Morphological Control of Periodic GaAs Hole Arrays by Simple Au-Mediated Wet Etching

In this study we report etched-GaAs morphologies with noble-metal layers embedded in the etching structures that are prepared by a simple wet process. Well-controlled n-GaAs (100) hole arrays are formed through metal-assisted chemical etching using a sputtered Au layer as an etching catalyst. GaAs exhibits anisotropic etching behavior, which originates from the substrate crystallography. The configuration of hole arrays is determined by the concentration of hydrofluoric acid included in the etching solution, the arrangement of Au catalysis layers relative to the preferential etching direction of the GaAs (100) substrate, and the etching time. The relationship between the etching process and the resultant hole structure is also discussed. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.021206jes] All rights reserved

Morphological Control of Periodic GaAs Hole Arrays by Simple Au-Mediated Wet Etching

In this study we report etched-GaAs morphologies with noble-metal layers embedded in the etching structures that are prepared by a simple wet process. Well-controlled n-GaAs (100) hole arrays are formed through metal-assisted chemical etching using a sputtered Au layer as an etching catalyst. GaAs exhibits anisotropic etching behavior, which originates from the substrate crystallography. The configuration of hole arrays is determined by the concentration of hydrofluoric acid included in the etching solution, the arrangement of Au catalysis layers relative to the preferential etching direction of the GaAs (100) substrate, and the etching time. The relationship between the etching process and the resultant hole structure is also discussed. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.021206jes] All rights reserved.ArticleJOURNAL OF THE ELECTROCHEMICAL SOCIETY. 159(5):D328-D332 (2012)journal articl

Bipolar anodic electrochemical exfoliation of graphite powders

The electrochemical exfoliation of graphite has attracted considerable attention as a method for large-scale, rapid production of graphene and graphene oxide (GO). As exfoliation typically requires direct electrical contact, and is limited by the shape and/or size of the starting graphite, treatment of small graphite particles and powders, the typical form available commercially, is extremely difficult. In this study, GO nanosheets were successfully prepared from small graphite particles and powders by a bipolar electrochemical process. Graphite samples were placed between two platinum feeder electrodes, and a constant current was applied between the feeder electrodes using dilute sulfuric acid as the electrolyte. Optical microscopy, atomic force microscopy, X-ray diffractometry, Raman spectroscopy, and X-ray photoelectron spectroscopy were employed to examine the samples obtained after electrolysis. The results obtained from these analyses confirmed that anodic electrochemical exfoliation occurs in the graphite samples, and the exfoliated samples are basically highly crystalline GO nanosheets with a low degree of oxidation (C/O = 3.6–5.3). This simple electrochemical method is extremely useful for preparing large amounts of graphene and GO from small particles of graphite

Degradation Behavior of Coatings Formed by the Plasma Electrolytic Oxidation Technique on AZ61 Magnesium Alloys Containing 0, 1 and 2 wt% Ca

The characteristics of coatings formed by Plasma Electrolytic Oxidation (PEO) are affected by the composition of metal substrates. In this work, the effect of alloying element Ca (0, 1 and 2 wt%) on the degradation behavior and apatite-forming ability of PEO coated AZ61 magnesium alloys was clarified by means of polarization measurements in 0.9% NaCl solution and an in-vitro test in Simulated Body Fluid (SBF), respectively. The AZ61 alloys were subjected to plasma electrolytic oxidation at a constant current of 200 A/m2 at 25°C for 8 min in 0.5 M Na3PO4 solution. The surface investigation suggested no significant effect of Ca content on the morphology of the PEO coating formed on the AZ61 specimens. The coatings exhibited an eruption-like structure decorated with micropores and microcracks. Their average thicknesses were 13.2, 17.4 and 14.3 µm for AZ61, AZ61-1Ca and AZ61-2Ca, respectively. The polarization measurements showed no significant difference in the corrosion potentials (-1.60 VAg/AgCl) and corrosion current densities (1.61×10-5 A cm-2) of all the coated specimens. Similarly, there was no significant effect of Ca on the apatite-forming ability in SBF, as indicated by the lack of apatite deposition on all the coated specimens after 14 days of immersion. Further sealing of the PEO coatings by chemical treatment in NaOH solution is suggested to enhance the corrosion resistance

Detection of the Oxidation Area by Spectrophotometry: Regional and Temporal Changes in Anodic Oxidation on Titanium in Bipolar Electrochemistry

This study investigated the temporal change in the oxidation area on a titanium (Ti) bipolar electrode (BPE) subjected to bipolar anodization in a direct current (DC) electric field using a spectrophotometer. The rectangular Ti sheet used as a BPE was horizontally positioned at the center of a cell. After the DC bipolar anodization, the oxidized area was detected nondestructively and visually using a specific interference color that depends on the thickness of the barrier-type oxide film formed on the Ti BPE. The change in the L*a*b* color space corresponding to each interference color revealed that the oxidation area increased along the longitudinal axis of the BPE with the increasing electrolysis time by reflecting the change in the potential distributions on the BPE. As visually demonstrated, the area where the anodic reaction proceeded reached saturation at 90% of the BPE surface area

Au-Capped GaAs Nanopillar Arrays Fabricated by Metal-Assisted Chemical Etching

Abstract GaAs nanopillar arrays were successfully fabricated by metal-assisted chemical etching using Au nanodot arrays. The nanodot arrays were formed on substrates by vacuum deposition through a porous alumina mask with an ordered array of openings. By using an etchant with a high acid concentration and low oxidant concentration at a relatively low temperature, the area surrounding the Au/GaAs interface could be etched selectively. Under the optimum conditions, Au-capped GaAs nanopillar arrays were formed with an ordered periodicity of 100 nm and pillar heights of 50 nm