Generally stories about very black materials will mention carbon nanotubes but not this time. A July 30, 2024 University of British Columbia (UBC) news release (also on EurekAlert and received via email) announces the discovery of a technique for making super-black wood,

Thanks to an accidental discovery, researchers at the University of British Columbia have created a new super-black material that absorbs almost all light, opening potential applications in fine jewelry, solar cells and precision optical devices. 

Professor Philip Evans and PhD student Kenny Cheng were experimenting with high-energy plasma to make wood more water-repellent. However, when they applied the technique to the cut ends of wood cells, the surfaces turned extremely black. 

Measurements by Texas A&M University’s department of physics and astronomy confirmed that the material reflected less than one per cent of visible light, absorbing almost all the light that struck it. 

Instead of discarding this accidental finding, the team decided to shift their focus to designing super-black materials, contributing a new approach to the search for the darkest materials on Earth.

“Ultra-black or super-black material can absorb more than 99 per cent of the light that strikes it – significantly more so than normal black paint, which absorbs about 97.5 per cent of light,” explained Dr. Evans, a professor in the faculty of forestry and BC Leadership Chair in Advanced Forest Products Manufacturing Technology.

Super-black materials are increasingly sought after in astronomy, where ultra-black coatings on devices help reduce stray light and improve image clarity. Super-black coatings can enhance the efficiency of solar cells. They are also used in making art pieces and luxury consumer items like watches.

The researchers have developed prototype commercial products using their super-black wood, initially focusing on watches and jewelry, with plans to explore other commercial applications in the future.

Wonder wood

The team named and trademarked their discovery Nxylon (niks-uh-lon), after Nyx, the Greek goddess of the night, and xylon, the Greek word for wood. 

Most surprisingly, Nxylon remains black even when coated with an alloy, such as the gold coating applied to the wood to make it electrically conductive enough to be viewed and studied using an electron microscope. This is because Nxylon’s structure inherently prevents light from escaping rather than depending on black pigments.

The UBC team have demonstrated that Nxylon can replace expensive and rare black woods like ebony and rosewood for watch faces, and it can be used in jewelry to replace the black gemstone onyx.

“Nxylon’s composition combines the benefits of natural materials with unique structural features, making it lightweight, stiff and easy to cut into intricate shapes,” said Dr. Evans.

Made from basswood, a tree widely found in North America and valued for hand carving, boxes, shutters and musical instruments, Nxylon can also use other types of wood such as European lime wood.

Breathing new life into forestry

Dr. Evans and his colleagues plan to launch a startup, Nxylon Corporation of Canada, to scale up applications of Nxylon in collaboration with jewellers, artists and tech product designers. They also plan to develop a commercial-scale plasma reactor to produce larger super-black wood samples suitable for non-reflective ceiling and wall tiles. 

“Nxylon can be made from sustainable and renewable materials widely found in North America and Europe, leading to new applications for wood. The wood industry in B.C. is often seen as a sunset industry focused on commodity products—our research demonstrates its great untapped potential,” said Dr. Evans.

Other researchers who contributed to this work include Vickie Ma, Dengcheng Feng and Sara Xu (all from UBC’s faculty of forestry); Luke Schmidt (Texas A&M); and Mick Turner (The Australian National University).

Here’s a link to and a citation for the paper (and hat’s off to the writers for an accessible introduction),

Super-Black Material Created by Plasma Etching Wood by Kenneth J. Cheng, Dengcheng Feng, Luke M. Schmidt, Michael Turner, Philip D. Evans. Advanced Sustainable Systems DOI: https://doi.org/10.1002/adsu.202400184 First published: 16 June 2024

This paper is open access.

I can’t resist; this is such a good introduction, keeping in mind it’s written for an academic journal, from Super-Black Material Created by Plasma Etching Wood.

Super-black materials have very low reflectivity due to structural absorption of light.^[1] They are attracting considerable scientific and industrial attention because of their important applications in many fields: astronomy,^{[2, 3]} photovoltaics,^{[4, 5]} and optical science,^[6] among others. In these applications, super-black materials minimize unwanted reflection of light enabling devices to operate more accurately or efficiently.^[6] In other fields, for example art and design, the attraction of super-black materials lies in their ability to create bizarre visual effects because of huge contrast between black and adjacent colored objects or surfaces.^[7] This artistic application of super-black materials is analogous to the juxtaposition of super-black and brightly colored courtship display patches in birds and peacock spiders.^{[8, 9]} In birds, super-black patches have been defined as those having less than 2% directional reflectance at normal incidence.^[8] Reflectance values of super-black patches in 32 bird species ranged from 0.045 to 1.97% with an average of 0.94% (300–700 nm).^[8] Other studies have associated super-blackness with reflectance values of 1%^[10] or 0.5%.^[3] Far lower reflectance values have been achieved with materials containing aligned carbon nanotubes (CNT), for example a low-density CNT array (0.045%),^[11] the coating Vantablack (0.035%)^[7] and a CNT-metal foil (0.005%).^[12] The current holder of the “record” for a low reflectivity material (<0.0002%) is an ion-track micro-textured polymer with anti-backscatter matrix.^[13]

The low reflectivity of materials such as Vantablack is due to the high absorption of light by graphene and the ability of vertical arrays of CNT to lower surface reflection.^{[6, 7]} In the case of a low-density CNT array, its low reflectivity was ascribed to its random surface profile and presence of a loose network of entangled nanotubes, in addition to vertically oriented nanotubes.^[11] Other structures can also be used to reduce reflectivity of synthetic materials including nanopores, and microcavities.^[6] Even more diverse structures are found in natural super-black materials, including complex barbule microstructures in birds,^[1] cuticular micro-lens arrays in peacock spiders,^[9] and polydisperse honeycomb configurations in the wings of butterflies.^[14] The structural features of butterfly wings have been used as biomimetic models to create super-black polymer films.^{[4, 10]} This biomimetic route to creating super-black materials has the advantages that “the films are thinner than known alternatives and can be fabricated at lower temperatures via plasma-enhanced chemical vapor deposition, instead of being grown from CNT.”^{[4, 14]}

Biomimicry of nature’s structural material par excellence, wood, is being used to create lightweight stiff and tough composites,^{[15, 16]} but wood is not a model for the creation of super-black materials because even the darkest woods such as ebony (Diospyros spp.) or African blackwood (Dalbergia melanoxylon Guill. & Perr.) lack structural features that reduce reflectivity. Nevertheless, there is interest in using wood in applications where blackness is advantageous such as solar steam generation and desalination of water,^[17-20] because wood is widely available, inexpensive, sustainable and can be fabricated into panels and objects. In these applications, wood is carbonized and retains its porous microstructure creating a black material with reflectivity of 3%.^[18] The creation of additional porosity by micro-drilling the wood prior to carbonization further reduced reflectivity to 2%.^[18] We serendipitously created a super-black wood during undirected investigations into the use of plasma etching to “machine” novel microstructures at basswood (Tilia americana L.) surfaces. We called this material Nxylon, a neologism created from Nyx (Greek goddess of the night) and xylon (Greek for wood materials). One of us published the reflectivity data for Nxylon in 2020.^[21] Here we report on the structural features responsible for the super-blackness of Nxylon, describe how it is made and discuss its possible practical uses. During the preparation of this manuscript, we became aware of a novel approach to creating super-black wood involving high temperature carbonization of delignified balsa wood (Ochroma pyramidale (Cav. ex Lam.) Urb.).^[22] This material is produced using “mature processing technologies” and can be used to create solid wood products with complex geometries. The surface plasma process we describe is liquid free, generates little waste and is more suited for the creation of super-black veneer which can be used on a small scale to manufacture luxury consumer products. Therein lies the novelty and significance of our work.

…

The most comprehensive piece I’ve published on the topic of the ‘really, really black’ is in a December 4, 2019 posting, “More of the ‘blackest black’.” At that point, some new work on creating the blackest black (up to 99.99% and 99.995% light absorption, respectively) had come from the US National Institute of Standards and Technology (NIST) and the Massachusetts Institute of Technology (MIT). I also included the latest about an artistic feud over Vantablack (mentioned in the paper’s introduction) and its 99.8% light absorption and provided a link back to my earliest stories on Vantablack.