Optical constants in the vacuum ultraviolet and electron energy losses

Abstract It is known that the complex dielectric constant ϵ for any material contains all information about the optical constants, n and k , as well as about the energy losses suffered by fast electrons in the solid. In principle, if the optical constants n and k are known, one should be able to calculate ϵ from the electron energy loss spectrum. The optical constants are relatively difficult to measure in the short wavelength range, whereas the electron energy losses are difficult to measure in the vicinity of the elastic peak. This fact alone is not entirely responsible, however, for the very poor agreement which is usually found in the intercomparison of the two types of data. Part of the discrepancy can be ascribed to the fact that none of the data have been gathered on the identical material. A few examples of such intercomparison are presented. The National Bureau of Standards' program is to measure the optical constants and the electron energy losses under ultra-high vacuum conditions and on the identical specimen.