Jiuxiang Dai

Nature Electronics, Published online: 21 April 2022; doi:10.1038/s41928-022-00746-6

Nature Electronics, Published online: 21 April 2022; doi:10.1038/s41928-022-00745-7

Nature Reviews Materials, Published online: 20 April 2022; doi:10.1038/s41578-022-00443-y

Nature, Published online: 20 April 2022; doi:10.1038/s41586-022-04472-z

npj 2D Materials and Applications, Published online: 21 April 2022; doi:10.1038/s41699-022-00302-y

Spontaneous Lattice Inversion

In article number 2200057, Zhiqiang Liu, Shenyuan Yang, Yong Zhang, Peng Gao, and co-workers confirm the polarity of AlN on sapphire prepared by metal–organic chemical vapor deposition is not inherited from the nitrides/sapphire interface as widely accepted, instead, experiences a spontaneous polarity inversion. Furthermore, a vertical 2D electron gas is revealed at the polarity inversion interface. This work identifies a new origin of high-density defects in nitride epilayers. It also points to a direction for polarity manipulation and hetero-polarity device design.

Author(s): Grisell Díaz Leines and Jutta Rogal

We present an atomistic study of heterogeneous nucleation in Ni employing transition path sampling, which reveals a template precursor-mediated mechanism of crystallization. Most notably, we find that the ability of tiny templates to modify the structural features of the liquid and promote the forma…

[Phys. Rev. Lett. 128, 166001] Published Tue Apr 19, 2022

Light: Science & Applications, Published online: 20 April 2022; doi:10.1038/s41377-022-00784-x

Common metal salts are used to realize the controlled phase transformation of transition metal dichalcogenides (TMDs) from the conventional thermodynamically stable 2H phase to unconventional metastable 1T′ phase. This work not only paves the way to prepare high-quality and high-purity unconventional metastable 1T′-TMDs for fundamental and practical investigations, but also greatly simplifies the procedure for the large-scale production of 1T′-TMDs.

Abstract

Phase engineering of nanomaterials (PEN) has demonstrated great potential in the fields of catalysis, electronics, energy storage and conversion, and condensed matter physics. Recently, transition metal dichalcogenides (TMDs) with unconventional metastable phases (e.g., 1T and 1T′) have attracted increasing research interest due to their unique and appealing physicochemical properties. However, there is still a lack of a simple, universal, and controlled method for the preparation of large-scale and high-purity unconventional-phase TMD crystals, restricting their further fundamental study and practical applications. Here, a facile, one-step salt-assisted general strategy is reported for the controlled phase transformation of commercially available TMDs with conventional 2H phase, yielding a large amount of metastable 1T′-phase TMDs, including WS₂, WSe₂, MoS₂, and MoSe₂. It is found that the easily accessible metal salts, such as K₂C₂O₄·H₂O, K₂CO₃, Na₂CO₃, Rb₂CO₃, Cs₂CO₃, KHCO₃, NaHCO₃, and NaC₂O₄, can be used to assist the 2H-to-1T′ phase transformation, greatly simplifying the synthetic process for producing metastable 1T′-TMDs. Importantly, this method can also be used to prepare 1T′-TMD alloys, such as 1T′-WS_{2 x} Se_{2(1− x )}. This newly developed strategy is robust and highly effective, which can also be used for the phase engineering of other materials with various polymorphs.

Transition between two topologically similar layered structures in In₂Se₃ breaks the speed and energy limitations of photonic memory, via reversible nonvolatile refractive index change induced by a single nanosecond pulse. In this work, the atomistic phase-change pathway between the layered structures is unraveled with in situ high-energy X-ray diffraction and integrated photonic switching with a transferred epitaxial layer is demonstrated. Detailed analysis on the volumetric effect and by nonlinear spectroscopy are provided to harness the mode coupling and loss in the hybrid device.

Abstract

The primary mechanism of optical memoristive devices relies on phase transitions between amorphous and crystalline states. The slow or energy-hungry amorphous–crystalline transitions in optical phase-change materials are detrimental to the scalability and performance of devices. Leveraging an integrated photonic platform, nonvolatile and reversible switching between two layered structures of indium selenide (In₂Se₃) triggered by a single nanosecond pulse is demonstrated. The high-resolution pair distribution function reveals the detailed atomistic transition pathways between the layered structures. With interlayer “shear glide” and isosymmetric phase transition, switching between the α- and β-structural states contains low re-configurational entropy, allowing reversible switching between layered structures. Broadband refractive index contrast, optical transparency, and volumetric effect in the crystalline–crystalline phase transition are experimentally characterized in molecular-beam-epitaxy-grown thin films and compared to ab initio calculations. The nonlinear resonator transmission spectra measure of incremental linear loss rate of 3.3 GHz, introduced by a 1.5 µm-long In₂Se₃-covered layer, resulted from the combinations of material absorption and scattering.

Nature Nanotechnology, Published online: 18 April 2022; doi:10.1038/s41565-022-01104-5

Nature Nanotechnology, Published online: 18 April 2022; doi:10.1038/s41565-022-01106-3

A large-scale multi-bridge channel field-effect transistor (MBC-FET) and complementary field-effect transistor (C-FET) arrays are demonstrated based on wafer-scale 2D semiconductors. Compared with conventional MoS₂ FETs, the MBC-FET structure exhibits improved electrical performance. By 3D integration of n-type MoS₂ and p-type MoTe₂, a C-FET is built with a voltage gain of 7 V/V when V _DD = 4 V.

Abstract

Two-dimentional semiconductors have shown potential applications in multi-bridge channel field-effect transistors (MBC-FETs) and complementary field-effect transistors (C-FETs) due to their atomic thickness, stackability, and excellent electrical properties. However, the exploration of MBC-FET and C-FET based on large-scale 2D semiconductors is still lacking. Here, based on a reliable vertical stacking of wafer-scale 2D semiconductors, large-scale MBC-FETs and C-FETs using n-type MoS₂ and p-type MoTe₂ are successfully fabricated. The drive current of an MBC-FET with two layers of MoS₂ channel (20 µm/10 µm) is up to 60 µA under 1 V bias. Compared with the single-gate MoS₂ FET, the carrier mobility of MBC-FET is 2.3 times higher and the sub-threshold swing is 70% smaller. Furthermore, NAND and NOR logic circuits are also constructed based on two vertically stacked MoS₂ channels. Then, C-FET arrays are fabricated by 3D integrating n-type MoS₂ FET and p-type MoTe₂ FET, which exhibit a voltage gain of 7 V/V when V _DD = 4 V. In addition, this C-FET device can directly convert light signals to an electrical digital signal within a single device. The demonstration of MBC-FET and C-FET based on large-scale 2D semiconductors will promote the application of 2D semiconductors in next-generation circuits.

Nature Communications, Published online: 19 April 2022; doi:10.1038/s41467-022-29771-x

The 2D electron gas at the surface of SrTiO₃ (001) can be turned on and off by depositing either SrO or TiO₂, which is observed by a combination of oxide molecular beam epitaxy with in situ synchrotron X-ray scattering and angle-resolved photoemission spectroscopy. Either way, the surface remains TiO₂-terminated.

Abstract

Bulk SrTiO₃ is a well-known band insulator and the most common substrate used in the field of complex oxide heterostructures. Its surface and interface with other oxides, however, have demonstrated a variety of remarkable behaviors distinct from those expected. In this work, using a suite of in situ techniques to monitor both the atomic and electronic structures of the SrTiO₃ (001) surface prior to and during growth, the disappearance and re-appearance of a 2D electron gas (2DEG) is observed after the completion of each SrO and TiO₂ monolayer, respectively. The 2DEG is identified with the TiO₂ double layer present at the initial SrTiO₃ surface, which gives rise to a surface potential and mobile electrons due to vacancies within the TiO_2−x adlayer. Much like the electronic reconstruction discovered in other systems, two atomic planes are required, here supplied by the double layer. The combined in situ scattering/spectroscopy findings resolve a number of longstanding issues associated with complex oxide interfaces, facilitating the employment of atomic-scale defect engineering in oxide electronics.