Laser induced desorption and ablation: mechanism of metal removal from an Al-Cu-Fe alloy and a quasicrystal of the same composition

Quasicrystals are a special class of metallic alloys that share some of the properties of crystals. Their structures reduce to a single repeating unit like that of the unit cell of a crystal. The quasi-unit-cell is representative of a cluster like structure where electrons cannot move with freedom as in metals. Quasicrystals are formed of metallic elements but they do not have metallic properties. The diversity of the fractionation behavior induced by laser desorption and ablation of the Al70Cu20Fe10 of the intermetallic alloy and of the Al65Cu23Fe12 quasicrystal has been examined in terms of the structural properties of the two compounds. Elemental fractionation during laser desorption and ablation sampling was investigated by using inductively coupled plasma mass spectrometry. The experiments were carried out in two different irradiance regimes by a Nd-YAG laser with 266 nm wavelength and single 6 nanosecond laser pulses. In the high irradiance regime (> 0.04, 0.07GW/cm(2)) the effect of the laser irradiance is not discriminating. In the low irradiance regime (< 0.04, 0.07GW/cm(2)) large differences have been found between the alloy and the quasicrystal. The results have been interpreted on the basis of a thermodynamic vaporization process for the intermetallic alloy. An electronic model of localized excitation is suggested for the physical process of surface material removal from a quasicrystal.