Atomically thin layers of B-N-C-O with tunable composition.

In recent times, atomically thin alloys of boron, nitrogen, and carbon have generated significant excitement as a composition-tunable two-dimensional (2D) material that demonstrates rich physics as well as application potentials. The possibility of tunably incorporating oxygen, a group VI element, into the honeycomb sp(2)-type 2D-BNC lattice is an intriguing idea from both fundamental and applied perspectives. We present the first report on an atomically thin quaternary alloy of boron, nitrogen, carbon, and oxygen (2D-BNCO). Our experiments suggest, and density functional theory (DFT) calculations corroborate, stable configurations of a honeycomb 2D-BNCO lattice. We observe micrometer-scale 2D-BNCO domains within a graphene-rich 2D-BNC matrix, and are able to control the area coverage and relative composition of these domains by varying the oxygen content in the growth setup. Macroscopic samples comprising 2D-BNCO domains in a graphene-rich 2D-BNC matrix show graphene-like gate-modulated electronic transport with mobility exceeding 500 cm(2) V(-1) s(-1), and Arrhenius-like activated temperature dependence. Spin-polarized DFT calculations for nanoscale 2D-BNCO patches predict magnetic ground states originating from the B atoms closest to the O atoms and sizable (0.6 eV < E g < 0.8 eV) band gaps in their density of states. These results suggest that 2D-BNCO with novel electronic and magnetic properties have great potential for nanoelectronics and spintronic applications in an atomically thin platform.

The changing colors of a quantum-confined topological insulator.

Bismuth selenide (Bi2Se3) is a 3D topological insulator, its strong spin-orbit coupling resulting in the well-known topologically protected coexistence of gapless metallic surface states and semiconducting bulk states with a band gap, Eg ≃ 300 meV. A fundamental question of considerable importance is how the electronic properties of this material evolve under nanoscale confinement. We report on catalyst-free, high-quality single-crystalline Bi2Se3 with controlled lateral sizes and layer thicknesses that could be tailored down to a few nanometers and a few quintuple layers (QLs), respectively. Energy-resolved photoabsorption spectroscopy (1.5 eV < E(photon) < 6 eV) of these samples reveals a dramatic evolution of the photon absorption spectra as a function of size, transitioning from a featureless metal-like spectrum in the bulk (corresponding to a visually gray color), to one with a remarkably large band gap (Eg ≥ 2.5 eV) and a spectral shape that correspond to orange-red colorations in the smallest samples, similar to those seen in semiconductor nanostructures. We analyze this colorful transition using ab initio density functional theory and tight-binding calculations which corroborate our experimental findings and further suggest that while purely 2D sheets of few QL-thick Bi2Se3 do exhibit small band gaps that are consistent with previous ARPES results, the presently observed large gaps of a few electronvolts can only result from a combined effect of confinement in all three directions.

A simple chemical vapor deposition method for the production of highly conductive polymer poly(3,4-ethylenedioxythiophene).

Conductive thin films of Poly(3,4-ethylenedioxythiophene) (PEDOT) have been successfully deposited on a variety of substrates by a simple chemical vapor deposition (CVD) method starting from the liquid monomer (EDOT) and using FeCl3 as a catalyst. Resistivity measurements indicated very good conductivity of the material, comparable with other previously reported values for PEDOT deposited by CVD. Further cyclic voltammetry measurements indicated a value of around -4.7 eV for the HOMO level of PEDOT in the deposited films, in agreement with other reported values. This value is within the bandgap of most semiconductors, and together with the relative low internal resistance makes our material an ideal candidate as a solid-state hole transport material for dye sensitized solar cells.

Growth of E18 rat hippocampal neuronal cells on nanostructured surfaces for enhanced electrical stimulation and recording.

We have prepared gold nanowire arrays inside nanoporous alumina templates with the goal towards neuronal interfacing and electrical recording from neurons. We have investigated biofunctionalization of such gold nanowire arrays (GNWs) and gold nanofilm (GNF) platforms to understand its impact on neuronal attachment and growth. Poly-D-Lysine (PDL) was coated on the nano-templates surfaces for adhesion of neurons which also enhanced the neuronal growth. Optical microscopy and scanning electron microscopy images revealed strong affinity and improved growth of neurons on PDL-coated surfaces. Such results will impact future investigation of stimulation and recording of electrical activity on nanoscale surfaces.

Synthesis of nanomaterials using self-assembled nanotemplates.

Nanoporous alumina templates and titania nanotube arrays have emerged as highly important materials due to their many potential applications in a variety of research areas. The templates are prepared using an electrochemical anodization process starting from metallic Al or Ti films. Several different synthesis routes for the deposition of such templates have been demonstrated in literature. This article provides an overview of the various synthesis routes that may be employed. The templates have diverse applications and may also be utilized in the electrodeposition of nanowire arrays of a variety of materials, such as metals, semiconductors, etc. A brief overview of these deposition methods is also provided.

High-aspect ratio nano-noodles of alumina and titania.

We report the formation of high-aspect ratio rod-like structures or 'nano-noodles' of alumina or titania. Such structures are formed either by rapid anodization of aluminum/titanium foil or by long-term post-anodization treatment of porous templates. Specifically, the nano-noodle structures form during anodization in highly acidic electrolytes and/or at high anodization voltages, or when porous templates are etched for long periods of time in an acid. Growth mechanism for such structures is also proposed.