Christopher J. Summers

Bio: Christopher J. Summers is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Photonic crystal & Photoluminescence. The author has an hindex of 40, co-authored 281 publications receiving 8688 citations. Previous affiliations of Christopher J. Summers include Georgia Tech Research Institute & Agilent Technologies.

Large-Scale Hexagonal-Patterned Growth of Aligned ZnO Nanorods for Nano-optoelectronics and Nanosensor Arrays

Abstract: An effective approach is demonstrated for growing large-area, hexagonally patterned, aligned ZnO nanorods. The synthesis uses a catalyst template produced by a self-assembled monolayer of submicron spheres and guided vapor-liquid-solid (VLS) growth on a single crystal alumina substrate. The ZnO nanorods have uniform shape and length, align vertically on the substrate, and are distributed according to the pattern defined by the catalyst template. The nanorods grow along [0001] with side surfaces defined by {2110}. This approach opens the possibility of creating patterned one-dimensional nanostructures for applications as sensor arrays, piezoelectric antenna arrays, optoelectronic devices, and interconnects.

Chemical reduction of three-dimensional silica micro-assemblies into microporous silicon replicas

Abstract: The carbothermal reduction of silica into silicon requires the use of temperatures well above the silicon melting point (> or =2,000 degrees C). Solid silicon has recently been generated directly from silica at much lower temperatures ( 500 m(2) g(-1)), and contained a significant population of micropores (< or =20 A). The silicon replicas were photoluminescent, and exhibited rapid changes in impedance upon exposure to gaseous nitric oxide (suggesting a possible application in microscale gas sensing). This process enables the syntheses of microporous nanocrystalline silicon micro-assemblies with multifarious three-dimensional shapes inherited from biological or synthetic silica templates for sensor, electronic, optical or biomedical applications.

Large-Scale Synthesis of Six-Nanometer-Wide ZnO Nanobelts

Abstract: Using a thin film of metallic tin as catalyst, ultrasmall single-crystalline zinc oxide nanobelts have been synthesized in large quantity using a simple solid-vapor technique. The nanobelts have an average width of 5.5 nm and a narrow size distribution of (1.5 nm. The nanobelts grew along the [0001] direction, with (21 h10) top/bottom surfaces and (011 h0) side surfaces. Photoluminescence measurement showed a blue shift in the emission spectrum compared to that acquired from ZnO nanobelts of 200 nm in width. These ultrafine nanobelts should be good candidates for investigating size-induced electrical and optical properties of functional oxides.

Rectangular Porous ZnO–ZnS Nanocables and ZnS Nanotubes

Abstract: ZnS, an important wide-bandgap semiconductor, is a photo-luminescence material. [1] Due to its wide bandgap of 3.8 eV, doping of ZnS with elements such as Tb and Eu, [2] can produce a wide range of exciting optical properties. Quantum dots of core±shell structured CdSe/ZnS have been found to exhibit a lasing effect and can be used for fluoro-immunoas-says, biological imaging, and biosensors. [3,4] Quantum confinement induced lasing has been observed in CdSe/ZnS. Semiconducting ZnO is one of the most important functional oxides for smart devices and optoelectronics. Recently, ultra-long nanobelt structures of ZnO, SnO 2 , In 2 O 3 , CdO, Ga 2 O 3 , and PbO 2 have been synthesized by simply evaporating the desired commercial metal oxide powders at high temperatures. [6,7] The as-synthesized oxide nanobelts are pure, structurally uniform, single crystalline, and most of them are free from dislocations. They have a rectangular cross section with typical widths of 100±300 nm, width-to-thickness ratios of 5±10 nm, and lengths of up to a few millimeters. The nano-belts are an ideal system for fully understanding dimensionally confined transport phenomena in functional oxides and for building functional devices along individual nanobelts. Nanosize sensors and field-effect transistors based on individual nanobelts have been fabricated. Colloid based methods are likely the most popular techniques for synthesis of semiconductor quantum dots. In this paper, using as-synthesized ZnO nanobelts as a template , nanostructured ZnS nanocables and nanotubes have been synthesized by chemical reaction. The structure of the ZnS has been analyzed and the corresponding photolumines-cence properties have been measured. A small blue shift is observed for the ZnO±ZnS cable structures, suggesting a small quantum-confinement effect. The template-assisted method is demonstrated to be a unique technique for producing ZnS nanostructures with controlled morphology. We first present the structural change of the ZnO nanobelt pre-and post-reaction with H 2 S. Figure 1a shows a scanning electron microscope (SEM) image of the as-synthesized ZnO nanobelts, which are pure and structurally uniform. A transmission electron microscope (TEM) image of the nanobelts is given in Figure 2a, clearly showing its uniformity in shape. The ZnO nanobelts have two fast growth directions, [0001] and [1010]. [6] For the [0001] ZnO nanobelts, the top surfaces are ± (21 10), and the side surfaces are ± (0110). The contrast observed on the nanobelts is due to bending induced strain, which is the so-called bending contour in electron diffrac-tion. Based …

Growth of uniformly aligned ZnO nanowire heterojunction arrays on GaN, AlN, and Al0.5Ga0.5N substrates.

Abstract: Vertically aligned single-crystal ZnO nanorods have been successfully fabricated on semiconducting GaN, Al0.5Ga0.5N, and AlN substrates through a vapor−liquid−solid process. Near-perfect alignment was observed for all substrates without lateral growth. Room-temperature photoluminescence measurements revealed a strong luminescence peak at ∼378 nm. This work demonstrates the possibility of growing heterojunction arrays of ZnO nanorods on AlxGa1-xN, which has a tunable band gap from 3.44 to 6.20 eV by changing the Al composition from 0 to 1, and opens a new channel for building vertically aligned heterojunction device arrays with tunable optical properties and the realization of a new class of nanoheterojunction devices.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

A comprehensive review of zno materials and devices

Abstract: The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

Dye-Sensitized Solar Cells

Abstract: Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...

Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays

Abstract: We have converted nanoscale mechanical energy into electrical energy by means of piezoelectric zinc oxide nanowire (NW) arrays. The aligned NWs are deflected with a conductive atomic force microscope tip in contact mode. The coupling of piezoelectric and semiconducting properties in zinc oxide creates a strain field and charge separation across the NW as a result of its bending. The rectifying characteristic of the Schottky barrier formed between the metal tip and the NW leads to electrical current generation. The efficiency of the NW-based piezoelectric power generator is estimated to be 17 to 30%. This approach has the potential of converting mechanical, vibrational, and/or hydraulic energy into electricity for powering nanodevices.