Abstract
Abstract We review the fundamental concepts of direct laser writing (DLW) of 3D metallic structures via photoreduction and give an overview over the state-of-the-art. On the one hand, metallic microstructures and nanostructures play an important role in photonic applications such as resonators, antennas, metamaterials, and polarizers. On the other hand, DLW offers a flexible and fast way to fabricate microstructures. Because the underlying mechanisms from the first photoreaction to the final 3D microstructure are quite complex and not yet well controlled, we believe that a review of the photochemistry and photophysics of the direct writing process of metal structures helps to promote development in this field. To this end, we first summarize the principles of electroplating and electroless plating as this helps understand the photoresist’s components. Next, we describe the different photoreducing agents and photoreactions that lead to metal seeds and in consequence to nanoparticles. This is followed by insights into the physics of nanoparticle agglomeration to the desired microstructure. Finally, we give an overview over the state-of-the-art of DLW metallic 3D microstructures.
Highlights
IntroductionThere exists a manifold of applications of metallic microstructures: from electrical wires and electrodes in, for example, electro-optic modulators or microelectromechanical systems (MEMS) [1,2,3], via metallic surfaces in which microstructures may lead to well-designed frictional and wear properties [4, 5], to structured magnets that are employed in spintronics [6]; often, metallic structures are among the key components of a functional device [7]
We review the fundamental concepts of direct laser writing (DLW) of 3D metallic structures via photoreduction and give an overview over the state-of-the-art
There exists a manifold of applications of metallic microstructures: from electrical wires and electrodes in, for example, electro-optic modulators or microelectromechanical systems (MEMS) [1,2,3], via metallic surfaces in which microstructures may lead to well-designed frictional and wear properties [4, 5], to structured magnets that are employed in spintronics [6]; often, metallic structures are among the key components of a functional device [7]
Summary
There exists a manifold of applications of metallic microstructures: from electrical wires and electrodes in, for example, electro-optic modulators or microelectromechanical systems (MEMS) [1,2,3], via metallic surfaces in which microstructures may lead to well-designed frictional and wear properties [4, 5], to structured magnets that are employed in spintronics [6]; often, metallic structures are among the key components of a functional device [7]. Direct photoreduction does not require these additional steps, does not limit the choice of substrate, and has the potential to enable the fabrication of, for example, complete MEMS with a single technology. It is based on the (multi)photon-induced reduction of dissolved metal precursors to neutral metal atoms and subsequent agglomeration of these atoms to a metal structure. Up to now, few of the directly written metal structures show a quality rivaling those of polymer or galvanically grown structures, preventing their application in photonics This is mostly due to so far not completely controllable thermal, light-matter interaction and chemical processes that take place during fabrication.
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