Broadband transverse electric surface wave in silicene

Transverse electric (TE) surface wave in silicine is theoretically investigated. The TE surface wave in silicene is found to exhibit better characteristics compared with that in graphene, in terms of a broader frequency range and more confinement to the surface which originate from the buckled structure of silicene. We found that even undoped silicene can support the TE surface wave. We expect the similar characteristics of the TE surface wave in other two-dimensional materials that have a slightly buckled honeycomb lattice. Selengkapnya

Fermi energy dependence of first- and second-order Raman spectra in graphene: Kohn anomaly and quantum interference effect

Intensities of the first- and the second-order Raman spectra are calculated as a function of the Fermi energy. We show that the Kohn anomaly effect, i.e., phonon frequency renormalization, in the first-order Raman spectra originates from the phonon renormalization by the interband electron-hole excitation, whereas in the second-order Raman spectra, a competition between the interband and intraband electron-hole excitations takes place. By this calculation, we confirm the presence of different dispersive behaviors of the Raman peak frequency as a function of the Fermi energy for the first- and the second-order Raman spectra, as observed in some previous experiments. Moreover, the… Selengkapnya

Multiple electronic Raman scatterings in a single metallic carbon nanotube

We observe multiple electronic Raman scatterings (ERSs) in a single suspended metallic single-walled carbon nanotube. The ERS process originates from the inelastic scattering of photoexcited excitons by a continuum of low-lying electron-hole pairs. In previous work, the observed Fano factor of the G band line shape is always negative; however, in this work we find that the Fano factor can be either positive or negative depending on the relative position of the nearest ERS with respect to the G band. This supports the idea that the origin of the G band asymmetry is an interference between the discrete G band… Selengkapnya

Quantum Effects in the Thermoelectric Power Factor of Low-Dimensional Semiconductors

We theoretically investigate the interplay between the confinement length L and the thermal de Broglie wavelength Λ to optimize the thermoelectric power factor of semiconducting materials. An analytical formula for the power factor is derived based on the one-band model assuming nondegenerate semiconductors to describe quantum effects on the power factor of the low dimensional semiconductors. The power factor is enhanced for one- and two-dimensional semiconductors when L is smaller than Λ of the semiconductors. In this case, the low-dimensional semiconductors having L smaller than their Λ will give a better thermoelectric performance compared to their bulk counterpart. On the… Selengkapnya

Anisotropic Electron-Photon and Electron-Phonon Interactions in Black Phosphorus

Orthorhombic black phosphorus (BP) and other layered materials, such as gallium telluride (GaTe) and tin selenide (SnSe), stand out among two-dimensional (2D) materials owing to their anisotropic in-plane structure. This anisotropy adds a new dimension to the properties of 2D materials and stimulates the development of angle-resolved photonics and electronics. However, understanding the effect of anisotropy has remained unsatisfactory to date, as shown by a number of inconsistencies in the recent literature. We use angle-resolved absorption and Raman spectroscopies to investigate the role of anisotropy on the electron–photon and electron–phonon interactions in BP. We highlight, both experimentally and theoretically, a… Selengkapnya

Gate Modulated Raman Spectroscopy of Graphene

A combination of electronic gating and inelastic scattering of light, known as Raman spectroscopy, elucidates interplay of electron, phonons, and photons in graphene because we can tune the Fermi energy of graphene while simultaneously probing phonon excitation. Spectral properties such as intensity, spectral linewidth, peak position, and lineshape of the Raman spectra can be modified by varying the gate voltage, indicating an interplay of the electron-phonon interaction. However, the physical consequence behind the change of spectral properties measured by experiment cannot be understood unless a theoretical calculation of Raman intensity is performed. Understanding detailed mechanism underlying the change of Raman… Selengkapnya

Photon energy dependence of angle-resolved photoemission spectroscopy in graphene

The photon energy dependence of angle-resolved photoemission spectroscopy (ARPES) in graphene is investigated experimentally and theoretically. By applying light with energy of around 46 eV, we found an unexpected increase in the ARPES relative intensity of graphene for the p branch (ARPES spectra brightened by the p-polarized light) with respect to the s branch (those brightened by the s-polarized light). The origin of the enhanced p-branch intensity is explained by first-principles calculations, in which we show (1) the optical dipole vector as a function of final-state energies of the excited electron, (2) the absorption intensity as a function of the… Selengkapnya

Ultraviolet Raman spectroscopy of graphene and transition‐metal dichalcogenides

Here, we overview Raman spectroscopy of graphene and transition‐metal dichalcogenides as a function of laser excitation energy , especially in the ultraviolet (UV) region. The double resonance G (or 2D) band of graphene is calculated for the laser energy range up to 7 eV. The intensity of the G band is proportional to  for eV. We also discuss electronic Raman spectra and the asymmetric Breit–Wigner–Fano lineshape of the G band in graphene for UV light. Finally, transition‐metal dichalcogenide materials show a strong optical absorption of the UV light at the M point at which we expect a two‐dimensional van… Selengkapnya

Diameter dependence of thermoelectric power of semiconducting carbon nanotubes

We calculate the thermoelectric power (or thermopower) of many semiconducting single wall carbon nanotubes (s-SWNTs) within a diameter range 0.5 – 1.5 nm by using the Boltzmann transport formalism combined with an extended tight-binding model. We find that the thermopower of s-SWNTs increases as the tube diameter decreases. For some s-SWNTs with diameters less than 0.6 nm, the thermopower can reach a value larger than 2000 μV/K at room temperature, which is about 6 to 10 times larger than that found in commonly used thermoelectric materials. The large thermopower values may be attributed to the one dimensionality of the nanotubes… Selengkapnya

Fermi energy-dependence of electromagnetic wave absorption in graphene

Undoped graphene is known to absorb 2.3% of visible light at a normal angle of incidence. In this paper, we theoretically demonstrate that the absorption of 10–100 GHz of an electromagnetic wave can be tuned from nearly 0 to 100% by varying the Fermi energy of graphene when the angle of incidence of the electromagnetic wave is kept within total internal reflection geometry. We calculate the absorption probability of the electromagnetic wave as a function of the Fermi energy of graphene and the angle of incidence of the wave. These results open up possibilities for the development of simple electromagnetic… Selengkapnya