Seminar: Adam Taylor, Swinburne University of Technology
Location
Physics : 401
Date & Time
July 31, 2015, 3:00 pm – 4:00 pm
Description
TITLE: Plasmonic nanostructure instability mediated by surface diffusion
ABSTRACT: Plasmonic gold nanorod instability and reshaping behavior below the bulk melting point is important for many future applications, but are yet to be fully understood, with existing nanoparticle melting theories unable to explain the observations.
We report here the photothermal reshaping behavior of gold nanorods irradiated with femtosecond laser pulses, and that the instability is driven by curvature induced surface diffusion, rather than threshold melting process, and that the stability dramatically decreases with increasing aspect ratio. We observed single particle, before and after reshaping via TEM imagery, and successfully utilized a surface diffusion model to explain observations. Activation energy for surface diffusion was found to be dependent on the aspect ratio of the rods, from 0.6 eV for aspect ratio of 5, to 1.5 eV for aspect ratio less than 3. This result indicates that the surface atoms are much easier to diffuse around in larger aspect ratio rods than shorter rods, and can induce reshaping at any given temperature. We additionally examine gold nanorods and bipyramids with in situ TEM heating, and observe similar reshaping trends.
These findings will be especially important for the field of gold nanorod photothermal therapy and two-photon biolabelling, plasmonic circuitry, solar cells using plasmonic structure, where increased laser power, and sharper geometric features are often seen as a mechanism for greater field enhancement. This work shows that surface diffusion based reshaping must be considered for plasmonic nanostructures for their stable operations, even at temperatures well below melting points.
ABSTRACT: Plasmonic gold nanorod instability and reshaping behavior below the bulk melting point is important for many future applications, but are yet to be fully understood, with existing nanoparticle melting theories unable to explain the observations.
We report here the photothermal reshaping behavior of gold nanorods irradiated with femtosecond laser pulses, and that the instability is driven by curvature induced surface diffusion, rather than threshold melting process, and that the stability dramatically decreases with increasing aspect ratio. We observed single particle, before and after reshaping via TEM imagery, and successfully utilized a surface diffusion model to explain observations. Activation energy for surface diffusion was found to be dependent on the aspect ratio of the rods, from 0.6 eV for aspect ratio of 5, to 1.5 eV for aspect ratio less than 3. This result indicates that the surface atoms are much easier to diffuse around in larger aspect ratio rods than shorter rods, and can induce reshaping at any given temperature. We additionally examine gold nanorods and bipyramids with in situ TEM heating, and observe similar reshaping trends.
These findings will be especially important for the field of gold nanorod photothermal therapy and two-photon biolabelling, plasmonic circuitry, solar cells using plasmonic structure, where increased laser power, and sharper geometric features are often seen as a mechanism for greater field enhancement. This work shows that surface diffusion based reshaping must be considered for plasmonic nanostructures for their stable operations, even at temperatures well below melting points.