Glass‐Channel Molding Assisted 3D Printing of Metallic Microstructures Enabled by Femtosecond Laser Internal Processing and Microfluidic Electroless Plating

Abstract

the trend of miniaturization, the 3D printing has become a power tool for producing various types of microstructures including photonics, microfluidics, micromechanics, and biostructures. [2][3][4][5][6] The most commonly used materials supporting 3D microprinting are based on polymer, as the polymer is easy to be processed. In the meantime, there is a high demand on the 3D metallic microstructures in applications such as microelectronics, terahertz photonics, microelectromechanical systems, and 3D electrodes, to name a few. [7][8][9][10] Generally speaking, the current additive manufacturing approach of 3D metal printing heavily relies on powder fusing methods such as laser selective melting and electron beam melting, [11] which is intrinsically a thermal process inevitably suffering from a thermal diffusion detrimental for high-resolution 3D printing. Therefore, several 3D metallic direct microprinting methods such as direct ink writing, [12] electrohydrodynamic printing, [13] local electrophoretic deposition, [14] laser induced forward transfer, [15] layer-by-layer electrodeposition, [16] laserinduced photoreduction, [17] and electrodeposition-based 3D printing [18] have been developed. Besides above-mentioned 3D 3D printing of metallic microstructures is highly desirable for many practical applications such as microelectronics, terahertz photonics, microelectromechanical systems, and electrochemisty. Unfortunately, high resolution microprinting of 3D metal structures with widely tunable feature sizes, high conductivities, high melting points, and highly smooth surfaces remains challenging for current microfabrication technologies. Herein, 3D printing of metallic microstructures of feature sizes ranging from ≈10 to ≈200 μm by combining femtosecond laser micromachining of 3D glass microchannels and microfluidic electroless plating is demonstrated. The proposed technique allows for producing 3D metallic structures of almost arbitrary geometries embedded in glass since the continuous flow of the plating solution enables controllable deposition of metal films inside the through microchannels. Moreover, freestanding metallic 3D microstructures are fabricated by removing the glass matrix with a wet chemical etching. As a nonthermal processing, the surface roughness of the fabricated metallic structures is as low as ≈20 nm. The 3D microstructures can be made of either silver or copper covered with a thin layer of silver, which are shown to have a high conductivity. As a proof-of-concept demonstration, a 3D metal scaffold structure with a size of ≈5 × 5 × 2 mm 3 is printed.

Electroless Plating of Metal Nanomaterials

“…The facility and flexibility of electroless plating is especially useful when working on laboratory and prototyping scales, and in conjunction with 3D printing. [17,38,50,51] Due to the reliance on chemical reducers and the more involved bath management, electroless plating reactions are more expensive than comparable electrodepositions.…”

“…Inversely, specific areas can be blocked to restrict metallization (e. g., with photolithography, [28] soft lithography, [145] simple printing, [121] or by confining the deposition through microfluidic channels). [17,146] For accurate nanoscale patterns, the process resolution is obviously critical, but the structural fidelity can also be obstructed by too large or misplaced deposit particles. If the patterning relies on seeds, they should be active, small, and attached to the chosen substrate areas in a dense, firm, homogeneous and selective fashion.…”

“…Not reliant on electrical contacting, the method is almost absurdly flexible regarding the substrate to be metallized, irrespective of its state of matter, composition, and morphology. Suitable substrates include gas nano-bubbles, [11] emulsified droplets, [12] dispersed nanoparticles, [13] artful three-dimensional lattices, [14] diatom shells, [15] spirulina filaments, [16] laser-written microfluidic channels [17] and block copolymer templates. [18] This astonishing flexibility allows constructing manifold nanomaterials, which range from quasi-zero-dimensional nanoparticles [13] over nanowires [19] and nanoplates [20] to monolithic nanostructured materials.…”

Electroless Nanoplating of Iridium: Template‐Assisted Nanotube Deposition for the Continuous Flow Reduction of 4‐Nitrophenol

“…While electroplating is limited to conductive substrates, electroless plating has proven to be particularly suitable for the conformal metal coating of various materials (including insulators) and complex substrates. [40][41][42] In electroless plating, metal ions are reduced by a reducing agent in an autocatalytic reaction without an external supply of electrons. [43] While most industrial electroless plating procedures focus on Ni deposits and are usually optimized for the fast coating of macroscale workpieces, [44,45] plating reactions suitable for nanomaterial production have been published for a variety of metals including Cu, [35] Ag, [32,38,[46][47][48] Au, [49,50] Pd, [51][52][53][54] and Pt.…”

3D-MID Technology for Surface Modification of Polymer-Based Composites: A Comprehensive Review

“…Generally, the surface modification of polymer substrate can be divided into two methods, chemical and physical modification. In chemical modification, the polymer substrate is modified on selective surface by using chemical solution as solvent such as potassium manganite (KMnO 4 ), nitric acid (HNO 3 ), and ethyl alcohol [ 207 , 208 , 209 ]. On the other hand, laser modification is one of the popular physical surface treatment methods used in order to prepare the polymer surface for metallization.…”