Pulsed laser deposition of oxide films by multi-kilowatt CO2 lasers

For realizing a high rate pulsed laser deposition (PLD) a pulsed 6 kW-CO2 laser conventionally used for laser machining was adapted by a suitable beam forming system. It allows intensities between 107 and 108 W/cm2 at a minimum pulse length of 100 μs. The targets consist of various compositions in the Al2O3–SiO2 system including the mullite phase. The deposition has been carried out in high vacuum. Even the average power of 200 W of the available 6 kW mostly used in these experiments due to the small sizes of the specially prepared targets yields mean deposition rates up to 100 nm/s. In-situ measurement of mass loss and momentum transfer on the target reveals that most of the material is ablated as microparticle, not as vapour. This corresponds with the cobblestone appearance of the films. Notwithstanding their rather coarse topography, they are dense without any kind of open porosity. This was also proved by mass loss investigations in oxidation experiments and by diffusion of 18O isotopes in combination with SNMS determination of the concentration profiles.