Van der Waals heterostructures, which are composed of layered two-dimensional materials, offer a platform to investigate a diverse range of physical phenomena and could be of use in a variety of applications. Heterostructures containing two-dimensional ferromagnets, such as chromium triiodide (CrI3), have recently been reported, which could allow two-dimensional spintronic devices to be developed. Here we study tunnelling through thin ferromagnetic chromium tribromide (CrBr3) barriers that are sandwiched between graphene electrodes. In devices with non-magnetic barriers, conservation of momentum can be relaxed by phonon-assisted tunnelling or by tunnelling through localized states. In contrast, in the devices with ferromagnetic barriers, the major tunnelling mechanisms are the emission of magnons at low temperatures and the scattering of electrons on localized magnetic excitations at temperatures above the Curie temperature. Magnetoresistance in the graphene electrodes further suggests induced spin–orbit coupling and proximity exchange via the ferromagnetic barrier. Tunnelling with magnon emission offers the possibility of spin injection.Electrons can tunnel through thin ferromagnetic CrBr3 barriers, sandwiched between graphene electrodes, via the emission of magnons, which suggests that these magnetic tunnel barriers could be used for spin injection.

Magnon-assisted tunnelling in van der Waals heterostructures based on CrBr 3

A grand family of two-dimensional (2D) materials and their heterostructures have been discovered through the extensive experimental and theoretical efforts of chemists, material scientists, physicists, and technologists. These pioneering works contribute to realizing the fundamental platforms to explore and analyze new physical/chemical properties and technological phenomena at the micro-nano-pico scales. Engineering 2D van der Waals (vdW) materials and their heterostructures via chemical and physical methods with a suitable choice of stacking order, thickness, and interlayer interactions enable exotic carrier dynamics, showing potential in high-frequency electronics, broadband optoelectronics, low-power neuromorphic computing, and ubiquitous electronics. This comprehensive review addresses recent advances in terms of representative 2D materials, the general fabrication methods, and characterization techniques and the vital role of the physical parameters affecting the quality of 2D heterostructures. The main emphasis is on 2D heterostructures and 3D-bulk (3D) hybrid systems exhibiting intrinsic quantum mechanical responses in the optical, valley, and topological states. Finally, we discuss the universality of 2D heterostructures with representative applications and trends for future electronics and optoelectronics (FEO) under the challenges and opportunities from physical, nanotechnological, and material synthesis perspectives.

2D Heterostructures for Ubiquitous Electronics and Optoelectronics: Principles, Opportunities, and Challenges.

With the increasing demand for multispectral information acquisition, infrared multispectral imaging technology that is inexpensive and can be miniaturized and integrated into other devices has received extensive attention. However, the widespread usage of such photodetectors is still limited by the high cost of epitaxial semiconductors and complex cryogenic cooling systems. Here, we demonstrate a noncooled two-color infrared photodetector that can provide temporal-spatial coexisting spectral blackbody detection at both near-infrared and mid-infrared wavelengths. This photodetector consists of vertically stacked back-to-back diode structures. The two-color signals can be effectively separated to achieve ultralow crosstalk of ~0.05% by controlling the built-in electric field depending on the intermediate layer, which acts as an electron-collecting layer and hole-blocking barrier. The impressive performance of the two-color photodetector is verified by the specific detectivity (D*) of 6.4 × 109 cm Hz1/2 W-1 at 3.5 μm and room temperature, as well as the promising NIR/MWIR two-color infrared imaging and absolute temperature detection. 

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Van der Waals two-color infrared photodetector

This paper demonstrated a hybrid SnO2–BNNTs (SnO2 decorated boron nitride nanotubes) for trace ppb-level sensing towards NO2. A facile way is utilized for the synthesis of SnO2–BNNTs in which BNNTs are consistently coated with SnO2 nanoparticles (NPs). The existence of SnO2 NPs onto BNNTs was confirmed by XRD, XPS, FESEM, and TEM. Sensing characteristics of SnO2–BNNTs sensor, including the sensor response, repeatability, long-term stability, and response–recovery times were studied by exposure to several NO2 gas concentrations varying from 250 ppb to 5 ppm at different operating temperatures form 25 °C–300 °C. As a result, the SnO2–BNNTs sensor showed an extremely low detection limit (DL) of 250 ppb, as well as a better sensor response as compared to the SnO2 sensor. The maximum sensor response of SnO2–BNNTs sensor was ∼2610 towards 5 ppm NO2 gas at low operating temperature (100 °C). Expanded variation of space charge depleted regions was created at p-n heterojunction which promoted tunneling effect caused by entrapment of NO2 gas molecule and offered conducting channels (CCs) through BNNTs for charge carriers towards an improved sensor response of SnO2–BNNTs sensor.

Selective ppb-level NO2 gas sensor based on SnO2-boron nitride nanotubes

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In neuromorphic hardware, peripheral circuits and memories based on heterogeneous devices are generally physically separated. Thus, exploration of homogeneous devices for these components is key fo...

2D materials-based homogeneous transistor-memory architecture for neuromorphic hardware.

Heterostructures based on diverse two-dimensional (2D) materials are effective for tailoring and further promoting device performance and exhibit considerable potential in photodetection. However, the problem of high-density thermionic carriers can be hardly overcome in most reported heterostructure devices based on type I and type II band alignment, which leads to an unacceptably small Iphoto/Idark and strong temperature dependence that limit the performance of photodetectors. Here, using the MoTe2/h-BN/MoTe2/h-BN heterostructure, we report the hole-dominated Fowler–Nordheim quantum tunneling transport in both on and off states. The state-of-the-art device operating at room temperature shows high detectivity of >108 Jones at a laser power density of

Runfeng Lin

Papers

2D materials-based homogeneous transistor-memory architecture for neuromorphic hardware.

Hole-dominated Fowler–Nordheim tunneling in 2D heterojunctions for infrared imaging