Extended Energy Loss Fine Structure Investigations

The Surface Extended Energy Loss Fine Structure (SEELFS) technique is complementary to the Extended X-ray Absorption Fine Structure (EXAFS) technique for determination of local structural parameters, such as bond length and coordination. It was used in the determination of local structural parameters for carbon in the form of diamond, graphite and a graphite suspension. Three silicon samples and (alpha)- and (beta)-silicon carbide have also been investigated using the SEELFS technique. An Auger electron spectrometer (double pass cylindrical mirror analyzer) was used to obtain energy loss spectra for SEELFS analysis and the Auger spectra to monitor the surface cleanliness of the samples. The phase and envelope references required for the SEELFS determination of coordination and bond length were obtained from a standard sample of known structure. First shell coordination and bond lengths were determined for pyrolytic graphite and Aguadag('TM) (graphite particle suspension) samples using a single crystal diamond as the standard. One of the silicon samples was used as standard to determine the phase and envelope functions. These were then used to determine the nearest neighbor bond length and coordination in the remaining two samples. The local structure parameters in (alpha)-silicon carbide were determined using (beta)-SiC as the standard. The coordination and radius determined by the SEELFS technique agree with known values to within uncertainties estimated. The factors contributing to uncertainties in the determination of bond length and coordination are probed. The validity of some of the theoretical assumptions is also discussed.