Subnanometer plasmonics

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dc.contributor.author Hajisalem, Ghazal
dc.date.accessioned 2016-09-19T16:00:05Z
dc.date.available 2016-09-19T16:00:05Z
dc.date.copyright 2016 en_US
dc.date.issued 2016-09-19
dc.identifier.uri http://hdl.handle.net/1828/7551
dc.description.abstract Plasmonic structures with nanometer scale gaps provide localized field enhancement and allow for engineering of the optical response, which is well described by conventional classical models. For subnanometer scale gaps, quantum effects and nonlocal effects become important and classical electromagnetics fail to describe the plasmonic coupling response. Coupled plasmonic system of gold nanoparticles on top of thin gold film separated with self-assembled monolayers (SAMs) provides a convenient geometry to experimentally explore plasmonic features in subnanometer scale gaps. However, the surface roughness of the thin metal film can significantly influence the plasmonic coupling properties. In this dissertation, I suggest modifying the coupled nanoparticles-film structures by using ultraflat thin metal films. Using these structures, I investigated the far-field optical response for gap size variations by dark field scattering measurements. A red-shift of the plasmon resonance wavelength was observed by reducing the gap width. However, I did not observe the previously reported saturation trend of the resonance shift for subnanometer scale gaps. I attribute the difference to surface roughness effects in past works since as they were not present in my studies with ultraflat films. To study the near-field enhancement in subnanometer scale gaps, I used third harmonic generation as a method that is highly sensitive (as the third power) to the local field intensity. The onset of the quantum tunneling regime was determined for gap thicknesses of 0.51 nm, where there was a sudden drop in the third harmonic when the gap width decreases from 0.69 nm to 0.51 nm. The experimental observations were consistent with analytical calculations that applied the quantum-corrected model for SAM separating two gold regions. In comparison to the gap without SAMs in which the onset of the tunneling regime was reported at 0.31 nm, the onset of tunneling across the gap with SAM occurred for larger gaps. This was an expected outcome because the material in the gap reduced the barrier height to tunneling. Furthermore, I investigated the wavelength dependence of the third harmonic generation for the gold plasmonic system to determine the role of the interband transitions in the nonlinear response of gold. Past works reported a strong wavelength dependence of the nonlinear response of gold for the fundamental wavelength at about 550 nm, attributed to the interband transitions between the 5d to 6s-6p bands. However, the roles of the interband transitions and wavelength-dependent field enhancement in the nonlinear response of gold was not investigated. In this dissertation, results showed the third harmonic generation enhanced by an order of magnitude by the interband transition (as compared to the non-resonant case). In my research I also used an analytic model for the dielectric function of gold in which contributions of the interband transitions were considered. This model was also consistent with the experimental observations. en_US
dc.language English eng
dc.language.iso en en_US
dc.rights Available to the World Wide Web en_US
dc.subject Plasmonics en_US
dc.subject Nanostructure en_US
dc.subject Nonlinear optical en_US
dc.subject Quantum tunneling en_US
dc.title Subnanometer plasmonics en_US
dc.type Thesis en_US
dc.contributor.supervisor Gordon, Reuven
dc.degree.department Department of Electrical and Computer Engineering en_US
dc.degree.level Doctor of Philosophy Ph.D. en_US
dc.identifier.bibliographicCitation G. Hajisalem, Q. Min, R. Gelfand, and R. Gordon, “Effect of surface roughness on self-assembled monolayer plasmonic ruler in nonlocal regime,” Opt. Express 22(8), 9604-9610 (2014). en_US
dc.identifier.bibliographicCitation G. Hajisalem, M. S. Nezami, and R. Gordon, "Probing the quantum tunneling limit of plasmonic enhancement by third harmonic generation," Nano Lett. 14(11), 6651-6654 (2014). en_US
dc.identifier.bibliographicCitation G. Hajisalem, D. K. Hore, and R. Gordon, "Interband transition enhanced third harmonic generation from nanoplasmonic gold," Opt. Mater. Express 5(10), 2217-2224 (2015). en_US
dc.identifier.bibliographicCitation G. Cao, G. Hajisalem, W. Li, F. Hof, and R. Gordon, "Quantification of an exogenous cancer biomarker in urinalysis by Raman spectroscopy," Analyst 139(21), 5375-5378 (2014). en_US
dc.identifier.bibliographicCitation J. Wu, W. Li, G. Hajisalem, A. Lukach, E. Kumacheva, F. Hof, and R. Gordon, "Trace cancer biomarker quantification using polystyrene-functionalized gold nanorods," Biomed. Opt. Express 5(12), 4101-4107 (2014). en_US
dc.identifier.bibliographicCitation H. Xu, G. Hajisalem, G. M. Steeves, R. Gordon, and B. C. Choi, "Nanorod surface plasmon enhancement of laser-induced ultrafast demagnetization," Sci. Rep. 5, (2015). en_US
dc.identifier.bibliographicCitation M. S. Nezami, D. Yoo, G. Hajisalem, S.-H. Oh, and R. Gordon, "Gap plasmon enhanced metasurface third harmonic generation in transmission geometry," ACS Photonics (2016). en_US
dc.description.scholarlevel Graduate en_US
dc.description.proquestcode 0752 en_US
dc.description.proquestcode 0544 en_US

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