The Application of Resonance Ionisation Mass Spectrometry to Trace Analysis in Solids

Borthwick, Ian Stewart (1993) The Application of Resonance Ionisation Mass Spectrometry to Trace Analysis in Solids. PhD thesis, University of Glasgow.

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Resonant ionisation mass spectrometry (RIMS) is a laser based technique which can detect gas phase atoms with a very high degree of selectivity and sensitivity. The basic concepts of the technique are detailed. For RIMS to be applied to the detection of trace quantities of elements in solid samples the sample must be atomised. If small areas of a surface are to be analysed then the atomisation technique must be able to be applied selectively to these areas. There are two suitable atomisation techniques which have been investigated; laser ablation and ion beam sputtering. Laser ablation is the less well characterised technique and the basic physical processes involved are detailed. This discussion then develops to detail the models which have been applied to the description of the velocity distribution of neutral atoms liberated by laser ablation. A brief review of the experimental investigations of laser ablation pertinent to the work discussed in this thesis is included. A detailed experimental study of laser ablation was undertaken by the author. After a discussion of the experimental arrangement involved this work is discussed in depth. The velocity distributions of neutral atoms liberated from solid samples by laser ablation have been studied as functions of laser wavelength for a variety of metal and non-metal samples. The effect of changing the ablation laser power on the velocity distribution has also been investigated. The results obtained from gold and lead foils indicate that a thermal mechanism can be applied to describe the laser ablation of these metals. This was also the case for the various elements ablated from a certified steel standard. It is shown that the relative sensitivity factors determined from this analysis are superior to those previously reported. The energy distribution of atoms liberated by the laser ablation of aluminium samples were in some instances unexpectedly high, and this is explained as being due to the contribution from an oxide film on the sample surface. Several methods which have been investigated in an attempt to reduce the interference from ions created by the ablation laser on the RIMS signal are detailed. A more efficient method of utilising the sample by laser ablation has been developed, this involves tuning the ablation laser wavelength to an atomic resonance of the atom being detected. This technique, called Resonant Laser Ablation, which can result in enhancements in the ion yield of three orders of magnitude, is discussed in detail. The results from other researchers, and workers in Glasgow are given to illustrate the important contribution that atomic collisions have in this process. The discussion also details the work of the author in applying the technique to the detection of small quantities of aluminium in a solid sample. The interfacing of an ion gun with a high current density to the RIMS system, by the author, is also discussed. The processes occurring during ion sputtering are understood more quantitatively than is the case for laser ablation. The essential results from sputtering theory are reported. Ion sputtering has been used to allow the quantification of the amount of material liberated by the laser ablation of a pure metal target. The two atomisation techniques are compared for trace analysis applications by undertaking a study of aluminium samples which each contain various concentrations of Mg and Mn.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: K WD Ledingham
Keywords: Optics, Analytical chemistry, Applied physics
Date of Award: 1993
Depositing User: Enlighten Team
Unique ID: glathesis:1993-74777
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 13 Nov 2019 15:58
Last Modified: 13 Nov 2019 15:58

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