scholarly journals Role of surface termination in realizing well-isolated topological surface states within the bulk band gap inTlBiSe2andTlBiTe2

2016 ◽  
Vol 93 (8) ◽  
Author(s):  
Bahadur Singh ◽  
Hsin Lin ◽  
R. Prasad ◽  
A. Bansil
Keyword(s):  
Band Gap ◽  
Surface States ◽  
Surface Termination ◽  
Topological Surface ◽  
Bulk Band

Optical and Electron Correlation Effects in Silicon Quantum Dots

2005 ◽  
Vol 23 ◽  
pp. 129-132 ◽  
Author(s):  
S.K. Ghoshal ◽  
K.P. Jain ◽  
R. Elliott
Keyword(s):  
Quantum Dots ◽  
Band Gap ◽  
Surface Passivation ◽  
Surface States ◽  
Hydrogen Atoms ◽  
Basis Expansion ◽  
Electron Correlation Effects ◽  
Homo Lumo ◽  
Pseudo Potential

We study (through computer simulation) the variation of the band gap as a function of sizes and shapes of small Silicon (Si) dots using pseudo-potential approach. We have used empirical pseudo-potential Hamiltonian and a plane wave basis expansion and a basic tetrahedral structure. It is found that the gap decreases for increasing dot size. Furthermore, the band gap increases as much as 0.13eV on passivation the surface of the dot with hydrogen. So both quantum confinement and surface passivation determine the optical and electronic properties of Si quantum dots. Visible luminescence is probably due to radiative recombination of electrons and holes in the quantum confined nanostructures. The effect of passivation of the surface dangling bonds by hydrogen atoms and the role of surface states on the gap energy as well as on the HOMO-LUMO states has also been examined. We have investigated the entire energy spectrum starting from the very low lying ground state to the very high lying excited states for silicon dots having 5, 18, 17 and 18 atoms. The results for the size dependence of the HOMO-LUMO gap and the wave functions for the bonding-antibonding states are presented and the importance of the confinement and the role of hydrogen passivation on the confinement are also discussed.

scholarly journals Ultrafast evolution of bulk, surface and surface resonance states in photoexcited $$\hbox {Bi}_{2}\hbox {Te}_{3}$$

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Hamoon Hedayat ◽  
Davide Bugini ◽  
Hemian Yi ◽  
Chaoyu Chen ◽  
Xingjiang Zhou ◽  
...  
Keyword(s):  
Surface States ◽  
Photoemission Spectroscopy ◽  
Time Resolved ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Interband Scattering ◽  
Surface Resonance ◽  
Bulk Surface ◽  
Unpolarized Electron ◽  
Topological Surface

AbstractWe use circular dichroism (CD) in time- and angle-resolved photoemission spectroscopy (trARPES) to measure the femtosecond charge dynamics in the topological insulator (TI) $$\hbox {Bi}_{2}\hbox {Te}_{3}$$ Bi 2 Te 3 . We detect clear CD signatures from topological surface states (TSS) and surface resonance (SR) states. In time-resolved measurements, independently from the pump polarization or intensity, the CD shows a dynamics which provides access to the unexplored electronic evolution in unoccupied states of $$\hbox {Bi}_{2}\hbox {Te}_{3}$$ Bi 2 Te 3 . In particular, we are able to disentangle the unpolarized electron dynamics in the bulk states from the spin-textured TSS and SR states on the femtosecond timescale. Our study demonstrates that photoexcitation mainly involves the bulk states and is followed by sub-picosecond transport to the surface. This provides essential details on intra- and interband scattering in the relaxation process of TSS and SR states. Our results reveal the significant role of SRs in the subtle ultrafast interaction between bulk and surface states of TIs.

scholarly journals New insight on the role of localisation in the electronic structure of the Si(111)(7 × 7) surfaces

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. E. Dávila ◽  
J. Ávila ◽  
I. R. Colambo ◽  
D. B. Putungan ◽  
D. P. Woodruff ◽  
...  
Keyword(s):  
Fermi Surface ◽  
Photoelectron Spectroscopy ◽  
Surface States ◽  
Emission Angle ◽  
Final State ◽  
Surface Mapping ◽  
Arpes Data ◽  
Reconstructed Surface ◽  
Bulk Band

AbstractNew angle-resolved photoelectron spectroscopy (ARPES) data, recorded at several different photon energies from the Si(111)(7 × 7) surface, show that the well-known S1 and S2 surface states that lie in the bulk band gap are localised at specific (adatom and rest atom) sites on the reconstructed surface. The variations in the photoemission intensity from these states as a function of polar and azimuthal emission angle, and incident photon energy, are not consistent with Fermi surface mapping but are well-described by calculations of the multiple elastic scattering in the final state. This localisation of the most shallowly bound S1 state is consistent with the lack of significant dispersion, with no evidence of Fermi surface crossing, implying that the surface is not, as has been previously proposed, metallic in character. Our findings highlight the importance of final state scattering in interpreting ARPES data, an aspect that is routinely ignored and can lead to misleading conclusions.

Surface States and Band Gap Correlation in Silicon Nanoclusters

2015 ◽  
Vol 1107 ◽  
pp. 308-313
Author(s):  
Sib Krishna Ghoshal ◽  
M.R. Sahar ◽  
R. Arifin ◽  
M.S. Rohani ◽  
K. Hamzah
Keyword(s):  
Band Gap ◽  
Surface Passivation ◽  
Light Emission ◽  
Radiative Lifetime ◽  
Surface States ◽  
Optical Gain ◽  
Visible Luminescence ◽  
Optical And Electronic Properties ◽  
Effect Of Oxygen

Tuning the visible emission of Si nanomaterials by modifying their size and shape is one of the key issue in optoelectronics. The observed optical gain in Si-nanoclusters (NCs) has given further impulse to nanosilicon research. We develop a phenomenological model by combining the effects of surface passivation, exciton states and quantum confinement (QC). The size and passivation dependent band gap, oscillator strength, radiative lifetime and photoluminescence (PL) intensity for NCs with diameter ranging from 1.0 to 6.0 nm are presented. By controlling a set of fitting parameters, it is possible to tune the optical band gap, PL peak and intensity. In case of pure clusters, the band gap is found to decrease with increasing NC size. Furthermore, the band gap increases on passivating the surface of the cluster with hydrogen and oxygen respectively in which the effect of oxygen is more robust. Both QC and surface passivation in addition to exciton effects determine the optical and electronic properties of silicon NCs. Visible luminescence is due to radiative recombination of electrons and holes in the quantum-confined NCs. The role of surface states on the band gap as well as on the HOMO-LUMO states is also examined and a correlation is established. Our results are in conformity with other observations. The model can be extended to study the light emission from other nanostructures and may contribute towards the development of Si based optoelectronics.

scholarly journals Role of topological surface states and mirror symmetry in topological crystalline insulator SnTe as an efficient electrocatalyst

Nanoscale ◽  
2021 ◽  
Author(s):  
Qing Qu ◽  
Bin Liu ◽  
Hongtao Liu ◽  
Jing Liang ◽  
Jiannong Wang ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Mirror Symmetry ◽  
Surface States ◽  
Topological Surface ◽  
Topological Crystalline Insulator

The intrinsic activities of SnTe (001) and (111) surfaces with robust topological surface states (TSSs) are superior to that of a (211) surface with fragile or without TSSs, attributing to the enhanced charge transfer between H atoms and TSSs.

scholarly journals Double band inversion in α -Sn: Appearance of topological surface states and the role of orbital composition

2017 ◽  
Vol 95 (16) ◽  
Author(s):  
Victor A. Rogalev ◽  
Tomáš Rauch ◽  
Markus R. Scholz ◽  
Felix Reis ◽  
Lenart Dudy ◽  
...  
Keyword(s):  
Surface States ◽  
Band Inversion ◽  
Topological Surface ◽  
Orbital Composition
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