Strong-field Photoionization of Sputtered Neutral Molecules for Chemical Imaging and Depth Profiling
Open Access
- Author:
- Willingham, David G
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- August 27, 2009
- Committee Members:
- Nicholas Winograd, Dissertation Advisor/Co-Advisor
Nicholas Winograd, Committee Chair/Co-Chair
Albert Welford Castleman Jr., Committee Member
Renee Denise Diehl, Committee Member
Barbara Jane Garrison, Committee Member - Keywords:
- ToF-SIMS
Laser Photoionization
Chemical Imaging
Depth Profiling - Abstract:
- Photoionization of molecules sputtered from molecular thin films and biological cells has been achieved using laser radiation in the short-wavelength/low-intensity and the long-wavelength/high-intensity regimes. In general, the interaction of intense radiation fields with molecules results in both emission of electrons to create intact molecular ions and often subsequent molecular dissociation resulting in fragment ions. Significant amounts of photodissociation is attributed to high amounts of internal energy imparted to the sputtered molecules during the ion desorption process coupled with above threshold absorption of photon energy as a result of high laser power density. Data presented in this thesis suggest that molecules subjected to cluster ion beam bombardment are desorbed with lower internal energies and high translational kinetic energies than those subjected to atomic ion bombardment. Molecules that posses lower internal energies are less likely to photodissociate resulting in less fragmented photoionization mass spectra. In addition, data presented in this thesis shows that it is possible to significantly reduce molecular fragmentation induced by the laser field by increasing the photoionization wavelength. The combination of C60 primary ion sources with strong-field, long-wavelength photoionization is observed to increase the efficacy of chemical imaging and molecular depth profiling time-of-flight secondary ion mass spectrometry (ToF-SIMS) experiments.