Journal
APPLIED PHYSICS LETTERS
Volume 96, Issue 8, Pages -Publisher
AMER INST PHYSICS
DOI: 10.1063/1.3291615
Keywords
chemical vapour deposition; epitaxial growth; graphene; high-speed optical techniques; hot carriers; insulating thin films; laser cooling; multilayers; nickel; phonons; silicon compounds
Categories
Funding
- National Science Foundation
- DARPA Young Faculty Award
- AFOSR [FA9550-07-1-0332]
- National Science Foundation [0520404]
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [0520404] Funding Source: National Science Foundation
- Div Of Electrical, Commun & Cyber Sys
- Directorate For Engineering [0824209] Funding Source: National Science Foundation
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Using ultrafast optical pump-probe spectroscopy, we study the relaxation dynamics of hot optical phonons in few-layer and multilayer graphene films grown by epitaxy on silicon carbide substrates and by chemical vapor deposition on nickel substrates. In the first few hundred femtoseconds after photoexcitation, the hot carriers lose most of their energy to the generation of hot optical phonons which then present the main bottleneck to subsequent cooling. Optical phonon cooling on short time scales is found to be independent of the graphene growth technique, the number of layers, and the type of the substrate. We find average phonon lifetimes in the 2.5-2.55 ps range. We model the relaxation dynamics of the coupled carrier-phonon system with rate equations and find a good agreement between the experimental data and the theory. The extracted optical phonon lifetimes agree very well with the theory based on anharmonic phonon interactions.
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