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ResearchProfessor Angus and co-workers at Case and the University of Louisville are studying charge transfer between diamond and adsorbed water films on the diamond surface. We have shown that charge exchange is to an electrochemical redox couple involving oxygen that acts as an electron acceptor or donor to the diamond. Transfer of electrons from the diamond to the redox couple is responsible for the highly unusual p-type surface conductivity observed on diamond; it also fixes the charge state of the diamond and influences other properties such as the adhesion of water to the diamond surface and the zeta potential. See Vidhya Chakrapani, John C. Angus, Alfred B. Anderson, Scott D. Wolter, Brian R. Stoner and Gamini U. Sumanasekera, “Charge Transfer Equilibria Between Diamond and an Aqueous Oxygen Electrochemical Redox Couple,” Science 318, 1424-1430 (2007).
We have shown that the effect can be used to change the conductivity of carbon nanotubes from n-type to p-type and that it modulates the yellow and green luminescence from both gallium nitride and zinc oxide. Charge transfer to adsorbed films may also play a previously unrecognized role in processes as diverse as sliding friction and contact electrification. Even more speculative is the possibility that certain animals and insects have evolved the capability of modulating the electrochemical potential in their feet to change the adhesive force to solid surfaces. Charge transfer to nano-structures not only can affect their properties, but will vary with the size of the structure because of quantum confinement effects. Professor Angus is also conducting research on novel methods for the synthesis of gallium nitride, indium nitride and related II-IV nitrides, such as zinc germanium nitride. Bulk growth of these materials from liquid metallic phases saturated with nitrogen from a nitrogen plasma is being attempted. A long-range goal is to grow large, bulk single crystals of GaN for use as a substrate for opto-electronic devices. The research programs are highly interdisciplinary and include collaborations with Professor Alfred B. Anderson (Chemistry), Professors Heidi B. Martin and Mohan Sankaran (Chemical Engineering) and Professor Kathleen Kash (Physics) as well as colleagues from the University of Louisville, Duke University and the Research Triangle Institute. Selected PublicationsS.C. Eaton, A.B. Anderson, J.C. Angus, Y.E. Evstefeeva, Y. Pleskov, “Diamond Growth in the Presence of Boron and Sulfur,” Diamond and Related Materials 12, 1627-1632 (2003). Alfred B. Anderson, Lubomir N. Kostadinov and John C. Angus, "Hydrogen Atom Pairs in Diamond Bulk and a the Surface: Hybrid Density Functional Theory and Cluster Models," Phys. Rev. B. 67, 233402 (2003) Tiberiu Fulop, Challa Bekele, Uziel Landau, John C. Angus and Kathleeen Kash, "Electrodeposition of Polycrystalline InSb from Aqueous Electrolytes," Thin Solid Films 449, 1-5 (2004). John C. Angus, Yuri V. Pleskov and Sally C. Eaton, "Electrochemistry of Diamond," Chapter in “Thin Film Diamond II,” J. Ristein and C. Nebel, Editors, pp. 545-567, Elsevier, Academic Press, Amsterdam, 2004. Heidi B. Martin, Sally C. Eaton, Uziel Landau and John C. Angus, "Electrochemical Effects on Diamond Surfaces: Wide Potential Window, Reactivity, Spectroscopy, Doping Levels and Surface Conductivity," pp. 26-50, Diamond Electrochemistry, Akira Fujishima et al., Editors, Elsevier/BKS Inc., Tokyo, 2005. Vidhya Chakrapani, Sally C. Eaton, Alfred B. Anderson, Massood Tabib-Azar, John C. Angus, “Studies of the Adsorbate-Induced Conductance of Diamond Surfaces,” Electrochem. and Solid State Lett. 8, E4-E8 (2005). Vidhya Chakrapani, John C. Angus, Alfred B. Anderson and Gamini Sumanasekera, “Electrochemical Charge Transfer to Diamond,” Mat. Res. Soc. Symp. Proc. 956, paper J15-01 (2007). Yu Cai, Tianhou Zhang, Alfred B. Anderson, John C. Angus, Lubomir N. Kostadinov and Titus V. Albu, “The Origin of Shallow n-type Conductivity in Boron-Doped Diamond with H or S Co-Doping: Density Functional Theory Study,” Diamond and Related Materials 15, 1868-77 (2007) Yu Cai, Alfred B. Anderson, John C. Angus, Lubomir N. Kostadinov, "Hydrogen Evolution on Diamond Electrodes by the Volmer-Heyrovsky Mechanism: Prediction of Reversible Potentials and Activation Energies," Journal of the Electrochemical Society 154, F30-F43 (2007) Vidhya Chakrapani, John C. Angus, Alfred B. Anderson, Scott D. Wolter, Brian R. Stoner and Gamini U. Sumanasekera, “Charge Transfer Equilibria Between Diamond and an Aqueous Oxygen Electrochemical Redox Couple,” Science 318, 1424-1430 (2007) Vidhya Chakrapani, Chandrasekhar Pendyala, Kathleen Kash, Alfred B. Anderson, Mahendra K. Sunkara, John C. Angus, “Electrochemical Pinning of the Fermi Level: Mediation of Photoluminescence from GaN and ZnO,” J. Am. Chem. Soc. 130, 12944-12952 (2008). |
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Since adsorbed water films are common on solids exposed to humid air, electrochemically induced charge transfer may appear in many other materials and processes. The figure shows the relationship of the energies of the electrochemical couple to the energy band structure of several common semiconductors.