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Investigation of Nanoelectrodes by Transmission Electron Microscopy M.S. Kabir1, S.H. Magnus Persson1, Yimin Yao2 , Jean Phillippe Bourgoin3, Serge Palacin3 1 Dept. of Micro Electronics and Nanoscience, Chalmers University of Technology, Gothenburg, Sweden. 2 Dept. of Microscopy and Microanalysis, Chalmers University of Technology, Gothenburg, Sweden. 3 Service de Chimie Mole:culaire, CEA Saclay, Centre d’Etudes de Saclay Bat 125, 91191 Gif sur Yvette, France Abstract Electrodes for making connections to single molecules and clusters must have separations smaller than 10 nm. They are therefore difficult or impossible to image with atomic force microscopes (AFM) or Scanning Electron Microscopes (SEM). We have fabricated nanoelelectrodes by different methods to contacts nanoclusters and conjugated molecules and investigated their properties in transmission electron microscope (TEM) and their electrical characteristics at room temperature and at 4.2K. The electrodes are made on SiN4 membranes, which is transparent to high energy electrons and which make it possible to image features of a few nanometers in TEM. Introduction The relentless downscaling of field effect transistors (FETs) is now reaching to an end. This is mainly due to the physical limitations, for example, unacceptable tunneling and leakage current through the different parts of the device [1]. This calls for investigating other alternatives, such as molecular electronic devices [2]. However, the fundamental properties of different kinds of molecules must be understood before single-molecule electronics can be realized. Function of this kind of devices is governed by the single molecule or molecules that is positioned between the electrodes. There are many fundamental challenges that are to be solved to study electrical properties of single molecules. One of the major problems that we are dealing with is the fabrication of electrodes with nanometer separation (1-5nm) to probe single molecules and to characterize them. In this paper we discuss two methods of fabricating electrodes with nanometer separation (1-5nm). We also have studied the electronic properties of alkanethiol terminated gold clusters and 2,5”-bis(acetylthio)-5.2’5’.2”-terthienyl (T3) which is a member of oligothienyl family. Molecules like T3 are interesting to study due to the conjugated π-orbitals, which mainly open the channels for conduction of electrons. Therefore oligomers with conjugated π-orbitals are expected to have higher conductivity than σ-type molecular orbitals like alkanethiol.

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2. Experimental Details 2.1 Electrodes fabrication: We had two different approaches to fabricate the electrodes with few nanometers separation. As a first choice we used angle evaporation method. Fig.1 shows the process sequence of this method. In this method, a thermally grown oxidized (200nm) Si wafer PMMA

Co-Polymer

SiO2 wafer

Spin coat e-beam

e-beam exposure

Development

1-5nm gap Metal evaporation

lift off

Fig:1 Schematic diagram of the process sequence of angle evaporation is s