Effect of Nanostructuring of the Surface of a Lead Sulfide Crystal in Plasma on the Optical Reflection Spectra

Abstract

A study of the optical-reflection spectra (250–2500 nm) for the surface of lead sulfide crystals in the initial state and after the formation of a homogeneous ensemble of nanostructures is conducted. Single crystals of PbS are grown using the vertical-zone-melting method, with the [100] orientation along the growth axis. Surface nanostructuring is realized in a reactor of high-density argon plasma with a low-pressure high-frequency inductive discharge (13.56 МHz) at the ion energy ~200 eV. The uniform array of stepped lead sulfide nanostructures formed due to plasma treatment is up to 140 nm in height, with cruciform bases having k100l-oriented lateral orthogonal elements 20–60 nm long. It is found that the specular-reflection- and diffuse-reflection spectra for the initial surface of the (100) PbS crystals and for that nanostructured in argon plasma differ significantly. Using the Kubelka–Munk theory of diffuse reflection and the Kumar theory of specular reflection, the band-gap value for the nanostructured surface of (100) PbS crystals is determined as 3.45–3.47 eV, exceeding the value for the initial surface of lead sulfide ~0.4 eV.