Topic
Absorption (logic)
About: Absorption (logic) is a research topic. Over the lifetime, 5733 publications have been published within this topic receiving 236302 citations.
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TL;DR: In this article, the authors investigated the electronic structure of the Cd and Te 4d core-level binding energies in the photon energy range from 20 to 140 eV by photoemission.
Abstract: The electronic structure of ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te (0\ensuremath{\le}x\ensuremath{\le}0.65) has been investigated by photoemission in the photon energy range from 20 to 140 eV. A sharp (\ensuremath{\approxeq}1 eV full width at half maximum) peak located 3.4 eV below the valence-band maximum (VBM) is assigned to emission from Mn 3${d}_{\ensuremath{\uparrow}}$ states with e symmetry. The ${t}_{2}$ components hybridize significantly with the Te 5p states and contribute therefore nearly uniformly to the top 6 eV of the valence bands. Weak structures below 6 eV of mixed Mn 3d--Te 5p character occur also due to the p-d hybridization. Cd and Te 4d core-level binding energies remain constant over the whole range of Mn concentrations when measured relative to the VBM. This implies that there are negligible chemical shifts and that the VBM is not affected by the replacement of Cd by Mn. The increase in the optical gap with x is thus due to an increase of the conduction-band energy, in agreement with a shift in the Te 4d absorption threshold as measured by partial-yield spectroscopy. A maximum of the Te 5p component in the density of empty conduction states is identified \ensuremath{\approxeq}2 eV above threshold. The Mn 3p\ensuremath{\rightarrow}3${d}_{\ensuremath{\downarrow}}$ excitations are atomiclike. The results are interpreted in terms of a schematic linear-combination-of-atomic-orbitals level scheme for the band structure of ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Mn}}_{\mathrm{x}}$Te.
79 citations
TL;DR: In this article, the authors measured the relaxation of photoinduced optical absorption following pulsed laser excitation and found that the diffusion coefficient of the excess carriers is time dependent, in agreement with the drift mobility of photocarriers and the predictions of the continuous-time random-walk theory of dispersive transport in disordered materials.
Abstract: Relaxation of photoinduced optical absorption following pulsed laser excitation was measured between 0.5 \ensuremath{\mu}s and 10 ms in doped and undoped $a$-Si: H as a function of temperature. The recombination was found to be bimolecular diffusion limited. The diffusion coefficient of the excess carriers is time dependent ($\ensuremath{\sim}{t}^{\ensuremath{-}0.3}$) in agreement with the drift mobility of photocarriers and the predictions of the continuous-time random-walk theory of dispersive transport in disordered materials.
79 citations
TL;DR: In this paper, a phenomenological band-theoretic model for photoelectric emission which includes the effects of energy loss due to phonon scattering is developed, which is applicable near threshold when the optical absorption depth is large compared to the phonon scatter length of hot electrons, and is particularly useful for cesiated surfaces with positive electron affinity.
Abstract: A phenomenological band-theoretic model for photoelectric emission which includes the effects of energy loss due to phonon scattering is developed. The model is applicable near threshold when the optical absorption depth is large compared to the phonon scattering length of hot electrons, and is particularly useful for cesiated surfaces with positive electron affinity. It is shown that in the low-photon-energy range one must include the dispersion of the optical constants in the yield expression. Formulas are given for photoelectric yield and for energy distribution curves in the cases of direct, indirect, and nondirect volume transitions; direct transitions give the commonly observed cube law for yield near threshold, changing to linear and square laws at higher energy. The theory is illustrated on experimental data for the following cesiated single crystals: Si (indirect transitions), GaAs, GaSb, ${\mathrm{Ga}}_{0.6}$${\mathrm{In}}_{0.4}$As, and Ge (all direct transitions), and is shown to provide in each case an excellent fit over a range of at least ${10}^{3}$ in the yield (1 eV in photon energy). Its applicability to amorphous materials is discussed and illustrated on Ge. Information on hot-electron scattering lengths in the above materials is also extracted and the voltage dependence (due to barrier lowering) of the yield predicted by this model is given.
79 citations
TL;DR: In this paper, a simple heuristic theory is used to calculate the shape of the free-induction decay and the form of the absorption at the normal resonance frequency of the spin system.
Abstract: A discussion is given of experimental results and theoretical considerations which apply in the case of complete adiabatic demagnetization in the rotating frame (ADRF) for nuclear spin systems in solids. Although the net magnetization in this state is zero, both continuous wave and pulse signals are predicted and readily observed at the normal resonance frequency. These signals appear to be much like the derivative of the signals observed in the normal nuclear magnetic resonance (NMR) cases with amplitudes comparable to normal NMR signal amplitudes and they persist for times comparable with ${T}_{1}$ at high fields even when the line is purely homogeneously broadened. A simple heuristic theory is used to calculate, after ADRF, the shape of the free-induction decay and the form of the absorption at $\ensuremath{\omega}\ensuremath{\approx}0, \ensuremath{\Omega}, \mathrm{and} 2\ensuremath{\Omega}$, where $\ensuremath{\Omega}$ is the resonance frequency of the spin system. The density matrix method is then used to calculate line shapes and free-induction decay signals which are found to be in agreement with experiment and the heuristic model calculation. The concept of spin temperature is used to calculate the effect of applying an rf field to produce a line asymmetry in a homogeneously broadened system. It is also shown that, in general, the free induction decay signal is not the Fourier transform of the line shape and homogeneously broadened lines do not saturate uniformly. In addition, it is found experimentally that ADRF is reversible, spin systems are coupled, spectra at low frequency and double the resonance frequency are observed, and spin-system relaxation times vary rapidly with field at low dc fields but are of order of ${T}_{1}$ at high fields.
79 citations
TL;DR: In this paper, the atomic and electronic structure, zone center phonon frequencies, and optical absorption of ferrolectric materials were calculated from first principles using the $GW$ approach and by solving the Bethe-Salpeter equation.
Abstract: The atomic and electronic structure, zone center phonon frequencies, and optical absorption of $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ are calculated from first principles. The structural and vibrational properties predicted from density functional theory are in good agreement with experiment and earlier theoretical work. The electronic band-structure and optical properties are found to be very sensitive to quasiparticle and electron-hole attraction effects, which are included here using the $GW$ approach and by solving the Bethe-Salpeter equation, respectively. We predict the fundamental gap to be more than $1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ larger than the $3.7\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ frequently cited for ferrolectric $\mathrm{Li}\mathrm{Nb}{\mathrm{O}}_{3}$ and calculate optical absorption spectra in good agreement with experiment.
79 citations