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20:16 EDT 26th April 2015 | BioPortfolio

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Showing PubMed Articles 1–25 of 2,300+ from Nano letters

1222801

Towards Ferroelectric Control of Monolayer MoS2.

The chemical vapor deposition (CVD) of molybdenum disulfide (MoS2) single-layer films onto periodically poled lithium niobate (PPLN) is possible while maintaining the substrate polarization pattern. The MoS2 growth exhibits a preference for the ferroelectric domains polarized "up" with respect to the surface so that the MoS2 film may be templated by the substrate ferroelectric polarization pattern, without the need for further lithography. MoS2 monolayers preserve the surface polarization of the "up" domain...

1221609

Single-Molecule Imaging of Activated Nitrogen Adsorption on Individual Manganese Phthalocyanine.

An atomic-scale understanding of gas adsorption mechanisms on metal-porphyrins or metal-phthalocyanines is essential for their practical application in biological processes, gas sensing and catalysis. Intensive research efforts have been devoted to the study of coordinative bonding with relatively active small molecules, such as CO, NO, NH3, O2 and H2. However, the binding of single nitrogen atoms has never been addressed, which is both of fundamental interest and indeed essential for revealing the elementa...

Friday 26th June 1220

Hexagonal Boron Nitride Cover on Pt(111) - A New Route to Tune Molecule-metal Interaction and Metal Catalyzed Reactions.

In heterogeneous catalysis molecule-metal interaction is often modulated through structural modifications at the surface or under the surface of the metal catalyst. Here, we suggest an alternative way towards this modulation by placing a two-dimensional (2D) cover on the metal surface. As an illustration, CO adsorption on Pt(111) surface has been studied under 2D hexagonal boron nitride (h-BN) overlayer. Dynamic imaging data from surface electron microscopy and in-situ surface spectroscopic results under ne...

Friday 8th May 1220

Complexation induced phase separation: preparation of composite membranes with a nanometer thin dense skin loaded with metal ions.

We present the development of a facile phase-inversion method for forming asymmetric membranes with a precise high metal ion loading capacity in only the dense layer. The approach combines the use of macromolecule-metal intermolecular complexes to form the dense layer of asymmetric membranes with nonsolvent-induced phase separation to form the porous support. This allows the independent optimization of both the dense layer and porous support while maintaining the simplicity of a phase-inversion process. Mor...

Wednesday 12th February 1220

Kondo effect in a neutral and stable all organic radical single molecule break junction.

Organic radicals are neutral, purely organic molecules exhibiting an intrinsic magnetic moment due to the presence of an unpaired electron in the molecule in their ground state. This property, added to the low spin-orbit coupling and weak hyperfine interactions, make neutral organic radicals good candidates for molecular spintronics insofar the radical character is stable in solid state electronic devices. Here we show that the paramagnetism of the polychlorotriphenylmethyl (PTM) radical molecule in the for...

1219990

Profound effect of substrate hydroxylation and hydration on electronic and optical properties of monolayer MoS2.

Atomic force microscopy, Kelvin probe force microscopy, and scanning photoluminescence spectroscopy image the progressive post-growth hydroxylation and hydration of atomically flat Al2O3(0001) under monolayer MoS2, manifested in large work function shifts (100 mV) due to charge transfer (>10(13) cm(-2)) from the substrate, and changes in PL intensity, energy, and peak width. In contrast, trapped water between exfoliated graphene and Al2O3(0001) causes surface potential and doping changes one and two orders ...

1219924

Electrically Configurable Graphene Field-Effect Transistors with a Graded-potential Gate.

A device architecture for electrically configurable graphene field-effect transistor (GFET) using a graded-potential gate is present. The gating scheme enables a linearly varying electric field that modulates the electronic structure of graphene and causes a continuous shift of the Dirac points along the channel of GFET. This spatially-varying electrostatic modulation produces a pseudo-bandgap observed as a suppressed conductance of graphene within a controllable energy range. By tuning the electrical gradi...

1219830

Tunable light-matter interaction and the role of hyperbolicity in graphene-hBN system.

Hexagonal boron nitride (hBN) is a natural hyperbolic material which can also accommodate highly dispersive surface phonon-polariton modes. In this paper, we examine theoretically the mid-infrared optical properties of graphene-hBN heterostructures derived from their coupled plasmon-phonon modes. We found that the graphene plasmon couples differently with the phonons of the two Reststrahlen bands, owing to their different hyperbolicity. This also leads to distinctively different interaction between an exter...

Wednesday 14th January 1215

Asynchronous Crystal Cell Expansion during Lithiation of K(+)-stabilized α-MnO2.

α-MnO2 is a promising material for Li-ion batteries and has unique tunneled structure that facilitates the diffusion of Li(+). The overall electrochemical performance of α-MnO2 is determined by the tunneled structure stability during its interaction with Li(+), the mechanism of which is, however, poorly understood. In this paper, a novel tetragonal-orthorhombic-tetragonal symmetric transition during lithiation of K(+)-stabilized α-MnO2 is observed using in-situ transmission electron microscopy. Atomic re...

1214888

Plasmon-enhanced Terahertz Photodetection in Graphene.

We report a large area terahertz detector utilizing a tunable plasmonic resonance in sub-wavelength graphene micro-ribbons on SiC(0001) to increase the absorption efficiency. By tailoring the orientation of the graphene ribbons with respect to an array of sub-wavelength bimetallic electrodes, we achieve a condition in which the plasmonic mode can be efficiently excited by an incident wave polarized perpendicular to the electrode array, while the resulting photothermal voltage can be observed between the out...

1214791

Symmetry-derived half-metallicity in atomic and molecular junctions.

Achieving highly spin-polarized electric currents in atomic-scale junctions is of great importance in the field of nanoelectronics and spintronics.
Based on robust symmetry considerations, we propose a mechanism to block completely one of spin conduction channels for a broad class of atomic and molecular junctions bridging two 
ferromagnetic electrodes. 
This particular behaviour is due to the wave-function orthogonality between spin up $s$-like states in ferromagnetic electrode and available $\pi$ ch...

1214709

Live-cell STED microscopy with genetically encoded biosensor.

Of the various super-resolution techniques, stimulated emission depletion (STED) microscopy achieves the best temporal resolution at high spatial resolution enabling live-cell imaging beyond the diffraction limit. However, STED and most other super-resolution imaging methods utilize a particular type of information extractable from the raw data, namely the positions of fluorophores. To expand on the use of super-resolution techniques, we here report live-cell STED microscopy of a dynamic biosensor. Using th...

Tuesday 11th November 1214

Probing and controlling liquid crystal helical nanofilaments.

We report the first in situ measurement of the helical pitch of the helical nanofilament B4 phase of bent-core liquid crystals, using linearly polarized, resonant soft x-ray scattering at the carbon K-edge. A strong, anisotropic scattering peak corresponding to the half-pitch of the twisted smectic layer structure was observed. The equilibrium helical half-pitch of NOBOW is found to be 120 nm, essentially independent of temperature. However, the helical pitch can be tuned by mixing guest organic molecules w...

Friday 31st January 1214

Strong enhancement of second harmonic emission by plasmonic resonances at the second harmonic wavelength.

We perform second harmonic spectroscopy of aluminum nanoantenna arrays that exhibit plasmonic resonances at the second harmonic wavelength between 450 and 570 nm by focusing sub-30 fs laser pulses tunable from 900 to 1140 nm onto the nanoantenna arrays. We find that a plasmonic resonance at the second harmonic wavelength boosts the overall nonlinear process by more than an order of magnitude. In particular, in the measurement the resonant second harmonic polarization component is a factor of about 70 strong...

1213500

Solvothermally synthesized Sb2Te3 platelets show unexpected optical contrasts in mid-infrared near-field scanning microscopy.

We report nanoscale-resolved optical investigations on the local material properties of Sb2Te3 hexagonal platelets grown by solvothermal synthesis. Using mid-infrared near-field microscopy, we find a highly symmetric pattern, which is correlated to a growth spiral and which extends over the entire platelet. As the origin of the optical contrast, we identify domains with different densities of charge carriers. On Sb2Te3 samples grown by other means we did not find a comparable domain structure.

Thursday 27th October 1211

Mechanical Tuning of LaAlO3/SrTiO3 Interface Conductivity.

In recent years, complex-oxide heterostructures and their interfaces have become the focus of significant research activity, primarily driven by the discovery of emerging states and functionalities that open up opportunities for the development of new oxide-based nanoelectronic devices. The highly conductive state at the interface between insulators LaAlO3 and SrTiO3 is a prime example of such emergent functionality, with potential application in high electron density transistors. In this report, we demonst...

Saturday 4th June 1211

Ballistic Phonon Transport in Holey Silicon.

When the size of semiconductors is smaller than the phonon mean free path, phonons can carry heat with no internal scattering. Ballistic phonon transport has received attention for both theoretical and practical aspects because Fourier's law of heat conduction breaks down and the heat dissipation in nanoscale transistors becomes unpredictable in the ballistic regime. While recent experiments demonstrate room-temperature evidence of ballistic phonon transport in various nanomaterials, the thermal conductivit...

1210437

Cathodoluminescence-Activated Nanoimaging: Noninvasive Near-Field Optical Microscopy in an Electron Microscope.

We demonstrate a new nanoimaging platform in which optical excitations generated by a low-energy electron beam in an ultrathin scintillator are used as a noninvasive, near-field optical scanning probe of an underlying sample. We obtain optical images of Al nanostructures with 46 nm resolution and validate the noninvasiveness of this approach by imaging a conjugated polymer film otherwise incompatible with electron microscopy due to electron-induced damage. The high resolution, speed, and noninvasiveness of ...

1208993

The Density of Trap States and Auger Mediated Electron Trapping in CdTe Quantum-Dot Solids.

Charge trapping is an ubiquitous process in colloidal Quantum-Dot Solids and a major limitation to the efficiency of quantum dot based devices such as solar cells, LEDs, and thermo-electrics. While empirical approaches led to a reduction of trapping and thereby efficiency enhancements, the exact chemical nature of the trapping mechanism remains largely unidentified. In this study, we determine the density of trap states in CdTe Quantum-Dot solids both experimentally, using a combination of electrochemical c...

1208897

Molten Au/Ge alloy migration in Ge nanowires.

Herein, we report time-resolved in-situ transmission electron microscopy (TEM) observation of Au particle melting at a Ge nanowire tip, subsequent forming of Au/Ge alloy liquid and its migrating within the Ge nanowire. The migration direction and position of the Au/Ge liquid can be controlled by the applied voltage and the migration speed shows a linear deceleration in the nanowire. In a migration model proposed, the relevant dynamic mechanisms (electromigration, thermodiffusion and viscous force, etc.) are...

1208479

Bringing macromolecules into cells and evading endosomes by oxidized carbon nanoparticles.

A great challenge exists in finding safe, simple and effective delivery strategies to bring matters across cell membrane. Popular methods such as viral vectors, positively charged particles and cell penetrating peptides possess some of the following drawbacks: safety issues, lysosome trapping, limited loading capacity and toxicity, while electroporation produces severe damages on both cargoes and cells. Here we show that a serendipitously discovered, relatively non-toxic, water dispersible, stable, negative...

Wednesday 4th April 1207

Vertically Aligned Sulfur-Graphene Nanowalls on Substrates for Ultrafast Lithium-Sulfur Batteries.

Although lithium-sulfur batteries have gained great interest owing to their high energy density, they lack suitable electrodes capable of rapid charging and discharging to enable a high power density critical for wide applications. Here, we demonstrate a simply electrochemical assembly strategy to achieve vertically aligned sulfur-graphene (S-G) nanowalls onto electrically conductive substrates. Remarkably, in each individual S-G nanowalls, sulfur nanoparticles are homogeneously anchored in between of graph...

Saturday 24th February 1207

Ultrafast Imaging of Surface Plasmons Propagating on a Gold Surface.

We record time-resolved nonlinear photoemission electron microscopy (tr-PEEM) images of propagating surface plasmons (PSPs) launched from a lithographically patterned rectangular trench on a flat gold surface. Our tr-PEEM scheme involves a pair of identical, spatially separated, and interferometrically-locked femtosecond laser pulses. Power dependent PEEM images provide experimental evidence for a sequential coherent nonlinear photoemission process, in which one laser source launches a PSP through a linear ...

Thursday 22nd February 1207

Nine New Phosphorene Polymorphs with Non-Honeycomb Structures: A Much Extended Family.

We predict a new class of monolayer phosphorous allotropes, namely, ε-P, ζ-P, η-P and θ-P. Distinctly different from the monolayer α-P (black) and previously predicted β-P (Phys. Rev. Lett. 112, 176802 (2014)), γ-P and δ-P (Phys. Rev. Lett. 113, 046804 (2014)) with buckled honeycomb lattice, the new allotropes are composed of P4 square or P5 pentagon units that favor tricoordination for P atoms. The new four polymorphs, together with 5 additional hybrid polymorphs, greatly enrich the phosphorene str...

1206979

Superior Conductive Solid-like Electrolytes: Nanoconfining Liquids within the Hollow Structures.

The growth and proliferation of lithium (Li) dendrites during cell recharge is unavoidable, which seriously hinders the development and application of rechargeable Li metal batteries. Solid electrolytes with robust mechanical modulus are regarded as a promising approach to overcome the dendrite problems. However, their room-temperature ionic conductivities are usually too low to reach the level required for normal battery operation. Here, a class of novel solid electrolytes with liquid-like room-temperature...


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