Thin film structural analysis using variable-period x-ray standing waves

Abstract

Variable period X-ray standing wave (VPXSW) studies have been carried out using 3 keV X-rays and photoelectron detection. Two model surfaces have been used, a native SiO 2 layer (20 Å thick) on bulk silicon, and a purpose built multilayer surface comprising a chloroform/water marker layer (12 Å thick) on an ionic liquid spacer layer (211 Å thick) deposited on a SiO 2 /Si substrate at 90 K. By using photoelectron detection, both chemical and elemental sensitivity were achieved. The surfaces were modelled using dynamic X-ray scattering for X-ray intensity, and attenuation of photoelectrons transmitted through the layers, to produce simulations which accurately reproduced the experimental VPXSW measurements. VPXSW measurements made using the substrate, spacer layer and marker layer photoelectron signatures produced consistent structural values. This work demonstrates that VPXSW can be used to determine chemically specific layer thicknesses within thick (≲ 300 Å) surface structures composed of the light elements B, C, N, O, F and Cl with an accuracy of 10 to 15 Å, perpendicular to the surface.

Insights from molecular dynamics simulations on structural organization and diffusive dynamics of an ionic liquid at solid and vacuum interfaces

“…92 It is heartening to know that our values of surface tension for all CHelpG methods, for RESP-HF with scaling factors of 1.0 and 0.9 and for RESP-B3LYP with full charges are still higher than the experimental value for n=4 for [C n C 1 Im][NTf 2 ] of 30.7 mN/m. 92 S-L-V -X-ray reflectivity: Several techniques, including atomic force microscopy, 93 infrared spectroscopy 94,95 or X-Ray scattering, 96,97,98 can provide information about the buried S-L interface and, at the same time, yield information on the structural ordering at this interface with sub-molecular accuracy. In our previous work 65 for the model system in S-L-S configuration this measurement was used to validate the Maginn / CL&P ff, along with the Lorentz-Berthelot mixing rule.…”