Optical emission and mass spectrometric diagnostics of laser-induced silicon plasmas

Optical Emission Spectroscopy (OES) and Mass Spectrometry (MS) were employed in tandem for diagnostic studies of Nd:YAG (532 nm) laser induced plasma plumes. OES measurements of laser-induced silicon plasmas were performed through a range of ambient pressure regimes from atmospheric pressure down to ~10-4 mbar. The temporal evolution of the plasmas was characterised in terms of electron excitation temperature Te, ionisation temperature Ti, and electron density Ne. Electron densities were determined in the range 2.86 × 1016 to 5.53 × 1019 cm-3, electron temperatures were calculated in the range 8794 to 21229 K, and ionic species temperatures calculated in the range 13658 to 22551K. The requirements for OES analysis based on the assumption of Local Thermal Equilibrium (LTE) conditions existing within the plasmas are discussed. The plasma morphology and expansion dynamics with respect to pressure are described. Response Surface Methodology (RSM) was employed to optimise Laser-Induced Breakdown Spectroscopy (LIBS) analyses of silicon at atmospheric pressure and under vacuum conditions. Multivariate analysis software was used to design and analyse several multi-level, full factorial RSM experiments. A Quality Factor (QF) was conceived as the response parameter for the experiments, representing the quality of the LIBS spectrum captured for a given hardware configuration. A full parametric study of the LIBS hardware configuration was performed to determine the true response of the system; the outcome of which compares favourably with the results yielded from the RSM investigation. MS analyses of silicon and copper laser-induced plasma plumes were performed using a commercially available Residual Gas Analyser (RGA). The RGA sampling configuration was investigated in order to maximise neutral and ionic species detection from the laser-induced plasmas.EThOS - Electronic Theses Online ServiceGBUnited Kingdo