Ultrathin polytyramine films by electropolymerisation on highly doped p-type silicon electrodes

In recent years, silicon-based materials have been used extensively in device fabrication for sensors, microfluidic and biomaterial applications. In order to enhance the performance of the material, a number of surface functionalisations are employed. However, until now, silicon has not been used as an electrode material for electrodeposition of functional polymers. Here, highly doped p-type silicon was used as an electrode facilitating the electropolymerisation of ultrathin polytyramine (PT) films by cyclic voltammetry. The influence of resistivity, pre-treatment of the silicon surface and electrochemical conditions on the electropolymerisation process was studied. The results show that ultrathin PT films with a controlled thickness from 2 to 15 nm exhibit good electrochemical stability in buffer solution (pH 6.8) over a large potential window (-1.5 V to 1.5 V) and passivating properties towards a redox probe. In terms of the film morphology, a pinhole-free smooth surface with a roughness below 0.5 nm and with dominantly globular features of 40-60 nm diameter was observed by AFM. XPS characterisation showed that PT films display amine functional groups at the coating surface. UV induced silicon oxidation was used to prepare patterned PT films.