Thermal Conductivity and Pressure-Dependent Raman Studies of Vertical Graphene Nanosheets
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2016-10-11 |
| Journal | The Journal of Physical Chemistry C |
| Authors | K. K. Mishra, Subrata Ghosh, T. R. Ravindran, S. Amirthapandian, M. Kamruddin |
| Institutions | Indira Gandhi Centre for Atomic Research |
| Citations | 36 |
Abstract
Section titled āAbstractāThermal 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 (E2g-in plane mode) is found to vary linearly with temperature. The first-order temperature coefficient for G-band is found to be 1.47(1) Ć 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) W m-1 K-1. The effect of pressure (P) on the G-mode frequency (Ļ) 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 Ļ 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 sp2-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.