Nonuniform Compressive Strain in Horizontally Aligned Single-Walled Carbon Nanotubes Grown on Single Crystal Quartz

Interactions with the substrate that allow near perfect horizontal alignment in combination with large difference in the coefficient of thermal expansion are shown to lead to uniaxial compressive strain in as-grown single-walled carbon nanotubes on single crystal quartz. Temperature dependence of Raman G-band spectra along the length of individual nanotubes reveals that the compressive strain is nonuniform and can be larger than 1% locally at room temperature. A response of 27 cm(-1) upshift per % compressive strain is estimated for the G-band longitudinal optical phonon mode of semiconducting nanotubes. Comparison of Raman and atomic force microscope images suggests that the nonuniformity of the compression arises from the surface roughness induced by polishing. Effects of device fabrication steps on the nonuniform strain are also examined and implications on electrical performance are discussed.