Prof. A. Subrahmanyam
Prof. A. Subrahmanyam
Indian Institute of Technology Madras, India
Title: Surface Work function measurements by Non-contact and Non-destructive Kelvin Probe technique: A Review
The solid surfaces have unique surface properties. Measurement of the work function of a surface is an important tool of surface characterization. Surface work function is a fundamental electronic property; it provides an understanding of the relative position of the surface Fermi level. For example, corrosion of metal surfaces (including bio-corrosion) can be studied by non-contact and non-destructive methods of measuring surface work function. Any charge insertion or removal, changes the surface work function, as in the case of electro-chromic materials. The electrical properties of modified surface form the basis of sensors working on surface electrical resistance. Presently, the surface modification and tuning of the work function is a requirement for several organic and inorganic semiconductor devices and metal surfaces. Surface modification can be achieved with chemical and physical methods; each method has its own charge transfer process at the surface dipole layer. The surface of even the degenerate semiconductors like tin doped indium oxide (ITO) thin films can be modified. Among the several techniques to measure the surface work function, Kelvin probe has the advantage of keeping the surface virgin even after the measurement because it is a non- contact and non-destructive technique. Kelvin probe technique gives the work function of a surface relative to a reference electrode. The Kelvin probe technique differs from the Kelvin Probe Force Microscopy (KPFM) though both the measurements give the surface work function. Present talk summarizes the basic principles of Kelvin probe technique and presents the status of surface work function measurements on several metals and semiconductor modified surfaces.
He has been awarded an Young Scientists Fellowship (BOYSCAST) by the Department of Science and Technology, Government of India in 1988; Humboldt Fellowship in 1989, Saint Gobain Chair in 2009 and DAAD Professor in TU Dresden in 2009-2010. Has established a laboratory for metal oxide thin films and surface engineering. Over the past ten years, his research efforts are on bio-medical engineering: development of Lung Assist devices (using the principles of photocatalysis) and on early warning systems in mechanical heart valve failures (executed an Indo – European project on mechanical heart valves). Has designed and developed Kelvin probe equipment for surface engineering and authored the first book. Presently he is expending efforts to commercialize the Kelvin probe machine for non-destructive surface analyses. Has six patents. His teaching experience spans over 35 years. He has guided 20 Doctoral Theses, published over 170 papers in International peer reviewed journals and executed 42 sponsored Research projects funded both from the Government of India and various Multinational companies. He is the Editor for Solar Energy materials and Solar Cells, an Elsevier Journal. His present effort are on (i) Copper Zinc Tin Sulfide (CZTS) solar cells by Reactive Dc magnetron sputtering, (ii) high efficiency electrochromic devices based on Tungsten oxide thin films and (iii) mixed metal oxide by sol gel technique to develop corrosion barrier coatings.