Search results for "absorption."

Ultrafast Charge Separation at the CdSe/CdS Core/Shell Quantum Dot/Methylviologen Interface: Implications for Nanocrystal Solar Cells

2011

Exciton separation dynamics in the electron transfer system containing highly photostable CdSe/CdS core/shell nanocrystal quantum dots and adsorbed methylviologen was investigated by means of femtosecond absorption spectroscopy. The experiments revealed that electron extraction from the photoexcited core is possible, and the rate of the ET reaction strongly depends on the CdS shell thickness. A CdS associated exponential decay constant β of 0.33 A−1 was obtained reflecting the electronic barrier effect of the shell. These findings show that core/shell structures are well suited for the design of optimized QD-based solar cells.

Local structure of ball-milled LaNi5 hydrogen storage material by Ni K-edge EXAFS

2010

Abstract Local structure of the nanostructured LaNi5 hydrogen storage alloys, prepared by ball-milling, has been studied using Ni K-edge extended X-ray absorption fine structure spectroscopy. Results indicate that the ball-milling up to 100 h results in the production of nanoparticles characterized by large atomic disorder and slightly reduced unit-cell volume, compared to the bulk LaNi5. High temperature annealing appears to help in partial recovery of atomic order in the ball-milled samples; however, long-time ball-milled samples retain large disorder even after the high temperature annealing. The results suggest that the large disorder and the reduced unit-cell volume might be causing a …

The local atomic structure and thermoelectric properties of Ir-doped ZnO: hybrid DFT calculations and XAS experiments

2021

We greatly acknowledge the financial support via the ERAF Project No. 1.1.1.1/18/A/073. Calculations have been performed under the Project HPC-EUROPA3 (INFRAIA-2016-1-730897), with the support of the EC Research Innovation Action under the H2020 Programme. A. C. gratefully acknowledges the technical support received from KTH-PDC. Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2

Structure and polarized absorption spectra of Mn3+-substituted andalusites (viridines)

1977

Treatment of disorder effects in X-ray absorption spectra beyond the conventional approach

2020

The contribution of static and thermal disorder is one of the largest challenges for the accurate determination of the atomic structure from the extended X-ray absorption fine structure (EXAFS). Although there are a number of generally accepted approaches to solve this problem, which are widely used in the EXAFS data analysis, they often provide less accurate results when applied to outer coordination shells around the absorbing atom. In this case, the advanced techniques based on the molecular dynamics and reverse Monte Carlo simulations are known to be more appropriate: their strengths and weaknesses are reviewed here.

CO2 laser-induced structure changes in lead zirconate titanate Pb(Zr0.58Ti0.42)O3 sol–gel films

2003

Based on absorption spectra of lanthanum modified lead zirconate titanate Pb0.9La0.1(Zr0.65Ti0.35)O3 (PLZT10/65/35) ferroelectric ceramics an idea of local and selective treatment of lead zirconite titanate Pb(ZrXTi1−X)O3 (PZT) sol–gel film in the multi-layer structure by CO2 laser radiation was formulated. The possibility to obtain PZT perovskite film on the SiO2/Si substrate by irradiation with CO2 laser was shown experimentally. X-ray studies revealed the PZT perovskite structure ratio growth at the expenses of pirochlore structure with an increased power density of laser radiation.

Vibrational spectroscopy of trans and cis deuterated formic acid (HCOOD): Anharmonic calculations and experiments in argon and neon matrices

2010

The absorption spectra of trans and cis conformers of deuterated formic acid (HCOOD) isolated in argon and neon matrices are analyzed in the mid-infrared and near-infrared spectral regions (7900–450 cm � 1 ). Vibrational excitation by narrow-band IR radiation is used to convert the lower-energy trans conformer to the higher-energy cis form. A large number of overtone and combination bands are identified. The results of anharmonic vibrational calculations (CC-VSCF) for both conformers are reported and compared to the experimental spectra.

Light absorption and electrical transport in Si:O alloys for photovoltaics

2010

Thin films (100-500 nm) of the Si:O alloy have been systematically characterized in the optical absorption and electrical transport behavior, by varying the Si content from 43 up to 100 at. %. Magnetron sputtering or plasma enhanced chemical vapor deposition have been used for the Si:O alloy deposition, followed by annealing up to 1250 °C. Boron implantation (30 keV, 3-30× 1014 B/cm2) on selected samples was performed to vary the electrical sheet resistance measured by the four-point collinear probe method. Transmittance and reflectance spectra have been extracted and combined to estimate the absorption spectra and the optical band gap, by means of the Tauc analysis. Raman spectroscopy was …

Luminescence and FTIR Spectroscopy of ZnO Nanocrystals

2006

Time-resolved luminescence and Furje Transformation Infrared (FTIR) absorption spectroscopy for ZnO nanocrystals prepared under different chemical reactions using microwave driven hydrothermal process was studied. OH- group stretching vibration frequency is considerably different in nanocrystals studied and in single ZnO crystal. It is shown that fractions of chemicals used in synthesis process could be found in nanopowders. Luminescence at ~2.0 eV (due to defect states in ZnO crystals and nanopowders) was suppressed in nanopowders obtained by urea method.

Raman Spectroscopic Fingerprints of Atomically Precise Ligand Protected Noble Metal Clusters: Au 38 (PET) 24 and Au 38− x Ag x (PET) 24

2021

Distinct Raman spectroscopic signatures of the metal core of atomically precise, ligand-protected noble metal nanoclusters are reported using Au38 (PET)24 and Au38- x Agx (PET)24 (PET = 2-phenylethanethiolate, -SC2 H4 C6 H5 ) as model systems. The fingerprint Raman features (occurring <200 cm-1 ) of these clusters arise due to the vibrations involving metal atoms of their Au23 or Au23- x Agx cores. A distinct core breathing vibrational mode of the Au23 core has been observed at 90 cm-1 . Whereas the breathing mode shifts to higher frequencies with increasing Ag content of the cluster, the vibrational signatures due to the outer metal-ligand staple motifs (between 200 and 500 cm-1 ) do not s…