Effect of charged deep states in hydrogenated amorphous silicon on the behavior of iron oxides nanoparticles deposited on its surface

Langmuir-Blodgett technique has been used for the deposition of ordered two-dimensional arrays of iron oxides (Fe₃O₄/Fe₂O₃) nanoparticles onto the photovoltaic hydrogenated amorphous silicon (a-Si:H) thin film. Electric field at the a-Si:H/iron oxides nanoparticles interface was directly in the electrochemical cell modified by light soaking and bias voltage (negative or positive) pretreatment resulting in the change of the dominant type of charged deep states in the a-Si:H layer. Induced reversible changes in the nanoparticle redox behavior have been observed. We suggest two possible explanations of the data obtained, both of them are needed to describe measured electrochemical signals. The first one consists in the electrocatalytical effect caused by the defect states (negatively or positively charged) in the a-Si:H layer. The second one consists in the possibility to manipulate the nanoparticle cores in the prepared structure immersed in aqueous solution via the laser irradiation under specific bias voltage. In this case, the nanoparticle cores are assumed to be covered with surface clusters of heterovalent complexes created onto the surface regions with prevailing ferrous or ferric valency. Immersed in the high viscosity surrounding composed of the wet organic nanoparticle envelope these cores are able to perform a field-assisted pivotal motion. The local electric field induced by the deep states in the a-Si:H layer stabilizes their “orientation ordering” in an energetically favourable position.