Phase Controlled Synthesis and Characterization of Large Area 2D Tin Sulfides

Abstract

Motivated by the increasing need to shift the energy sector from fossil fuels towards renewables, two-dimensional (2D) layered material systems have been explored as potential candidates for energy harvesting and storage applications.[1] In particular, 2D tin sulfides (SnS and SnS2) have emerged as promising candidate materials for photovoltaic and battery applications due to their high earth abundance and non-toxic nature.[2,3] The dual valency of tin and the numerous oxidation states of sulfur can result in three thermodynamically stable polymorphic phases namely SnS, SnS2 and Sn2S3. Thus, phase-controlled synthesis of SnSx materials can be challenging. A detailed investigation of material properties of SnSx is essential to correlate the structure property relationship. Gas phase synthesis such as chemical vapor deposition (CVD) enables the tuning of material phase by choosing suitable precursor chemistries, substrates as well as varying the process parameters such as temperature and pressure. In this study we have developed a new CVD process for the synthesis of SnSx thin films on Si and mica substrates using a combination of a metalorganic precursor for tin and elemental sulfur under mild process conditions. Complementary thin film analysis using X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), nuclear reaction analysis (NRA) and X-ray photoelectron spectroscopy (XPS) were performed. While XRD and Raman revealed the fabrication of phase pure crystalline SnS2 on both Si(100) and mica, XPS indicated inclusion of SnS species that couldn’t be identified unambiguously via XRD (Figure 1). A band gap of 2.2 eV estimated via UV-Vis spectroscopy further confirms the deposition of phase pure crystalline SnS2 layers. These new findings are very promising and pave a way to grow large area and phase controlled SnSx layers that can be suitable for potential functional applications such as batteries, photovoltaics, sensors etc. Figure 1