This PDF file contains the front matter associated with SPIE Proceedings Volume 8106, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

In this paper the fundamental properties of heterostructures based on semiconductor nanowires synthesized with molecular beam epitaxy are reviewed. Special focus is given on surface passivation mechanisms with radial epitaxial passivation shells. The growth of radial p-i-n junctions in GaAs nanowires is discussed. Characterization of such nanowires on a single nanowire level is presented. The fundamental limits of single nanowire optical device performance are obtained by numerical simulation and discussed.

Devices fabricated using nanowire structures can provide performance enhancement as well as open new applications. Integration of electronics into textile, referred to as e-textile, offers an opportunity for future electronics. Herein, copper and copper oxide based nanostructures are embedded for e-textile. Metallic copper wire is utilized as a growth substrate, which is simultaneously used as the fiber of mesh textiles. Among various metals, copper is promising as it is non-toxic and relatively abundant on earth. The motivating factor is ease of growth of nanostructures; the nanowire and thin-film forms are synthesized by self-catalytic vapor-solid growth. Simply heating with oxygen gas can form copper oxide nanowires or thin-film depending on the growth conditions. As key building blocks in e-textile, memory, transistor, and interconnect are presented. The resistive memory is comprised of copper oxide thin-film sandwiched within two orthogonal fibers. For a metal semiconductor field effect transistor (MESFET), a Schottky junction is used as the gate to channel barrier. The copper fiber and copper oxide thin-film are devoted to the gate and channel, respectively. For an interconnection, the neighboring fibers are electrically connected by transforming copper oxide nanowires into copper nanowires. Hydrogen thermal reduction of copper oxide is proved to be effective to make conductive nanowires.Inp

For over one decade, numerous research have been performed on field-effect transistor (FET) sensors with a quasi-onedimensional (1D) nanostructure channel demonstrating highly sensitive surface and bulk sensing. The high surface and bulk sensing sensitivity respectively arises from the inherently large surface area-to-volume ratio and tiny channel volume. The generic nanowire FET sensors, however, have limitations such as impractically low output current levels especially near the limit of detection (LOD) that would require downstream remote amplification with an appreciable amount of added noise. We have recently proposed and experimentally demonstrated an innovative amplifying nanowire FET sensor structure that seamlessly integrates therein a sensing nanowire and a nanowire FET amplifier. This novel sensor structure embraces the same geometrical advantage in quasi-1D nanostructure yet it offers unprecedented closeproximity signal amplification with the lowest possible added noise. In this paper, we review the device operating principle and amplification mechanism. We also present the prototype fabrication procedures, and surface and bulk sensing experimental results showing significantly enhanced output current level difference as predicted.

This paper presents our on-going nano-epitaxial efforts to grow tin oxide (SnO₂), zinc oxide (ZnO), and lead zirconate titanate (PZT) for nanotechnology-enhanced devices. The applicable devices involve piezoelectric energy harvesting devices and nanomaterial-enhanced chemical sensors, with the Systems-level vision involving the piezoelectric energy harvesting devices that could self-power chemical sensors for a stand-alone, self-powered device that could harvest its own power from mechanical vibrations. To this end, device concepts are presented herein and preliminary details for ZnO, SnO₂, and PZT material synthesis are presented. The growth of nanowires and nanotetrapods are presented for said device applications using vapor-liquid-solid (VLS), solution synthesis, as well as the results from other synthesis processes. Characterization was done by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).

In this paper, we report on a new method of synthesis for ZnO nanowires on arbitrary substrates and nanowalls on aluminum coated substrates at ambient conditions. Our method is based on sonochemical reaction of Zinc acetate dihydrate (Zn(O2CCH3)2-2H2O) Zinc nitrate hexahydrate (Zn(NO3)2-6H2O) and hexamethylenetetramine (HMT, (CH2).6N4) in aqueous solutions. Repetitive growth cycles resulted in synthesis of ZnO nanowires and nanowalls with controlled dimensions and large aspect ratios. Extensive analysis by transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS) and UV-Visible spectroscopy revealed the crystalline ZnO composition of the synthesized nanostructures. The proposed method is a rapid, inexpensive, low-temperature, catalyst-free, CMOS compatible and environmentally benign alternative to existing growth techniques.

Electron transport is discussed for an ensemble of fused conical indium phosphide nanowires bridging two hydrogenated n⁺-silicon electrodes. The current-voltage (I_d-V_d) characteristics exhibit a Coulomb staircase in dark with a period of ~ 1 V but it disappears under light illumination in some devices, while I_d-V_d is featureless smooth monotonic curve in other devices. It is shown that transport is dominated by a single NW pair in dark, while many NW pairs will contribute to transport under illumination.sentati

Scanning photocurrent microscopy (SPCM) is a powerful technique for investigating local electronic structures and charge transport in semiconductor nanowires. Here we apply this technique to explore colloidal PbSe nanowires and VO₂ nanobeams. Field effect transistors incorporating single colloidal PbSe nanowires were fabricated. A fast, sensitive polarization-dependent photoresponse was observed. SPCM of as-grown PbSe nanowires showed a downward band bending towards the metal electrodes, consistent with their p-type nature. At 54 °C, SPCM of VO₂ nanobeams revealed band bending at the metallic/insulating domain boundaries. At room temperature, we observed photocurrent spots in the middle of the VO₂ nanobeams, indicating local electric fields likely caused by defects.

We have investigated the growth of ZnO nanowires on curved BaTiO3 retroreflector beads, as well as growth of ZnO nanowires on flat substrates. Results indicate that the growth of ZnO aligned nanowire arrays occurs farther away from the Zn source in the retroreflectors, while the results are opposite for the flat Si substrates. In the case of the ZnO nanowires on flat Si, the nanowires formed in nearly aligned arrays are short and significantly thicker, suggesting that the growth occurs both longitudinally and laterally in this process, which is not the case for the growth on the retroreflector beads. The SERS response of the nanowire arrays on the retroreflectors has been compared to random nanowires on flat Si substrates, and results show that the signal strength is 29 times greater in the case of the wires grown on the retroreflectors. Since one would only expect a factor of 4 enhancement due to the light reflecting properties of the retroreflector, it is believed that the enhancement in the SERS signal is due to light channeling by the aligned nanowire arrays.

This proceeding summarizes the materials preparation of position-controlled ZnO-based nanorod heterostructures and fabrication of vertically-aligned wide band gap semiconductor nanorod light-emitting devices. Especially the fabrication of GaN/In_xGa_1-xN/GaN/ZnO nanorod heterostructured visible-light-emitter arrays on sapphire and Si substrates, representing important progress in the field of nanoheteroepitaxy and photonic devices in nanoscale, are reported. Particularly, position-controlled vertical nanostructure arrays make those possible to prepare high-quality material systems without stress or strain accumulation and to fabricate high-performance light-emitting devices (LEDs) with a three-dimensional device configuration. Our method based on nanoheteroepitaxy and position-controlled nanodevice integration for fabricating GaN-based micro-LED arrays constitutes a promising strategy for resolving the issues of conventional GaN LEDs and fabricating high-performance LEDs on various substrates for potential optoelectronic integrated circuits and solid-state lighting applications.

We investigate the electrical conductivity of GaAs-based tunnel junctions enhanced with semimetallic ErAs nanoparticles. In particular, we examine the effects of digitally-graded InGaAs alloys on the n-type side of the tunnel junction, along with different p-type doping levels. Device characteristics of the graded structures indicate that the n-type Schottky barrier may not be the limiting factor in the tunneling current as initially hypothesized. Moreover, significantly improved forward and reverse bias tunneling currents were observed with increased p-type doping, suggesting p-side limitation.

Thermoelectric figure of merit (ZT) depends on three material properties; electrical conductivity, thermal conductivity, and Seebeck coefficient. Maximizing ZT simply requires that electrical conductivity and Seebeck coefficient be high to reduce Joule heating and to increase energy conversion efficiency while thermal conductivity needs to be low to maintain temperature gradient across a thermoelectric material. Unfortunately these three material properties are closely correlated each other in homogeneous bulk semiconductors. Recent demonstrations that employ various semiconductor materials tuned at the nanometer-scale (nanomaterials) have shown great promise in advancing thermoelectrics. Among a wide range of nanomaterials, we focus on "nanocomposites" in which semimetallic nanostructures are epitaxially embedded in a ternary compound semiconductor matrix to attempt tuning the three material properties independently. We demonstrated co-deposition of erbium monoantimonide (ErSb) and In_1-xGa_xSb or InSb_1-yAsy ternary alloy to form nanometer-scale semimetallic ErSb structures within these ternary alloys "nanocomposite" using low-pressure metal organic chemical vapor deposition. The grown nanocomposites were structurally and thermoelectrically analyzed to assess their potential for advanced thermoelectric power generation.

We present models for the growth and electrical conductivity of ErAs films grown with the nanoparticle-seeded film growth technique. This growth mode overcomes the mismatch in rotational symmetry between the rocksalt ErAs crystal structure and the zincblende GaAs crystal structure. This results in films of ErAs grown through a thin film of GaAs that preserves the symmetry of the substrate. The conductivity of the films, as a function of film thickness, are investigated and a surface roughness model is used to explain observed trends. Transmission electron micrographs confirm the suppression of anti-phase domains. A simple diffusion model is developed to describe the diffusion and incorporation of surface erbium into subsurface ErAs layers and predict potential failure mechanisms of the growth method.

We have demonstrated the growth of a group III-V semiconductor binary alloy, indium phosphide (InP), directly on carbon fibers thereby enabling a union of semiconductor and structural materials. Carbon fibers were prepared by electrospinning solutions of polyacrilonitrile (PAN) and dimethylformamide (DMF) followed by carbonization at 750 °C in inert atmosphere. Gold nanoparticles dispersed on the fibers catalyzed nanowire growth by metal organic chemical vapor deposition. X-ray diffraction suggests that the nanowires appear to be epitaxially grown along the (110) direction. Geometrical parameters have been determined by scanning electron microscopy and transmission electron microscopy and elemental analysis has been carried out using energy dispersive spectroscopy. The nanowires grown from carbon fibers are composed of an amorphous shell and crystalline core which alternates at high spatial frequency.mountai