Nanomolding of Gold and Gold–Silicon Heterostructures at Room Temperature

Abstract

Nanofabrication techniques are limited by at least one of the required characteristics such as choice of material, control over geometry, fabrication requirements, yield, cost, and scalability. Our previously developed method of thermomechanical nanomolding fulfills these requirements, although it requires high processing temperatures. Here, we demonstrate low-temperature molding where we utilize the enhanced diffusivity on "eutectic interfaces". Gold nanorods are molded at room temperature using Au−Si alloy as feedstock. Instead of using alloy feedstock, these "eutectic interfaces" can also be established through a feedstock−mold combination. We demonstrate this by using pure Au as feedstock, which is molded into Si molds at room temperature, and also the reverse, Si feedstock is molded into Au molds forming high aspect ratio Au−Si core−shell nanorods. We discuss the mechanism of this low-temperature nanomolding in terms of lower homologous temperature at the eutectic interface. This technique, based on enhanced eutectic interface diffusion, provides a practical nanofabrication method that eliminates the previous high-temperature requirements, thereby expanding the range of the materials that can be practically nanofabricated.

Thin-Film-Assisted Photothermal Deformation of Gold Nanoparticles: A Facile and In-Situ Strategy for Single-Plate-Based Devices

“…Irradiation of the Au NP on the bare Si substrate only results in red shift of the scattering peak (Figure a) and the spherical Au deforms into a NP with a small plate underneath (inset of Figure a and Figure S4). This is largely because Au–Si alloys can be formed at the interface, which significantly lowers the melting point of Au and the interfacial tensions . Thus, partial wetting of the molten Au is formed on the Si substrate, which forms the small plate on Si.…”

“…This is largely because Au−Si alloys can be formed at the interface, which significantly lowers the melting point of Au and the interfacial tensions. 27 Thus, partial wetting of the molten Au is formed on the Si substrate, which forms the small plate on Si. The large surface tension of the molten Au droplet still retains its hemispherical shape, rendering the formation of NP on plate structure.…”

Longitudinal Assembly of Gold Nanorods on Various Templates for Optoelectronics

“…According to Liang et al [53], the optimal temperature for achieving nematic, curved end-to-end assembly and transition mode is 30 ° C-50 ° C on a wrinkled template. Moreover, GNRs can be molded at room temperature using Au-Si alloy as feedstock [54]. By thermal annealing the GNRs after the evaporation of the solvent and gradually increasing the temperature from 20°C to 140°C, a quasicontinuous wire-like structure was obtained [28].…”

“…In low humidity, GNRs tend to form the nematic arrangement, while in high humidity, GNRs prefer the curved end-to-end fashion as mentioned in ref. [54].…”

Single-Crystal Nanostructure Arrays Forming Epitaxially through Thermomechanical Nanomolding

“…The nanowires’ length and diameter are limited practically by the mold dimensions, but there is no fundamental limit to these features. We have demonstrated that TMNM can be applied to a wide range of materials, including metals, alloys, and ordered phases. ,− The underlying mechanism of TMNM is based on diffusion, specifically on interface diffusion (see Figure S2 Supporting Information) for temperatures above ∼0.4 T M , where T M is the melting temperature of the material. Notably, functional nanostructures fabricated by TMNM include superconductors, topological insulators, semiconductors, and phase change materials .…”