Graduate student Kent Hallman checks the sample alignment in the vapor deposition machine in Vanderbilt Institute for Nanoscale Science and Engineering's clean room. (Credit: Joe Howell/Vanderbilt)

This optical switch is super small and crazy fast

A new optical switch can turn on and off trillions of times a second—and it’s remarkably small.

The device consists of individual switches that are only one five-hundredth the width of a human hair (200 nanometers) in diameter. This size is much smaller than the current generation of optical switches and it easily breaks one of the major technical barriers to the spread of electronic devices that detect and control light: miniaturizing the size of ultrafast optical switches.

Graduate student Christina McGahan holds a disk on which centimeter square samples are grown. (Credit: Joe Howell/Vanderbilt)
Graduate student Christina McGahan holds a disk on which centimeter square samples are grown. (Credit: Joe Howell/Vanderbilt)

The ultrafast switch is made out of an artificial material engineered to have properties that are not found in nature. In this case, the “metamaterial” consists of nanoscale particles of vanadium dioxide (VO2)—a crystalline solid that can rapidly switch back and forth between an opaque, metallic phase and a transparent, semiconducting phase—which are deposited on a glass substrate and coated with a “nanomesh” of tiny gold nanoparticles.

The scientists report in the journal Nano Letters that bathing these gilded nanoparticles with brief pulses from an ultrafast laser generates hot electrons in the gold nanomesh that jump into the vanadium dioxide and cause it to undergo its phase change in a few trillionths of a second.

“We had previously triggered this transition in vanadium dioxide nanoparticles directly with lasers and we wanted to see if we could do it with electrons as well,” says Richard Haglund, a physics professor at Vanderbilt University, who led the study. “Not only does it work, but the injection of hot electrons from the gold nanoparticles also triggers the transformation with one fifth to one tenth as much energy input required by shining the laser directly on the bare VO2.”

Both industry and government are investing heavily in efforts to integrate optics and electronics, because it is generally considered to be the next step in the evolution of information and communications technology.

Intel, Hewlett-Packard, and IBM have been building chips with increasing optical functionality for the last five years that operate at gigahertz speeds, one thousandth that of the VO2 switch.

Left: Illustration of terahertz optical switches shows the vanadium dioxide nanoparticles coated with a "nanomesh" of smaller gold particles. Right: Scanning electron microscope image of the switches at two resolutions. (Credit: Haglund Lab/Vanderbilt)
Left: Illustration of terahertz optical switches shows the vanadium dioxide nanoparticles coated with a “nanomesh” of smaller gold particles. Right: Scanning electron microscope image of the switches at two resolutions. (Credit: Haglund Lab/Vanderbilt)

“Vanadium dioxide switches have a number of characteristics that make them ideal for optoelectronics applications,” says Haglund. In addition to their fast speed and small size, they:

  • Are completely compatible with current integrated circuit technology, both silicon-based chips and the new “high-K dielectric” materials that the semiconductor industry is developing to continue the miniaturization process that has been a major aspect of microelectronics technology development.
  • Operate in the visible and near-infrared region of the spectrum that is optimal for telecommunications applications.
  • Generate an amount of heat per operation that is low enough so that the switches can be packed tightly enough to make practical devices: about ten trillionths of a calorie (100 femtojoules) per bit.

“Vanadium dioxide’s amazing properties have been known for more than half a century. . . . It is only in the last few years that intensive computational studies have illuminated the physics that underlies its semiconductor-to-metal transition,” says Haglund.

Scientists from the University of Alabama-Birmingham and Los Alamos National Laboratory worked on the project. Grants from the Defense Threat-Reduction Agency, US Department of Energy, US Department of Education, and the National Science Foundation helped support the research.

Source: Vanderbilt University

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