Formation and depth profiling analysis of multilayers derived from sol-gelprocessing using dynamic SIMS, RBS, and TEM

Silica sol-gel single layer AR coatings are used in high peak power pulsed lasers due to their high laser induced damage threshold (LIDT) and their lo w refractive index (1.22). We have used sol-gel processing to spin and dip coat multilayers of alternating high index (zirconia/hafnia) and low index (base catalysed silica) sol-gels on to fused silica substrates. When tailor ed at the correct thickness these stacks have shown > 95% reflectivity at 3 55 nm and normal incidence whilst retaining a high LIDT. Depth profiling us ing Dynamic Secondary Ion Mass Spectrometry (DSIMS) and Rutherford back sca ttering (RBS) through these multilayer coatings has revealed the effect of increasing the number of layers in the stack. Results are presented for bot h spin and dip coated multilayers and a significant difference in the inter facial boundary is seen between the two coating processes. These difference s are related to changes in the LIDT of the coatings. Individual layer thic knesses were estimated using this technique and compared to values gained f rom UV-Visible spectroscopy. TEM analysis of an ion-milled cross-section of the multilayers was performed showing the colloidal silica coatings and th e depth of interpenetration of the interfaces.