Kinetics of Graphite Oxidation:  Monolayer and Multilayer Etch Pits in HOPG Studied by STM

Abstract

Oxidation experiments using a particular grade of highly oriented pyrolytic graphite have allowed observation of large numbers of both monolayer and multilayer etch pits on the same samples, formed under identical conditions. Scanning tunneling microscopy was used to measure pits produced after various etch times, temperatures, and O2 pressures. From these data pit growth rates, activation energies, and reaction orders were derived. Although multilayer pits were observed to grow over 3 times faster than monolayer pits in air, both types of pits had the same activation energy. Multilayer etch pits were sometimes observed to form at screw dislocations in the graphite but were also seen in the absence of such defects. The experimentally determined reaction rates and activation energies were not consistent with a direct reaction of edge-carbon atoms with atmospheric oxygen, but instead suggest a chain reaction or preequilibrium process. A mechanism for oxidation of multilayer pits involving reaction of partially oxidized sites on adjacent graphite layers is suggested.

Evaluation of crystalline perfection degree of multi‐walled carbon nanotubes: correlations between thermal kinetic analysis and micro‐Raman spectroscopy

“…The E A values obtained for MWCNTs, ranging between 203 and 219 kJ/mol, are in good agreement with that (∼225 kJ/mol) found for MWCNTs in isothermal experiments by Ajayan et al [37] Also, the values obtained for graphite samples fall in the broad range (100-300 kJ/mol) reported for graphite oxidation. [38] The highest activation energy (236 kJ/mol) pertains to sample G1, whereas the lower value of sample G2 is consistent with the increase in fraction of edge sites and the partial loss of 3D order.…”

Transition metals on the (0 0 0 1) surface of graphite: Fundamental aspects of adsorption, diffusion, and morphology

“…Often, these graphite surfaces exhibit flat, micron-size terraces, but defects can be found. These defects fall into two classes: (1) long-range imperfections, including dislocations and associated stacking faults [25,[34][35][36][37][38][39][40][41][42], as well as folds of the top carbon sheet [39]; and (2) small localized defects which may be single-atom vacancies in the top carbon sheet, inclusions, or adsorbates [43][44][45][46][47][48]. For illustration, an extensively-folded region (type 1 defect) is illustrated in Fig.…”

“…Defects of type 1 can be modified or even created under the influence of a scanning probe tip. Defects of type 2 occur at densities ranging from 1 x 10 -8 nm -2 to 1 x 10 -4 nm -2 [43][44][45][46][47][48], with no obvious NOTICE: This is the author's version of a work that was accepted for publication in Progress in Surface Science. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document.…”

Combined Theoretical and Experimental Investigation of Mechanisms and Kinetics of Vapor-Phase Mercury Uptake by Carbonacoues Surfaces

“…In order to introduce defect sites and etch pits on HOPG, an air-cleaved HOPG sample was subjected to plasma treatment at controlled oxygen pressure. It has been shown previously that high temperature oxidation in air creates low density (< 1% by surface area) of monolayer deep etch pits at existing defects of HOPG, while maintaining the flatness of the graphite surface (105,(126)(127)(128)(129) .…”

“…It has been shown that high temperature oxidation in air creates low density (< 1% by surface area) of monolayer deep etch pits at existing defects of HOPG, while maintaining the flatness of the graphite surface. (105,126,127,133) Plasma oxidation, however, creates mechanical damage on initially flat surface that augments pre-existing defect sites. (105) Plasma oxidation etches the surface, resulting in highly roughened surfaces as confirmed by AFM measurements.…”