We are studying the electronic structures of new and advanced materials. We are using synchrotron radiation to perform soft x-ray emission and absorption spectroscopy of systems like biomaterials, superconductors and transition metal compounds.

Regan G. Wilks, Doctor of Philosophy

Regan Wilks

[Regan.Wilks@usask.ca]

Education

  • University of Saskatchewan
    Saskatoon, Saskatchewan
    B.E. in Engineering Physics
    April 2002
  • M.Sc. in Physics
    July 2005
  • Ph.D. in Physics
    June 2009

Current Affiliation

  • Helmholtz-Zentrum Berlin, Division Solar Energy Research (Berlin, Germany)

Ph.D. Thesis

  • X-ray spectroscopy of organic materials

Abstract

A combined experimental and theoretical examination of the electronic structures of a number of modified helical peptides, specifically ferrocene-(proline)x-benzyl ester (referred to as Fc-Prox-OBz), is presented. Soft X-ray absorption (XAS) and emission (XES) spectroscopy using synchrotron radiation are used to probe the unoccupied and occupied partial densities of electronic states, respectively. The identities of the final-state orbitals corresponding to all near-edge features in the XAS spectra of all elements in the molecules are determined by comparison with published results for other systems, as well as density functional theory (DFT) spectral simulations. Experimental evidence of the splitting of the Fc 3e2u orbital due to the presence of a substituent is observed for the first time. The 3e2u orbital is also found to contribute to a delocalized orbital that extends throughout the peptide, suggesting a possible electron transfer pathway. Analysis of the Fe 2p XAS spectrum leads to the reassignment of the origin of the prominent 711.4 eV resonance to transitions into hybridized orbitals involving Fe 4s levels and the s* orbitals associated with the Fc C-H bonds. Previous studies incorrectly described this feature.

Comparison of the DFT-simulated ground-state DOS of Fc-Pro2-OBz and Fc-Pro3-OBz shows a major reorganization of the orbitals of the benzyl ester, which acts as the reduction centre in redox reactions. In Fc-Pro3-OBz, the orbitals closely resemble those of a gaseous substituted benzene ring and were found at a lower energy than the equivalent orbitals of Fc-Pro2-OBz. This shift is proposed as a possible explanation for the decrease in redox potential observed upon the addition of a third proline residue to the peptide.

Project

My current research involves the study of a variety of organometallic materials using soft X-ray absorption and emission spectroscopy. A series of sarcophagine molecules that include transition metals held in place by encapsulating ligands are being studied. It has been shown that the oxidation state of the metal sites of these molecules can be altered through chemical means, suggesting that these molecules may have applications as charge storage centres in molecular electronic devices. I am also examining a series of nanoporous ferrocene-peptide complexes. The pores of these molecules are hydrophilic, and the goal of the study is to understand the interaction between the H2O and the host peptide. These structures have possible applications in trans-membrane transport, separation science, supramolecular host-guest chemistry, and molecular electronics.

Publications

  • 1. Fast electron dynamics in vanadates measured by resonant inelastic x-ray scattering G. Herrera, J. Jimenez-Mier, R.G. Wilks, A. Moewes, W. Yang, J. Denlinger, Materials Letters. 107, 144-146 (2013).

  • 2. Excited states in yttrium orthovanadate YVO4 measured by soft X-ray absorption spectroscopy G. Herrera, J. Jimenez-Mier, R.G. Wilks, A. Moewes, W. Yang, J. Denlinger, J. Mat. Sci. 48, 6437-6444 (2013).

  • 3. Molecular orientation and optical luminescence properties of soluble star-shaped oligothiophene molecules for organic electronics applications R.G. Wilks, G.S. Chang, K.H. Kim, D.H. Choi, and A. Moewes, J. Electr. Spectr. Rel. Phen. 184, 355-359 (2011).

  • 4. Electron dynamics of transition metal compounds studied with resonant soft x-ray scattering J. Jimenez-Mier, G. Herrera-Perez, P. Olalde-Velasco, G. Carabali, E. Chavira, P. de la Mora, W.L. Yang, J. Denlinger, A. Moewes, R. Wilks, Proceedings of 6th International Symposium on Radiation Physics, March 7-10, 2010 Zacatecas, Mexico) – Revista Mexicana de la Fisica 57, 6-13 (2011).

  • 5. Charge transfer and band gap of ferrocene intercalated into TiSe2 A.N. Titov, Y.M. Yarmoshenko, P. Bazylewski, M.V. Yablonskikh, E.Z. Kurmaev, R. Wilks, A. Moewes, V.A. Tsurin, V.V. Fedorenko, O.N. Suvorova, S.Yu. Ketkov, M. Neumann, and G.S. Chang, Chem. Phys. Lett. 497, 187-190 (2010).

  • 6. Correlation effects in Ni 3d states of LaNiPO A.V. Lukoyanov, S.L. Skornyakov, J.A. McLeod, M. Abu-Samak, R.G. Wilks, E.Z. Kurmaev, and A. Moewes, N.A. Skorikov, Yu.A. Izyumov, L.D. Finkelstein, V.I. Anisimov, and D. Johrendt, Phys. Rev. B 81, 235121-1-5 (2010).

  • 7. Band gaps and Electronic structure of alkaline-earth and post-transition metal oxides J.A. McLeod, R.G. Wilks, N.A. Skorikov, L.D. Finkelstein, M. Abu-Samak, E.Z. Kurmaev, and A. Moewes, Phys. Rev. B 81, 245123-1-9 (2010).

  • 8. Electronic structure of BiMeO3 multiferroics and related oxides J.A. McLeod, Z.V. Pchelkina, L.D. Finkelstein, E.Z. Kurmaev, R.G. Wilks, A. Moewes, I.V. Solovyev, A.A. Belik, and E. Takayama-Muromachi, Phys. Rev. B 81, 144103-1-10 (2010).

  • 9. A comparative theoretical and experimental study of the radiation induced decomposition of Glycine R.G. Wilks, J.B. MacNaughton, H.-B. Kraatz, T. Regier, R.I.R. Blyth, and A. Moewes J. Phys. Chem. A 113, 5360-5366 (2009).

  • 10. Determining the sp2/sp3 bonding concentrations of carbon films using X-ray absorption spectroscopy T. Hamilton, R.G. Wilks, M.V. Yablonskikh, Q. Yang, M. Foursa, A. Hirose, V.N. Vasilets, and A. Moewes, Canadian Journal of Physics 86, 1401-1407 (2008).

  • 11. Characterization of oxide layers formed on chemically treated Ti by using soft X-ray absorption measurements R.G. Wilks, E.Z. Kurmaev, E. Santos, M.V. Yablonskikh, A. Moewes, N.K. Kuromoto, and G.A. Soares, J. Electr. Spectr. Rel. Phen. 169, 46-50 (2009).

  • 12. X-ray emission and photoluminescence Spectroscopy of nanostructured Silica with implanted copper ions D.A. Zatsepin, V.S. Kortov, E.Z. Kurmaev, N.V. Gavrilov, R.G. Wilks, and A. Moewes, Phys. Solid State 50, 2322-2326 (2008).

  • 13. Unipolar-to-ambipolar conversion of rubrene thin-film transistors by organosilene self-assembled monolayer J.H. Seo, G.S. Chang, R.G. Wilks, C.N. Whang, K.H. Chae, S.J. Cho, K.-H. Yoo, and A. Moewes, J. Phys. Chem. B 112, 16266 (2008).

  • 14. X-ray spectra and electronic structures of the iron arsenide superconductors RFeAsO1-xFx (R=La, Sm) E.Z. Kurmaev, R.G. Wilks, A. Moewes, N.A. Skorikov, Yu.A. Izyumov, L.D. Finkelstein, R.H. Li, and X.H. Chen, Phys. Rev. B 78, 220503R 1-4 (2008).

  • 15. RIXS spectra and electronic structure of Sc and Ti dihydrides A.V. Galakhov, L.D. Finkelstein, E.Z. Kurmaev, R.G. Wilks, A. Moewes, V.K. Fedotov J. Phys.: Cond. Matt. 20, 335224-1-6 (2008).

  • 16. Characterization of chemically treated bioactive Ti using soft X-ray fluorescence E.Z. Kurmaev, R.G. Wilks, R. Filby, A. Moewes, L. Müller, and F.A. Müller, Materials Science and Engineering C 29, 136-139 (2009).

  • 17. X-ray spectra and electronic structure of FeAs superconductors E.Z. Kurmaev, R.G. Wilks, A. Moewes, N.A. Skorikov, Yu.A. Izyumov, L.D. Finkelstein, R.H. Li, and X.H. Chen, arXiv:0805.0668v1 [cond-matt.supr-con] 2008.

  • 18. Oxygen X-ray emission and absorption spectra as a probe of electronic structure in strongly correlated systems E.Z. Kurmaev, R.G. Wilks, A. Moewes, L.D. Finkelstein, and S.N. Shamin, Phys. Rev. B 77, 165127-1-5 (2008).

  • 19. Energy Band structure and X-ray Spectra of Phenakite Be2SiO4 I.R. Shein, R. Wilks, A. Moewes, E.Z. Kurmaev, D.A. Zatsepin, A.I. Kukharenko, and S.O. Cholakh, Phys. Sol. State 50, 615-620 (2008).

  • 20. The attachment of Amino Fragment to purine: Inner-shell structures and spectra S. Saha, F. Wang, J.B. MacNaughton, A. Moewes, and D.P. Chong, Journal of Synchrotron Radiation 15, 151-157 (2008).

  • 21. Substituent Effects in the Iron 2p and Carbon 1s edge Near-Ede X-ray Absorption Fine Structure (NEXAFS) Spectroscopy of Ferrocene Compounds E. Otero, R.G. Wilks, T. Regier, R. Blyth, A. Moewes, and S.G. Urquhart, J. Phys. Chem. A 112, 624-634 (2008).

  • 22. An X-ray emission and density functional theory study of Zn1-xMnxS R.G. Wilks, E.Z. Kurmaev, L.M. Sandratskii, A.V. Postnikov, L.D. Finkelstein, T.P. Surkova, S.A. Lopez-Rivera, and A. Moewes, J. Phys.: Cond. Matt. 18, 10405-10412 (2006).

  • 23. Experimental and Theoretical Investigation of the Electronic Structure of 5-Fluorouracil Compounds J.B. MacNaughton, R.G. Wilks, J.S. Lee, and A. Moewes, J. Phys. Chem. B 110, 18180-18190 (2006).

  • 24. Combined X-ray absorption spectroscopy and density functional theory examination of Ferrocene labeled peptides R.G. Wilks, J.B. MacNaughton, H.-B. Kraatz, T. Regier, and A. Moewes, J. Phys. Chem. B 110, 5955-5965 (2006).

  • 25. Electronic structure of boron nitride single crystals and films J.B. MacNaughton, A. Moewes, R.G. Wilks, X.T. Zhou, T.K. Sham, T. Taniguchi, C.Y. Chan, W.J. Zhang, I. Bello, S.T. Lee, and H. Hofsäss, Phys. Rev. B 72, 195113-1-8 (2005).

  • 26. Ion irradiation induced reduction of Fe3+ to Fe2+ in triethoxysilane films R.G. Wilks, E.Z. Kurmaev, J.C. Pivin, A. Hunt, M.V. Yablonskikh, D.A. Zatsepin, A. Moewes, S. Shin, P. Palade, and G. Principi, J. Phys.: Cond. Matt. 17, 7023-7028 (2005).

  • 27. Resonantly Excited Cascade X-ray Emission from La A. Moewes, R. Wilks, A.G. Kochur, and E.Z. Kurmaev, Phys. Rev. B 72, 075129-1-6 (2005).

  • 28. Local Environment of Fluorine Atoms in Sr2Can-1CunO2n+δF2±y (n=2,3) High-Temperature Superconductors Grown under High Pressure E.Z. Kurmaev, A. Moewes, R. Wilks, L.D. Lechkina, D.A. Zatsepin, T. Kawashima, and E. Takayama-Muromachi, Phys. Solid State 47, 1211 – 1215 (2005).

  • 29. Monitoring 5p–4d soft X-ray emission of La when exciting through the low-lying 3d – 4f threshold A. Moewes, R. Wilks, A. Kochur, and E.Z. Kurmaev, J. Electr. Spectr. Rel. Phenom. 144-147, 577-580 (2005).

  • 30. Soft X-ray Spectroscopy of Nucleobases, B-DNA and Ferrocene-proline conjugates A. Moewes, J. MacNaughton, R. Wilks, J.S. Lee, S.D. Wettig, H.-B. Kraatz, and E.Z. Kurmaev, J. Electr. Spec. Rel. Phen. 137-140, 817-822 (2004).