Surface ripple, as an important factor of corrugations in two-dimensional (2D) atomic crystals, plays important roles in determining their mechanical and physical properties. Here, we systematically investigated the strain-engineered rippling structure and manipulation of the rippling domain in monolayer WS2 flakes via atomic force microscopy (AFM). The rippling structure was introduced by the in-plane compression applied through the underlying SiO2/Si substrate during the rapid cooling process of post-growth. The zigzag-orientated rippling domains with three-equivalent directions were visualized by transverse shear microscopy (TSM) and friction force microscopy and further determined via angle-dependent TSM. Furthermore, these rippling domains can be precisely manipulated by controlling the AFM scanning, and various rippling patterns were formed by the AFM lithography. The manipulation mechanisms were phenomenally discussed based on their strain-induced anisotropic mechanical properties, the film–substrate mechanical model, and the dynamic strain-induced anisotropic puckering effects. Our study will be beneficial in understanding and controlling not only the rippling structures but also the rippling-related electronic and optical properties of 2D materials.

Cryogenic temperature detection underlies the understanding of important physical phenomena and is crucial for material science and space exploration. Simple, facile, and accurate assessment of temperature, especially for surface or body thermal mapping, is one of the challenges that must be addressed when developing new materials or technologies for thermometers. Here, we introduce a temperature detection strategy based on a 3D cross-correlative matrix derived from fluorescence response patterns of an organic probe in three solvation envelopes. The intermolecular interactions, such as excimer or exciplex formation, intramolecular charge transfer and solvent relaxation processes, between the probe and molecule surroundings, are attributed to the unique temperature-dependent optical behaviors in different solutions. The precise temperature detection originated from apparent variations in fluorescence intensity and wavelength upon temperature change in these solvents. This enabled the construction of a comprehensive temperature sensor array, which gives a unique visible color pattern of signals as a read-output discernible by the naked eye. Furthermore, as a proof-ofconcept, a new strategy for facile and non-destructive thermal mapping of a crystal surface is presented.

Three tetra-aryl substituted 1,3-butadiene derivatives with aggregation enhanced emission (AEE) and mechanochromic fluorescence behavior have been rationally designed and synthesized. The results suggest an effective design strategy for developing diverse materials with aggregation induced emission (AIE) and significant mechanochromic performance by employing D-π-A structures with large dipole moments.

The strain has been employed for controlled modification of electronical and mechanical properties of two-dimensional (2D) materials. However, the thermal strain-engineered behaviors of the CVD-grown MoS 2 have not been systematically explored. Here, we investigated the strain-induced structure and properties of CVD-grown triangular MoS 2 flakes by several advanced atomic force microscopy. Two different kinds of flakes with sharp-corner or vein-like nanostructures are experimentally discovered due to the size-dependent strain behaviors. The critical size of these two kinds of flakes can be roughly estimated at∼17 μm. Within the small flakes, the sharp-corner regions show specific strain-modified properties due to the suffering of large tensile strain. While in the large MoS 2 flakes, the complicated vein-like nanoripple structures were formed due to the interface slipping process under the larger tensile strain. Our work not only demonstrates the size-specific strain behaviors of MoS 2 flakes but also sheds light on the artificial design and preparation of strain-engineered nanostructures for the devices based on the 2D materials.

Thermal conductivity (κ) of the single-crystalline bilayer graphene (BLG) is investigated experimentally as a function of the interlayer twist angle (θ) and temperature using the optothermal Raman technique. The results show that a slight 2° twist angle leads to a κ decrease in 15% at ∼320 K. With the regulation of θ from 0° to 30°, the in-plane κ of the BLG decreases first and then increases showing an asymmetry V shape. The local maximum value of κ was reached when the twist angle is 30° and the highest value was found on the Bernal stacked BLG. The obtained κ is further found to be sensitive to the Moire periodicity but insensitive to the commensurate lattice constant of the twisted BLG. The non-equilibrium molecular dynamics simulation reveals that the twist angle in t-BLG affects the proportion of low-frequency phonons and finally changes the κ. The quantitative study validates the regulation of thermal conduction through the interlayer twist angle and favors the further understanding of thermal transport in the van der Waals bilayer systems.