833wileyonlinelibrary.com fi lm solar cells, and smart windows. [ 4 ] The main disadvantage of ITO is its limited optical performance at very low sheet resistances. Moreover, the brittleness of the ceramic ITO fi lms can present a bottleneck in the fabrication of highly fl exible devices. [ 5 ] These disadvantages have motivated recent research efforts toward alternative material systems such as carbon nanotube [ 6 ] or silver nanowire (AgNW) networks, [ 7,8 ] metallized electrospun nanowires, [ 9,10 ] graphene layers, [ 11 ] ultrathin metal fi lms, [ 12 ] self-forming [ 13 ] or patterned metal grids. [14][15][16][17][18][19][20] Ideally, besides having very good electrical and optical performance, the new system should be low cost, fl exible and include direct patterning. The former two can be achieved by the additive solution-processing of silver nanowire networks that show remarkable fl exibility. [ 8 ] Depending on the application, this method however requires a post deposition structuring step. Direct patterning can be implemented with metal-wire grid electrodes when considering suitable printing technologies. While grids have been realized with nanoscale lines in several studies, the fabrication relied on subtractive multistep patterning methods such as imprinting, [ 14,15,20 ] lithography, [ 15 ] or evaporative self-assembly. [ 16 ] For microscale line widths, although not completely additive, an elegant method using selective laser sintering of a silver or nickel nanoparticle fi lm has been presented by Hong et al. [ 17 ] and Lee et al., [ 18 ] respectively. A direct ink writing approach of concentrated silver inks has been shown by Ahn et al., demonstrating linewidths around 5 µm. [ 19 ] TCE of very high performance have been demonstrated by electrospinning of polymer nanowires followed by the metal evaporation resulting in nanotrough networks of various metals. [ 9 ] A similar procedure was used to fabricate a network of copper wires about 1 µm in diameter that can be transferred onto a fi ner mesh of solution-deposited nanowires. [ 10 ] However, this interesting method is neither additive nor does it have the ability for direct patterning.Electrohydrodynamic (EHD) printing, the technique used in this work, has been applied as a viable additive and noncontact printing technique. Conventional additive printing methods such as screen printing or inkjet printing simply lack the resolution needed for invisible metal grid TCE applications. Electrohydrodynamic NanoDrip Printing of High Aspect Ratio Metal Grid Transparent Electrodes

An extensive range of metals can be dissolved and re-deposited in liquid solvents using electrochemistry. We harness this concept for additive manufacturing, demonstrating the focused electrohydrodynamic ejection of metal ions dissolved from sacrificial anodes and their subsequent reduction to elemental metals on the substrate. This technique, termed electrohydrodynamic redox printing (EHD-RP), enables the direct, ink-free fabrication of polycrystalline multi-metal 3D structures without the need for post-print processing. On-the-fly switching and mixing of two metals printed from a single multichannel nozzle facilitates a chemical feature size of <400 nm with a spatial resolution of 250 nm at printing speeds of up to 10 voxels per second. As shown, the additive control of the chemical architecture of materials provided by EHD-RP unlocks the synthesis of 3D bi-metal structures with programmed local properties and opens new avenues for the direct fabrication of chemically architected materials and devices.

Many emerging applications in microscale engineering rely on the fabrication of 3D architectures in inorganic materials. Small-scale additive manufacturing (AM) aspires to provide flexible and facile access to these geometries. Yet, the synthesis of device-grade inorganic materials is still a key challenge toward the implementation of AM in microfabrication. Here, a comprehensive overview of the microstructural and mechanical properties of metals fabricated by most state-of-the-art AM methods that offer a spatial resolution ≤10 μm is presented. Standardized sets of samples are studied by cross-sectional electron microscopy, nanoindentation, and microcompression. It is shown that current microscale AM techniques synthesize metals with a wide range of microstructures and elastic and plastic properties, including materials of dense and crystalline microstructure with excellent mechanical properties that compare well to those of thin-film nanocrystalline materials. The large variation in materials' performance can be related to the individual microstructure, which in turn is coupled to the various physico-chemical principles exploited by the different printing methods. The study provides practical guidelines for users of small-scale additive methods and establishes a baseline for the future optimization of the properties of printed metallic objects-a significant step toward the potential establishment of AM techniques in microfabrication.

Colloidal quantum dots in silver cavities result in a versatile class of laser-like plasmonic devices for on-chip use.

Organic compounds present a powerful platform for nanotechnological applications. In particular, molecules suitable for optical functionalities such as single photon generation and energy transfer have great promise for complex nanophotonic circuitry due to their large variety of spectral properties, efficient absorption and emission, and ease of synthesis. Optimal integration, however, calls for control over position and orientation of individual molecules. While various methods have been explored for reaching this regime in the past, none satisfies requirements necessary for practical applications. Here, we present direct non-contact electrohydrodynamic nanoprinting of a countable number of photostable and oriented molecules in a nanocrystal host with subwavelength positioning accuracy. We demonstrate the power of our approach by writing arbitrary patterns and controlled coupling of single molecules to the near field of optical nanostructures. Placement precision, high yield and fabrication facility of our method open many doors for the realization of novel nanophotonic devices.