High Aspect Ratio Au Microflakes via Gap-Assisted Synthesis

Abstract

Ultrathin and extra-large single-crystalline Au microflakes (Au MFs) have a huge potential in applications ranging from nanophotonics to catalysis. Yet, wet chemical synthesis approaches cannot access this size range due to the proportionality between growth time, thickness, and lateral size. Concurrently, complexity and small MF areas restrict the use of 2D template-based methods. In all cases, subsequent transfer to a substrate remains challenging. Here, we demonstrate a facile, gap-assisted synthesis method that enables on-substrate growth of ultrathin and extra-large Au MFs. In particular, using a 43 μm gap-size between two glass substrates and leveraging the directed-growth effect of halide ions, we achieve a high yield (∼90%) of Au MFs on glass with lateral sizes as high as 0.25 mm and thicknesses as low as 10 nm. Interestingly, for up to 25 h growth time, we observe a time-independent, ultralow average thickness of just 21 nm. A parametric synthesis study and an in-depth material characterization provide mechanistic insights into this extreme 2D growth mode. Overall, our gap-assisted approach greatly enhances the halide effect and results in a record-high aspect ratio of ∼104. It thus opens new opportunities for on-substrate anisotropic growth strategies that would benefit emerging optoelectronic and photoelectrochemical devices.

Effect of Mirror Quality on Optical Response of Nanoparticle‐on‐Mirror Plasmonic Nanocavities

“…The nonperiodic lattice fringes observed in the high-resolution TEM image of the sputtered gold film (Figure 1i) indicate that both SGFs and TSGFs have a polycrystalline structure. Different from SGFs and TSGFs, in agreement with previous works, [39,41] chemically grown GMFs have a single-crystalline structure and an atomically smooth surface with an RMS roughness as low as ≈0.16 nm (Figure 1f).…”

Nonlinear Photoluminescence in Gold Thin Films

“…To obtain additional insight into the NPL dynamics, we perform two-pulse correlation experiments on a monocrystalline gold flake sample that has a varying thickness (similar to the samples in ref ). The crystallinity and (111) orientation of this type of sample are conclusively established. , Further details about the sample preparation and optical characterization can be found in Methods. The measured two-pulse correlation traces of the NPL signal for gold thicknesses of approximately 22, 26, and 32 nm obtained at ∼10 mJ/cm 2 fluence are shown in Figure .…”

“…The crystallinity and (111) orientation of this type of sample are conclusively established. 53,54 Further details about the sample preparation and optical characterization can be found in Methods. The measured two-pulse correlation traces of the NPL signal for gold thicknesses of approximately 22, 26, and 32 nm obtained at ∼10 mJ/cm 2 fluence are shown in Figure 6.…”

Ultimate Limit for Optical Losses in Gold, Revealed by Quantitative Near-Field Microscopy

“…We measured ∼0.2 nm, which is in agreement with other reported values (<1, 0.1, and ∼0.2 nm). We further applied plasma cleaning for 1 h prior to our measurements to remove a miniscule organic layer that is residual from the crystal synthesis . Note that gold atoms are packed in a face-centered cubic (FCC) lattice, resulting in a nonrectangular, tapered-edge profile of the flake (see the side facets in the inset of Figure b; discussion concerning the geometry of the flake edges and their optical properties can be found in a recent work).…”