By Steve Sampsell
Eberly College of Science
Scientists have discovered an effective and precise way to make ultraminiature metal wires in very close proximity to each other. Their work -- important because nanoscale construction methods have been limited to structures with larger, less controlled spacings -- is expected to be useful in the effort to further miniaturize electronic and opto-electronic devices used for circuits, high-density data storage and sensors.
The results describe the use of organic molecules as "molecular rulers" that permit the fabrication of useful wires dozens of times smaller than the period at the end of this sentence. The scientists measure their results in nanometers, equal to one billionth of a meter, and micrometers, equal to one millionth of a meter. They have proven they can make extremely thin wires from 15 to 70 nanometers wide and a few micrometers long that are spaced 10 to 40 nanometers apart.
Paul Weiss, associate professor of chemistry, and Amat Hatzor, a post-doctoral fellow, co-authored a paper describing the project.
The "molecular ruler" construction process requires some existing nanoscale structures to "grow" in order to produce the even smaller structures. The scientists started with two parallel gold nanostructures on a silicate substrate. Those structures were formed by electron-beam lithography, one of several widely used nanoscale construction techniques. Layers of organic molecules then were applied atop the initial structures to make them bigger and wider, at the same time reducing the gap between the structures.
Imagine two cookies rising beside each other while baking, with the space between the cookies getting smaller as they cook, and you get a sense of how each of the initial structures grows by the addition of organic molecules and how the space between the structures gets narrower.
Because the scientists knew the size and spacing of the initial structures and the thickness of the layers of films created by the molecules atop the structures, they could calculate the size of the narrowing space between the structures. As a result, the organic molecules, which selectively bind to each other and to the substrate materials, provide "molecular rulers" that precisely determine the size of the resulting space between the initial structures. Scientists use the resulting space for forming even smaller wires by filling the space with gold.