Sol-gel synthesis of nanocrystalline magnesium fluoride: Its use in the preparation of MgF2 films and MgF2-SiO2 composites

Thin, protective films of nanocrystalline MgF2 were formed by spin-coating a sol that contained nanocrystalline MgF2, which was formed by the action of KF on a sol prepared from methanolic H2O2 and Mg(OCH3)(2). These thin films on Si(100) lost fluoride to form MgO when heated at 550 degrees C. When the films on two such substrates were placed together face to face and heated at 550 degrees C, rough, abrasion resistant MgF2 films were obtained. To form composites, nanocrystalline MgF2 sols were mixed with silicate sols prepared from the acid catalyzed hydrolysis and condensation of tetramethyl orthosilicate (TMOS). X-ray diffraction and TEM analysis of xerogels and films obtained from these biphasic sols indicated nanocrystals of MgF2 dispersed in an amorphous matrix. On heating, fluoride loss and MgF2 crystal growth were both greatly retarded in powders and thin films prepared from silicate-MgF2 sols.