One-dimensional (1D) ZnO nanostructures have been studied intensively and extensively over the last decade not only for their remarkable chemical and physical properties, but also for their current and future diverse technological applications. This article gives a comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods. We will cover the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, position-controlled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronic, and energy harvesting devices.

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One-dimensional ZnO nanostructures: Solution growth and functional properties

Optical transparency, tunable conducting properties and easy processability make metal oxides key materials for advanced optoelectronic devices. This Review discusses recent advances in the synthesis of these materials and their use in applications. Metal oxides (MOs) are the most abundant materials in the Earth's crust and are ingredients in traditional ceramics. MO semiconductors are strikingly different from conventional inorganic semiconductors such as silicon and III–V compounds with respect to materials design concepts, electronic structure, charge transport mechanisms, defect states, thin-film processing and optoelectronic properties, thereby enabling both conventional and completely new functions. Recently, remarkable advances in MO semiconductors for electronics have been achieved, including the discovery and characterization of new transparent conducting oxides, realization of p-type along with traditional n-type MO semiconductors for transistors, p–n junctions and complementary circuits, formulations for printing MO electronics and, most importantly, commercialization of amorphous oxide semiconductors for flat panel displays. This Review surveys the uniqueness and universality of MOs versus other unconventional electronic materials in terms of materials chemistry and physics, electronic characteristics, thin-film fabrication strategies and selected applications in thin-film transistors, solar cells, diodes and memories.

Metal oxides for optoelectronic applications

Flexible graphene fi ber (GF) stands for a new type of fi ber of practical importance, which integrates such unique properties as high strength, electrical and thermal conductivities of individual graphene sheets into the useful, macroscopic ensembles. GFs possess the common characteristics of fi bers like the mechanical fl exibility for textiles, while maintaining the uniqueness such as low cost, light weight, and ease of functionalization in comparison with conventional carbon fi bers. [ 1–3 ] Due to the extraordinary challenge to assemble two-dimensional (2D) microcosmic graphene sheets with irregular size and shape into macroscopic fi brillar confi guration, however, the success in fabrication of neat graphene fi bers only comes true recently. [ 1–4 ]

All‐Graphene Core‐Sheath Microfibers for All‐Solid‐State, Stretchable Fibriform Supercapacitors and Wearable Electronic Textiles

In this paper, in order to increase the power conversion efficiency we demonstrated the selective growth of "nanoforest" composed of high density, long branched "treelike" multigeneration hierarchical ZnO nanowire photoanodes. The overall light-conversion efficiency of the branched ZnO nanowire DSSCs was almost 5 times higher than the efficiency of DSSCs constructed by upstanding ZnO nanowires. The efficiency increase is due to greatly enhanced surface area for higher dye loading and light harvesting, and also due to reduced charge recombination by providing direct conduction pathways along the crystalline ZnO "nanotree" multi generation branches. We performed a parametric study to determine optimum hierarchical ZnO nanowire photoanodes through the combination of both length-wise growth and branched growth processes. The novel selective hierarchical growth approach represents a low cost, all solution processed hydrothermal method that yields complex hierarchical ZnO nanowire photoanodes by utilizing a simple engineering of seed particles and capping polymer.

http://pubs.acs.org/doi/pdf/10.1021/nl1037962

Nanoforest of hydrothermally grown hierarchical ZnO nanowires for a high efficiency dye-sensitized solar cell.

A highly stretchable metal electrode is developed via the solution-processing of very long (>100 μm) metallic nanowires and subsequent percolation network formation via low-temperature nanowelding. The stretchable metal electrode from very long metal nanowires demonstrated high electrical conductivity (~9 ohm sq(-1) ) and mechanical compliance (strain > 460%) at the same time. This method is expected to overcome the performance limitation of the current stretchable electronics such as graphene, carbon nanotubes, and buckled nanoribbons.

Highly Stretchable and Highly Conductive Metal Electrode by Very Long Metal Nanowire Percolation Network

Modern means of communication rely on electric fields and currents to carry the flow of information. In contrast, biological systems follow a different paradigm that uses ion gradients and currents, flows of small molecules, and membrane electric potentials. Living organisms use a sophisticated arsenal of membrane receptors, channels, and pumps to control signal transduction to a degree that is unmatched by manmade devices. Electronic circuits that use such biological components could achieve drastically increased functionality; however, this approach requires nearly seamless integration of biological and manmade structures. We present a versatile hybrid platform for such integration that uses shielded nanowires (NWs) that are coated with a continuous lipid bilayer. We show that when shielded silicon NW transistors incorporate transmembrane peptide pores gramicidin A and alamethicin in the lipid bilayer they can achieve ionic to electronic signal transduction by using voltage-gated or chemically gated ion transport through the membrane pores.

https://www.pnas.org/content/pnas/106/33/13780.full.pdf

Bioelectronic silicon nanowire devices using functional membrane proteins

All-solution processed, low-temperature zinc oxide nanowire network transistor fabrication on a polymer substrate was demonstrated. This simple process can produce high resolution metal electrode transistors with inorganic semiconductor nanowire active material in a fully maskless sequence, eliminating the need for lithographic and vacuum processes. The temperature throughout the processing was under 140°C, which will enable further applications to electronics on low-cost, large-area flexible polymer substrates.

ZnO nanowire network transistor fabrication on a polymer substrate by low-temperature, all-inorganic nanoparticle solution process

We report a rapid and low temperature process for fabricating composite TiO2 electrodes for dye-sensitized solar cells on glass and plastics by in tandem spray deposition and laser annealing. A homogenized KrF excimer laser beam (248 nm) was used to layer-by-layer anneal spray deposited TiO2 nanoparticles. The produced TiO2 film is crack free and contains small particles (30 nm) mixed with different fractions of larger particles (100–200 nm) controlled by the applied laser fluence. Laser annealed double-layered structure is demonstrated for both doctor-blade deposited and spray-deposited electrodes and performance enhancement can be observed. The highest demonstrated all-laser-annealed cells utilizing ruthenium dye and liquid electrolyte showed power conversion efficiency of ∼3.8% under simulated illumination of 100 mW/cm2.

Laser annealed composite titanium dioxide electrodes for dye-sensitized solar cells on glass and plastics

A liner for a semiconductor processing chamber and a semiconductor processing chamber are provided. In one embodiment, a liner for a semiconductor processing chamber includes a body having an outwardly extending flange. A plurality of protrusions extend from a bottom surface of the flange. The protrusions have a bottom surface defining a contact area that is asymmetrically distributed around the bottom surface of the flange.

Temperature controlled chamber liner

Nanoscale electrodes based on one-dimensional inorganic conductors could possess significant advantages for electrochemical measurements over their macroscopic counterparts in a variety of electrochemical applications. We show that the efficiency of the electrodes constructed of individual highly doped silicon nanowires greatly exceeds the efficiency of flat Si electrodes. Modification of the surfaces of the nanowire electrodes with phospholipid bilayers produces an efficient biocompatible barrier to transport of the solution redox species to the nanoelectrode surface. Incorporating functional α-hemolysin protein pores in the lipid bilayer results in a partial recovery of the Faradic current due to the specific transport through the protein pore. These assemblies represent a robust and versatile platform for building a new generation of highly specific biosensors and nano/bioelectronic devices.

Nipun Misra

Papers

Bioelectronic silicon nanowire devices using functional membrane proteins

ZnO nanowire network transistor fabrication on a polymer substrate by low-temperature, all-inorganic nanoparticle solution process

Laser annealed composite titanium dioxide electrodes for dye-sensitized solar cells on glass and plastics

Temperature controlled chamber liner

Highly Efficient Biocompatible Single Silicon Nanowire Electrodes with Functional Biological Pore Channels