Highly oriented pyrolytic graphite

About: Highly oriented pyrolytic graphite is a research topic. Over the lifetime, 3145 publications have been published within this topic receiving 76715 citations. The topic is also known as: Highly oriented pyrolytic graphite, HOPG.

First- and second-order Raman scattering from finite-size crystals of graphite

Abstract: First- and second-order Raman scattering from graphite has been studied. The second-order spectra of single crystals and of highly oriented pyrolytic graphite are continuous and exhibit several well-defined bands which can be attributed to features in the density of vibrational states as determined from current lattice-dynamics models. The density of states deduced from the lattice-dynamics model of Nicklow, Wakabayashi, and Smith provides the best replication of the second-order Raman spectrum, but is nevertheless somewhat deficient in this regard, and in need of improvement. The dependence of the first- and second-order graphite Raman spectra on crystallite size has also been studied for a series of samples with typical dimensions ${L}_{c}$ and ${L}_{a}$ as small as 30 \AA{}. With decreasing crystal size the features in the second-order spectrum broaden noticeably and additional broad features appear in both the first- and second-order spectra. The additional first- and second-order features are also attributed to structure in the vibrational density of states and arise from the wave-vector selection-rule relaxation that results from finite-crystal-size effects. Evidence is presented to demonstrate that the above described spectral features are intrinsic and not associated with impurity excitations.

Covalent Modification of Carbon Surfaces by Aryl Radicals Generated from the Electrochemical Reduction of Diazonium Salts

Abstract: Electrochemical reduction of a wide variety of aromatic diazonium salts on carbon electrodes (glassy carbon, highly oriented pyrolytic graphite) leads to the covalent attachment of the corresponding aromatic radicals The films thus deposited on glassy carbon surfaces require mechanical abrasion to be removed Cyclic voltammetry, X-ray photoelectron spectroscopy, polarization modulation IR reflection absorption spectroscopy, Auger spectroscopy, and Rutherford backscattering spectroscopy allow the characterization of the overlayer and an estimate of the surface coverage The latter can be controlled through diazonium concentration and electrolysis duration The mechanism of derivatization is discussed on the basis of the kinetic data obtained from cyclic voltammetry and preparative electrolysis This versatile method of surface modification may find applications in the field of carbon−epoxy composites as attested by the successful binding of grafted p-aminophenyl groups with epichlorhydrin

Work Functions and Surface Functional Groups of Multiwall Carbon Nanotubes

Abstract: We have studied the work function and density of states (DOS) of multiwall carbon nanotubes (MWNTs) using ultraviolet photoelectron spectroscopy (UPS) Raw MWNTs were purified by successive sonication, centrifugation, sedimentation, and filtration processes with the aid of a nonionic surfactant The purified MWNTs showed a slightly lower work function (43 eV) than that of highly oriented pyrolytic graphite (44 eV) Effects of three different oxidative treatments, air-, oxygen plasma-, and acid-oxidation, have also been studied It was found that oxidative treatments affect the DOS of valence bands and increase the work function X-ray photoelectron spectroscopy (XPS) measurements have suggested that gas-phase treatment preferentially forms hydroxyl and carbonyl groups, while liquid-phase treatment forms carboxylic acid groups on the surface of MWNTs These surface chemical groups disrupt the π-conjugation and introduce surface dipole moments, leading to higher work functions up to 51 eV We expect the

Induced magnetic ordering by proton irradiation in graphite.

Abstract: We provide evidence that proton irradiation of energy 2.25 MeV on highly oriented pyrolytic graphite samples triggers ferro- or ferrimagnetism. Measurements performed with a superconducting quantum interferometer device and magnetic force microscopy reveal that the magnetic ordering is stable at room temperature.

Lithium Diffusion in Graphitic Carbon

Abstract: Graphiticcarboniscurrentlyconsideredthestate-of-the-artmaterial for the negative electrode in lithium ion cells, mainly due to its high reversibility and low operating potential. However, carbon anodes exhibit mediocre charge/ discharge rate performance, which contributes to severe transport-induced sur- face structural damage upon prolonged cycling and limits the lifetime of the cell. Lithium bulkdiffusion in graphitic carbon is not yet completely understood, partly due to the complexity of measuring bulk transport properties in finite-sized nonisotropic particles. To solvethis problem forgraphite, weuse the Devanathan- Stachurski electrochemical methodology combined with ab initio computations to deconvolute and quantify the mechanism of lithium ion diffusion in highly oriented pyrolytic graphite (HOPG). The results reveal inherent high lithium ion diffusivityinthedirectionparalleltothegrapheneplane(∼10 -7 -10 -6 cm 2 s -1 ),as comparedtosluggishlithiumiontransportalonggrainboundaries(∼10 -11 cm 2 s -1 ), indicating the possibility of rational design of carbonaceous materials and com- posite electrodes with very high rate capability. SECTION Energy Conversion and Storage