Organic molecules as charge carriers play a key role in the developing field of “plastic electronics”. Note that flow processing has recently [1] been suggested as a means of orienting and placing such molecules to create bridges between electrodes – i.e. creating molecular wires. We wish to develop a simple, repeatable process to create such wires using DNA as a scaffold. We are developing this process by using dip-pen nanolithography (DPN) to first control the placement of mercaptohexanoic acid on gold electrodes. We then functionalize the acid with N-hydroxy-succinimide, thus creating amine linkages to tether a 3µm NH2-DNA-conducting organic molecule-DNA-H2N (DOD) sandwich between two gold electrodes. The DNA segments in the bridge are subsequently metallized, creating conducting wires separated by an organic single molecule. Thus the key processing step is tethering one end of the DOD chain to an electrode and exposing it to shear flow to stretch the chain and create contact between the free end and a second electrode. The free end is subsequently tethered via an additional chemical functionalization.

In this talk, we will first demonstrate experiments which show the first steps in this process, i.e. end tethering of the DNA using the DPN process, followed by shear stretching. Subsequently, the dynamics of the molecule in flow are examined through simulations and experiments in the flow-gradient plane. Using Brownian Dynamic simulations, we have developed a statistical description of the contact of a wall-tethered polymer's free end with the wall. For example, based on simulation results for the probability distribution of contact distance in the flow direction, 90% extension with a 2.3% standard deviation of a 22 Kuhn step (3µm) Kratky-Porod chain is obtained for Wi=88. We demonstrate that the extension deficit and its standard deviation upon wall contact scales with Wi-1/3 for Wi >> 1, which corresponds to results obtained by Ladoux et al. [2], and the contact frequency scales as Wi2/3. For Wi<10, there exists a regime of cyclic dynamics where the chain end will stretch, approach the wall, and recoil with a characteristic frequency as shown by the power spectral density of the polymer orientation angle, supporting previous results obtained for tethered polymers by Schroeder et al [3]. Ultimately, our results will afford precise control over the creation of the DOD bridges.

REF:

1) E. Braun, Y. Eichen, U. Sivan, G. Ben-Yoseph, Nature. 391, 775 (1998)

2) B. Ladoux and P.S. Doyle, Europhys. Lett. 52, 511 (2000)

3) C.M. Schroeder, R.E. Teixeira, E.S.G. Shaqfeh, S. Chu, Phys. Rev. Lett. 95, 018301 (2005)