In some aspects, a method of fabricating a memory cell is provided that includes (1) fabricating a steering element above a substrate; and (2) fabricating a reversible-resistance switching element coupled to the steering element by selectively fabricating carbon nano-tube (CNT) material above the substrate. Numerous other aspects are provided.

Memory cell that employs a selectively fabricated carbon nano-tube reversible resistance-switching element and methods of forming the same

ZnO nanorod arrays on an ITO substrate and nanorod powder have been prepared via a chemical method in aqueous solution at low temperature. Two dimensions of composite nanorods in the arrays were obtained by controlling the reaction time. SEM, XRD, UV−vis transmission, and PL measurements have been utilized to characterize the samples. The surface photovoltage (SPV) spectra of the three samples have been comparatively investigated by a lock-in amplifier with dc bias and Kelvin probe (KP) based measurements. The kinetic features of SPV responses are interpreted in terms of ac SPV phase spectra and SPV transients on a KP. We demonstrate that the photovoltaic properties of ZnO nanorods not only depend on the rod size, but also rely on the crystallographic orientation. The mechanisms therein have been discussed in detail. Our results could lead to better understanding of the photovoltaic properties in ZnO nanostructures.

Size- and Orientation-Dependent Photovoltaic Properties of ZnO Nanorods

Preparation of ZnO nanorods through wet chemical method

Two-step preparation of Ag/tetrapod-like ZnO with photocatalytic activity by thermal evaporation and sputtering

Localized heating has emerged as a viable technique for the site specific synthesis of one-dimensional (1D) nanostructures. By localizing the heat source, the extent of chemical vapor deposition synthesis reactions can be confined to well-defined, microscale regions. Resistive heating has been extensively used to realize highly localized regions of elevated temperature while maintaining a microelectronics-compatible thermal environment elsewhere. Other localized heating methods are being pursued as well. Overall, the approach is simple, flexible, and robust, and offers unique opportunities in 1D nanostructure synthesis, characterization, and integration. Herein, the recent progress of these techniques is reviewed and discussed.

Localized heating induced chemical vapor deposition for one-dimensional nanostructure synthesis

At room-temperature ambient, carbon nanotubes (CNTs) were selectively synthesized on each bridge of the microheater array (MHA) formed on a glass substrate. Both multiwalled (MW) and single-walled CNTs could be formed by controlling the MHA temperature, which was confirmed from Raman spectroscopy. By incorporating the selectively grown MW CNTs into the lateral-gated field-emitter arrays, high current density of electron emission was observed with low device leakage.

Selective Formation of Carbon Nanotubes and Its Application to Field-Emitter Arrays

The one-dimensional ZnO nanostructures prepared through thermal evaporation under various cooling down procedures by changing the flow rates of the carrier gas and the reactive gas were investigated. The nanorod structures were changed into the nanonail types with a broad head through the reduction of the flow rate of the carrier gas. The decrease of the reactive gas reduced the length of the nail heads due to the limited mass transport of reactive gas. The intensity ratio of the ultraviolet emission/green emission of photoluminescence was proportional to the length of the broad head showing a larger surface area. The vertically aligned nanostructures were grown along the [0 0 0 1] direction of ZnO regardless of the aligned directions. The crystal direction of the nanostructures was determined by that of the initial ZnO crystal.

Shape control and characterization of one-dimensional ZnO nanostructures through the synthesis procedure

Neutron shielding simulations by using GEANT4 and PHITS code are performed. As a neutron source, $^{252}$Cf is considered and the energy distribution of the neutrons emitted from $^{252}$Cf is assumed the Watt fission spectrum. The neutron dose equivalent rates with and without the shield are estimated for shielding materials such as graphite, iron, polyethylene, NS-4-FR and KRAFTON-HB. For the neutron shielding simulations by using GEANT4, high precision (G4HP) model with G4NDL 4.2 based on ENDF-VII data are used. And for PHITS simulations, JENDL-4.0 library are used for the same purpose. It is found that differences between the shielding calculations by using GEANT4 with G4NDL 4.2 and PHITS with JENDL-4.0 library are not significant for all cases considered in this work. We investigate the accuracy of the neutron dose equivalent rates obtained from GEANT4 and PHITS by comparing our simulation results with experimental data and other values calculated earlier. Calculated neutron dose equivalent rates agree well with the experimental dose equivalent rates within 20% errors except for polyethylene. For polyethylene material, discrepancy between the calculations and the experiments are up to 40% but all simulations show consistent features.

GEANT4 and PHITS simulations of the shielding of neutrons from $^{252}$Cf source

We investigated the optical properties of ZnO nanorods on nanosilicon-on-insulator using variable temperature photoluminescence (PL) spectroscopy, and explored the contribution of exciton–phonon coupling and surface resonance effect on the emission characteristics of the nanorods The low-temperature (<100 K) PL spectra revealed different strengths of exciton–phonon interaction for nanorods of different surface structures The exciton–phonon coupling strength was stronger for nanorods of rougher surfaces with enhanced contribution of longitudinal optical phonon replicas of free exciton Despite exhibiting different coupling strengths of exciton–phonon interactions, the room-temperature PL showed an unchanged energy position at 328 eV for nanorods of different surface structures The unchanged energy position of band-edge emission was caused by the competitive effect of the surface defects induced exciton–phonon interaction and the surface resonance effect in faceted nanorods

Do-Yoon Kim

Papers

Selective Formation of Carbon Nanotubes and Its Application to Field-Emitter Arrays

Shape control and characterization of one-dimensional ZnO nanostructures through the synthesis procedure

GEANT4 and PHITS simulations of the shielding of neutrons from $^{252}$Cf source

Emission characteristics of ZnO nanorods on nanosilicon-on-insulator: competition between exciton–phonon coupling and surface resonance effect

Simulation and measurement of characteristics of MICROMEGAS gaseous detectors.