2D Tellurium Films Based Self-drive Near Infrared Photodetector.

To reduce the amount of energy consumed in integrated circuits, high efficiency with the lowest energy is always expected. Self-drive device is one of the options in the pursuit of low power nanodevices. It is a typical strategy to form an internal electric field by constructing a heterojunction in self-drive semiconductor system. Here, a two-step method is proposed to prepare high quality centimeter-sized 2D tellurium (Te) thin film with hall mobility as high as 37.3 cm2V-1s-1, and the 2D Te film is further assembled with silicon to form a heterojunction for self-drive photodetector, which can realize effective detection from visible to near infrared bands. The photodetectivity of the heterojunctions can reach 1.58 × 1011 Jones under the illumination of 400 nm@ 1.615 mW/cm2 and 2.08 x 108 Jones under the illumination of 1550 nm@ 1.511mW/cm2 without bias. Our experiments demonstrate the potential of 2D tellurium thin films for wide band and near infrared integrated device applications.

Robust Magnetic Proximity Induced Anomalous Hall Effect in a Room Temperature van der Waals Ferromagnetic Semiconductor Based 2D Heterostructure.

Developing novel high-temperature van der Waals ferromagnetic semiconductor materials and investigating their interface coupling effects with 2D topological semimetals are pivotal for advancing next-generation spintronic and quantum devices. However, most van der Waals ferromagnetic semiconductors exhibit ferromagnetism only at low temperatures, limiting the proximity research on their interfaces with topological semimetals. Here, an intrinsic, van der Waals layered room-temperature ferromagnetic semiconductor crystal, FeCr0.5 Ga1.5 Se4 (FCGS), is reported with a Curie temperature (TC ) as high as 370 K, setting a new record for van der Waals ferromagnetic semiconductors. The saturation magnetization at low temperature (2 K) and room temperature (300 K) reaches 8.2 and 2.7 emu g-1 , respectively. Furthermore, FCGS possesses a bandgap of ≈1.2 eV, which is comparable to the widely used commercial silicon. The FCGS/graphene 2D heterostructure exhibits an impeccably smooth and gapless interface, thereby inducing a robust van der Waals magnetic proximity coupling effect between FCGS and graphene. After the proximity coupling, graphene undergoes a charge carrier transition from electrons to holes, accompanied by a transition from non-magnetic to ferromagnetic transport behavior with robust anomalous Hall effect (AHE). Notably, the van der Waals magnetic proximity-induced AHE remains robust even up to 400 K.

Room-Temperature van der Waals Ferromagnet Switching by Spin-Orbit Torques.

The emerging wide varieties of the van der Waals (vdW) magnets with atomically thin and smooth interfaces hold great promise for next-generation spintronic devices. However, due to the lower Curie temperature of the vdW ferromagnets than room temperature, electrically manipulating its magnetization at room temperature has not been realized. In this work, it is demonstrated that the perpendicular magnetization of the vdW ferromagnet Fe3 GaTe2 can be effectively switched at room temperature in the Fe3 GaTe2 /Pt bilayer by spin-orbit torques (SOTs) with a relatively low current density of 1.3 × 107 A cm-2 . Moreover, the high SOT efficiency of ξDL ≈ 0.28 is quantitatively determined by harmonic measurements, which is higher than those in Pt-based heavy metal/conventional ferromagnet devices. The findings of room-temperature vdW ferromagnet switching by SOTs provide a significant basis for the development of vdW-ferromagnet-based spintronic applications.

MASCN Surface Treatment to Reduce Phase Transition Temperature and Regulate Strain for Efficient and Stable α-FAPbI3 Perovskite Solar Cells.

The fabrication of α-FAPbI3 perovskite films usually requires high temperature annealing above 150 °C, and the residual tensile strain in the films seriously affects the stability of α-FAPbI3 by converting to δ-phase FAPbI3. Here, we use MASCN surface treatment of FAPbI3 films to induce a rotation of the coplanar octahedron [PbI6]4- to the metric octahedron for the strong interaction of SCN- with Pb2+, converting δ-FAPbI3 into α-FAPbI3 highly crystalline films at room temperature. The optimized FAPbI3 films have high stability due to releasing residual tensile strains after MASCN treatment. The efficiency of the MASCN-treated unannealed FAPbI3 PSC is 19.03%, while the optimized FAPbI3 annealed at 100 °C shows a maximum PCE of 21.95% on a small area. The solar cell stability for humidity, light, and thermal stability are significantly improved. The MASCN treated FAPbI3 achieves a PCE of 15.32% on a PSC module with an effective area of 9.6 cm2 and maintains an initial efficiency of 94.1% after 100 days of ageing at 85 °C and 85% humidity.

Evaluation of validity and reliability of novel rapid measurement for infundibulopelvic angle: a comparison with PACS system.

BACKGROUND: For patients with lower pole renal calculi (LPC), preoperative evaluation of infundibulopelvic angles (IPA) is of great significance; however, conventional measuring method is often inconvenient in clinical setting. Here we introduce a rapid novel method using built-in inclinometer in smartphone which is often used in anatomical parameters evaluating to implement the measurement of IPA. MATERIALS AND METHODS: The randomized, self-controlled study on evaluating inclinometer application measured IPA on urography films collected from enrolled LPC patients. Results of statistical analysis for its validity and reliability compared to conventional PACS system are reported. Predictive performance of postoperative stone-free rates by IPA measured with the novel method was also evaluated in this study. RESULTS: Bland-Altman plot result shows that there is favorable agreement between IPA values of these two methods. The time required to utilize the PACS was considerably greater than time required to take similar measure using smartphones. The precision-recall curve (PRC) indicates that the new method has similar predictive performance for postoperative clearance rates as PACS. CONCLUSIONS: In summary, measurement of IPA implemented by integrated inclinometer of smartphone is rapid, convenient, accurate and reliable in evaluating renal anatomy parameters of LPC patients.

Room-Temperature and Tunable Tunneling Magnetoresistance in Fe3GaTe2-Based 2D van der Waals Heterojunctions.

Magnetic tunnel junctions (MTJs) based on van der Waals (vdW) heterostructures with sharp and clean interfaces on the atomic scale are essential for the application of next-generation spintronics. However, the lack of room-temperature intrinsic ferromagnetic crystals with perpendicular magnetic anisotropy has greatly hindered the development of vertical MTJs. The discovery of room-temperature intrinsic ferromagnetic two-dimensional (2D) crystal Fe3GaTe2 has solved the problem and greatly facilitated the realization of practical spintronic devices. Here, we demonstrate a room-temperature MTJ based on a Fe3GaTe2/WS2/Fe3GaTe2 heterostructure for the first time. The tunneling magnetoresistance (TMR) ratio is up to 213% with a high spin polarization of 72% at 10 K, the highest ever reported in Fe3GaTe2-based MTJs up to now. A tunneling spin-valve signal robustly persists at room temperature (300 K) with a bias current down to 10 nA. Moreover, the spin polarization can be modulated by bias current and the TMR shows a sign reversal at a large bias current. Our work sheds light on the potential application of low-energy consumption in all-2D vdW spintronics and offers alternative routes for the electronic control of spintronic devices.

Room-temperature spin-valve devices based on Fe3GaTe2/MoS2/Fe3GaTe2 2D van der Waals heterojunctions.

The spin-valve effect has been the focus of spintronics over the last decades due to its potential for application in many spintronic devices. Two-dimensional (2D) van der Waals (vdW) materials are highly efficient to build spin-valve heterojunctions. However, the Curie temperatures (TC) of the vdW ferromagnetic (FM) 2D crystals are mostly below room temperature (∼30-220 K). It is very challenging to develop room-temperature, FM 2D crystal-based spin-valve devices. Here, we report room-temperature, FM 2D-crystal-based all-2D vdW Fe3GaTe2/MoS2/Fe3GaTe2 spin-valve devices. The magnetoresistance (MR) of the device was up to 15.89% at 2.3 K and 11.97% at 10 K, which are 4-30 times the MR of the spin valves of Fe3GeTe2/MoS2/Fe3GeTe2 and conventional NiFe/MoS2/NiFe. The typical spin valve effect showed strong dependence on the MoS2 spacer thickness in the vdW heterojunction. Importantly, the spin valve effect (0.31%) robustly existed even at 300 K with low working currents down to 10 nA (0.13 A cm-2). This work provides a general vdW platform to develop room-temperature, 2D FM-crystal-based 2D spin-valve devices.

Highly Tunable Beyond-Room-Temperature Intrinsic Ferromagnetism in Cr-Doped Topological Crystalline Insulator SnTe Crystals.

The combination of topological phase and intrinsic beyond-room-temperature ferromagnetism is expected to realize the quantum anomalous Hall effect at a high temperature. However, no beyond-room-temperature intrinsic ferromagnetism has been reported in either topological insulator or topological crystalline insulator (TCI) so far. Here, we report Cr-doping in TCI-phase SnTe crystals which possess highly tunable beyond-room-temperature intrinsic ferromagnetism including Tc, magnetic moment, and coercivity by varying Cr contents and crystal thickness. With the increase of the Cr content, the Tc increases by 159 K from 221 to 380 K and the saturation magnetic moments increase by ∼23.6 times from 0.018 to 0.421 µB/f.u. This intrinsic beyond-room-temperature ferromagnetism is fully demonstrated by the anomalous Hall effect and magneto-optical Kerr effect in a single CrxSn1-xTe nanosheet. Moreover, the room-temperature tunneling magnetoresistance effect has been realized by using a CrxSn1-xTe flake, a Fe thin film, and a commercially compatible ultrathin AlOx tunneling barrier. This work indicates a great potential of CrxSn1-xTe crystals in room-temperature magnetoelectronic and spintronic devices.

Two-Dimensional Van Der Waals Topological Materials: Preparation, Properties, and Device Applications.

Over the past decade, 2D van der Waals (vdW) topological materials (TMs), including topological insulators and topological semimetals, which combine atomically flat 2D layers and topologically nontrivial band structures, have attracted increasing attention in condensed-matter physics and materials science. These easily cleavable and integrated TMs provide the ideal platform for exploring topological physics in the 2D limit, where new physical phenomena may emerge, and represent a potential to control and investigate exotic properties and device applications in nanoscale topological phases. However, multifaced efforts are still necessary, which is the prerequisite for the practical application of 2D vdW TMs. Herein, this review focuses on the preparation, properties, and device applications of 2D vdW TMs. First, three common preparation strategies for 2D vdW TMs are summarized, including single crystal exfoliation, chemical vapor deposition, and molecular beam epitaxy. Second, the origin and regulation of various properties of 2D vdW TMs are introduced, involving electronic properties, transport properties, optoelectronic properties, thermoelectricity, ferroelectricity, and magnetism. Third, some device applications of 2D vdW TMs are presented, including field-effect transistors, memories, spintronic devices, and photodetectors. Finally, some significant challenges and opportunities for the practical application of 2D vdW TMs in 2D topological electronics are briefly addressed.

Above-room-temperature strong intrinsic ferromagnetism in 2D van der Waals Fe3GaTe2 with large perpendicular magnetic anisotropy.

The absence of two-dimensional (2D) van der Waals (vdW) ferromagnetic crystals with both above-room-temperature strong intrinsic ferromagnetism and large perpendicular magnetic anisotropy (PMA) severely hinders practical applications of 2D vdW crystals in next-generation low-power magnetoelectronic and spintronic devices. Here, we report a vdW intrinsic ferromagnetic crystal Fe3GaTe2 that exhibits record-high above-room-temperature Curie temperature (Tc, ~350-380 K) for known 2D vdW intrinsic ferromagnets, high saturation magnetic moment (40.11 emu/g), large PMA energy density (~4.79 × 105 J/m3), and large anomalous Hall angle (3%) at room temperature. Such large room-temperature PMA is better than conventional widely-used ferromagnetic films like CoFeB, and one order of magnitude larger than known 2D vdW intrinsic ferromagnets. Room-temperature thickness and angle-dependent anomalous Hall devices and direct magnetic domains imaging based on Fe3GaTe2 nanosheet have been realized. This work provides an avenue for room-temperature 2D ferromagnetism, electrical control of 2D ferromagnetism and promote the practical applications of 2D-vdW-integrated spintronic devices.

Highly-Tunable Intrinsic Room-Temperature Ferromagnetism in 2D van der Waals Semiconductor Crx Ga1- x Te.

The combination of semiconductivity and tunable ferromagnetism is pivotal for electrical control of ferromagnetism and next-generation low-power spintronic devices. However, Curie temperatures (TC ) for most traditional intrinsic ferromagnetic semiconductors (≤200 K) and recently discovered two-dimensional (2D) ones (<70 K) are far below room temperature. 2D van der Waals (vdW) semiconductors with intrinsic room-temperature ferromagnetism remain elusive considering the unfavored 2D long-range ferromagnetic order indicated by Mermin-Wagner theorem. Here, vdW semiconductor Crx Ga1- x Te crystals exhibiting highly tunable above-room-temperature ferromagnetism with bandgap 1.62-1.66 eV are reported. The saturation magnetic moment (Msat ) of Crx Ga1- x Te crystals can be effectively regulated up to ≈5.4 times by tuning Cr content and ≈75.9 times by changing the thickness. vdW Crx Ga1- x Te ultrathin semiconductor crystals show robust room-temperature ferromagnetism with the 2D quantum confinement effect, enabling TC 314.9-329 K for nanosheets, record-high for intrinsic vdW 2D ferromagnetic semiconductors. This work opens an avenue to room-temperature 2D vdW ferromagnetic semiconductor for 2D electronic and spintronic devices.

Two-dimensional magnetic atomic crystals.

Two-dimensional (2D) magnetic crystals show many fascinating physical properties and have potential device applications in many fields. In this paper, the preparation, physical properties and device applications of 2D magnetic atomic crystals are reviewed. First, three preparation methods are presented, including chemical vapor deposition (CVD) molecular beam epitaxy (MBE) and single-crystal exfoliation. Second, physical properties of 2D magnetic atomic crystals, including ferromagnetism, antiferromagnetism, magnetic regulation and anomalous Hall effect are presented. Third, the application of 2D magnetic atomic crystals in heterojunctions reluctance and other aspects are briefly introduced. Finally, the future development direction and possible challenges of 2D magnetic atomic crystals are briefly addressed.

Tunable and Robust Near-Room-Temperature Intrinsic Ferromagnetism of a van der Waals Layered Cr-Doped 2H-MoTe2 Semiconductor with an Out-of-Plane Anisotropy.

The intrinsically nonmagnetic feature of van der Waals (vdW) layered transition-metal dichalcogenide (TMDC) semiconductors limits the spintronic applications of these semiconductors. In this paper, we demonstrate a facile Te flux strategy to induce intrinsic ferromagnetism in the vdW layered 2H-MoTe2 semiconductor by magnetic chromium (Cr) doping. The Curie temperature (Tc) and saturation magnetization (Ms) can be well tuned by adjusting the Cr doping concentration. A notable Tc up to 275 K can be achieved for the vdW layered Cr-doped 2H-MoTe2 bulk crystals, which is much higher than that of recently reported van der Waals ferromagnetic semiconductors (Tc is mostly less than 70 K), in contrast to the diamagnetic feature of the pristine MoTe2. Meanwhile, the highest Ms of the vdW layered Cr-doped 2H-MoTe2 bulk crystals can reach 4.78 emu g-1, which is stronger than most values reported for magnetic-element-doped van der Waals materials. In addition, all of the as-grown semiconducting Cr-doped 2H-MoTe2 (Cr-2H-MoTe2) single crystals display a large magnetic anisotropy with an out-of-plane easy axis of magnetization. The observed ferromagnetism in the Cr-2H-MoTe2 has intrinsic characteristics, which can be mainly attributed to the spin polarization caused by Cr doping as confirmed by the density functional theory (DFT) calculations. Our approach offers an avenue to tune the ferromagnetism in the vdW layered semiconductor and explore its diverse spintronic and magnetoelectric applications.