Dandelion-Like Carbon Nanotubes for Near-Perfect Black Surfaces

Abstract

A variety of complex and expensive techniques, which usually work efficiently in the visible range only, have been developed to make a near-perfect blackbody. In this work, novel hierarchical dandelion-like flower carbon nanostructure (FCNTs) are synthesized by using a two-step growth protocol. FCNTs show near-perfect absorption of ≥99.9% in the wavelength range of 300–2000 nm at varying beam angles (10° to 60°). Coupled with the emissivity of 0.98, FCNTs are qualified as one of the darkest artificial materials. The observed behavior originates from multiple scattering and subsequent trapping of incident beam inside the FCNT microstructure. The contact angle (172°) and roll-off angle (2°) of water droplets reveal the superhydrophobic and self-cleaning behavior of the fabricated surface. The combination of properties demonstrated by FCNTs are envisaged to be a significant step toward developing better materials for stray light absorption and a light trapping layer in a photovoltaic system.

Near perfect thin film flexible broadband optical absorber with high thermal/electrical conductivity

“…It is observed that VACNTs are having refractive index close to air due to the presence of more than 96% air in the VACNT structure. VACNT array having a low filling fraction of 3.2% when added in pure PDMS, the overall reflective index of composite decrease to 1.36 compared to 1.6 of pure PDMS. Due to the lowering of refractive index, the reflection losses from air‐flexible absorber interface are reduced to 3% in UV–Vis spectrum and around 4% in NIR wavelength region [see Figure (a)].…”

“…In addition to absorption behavior, emissivity of pure PDMS and PDMS‐VACNT composites is measured using a Scotch™ Brand 88 black vinyl electrical tape of known emissivity (0.96) as per our previous work . Scotch tape with known emissivity and PDMS or PDMS‐VACNT sample with unknown emissivity are heated up to a set temperature and emissivity is calculated using Boltzmann's law as given in equation .…”

“…Recently, Ghai et al . shown that absorption capacity of as high as 99.98% in UV–Vis–NIR wavelength range is possible with hierarchical dandelion‐like flower carbon nanostructure . It should be pointed out here that most of the existing ultra‐black absorbers are fabricated on rigid substrates .…”

“…shown that absorption capacity of as high as 99.98% in UV–Vis–NIR wavelength range is possible with hierarchical dandelion‐like flower carbon nanostructure . It should be pointed out here that most of the existing ultra‐black absorbers are fabricated on rigid substrates . For real life applications, absorber needs to be flexible in nature so that it can be mounted on any surface having different curvatures without any damage or creasing failure.…”

Mechanically Robust Vertically Aligned Carbon Nanotube Composites for Applications in Ultralow Reflectance Optical Elements

“…Ultrablack materials can reflect less than 1% of incident light and can be used to reduce stray light in low signal detector systems (e.g., deep space images) − and as broad-band absorbers. − Vertically aligned carbon nanotube (VACNT) forests are currently the darkest manmade material − and have resulted in a reflectance down to ∼0.012% for red light. The low reflectance is caused by two factors: first, the extremely low carbon density in the VACNT forests , (they are mostly air) resulting in an effective refractive index very close to the index of air and second a high coefficient of optical absorption.…”