Surface states

About: Surface states is a research topic. Over the lifetime, 11143 publications have been published within this topic receiving 307395 citations.

Formation of Fabry-Perot cavity in one-dimensional and two-dimensional GaAs nanostructures

Abstract: We report formation of an optical cavity and observation of Fabry-Perot resonance in GaAs nanowires and nanosheets grown by metal organic chemical vapor deposition (MOCVD) with selective area growth (SAG). These nanostructures are grown along the (111)B direction. The formation of an optical cavity in the nanowires and nanosheets are fundamentally different from each other. In nanowires the optical cavity is formed along the length of the nanowire with ends of the nanowire behaving as two parallel mirrors. In nanosheets, however, the three non-parallel edges of the GaAs nanosheets are involved in trapping of the light through total internal reflection, thus forming a 2D cavity. We show that through surface passivation and local field enhancement, both the photoluminescence intensity and hence Fabry-Perot peak intensity increases significantly. Transferring the GaAs nanowires and nanosheets to the gold substrate (instead of Si/SiO2 substrate) leads to substantial enhancement in the photoluminescence intensity by 5X (for nanowires) and 3.7X (for nanosheets) to infinite enhancement of the FP peaks intensities. In order to reduce the non-radiative recombination in these nanowires the surface states in the nanowires can be passivated by either an ionic liquid (EMIM-TFSI) or an AlGaAs surface layer. Both passivations methods lead to an enhancement of the optical response by up to 12X.

Surface States Dominated Infrared Conductivity in a Topological Crystalline Insulator

Abstract: Topological crystalline insulators (TCIs) are insulating materials that possess metallic surface states protected by crystalline symmetry. The (001) surface states have been predicted to exhibit many novel physical properties (such as superconductivity, quantum anomalous Hall effect and Weyl fermions) that are widely tunable under various perturbations, rendering these materials a versatile platform for exploring topological phenomena and potential applications. However, progress in this field has been hindered by the challenge to probe the optical and transport properties of the surface states owing to the presence of bulk carriers. Here we report infrared reflectance measurements of a TCI, (001) oriented $Pb_{0.7}Sn_{0.3}Se$ in zero and high magnetic fields. We demonstrate that the far-infrared conductivity is dominated by the surface states as a result of their unique band structure and the consequent high surface carrier density. Moreover, our experiments yield a surface mobility of 40,000 $cm^2 V^{-1} s^{-1}$, which is one of the highest reported values in topological materials. The transport parameters obtained from our experiments suggest the viability of surface-dominated conduction in thin TCI crystals. These findings open up new opportunities for exploring the exotic physics predicted for TCIs.

First-principles study of the H2S passivation on 6H-SiC (0001) surface

Abstract: Passivation is an effective way to reduce density of states (DOS) on the surface. In order to verify the differences and stabilities of H2S passivation on Si- and C-face of 6H-SiC, the adsorption of H2S on surface is studied by the first principles method, which is based on the density functional theory. Adsorption configuration and stability are researched with the coverage changing from 1/9monolayer (ML) to 1/3ML on Si-face while 1/9ML to 5/9ML on C-face. Adsorption energy, DOS and charge population of the system are calculated separately. On Si-face, energy calculations show that H2S which is adsorbed at the bridge (BR) site is more stable than that adsorbed at the on-top (OT) site. After H2S is decomposed, S atoms are combined at the BR site, while H atoms are adsorbed at the OT site. The surface states are noticeably reduced after passivation. Surface states are reduced to the lowest when the coverage is 2/9ML. On C-face, H2S which is adsorbed at the OT site is more stable than that adsorbed at the BR site. After H2S is decomposed, HS bonds and H atoms are all combined at the OT site. The surface states are noticeably reduced to the lowest when the coverage is 4/9ML.