Kinetically controlled vapor-diffusion synthesis of novel nanostructured metal hydroxide and phosphate films using no organic reagents

Abstract

Nanostructured Co₅(OH)₈Cl₂·3H₂O, Co₅(OH)₈(NO₃)₂·2H₂O, Co₅(OH)₈SO₄·2H₂O, Zn₅(OH)₈(NO₃)₂·2H₂O, Cu₂(OH)₃(NO₃) and Mn₃(PO₄)₂·7H₂O thin films have been prepared using a kinetically controlled vapor-diffusion method. Vectorial control by diffusion of ammonia as a base catalyst into an aqueous metal salt solution yields large area (2 cm²) metal hydroxide and metal phosphate films with unique structures. No supporting substrate for growth of the films is necessary in this approach. The films were characterized using X-ray powder diffraction and scanning electron microscopy. The cobalt containing films were studied in more detail using transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption near edge structure and various chemical analysis techniques. For the first time the electronic properties and crystal structure of these materials could be studied in thin films not influenced by the presence of an underlying substrate. For Co₅(OH)₈(NO₃)₂·2H₂O films, which crystallize in a layered hydrotalcite-like structure that is homogeneous from the nanoscale to the macroscale, unprecedented photoconductivity properties were observed. Resistivity measurements show that this material is a p-type semiconductor with an unusually long minority carrier lifetime and high carrier density.