Epitaxial thin films of ZnMn2O4, grown from an aqueous solution on (100) and (111) spinel MgAl2O4 substrates, have been topotactically reduced and leached to produce epitaxial rock salt MnO on the same substrates. The volume change accompanying the conversion of ZnMn2O4 to 2MnO associated with a loss of Zn and O2 manifests as a network of interconnected, 50-100 nm pores. The topotactic nature o...