Thermal Etching of NaF Cleavages

Abstract

Freshly cleaved surfaces of sodium fluoride have been thermally etched in the range of temperature between 860°C and 930°C for the required time. The formation of circularly terraced pits has been discussed. The topography of thermal etch patterns is studied by multiple beam interferometry. Interaction of circular etch fronts from the point of nucleation of two or more dislocations is illustrated. Under controlled conditions of thermal etching, in addition to the thermal etch pits, spiral structures have been observed. It is conjectured that these spirals might have been formed as explained by Lang (1957). It is conjectured that the etch patterns appearing similar to the pattern observed at the Frank-Read sources might have been formed due to a pair of dislocations of opposite sign.