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.