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Prof. John Okumu

Professor & Acting Vice Chancellor, Department of Physics

Home School of Pure & Applied Sciences Department of Physics Prof. John Okumu

Prof. John Okumu

Professor & Acting Vice Chancellor, Department of Physics

Department of Physics · PhD, University of Leeds, UK (1996)

Administrative Position
Acting Vice Chancellor, Kenyatta University

Research Interests

Prof. Okumu's research focuses on sputter deposition techniques applied to thin films of transition metal oxides, with the goal of understanding novel materials for device applications. His work involves characterising optical and structural properties using optical spectroscopy and x-ray diffraction, in collaboration with the 1st Institute of Physics at RWTH-Aachen, Germany.

Thin film deposition & transition metal oxides
Nanoparticle fabrication via sputter deposition
Gasochromic & photochromic smart window coatings
Optical data storage, hard coatings & mirrors

Academic Qualifications

PhD — Electronic Properties of Amorphous Semiconductors & Liquid Metals
University of Leeds, UK (1996)

Refereed Journal Articles

  1. Lawrence Ochoo, Charles Migwi and John Okumu: "Impact Parameters for optimized metal nanoparticles – aided electromagnetic field (EMF) effect on cancer", Cancer Nanoparticles (2018) 9:2
  2. P.K. Kariuki, J. Okumu, and C.S. Singh: "Distorted Wave Born and Optical Potential Calculation Methods for Electron-Sodium Elastic Scattering Cross-section at Intermediate Energies", The African Review of Physics, 10, 131–138 (2015)
  3. P.K. Kariuki, J. Okumu and C.S. Singh: "Calculation of cross-sections for elastic scattering of electrons at Intermediate energies by a magnesium atom", African Review of Physics 9:39 (2014)
  4. W.M. Ndeke, J. Okumu, C.S. Singh: "Distorted Wave Method Calculations of Positron Impact Excitation of 2¹S State of Helium atom", Advances in Physics Theories and Applications, Vol 35, 49–57 (2014)
  5. Ochoo L.O., Migwi C.M. and Okumu J.: "Damping effect of the inner band electrons on the optical absorption and bandwidth of metal nanoparticles", Journal of Nanoparticle Research, 14, 1–14 (2012)
  6. E. Jobunga, J. Okumu and C.S. Singh: "Excitation cross section evaluation for the lowest autoionizating state of potassium", African Review of Physics 7, 0001 (2012)
  7. Agumba J.O., Karimi P.M., Okumu J., and Njoroge W.K.: "Design and Fabrication of simple Four point probe system for electrical characterization of thin films", International Journal of Current Research, vol. 3, issues 7, 135–139 (2011)
  8. J.M. Linturi, J. Okumu, and C.S. Singh: "A distorted wave method applied to study the 2³P excitation of helium atom by electron impact", Indonesian Journal of Physics 22, 35 (2011)
  9. J. Okumu, D. Kohl, A. Sprafke, G. von Plessen, and M. Wuttig: "Formation mechanism of noble metal nanoparticles in reactively sputtered TiO₂", Journal of Applied Physics 108, 063529 (2010)
  10. E.O. Jobunga, J. Okumu and C.S. Singh: "Electron Impact Excitation of the lowest autoionization states of alkalis using distorted wave method", African Journal of Science and Technology 11, 24 (2010)
  11. C.K. Wangati, W.K. Njoroge and J. Okumu: "Influence of Deposition parameters on the Optical properties of thin tungsten oxide films prepared by reactive DC magnetron sputtering", East African Journal of Physical Sciences, 8(1): 55–74 (2008)
  12. J. Okumu, F. Koerfer, C. Salinga, T.P. Pedersen and M. Wuttig: "Gasochromic switching of reactively sputtered molybdenum oxide films", Thin Solid Films, 515, 1327–1333 (2006)
  13. E.U.O. Mapesa, J.M. Odote and J. Okumu: "Optical properties of indium-tin-oxide thin films prepared by non-reactive DC magnetron sputtering", East African Journal of Physical Sciences, 7(1/2): 13–23 (2006)
  14. J. Okumu, C. Dahmen, A.N. Sprafke, M. Lysberg, G. von Plessen and M. Wuttig: "Photochromic silver nanoparticles fabricated by sputter deposition", J. Appl. Phys. 97, 094305-1 (2005)
  15. J.G. Gitonga, J.W. Waithaka, J. Okumu, and R.L. Stangl: "Gravity Survey of Lake Magadi Area", East African Journal of Physical Sciences, 6(2): 89–100 (2005)
  16. J. Okumu, F. Koerfer and M. Wuttig: "In-situ measurements of thickness changes and mechanical stress upon gasochromic switching of thin MoOx films", J. Appl. Phys. 95, 7632–7636 (2004)
  17. Y.M. Wambua, J. Okumu and T.S. Dod: "Computation of Electronic properties of a-Si", East African Journal of Science 3(1), 35–42 (2001)
  18. J. Okumu and G.J. Morgan: "Calculation of linear and non-linear optical properties of amorphous silicon", East African Journal of Science 3(1), 25–33 (2001)
  19. J. Okumu and G.J. Morgan: "Linear and non-linear optical properties of amorphous silicon", J. Non-Cryst. Solids 272, 67–70 (2000)
  20. G.J. Morgan and J. Okumu: "Electron confinement in a-Si:H and effective mass theorem for amorphous semiconductors", Phys. Rev. B, 53, 13254–13256 (1996)
  21. G.J. Morgan and J. Okumu: "The nature of the band gap in amorphous Si:H", Solid State Phenomena, 44–46, 669–674 (1995)
  22. J. Okumu, J.M. Holender and G.J. Morgan: "Hall Effect and Electronic conduction in amorphous silicon", Phil. Mag. Lett., 72, 135–142 (1995)
  23. G.J. Morgan, J. Okumu, J.M. Holender, D. Weaire and D. Hobbs: "Electron, Holes and the Hall Effect in amorphous silicon", J. Non-Cryst. Solids, 164–166, 457–460 (1993)

Books

James Mugambi Linturi, Singh C.S. and J. Okumu: Electron Impact Excitation of Helium Atom. Lambert Academic Publishing GmbH & Co. KG, Germany (2010). ISBN: 978-3-8433-7517-7
Erick Ouma Jobunga, J. Okumu and C.S. Singh: Electron Impact: Excitation of the Lowest Autoionizing States of Alkalis using the Distorted Wave Method. VDM Verlag Dr. Muller Publishing Company, Germany (2010). ISBN: 978-3-6392-9573-3

Conference Papers

  1. J.M. Linturi, J. Okumu and C.S. Singh: Paper presented at the 1st East African Regional Scientific Conference of Pure and Applied Sciences, Kenyatta University, Nairobi, Kenya.
  2. E. Jobunga, J. Okumu and C.S. Singh: "Electron impact excitation of the lowest autoionizing state of potassium using distorted wave method", XXVII International Conference on Photonic, Electronic and Atomic Collisions, Belfast, Northern Ireland, UK (27 July 2011)
  3. J.O. Agumba, P.M. Karimi, J. Okumu, and W.K. Njoroge: "Design and fabrication of a simple four point probe for electrical characterization of thin films", 1st East African Regional Conference of Pure and Applied Sciences, Kenyatta University, Nairobi, Kenya (10–14 August 2010)
  4. E.O. Jobunga, J. Okumu and C.S. Singh: "Electron Impact Excitation of the lowest autoionization states of sodium using distorted wave method", 1st East African Regional Conference of Pure and Applied Sciences, Kenyatta University, Nairobi, Kenya (10–14 August 2010)
  5. W.K. Njoroge, C.K. Wangati, and J. Okumu: "Influence of sputter power and chamber pressure on the optical properties of tungsten thin films deposited by magnetron sputtering", International Conference on Solar Energy Materials, Dar es Salaam, Tanzania (13–15 October 2009)
  6. J. Okumu, C. Dahmen, A.N. Sprafke, M. Lysberg, G. von Plessen and M. Wuttig: "Multicolor Photochromism in Silver nanoparticles in TiO2 matrix", International Conference on Solar Energy Materials, Dar es Salaam, Tanzania (13–15 October 2009)
  7. E.U.O. Mapesa, J.M. Odote and J. Okumu: "Optical properties of indium-tin-oxide thin films prepared in a non-reactive ambient", Proceedings of the Ninth College on Thin Film Technology, University of Dar es Salaam, Tanzania (24 July – 4 August 2006)
  8. J. Okumu and M. Wuttig: "Optical properties of TiO2 loaded with silver nanoparticles", World Conference on Physics and Sustainable Development, Durban, South Africa (31 October – 2 November 2005)
  9. J. Okumu, C. Dahmen, A.N. Sprafke, M. Lysberg, G. von Plessen and M. Wuttig: "Photochromic silver in TiO2 matrix", 8th European Vacuum Congress, Berlin, Germany (23–26 June 2003)
  10. J. Okumu, C. Salinga, and M. Wuttig: "Gasochromic Switching in MoOx Thin Films", Deutschen Physikalischen Gesellschaft (German Physical Society) Meeting, Dresden, Germany (24–28 March 2003)
  11. J. Okumu, H. Weis, T. Petersen and M. Wuttig: "Hydrogenation of Mg films for Optical Switches", Regional Workshop of Thin Film Technology, Dar es Salaam (2000), p. 52–56
  12. G.A. Ibitola, J. Okumu and P.K. Karimi: "High Electron Mobility Transistors: A review", Proceedings of the 5th Regional Conference on Material Science and Device Technology, Nairobi (2000)
  13. J. Okumu: "Theory of the band gap formation in amorphous silicon", Proceedings of Regional Conference on Developments in Material Science and Physics Education, Nairobi (1996)