Photonic crystals in biology - NanoTR-VI

PP andPoster Session, Thursday, June 17Theme F686 - N1123Photon Scanning Tunneling Microscopy System for Observing Optical Excitations at NanoscaleTunnel Junctions111Tansu ErsoyP P, Mehmet Selman TamerPUOuzhan GürlüUP P*1Pstanbul Technical University, Department of Physics, Maslak, 34469, stanbul, TurkeyAbstract-We are developing an optical system which is capable of collecting the photons emitted from the tunnel junction of a scanningtunneling microscope. These systems allow mapping the photon emission from a surface with sub nanometer spatial resolution. Electronic andoptical properties of nanostructures like quantum dots or quantum wires will be studied by this system.Images with atomic resolution of semiconductor and metalsurfaces can be obtained using scanning tunneling microscopy(STM) [1]. Moreover optical and electronic properties of thesesurfaces can be examined by STM at nanoscale [2]. Thetunneling current between the tip and the surface can exciteoptical transitions on the surface [3]. This is calledelectroluminescence due to inelastic tunneling. STM-lightemission experiment is a recently emerging and very usefultechnique for investigating optical properties of surfaces withnanometer resolution [4].Nanostructures have different characteristics from bulkmaterials. As the size of the materials approach to nanoscale,quantum effects appear, which is very important for deviceapplications [5]. If a semiconductor crystal becomes verysmall, motion of the charge carriers is restricted. Thisphenomenon is known as quantum confinement. This resultsin sharp electronic states in these structures. In order tounderstand quantum effects there are numerous studies fordeveloping nanostructures and methods for investigating theirelectronic and optical properties [4,5,6].Metals also behave unconventionally physical properties atnano scale. For instance Ag films coated on glass or mica hasa rough structure due to which the surface plasmon polaritonsare confined. These effects the optical properties of the filmsgreatly like giving the film unexpected color. Using thephoton scanning microscope one can study the local electroopticalproperties [7] of these films and their interaction withadsorbates.most efficient way [10] and they have to be spectroscopically.analyzed. Thus, electroluminescence spectroscopy atnanoscale can be performed.Figure 2. In inelastic tunneling, electrons that tunnel from the tip tothe surface lose some of their energy. Photons are generated in thisprocess. Energy lost due to excitations can be observed byconductivity measurements. They appear as peaks in the secondderivative of the tunneling current with respect to sample bias [9].Figure 3. A simple representation of photon STM setup.First we are planning to investigate optical properties ofmetal surfaces like vacuum evaporated rough Au or Ag filmson glass. Later on we will investigate core/shell quantum dotslike CdSe/ZnS. Optical behavior of QDs on gold surfaces willbe observed by STM induced light emission technique.Depending on structures and positions of QDs on gold surfacewe are expecting variations in their optical behaviors.Moreover, we will investigate the results of the interactions ofQDs with various surfaces and with their environments.*Corresponding author: HTgurlu@itu.edu.trTHFigure.1. (a) STM image of sputter coated Ag film on glass.(500 nm x 500 nm at Vs = 2.0 V and I = 5.0 nA.). (b) Photonmap of the surface due to inelastic tunneling [7].In this work, we are designing a setup which is suitable forSTM light emission experiments. When inelastic electrontunneling occurs at nanoscale tunnel junctions, photonemission is possible [8] (Figure.2). Our aim is to develop theexperimental setup which will allow investigating the systemsthat cause photon emission from these tunnel junctions.The main problem in these experiments is low photonefficiency in most of the physical systems to be investigated.Therefore the generated photons have to be collected in the[1] G. Binning, H. Rohrer, Ch. Gerber and E. Weibel, Phys. Rev.Lett. 50, p 120 (1983).[2] R. Berndt, R. Gaisch and W. D. Schneider, Phys. Rev. Lett. 74,102 (1995).[3] M,J. Romero, et al., Nanoletters 6, 2833 (2006).[4] T. Tsuruoka, Y. Ohizumi and S. Ushioda, App. Phys. Lett. 82,3257 (2003).[5] L. Turyanska, et al., App. Phys. Lett. 89, 092106, (2006)[6] R. Cingolani and R. Rinaldi, Phys. Stat. Sol. 234, 411 (2002).[7] T. Arai, K. Nakayama, Applied Surface Science 246, 193 (2005)[8] D. Fujita, K. Onishi, and N. Niori, Nanotechnology 15, 355(2004).[9] http://www.fkf.mpg.de/kern/research/nanooptics/pstm.1.html[10] N. J. Watkins, J. P. Long, Z. H. Kafafi, and A. J. Makinen, Rev.Sci. Inst. 78, 053707 (2007).6th Nanoscience and Nanotechnology Conference, zmir, 2010 623