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11:08 EST 31st January 2015 | BioPortfolio

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Showing PubMed Articles 1–25 of 2,200+ from Nano letters

Tuesday 25th March 1157

Dopant Segregation in Polycrystalline Monolayer Graphene.

Chemical Vapor Deposition (CVD) has emerged as the chief method to grow large-area two-dimensional (2D) van der Waals materials. Doping or alloying with foreign atoms or molecules has been extensively used to modify the structure and electronic properties, but the spatial homogeneity of such doping processes is largely unexplored in 2D systems. Here, we use a combination of micro-Raman spectroscopy, x-ray spectroscopy and scanning tunneling microscopy (STM) to map the dopant concentration from the atomic to...

Tuesday 7th January 1157

Nanoporous Ionic Organic Networks: Stabilizing and Supporting Gold Nanoparticles for Catalysis.

Nanoporous ionic organic networks (PIONs) with a high ionic density (three cation-anion pairs per unit) have been synthesized by a facile SN2 nucleophilic substitution reaction. Owing to the electrostatic and steric effect, those ionic networks with porous channels can stabilize and support gold (Au) nanoparticles (NPs) in 1-2 nm. The Au@PION hybrid materials used as a heterogeneous catalyst were highly active, selective, and stable in the aerobic oxidation of saturated alcohols.


Control of strong light-matter coupling using the capacitance of metamaterial nanocavities.

Metallic nanocavities with deep subwavelength mode volumes can lead to dramatic changes in the behavior of emitters placed in their vicinity. This collocation and interaction often leads to strong coupling. Here, we present for the first time experimental evidence that the Rabi splitting is directly proportional to the electrostatic capacitance associated with the metallic nanocavity. The system analyzed consists of different metamaterial geometries with the same resonance wavelength coupled to intersubband...


Microwave Near-Field Imaging of Two-Dimensional Semiconductors.

Optimizing new generations of 2D devices based on van der Waals materials will require techniques capable of measuring variations in electronic properties in situ and with nanometer spatial resolution. We perform scanning microwave microscopy (SMM) imaging of single layers of MoS2 and n- and p-doped WSe2. By controlling the sample charge carrier concentration through the tip bias, we are able to reversibly control and optimize the SMM contrast to image variations in electronic structure and the localized ef...


Giant Topological Nontrivial Band Gaps in Chloridized Gallium Bismuthide.

Quantum spin Hall (QSH) effect is promising for achieving dissipationless transport devices but presently is achieved only at extremely low temperature. Searching for the large-gap QSH insulators with strong spin-orbit coupling (SOC) is the key to increase the operating temperature. We demonstrate theoretically that this can be solved in the chloridized gallium bismuthide (GaBiCl2) monolayer, which has nontrivial gaps of 0.95 eV at the Γ point, and 0.65 eV for bulk, as well as gapless edge states in the na...


Nanophotonic Force Microscopy: Characterizing Particle-Surface Interactions Using Near-Field Photonics.

Direct measurements of particle-surface interactions are important for characterizing the stability and behavior of colloidal and nanoparticle suspensions. Current techniques are limited in their ability to measure pico-Newton scale interaction forces on submicrometer particles due to signal detection limits and thermal noise. Here we present a new technique for making measurements in this regime, which we refer to as nanophotonic force microscopy. Using a photonic crystal resonator, we generate a strongly ...

Saturday 23rd November 1156

Electrically Driven Reversible Insulator-Metal Phase Transition in 1T-TaS2.

In this work, we demonstrate abrupt, reversible switching of resistance in 1T-TaS2 using DC and pulsed sources, corresponding to an insulator-metal-transition between the insulating Mott and equilibrium metallic states. This transition occurs at a constant critical resistivity of 7 mohm-cm regardless of temperature or bias conditions and the transition time is significantly smaller than abrupt transitions by avalanche breakdown in other small gap Mott insulating materials. Furthermore, this critical resisti...

Thursday 8th August 1156

Quantum confined electron-phonon interaction in silicon nanocrystals.

We study the micro-Raman spectra of colloidal silicon nanocrystals as a function of size, excitation wavelength, and excitation intensity. We find that the longitudinal (LO) phonon spectrum is asymmetrically broadened towards the low energy side and exhibits a dip or anti-resonance on the high-energy side, both characteristics of a Fano lineshape. The broadening depends on both nanocrystal size and Raman excitation wavelength. We propose that the Fano lineshape results from interference of the optical phono...

Saturday 16th March 1156

Light-controlled spin filtering in bacteriorhodopsin.

The role of the electron spin in chemistry and biology has been receiving much attention owing to a plausible relation to electromagnetic field effects on living organisms and the prospect of using molecules in the emerging field of spintronics. Recently the chiral-induced spin selectivity effect was observed by electron transmission through organic molecules. In the present study, we demonstrate the ability to control the spin filtering of electrons by light transmitted through purple membranes containing ...


Direct observation of ordered configurations of hydrogen adatoms on graphene.

Ordered configurations of hydrogen adatoms on graphene have long been proposed, calculated and searched for. Here we report direct observation of several ordered configurations of H adatoms on graphene by scanning tunneling microscopy. On the top side of the graphene plane, H atoms in the configurations appear to stick to carbon atoms in the same sublattice. Scanning tunneling spectroscopy measurements revealed a substantial gap in the local density of states in H-contained regions as well as in-gap states ...


Generation of Ensembles of Individually Resolvable Nitrogen Vacancies Using Nanometer-Scale Apertures in Ultrahigh-Aspect Ratio Planar Implantation Masks.

A central challenge in developing magnetically coupled quantum registers in diamond is the fabrication of nitrogen vacancy (NV) centers with localization below ~20 nm to enable fast dipolar interaction compared to the NV decoherence rate. Here, we demonstrate the targeted, high throughput formation of NV centers using masks with a thickness of 270 nm and feature sizes down to ~1 nm. Super-resolution imaging resolves NVs with a full-width maximum distribution of 26±7 nm and a distribution of NV-NV separatio...


Optical Phonons in Twisted Bilayer Graphene with Gate-Induced Asymmetric Doping.

Twisted bilayer graphene (tBLG) devices with ion gel gate dielectrics are studied using Raman spectroscopy in the twist angle regime where a resonantly enhanced G band can be observed. We observe prominent splitting and intensity quenching on the G Raman band when the carrier density is tuned away from charge neutrality. This G peak splitting is attributed to asymmetric charge doping in the two graphene layers, which reveals individual phonon self-energy renormalization of the two weakly-coupled layers of g...


Optical Magnetism and Plasmonic Fano Resonances in Metal-Insulator-Metal Oligomers.

The possibility of achieving optical magnetism at visible frequencies using plasmonic nanostructures has recently been subject of great interest. The concept is based on designing structures that support plasmon modes with electron oscillation patterns that imitate current loops, that is, magnetic dipoles. However, the magnetic resonances are typically spectrally narrow, thereby limiting their applicability in, for example, metamaterial designs. We show that a significantly broader magnetic response can be ...


Scalable Exfoliation Process for Highly Soluble Boron Nitride Nanoplatelets by Hydroxide-assisted Ball Milling.

The scalable preparation of two-dimensional hexagonal boron nitride (h-BN) is essential for practical applications. Despite intense research in this area, high-yield production of two-dimensional h-BN with large-size and highly-soluble remains a key challenge. In the present work, we propose a scalable exfoliation process for hydroxyl-functionalized BN nanoplatelets (OH-BNNPs) by a simple ball milling of BN powders in presence of sodium hydroxide via the synergetic effect of chemical peeling and mechanical ...

Friday 20th October 1155

Near-field Energy Extraction with Hyperbolic Metamaterials.

Although blackbody radiation described by Planck's law is commonly regarded as the maximum of thermal radiation, thermal energy transfer in the near-field can exceed the blackbody limit due to the contribution from evanescent waves. Here, we demonstrate experimentally a broadband thermal energy extraction device based on hyperbolic metamaterials that can significantly enhance near-field thermal energy transfer. The thermal extractor made from hyperbolic metamaterials does not absorb or emit any radiation bu...

Friday 11th August 1155

Plasmonic lasing of nanocavity embedding in metallic nanoantenna array.

Plasmonic nanolasers have ultrahigh lasing thresholds, especially those devices for which all three dimensions are truly subwavelength. Because of a momentum mismatch between the propagating light and localized optical field of the subwavelength nanocavity, poor optical pumping efficiency is another important reason for the ultrahigh threshold but is normally always ignored. Based on a cavity-embedded nanoantenna array design, we demonstrate a room-temperature low-threshold plasmonic nanolaser that is robus...

Monday 12th June 1155

Generation-Dependent Templated Self-Assembly of Biohybrid Protein Nanoparticles around Photosensitizer Dendrimers.

In this article we show the great potential of dendrimers for driving the self-assembly of biohybrid protein nanoparticles. Dendrimers are periodically branched macromolecules with a perfectly defined and monodisperse structure. Moreover, they allow the possibility to incorporate functional units at predetermined sites, either at their core, branches or surface. On these bases, we have designed and synthesized negatively charged phthalocyanine (Pc) dendrimers that behave as photosensitizers for the activati...

Thursday 5th January 1155

Electron Pairing in Designer Materials: A Novel Strategy for a Negative Effective Hubbard U.

We propose a set of design rules with a model Hamiltonian that allows electrons to form attracting pairs through the exploitation of a new combination of resonant band alignment and Coulombic repulsion. The pair bands and single particle bands in various lattices are calculated and compared in energy, and regions of net attraction are identified. This work provides guidelines for the construction of molecular systems, nanocrystals, and nanoparticle arrays with the potential for superconductivity.


Interfacial Effects on Lithium Superoxide Disproportionation in Li-O2 Batteries.

During the cycling of Li-O2 batteries the discharge process gives rise to dynamically evolving agglomerates composed of lithium-oxygen nanostructures; however, little is known about their composition. In this paper, we present results for a Li-O2 battery based on an activated carbon cathode that indicate interfacial effects can suppress disproportionation of a LiO2 component in the discharge product. High-intensity X-ray diffraction and transmission electron microscopy measurements are first used to show th...


Microscopic view on the ultrafast photoluminescence from photo-excited graphene.

We present a joint theory-experiment study on ultrafast photoluminescence from photo-excited graphene. Based on a microscopic theory, we reveal two distinct mechanisms behind the occurring photoluminescence: Besides the well-known incoherent contribution driven by non-equilibrium carrier occupations, we found a coherent part that spectrally shifts with the excitation energy. In our experiments, we demonstrate for the first time the predicted appearance and spectral shift of the coherent photoluminescence.

Monday 2nd May 1154

DNA-assembled nanoparticle rings exhibit electric and magnetic resonances at visible frequencies.

Metallic nanostructures can be used to manipulate light on the sub-wavelength scale to create tailored optical material properties. Next to electric responses, artificial optical magnetism is of particular interest but difficult to achieve at visible wavelengths. DNA-self-assembly has proved to serve as a viable method to template plasmonic materials with nanometer precision and to produce large quantities of metallic objects with high yields. We here present the fabrication of self-assembled ring-shaped pl...


Comparing graphene growth on Cu(111) vs. oxidized Cu(111).

The epitaxial growth of graphene on catalytically active metallic surfaces via chemical vapor deposition (CVD) is known to be one of the most reliable routes towards high-quality large-area graphene. This CVD-grown graphene is generally coupled to its metallic support resulting in a modification of its intrinsic properties. Growth on oxides is a promising alternative that might lead to a decoupled graphene layer. Here, we compare graphene on a pure metallic to graphene on an oxidized copper surface, in both...

Friday 14th May 1153

Quantum thermopower of metallic atomic-size contacts at room temperature.

We report conductance and thermopower measurements of metallic atomic-size contacts, namely gold and platinum, using a scanning tunneling microscope (STM) at room temperature. We find that few-atom gold contacts have an average negative thermopower, whereas platinum contacts present a positive thermopower, showing that for both metals, the sign of the thermopower in the nanoscale differs from that of bulk wires. We also find that the magnitude of the thermopower exhibits minima at the maxima of the conducta...


Switching a Normal Insulator into a Topological Insulator via Electric Field with Application to Phosphorene.

The study of topological insulators has generally involved search of materials that have this property as an innate quality, distinct from normal insulators. Here we focus on the possibility of converting a normal insulator into a topological one by application of an external electric field that shifts different bands by different energies and induces a specific band inversion, which leads to a topological state. Phosphorene is a two-dimensional (2D) material that can be isolated through mechanical exfoliat...


Electrostatically induced superconductivity at the surface of WS2.

We investigate transport through ionic liquid gated field effect transistors (FETs) based on exfoliated crystals of semiconducting WS2. Upon electron accumulation, at surface densities close to -or just larger than- 10(14) cm(-2), transport exhibits metallic behavior, with the surface resistivity decreasing pronouncedly upon cooling. A detailed characterization as a function of temperature and magnetic field clearly shows the occurrence of a gate-induced superconducting transition below a critical temperatu...

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