Search results for "Band structure"
showing 10 items of 215 documents
Electronic structure of CuAlO2 and CuScO2 delafossites under pressure
2007
The electronic structure of CuAlO 2 and CuScO 2 delafossites is investigated by means of optical absorption measurements under pressure and ab initio band structure calculations. Measurements are carried out on CuAlO 2 monocrystals and pulsed laser deposited CuAlO 2 and CuScO 2 thin films up to 20 GPa. CuAlO 2 is an indirect semiconductor that is stable in the pressure range explored here. The pressure coefficients of the indirect and direct gaps are found to be 15 meV/GPa and 2 meV/GPa respectively. CuScO 2 is a direct semiconductor and the pressure coefficient of the excitonic peak energy is -5.5 meV/GPa. Two reversible phase transitions are observed in CuScO 2 . At 13 GPa the delafossite…
Verwey-type transition in EuNiP
2006
High temperature 151Eu Mossbauer measurements provide proof for inhomogeneous mixed-valent behaviour in EuNiP. We observed that EuNiP undergoes a Verwey-type charge delocalisation transition when heated above 470 K prior to the structural γ-β phase transition at T ≈ 510 K. This finding confirms the results of photoemission spectroscopy in the isostructural compound EuPdP and of TB-LMTO-ASA band structure calculations. We discuss the role of a van Hove singularity associated with a high density of 4f states close to the Fermi energy in inhomogeneous mixed europium valency, and the microscopic mechanism of γ-β phase transition in compounds analogous to EuNiP.
Photoelectrochemical characterization of photocatalysts
2021
Abstract This chapter aims to provide an overview of the photoelectrochemical characterization of semiconducting photocatalysts and, in particular, present Photocurrent Spectroscopy (PCS) as a useful tool in determining the band structure of semiconducting/insulating materials. Some fundamentals on PCS will be provided looking at the experimental setup and underlying its advantages and disadvantages. Then, the photoelectrochemical behavior of a semiconductor/electrolyte junction under irradiation will be presented, also taking into account its crystalline or amorphous nature, highlighting how it is possible to get information on the energetics of the junction. This will be exploited to show…
Photoluminescence from silicon nanocrystals initiated by Auger recombination
2006
Abstract The mechanism of intense photoluminescence (PL) of silicon nanocrystals (nc-si), so interpreted as recombinative emission is reconsidered. Analysis of available theoretical and experimental data is presented to show that nc-si have an indirect band structure and, therefore, it is doubtful that electron–hole recombination is the only mechanism of intense emission. A model is proposed according to which a fraction of electrons reaches the second conduction sub-band by Auger recombination, a part of intense visible radiation being caused by direct electron transitions from the second conduction sub-band to the first one. Continuity equations are constructed in the first and the second…
Photonic Crystals from Core-Shell Colloids with Incorporated Highly Fluorescent Quantum Dots
2005
We report the preparation of nanoscaled PS/PMMA core-shell spheres with highly fluorescent CdS/ZnS coated CdSe quantum dots (QDs) integrated in the core. Core-shell spheres of different diameters have been self-assembled to colloidal photonic crystals (PCs) with photonic stop bands located in the visible range of the electromagnetic spectrum. For the synthesis of the core, a modified miniemulsion polymerization has been used; the shell was prepared by a newly developed core-shell polymerization. The CdSe QDs embedded in the core were coated with the higher band gap semiconductor materials CdS and ZnS in a successive ion layer adsorption reaction (SILAR) keeping up the light-emitting propert…
Anisotropic photoluminescence of nonpolar ZnO epilayers and ZnO/Zn1 −xMgxO multiple quantum wells grown on LiGaO2 substrate
2020
Ministry of Science and Technology, Taiwan (104-2221-E-110-012-MY3, 107-2221-E-110-004-MY3); National Natural Science Foundation of China (51602309, U1605245).
VIS-UV ZnCdO/ZnO multiple quantum well nanowires and the quantification of Cd diffusion.
2014
International audience; We report on the growth and microstructure analysis of high Cd content ZnCdO/ZnO multiple quantum wells (MQW) within a nanowire. Heterostructures consisting of ten wells with widths from 0.7 to 10nm are demonstrated, and show photoluminescence emissions ranging from 3.03 to 1.97eV. The wells with thicknesses⩽2nm have high radiative efficiencies compared to the thickest ones, consistent with the presence of quantum confinement. However, a nanometric analysis of the Cd profile along the heterostructures shows the presence of Cd diffusion from the ZnCdO well to the ZnO barrier. This phenomenon modifies the band structure and the optical properties of the heterostructure, an…
γ-Ray Spectroscopy at the Limits: First Observation of Rotational Bands inLr255
2009
The rotational band structure of Lr-255 has been investigated using advanced in-beam gamma-ray spectroscopic techniques. To date, Lr-255 is the heaviest nucleus to be studied in this manner. One ro ...
Shell-Structure and Pairing Interaction in Superheavy Nuclei: Rotational Properties of theZ=104NucleusRf256
2012
The rotational band structure of the $Z=104$ nucleus $^{256}\mathrm{Rf}$ has been observed up to a tentative spin of $20\ensuremath{\hbar}$ using state-of-the-art $\ensuremath{\gamma}$-ray spectroscopic techniques. This represents the first such measurement in a superheavy nucleus whose stability is entirely derived from the shell-correction energy. The observed rotational properties are compared to those of neighboring nuclei and it is shown that the kinematic and dynamic moments of inertia are sensitive to the underlying single-particle shell structure and the specific location of high-$j$ orbitals. The moments of inertia therefore provide a sensitive test of shell structure and pairing i…
XMM‐NewtonObservations of the Supernova Remnant IC 443. I. Soft X‐Ray Emission from Shocked Interstellar Medium
2006
The shocked interstellar medium around IC443 produces strong X-ray emission in the soft energy band (E<1.5 keV). We present an analysis of such emission as observed with the EPIC MOS cameras on board the XMM-Newotn observatory, with the purpose to find clear signatures of the interactions with the interstellar medium (ISM) in the X-ray band, which may complement results obtained in other wavelenghts. We found that the giant molecular cloud mapped in CO emission is located in the foreground and gives an evident signature in the absorption of X-rays. This cloud may have a torus shape and the part of torus interacting with the IC443 shock gives rise to 2MASS-K emission in the southeast. The…