Two-dimensional (2D) materials are potential candidates for electronic devices due to their unique structures and exceptional physical properties, making them a focal point in nanotechnology research. Accurate assessment of the mechanical and tribological properties of 2D materials is imperative to fully exploit their potential across diverse applications. However, their nanoscale thickness and planar nature pose significant challenges in testing and characterizing their mechanical properties. Among the in situ characterization techniques, atomic force microscopy (AFM) has gained widespread applications in exploring the mechanical behaviour of nanomaterials, because of the easy measurement capability of nano force and displacement from the AFM tips. Specifically, AFM-based force spectroscopy is a common approach for studying the mechanical and tribological properties of 2D materials. This review comprehensively details the methods based on normal force spectroscopy, which are utilized to test and characterize the elastic and fracture properties, adhesion, and fatigue of 2D materials. Additionally, the methods using lateral force spectroscopy can characterize the interfacial properties of 2D materials, including surface friction of 2D materials, shear behaviour of interlayers as well as nanoflake-substrate interfaces. The influence of various factors, such as testing methods, external environments, and the properties of test samples, on the measured mechanical properties is also addressed. In the end, the current challenges and issues in AFM-based measurements of mechanical and tribological properties of 2D materials are discussed, which identifies the trend in the combination of multiple methods concerning the future development of the in situ testing techniques.

Strain engineering, as a cutting-edge method for modulating the electronic structure of catalysts, plays a crucial role in regulating the interaction between the catalytic surface and the adsorbed molecules. The electrocatalytic performance is influenced by the electronic structure, which can be achieved by introducing the external forces or stresses to adjust interatomic spacing between surface atoms. The challenges in strain engineering research lie in accurately understanding the mechanical impact of strain on performance. This paper first introduces the basic strategy for generating the strain, summarizes the different strain generation forms and their advantages and disadvantages. The progress in researching the characterization means for the lattice strains and their applications in the field of electrocatalysis is also emphasized. Finally, the challenges of strain engineering are introduced, and an outlook on the future research directions is provided.

The high sensitivity of room-temperature gas sensors is the key to innovation in the areas of environment, energy conservation and safety. However, metal-oxide-based sensors generally operate at high temperatures. Herein, we designed three ZrO₂-based sensors and explored their NO₂ sensing properties at room temperature. ZrO₂ with three different morphologies and microstructure were synthesized by simple hydrothermal methods. The microstructures of sensing materials are expected to significantly affect gas sensing properties. The rod-shaped ZrO₂ (ZrO₂-R) displayed the advantages such as higher crystallinity, larger pore size, narrower band gap and more chemisorbed adsorbed oxygen, compared to hollow sphere-shaped ZrO₂ (ZrO₂-HS), stellate-shaped ZrO₂ (ZrO₂–S). The ZrO₂-R sensor showed the highest response towards 30 ​ppm NO₂ (423.8%) at room temperature, and a quite high sensitivity of 198.0% for detecting 5 ​ppm NO₂. Although ZrO₂-HS and ZrO₂–S sensors exhibited lower response towards 30 ​ppm NO₂ (232.9% and 245.1%), the response time and recovery time of these two sensors are 5 ​s/19 ​s and 4 ​s/3 ​s, respectively. This work can provide a new strategy for the development of room-temperature metal-oxide-based sensors.