Two-dimensional materials from layered van der Waals (vdW) crystals hold great promise for electronic, optoelectronic, and quantum devices, but technological implementation will be hampered by the lack of high-throughput techniques for exfoliating single-crystal monolayers with sufficient size and high quality. Here, we report a facile method to disassemble vdW single crystals layer by layer into monolayers with near-unity yield and with dimensions limited only by bulk crystal sizes. The macroscopic monolayers are comparable in quality to microscopic monolayers from conventional Scotch tape exfoliation. The monolayers can be assembled into macroscopic artificial structures, including transition metal dichalcogenide multilayers with broken inversion symmetry and substantially enhanced nonlinear optical response. This approach takes us one step closer to mass production of macroscopic monolayers and bulk-like artificial materials with controllable properties.

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Excitons play a dominant role in the optoelectronic properties of atomically thin van der Waals (vdW) semiconductors. These excitons are amenable to on-demand engineering with diverse control knobs, including dielectric screening, interlayer hybridization, and moiré potentials. However, external stimuli frequently yield heterogeneous excitonic responses at the nano- and meso-scales, making their spatial characterization with conventional diffraction-limited optics a formidable task. Here, we use a scattering-type scanning near-field optical microscope (s-SNOM) to acquire exciton spectra in atomically thin transition metal dichalcogenide microcrystals with previously unattainable 20 nm resolution. Our nano-optical data revealed material- and stacking-dependent exciton spectra of MoSe2, WSe2, and their heterostructures. Furthermore, we extracted the complex dielectric function of these prototypical vdW semiconductors. s-SNOM hyperspectral images uncovered how the dielectric screening modifies excitons at length scales as short as few nanometers. This work paves the way towards understanding and manipulation of excitons in atomically thin layers at the nanoscale.

The optical properties of transition metal dichalcogenides have previously been modified at the nanoscale by using mechanical and electrical nanostructuring. However, a clear experimental picture relating the local electronic structure with emission properties in such structures has so far been lacking. Here, we use a combination of scanning tunneling microscopy (STM) and near-field photoluminescence (nano-PL) to probe the electronic and optical properties of single nano-bubbles in bilayer heterostructures of WSe 2 on MoSe 2 . We show from tunneling spectroscopy that there are electronic states deeply localized in the gap at the edge of such bubbles, which are independent of the presence of chemical defects in the layers. We also show a significant change in the local bandgap on the bubble, with a continuous evolution to the

With the continual increasing application requirements of broadband vibration energy harvesters (VEHs), many attempts have been made to broaden the bandwidth. As compared to adopted only a single approach, integration of multi-approaches can further widen the operating bandwidth. Here, a novel two-degree-of-freedom cantilever-based vibration triboelectric nanogenerator is proposed to obtain high operating bandwidth by integrating multimodal harvesting technique and inherent nonlinearity broadening behavior due to vibration contact between triboelectric surfaces. A wide operating bandwidth of 32.9 Hz is observed even at a low acceleration of 0.6 g. Meanwhile, the peak output voltage is 18.8 V at the primary resonant frequency of 23 Hz and 1 g, while the output voltage is 14.9 V at the secondary frequency of 75 Hz and 2.5 g. Under the frequencies of these two modes at 1 g, maximum peak power of 43.08 µW and 12.5 µW are achieved, respectively. Additionally, the fabricated device shows good stability, reaching and maintaining its voltage at 8 V when tested on a vacuum compression pump. The experimental results demonstrate the device has the ability to harvest energy from a wide range of low-frequency (<100 Hz) vibrations and has broad application prospects in self-powered electronic devices and systems.Currently, most vibrational energy harvesters (VEHs) are usually designed as resonance systems for higher power output. However, one of the main problems for VEHs with the resonant behavior is the narrow operating bandwidth. Thus, when operated under irregular mechanical vibration sources with low and variable frequencies, most VEHs yield very low and irregular output power, which lowers their practical application possibilities.To solve the problem of narrow bandwidth, many researchers have demonstrated some broadband harvesters by applying multimodal harvesting technique [17][18][19][20][21][22][23]. Multimodal energy harvesters are considered more efficient in matching multiple frequencies to better utilize kinetic energy. Sari et al. [17], Liu et al. [18], and Qi et al. [19] reported the use of multiple cantilevers or a cantilever array as one solution to increase the bandwidth. However, this type of energy harvester has the disadvantage of being bulky and complex in structure, thus overshadowing its advantages in broadband behavior. Another multimodal system was developed with multiple bending modes in a continuous beam, rather than using arrays of cantilevers configuration [20][21][22][23]. Ou et al. presented a broadband energy harvester with a two-mass cantilever beam structure [20]. Due to the addition of an extra mass, two useful working modes can be obtained. Arafa et al. developed a two-degree-of-freedom (2DOF) cantilever-based piezoelectric generator which used the proof mass as a dynamic amplifier [21]. However, the multimodal harvester only increases the number of peak amplitudes, and the bandwidth of each peak is relatively narrow, which still causes a sharp drop in power generation when the excitation...