Acoustoelectric Conversion Efficiency In Fluorine-Doped Single-Walled Carbon Nanotubes

Abstract

This study presents a comprehensive theoretical investigation of the acoustoelectric conversion efficiency (𝜂) in fluorine-doped single-walled carbon nanotubes (FSWCNTs) subjected to combined dc and ac electric fields in the hypersound regime (𝑞𝓁 ≫ 1). A microscopic transport model is developed within the semiclassical Boltzmann transport formalism by incorporating electron–phonon interactions, Bloch oscillations, nonlinear field modulation, and temperature-dependent carrier scattering. Analytical expressions for the acoustoelectric current density (𝐽AE) and the corresponding conversion efficiency are derived, while the electronic and lattice properties are discussed within the framework of density functional perturbation theory (DFPT) to establish the microscopic origin of the transport parameters. The model explicitly accounts for the effects of nanotube chirality, axial and circumferential overlap integrals (𝛥𝑧 and 𝛥𝑠), carrier relaxation time, nanotube length, carrier concentration, and fluorination-induced lattice modifications. The results reveal that the acoustoelectric conversion efficiency increases approximately linearly with the applied dc electric field and exhibits pronounced resonant enhancements whenever the Bloch frequency approaches integer multiples of the applied ac frequency. The oscillatory dependence on the ac field amplitude originates from multiphoton assisted sideband formation described by Bessel-function modulation of the carrier dynamics. The conversion efficiency displays a non-monotonic temperature dependence with a well-defined optimum temperature arising from the competition between thermally activated carrier transport and enhanced electron–phonon scattering. A detailed sensitivity analysis demonstrates that increasing the phenomenological damping factor broadens the resonance linewidth, suppresses the peak conversion efficiency, and reduces the resonance quality factor without significantly shifting the resonance frequency, thereby confirming that damping primarily governs carrier coherence rather than the intrinsic Bloch dynamics. The analysis further shows that electron–phonon scattering, impurity scattering, fluorine-induced lattice disorder, and phonon lifetime collectively determine the effective relaxation rate and consequently the efficiency of acoustoelectric energy conversion. Furthermore, the axial overlap integral, nanotube length, carrier concentration, and carrier relaxation time are identified as the dominant parameters controlling the acoustoelectric response. Enhanced conversion efficiency is obtained under conditions of low damping, long carrier relaxation times, optimised Bloch frequency, and moderate fluorination, where coherent momentum transfer between acoustic phonons and charge carriers is maximised. These findings provide a comprehensive physical framework for understanding resonant acoustoelectric transport in fluorinated carbon nanotubes and offer practical design guidelines for developing high-efficiency nanoscale acoustoelectric energy harvesters, high-frequency sensors, phononic devices, and next-generation nanoelectromechanical systems.