Strong infrared absorber: surface-microstructured Au film replicated from black silicon

Area of Science:

• Materials Science
• Optics
• Nanotechnology

Background:

• Broadband infrared light absorption is crucial for applications like thermal detectors and energy harvesting.
• Traditional methods often struggle to achieve high absorption over wide spectral ranges.
• Controlling material microstructure is key to tailoring optical properties.

Purpose of the Study:

• To experimentally demonstrate enhanced broadband infrared light absorption in gold (Au) films.
• To investigate the role of quasi-periodic microstructures in achieving this enhanced absorption.
• To understand the underlying mechanism responsible for the broad absorption characteristics.

Main Methods:

• Fabrication of microstructured Au films using replica molding of femtosecond (fs) laser microstructured silicon (black silicon).
• Experimental characterization of infrared light absorption over a broad wavelength band (2.7–15.1 μm).
• Surface analysis using X-ray photoelectron spectroscopy (XPS) to identify surface components.

Main Results:

• Achieved significant enhancement of infrared light absorption in Au films over a broad wavelength range (2.7–15.1 μm).
• Demonstrated that quasi-periodic microstructures are responsible for the broadband absorption.
• Identified the primary cause of absorption as a good impedance match from free space to the Au film.
• XPS analysis revealed peaks attributed to residual polydimethylsiloxane (PDMS), H2SO4, adsorbed water, and CO2.

Conclusions:

• Quasi-periodic microstructures are an effective strategy for realizing broadband infrared light absorption in Au films.
• The observed absorption enhancement is attributed to impedance matching, facilitating efficient light coupling.
• Surface contaminants can influence optical characterization, necessitating careful analysis.