Static Secondary Ion Mass Spectrometry Studies of the Formation and Stability of Metal Oxide Clusters

• Main Author: Reed, Nicola M
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1990
• Subjects: Atomic physics; Molecular physics; Particle physics
• ISBN: 9798426843912

The technique of static SIMS is becoming more widely used in a number of areas. In spite of the growth of this analytical technique there still remains some uncertainty as to the precise mechanism of secondary ion formation. This study attempts to elucidate some of these mechanisms and to address the question of whether ions can form by recombination (ACM) or only direct emission (DEM). A review of the basic theories of sputtering and ionization mechanisms is presented.The problem of suitable analysis parameters is investigated, with particular attention being paid to the problem of changing sample potential. If sample charging is severe then the degree and quality of spectral information may be seriously reduced. Negative ions are particularly susceptible to this effect, since under a positive primary ion beam the sample will charge positively due to an input of charge and loss of electrons, thus reducing the ease with which negative ions can escape from the surface. Compensation of this effect is studied using a neutral primary beam, Ar°, and simultaneous electron beam bombardment.SIMS studies of metal oxide cluster formation are shown for a number of oxides of different structures. The results are discussed in terms of oxide parameters, surface compositional changes, valency, M-0 bond strength, electron configuration and the resulting partial charges on the metal and oxygen ions. The distribution of energies with which the clusters are formed is discussed and related to the oxide structures.Tandem mass spectrometry studies (MS/MS) allow the stability of the secondary ions, i.e. the parent ions, to be estimated and an analysis of the fragments of these ions i.e. the daughter ions to be performed.The possibility of surface reduction following sample heating and/or argon etching is studied for V2O5, SnO2 and TiO2, combining SIMS and ESCA data. An assessment of sample damage under different primary beam conditions is also shown for these three oxides. Further experiments to determine the likelihood of cluster ion emission by DEM or ACM are performed in the study of the mixed oxide solid solutions Mg1-xNixO, Mg1-xCoxO and Al2-xCrxO3.