Four Nature articles are mad every day. What is the magic of this semiconductor nanomaterial?

Two-dimensional materials are undoubtedly the treasure of today‘s scientific research community. Not only graphene, but various other non-graphene two-dimensional materials have also played an increasing role in the fields of catalysis, optics, and electronic devices. In the early morning of March 5, Nature Magazine published four papers (3 research papers and 1 prospective article) on the same day, covering a series of breakthroughs in two-dimensional materials.

Below, we briefly introduce this, hoping to inspire researchers in related fields.

1-2. Nature: Two-dimensional materials make ultra-fast image recognition sensors possible!
Whether in autonomous driving or emerging technologies such as face recognition, ultra-fast visual image sensing technology has become a key component of intelligent systems. The problem is that the ultra-fast conversion of optical images into the electrical signal domain is still one of the bottlenecks in the field. With artificial neural network technology that mimics the structure of the human eye, it has great potential in enhancing image contrast, noise reduction or data acquisition, and is expected to make breakthroughs in this field.

In view of this, Lukas Mennel and Thomas Mueller et al from Vienna University of Technology reported the latest results of ultra-fast image recognition based on two-dimensional materials. Professor Yang Chai of the Hong Kong Polytechnic University was invited to comment on this in Nature and made a prospect.

Highlights of this article:
1) It is proved that the image sensor itself can constitute an artificial neural network, and simultaneously sense and process optical images without delay.
2) Based on the WSe2 two-dimensional semiconductor as a photosensitive material, a reconfigurable photodiode array was constructed, showing strong light-matter interaction and excellent photoelectric characteristics.
3) Achieved supervised and unsupervised learning, and trained the sensors to classify and encode the images projected on the chip optically, with a processing capacity of 20 million bins per second.

references:
1. Lukas Mennel et al. Ultrafast machine vision with 2D material neural networkimage sensors. Nature 2002.
https://www.nature.com/articles/s41586-020-2038-x
2.Yang Chai et al. In-sensor computing for machine vision. Nature 2002.
https://www.nature.com/articles/d41586-020-00592-6

3. Nature: New strategy for growing wafer-level single-layer hexagonal boron nitride single crystals
In integrated circuits, ultrathin two-dimensional semiconductor materials offer great potential for extending Moore‘s Law. One of the key issues is how to avoid the formation of charge scattering and trap sites between adjacent dielectrics. The hexagonal boron nitride (hBN) insulating van der Waals layer provides an excellent interfacial dielectric, effectively reducing the scattering of charge. Single crystal hexagonal boron nitride is usually grown on the surface of molten gold or on bulk copper foil. However, the high cost of molten gold, cross-contamination, and potential problems with process control and scalability are not welcomed by companies. Copper foil may be suitable for roll-to-roll processes, but is unlikely to be compatible with advanced microelectronics manufacturing on wafers. Therefore, how to reliably grow single crystal hBN directly on a wafer is one of the key technologies in the semiconductor field.

Also on March 4, 2020, Taiwanese scientists Lain-Jong Li, Wen-Hao Chang, and American scientist Boris I. Yakobson et al. Reported a wafer-level single-layer hexagonal growth on the surface of Cu (111) single crystal. The new strategy of boron nitride single crystal has laid the foundation for the application of two-dimensional materials in the field of electronic devices.

Highlights of this article:
1) Using a two-inch c-plane sapphire wafer as the substrate, a single crystal hBN single layer was successfully prepared by epitaxial growth on a Cu (111) single crystal film.
2) First-principles calculations show that the Cu (111) step of hBN lateral docking can enhance epitaxial growth, thereby ensuring the unidirectionality of the hBN monolayer.
3) The single crystal hBN is used as the interface layer between MoS2 and HfO2, which effectively improves the electrical performance of the transistor.

references:
Tse-AnChen et al. Wafer-scale single-crystal hexagonal boron nitride monolayers on Cu (111). Nature 2020.
https://www.nature.com/articles/s41586-020-2009-2

4. Nature: Tunable Correlative Chen Insulators and Ferromagnetism in the Mohr Superlattice
The two-dimensional electronic system in a strong magnetic field can realize the quantum Hall effect, a class of topological states of matter, which has a finite Chen number C (Chern number) and a chiral edge state. Haldane then reasoned that stale insulators with integer quantum Hall effect may appear in lattice models with complex jump parameters, even in the case of zero magnetic fields. The ABC-three-layer graphene / hexagonal boron nitride (ABC-TLG / hBN) Moire superlattice is an ideal platform for exploring aging insulators because it has a nearly flat Moire microstrip, and the corresponding aging numbers follow Changeable and electrically tunable.

In view of this, Lawrence Berkeley National Laboratory / University of California, Berkeley Wang Feng‘s team, Fudan University Zhang Yuanbo‘s team, and SLAC National Accelerator Lab David Goldhaber-Gordon‘s team have jointly reported the associated BBC-TLG / hBN Mohr superlattice with insulator Experimental observations.

Highlights of this article:
1) Magnetic transport tests have found that changing the direction of the applied vertical electric field enables the ABC-TLG / hBN Moore microstrip to switch between zero and non-zero finite Chen numbers.
2) For the topological hole microstrip tuned with a finite Chen number, the author focuses on the study of its quarter-filling, that is, one hole in each Moire cell.
3) When the magnetic field is greater than 0.4T, the Hall resistor has a quantization interval of h / 2e2, indicating that C = 2.
4) Associated topological insulators are ferromagnetic and exhibit great hysteresis and anomalous Hall signals at zero magnetic fields.

In summary, the discovery of C = 2 Chen insulators under zero magnetic fields provides an opportunity to explore new associated topological states.

references:
Guorui Chen et al. Tunable correlated Chern insulator and ferromagnetism in a moiré superlattice. Nature, 2020.
DOI: 10.1038 / s41586-020-2049-7
https://www.nature.com/articles/s41586-020-2049-7