Effects of laser power and substrate on the Raman shift of carbon-nanotube papers

The progress in the fabrication of carbon-nanotube-based structures has made it possible to use Raman spectroscopy to measure the deformation states of carbon nanotubes and abutting materials. In this work, we investigate the effects of laser power and surrounding materials on the Raman shift of carbon-nanotube (CNT) papers for the laser intensity in a range of 0.071 to 1.415 kW/mm2 without action of mechanical loading. Two different configurations of the CNT papers are used in the Raman measurement; one uses a suspended CNT paper, and the other places a CNT paper on a glass or aluminum substrate. The experimental results reveal that there exist combinational effects of the laser power and abutting materials on the changes of the wavenumbers of the D, G and G′ bands of the CNT papers. We derive an analytical relation between the strain components, temperature and the change of the wavenumber of the Raman peak, which yields a proportional relationship between the change of the wavenumber of the Raman peak and the laser power. Such a relationship is supported by the experimental results.