Controllable Synthesis of Transferable Ultrathin Bi2Ge(Si)O5 Dielectric Alloys with Composition-Tunable High-κ Properties.

Two-dimensional (2D) alloys hold great promise to serve as important components of 2D transistors, since their properties allow continuous regulation by varying their compositions. However, previous studies are mainly limited to the metallic/semiconducting ones as contact/channel materials, but very few are related to the insulating dielectrics. Here, we use a facile one-step chemical vapor deposition (CVD) method to synthesize ultrathin Bi2SixGe1-xO5 dielectric alloys, whose composition is tunable over the full range of x just by changing the relative ratios of the GeO2/SiO2 precursors. Moreover, their dielectric properties are highly composition-tunable, showing a record-high dielectric constant of >40 among CVD-grown 2D insulators. The vertically grown nature of Bi2GeO5 and Bi2SixGe1-xO5 enables polymer-free transfer and subsequent clean van der Waals integration as the high-κ encapsulation layer to enhance the mobility of 2D semiconductors. Besides, the MoS2 transistors using Bi2SixGe1-xO5 alloy as gate dielectrics exhibit a large Ion/Ioff (>108), ideal subthreshold swing of ∼61 mV/decade, and a small gate hysteresis (∼5 mV). Our work not only gives very few examples on controlled CVD growth of insulating dielectric alloys but also expands the family of 2D single-crystalline high-κ dielectrics.

Above-Room-Temperature Ferromagnetism in Copper-Doped Two-Dimensional Chromium-Based Nanosheets.

Two-dimensional ferromagnetic materials (2D-FMs) are expected to become ideal candidates for low-power, high-density information storage in next-generation spintronics devices due to their atomically ultrathin and intriguing magnetic properties. However, 2D-FMs with room-temperature Curie temperatures (Tc) are still rarely reported, which greatly hinders their research progress and practical applications. Herein, ultrathin Cu-doped Cr7Te8 FMs were successfully prepared and can achieve above-room-temperature ferromagnetism with perpendicular magnetic anisotropy via a facile chemical vapor deposition (CVD) method, which can be controlled down to an atomic thin layer of ∼3.4 nm. STEM-EDX quantitative analysis shows that the proportion of Cu to metal atoms is ∼5%. Moreover, based on the anomalous Hall effect (AHE) measurements in a six-terminal Hall bar device without any encapsulation as well as an out-of-plane magnetic field, the maximum Tc achieved ∼315 K when the thickness of the sample is ∼28.8 nm; even the ultrathin 7.6 nm sample possessed a near-room-temperature Tc of ∼275 K. Meanwhile, theoretical calculations elucidated the mechanism of the ferromagnetic enhancement of Cu-doped Cr7Te8 nanosheets. More importantly, the ferromagnetism of CVD-synthesized Cu-doped CrSe nanosheets can also be maintained above room temperature. Our work broadens the scope on room-temperature ferromagnets and their heterojunctions, promoting fundamental research and practical applications in next-generation spintronics.

Efficient Suppression of Persistent Photoconductivity in ß-Ga2O3-Based Photodetectors with Square Nanopore Arrays.

In this work, square nanopore arrays were developed on the surface of ß-Ga2O3 microflakes using focused ion beam (FIB) etching, and solar-blind photodetectors (PDs) were fabricated based on the ß-Ga2O3 microflakes with square nanopore arrays. The ß-Ga2O3 microflake-based device was transformed from a gate voltage depletion mode to an oxygen depletion mode by FIB etching. The developed device exhibited excellent solar-blind PD performance with extremely high responsivity (1.8 × 105 at 10 V), detectivity (3.4 × 1018 Jones at 10 V), and light-to-dark ratio (9.3 × 108 at 5 V) as well as good repeatability and excellent stability. The intrinsic mechanism responsible for this performance was then systematically discussed. This work opens up a new avenue for the fabrication of high-performance ß-Ga2O3-based low-dimensional PDs with high reproducibility by employing the FIB etching process.

Enhanced Faraday rotation by a Fano resonance in substrate-free three-dimensional magnetoplasmonic structures.

Three-dimensional magnetoplasmonic nanostructures possess more novel and richer optical and magneto-optical (MO) behaviors compared with planar nanostructures, and exhibit attractive potential applications in micro-nano non-reciprocal photonic devices. However, fabrication of three-dimensional magnetoplasmonic nanostructures is difficult using the usual nanofabrication methods. This work constructs three-dimensional substrate-free Au/Co/Au structures prepared using focused ion beam (FIB) technology. In the three-dimensional split-ring structure, with y-polarized light normal incidence, a three-dimensional coupling current is formed between the vertical split-ring and the bottom square hole, which causes excitation of the Fano resonance. The Fano resonance causes a significant enhancement of the local magnetic field, resulting in a larger Faraday rotation (FR). The resonance also brings about a sign reversal of FR, which is related to the direction of the Lorentz force on electrons. Similar effects also exist in the three-dimensional nanopillar structure and the three-dimensional nanoring structure in the simulation results. Due to the high flexibility of FIB machining, the height and shape of the three-dimensional split-ring can be arbitrarily changed, which means the FR intensity and the position of the FR null point are tunable. The designed three-dimensional structures provide a new route to regulate the Faraday effect, and broaden the possibilities for the design and construction of MO devices.