Deposition of SnS Thin Films from Sn(II) Thioamidate Precursors

Two thioamide pro-ligands, R1N(H)C(S)R2 (R1 = t-Bu, R2 = i-Pr and R1 = i-Pr, R2 = i-Pr), were synthesized by treatment of the corresponding amides with Lawesson’s reagent. Reactions of [Sn{N(SiMe3)2}2] with two molar equivalents of 7 each thioamide pro-ligand yielded the tin(II) thioamidate species, bis(2-methyl-N-(1-methylethyl)-propanethioamide)tin(II) and bis[N-(1,1-dimethylethyl)-2-methylpropanethioamide]tin(II). Both of the new tin compounds have been characterized by 1H, 1C, and 119Sn NMR spectroscopy and elemental analysis. In addition, the solid-state structure of bis(2-methyl-N-(1-methylethyl)-10 propanethioamide)tin(II) has been determined through a single crystal X-ray diffraction analysis and shown to display a 11 monomeric constitution in which the tin(II) center occupies a distorted pseudosquare pyramidal geometry defined by the N2S2 donors and the stereochemically active lone pair. Both tin(II) derivatives have been assessed for their potential as single source precursors to SnS by TGA and by NMR spectroscopic analysis of the volatile organic products produced during their thermolysis. Both compounds have been utilized in the growth of thin films by aerosol-assisted chemical vapor deposition (AACVD). These latter studies provided film growth at temperatures as low as 200 °C. The films have been analyzed by pXRD, Raman spectroscopy, XPS, AFM, and SEM and are shown to comprise primarily the orthorhombic (Herzenbergite) phase of SnS, which is contaminated by only low levels of residual carbon (<5 at %). Although further films deposited onto Mo-coated substrates produced only limited photocurrents when illuminated, these results demonstrate the potential of such simple thioamidate derivatives to act as single source precursors to useful metal sulfide thin film materials.