Hierarchical WO_3–x Ultrabroadband Absorbers and Photothermal Converters Grown from Femtosecond Laser-Induced Periodic Surface Structures

Abstract

Oxygen-vacancy-rich WO3–x absorbers are gaining increasing attention because of their extensive absorbance-based applications in near-infrared shielding, photocatalysis, sterilization, interfacial evaporator and electrochromic, photochromic, and photothermal fields. Thermal treatment in an oxygen-deficient atmosphere enables us to prepare WO3–x but lacks the capacity for finely manipulating the grown structures. In this work, we present that laser-induced periodic surface structure (LIPSS) obtained by femtosecond laser ablation is a good template to grow various hierarchical WO3–x ultrabroadband absorbers and photothermal converters by thermal oxidation annealing in air. Increasing annealing temperature from 600 to 1000 °C allows the manipulation of WO3–x crystal sizes from ∼70 nm to ∼4 μm, accompanied by a color transition from brown to dark blue and finally to yellow. Benefiting from annealing-induced surface cracks and phase transition into WO3–x (containing both WO3 and W18O49) at 600 °C, excellent UV–vis–NIR–MIR ultrabroadband absorbers were produced: >90% UV–NIR absorbance (0.3–2.5 μm) and 50–90% MIR absorbance (2.5–16 μm), much better than most W-based metamaterial absorbers. The higher the annealing temperature (1000 > 800 > 600 °C), the better the photothermal performances (sample temperature as the indicator) of annealed interfaces due to the increased oxidation rates and resultant thicker oxide layers (6, 150, and 507 μm), a trend which is more apparent upon the irradiation of high-density (3160 mW/cm2) and ultrabroadband (200–2500 nm) light but much less apparent for shorter-band (200–800, 420–800, 800–2500 nm, etc.) and less-intensity (1694, 1540, 1460 mW/cm2, etc.) light irradiation. This phenomenon indicates that (1) higher-performance ultrabroadband absorbers possess a higher photothermal conversion capacity; (2) thicker-WO3–x oxide layer converters are more effective in preserving photothermal heat; and (3) both the W-LIPSS and metal tungsten substrate can quickly dissipate the photothermal heat to inhibit heat accumulation in the oxide photothermal converters. It is also proved that ablation-induced high-pressure shockwaves can produce deformation layers in the subsurfaces to release annealing-induced stresses, beneficial for the formation of less-cracked non-stoichiometric WO3–x interfaces upon annealing. High-pressure shockwaves are also capable of inducing grain refinement of LIPSS, which facilitates a homogeneous growth of small non-stoichiometric metal-oxide crystals upon annealing. Our results indicate that femtosecond laser ablation is a convenient upstream template-fabrication technique compatible with the thermal oxidation annealing method to develop advanced functional oxygen-vacancy metal-oxide interfaces.

Chelating Coordination Regulated Photochromic Electrospun Nanofibers for Waterproof and Long-Color-Retention Rewritable Wearables

“…39 In the high-resolution XPS spectrum of tungsten (W 4f), four peaks at 33.8, 35.4, 36.3, and 37.4 eV are identifiable, which are contributing to W 4f 7/2 and W 4f 5/2 . 56 The splitting of the 4f doublets is 2.0 eV (35.4 to 37.4 eV), indicating that the valence state of W is +6, which corresponds to the typical binding energies of W 6+ oxidation states in WO 3 (Figure 6b). Moreover, the peak at 41.0 eV is considered as tungsten (W 5p).…”

“…The existence of Al is attributed to the 2s and 2p peaks, which might be ascribed to the substrate (Al foil) (Figure a) . In the high-resolution XPS spectrum of tungsten (W 4f), four peaks at 33.8, 35.4, 36.3, and 37.4 eV are identifiable, which are contributing to W 4f 7/2 and W 4f 5/2 . The splitting of the 4f doublets is 2.0 eV (35.4 to 37.4 eV), indicating that the valence state of W is +6, which corresponds to the typical binding energies of W 6+ oxidation states in WO 3 (Figure b).…”

Pd Decoration with Synergistic High Oxygen Mobility Boosts Hydrogen Sensing Performance at Low Working Temperature on WO3 Nanosheet

“…As shown in Figure 7a, the deconvoluted peaks at 35.7 and 37.8 eV corresponded to W 6+ 4f 7/2 and W 6+ 4f 5/2 . 58,59 Notably, the Pd 3d spectra showed two different states (Pd 2+ and Pd 0 ) of Pd species, and the peaks corresponded to Pd 2+ at 336.6 eV (3d 5/2 ) and 341.9 eV (3d 3/2 ) and to Pd 0 at 335.4 eV (3d 5/2 ) and 340.7 eV (3d 3/2 ) (Figure 7b−d). 30 Particularly, the amount of Pd 2+ species considerably increased at the elevation of annealing temperature, further proving the MSI between Pd nanoparticle and WO 3 nanosheet.…”

Advances in Photothermal Catalysis: Mechanisms, Materials, and Environmental Applications

“…proposed femtosecond laser-induced periodic surface structure hierarchical WO 3−x (x ranged from 0 to 1) for enhanced photothermal conversion owing to the broadband light absorption ability. 132 After WO 3−x crystal endowment, NIR absorbance was significantly increased on account of oxygenvacancy-enhanced absorbance and light trapping effect (Figure 7d), which was higher than those of W/SiO 2 /W 137 and Wcoated anodic aluminum oxide (AAO) nanowires. 138 The NIR region absorption of WO 3−x /C (x ranged from 0 to 1) was strongly improved, aroused by OVs and carbon coating, which further promoted the carrier separation efficiency.…”