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16:25 EDT 2nd August 2015 | BioPortfolio

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Showing PubMed Articles 1–25 of 2,500+ from Nano letters

Tuesday 30th November 1305

Hexagonal Silicon Realized.

Silicon, arguably the most important technological semiconductor, is predicted to exhibit a range of new and interesting properties when grown in the hexagonal crystal structure. To obtain pure hexagonal silicon is a great challenge since it naturally crystallizes in the cubic structure. Here, we demonstrate the fabrication of pure and stable hexagonal silicon evidenced by structural characterization. In our approach we transfer the hexagonal crystal structure from a template hexagonal gallium phosphide nan...

Saturday 25th September 1305

Optical Epitaxial Growth of Gold Nanoparticle Arrays.

We use an optical analogue of epitaxial growth to assemble gold nanoparticles into 2D arrays. Particles are attracted to a growth template via optical forces and interact through optical binding. Competition between effects determines the final particle arrangements. We use a Monte Carlo model to design a template that favors growth of hexagonal particle arrays. We experimentally demonstrate growth of a highly stable array of fifty, 200-nm-diameter gold particles with spacing of 1.1 μm.

Monday 28th December 1304

Adhesion and Atomic Structures of Gold on Ceria Nanostructures: The Role of Surface Structure and Oxidation State of Ceria Supports.

We report an aberration-corrected electron microscopy analysis of the adhesion and atomic structures of gold nanoparticle catalysts supported on ceria nanocubes and nanorods. Under oxidative conditions, the as-prepared gold nanoparticles on the ceria nanocubes have extended atom layers at the metal-support interface. In contrast, regular gold nanoparticles and rafts are present on the ceria nanorod supports. Under the reducing conditions of water-gas shift reaction, the extended gold atom layers and rafts v...

Tuesday 1st September 1304

Tunable optical excitations in twisted bilayer graphene form strongly bound excitons.

When two sheets of graphene stack in a twisted bilayer graphene (tBLG) configuration, the resulting constrained overlap between interplanar 2p orbitals produce angle-tunable electronic absorption resonances.By applying a novel combination of multiphoton transient absorption (TA) microscopy and TEM, we resolve the electronic structure and ensuing relaxation by probing resonant excitations of single tBLG domains. Strikingly, we find that the transient electronic population in resonantly excited tBLG domains i...

Saturday 9th May 1304

Tunneling Plasmonics in Bilayer Graphene.

We report experimental signatures of plasmonic effects due to electron tunneling between adjacent graphene layers. At sub-nanometer separation, such layers can form either a strongly coupled bilayer graphene with a Bernal stacking or a weakly coupled double-layer graphene with a random stacking order. Effects due to interlayer tunneling dominate in the former case but are negligible in the latter. We found through infrared nano-imaging that bilayer graphene supports plasmons with a higher degree of confinem...


Magnetically Actuated Single-Wall Carbon Nanotubes.

We couple magnetic tweezer techniques with standard lithography methods to make magnetically actuated single-wall carbon nanotube (SWNT) devices. Parallel arrays of 4-10 micron-long SWNT cantilevers are patterned with one end anchored to the substrate and the other end attached to a micron-scale iron magnetic tag that is free to move in solution. Thermal fluctuations of this tag provide a direct measurement of the spring constant of the SWNT cantilevers, yielding values of 10-7‒10-8 N/m. This tag is also ...


Relaxometry and dephasing imaging of superparamagnetic magnetite nanoparticles using a single qubit.

The dynamics of single magnetic particles play a vital role in their response to external stimuli. Specifically, thermally-driven random spin flips in superparamagnetic nanoparticles generate a unique spin-noise fingerprint, which can be used to localize them in a host matrix and also serve as an identifier in a heterogeneous environment. In this paper, we use scanning probe relaxometry and dephasing of the nitrogen-vacancy (NV) center in diamond to characterize the spin-noise of a single 10-nm magnetite pa...


Fabrication of Sub-25 nm Diameter GaSb Nanopillar Arrays by Nanoscale Self-Mask Effect.

GaSb individual nanowires and nanowire arrays are considered as intriguing candidates for electronic and photonic applications. In this paper, we report a new mask-free method to fabricate large area GaSb nanopillar arrays through reactive ion etching of GaSb substrates facilitated by O2 plasma. We have shown that nanoscale oxide self-masks could form thereby facilitating the formation of GaSb nanopillars. We have achieved GaSb nanowires with diameters less than 25 nm and an aspect ratio of 24. Additionally...


Steep Subthreshold Swing n- and p-Channel Operation of Bendable Feedback Field-Effect Transistors with p(+)-i-n(+) Nanowires by Dual-Top-Gate Voltage Modulation.

In this study, we present the steep switching characteristics of bendable feedback field-effect transistors (FBFETs) consisting of p(+)-i-n(+) Si nanowires (NWs) and dual-top-gate structures. As a result of a positive feedback loop in the intrinsic channel region, our FBFET features the outstanding switching characteristics of an on/off current ratio of approximately 10(6), and point subthreshold swings (SSs) of 18-19 mV/dec in the n-channel operation mode and of 10-23 mV/dec in the p-channel operation mode...


Competing forces during contact formation between a tip and a single molecule.

Sn-phthalocyanine adsorbs on Ag(111) in a physisorbed or a chemisorbed configuration. Both structures are contacted with the tip of a combined scanning tunneling and atomic force microscope. The tunneling conductances of both configurations exhibit similar exponential variations with the tip-molecule distance. The short-range forces, however, display non-trivial distance dependencies. First-principles calculations reproduce the experimental results. Both attractive and repulsive interactions occur between t...

Sunday 22nd September 1303

Torsional detwinning domino in nanotwinned one-dimensional nanostructures.

How to maintain sustained deformation in one-dimensional nanostructures without localized failure is an important question for many applications of nanotechnology. Here we report a phenomenon of torsional detwinning domino which leads to giant rotational deformation without localized failure in nanotwinned one-dimensional metallic nanostructures. This mechanism is demonstrated in nanotwinned Cu nanorods via molecular dynamics simulations, where coherent twin boundaries are transformed into twist boundaries ...

Thursday 2nd May 1303

Controlled Three-Dimensional Hierarchical Structuring by Memory-Based, Sequential Wrinkling.

This paper describes how a memory-based, sequential wrinkling process can transform flat polystyrene sheets into multi-scale, three-dimensional hierarchical textures. Multiple cycles of plasma-mediated skin growth followed by directional strain relief of the substrate resulted in hierarchical architectures with characteristic generational (G) features. Independent control over wrinkle wavelength and wrinkle orientation for each G was achieved by tuning plasma treatment time and strain-relief direction for e...

Tuesday 26th February 1303

Uniaxial strain redistribution in corrugated graphene - clamping, sliding, friction and 2D band splitting.

Graphene is a promising material for strain engineering based on its excellent flexibility and elastic properties, coupled with very high electrical mobility. In order to implement strain devices, it is important to understand and control the clamping of graphene to its support. Here we investigate the limits of the strong van der Waals interaction on friction clamping. We find that the friction of graphene on a SiO2 substrate can support a maximum local strain gradient, and that higher strain gradients res...


Combining 2 nm spatial resolution and 0.02 % precision for deformation mapping of semiconductor specimens in a transmission electron microscope by precession electron diffraction.

Precession electron diffraction has been used to provide accurate deformation maps of a device structure showing that this technique can provide a spatial resolution of better than 2 nm and a precision of better than 0.02 %. The deformation maps have been fitted to simulations that account for thin specimen relaxation. By combining the experimental deformation maps and simulations, we have been able to separate the effects of the stressor and recessed sources and drains and show that the Si3N4 stressor incr...


Antenna enhanced graphene THz emitter and detector.

Recent intense electrical and optical studies of graphene have pushed the material to the forefront of optoelectronic research. Of particular interest is the few terahertz (THz) frequency regime where efficient light sources and highly sensitive detectors are very challenging to make. Here we present THz sources and detectors made with graphene field effect transistors (GFETs) enhanced by a double-patch antenna and an on-chip silicon lens. We report the first experimental observation of 1-3 THz radiation fr...


Robust and Soft Elastomeric Electronics Tolerant to Our Daily Lives.

Clothes represent a unique textile, as they simultaneously provide robustness against our daily activities and comfort (i.e., softness). For electronic devices to be fully integrated into clothes, the devices themselves must be as robust and soft as the clothes themselves. However, to date, no electronic device has ever possessed these properties, because all contain components fabricated from brittle materials, such as metals. Here, we demonstrate robust and soft elastomeric devices where every component p...


Peptide Bioink: Self-Assembling Nanofibrous Scaffolds for 3D Organotypic Cultures.

Printable scaffolds with adequate mechanical strength and stiffness are sought after to ensure viability of printed cells and tissues. We report the first peptide bioinks - lysine-containing hexapeptides which self-assemble into stable, nanofibrous three-dimensional hydrogels with unprecedented stiffness of up to 40kPa. These biocompatible scaffolds support the 3D culture of human stem cells and differentiation of primary cells into organotypic (gastrointestinal and skin) structures for high-throughput scre...


Hybridization in 3D: a novel route towards plasmonic metamolecules.

Plasmonic metamolecules have received much interest in the last years since they can produce a wide spectrum of different hybrid optical resonances. Most of the configurations presented so far, however, considered planar resonators lying on a dielectric substrate. This typically yields high damping and radiative losses, which severely limit the performance of the system. Here we show that these limits can be overcome by considering a 3D arrangement made from slanted nanorod dimers extruding from a silver ba...

Friday 28th September 1302

Plasmonic Properties of Silicon Nanocrystals Doped with Boron and Phosphorus.

Degenerately doped silicon nanocrystals are appealing plasmonic materials due to silicon's low cost and low toxicity. While surface plasmonic resonances of boron-doped and phosphorus-doped silicon nanocrystals were recently observed, there currently is poor understanding of the effect of surface conditions on their plasmonic behavior. Here, we demonstrate that phosphorus-doped silicon nanocrystals exhibit a plasmon resonance immediately after their synthesis but may lose their plasmonic response with oxidat...

Saturday 2nd June 1302

Optically pumped two-dimensional MoS2 lasers operating at room-temperature.

The discovery of direct bandgap semiconducting two-dimensional (2D) transition metal dichalcogenides (TMDCs) has opened a new era in flexible optoelectronic devices. Critical to this development is the realization of a semiconductor laser using the emerging 2D TMDCs. Here, by embedding 2D MoS2 at the interface between a free-standing microdisk and microsphere, we have demonstrated, for the first time, room-temperature lasing from 2D TMDCs. The devices exhibit multiple lasing peaks in the wavelength range of...


Spontaneous hot-electron light emission from electron-fed optical antennas.

Nanoscale electronics and photonics are among the most promising research areas providing functional nano-components for data transfer and signal processing. By adopting metal-based optical antennas as a disruptive technological vehicle, we demonstrate that these two device-generating technologies can be interfaced to create an electronically-driven self-emitting unit. This nanoscale plasmonic transmitter operates by injecting electrons in a contacted tunneling antenna feedgap. Under certain operating condi...


Integrating substrate-less electrospinning with textile technology for creating biodegradable 3D structures.

The present study describes a unique way of integrating substrate-less electrospinning process with textile technology. We developed a new collector design that provided a pressure-driven, localized cotton-wool structure in free space from which continuous high strength yarns were drawn. An advantage of this integration was that the textile could be drug/dye loaded and be developed into a core-sheath architecture with greater functionality. This method could produce potential nano-textiles for various biome...

Sunday 11th October 1299

Fast anion-exchange in highly luminescent nanocrystals of cesium lead halide perovskites (CsPbX3, X=Cl, Br, I).

Post-synthestic chemical transformations of colloidal nanocrystals, such as ion-exchange reactions, provide an avenue to compositional fine tuning or to otherwise inaccessible materials and morphologies. While cation-exchange is facile and commonplace, anion-exchange reactions have not received substantial deployment. Here we report fast, low-temperature, deliberately partial or complete anion-exchange in highly luminescent semiconductor nanocrystals of cesium lead halide perovskites (CsPbX3, X=Cl, Br, I). ...

Sunday 5th July 1299

Control of Electron Beam-Induced Au Nanocrystal Growth Kinetics through Solution Chemistry.

Measurements of solution-phase crystal growth provide mechanistic information that is helpful in designing and synthesizing nanostructures. Here, we examine the model system of individual Au nanocrystal formation within a defined liquid geometry during electron beam irradiation of gold chloride solution, where radiolytically formed hydrated electrons reduce Au ions to solid Au. By selecting conditions that favor the growth of well-faceted Au nanoprisms, we measure growth rates of individual crystals. The vo...

Friday 17th April 1299

Systematic enumeration of sp(3) nanothreads.

Slow decompression of crystalline benzene in large-volume high-pressure cells has recently achieved synthesis of a novel one-dimensional allotrope of sp(3) carbon in which stacked columns of benzene molecules rehybridize into an ordered crystal of nanothreads. The progeniter benzene molecules function as six-valent one-dimensional super-atoms with multiple binding sites. Here we enumerate their hexavalent bonding geometries -- recognizing that the repeat unit of interatomic connectivity ("topological unit c...