Highly Robust Room-Temperature Interfacial Ferromagnetism in Ultrathin Co2Si Nanoplates.

The reduced dimensionality and interfacial effects in magnetic nanostructures open the feasibility to tailor magnetic ordering. Here, we report the synthesis of ultrathin metallic Co2Si nanoplates with a total thickness that is tunable to 2.2 nm. The interfacial magnetism coupled with the highly anisotropic nanoplate geometry leads to strong perpendicular magnetic anisotropy and robust hard ferromagnetism at room temperature, with a Curie temperature (TC) exceeding 950 K and a coercive field (HC) > 4.0 T at 3 K and 8750 Oe at 300 K. Theoretical calculations suggest that ferromagnetism originates from symmetry breaking and undercoordinated Co atoms at the Co2Si and SiO2 interface. With protection by the self-limiting intrinsic oxide, the interfacial ferromagnetism of the Co2Si nanoplates exhibits excellent environmental stability. The controllable growth of ambient stable Co2Si nanoplates as 2D hard ferromagnets could open exciting opportunities for fundamental studies and applications in Si-based spintronic devices.

Low Temperature Synthesis of 2D p-Type α-In2 Te3 with Fast and Broadband Photodetection.

2D A 2 III B 3 VI ${\mathrm{A}}_2^{{\mathrm{III}}}{\mathrm{B}}_3^{{\mathrm{VI}}}$ compounds (A = Al, Ga, In, and B = S, Se, and Te) with intrinsic structural defects offer significant opportunities for high-performance and functional devices. However, obtaining 2D atomic-thin nanoplates with non-layered structure on SiO2 /Si substrate at low temperatures is rare, which hinders the study of their properties and applications at atomic-thin thickness limits. In this study, the synthesis of ultrathin, non-layered α-In2 Te3  nanoplates is demonstrated using a BiOCl-assisted chemical vapor deposition method at a temperature below 350 °C on SiO2 /Si substrate. Comprehensive characterization results confirm the high-quality single crystal is the low-temperature cubic phase α-In2 Te3 , possessing a noncentrosymmetric defected ZnS structure with good second harmonic generation. Moreover, α-In2 Te3 is revealed to be a p-type semiconductor with a direct and narrow bandgap value of 0.76 eV. The field effect transistor exhibits a high mobility of 18 cm2 V-1  s-1 , and the photodetector demonstrates stable photoswitching behavior within a broadband photoresponse from 405 to 1064 nm, with a satisfactory response time of τrise = 1 ms. Notably, the α-In2 Te3 nanoplates exhibit good stability against ambient environments. Together, these findings establish α-In2 Te3 nanoplates as promising candidates for next-generation high-performance photonics and electronics.

Terminal Atom-Controlled Etching of 2D-TMDs.

The controlled etching of 2D transition metal dichalcogenides (2D-TMDs) is critical to understanding the growth mechanisms of 2D materials and patterning 2D materials but remains a major comprehensive challenge. Here, a rational strategy to control the terminal atoms of 2D-TMDs etched holes is reported. Using laser irradiation combined with an improved anisotropic thermal etching process under a determined atmosphere, terminal atom-controlled etched hole arrays are created on 2D-TMDs. By adjusting the gas atmosphere during the thermal etching stage, triangular etched hole arrays terminated by the tungsten zigzag (W-ZZ) edge (in an Ar/H2 atmosphere), hexagonal etched hole arrays terminated alternately by the W-ZZ edge and sulfur (selenium) zigzag (S-ZZ or Se-ZZ) edge (in a pure Ar atmosphere), and triangular etched hole arrays terminated by the S-ZZ (Se-ZZ) edge (in an Ar/sulfur [selenium] vapor atmosphere) can be obtained. Density functional theory reveals the forming energy of different edges and the different activities of metal atoms and chalcogenide atoms under different atmospheres, which determine the terminal atoms of the holes. This work may enhance the understanding of the etching and growth of 2D-TMDs. The 2D-TMDs hole arrays constructed by this work may have important applications in catalysis, nonlinear optics, spintronics, and large-scale integrated circuits.

Wafer-scale and universal van der Waals metal semiconductor contact.

Van der Waals (vdW) metallic contacts have been demonstrated as a promising approach to reduce the contact resistance and minimize the Fermi level pinning at the interface of two-dimensional (2D) semiconductors. However, only a limited number of metals can be mechanically peeled and laminated to fabricate vdW contacts, and the required manual transfer process is not scalable. Here, we report a wafer-scale and universal vdW metal integration strategy readily applicable to a wide range of metals and semiconductors. By utilizing a thermally decomposable polymer as the buffer layer, different metals were directly deposited without damaging the underlying 2D semiconductor channels. The polymer buffer could be dry-removed through thermal annealing. With this technique, various metals could be vdW integrated as the contact of 2D transistors, including Ag, Al, Ti, Cr, Ni, Cu, Co, Au, Pd. Finally, we demonstrate that this vdW integration strategy can be extended to bulk semiconductors with reduced Fermi level pinning effect.

General low-temperature growth of two-dimensional nanosheets from layered and nonlayered materials.

Most of the current methods for the synthesis of two-dimensional materials (2DMs) require temperatures not compatible with traditional back-end-of-line (BEOL) processes in semiconductor industry (450 °C). Here, we report a general BiOCl-assisted chemical vapor deposition (CVD) approach for the low-temperature synthesis of 27 ultrathin 2DMs. In particular, by mixing BiOCl with selected metal powders to produce volatile intermediates, we show that ultrathin 2DMs can be produced at 280-500 °C, which are ~200-300 °C lower than the temperatures required for salt-assisted CVD processes. In-depth characterizations and theoretical calculations reveal the low-temperature processes promoting 2D growth and the oxygen-inhibited synthetic mechanism ensuring the formation of ultrathin nonlayered 2DMs. We demonstrate that the resulting 2DMs exhibit electrical, magnetic and optoelectronic properties comparable to those of 2DMs grown at much higher temperatures. The general low-temperature preparation of ultrathin 2DMs defines a rich material platform for exploring exotic physics and facile BEOL integration in semiconductor industry.