Abstract
A very quick, reliable and reproducible procedure for preparing 'holey' films with various ranges of hole diameters (0.05-20 mu m), as test objects for correction of astigmatism in high resolution instruments, and Formvar nets for mounting ultrathin microtome sections for high resolution electron microscopy is presented. It has been possible to control the hole diameter within limits under the stated conditions. The physical explanation for the mechanism of hole formation has also been given.