Laser ablation plume of FeSi 2 alloy target studied by TOF mass and optical emission spectroscopies

Abstract

Time-of-flight (TOF) mass and optical emission spectroscopies have been performed on the ablation plume from a-FeSi2 alloy target under KrF excimer laser irradiation at a fluence of 0.35-2.5 J/cm2 to characterize the mass, kinetic energies and excited states of the ej ected species. According to the TOF mass measurements in vacuum, the most prominent species were Si and Fe atoms and ions over the entire fluence range, in addition to Si dimer. At 0.4-0.7 J/cm2, only neutrals of Si, Fe and Si2 with the kinetic energy of around 0.2 eV were observed. At the fluences above 0.7 JIcm2 , doubly and singly charged Si and Fe ions appeared and abruptly increased their number density and kinetic energies from 6 eV at 0.7 J/cm2 to over 100 eV at 2.5 J/cm2. Consistent with the TOF mass spectra, the optical emission lines stemmed from the monatomic Si and Fe as well as Si dimer in the wavelength range of 240-800 nm in vacuum. On the other hand, we confirmed some luminescent lines appeared only in helium atmosphere of 10 Torr, suggesting the cluster formation such as FeSi.