Absorption (logic)

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

Magnetic and charge dynamics in a doped one-dimensional transition metal oxide.

Abstract: We have measured the electrical resistivity, polarized x-ray absorption, and magnetic neutron scattering for ${\mathrm{Y}}_{2\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Ba}{\mathrm{Ni}}_{1\ensuremath{-}y}{\mathrm{Zn}}_{y}{\mathrm{O}}_{5}$ to determine how doping affects the charge and spin dynamics of a Haldane chain compound. While Zn doping, which severs the NiO chains, increases the resistivity beyond that of the pure material, Ca doping introduces holes, residing mainly in the ${2p}_{z}$, orbital of the oxygens in the NiO chains. Both dopants lead to simple finite size effects above the Haldane gap. In addition, we have discovered that Ca doping yields substantial magnetic states below the Haldane gap.

Compensation in Al-Doped ZnO by Al-Related Acceptor Complexes: Synchrotron X-Ray Absorption Spectroscopy and Theory

Abstract: The synchrotron x-ray absorption near edge structures (XANES) technique was used in conjunction with first-principles calculations to characterize Al-doped ZnO films. Standard characterizations revealed that the amount of carrier concentration and mobility depend on the growth conditions, i.e. ${\mathrm{H}}_{2}$ $(\mathrm{or}\text{ }\text{ }{\mathrm{O}}_{2})/\mathrm{Ar}$ gas ratio and Al concentration. First-principles calculations showed that Al energetically prefers to substitute on the Zn site, forming a donor ${\mathrm{Al}}_{\mathrm{Zn}}$, over being an interstitial (${\mathrm{Al}}_{i}$). The measured Al $K$-edge XANES spectra are in good agreement with the simulated spectra of ${\mathrm{Al}}_{\mathrm{Zn}}$, indicating that the majority of Al atoms are substituting for Zn. The reduction in carrier concentration or mobility in some samples can be attributed to the ${\mathrm{Al}}_{\mathrm{Zn}}\mathrm{\text{\ensuremath{-}}}{V}_{\mathrm{Zn}}$ and $2{\mathrm{Al}}_{\mathrm{Zn}}\mathrm{\text{\ensuremath{-}}}{V}_{\mathrm{Zn}}$ complex formations that have similar XANES features. In addition, XANES of some samples showed additional features that are the indication of some $\ensuremath{\alpha}\mathrm{\text{\ensuremath{-}}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ or $n{\mathrm{Al}}_{\mathrm{Zn}}\mathrm{\text{\ensuremath{-}}}{\mathrm{O}}_{i}$ formation, explaining their poorer conductivity.

Complex magnetic properties of the rare-earth copper oxides, R2CuO4, observed via measurements of the dc and ac magnetization, EPR, microwave magnetoabsorption, and specific heat

Abstract: We report the results of an extensive investigation of the magnetic properties of a large series of undoped ${R}_{2}$${\mathrm{CuO}}_{4}$ single crystals with R==Pr, Nd, Sm, Eu, and Gd (which are the host compounds for the newly discovered series of electron cuprate superconductors) and mixture versions of the form ${A}_{2\mathrm{\ensuremath{-}}x}$${B}_{x}$${\mathrm{CuO}}_{4}$, with A==Pr, Nd, Sm, Eu, or Gd, and B==Gd, Tb, or Dy. We have measured dc and ac magnetization, microwave magnetoabsorption, EPR, and specific heat. These measurements reveal two characteristic transition temperatures associated with a novel complex magnetic behavior, including weak ferromagnetism, two sharp peaks in the low-field dc magnetization, an unusual anisotropy in the EPR resonance field for R=Gd, and two additional anisotropic microwave absorption modes. The higher characteristic transition temeperature at \ensuremath{\sim}270 K is associated with antiferromagnetic ordering of the Cu moments which are strongly coupled within the ${\mathrm{CuO}}_{2}$ layers. The lower, at \ensuremath{\le}20 K, cannot be attributed to antiferromagnetic ordering of the R moments and is tentatively attributed to a spontaneous canted spin reorientation. An understanding of this magnetic behavior is important in order to ascertain its relationship to possible mechanisms of high-temperature superconductivity.

Spontaneous-Raman-Scattering Efficiency and Stimulated Scattering in Silicon

Abstract: The absolute spontaneous-Raman-scattering efficiency and linewidth of the 521-${\mathrm{cm}}^{\ensuremath{-}1}$ optical mode of silicon have been measured at 77 K using a continuous laser (Nd in yttrium aluminum garnet) operating at 1.064 \ensuremath{\mu}m. The measured scattering efficiency (5.1 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$/cm sr for unpolarized forward scattering along the crystal [111] direction) and narrow linewidth yield a calculated value of the stimulated Raman gain coefficient which is considerably larger than those reported for other media, both solid and liquid. Stimulated Raman scattering in Si at 77 K has also been observed using a focused multimode $Q$-switched YAG: Nd laser. Inaccuracy in the measured stimulated gain resulted mainly from the uncertainty in the effective focal volume inside the silicon. Multiphoton absorption at the incident laser frequency has been considered and found to modify the measured stimulated gain by a significant amount. The estimated gain from the stimulated Raman effect was found to be in satisfactory agreement with that calculated from the absolute spontaneous-Raman-scattering efficiency.

General Model of Electrochemical Hydrogen Absorption into Metals

Abstract: A general model for the hydrogen adsorption and hydrogen absorption into metals has been proposed. It includes reactions of hydrogen evolution M+H{sub 2}O+e=MH{sub ads}+OH{sup {minus}}; MH{sub ads}+H{sub 2}O+e=M+H{sub 2}+OH{sup {minus}}; and 2MH{sub ads}+2M+H{sub 2}; hydrogen absorption MH{sub ads}+MH{sub abs}; and hydrogen diffusion into metal. This problem leads to a system of differential equations which was solved using the differential algebraic equations method. Solutions were obtained for constant potential and constant current charging/discharging in the case of semi-infinite and finite length diffusion for planar, spherical, and cylindrical diffusion. Numerical solutions give new information about the reaction mechanism and may be useful in the determination of the kinetics of these processes.