Ft ir 6000

In this study, the CuNP solution samples without any rinsing were directly analyzed by UV–vis (Gensys 10 Series, Thermo Scientific, Waltham, MA, USA). The morphological properties of the CuNPs were studied using an H-7100 TEM (Hitachi, Tokyo, Japan). Measurement of the Cu conductive ink viscosity was carried out using a DV3T viscometer (Brookfield Engineering Laboratories, Middleboro, MA, USA). XRD (Empyrean, Malvern Panalytical, Malvern, UK) was used to further characterize the CuNPs. The surface tension of Cu conductive ink was assessed using a Model 100SB device (Sindatek Instruments, New Taipei, Taiwan). Fourier-transform infrared (FTIR) spectroscopy (FT/IR-6000, Jasco International Co., Tokyo, Japan) was used to confirm the functional groups change of PET before and after surface modification, and atomic force microscopy (AFM; XE-100, Park Scientific Instruments, Sunnyvale, CA, USA) was used to measure the surface roughness. Finally, the electrical resistivity of the patterns was measured using a Surfcorder ET3000 microfigure measuring instrument (Kosaka Laboratory, Tokyo, Japan) and a Keithley 2000-EM4P four-point probe analyzer (Tektronix, Beaverton, OR, USA).

The surface morphology of butterfly wings and biomimetic samples were observed using a digital camera (EOS7D, CANON, Tokyo, Japan), a digital microscope (VHX-6000, KEYENCE, Tokyo, Japan), and a scanning electron microscope (SEM, JEOL Ltd., Tokyo, Japan). In addition, the chemical composition of butterfly wing scales and biomimetic samples were tested using EDS (equipped on SEM, JEOL Ltd., Tokyo, Japan), XRD (Bruker-AXS, Billerica, America. X-ray diffractometer system, recorded in the lower angle), and FTIR (FT/IR-6000, JASCO, Tokyo, Japan). The contact angles of butterfly wings, biomimetic samples, and ordinary glass were measured using a contact angle measuring instrument (JC2000A, Biolin Scientific, Espoo, Finland). The reflectivity of the butterfly wings, biomimetic samples, and ordinary glass were tested using a spectrometer (USB 4000, Ocean Optics, Dunedin, FL, USA), which was carefully calibrated using STD-WS. Fog droplets were generated at a speed of 30 cm·s⁻¹ using an ultrasonic humidifier (YC-X100E, YADU, Beijing, China).

CeO₂ NPs were synthesized using a homogeneous precipitation method. Ce(NO₃)₃ 6H₂O (4 mmol) and urea (50 g) were mixed and dissolved in distilled water (300 mL) and heated at 90°C for 60 min in a hot water bath. After cooling to 20°C, the precipitate was collected as a precursor by centrifugation (10,000 g, 10 min) and washed with distilled water (10,000 g, 10 min, ×3). After drying the precursor at 80°C for 24 h, it was calcined by increasing the temperature to 800°C at a rate of 10°C/min and maintaining it at 800°C for 1 h in an electric furnace (NHK-170; Nitto Kagaku Co., Ltd., Nagoya, Japan). Calcined samples (1 g) were milled using Pulverrisette 7 Classic Line (Fritsch GmbH, Idar-Oberstein, Germany) at 250 rpm for 60 min. The obtained samples were analyzed using an FT-IR spectrometer (FT/IR-6000; JASCO Co., Tokyo, Japan), X-ray diffraction (XRD; RINT-TTR III; Rigaku Co., Tokyo, Japan), dynamic light scattering (DLS; ELSZ-2000ZS; Otsuka Electronics Co., Ltd., Osaka, Japan), and scanning electron microscopy (SEM; S-4200; Hitachi High-Tech Co., Tokyo, Japan). The crystalline size of samples was also determined by the half-width of XRD peaks according to the Scherrer formula (Patterson, 1939 (link)).