The Study of Acoustic Effects in Carbon Allotropes

ABSTRACT

Acoustic effects such as absorption/amplification of acoustic phonons, Acoustoelectric Effect (AE) and Acoustomagnetoelectric Effect (AME) were studied in Carbon Allotropes. In this thesis, the Carbon Allotropes considered are Graphene Nanoribbon (GNR), 2-dimensional Graphene sheet, and Carbon Nanotubes (CNT). The Boltzmann transport equation (BTE) and the phonon kinetic equation (PKE) were used. All results were analysed numerically and graphically presented. Using BTE for Armchair Graphene Nanoribbon (AGNR), amplification of acoustic waves (Γ/Γ0) and acoustomagnetoelectric field (Esame) were studied in the presence of an external electric and magnetic fields. Γ/Γ0 and Esame were found to depend on the sub-band index (pi), the nanoribbon width (N), and the dimensionless factor (η = Ωτ). Using the PKE, amplification (absorption) and AE in 2D graphene and Carbon Nanotubes (CNTs) were studied. On hypersound amplification, a mechanism due Cerenkov emission was employed where the ratio of the drift velocity (Vd) to the velocity of sound (Vs) was considered. In both materials, the dependence of amplification (absorption) on frequency (ωq) were analysed. Here the acoustic waves were considered as phonons in the hypersound regime. In CNT, it was observed that the maximum amplification was attained as Vd = 1.1Vs which occurred at E = 51.7 Vcm−1 . For n = 2, (where n is an integer) the absorption obtained qualitatively agree with an experimental measurement.