Pitaya-Structured Microspheres with Dual Laser Wavelength Responses for Polymer Laser Direct Writing

Autocatalytic Laser Activator for Both UV and NIR Lasers: Preparation of Circuits on Polymer Substrates by Selective Metallization

In laser-induced selective metallization (LISM), conventional laser activators only work at a single laser wavelength. This study reported a new laser activator (MoO₃) very suitable for both 355 nm UV and 1064 nm near-infrared (NIR) lasers for the first time. When applying MoO₃ to polymers, the prepared Cu layer on laser-activated polymers showed a good conductivity (2.63 × 10⁶ Ω^-1·m^-1) and excellent adhesion. Scanning electron microscopy, optical microscopy, and resistance analysis revealed the excellent LISM performance of the polymer/MoO₃ composites, and the quality of the Cu layer prepared using the UV laser is much better than that using the NIR laser. The limit width of the copper wire prepared by the UV laser is as narrow as 30.1 μm. We also confirmed the mechanism of MoO₃ initiating electroless copper plating after laser activation to be the autocatalytic mechanism, which is very different from the conventional reduction mechanism. The effect of laser activation was only to expose the MoO₃ active species to the polymer surface. X-ray diffraction and tube experiments revealed that the activity of α·h-MoO₃ was higher than that of α-MoO₃. X-ray photoelectron spectroscopy indicated that a part of Mo⁶⁺ was reduced to Mo⁵⁺ during laser activations, leading to the increase of the oxygen vacancies in MoO₃ and possibly further enhancing the activity of MoO₃. Besides, the micro-rough structures caused by the laser on the polymer surface provided riveting points for successfully depositing the copper layer. The Ni-Cu, Ag-Cu, and Au-Ni-Cu layers were obtained via the continued deposit of other metals on the Cu layer. The resistances of these metal layers had much better stability than that of the neat Cu layer. Furthermore, the Au layer further enhanced the conductivity of the circuit. The proposed strategy is easy for large-scale industrial applications, which will greatly expand the application scenarios of the LISM field.