A research team with members from the University, Pennsylvania State University and Rice University has developed single-molecule switches that could someday be used in electronics.
“If we think about the ultimate miniaturization of electronics, a single molecule as a switch is just about as small as it gets,” University chemistry professor Jim Hutchison said.
And small it is.
University graduate student Christina Inman said the number of these molecules that can fit across a human hair is equivalent to the number of human hairs that can fit across a football field.
The existence of molecules that can reverse charge from positive to negative has been recognized for some time. The innovation of this particular study, Hutchison said, is that the switches can now be controlled by humans and reliably remain on or off when turned on or off.
The molecules are specially engineered to have the necessary properties to work in the system. Inman said the double and triple bonds between the carbon atoms make the molecules rigid and highly conductive electrically.
A key component of the switch system is a scanning tunneling microscope, which functions as the “nanofinger that switches (the molecules) on and off,” Hutchison said.
The tip of the switch molecule is always positively charged. The tip of the scanning tunneling microscope can have either a positive or a negative charge, and modulating this charge is what turns the switch on and off. Because opposite charges attract and similar charges repel, when the scanning tunneling microscope has a negative charge, the tip of the switch molecule will be pulled toward it and the switch will turn on, Hutchison said.
When the tip of the scanning tunneling microscope has a positive charge, the switch molecule falls away from it into the matrix molecules nearby. This is the switch’s off position, and it is held in this position by hydrogen bonding between the switch molecule and the matrix molecules.
Paul Weiss, a professor of chemistry and physics at Penn State, said the researchers tried turning the molecule upside down to put the negatively charged end at the top but found that this did not produce similar results because the position of certain important parts of the molecule cannot be changed.
Each school involved in the research contributed to a specific aspect of the project.
Rice University worked on molecular electronic functions in the switches, the University worked on the matrix molecules, and Penn State worked on improving the switch molecules, Weiss said.
Weiss said the University and Penn State began collaborating on projects related to these issues in 2001, when his graduate student Rachel Smith, who graduated from the University’s Robert D. Clark Honors College in 1999 and wrote her honors thesis in Hutchison’s lab, visited Eugene to see old friends.
“She came back with the molecules in her pocket, basically,” Weiss said.
Hutchison said it is too early to predict exactly how the recent study’s findings, which will be published in the December issue of the Journal of the American Chemical Society, will be used.
Inman, who will earn her doctorate in chemistry at the end of this term, said a possible application of single-molecule switches could be computer memory cards. Computers encode information in a language made of zeroes and ones, two commands that could also be interpreted as on and off. The scanning tunneling microscope could encode information onto the memory chip by turning switches on and off in designated patterns and then read the information later.

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