Designing Novel LiDAR-Detectable Plate-Type Materials: Synthesis, Chemistry, and Practical Application for Autonomous Working Environment

Abstract

Plate-type hollow black TiO₂ (HL/BT) with a high NIR reflectance was fabricated for the first time as a LiDAR-detectable black material. A TiO₂ layer was formed on commercial-grade glass by using the sol-gel method to obtain a plate-type structure. The glass template was then etched with hydrofluoric acid to form a hollow structure, and blackness was further achieved through NaBH₄ reduction, which altered the oxidation state of TiO₂ to black Ti_<i>x</i>O_2<i>x</i>-1 or Ti⁴⁺ to Ti³⁺ and Ti²⁺. The blackness of the HL/BT material was maintained by a novel approach that involved etching prior to reduction. The thickness of the TiO₂ layer was controlled to maximize the NIR reflectance when applied as paint. The HL/BT material with a thickness of 140 nm (HL/BT140) showed a blackness (<i>L</i>*) of 13.3 and high NIR reflectance of 23.6% at a wavelength of 905 nm. This is attributed to the effective light reflection at the interface created by the TiO₂ layer and the hollow structure. Plate-type HL/BT140 provides excellent spreadability, durability, and thermal stability in practical paint applications compared with sphere-type materials due to the higher contacting area to the applied surface, making it suitable for use as a LiDAR-detectable inorganic black pigment in autonomous environments.