Formation of Microcracks on the Surface of a Glass Irradiated with 30-Kev Protons

Changes in the surface structure of K-208 glass irradiation with 20- and 30-keV protons in a vacuum chamber with a residual pressure of 10–4 Pa are studied using atomic-force microscopy. It is found that on the surface of K-208 glass irradiated with 30-keV protons at a flux density of φp = 4.5 × 1010 cm–2 s–1 and fluences Φp = (1.1 × 1015–6.6 × 1015) cm–2, microcracks are formed, the size of which grows with increasing fluence. We believe that the formation of microcracks is due to: the appearance of tensile stresses in the surface layer as a result of restructuring of the glass microstructure caused by the migration of sodium ions in the field of the introduced charge; the formation of gas-filled bubbles; mass transfer to the irradiated surface; and, possibly, access to the irradiated surface of percolation channels of sodium and oxygen. For those values of φp and Φp, irradiation of K-208 glass with 20-keV protons is shown to not lead to the formation of microcracks.