Development of a measurement base for static secondary ion mass spectrometry
thesisposted on 06.12.2012 by Ian S. Gilmore
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
This work sets out a framework to provide a metrological basis for static SIMS measurements. This surface analytical technique has been is use for over thirty years but, because of the lack of an infrastructure, has not achieved its full potential in industry. To build this basis, the measurement chain is studied from the sample through to the detector and data processing. By understanding the effects of each link in the chain, repeatabilities are reduced by orders of magnitude to below 1%, the ion beam current and flux density are calibrated to better than 2%, ion beam damage in polymers is controlled and detection efficiencies calculated. Utilising these developments, a characterised and calibrated SIMS spectrometer is used to establish reference materials. An inter-laboratory study to assess the extent of spectrum variability between spectrometers was conducted involving over twenty laboratories worldwide. Analysis of the data gives the level of repeatability and reproducibility using current procedures. Repeatabilities for some laboratories are as good as 1% but many are at 10% and a few as poor as 80%. A Relative Instrument Spectral Response, RISR, is developed to facilitate the comparison of spectra from one instrument to another or library data. For most instruments reproducibilities of 14% are achievable. Additionally, the wide variety of ion beam sources and energies, presently in use, result in spectra that are only broadly comparable. A detailed study of these effects provides, for the first time, a unified method to relate the behaviour for all ion species and energies. A development of this work gives a totally new spectroscopy, known as G-SIMS or gentle-SIMS. Here, the static SIMS spectrum for a low surface plasma temperature is calculated which promotes those spectral intensities truly representative of the analysed material and reduces those caused by additional fragmentation and rearrangement mechanisms. The resulting GSIMS spectra are easier to identify and are interpreted more directly. This work provides the essential basis for the development of static SIMS. Future work will improve the consistency of library data so that the valid data for molecular identification can be uniquely extracted. The measurement base will be developed to meet the growing requirements for static SIMS analysis of complex organic and biomaterials.