Prof. John Okumu
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Current Research
My recent work has focused on sputter deposition technique to thin films of transition metal oxides. The main goal is to have a better understanding of novel materials for device development. This involves the characterization of materials for various applications through the study of optical and structural properties using optical spectroscopy and x-ray diffraction analysis. The study of these materials has immediate applications in optical data storage, hard coatings and mirrors, and coatings for smart windows.
I have also recently started a project on fabrication of nanoparticles especially by sputter deposition in transition metal oxides. We research on a method that can produce a broad plasmon resonance band which is suited for photochromic applications. We try to understand these properties using x-ray diffraction, transmission electron microscopy and optical spectroscopy. In this work we collaborate with the 1st Institute of Physics, RWTH-Aachen, Germany.
Publications
Internationally Refereed Journals
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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
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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)
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P.K. Kariuki, J. Okumu and C.S. Singh, “Calculation of cross-sections for elastic scattering of electrons at Intermediate energies by a magnetsium atom”, African Review of Physics 9.39(2014)
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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
- 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).
- 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).
- 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).
- 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).
- 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).
- 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).
- 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)
- J. Okumu, F. Koerfer, C. Salinga, T.P. Pedersen and M. Wuttig; “Gasochromic switching of reactively sputtered molybdenum oxide films: A correlation between film properties and deposition pressure.” Thin Solid films, 515, 1327-1333 (2006).
- 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).
- 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).
- 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).
- 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).
- 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)
- 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).
- J. Okumu and G.J. Morgan; ''Linear and non-linear optical properties of amorphous silicon.'' J. Non-Cryst. Solids 272, 67-70 (2000)
- J.M. Ngaruiya, J.M. Odote, J. Okumu and R.T. Kivaisi," Effects of Thermal Switching on Reactively Sputtered VO2 Films." Pro. Regional Conference on Material Science, Makarere University, Kampala-Uganda (1999).p 29-37.
- J. Okumu, ‘’Electronic Properties of Amorphous Semiconductors and Liquid Metals’’. Ph.D thesis, University of Leeds, UK (1996)
- 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).
- G.J. Morgan and J. Okumu; ''The nature of the band gap in amorphous Si:H''. Solid State phenomena, 44-46, 669-674 (1995).
- J. Okumu, J.M. Holender and G.J. Morgan; ''Hall Effect and Electronic conduction in amorphous silicon''. Phil. Mag. Lett., 72, 135-142 (1995).
- 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).
Other Publications
Books
- 2010 - James Mugambi Linturi, Singh CS and J. Okumu, Electron Impact Excitation of Helium Atom, published by Lambert Academic publishing GmbH & Co, KG, Germany (2010) ISBN: 978-3-8433-7517-7
- 2010- 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
- J.M. Linturi, J. Okumu and C.S. Singh, paper presented in the 1st East African Regional Scientific conference of Pure and Applied sciences held at Kenyatta University, Nairobi , Kenya.
- E Jobunga, J. Okumu and C.S. Singh, “Electron impact excitation of the lowest autoionizing state of potassium using distorted wave method. Presented in the XXVII international conference on Photonic, Electronic and Atomic collisions held in Belfast, Northern Ireland, UK on 27th July 2011.
- 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, 10th -14th August 2010, Kenyatta University, Nairobi-Kenya.
- 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, 10th -14th August 2010, Kenyatta University, Nairobi-Kenya
- 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”. Pro. International Conference on Solar Energy Materials, 13th- 15th October, 2009, Dar es Salaam, Tanzania.
- J. Okumu, C. Dahmen, A.N. Sprafke M. Lysberg, G. von Plessen and M. Wuttig, “Multicolor Photochromism in Silver nanoparticles in TiO2 matrix”. Pro. International Conference on Solar Energy Materials, 13th-15th October, 2009, Dar es Salaam,Tanzania.
- 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 onThin Film Technology, July 24th to 4th August 2006, University of Dar es Salaam,Tanzania.
- J. Okumu and M. Wuttig, Optical properties of TiO2 loaded with silver nanopartiles,World Conference on Physics and Sustainable Development (31st October-2nd November 2005), Durban, South Africa.
- 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 2003 (23rd -26th June 2003)-Berlin (Germany).
- J. Okumu, C. Salinga, and W. Wuttig, Gasochromic Switching in MoOx Thin Films Deutschen Physikalischen Gesellschaft (German Physical Society) meeting-Dresden (24th -28th March 2003) Dresden (Germany).
- J. Okumu, H. Weis, T. Petersen and M. Wuttig, '' Hydrogenation of Mg films for Optical Switches''. Pro. Regional workshop of Thin film Technology -Dar es Salaam (2000) p 52-56.
- G.A. Ibitola J. Okumu and P.K. Karimi, ''High electron mobility Transistors: A review. Proc. 5th Regional Conference on Material Science and Device Technology. Nairobi (2000).
- J. Okumu, "Theory of the band gap formation in amorphous silicon." Proc. Regional Conference on Developments in material science and Physics Education (Nairobi) (1996).
