Molecules are the smallest possible switching elements for future electronic devices. However, fabrication and wiring of these molecules, the so-called molecular junctions [1, 2], remains challenging. In fact, most molecular electronic properties were demonstrated based on scanning tunneling microscopy (STM). Although the fundamental chemical and electronic properties of these molecules can be conveniently demonstrated by using STM, these properties may be altered by integration of these molecules into devices. Molecular devices reported thus far can be classified into two main categories. The first is based on individual junctions, which is excellent for the study of molecule properties, but does not compatible with formation into arrays of junctions [2, 3]. In contrast, the second category is based on arrays of junctions, but these are extremely difficult or complicated to assemble and not reproducible by others [4].

Here we demonstrate a simple fabrication scheme for arrays of molecular junctions by using carbon nanotubes (CNTs) as the electrodes. Our scheme uses commonly available techniques that are readily reproducible by others. We shown that the electronic properties of our devices are identical to those measured by our STM, signifying that our fabrication scheme maintains the chemical and electronic properties of the molecules. Arrays of gold electrodes are first deposited on oxidized Si substrates. Self-assembled monolayers (SAMs) of organothiol SAM octadecanethiol (ODT) molecules are then deposited on these electrodes. Multiwalled CNTs (MWCNTs) grown by chemical vapor deposition [5, 6] were then dispersed in ethanol and deposited on these SAM by our surfactant-free dielectrophoresis (DEP) [7]. Array of well dispersed MWCNTs are successfully deposited by AC potential of 3-30V and 2kHz-2MHz, well below the critical frequency predicted by the Clausius–Mossotti factor. Current-voltage (I-V) measurements show that MWCNTs are capable of forming stable contact with ODT without destructing the molecules. We found that I-V characters of our devices are very reproducible within the bias range of ±5V, with a well-defined “off” state at ±2V [8]. This means, these devices are reliable within the indentified operation range, beyond which degradation of devices are detected. Our results suggest that the demonstrated scheme can be extended to all carbon molecular electronics.

Y. K. Yap acknowledges supports from the Defense Advanced Research Projects Agency (DARPA, Contract No.: DAAD17-03-C-0115, through Army Research Laboratory).

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