Optimisation of the wire-shadow TEM cross-section preparation technique

The wire-shadow technique is a simple and easy-to-use preparation method of cross-section specimens for TEM investigations. The method has been optimised for thin films on silicon and oxide (sapphire, MgO) substrates. A wire is glued onto the film. During thinning in a modified commercial ion-milling sample holder the shadow of the small wire protects part of the film. Non-shadowed areas of film and substrate are removed by ion sputtering. During ion thinning a sharp edge evolves in the wire shadow. As a consequence, the interface between film and substrate becomes transparent to electrons just at the point at which the wire is eroded away. Different wire materials (tungsten, Al2O3, carbon, nicalon (SiC) and nylon) and thinning geometries were tested. The best results were achieved using an amorphous carbon fibre with a diameter of 7 μm.