Possibility of a double-well potential formation in diamondlike amorphous carbon

Abstract

A microscopic model, which describes specific features of the electronic spectrum of various allotropic forms of amorphous carbon as being responsible for their structure peculiarities, is presented. It is shown that the formation of a double-well potential is a possible driving force for this behavior.71.23.Cq and 61.43.Dq

Micro-Raman study of CNx composites subjected to high pressure treatment

“…4) are similar to the ones reported in polycrystalline graphite [17,18]. Now we are going to discuss the results obtained on the basis of the theoretical model proposed by us in a previous work [10]. Let us start from prerequisites pointed out earlier concerning the graphite-diamond phase structural transformation [19]: 1) the transition from a sp 2 to a sp 3 coordinated phase is readily realized under a high pressure and high temperature treatments only if the initial material is graphite with a high degree of crystallinity; 2) the rombohedral structural modification of graphite is the appropriate initial structure for a direct transformation along the stacking (c-axis) direction to form the diamond structure.…”

“…Taking the broadening of the 1332 cm -1 Raman line as a measure of the degree of ordering, we show that the diamond crystals obtained in this work are better than the ones described in [9]. For a qualitative explanation of the phase structural transition from amorphous carbon to diamond crystals, we use the double-well potential model recently proposed by us to describe structural peculiarities of amorphous carbon [10]. For completeness, X-ray diffraction and microhardness measurements were also carried out.…”

“…Let us consider the second prerequisite. In terms of the proposed double-well potential model [10], the appearance of sp 3 coordination in graphite may be the result of the displacement of some carbon atoms in a direction perpendicular to the layer (parallel to the optic axis). Keeping it in mind we shall compare the structure of the hexagonal and rombohedral modification of graphite [19].…”

“…For the second half of atoms the displacement is relieved but is equiprobable for opposite directions. In terms of a dynamical approach [10], the mean equilibrium for the atomic position is within the layer. However, from this point of view there are fundamental differences between rombohedral and hexagonal graphite.…”

“…However, a number of recent works testify that there are some problems using the I D /I G ratio as a quantitative criterion for sp 2 cluster size in amorphous a-C and a-C:H films [14,15]. In this connection, it is appropriate to note that the doublewell potential model describing the coexistence of sp 2 -and sp 3 -bonds in amorphous carbon [10] does not deal with nano-sized sp 2 -coordinated graphite clusters. Nevertheless, the spectrum of the initial film (see curve a in Fig.…”