Appl. Phys. Lett. 102, 251105 (2013)

Credit: © 2013 AIP

Mihail Bora and colleagues at Lawrence Livermore National Laboratory, USA, have investigated a metallic structure that absorbs more than 95% of incident light. Their work builds on other recent research that typically uses metallic grooves or 'funnels' to minimize the impedance mismatch or reflection with the surroundings with the aim of trapping or nanofocusing light in the sample. Using a square array of metal-coated nanowires, the team showed that absorbance of the substrates can be increased above 75% in the 400–800 nm range. The use of structures fabricated from wires with more pronounced matchstick-like tops formed more pronounced funnels, resulting in absorbances of over 90%. Nanowire arrays were patterned on 4-inch wafers by laser interference lithography and were transferred to a silicon substrate by directional deep reactive ion etching. The wire length and profile are determined by the etch time. Such structures that employ nanofocusing and dissipation to absorb light have been dubbed 'black metals'.