Materials chemists in the UK have made important advances in understanding how to control the growth of films of zinc oxide crystals on a range of substrates.
Materials chemists in the UK have made important advances in understanding how to control the growth of films of zinc oxide crystals on a range of substrates. The new work is significant because the same team previously demonstrated that nano-scale, columnar crystals of ZnO grown by wet-chemical methods can exhibit important optical properties at room temperature, including emission of white light and lasing.
Crucially, and for the first time, the team, from the Manchester Materials Science Centre and the department of chemistry at the University of Manchester, has derived a simple theoretical framework for the growth of films of columnar ZnO crystals that may be applied to many different systems using chemical bath deposition (CBD). The films can be grown under relatively mild conditions using CBD, raising the possibility of incorporating ordered crystal arrays into sensitive substrates such as semiconducting polymers. Such a system could eventually have applications in display technologies, high-density optical storage and optical computing.
CBD essentially involves immersing a substrate in a bath of solution containing the necessary ions to enable crystals to form on the substrate.
However, say researchers, controlling the deposition and growth of the crystals is tricky. Many complex chemical interactions take place simultaneously involving numerous intermediate species, they warn.
In work that is about to be submitted for publication, the Manchester research team of Kuveshni Govender, David Smyth-Boyle, Peter Kenway and Paul O’Brien has shown how subtle control can be exerted over the size, morphology and configuration of the crystals grown by CBD by varying the reaction conditions.
By systematically changing a range of parameters, the Manchester researchers have shown that a range of crystal formations - from flat ’platelets’ to needle-like morphologies - can be deposited on a variety of substrates.
The team has demonstrated that unrelated parameters such as pH, ionic strength, growth time, the nature of the substrate and the point at which the substrate is introduced into the bath can all influence crystal morphology.