Manipulation of a Single Crystal Nanowire on an Atomic Level

Abstract

In recent years, metal oxide nanostructures (MO) have been intensively studied due to a wide variety of applications on multiple fields, for example in optoelectronics, gas sensing, photovoltaics, field-effect transistors, UV lasers, field emission sources etc. [1]. However, for applications, other types of structures are also interesting such as sulfides and nitrides. Here the question that raises is can we manipulate nanomaterials like nanowires on an atomic level. Knowing the exact mechanism of sulfur-oxygen exchange in the metal oxide crystal lattice can be utilized for the synthesis of metal sulfides with specific morphologies. When compared to metal oxides, single-crystalline metal sulfide nanostructures of specific morphologies are usually harder to produce than MOs. Generally, metal sulfide nanostructures represent unconventional materials in areas such as batteries or photovoltaics with yet unexploited potential, where their efficiency is mainly limited by the purity of crystalline phases and structural defects [2]. A promising path for novel synthesis route is incorporation of the sulfur in the crystal structure of a metal oxide nanoparticle, while during this transition the morphology of the nanostructure does not change. In this way, it is possible to obtain single crystal metal sulfide nanostructures from metal oxide nanostructures in the single crystal to single crystal (SCSC) transformation. A promising method to achieve such transformation in a short period of time is a treatment of metal oxide nanostructures with the plasma of sulfur-containing gas. In this research, we studied the mechanism of sulfur incorporation in the metal oxide crystal structure. The procedure was carried out by synthesis of ultra-thin metal oxide nanowires, which were then treated with sulfur-containing gases under increased temperature (in thermodynamic equilibrium conditions) and in the plasma of the same gases (under thermodynamically non-equilibrium conditions). Experiments were conducted at different temperatures and pressures to evaluate the influence of plasma on transformation process. Mechanisms involved in the interaction of sulfur-containing species with metal oxides were studied on isolated single ultra-thin metal oxide nanowire. Furthermore, changes in crystal structures and their effect on the material properties before and after sulfurization were studied. [1] Umar A. & Hahn Y. B. (Eds.). (2010), Metal Oxide Nanostructures and their Applications. American Scientific Publishers, CA, USA [2] Zavašnik, J., & Rečnik, A. (2013). Electron microscopy study of CVT grown Fe-sulphides. Journal of Crystal Growth, 367, 18-23.