Assemblies of Metal Nanoparticles and Single Quantum Dots with Low-Power, Ultrafast Nonlinear Optical Response

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The ability to continue to build faster, more powerful computers is reaching a limit set by the amount of energy needed to run the computers. It may be possible to overcome this energy barrier by replacing electronic components, which use electrical current to process information, with photonic components, which use light to process information, but only if ultrafast, ultrasmall, and ultra-low-power photonic devices can be built. This project develops one class of these devices, which can serve to control the flow of light in future all-optical computers. This is accomplished by using chemical means to produce nanometer-scale metal and semiconductor particles and to induce strong optical interactions among the particles by assembling them into controlled hybrid arrangements. These scientific goals are integrated with efforts to broaden the diversity of the scientific workforce, through the involvement of high-school, undergraduate, and graduate students in cutting-edge research, particularly students from underrepresented groups, female students, and veterans.The objective of this project is to produce assemblies of metal nanoparticles (MNPs) and single quantum dots (QDs) with nonlinear optical response at ultralow incident powers. The nonlinearity arises due to near-field optical interactions among the nanoparticles and is qualitatively different from the response of the components separately. Assemblies of colloidal QDs and MNPs with strong interparticle interactions are fabricated through the chemical synthesis of QDs and anisotropic gold nanoparticles (nanorods or bipyramids), the selective covalent binding of single QDs to the ends of the MNPs to form MNP-QD-MNP trimers, and the separation of these trimers from smaller and larger assemblies. Optical functionality is verified by correlated linear and nonlinear optical spectroscopy and electron-microscope imaging of individual assemblies. Experimental results are compared to numerical simulations, enabling detailed understanding of structure-property relationships and optimization of the nonlinear response.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.