Molecular Electronics : A Review of Experimental Results

Abstract

Molecular electronics aims for scaling down electronics to its ultimate limits by choosing single molecules as the building blocks of active devices. The advantages of this approach are the high reproducibility of molecular synthesis on the nanometer scale, the ability of molecules to form large structures by self-assembly, and the huge versatility of molecular complexes. On the other hand, conventional contacting techniques cannot form contacts on the single molecule scale and imaging techniques nowadays cannot provide a detailed image of such junctions. Therefore, the fabrication has to rely to some degree on self-organization of the constituents. The proof that a molecule has been contacted successfully can only be given by indirect methods, for example by measuring the current transport through the junctions. Here we give an overview of various techniques that were used successfully to contact molecules and to characterize them electrically. The techniques range from methods to contact single molecules to such which can be used to characterize ensembles of molecules. Especially, the comparison between such different techniques shows that a single measurement is always prone to artefacts originating from the unknown microscopic details of the junctions. It is therefore necessary to perform a statistically relevant number of measurements in order to resolve molecular properties. Various properties of the molecules can be studied. Special examples are the influence of conformational changes of the molecules, differences between various coupling endgroups of the molecules and effects of light-irradiation onto the molecular junctions.