Browsing by Subject "Valence band"

Now showing 1 - 3 of 3

Open Access
Dynamics of sliding and loading bilayer graphene
(2022-09) Edun, Benjamin
Sliding and loading bilayer graphene is investigated using the Tight Binding method. We develop interaction-distance dependent tight binding parameter functions to allow for the calculation of band structure for different interacting distances. We investigate the band structures of sliding graphene and loading bilayer graphene, in which case the latter consists of varying interlayer distances between monolayers. We show that based on developed parameter models, band splittings can be seen to emerge in the band structures, which follow different patterns for different sliding directions. As expected we con rm that for varying vertical interlayer distances, monolayer graphene band structure is the limit for both AA and AB stacking con gurations. By applying a quadratic energy model to the curvature of the band structures in the vicinity of the K-point for AB stacking con guration we predict the effective mass of electrons and holes in bilayer graphene, and electrons in monolayer graphene. We also show the pattern of change of effective mass with respect to changing interlayer distance, and try to investigate where our prescribed quadractic energy model breaks down, as we approach the limit of the monolayer band structure.
Open Access
Optoelectronic properties of layered titanate nanostructure and polyaniline impregnated devices
(Wiley - V C H Verlag GmbH & Co. KGaA, 2016) Vempati S.; Ertas Y.; Babu, V. J.; Uyar, Tamer
Integrated structure of titanate nanotubes and nanosheets is investigated for their optical, electronic and optoelectronic properties when combined with HCl doped polyaniline (PANI). HR-TEM, SEM and XRD were employed for detailed morphological and microstructural understanding of the orthorhombic titanate nanostructure. Chemisorbed oxygeneous groups are probed with Raman spectroscopy which are found to desorb under UV-Vis treatment. We note a blue shift of Ti-O-Ti Raman frequency in contrast to Na-O-Ti stretching. Valence band region of titanate is analyzed for contribution of O2p, O2s, Na2p and Ti3p. Photoluminescence with different excitation energies revealed the presence of oxygen vacancy related defects in titanate. The highly occupied electronic states of PANI were also analyzed until 40 eV below the Fermi energy. XPS core-level analyses revealed ∼25 % doping density in PANI. Edges of valence band and HOMO are determined to be at 2.45 eV and 2.54 eV below Fermi energy for titanate and PANI, respectively. ITO/PANI/ITO has depicted negative photoresponse and the magnitude of which is reduced ∼4 times after combining with titanate nanostructure. Essentially the nanoscale architecture separates the emeraldine base and salt regions of PANI. This separation channelizes the charge carriers before trapping which reduces the magnitude of the negative photoresponse.
Open Access
Temperature-and excitation intensity-dependent photoluminescence in TlInSeS single crystals
(American Institute of Physics, 2002) Gasanly, N. M.; Aydınlı, Atilla; Yuksek, N. S.
Photoluminescence (PL) spectra of TlInSeS layered single crystals were investigated in the wavelength region 460-800 nm and in the temperature range 10-65 K. We observed one wide PL band centred at 584 nm (2.122 eV) at T = 10 K and an excitation intensity of 7.5 W cm-2. We have also studied the variation of the PL intensity versus excitation laser intensity in the range from 0.023 to 7.5 W cm-2. The red shift of this band with increasing temperature and blue shift with increasing laser excitation intensity was observed. The PL was found to be due to radiative transitions from the moderately deep donor level located at 0.243 eV below the bottom of the conduction band to the shallow acceptor level at 0.023 eV located above the top of the valence band. The proposed energy-level diagram permits us to interpret the recombination processes in TlInSeS layered single crystals.