My research interests involve investigating and correlating the morphological and electrical properties of promising organic s

Research Statement by Serkan Zorba

My research interests involve investigating and correlating the morphological and electrical properties of promising organic semiconductors= such as pentacene, perylene, CuPc, sexithiophenes, Alq, TPD etc., at nanoscale.<= o:p>

Organic semiconductor materials have been shown to be very favorable in optoelectronic devices due to their low-cost, mechanical flexibility, lower power consumption, and large-area applications. These no= vel materials are already being used as the active elements in various commerci= ally available devices such as displays in car stereos, cell phones, and digital cameras. However, applications for organic transistors are not yet as immediate, which is not very good because the realization of organic-field effect transistors (OFETs) is a necessary requirement for the promising all-plastic electronics. OFETs with conventional structure have still low-mobility, and relatively high operational voltages. The culprits for su= ch lousy device performances are their morphology and device structure.

It is, therefore, plausible and necessary to try to improve bot= h of these factors if one wants to utilize full potential of organic semiconduct= or materials and have practical device applications. I believe that we have to understand the mechanisms behind the morphology of such materials if we hope to improve their charge transport properties, and hence have practical applications.

To this end, I investigated, as part of my Ph.D. research, the morphology of pentacene and perylene using kinetic roughening theory and computer simulations. My results reveal the mechanisms behind their peculiar morphology that is responsible for the relatively high charge carrier mobilities in these substances, and may point to possible ways of controlli= ng the morphology in favor of electrical properties.

As an undergraduate, I did my internship in the area of critical phenomena, which involved the theoretical study of phase transitions using stochastic methods via computer simulations. I still employ computer simulations and numerical analysis in my study of the morphology of organic semiconductors.

In order to study the correlation between electrical and morphological properties of promising organic materials at nanoscale, I have fabricated nanoscale gold electrodes at Cornell NanoScale Science&Technology Facility (CNF) (a class 1000 clean-room facility) us= ing electron beam lithography.

I did study the current-voltage characteristics of pentacene us= ing conductive probe atomic force microscopy (CAFM). It turned out that the transport in pentacene occurs, at relatively high voltages, via hoping of charge carriers as evidenced by the square-root dependence of log current o= n electric field.

I have also pursued the path of modifying the FET device struct= ure in hopes of getting better performing transistors. I realized that goal by switching from metal-insulator-semiconductor (MIS) structure to static induction transistor (SIT) geometry, and obtained very promising figures. T= he resulting promising characteristics are mainly due to the very short channel length between the source, drain, and gate electrodes in SIT structure. I u= sed pentacene, perylene, Alq, and TPD as the active elements in our SITs. I was able to get successful transistor operation with Alq and TPD. Pentacene and perylene failed to produce any successful operation. The failure of these promising materials was because of a short circuit that arose due to the pi= nhole like structures in the thin films. This further demonstrates the significan= ce of understanding and controlling the morphology of organic semiconductor th= in films to fully realize and utilize the potential of such promising material= s.

The Defense Advanced Research Projects Agency (DARPA) and the National Science Foundation (NSF) are some of the potential funding agencies for such a research. Hi-tech companies such as Lucent Technologies, Bell Laboratories (now under Lucent), Kodak, IBM, Xerox, Motorola, Pioneer, Universal Display Corporation are already investing billions of dollars into such research projects with some commercial products already in the market.=

I have involved in research with the undergraduates and supervi= sed them as part of Research Experience for Undergraduates (REU) program. Some = of the projects in which I supervised REU students are DNA-stretching with AC electric fields, customizing scanning probe microscopy software, and various atomic force microscopy applications.

My future research goals center around further exploration of morphology-transport relationship, and improving the mobility of organic materials and device performance. I would like to employ both experimental = and simulation techniques in this exploration. I want to keep my research close= to the application-oriented side such as making better organic transistors or organic light emitting diodes or organic lasers. I would also like to tackle the morphology problem from theoretical perspective such as renormalization group approach and scaling theory. In some of the surfaces we studied, a nontrivial interplay between fractal growth, diffusion, and mound growth revealed peculiar behaviors such as that of pentacene, which is one of the = most promising small organic semiconductor materials. Due to the close relations= hip between the latter subjects and chaos and non-linear physics, I would like = to become also involved in the area of non-linear science, which I deem as a v= ery promising field. Involvement of undergraduate students in all these research undertakings, be it experimental and/or theoretical, is going to be a significant part in all my projects.

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