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In the emergence of graphene and many two-dimensional (2D) materials, the most exciting applications come from stacking them into 3D devices, promising many excellent possibilities for neoteric electronics and optoelectronics. Layers of semiconductors, insulators, and conductors can be stacked to form van der Waals heterostructures, after the weak bonds formed between the layers. However, the interlayer coupling in these heterostructures is usually hard to modulate, resulting in difficulty to realize their emerging optical or electronic properties. Especially, the relationship between interlayer distance and interlayer coupling remains to be investigated, due to the lack of effective technology. In this work, we have used laser shocking to controllably tune the interlayer distance between graphene (Gr) and boron nitride (BN) in the Gr/BN/Gr heterostructures and the strains in the 2D heterolayers, providing a simple and effective way to modify their optic and electronic properties. After lase shocking, the reduction of interlayer distance is calculated by molecular dynamics (MD) simulation. Some atoms in Gr or BN are out-of-plane as well. In Raman measurements, the G peak in the heterostructure shows a red-shifted trend after laser shocking, indicating the strong phonon coupling in the interlayer. Moreover, the larger transparency after laser shocking also verifies the stronger photon coupling in the heterostructure. To investigate the effects of the interlayer coupling of heterostructure on its out-of-plane electronic behavior, we have investigated the electronic tunneling behavior. The heterostructure after laser shock reveals a lager tunneling current and lower tunneling threshold, proving an unexpected better electrical property. From DFT calculations, laser shocking can modulate the band gap structure of graphene in Gr/BN/Gr heterostructures; therefore, the heterostructures can be implemented as a unique photonic platform to modulate the emission characters of the anchored CdSe/ZnS core-shell quantum dots. Remarkably, the effective laser shocking method is also applicable to various otherwise noninteracting 2D materials, resulting in many new phenomena, which will lead science and technology to unexplored territories.

Perovskite semiconductor nanocrystals with different compositions have shown promise for applications in light-emitting devices. Dark excitonic states may suppress light emission from such nanocrystals by providing an additional nonradiative recombination channel. Here, we study the composition dependence of dark exciton dynamics in nanocrystals of lead halides by time-resolved photoluminescence spectroscopy at cryogenic temperatures. The presence of a spin-related dark state is revealed by magneto-optical spectroscopy. The energy splitting between bright and dark states is found to be highly sensitive to both halide elements and organic cations, which is explained by considering the effects of size confinement and charge screening, respectively, on the exchange interaction. These findings suggest the possibility of manipulating dark exciton dynamics in perovskite semiconductor nanocrystals by composition engineering, which will be instrumental in the design of highly efficient light-emitting devices.

Metal oxides and carbon-based materials are the most promising electrode materials for a wide range of low-cost and highly efficient energy storage and conversion devices. Creating unique nanostructures of metal oxides and carbon materials is imperative to the development of a new generation of electrodes with high energy and power density. Here we report our findings in the development of a novel graphene aerogel assisted method for preparation of metal oxide nanoparticles (NPs) derived from bulk MOFs (Co-based MOF, Co(mIM)2 (mIM = 2-methylimidazole). The presence of cobalt oxide (CoOx) hollow NPs with a uniform size of 35 nm monodispersed in N-doped graphene aerogels (NG-A) was confirmed by microscopic analyses. The evolved structure (denoted as CoOx/NG-A) served as a robust Pt-free electrocatalyst with excellent activity for the oxygen reduction reaction (ORR) in an alkaline electrolyte solution. In addition, when Co was removed, the resulting nitrogen-rich porous carbon–graphene composite electrode (d...

We present and demonstrate a novel imprint method, electrostatic force-assisted nanoimprint lithography (EFAN), where a voltage applied between a mold and a substrate generates an electrostatic force that presses the mold into a resist on the substrate. We have successfully used EFAN to pattern nanostructures in a photocurable resist spin-coated on a wafer, with high fidelity and excellent uniformity over the entire substrate, in ambient atmosphere without using a vacuum chamber. In initial tests without any process optimization, 100 nm half-pitch gratings with a residual layer thickness of 22 ± 5 nm were imprinted across a 100 mm diameter wafer in about 2 s. Furthermore, numerical calculations show that the field magnitude experienced by the dielectric layers on the substrate is much less than their breakdown limit. Hence, EFAN is well suited for step-and-repeat nanoimprint lithography, and its simple operation can simplify and speed up multilayer alignment process.