Electromagnetic Field Tapering in the High-Roughness Substrates Coated by a Thin Film of Manganese: A Lithography-Free Approach to Ultra-Broadband, Wide-Angle, UV to FIR Perfect Absorption

TL;DR

This paper demonstrates a lithography-free method using a single manganese layer on high-roughness substrates to achieve near-perfect, ultra-broadband absorption from UV to FIR, leveraging electromagnetic field tapering and graded-index effects.

Contribution

It introduces a novel, simple, and cost-effective approach for ultra-broadband perfect absorption using a single metal layer on rough substrates, eliminating complex multilayer structures.

Findings

Achieved approximately 99% average absorption across UV to FIR spectrum.

Demonstrated the effectiveness of manganese as a broadband absorber due to its optical properties.

Validated the approach with full experimental characterization and physical analysis.

Abstract

Metallic layers are known to be used for the suppression of wave transmission when their thickness is sufficiently higher than the skin depth of metal. If in addition to blocking the transmission, metallic layers have the feature of blocking the reflection, too, they would make perfect absorbers. In this work, we propose an experimental approach of using a single thin layer of Manganese (Mn) as both the transmission suppresser and the reflection suppresser. This approach leads to obtaining lithography-free ultra-broadband perfect absorption in an ultra-wide spectrum ranging from Ultraviolet (UV) to Far Infrared (FIR). The measured average absorption is approximately 99%. Such a promising result can be achieved by only coating a single Mn layer on high-roughness substrates that include random nano-pyramids on it. In other words, we do not need a stack of different materials and combinations of geometrical features. The high roughness is realized on a commercial Silicon wafer substrate by inductively coupled plasma (ICP) etching. The key to this ultra-wideband absorption is electromagnetic field tapering which exists due to the graded-index feature of the structure (known as moth-eye effect), along with the ideal optical properties of Mn which makes it an excellent metal for broadband absorption applications. A full experimental characterization of the fabricated samples is presented along with the physical analysis of the phenomena. The findings of this paper can be used for the realization of lithography-free, cost-effective and high-throughput mass production of broadband absorbers.