Laser-induced desorption of atomic and molecular fragments from a tin dioxide surface modified by a thin organic covering of copper phthalocyanine

The systematic features of laser-induced desorption from an SnO$_2$ surface exposed to 10-ns pulsed neodymium laser radiation are studied at the photon energy 2.34 eV, in the range of pulse energy densities 1 to 50 mJ/cm$^2$. As the threshold pulse energy 28 mJ/cm$^2$ is achieved, molecular oxygen O$_2$ is detected in the desorption mass spectra from the SnO$_2$ surface; as the threshold pulse energy 42 mJ/cm$^2$ is reached, tin Sn, and SnO and (SnO)$_2$ particle desorption is observed. The laser desorption mass spectra from the SnO$_2$ surface coated with an organic copper phthalocyanine (CuPc) film 50 nm thick are measured. It is shown that laser irradiation causes the fragmentation of CuPc molecules and the desorption of molecular fragments in the laser pulse energy density range 6 to 10 mJ/cm$^2$. Along with the desorption of molecular fragments, a weak desorption signal of the substrate components O$_2$, Sn, SnO, and (SnO)$_2$ is observed in the same energy range. Desorption energy thresholds of substrate atomic components from the organic film surface are approximately five times lower than thresholds of their desorption from the atomically clean SnO$_2$ surface, which indicates the diffusion of atomic components of the SnO$_2$ substrate to the bulk of the deposited organic film.