Understanding and Reducing Photothermal Forces for the Fabrication of Au Nanoparticle Dimers by Optical Printing

Abstract

Optical printing holds great potential to enable the use of the vast variety of colloidal nanoparticles (NPs) in nano- and microdevices and circuits. By means of optical forces, it enables the direct assembly of NPs, one by one, onto specific positions of solid surfaces with great flexibility of pattern design and no need of previous surface patterning. However, for unclear causes it was not possible to print identical NPs closer to each other than 300 nm. Here, we show that the repulsion restricting the optical printing of close by NPs arises from light absorption by the printed NPs and subsequent local heating. By optimizing heat dissipation, it is possible to reduce the minimum separation between NPs. Using a reduced graphene oxide layer on a sapphire substrate, we demonstrate for the first time the optical printing of Au-Au NP dimers. Modeling the experiments considering optical, thermophoretic, and thermo-osmotic forces we obtain a detailed understanding and a clear pathway for the optical printing fabrication of complex nano structures and circuits based on connected colloidal NPs.

Nanoscale Optical Trapping: A Review

“…The fixation process can rely on different mechanisms: hydrophobic or van der Waals interactions between the nanoparticle and the substrate, laser‐induced adhesion (transient melting) or laser‐induced photopolymerization . Other techniques exploiting similar approaches include optical printing of nanostructures onto a substrate from colloidal nanoparticles, and multiphoton polymerization of 3D patterns (e.g., waveguides) in colloidal crystals . Working electronic devices have been fabricated from nanowires tweezed and fused together (Figure c) or fused onto other structures (Figure d) …”

High‐Rate Printing of Micro/Nanoscale Patterns Using Interfacial Convective Assembly

“…However, previous work has reported that Rayleigh–Benard convection is negligible in micrometer length scale. [ 46–48 ] To verify the existence of the Rayleigh–Benard convection, a dimensionless number, Rayleigh number ( R ), is calculated as where g is the acceleration due to gravity, ρ m , α m , η m , and κ m are the density, thermal volume expansion coefficient, dynamic viscosity, and thermal diffusivity of the mixed suspension, respectively, Δ T is the vertical temperature difference between the bottom (substrate temperature, T s ) and the top (room temperature, 20 °C) of the suspension, and h is the thickness of the suspension. The thermal diffusivity κ m can be obtained as where λ m and Cp m are the thermal conductivity and heat capacity of the mixed suspension.…”

“…The thermal Marangoni convection is reported to be prominent in micrometer length scale. [ 47 ] To validate this conclusion, another dimensionless number, thermal Marangoni number ( Ma T ), is calculated as where γ m is the surface tension of the mixed suspension. [ 52,53 ] The thermal Marangoni number also increases with the substrate temperature and ranges between 540 and 6000 (Figure 2d).…”

Particle‐in‐a‐Frame Nanostructures with Interior Nanogaps

“…Thegeometric model for each structure was built based on the experimentally determined average edge length, inner NP size,i nterior nanogap size,a nd frame thickness of the Au PIAFs.F rom the calculated extinction spectra of the model structures and corresponding simulated charge distributions at the respective resonance wavelengths,i tc an be corroborated that the LSPR peaks of the Au PIAFs correspond to the collection of coupled plasmon modes between the dipole plasmon modes of the inner NPs and outer frames. [32,33] This technique allows to aid identifying unambiguously the plasmonic response of the Au PIAF avoiding interparticle coupling effects (that is,external hot spots). Single-particle spectroscopy is apowerful tool for interpreting the physicochemical phenomena precisely in nanoparticle systems.…”