Controlling Optoelectronic Properties of NiO x Thin Films Using Surface Chemical Modification with Acetylacetone and Hexafluoroacetylacetone

Abstract

Nickel oxides (NiOx) are considered prime materials for tuning the physical properties, such as work function, conductivity, and transparency (optical transmittance), of thin films with applications in optoelectronics and energy conversion. However, deposition methods for this material often yield complex structures with varying oxidation states and nickel vacancies. In order to control and tune their properties, chemical modification can be used. In this work, NiOx films deposited onto solid substrates are chemically modified with acetylacetone and hexafluoroacetylacetone. The modification process is followed by X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and measurements of the conductivity and transparency of the resulting films to evaluate the role of surface chemistry, decomposition, and stability of the surface chemical species resulting from this modification. The work function of the films and the conductivity are indeed affected by the surface chemistry of these compounds, and the pronounced electronic effect is related to the surface modification process for acetylacetone and to a combination of surface decomposition followed by diffusion of fluorine into bulk NiOx for hexafluoroacetylacetone.