Nanoparticle Tuning for New Optomechanical Applications

Placing nanodisks in groups can change their vibrational frequencies

Like a tuning fork struck with a mallet, gold nanodisks on a glass surface can be made to vibrate at resonant frequencies with a pulse of laser light. Rice University researchers found that acoustic vibrations from larger particles modified the resonant frequencies of smaller particles nearby.

December 4, 2017 | Source: Rice University, news.rice.edu, 16 Oct 2017, Jade Boyd

Like a tuning fork struck with a mallet, tiny gold nanodisks can be made to vibrate at resonant frequencies when struck by light. In new research, Rice University researchers showed they can selectively alter those vibrational frequencies by gathering different-sized nanodisks into groups.

Researchers tested more than a dozen sample groupings of nanodisks using electron beam lithography. Each group of tiny gold disks sat atop a flat surface called a substrate, which was sometimes ordinary glass and sometimes aluminum oxide.

A pulse laser was used to strike the disks, which added a burst of energy analogous to the mallet striking the tuning fork. The light pulse provided an almost instant burst of heat, which caused the metal disks to expand and contract very fast, several billion times each second. A second laser beam was used to probe these vibrations by detecting tiny changes in their color in a microscope.

Experiments showed the resonant frequency of smaller disks shifted about 20 percent when they were placed near larger disks. The research points to a new way for engineers to convert light energy into mechanical energy and vice versa at the nanoscale, which may open the door for new applications in secure communications, sensing and more.