▎ 摘　　要

Thermal and mechanical properties of graphene sheet are of significant importance in the areas of thermal and stress management, respectively. Here, we report the thermal conductivity and high-pressure behaviors of unsupported vertical graphene nanosheets (VGNs) grown by electron cyclotron resonance-plasma enhanced chemical vapor deposition method. Structural morphology of the as-grown VGNs on SiO2/Si substrate suggests a homogeneous, uniformly interconnected network of graphene sheets standing vertically on a basal nanographitic layer. On examination of edges of exfoliated sheets using transmission electron microscopy, seven layers of graphene is estimated. The frequency of the G-band (E-2g-in plane mode) is found to vary linearly temperature. The first-order temperature coefficient for G-band is found to be 1.47(1) X 10(-2) cm(-1) K-1. Using the G-band temperature coefficient and its position dependence on excitation laser power, the thermal conductivity of the VGNs at room temperature is estimated to be 250 (19) Wm(-1) K-1. The effect of pressure (P) on the G-mode frequency (omega) of unsupported VGNs is investigated by in situ Raman spectroscopic studies up to 40 GPa using a diamond anvil cell. Above 16 GPa, discontinuity in the w versus P curve suggests a disruption of long-range order in the graphene layers resulting in a deviation from two-dimensional layer structure. Persistence of local sp(2)-hybridization up to 40 GPa is evident from the presence of G-band at this highest pressure. Upon decompression, VGN is found to recover its original ordered structure.