Performing quantitative MFM measurements on soft magnetic nanostructures.

We have extended our previous work (Rawlings et al 2010 Phys. Rev. B 82 085404) on simulating magnetic force microscopy (MFM) images for magnetically soft samples to include an accurate representation of coated MFM tips. We used an array of square 500 nm nanomagnets to evaluate our improved MFM model. A quantitative comparison between model and experiment was performed for lift heights ranging from 20 to 100 nm. No fitting parameters were used in our comparison. For all lift heights the qualitative agreement between model and experiment was significantly improved. At low lift heights, where the magnetic signal was strong, the difference between theory and experiment was less than 30%.

Optimized vertical carbon nanotube forests for multiplex surface-enhanced raman scattering detection

The highly sensitive and molecule-specific technique of surface-enhanced Raman spectroscopy (SERS) generates high signal enhancements via localized optical fields on nanoscale metallic materials, which can be tuned by manipulation of the surface roughness and architecture on the submicrometer level. We investigate gold-functionalized vertically aligned carbon nanotube forests (VACNTs) as low-cost straightforward SERS nanoplatforms. We find that their SERS enhancements depend on their diameter and density, which are systematically optimized for their performance. Modeling of the VACNT-based SERS substrates confirms consistent dependence on structural parameters as observed experimentally. The created nanostructures span over large substrate areas, are readily configurable, and yield uniform and reproducible SERS enhancement factors. Further fabricated micropatterned VACNTs platforms are shown to deliver multiplexed SERS detection. The unique properties of CNTs, which can be synergistically utilized in VACNT-based substrates and patterned arrays, can thus provide new generation platforms for SERS detection. © 2012 American Chemical Society.

Synthesis of zinc oxide nanostructures by microheaters in the ambient environment

A catalyst-free synthesis of ZnO nanostructures using platinum microheaters under ambient environmental conditions has been developed. Different types of ZnO nanostructures are synthesized from the oxidization of Zn thin film by local heating. The characterization of two shapes of Pt microheaters is investigated and the relationship between the applied power for heat generation and ZnO nanostructure synthesis is investigated by local heating experiments under ambient conditions. Based on the developed heating approach, synthesis area, location, and morphologies of ZnO nanostructures can be controlled through the deposited thickness of Zn layer and applied heating voltages. Furthermore, a connected multiple-structure (Zn-ZnO-Zn) layer is synthesized using combinative multimicroheaters. © 2002-2012 IEEE.

Multiwall nanotubes, multilayers, and hybrid nanostructures: new frontiers for technology and Raman spectroscopy.

Technological progress is determined, to a great extent, by developments in material science. Breakthroughs can happen when a new type of material or new combinations of known materials with different dimensionality and functionality are created. Multilayered structures, being planar or concentric, are now emerging as major players at the forefront of research. Raman spectroscopy is a well-established characterization technique for carbon nanomaterials and is being developed for layered materials. In this issue of ACS Nano, Hirschmann et al. investigate triple-wall carbon nanotubes via resonant Raman spectroscopy, showing how a wealth of information can be derived about these complex structures. The next challenge is to tackle hybrid heterostructures, consisting of different planar or concentric materials, arranged "on demand" to achieve targeted properties.

Engineering hierarchical nanostructures by elastocapillary self-assembly

Surfaces coated with nanoscale filaments such as silicon nanowires and carbon nanotubes are potentially compelling for high-performance battery and capacitor electrodes, photovoltaics, electrical interconnects, substrates for engineered cell growth, dry adhesives, and other smart materials. However, many of these applications require a wet environment or involve wet processing during their synthesis. The capillary forces introduced by these wet environments can lead to undesirable aggregation of nanoscale filaments, but control of capillary forces can enable manipulation of the filaments into discrete aggregates and novel hierarchical structures. Recent studies suggest that the elastocapillary self-assembly of nanofilaments can be a versatile and scalable means to build complex and robust surface architectures. To enable a wider understanding and use of elastocapillary self-assembly as a fabrication technology, we give an overview of the underlying fundamentals and classify typical implementations and surface designs for nanowires, nanotubes, and nanopillars made from a wide variety of materials. Finally, we discuss exemplary applications and future opportunities to realize new engineered surfaces by the elastocapillary self-assembly of nanofilaments. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Characterisation of nanostructures via terahertz spectroscopy

We have used terahertz spectroscopy to measure the conductivity and time-resolved photoconductivity of a range of semiconducting nanostructures. This article focuses on our recent terahertz conductivity studies on semiconductor nanowires and single walled carbon nanotubes. © 2010 IEEE.

Optical trapping and manipulation of nanostructures

Optical trapping and manipulation of micrometre-sized particles was first reported in 1970. Since then, it has been successfully implemented in two size ranges: the subnanometre scale, where light-matter mechanical coupling enables cooling of atoms, ions and molecules, and the micrometre scale, where the momentum transfer resulting from light scattering allows manipulation of microscopic objects such as cells. But it has been difficult to apply these techniques to the intermediate-nanoscale-range that includes structures such as quantum dots, nanowires, nanotubes, graphene and two-dimensional crystals, all of crucial importance for nanomaterials-based applications. Recently, however, several new approaches have been developed and demonstrated for trapping plasmonic nanoparticles, semiconductor nanowires and carbon nanostructures. Here we review the state-of-the-art in optical trapping at the nanoscale, with an emphasis on some of the most promising advances, such as controlled manipulation and assembly of individual and multiple nanostructures, force measurement with femtonewton resolution, and biosensors.

On-chip focusing of light by metallic nanotip

We present a numerical simulations, fabrication and experimental results for on-chip focusing of surface plasmon polaritons (SPPs) in metal nanotip coupled to the silicon waveguide © 2011 OSA.

Calculation of metallic and insulating phases of V2O3 by hybrid density functionals.

The electronic structure of vanadium sesquioxide V2O3 in its different phases has been calculated using the screened exchange hybrid density functional. The hybrid functional accurately reproduces the experimental electronic properties of all three phases, the paramagnetic metal (PM) phase, the anti-ferromagnetic insulating phase, and the Cr-doped paramagnetic insulating (PI) phase. We find that a fully relaxed supercell model of the Cr-doped PI phase based on the corundum structure has a monoclinic-like local strain around the substitutional Cr atoms. This is found to drive the PI-PM transition, consistent with a Peierls-Mott transition. The PI phase has a calculated band gap of 0.15 eV, in good agreement with experiment.

On-chip focusing of light by metallic nanotip

We present a numerical simulations, fabrication and experimental results for on-chip focusing of surface plasmon polaritons (SPPs) in metal nanotip coupled to the silicon waveguide. © 2011 Optical Society of America.

Multi-walled carbon nanotube conductivity enhancement and band gap widening via rapid pulsed thermal annealing

Herein we report on the transport characteristics of rapid pulsed vacuum-arc thermally annealed, individual and network multi-walled carbon nanotubes. Substantially reduced defect densities (by at least an order of magnitude), measured by micro-Raman spectroscopy, and were achieved by partial reconstruction of the bamboo-type defects during thermal pulsing compared with more traditional single-pulse thermal annealing. Rapid pulsed annealed processed networks and individual multi-walled nanotubes showed a consistent increase in conductivity (of over a factor of five at room temperature), attributed to the reduced number density of resistive axial interfaces and, in the case of network samples, the possible formation of structural bonds between crossed nanotubes. Compared to the highly defective as-grown nanotubes, the pulsed annealed samples exhibited reduced temperature sensitivity in their transport characteristics signifying the dominance of scattering events from structural defects. Transport measurements in the annealed multi-walled nanotubes deviated from linear Ohmic, typically metallic, behavior to an increasingly semiconducting-like behavior attributed to thermally induced axial strains. Rapid pulsed annealed networks had an estimated band gap of 11.26 meV (as-grown; 6.17 meV), and this observed band gap enhancement was inherently more pronounced for individual nanotubes compared with the networks most likely attributed to mechanical pinning effect of the probing electrodes which possibly amplifies the strain induced band gap. In all instances the estimated room temperature band gaps increased by a factor of two. The gating performance of back-gated thin-film transistor structures verified that the observed weak semiconductivity (p-type) inferred from the transport characteristic at room temperature. © 2014 Copyright Taylor & Francis Group, LLC.

On-chip focusing of light by Metallic Nanotip

We investigate numerically and experimentally the on-chip nanoscale focusing of surface plasmon polaritons (SPPs) in metallic nanotip coupled to the silicon waveguide. Strong field enhancement is observed at the apex of the tip. © 2010 Optical Society of America.

Top down scale-up of semiconducting nanostructures for large area electronics

In this paper, we present a study on electrical and optical characteristics of n-type tin-oxide nanowires integrated based on top-down scale-up strategy. Through a combination of contact printing and plasma based back-channel passivation, we have achieved stable electrical characteristics with standard deviation in mobility and threshold voltage of 9.1% and 25%, respectively, for a large area of 1× 1 cm2 area. Through use of contact printing, high alignment of nanowires was achieved thus minimizing the number of nanowire-nanowire junctions, which serve to limit carrier transport in the channel. In addition, persistent photoconductivity has been observed, which we attribute to oxygen vacancy ionization and subsequent elimination using a gate pulse driving scheme. © 2014 IEEE.