PubMed Journal Database | Nano letters RSS

11:26 EDT 24th October 2014 | BioPortfolio

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

Monday 12th June 1104

Atomic Level Spatial Variations of Energy States along Graphene Edges.

The local atomic bonding of carbon atoms around the edge of graphene is examined by aberration-corrected scanning transmission electron microscopy (STEM) combined with electron energy loss spectroscopy (EELS). High-resolution 2D maps of the EELS combined with atomic resolution annular dark field STEM images enables correlations between the carbon K-edge EELS and the atomic structure. We show that energy states of graphene edges vary across individual atoms along the edge according to their specific C-C bond...


Rapid Estimation of Catalyst Nanoparticle Morphology and Atomic-coordination by High-resolution Z-contrast Electron Microscopy.

Heterogeneous nanoparticle catalyst development relies on an understanding of their structure-property relationships, ideally at atomic resolution and in three-dimensions. Current transmission electron microscopy techniques such as discrete tomography can provide this, but require multiple images of each nanoparticle and are incompatible with samples that change under electron irradiation, or with surveying large numbers of particles to gain significant statistics. Here we make use of recent advances in qua...


Solid-Solid Phase Transformations Induced through Cation Exchange and Strain, in 2D Heterostructured Copper Sulfide Nanocrystals.

We demonstrate dual interface formation in nanocrystals (NCs) through cation exchange, creating epitaxial heterostructures within spherical NCs. The thickness of the inner-disk layer can be tuned to form two-dimensional (2D), single atomic layers (


Spontaneous formation of high index planes in gold single domain nanocrystal superlattices.

Crystals of nanocrystals, also called supracrystals and nanocrystal superlattices are expected to exhibit specific properties that differ from both the corresponding bulk material and nanosized elementary units. In particular, their surfaces have a great potential as nanoscale interaction plateforms. However, control of the symmetry, compacity and roughness of their surfaces remains an open question. Here, we describe the spontaneous formation of upper vicinal surfaces for supracrystals of Au nanocrystals g...


Comparing the Catalytic Oxidation of Ethanol at the Solid-Gas and Solid-Liquid Interfaces over Size-Controlled Pt Nanoparticles - Striking Differences in Kinetics and Mechanism.

Pt nanoparticles with controlled size (2 nm, 4 nm, 6 nm) are synthesized and tested in ethanol oxidation by molecular oxygen at 60 ⁰C to acetaldehyde and carbon-dioxide both in the gas and liquid phases. The turnover frequency of the reaction is ~ 80 times faster, and the activation energy is ~ 5 times higher at the gas-solid interface compared to the liquid-solid interface. The catalytic activity is highly dependent on the size of the Pt nanoparticles, however the selectivity is not size sensitive. Aceta...


The Gold-Copper Nano-Alloy, "Tumbaga" in the Era of Nano: Phase Diagram and Segregation.

Gold-copper (Au-Cu) phases were employed already by pre-Columbian civilizations, essentially in decorative arts, while nowadays they emerge in nanotechnology as an important catalyst. The knowledge of the phase diagram is critical to understanding the performance of a material. However, experimental determination of nano-phase diagrams is rare because calorimetry remains quite challenging at the nanoscale; theoretical investigations are therefore welcomed. Using nano-thermodynamics, this paper presents the ...

Saturday 29th August 1102

Porous Ice Phases with VI and Distorted VII Structures Constrained in Nanoporous Silica.

High-pressure compression of water contained in nanoporous silica allowed fabrication of novel porous ice phases as a function of pressure. The starting liquid nanoporous H2O transformed to ice VI and VII at 1.7 GPa and 2.5 GPa, respectively, which are 0.6 GPa and 0.4 GPa higher than commonly accepted pressures for bulk H2O. Continuous increase of pressure drives the formation of a tetragonally distorted VII structure with the space group I4mm, rather than a cubic Pn3m phase in bulk ice. The enhanced incomp...


Nucleation of Graphene and its Conversion to Single Walled Carbon Nanotubes.

We use an environmental transmission electron microscope to record atomic-scale movies showing how carbon atoms assemble together on a catalyst nanoparticle to form a graphene sheet that progressively lifts-off to convert into a nanotube. Time-resolved observations combined with theoretical calculations confirm that some nanoparticle facets act like a vice-grip for graphene, offering anchoring sites, while other facets allow the graphene to lift-off, which is the essential step to convert into a nanotube..


An Advanced Lithium-Air Battery Exploiting an Ionic Liquid-based Electrolyte.

A novel lithium-oxygen battery exploiting a PYR14TFSI-LiTFSI ionic liquid as the electrolyte medium is reported. The Li/PYR14TFSI-LiTFSI/O2 battery was fully characterized by electrochemical impedance spectroscopy, capacity-limited cycling, field emission scanning electron microscopy, high resolution transmission electron microscopy, and x-ray photoelectron spectroscopy. The results of this extensive study demonstrate that this new Li/O2 cell is characterized by a stable electrode-electrolyte interface and ...


Ligand-Exchange Assisted Formation of Au/TiO2 Schottky Contact for Visible-Light Photocatalysis.

Plasmonic noble metal nanoparticles have emerged as a promising material in sensitizing wide-bandgap semiconductors for visible-light photocatalysis. Conventional methods in constructing such hetero-catalysts suffer from either poor control over the size of the metal nanoparticles or inefficient charge transfer through the metal/semiconductor interface, which limit their photocatalytic activity. To solve this problem, in this work we construct Au/TiO2 photocatalysts by depositing pre-synthesized colloidal A...


Electrical detection of the spin polarization due to charge flow in the surface state of the topological insulator Bi1.5Sb0.5Te1.7Se1.3.

We detected the spin polarization due to charge flow in the spin non-degenerate surface state of a three dimensional topological insulator by means of an all-electrical method. The charge current in the bulk-insulating topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) was injected/extracted through a ferromagnetic electrode made of Ni80Fe20, and an unusual current-direction-dependent magnetoresistance gives evidence for the appearance of spin polarization which leads to a spin-dependent resistance at the BS...


Atomic Scale Strain Relaxation in Axial Semiconductor III-V Nanowire Heterostructures.

Combination of mismatched materials in semiconductor nanowire heterostructures offers a freedom of bandstructure engineering that is impossible in standard planar epitaxy. Nevertheless, the presence of strain and/or structural defects directly control the optoelectronic properties of these nanomaterials. Understanding with atomic accuracy how mismatched heterostructures release or accommodate strain is therefore highly desirable. By using atomic resolution high angle annular dark field scanning transmission...


Time-lapse nanoscopy of friction in the non-Amontons and non-Coulomb regime.

Originally discovered by Leonard da Vinci in the 15th century, the force of friction is directly proportional to the applied load (known as Amontons' first law of friction). Furthermore, kinetic friction is independent of the sliding speed (known as Coulomb's law of friction). These empirical laws break down at high normal pressure (due to plastic deformation) and low sliding speed (in the transition regime between static friction and kinetic friction). An important example of this phenomenon is friction be...


Nanoscale strain engineering on the surface of a bulk TiO2 crystal.

Arrays of highly strained 5 - 25 nm-wide regions have been prepared on rutile TiO2(110) surface through a low energy Ar ion bombardment technique. Using scanning tunneling microscopy (STM) and an innovative STM tip-triggered nano-explosion approach we show experimentally that the protrusions arise from subsurface Ar-filled pockets. Continuum mechanics modeling gives good estimates of the corresponding elastic deformation. Surface strain values of up to 4 % have been deduced.


Grain Boundaries in Graphene on SiC(000-1) Substrate.

Grain boundaries in epitaxial graphene on the SiC(000-1) substrate are studied using scanning tunneling microscopy and spectroscopy. All investigated small-angle grain boundaries show pronounced out-of-plane buckling induced by the strain fields of constituent dislocations. The ensemble of observations allows to determine the critical misorientation angle of buckling transition θC=19±2°. Periodic structures are found among the flat large-angle grain boundaries. In particular, the observed θ=3±2° highl...


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...

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