NER: Deposition of Molecular Nanostructures with Controlled in-plane Orientation

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This project was received in response to Nanoscale Science and Engineering initiative, NSF 01-157, category NER. Nanoscale materials are now fabricated by a variety of means, but the dominant methods rely on self-assembly or advanced lithography. These and other fabrication schemes, especially self-assembly, can create structures in which the molecular orientation perpendicular to the surface is controlled by the chemistry, conferring the functionality. This project will take control of orientation one step further - so that the molecules can also be locally oriented in the plane of the surface. Variations of the orientation on a 100 nm length scale permits nanoscale functionality based on the relative orientation of molecules to be obtained. This is a powerful concept for high performance molecular devices, since the properties of molecules are highly anisotropic. The 'nanopoling' scheme should be much more effective at orienting molecules than current poling methods due to the larger electric field that can be generated locally. The central task of this project is to demonstrate the attachment of oriented molecules to a surface. Major tasks will be the identification of the best method for each of a few classes of molecules (conjugated polymers, porphyrins, DNA), to model the orientation and attachment processes, and to study the dependence of these processes on field strength and electrode geometry. The latter will require the facile scanning probe microscope. Topography and orientation of the molecules is characterized with polarization-sensitive near-field optical microscopy (NSOM) utilizing the same probe as deposited the oriented molecules, and the electrical properties are obtained via lithographically-defined contacts. The novelty and importance of this project evolves from the breaking of the in-plane symmetry within the nanostructures. It will result in new types of nanostructures with novel properties and functionality. This will lead to new devices. In this project we will focus on the science of the growth process with a scanning probe microscope. Ultimate usage for fabrication of the novel devices engendered by this deposition technique will require much faster fabrication methods. The prospects for large-scale fabrication once the processes are understood are good, and we have defined a possible route to a mask-based technology resulting from these studies.