Ok-Joo Lee

Fabrication of Highly Ordered Pore Array in Anodic Aluminum Oxide

Highly ordered pore array in anodic aluminum oxide was fabricated by anodizing pure aluminum. The order of a pore array was affected by anodizing voltage, electrolyte temperature, and first anodizing time. A regular pore array with mean diameter of 24 nm and interpore distance of 109 nm could be formed by two-step anodization at 40 V., oxalic acid concentration of 0.3 M and electrolyte temperature of 15 ‡C. The measured interpore distance showed linearity with anodizing voltage. The diameter of pores was adjusted by pore widening treatment in a 5 wt% phosphoric acid solution at 30 ‡C after two step anodization. The mechanism of self-arrangement of pores could be explained by the repulsive interaction between the pore walls.

Fabrication of flexible field emitter arrays of carbon nanotubes using self-assembly monolayers

This letter reports on flexible field emitter arrays of single-walled carbon nanotubes (SWNTs) aligned on organic polymer substrates. An array of gold electrodes was patterned on the Ti-coated polymer substrate by sputtering gold through a shadow mask. A self-assembly monolayer of organic molecules was then formed on the gold electrodes using thiol chemistry. Cut SWNTs prepared by acidic treatment were attached to the end of the organic molecules. The field emission measurement showed that the turn-on field was 3.88 V/μm at the emission current density of 10 μA/cm2. The current density was 1.6 mA/cm2 at 6 V/μm. This room temperature process is suitable for the fabrication of flexible electronic devices with carbon nanotubes.

Template‐based carbon nanotubes field emitter

Abstract The growth of carbon nanotubes(CNTs) in anodic aluminum oxide(AAO) template and their application to a field emitter are described. AAO templates were fabricated by anodizing bulk aluminum and sputtered thin Al film on Nb‐coated Si wafers. After Co catalyst had been electrochemically deposited into the bottom of the pores in AAO template, CNTs were grown by pyrolyzing C2H2. Depending on the reaction conditions, CNTs grew up to or over the top of the pores in AAO template with different structures. The morphology and structure of CNTs were observed with a scanning electron microscope and a transmission electron microscope. The diameter of CNTs strongly depended on the size of the pores in AAO template and the growing conditions. The electron field emission measurement of the samples resulted in the turn‐on field of 1.9–2.2 V/μm and the field enhancement factor of 2450–5200. The observation of high field enhancement factors is explained in terms of low field screening effect.

Synthesis, characterisation, and thermal conductivity of resorcinol - formaldehyde aerogel

Resorcinol-formaldehyde (RF) organic aerogels were synthesised by sol-gel processing and supercritical carbon dioxide drying over a wide range of processing conditions. The thermal conductivity was measured by a transient hot-wire method for aerogels prepared at various conditions. In general, the thermal conductivity of RF aerogels tends to decrease with decreasing density. When the density of RF aerogels is lower than 67 kg m -3 , the thermal conductivity tends to increase. The RF aerogel obtained by a resorcinol/catalyst (R/C) ratio of 300 shows a lower thermal conductivity compared to other R/C ratios. With respect to low thermal conductivity, we found that the R/C ratio is one of the most important process variables. The aerogel prepared by an R/C ratio of 300 and a density of 67 kg m -3 shows a lower thermal conductivity than those obtained by other conditions.