New Metal-Organic Chemistry of Barium, AN Aqueous Synthesis for Volatile Alkaline Earth Complexes, and Synthesis and Characterization of Thallium-Barium - Thin Films by Metal-Organic Chemical Vapor Deposition

The synthesis and characterization of six fluorine -free barium MOCVD (metal-organic chemical vapor deposition) precursors based upon encapsulating beta -ketoiminate-polyether ligation and having the general formula Ba(RCOCHC(NR^')R ^{''})_2 (R^' = ^{rm t}butyl, R^ ' = polyether, and R^{ ''} = methyl or ^{rm t}butyl) is reported. The complexes were prepared by a nonaqueous approach which employs BaH_2 and the corresponding beta-ketoimine. These complexes have been characterized by ^1H and ^{13}C NMR spectroscopy, elemental analysis, mass spectroscopy, cryoscopic molecular weight determination, thermogravimetric analysis, and single crystal X-ray structural analysis. These complexes serve as volatile barium MOCVD precursors. Thus, BaPbO _3 films have been grown using the aforementioned barium beta-ketoiminate complexes and Pb(dipivaloylmethanate)_2 as the respective barium and lead sources, and have been characterized by X-ray diffraction, scanning electron microscopy energy dispersive X-ray spectroscopy, and variable-temperature resistivity measurements. Investigation of thermolytic decomposition of the barium beta -ketoiminate complexes led to identification of 2-methyl -4-^{rm t}butylpyridine (17), pinacolone, and 2,2-dimethyl-5-imino-3-hexanone as the major organic thermolysis products of 11, 12, and 13. The MOCVD synthesis of Tl-Ba-Ca-Cu-O thin films on novel substrates, a growth method and film configuration which is potentially applicable toward device technologies, has been investigated. These films were prepared in three steps: first, deposition of Ba-Ca-Cu-O-(F) thin films by MOCVD; next, defluorination via water/oxygen anneal; and finally, thallination using volatile thallium oxides. Films were characterized by X-ray diffraction (theta/2 theta, omega, and phi scans), variable temperature magnetization, variable temperature conductivity, and scanning and transmission electron microscopy. Attempts at preparing Tl-Ba-Ca-Cu -O thin films on Pt resulted in the formation of rm Tl_2Pt_2O_7 while attempts using Ag substrate led to the formation of a non -contiguous Ba-Ca-Cu-O film during the thallination step. rm Tl_2Ba_2Ca_1Cu_2O _{x} on Au/YSZ, Au, and LaAlO _3 show preferential orientation of crystallite c-axes and exhibit T_{rm c} equal to 94, 80, and 97 K, respectively. Au-Cu alloy formation was confirmed by TEM/EDS for rm Tl_2Ba_2Ca_1Cu_2O_{x } thin films on Au.