Absorption (logic)

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

Ultranarrow Luminescence Lines from Single Quantum Dots.

Abstract: We report ultranarrow $(l0.15\mathrm{meV})$ cathodoluminescence lines originating from single InAs quantum dots in a GaAs matrix for temperatures up to 50 K, directly proving their $\ensuremath{\delta}$-function-like density of electronic states. The quantum dots have been prepared by molecular beam epitaxy utilizing a strain-induced self-organizing mechanism. A narrow dot size distribution of width $12\ifmmode\pm\else\textpm\fi{}1\mathrm{nm}$ is imaged by plan-view transmission electron microscopy. Cathodoluminescence images directly visualize individual dot positions and recombination from a single dot. A dense dot array $(\ensuremath{\sim}{10}^{11}\mathrm{dots}/{\mathrm{cm}}^{2})$ gives rise to a distinct absorption peak which almost coincides with the luminescence maximum.

Electron Spin Resonance Absorption in Metals. I. Experimental

Abstract: The electron spin resonance absorption in metals was investigated at 300 and 9000 Mc/sec, in the temperature range from 4\ifmmode^\circ\else\textdegree\fi{}K to 296\ifmmode^\circ\else\textdegree\fi{}K. The metals investigated were: Li, Na, K, Be, Mg, Al, Pd, W. Resonances were observed in Li, Na, Be, for which accurate $g$ values and relaxation times were obtained and compared with existing theories. K gave a signal only at 4\ifmmode^\circ\else\textdegree\fi{}K and 300 Mc/sec, with too poor a signal-to-noise ratio to make accurate measurements. No resonances were observed in Mg, Al, Pd, W. The line shapes predicted by Dyson's theory for the resonance absorption in metals were checked experimentally for different diffusion times and relaxation times. A satisfactory agreement between the theory and experiment is obtained for both the normal and the anomalous skin effect region.

Infrared absorption strength and hydrogen content of hydrogenated amorphous silicon.

Abstract: We have used infrared transmission and nuclear-reaction analysis to determine the ir absorption strength of the Si-H wagging and stretching modes in hydrogenated amorphous silicon (a-Si:H). The films were deposited by plasma-assisted chemical vapor deposition and reactive magnetron sputtering. We show that the widely used ir-data-analysis method of Brodsky, Cardona, and Cuomo can lead to significant errors in determining the absorption coefficients, particularly for films less than \ensuremath{\sim}1 \ensuremath{\mu}m thick. To eliminate these errors we explicitly take into account the effects of optical interference to analyze our data. We show that the hydrogen content can be determined from the stretching modes at \ensuremath{\omega}=2000 and 2100 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ as well as the wagging mode at \ensuremath{\omega}=640 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. By assigning different oscillator strengths to the 2000- and 2100-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ modes, we show that the absorption strength of the stretching modes does not depend on the details of sample preparation, contrary to hypotheses previously invoked to explain experimental data. We obtain ${\mathit{A}}_{640}$=(2.1\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$, ${\mathit{A}}_{2000}$=(9.0\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$, and ${\mathit{A}}_{2100}$=(2.2\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ for the proportionality constants between the hydrogen concentration and the integrated absorbance of the wagging and stretching modes. The value of ${\mathit{A}}_{640}$ is \ensuremath{\sim}30% larger than the generally used value. We show that previously published data for both the wagging and stretching modes are consistent with the proportionality factors determined in the present study.

Measurement of Dispersive Properties of Electromagnetically Induced Transparency in Rubidium Atoms

Abstract: The dispersive properties of the atomic transition in the rubidium ${D}_{2}$ line ($5{S}_{\frac{1}{2}}\ensuremath{-}5{P}_{\frac{3}{2}}$) at 780.0 nm are measured with a Mach-Zehnder interferometer when an additional coupling field at 775.8 nm is applied to an upper transition ($5{P}_{\frac{3}{2}}\ensuremath{-}5{D}_{\frac{5}{2}}$). This ladder-type system is observed to exhibit electromagnetically induced transparency together with a rapidly varying refractive index. A reduction in group velocity for the probe beam (${v}_{g}=\frac{c}{13.2}$) is inferred from the measured dispersion curve with 52.5% suppressed absorption on resonance.

Fine structure in the absorption-edge spectrum of si

Abstract: Measurements of the absorption spectrum of Si, made with high resolution, near the main absorption edge, at various temperatures between 4.2\ifmmode^\circ\else\textdegree\fi{}K and 415\ifmmode^\circ\else\textdegree\fi{}K, have revealed fine structure in the absorption on the long-wavelength side of this edge. This structure has been analyzed and can be interpreted in terms of indirect transitions involving, in general, phonons with energies corresponding to temperatures of 212\ifmmode^\circ\else\textdegree\fi{}K, 670\ifmmode^\circ\else\textdegree\fi{}K, 1050\ifmmode^\circ\else\textdegree\fi{}K, and 1420\ifmmode^\circ\else\textdegree\fi{}K. The form of the absorption associated with each type of phonon indicates that, as well as the formation of free electron-hole pairs taking place, excitons with a binding energy \ensuremath{\sim}0.01 ev are produced in the absorption process. The temperature dependence of the indirect energy band gap has been found and using this along with data on the intrinsic carrier density indicates an increase with temperature of the combined density-of-states effective mass of the electrons and holes. A smoothing out of the basic features of the curves is observed and shown to be consistent with relaxation broadening. A discussion of the significance of the energies of the phonons taking part in the indirect transitions to the lattice vibrational spectrum of Si is given.