Recently, we published our early results on laser microprinting of functional microelectronics (Nature Commun. 14, 1103 (2023)). Here, we report our progress beyond this work. First, we present a simplified photothermal print scheme – again without the need for post-processing. This scheme includes the purposeful choice of the printing substrate as well as new inks. Second, we present our early results on in-situ monitoring of the metal- and semiconductor-growth processes by time-resolving a weak co-focused reflected probe laser beam. Third, we discuss how the print parameters such as focus speed and laser power influence the morphology of the printed material.
Recently, the necessary average total laser power for rapid multi-photon multi-focus applications has exceeded the Watt level. To enable even faster 3D printing, we have developed new sensitive photoresists by adding co-initiators to commonly used standard systems. We yet exceed these advances in sensitivity using a novel photoresist system based on a modified benzylidene ketone photoinitiator, making it a very attractive system for advanced rapid 3D laser nanoprinting. To compare our original results to more than 70 different published systems from the literature, we define a photoresist-sensitivity figure-of-merit, enabling a fair comparison to measurements taken under vastly different conditions.
Organic light emitting diodes (OLEDs) are thin, lightweight and flexible whilst still maintaining high efficiencies. Therefore, OLEDs are at the forefront of display technology and recently, applications of OLEDs have emerged in solid state lighting. Additionally, OLEDs can be made extremely flexible and stretchable, making them suitable for use in wearable electronics. Among light emitting materials for OLEDs, thermally activated delayed fluorescent (TADF) materials have shown great promise in the last few years. In this study, we report a solution processable TADF emitting polymer as an emissive material for OLEDs. The bespoke polymer structure has the TADF emitter 4-(9H-carbazol9-yl)-2-(3′-hydroxy-[1,1′- biphenyl]-3-yl)isoindoline-1,3-dione as a pendant group on a poly(methyl methacrylate) based polymer chain. We demonstrate ink-jet printed OLEDs using our TADF polymer, which allows for precise patterning without masks, deposition of nanometer scale thicknesses, and minimal wastage
We introduce stimuli-responsive structures fabricated by 3D laser lithography. The key material is a responsive hydrogel. It is based on supramolecular host-guest chemistry, which allows reversible actuation under physiological conditions. Combined with other photoresists, multi-material scaffolds are used to directly study live cell behavior during spatially and temporally well-defined changes in the extracellular surrounding. Digital image correlation enables us to precisely track and analyze the behavior of a multitude of cells in a single experiment. With this versatile technique we will study the mechanoresponse of cells and the role of different proteins in the mechanotransduction.
Additive manufacturing – specifically 3D laser lithography – is a powerful technology for the fabrication of functional devices on the micro- and nanoscale. This technique has already been applied in a broad range of fields, including metamaterials, biomedicine, and others. While significant progress has being made in chemically tailored photoresist systems for additive manufacturing, the design of photoresists for subtractive manufacturing on the microscale is still in its infancy. Existing resists for 3D laser lithography can only be removed under harsh conditions, such as calcination, oxygen-plasma etching, or etching with hydrofluoric acid.
Herein, we present a new class of on-demand cleavable photoresists for 3D laser lithography. Multifunctional monomers containing disulfide, thioether or silane moieties, which can be specifically cleavage in the presence of a reducing agent or a mild base, are employed. Particularly, dithiothreitol (DTT) causes a thiol–disulfide exchange, erasing the written structure in the first case and sodium bicarbonate (NaHCO3), potassium carbonate (K2CO3) and a fluorine salt (KF) have been proved to sequentially degrade slightly chemically different silane-based microsctructures in the latter case. Thus, these photoresists can be cleaved selectively, which enables the sequential degradation of laser written structures and thereby allows for subtractive manufacturing at the micro- and nanoscale.
During the last years there has been significant interest in the fabrication of conductive three-dimensional (3D) structures on the micrometer scale due to their potential applications in microelectronics or emerging fields such as flexible electronics, nanophotonics, and plasmonics. Two-photon direct laser writing (DLW) has been proposed as a potential tool for the fabrication of 3D microstructures in various contexts. The majority of these two-photon processes involve the preparation of insoluble polymeric networks using photopolymerizable photoresins based on acrylate or epoxy groups. Nevertheless, the preparation of conductive 3D microstructures is still very challenging.
The aim of the current work has been the preparation of conductive 3D microstructures via DLW by employing a newly developed photoresist. The photoresist consists of acrylate-functionalized poly(ethylene glycol) derivates and HAuCl4 as the gold precursor. By varying the gold content of the photoresist, different structures have been prepared and characterized by SEM and XPS. Conductivity of individual wires between prefabricated macroelectrodes has been measured too. Subsequently, the material has been employed to demonstrate the possibility of true 3D microscale connections.
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