Ceramic aerogels, which present a unique combination of low thermal conductivity and excellent high-temperature stability, are attractive for thermal insulation under extreme conditions. However, most ceramic aerogels are constructed by oxide ceramic nanoparticles and thus are usually plagued by their brittleness and structural collapse at elevated temperatures (less than 1000 °C). Despite great progress achieved in this regard recently, it still remains a big challenge to design and fabricate intriguing ceramic aerogels with enhanced mechanical strength and remarkable thermal stability at ultrahigh temperature up to 1400 °C. To this end, we herein report a facile and scalable strategy to manufacture ceramic nanorod aerogels (CNRAs) with hierarchically macroporous and mesoporous structures by the controllable assembly of Al2O3 nanorods and SiO2 nanoparticles. Subsequently, the high-temperature annealing treatment of CNRAs significantly maximizes mechanical strength and promotes thermal tolerance. The obtained CNRAs demonstrate the integrated properties of super-strong heat resistance (up to 1400 °C), low thermal conductivity (0.026 W/m·K at 25 °C and 0.089 W/m·K at 1200 °C), high mechanical robustness (compressive strength 1.5 MPa), and low density (0.146 g/cm3). We envision that this novel nanorod-assembled ceramic aerogels offer considerable advantages than most of the state-of-the-art ceramic aerogels for thermal superinsulation upon exposure to extremely harsh environments.

Ultrafast all-optical switches based on epsilon-near-zero (ENZ)-enhanced nonlinear refraction in transparent conducting oxides have achieved exciting results in realizing large absolute modulations. However, broad-band, polarization-independent, and wide-angle ultrafast all-optical switches have been challenging to produce, due to the inherent narrow band, polarization-dependent, and angle-dependent characteristics of the ENZ effect. To this end, we propose an ultrafast all-optical switch based on the enhanced nonlinear absorption of corrugated indium tin oxide (ITO) thin films. Taking advantage of the perfect absorption and localized field enhancement of the ENZ and localized surface plasmon resonance modes, we significantly enhanced the nonlinear absorption of the corrugated ITO film in the 1450–1650 nm telecom band. The experimental results show that the nonlinear saturable absorption coefficient of the corrugated ITO film at 1450 nm was as high as −1.5 × 105 cm GW–1, enabling all-optical switching to obtain an extinction ratio of 14.32 dB and an ultrafast switching time of 350 fs at a pump fluence of 18.51 mJ cm–2. Furthermore, the all-optical switch achieved an extinction ratio of over 15 dB and an insertion loss of approximately 2.6 dB within the 200 nm absorption band and exhibited polarization-independent and wide-angle features. The ultrafast temporal response can be attributed to intraband transient bleaching of the corrugated ITO film. Our findings demonstrate that corrugated ENZ films can overcome the inherent narrow-band, polarization-dependent, and angle-dependent problems of natural ENZ materials without increasing the response time, making them a potential ENZ ultrafast all-optical switching material platform.

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