Absorption (logic)

Abstract: We report values of pseudodielectric functions $〈\ensuremath{\epsilon}〉=〈{\ensuremath{\epsilon}}_{1}〉+i〈{\ensuremath{\epsilon}}_{2}〉$ measured by spectroscopic ellipsometry and refractive indices $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{n}=n+ik$, reflectivities $R$, and absorption coefficients $\ensuremath{\alpha}$ calculated from these data. Rather than correct ellipsometric results for the presence of overlayers, we have removed these layers as far as possible using the real-time capability of the spectroscopic ellipsometer to assess surface quality during cleaning. Our results are compared with previous data. In general, there is good agreement among optical parameters measured on smooth, clean, and undamaged samples maintained in an inert atmosphere regardless of the technique used to obtain the data. Differences among our data and previous results can generally be understood in terms of inadequate sample preparation, although results obtained by Kramers-Kronig analysis of reflectance measurements often show effects due to improper extrapolations. The present results illustrate the importance of proper sample preparation and of the capability of separately determining both ${\ensuremath{\epsilon}}_{1}$ and ${\ensuremath{\epsilon}}_{2}$ in optical measurements.

Abstract: The infrared spectra of 7 ferrites of the formula $M{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$, where $M$ designates a divalent metal, are presented and analyzed. Electronic absorption was observed in the visible and near-infrared regions. Two absorption bands arising from interatomic vibrations were measured and force constants calculated for the stretching of bonds between octahedral or tetrahedral metal ions and oxide ions. These force constants are in agreement with the elastic and thermodynamic properties of these compounds and are sensitive to distribution of metal ions between the alternate sites. The integrated vibrational band intensities were measured: they are compatible with predominantly ionic bonding for these structures.

Abstract: The intensity of optical absorption close to the edge in semiconductors is examined using band theory together with the effective-mass approximation for the excitons. Direct transitions which occur when the band extrema on either side of the forbidden gap are at the same K, give a line spectrum and a continuous absorption of characteristically different form and intensity, according as transitions between band states at the extrema are allowed or forbidden. If the extrema are at different K values, indirect transitions involving phonons occur, giving absorption proportional to ${(\ensuremath{\Delta}E)}^{\frac{1}{2}}$ for each exciton band, and to ${(\ensuremath{\Delta}E)}^{2}$ for the continuum. The experimental results on ${\mathrm{Cu}}_{2}$O and Ge are in good qualitative agreement with direct forbidden and indirect transitions, respectively.

Abstract: The current commutation ${\mathrm{relations}}^{1}$ and partially conserved axial-vector current (PCAC) ${\mathrm{assumption}}^{2,3}$ allow the calculation of the matrix elements for emission and absorption of any number of soft ${\mathrm{pions}}^{4}$ and, therefore, in particular, determine the scattering length of a pion on any target particle In this note we give a simple formula for pion scattering on any particle but a ${\mathrm{pion}}^{5}$, and then extend this result to the more difficult case of pion-pion scattering