In Situ Temperature Dependent Optical Characterization and Modeling of Dealloyed Thin‐Film Nanoporous Gold Absorbers

Abstract

Nanostructured noble metals such as gold exhibit unique size‐dependent plasmonic and optical properties which is an enabling factor for designing nanophotonic devices. However, for its deployment in high temperature applications such as solar thermal energy harvesting and optothermal conversion, it requires understanding of its temperature dependent optical properties. This paper investigates the in situ specular reflectance of nanoporous gold (NPG) thin films in the wavelength range between 400 and 1000 nm at temperatures ranging from 25 to 500 °C via a home‐built fiber‐based optical spectrometer. During heating, the NPG's ligaments coalesce from an initial size of 39 ± 12 nm to a final size of up to 299 ± 114 nm, and its ligament scales with temperature closely matching an Arrhenius dependence. The surface roughness of NPG is empirically correlated to ligament size and temperature to allow for the theoretical prediction of the relative specular reflectance using scattering coefficients and effective medium theory which closely matches the experimental results. These results represent a step forward in using in situ optical spectroscopic methods to monitor the ligament size evolution of NPG thin‐films and to understand its stability and optical properties for applications at elevated temperatures.

Synthesizing Nanoporous Stainless Steel Films via Vacuum Thermal Dealloying

“…Nanoporous materials can be applied in numerous fields, e.g., sensors [1][2][3], actuators [4,5], catalysts [6][7][8][9][10], biomaterials [11][12][13], and energy conversion and storage [14][15][16][17], due to their unique bi-continuous open porous structure and high surface-area-to-volume ratio. As a result, this type of material has received significant attention, leading to a wide variety of approaches for the fabrication of nanoporous metals, which have emerged in the past decades.…”

Enhanced Molecular Interaction of 3D Plasmonic Nanoporous Gold Alloys by Electronic Modulation for Sensitive Molecular Detection

“…Nanoporous gold has garnered significant attention in a multitude of applications ranging from catalysis to photonics due to its excellent physical and chemical properties. − For example, it exhibits a broad optical response ranging from ultraviolet (UV) to near-infrared (NIR) as well as electric field confinement and enhancement in high-density nanopores, which makes it one of ideal substrates for various sensing applications. − ,, Such porous structure has been commonly prepared by a dealloying method, which involves the selective removal of less noble metals such as silver, copper, and aluminum from gold-based alloys. − Because of the residual less noble metal during the dealloying, the resulting nanoporous structure turns out to have alloy compositions to some extent. ,− Interestingly, these gold-based alloys are found to enhance plasmonic properties due to modulation of their permittivity by other metals. − …”