Carmichael’s Concise Review Coming Events
Due to COVID-19, please check to see if the listed events have been postponed or cancelled.
2021
ABRF 2021 March 7–10, 2021
Boston, MA
https://web.cvent.com/event/8eb4a085-b3c5-464a- ba49-023f033a7ee4/ summary?RefId=ABRF%20 2021%20 Annual%20Meeting%20Home
Focus on Microscopy 2021 March 28–31, 2021
Porto, Portugal
www.focusonmicroscopy.org
EMAS 2021 – 17th European Workshop on Modern Developments and Applications in Microbeam Analysis
May 16–20, 2021 Krakow, Poland
www.microbeamanalysis.eu/events/event/60- emas-2021-17th-european- workshop-on-modern- developments-and- applications-in-microbeam-analysis
IUMAS-8: 8th Meeting of the International Union of Microbeam Analysis Societies
May 24–28, 2021 Banff, Alberta, Canada
www.microbeamanalysis.eu/events/event/ 74-iumas-8-8th-meeting-of-the-international- union-of-microbeam- analysis-societies
mmc2021: Microscience Microscopy Congress 2021
July 5–8, 2021 Manchester, UK
www.mmc-series.org.uk
Microscopy & Microanalysis 2021 August 1–5, 2021
Pittsburgh, PA
www.microscopy.org/events/future.cfm
2022
Microscopy & Microanalysis 2022 July 31–August 4, 2022
Portland, OR
www.microscopy.org/events/future.cfm
2023 Microscopy & Microanalysis 2023 July 24–28, 2023
Minneapolis, MN
www.microscopy.org/events/future.cfm 2024
Microscopy & Microanalysis 2024 July 28–August 1, 2024
Cleveland, OH
www.microscopy.org/events/future.cfm
Ultra-black materials are characterized both by exceptionally low reflectance
and high absorbance. Teir industrial uses include, among others, the potential to increase photovoltaic cell efficiency, improve stray light capture in telescopes, and inform the design of infrared or radar camouflage. Currently, most synthetic ultra-black materials are made from nano-patterned metals or carbon nanotubes, but these are challenging to manufacture. Te nanotubes are extremely susceptible to abrasion and other forms of damage, making them unsuitable for many uses. Alexander Davis, H. Frederik Nijhout, and Sönke Johnsen reasoned that naturally occurring ultra-black materials could offer insight into more robust absorbers for future applications [1]. Some animals have evolved micro- or nanostructures that reflect as little as
0.05% of visible light. Tese include several species of birds of paradise, certain peacock jumping spiders, and some swallowtail butterflies. Davis et al. chose to study the structure of ultra-black areas of butterfly wings for three reasons: (i) their scales have evolved several different optical specializations, (ii) the scales are much thinner than other naturally occurring ultra-black materials or synthetic alterna- tives, and (iii) butterfly scales are both light and robust to be useful in flight. To investigate the general design principles of natural ultra-black materials, they used scanning electron microscopy (SEM), spectrophotometry, and a complex math- ematical calculation called finite-difference time-domain modeling. Tey exam- ined four subfamilies of butterflies: (i) other species of swallowtails, (ii) a group that includes tropical brushfoots, (iii) a group that includes a few of the almost 300 species of milkweed butterflies, and (iv) a group commonly called longwings. As controls, they examined brown or less black butterflies from four genera that contain ultra-black species. Davis et al. first characterized the structure of scales of 11 butterflies (7 ultra-
black, 4 controls) using SEM. All of the butterflies had scales with an upper lamina perforated by holes. Te holes were honeycombed, chevron-shaped, or rectangu- lar, varying in size from 500 × 330 nm to 750 × 500 nm. Various observations led to the conclusion that shape and size of the holes did not play an important role in ultra-blackness. Structural features that were consistently found in all the ultra-black speci-
mens were steep longitudinal ridges and robust trabeculae connecting the upper and lower laminae. Control butterflies either lacked or showed significantly reduced trabeculae. Finite-difference time-domain modeling was consistent with the hypothesis that trabeculae or ridges are key structural components for making an ultra-black structure. Other studies led to the conclusion that trabeculae are a more important feature than ridges. Aſter characterizing the underlying structure, Davis et al. examined the
absorbing pigment, melanin. Various studies suggested that melanin’s particular optical properties are not necessary to make ultra-black butterfly scales; only a strongly absorbing material is needed.
8 doi:10.1017/S1551929520001522 2020 November
The Microscopic Structure of Natural Ultra-Black Material
Stephen W. Carmichael Mayo Clinic, Rochester, MN 55905
carmichael.stephen@
mayo.edu
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