Nanoscopic observations of stress-induced formation of graphitic nanocrystallites at amorphous carbon surfaces

Nanocrystalline Graphite Formed at Fullerene‐Like Carbon Film Frictional Interface

“…And these two peaks were broader and one‐to‐one corresponding to the D GR (1330 cm −1 ) and G GR (1580 cm −1 ). According to previous studies, G E 2g symmetry breathing presented the in‐plane stretching breathing mode of sp 2 ‐C pair‐atoms in aromatic and olefinic molecules more than in sixfold rings. While the symmetry breathing D band intensity arouse signifies the presence of sp 2 atoms in clusters or sixfold aromatic rings in disordered structure .…”

“…Similar research also suggests that sp 3 networks could be compressed and transform into a thermodynamically stable graphitic structure due to shear strain . And the graphitic phase transformation process could be only induced by stress in the absence of heat . Moreover, FL networks also include sp 3 hybrid carbon bonds within the clusters and on the grain boundaries besides the pentagonal and heptagonal carbon rings .…”

“…For typical diamond‐like carbon films, the micro‐Raman spectra involves a G peak of symmetry in‐plane bond‐stretching vibration of sp 2 carbon atoms and a D peak of breathing vibration of sp 2 carbon rings . And it presented in disordered extent that differs from the sixfold rings in perfect NG, in which the D and G peaks were sharp centered at 1330 and 1580 cm −1 . Micro‐Raman spectrum of FL‐C:H film from wavenumber of 800–2000 cm −1 were shown in Figure , which showed a weak shoulder peak at 1200 cm −1 apart from the typical D and G peaks.…”

“…While the symmetry breathing D band intensity arouse signifies the presence of sp 2 atoms in clusters or sixfold aromatic rings in disordered structure . Therefore, this indicates the tribofilm possess a possible existence of graphitic nanocrystallines or short ordered multi‐layered graphene islands . Moreover, the peak width are broader than perfect graphite in reference, which means the graphitic nano structures are embedded in amorphous matrix and are not ordered as perfect NG .…”

Temperature‐driven wear behavior of Si3N4‐based ceramic reinforced by in situ formed TiC0.3N0.7 particles

“…Here it is worth noting that the characteristic D peak (1360 cm −1 ) and G peak (1600 cm −1 ) of graphite are detected, where the intensity of D peak is higher than that of G peak, indicating that the graphite has the severe defect and disorder . In fact, graphite‐like carbon cluster can be formed through unstable sp 3 bonds break and stable sp 2 bonds reconstruction . Here a reasonable explanation for the phenomenon is that the replaced carbon atoms (Figure C) driven by large shear stress and frictional heat achieve graphitization through self‐assembly method.…”