Phonon anharmonicities in 7-armchair graphene nanoribbons

Graphene nanoribbons (GNRs) provide a potential alternative to overcome the shortcoming of gapless graphene and have been applied into next-generation nanoelectronic devices like FETs. The phonon anharmonicities in functional materials usually play a key role in the device performance. Here, temperature dependent Raman scattering measurements on high quality 7-armchair GNRs (7-AGNRs) on Au(111) synthesized by on-surface method were conducted in the temperature range from 80 to 520 K. The frequency of optical phonon G mode (collective acoustic phonon RBLM mode) linearly (nonlinearly) downshifts with temperature. The first-order temperature coefficient of G mode of 7-AGNR is calculated to be −0.026 cm−1K−1, almost twice that of freestanding graphene of −0.015 cm−1K−1 and half of that of CVD grown single layer graphene on Cu foils of −0.056 cm−1K−1. For RBLM, the anharmonicity is much weaker and attributed to the intrinsic quartic-phonon decay processes rather than the cubic-phonon ones. Our findings make a first step to the thermal properties of atomically precise GNRs. [Display omitted]