In this paper, a facile method was introduced to fabricate fine conductive patterns by low-temperature selective laser sintering of Cu nanoparticles. By virtue of a nanosecond-pulsed ultraviolet laser source, fine circuits with a thickness of ∼8 µm and a conductivity of 3-6.5 × 10 6 S m −1 was successfully fabricated from Cu nanoparticle paste with a high metal content >80 wt.% on a flexible substrate at a wide scan rate range of 5-500 mm s −1 . The sintered circuits exhibited a special sandwich morphology, with fully melted features in the centre and thermally sintered neck-connected features on the edges. A twofold linear relationship between the width of thermally sintered region and the reciprocal of the laser scan rate was revealed, indicating a heat dissipation mode transition from metal layer dominated dissipation to substrate dominated dissipation with the decrease of the laser scan rate. Finite element simulations were carried out to study the evolutions of temperature field and heat dissipation with changing laser scan rate and power, and the results fitted well with experimental results. On this basis, a relational expression was further proposed to determine the optimal processing window for laser sintering of metal nanoparticle layers. Our method extends the producible thickness and improves the fabrication efficiency of laser-printed circuits with desirable conductivity. The findings of this study can provide a guidance for understanding and controlling the sintering and heat transfer process of printing methods with similar materials and techniques.
In this paper, isotropic copper nanoparticles (CuNPs) were successfully sythesized by using Cu(CH3COO)2 and ascorbic acid in absolute ethanol solution. With the addition of polyvinylpyrrolidone (PVP) protective additive, the size distribution range of the synthesized CuNPs was significantly reduced from 650±415 nm to 51±12 nm. Electrodeposition analysis revealed that PVP could greatly suppress the reduction of Cu but had no prominent effects on the deposition mechanism. Based on the potentiostatic deposition results, a growth model was proposed to improve the applicability of the Scharifker‐Hills model by considering both the surface inhibition effect and the mass diffusion during the growth process of Cu nuclei. The experimental data fitted well with the prediction results from the proposed model, indicating that the electrodeposition of Cu followed the progressive nucleation process. The PVP additive could inhibit the deposition and growth of Cu by increasing the surface inhibition for cation incorporation on the nuclei, which was probably the main reason for the refinement of the sythesized CuNPs. Our findings can provide insights for the preparation of metallic nanoparticles and the understanding of their deposition mechanism.
The Cover Feature illustrates a wet‐chemical synthesis method using Cu(CH3COO)2 and ascorbic acid in absolute ethanol solution for the preparation of isotropic copper nanoparticles. A strong surface inhibition effect of the PVP protective additive remarkably refines the particle size. Electrodeposition analysis provides insights for the preparation of metallic nanoparticles and an understanding of their deposition mechanism. More information can be found in the Aricle by G. Yang, X. Zeng et al.
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