Designing Strong Optical Absorbers via Continuous Tuning of Interparticle Interaction in Colloidal Gold Nanocrystal Assemblies

Abstract

We program the optical properties of colloidal Au nanocrystal (NC) assemblies via an unconventional ligand hybridization (LH) strategy to precisely engineer interparticle interactions and design materials with optical properties difficult or impossible to achieve in bulk form. Long-chain hydrocarbon ligands used in NC synthesis are partially exchanged, from 0% to 100%, with compact thiocyanate ligands by controlling the reaction time for exchange. The resulting NC assemblies show transmittance, reflectance, optical permittivity, and directcurrent (DC) resistivity that continuously traverse a dielectric-metal transition, providing analog tuning of their physical properties, unlike the digital control realized by complete exchange with ligands of varying length. Exploiting this LH strategy, we create Au NC assemblies that are strong, ultrathin film optical absorbers, as seen by a 6× increase in the extinction of infrared light compared to that in bulk Au thin films and by a temperature rise of 20 °C upon illumination with 808 nm light. Our LH strategy may be applied to the design of materials constructed from NCs of different size, shape, and composition for specific applications.

Simultaneous Photonic and Excitonic Coupling in Spherical Quantum Dot Supercrystals

“…Distributions of the electric field density at the peak are shown in Figure S2. The maximum absorption efficiency is therefore limited by the penetration of the electric field within the SC and may be further optimized by tuning the refractive index by varying QD core material, 36,39 surface ligands, 40 architectural morphology, 8,41 and postprocessing treatments. 42 While Figure 2c provides a visual illustration of the absorption efficiency and its saturation in the spectral range of λ < 550 nm, a quantitative prediction of the wavelengthdependent absorption cross section and its saturation for increasing SC diameters is shown in Figure 2d.…”

Macroscopic Orientational Gold Nanorods Monolayer Film with Excellent Photothermal Anticounterfeiting Performance

“…When the energy density rose to 0.4 W cm −2 , the temperature went up to 50 °C in 10 s. In other words, the proposed SS assemblies showed higher efficiency of photothermal conversion under the energy density several times or even dozens of times lower than other similar works. [ 36,71,72 ]…”

“…Furthermore, the controllable UV adsorption from the macroscopic orientational Au NRs arrays makes this system extremely attractive and match the light source to reach optimum photothermal conversion, as demonstrated by previous similar works. [ 36 ] Under low laser energy density, the Au NRs side by side (SS) assembly shows high and rapid photothermal response. With the assistance of thermochromic dyes, photothermal anticounterfeiting performance of different patterns and writing performance of Au NRs SS assembly were investigated.…”

Fused Silica with Embedded 2D‐Like Ag Nanoparticle Monolayer: Tunable Saturable Absorbers by Interparticle Spacing Manipulation

“…Interparticle spacing manipulation has become a key technique for noble metallic NPs to modulate LSPR response in a fast, industrialized and environmentally friendly way . Several attempts have been proposed for NPs on chip or in solution, including angle‐resolved nanosphere lithography, temperature control, nanometer precision, and directed self‐assembly .…”