van der Waals heterostructures stacked by transition metal dichalcogenides and graphene provide a new opportunity for exploring superlubricity. However, the further reduction of friction is limited by the unavoidable charge transfer in the heterostructures. The dynamics of charge transfer occur at picosecond time scale, which cannot be detected by traditional friction instruments, making the friction mechanism of charge transfer unclear. Here, we investigate friction-induced charge transfer in WS₂/graphene heterostructures with ultrafast friction energy dissipation detecting technique. The observed friction exhibits a strong linear relationship with the dissipation rate of interlayer charge transfer. By modulating the band structure of heterostructures, the dissipation rate of interlayer charge transfer can be efficiently tuned from 0.72 to 0.17 ps⁻¹, resulting in a ~ 35% reduction in friction. This work gives the direct explanation of friction-induced charge transfer, which enables the high-performance micro-electro-mechanical systems and new insight into the origin of friction from the perspective of ultrafast electron dynamics.

The boundary slip condition is pivotal for nanoscale fluid motion. Recent research has primarily focused on simulating the interaction mechanism between the electronic structure of two-dimensional materials and slip of water at the nanoscale, raising the possibility for ultralow friction flow of water at the nanoscale. However, experimentally elucidating electronic interactions at the dynamic solid–liquid interface to control boundary slip poses a significant challenge. In this study, the crucial role of electron structures at the dynamic solid–liquid interface in regulating slip length was revealed. Notably, the slip length of water on the molybdenum disulfide/graphene (MoS₂/G) heterostructure (100.9 ± 3.6 nm) significantly exceeded that of either graphene (27.7 ± 2.2 nm) or MoS₂ (5.7 ± 3.1 nm) alone. It was also analyzed how electron transfer significantly affected interface interactions. Excess electrons played a crucial role in determining the type and proportion of excitons at both MoS₂–water and MoS₂/G–water interfaces. Additionally, by applying voltage, distinct photoluminescence (PL) responses at static and dynamic interfaces were discovered, achieving a 5-fold modulation in PL intensity and a 2-fold modulation in the trion to exciton intensity ratio. More electrons transfer from the top graphene to the bottom MoS₂ at the MoS₂/G–water interface, reducing surface charge density. Thus, the reduction of electrostatic interactions between the solid and water leads to an increased slip length of water on the MoS₂/G heterostructure. The process aids in comprehending the origin of frictional resistance at the subatomic scale. This work establishes a foundation for actively controlling and designing of fluid transport at the nanoscale.

Robust superhydrophobic surfaces with excellent capacities of repelling water and anti-frosting are of importance for many mechanical components. In this work, wear-resistant superhydrophobic surfaces were fabricated by curing a mixture of polyurethane acrylate (PUA) coating and 1H,1H,2H,2H-Perfluorodecyltrichlorosilane (HFTCS) on titanium alloy (TC4) surfaces decorated with micropillars pattern, thus, composite functional surfaces with PUA coating in the valleys around the micropillars pattern of TC4 were achieved. Apparent contact angle on fabricated surfaces could reach 167°. Influences of the geometric parameters of micropillars pattern on the apparent contact angle were investigated, and the corresponding wear-resistant property was compared. Droplet impact and anti-frosting performances on the prepared surfaces were highlighted. An optimized design of surface texture with robust superhydrophobicity, controllable droplet impact, and anti-frosting performances was proposed. This design principle is of promising prospects for fabricating superhydrophobic surfaces in traditional mechanical systems.

About 30% of the world’s primary energy consumption is in friction. The economic losses caused by friction energy dissipation and wear account for about 2%–7% of its gross domestic product (GDP) for different countries every year. The key to reducing energy consumption is to control the way of energy dissipation in the friction process. However, due to many various factors affecting friction and the lack of efficient detection methods, the energy dissipation mechanism in friction is still a challenging problem. Here, we firstly introduce the classical microscopic mechanism of friction energy dissipation, including phonon dissipation, electron dissipation, and non-contact friction energy dissipation. Then, we attempt to summarize the ultrafast friction energy dissipation and introduce the high-resolution friction energy dissipation detection system, since the origin of friction energy dissipation is essentially related to the ultrafast dynamics of excited electrons and phonons. Finally, the application of friction energy dissipation in representative high-end equipment is discussed, and the potential economic saving is predicted.

The thickness of two-dimensional (2D) nanomaterials shows a significant effect on their optical and electrical properties. Therefore, a rapid and automatic detection technology of 2D nanomaterials with desired layer-number is required to extend their practical application in optoelectronic devices. In this paper, an image recognition technology was proposed for rapid and reliable identification of thin-layer WS₂ samples, which combining a layer-thickness identification criterion and a novel image segmentation algorithm. The criterion stemmed from optical contrast study of monochromatic illumination photographs, and the algorithm was based on Canny operator and edge connection iteration. This optical identification method can seek out thin-layer WS₂ samples on complex surfaces, which provides a promising approach for automatic search of thin-layer nanomaterials.

Two-dimensional (2D) transition-metal dichalcogenide (TMD) materials have aroused noticeable interest due to their distinguished electronic and optical properties. However, little is known about their complex exciton properties together with the exciton dynamics process which have been expected to influence the performance of optoelectronic devices. The process of fluorescence can well reveal the process of exciton transition after excitation. In this work, the room-temperature layer-dependent exciton dynamics properties in layered WSe₂ are investigated by the fluorescence lifetime imaging microscopy (FLIM) for the first time. This paper focuses on two mainly kinds of excitons including the direct transition neutral excitons and trions. Compared with the lifetime of neutral excitons (< 0.3 ns within four-layer), trions possess a longer lifetime (~ 6.6 ns within four-layer) which increases with the number of layers. We attribute the longer-lived lifetime to the increasing number of trions as well as the varieties of trion configurations in thicker WSe₂. Besides, the whole average lifetime increases over 10% when WSe₂ flakes added up from monolayer to four-layer. This paper provides a novel tuneable layer-dependent method to control the exciton dynamics process and finds a relatively longer transition lifetime of trions at room temperature, enabling to investigate in the charge transport in TMD-based optoelectronics devices in the future.