2, University of Minnesota, Twin Cities, Minnesota, United States
Herein, we have reported on structural, chemical and electronic properties of two-dimensional (2D) tin disulfide (SnS2) crystals grown on silicon dioxide (SiO2) substrates by vapor-phase method. High-resolution annular dark-field (ADF) scanning transmission electron microscope (STEM) analysis indicate that the SnS2 crystals crystallize in 1T phase, which is in consistent with the ab-initio density functional theory (DFT) calculations predicting that SnS2 stabilizes 1T phase at ground state. Photoluminescence (PL) and ultraviolet-visible (UV-vis) spectroscopy measurements suggest that the SnS2 crystals have an indirect band gap of 2.20 eV and 2.35 eV, respectively, which is in good agreement with the DFT-calculated band gap of 2.31 eV. The electrical transport measurements performed on back-gated field-effect transistors (FETs) exhibit n-type semiconductor characteristics of the SnS2 crystals. High-angle annular dark-field (HAADF) STEM imaging and STEM energy dispersive X-ray (EDX) chemical analysis demonstrate that the SnS2 crystals are chemically homogeneous with a stoichiometric S/Sn atomic ratio of 2. Electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) analysis present the characteristic Sn and S peaks of SnS2, confirming the phase purity of the SnS2 crystals. Ultraviolet photoelectron spectroscopy (UPS) measurements of the SnS2 crystals provide an ionization potential of 7.51 eV, which is in a perfect agreement with the DFT-calculated ionization potential of 7.51 eV. Resonance Raman spectroscopy in conjunction with ab-initio DFT calculations reveal the characteristic first-order and second-order Raman modes of 1T phase of the SnS2 crystals. Angle-resolved polarized Raman spectroscopy (ARPRS) mappings with different polarization angles show unique edge features of the SnS2 crystals.