Abstract
The molecular Sn(iv) complexes, [SnCl4{nBuS(CH2)3SnBu}] (2), [SnCl4(nBu2S)2] (3) and [SnCl4(nBu2Se)2] (4) have been prepared in good yield from reaction of SnCl4 with the appropriate chalcogenoether ligand in anhydrous hexane and, together with the known [SnCl4{nBuSe(CH2)3SenBu}] (1), employed as single source precursors for the low pressure chemical vapour deposition of the corresponding tin dichalcogenide thin films. At elevated temperatures the bidentate ligand precursors, (1) and (2), also form the tin monochalcogenides, SnSe and SnS, respectively. In contrast, (3) gave a mixture of phases, SnS2, Sn2S3 and SnS and (4) gave SnSe2 only. The morphologies, elemental compositions and crystal structures of the resulting films have been determined by scanning electron microscopy, energy dispersive X-ray spectroscopy, grazing incidence X-ray diffraction and Raman spectroscopy. Van der Pauw measurements on the SnS2, SnS and SnSe2 films confirm their resistivities to be 2.9(9), 266(3) and 4.4(3) Ω cm, respectively.
Highlights
[SnCl4(Et2Se)2]19 and [SnCl4{nBuSe(CH2)3SenBu}],20 have been shown to produce polycrystalline SnSe2 thin films, whilst low pressure chemical vapour deposition (LPCVD) of [SnCl4{o-C6H4(CH2SeMe)2}] at 600 °C resulted in SnSe,[19] and, despite the S–C bonds in thioethers being stronger than Se–C bonds,25 [SnCl4{o-C6H4(CH2SMe)2}] has been shown to be suitable as a single source precursor for the deposition of tin sulfide thin films, forming SnS2 at 650 °C, with some SnS forming further into the hot zone.[19]
By modifying the precursor to be more volatile, as well as incorporating nBu substituents in place of Me groups, we proposed that the temperature difference between sublimation of precursor and deposition of the metal chalcogenide would be increased and better film quality achieved
Precursors containing the monodentate nBu2E (E = S, Se) ligands would be more convenient to synthesise and easier to access than bidentate ligands
Summary
The reflections marked are from the TiN layer underlying the top SiO2 on the substrate, whilst * is from the Si; (right) SEM image of the SnS2 film grown from [SnCl4(nBu2S)2] (3). The orthorhombic SnS phase is further confirmed by XRD analysis (Fig. 6) and the refined lattice parameters (Table 1) match well with the literature values (a = 11.20, b = 3.99, c = 4.30).[12] The Raman spectrum (Fig. 6) of the film clearly shows SnS with peaks at 220, 190 and 165 cm−1.
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