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PubMed Journal Database | Nano letters RSS

07:55 EST 10th February 2016 | BioPortfolio

The US National Library of Medicine and National Institutes of Health manage PubMed.gov which comprises of more than 21 million records, papers, reports for biomedical literature, including MEDLINE, life science and medical journals, articles, reviews, reports and  books.  BioPortfolio aims to publish relevant information on published papers, clinical trials and news associated with users selected topics.

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Showing PubMed Articles 1–25 of 2,900+ from Nano letters

Van der Waals Heterostructures with High Accuracy Rotational Alignment.

We describe the realization of van der Waals (vdW) heterostructures with accurate rotational alignment of individual layer crystal axes. We illustrate the approach by demonstrating a Bernal-stacked bilayer graphene formed using successive transfers of monolayer graphene flakes. The Raman spectra of this artificial bilayer graphene possess a wide 2D band which is best fit by four Lorentzians, consistent with Bernal stacking. Scanning tunneling microscopy reveals no moiré pattern on the artificial bilayer gr...

Effects of surface electron doping and substrate on the superconductivity of epitaxial FeSe films.

Superconductivity in FeSe is greatly enhanced in films grown on SrTiO3 substrates, although the mechanism behind remains unclear. Recently, surface potassium (K) doping has also proven able to enhance the superconductivity of FeSe. Here by using scanning tunneling microscopy, we compare the K doping dependence of the superconductivity in FeSe films grown on two substrates: SrTiO3 (001) and graphitized SiC (0001). For thick films (20 unit cells (UC)), the optimized superconducting (SC) gaps are of similar si...

Shot noise of 1,4-benzenedithiol single-molecule junctions.

We report measurements of the shot noise on single-molecule Au-1,4-benzenedithiol (BDT)-Au junctions, fabricated with the mechanically controllable break junction (MCBJ) technique at 4.2 K in a wide range of conductance values from 10(-2) to 0.24 conductance quanta. We introduce a simple measurement scheme using a current-amplifier and a spectrum analyzer, and that does not imply special requirements regarding the electrical leads. The experimental findings provide evidence that the current is carried by a ...

Voltage Scaling of Graphene Device on SrTiO3 Epitaxial Thin Film.

Electrical transport in monolayer graphene on SrTiO3 (STO) thin film is examined in order to promote gate-voltage scaling using a high-k dielectric material. The atomically flat surface of thin STO layer epitaxially grown on Nb-doped STO single-crystal substrate offers good adhesion between the high-k film and graphene, resulting in non-hysteretic conductance as a function of gate voltage at all temperatures down to 2 K. The two-terminal conductance quantization under magnetic fields corresponding to quantu...

Chemical bath deposition of p-type transparent, highly conducting (CuS)x:(ZnS)1-xnanocomposite thin films and fabrication of Si heterojunction solar cells.

P-type transparent conducting films of nanocrystalline (CuS)x:(ZnS)1-x were synthesized by facile and low-cost chemical bath deposition. Wide angle x ray scattering (WAXS) and high resolution transmission electron microscopy (HRTEM) were used to evaluate the nanocomposite structure, which consists of sub-5-nm crystallites of sphalerite ZnS and covellite CuS. Film transparency can be controlled by tuning the size of the nanocrystallites which is achieved by adjusting the concentration of the complexing agent...

Optical manipulation and spectroscopy of silicon nanoparticles exhibiting dielectric resonances.

We demonstrate that Si nanoparticles with scattering properties exhibiting strong dielectric resonances can be successfully manipulated using optical tweezers. The large dielectric constant of silicon has a distinct advantage over conventional colloids nanoparticles in that it leads to enhanced trapping forces without the heating associated with metallic nanoparticles. Further, the spectral features of the trapped nanoparticles provide a unique marker for probing size, shape, orientation and local dielectri...

Helical Growth of Ultrathin Gold-Copper Nanowires.

In this work, we report the synthesis and detailed structural characterization of novel helical gold-copper nanowires. The nanowires possess the Boerdijk-Coxeter-Bernal structure, based on the pile up of octahedral, icosahedral, and/or decahedral seeds. They are self-assembled into a coiled manner as individual wires or into a parallel-ordering way as groups of wires. The helical nanowires are ultrathin with a diameter of less than 10 nm and variable length of several micrometers, presenting a high density ...

Dynamics of Spatially Confined Bisphenol A Trimers in a Unimolecular Network on Ag(111).

Bisphenol A (BPA) aggregates on Ag(111) shows a polymorphism between two supramolecular motifs leading to formation of distinct networks depending on thermal energy. With rising temperature a dimeric pairing scheme reversibly converts into a trimeric motif, which forms a hexagonal superstructure with complex dynamic characteristics. The trimeric arrangements notably organize spontaneously into a self-assembled one-component array with supramolecular BPA rotors embedded in a two-dimensional stator sublattice...

A 250 mV Cu/SiO2/W memristor with half-integer quantum conductance states.

Memristive devices, whose conductance depends on previous programming history are of significant interest for building non-volatile memory and brain-inspired computing systems. Here, we report half-integer quantized conductance transitions G = (n/2)(2e(2)/h) for n = 1, 2, 3, . . . in Cu/SiO2/W memristive devices observed below 300 mV at room temperature. This is attributed to the nanoscale filamentary nature of Cu conductance pathways formed inside SiO2. Retention measurements also show spontaneous filament...

Low-Resistance 2D/2D Ohmic Contacts: A Universal Approach to High-Performance WSe2, MoS2, and MoSe2 Transistors.

We report a new strategy for fabricating 2D/2D low-resistance ohmic contacts for a variety of transition metal dichalcogenides (TMDs) using van der Waals assembly of substitutionally doped TMDs as drain/source contacts and TMDs with no intentional doping as channel materials. We demonstrate that few-layer WSe2 field-effect transistors (FETs) with 2D/2D contacts exhibit low contact resistances of ~ 0.3 kΩ µm, high on/off ratios up to > 10(9), and high drive currents exceeding 320 µA µm(-1). These favorab...

Stark effect spectroscopy of mono- and few-layer MoS2.

We demonstrate electrical control of the A-exciton interband transition in mono- and few-layer MoS2 crystals embedded into photocapacitor devices via the DC Stark effect. Electric field dependent low-temperature photoluminescence spectroscopy reveals a significant tuneability of the A-exciton transition energy, up to ∼ 16 meV, from which we extract the mean DC exciton polarisability 〈β〉N = (0.58 ± 0.25) × 10(-8) DmV(-1). The exciton polarisability is shown to be layer-independent, indicating a stro...

Imaging Cyclotron Orbits of Electrons in Graphene.

Electrons in graphene can travel for several microns without scattering at low temperatures, and their motion becomes ballistic, following classical trajectories. When a magnetic field B is applied perpendicular to the plane, electrons follow cyclotron orbits. Magnetic focusing occurs when electrons injected from one narrow contact focus onto a second contact located an integer number of cyclotron diameters away. By tuning the magnetic field B and electron density n in the graphene layer, we observe magneti...

Unveiling in vivo subcutaneous thermal dynamics by infrared luminescent nanothermometers.

The recent development of core/shell engineering of rare earth doped luminescent nanoparticles has ushered a new era in fluorescence thermal biosensing, allowing for the performance of minimally invasive experiments, not only in living cells but also in more challenging small animal models. Here, the potential use of active-core/active-shell Nd3+- and Yb3+-doped nanoparticles as subcutaneous thermal probes has been evaluated. These temperature nanoprobes operate in the infrared transparency window of biolog...

Photoelectrochemistry of Pristine Mono- and Few-layer MoS2.

Two-dimensional crystals are promising building blocks for the new generation of energy materials due to their low volume, high surface area and high transparency. Electrochemical behavior of these crystals determines their performance in applications such as energy storage/conversion, sensing, and catalysis. Nevertheless, the electrochemistry of an isolated monolayer of molybdenum disulfide, which is one of the most promising semiconducting crystals, has not been achieved to date. We report here on photoel...

The electric field of CO tips and its relevance for atomic force microscopy.

Metal tips decorated with CO molecules have paved the way for an impressively high resolution in Atomic Force Microscopy (AFM). Although Pauli repulsion and the associated CO tilting play a dominant role at short distances, experiments on polar and metallic systems show that electrostatic interactions are necessary to understand the complex contrast observed and its distance evolution. Attempts to describe those interactions in terms of a single electrostatic dipole replacing the tip have led to contradicto...

Gate-optimized thermoelectric power factor in ultrathin WSe2 single crystals.

We report an electric field tuning of the thermopower in ultrathin WSe2 single crystals over a wide range of carrier concentration by using electric double-layer (EDL) technique. We succeeded in the optimization of power factor not only in the hole but also in the electron side, which has never been chemically accessed. The maximized values of power factor are one-order larger than that obtained by changing chemical composition, reflecting the clean nature of electrostatic doping.

Harnessing a Quantum Design Approach for making Low-loss Superlenses.

Recently, so-called "superlenses", made from metamaterials that are structured on a length scale much less than an optical wavelength, have shown impressive diffraction-beating image resolution, but they use materials with negative dielectric responses, and they absorb much of the light in a way that seriously degrades both the resolution and brightness of the image. Here we demonstrate an alternative "quantum metamaterials" (QM) approach that uses materials structured at the nanoscale, i.e. comparable to a...

Synthesis of Cesium Lead Halide Perovskite Nanocrystals in a Droplet-Based Microfluidic Platform: Fast Parametric Space Mapping.

Prior to this work, fully inorganic nanocrystals of cesium lead halide perovskite (CsPbX3, X = Br, I and Cl and Cl/Br and Br/I mixed halide systems), exhibiting bright and tunable photoluminescence, have been synthesized using conventional batch (flask-based) reactions. Unfortunately, our understanding of the parameters governing the formation of these nanocrystals is still very limited due to extremely fast reaction kinetics and multiple variables involved in ion-metathesis-based synthesis of such multinar...

Continuously controlled optical band gap in oxide semiconductor thin films.

The optical band gap of the prototypical semiconducting oxide SnO2 is shown to be continuously controlled through single axis lattice expansion of nanometric films induced by low-energy helium implantation. While traditional epitaxy induced strain results in Poisson driven multi-directional lattice changes shown to only allow discrete increases in bandgap, we find that a downward shift in the band gap can be linearly dictated as a function of out-of-plane lattice expansion. Our experimental observations clo...

van der Waals Solids from Self-Assembled Nanoscale Building Blocks.

Traditional atomic van der Waals materials such as graphene, hexagonal boron-nitride, and transition metal dichalcogenides have received widespread attention due to the wealth of unusual physical and chemical behaviors that arise when charges, spins, and vibrations are confined to a plane. Though not as widespread as their atomic counterparts, molecule-based two-dimensional (2D) layered solids offer significant benefits; their structural flexibility will enable the development of materials with tunable prop...

Frictional properties of nano-junctions including atomically thin sheets.

Using non-equilibrium molecular dynamics simulations and a coarse-grained description of a system, we have investigated frictional properties of nano-junctions including atomically thin sheets embedded between metal surfaces. We found that the frictional properties of the junctions are determined by the interplay between the lattice mismatch of the contacting surfaces and out-of-plane displacements of the sheet. The simulations provide insight into how and why the frictional characteristics of the nano-junc...

Self-assembly of graphene nanoblisters sealed to a bare metal surface.

The possibility to intercalate noble gas atoms below epitaxial graphene monolayers coupled with the instability at high temperature of graphene on the surface of certain metals has been exploited to produce Ar filled graphene nanosized blisters evenly distributed on the bare Ni(111) surface. We have followed in real time the self assembling of the nanoblisters during the thermal annealing of the Gr/Ni(111) interface loaded with Ar and characterized their morphology and structure at the atomic scale. The nan...

Spider silk peptide is a compact, linear nano-spring ideal for intracellular tension sensing.

Recent development and applications of calibrated, FRET-based tension sensors have led to a new understanding of single molecule mechanotransduction in a number of biological systems. To expand the range of accessible forces, we systematically measured FRET vs. force trajectories for 25, 40 and 50 amino acid peptide repeats derived from spider silk. Single molecule fluorescence-force spectroscopy showed that the peptides behaved as linear springs instead of the nonlinear behavior expected for a disordered p...

Sequence-specific recognition of microRNAs and other short nucleic acids with solid-state nanopores.

The detection and quantification of short nucleic acid sequences has many potential applications in studying biological processes, monitoring disease initiation and progression, and evaluating environmental systems, but is challenging by nature. We present here an assay based on the solid-state nanopore platform for the identification of specific sequences in solution. We demonstrate that hybridization of a target nucleic acid with a synthetic probe molecule enables discrimination between duplex and single-...

Magnetic propulsion of microswimmers with DNA-based flagellar bundles.

Many motile micro-organisms possess flagella to propel or swim through viscous fluids. Mimicking these highly evolved micro-structures with nanoscale features is challenging, but would enable the realization of functional microswimmers. Here we show that DNA-based self-assembly can serve as a general and flexible tool to construct artificial flagella of several micrometers in length and only tens of nanometers in diameter. By attaching the DNA flagella to biocompatible magnetic microparticles, we provide a ...


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