Metal nanoparticles: near and far field manipulation of light
A unique research system for nanoscale physics
Nano-sized metal objects possess a localized surface plasmon resonance (LSPR) -- that is, resonant optical energy can be absorbed and excite a coherent oscillation of conduction electrons ("plasmon"). While it persists, this oscillation enhances the local electric field around the nanostructure, which correspondingly then also influences the properties of other objects located close to the metal structure. For isotropically-shaped objects (e.g., nanospheres), a single LSPR exists, whereas for anisotropic objects (e.g., nanorods) each spatial axis of symmetry has a distinct resonance such as the longitudinal (l-LSPR) and transverse (t-LSPR) directions.
On fairly short time scales, the plasmon damps out and thereby releases the absorbed light energy as heat within the metal nanostructure, which through thermal transport processes, propagates outwards from the nanoscale object into the surrounding environment. This "light-to-heat" conversion process is referred to as the photothermal effect of metal nanoparticles. Our research efforts have utlized sample systems when these "nano-heaters" are dilutely embedded within solid materials and subsequently illuminated with appropriate wavelength light to excite the LSPRthen relaxed as released heat, demonstrating thermal processing outcomes which are unrealizeable by conventional heating methods which typically occur 1) from the outer surface of a material to the inside rather than from the inside outwards, and 2) not originally localized from nano-sized structures.
Our research team and collaborators have developed unique optically-based research tools to subsequently measure the spatial temperature distribution at nanoscale length scales which arise under such photothermal heating. These research efforts in nanothermometry employ the unique and robust absorptive properties of the metal nanoparticles themselves, as well as independent signals generated from molecular fluorophores, randomly-distributive within the material matrix.
Other work focuses on fundamental light-matter interactions by exploring the influence of metal nanoparticles on the emission properties of nearby quasi-resonant light-emitters. In this regime, the extremely strong local electric field generated by a nanoparticle's LSPR dramatically modifies the emissive and absorptive properties of the light-emitters.
Most recent papers: (See Publications for a complete list of papers.)
"Facile Measurement of Surface Heat Loss from Polymer Thin Films via Fluorescence Thermometry,"
J. Polymer Science, Part B: Polymer Physics 56, 643 (2018).
(journal) [paper] [DOI: 10.1002/polb.24571]
"Nanoscale Steady-state Temperature Gradients within Polymer Nanocomposites Undergoing Continuous-Wave Photothermal Heating from Gold Nanorods,"
Nanoscale 9, 11605 (2017).
(journal) [paper] [DOI: 10.1039/C7NR04613H]
"In-situ curing of liquid epoxy via gold-nanoparticle mediated photothermal heating,"
Nanotechnology 28, 065601 (2017).
(journal) [paper] [DOI: 10.1088/1361-6528/aa521b]
"Enhanced crystallinity of polymer nanofibers without loss of nanofibrous morphology via heterogeneous photothermal annealing,"
Macromolecules 49, 9484 (2016).
(journal) [paper] [DOI: 10.1021/acs.macromol.6b01655]
"Spatial Temperature Mapping within Polymer Nanocomposites Undergoing Ultrafast Photothermal Heating via Gold Nanorods,"
Nanoscale 6, 15236 (2014).
(journal) [paper] [DOI: 10.1039/C4NR05179C]