Defense Presentation

Scott Heinbuch

Ph.D. Final
April 06, 2009, 4:00
ERC 3rd floor conference room

Abstract:  This dissertation reports the study of the structure and reactivity of clusters using a new mass spectrometry approach in which the ionization is produced by high energy photons generated by a desk-top size soft x-ray (SXR) laser. The work was motivated by the importance that catalytic processes have in enhancing the rate of gas phase chemical reactions such as the manufacture of hydrocarbons, polymers, drugs, sulfuric acid, fertilizers, pesticides, etc., many forms of pollution control, development of robust mirror coatings for extreme ultraviolet (EUV) lithography, and hydrogen storage for clean energy applications. Extensive mass spectrometry studies have shown that gas phase nanoclusters are effective model systems to study surface reactions in the bulk phase. However, the use of multi-photon ionization or electron impact ionization sources results in cluster fragmentation, limiting the information gained about the neutral cluster parent. Our approach uses the 26.5 eV photons of a compact capillary discharge driven laser to ionize clusters by single photon events, avoiding the cluster fragmentation associated with multi-photon ionization. The high photon energy also allows the detection of neutral clusters and small molecule reaction products with high ionization energies. Experiments were conducted for several types of clusters including van der Waals clusters, metal oxides, and metal oxide reactions. Density Functional Theory (DFT) calculations were employed to elucidate cluster geometries, properties, and reaction mechanisms. For hydrogen/van der Waals clusters, the unimolecular dissociation rate constants for reactions involving loss of one neutral molecule were calculated and neutral cluster temperature were estimated. The results of metal oxide clusters experiments and calculations suggest that SO2 can be reduced and oxidized by oxygen deficient and oxygen rich vanadium oxide clusters, respectively. Three SO3 formation mechanisms are proposed, and several condensed phase catalytic cycles are suggested based on SO3 formation mechanisms. Other experiments showed that C=C bonds of alkenes can be broken on neutral vanadium oxide oxygen rich clusters with the general structure VO3(V2O5)n=0,1,2…. DFT calculations provide a mechanistic explanation for the general reaction in which the C=C double bond of alkenes are broken. New results also help to elucidate the selective catalytic reduction of NO using NH3 on a vanadium oxide catalyst. A separate set of experiments to identify capping layer materials for extreme EUV optical coatings that are resistive to carbon contamination. Results show that oxidized Hf and Zr are much less reactive than Ti or Si oxide, and might lead to capping layers that might extend lifetimes of EUV mirror coating upon EUV irradiation. Zr oxide was found to be less reactive than Hf oxide. The set of results demonstrate the potential of compact soft-ray lasers as new tools for chemistry and photo-physics studies with intense soft x-ray light in small laboratory environments.

Adviser: Jorge Rocca
Co-adviser: Elliot Bernstein
Non-ECE member: Elliot Bernstein
Member3: Carmen Menoni
Member4: Mario Marconi
Additional member: NA

Publications:
1. S. Heinbuch, F. Dong, J.J. Rocca, and E.R. Bernstein, “Gas phase study of the reactivity of optical coating materials with hydrocarbons using a desk-top size EUV laser,” SPIE 6921, 69213F (2008).
2. S. Heinbuch, F. Dong, J.J. Rocca, and E.R. Bernstein, “Gas phase study of the reactivity of optical coating materials with hydrocarbons using a desk-top size EUV laser,” JOSA B 25, B85 (2008).
3. S. Heinbuch, F. Dong, J.J. Rocca, and E.R. Bernstein, “Neutral nanocluster chemistry studied by soft x-ray laser single-photon ionization: Application to soft x-ray optical surface contamination studies: SimOn and TimOn,” SPIE 6702, 67020K (2007).
4. S. Heinbuch, F. Dong, J.J. Rocca, and E.R. Bernstein, “Single photon ionization of hydrogen bonded clusters with a soft x-ray laser: (HCOOH)x and (HCOOH)y(H2O)z,” J. Chem. Phys. 126, 244301 (2007).
5. S. Heinbuch, F. Dong, J.J. Rocca, and E.R. Bernstein, “Single photon ionization of van der Waals clusters with a soft x-ray laser: (CO2)n and (CO2)n(H2O)m,” J. Chem. Phys. 125, 154316 (2006).
6. S. Heinbuch, F. Dong, J.J. Rocca, and E.R. Bernstein, “Single photon ionization of van der Waals clusters with a soft x-ray laser: (CO2)n and (CO2)n(H2O)m,” J. Chem. Phys. 125, 154316 (2006).
7. S. Heinbuch, M. Grisham, D. Martz, and J. J. Rocca, "Demonstration of a desk-top size high repetition rate soft x-ray laser," Optics Express 13, 4050 (2005).
8. S. Heinbuch, M. Grisham, D. Martz, F. Dong, E.R. Bernstein, and J. J. Rocca, “Desk-top Size High Repetition Rate 46.9 nm Capillary Discharge Laser as Photoionization Source for Photochemistry Applications,” SPIE 5919, 591907 (2005).
9. F. Dong, S. Heinbuch, Y. Xie, J.J. Rocca, Z. Wang, K. Deng, S. He, and E.R. Bernstein, “C=C bond cleavage on neutral VO3(V2O5)n clusters,” JACS (submitted).
10. F. Dong, S. Heinbuch, Y. Xie, J. J. Rocca, and E. R. Bernstein, "Reaction of Neutral Vanadium Oxide Clusters With methanol and Ethanol", J. Chem. Phys. submitted.
11. F. Dong, S. Heinbuch, Y. Xie, J.J. Rocca, Z. Wang, K. Deng, S. He, and E.R. Bernstein, “Experimental and theoretical study of the reactions between neutral vanadium oxide clusters and ethane, ethylene, and acetylene,” J. Am. Chem. Soc. 130(6), 1932 (2008).
12. F. Dong, S. Heinbuch, J.J. Rocca, and E.R. Bernstein, “Dynamics and fragmentation of van der Waals clusters: (H2O)n, (CH3OH)n, and (NH3)n upon ionization by a 26.5 eV soft x-ray laser,” J. Chem. Phys. 124, 224319


Program of Study:
EE 777 X-Ray Lasers
EE 795 Independent Study
EE 799 Dissertation
EE 535 Analog Integrated Circuit Lab
EE 534 Analog Integr Circuit Design
EE 580 Physical Optics
EE 580 Opt. Int. and Laser Metrology
C 773 Atomic& Molecular Spectroscopy