Formation of Nanoporous Films during Solid-Phase Reactions

Specific features of the formation of nanoporous Al2O3, AlN, and Ni(Fe+Al)2O4 films on sapphire substrates by thermal sputtering of metals with subsequent firings in an appropriate gas medium are studied. This synthesis process involves interaction of the metal solid phase with an active ambient gas medium (oxygen or nitrogen), some other chemical reactions, diffusion, and crystallization. It can be controlled via a set of synthesis parameters to achieve desired film properties and structure. It is shown that variations in the thickness of initial metal films, annealing temperature and time, and sample heating rate affect the run and completeness of the above processes and allow one to obtain films with a required structure (in particular, films with a nanoporous structure with pores 10–200 nm in size).