Synthesis and properties of MoCl4 complexes with thio- and seleno-ethers and their use for chemical vapour deposition of MoSe2 and MoS2 films

Abstract

Treatment of trans-[MoCl₄(MeCN)₂] with L (L = Me₂S, Me₂Se, THT, ½MeSCH₂CH₂SMe) in CH₂Cl₂ solution, or reaction of MoCl₅ with excess L′ (L′ = ⁿBu₂S, ⁿBu₂Se, ½MeSCH₂CH₂SMe, ½ⁱPrSCH₂CH₂SⁱPr, ½MeSCH₂CH₂CH₂SMe, ½MeSeCH₂CH₂CH₂SeMe) in MeCN, produces the Mo(IV) complexes, [MoCl₄(L)₂] and [MoCl₄(L′)₂], respectively, in good yield. The new complexes have been characterised by IR and UV-vis spectroscopy, elemental analysis and magnetic measurements, whilst crystal structure analyses of trans-[MoCl₄(Me₂S)₂], cis-[MoCl₄{RS(CH₂)₂SR}] (R = Me, ⁱPr) and cis-[MoCl₄{MeS(CH₂)₃SMe}] confirmed their identities and distorted octahedral geometries. The potential of [MoCl₄(ⁿBu₂E)₂] (E = S, Se) as the first examples of molybdenum halide derived single source CVD precursors for the growth of MoE₂ thin films was first probed by TGA, which showed multi-step decomposition processes, with the masses of the final residues consistent with MoSe₂ (E = Se) and MoCl₄ (E = S), respectively. Low pressure CVD experiments conducted at 750 °C (E = S) and 525 °C (E = Se) gave silvery and golden yellow films, respectively. Grazing incidence and in plane XRD data confirmed these to be 2H-MoE₂, whilst the texture of the MoSe₂ was investigated using pole figure measurements. SEM and EDX data, optical and Raman data on the films are also reported.