The development and evaluation of coincidence counting TOF-MS /.
| Main Author: | |
|---|---|
| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1991.
|
| Subjects: | |
| Online Access: | Link to ProQuest copy Link to OAKTrust copy ProQuest, Abstract |
| Abstract: | Coincidence counting has been combined with time-of-flight mass spectrometry (TOF-MS) in a study of the relationships of secondary ions desorbed by keV and MeV energy primary ions. Secondary ions are in coincidence with one another when they are desorbed by the same primary ion impact on the sample. Such secondary ions are recorded in coincidence spectra. During an analysis, the results of many (~10^6) primary ion impacts are recorded in conventional and coincidence TOF mass spectra. The relationships between secondary ions are observed by comparing the number of counts in the peaks of conventional mass spectra with those in corresponding coincidence mass spectra. Since the observed coincidences are dependent on many properties of the sample, and of the primary and secondary ions, information about these properties can be gained through coincidence counting. The first goal of this study was to develop the necessary instrumentation and methods of data acquisition and analysis. We then used this instrumentation to study the properties that affect coincidence counting results. Among these are the spatial relationships of sample components on surfaces (i.e. common spatial origin) and the chemical relationships of secondary ions (i.e. common chemical origin). The measure of common spatial origin took the form of a test for the chemical microhomogeneity of the sample surface. The validity of this approach was demonstrated with the detection of 500nm surface segregations. In the examination of chemical relationships, we found that secondary ions of a common chemical origin could be produced via either the prompt or metastable decay of larger species. The chemical relationships observed due to prompt decays can be used to identify certain functional groups. Coincidence counting is also useful for measuring secondary ion yields. The measured yields in turn are useful for the quantitative analysis of samples. Finally, we found coincidence counting useful in the examination of the fundamental processes of secondary ion desorption. In the examination of the desorption of secondary ions due to MeV/amu energy ion impacts, we obtained data which is consistent with a Coulomb explosion model of desorption. In desorption studies with keV energy polyatomic projectiles, we found that, in the energy range studied, the linearity of the collision cascade is not a function of the primary ion kinetic energy, but primarily of the number of atoms in the primary ion... |
|---|---|
| Item Description: | "Major subject: Chemistry." Typescript (photocopy). Vita. |
| Physical Description: | xv, 252 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |