Preparation of Dispersed Copper(II) Oxide Nanosuspensions as Precursor for Femtosecond Reductive Laser Sintering by High-Energy Ball Milling

Abstract

This contribution demonstrates and discusses the preparation of finely dispersed copper(II) oxide nanosuspensions as precursors for reductive laser sintering (RLS). Since the presence of agglomerates interferes with the various RLS sub-processes, fine dispersion is required, and oversized particles must be identified by a measurement methodology. Aside from the established method of scanning electron microscopy for imaging individual dried particles, this work applies the holistic and statistically more significant laser diffraction in combination with dynamic image analysis in wet dispersion. In addition to direct ultrasonic homogenization, high-energy ball milling is introduced for RLS, to produce stable nanosuspensions with a high fine fraction, and, above all, the absence of oversize particles. Whereas ultrasonic dispersion stagnates at particle sizes between 500 nm and 20 μm, even after 8 h, milled suspension contains a high proportion of finest particles with diameters below 100 nm, no agglomerates larger than 1 μm and a trimodal particle size distribution with the median at 50 nm already, after 100 min of milling. The precursor layers produced by doctor blade coating are examined for their quality by laser scanning microscopy. The surface roughness of such a dry film can be reduced from 1.26 μm to 88 nm by milling. Finally, the novel precursor is used for femtosecond RLS, to produce homogeneous, high-quality copper layers with a sheet resistance of 0.28Ω/sq and a copper mass concentration of 94.2%.

Rheological Investigation of Highly Filled Copper(II) Oxide Nanosuspensions to Optimize Precursor Particle Content in Reductive Laser-Sintering

“…Only when sufficiently diluted to a ratio of 1.33 or less, the PC has a high flowability immediately after shearing, so that the grooves formed during coating are smoothed out. Previous work [22] has shown, in connection with the presence of large agglomerates in the PC, that a homogeneous surface is urgently required in order to produce reproducible, homogeneous and defect-free Cu structures. Shestakov et al also showed in the context of RLS with deep eutectic solvents that the layer thickness of the PC has a significant influence on the laser-generated Cu structure [30].…”

“…The results shown in this work deviate from previous observations and show that a homogeneous surface can only be formed when the particle content is reduced to about 50 wt%. In addition to the different coating technique, we presume that this is primarily due to the milling process, which is associated with highly dispersed PC [22]. The degassing of the PC also prevents the formation of fine air bubbles during the drying process of the PC layer.…”

“…The size measurement of the SEM images was performed using the software Gwyddion (Czech Metrology Institute, Jihlava, Czech Republic). For further details on the PC preparation and measurement, we refer readers to our previous publication [22]. After its characterization, the stock PC was diluted stepwise by adding EG.…”

“…Recently, the production of highly filled, finely dispersed CuO PC for RLS was demonstrated by high-energy ball milling, so that ultra-homogeneous PC layers can be produced without interfering agglomerates. As in other works, the coating composition had to be finely adjusted by adding solvent in order to achieve good coatability [22].…”

Commercial-Grade Dielectrics Surface Metallization by Direct Laser Deposition from Deep Eutectic Solvents

“…For example, selective surface activation induced by laser (SSAIL) is a prominent representative of the first group, and laser scribing is used for dielectric surface activation − to facilitate further selective metallization. On the contrary in reductive laser sintering (rSLS), , lasers are directly employed for the chemical reduction of CuO nanoparticles (NPs), as well as for sintering these particles to form copper patterns . This approach has a great perspective for the fabrication of micro-thermocouples and tactile and electrochemical sensors based on copper, nickel, cobalt, and composite films. , …”