Associate Professor of Chemistry and of Electrical and Computer Engineering
The overall goal of our research is to understand the physical principles that govern the interaction of plasmonic nanoparticles (NPs) with each other and their molecular environment and determine the collective optical properties of novel composite nanomaterials as a function of size, shape, and especially ordering of the constituent NPs in large one-dimensional (1D) assemblies prepared from chemically synthesized NPs.
Building new photonic materials and devices from the bottom up is a central goal in nanoscience. Using plasmonic NPs as building blocks requires a detailed understanding of how the optical properties of the individual NPs change as they are assembled into complex, higher order structures. These changes occur because interactions between plasmonic NPs lead to new phenomena that depend not only on the dimensions and shapes of the individual NPs, but also their relative distances and orientations. An additional level of complexity exists when NPs are prepared and assembled by chemical synthesis and soft lithography methods because irregularities or ‘defects’ in particle size, shape, and ordering are inherently present in those systems. Despite these challenges, the advantages of chemically prepared NPs include highly crystalline structures and small interparticle distances, allowing for the strongest plasmon coupling. Therefore, the advantageous properties of chemically prepared NPs make it worthwhile to understand and control the challenges introduced by polydispersity, especially given the many assembly strategies already developed so far. To fully exploit these NP assemblies and to advance the field, it is first necessary to determine the effect of imperfections on the functional properties of nanomaterials consisting of many interacting plasmonic NPs. In addition to plasmon coupling between NPs, their interaction with the environment is also a key factor for many applications of plasmonic NPs. To address these complex issues on a microscopic scale, we are applying and developing single molecule and particle spectroscopy techniques, which, when correlated with structural characterization of the same NP system and detailed electromagnetic modeling, allow us to address the following important thematic questions:
1) How do the optical properties of 1-D NP assemblies depend on the morphology of the overall structure and what is the role of disorder with respect to NP size, shape, and positioning?
2) How can plasmonic NPs be integrated with liquid crystals to achieve active control over the optical properties?
3) How can the diffusion of NPs in solution be exploited to understand the interaction with heterogeneous media?
While these questions address mainly fundamental issues, our long term research is strongly guided by possible applications of assembled nanomaterials as plasmonic waveguides and antennas, active plasmonic devices, and drug delivery agents based on the principles learned from understanding coupling between plasmonic NPs as well as interactions with the surrounding environment.
1. W.-S. Chang, F. Wen, D. Chakraborty, M.-N. Su, Y. Zhang, B. Shuang, P. J. Nordlander, J. E. Sader, N. J. Halas, S. Link, Tuning the acoustic frequency of a gold nanorisk through its adhesion layer. Nat. Comm. DOI 10.1038/ncomms8022 (2015).
2. M. Yorulmaz, S. Nizzero, A. Hoggard, L.-Y. Wang, Y.-Y. Cai, M. N. Su, W.-S. Chang,S. Link, Single-particle absorption spectroscopy by photothermal contrast. Nano Lett. 15, 3041 (2015).
3. J. Olson, A. Manjavacas, L. Liu, W.-S. Chang, B. Foerster, N. King, M. W. Knight, P. Nordlander, N. J. Halas, S. Link, Vivid, Full-Color Aluminum Plasmonic Pixels. Proc. Natl. Acad. Sci. USA, 111, 14348 (2014).
4. A. R. Hoggard, L.-Y. Wang, L. Ma, Y. Fang, J. M. Olson, W.-S. Chang, P. M. Ajayan, S. Link, Using the Plasmon Linewidth to Calculate the Time and Efficiency of Electron Transfer Between Gold Nanorods and Graphene. ACS Nano 7, 11209 (2013).
5. W. Ma, H. Kuang, L. Wang, L. Xu, W.-S. Chang, H. Zhang, M. Sun, Y. Zhu, Y. Zhao, L. Liu, C. Xu, S. Link, N. A. Kotov, Chiral plasmonics of self-assembled nanorod dimers. Scientific Reports 3, 1934, (2013).
6. L. S. Slaughter, B. A. Willingham, W.-S. Chang, M. H. Chester, N. Ogden, S. Link, Toward Plasmonic Polymers. Nano Lett. 12, 3967 (2012).
7. S. Dominguez-Medina, S. McDonough, P. Swanglap, C. F. Landes, S. Link, In situ measurement of bovine serum albumin interaction with gold nanospheres. Langmuir 28, 9131 (2012).
8. S. Khatua, W.-S. Chang, P. Swanglap, J. Olson, S. Link, Active Modulation of Nanorod Plasmons. Nano Lett.11, 3797 (2011).
9. A. Tcherniak, S. Dominguez-Medina, W.-S. Chang, P. Swanglap, L. S. Slaughter, C. F. Landes, S. Link, One-photon plasmon luminescence and its application to correlation spectroscopy as a probe for rotational and translational dynamics of gold nanorods. J. Phys. Chem. C 115, 15938 (2011).
10. W.-S. Chang, J. W. Ha, L. S. Slaughter, S. Link, Plasmonic Nanorod Absorbers as Orientation Sensors. Proc. Natl. Acad. Sci. USA 107, 2781 (2010).
D. Huang, C. P. Byers, L.-Y. Wang, A. Hoggard, B. Hoener, S. Dominguez-Medina, S. Chen, W.-S. Chang, C. F. Landes, S. Link, Photoluminescence of a Plasmonic Molecule. ACS Nano 9, 7072 (2015).