bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoemission yield and the electron escape depth determination in metal–oxide–semiconductor structures on N+-type and P+-type silicon substrates
Authors: Przewlocki H. M. , Brzezinska D. , Engstrom O.
Published: June 2012

This article gives a quantitative analysis of electron photoemission yield from N+-type and P+-type substrates of MOS structures. Based on this analysis, a method is presented to estimate both the scattering length, ℓ, of electrons in the image force potential well and of photoelectron escape depth, xesc, from the semiconductor substrate. This method was used to estimate the scattering length and the escape depth from the substrates of Al-SiO2-Si (N+-type and P+-type) structures. It was found that for N+-type substrate structures the scattering in the image force potential well has a dominating influence on the photoemission yield while for P+-type substrate structures both the scattering in the image force potential well and the photoemission from the subsurface regions of the photoemitter play important roles. It was found that the scattering length in the image force potential well was equal to ℓ = 6.7–6.9 nm for structures on both N+ and P+ substrates, produced in the same processing conditions. For structures on P+ substrates, the escape depth was found to be equal to xesc = 8–9 nm. The scattering length, ℓ, determined in this study is considerably larger than the one reported previously (ℓ = 3.4 nm) for similar MOS structures. The escape depth xesc determined in this study is also considerably larger than the escape depth determined previously (xesc = 1.2–2.5 nm) for the external photoemission from uncovered silicon surfaces into vacuum.
Phase transition in BCx system under high-pressure and high-temperature: Synthesis of cubic dense BC3 nanostructured phase
Authors: Zinin P. V. , Ming L. C. , Ishii H. A. , Jia R. , Acosta T. , Hellebrand E.
Published: June 2012

We synthesized a cubic BC3 (c-BC3) phase, by direct transformation from graphitic phases at a pressure of 39 GPa and temperature of 2200 K in a laser-heated diamond anvil cell. A combination of x-ray diffraction, electron diffraction, transmission electron microscopy (TEM) imaging, and electron energy loss spectroscopy (EELS) measurements lead us to conclude that the obtained phase is hetero-nano-diamond, c-BC3. High-resolution TEM imaging of the c-BC3 specimen recovered at ambient conditions demonstrates that the c-BC3 is a single, uniform, nanocrystalline phase with a grain size of about 3–5 nm. The EELS measurements show that the atoms inside the cubic structure are bonded by sp3 bonds. The zero-pressure lattice parameter of the c-BC3 calculated from diffraction peaks was found to be a = 3.589 ± 0.007 Å. The composition of the c-BC3 is determined from EELS measurements. The ratio of carbon to boron, C/B, is approximately 3 (2.8 ± 0.7).
Photofragmentations, state interactions, and energetics of Rydberg and ion-pair states: Two-dimensional resonance enhanced multiphoton ionization of HBr via singlet-, triplet-, Ω = 0 and 2 states
Authors: Long Jingming , Hróðmarsson Helgi Rafn , Wang Huasheng , Kvaran Ágúst
Published: June 2012

Mass spectra were recorded for one-colour resonance enhanced multiphoton ionization (REMPI) of HiBr (i = 79, 81) for the two-photon resonance excitation region 79 040–80 300 cm−1 to obtain two-dimensional REMPI data. The data were analysed in terms of rotational line positions, intensities, and line-widths. Quantitative analysis of the data relevant to near-resonance interactions between the F1Δ2(v′ = 1) and V1Σ+(v′ = m + 7) states gives interaction strengths, fractional state mixing, and parameters relevant to dissociation of the F state. Qualitative analysis further reveals the nature of state interactions between ion-pair states and the E1Σ+ (v′ = 1) and H1Σ+(v′ = 0) Rydberg states in terms of relative strengths and J′ dependences. Large variety in line-widths, depending on electronic states and J′ quantum numbers, is indicative of number of different predissociation channels. The relationship between line-widths, line-shifts, and signal intensities reveals dissociation mechanisms involving ion-pair to Rydberg state interactions prior to direct or indirect predissociations of Rydberg states. Quantum interference effects are found to be important. Moreover, observed bromine atom (2 + 1) REMPI signals support the importance of Rydberg state predissociation channels. A band system, not previously observed in REMPI, was observed and assigned to the k3Π0(v′ = 0) ←← X transition with band origin 80 038 cm−1 and rotational parameter $B_{v^\prime } = 7.238\;{\rm cm}^{ - 1}$Bv′=7.238 cm −1.
Electronic transport properties on transition-metal terminated zigzag graphene nanoribbons
Authors: Cao Can , Chen Ling-Na , Long Meng-Qiu , Huang Wei-Rong , Xu Hui
Published: June 2012

By using non-equilibrium Green’s functions in combination with the density-functional theory, we investigate the spin transport properties of molecular junctions based on 3d transition terminated zigzag graphene nanoribbons. The results show that the electronic transport properties are strongly depending on the type of terminated atom at the edge of ribbon. The currents of spin-up and spin-down display different behaviors, and the spin-filter effects can be observed. These unconventional doping effects could be used to design novel nanospintronics devices.
Routh reduction and the class of magnetic Lagrangian systems
Authors: Langerock B. , Andrés E. García-Toraño , Cantrijn F.
Published: June 2012

In this paper, some new aspects related to Routh reduction of Lagrangian systems with symmetry are discussed. The main result of this paper is the introduction of a new concept of transformation that is applicable to systems obtained after Routh reduction of Lagrangian systems with symmetry, so-called magnetic Lagrangian systems. We use these transformations in order to show that, under suitable conditions, the reduction with respect to a (full) semi-direct product group is equivalent to the reduction with respect to an Abelian normal subgroup. The results in this paper are closely related to the more general theory of Routh reduction by stages.
Degradation of AlGaN/GaN high electron mobility transistors related to hot electrons
Authors: Meneghini Matteo , Stocco Antonio , Silvestri Riccardo , Meneghesso Gaudenzio , Zanoni Enrico
Published: June 2012

This paper reports on an extensive analysis of the degradation of AlGaN/GaN high electron mobility transistors (HEMTs) submitted to on-state and off-state stresses. The results of this study indicate that: (i) the analyzed devices do not show any degradation when submitted to off-state stress tests up to 100 V; (ii) during on-state stress, devices show a significant decrease in drain current and in the electroluminescence (EL) signal; (iii) degradation rate is strongly dependent on the intensity of the EL signal measured during stress on the devices, which is related to the concentration of hot electrons in the channel. Based on the experimental evidence collected within this paper, the on-state degradation of HEMTs is ascribed to the trapping of negative charge in the gate-drain access region, triggered by hot electrons. By considering the intensity of the EL signal as a measure of the stress acceleration factor, we have derived an acceleration law for the hot-electron induced degradation.
A note on the Liouvillian integrability and the qualitative properties of the mass rate equation for black holes
Authors: Giné Jaume , Peralta-Salas Daniel
Published: June 2012

In this paper, we study the qualitative properties of the mass rate equation for black holes introduced by Bean and Magueijo. These authors claimed that this equation does not admit solutions which can be expressed in terms of elementary functions (or quadratures of elementary functions). We provide a proof of this claim by showing that an associated planar polynomial system is not Liouville integrable and has no (nontrivial) invariant algebraic curves. We also describe the qualitative phase portrait of this system showing that the black holes evaporate in finite time or they grow indefinitely, depending on the initial mass.
Graphene folds by femtosecond laser ablation
Authors: Yoo Jae-Hyuck , Bin In Jung , Bok Park Jong , Jeon Hojeong , Grigoropoulos Costas P.
Published: June 2012

We report the production of graphene folds induced by femtosecond laser ablation. A single laser pulse irradiation on graphene produced an ablated spot featuring in its proximity circumferentially periodic graphene folds. The graphene fold structure was constructed through folding of a single layer graphene segment. We investigated the laser fluence effect on the graphene fold structure. We also performed ablation on suspended graphene and verified that interaction with the underlying substrate is required for the formation of graphene folds. We expect this one-step folding method may provide a controlled process to explore properties of graphene folds.
Frequency dispersion in III-V metal-oxide-semiconductor capacitors
Authors: Stemmer Susanne , Chobpattana Varistha , Rajan Siddharth
Published: June 2012

A recombination-controlled tunneling model is used to explain the strong frequency dispersion seen in the accumulation capacitance and conductance of dielectric/n-In0.53Ga0.47As metal-oxide-semiconductor capacitors. In this model, the parallel conductance is large when, at positive gate biases, the metal Fermi level lines up with a large density of interface states in the In0.53Ga0.47As band gap. It is shown that the model explains in a semi-quantitative manner the experimentally observed capacitor characteristics, including a peak in parallel conductance/frequency (Gp/ω) versus log frequency curves at positive gate bias and the dependence of the frequency dispersion on the dielectric thickness.
Parameterisation of injection-dependent lifetime measurements in semiconductors in terms of Shockley-Read-Hall statistics: An application to oxide precipitates in silicon
Authors: Murphy J. D. , Bothe K. , Krain R. , Voronkov V. V. , Falster R. J.
Published: June 2012

Injection-dependent minority carrier lifetime measurements are a valuable characterisation method for semiconductor materials, particularly those for photovoltaic applications. For a sample containing defects which obey Shockley-Read-Hall statistics, it is possible to use such measurements to determine (i) the location of energy levels within the band-gap and (ii) the ratios of the capture coefficients for electrons and holes. In this paper, we discuss a convenient methodology for determining these parameters from lifetime data. Minority carrier lifetime is expressed as a linear function of the ratio of the total electron concentration to the total hole concentration for p-type (or vice versa for n-type) material. When this is plotted on linear scales, a single-level Shockley-Read-Hall centre manifests itself as a straight line. The gradient and intercepts of such a plot can be used to determine recombination parameters. The formulation is particularly instructive when multiple states are recombination-active in a sample. To illustrate this, we consider oxide precipitates in silicon as a case study and analyse lifetime data for a wide variety of p-type and n-type samples as a function of temperature. We fit the data using both a single two-level defect and two independent single-level defects and find the latter can fit the lifetime curves in all cases studied. The first defect is at EV + 0.22 eV and has a capture coefficient for electrons ∼157 times greater than that for holes at room temperature. The second defect is at EC − 0.08 eV and has a capture coefficient for holes ∼1200 times greater than that for electrons at room temperature. We find that the presence of dislocations and stacking faults around the precipitates acts to increase the density of both states without introducing new levels. Using the analysis method described, we present a parameterisation of the minority carrier lifetime in silicon containing oxide precipitates.
Ultrafast carrier and coherent phonon dynamics in semi-insulated and n-type 4H-SiC
Authors: Kato Keiko , Oguri Katsuya , Ishizawa Atsushi , Nakano Hidetoshi , Sogawa Tetsuomi
Published: June 2012

We investigated ultrafast carrier and phonon dynamics in semi-insulated (SI) and n-type 4H-SiC using time-resolved reflectivity measurements. In the n-type 4H-SiC, carriers are excited by an inter-conduction band transition, and thermalized by electron-electron scattering within 20 fs. We observed coherent phonons of folded phonon modes, which become Raman active as a result of the zone folding, and those of A1-symmetry longitudinal optical (A1-LO) phonon mode. In the n-type SiC, the A1-LO coherent phonon forms a coupled mode with a plasmon, resulting in an asymmetrically broadened Fourier transform spectrum. The polarization dependence and the sine-type initial phase indicate that the impulsive stimulated Raman scattering is the mechanism generating coherent phonons of E2-symmetry transverse optical and A1-LO modes in both the SI and n-type 4H-SiC.
Sound propagation in periodic urban areas
Authors: Molerón Miguel , Félix Simon , Pagneux Vincent , Richoux Olivier
Published: June 2012

This paper presents an experimental and numerical study of low frequency sound propagation in regular urban areas, under the assumption of a periodic distribution of buildings. Although the radiation losses above the urban canyons are generally significant, our results show that the effects of the periodicity still occur. Band diagrams are notably characterized, both numerically and experimentally, to investigate the effect of the radiation above the periodic structure. The problem is tackled using a coupled modal-finite elements method. The main idea is to turn the original unbounded domain into an equivalent waveguiding structure, with PML bounding the originally open region. The experimental study is performed in a scale model of urban area. Numerical and experimental results on both the band diagrams and the wavefield propagating through the lattice are in good agreement.
Vector control of induced magnetic anisotropy using an in situ quadrupole electromagnet in ultrahigh vacuum sputtering
Authors: Cheng Cheng , Sturcken Noah , Shepard Kenneth , Bailey William E.
Published: June 2012

We demonstrate the incorporation of a quadrupole electromagnet into an ultrahigh vacuum sputtering system for the vector control of induced magnetic anisotropy in magnetic thin-film heterostructures. A stationary quadrupole electromagnet is used to generate a magnetic field, which rotates synchronously with the physical axes of the substrate in situ during sputtering. An arbitrary anisotropy direction can be set for successive ferromagnetic layers by adjusting the phase difference of substrate and field rotation. The ability to rotate the substrate during deposition and change anisotropy without breaking vacuum enables the deposition of magnetically soft heterostructures with arbitrary in-plane anisotropy axes.
Broad photoelectron spectrum and lowered electron affinity due to hydrogen in ZnOH: A joint experimental and theoretical study
Authors: Iordanov I. , Gunaratne K. D. D. , Harmon C. L. , Sofo J. O. , Castleman A. W.
Published: June 2012

We report a combined experimental and theoretical photoelectron spectroscopy study of ZnOH−. We find that the electron binding energy spectrum of ZnOH− reveals a broad and featureless peak between 1.4 and 2.4 eV in energy. The vertical detachment energy (VDE) of ZnOH− is determined to be 1.78 eV, which is lower than the 2.08 eV VDE of ZnO−. Our theoretical calculations match the VDE of ZnOH− accurately, but we find that the broadness of the peak cannot be explained by rotational or vibrational state excitation. The broadness of this peak is in strong contrast to the narrow and easily understood first peak of the ZnO spectrum, which features a well-resolved vibrational progression that can be readily explained by calculating the Franck-Condon transition factors. This study provides spectroscopic evidence of the effect of hydrogen on diatomic ZnO.
Simple model for the simulation of peptide folding and aggregation with different sequences
Authors: Enciso Marta , Rey Antonio
Published: June 2012

We present a coarse-grained interaction potential that, using just one single interaction bead per amino acid and only realistic interactions, can reproduce the most representative features of peptide folding. We combine a simple hydrogen bond potential, recently developed in our group, with a reduced alphabet for the amino acid sequence, which takes into account hydrophobic interactions. The sequence does not pose any additional influence in the torsional properties of the chain, as it often appears in previously published work. Our model is studied in equilibrium simulations at different temperatures and concentrations. At low concentrations the effect of hydrophobic interactions is determinant, as α-helices (isolated or in bundles) or β-sheets are the most populated conformations, depending on the simulated sequence. On the other hand, an increase in concentration translates into a higher influence of the hydrogen bond interactions, which mostly favor the formation of β-type aggregates, in agreement with experimental observations. These aggregates, however, still keep some distinct characteristics for different sequences.
Fast crystal nucleation induced by surface oxidation in Si-doped GeTe amorphous thin film
Authors: Saito Yuta , Sutou Yuji , Koike Junichi
Published: June 2012

Fast crystallization in the phase change materials (PCMs) used for optical and electrical phase change memory improves their data recording rate. In the present work, it was found that the preferential surface oxidation of Si shortens the nucleation time of Ge46.55Te46.55Si6.9 amorphous films. The nucleation time of a surface-oxidized film was approximately 20% faster than that of a non-oxidized film. This was due to the formation of inhomogeneous nucleation sites at the film surface. These results suggest that preferential surface oxidation of PCM is an effective method to enhance the data recording rate of phase change memory devices.
Origin of magneto-optic enhancement in CoPt alloys and Co/Pt multilayers
Authors: Višňovský Štefan , Jakubisová Lišková Eva , Nývlt Miroslav , Krishnan Ramanathan
Published: June 2012

The magneto-optical (MO) Kerr effect in CosPt1−s alloys follows from the permittivity tensor component ɛxy times the function v(N) of the refractive index, N. Re(ɛxy) displays a maximum at the photon energy ℏω ≈ 1 eV, |v[N(ℏω)]| increases 30 × from 1 to 6 eV. Re(ɛxy) creates a low ℏω peak in polar Kerr rotation (PKR). The PKR peak above 3.6 eV results from v[N(ℏω)] that modulates Re(ɛxy). The Re(ɛxy) maximum reduces with s while |v[N(ℏω)]| above 4 eV becomes steeper. PKR peak at ℏω > 3.6 eV originate mostly from v(N). The mechanism affects MO effects in other ferromagnetic metals and alloys.
Sub-femtosecond absolute timing jitter with a 10 GHz hybrid photonic-microwave oscillator
Authors: Fortier T. M. , Nelson C. W. , Hati A. , Quinlan F. , Taylor J. , Jiang H. , Chou C. W. , Rosenband T. , Lemke N. , Ludlow A. , Howe D. , Oates C. W. , Diddams S. A.
Published: June 2012

We present an optical-electronic approach to generating microwave signals with high spectral purity. By circumventing shot noise and operating near fundamental thermal limits, we demonstrate 10 GHz signals with an absolute timing jitter for a single hybrid oscillator of 420 attoseconds (1 Hz–5 GHz).
GaN-based light-emitting diodes on origami substrates
Authors: Jung Younghun , Wang Xiaotie , Kim Jiwan , Hyun Kim Sung , Ren Fan , Pearton Stephen J. , Kim Jihyun
Published: June 2012

GaN-based light-emitting diodes (LEDs) were transferred to paper substrates after a laser lift-off (LLO) process with an ArF excimer laser system (λ = 193 nm) to remove the sapphire substrate and produce freestanding blue LED templates. The threshold voltage (∼2.7 V), current-voltage characteristics, and peak emission wavelength (442 nm) were not changed after the paper substrate was subsequently wrinkled. We were able to demonstrate transfers to both planar and folded (origami) paper structures, showing the promise of the LLO process for transferring LEDs to arbitrary surfaces.
Interfacial layer growth condition dependent carrier transport mechanisms in HfO2/SiO2 gate stacks
Authors: Sahoo S. K. , Misra D.
Published: June 2012

The temperature and field dependent leakage current in HfO2/SiO2 gate stack for in situ steam grown and chemical interfacial layers (ILs) are studied in the temperature range of 20 °C to 105 °C. Poole-Frenkel mechanism in high field whereas Ohmic conduction in low field region are dominant for both devices. Leakage current decreases whereas both trap energy level (ϕt) and activation energy (Ea) increase for chemically grown IL devices. The trap level energy, (ϕt) ∼ 0.2 eV, indicates that doubly charged oxygen vacancies (V2−) are the active electron traps which contribute to the leakage current in these gate stacks.
High temperature single photon emitter monolithically integrated on silicon
Authors: Cavigli L. , Bietti S. , Accanto N. , Minari S. , Abbarchi M. , Isella G. , Frigeri C. , Vinattieri A. , Gurioli M. , Sanguinetti S.
Published: June 2012

We report on triggered single photon emission from GaAs quantum dots, grown on Si substrates and obtained by means of fabrication protocols compatible with the monolithic integration on Si based microelectronics. Very bright and sharp individual exciton lines are resolved in the spectra and can be followed up to 150 K. The nature of quantum emitters of single photon pulses can be measured up to liquid nitrogen temperature by Hanbury Brown and Twiss interferometric correlations.
Symmetry-dependent transport properties and magnetoresistance in zigzag silicene nanoribbons
Authors: Kang Jun , Wu Fengmin , Li Jingbo
Published: June 2012

First principles calculations are performed to study the transport properties of zigzag silicene nanoribbons (ZSiNRs). ZSiNRs show symmetry-dependent transport properties similar to those of zigzag graphene nanoribbons, although the σ mirror plane is absent. Even-N and odd-N ZSiNRs have very different current-voltage relationships, which can be attributed to the different parity of their π and π* bands under c2 symmetry operation with respect to the center axis. Moreover, magnetoresistance effect is observed in even-N ZSiNRs, and the order can reach 1 000 000%. On the basis of these interesting transport properties, ZSiNR-based logic devices, such as not, and, and or gates, are proposed.
Spatio-temporal analysis of tamoxifen-induced bystander effects in breast cancer cells using microfluidics
Authors: Rios-Mondragon Ivan , Wang Xiang , Gerdes Hans-Hermann
Published: June 2012

The bystander effect in cancer therapy is the inhibition or killing of tumor cells that are adjacent to those directly affected by the agent used for treatment. In the case of chemotherapy, little is known as to how much and by which mechanisms bystander effects contribute to the elimination of tumor cells. This is mainly due to the difficulty to distinguish between targeted and bystander cells since both are exposed to the pharmaceutical compound. We here studied the interaction of tamoxifen-treated human breast cancer MCF-7 cells with their neighboring counterparts by exploiting laminar flow patterning in a microfluidic chip to ensure selective drug delivery. The spatio-temporal evolution of the bystander response in non-targeted cells was analyzed by measuring the mitochondrial membrane potential under conditions of free diffusion. Our data show that the bystander response is detectable as early as 1 hour after drug treatment and reached effective distances of at least 2.8 mm. Furthermore, the bystander effect was merely dependent on diffusible factors rather than cell contact-dependent signaling. Taken together, our study illustrates that this microfluidic approach is a promising tool for screening and optimization of putative chemotherapeutic drugs to maximize the bystander response in cancer therapy.
Note: A monolithic filter cavity for experiments in quantum optics
Authors: Palittapongarnpim Pantita , MacRae Andrew , Lvovsky A. I.
Published: June 2012

By applying a high-reflectivity dielectric coating on both sides of a commercial plano-convex lens, we produce a stable monolithic Fabry-Perot cavity suitable for use as a narrow band filter in quantum optics experiments. The resonant frequency is selected by means of thermal expansion. Owing to the long term mechanical stability, no optical locking techniques are required. We characterize the cavity performance as an optical filter, obtaining a 45dB suppression of unwanted modes while maintaining a transmission of 60%.
On the best bandstructure for thermoelectric performance: A Landauer perspective
Authors: Jeong Changwook , Kim Raseong , Lundstrom Mark S.
Published: June 2012

The question of what bandstructure produces the best thermoelectric device performance is revisited from a Landauer perspective. We find that a delta-function transport distribution function (TDF) results in operation at the Mahan-Sofo upper limit for the thermoelectric figure-of-merit, ZT. We show, however, the Mahan-Sofo upper limit itself depends on the bandwidth (BW) of the dispersion, and therefore, a finite BW dispersion produces a higher ZT when the lattice thermal conductivity is finite. Including a realistic model for scattering profoundly changes the results. Instead of a narrow band, we find that a broad BW is best. The prospects of increasing ZT through high valley degeneracy or by distorting the density-of-states are discussed from a Landauer perspective. We conclude that while there is no simple answer to the question of what bandstructure produces the best thermoelectric performance, the important considerations can be expressed in terms of three parameters derived from the bandstructure—the density-of-states, D(E), the number of channels, M(E), and the mean-free-path, λ(E).
Graphene sheets embedded carbon film prepared by electron irradiation in electron cyclotron resonance plasma
Authors: Wang Chao , Diao Dongfeng , Fan Xue , Chen Cheng
Published: June 2012

We used a low energy electron irradiation technique to prepare graphene sheets embedded carbon (GSEC) film based on electron cyclotron resonance plasma. The particular π electronic structure of the GSEC film similar to bilayer graphene was verified by Raman spectra 2D band analyzing. The phase transition from amorphous carbon to GSEC was initiated when electron irradiation energy reached 40 eV, and the growth mechanism of GSEC was interpreted as inelastic scattering of low energy electrons. This finding indicates that the GSEC film obtained by low energy electron irradiation can be excepted for widely applications with outstanding electric properties.
Biofunctionalized AlGaN/GaN high electron mobility transistor for DNA hybridization detection
Authors: Thapa Resham , Alur Siddharth , Kim Kyusang , Tong Fei , Sharma Yogesh , Kim Moonil , Ahyi Claude , Dai Jing , Wook Hong Jong , Bozack Michael , Williams John , Son Ahjeong , Dabiran Amir , Park Minseo
Published: June 2012

Label-free electrical detection of deoxyribonucleic acid (DNA) hybridization was demonstrated using an AlGaN/GaN high electron mobility transistor (HEMT) based transducer with a biofunctionalized gate. The HEMT DNA sensor employed the immobilization of amine-modified single strand DNA on the self-assembled monolayers of 11-mercaptoundecanoic acid. The sensor exhibited a substantial current drop upon introduction of complimentary DNA to the gate well, which is a clear indication of the hybridization. The application of 3 base-pair mismatched target DNA showed little change in output current characteristics of the transistor. Therefore, it can be concluded that our DNA sensor is highly specific to DNA sequences.
Bandwidth enhancement and optical performances of multiple quantum well transistor lasers
Authors: Taghavi Iman , Kaatuzian Hassan , Leburton Jean-Pierre
Published: June 2012

A detailed rate-equation-based model is developed to study carrier transport effects on optical and electrical characteristics of the multiple quantum well heterojunction bipolar transistor laser in time-domain. Simulation results extracted using numerical techniques in small-signal regime predict significant enhancement in device optical bandwidth when multiple quantum wells are used. Cavity length and base width are also modified to optimize the optoelectronic performances of the device. An optical bandwidth of ≈60 GHz is achieved in the case of 5 quantum wells each of 70 Å widths and a cavity length of 200 μm.
Mechanism of the enhancement of mid-infrared emission from GeS2-Ga2S3 chalcogenide glass-ceramics doped with Tm3+
Authors: Lin Changgui , Dai Shixun , Liu Chao , Song Bao’an , Xu Yinsheng , Chen Feifei , Heo Jong
Published: June 2012

We report the fabrication and characterization of 80GeS2·20Ga2S3:0.5Tm2S3 chalcogenide glass-ceramics. A careful thermal process has led to the formation of ∼50 nm Ga2S3 nanocrystals. By monitoring the 3H5→3F4 Tm3+ transition, an almost fivefold increase of in the intensity and ∼76 μs prolongation in the lifetime of mid-infrared fluorescence at 3.8 μm have been observed after crystallization. Element mapping evidenced that enhancement in the mid-infrared emission intensity was related to the formation of Ge-rich region in the glass-ceramics, consistent with spectroscopic results from glasses with different levels of GeS2 content and β-GeS2 precipitation.
Study on spin-splitting phenomena in the band structure of GdN
Authors: Vidyasagar R. , Kitayama S. , Yoshitomi H. , Kita T. , Sakurai T. , Ohta H.
Published: June 2012

An exceptional kind of spin splitting in the band structure of AlN/GdN/AlN double heterostructures has been studied by employing temperature-dependent spectroscopy. This spin splitting can be attributed to both the band-gap shrink and the difference between minority and majority band energies in GdN below the Curie point; these results have been established by evaluating the optical band gaps at the X-point. The temperature-dependent magnetization measurements that provide direct evidence of the magnetic ordering below 32 K and it is described by long-range spin correlation in GdN.
Soft x-ray backlighting of direct-drive implosions using a spherical crystal imager on OMEGA
Authors: Stoeckl C. , Delettrez J. A. , Epstein R. , Fiksel G. , Guy D. , Hohenberger M. , Jungquist R. K. , Mileham C. , Nilson P. M. , Sangster T. C. , Shoup M. J. , Theobald W.
Published: June 2012

Using a spherically bent quartz crystal for the Si Heα line at ∼1.865 keV, a narrowband x-ray imager has been deployed at the Omega Laser Facility to record backlit images of direct-drive laser implosions. The crystal was cut along the $10\bar 11$101¯1 planes for a 2d spacing of 0.687 nm, resulting in a Bragg angle of 83.9°. Apertures in front of the crystal were used to control the astigmatism of the imaging system. The backlit images show a high signal-to-background ratio of >10:1 with backlighter laser energies ≥1.5 kJ at a 10-ps pulse duration and a spatial resolution of better than 20 μm.
Topology optimization of viscoelastic rectifiers
Authors: Ejlebjerg Jensen Kristian , Szabo Peter , Okkels Fridolin
Published: June 2012

An approach for the design of microfluidic viscoelastic rectifiers is presented based on a combination of a viscoelastic model and the method of topology optimization. This presumption free approach yields a material layout topologically different from experimentally realized rectifiers, and simulations indicate superior performance for the optimized design in the regime of moderate elasticity.
Laterally confined two-dimensional electron gases in self-patterned LaAlO3/SrTiO3 interfaces
Authors: Foerster M. , Bachelet R. , Laukhin V. , Fontcuberta J. , Herranz G. , Sánchez F.
Published: June 2012

A bottom-up process has been used to engineer the LaAlO3/SrTiO3 interface atomic composition and locally confine the two-dimensional electron gas to lateral sizes in the order of 100 nm. This is achieved by using SrTiO3(001) substrate surfaces with self-patterned chemical termination, which is replicated by the LaAlO3 layer, resulting in a modulated LaO/TiO2 and AlO2/SrO interface composition. We demonstrate the confinement of the conducting interface forming either long-range ordered nanometric stripes or isolated regions. Our results demonstrate that engineering the interface chemical termination is a suitable strategy towards nanoscale lateral confinement of two-dimensional high-mobility systems.
Momentum matching in the tunneling between 2-dimensional and 0-dimensional electron systems
Authors: Beckel Andreas , Zhou Daming , Marquardt Bastian , Reuter Dirk , Wieck Andreas D. , Geller Martin , Lorke Axel
Published: June 2012

We investigate the tunneling rates from a 2-dimensional electron gas (2DEG) into the ground state of self-assembled InGaAs quantum dots. These rates are strongly affected by a magnetic field perpendicular to the tunneling direction. Surprisingly, we find an increase in the rates for fields up to 4 T before they decrease again. This can be explained by a mismatch between the characteristic momentum of the quantum dot ground state and the Fermi momentum kF of the 2DEG. Calculations of the tunneling probability can account for the experimental data and allow us to determine the dot geometry as well as kF.
Growth of AlN/SiC/AlN quantum wells on Si(111) by molecular beam epitaxy
Authors: Cheng Yana , Beresford Roderic
Published: June 2012

AlN/SiC/AlN quantum well structures have been grown on Si(111) by molecular beam epitaxy at 700 °C. The microstructure is single-crystal wurtzite AlN and cubic SiC with stacking sequence disorder. Depth profiles taken by Auger electron spectroscopy indicate that the ratio of Si to C is about 5:4. Layers with lower carbon content exhibit regions with five-fold superstructures. Fourier transform infrared spectroscopy confirms the presence of Al-N and Si-C bonds. Our work demonstrates the feasibility of a low-temperature synthesis route for epitaxial SiC and AlN/SiC heterostructures on Si.
Influence of isochronal annealing on the microstructure and magnetic properties of Cu-free HITPERM Fe40.5Co40.5Nb7B12 alloy
Authors: Gupta P. , Ganguli Tapas , Gupta A. , Sinha A. K. , Deb S. K. , Svec P. , Franco V.
Published: June 2012

Systematic study of the effect of isochronal annealing on the structure and magnetic properties of Cu-free HITPERM alloy (Fe40.5Co40.5Nb7B12) is described herein. Mössbauer spectroscopy (MS) and anomalous x-ray diffraction (XRD) measurement at Fe K-edge (7.112 keV) jointly provide clear evidence for the presence of atomically ordered α′-FeCo (B2 structure) phase as a nanocrystalline ferromagnetic phase. Being a short range order probe, Mössbauer spectroscopy also confirms the development of an additional non-magnetic Nb-rich phase in the nanocrystalline specimens (annealed above 723 K) with simultaneous lowering of the volume fraction of ferromagnetic phases. The fraction of Fe atoms in the non-magnetic phase is ∼15% upon annealing at 773 K for 1 h, which increases gradually and reaches to as high as ∼19% after annealing at 923 K. This phase was not detected by XRD and transmission electron microscopy (TEM) measurements, which may be attributed to tiny crystallite size and/or high degree of disorder. In the second stage of crystallization, i.e., above 923 K, the alloy becomes fully crystalline and a stable, hard magnetic fcc-(FeCo)23B6 type phase was observed as a main boride phase along with soft magnetic α′-FeCo phase and Nb rich non-magnetic phase. Thermo magnetic measurement evidenced re-crystallization process as a considerable decrease in magnetization at the second transformation stage. Simultaneous lowering of the volume fraction of magnetic phases with the formation of non-magnetic phase provides convincing origin for the decrease in magnetization at the second crystallization stage.
An easy way to prepare layered nanoplatelets: Fragment of nanostructured multilayers
Authors: Zhang J. Y. , Wu K. , Zhang P. , Wang R. H. , Liu G. , Zhang G. J. , Sun J.
Published: June 2012

In this study, we present an easy way to create layered-nanoplatelets with well-defined geometry by controlling the cracking process of nanostructured multilayers. The geometrical dimension of layered-nanoplatelets is determined by the multilayer intrinsic size, the total strain, and the elastic mismatch between the substrate and multilayers, which was analyzed by statistical approach. Fracture behaviors characterized by critical strain to nucleate microcrack, fracture toughness, and evolution of fragment width were also studied for nanostructured Cu/Cr multilayers with modulation period (λ) spanning from of 5 to 250 nm and were quantified based on linear elastic theory and shear-lag theory. An optimal modulation period seems to be likely favorable for maximizing the ductility, strength, and fracture toughness of the nanolayered materials.
Molecular driving forces defining lipid positions around aquaporin-0
Authors: Aponte-Santamaría Camilo , Briones Rodolfo , Schenk Andreas D. , Walz Thomas , de Groot Bert L.
Published: June 2012

Lipid–protein interactions play pivotal roles in biological membranes. Electron crystallographic studies of the lens-specific water channel aquaporin-0 (AQP0) revealed atomistic views of such interactions, by providing high-resolution structures of annular lipids surrounding AQP0. It remained unclear, however, whether these lipid structures are representative of the positions of unconstrained lipids surrounding an individual protein, and what molecular determinants define the lipid positions around AQP0. We addressed these questions by using molecular dynamics simulations and crystallographic refinement, and calculated time-averaged densities of dimyristoyl-phosphatidylcholine lipids around AQP0. Our simulations demonstrate that, although the experimentally determined crystallographic lipid positions are constrained by the crystal packing, they appropriately describe the behavior of unconstrained lipids around an individual AQP0 tetramer, and thus likely represent physiologically relevant lipid positions.While the acyl chains were well localized, the lipid head groups were not. Furthermore, in silico mutations showed that electrostatic interactions do not play a major role attracting these phospholipids towards AQP0. Instead, the mobility of the protein crucially modulates the lipid localization and explains the difference in lipid density between extracellular and cytoplasmic leaflets. Moreover, our simulations support a general mechanism in which membrane proteins laterally diffuse accompanied by several layers of localized lipids, with the positions of the annular lipids being influenced the most by the protein surface. We conclude that the acyl chains rather than the head groups define the positions of dimyristoyl-phosphatidylcholine lipids around AQP0. Lipid localization is largely determined by the mobility of the protein surface, whereas hydrogen bonds play an important but secondary role.
Molecular simulations elucidate electric field actuation in swollen liquid crystal elastomers
Authors: Skačej Gregor , Zannoni Claudio
Published: June 2012

Swollen elastomer liquid crystals undergo significant deformations by application of an electric field perpendicular to their alignment axis, as shown in experiments by Urayama et al. [Urayama K, Honda S, Takigawa T (2006)Macromolecules39:1943–1949]. Here we clarify this surprising effect at the molecular level using large-scale Monte Carlo simulations of an off-lattice model based on a soft Gay–Berne potential. We provide the internal change of molecular organization, as well as the key observables during the actuation cycle.
Inhibition of the MRP1-mediated transport of the menadione-glutathione conjugate (thiodione) in HeLa cells as studied by SECM
Authors: Koley Dipankar , Bard Allen J.
Published: June 2012

Oxidative stress induced in live HeLa cells by menadione (2-methyl-1,4-napthaquinone) was studied in real time by scanning electrochemical microscopy (SECM). The hydrophobic molecule menadione diffuses through a living cell membrane where it is toxic to the cell. However, in the cell it is conjugated with glutathione to form thiodione. Thiodione is then recognized and transported across the cell membrane via the ATP-driven MRP1 pump. In the extracellular environment, thiodione was detected by the SECM tip at levels of 140, 70, and 35 µM upon exposure of the cells to menadione concentrations of 500, 250, and 125 µM, respectively. With the aid of finite element modeling, the kinetics of thiodione transport was determined to be 1.6 × 10
-7
 m/s, about 10 times faster than menadione uptake. Selective inhibition of these MRP1 pumps inside live HeLa cells by MK571 produced a lower thiodione concentration of 50 µM in presence of 500 µM menadione and 50 µM MK571. A similar reduced (50% drop) thiodione efflux was observed in the presence of monoclonal antibody QCRL-4, a selective blocking agent of the MRP1 pumps. The reduced thiodione flux confirmed that thiodione was transported by MRP1, and that glutathione is an essential substrate for MRP1-mediated transport. This finding demonstrates the usefulness of SECM in quantitative studies of MRP1 inhibitors and suggests that monoclonal antibodies can be a useful tool in inhibiting the transport of these MDR pumps, and thereby aiding in overcoming multidrug resistance.
Analytical theory of polymer-network-mediated interaction between colloidal particles
Authors: Di Michele Lorenzo , Zaccone Alessio , Eiser Erika
Published: June 2012

Nanostructured materials based on colloidal particles embedded in a polymer network are used in a variety of applications ranging from nanocomposite rubbers to organic-inorganic hybrid solar cells. Further, polymer-network-mediated colloidal interactions are highly relevant to biological studies whereby polymer hydrogels are commonly employed to probe the mechanical response of living cells, which can determine their biological function in physiological environments. The performance of nanomaterials crucially relies upon the spatial organization of the colloidal particles within the polymer network that depends, in turn, on the effective interactions between the particles in the medium. Existing models based on nonlocal equilibrium thermodynamics fail to clarify the nature of these interactions, precluding the way toward the rational design of polymer-composite materials. In this article, we present a predictive analytical theory of these interactions based on a coarse-grained model for polymer networks. We apply the theory to the case of colloids partially embedded in cross-linked polymer substrates and clarify the origin of attractive interactions recently observed experimentally. Monte Carlo simulation results that quantitatively confirm the theoretical predictions are also presented.
Structural engineering of a phage lysin that targets Gram-negative pathogens
Authors: Lukacik Petra , Barnard Travis J. , Keller Paul W. , Chaturvedi Kaveri S. , Seddiki Nadir , Fairman James W. , Noinaj Nicholas , Kirby Tara L. , Henderson Jeffrey P. , Steven Alasdair C. , Hinnebusch B. Joseph , Buchanan Susan K.
Published: June 2012

Bacterial pathogens are becoming increasingly resistant to antibiotics. As an alternative therapeutic strategy, phage therapy reagents containing purified viral lysins have been developed against Gram-positive organisms but not against Gram-negative organisms due to the inability of these types of drugs to cross the bacterial outer membrane. We solved the crystal structures of a
Yersinia pestis
outer membrane transporter called FyuA and a bacterial toxin called pesticin that targets this transporter. FyuA is a β-barrel membrane protein belonging to the family of TonB dependent transporters, whereas pesticin is a soluble protein with two domains, one that binds to FyuA and another that is structurally similar to phage T4 lysozyme. The structure of pesticin allowed us to design a phage therapy reagent comprised of the FyuA binding domain of pesticin fused to the N-terminus of T4 lysozyme. This hybrid toxin kills specific
Yersinia
and pathogenic
E. coli
strains and, importantly, can evade the pesticin immunity protein (Pim) giving it a distinct advantage over pesticin. Furthermore, because FyuA is required for virulence and is more common in pathogenic bacteria, the hybrid toxin also has the advantage of targeting primarily disease-causing bacteria rather than indiscriminately eliminating natural gut flora.
Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces
Authors: Oze Christopher , Jones L. Camille , Goldsmith Jonas I. , Rosenbauer Robert J.
Published: June 2012

Molecular hydrogen (H
2
) is derived from the hydrothermal alteration of olivine-rich planetary crust. Abiotic and biotic processes consume H
2
to produce methane (CH
4
); however, the extent of either process is unknown. Here, we assess the temporal dependence and limit of abiotic CH
4
related to the presence and formation of mineral catalysts during olivine hydrolysis (i.e., serpentinization) at 200 °C and 0.03 gigapascal. Results indicate that the rate of CH
4
production increases to a maximum value related to magnetite catalyzation. By identifying the dynamics of CH
4
production, we kinetically model how the H
2
to CH
4
ratio may be used to assess the origin of CH
4
in deep subsurface serpentinization systems on Earth and Mars. Based on our model and available field data, low H
2
/CH
4
ratios (less than approximately 40) indicate that life is likely present and active.
HOW DOES THE WELFARE STATE INFLUENCE INDIVIDUALS' SOCIAL CAPITAL?
Authors: Gelissen John P.T.M. , van Oorschot Wim J.H. , Finsveen Ellen
Published: June 2012

In the current literature there is emerging consensus about a positive correlation between countries' welfare efforts and the social capital of their inhabitants: the larger the welfare state, the more social capital its inhabitants have. This paper pulls the discussion an important step further by asking what mechanisms can be responsible for this correlation. Based on theory and previous findings, we formulate a conceptual model of how the macro–micro relationship could come about. The hypotheses are tested using Eurobarometer data. While most of the mechanisms hypothesised are also found empirically, a substantial part of the direct macro-to-micro effect remains after controlling for the presumed most important intervening factors. Our conclusion is that the relationship is still not well understood and needs more academic attention in future research.
ANALYSING INTERGENERATIONAL INFLUENCES ON INCOME POVERTY AND ECONOMIC VULNERABILITY WITH EU-SILC
Authors: Whelan Christopher T. , Nolan Brian , Maître Bertrand
Published: June 2012

The European Union Statistics of Income and Living Conditions (EU-SILC) 2005 wave includes a special module on inter-generational transmission of poverty. In addition to the standard data relating to income and material deprivation, information relating to parental background and childhood circumstances was collected for all household members aged over 24 and less than 66 at the end of the income reference period. In principle, the module provides an unprecedented opportunity to apply a welfare regime perspective to a comparative European analysis of the relationship between poverty and social exclusion and parental characteristics and childhood economic circumstances. In this paper, we seek to exploit such potential. In pursuing this objective, it is necessary to take into account some of the limitations of the data. We do by restricting our attention to a set of countries where data issues seem less extreme. Finally, we compare findings from one dimensional and multidimensional approaches to poverty and social exclusion in order to provide an assessment of the extent to which our analysis of welfare regime variation provides a coherent account of the intergenerational transmission of disadvantage.