ABSTRACT
We perform self-consistent analysis of the Boltzmann transport equation for momentum and energy in the hypersound regime i.e., [Formula: see text] ([Formula: see text] is the acoustic wavenumber and l is the mean free path). We investigate the Landau damping of acoustic phonons ([Formula: see text]) in graphene nanoribbons, which leads to acoustoelectric current generation. Under a non-quantized field with drift velocity, we observed an acoustic phonon energy quantization that depends on the energy gap, the width, and the sub-index of the material. An effect similar to Cerenkov emission was observed, where the electron absorbed the confined acoustic phonon energy, causing the generation of acoustoelectric current in the graphene nanoribbon. A qualitative analysis of the dependence of the absorption coefficient and the acoustoelectric current on the phonon frequency is in agreement with experimental reports. We observed a shift in the peaks when the energy gap and the drift velocity were varied. Most importantly, a transparency window appears when the absorption coefficient is zero, making graphene nanoribbons a potential candidate for use as an acoustic wave filter with applications in tunable gate-controlled quantum information devices and phonon spectrometers.
ABSTRACT
Raman microprobe studies of long crystalline Si nanowires reveal for the first time the evolution of phonon confinement with wire diameter. The Raman band at approximately 520 cm-1 in bulk Si is found to downshift and asymmetrically broaden to lower frequency with decreasing wire diameter D, in good agreement with a phenomenological model first proposed by Richter et al. An adjustable parameter (alpha) is added to the theory that defines the width of the Gaussian phonon confinement function. We find that this parameter is not sensitive to diameter over the range 4-25 nm.
Subject(s)
Crystallization/methods , Models, Chemical , Nanotechnology/methods , Nanotubes/chemistry , Silicon/chemistry , Spectrum Analysis, Raman/methods , Computer Simulation , Materials Testing , Models, Molecular , Molecular Conformation , Nanotubes/analysis , Nanotubes/ultrastructure , Particle Size , Silicon/analysis , Structure-Activity Relationship , VibrationABSTRACT
Gallium phosphide nanowires with a most probable diameter of approximately 20.0 nm and more than 10 microns in length have been synthesized by pulsed laser vaporization of a heated GaP/5% Au target. The morphology and microstructure of GaP nanowires have been investigated by scanning electron microscopy and transmission electron microscopy. Twins have been observed along the crystalline nanowires, which have a growth direction of [111]. Raman scattering shows a 4 cm-1 downshift of the longitudinal optical phonon peak in the nanowire with respect to the bulk; the transverse optical phonon frequency and line width are, however, the same as in the bulk. The quantum confinement model first proposed by Richter et al. cannot explain the observed behavior of the Raman modes.
Subject(s)
Crystallography/methods , Gallium/chemistry , Nanotechnology/instrumentation , Nanotechnology/methods , Nanotubes/chemistry , Nanotubes/ultrastructure , Phosphines/chemistry , Spectrum Analysis, Raman/methods , Electric Conductivity , Electric Wiring , Molecular Conformation , Phosphines/chemical synthesis , SemiconductorsABSTRACT
Results are presented of in situ studies of the thermoelectric power and four-probe resistance of single-walled carbon nanotube films during the adsorption of cyclic hydrocarbons C(6)H(2n) (n=3-6). The size of the change in these transport parameters is found to be related to the pi electron population of the molecule, suggesting the coupling between these pi electrons and those in the nanotube wall may be responsible for the observed effects. A transport model for the SWNT film behavior is presented, incorporating the effects of a new scattering channel associated with the adsorbed molecules.
