Mass Transport via Thermoplasmonics
Doktorsavhandling, 2020

When a metallic nanoparticle is illuminated with light under resonant conditions, the free electron gas oscillates in such a way that substantial amplification of the local electric field amplitude is achieved – this is known as a plasmonic resonance. This resonance enhances both the optical scattering as well as absorption. In many applications, the enhanced scattering can facilitate efficient coupling between the near-field and the far-field, which enables optical interrogation of nanoscale volumes. Simultaneously, however, the enhanced absorption results in localized heating and substantial temperature gradients. The resulting temperature profile can drive other thermal processes, some beneficial others detrimental. Thermoplasmonics is the study of these plasmonically enhanced thermal processes.

Elevated temperatures increase the Brownian motion of small particles. Moreover, if large temperature gradients are present, then a process known as thermophoresis is likely to occur. Thermophoresis tends to cause a local depletion of Brownian particles around a hot region. From the context of “conventional” plasmonic applications (like molecular sensing), these thermally driven mass transport mechanisms are adverse side effects since they reduce the interaction rate between the plasmonic system and the analyte. An investigation of thermal effects in plasmonic optical tweezers showed that the increased Brownian motion essentially negated the optical tweezing effect, resulting in an overall insensitivity between the resonance condition of the antenna and the particle confinement when evaluated in terms of the local temperature increase. Additionally, a significant thermophoretic depletion of analytes occurred, extending tens of microns from the plasmonic structure. This depletion acts in opposition to the plasmonically enhanced optical forces, which are restricted to a region of only a few hundred nanometres.

However, thermoplasmonic effects can also be used for advantageous means. Once example is by driving thermocapillary flows directed towards the plasmonic system, thereby facilitating the efficient accumulation of analytes. One method of employing this effect is to superheat a plasmonic particle to a high enough temperature such that a bubble is nucleated. Once a bubble is formed, thermocapillary effects at the bubble interface drive fluid motion with a flow profile similar to that of a Stokeslet. This fluid flow can be utilized for analyte accumulation near the plasmonic structure. In addition to the thermocapillary induced flow, it was found that even more intense flow speeds were achieved immediately upon nucleation due to the mechanical action of the bubble. This transient peak in flow speed was approximately an order of magnitude faster than the subsequent persistent (thermocapillary) flow. By designing the plasmonic nanoparticle so that the Laplace pressure restricted the ultimate bubble size, these bubbles could be kept small enough to permit high modulation rates and maximize the relative effect of the peak transient flow.

contact steven.jones@chalmers.se for zoom password
Opponent: Prof. Jochen Feldmann, Ludwig-Maximilians-Universität, München, Germany

Författare

Steven Jones

Chalmers, Fysik, Nano- och biofysik

Jones S., Andrén D., Antosiewicz T. J., Stilgoe A., Rubinsztein-Dunlop H., & Käll M., Strong Transient Flows Generated by Thermoplasmonic Bubble Nucleation

Photothermal Heating of Plasmonic Nanoantennas: Influence on Trapped Particle Dynamics and Colloid Distribution

ACS Photonics,; Vol. 5(2018)p. 2878-2887

Artikel i vetenskaplig tidskrift

Ultrafast Modulation of Thermoplasmonic Nanobubbles in Water

Nano Letters,; Vol. 19(2019)p. 8294-8302

Artikel i vetenskaplig tidskrift

Thermoplasmonics: the potential of losses

Losses are a ubiquitous feature of our universe. They are encoded in the fundamental laws of thermodynamics. In our everyday lives we experience these losses as friction, air resistance, etc. Generally speaking, losses are the effects that occur in any physical process that cause a decrease in efficiency and result in the generation of heat.

Plasmonics is no different.

Plasmonics is the study of how light interacts with metallic nanostructures (e.g. gold nanoparticles). Small gold structures can act as optical antennas and allow scientists to probe nanoscopic environments. However, because of losses, these nanoantennas can also generate a significant amount of heat.

Thermoplasmonics concerns itself with studying the effects of heat generated by plasmonic interactions. Historically this heat generation has often been viewed as an unwelcome side-effect, and thus it is imperative to study these processes to understand ways to design systems to mitigate heat generation. However, there are also new and exciting ways that these losses can be utilized for entirely new purposes.

This thesis explores both the detrimental and beneficial aspects of thermoplasmonics. In particular, the adverse effects of thermally enhanced Brownian motion and thermophoretic depletion are examined in the context of conventional plasmonic systems. Additionally, the use of thermally nucleated bubbles is explored as a potential means of efficient mass transport in microfluidic systems.

Styrkeområden

Nanovetenskap och nanoteknik (SO 2010-2017, EI 2018-)

Ämneskategorier

Fysik

Nanoteknik

Infrastruktur

Chalmers materialanalyslaboratorium

ISBN

978-91-7905-395-6

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4862

Utgivare

Chalmers tekniska högskola

contact steven.jones@chalmers.se for zoom password

Online

Opponent: Prof. Jochen Feldmann, Ludwig-Maximilians-Universität, München, Germany

Mer information

Senast uppdaterat

2020-12-03