Quantum Dots Used to 'Draw' Circuits for Molecular Computers

By using tiny quantum dots to create trails of altered molecules, UCLA researchers are developing a method of producing nanoscale circuitry for the molecular computers of the future that will use molecular switches in place of transistors.
“This technology, although still in the unpublished, proof-of-concept stage, could eventually lead to a relatively inexpensive means of patterning interconnections between the logic gates of a molecular computer,” according to Harold G. Monbouquette, professor of chemical engineering at UCLA’s Henry Samueli School of Engineering and Applied Science, who leads the team.From UCLA:Quantum Dots Used to ‘Draw’ Circuits for Molecular Computers

Date: March 28, 2003
Contact: David Brown ( dbrown@ea.ucla.edu )
Phone: 310-206-0540

By using tiny quantum dots to create trails of altered molecules, UCLA researchers are developing a method of producing nanoscale circuitry for the molecular computers of the future that will use molecular switches in place of transistors.

“This technology, although still in the unpublished, proof-of-concept stage, could eventually lead to a relatively inexpensive means of patterning interconnections between the logic gates of a molecular computer,” according to Harold G. Monbouquette, professor of chemical engineering at UCLA’s Henry Samueli School of Engineering and Applied Science, who leads the team.

The method represents a drastic departure from the current lithographic method of creating interconnecting lines on silicon chips.

Instead, Monbouquette said, his goal is to develop a means to make patterns on a surface “on the order of a nanometer or two and these quantum dots serve as the pens to do it.”

Quantum dots, nanoparticles of semiconductor material, were selected because of their photocatalytic properties. By moving them around using an electrical force and simultaneously shining light on the surface, a “trail” of molecules will be left behind. These trails could eventually serve as interconnections for nanoscale circuitry, Monbouquette said.

Monbouquette and UCLA chemistry professor Miguel Garcia-Garibay, an organic chemist who focuses on photochemistry, are also breaking new ground with a potential method to create circuitry that relies primarily on organic chemistry. The process creates a chemical reaction on the surface, but only where the photocatalyst is present. Garcia-Garibay is co-principal investigator on the project.

“In the presence of a photocatalyst, the quantum dots and blue light, you can convert the substance on the surface to something else,” Monbouquette said. “If you shine blue light on the surface in the absence of a photocatalyst, nothing happens, or very little happens. In the presence of a photocatalyst, the reaction actually takes place at an appreciable rate.”

By using more quantum dots, multiple patterns can be created simultaneously.

“The idea is we put a large number of these particles on a surface. We shine light on the surface and move the particles in a pre-programmed way under the influence of an electric field that moves each particle roughly the same way. Wherever the particles go, the underlying surface gets converted thereby generating a repetitive pattern written.”

In order to create actual circuitry, the researchers will have to make the “trails” capable of conducting electricity. Monbouquette said they “have ideas about how to do that. But for now, we want to show we can do patterning on the surface.”

The goal of this research is to demonstrate that complex patterns can be created on a surface with a feature size of only a few nanometers.

“Right now the state of the art in microelectronics is around 100 nanometers. So if we want to use the molecular transistors that you hear about, we need to be able to pattern surfaces with a feature size corresponding to molecular dimensions,” Monbouquette said.

Not only could the process be carried out in relatively inexpensive production facilities, Monbouquette said, it could also lead to ways of creating new materials.

“At first we called this ‘molecular Etch A Sketch,'” like the toy used to draw designs on a screen covered with powdered aluminum by moving a stylus horizontally and vertically, Monbouquette said.

“But it’s better than Etch A Sketch because not only can you have as many pens as you want by putting down more quantum dots, but you can also have a ‘pen-up.’ One of the most annoying things about Etch A Sketch is that you can’t lift the pen. It’s impossible to get from one point to another without drawing a line.”

So how does he execute a “pen-up”?

“You just turn the light off and keep the quantum dot moving,” Monbouquette said. “While the light’s off, it’s not going to catalyze the reaction. So you can get it from one spot on the surface to another.”

Because this is an electron transfer reaction, the quantum dot cannot continually give up an electron for the desired reaction unless it can get an electron from some other place. So at the same time the quantum dot is catalyzing the reaction, it also picks up an electron from sacrificial compounds in solution.

Nano-patterned organic surfaces may also provide structures for creating molecular devices that mimic biological systems such as those for photo energy transduction, vision, sensing and complex-molecule synthesis, Monbouquette said.

The research is funded by the Office of Naval Research.

-UCLA-

DB114



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