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 (G=G0) and acoustomagnetoelectric

field (Esame) were studied in the presence of an external electric and magnetic

fields. G=G0 and Esame were found to depend on the sub-band index (pi), the

nanoribbon width (N), and the dimensionless factor (h = Ωt ).

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 (wq) 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.

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