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15:09 EST 20th December 2014 | BioPortfolio

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Showing PubMed Articles 1–25 of 2,100+ from Nano letters


Inverse Metal-Assisted Chemical Etching Produces Smooth High Aspect Ratio InP Nanostructures.

Creating top-down high aspect ratio (AR) nanostructures without surface damage remains challenging for III-V semiconductors. Here, we demonstrate uniform, array-based InP nanostructures with lateral dimensions as small as sub-20 nm and AR > 35 using inverse metal-assisted chemical etching (I-MacEtch) in hydrogen peroxide (H2O2) and sulfuric acid (H2SO4), a purely solution-based yet anisotropic etching method. The mechanism of I-MacEtch, in contrast to regular MacEtch, is explored through surface characteriz...


Second-harmonic generation from metal nanoparticles - resonance enhancement vs. particle geometry.

We demonstrate that optical second-harmonic generation (SHG) from arrays of noncentrosymmetric gold nanoparticles depends essentially on particle geometry. We prepare nanoparticles with different geometrical shapes (L and T) but similar wavelengths for the polarization-dependent plasmon resonances. In contrast to recent interpretations emphasizing resonances at the fundamental frequency, the T shape leads to stronger SHG when only one, instead of both, polarization component of the fundamental field is reso...


Analog computing using reflective plasmonic metasurfaces.

Motivated by the recent renewed interest in compact analog computing using light and metasurfaces (Silva, A. et al., Science 2014, 343, 160-163), we suggest a practical approach to its realization that involves reflective metasurfaces consisting of arrayed gold nanobricks atop a subwavelength-thin dielectric spacer and optically-thick gold film, a configuration that supports gap-surface plasmon resonances. Using well established numerical routines, we demonstrate that these metasurfaces enable independent c...


Designing new lithium-excess cathode materials from percolation theory: Nanohighways in LixNi2-4x/3Sbx/3O2.

Increasing lithium content is shown to be a successful strategy for designing new cathode materials. In layered LixNi2-4x/3Sbx/3O2 (x=1.00-1.15), lithium excess improves both discharge capacity and capacity retention at 1C. Structural studies reveal a complex nanostructure pattern of Li-Sb and Ni-Sb ordering where the interface between these domains forms the correct local configuration for good lithium mobility. The < 1nm Li-Sb stripe domains and their interfaces thereby effectively act as nanohighways for...


Optoelectronic Memory Using Two-Dimensional Materials.

An atomically thin optoelectronic memory array for image sensing is demonstrated with layered CuIn7Se11 and extended to InSe and MoS2 atomic layers. Photogenerated charge carriers are trapped and subsequently retrieved from the potential well formed by gating a 2D material with Schottky barriers. The atomically thin layered optoelectronic memory can accumulate photon-generated charges during light exposure, and the charges can be read out later for data processing and permanent storage. An array of atomical...


Solution-Processable Singlet Fission Photovoltaic Devices.

We demonstrate the successful incorporation of a solution-processable singlet fission material, 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), into photovoltaic devices. TIPS-pentacene rapidly converts high-energy singlet excitons into pairs of triplet excitons via singlet fission, potentially doubling the photocurrent from high-energy photons. Low-energy photons are captured by small-bandgap electron-accepting lead chalcogenide nanocrystals. This is the first solution-processable singlet fis...

Tuesday 20th August 1128

Twin Boundary-Assisted Lithium Ion Transport.

With the increased need for high-rate Li-ion batteries, it has become apparent that new electrode materials with enhanced Li-ion transport should be designed. Interfaces, such as twin boundaries (TBs), offer new opportunities to navigate the ionic transport within nanoscale materials. Here, we demonstrate the effects of TBs on the Li-ion transport properties in single crystalline SnO2 nanowires. It is shown that the TB-assisted lithiation pathways are remarkably different from the previously reported lithia...

Monday 15th April 1128

Low-Voltage Organic Electronics Based on a Gate‒Tunable Injection Barrier in Vertical Graphene-Organic Semiconductor Heterostructures.

The vertical integration of graphene with inorganic semiconductors, oxide semiconductors, and newly-emerging layered materials has recently been demonstrated as a promising route towards novel electronic and optoelectronic devices. Here, we report organic thin film transistors based on vertical heterojunctions of graphene and organic semiconductors. In these thin heterostructure devices current modulation is accomplished by tuning the injection barriers at the semiconductor/graphene interface with the appli...


Integrated Perovskite/Bulk-Heterojunction toward Efficient Solar Cells.

We successfully demonstrated an integrated perovskite/bulk-heterojunction (BHJ) photovoltaic device for efficient light harvesting and energy conversion. Our device efficiently integrated two photovoltaic layers, namely a perovskite film and organic BHJ film, into the device. The device structure is ITO/TiO2/perovskite/BHJ/MoO3/Ag. A wide bandgap small molecule DOR3T-TBDT was used as donor in the BHJ film, and a power conversion efficiency (PCE) of 14.3% was achieved in the integrated device with a high sho...


Sphere Shaped Hierarchical Cathode with Enhanced Growth of Nano-Crystal Planes for High-Rate and Cycling-Stable Li-Ion Batteries.

High-energy and high-power Li-ion batteries have been intensively pursued as power sources in electronic vehicles and renewable energy storage systems in smart grids. With this purpose, developing high-performance cathode materials is urgently needed. Here we report an easy and versatile strategy to fabricate high-rate and cycling-stable hierarchical sphered cathode Li1.2Ni0.13Mn0.54Co0.13O2, by using an ionic interfusion method. The sphere shaped hierarchical cathode is assembled with primary nano-plates w...


Preparation and Size Control of sub-100 nm Pure Nanodrugs.

Pure nanodrugs (PNDs) - nanoparticles consist entirely of drug molecules, become potential candidates for the next generation of nanodrugs. However, the traditional reprecipitation method faces critical challenges including poor reproducibility, low production rates, relatively large sizes and batch-to-batch variations. Here, for the first time, we successfully develop a novel, universal, controllable strategy for preparation of PNDs by an anodized aluminium oxide (AAO) template-assisted method. (1) With th...


Regio-selective Plasmonic Coupling in Metamolecular Analogs of Benzene Derivatives.

In analogy with benzene-derived molecular structures, we construct plasmonic metamolecules by attaching Au nanospheres to specific sites on a hexagonal Au nanoplate. We employ a ligand exchange strategy that allows regio-selective control of nanosphere attachment and study resulting structures using correlated electron microscopy/optical spectroscopy at the single-metamolecule level. We find that plasmonic coupling within the resulting assembly is strongly dependent on the structure of the metamolecule, in ...


Directionally-Controlled Periodic Collimated Beams of Surface Plasmon Polaritons on Metal Film in Ag Nanowire/Al2O3/Ag Film Composite Structure.

Plasmonics holds promise for the realization of miniaturized photonic devices and circuits in which light can be confined and controlled at the nanoscale using surface plasmon polaritons (SPPs) - surface waves of collective oscillations of electrons at a metal/dielectric interface. But realizing plasmonic applications fundamentally requires the ability to guide and transfer SPPs in different plasmonic structures. Here the generation and control of periodic collimated SPP-beams are reported in composite stru...


Magic-Number Gold Nanoclusters with Diameters from 1 to 3.5 nm: Relative Stability and Catalytic Activity for CO Oxidation.

Relative stability of geometric magic-number gold nanoclusters with high point-group symmetry (Ih, D5h, Oh) and size up to 3.5 nm, as well as structures obtained by global optimization using an empirical potential, is investigated using density functional theory (DFT) calculations. Among high-symmetry nanoclusters, our calculations suggest that from Au(147) to Au(923), the stability follows the order Ih > D5h > Oh. However, at the largest size of Au(923), the computed cohesive energy differences among high-...


Nanoscale charge localization induced by random orientations of organic molecules in hybrid perovskite CH3NH3PbI3.

Perovskite-based solar cells have achieved high solar-energy conversion efficiencies and attracted wide attentions nowadays. Despite the rapid progress in solar-cell devices, many fundamental issues of the hybrid perovskites have not been fully understood. Experimentally, it is well known that in CH3NH3PbI3, the organic molecules CH3NH3 are randomly orientated at the room temperature, but the impact of the random molecular orientation has not been investigated. Due to the dipole moment of the organic molecu...

Sunday 13th November 1126

Nano-optics of molecular-shunted plasmonic nanojunctions.

Gold nanoparticles on a planar gold film are separated by 1.1nm thick self-assembled monolayers of different conductivity. Incremental replacement of the non-conductive molecules with a chemically-equivalent conductive version differing by only one atom produces a strong 50nm blue-shift of the coupled plasmon. With modelling this gives conductance of 0.17G0 per biphenyl-4,4'-dithiol molecule, and total conductance across the plasmonic junction of 30G0. Our approach provides a reliable tool quantifying the n...

Tuesday 12th July 1126

Implantation and atomic scale investigation of self-interstitials in graphene.

Crystallographic defects play a key role in determining the properties of crystalline materials. The new class of two-dimensional materials, foremost graphene, have enabled atomically resolved studies of defects, such as vacancies, grain boundaries, dislocations, and foreign atom substitutions. However, atomic resolution imaging of implanted self-interstitials has so far not been reported in any three- but also not in any two-dimensional material. Here, we deposit extra carbon into single-layer graphene at ...

Monday 21st March 1126

Chemical vapor deposition of thin crystals of layered semiconductor SnS2 for fast photo-detection application.

Layered two-dimensional (2D) semiconductors, such as MoS2 and SnS2, have been receiving intensive attention due to their technological importance for the next-generation electronic/photonic applications. We report a novel approach to the controlled synthesis of thin crystal arrays of SnS2 at predefined locations on chip by chemical vapor deposition with seed engineering, and have demonstrated their application as fast photo-detectors with photo-current response time ~ 5 μs. This opens a pathway for the lar...

Wednesday 5th January 1126

High-speed planar GaAs nanowire arrays with fmax >70 GHz by wafer-scale bottom-up growth.

Wafer-scale defect-free planar III-V nanowire (NW) arrays with ~100% yield and precisely defined positions are realized via a patterned vapor-liquid-solid (VLS) growth method. Long and uniform planar GaAs NWs were assembled in perfectly parallel arrays to form double-channel T-gated NW array-based high electron mobility transistors (HEMTs) with DC and RF performance surpassing those for all field-effect transistors (FETs) with VLS NWs, carbon nanotubes (CNTs) or graphene channels in-plane with the substrate...


Magnetic bistability in a submonolayer of sublimated Fe4 Single-Molecule Magnets.

We demonstrate that Fe4 molecules can be deposited on gold by thermal sublimation in ultra-high vacuum with retention of single molecule magnet behavior. A magnetic hysteresis comparable to that found in bulk samples is indeed observed when a submonolayer film is studied by X-ray magnetic circular dichroism. Scanning tunneling microscopy evidences the coexistence of Fe4 molecules assembled in a 2D lattice with short-range hexagonal order and traces of a smaller contaminant. The presence of intact Fe4 molecu...


Tailoring 10-nm-scale Suspended Graphene Junctions and Quantum Dots.

The possibility to make 10-nm-scale, and low-disorder, suspended graphene devices would open up many possibilities to study and make use of strongly coupled quantum electronics, quantum mechanics and optics. We present a versatile method, based on the electromigration of gold-on-graphene bow-tie bridges, to fabricate low-disorder suspended graphene junctions and quantum dots with lengths ranging from 6 nm up to 55 nm. We control the length of the junctions, and shape of their gold contacts by adjusting the ...


Electroosmotic flow reversal outside glass nanopores.

We report observations of a striking reversal in the direction of electroosmotic flow (EOF) outside a conical glass nanopore as a function of salt concentration. At high ionic strengths we observe EOF in the expected direction as predicted by classical electrokinetic theory, while at low salt concentrations the direction of the flow is reversed. The critical crossover salt concentration depends on the pore diameter. Finite-element simulations indicate a competition between the EOF generated from the inner a...


Optically triggered infrared photodetector.

We present, manufacture and characterize the first demonstration of a new class of semiconductor photodetector that we call "Optically Triggered Infrared Photodetector" (OTIP). This photodetector is based on a new physical principle that allows the detection of infrared light to be switched ON and OFF by means of an external light. Our experimental device, fabricated using InAs/AlGaAs quantum dot technology, demonstrates normal incidence infrared detection in the 2-6 μm range. The detection is optically tr...

Sunday 21st November 1125

Manganese Oxide/Carbon Yolk-Shell Nanorod Anodes for High Capacity Lithium Batteries.

Transition metal oxides have attracted a lot of interest for their high energy density in lithium batteries. However, the fast capacity fading and the low power density still limit their practical implementation. In order to overcome these challenges, one dimensional yolk-shell nanorods have been successfully constructed using manganese oxide as an example through a facile two-step sol-gel coating method. Dopamine and tetraethoxysilane are used as precursors to obtain uniform polymer coating and silica laye...

Monday 12th July 1125

Single Nanowire Photoconductive Terahertz Detectors.

Spectroscopy and imaging in the terahertz (THz) region of the electromagnetic spectrum has proven to provide important insights in fields as diverse as chemical analysis, materials characterization, security screening and non-destructive testing. However, compact optoelectronics suited to the most powerful terahertz technique - time-domain spectroscopy - are lacking. Here, we implement single GaAs nanowires as microscopic coherent THz sensors and for the first time incorporated them into the pulsed time-dom...

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