bluuebunny/crossref_metadata_2025 huggingface dataset:
Interfacial reaction-dominated full oxidation of 5 nm diameter silicon nanowires
Authors: Kim Ilsoo , Park Tae-Eon , Lee Ki-Young , Ha Ryong , Kim Byung-Hyun , Chung Yong-Chae , Lee Kwang-Ryeol , Choi Heon-Jin
Published: November 2012

While almost all Si nanostructures, including Si nanowires (SiNWs), Si nanocrystals, and Si nanotrench-like structures on a supra- or sub-10 nm scale exhibit self-limiting oxidative behavior, herein we report full oxidation of SiNWs 5 nm in diameter. We investigated the oxidative behavior of SiNWs with diameters of 5 nm and compared our findings with those for SiNWs with diameters of 30 nm. Single-crystalline SiNWs 5 and 30 nm in diameter were grown by a chemical vapor deposition (CVD) process using Ti as a catalyst. The SiNWs were then oxidized at 600–1000 °C for 30 min to 240 min in O2. The thicknesses of the resulting oxide layers were determined by transmission electron microscopy (TEM). As expected, the SiNWs 30 nm in underwent self-limiting oxidation that was parabolic in nature. However, under the same conditions, the SiNWs 5 nm in diameter underwent full oxidation that was linear in nature. Atomic-scale molecular dynamic simulations revealed that the compressive stress in the oxide layer, which is generated owing to the increase in the volume of the oxide formed, decreased in the case of the SiNWs 5 nm in diameter. It is likely that this decrease in the compressive stress results in a lowering of the energy barrier for the diffusion of oxygen into the oxide layer, leading to the full oxidation of the SiNWs 5 nm in diameter. It is also responsible for the oxidation in the case of SiNWs 5 nm in diameter being interfacial reaction-dominated as opposed to the diffusion dominated-oxidation typical for SiNWs.
Dynamics and collective state of ordered magnetic nanoparticles in mesoporous systems
Authors: Vargas José M. , Srivastava Abhishek , Garza Ezra , Yourdkhani Amin , Caruntu Gabriel , Spinu Leonard
Published: November 2012

In this paper we present a study of superparamagnetic and superspin glass states of magnetic nanoparticles confined in mesoporous templates. Characterization utilizes dynamic magnetization techniques, ac susceptibility, and ferromagnetic resonance, in addition to dc magnetization curves. In order to differentiate between the intrinsic and collective properties, we considered three magnetic nanoparticles systems with comparable size, shape, and crystallinity but with different intrinsic magnetocrystalline anisotropy. Further, confinement effects were studied by considering three different geometries of nanoparticles. The effect of the geometrical confinement and intrinsic anisotropy of the nanoparticles are discussed based on known theoretical predictions.
Towards an understanding of light activation processes in titanium oxide based inverted organic solar cells
Authors: Chambon S. , Destouesse E. , Pavageau B. , Hirsch L. , Wantz G.
Published: November 2012

The light activation phenomenon in inverted P3HT:PCBM bulk heterojunction organic solar cells based on titanium oxide sublayer (TiOx) is characterized by fast acquisition of current-voltage (J-V) curves under light bias as function of time. TiOx layers were thermally treated under inert atmosphere at different temperatures prior active layer deposition and for every device an activation time was extracted. It is shown that the higher the TiOx annealing temperature, the faster the activation. The improvement of the overall device performances is also observed for devices with TiOx layers baked above 100 °C. The evolution of the characteristic of the organic semiconductors (OSC) device, from dielectric to diode, is attributed to the increase of TiOx conductivity by three orders of magnitude upon white light illumination. Additionally, devices based on baked TiOx present higher conductivity than those based on unbaked TiOx which would explain the gain in performances and the short activation time of the OSC. In order to understand the origin of the phenomenon, deactivation experiments were also performed under different conditions on OSC. The deactivation process was shown to be thermally dependent and fully reversible under inert atmosphere, which suggest that deep traps are responsible for the activation phenomenon. An optimal annealing temperature was found at 120 °C and gives a reasonable short activation time of approximately 1 min and photo conversion efficiency up to 4%.
Effect of Li+ ions on enhancement of near-infrared upconversion emission in Y2O3:Tm3+/Yb3+ nanocrystals
Authors: Li Dongyu , Wang Yuxiao , Zhang Xueru , Dong Hongxing , Liu Lu , Shi Guang , Song Yinglin
Published: November 2012

Near-infrared (NIR) to NIR upconversion emission is investigated in Tm3+/Yb3+/Li+ triply doped Y2O3 nanocrystals. Li+ ions doped in Y2O3:Tm3+/Yb3+ nanocrystals can greatly enhance the NIR upconversion emission intensity of Tm3+ ions. The abnormal shift of the (222) diffraction peak position determined from x-ray diffraction measurements is discussed, by introducing Li+ ions in the Y2O3:Tm3+/Yb3+ nanocrystals. The cause of the enhancement is the modification of the local symmetry induced by the Li+ ions, which increases the intra-4f transitions of Tm3+ ion. Li+ ions doped in Y2O3:Tm3+/Yb3+ nanocrystals also can reduce the OH groups, dissociate the Yb3+ and Tm3+ ion clusters, and create the oxygen vacancies, which are the other reasons for enhancing the upconversion emission intensities. This material may be promising for in vitro and in vivo bioimaging probes.
Extremely long carrier lifetime at intermediate states in wall-inserted type II quantum dot absorbers
Authors: Sato Daisuke , Ota Junya , Nishikawa Kazutaka , Takeda Yasuhiko , Miyashita Naoya , Okada Yoshitaka
Published: November 2012

To realize highly efficient intermediate-band solar cells (IB-SCs), a long lifetime of photo-generated carriers in the IB is essential. We propose a new concept for this purpose based on IB absorbers using quantum-dots (QDs). By inserting potential walls between QDs and barriers that form a type II band alignment, electrons in the IB and holes in the valence band are farther separated compared to those in a conventional type II QD material, leading to significant reduction of radiative recombination. We designed a concrete structure using InAs QDs, GaAs1−xSbx barriers, and GaAs walls to find the suitable GaAs wall thickness and Sb content being 2 nm and x = 0.18, respectively, and demonstrated a lifetime of electrons excited to the IB as long as 220 ns.
The influence of demagnetizing effects on the performance of active magnetic regenerators
Authors: Nielsen Kaspar K. , Smith Anders , Bahl Christian R. H. , Olsen Ulrik L.
Published: November 2012

Active magnetic regenerators (AMR) comprise an involved, multi-physics problem including heat transfer, fluid flow, magnetocaloric properties, and demagnetizing fields. In this paper a method is developed that combines previously published models that simulate a parallel-plate AMR and the magnetostatics of a stack of parallel plates, respectively. Such a coupling is non-trivial due to the significant increase in computational time, and a simplified scheme is thus developed and validated resulting in little extra computational effort needed. A range of geometrical and operating parameters are varied, and the results show that not only do demagnetizing effects have a significant impact on the AMR performance, but the magnitude of the effect is very sensitive to a range of parameters such as stack geometry (number of plates, dimensions of the plates and flow channels, and overall dimensions of the stack), orientation of the applied field, and the operating conditions of the AMR (such as thermal utilization).
Dynamics of femto- and nanosecond laser ablation plumes investigated using optical emission spectroscopy
Authors: Verhoff B. , Harilal S. S. , Freeman J. R. , Diwakar P. K. , Hassanein A.
Published: November 2012

We investigated the spatial and temporal evolution of temperature and electron density associated with femto- and nanosecond laser-produced plasmas (LPP) from brass under similar laser fluence conditions. For producing plasmas, brass targets were ablated in vacuum employing pulses either from a Ti:Sapphire ultrafast laser (40 fs, 800 nm) or from a Nd:YAG laser (6 ns, 1064 nm). Optical emission spectroscopy is used to infer the density and temperature of the plasmas. The electron density (ne) was estimated using Stark broadened profiles of isolated lines while the excitation temperature (Texc) was estimated using the Boltzmann plot method. At similar fluence levels, continuum and ion emission are dominant in ns LPP at early times (<50 ns) followed by atomic emission, while the fs LPP provided an atomic plume throughout its visible emission lifetime. Though both ns and fs laser-plasmas showed similar temperatures (∼1 eV), the fs LPP is found to be significantly denser at shorter distances from the target surface as well as at early phases of its evolution compared to ns LPP. Moreover, the spatial extension of the plume emission in the visible region along the target normal is larger for fs LPP in comparison with ns LPP.
Critical behavior and magnetic-entropy change of orthorhombic La0.7Ca0.2Sr0.1MnO3
Authors: Phan The-Long , Zhang Y. D. , Zhang P. , Thanh T. D. , Yu S. C.
Published: November 2012

We prepared a polycrystalline sample of orthorhombic La0.7Ca0.2Sr0.1MnO3 and then investigated its magnetic properties. Detailed studies and analyses in the vicinity of the ferromagnetic (FM)-paramagnetic phase-transition temperature prove the sample undergoing a second-order phase transition, where variations of the saturation magnetization and the initial susceptibility versus temperature obey asymptotic relations. Basing on the modified Arrott plot, we have determined the critical parameters (TC, β, γ, and δ) in the two characteristic regions of low- and high-magnetic fields, and in the cases of no-subtracting and subtracting the demagnetization field (Hd). The experimental results reveal that values of the critical parameters depend remarkably on analysis routes of isothermal-magnetization data. Intrinsically, β keeps close to the value expected for the 3D Heisenberg ferromagnets with ferromagnetic short-range interactions, while γ is close to the value of the mean-field theory. These results are different from those reported previously on a La0.7Ca0.2Sr0.1MnO3 single crystal exhibiting a tri-critical point. The effects related to grain boundaries and isotropic properties existing in the polycrystalline sample are assigned to cause such the phenomena. Particularly, around TC, the magnetic-entropy change reaches a maximum value of 4.3 J kg−1 K−1 under an applied field of 30 kOe, which corresponds to a relative cooling power ∼150 J/kg suitable for magnetic refrigeration applications.
Experimental investigations on the magneto-hydro-dynamic interaction around a blunt body in a hypersonic unseeded air flow
Authors: Cristofolini Andrea , Borghi Carlo A. , Neretti Gabriele , Schettino Antonio , Trifoni Eduardo , Battista Francesco , Passaro Andrea , Baccarella Damiano
Published: November 2012

This paper deals with the experimental investigation on the MHD (magneto-hydro-dynamic or magneto-fluid-dynamic) interaction around a test body immersed into a hypersonic unseeded air flow. The experiments have been carried out in the CIRA plasma wind tunnel SCIROCCO. Two test conditions have been utilized for the experiments with a total pressure of 2.5 and 2.3 bar respectively, a total specific enthalpy of 16 and 12.1 MJ/kg respectively. The air flow was accelerated in the nozzle up to Mach 10. The magnetic induction field is generated by an electromagnet enclosed in the test body and reaches a 0.8 T maximum value in the interaction region.
Microstructure and oxidation states in multiferroic Lu2(Fe,Mn)3O7
Authors: Ma Chao , Qin Yuanbin , Yang Huaixin , Tian Huanfang , Li Jianqi , Sardar Kripasindhu , Walton Richard I. , Su Dong , Wu Lijun , Zhu Yimei
Published: November 2012

Microstructural features and oxidation states in multiferroic Lu2Fe2.1Mn0.9O7 have been investigated by neutron diffraction, transmission electron microscopy (TEM), and x-ray absorption near edge spectroscopy. Our experimental results demonstrate the disordered distribution of Mn atoms in the FeO double (W) layers, indicating that structural modulations originate from the charge disproportionation, which is evidenced by the mixed-valence states of Fe ions. TEM measurements clearly reveal Mn doping induced chemical inhomogeneity and local distortions which are associated with the charge disproportionation in the W layers. In addition, the polarization is discussed in association with the lattice distortions and charge disproportionation.
Observation of rotatable stripe domain in permalloy films with oblique sputtering
Authors: Wang Gaoxue , Dong Chunhui , Wang Wenxi , Wang Zhiling , Chai Guozhi , Jiang Changjun , Xue Desheng
Published: November 2012

Stripe domain (SD) in obliquely sputtered permalloy films were investigated by comparing with normally sputtered ones. The critical thickness for SD formation of obliquely sputtered films was about 100 nm thinner than that of normally sputtered films. The hysteresis loops of obliquely sputtered films showed a peculiar shape. A rotation of SD towards easy axis was observed in the obliquely sputtered films, which was confirmed by permeability spectra under a bias field. The origin of the rotation could result from in-plane uniaxial anisotropy, which is induced by the shape effect of the oblique columnar growth of permalloy grains.
Time-resolved photoluminescence spectroscopy of excitons in layered semiconductor PbI2 nanoclusters
Authors: Gnatenko Yu. P. , Bukivskij P. M. , Piryatinski Yu. P. , Bukivskii A. P. , Skubenko P. A. , Gamernyk R. V.
Published: November 2012

We studied the dynamics of excitons excited in layered semiconductor PbI2 nanoclusters (NCLs) using time-resolved photoluminescence (TRPL) spectroscopy. TRPL spectra reveal formation of self-trapped excitons (STEs). It was shown that the formation of the STEs for larger [more than the Bohr radius of exciton in bulk PbI2 (RB = 1.9 nm)] NCLs occurs in sub-nanosecond time scale, while in the case of small NCLs with sizes about RB, it takes place in nanosecond scale. The effective energy transfer from the small to the larger semiconductor NCLs, which arises from dipole-dipole intercluster interactions, takes place in sub-nanosecond scale. We demonstrate that the STEs are stable states and they define effective radioluminescence of the investigated Pb1−XCdXI2 alloys.
Magnetic properties of the magnetophotonic crystal based on bismuth iron garnet
Authors: Popova Elena , Magdenko Liubov , Niedoba Halina , Deb Marwan , Dagens Béatrice , Berini Bruno , Vanwolleghem Mathias , Vilar Christèle , Gendron François , Fouchet Arnaud , Scola Joseph , Dumont Yves , Guyot Marcel , Keller Niels
Published: November 2012

This article reports on the magnetism of continuous and patterned bismuth iron garnet (Bi3Fe5O12 or BIG) thin films for magnetophotonic crystal (MPC) applications. The exact knowledge of the magnetic properties is crucial for the design of fully functional MPC. BIG thin films were grown on several types of isostructural substrates by pulsed laser deposition. The growth conditions and bismuth transfer were optimized to obtain good quality magneto-optically active films compatible with nanostructuring process. MPC were successfully fabricated from BIG/GGG(001) films with low roughness and high Faraday rotation. Magnetic characteristics (magnetization, anisotropy, magnetic domains, magnetization reversal) of the continuous BIG films and MPC were extensively studied and compared to the results of the micromagnetic simulations performed for MPC with different anisotropy. The present study shows that the fabrication of the MPC structure lowers the magnetocrystalline and uniaxial in-plane anisotropies and induces a partial out-of-plane magnetization. External field smaller than 2000 G is sufficient to ensure the out-of-plane saturation of magnetization for optimum device operation, in agreement with micromagnetic calculations. The experimentally determined magnetic properties of MPC are fully compatible with the device operation.
Dynamics of positronium formation in positron-hydrogen collisions embedded in weakly coupled plasmas
Authors: Nayek Sujay , Ghoshal Arijit
Published: November 2012

Dynamics of positronium (Ps) formation in an arbitrary s-state from an arbitrary s-state of the hydrogen atom in weakly coupled plasma has been investigated within the framework of a distorted-wave theory. The interactions among the charged particles in the plasma have been represented by Debye-Huckel potentials. Using simple variational hydrogenic wave functions and arbitrary order derivatives of the general three-denominator Lewis integral partial-wave scattering amplitudes have been obtained in closed forms. These distorted-wave scattering amplitudes have been used to make a detailed study on differential and total cross sections. It has been found that screening of the interaction potentials has significant effect on the scattering dynamics. Some notable features of cross sections have also been revealed.
Exploring the p-n junction region in Cu(In,Ga)Se2 thin-film solar cells at the nanometer-scale
Authors: Cojocaru-Mirédin O. , Choi P. , Wuerz R. , Raabe D.
Published: November 2012

In this work we study the CdS/Cu(In,Ga)Se2 p-n junction region in Cu(In,Ga)Se2 thin-film solar cells using atom probe tomography. A Cu-, Ga-depleted, and Cd-doped region of about 1 nm thickness is detected at the Cu(In,Ga)Se2 side of the CdS/Cu(In,Ga)Se2 interface. Furthermore, Cd is also found to be enriched at Cu(In,Ga)Se2 grain boundaries connected to the CdS layer. Na and O impurities decorate the CdS/CIGS interface, where Na-rich clusters are preferentially located in CdS regions abutting to Cu(In,Ga)Se2 grain boundaries. The experimental findings of this work demonstrate the capability of atom probe tomography in studying buried interfaces and yield vital information for understanding and modeling the p-n junction band structure in Cu(In,Ga)Se2 solar cells.
Fastin situphase and stress analysis during laser surface treatment: A synchrotron x-ray diffraction approach
Authors: Kostov V. , Gibmeier J. , Wilde F. , Staron P. , Rössler R. , Wanner A.
Published: November 2012

An in situ stress analysis by means of synchrotron x-ray diffraction was carried out during laser surface hardening of steel. A single exposure set-up that based on a special arrangement of two fast silicon strip line detectors was established, allowing for fast stress analysis according to the sin2ψ x-ray analysis method. For the in situ experiments a process chamber was designed and manufactured, which is described in detail. First measurements were carried out at the HZG undulator imaging beamline (IBL, beamline P05) at the synchrotron storage ring PETRA III, DESY, Hamburg (Germany). The laser processing was carried out using a 6 kW high power diode laser system. Two different laser optics were compared, a Gaussian optic with a focus spot of ø 3 mm and a homogenizing optic with a rectangular spot dimension of 8 × 8 mm2. The laser processing was carried out using spot hardening at a heating-/cooling rate of 1000 K/s and was controlled via pyrometric temperature measurement using a control temperature of 1150 °C. The set-up being established during the measuring campaign allowed for this first realization data collection rates of 10Hz. The data evaluation procedure applied enables the separation of thermal from elastic strains and gains unprecedented insight into the laser hardening process.
Three-dimensional modeling of beam emission spectroscopy measurements in fusion plasmas
Authors: Guszejnov D. , Pokol G. I. , Pusztai I. , Refy D. , Zoletnik S. , Lampert M. , Nam Y. U.
Published: November 2012

One of the main diagnostic tools for measuring electron density profiles and the characteristics of long wavelength turbulent wave structures in fusion plasmas is beam emission spectroscopy (BES). The increasing number of BES systems necessitated an accurate and comprehensive simulation of BES diagnostics, which in turn motivated the development of the Rate Equations for Neutral Alkali-beam TEchnique (RENATE) simulation code that is the topic of this paper. RENATE is a modular, fully three-dimensional code incorporating all key features of BES systems from the atomic physics to the observation, including an advanced modeling of the optics. Thus RENATE can be used both in the interpretation of measured signals and the development of new BES systems. The most important components of the code have been successfully benchmarked against other simulation codes. The primary results have been validated against experimental data from the KSTAR tokamak.
An alternative scaling model for neutron production in Z-pinch devices
Authors: Bures Brian L. , Krishnan Mahadevan
Published: November 2012

The DD neutron yield (Yn) from z-pinches, either dense plasma foci or fast radial pinches, has been fitted for decades to the scaling model Yn ∼ α(Imax)δ, where α is a numerical scaling coefficient, Imax the peak current, and 3 < δ < 5. The data from 12 000 pulses analyzed from eight different z-pinches presented in this paper show that Yn varies by as much as ±15 000% about the best fit value of the conventional scaling model with δ = 4. A revised scaling model derived from the reaction rate equation and a circuit model that includes the time derivative of the current dI/dt (normalized to its initial value) reduces the scatter in data from ±15 000% to ±100%. For the special case of very high normalized dI/dt, the standard deviation between the revised scaling prediction and the measured neutron yields is reduced to just ±30%. Implications of this revised scaling for higher current pinches are discussed.
Growth and characterization of n-type electron-induced ferromagnetic semiconductor (In,Fe)As
Authors: Nam Hai Pham , Duc Anh Le , Mohan Shyam , Tamegai Tsuyoshi , Kodzuka Masaya , Ohkubo Tadakatsu , Hono Kazuhiro , Tanaka Masaaki
Published: November 2012

We show that by introducing isoelectronic iron (Fe) magnetic impurities and Beryllium (Be) double-donor atoms into InAs, it is possible to grow an n-type ferromagnetic semiconductor (FMS) with the ability to control ferromagnetism by both Fe and independent carrier doping by low-temperature molecular-beam epitaxy. We demonstrate that (In,Fe)As doped with electrons behaves as an n-type electron-induced FMS. This achievement opens the way to realize spin-devices such as spin light-emitting diodes or spin field-effect transistors, as well as helps to understand the mechanism of carrier-mediated ferromagnetism in FMSs.
Surface relief grating in azo-polymer obtained for s-s polarization configuration of the writing beams
Authors: Sobolewska Anna , Bartkiewicz Stanislaw
Published: November 2012

The paper reports on the formation of the surface relief gratings in thin films of the azobenzene-functionalized polymer. We evidence that the efficiency of the formation process of the surface relief gratings strongly depends on the length of the main polymer chains in the case of the s-s configuration. The explanation of this relationship is given and is based on the revealing of the differences in the ability of the motion of the main chain which is strictly related to its length.
Upper limit power for self-guided propagation of intense lasers in plasma
Authors: Wang Wei-Min , Sheng Zheng-Ming , Zeng Ming , Liu Yue , Hu Zhi-Dan , Kawata Shigeo , Zheng Chun-Yang , Mori Warren B. , Chen Li-Ming , Li Yu-Tong , Zhang Jie
Published: November 2012

It is shown that there is an upper-limit laser power for self-focusing of a laser pulse in plasma in addition to the well-known lower-limit critical power set by the relativistic effect. This upper limit is caused by the transverse ponderomotive force of the laser, which tends to expel plasma electrons from the laser propagating area. Furthermore, there is a lower-limit plasma density for a given laser spot size, below which self-focusing does not occur for any laser power. Both the lower-limit density and the upper-limit power are derived theoretically and verified by two-dimensional and three-dimensional particle-in-cell simulations. It is also found that plasma channels may be unfavorable for stable guiding of lasers above the upper-limit power.
Design of remnant magnetization FeCoV films as compact, heatless neutron spin rotators
Authors: Abutaleb M. O. , Pushin D. A. , Huber M. G. , Majkrzak C. F. , Arif M. , Cory D. G.
Published: November 2012

We introduce a design of a neutron spin rotator for applications with space and temperature constraints. These passive devices employ remnant magnetization FeCoV thin films and can be tuned experimentally to achieve arbitrary rotation of an incident neutron with a known spin state. Polarized neutron reflectometry measurements are reported for FeCoV monolayer films at thicknesses of 0.5 μm and 5.3 μm to characterize the depth-dependent vector magnetization in the films. Results for a prototype set of film rotators are presented, and the stray field near such films is characterized.
Tunable bandgap and ferromagnetism in sputtered epitaxial Sn1−xMgxO2 thin films
Authors: Zhou Baozeng , Wu Ping , Zhou Wei
Published: November 2012

Room-temperature magnetic behavior and tunable bandgap of epitaxial Sn1−xMgxO2 films were investigated. The Mg dopants can enhance the ferromagnetism and the largest saturation magnetization of 7.0 emu/cm3 has been observed in Sn0.94Mg0.06O2 film which has the narrowest bandgap. The ferromagnetism decreases with further doping but increases in Sn0.84Mg0.16O2 film after air annealing at 700 °C. The ferromagnetism is likely due to the double exchange mechanism through the p-p interaction. Mg interstitials can irreversibly transform to Mg substitutions by thermal treatment. The generated oxide alloys will decrease the optical bandgap and ferromagnetism of the samples.
Effect of hydrogen/deuterium incorporation on electroforming voltage of SiOx resistive random access memory
Authors: Wang Yanzhen , Fowler Burt , Chen Yen-Ting , Xue Fei , Zhou Fei , Chang Yao-Feng , Lee Jack C.
Published: November 2012

The electroforming voltage (Vef) of silicon oxide resistive random access memories treated with post-deposition-anneal (PDA) and/or post-metal-anneal in different gas ambients is compared. Secondary ion mass spectroscopy result shows significant incorporation of H/D atoms in SiOx after anneals in H2/N2 and D2/N2. Vef is significantly reduced after anneal in H2/N2 or D2/N2, but D2/N2 anneal results in even lower Vef, which could be due to more stable Si passivation in the Si-D/O+ pair as compared to the Si-H/O+ pair. On and off state currents are measured at 200 mV gate bias every 60 s for a total time of 6000 s with results showing good data retention for both on and off states. On and off state currents are observed to decrease when using PDA resulting in lower overall power dissipation.
Removing the effects of elastic and thermal scattering from electron energy-loss spectroscopic data
Authors: Lugg N. R. , Haruta M. , Neish M. J. , Findlay S. D. , Mizoguchi T. , Kimoto K. , Allen L. J.
Published: November 2012

Electron energy-loss spectroscopy (EELS) studies in scanning transmission electron microscopy are widely used to investigate the location and bonding of atoms in condensed matter. However, the interpretation of EELS data is complicated by multiple elastic and thermal diffuse scattering of the probing electrons. Here, we present a method for removing these effects from recorded EELS spectrum images, producing visually interpretable elemental maps and enabling direct comparison of the spectral data with established first-principles energy-loss fine structure calculations.
Direct intensity sampling of a modelocked terahertz quantum cascade laser
Authors: Freeman Joshua R. , Maysonnave Jean , Jukam Nathan , Cavalié Pierrick , Maussang Kenneth , Beere Harvey E. , Ritchie David A. , Mangeney Juliette , Dhillon Sukhdeep S. , Tignon Jérôme
Published: November 2012

Pulses from an actively modelocked terahertz quantum cascade laser are fully characterized using an optical sampling technique to detect the total instantaneous terahertz intensity. By triggering the quantum cascade laser electronics with a femtosecond laser, we are able to measure both the formation of modelocked pulses and the quasi-steady state. The dependence of the pulse width on the modulation power and drive current are investigated. At low drive currents, we measure transform-limited gaussian-shaped pulses with a FWHM of 19 ps.
Direct observation of blocked nanoscale surface evaporation on SiO2 nanodroplets
Authors: Wan Neng , Xu Jun , Sun Li-Tao , Martini Matteo , Huang Qing-An , Hu Xiao-Hui , Xu Tao , Bi Heng-Chang , Sun Jun
Published: November 2012

Nano-scale surface evaporation of SiO2 nanodroplets from a volcano-shaped tip (tip diameter d ∼ 20 nm to 70 nm) was observed directly using an in situ transmission electron microscopy method. Au nanoparticles, those precipitated in the SiO2 matrix after an Au catalyzed growth, diffused and pinned onto the evaporation surface, which induced blocked evaporation dynamics. Our observations provide direct evidences of blocked evaporation dynamics caused by small-sized nanoparticles at the nanometer scale.
Sub-micron mapping of GHz magnetic susceptibility using scanning transmission x-ray microscopy
Authors: Cheng Cheng , Bailey William E.
Published: November 2012

We report submicron imaging (∼0.75 μm resolution) of complex magnetic susceptibility in a micron-size ferromagnetic heterostructure using time-resolved scanning transmission x-ray microscopy. The real and imaginary parts of the susceptibility are extracted from the phase and amplitude of the small-angle (<20°) rotational response of the local magnetization under microwave excitation. Frequency-dependent response patterns were observed in an incompletely saturated bilayer element. The technique is extensible to higher frequencies (to ∼10 GHz), better spatial resolution, and layer-specific measurement.
Silicon nanowire based Pirani sensor for vacuum measurements
Authors: Brun T. , Mercier D. , Koumela A. , Marcoux C. , Duraffourg L.
Published: November 2012

Nano-Pirani vacuum gauges based on the physical properties of suspended silicon nanowires have been fabricated and characterized. With a 160 × 260 nm2 rectangular section and a 5.2 μm length, they are 50 times smaller than the smallest silicon based vacuum sensor and they exhibits much lower power consumption. The nano-Pirani constructed are capable of measuring pressures from 50 to 105 Pa. Moreover, their fabrication is compatible with microelectronic and micromachining fabrication techniques making them suitable for in-situ monitoring of micro and nano systems vacuum packaging.
Silicon coding-decoding photonic device by electron irradiation and light down conversion
Authors: Malyutenko V. K. , Tykhonov A. N. , Malyutenko O. Yu. , Rohutskii I. S. , Danilchenko B. A.
Published: November 2012

We propose and demonstrate a coding-decoding procedure as an important step to realize one more Si-based photonic device. Low-fluence (<1014 e/cm2) high-energy (1 MeV) electron irradiation of a bulk Si matrix is used to code an information by forming local regions with lower free carrier lifetime that are hidden under the surface and invisible to the eye. Short-wavelength (<1 μm) free carrier generation stands for multiple, remote, and nondestructive decoding process, which makes it easy to dynamically (ms range) visualize a code by capturing two-dimensional pattern of thermal emission in the longer-wavelength (3–12 μm) band (light down conversion).
Tunable photovoltaic effect and solar cell performance of self-doped perovskite SrTiO3
Authors: Jin K. X. , Li Y. F. , Wang Z. L. , Peng H. Y. , Lin W. N. , Kyaw A. K. K. , Jin Y. L. , Jin K. J. , Sun X. W. , Soci C. , Wu Tom
Published: November 2012

We report on the tunable photovoltaic effect of self-doped single-crystal SrTiO3 (STO), a prototypical perovskite-structured complex oxide, and evaluate its performance in Schottky junction solar cells. The photovaltaic characteristics of vacuum-reduced STO single crystals are dictated by a thin surface layer with electrons donated by oxygen vacancies. Under UV illumination, a photovoltage of 1.1 V is observed in the as-received STO single crystal, while the sample reduced at 750 °C presents the highest incident photon to carrier conversion efficiency. Furthermore, in the STO/Pt Schottky junction, a power conversion efficiency of 0.88% was achieved under standard AM 1.5 illumination at room temperature. This work establishes STO as a high-mobility photovoltaic semiconductor with potential of integration in self-powered oxide electronics.
Photoluminescence under high-electric field of PbS quantum dots
Authors: Ullrich B. , Wang J. S. , Brown G. J.
Published: November 2012

The effect of a laterally applied electric field (≤10 kV/cm) on the photoluminescence of colloidal PbS quantum dots (diameter of 2.7 nm) on glass was studied. The field provoked a blueshift of the emission peak, a reduction of the luminescent intensity, and caused an increase in the full width at half maximum of the emission spectrum. Upon comparison with the photoluminescence of p-type GaAs exhibits the uniqueness of quantum dot based electric emission control with respect to bulk materials.
Effect of Co-doping on the resistivity and thermopower of SmFe1-xCoxAsO (0.0≤x≤0.3)
Authors: Okram Gunadhor S. , Kaurav Netram , Soni Ajay , Pal Anand , Awana V. P. S.
Published: November 2012

We report structure, electrical resistivity and thermopower of polycrystalline SmFe1-x CoxAsO samples for 0.0 ≤ x ≤ 0.3. The XRD data revealed full Co substitution at Fe-site with slight compression of the unit cell. Resistivity data showed that the spin-density wave observed at 130 K for x = 0 is suppressed when x = 0.05, above which superconductivity emerges due to injection of mobile electrons, supporting the substitution of Co3+ at Fe2+ site but disappears for x = 0.3. The thermopower (S) data indicate that the majority of charge carriers is electron-like and its value reaches −81 μV/K (at 300 K) for x = 0.3. Noticeable deviations from the expected linear behavior in S(T) at low temperatures and S/T against temperature curves at intermediate temperatures were observed. These observations were interpreted on the basis of nested Fermi surface and Umklapp processes.
Solar electron source and thermionic solar cell
Authors: Yaghoobi Parham , Vahdani Moghaddam Mehran , Nojeh Alireza
Published: November 2012

Common solar technologies are either photovoltaic/thermophotovoltaic, or use indirect methods of electricity generation such as boiling water for a steam turbine. Thermionic energy conversion based on the emission of electrons from a hot cathode into vacuum and their collection by an anode is also a promising route. However, thermionic solar conversion is extremely challenging as the sunlight intensity is too low for heating a conventional cathode to thermionic emission temperatures in a practical manner. Therefore, compared to other technologies, little has been done in this area, and the devices have been mainly limited to large experimental apparatus investigated for space power applications. Based on a recently observed “Heat Trap” effect in carbon nanotube arrays, allowing their efficient heating with low-power light, we report the first compact thermionic solar cell. Even using a simple off-the-shelf focusing lens, the device delivered over 1 V across a load. The device also shows intrinsic storage capacity.
Perch substrate use by the threatened wallum sedge frog (Litoria olongburensis) in wetland habitats of mainland eastern Australia
Authors: Shuker Jon D. , Hero Jean-Marc
Published: November 2012

Understanding habitat requirements for a threatened species is important for recovery planning and management of threatening processes. This study examines utilisation of wetland habitat by the threatened wallum sedge frog (Litoria olongburensis), which breeds in acidic waters of coastal sandy lowlands in subtropical eastern Australia. Habitat utilisation was determined by comparing perch substrate observations with perch substrate availability in wetlands occupied by the species throughout its mainland distribution range. A high proportion (75.3%) of adult wallum sedge frogs perched on upright sedges, comprising Baumea, Schoenus and Chorizandra species, which was much higher than expected on the basis of availability (P < 0.001). Baloskion pallens, a thin sedge-like herbaceous plant, was utilised by 12.1% of the frogs, which was lower than expected on the basis of availability (P = 0.020). Other herbaceous species and shrubs were also utilised significantly less than expected. The identification of preferred perch species is critical for impact assessment and mitigation activities, including design, construction, restoration and maintenance of wetlands suitable for the survival and reproduction of the wallum sedge frog.
Dilatational band formation in bone
Authors: Poundarik Atharva A. , Diab Tamim , Sroga Grazyna E. , Ural Ani , Boskey Adele L. , Gundberg Caren M. , Vashishth Deepak
Published: November 2012

Toughening in hierarchically structured materials like bone arises from the arrangement of constituent material elements and their interactions. Unlike microcracking, which entails micrometer-level separation, there is no known evidence of fracture at the level of bone’s nanostructure. Here, we show that the initiation of fracture occurs in bone at the nanometer scale by dilatational bands. Through fatigue and indentation tests and laser confocal, scanning electron, and atomic force microscopies on human and bovine bone specimens, we established that dilatational bands of the order of 100 nm form as ellipsoidal voids in between fused mineral aggregates and two adjacent proteins, osteocalcin (OC) and osteopontin (OPN). Laser microdissection and ELISA of bone microdamage support our claim that OC and OPN colocalize with dilatational bands. Fracture tests on bones from OC and/or OPN knockout mice (OC
−/−
, OPN
−/−
, OC-OPN
−/−;−/−
) confirm that these two proteins regulate dilatational band formation and bone matrix toughness. On the basis of these observations, we propose molecular deformation and fracture mechanics models, illustrating the role of OC and OPN in dilatational band formation, and predict that the nanometer scale of tissue organization, associated with dilatational bands, affects fracture at higher scales and determines fracture toughness of bone.
Meltwater routing and the Younger Dryas
Authors: Condron Alan , Winsor Peter
Published: November 2012

The Younger Dryas—the last major cold episode on Earth—is generally considered to have been triggered by a meltwater flood into the North Atlantic. The prevailing hypothesis, proposed by Broecker et al. [1989
Nature
341:318–321] more than two decades ago, suggests that an abrupt rerouting of Lake Agassiz overflow through the Great Lakes and St. Lawrence Valley inhibited deep water formation in the subpolar North Atlantic and weakened the strength of the Atlantic Meridional Overturning Circulation (AMOC). More recently, Tarasov and Peltier [2005
Nature
435:662–665] showed that meltwater could have discharged into the Arctic Ocean via the Mackenzie Valley ∼4,000 km northwest of the St. Lawrence outlet. Here we use a sophisticated, high-resolution, ocean sea-ice model to study the delivery of meltwater from the two drainage outlets to the deep water formation regions in the North Atlantic. Unlike the hypothesis of Broecker et al., freshwater from the St. Lawrence Valley advects into the subtropical gyre ∼3,000 km south of the North Atlantic deep water formation regions and weakens the AMOC by <15%. In contrast, narrow coastal boundary currents efficiently deliver meltwater from the Mackenzie Valley to the deep water formation regions of the subpolar North Atlantic and weaken the AMOC by >30%. We conclude that meltwater discharge from the Arctic, rather than the St. Lawrence Valley, was more likely to have triggered the Younger Dryas cooling.
Kinetic mechanism for viral dsRNA length discrimination by MDA5 filaments
Authors: Peisley Alys , Jo Myung Hyun , Lin Cecilie , Wu Bin , Orme-Johnson McGhee , Walz Thomas , Hohng Sungchul , Hur Sun
Published: November 2012

The viral sensor MDA5 distinguishes between cellular and viral dsRNAs by length-dependent recognition in the range of ∼0.5–7 kb. The ability to discriminate dsRNA length at this scale sets MDA5 apart from other dsRNA receptors of the immune system. We have shown previously that MDA5 forms filaments along dsRNA that disassemble upon ATP hydrolysis. Here, we demonstrate that filament formation alone is insufficient to explain its length specificity, because the intrinsic affinity of MDA5 for dsRNA depends only moderately on dsRNA length. Instead, MDA5 uses a combination of end disassembly and slow nucleation kinetics to
“
discard
”
short dsRNA rapidly and to suppress rebinding. In contrast, filaments on long dsRNA cycle between partial end disassembly and elongation, bypassing nucleation steps. MDA5 further uses this repetitive cycle of assembly and disassembly processes to repair filament discontinuities, which often are present because of multiple, internal nucleation events, and to generate longer, continuous filaments that more accurately reflect the length of the underlying dsRNA scaffold. Because the length of the continuous filament determines the stability of the MDA5–dsRNA interaction, the mechanism proposed here provides an explanation for how MDA5 uses filament assembly and disassembly dynamics to discriminate between self vs. nonself dsRNA.
Conductivity of an atomically defined metallic interface
Authors: Oliver David J. , Maassen Jesse , El Ouali Mehdi , Paul William , Hagedorn Till , Miyahara Yoichi , Qi Yue , Guo Hong , Grütter Peter
Published: November 2012

A mechanically formed electrical nanocontact between gold and tungsten is a prototypical junction between metals with dissimilar electronic structure. Through atomically characterized nanoindentation experiments and first-principles quantum transport calculations, we find that the ballistic conduction across this intermetallic interface is drastically reduced because of the fundamental mismatch between s wave-like modes of electron conduction in the gold and d wave-like modes in the tungsten. The mechanical formation of the junction introduces defects and disorder, which act as an additional source of conduction losses and increase junction resistance by up to an order of magnitude. These findings apply to nanoelectronics and semiconductor device design. The technique that we use is very broadly applicable to molecular electronics, nanoscale contact mechanics, and scanning tunneling microscopy.
Autotrophy as a predominant mode of carbon fixation in anaerobic methane-oxidizing microbial communities
Authors: Kellermann Matthias Y. , Wegener Gunter , Elvert Marcus , Yoshinaga Marcos Yukio , Lin Yu-Shih , Holler Thomas , Mollar Xavier Prieto , Knittel Katrin , Hinrichs Kai-Uwe
Published: November 2012

The methane-rich, hydrothermally heated sediments of the Guaymas Basin are inhabited by thermophilic microorganisms, including anaerobic methane-oxidizing archaea (mainly ANME-1) and sulfate-reducing bacteria (e.g., HotSeep-1 cluster). We studied the microbial carbon flow in ANME-1/ HotSeep-1 enrichments in stable-isotope–probing experiments with and without methane. The relative incorporation of13C from either dissolved inorganic carbon or methane into lipids revealed that methane-oxidizing archaea assimilated primarily inorganic carbon. This assimilation is strongly accelerated in the presence of methane. Experiments with simultaneous amendments of both13C-labeled dissolved inorganic carbon and deuterated water provided further insights into production rates of individual lipids derived from members of the methane-oxidizing community as well as their carbon sources used for lipid biosynthesis. In the presence of methane, all prominent lipids carried a dual isotopic signal indicative of their origin from primarily autotrophic microbes. In the absence of methane, archaeal lipid production ceased and bacterial lipid production dropped by 90%; the lipids produced by the residual fraction of the metabolically active bacterial community predominantly carried a heterotrophic signal. Collectively our results strongly suggest that the studied ANME-1 archaea oxidize methane but assimilate inorganic carbon and should thus be classified as methane-oxidizing chemoorganoautotrophs.
Quantifying transient binding of ISWI chromatin remodelers in living cells by pixel-wise photobleaching profile evolution analysis
Authors: Erdel Fabian , Rippe Karsten
Published: November 2012

Interactions between nuclear proteins and chromatin frequently occur on the time scale of seconds and below. These transient binding events are important for the fast identification of target sites as concluded from our previous analysis of the human chromatin remodelers Snf2H and Snf2L from the imitation switch (ISWI) family. Both ATP-driven molecular motor proteins are able to translocate nucleosomes along the DNA and appear to exert this activity only on a small number of nucleosomes to which they bind more tightly. For mechanistic studies, one needs to distinguish such translocation reactions or other long-lived interactions associated with conformational changes and/or ATP hydrolysis from nonproductive chromatin sampling during target search. These processes can be separated by measuring the duration of nucleosome binding with subsecond time resolution. To reach this goal, we have developed a fluorescence bleaching technique termed pixel-wise photobleaching profile evolution analysis (3PEA). It exploits the inherent time structure of confocal microscopy images and yields millisecond resolution. 3PEA represents a generally applicable approach to quantitate transient chromatin interactions in the 2- to 500-ms time regime within only ∼1 s needed for a measurement. The green autofluorescent protein (GFP)-tagged Snf2H and Snf2L and the inactive Snf2L+13 splice variant were studied by 3PEA in comparison to the isolated GFP or red autofluorescent protein and a GFP pentamer. Our results reveal that the residence time for transient chromatin binding of Snf2H and Snf2L is <2 ms, and strongly support the view that ISWI-type remodelers are only rarely active in unperturbed cells during G1 phase.