USE OF SUM-RULES ON THE ENERGY-LOSS FUNCTION FOR THE EVALUATION OF EXPERIMENTAL OPTICAL-DATA

We present an evaluation of optical data for Al, Si, Ti, Mo, W, and Ir based on two sum rules for the energy-loss function, the familiar f-sum rule and another sum rule based on a limiting form of the Kramers-Kronig integral. These sum rules were used to evaluate sets of energy-loss function data constructed first from tabulated optical data which have been supplemented by interpolations in the 40-100 eV range for Ti, Mo, W, and Ir. A second set of energy-loss function data was constructed for each material by substituting energy-loss function values calculated from the optical data of Windt et al. (Appl. Opt., 27 (1988) 246, 279) in the 10-525 eV range. The deviations in the results of the sum-rule tests with the second set of optical data were about twice those found for the first set. We conclude that the first set of optical data is preferred over the second set.