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Hole accumulation in Ge/Si core/shell nanowires (NWs) has been observed and quantified using off-axis electron holography and other electron microscopy techniques. The epitaxial ⟨110⟩-oriented Ge/Si core/shell NWs were grown on Si (111) substrates by chemical vapor deposition through the vapor−liquid−solid growth mechanism. High-angle annular-dark-field scanning transmission electron microscopy images and off-axis electron holograms were obtained from specific NWs. The excess phase shifts measured by electron holography across the NWs indicated the presence of holes inside the Ge cores. Calculations based on a simplified coaxial cylindrical model gave hole densities of (0.4 ± 0.2) /nm3in the core regions. [ABSTRACT FROM AUTHOR]

AbstractSpacecraft launched to Mars can retain viable terrestrial microorganisms on board that may survive the interplanetary transit. Such biota might compromise the search for life beyond Earth if capable of propagating on Mars. The current study explored the survivability of Psychrobacter cryohalolentisK5, a psychrotolerant microorganism obtained from a Siberian permafrost cryopeg, under simulated martian surface conditions of high ultraviolet irradiation, high desiccation, low temperature, and low atmospheric pressure. First, a desiccation experiment compared the survival of P. cryohalolentiscells embedded, or not embedded, within a medium/salt matrix (MSM) maintained at 25°C for 24 h within a laminar flow hood. Results indicate that the presence of the MSM enhanced survival of the bacterial cells by 1 to 3 orders of magnitude. Second, tests were conducted in a Mars Simulation Chamber to determine the UV tolerance of the microorganism. No viable vegetative cells of P. cryohalolentiswere detected after 8 h of exposure to Mars-normal conditions of 4.55 W/m2UVC irradiation (200–280 nm), −12.5°C, 7.1 mbar, and a Mars gas mix composed of CO2(95.3), N2(2.7), Ar (1.6), O2(0.2), and H2O (0.03). Third, an experiment was conducted within the Mars chamber in which total atmospheric opacities were simulated at τ 0.1 (dust-free CO2atmosphere at 7.1 mbar), 0.5 (normal clear sky with 0.4 dust opacity and 0.1 CO2-only opacity), and 3.5 (global dust storm) to determine the survivability of P. cryohalolentisto partially shielded UVC radiation. The survivability of the bacterium increased with the level of UVC attenuation, though population levels still declined several orders of magnitude compared to UVC-absent controls over an 8 h exposure period. Astrobiology 9, 221–228. [ABSTRACT FROM AUTHOR]

Electric-discharge plasmas in gallium-iodide vapours are experimentally found to convert 40% of input electric power into ultraviolet and visible radiation (200-800 nm). The conditions are a weakly ionized positive column consisting of 5-10 Torr argon, and the gallium-iodide vapour is formed by heating condensed gallium-iodide to 100-120 degC. The input power density is 50-100 mW cm[?]3. The plasma is contained in a sealed silica tube and excited by an external radiofrequency antenna. Computational analysis and plasma diagnostics lead to a quantitative understanding that gallium atoms are formed by electron-impact dissociation of gallium-iodide compounds that evaporate into the plasma volume, and that further electron collisions excite the gallium atoms, which then decay by photon emission. High efficiency is possible only because several photons are emitted per dissociation event, and because nonradiative power channels such as electron-impact elastic heating and vibrational excitation are not dominant. The dissociated species recombine on the wall to reform the species that evaporates. The plasma properties change discontinuously as the molar ratio of iodine to gallium (I/Ga) in the system crosses the values I/Ga = 3 and I/Ga = 2, consistent with the thermodynamic properties of condensed gallium-iodide compounds. [ABSTRACT FROM AUTHOR]

The interactions of nanoparticles (NPs) with cellular membranes and subsequent transport processes have major implications for the biology, toxicology, and pharmacology of nanoscale materials. Moreover, understanding and predicting the behaviors of diverse NP designs in a physiological setting is of increasing technological and regulatory importance. Still, the current complexity of experiments and lack of a consensus in modeling and simulation preclude a clear picture of relevant NP-membrane interaction modes and mechanisms, particularly for particles on the ~1–10 nm scale. Here, we leverage detailed coarse-grained molecular dynamics simulations with advanced sampling strategies to uncover the thermodynamic driving forces and possible kinetic pathways of approximately 0.5–2.0 nm hydrophilic, hydrophobic, and ‘interfacially active’ particles with model lipid bilayer membranes. Using the simulations, we test the applicability of well-established theoretical models for the permeability of small molecule transport—Overton’s rule and the inhomogeneous solubility-diffusion model—and conclude that the former is overly-simplified for fluctuating lipid bilayers, while the latter breaks down at the larger particle sizes due to the influence of other physics like membrane undulations. We place this work in the context of recent simulation studies, and conclude with critical physical and methodological insights to guide future thermodynamic and kinetic studies of NP-membrane interactions. [ABSTRACT FROM AUTHOR]

Viscosity is a key parameter for characterising the behaviour of liquids and their flow. It is, however, difficult to measure precisely, reproducibly and accurately for aqueous solutions on a micro-litre volume scale, which is what is usually needed for biological samples. We report the development of a new method for measuring dynamic viscosity by measuring dynamic light scattering (DLS) data for a range of particles of well-defined size. Most applications of DLS involve determining particle size for samples of known viscosity. We inverted the usual protocol and endeavoured to determine viscosity for samples of known particle size. Viscosity measurements for water and aqueous solutions of calf thymus DNA made using DLS were compared with those from a U-tube viscometer. The styrene particles, frequently used as particle size standards, gave unsatisfactory results for our DNA samples as did C-6 derivatized silica and positively charged amino polystyrene microspheres. However, negatively charged carboxylate polystyrene microspheres particles readily gave accurate viscosity measurements over a range of temperatures (0–100 °C). The sample volume required depends on the cuvette used to measure DLS, but can be performed with samples sizes ranging from 40 to 3000 μL. The sample can then be recovered for subsequent experiments. The DLS method is simple to perform at different temperatures and provides data of accuracy significantly above that of a U-tube viscometer. Our results also indicate a way forward to account accurately for solution viscosity in the normal applications of DLS to particle size determination by including the appropriate non-interacting particles as an internal standard. [ABSTRACT FROM AUTHOR]

We use two different techniques to derive the two parameters describing conduction electron scattering and spin-flipping at sputtered Al/Cu interfaces in the current-perpendicular-to-plane (CPP) geometry. These parameters are: 2ARAl/Cu, twice the interface specific resistance, where A is the area through which the CPP current flows; and δAl/Cu, which gives the probability P of spin-flipping from P = 1 - exp(-δ). A technique involving simple multilayers, and sample temperature not exceeding room temperature, gives 2ARAl/Cu = 2.3 ± 0.2 fΩm2. A technique involving exchange-biased spin-valves (EBSVs), where the sample is annealed briefly to 453 K, gives 2ARAl/Cu = 2.0 ± 0.15 fΩm2. Averaging the two values, but increasing the uncertainty for reasons explained, gives the best estimate of 2ARAl/Cu = 2.15 ± 0.4 fΩm2. This average is comparable to, but smaller than, the published value of 2ARAl/Cu = 3.6 ± 1 fΩm2 derived from thermal conductance measurements, and larger than our calculated values for interface thicknesses up to 6 monolayers (ML). However, it is similar to our calculated values for an interface thickness of 8 ML. Combining extrapolation of higher temperature bulk diffusion data for Al in Cu and vice-versa, with x-ray and transmission electron microscope (TEM) studies of similarly sputtered multilayers, indicates that such interface thicknesses are possible, especially for annealed multilayers. CPP-magnetoresistance (MR) measurements of the EBSV samples give only very small spin-flipping at the Al/Cu interface-δAl/Cu = 0.05-0.05+0.02. Such a small value is consistent with expected small spin-orbit interactions in both Al and Cu. Supplementary studies of CPP-MR of Permalloy (Py)-based EBSVs containing [Cu/Al/Cu] trilayers, show unusual behavior when the central Al layer is at least 10 nm thick, giving a CPP-MR like that for Py/Al, independent of Cu layer thicknesses from 0 to 10 nm. MR, x-ray, and TEM results give some clues as to the origins of this behavior, but a completely satisfactory explanation is not yet available. [ABSTRACT FROM AUTHOR]

We report the fabrication of a new class of Sn/P-doped Ge-like materials with high quality optical, structural, and device properties. A flux of Ge2H6with trace amounts of SnD4is used to deposit thick Sn-doped Ge films via chemical vapor deposition (CVD) at low temperatures (∼390–370 °C) directly on Si(100) substrates. The presence of Sn in the gas mixture alters the standard Ge growth mechanism (Stranski–Krastanov) to yield atomically smooth layers with minimal threading defects at growth rates as high as 15–30 nm/min. The films, dubbed “quasi-Ge”, contain ∼1019cm–3Sn “impurities”, which do not produce any measurable shift in the lattice constant or emission wavelength. This new method represents a low-cost, high-performance alternative to the standard CVD approaches to grow high-quality Ge-on-Si for optoelectronic applications. In this regard, the optical quality of the materials is corroborated by studying photoluminescence (PL) of both intrinsic samples and n-type analogues doped well above 1019atoms cm–3, using the single-source P(GeH3)3. Heavy n-doping significantly enhances the PL intensity, allowing the observation of distinct indirect and direct gap peaks. The device quality of the material was evaluated by fabricating prototype heterostructure photodetectors in n-i-pgeometry. These are found to exhibit significantly higher responsivities than pure Ge p-i-nanalogues and dark current densities comparable to the state of the art. [ABSTRACT FROM AUTHOR]

Highly oriented, single-crystal Ni nanowire arrays have been synthesized atop amorphous SiO2∥Si substrates using a single-step chemical vapor deposition method in the absence of any foreign catalyst. Electron and X-ray diffraction confirm the crystalline quality of the Ni nanowires while magnetoresistance measurements probe the magnetic response and the behavior is explained using simulation results for nanoscale, single-crystal Ni. A growth mechanism involving competing chemical, energetic, and kinetic influences is presented. [ABSTRACT FROM AUTHOR]

We found that multiwalled carbon nanotubes (MWNTs) can be opened longitudinally by intercalation of lithium and ammonia followed by exfoliation. Intercalation of open-ended tubes and exfoliation with acid treatment and abrupt heating provided the best results. The resulting material consists of: (i) multilayered flat graphitic structures (nanoribbons), (ii) partially open MWNTs, and (iii) graphene flakes. We called the completely unwrapped nanotubes ex-MWNTs, and their large number of edge atoms makes them attractive for many applications. [ABSTRACT FROM AUTHOR]

We report the use of chemical vapor deposition (CVD) for the bulk production (grams per day) of long, thin, and highly crystalline graphene ribbons (<20−30 μm in length) exhibiting widths of 20−300 nm and small thicknesses (2−40 layers). These layers usually exhibit perfect ABAB... stacking as in graphite crystals. The structure of the ribbons has been carefully characterized by several techniques and the electronic transport and gas adsorption properties have been measured. With this material available to researchers, it should be possible to develop new applications and physicochemical phenomena associated with layered graphene. [ABSTRACT FROM AUTHOR]

This study reports the observation of six different zincblende compound semiconductors in [110] projection using large-collection-angle bright-field (LABF) imaging with an aberration-corrected scanning transmission electron microscope. Phase contrast is completely suppressed when the collection semi-angle is set equal to the convergence semi-angle and there are no reversals in image contrast with changes in defocus or thickness. The optimum focus for imaging closely separated pairs of atomic columns (‘dumbbells’) is unique and easily recognized, and the positions of atomic columns occupied by heavier atoms always have darker intensity than those occupied by lighter atoms. Thus, the crystal polarity of compound semiconductors can be determined unambiguously. Moreover, it is concluded that the LABF imaging mode will be highly beneficial for studying other more complicated heterostructures at the atomic scale. [ABSTRACT FROM AUTHOR]