Enhancement of carrier lifetime by spin-orbit coupling in a topological insulator of an SbTe thin film.

Electrons and phonons in chalcogenide-based materials are important factors in the performance of optical data-storage media and thermoelectric devices. However, the fundamental kinetics of carriers in chalcogenide materials remains controversial, and active debate continues over the mechanism responsible for carrier relaxation. In this study, we used optical-pump terahertz-probe spectroscopy, which permits the relationship between structural phase transition and optical property transitions to be examined, to investigate the ultrafast carrier dynamics in a multilayered [Sb(3 Ã…)/Te(9 Ã…)] thin film during the transition from the disordered to crystalline phase.

Electron transport mechanism of bathocuproine exciton blocking layer in organic photovoltaics.

Efficient exciton management is a key issue to improve the power conversion efficiency of organic photovoltaics (OPVs). It is well known that the insertion of an exciton blocking layer (ExBL) having a large band gap promotes the efficient dissociation of photogenerated excitons at the donor-acceptor interface. However, the large band gap induces an energy barrier which disrupts the charge transport.

Tuning the Fermi level with topological phase transition by internal strain in a topological insulator Bi2Se3 thin film.

In a three-dimensional topological insulator Bi2Se3, a stress control for band gap manipulation was predicted but no systematic investigation has been performed yet due to the requirement of large external stress. We report herein on the strain-dependent results for Bi2Se3 films of various thicknesses that are grown via a self-organized ordering process. Using small angle X-ray scattering and Raman spectroscopy, the changes of d-spacings in the crystal structure and phonon vibration shifts resulted from stress are clearly observed when the film thickness is below ten quintuple layers.

Evolution of the surface state in Bi2Se2Te thin films during phase transition.

Topological insulators, a new quantum state of matter, have created exciting opportunities for studies in topological quantum physics and for exploring spintronics applications due to their gapless helical metallic surface states. In this study, thin films composed of alternate layers of Bi and Se (Te) ({Bi(3 Ã…)Te(9 Ã…)}n/{Bi(3 Ã…)Se(9 Ã…)}n) were fabricated by controlling the layer thickness within the atomic scale using thermal evaporation techniques. The high-purity growth of uniform Bi2Se2Te1 thin films has not yet been achieved using a thermal evaporation method.

Terahertz single conductance quantum and topological phase transitions in topological insulator Bi₂Se₃ ultrathin films.

Strong spin-orbit interaction and time-reversal symmetry in topological insulators generate novel quantum states called topological surface states. Their study provides unique opportunities to explore exotic phenomena such as spin Hall effects and topological phase transitions, relevant to the development of quantum devices for spintronics and quantum computation. Although ultrahigh-vacuum surface probes can identify individual topological surface states, standard electrical and optical experiments have so far been hampered by the interference of bulk and quantum well states.

Theoretical study on the effects of nitrogen and methyl substitution on tris-(8-hydroxyquinoline) aluminum: an efficient exciton blocking layer for organic photovoltaic cells.

We studied the effect of nitrogen and methyl substitution on tris-(8-hydroxyquinoline) aluminum (Alq(3)) with density functional theory, which has been adopted as an exciton blocking layer (EBL) in organic photovoltaic cells (OPVCs). The substitution of electron withdrawing nitrogen on the phenoxide moiety of Alq(3) lowers the highest molecular orbital (HOMO) level, thus photogenerated excitons can be effectively blocked in OPVC. Additional substitution of methyl on the pyridine moiety makes that Alq(3) has a smaller electron reorganization energy, which results in higher electron mobility with keeping HOMO level almost intact.

Electronic structure of Te/Sb/Ge and Sb/Te/Ge multi layer films using photoelectron spectroscopy.

Te/Sb/Ge and Sb/Te/Ge multilayer films with an atomically controlled interface were synthesized using effusion cell and e-beam techniques. The layers interacted during the deposition, resulting in films composed of Sb-Te+Sb-Sb/Ge and Sb/Sb-Te/Ge-Te/Ge respectively. Atomic diffusion and chemical reactions in films during the annealing process were investigated by photoemission spectroscopy.

The interface state assisted charge transport at the MoO(3)/metal interface.

The interface formation between a metal and MoO(3) was examined. We carried out in situ ultraviolet and x-ray photoemission spectroscopy with step-by-step deposition of MoO(3) on clean Au and Al substrates. The MoO(3) induces huge interface dipoles, which significantly increase the work functions of Au and Al surfaces.