Absorption (logic)

About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.

Hopping and clustering of oxygen vacancies in SrTiO3 by anelastic relaxation

Abstract: The complex elastic compliance ${s}_{11}(\ensuremath{\omega},T)$ of $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ has been measured as a function of the O deficiency $\ensuremath{\delta}l0.01$. The two main relaxation peaks in the absorption are identified with hopping of isolated O vacancies over a barrier of $0.60\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and reorientation of pairs of vacancies involving a barrier of $1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The pair binding energy is $\ensuremath{\simeq}0.2\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, and indications for additional clustering, possibly into chains, is found already at $\ensuremath{\delta}\ensuremath{\sim}0.004$. The anisotropic component of the elastic dipole of an O vacancy is $\ensuremath{\Delta}\ensuremath{\lambda}=0.026$. The possible role of electrostatic repulsion between vacancies in slowing the kinetics for their aggregation is discussed.

Electronic states and optical properties of porphyrins in van der Waals contact: thorium(IV) sandwich complexes

Abstract: Ground-state and time-resolved excited-state absorption spectra and fluorescence and phosphorescence spectra of three Th{sup IV} sandwich complexes, Th{sup IV}(TPP){sub 2}, Th{sup IV}(OEP){sub 2}, and Th{sup IV}(OEP)(TPP), are reported (OEP = 2,3,7,8,12,13,17,18-octaethylporphyrinate, TPP = 5,10,15,20-tetraphenylporphyrinate). These complexes, in which the nitrogen planes of the two porphyrin macrocycles are {approximately}2.9 {Angstrom} apart, exhibit a number of prominent optical characteristics: (1) monoporphyrin-like Q and B absorption bands, (2) a new absorption between the Q and B bands, (3) a weak, low-energy absorption that is substantially red-shifted relative to the Q bands of analogous monoporphyrin complexes, (4) fluorescence and phosphorescence emission bands that are even further red-shifted relative to typical emission bands from porphyrin monomers, and (5) a moderately intense near-infrared {sup 3}({pi},{pi}*) excited-state absorption not observed in monomeric porphyrins. These characteristic optical properties of the sandwich complexes are all accounted for by a relatively simple molecular orbital configuration-interaction model. Additionally, the spectral data and molecular orbital model identify the energies of charge-transfer configurations and delineate their contribution to the electronic states of these strongly-coupled {pi} systems. These results provide insights into the interactions that can take place between other pairs of chromophores brought within van der Waals contact, such as the bacteriochlorophyll dimermore » of the photosynthetic reaction center. 49 refs., 9 figs., 1 tab.« less

Charge transfer in collisions of atomic hydrogen with O/sup 8 +/, He/sup + +/, and H/sup +/

Abstract: The charge-transfer process ${\mathrm{O}}^{8+}+\mathrm{H}(1s)\ensuremath{\rightarrow}{\mathrm{O}}^{7+}+{\mathrm{H}}^{+}$ is considered for ${\mathrm{O}}^{8+}$ impact energies from 0.025 to 200 keV/amu, using the atomic base $S$ matrix formulation represented by time-dependent bases which denote moving atomic orbitals. In the evaluation of the $S$ matrix, models of two extreme types, the unitarized model and the absorption model, are introduced. The numerical results show that there is only a small difference between the cross sections obtained using the respective models for impact energies above 0.5 keV/amu, while the cross section due to the unitarized model becomes smaller than one-half of that obtained with the absorption model at an impact energy of 0.05 keV/amu. The data are also compared with other calculations of the same process. For the investigation of the validity of our formula, the unitarized formula is also applied to the processes ${\mathrm{H}}^{+}+\mathrm{H}(1s)\ensuremath{\rightarrow}\mathrm{H}+{\mathrm{H}}^{+}$ and ${\mathrm{He}}^{2+}+\mathrm{H}(1s)\ensuremath{\rightarrow}{\mathrm{He}}^{+}+{\mathrm{H}}^{+}$. The results are in good agreement with the experimental data.

Range of heavy ions in solids

Abstract: The ranges of N, Ne, Ar, Kr, and Xe ions in Be, B, C, and Al have been measured to \ifmmode\pm\else\textpm\fi{}10% for incident ion energy 50-500 kev. A monoenergetic ion beam from an electrostatic accelerator strikes a thick target of the absorber, and the penetration depth is determined by a momentum analysis of monoenergetic protons elastically scattered from the target and the embedded atoms. An expression relating the penetration depth to the actual path length is derived. A linear range-energy behavior is found for Ar, Kr, and Xe ions; for N and Ne ions $\frac{\mathrm{dE}}{\mathrm{dX}}$ increases with ion energy. The experimental ranges are 20% shorter than theoretical values based on energy loss by elastic nuclear collisions. By including electronic contributions to the stopping process, good agreement with experiment is achieved.

Probing outer-sphere adsorption of aqueous metal complexes at the oxide-water interface with resonant anomalous x-ray reflectivity.

Abstract: Resonant anomalous x-ray reflectivity near the Pt ${L}_{\mathrm{I}\mathrm{I}\mathrm{I}}$ edge simultaneously revealed the geometric and spectroscopic structures of $\mathrm{P}\mathrm{t}({\mathrm{N}\mathrm{H}}_{3})_{4}{}^{2+}$ ions adsorbed at the quartz(100)-water interface. The derived Pt geometric subprofile shows two discrete ``outer-sphere'' adsorbed layers, and the interface-specific x-ray absorption edge profile exhibits a significant white-line enhancement compared to the bulk-solution species.