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Carlos S. Ruiz-vargas - One of the best experts on this subject based on the ideXlab platform.

  • Ultrafast relaxation dynamics of hot Optical Phonons in graphene
    Applied Physics Letters, 2010
    Co-Authors: Haining Wang, Farhan Rana, Virgil B. Shields, Paul A. George, Jared H. Strait, Shriram Shivaraman, M V S Chandrashekhar, Jeonghyun Hwang, Michael G. Spencer, Carlos S. Ruiz-vargas
    Abstract:

    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.

  • Ultrafast relaxation dynamics of hot Optical Phonons in graphene
    Applied Physics Letters, 2010
    Co-Authors: Haining Wang, Farhan Rana, Virgil B. Shields, Paul A. George, Jared H. Strait, Shriram Shivaraman, M V S Chandrashekhar, Jeonghyun Hwang, Michael G. Spencer, Carlos S. Ruiz-vargas
    Abstract:

    Using ultrafast Optical pump-probe spectroscopy, we study the relaxation dynamics of hot Optical Phonons in few-layer and multi-layer 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 carrier 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.

Haining Wang - One of the best experts on this subject based on the ideXlab platform.

  • Ultrafast relaxation dynamics of hot Optical Phonons in graphene
    Applied Physics Letters, 2010
    Co-Authors: Haining Wang, Farhan Rana, Virgil B. Shields, Paul A. George, Jared H. Strait, Shriram Shivaraman, M V S Chandrashekhar, Jeonghyun Hwang, Michael G. Spencer, Carlos S. Ruiz-vargas
    Abstract:

    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.

  • Ultrafast relaxation dynamics of hot Optical Phonons in graphene
    Applied Physics Letters, 2010
    Co-Authors: Haining Wang, Farhan Rana, Virgil B. Shields, Paul A. George, Jared H. Strait, Shriram Shivaraman, M V S Chandrashekhar, Jeonghyun Hwang, Michael G. Spencer, Carlos S. Ruiz-vargas
    Abstract:

    Using ultrafast Optical pump-probe spectroscopy, we study the relaxation dynamics of hot Optical Phonons in few-layer and multi-layer 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 carrier 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.

Tony F. Heinz - One of the best experts on this subject based on the ideXlab platform.

  • temperature dependence of the anharmonic decay of Optical Phonons in carbon nanotubes and graphite
    Physical Review B, 2011
    Co-Authors: Ioannis Chatzakis, Hugen Yan, Daohua Song, Stephane Berciaud, Tony F. Heinz
    Abstract:

    We report on the temperature dependence of the anharmonic decay rate of zone-center (G mode) Optical Phonons in both single-walled carbon nanotubes and graphite. The measurements are performed using a pump-probe Raman scattering scheme with femtosecond laser pulses. For nanotubes, measured over a temperature range of 6 K–700 K, we observe little temperature dependence of the decay rate below room temperature. Above 300 K, the decay rate increases from 0.8 to 1.7 ps −1 . The decay rates observed for graphite range from 0.5 to 0.8 ps −1 for temperatures from 300 K–700 K. We compare the behavior observed in carbon nanotubes and graphite and discuss the implications of our results for the mechanism of the anharmonic decay of Optical Phonons in both systems.

  • longitudinal Optical Phonons in metallic and semiconducting carbon nanotubes
    Physical Review Letters, 2009
    Co-Authors: Martin Fouquet, Janina Maultzsch, Tony F. Heinz, Hagen Telg, Bhupesh Chandra, James Hone, C Thomsen
    Abstract:

    We analyze the high-energy Raman modes, G + and G - , in a pair of one metallic and one semiconducting nanotubes. By combining Rayleigh scattering with Raman resonance profiles of the radial breathing mode and the high-energy modes, we show that the observed G - and G + peaks can originate from longitudinal Optical Phonons of different tubes. The G - peak is the longitudinal mode of the metallic tube; it is broadened and downshifted due to strong electron-phonon coupling in the metallic nanotube. The G + peak is due to the longitudinal mode in the semiconducting tube. This result resolves an ongoing debate in the literature.

  • direct measurement of the lifetime of Optical Phonons in single walled carbon nanotubes
    Physical Review Letters, 2008
    Co-Authors: Daohua Song, Feng Wang, Gordana Dukovic, Ming Zheng, E D Semke, Louis E Brus, Tony F. Heinz
    Abstract:

    Time-resolved anti-Stokes Raman spectroscopy has been applied to probe the dynamics of Optical Phonons created in single-walled carbon nanotubes by femtosecond laser excitation. From measurement of the decay of the anti-Stokes Raman signal in semiconducting nanotubes of $(6,5)$ chiral index, a room-temperature lifetime for $G$-mode Phonons of $1.1\ifmmode\pm\else\textpm\fi{}0.2\text{ }\text{ }\mathrm{ps}$ has been determined. This lifetime, which reflects the anharmonic coupling of the $G$-mode Phonons to lower-frequency Phonons, is important in assessing the role of nonequilibrium phonon populations in high-field transport phenomena.

  • The Lifetime of Optical Phonons in Graphite
    Frontiers in Optics 2008 Laser Science XXIV Plasmonics and Metamaterials Optical Fabrication and Testing, 2008
    Co-Authors: Hugen Yan, Daohua Song, Kin Fai Mak, Ioannis Chatzakis, Janina Maultzsch, Tony F. Heinz
    Abstract:

    Femtosecond pump-probe Raman spectroscopy has been applied to monitor the decay of non-equilibrium Optical Phonons in graphite. A lifetime of 2.2 ps is found.

Farhan Rana - One of the best experts on this subject based on the ideXlab platform.

  • Ultrafast relaxation dynamics of hot Optical Phonons in graphene
    Applied Physics Letters, 2010
    Co-Authors: Haining Wang, Farhan Rana, Virgil B. Shields, Paul A. George, Jared H. Strait, Shriram Shivaraman, M V S Chandrashekhar, Jeonghyun Hwang, Michael G. Spencer, Carlos S. Ruiz-vargas
    Abstract:

    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.

  • Ultrafast relaxation dynamics of hot Optical Phonons in graphene
    Applied Physics Letters, 2010
    Co-Authors: Haining Wang, Farhan Rana, Virgil B. Shields, Paul A. George, Jared H. Strait, Shriram Shivaraman, M V S Chandrashekhar, Jeonghyun Hwang, Michael G. Spencer, Carlos S. Ruiz-vargas
    Abstract:

    Using ultrafast Optical pump-probe spectroscopy, we study the relaxation dynamics of hot Optical Phonons in few-layer and multi-layer 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 carrier 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.

Virgil B. Shields - One of the best experts on this subject based on the ideXlab platform.

  • Ultrafast relaxation dynamics of hot Optical Phonons in graphene
    Applied Physics Letters, 2010
    Co-Authors: Haining Wang, Farhan Rana, Virgil B. Shields, Paul A. George, Jared H. Strait, Shriram Shivaraman, M V S Chandrashekhar, Jeonghyun Hwang, Michael G. Spencer, Carlos S. Ruiz-vargas
    Abstract:

    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.

  • Ultrafast relaxation dynamics of hot Optical Phonons in graphene
    Applied Physics Letters, 2010
    Co-Authors: Haining Wang, Farhan Rana, Virgil B. Shields, Paul A. George, Jared H. Strait, Shriram Shivaraman, M V S Chandrashekhar, Jeonghyun Hwang, Michael G. Spencer, Carlos S. Ruiz-vargas
    Abstract:

    Using ultrafast Optical pump-probe spectroscopy, we study the relaxation dynamics of hot Optical Phonons in few-layer and multi-layer 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 carrier 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.