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We present a Ge/MoS2 van der Waals heterojunction photodetector with a short active region constructed using a transfer process. The device exhibits broadband, self-powered, superior device performance within the visible to infrared wavelength (500–1700 nm) operated in a photovoltaic mode. Intriguingly, a sharp increased gain of 10 556 (93) with a varied breakdown voltage of −8.02 V (−6.25 V) under the 700 nm (1550 nm) laser illumination was observed, which was interpreted as the synergistic effect of both soft and avalanche breakdown behavior. These results imply disposable high-sensitivity broadband light-detection potentials with a simple Ge/MoS2 heterojunction, exempting it from the complex and strict construction requirement of conventional avalanche photodetectors. [ABSTRACT FROM AUTHOR]

Graphene, the first isolated two-dimensional atomic crystal, is about to pass its 20th year. The last decade has been a critical period for graphene to gradually move from the laboratory to practical applications, and the research on the spin-related physical properties and various spintronic applications of graphene is still enduring. In this review, we systematically retrospect the important and state-of-art progresses about graphene-based spintronics. First, spin–orbit coupling and various tuning means in graphene have been introduced, such as adatoms, electrical control, and the proximity effect. Second, several methods for inducing magnetism in graphene are summarized, including defect, atom doping, proximity effect, and the recently attractive twisted magic-angle. Third, graphene-based lateral and vertical spin valves are discussed, along with some emergent spin transport properties, including spin injection, scattering, and relaxation. Fourth, graphene-based spin logic circuits for spin communications and multifunctional spin logic devices are exhibited. Finally, some significant opportunities and challenges of graphene-based spintronics for the fundamental physics and practical applications in the future are briefly discussed. [ABSTRACT FROM AUTHOR]

An efficient visible-light photoelectrochemical photodetector based on a compact In-rich n-InGaN layer activated by p-Cu2O microcrystals operating as photoanode in the self-powered mode is demonstrated. The photocurrent density of 80 µA/cm2 under one-sun illumination is more than 10 times larger than that of a bare InGaN layer. Moreover, the photocurrent density, responsivity of 0.8 mA/W, specific detectivity of 4 × 109 Jones, and response times of 5–8 ms are more than five times better compared to those of our previously reported nanowire counterpart. The excellent performance is attributed to maximized photocarrier separation in the built-in electric field of the internal p–n junction for fully depleted Cu2O microcrystals with maximized height and the planar geometry, guaranteeing unhindered diffusion of the electrolyte to and from the photoanode surface. [ABSTRACT FROM AUTHOR]

We demonstrated that ternary HfAlO2 amorphous film prepared with common co-sputtering technology can be a suitable gate dielectric for bilayer MoTe2 transistors. The film quality can be improved by optimizing the sputtering process and post-annealing treatment, which is superior to its binary Al2O3 and HfO2 components and satisfies gate dielectric criteria. The bilayer MoTe2 transistors with ∼29-nm-thick HfAlO2 gate dielectric exhibit an Ion/Ioff ratio of over 108 by a low operating voltage, together with a small subthreshold swing ≈ 71.22 mV/dec. These promising characteristics favor the development of high-performance and low-power ultrathin MoTe2-based beyond-silicon electronics. [ABSTRACT FROM AUTHOR]

We demonstrated that the carrier polarity of MoTe2 transistors can be modulated by controlling the channel thickness with NiTe2 semimetal contacts. The multilayer MoTe2 transistors (thickness >7.1 nm) exhibit a symmetric ambipolar conduction, and a transition to unipolar p-type polarity occurs as the channel thickness decreased down to ∼2.3 nm. The position of the semimetal NiTe2 work function was verified to be located at the mid-gap of multilayer MoTe2, and the observed transition was interpreted by a synergistic effect of the channel thickness-dependent band alignment and charge transfer behavior with unique NiTe2 semimetal contacts. [ABSTRACT FROM AUTHOR]

Field-free room-temperature modulating magnetic domain structures and realizing stable nanoscale magnetic bubbles in 2D van der Waals (vdW) intrinsic ferromagnets are fundamentally important for 2D spintronic devices. However, it is still very challenging for the absence of a proper room-temperature 2D vdW ferromagnet with suitable perpendicular magnetic anisotropy. Here, by using a 2D vdW intrinsic room-temperature ferromagnetic Fe3GaTe2 crystal with Curie temperature of over ∼340 K and large perpendicular magnetic anisotropy, we study field-free thickness-dependent magnetic domain structure evolution in Au-capped 2D Fe3GaTe2 nanosheets by magnetic force microscopy at room temperature. The magnetic domain varies from a labyrinth-like stripe domain to a single domain in Au/Fe3GaTe2 (20/x nm) with decreasing Fe3GaTe2 thickness from 129 to 17.8 nm. Importantly, the field-free, spontaneous, stable, nanoscale magnetic bubbles can be realized in Au/Fe3GaTe2 (8/x nm) with a wide range of Fe3GaTe2 thickness over 30 nm. The highest bubble density and smallest diameter are measured as ∼2.65 μm−1 and ∼130 nm, respectively, superior to that of most room-temperature magnetic bubble materials. This work paves the way for field-free, room-temperature magnetic domain modulation and vdW-integrated spintronic applications of 2D vdW crystals. [ABSTRACT FROM AUTHOR]

With designing stator teeth by using grain oriented silicon sheets (GO) and other parts still with non-grain oriented silicon sheets (NGO), the electromagnetic performance of interior permanent magnet synchronous machine (GO-IPMSM) can be improved greatly, however its torque ripple will be increased as well. For reducing its torque ripple, optimizing its rotor barrier shape is an effective way. In this paper, the polynomial method is proposed to establish the rotor barrier shape, and the genetic algorithm (GA) method is employed for the optimization process. In case the optimized GO-IPMSM can work normally, its anti irreversible demagnetization ability is analyzed as well. As shown, with the GO is adopted for designing the stator teeth and its rotor barrier shape is optimized, though its torque ability and efficiency have been increased, its anti irreversible demagnetization risk ability is reduced, however the proposed machine can still operate safely. [ABSTRACT FROM AUTHOR]

We demonstrated a feasible strategy to fabricate MoTe2/Ge heterojunction by direct growth of Ge flake on a MoTe2 film substrate with a two-step chemical vapor deposition method. A thin transition layer (∼4 nm) mainly composed of polycrystalline germanium at the MoTe2/Ge interface was verified during the Ge flake growth. The MoTe2/Ge heterojunction-based photodetector exhibits both the response speed with a rise/fall time of 7/4 μs and the photoresponsivity and detectivity with 4.87 A W−1 and 5.02 × 1011 Jones under zero bias in the near-infrared regime, respectively. The characteristics of device performance imply its practical applicability as building block for potential near-infrared integrated photonics. [ABSTRACT FROM AUTHOR]

We demonstrated that Schottky barrier height (SBH) at the metal/CVD-grown MoTe2 interface can be significantly reduced with tunnel contact by inserting a thin Al2O3 layer regardless of the metal work function. The existence of strong Fermi level pinning (FLP) at the metal/MoTe2 interface was verified, while depinning cannot be achieved with Al2O3 insertion. Thus, the fixed charges inside the Al2O3 were proposed to be responsible for the effective SBH reduction in virtue of the eliminated SBH reduction after the post-annealing treatment. This work provides a feasible way to solve the contact issue and favors for the fabrication of high performance MoTe2-based electronic devices. [ABSTRACT FROM AUTHOR]

We report the fabrication of high performance MoTe2/Si heterojunction photodiodes by direct growth of MoTe2 patterns on a commercial Si substrate by a feasible chemical vapor deposition method. The devices exhibit an ultrafast response speed with a rise/fall time of 5/8 μs, a broadband (400–1550 nm) photoresponse, a high on/off ratio of ∼104, and self-powered photo-detection with a zero bias responsivity of 0.26 A W−1 and a detectivity of 2 × 1013 Jones at 700 nm wavelength. The devices further show high stability in air for one month. This investigation offers the feasibility to fabricate high performance MoTe2/Si photodiodes for future vital optoelectronic applications. [ABSTRACT FROM AUTHOR]

Field-free room-temperature modulating magnetic domain structures and realizing stable nanoscale magnetic bubbles in 2D van der Waals (vdW) intrinsic ferromagnets are fundamentally important for 2D spintronic devices. However, it is still very challenging for the absence of a proper room-temperature 2D vdW ferromagnet with suitable perpendicular magnetic anisotropy. Here, by using a 2D vdW intrinsic room-temperature ferromagnetic Fe3GaTe2 crystal with Curie temperature of over ∼340 K and large perpendicular magnetic anisotropy, we study field-free thickness-dependent magnetic domain structure evolution in Au-capped 2D Fe3GaTe2 nanosheets by magnetic force microscopy at room temperature. The magnetic domain varies from a labyrinth-like stripe domain to a single domain in Au/Fe3GaTe2 (20/x nm) with decreasing Fe3GaTe2 thickness from 129 to 17.8 nm. Importantly, the field-free, spontaneous, stable, nanoscale magnetic bubbles can be realized in Au/Fe3GaTe2 (8/x nm) with a wide range of Fe3GaTe2 thickness over 30 nm. The highest bubble density and smallest diameter are measured as ∼2.65 μm−1 and ∼130 nm, respectively, superior to that of most room-temperature magnetic bubble materials. This work paves the way for field-free, room-temperature magnetic domain modulation and vdW-integrated spintronic applications of 2D vdW crystals. [ABSTRACT FROM AUTHOR]