An X-ray diffraction topographic study of highly oriented pyrolytic graphite

Abstract

Highly oriented pyrolytic graphite is a very efficient and well-known X-ray and neutron monochromator that is obtained by thermal cracking of a hydrocarbon gas and a subsequent graphitization treatment. Its microstructure is still, however, a matter of controversy. Several samples of different quality were extensively studied by X-ray diffraction topography. The contrast obtained on OOL reflections is mainly explained in terms of 'primary extinction' and orientation contrast. This implies that the interlayer spacing of the graphite lattice planes remains constant over distances of several tens of micrometres. Graphitization mechanisms are discussed in the light of this interpretation. A microstructural model, closely related to that of as-deposited pyrolytic carbon, is proposed.

Understanding the intrinsic water wettability of graphite

“…Then most people never think of graphite again without realizing how prevalent its use is in our world with applications ranging from a simple writing utensil to being a very good solid lubricant to integration into battery electrodes. 1,2 As the most stable allotrope of carbon, graphite forms naturally in the Earth and is considered to be the highest grade of coal. Placed under high temperature and extreme pressure (900-1300°C and 4.5-6 GPa), the crystallographic structure of graphite can rearrange to form diamond.…”

“…3.35 Å which changes slightly with temperature. 2,[9][10][11] Notably, graphite is a lamellar material with weak interlayer bonding due to van der Waals forces and strong intralayer bonding due to non-polar C-C bonds. This classifies graphite as part of a larger class of materials known as lamellar or van der Waals materials that have strong intralayer bonding and weak interlayer bonding where the uppermost surface can be removed through facile methods such as applying tape and pulling away, thus exposing a fresh or pristine surface.…”

“…The lowest quality sp 2 -hybridzed carbon used in this study is PG which has mosaicity of 30°-60°. 2 Table 1 shows graphite samples used in this study. Optical and AFM scans of the samples are shown in Figure 1.…”

“…The number of defects typically correlates proportionally to the mosaicity of a sample, i.e., a low mosaicity sample will have fewer defects and larger grain sizes than a high mosaicity sample. 2,7 It is worth noting that the optical and AFM images of SPI-1 were taken on a sample that had been cleaved numerous times, thus the surface shows substantially more "damage" than the surface of a brand new sample. Images of the other samples were taken when the sample was relatively new.…”

“…where α=4πk/λ, k is the extinction coefficient of graphite (k=1.3), and λ is the laser wavelength (λ=532 nm With these assumptions, contribution of each graphene layer to the observed G peak intensity will decrease by (1-0.023) 2 for each increase of layer depth; contribution from the top layer of graphene accounts for 4.5% of the observed G peak intensity. 76 This is reflected in Table 7 where I G is 4.5% of the actual experimental peak height to correct for surface sensitivity.…”