Influence of precursors chemistry on ALDgrowth of cobalt–molybdenum oxide films

Abstract

Cobalt molybdenum compounds are important catalytic materials in many processes, e.g. in splitting of ammonia to form CO free hydrogen fuel. We here report on deposition of such cobalt molybdenum oxides by atomic layer deposition (ALD) using different types of metal precursors CoCp₂ (Cp = cyclopentadienyl), Co(thd)₂ (Hthd = 2,2,6,6-tetramethylheptan-3,5-dione), Mo(CO)₆ and oxygen precursors O₃, H₂O, and (O₃ + H₂O). The growth dynamics have been investigated using quartz crystal microbalance (QCM) methods. It is evident that mixing of the different precursor chemistries affect the growth patterns. When water is introduced to the reactions, a surface controlled mechanism takes place which guides the deposited stoichiometry towards the CoMoO₄ phase over a wide range of cobalt rich pulsed compositions. This is a rare example of how surface chemistry can control stoichiometry of depositions in ALD. The deposited films have been investigated by X-ray diffraction, Raman spectroscopy and atomic force microscopy. The catalytic activity of selected films have been characterized by temperature programmed ammonia decomposition, proving the films to be catalytically active and lowering the decomposition temperature by some 200 °C.