Abstract
Plasmon-enhanced photothermal and optomechanical effects on deforming and reshaping a gold nanoparticle (NP) are studied theoretically. A previous paper (Wang and Ding, ACS Nano 13, 32–37, 2019) has shown that a spherical gold nanoparticle (NP) irradiated by a tightly focused laser beam can be deformed into an elongated nanorod (NR) and even chopped in half (a dimer). The mechanism is supposed to be caused by photothermal heating for softening NP associated with optical traction for follow-up deformation. In this paper, our study focuses on deformation induced by Maxwell’s stress provided by a linearly polarized Gaussian beam upon the surface of a thermal-softened NP/NR. We use an elastic model to numerically calculate deformation according to optical traction and a viscoelastic model to theoretically estimate the following creep (elongation) as temperature nears the melting point. Our results indicate that a stretching traction at the two ends of the NP/NR causes elongation and a pinching traction at the middle causes a dent. Hence, a bigger NP can be elongated and then cut into two pieces (a dimer) at the dent due to the optomechanical effect. As the continuous heating process induces premelting of NPs, a quasi-liquid layer is formed first and then an outer liquid layer is induced due to reduction of surface energy, which was predicted by previous works of molecular dynamics simulation. Subsequently, we use the Young–Laplace model to investigate the surface tension effect on the following deformation. This study may provide an insight into utilizing the photothermal effect associated with optomechanical manipulation to tailor gold nanostructures.
Highlights
Studies of light–matter interaction in physics and chemistry at the nanoscale have attracted lots of attention for decades [1,2,3,4,5]
Interesting experimental results [1] have shown that a spherical gold nanoparticle (NP) can be deformed into an elongated NR or even a dimer as irradiated by a tightly focused linearly polarized (LP) continuous-wave (CW) laser beam of 446 nm in air, where a P(VDF-TrFE) layer was coated on a Si substrate to reduce adhesion
The mechanism could be due to the combination of the photothermal effect for softening the NP with optical stress (Maxwell’s stress) for the follow-up optomechanical deformation
Summary
Studies of light–matter interaction in physics and chemistry at the nanoscale have attracted lots of attention for decades [1,2,3,4,5]. The mechanism could be due to the combination of the photothermal effect for softening the NP with optical stress (Maxwell’s stress) for the follow-up optomechanical deformation. The mechanism of V-shaped deformation of an NR was theoretically explained in [7]; photothermal heating softens gold NR, and optical stress (Maxwell’s stress on surface) induces an optical bending on the NR by a LP Gaussian beam. Most previous experiments showed that a gold NR can be heated to become a spherical NP by irradiation of CW or pulsed lasers [8,9,10,11,12,13,14,15] This is because as the power of laser is high enough to melt the NR the surface tension of liquid metal spherifies the NR [8]. Precise control of heating conditions (e.g., laser power) is very crucial to manipulate photothermal and optomechanical deformation of plasmonic nanostructures by means of light on demand
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