3D printing of reduced graphene oxide (rGO) nanowires is realized at room temperature by local growth of GO at the meniscus formed at a micropipette tip followed by reduction of GO by thermal or chemical treatment. 3D rGO nanowires with diverse and complicated forms are successfully printed, demonstrating their ability to grow in any direction and at the selected sites.

Organic electronics increasingly impacts our everyday life with a variety of devices such as displays for TV or mobile appliances, smart cards and radio-frequency identifi cation (RFID) tags. [ 1 , 2 ] This blossoming domain could greatly profi t from effective ways to fabricate conducting or semiconducting organic nanowires. [ 3 ] Specifi cally, the three-dimensional (3D) and individual integration of each nanowire is essential [ 4 ] for many new device concepts, but so far this was not possible. Here we show the demonstration of accurate and versatile 3D direct writing of conducting polymer nanowires based on guiding a monomer meniscus by pulling a micropipette during oxidative polymerization. This is an important step for organic electronic integration with high density and enhanced freedom in circuit design.Conducting polymers such as polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) are very interesting materials because they combine tunable electrical transport characteristics and excellent mechanical properties. [ 5 ] In particular, conducting polymer nanowires are quite important for a broad range of nanodevices such as fi eld effect transistors, [ 3 ] bio-and chemical sensors, [ 6 , 7 ] and non-volatile memories. [ 8 ] Such nanowires are fabricated by soft lithography, [ 9 , 10 ] dip-pen lithography [ 11 ] and electrospinning. [ 12 ] However, these methods are still limited to in-plane patterning of low-aspect-ratio nanowires, whereas for advanced applications 3D patterning is essential.Direct ink writing and probe-based drawing are used for 3D wire patterning. The fi rst method, based on the extrusion of concentrated ink through a nozzle, was applied for 3D microfabrication with metals, oxides, and polymers. [13][14][15][16] However, bringing the wire diameter below micrometer-level is not easy due to the size and concentration of the ink particles. Probe-based drawing can fabricate polymer nanowires. [ 17 ] However, high-density integration is limited by the large pre-deposited polymer droplet (a few tens to hundreds of micrometers).An alternate technique for 3D electrodeposition was recently developed: writing nanowires with a nanoscale electrolyte meniscus. [ 18 , 19 ] This method was so far demonstrated for 3D metallic nanowires but not for conducting polymers.Here we show that this type of technique can in fact be used for conducting polymers offering high accuracy, excellent versatility and marked advantages with respect to alternate solutions. In essence, we obtained a stretched monomer meniscus by pulling a micropipette fi lled with a Py solution, exploiting oxidative polymerization in air. The wire radius so produced was accurately controlled down to ∼ 50 nm by tuning the pulling speed.The technique was successfully tested with specifi c focus on essential features for advanced organic nanodevice integration. Specifi cally, we produced dense arrays of different types of freestanding nanocomponents: straight wires, complex-shape wires, branche...

3D printing of metallic microarchitectures with controlled internal structures is realized at room temperature in ambient air conditions by the manipulation of metal ion concentration and pulsed electric potentials in the electrolyte meniscus during the meniscus-guided electrodeposition. Precise control of the printing nozzle enables the drawing of complex 3D microarchitectures with well-defined geometries and positions.

Moving printed electronics to three dimensions essentially requires advanced additive manufacturing techniques yielding multifunctionality materials and high spatial resolution. Here, we report the meniscus-guided 3D printing of highly conductive multiwall carbon nanotube (MWNT) microarchitectures that exploit rapid solidification of a fluid ink meniscus formed by pulling a micronozzle. To achieve high-quality printing with continuous ink flow through a confined nozzle geometry, that is, without agglomeration and nozzle clogging, we design a polyvinylpyrrolidone-wrapped MWNT ink with uniform dispersion and appropriate rheological properties. The developed technique can produce various desired 3D microstructures, with a high MWNT concentration of up to 75 wt % being obtained via post-thermal treatment. Successful demonstrations of electronic components such as sensing transducers, emitters, and radio frequency inductors are also described herein. We expect that the technique presented in this study will facilitate selection of diverse materials in 3D printing and enhance the freedom of integration for advanced conceptual devices.

Coherent x-rays from synchrotron sources are increasingly used in non-conventional radiological techniques ('phase-contrast' radiology). Our experiments demonstrate that by using white (unmonochromatic) radiation and a time-resolving system, it is possible to image microscopic details of moving blood vessels in different live animals without using any contrast agent. The images have excellent contrast plus unprecedented spatial resolution for microangiography (< 10 microm). This result is likely to impact many different areas of biological and medical research and of diagnostic radiology.

Organic-inorganic metal halide perovskites, particularly CH 3 NH 3 PbX 3 (X = Cl, Br, and I), have recently emerged as a promising optoelectronic material [1] because of their excellent properties such as large optical absorption, long carrier diffusion length, high carrier mobility, and low-cost solution production process. [2][3][4][5][6] Over the past decade, there have been conducted substantial research to utilize perovskites for diverse applications as solar cells, [2,7,8] photodetectors, [9,10] light emitting diodes, [11,12] and lasers. [13,14] Most of the research has focused on the control over crystallinity or chemical composition in a thin film form, in result, making great advances in material performance. [15][16][17][18][19] Continuous demands on optoelectronic devices with high integration density and new functions have raised the need for nanostructured perovskites. [20] Especially, nanowires, 1D nanostructures with controlled diameters and lengths, are the basic building blocks for creating miniaturized devices. Techniques to fabricate perovskite nanowires mainly rely on i) vapor-phase deposition [21,22] or ii) solution-mediated crystallization. [14,[23][24][25][26] The former offers an excellent crystal quality but lacks the ability to precisely position individual nanowires. In the latter that is based on supersaturation of solutes, there have been several remarkable attempts to fabricate and align individual nanowires by confinement of solution inside templates, [23,24] nanoimprint molds, [25] or nanofluidic channels [26] under evaporation of solvent.Recently, some clever methods based on inkjet printing have been devised for patterning perovskite micro/nanostructures. [27,28] These attempts have enhanced the freedom of nanostructures design beyond straight nanowires, potentially enabling a high-level integration of perovskite circuitries and devices. However, the developed patterning techniques for perovskites are still limited to in-plane fabrication and alignment.Since its invention in the 1980s, 3D printing, known as additive manufacturing, has attracted great attention as a facile method to produce tangible freeform structures. Beyond simple prototyping, there have recently been enormous efforts to improve or diversify the properties of 3D printed objects-for their practical use-by engineering materials' crystallinity [29,30] or molecular orientation. [31][32][33] In this context, owing to their As competing with the established silicon technology, organic-inorganic metal halide perovskites are continually gaining ground in optoelectronics due to their excellent material properties and low-cost production. The ability to have control over their shape, as well as composition and crystallinity, is indispensable for practical materialization. Many sophisticated nanofabrication methods have been devised to shape perovskites; however, they are still limited to in-plane, low-aspect-ratio, and simple forms. This is in stark contrast with the demands of modern optoelectronics with freeform circui...

Printed strain sensors have promising potential as a human-machine interface (HMI) for health-monitoring systems, human-friendly wearable interactive systems, and smart robotics. Herein, flexible strain sensors based on carbon nanotube (CNT)-polymer composites were fabricated by meniscus-guided printing using a CNT ink formulated from multiwall nanotubes (MWNTs) and polyvinylpyrrolidone (PVP); the ink was suitable for micropatterning on nonflat (or curved) substrates and even three-dimensional structures. The printed strain sensors exhibit a reproducible response to applied tensile and compressive strains, having gauge factors of 13.07 under tensile strain and 12.87 under compressive strain; they also exhibit high stability during ∼1500 bending cycles. Applied strains induce a contact rearrangement of the MWNTs and a change in the tunneling distance between them, resulting in a change in the resistance (Δ R/ R) of the sensor. Printed MWNT-PVP sensors were used in gloves for finger movement detection; these can be applied to human motion detection and remote control of robotic equipment. Our results demonstrate that meniscus-guided printing using CNT inks can produce highly flexible, sensitive, and inexpensive HMI devices.

Despite sufficient spatial resolution and routine operation, traditional electron microscopy (SEM and TEM) of polymer blend morphologies is limited to two dimensions (2D) and often requires tedious sample preparation. We have used a powerful X-ray imaging technique to visualize the morphology of polymer blends in three dimensions (3D). Images of polystyrene/high-density polyethylene (PS/HDPE) blend samples were constructed with microtomography using coherent synchrotron X-rays. Good contrast for blends with and without the PS phase removed (no other sample preparation was needed) was accomplished, and image quality is compared in the paper. High resolution (1 µm) images of relatively thick (∼1 mm) blend samples were possible by adapting a sample stage equipped with high precision motor controls, by enhancing phase contrast through optimization of sample-scintillator distance, and by taking a large number of projection images (up to 1000) along different angles. Reconstructed slices were used to create 3D volume-rendered images of the blends. Coarsening of the cocontinuous morphology during annealing was monitored using extraction-free microtomography. Measurements of interfacial area per volume at varying annealing times agree with experimental results obtained using mercury porosimetry. It was also shown that SEM quantitative annealing results are limited at long annealing times due to the limitations of two-dimensional images of a three-dimensional morphology.