TUNGSTEN THIN FILM DEPOSITION BY 5 μm MULTIPHOTON DISSOCIATION OF W(CO)₆

Abstract

Summed frequency radiation from two synchronised CO₂ transversely excited atmospheric lasers in an AgGaSe₂ crystal, with energies up to 50 mJ at frequencies of ∼2000 cm_–1 has been used to study infrared multiple photon dissociation of W(CO)₆ and to induce tungsten thin film deposition. The cross-section of multiphoton absorption saturates, but at a flux close to 40 mJ cm_–2 is still high enough (2 x 10^–17 cm²) to allow absorption, on average, of more than 20 photons per molecule, overcoming the dissociation threshold. In parallel beam configuration the multiphoton dissociation yield is proportional to the beam flux raised to the power 1·6 and the critical flux is ⋜120 mJ cm^–2.Averaged energy absorbed per molecule at this flux, calculated on the basis of Judd s absorption law, overcomes total bond dissociation energy by only ∼ 1·4 eV. A transmission electron microscopy study of the deposited tungsten thin film shows that the film is amorphous and homogeneous with a grain size <1 nm.