Fabrication and Characterization of Electrical Contacts for Charge Transport Study in Molecular Electronics.

Abstract

Nanoscale imprint lithography (NIL) is investigated in the view point of the ability to form nanoscale feature. NIL at room temperature is proposed and demonstrated on thermoplastic substrate that has a restriction of heating. Anisotropic oxygen-based plasma etch performance is evaluated to remove the residual resist at the bottom of impressed pattern and to achieve the thinner patterns with various etching molecules. The patterning fidelity in nano-imprint lithography including the ability of polymer deformation is studied, and based on the results a mechanism for the polymeric behavior of imprinted resist is discussed.

A procedure using geometrical shadowing in common metal-evaporation tools to form nanoscale metal electrodes with controlled width-to-pitch ratios is demonstrated and characterized for feature sizes near 50 nm. Successive formation of metallic bridge with the metallic nanoparticle for the conductance study and the electrical characterization are described. From the results of electrical conduction, we estimate the contact area (~20.1 nm2) and the number of molecules between nanoparticle and surface-bound molecules, and then calculate the resistances of single molecules, contact resistance, the tunneling probabilities in contacts. The electrical characterization of the conjugated molecules has been accomplished using the same nanoscale test-bed in terms of surface bound head groups.

As a new approach for the interconnecting elementary molecular devices, Au nanoparticle dimer bridged by conjugated molecule is assembled on the nanoscale electrode gap. Oligo Phenylacetylene-bridged gold nanoparticle dimer was prepared for the demonstration. Resistance measured at low bias regime is 2.2 ± 0.64 GΩ at room temperature, which is comparable with the single molecule conduction. The selective adsorption of SAM on Au plates by means of electron supply is proposed to develop the pliable manipulation of self-assembling molecular elementary devices. The method is applied to the two metal patterns, which is an electrical test-bed for the molecular resistors. The electrical characterization is in good agreement with the selective formation of molecular layer on metal.