Microcolumn development on titanium by multipulse laser irradiation in nitrogen

We report the growth of titanium nitride microcolumns under multipulse Nd:yttrium aluminum garnet (λ = 1.064 μm, τ ∼ 300 ns, ν = 30 kHz) laser irradiation of titanium targets in nitrogen atmosphere. The laser intensity value was chosen below the single-pulse melting threshold of titanium. The evolution with the number of laser pulses of the target morphology, crystalline state, and chemical composition at the surface as well as in depth were investigated by scanning electron microscopy, x-ray diffractometry, Raman spectroscopy, and wavelength dispersive x-ray spectroscopy. Under the action of the laser pulses, during progressive surface nitridation, an initial rippled morphology developed, which evolved with further irradiation to TiN microcolumns. In-depth investigations showed a granular zone beneath the surface consisting of rutile and anatase phase TiO₂, followed by a compact needlelike layer of titanium until the interface with the unaffected target material.