Two-dimensional (2D) materials have emerged as promising candidates for various optoelectronic applications based on their diverse electronic properties, ranging from insulating to superconducting. However, cooperative phenomena such as ferroelectricity in the 2D limit have not been well explored. Here, we report room-temperature ferroelectricity in 2D CuInP2S6 (CIPS) with a transition temperature of ∼320 K. Switchable polarization is observed in thin CIPS of ∼4 nm. To demonstrate the potential of this 2D ferroelectric material, we prepare a van der Waals (vdW) ferroelectric diode formed by CIPS/Si heterostructure, which shows good memory behaviour with on/off ratio of ∼100. The addition of ferroelectricity to the 2D family opens up possibilities for numerous novel applications, including sensors, actuators, non-volatile memory devices, and various vdW heterostructures based on 2D ferroelectricity.

Wearable or attachable health monitoring smart systems are considered to be the next generation of personal portable devices for remote medicine practices. Smart flexible sensing electronics are components crucial in endowing health monitoring systems with the capability of real-time tracking of physiological signals. These signals are closely associated with body conditions, such as heart rate, wrist pulse, body temperature, blood/intraocular pressure and blood/sweat bio-information. Monitoring such physiological signals provides a convenient and non-invasive way for disease diagnoses and health assessments. This Review summarizes the recent progress of flexible sensing electronics for their use in wearable/attachable health monitoring systems. Meanwhile, we present an overview of different materials and configurations for flexible sensors, including piezo-resistive, piezo-electrical, capacitive, and field effect transistor based devices, and analyze the working principles in monitoring physiological signals. In addition, the future perspectives of wearable healthcare systems and the technical demands on their commercialization are briefly discussed.

Single-layer single-crystalline SnSe nanosheet with four-atomic thickness of ~1.0 nm and lateral size of ~300 nm is presented here by using a one-pot synthetic method. It is found that 1,10-phenanthroline plays an important role in determining the morphology of the SnSe product as three-dimensional SnSe nanoflowers are obtained in the absence of 1,10-phenanthroline while keeping other reaction parameters the same. The evolution process study discloses that single-crystalline nanosheets are obtained from the coalescence of the SnSe nucleus in an orientated attachment mechanism. Band gap determination and optoelectronic test based on hybrid films of SnSe and poly(3-hexylthiophene) indicate the great potential of the ultrathin SnSe nanosheets in photodector and photovoltaic, and so forth.

We demonstrated a facile route for one-pot synthesis of visible light responsive nitrogen doped anatase TiO(2) sheets with dominant {001} facets from TiN. The synthesized anatase TiO(2) sheets show a strong and stable capability of generating photocatalysis active species of *OH radicals and hydrogen evolution from splitting water under visible light irradiation.