A ferroelectric semiconductor field-effect transistor (FeS-FET) was proposed and experimentally demonstrated for the first time. In this novel FeS-FET, a two-dimensional (2D) ferroelectric semiconductor α-In2Se3 is used to replace conventional semiconductor as channel.α-In2Se3 is identified due to its proper bandgap, room temperature ferroelectricity, the ability to maintain ferroelectricity down to a few atomic layers and the feasibility for large-area growth.An atomic-layer deposition (ALD) Al2O3 passivation method was developed to protect and enhance the performance of the α-In2Se3 FeS-FETs. The fabricated FeS-FETs exhibit high performance with a large memory window, a high on/off ratio over 10 8 , a maximum on-current of 671 μA/μm, high electron mobility of 488 cm 2 /V•s, and the potential to exceed the existing Fe-FETs for non-volatile memory applications.

Selenium has attracted intensive attention as a promising material candidate for future optoelectronic applications. However, selenium has a strong tendency to grow into nanowire forms due to its anisotropic atomic structure, which has largely hindered the exploration of its potential applications. In this work, using a physical vapor deposition method, we have demonstrated the synthesis of large-size, high-quality 2D selenium nanosheets, and the minimum thickness of which could be as thin as 5 nm. The Se nanosheet exhibits a strong in-plane anisotropic property, which is determined by angle-resolved Raman spectroscopy. Back-gating field-effect transistors (FETs) based on Se nanosheet exhibit p-type transport behaviors with on-state current density around 20 mA/mm at Vds=3V. Four-terminal field-effect devices are also fabricated to evaluate the intrinsic hole mobility of selenium nanosheet, and the value is determined to be 0.26 cm 2 V -1 s -1 at 300 K. The selenium nanosheet phototransistors show an excellent photoresponsivity up to 263 A/W, with the rise time of 0.1s and fall time of 0.12s. These results suggest that crystal selenium as a 2D form of 1D van der Waals solid, opens more feasibility to explore device applications.

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2D transition metal dichalcogenides materials are explored as potential surface-enhanced Raman spectroscopy substrates. Herein, a systematic study of the Raman enhancement mechanism on distorted 1T (1T') rhenium disulfide (ReS ) nanosheets is demonstrated. Combined Raman and photoluminescence studies with the introduction of an Al O dielectric layer unambiguously reveal that Raman enhancement on ReS materials is from a charge transfer process rather than from an energy transfer process, and Raman enhancement is inversely proportional while the photoluminescence quenching effect is proportional to the layer number (thickness) of ReS nanosheets. On monolayer ReS film, a strong resonance-enhanced Raman scattering effect dependent on the laser excitation energy is detected, and a detection limit as low as 10 m can be reached from the studied dye molecules such as rhodamine 6G and methylene blue. Such a high enhancement factor achieved through enhanced charge interaction between target molecule and substrate suggests that with careful consideration of the layer-number-dependent feature and excitation-energy-related resonance effect, ReS is a promising Raman enhancement platform for sensing applications.