Plasmon-Enhanced Photothermal and Optomechanical Deformations of a Gold Nanoparticle

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.

NIR-Absorbing Mesoporous Silica-Coated Copper Sulphide Nanostructures for Light-to-Thermal Energy Conversion

“…A large body of literature deals with the fabrication of anisotropic Au NPs, such as nanorods [ 1 , 12 ], nanostars [ 17 ], or spiky nanostructures [ 19 ] for in vitro and in vivo investigation of their PT properties, using minimally invasive NIR radiation as excitation. However, nanostructures, featuring high curvature (i.e., nanorods, nanostars, spiky NPs), present limited stability under prolonged light exposure, as they may undergo deformation and reshaping phenomena [ 19 , 20 , 21 , 22 , 23 , 24 ].…”

Laser-Induced Plasmonic Nanobubbles and Microbubbles in Gold Nanorod Colloidal Solution

“…The intensity of the optical signal at the early stage of laser shining is evidence of the nanobubbles caused by the photothermal effect of GNRs within the focal spot of the pulsed laser. On the other hand, if the pulsed energy is too high, the transient temperature in GNR could be over 600 °C to melt and re-sharpen GNR [ 14 ]. Consequently, overheating may cause the change in SPR performance, which is not suitable for several shots of laser on the same GNR colloid.…”

“…The specific heat of gold is 0.126 J/g-K, and the melting point of GNP/GNR is about 590 °C, which is much lower than that of bulk gold (1064 °C) [ 14 ]. The latent heat of fusion for gold is 67 J/g, and the latent heat of vaporization is 1578 J/g.…”

“…If the SPR of GNRs is within the near-infrared (NIR) region, they are particularly useful for biomedical applications [ 13 ]. Recently, a variety of applications of GNP have been developed based on the plasmonic photothermal, optomechanical, and photochemical effects [ 14 , 15 , 16 ]. An important application of GNP is to utilize the plasmon-enhanced photothermal effect for generating plasmonic nanobubbles [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ].…”