Absorption (logic)

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

Hole-doping-induced changes in the electronic structure of La 1 − x Sr x FeO 3 : Soft x-ray photoemission and absorption study of epitaxial thin films

Abstract: We have studied the electronic structure of epitaxially grown thin films of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{FeO}}_{3}$ by in situ photoemission spectroscopy (PES) and x-ray-absorption spectroscopy (XAS) measurements. The $\mathrm{Fe}$ $2p$ and valence-band PES spectra and the $\mathrm{O}$ $1s$ XAS spectra of ${\mathrm{LaFeO}}_{3}$ have been successfully reproduced by configuration-interaction cluster-model calculation and, except for the satellite structure, by band-structure calculation. From the shift of the binding energies of core levels, the chemical potential was found to be shifted downward as $x$ was increased. Among the three peaks in the valence-band spectra of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{FeO}}_{3}$, the peak nearest to the Fermi level $({E}_{F})$, due to the ``${e}_{g}$ band,'' was found to move toward ${E}_{F}$ and became weaker as $x$ was increased, whereas the intensity of the peak just above ${E}_{F}$ in the $\mathrm{O}$ $1s$ XAS spectra increased with $x$. The gap at ${E}_{F}$ was seen for all values of $x$. These results indicate that changes in the spectral line shape around ${E}_{F}$ are dominated by spectral weight transfer from below to above ${E}_{F}$ across the gap and are therefore highly nonrigid-bandlike changes.

Temperature-dependent photoluminescence from single-walled carbon nanotubes

Abstract: Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy of pillar-suspended single-walled carbon nanotubes has been measured for temperatures between 300 and $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The atmospheric environment strongly affects the low-temperature luminescence. The PL intensity is quenched at temperatures below $\ensuremath{\sim}40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for nanotubes in high vacuum, while nanotubes in helium ambient remain luminescent. The PL peak emission energy is only very weakly dependent on temperature, with a species-dependent blueshift upon cooling corresponding to a relative shift in bandgap of $\ensuremath{-}3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.3em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ or less. The integrated peak intensities change by only a factor of 2, with linewidths showing a moderate temperature dependence. In PLE, the second absorption peak energy $({E}_{22})$ is also only weakly temperature dependent, with no significant shift and a limited reduction in linewidth upon cooling to $20\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. In addition to the previously assigned nanotube PL peaks seen at room temperature, at least two distinct new classes of PL peaks are observed at cryogenic temperatures.

Energy levels and line intensities of Pr 3 + in LiY F 4

Abstract: High-resolution polarized absorption and fluorescence spectra of ${\mathrm{Pr}}^{3+}$ in LiY${\mathrm{F}}_{4}$ were measured at temperatures between 10 and 300\ifmmode^\circ\else\textdegree\fi{}K. Energy-level assignments were made assuming electric-dipole transition selection rules for ${S}_{4}$ site symmetry. Forty-six energy levels of the $4{f}^{2}$ ground configuration were established, including 44 in the lowest nine multiplets. Crystal-field parameters were determined that gave a rms deviation of 15.8 ${\mathrm{cm}}^{\ensuremath{-}1}$ between 41 of the experimental energy levels and calculated values. The parameters were ${B}_{20}=488.9$, ${B}_{40}=\ensuremath{-}1043$, ${B}_{44}=1242$, ${B}_{60}=\ensuremath{-}42$, Re ${B}_{64}=1213$, and Im ${B}_{64}=22.5$ ${\mathrm{cm}}^{\ensuremath{-}1}$. These parameters were used to obtain the remaining energy levels, yielding a complete energy-level scheme for the $4{f}^{2}$ configuration of ${\mathrm{Pr}}^{3+}$. The crystal-field parameters for ${\mathrm{Pr}}^{3+}$ in LiY${\mathrm{F}}_{4}$ were compared to those for other ions in this host. A theoretical calculation of line intensities was performed in which the odd-fold crystal-field parameters were obtained from a lattice sum. Line intensities were measured and compared with theory.

Absorption and Scattering of X-Rays

Abstract: X-rays are absorbed by materials in differing degrees; absorption coefficients are defined to quantitatively describe the magnitudes of this process. Let us assume that when an x-ray beam passes through a thin layer of material a fraction dN/N of the pulse rate N is absorbed. This fraction is proportional to the thickness dx of the layer $$\frac{{d N}} {N} = - \mu dx$$ where μ is a proportionality factor. The negative sign indicates that x-rays are reduced in intensity when passing through matter. If the factor μ is independent of x, we then obtain by integration $$N = {N_0}\exp \left[ { - \mu x} \right]$$ where N 0 is the pulse rate of the primary incident radiation and N the pulse rate after passage through the layer of the thickness x. The term μ is known as the linear absorption coefficient and, in the following, is therefore always written as μ l . It is $$\frac{{mu _l}} = - {\{{1}} {N}{{dN}} {dx}\left[ {{\mu _l}} \right] = c{m^-1}$$ where μ l describes the magnitude of absorption after passage through one centimeter of matter.

Ultrafast Optical Nonlinearity in the Quasi-One-Dimensional Mott Insulator Sr 2 CuO 3

Abstract: We report strong instantaneous photoinduced absorption in the quasi-one-dimensional Mott insulator ${\mathrm{Sr}}_{2}{\mathrm{CuO}}_{3}$ in the IR spectral region. The observed photoinduced absorption is to an even-parity two-photon state that occurs immediately above the absorption edge. Theoretical calculation based on a two-band extended Hubbard model explains the experimental features and indicates that the strong two-photon absorption is due to a very large dipole coupling between nearly degenerate one- and two-photon states. Room temperature picosecond recovery of the optical transparency suggests the strong potential of ${\mathrm{Sr}}_{2}{\mathrm{CuO}}_{3}$ for all-optical switching.