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23:47 EDT 20th October 2014 | BioPortfolio

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Showing PubMed Articles 1–25 of 2,000+ from Nano letters


Strong Reciprocal Interaction Between Polarization and Surface Stoichiometry in Oxide Ferroelectrics.

We present a systematic evaluation of the effects of polarization switchability on surface structure and stoichiometry in BaTiO3 and PbTiO3 ferroelectric oxides. We show that charge passivation, mostly by ionic surface reconstructions, is the driving force for the stability of the surfaces, which suggests that varying the substrate polarization offers a new mechanism for controlling surface reconstructions in polar systems and inducing highly non-stoichiometric structures. Conversely, for thin-films, the ch...


Broadband Up-Conversion at Sub-Solar Irradiance: Triplet-Triplet Annihilation Boosted by Fluorescent Semiconductor Nanocrystals.

Conventional solar cells exhibit limited efficiencies in part due to their inability to absorb the entire solar spectrum. Sub-band-gap photons are typically lost but could be captured if a material that performs up-conversion, which shifts photon energies higher, is coupled to the device. Recently, molecular chromophores that undergo triplet-triplet annihilation (TTA) have shown promise for efficient up-conversion at low irradiance, suitable for some types of solar cells. However, the molecular systems that...

Wednesday 21st September 1097

Enhanced third-harmonic generation in silicon nanoparticles driven by magnetic response.

We observe enhanced third-harmonic generation from silicon nanodisks exhibiting both electric and magnetic dipolar resonances. Experimental characterization of the nonlinear optical response through third-harmonic microscopy and spectroscopy reveals that the third-harmonic generation is significantly enhanced in the vicinity of the magnetic dipole resonances. The field localization at the magnetic resonance results in two-orders-of-magnitude enhancement of the harmonic intensity with respect to unstructured...

Monday 23rd May 1097

Probing the quantum tunneling limit of plasmonic enhancement by third harmonic generation.

Metal nanostructures provide extreme focusing of optical energy that is limited fundamentally by quantum tunneling. We probe directly the onset of the quantum tunneling regime observed by a sharp reduction in the local field intensity in sub-nanometer self-assembled monolayer gaps using third harmonic generation. Unlike past works that have inferred local limits from far-field spectra, this nonlinear measurement is sensitive to the near-field intensity as the third power. We calculate the local field intens...


Multi-shelled TiO2 Hollow Microspheres as Anodes with Superior Reversible Capacity for Lithium Ion Batteries.

Herein uniform multi-shelled TiO2 hollow microspheres were synthesized, especially 3- and 4-shelled TiO2 hollow microspheres were synthesized for the first time by a simple sacrificial method capable of controlling the shell thickness, inter-shell spacing and number of internal multi-shells which are achieved by controlling the size, charge and diffusion rate of the titanium coordination ions as well as the calcination process. Used as anodes for lithium ion batteries, the multi-shelled TiO2 hollow microsph...


Electrically continuous graphene from single crystal copper verified by terahertz conductance spectroscopy and micro four-point probe.

The electrical performance of graphene synthesized by chemical vapour deposition and transferred to insulating surfaces may be compromised by extended defects, including for instance grain boundaries, cracks, wrinkles and tears. In this study we experimentally investigate and compare the nano- and micro-scale electrical continuity of single layer graphene grown on cm-size single crystal copper with that of previously studied graphene films, grown on commercially available copper foil. The electrical continu...

Saturday 7th February 1096

Hot-Electron Injection in Au Nanorod-ZnO Nanowire Hybrid Device for Near-Infrared Photodetection.

In this paper we present a new class of near-infrared photodetectors comprising Au nanorods - ZnO nanowire hybrid systems. Fabricated hybrid FET devices showed a large photoresponse under radiation wavelengths between 650 nm and 850 nm, accompanied by an "ultrafast" transient with a time scale of 250 ms, more than one order of magnitude faster than the ZnO response under radiation above band-gap. The generated photocurrent is ascribed to plasmonic-mediated generation of hot electrons at the metal-semiconduc...

Friday 29th August 1095

Amorphous Vanadium Oxide Matrixes Supporting Hierarchical Porous Fe3O4/Graphene Nanowires as a High-Rate Lithium Storage Anode.

Developing electrode materials with both high energy and power densities holds the key for satisfying the urgent demand of energy storage worldwide. In order to realize the fast and efficient transport of ions/electrons and stable structure during the charging/discharging process, hierarchical porous Fe3O4/Graphene nanowires supported by amorphous vanadium oxide matrixes has been rationally synthesized with a facile phase separation process. The porous structure is directly in situ constructed from the FeVO...

Wednesday 16th July 1095

Toward practical application of functional conductive polymer binder for a high-energy lithium-ion battery design.

Silicon alloys have the highest specific capacity when used as anode material for lithium-ion batteries, however, the drastic volume change inherent in their use causes formidable challenges toward achieving stable cycling performance. Large quantities of binders and conductive additives are typically necessary to maintain good cell performance. In this report, an only 2% (by weight) functional conductive polymer binder without any conductive additives was successfully used with a micron-size silicon monoxi...


Mössbauer study of temperature dependent cycloidal ordering in BiFeO3 nanoparticles.

To study the effect of different temperatures and particle sizes on the anharmonic cycloidal spin structure in BiFeO3 nanoparticles, Mössbauer spectroscopy was applied to three sets of particles in the range of 4 - 800 K. The paramagnetic transition showed a distinct broadening upon decreasing particle size with Néel temperatures decreasing from 652 K to 631 K. The anharmonicity of the long range cycloidal structure, calculated from experimental Mössbauer spectra, is revealed to decrease upon rising temp...


Chloride Molecular Doping Technique on 2D Materials: WS2 and MoS2.

Low-resistivity metal-semiconductor (M-S) contact is one of the urgent challenges in the research of 2D transition metal dichalcogenides (TMDs). Here, we report a chloride molecular doping technique which greatly reduces the contact resistance (Rc) in the few-layer WS2 and MoS2. After doping, the Rc of WS2 and MoS2 have been decreased to 0.7 kΩ•μm and 0.5 kΩ•μm, respectively. The significant reduction of the Rc is attributed to the achieved high electron doping density thus significant reduction of ...


A three-junction SQUID-on-tip with tunable in-plane and out-of-plane magnetic field sensitivity.

Nanoscale superconducting quantum interference devices (SQUIDs) demonstrate record sensitivities to small magnetic moments, but are typically sensitive only to the field component that is normal to the plane of the SQUID and out-of-plane with respect to the scanned surface. We report on a nanoscale three-junction Pb SQUID which is fabricated on the apex of a sharp tip. Because of its three-dimensional structure, it exhibits a unique tunable sensitivity to both in-plane and out-of-plane fields. We analyze th...


Experimental Realization of a Polarization-Independent Ultraviolet/Visible Coaxial Plasmonic Metamaterial.

We report the experimental realization of an optical metamaterial composed of a hexagonal array of coaxial plasmonic metal/insulator/metal waveguides that shows strong polarization-independent optical mode index dispersion in the ultraviolet/blue. The metamaterial is composed of silicon coaxes with a well defined diameter in the range of 150-168 nm with extremely thin sidewalls (13-15 nm), embedded in a silver film, fabricated using a combination of electron beam lithography, physical vapor deposition, reac...


Self-trapping of excitons, violation of Condon approximation and efficient fluorescence in conjugated cycloparaphenylenes.

Cycloparaphenylenes, the simplest structural unit of armchair carbon nanotubes, have unique optoelectronic properties counterintuitive in the class of conjugated organic materials. Our time-dependent density functional theory study and excited state dynamics simulations of cycloparaphenylene chromophores provide a simple and conceptually appealing physical picture explaining experimentally observed trends in optical properties in this family of molecules. Fully delocalized degenerate second and third excito...


One-step Synthesis of Hybrid Nanocrystals with Rational Tuning of the Morphology.

Metal-sulfide hybrid nanocrystals (HNCs) have been of great interest for their distinguished interfacial effect which gives rise to unique catalytic properties. However, most of the reported metal-sulfide HNCs were synthesized via two-step approaches and few were fabricated based on the one-step strategies. Herein, we report a facile one-pot synthesis of CuPt-Cu2S, Pt-Cu2S HNCs, and CuPt nanocubes by simply changing the Pt precursor types. 1-hexadecanethiol (HDT) was employed in this system to mediate the r...

Thursday 24th October 1094

Nanoparticle Facilitated Extracellular Electron Transfer in Microbial Fuel Cells.

Microbial fuel cells (MFCs) have been the focus of substantial research interest due to their potential for long-term, renewable electrical power generation via the metabolism of a broad spectrum of organic substrates, although the low power densities have limited their applications to date. Here, we demonstrate the potential to improve the power extraction by exploiting biogenic inorganic nanoparticles to facilitate extracellular electron transfer in MFCs. Simultaneous short-circuit current recording and o...

Friday 12th July 1094

Electrically tunable metasurface perfect absorbers for ultra-thin mid-infrared optical modulators.

Dynamically reconfigurable metasurfaces open up unprecedented opportunities in applications such as high capacity communications, dynamic beam shaping, hyperspectral imaging and adaptive optics. The realization of high performance metasurface-based devices remains a great challenge due to very limited tuning ranges and modulation depths. Here we show that a widely tunable metasurface composed of optical antennas on graphene can be incorporated into a subwavelength-thick optical cavity to create an electrica...


Optical Properties and Band Gap of Single- and Few-Layer MoTe2 Crystals.

Single- and few-layer crystals of exfoliated MoTe2 have been characterized spectroscopically by photoluminescence, Raman scattering, and optical absorption measurements. We find that MoTe2 in the monolayer limit displays strong photoluminescence. Based on complementary optical absorption results, we conclude that monolayer MoTe2 is a direct-gap semiconductor, with an optical band-gap of 1.10 eV. This new monolayer material extends the spectral range of atomically thin direct-gap materials from the visible t...


Multi-mode silicon nanowire transistors.

The combined capabilities of both a non-planar design and non-conventional carrier injection mechanisms are subject to recent scientific investigations to overcome the limitations of silicon MOSFETs. In this letter we present a multi-mode FET device using silicon nanowires that feature an axial n-type/intrinsic doping junction. A heterostructural device design is achieved by employing a self-aligned nickel-silicide source contact. The polymorph operation of the dual-gate device enabling the configuration of...


Granularity Controlled Non-Saturating Linear Magneto-resistance in Topological Insulator Bi2Te3 Films.

We report on the magneto-transport properties of chemical vapor deposition grown films of interconnected Bi2Te3 nanoplates. Similar to many other topological insulator (TI) materials, these granular Bi2Te3 films exhibit a linear magneto-resistance (LMR) effect which has received much recent attention. Studying samples with different degree of granularity, we find a universal correlation between the magnitude of the LMR and the average mobility () of the films over nearly two orders of magnitude change of . ...


Transporting a Tube in a Tube.

LbL assembled tubes were employed for the micro/nano scale cargoes transportation through the kinesin-microtubule system. Selectively modified with kinesins onto inner tube walls through Ni-NTA complexes, these tubes can work as channels for microtubules. A motility assay shows the smooth movement of microtubules along the tube inner wall powered by the inside immobilized kinesins. It could be envisioned that cargoes with different sizes can be transported through these tubular channels with little outside ...


Bonding Pathways of Gold Nanocrystals in Solution.

Nanocrystal bonding is an important phenomenon in crystal growth, and nanoscale welding. Here, we show that for gold nanocrystals bonding in solution can follow two distinct pathways: 1) coherent, defect-free bonding occurs when two nanocrystals attach with their lattices aligned to within a critical angle; 2) beyond this critical angle, defects form at the interfaces where the nanocrystals merge. The critical misalignment angle for ~10 nm crystals is ~15o in both in-situ experiments and full-atom molecular...


A black phosphorus photo-detector for multispectral, high-resolution imaging.

Black phosphorus is a layered semiconductor that is intensely researched in view of applications in optoelectronics. In this Letter, we investigate a multi-layer black phosphorus photo-detector that is capable of acquiring high-contrast (V>0.9) images both in the visible (λVIS=532nm) as well as in the infrared (λIR=1550nm) spectral regime. In a first step, by using photocurrent microscopy, we map the active area of the device and we characterize responsivity and gain. In a second step, by deploying the bl...

Monday 9th August 1091

Multimetallic Core/Interlayer/Shell Nanostructures as Advanced Electrocatalysts.

The fine balance between activity and durability is crucial for the development of high performance electrocatalysts. The importance of atomic structure and compositional gradients is a guiding principle in exploiting the knowledge from well-defined materials in the design of novel electrocatalysts with a Ni core, Au interlayer and PtNi shell nanostructure (Ni@Au@PtNi). This multimetallic system is found to have the optimal balance of activity and durability due to the synergy between stabilizing effect of ...

Friday 29th January 1091

Mechanisms of photoconductivity in atomically thin MoS2.

Atomically thin transition metal dichalcogenides have emerged as promising candidates for sensitive photodetection. Here, we report a photoconductivity study of biased mono- and bilayer molybdenum disulphide field- effect transistors. We identify photovoltaic and photoconductive effects, which both show strong photogain. The photovoltaic effect is described as a shift in transistor threshold voltage due to charge transfer from the channel to nearby molecules, including SiO2 surface-bound water. The photocon...

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