Characterizing top gated bilayer graphene interaction with its environment by Raman spectroscopy

In this work we study the behavior of the optical phonon modes in bilayer graphene devices by applying top gate voltage, using Raman scattering. We observe the splitting of the Raman G band as we tune the Fermi level of the sample, which is explained in terms of mixing of the Raman (Eg) and infrared (Eu) phonon modes, due to different doping in the two layers. We theoretically analyze our data in terms of the bilayer graphene phonon self-energy which includes non-homogeneous charge carrier doping between the graphene layers. We show that the comparison between the experiment and theoretical model not only gives information about the total charge concentration in the bilayer graphene device, but also allows to separately quantify the amount of unintentional charge coming from the top and the bottom of the system, and therefore to characterize the interaction of bilayer graphene with its surrounding environment

Continuous-distribution puddle model for conduction in trilayer graphene

An insulator-to-metal transition is observed in trilayer graphene based on the temperature dependence of the resistance under different applied gate voltages. At small gate voltages the resistance decreases with increasing temperature due to the increase in carrier concentration resulting from thermal excitation of electron-hole pairs. At large gate voltages excitation of electron-hole pairs is suppressed, and the resistance increases with increasing temperature because of the enhanced electron-phonon scattering. We find that the simple model with overlapping conduction and valence bands, each with quadratic dispersion relations, is unsatisfactory. Instead, we conclude that impurities in the substrate that create local puddles of higher electron or hole densities are responsible for the residual conductivity at low temperatures. The best fit is obtained using a continuous distribution of puddles. From the fit the average of the electron and hole effective masses can be determined.Comment: 18 pages, 5 figure

Crystal Structure Of Fluorite-related Ln3sbo7 (ln = La-dy) Ceramics Studied By Synchrotron X-ray Diffraction And Raman Scattering

Ln3SbO7 (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb and Dy) ceramics were synthesized by solid-state reaction in optimized conditions of temperature and time to yield single-phase ceramics. The crystal structures of the obtained ceramics were investigated by synchrotron X-ray diffraction, second harmonic generation (SHG) and Raman scattering. All samples exhibited fluorite-type orthorhombic structures with different oxygen arrangements as a function of the ionic radius of the lanthanide metal. For ceramics with the largest ionic radii (La-Nd), the ceramics crystallized into the Cmcm space group, while the ceramics with intermediate and smallest ionic radii (Sm-Dy) exhibited a different crystal structure belonging to the same space group, described under the Ccmm setting. The results from SHG and Raman scattering confirmed these settings and ruled out any possibility for the non-centrosymmetric C2221 space group describing the structure of the small ionic radii ceramics, solving a recent controversy in the literature. Besides, the Raman modes for all samples are reported for the first time, showing characteristic features for each group of samples. © 2013 Elsevier Inc. All rights reserved.203326332Abe, R., Higashi, M., Zou, Z.G., Sayama, K., Abe, Y., Arakawa, H., (2004) J. Phys. Chem. B, 108, pp. 811-814Cai, L., Nino, J.C., (2007) J. Eur. Ceram. Soc., 27, pp. 3971-3976Cai, L., Nino, J.C., (2010) J. Eur. Ceram. Soc., 30, pp. 307-313Doi, Y., Harada, Y., Hinatsu, Y., (2009) J. Solid State Chem., 182, pp. 709-715Wakeshima, M., Nishimine, H., Hinatsu, Y., (2004) J. Phys. Condens. Matter, 16, pp. 4103-4120Wakeshima, M., Hinatsu, Y., (2010) J. Solid State Chem., 183, pp. 2681-2688Hinatsu, Y., Ebisawa, H., Doi, Y., (2009) J. Solid State Chem., 182, pp. 1694-1699Cai, L., Denev, S., Gopalan, V., Nino, J.C., (2010) J. Am. Ceram. Soc., 93, pp. 875-880Hinatsu, Y., Doi, Y., Nishimine, H., Wakeshima, M., Sato, M., (2009) J. Alloys Compd., 488, pp. 541-545Rossell, H.J., (1979) J. Solid State Chem., 27, pp. 115-122Kahn-Harari, A., Mazerolles, L., Michel, D., Robert, F., (1995) J. Solid State Chem., 116, pp. 103-106Khalifah, P., Huang, Q., Lynn, J.W., Erwin, R.W., Cava, R.J., (2000) Mater. Res. Bull., 35, pp. 1-7Wiss, F., Raju, N.P., Wills, A.S., Greedan, J.E., (2000) Int. J. Inorg. Mater., 2, pp. 53-59Harada, D., Hinatsu, Y., Ishii, Y., (2001) J. Phys. Condens. Matter, 13, pp. 10825-10836Harada, D., Hinatsu, Y., (2001) J. Solid State Chem., 158, pp. 245-253Lam, R., Langet, T., Greedan, J.E., (2002) J. Solid State Chem., 171, pp. 317-323Hinatsu, Y., Wakeshima, M., Kawabuchi, N., Taira, N., (2004) J. Alloys Compd., 374, pp. 79-83Plaisier, J.R., Drost, R.J., Ijdo, D.J.W., (2002) J. Solid State Chem., 169, pp. 189-198Gemmill, W.R., Smith, M.D., Mozharivsky, Y.A., Miller, G.J., Zur Loye, H.-C., (2005) Inorg. Chem., 44, pp. 7047-7055Lam, R., Wiss, F., Greedan, J.E., (2002) J. Solid State Chem., 167, pp. 182-187Vente, J.F., Helmholdt, R.B., Ijdo, D.J.W., (1994) J. Solid State Chem., 108, pp. 18-23Vente, J.F., Ijdo, D.J.W., (1991) Mater. Res. Bull., 26, pp. 1255-1262Nishimine, H., Wakeshima, M., Hinatsu, Y., (2004) J. Solid State Chem., 177, pp. 739-744Greedan, J.E., Raju, N.P., Wegner, A., Gougeon, P., Padiou, J., (1997) J. Solid State Chem., 129, pp. 320-327Nishimine, H., Wakeshima, M., Hinatsu, Y., (2005) J. Solid State Chem., 178, pp. 1221-1229Nath, D.K., (1970) Inorg. Chem., 9, pp. 2714-2718Fennell, T., Bramwell, S.T., Green, M.A., (2001) Can. J. Phys., 79, pp. 1415-1419Fu, W.T., Ijdo, D.J.W., (2009) J. Solid State Chem., 182, pp. 2451-2455Gemmill, W.R., Smith, M.D., Zur Loye, H.-C., (2004) Inorg. Chem., 43, pp. 4254-4261Moreira, R.L., Lobo, R.P.S.M., Subodh, G., Sebastian, M.T., Matinaga, F.M., Dias, A., (2007) Chem. Mater., 19, pp. 6548-6554Dias, A., Sá, R.G., Moreira, R.L., (2008) J. Raman Spectrosc., 39, pp. 1805-1810Dias, A., Siqueira, K.P.F., (2010) J. Raman Spectrosc., 41, pp. 93-97Dias, A., Subodh, G., Sebastian, M.T., Moreira, R.L., (2010) J. Raman Spectrosc., 41, pp. 702-706Larson, A.C., Von Dreele, R.B., (2000) Los Alamos National Laboratory Report LAUR 86-748Toby, B.H., (2001) J. Appl. Crystallogr., 34, pp. 210-213Boyd, R.W., (2008) Non Linear Optics, , third ed., Academic Press, Burlington, MAHayes, W., Loudon, R., (1978) Scattering of Light by Crystals, , Wiley, New YorkRousseau, D.L., Bauman, R.P., Porto, S.P.S., (1981) J. Raman Spectrosc., 10, pp. 253-290Shannon, R.D., (1976) Acta Crystallogr. Sect. A: Found. Crystallogr., 32, pp. 751-767Siqueira, K.F.P., Moreira, R.L., Dias, A., (2010) Chem. Mater., 22, pp. 2668-267

Femtosecond energy relaxation in suspended graphene: Phonon-assisted spreading of quasiparticle distribution

10.1007/s00340-011-4853-0Applied Physics B: Lasers and Optics1071131-136APBO