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

Abstract

A family of 12 zinc(II) thoureide complexes, of the general form [{L}ZnMe], [{L}Zn{N(SiMe 3 ) 2 }], and [{L} 2 Zn], have been synthesized by direct reaction of the thiourea pro-ligands i PrN(H)CS(NMe 2 ) H[L 1 ], CyN(H)CS(NMe 2 ) H[L 3 ], t BuN(H)CS(NMe 2 ) H[L 2 ], and MesN(H)CS(NMe 2 ) H[L 4 ] with either ZnMe 2 (1:1) or Zn{N(SiMe 3 ) 2 } 2 (1:1 and 2:1) and characterized by elemental analysis, NMR spectroscopy, and thermogravimetric analysis (TGA). The molecular structures of complexes [{L 1 9), and [{L 4 } 2 Zn] 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 (E g = 3.711−3.772 eV) values between those expected for bulk cubic-ZnS (E g = 3.54 eV) and hexagonal-ZnS (E g = 3.91 eV).

Synthesis, solution dynamics and chemical vapour deposition of heteroleptic zinc complexes via ethyl and amide zinc thioureides

“…Both structures are analogous to each other and also to reported methyl zinc thioureides, with dimerization occurring through S atoms and formation of a Zn–S–Zn–S ring structure. 30 The C–S bond in 2 was significantly lengthened as compared to the free ligand HL 1 * (1.7678(16) Å and 1.6852(15) Å respectively) whilst the C–N(Ph) bond was shortened (1.323(2) Å and 1.3715(18) Å) upon coordination to the zinc centre. The C–N(Me 2 ) bond in HL 1 * was also significantly shorter than in 2 .…”

“…Taking inspiration from Sullivan et al , 30 thiourea ligands were chosen as the sulfur source due to their facile, high yielding synthesis which circumvents issues with usage of H 2 S gas and other malodourous sulfur containing compounds. Their work also showed that zinc thioureides were effective SSPs towards phase pure zinc sulfide.…”

“…Crystals suitable for single crystal XRD were obtained after recrystallisation from a concentrated toluene solution and confirmed the structure as a dimeric species in the solid state, in agreement with previous literature. 30 …”

“…Crystals suitable for single crystal XRD were obtained after recrystallisation from a concentrated toluene solution and confirmed the structure as a dimeric species in the solid state, in agreement with previous literature. 30 Reactions of ethyl zinc and amide zinc thioureides with HL 2 and HL 3 . Initially, -ketoiminates (BKI) ligands were chosen as the oxygen source as they have facile, high yielding syntheses and BKI metal complexes have been shown to be excellent CVD precursors towards metal oxides.…”

Synthetic and Structural Studies of Ethyl Zinc β-Amidoenoates and β-Ketoiminates

“…Both the complexes dimerise analogously, with dative interactions between the zinc atom on one monomeric unit and the methine carbon on the ligand of the second monomeric unit ( Figure 3 ). This dimerisation is uncommon in zinc alkyl complexes, with most dimerisation occurring through a [Zn–L] 2 (L = donor atom) ring interaction ( Figure 3 , left) [ 21 , 22 , 23 , 24 ]. A bis (N-heterocyclic carbene) zinc ethyl complex previously reported dimerises in a similar fashion to 1 and 2 , though this was due to the unusual deprotonation of the methylene proton of the ligand backbone by diethylzinc, and the formation of a formal Zn–C bond ( Figure 3 , right) [ 25 ].…”