nanotechnology, with its broad impact on societally relevant applications, relies heavily on the availability of accessible nanofabrication methods. Even though a host of such techniques exists, the flexible, inexpensive, on-demand and scalable fabrication of functional nanostructures remains largely elusive. Here we present a method involving nanoscale electrohydrodynamic ink-jet printing that may significantly contribute in this direction. A combination of nanoscopic placement precision, soft-landing fluid dynamics, rapid solvent vapourization, and subsequent self-assembly of the ink colloidal content leads to the formation of scaffolds with base diameters equal to that of a single ejected nanodroplet. The virtually material-independent growth of nanostructures into the third dimension is then governed by an autofocussing phenomenon caused by local electrostatic field enhancement, resulting in large aspect ratio. We demonstrate the capabilities of our electrohydrodynamic printing technique with several examples, including the fabrication of plasmonic nanoantennas with features sizes down to 50 nm.

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

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By means of high-resolution scanning tunneling microscopy (STM), we have revealed unprecedented details about the intermediate steps for a surface-catalyzed reaction. Specifically, we studied the oxidation of H adatoms by O(2) molecules on the rutile TiO(2)(110) surface. O(2) adsorbs and successively reacts with the H adatoms, resulting in the formation of water species. Using time-lapsed STM imaging, we have unraveled the individual reaction intermediates of HO(2), H(2)O(2), and H(3)O(2) stoichiometry and the final reaction product-pairs of water molecules, [H(2)O](2). Because of their different appearance and mobility, these four species are discernible in the time-lapsed STM images. The interpretation of the STM results is corroborated by density functional theory calculations. The presented experimental and theoretical results are discussed with respect to previous reports where other reaction mechanisms have been put forward.

Colloidal quantum-dots are bright, tunable emitters that are ideal for studying near-field quantum-optical interactions. However, their colloidal nature has hindered their facile and precise placement at desired near-field positions, particularly on the structured substrates prevalent in plasmonics. Here, we use high-resolution electro-hydrodynamic printing (<100 nm feature size) to deposit countable numbers of quantum dots on both flat and structured substrates with a few nanometer precision. We also demonstrate that the autofocusing capability of the printing method enables placement of quantum dots preferentially at plasmonic hot spots. We exploit this control and design diffraction-limited photonic and plasmonic sources with arbitrary wavelength, shape, and intensity. We show that simple far-field illumination can excite these near-field sources and generate fundamental plasmonic wave-patterns (plane and spherical waves). The ability to tailor subdiffraction sources of plasmons with quantum dots provides a complementary technique to traditional scattering approaches, offering new capabilities for nanophotonics.