Aerosol-Assisted Chemical Vapor Deposition of ZnS from Thioureide Single Source Precursors

A family of 12 zinc­(II) thoureide complexes, of the general form [{L}­ZnMe], [{L}­Zn­{N­(SiMe3)2}], and [{L}2Zn], have been synthesized by direct reaction of the thiourea pro-ligands iPrN­(H)­CS­(NMe2) H­[L1 ], CyN­(H)­CS­(NMe2) H­[L 3], tBuN­(H)­CS­(NMe2) H­[L2 ], and MesN­(H)­CS­(NMe2) H­[L4 ] with either ZnMe2 (1:1) or Zn­{N­(SiMe3)2}2 (1:1 and 2:1) and characterized by elemental analysis, NMR spectroscopy, and thermogravimetric analysis (TGA). The molecular structures of complexes [{L1 }­ZnMe]2 (1), [{L2 }­ZnMe]2] (2), [{L3 }­ZnMe]∞ (3), [{L4 }­ZnMe]2] (4), [{L1 }­Zn­{N­(SiMe3)2}]2 (5), [{L2 }­Zn­{N­(SiMe3)2}]2 (6), [{L3 }­Zn­{N­(SiMe3)2}]2] (7), [{L4 }­Zn­{N­(SiMe3)2}]2] (8), [{L1 }2Zn]2 (9), and [{L4 }2Zn]2 (12) have been unambiguously determined using single crystal X-ray diffraction studies. Thermogravimetric analysis has been used to assess the viability of complexes 1–12 as single source precursors for the formation of ZnS. On the basis of TGA data compound 9 was investigated for its utility as a single source precursor to deposit ZnS films on silica-coated glass and crystalline silicon substrates at 150, 200, 250, and 300 °C using an aerosol assisted chemical vapor deposition (AACVD) method. The resultant films were confirmed to be hexagonal-ZnS by Raman spectroscopy and PXRD, and the surface morphologies were examined by SEM and AFM analysis. Thin films deposited from (9) at 250 and 300 °C were found to be comprised of more densely packed and more highly crystalline ZnS than films deposited at lower temperatures. The electronic properties of the ZnS thin films were deduced by UV–Vis spectroscopy to be very similar and displayed absorption behavior and band gap (Eg = 3.711–3.772 eV) values between those expected for bulk cubic-ZnS (Eg = 3.54 eV) and hexagonal-ZnS (Eg = 3.91 eV).