Mass Sensing, Strong Vibrational Coupling and Super-Resolution Imaging of Noble Metal Nanostructures

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The Macromolecular, Supramolecular, and Nanochemistry Program in the Chemistry Division supports Professor Gregory V. Hartland and his group at the University of Notre Dame to create ultra-small, nanometer-sized mass balances that can operate at room temperature. All objects vibrate and the vibration frequencies depend on the size and shape of the object. These vibration frequencies are very high for nanoparticles and they change when two particles are attached to each other. Using this effect, this project contributes to sensing particles whose sizes make them very difficult to detect with conventional techniques. By accurately measuring mass, the researchers are able to identify unknown particles such as viruses. The fundamental knowledge gained from this study can also enable the detection of a variety of chemicals and particles in the environment. The accurate detection of chemicals and particles is important for assessing potential risks from environmental and biological hazards. This research provides training and education to graduate and undergraduate students at the University of Notre Dame as well as from local primarily undergraduate institutions (PUIs). This project also provides research experience for high school students and teachers from Elkhart Community Schools. The vibrational modes of metal nanostructures suspended in air or placed on low density substrates have very high quality factors which allows their frequencies to be accurately measured. With this award from the Macromolecular, Supramolecular, and Nanochemistry Program, Professor Hartland and his group at the University of Notre Dame use suspended nanostructures to study how the vibrational modes of the nanostructures are affected by adsorbed mass. They also examine the coupling between the vibrational modes of different nanostructures, and coherently control the vibrational motion of coupled nanostructures. These experiments are performed by transient absorption microscopy implemented with asynchronous optical sampling, a dual laser technique that avoids the use of a mechanical delay line to record data. The results of the measurements allow the masses of large uncharged particles to be directly determined, which is a challenge for conventional mass spectrometers. In addition, ultrafast mid-infrared pump transient absorption microscopy is used to image the plasmon resonances of single metal nanostructures. These experiments generate new information about the form of the plasmon modes of these structures, which is important for understanding the field enhancements that are central to surface enhanced spectroscopies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.