Piezomaterials are known to display enhanced energy conversion efficiency at nanoscale due to geometrical effect and improved mechanical properties. Although piezoelectric nanowires have been the most widely and dominantly researched structure for this application, there only exist a limited number of piezomaterials that can be easily manufactured into nanowires, thus, developing effective and reliable means of preparing nanostructures from a wide variety of piezomaterials is essential for the advancement of self-powered nanotechnology. In this study, we present nanoporous arrays of polyvinylidene fluoride (PVDF), fabricated by a lithography-free, template-assisted preparation method, as an effective alternative to nanowires for robust piezoelectric nanogenerators. We further demonstrate that our porous PVDF nanogenerators produce the rectified power density of 0.17 mW/cm3 with the piezoelectric potential and the piezoelectric current enhanced to be 5.2 times and 6 times those from bulk PVDF film nanogenerators under the same sonic-input.

Layered assembly structures composed of nanomaterials, such as nanocrystals, have attracted considerable attention as promising candidates for new functional devices whose optical, electromagnetic and electronic behaviours are determined by the spatial arrangement of component elements. However, difficulties in handling each constituent layer in a materialspecific manner limit the 3D integration of disparate nanomaterials into the appropriate heterogeneous electronics. Here we report a pick-and-place transfer method that enables the transfer of large-area nanodot assemblies. This solvent-free transfer utilizes a lifting layer and allows for the reliable transfer of a quantum dot (QD) monolayer, enabling layer-by-layer design. With the controlled multistacking of different bandgap QD layers, we are able to probe the interlayer energy transfer among different QD monolayers. By controlling the emission spectrum through such designed monolayer stacking, we have achieved white emission with stable optoelectronic properties, the closest to pure white among the QD lightemitting diodes reported so far.

The energy harvesting efficiency is of tremendous importance for the realization of a high output-power nanogenerator serving as the basis for self-powered electronics. Here we report that the device performance of a sound-driven piezoelectric energy nanogenerator (SPENG) is remarkably improved by controlling both the carrier density and the interfacial energy in a semiconducting ZnO nanowire (NW), thereby achieving its intrinsic efficiency limits. A SPENG with carrier-controlled ZnO NWs exhibits excellent energy harvesting characteristics with an average power density of 0.9 mW cm À3 , as well as a near 50 fold increase in both output voltage and current compared to those of a conventional ZnO NW. In addition, we demonstrate for the first time that an optimized SPENG is large enough and very suitable to drive electrophoretic ink displays based on voltage-drive systems. This fundamental progress makes it possible to fabricate high performance nanogenerators for viable industrial applications in portable/wearable personal electronics such as electronic papers and smart identity cards.Recent developments in piezoelectric power generators harvesting energy steadily from ambient mechanical vibrations without regard to time, place, or any external conditions, present innovative and emerging research topics in the area of a green energy technology. 6,10,11,13 In particular, a ZnO nanowire (NW) has been intensively studied as one of the most attractive piezoelectric materials for widespread use as a clean and inexhaustible power source in future self-powered nanosystems, including implantable chips, exible/ portable electronics, and environmental and heath monitoring sensors, because of its unique dimensionality and superior transparent and piezoelectric semiconducting properties coupled with biocompatibility, environmental friendliness, and geometrical versatility. 6,10,11 To date various approaches have been reported demonstrating and enhancing unique capabilities for a ZnO NW-based piezoelectric energy generator by introducing various NW arrays and device congurations, exible/textile electrodes and substrates, and diverse types of ambient mechanical energy sources. 6,11,[13][14][15][16][17] However, despite the demonstrated ability and fascinating piezoelectric

When deposited from an evaporating solution onto a substrate, even nondescript nanoparticles can organize into intricate spatial patterns. Here we show that a simple but long-ranged anisotropy in nanoparticles' interactions can greatly enrich this scenario. In experiments with colloidal Co nanocrystals, which bear a substantial magnetic dipole, we observe assemblies quite distinct from those formed by nonmagnetic particles. Reflecting the strongly nonequilibrium nature of this process, nanocrystal aggregates also differ substantially from expected low-energy arrangements. Using coarse-grained computer simulations of dipolar nanoparticles, we have identified several dynamical mechanisms from which such unusual morphologies can arise. For particles with modest dipole moments, transient connections between growing domains frustrate phase separation into sparse and dense regions on the substrate. Characteristic length scales of the resulting cellular networks depend non-monotonically on the depth of quenches we use to mimic the effects of solvent evaporation. For particles with strong dipole moments, chain-like aggregates formed at early times serve as the agents of assembly at larger scales. Their effective interactions drive the formation of layered loop structures similar to those observed in experiments.

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