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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Enhancement of oxygen ion conductivity in oxides is important for low-temperature (<500 °C) operation of solid oxide fuel cells, sensors and other ionotronic devices. While huge ion conductivity has been demonstrated in planar heterostructure films, there has been considerable debate over the origin of the conductivity enhancement, in part because of the difficulties of probing buried ion transport channels. Here we create a practical geometry for device miniaturization, consisting of highly crystalline micrometre-thick vertical nanocolumns of Sm-doped CeO2 embedded in supporting matrices of SrTiO3. The ionic conductivity is higher by one order of magnitude than plain Sm-doped CeO2 films. By using scanning probe microscopy, we show that the fast ion-conducting channels are not exclusively restricted to the interface but also are localized at the Sm-doped CeO2 nanopillars. This work offers a pathway to realize spatially localized fast ion transport in oxides of micrometre thickness.

Same-spot Raman-photoluminescence with two lasers in a diamond anvil cell under hydrostatic pressure reveals that CsPbBr 3 nanocrystals, mostly located on the edges of CsPb 2 Br 5 2D platelets, are responsible for CsPb 2 Br 5 's green emission. This sensitive non-invasive technique combining static and dynamic probes establishes a one-toone property-structure relationship and distinguishes light emission from point defects versus nano-inclusions.