Search results for "surface states"
showing 10 items of 47 documents
Unification of the electrical behavior of defects, impurities, and surface states in semiconductors: Virtual gap states in CdO
2009
In contrast to conventional semiconductors, native defects, hydrogen impurities, and surface states are all found to be donors in $n$-type CdO. Using this as a model system, the electrical behaviors of defects, dopants, and surface states in semiconductors are unified by a single energy level, the charge neutrality level, giving much insight into current materials and allowing a band-structure engineering scheme for obtaining desired custom electronic properties in new compound semiconductors.
Time-Resolved Luminescence Characteristics of Cerium Doped YAG Nanocrystals
2007
Time-resolved luminescence characteristics have been studied for cerium doped YAG nanopowders (NP) and nanostructured ceramics (NC). The results obtained have been compared to the luminescence characteristics for the well studied YAG:Ce3+ single crystal (SC). It was detected that the luminescence decay kinetics of Ce3+ related emission in nanocrystals can be closely approximated by two exponents, whereas a single exponential decay was observed in the single crystal. It was also found that the luminescence decay time and light yield of Ce3+ emission are strongly dependent on the cerium concentration and an unusual concentration quenching of Ce3+ emission was observed in YAG nanocrystals. The…
Dynamic modification of Fermi energy in single-layer graphene by photoinduced electron transfer from carbon dots
2020
Graphene (Gr)&mdash
Multi-MHz time-of-flight electronic bandstructure imaging of graphene on Ir(111)
2016
In the quest for detailed spectroscopic insight into the electronic structure at solid surfaces in a large momentum range, we have developed an advanced experimental approach. It combines the 3D detection scheme of a time-of-flight momentum microscope with an optimized filling pattern of the BESSY II storage ring. Here, comprehensive data sets covering the full surface Brillouin zone have been used to study faint substrate-film hybridization effects in the electronic structure of graphene on Ir(111), revealed by a pronounced linear dichroism in angular distribution. The method paves the way to 3D electronic bandmapping with unprecedented data recording efficiency.
Comparative study of polar perovskite surfaces
2004
A novel model of the ‘‘zig–zag’’ (1 1 0) polar surface termination of ABO3 perovskites is suggested and analyzed. Classical shell model calculations for BaTiO3, SrTiO3 and LaMnO3 show that such the (1 · 2) (1 1 0) surface reconstruction has the lowest energy, comparable to that for the (1 0 0) surfaces. The calculated surface energy reaches the saturation only when 6–8 atomic near-surface planes are allowed to relax. Surface relaxation leads to the formation of considerable dipole moment perpendicular to the surface. The predicted surface polarization of thin perovskite films, even in the cubic phase, could affect their dielectric properties. � 2004 Elsevier B.V. All rights reserved.
Ultrafast spectroscopic investigation on fluorescent carbon nanodots: the role of passivation.
2019
Disentangling the respective roles of the surface and core structures in the photocycle of carbon nanodots is a critical open problem in carbon nanoscience. While the need of passivating carbon dot surfaces to obtain efficiently emitting nanoparticles is very well-known in the literature, it is unclear if passivation introduces entirely new surface emitting states, or if it stabilizes existing states making them fluorescent. In this multi-technique femtosecond spectroscopy study, the relaxation dynamics of non-luminescent (non-passivated) carbon dots are directly compared with their luminescent (passivated) counterparts. Non-passivated dots are found to host emissive states, albeit very sho…
Band unpinning and photovoltaic model for P3HT:PCBM organic bulk heterojunctions under illumination
2008
Capacitance analysis of P3HT:PCBM bulk heterojunction solar cells, in dark and under illumination, shows a linear Mott-Schottky characteristic at moderate reverse bias, indicating p-doping of the organic blend. The flatband potential under illumination is displaced negatively about 0.6 V with respect to dark conditions. A basic photovoltaic model is developed to explain this, in terms of electron transfer via surface states at the metal/organic interface. Surface states with a slow exchange kinetics, become charged under illumination, unpinning the band and decreasing the depletion layer at the electron extraction contact. This becomes a major factor limiting the performance of bulk heteroj…
Periodic unmixing of a binary metallic vapor
2005
We report on a type of surface structuring after short pulse laser ablation of a binary alloy. We observe the emergence of a concentric ring structure with changing elemental composition. The composition changes are interpreted by condensation of the ambient ablation vapor due to stress wave excitations in the ablation spot.
Ligand removal from soluble CdTe nanocrystals evidenced by time-resolved photoluminescence spectroscopy
2008
We present experimental studies on the effect of pyridine treatment on the optical properties of ligand-stabilized colloidal CdTe nanocrystals. We demonstrate, by quasi-stationary and time-resolved photoluminescence (PL) spectroscopy, a drastic reduction in the PL lifetime and a concomitant decrease in the PL yield by more than 90% when dissolving the nanocrystals in pyridine. The pyridine solvent efficiently removes the ligand shell and thus enables a rapid energy transfer from the quantum dot to optically dark surface states or into the solvent. The demonstrated removal of the ligand shell is a key step towards integrating such CdTe nanocrystals in hybrid organic/inorganic nanocomposites,…
Catalyst-free vapour-solid technique for deposition of Bi2Te3 and Bi2Se3 nanowires/nanobelts with topological insulator properties.
2015
We present a simple two-stage vapour–solid synthesis method for the growth of bismuth chalcogenide (Bi2Te3, Bi2Se3) topological insulator nanowires/nanobelts by using Bi2Se3 or Bi2Te3 powders as source materials. During the first stage of the synthesis process nanoplateteles, serving as “catalysts” for further nanowire/nanobelt growth, are formed. At a second stage of the synthesis, the introduction of a N2 flow at 35 Torr pressure in the chamber induces the formation of free standing nanowires/nanobelts. The synthesised nanostructures demonstrate a layered single-crystalline structure and Bi : Se and Bi : Te ratios 40 : 60 at% for both Bi2Se3 and Bi2Te3 nanowires/nanobelts. The presence of…