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We study the thermal transport properties of twisted-layer graphite nanofibers. We show that in the presence of a twisted layer, the phonon thermal conductance of a graphite nanofiber of rectangular cross-section varies remarkably with the twist angle and can reach minimum values either at two critical angles θ 1 and θ 2 that conform to the rule θ 1 + θ 2 = 180 0 or exactly at the angle θ = 900. A reduction of roughly 50% of the phonon thermal conductance can be achieved in some structures. We unveil that the twisting effect mainly influences the optical modes, more precisely, the breathing modes ZOꞌ, and leaving almost unaltered the acoustic ones. The effect is also visible in the higher and more numerous van Hove singularities of the phonon density of states. We also point out that the behavior of the thermal conductance with the twist angle is associated with and dominated by the alteration in the overlap area between the twisted and non-twisted layers. The finite-size effect is demonstrated to play an essential role in defining the critical angles at the local minima, where these angles are dependent on the size of the investigated nanofibers, in particular on the proportion between the widths of zigzag and armchair edges. We also analyze the behavior of circular nanofibers where the correlation between the overlap area and the thermal conductance is much smaller. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, by combining the tight-binding description with the gradient approximation, we investigated the impacts of electric gating and divacancies on the optical characteristics of zigzag buckling silicene nanoribbons. Our results show that the back-gate electric potential tends to shift the peak structure to higher frequencies in the free-defective structures, while the side-gate electric potentials intensify the intensity of the excitation channels obeying the selection rule Δ J = even. In particular, applying the potentials in a suitable range can improve the optical absorption efficiency at a certain frequency with the back gate or widen the threshold absorption intensity from J v = 1 to J c = 1 with the side gates. Besides, the defective structures' absorption spectra exhibit richer features than the perfect one, with the appearance of new optical excitations due to the transitions between the local minimum or maximum in the low-energy bands around the Fermi level. Moreover, applying electric gating in defective structures can also tune the absorption spectra with additional features. • The impact of electric gating on physical properties of both free-defective and defective BSiNRs. • The resemblance and disparity in the effects of back and side gates on optical characteristics. • The mutual impact of divacancies and electric fields on optical and electronic properties. • An insightful comparison of variations in spectral structure in free-defective and defective structures. [ABSTRACT FROM AUTHOR]