Synthesis of Mg and Zn diolates and their use in metal oxide deposition

The synthesis of complexes [M(OCHMeCH₂NMeCH₂)₂] (5, M = Mg; 7, M = Zn) is described. Treatment of MeHNCH₂CH₂NMeH (1) with 2-methyloxirane (2) gave diol (HOCHMeCH₂NMeCH₂)₂ (3), which upon reaction with equimolar amounts of MR₂ (4, M = Mg, R = Bu; 6, M = Zn, R = Et) gave 5 and 7. The thermal behavior and vapor pressure of 5 and 7 were investigated to show whether they are suited as CVD (= chemical vapor deposition) and/or spin-coating precursors for MgO or ZnO layer formation. Thermogravimetric (TG) studies revealed that 5 and 7 decompose between 80-530 °C forming MgO and ZnO as evidenced by PXRD studies. In addition, TG-MS-coupled experiments were carried out with 7 proving that decomposition occurs by M-O, C-O, C-N and C-C bond cleavages, as evidenced from the detection of fragments such as CH₄N⁺, C₂H₄N⁺, C₂H₅N⁺, CH₂O⁺, C₂H₂O⁺ and C₂H₃O⁺. The vapor pressure of 7 was measured at 10.4 mbar at 160 °C, while 5 is non-volatile. The layers obtained by CVD are dense and conformal with a somewhat granulated surface morphology as evidenced by SEM studies. In addition, spin-coating experiments using 5 and 7 as precursors were applied. The corresponding MO layer thicknesses are between 7-140 nm (CVD) or 80 nm and 65 nm (5, 7; spin-coating). EDX and XPS measurements confirm the formation of MgO and ZnO films, however, containing 12-24 mol% (CVD) or 5-9 mol% (spin-coating) carbon. GIXRD studies verify the crystalline character of the deposited layers obtained by CVD and the spin-coating processes.