable, namely, the oscillatory amplitude is small; besides, the radial mode and shape modes are out of resonance so that no deformation emerges. As the bubble becomes larger, the natural frequencies of encapsulated and gas bubbles get closer, leading to the less apparent difference in oscillatory amplitude between them. Furthermore, shape modes of an encapsulated bubble are prone to be induced when twice of the higher-order natural frequency is approximately equal to the frequency of radial mode particularly when the bubble is at radial resonance for which the large-amplitude pulsation enhances the compressive stress developing in the membrane. In contrast, the shape oscillation is less likely to occur for a gas bubble with micrometer size since the surface tension suppresses the developments of nonspherical shape modes.
Optical trapping of synaptic vesicles in neurons
Authors: Hosokawa Chie , Kudoh Suguru N. , Kiyohara Ai , Taguchi Takahisa
Published: April 2011

We demonstrate intracellular manipulation of synaptic vesicles in living neurons by optical trapping. When an infrared trapping laser is focused on synapses of a neuronal cell labeled with a fluorescent endocytic marker, fluorescence is observed at the focal spot. The fluorescence spectrum is attributed to fluorescent dye in the synaptic vesicles, indicating excitation by two-photon absorption of the trapping laser. The fluorescence intensity increases gradually within ∼100 s of laser irradiation, suggesting that trapping force causes vesicles assembly at the focus. Our method can be applied to manipulate synaptic transmission of a particular neuron in a neuronal network.
Promising thermoelectric properties in AgxMo9Se11 compounds (3.4≤x≤3.9)
Authors: Zhou Tong , Lenoir Bertrand , Colin Malika , Dauscher Anne , Al Orabi Rabih Al Rahal , Gougeon Patrick , Potel Michel , Guilmeau Emmanuel
Published: April 2011

Polycrystalline Mo9 cluster chalcogenides AgxMo9Se11 (3.4≤x≤3.9) have been prepared by powder metallurgy techniques, sintered by spark plasma sintering and characterized by x-ray diffraction. Their thermoelectric properties (electrical resistivity, thermopower, thermal conductivity) have been determined in the 300–800 K temperature range. The AgxMo9Se11 compounds show p-type conduction characteristics. The outstanding low lattice thermal conductivities give rise to a rather high value of the dimensionless thermoelectric figure of merit ZT of ∼0.65 at 800 K for x=3.8–3.9, making this family of materials particularly promising for thermoelectric power generation applications.
Note: Discharging fused silica test masses with ionized nitrogen
Authors: Ugolini D. , Funk Q. , Amen T.
Published: April 2011

We have developed a technique for discharging fused silica test masses in a gravitational-wave interferometer with nitrogen ionized by an electron beam. The electrons are produced from a heated filament by thermionic emission in a low-pressure region to avoid contamination and burnout. Some electrons then pass through a small aperture and ionize nitrogen in a higher-pressure region, and this ionized gas is pumped across the test mass surface, neutralizing both polarities of charge. The discharge rate varies exponentially with charge density and filament current, quadratically with filament potential, and has an optimal working pressure of ∼8 mT. Adapting the technique to larger test mass chambers is also discussed.
Quadratic algebra approach to relativistic quantum Smorodinsky–Winternitz systems
Authors: Marquette Ian
Published: April 2011

There exists a relation between the Klein–Gordon and the Dirac equations with scalar and vector potentials of equal magnitude and the Schrödinger equation. We obtain the relativistic energy spectrum for the four relativistic quantum Smorodinsky–Winternitz systems from their quasi-Hamiltonian and the quadratic algebras studied by Daskaloyannis in the nonrelativistic context. We also apply the quadratic algebra approach directly to the initial Dirac equation for these four systems and show that the quadratic algebras obtained are the same than those obtained from the quasi-Hamiltonians. We point out how results obtained in context of quantum superintegrable systems and their polynomial algebras can be applied to the quantum relativistic case.