Announcing a new publication from Opto-Electronic Sciences; DOI 10.29026/oes.2026.260023.

The “Janus” concept, integrating asymmetric functions like radiative cooling (RC) and photothermal (PT) effects is gaining prominence for multi-scenario applications. In this work, we present a novel “Janus-material/functional” processing paradigm by femtosecond laser nanomaterial synthesis and 600°C post thermal annealing. This technique enables universal preparation of PT-active surfaces and in situ white (colorful) RC functional transition on transition metals of Nb, Mo, Ta, and W, while Ti-based PT interface exhibits uniquely 600°C-annealing thermal resistance.

"Janus" concept, inspired by the two-faced Roman deity, enables interfaces with dual functionalities. Motivated by harsh environmental applications, advanced thermal regulation materials like black photothermal (PT) and white/colorful radiative cooling (RC) materials are gaining increasing worldwide attraction, particularly for interfacial heat dissipation. However, the most frequently investigated oxide-polymer RC composites lack functional diversity and environmental durability. To enable scenario-adaptive thermal control and enhance environmental resistance, metal-based Janus thermal regulation is urgently needed. Although femtosecond laser machining excels at metal "blackening" through micro/nano-texturing and in situ nanomaterial synthesis, processes for "black-to-white" and "white-to-black" Janus conversions, as well as single/double-sided black-white integration (Figure 1), require breakthroughs. Additionally, the validation of black-to-colorful Janus thermal regulation remains an open challenge.

To address these technical bottlenecks, the research team led by Associate Professor Dongshi Zhang and Professor Zhuguo Li at Shanghai Jiao Tong University innovatively proposed a new processing paradigm for metal-based Janus materials and functionalization: femtosecond laser micro/nano-machining followed by thermal oxidation treatment. This approach enables monolithic fabrication of tungsten-based PT/RC black/white tungsten oxide interfaces and integrated manufacturing of single-, double-, and integrated single/double-sided Janus PT/RC interfaces as illustrated in Figure 1, also expandable for fabricating colorful RC-interfaces on various metals. This work was recently published in Opto-Electronic Science entitled by “Femtosecond laser-based ‘Janus-material/function’ processing paradigm for photothermal and radiative cooling modulation.”

Femtosecond laser processing of a tungsten (W) metal plate synthesizes and deposits black WO_3-x nanomaterials, which can be transformed into white WO_3-x interface through thermal annealing (Figure 2) under optimized annealing temperature and duration conditions. The significant differences in thermal conductivity and infrared emissivity between the metal substrate and the interfacial oxides constitute the Janus thermal regulation material/function system. The regulation of black and white tungsten oxide further endows the metal substrate with either PT or RC function (Figure 2). Under 1-sun irradiation, PT/RC- interfaces raise the temperature of the tungsten metal by 9 °C and lower it by 2 °C, respectively, providing strong support for development of 24-hour (day/night) photo-thermal electric generation (PTEG) interfaces.

This processing paradigm exhibits high flexibility, enabling double-sided black/white PT-RC functionalization and single-sided “LASER JANUS” black/white patterning on the metal tungsten substrate. The black PT and white RC interfaces can withstand thermal oxidation at 100°C and 200°C for 4 hours, are as well resistant to hand shaking and tape scratching. Furthermore, this paradigm shows excellent material universality and potential for extending to colorful RC interfaces, which has been verified using Ta, Mo, and Nb substrates (Figure 3). The experiments also reveal the thermal oxidation resistance of the Ti-based (TiO_2-x) PT interface, which retained their black color after annealing at 600°C for two hours, highlighting the diversity of Janus thermal regulation and the distinct characteristics of different materials. Given the wide variety of metal-based materials (elements, alloys, and composites), it can be inferred that this new processing paradigm enabling Janus thermal regulation will facilitate the development of gradient thermal-regulation materials and interfaces.

Keywords: Janus matrix, femtosecond laser synthesis, photothermal, radiative cooling, photo-thermoelectric generation

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This work was carried out under the joint supervision of Assoc. Prof. Dongshi Zhang and Prof. Zhuguo Li, with Dr. Jianing Liao as the first author. The research was supported by Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University. The team has long been dedicated to exploring the application potential of femtosecond laser micro/nano-processing in multidisciplinary fields, with a particular focus on optical/photothermal modulation, metamaterials/metasurfaces fabrication, and development of multifunctional thermal regulation materials and interfaces.
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Liao JN, Li ZG, Zhang DS. Femtosecond laser based “Janus-material/function” processing paradigm for photothermal and radiative cooling modulation. Opto-Electron Sci 5, 260023 (2026). DOI: 10.29026/oes.2026.260023