Manipulation of ferroelectric domains is essential for advancing ferroelectric electronics. Mechanical switching offers an effective route for nanoscale domain control, yet conventional inorganic ferroelectrics typically require micronewton-level forces applied by nanoscale probes, generating GPa local pressures that risk material damage and make it challenging to mechanically generate large-area ferroelectric domain patterns. Overcoming this limitation demands ferroelectrics capable of responding to extremely small mechanical stimuli. Here, we demonstrate ultralow-force-driven polarization switching in the molecular ferroelectric (3,3-difluorocyclobutylammonium)₂CuCl₄, a two-dimensional organic–inorganic hybrid perovskite. Domain switching is achieved with an applied force of only 25 nN—corresponding to a local pressure below 20 MPa, orders of magnitude lower than that required for inorganic oxide ferroelectrics. This exceptionally low mechanical threshold arises from the intrinsic structural compliance and flexibility of molecular ferroelectrics. Moreover, the remarkably small switching force also enables ultrasound-driven domain modification. These results create new opportunities for molecular ferroelectrics in mechanoelectrical electronics, energy harvesting, and ultrasonic catalysis.

Optical emission efficiency of two-dimensional layered transition metal dichalcogenides (TMDs) is one of the most important parameters affecting their optoelectronic performance. The optimization of the growth parameters by chemical vapor deposition (CVD) to achieve optoelectronic-grade quality TMDs is, therefore, highly desirable. Here, we present a systematic photoluminescence (PL) spectroscopic approach to assess the intrinsic optical and crystalline quality of CVD grown MoS₂ (CVD MoS₂). We propose the use of the intensity ratio between the PL measured in air and vacuum as an effective way to monitor the intrinsic optical quality of CVD MoS₂. Low-temperature PL measurements are also used to evaluate the structural defects in MoS₂, via defect-associated bound exciton emission, which well correlates with the field-effect carrier mobility of MoS₂ grown at different temperatures. This work therefore provides a sensitive, noninvasive method to characterize the optical properties of TMDs, allowing the tuning of the growth parameters for the development of optoelectronic devices.

The electrical performance of two-dimensional transition metal dichalcogenides (TMDs) is strongly affected by the number of structural defects. In this work, we provide an optical spectroscopic characterization approach to correlate the number of structural defects and the electrical performance of WSe₂ devices. Low-temperature photoluminescence (PL) spectra of electron-beam-lithographyprocessed WSe₂ exhibit a clear defect-induced PL emission due to excitons bound to defects, which would strongly degrade the electrical performance. By adopting an electron-beam-free transfer-electrode technique, we successfully prepared a backgated WSe₂ device containing a limited amount of defects. A maximum hole mobility of approximately 200 cm²·V^-1·s^-1 was achieved because of the reduced scattering sources, which is the highest reported value for this type of device. This work provides not only a versatile and nondestructive method to monitor the defects in TMDs but also a new route to approach the room-temperature phonon-limited mobility in high-performance TMD devices.