Laser-induced photochemistry of nickel chelate thin films

This work is devoted to the investigation of laser-induced decomposition mechanism of solid films and powders of nickel(II) chelate complexes with dimethylglyoxime Ni(DMG)2 and with dehydrogenated free—radical methyl derivative of 1,2—hydroxylaminooxime Ni(HAO)2. A comparison of stable gaseous products of laser-induced decay of these complexes with those of thermal decomposition have shown considerable difference between them. Sufficiently threshold character of the conversion degree dependence on the power density of XeCl excimer laser irradiation was revealed in the experiments. These two facts being correlated with the data on positive and negative ion chemical ionization mass spectrometry allow to propose a primary process to be predominantly photochemical with two-photon initiation mechanism. The vertical photoionization of one of chelate molecules is suggested to be accompanied by electron transfer to lattice and then by localization of excess electron on antibonding level of neighbouring chelate molecule resulting in its fragmentation. The secondary processes of solid chelate decomposition are determined by the pecularities of electronic and stereochemical structure of the complexes. Thin layers of these chelates applied onto Si and Si02 substrates decompose explosion-like in air under the influence of radiation pulse of XeC1 excimer laser. A plume of decomposition products is thrown from the substrate into atmosphere, and a thin layer of dielectric film with refractive index close to the value for nickel hydroxide is deposited on the substrate.