Tailoring thermal radiation using low‐infrared‐emissivity materials has drawn significant attention for diverse applications, such as passive radiative heating and thermal camouflage. However, the previously reported low‐infrared‐emissivity materials have the bottleneck of lacking independent control over visible optical properties. Here, a novel visibly transparent and infrared reflective (VTIR) coating by exploiting a nano‐mesh patterning strategy with an oxide–metal–oxide tri‐layer structure is reported. The VTIR coating shows simultaneously high transmittance in the visible region (>80% at 550 nm) and low emissivity in the mid‐infrared region (< 20% in 7–14 µm). The VTIR coating not only achieves a radiative heating effect of 6.6 °C for indoor conditions but also enables a synergetic effect with photothermal materials to keep human body warm at freezing temperatures for outdoor conditions, which is 10–15 °C warmer than normal cotton and Mylar film. Moreover, it demonstrates an excellent thermal camouflage effect at various temperatures (34–250 °C) and good compatibility with visible camouflage on the same object, making it ideal for both daytime and nighttime cloaking. With its unique and versatile spectral features, this novel VTIR design has great potential to make a significant impact on personal heat management and counter‐surveillance applications.
Nanocrystalline diamonds (NCDs) are one of the many carbon
allotropes
that have attracted great attention for the advancement of many technologies
owing to their superior mechanical, thermal, and optical properties.
Yet, their synthesis must be improved for availability at low costs
and their widespread application. Here, we report the atmospheric-pressure
flame vapor deposition (FVD) synthesis of NCD particles and thin films
over an area of more than 27 cm2 using methane–hydrogen–air
flat flames. Synthesis at atmospheric pressure is beneficial as it
can lower costs and be more time-efficient when compared to the batch-by-batch
synthesis of low-pressure and high-pressure processes. Also, the abundance
of methane gas available can further lower costs and improve scalability,
while generating lower flame temperatures to mitigate the need of
extensive cooling. Notably, the FVD method unlocks conditions for
diamond growth beyond the previously considered diamond-growth region
of the C–H–O phase diagram. By modeling the flame radical
species as a guidance, we experimentally demonstrate that the FVD
growth of NCDs can be facilely controlled by tuning the reactant gas
composition, substrate material, and seeding density. Moreover, we
show that the addition of an external electric bias was influential
in controlling the porosity and thickness of the NCD films. Overall,
with the low cost and simplicity for operation without the need of
vacuum, this atmospheric-pressure FVD approach will offer opportunities
to facilitate the scaling-up of NCD synthesis for applications in
optical, tribological, thermal, and biomedical coatings.
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