Jiuxiang Dai

Photo-reactive DNA-cross-linked hydrogels are presented that enable polymorphing under patterned light. The photo-reactive DNA crosslinks act as a regulator in morphing of the hydrogels, adjusting the lengths of the cross-links depending on the wavelength of light. Spatiotemporal controllability and reprogrammable features of the polymorphing hydrogels within a one-pot system offer advanced solutions for applications in soft robotics and 4D printing.

Abstract

Polymorphing hydrogels can morph into another structure on demand with reprogrammable features. This concept extends the degree of morphing beyond that of traditional shape-morphing hydrogels, which predetermine their morphing capabilities at the fabrication stage. However, current polymorphing hydrogels face limitations due to the need for complex, non-sustained responsiveness or additional chemical steps for reconfigurable morphing. Here, photo-reactive DNA-cross-linked polymorphing hydrogels are presented that enable polymorphing under patterned light. The photo-reactive DNA cross-links act as a regulator in changing the shapes of the hydrogels by adjusting the lengths of the cross-links depending on the wavelength of light, which allows precise and dynamic morphing in a programmable way through a one-pot reaction. The high programmability involving spatiotemporal controllability and reprogrammable features offers advanced solutions for multifunctional soft machines and applications requiring complex processes.

Strain engineering is a powerful tool, that can strongly modulate the physical and physicochemical properties of 2D materials. Particularly, the lattice distortion-induced modification in the electronic band structure enables the emergence of many excellent properties that greatly expand the applicability of 2D materials in the fields of flexible electronics, flexible photo-/image-sensors, flexible strain sensors, and wearable bioelectronics devices.

Abstract

Strain engineering is a powerful strategy that can strongly influence and tune the intrinsic characteristics of materials by incorporating lattice deformations. Due to atomically thin thickness, 2D materials are excellent candidates for strain engineering as they possess inherent mechanical flexibility and stretchability, which allow them to withstand large strains. The application of strain affects the atomic arrangement in the lattice of 2D material, which modify the electronic band structure. It subsequently tunes the electrical and optical characteristics, thereby enhances the performance and functionalities of the fabricated devices. Recent advances in strain engineering strategies for large-area flexible devices fabricated with 2D materials enable dynamic modulation of device performance. This perspective provides an overview of the strain engineering approaches employed so far for straining 2D materials, reviewing their advantages and disadvantages. The effect of various strains (uniaxial, biaxial, hydrostatic) on the characteristics of 2D material is also discussed, with a particular emphasis on electronic and optical properties. The strain-inducing methods employed for large-area device applications based on 2D materials are summarized. In addition, the future perspectives of strain engineering in functional devices, along with the associated challenges and potential solutions, are also outlined.

The surface-assisted passivation growth strategy is designed to synthesize ultrathin and large size β-Bi₂O₃ crystals with the thickness down to 0.77 nm and the lateral size up to 163 µm. Experiments and theoretical calculations substantiate the growth mechanism. Remarkably, β-Bi₂O₃ flakes based photodetectors exhibit excellent performance and anisotropic photodetection that surpass or are comparable to other 2D materials devices.

Abstract

2D nonlayered materials (NLMs) have garnered considerable attention due to unique surface structure and bright application prospect. However, owing to the strong interatomic forces caused by intrinsic isotropic chemical bonds in all directions, the direct synthesis of ultrathin and large area 2D NLMs remains a tremendous challenge. Here, the surface-assisted passivation growth strategy is designed to synthesize ultrathin and large size β-Bi₂O₃ crystals with the thickness down to 0.77 nm and the lateral size up to 163 µm. These results are primarily ascribed to the bonding between Se atoms and the unsaturated Bi atoms on the surface of β-Bi₂O₃, resulting in the surface passivation and promoting the obtaining of ultrathin β-Bi₂O₃. Strikingly, the photodetectors based on β-Bi₂O₃ flakes exhibit a high photoresponsivity of 71.91 A W⁻¹, an excellent detectivity of 6.09 × 10¹³ Jones, a remarkable external quantum efficiency of 2.4 × 10⁴%, an outstanding anisotropic photodetection and excellent UV imaging capability at 365 nm. This work sheds light on the synthesis of 2D ultrathin NLMs and promotes their applications in multifunctional optoelectronics.

Author(s): Guangyao Miao (苗光耀), Nuoyu Su (苏诺雨), Ze Yu (喻泽), Bo Li (李博), Xiaochun Huang (黄筱淳), Weiliang Zhong (衷惟良), Qinlin Guo (郭沁林), Miao Liu (刘淼), Weihua Wang (王炜华), and Jiandong Guo (郭建东)

The development of two-dimensional (2D) semiconductors is limited by the lack of doping methods. We propose surface isovalent substitution as an efficient doping mechanism for 2D semiconductors by revealing the evolution of the structure and electronic properties of 2D Se/Te. Because of the differen…

[Phys. Rev. Lett. 133, 236201] Published Tue Dec 03, 2024

Ising superconductors are known for remarkable resilience to external in-plane magnetic fields (B _∥) due to the protection of strong spin-orbit coupling fields α_SOC. By forming Cooper pairing states in mirror-symmetric Fermi surfaces with highly anisotropic α_SOC, a new type-III Ising superconductivity is discovered in atomically-thin natural van der Waals heterostructures of TaSe₂/SnSe with anomalous B _∥-enhanced T _c .

Abstract

Van der Waals (vdW) crystals with strong spin-orbit coupling (SOC) provide great opportunities for exploring unconventional 2D superconductors, wherein new pairing states emerge due to the interplay of SOC with crystalline symmetries, electronic correlations, quenched disorders and external modulation forces, etc. Here, a distinct mirror-symmetry protected Ising pairing state with unprecedented Γ- and M-valley symmetries in natural vdW heterostructures (vdWH) of interweaving tetragonal SnSe and trigonal 1H-TaSe₂ monolayers is reported, in which the unidirectional lattice interlocking effectively suppresses the K-valley Ising pairing mechanism by incommensurate charge-density-wave (CDW) transitions. In the 2D limit of an TaSe₂/SnSe bilayer with intact basal mirror symmetry (M _z ), the mirror-symmetric vdWH Ising superconductors show anomalous in-plane magnetic field B _‖-controlled enhancements in the critical temperature T _c, which is completely absent for multilayer vdWHs with broken M _z induced by orthorhombic stacking between nearest-neighbour TaSe₂ monolayers. The experimental observations consistently reveal a mirror symmetry-protected type-III Ising state in the inversion asymmetric lattice of 1H-TaSe₂, which is predicted to be a mixture of spin-singlet and spin-triplet states.

Nature Nanotechnology, Published online: 05 December 2024; doi:10.1038/s41565-024-01821-z

Nature Electronics, Published online: 05 December 2024; doi:10.1038/s41928-024-01307-9

Light: Science & Applications, Published online: 02 December 2024; doi:10.1038/s41377-024-01642-8

Nature Materials, Published online: 06 December 2024; doi:10.1038/s41563-024-02081-x

npj 2D Materials and Applications, Published online: 05 December 2024; doi:10.1038/s41699-024-00518-0

Nature Synthesis, Published online: 03 December 2024; doi:10.1038/s44160-024-00690-7

Nature Reviews Methods Primers, Published online: 05 December 2024; doi:10.1038/s43586-024-00366-8

InAs-on-Insulator (InAsOI) is a new platform for developing superconducting electronics. An epilayer of semiconducting InAs with different electron densities is grown onto a cryogenic insulating InAlAs metamorphic buffer, used to decouple adjacent devices electrically. Josephson Junctions with various lengths and widths are fabricated employing Al as a superconductor and InAs with different electron densities.

Abstract

Superconducting circuits based on hybrid InAs Josephson Junctions (JJs) play a starring role in the design of fast and ultra-low power consumption solid-state quantum electronics and exploring novel physical phenomena. Conventionally, 3D substrates, 2D quantum wells (QWs), and 1D nanowires (NWs) made of InAs are employed to create superconducting circuits with hybrid JJs. Each platform has its advantages and disadvantages. Here, the InAs-on-insulator (InAsOI) is proposed as a groundbreaking platform for developing superconducting electronics. An epilayer of semiconducting InAs with different electron densities is grown onto an InAlAs metamorphic buffer, efficiently used as a cryogenic insulator to decouple adjacent devices electrically. JJs with various lengths and widths are fabricated employing Al as a superconductor and InAs with different electron densities. A switching current density of 7.3 µA µm⁻¹, a critical voltage of 50-to-80 µV, and a critical temperature equal to that of the superconductor used are achieved. For all the JJs, the switching current follows a Fraunhofer-like pattern with the out-of-plane magnetic field. These achievements enable the use of InAsOI to design and fabricate surface-exposed Josephson Field Effect Transistors with high critical current densities and superior gating properties.

A reliable one-step van der Waals integration technique is developed for centimeter-scale transfer printing of multilayer top-gate stacks. This technique enables the realization of superior electrical performance and threshold voltage control in MoS₂ transistors. Depletion-mode Al-gated transistors and enhancement-mode Au-gated transistors are utilized to construct inverters, logic gates, static random-access memory, and ring oscillators, demonstrating the functionality of multi-threshold 2D circuits.

Abstract

Transition-metal dichalcogenides (TMDs), as atomically thin semiconductors, have shown immense promise for next-generation electronics due to their high mobility and potential for creating van der Waals heterostructures. However, precise control of the threshold voltage (V _th) in field-effect transistors (FETs) remains a significant challenge, impeding the development of 2D material circuits with tailored electronic functions. Herein, a graphene-assisted one-step van der Waals integration technique is presented for fabricating multi-threshold 2D functional circuits. Graphene's unique property of having a surface without dangling bonds is utilized as an intermediary layer, allowing for the transfer of electrodes with various work functions and high-κ dielectric layers onto 2D channel materials in a single step. This technique has successfully produced Al-gated MoS₂ FETs with a V _th of −0.2 V and Au-gated MoS₂ FETs with a V _th of 1.9 V. This precision enables the development of functional devices such as rail-to-rail inverters with large noise margins. Furthermore, more complex multi-threshold 2D circuits are achieved, including basic logic gates (NOT, NAND, NOR), six-transistor static random-access memory (6T-SRAM), and ring oscillators (RO). This work showcases a scalable and effective strategy for threshold voltage engineering in 2D material-based circuits, paving the way for sophisticated electronic and optoelectronic applications.

This work reports the confined template growth of well-crystallized MoS₂ nanotubes encapsulated within carbon nanotubes, forming 1D van der Waals heterostructures. The growth of MoS₂ nanotubes is catalyzed by iron carbide. Free-standing MoS₂ nanotubes can be obtained by removing outer carbon nanotubes with gentle plasma etching.

Abstract

Single-crystal MoS₂ nanotubes possess outstanding electronic and optoelectronic properties. However, previous attempts to synthesize MoS₂ nanotubes are hindered by poor crystallinity and the high strain energy required to roll a sheet with three atomic layers into a tubular structure. Here, the confined template growth of well-crystallized MoS₂ nanotubes encapsulated within carbon nanotubes, forming 1D van der Waals heterostructures, is reported. The growth of MoS₂ nanotubes is catalyzed by iron carbide. CNTs serve as nanoreactors and structurally confined templates, ensuring the growth of fine MoS₂ nanotubes. Water vapor is employed to manipulate the structure and morphology of resultant MoS₂. Free-standing MoS₂ nanotubes are obtained by removing outer CNTs with gentle plasma etching. This method demonstrate the power of coupling the catalytic effect and the space confinement in the growth of high-quality MoS₂ nanotubes, which may become a common strategy for the preparation of general 1D nanostructures of various transition metal dichalcogenides and other materials.

β-Nb₂N films are grown with molecular beam epitaxy and their physical properties are studied with various techniques. The superconducting transition initiates at 10 K with an upper critical field of ≈5 T. Its 3D electronic structure is elucidated experimentally and theoretically. It is confirmed that crystal structure of Nb₂N is β_B phase, correcting previous misconceptions. These findings facilitate future applications.

Abstract

Niobium nitrides have garnered significant research interest since their discovery due to their exceptional properties and broad applications. In this study, NbNx thin films are successfully grown on 4H(6H)-SiC(001) substrates using nitrogen-assisted molecular beam epitaxy. Through scanning transmission electron microscopy and X-ray diffraction, it is confirmed that the crystal structure of the thin films corresponds to the β-Nb₂N. Different from the previously reported structure of the β_A phase (P6₃/mmc) of β-Nb₂N, the results clearly match with the β_B phase (P3¯m1${\mathrm{P}}\bar{3}{\mathrm{m}}1$). Resistivity measurements reveal that β-Nb₂N exhibits superconductivity at ≈10 K with an upper critical field of ≈5 T. Its 3D electronic structure is further elucidated using angle-resolved photoemission spectroscopy combined with theoretical calculations. The observed superconductivity in β-Nb₂N is attributed to its relatively high electron–phonon coupling strength and density of states at Fermi level. Interestingly, it is found that the sample is close to a Lifshitz transition, suggesting potential for tunable physical properties. The results provide a comprehensive understanding of the crystal and electronic structures of β-Nb₂N, facilitating its future applications.

Two-dimensional (2D) materials have been extensively utilized in catalytic reactions due to their fully exposed active sites and special electronic structure. This review summarizes the progress of 2D materials from model studies to application in catalysis and illustrates how 2D materials serve as models to explore structure–activity relationships by combining theoretical calculations and surface research.

Abstract

Two-dimensional (2D) materials have been utilized broadly in kinds of catalytic reactions due to their fully exposed active sites and special electronic structure. Compared with real catalysts, which are usually bulk or particle, 2D materials have more well-defined structures. With easily identified structure-modulated engineering, 2D materials become ideal models to figure out the catalytic structure-function relations, which is helpful for the precise design of catalysts. In this review, the unique function of 2D materials was summarized from model study to reality catalysis and application. It includes several typical 2D materials, such as graphene, transition metal dichalcogenides, metal, and metal (hydr)oxide materials. We introduced the structural characteristics of 2D materials and their advantages in model researches. It emphatically summarized how 2D materials serve as models to explore the structure-activity relationship by combining theoretical calculations and surface research. The opportunities of 2D materials and the challenges for fundamentals and applications they facing are also addressed. This review provides a reference for the design of catalyst structure and composition, and could inspire the realization of two-dimensional materials from model study to reality application in industry.

In-plane and out-of-plane Raman shifts of 2D tetragonal and hexagonal FeTe exceptionally harden (soften) under uniaxial tensile (compressive) strain, distinguished from the common behaviors of many conventional 2D systems. This anomalous Raman response of FeTe is attributed to its strong spin-phonon coupling. These results may shed light on the exotic properties of 2D magnetic materials.

Abstract

2D Fe-chalcogenides emerge with rich structures, magnetisms, and superconductivities, which spark the growing research interests in the torturous transition mechanism and tunable properties for their potential applications in nanoelectronics. Uniaxial strain can produce a lattice distortion to study symmetry breaking induced exotic properties in 2D magnets. Herein, the anomalous Raman spectrum of 2D tetragonal (t−) and hexagonal (h−) FeTe is systematically investigated via uniaxial strain engineering strategy. It is found that both t- and h-FeTe keep the structural stability under different uniaxial tensile or compressive strain up to ± 0.4%. Intriguingly, the lattice vibrations along both in-plane and out-of-plane directions exceptionally harden (softened) under tensile (compressive) strain, distinguished from the behaviors of many conventional 2D systems. Further, the difference in thickness-dependent strain effect can be well explained by their structural discrepancy between two polymorphs of FeTe. These results can supply a unique platform to explore the vibrational properties of many novel 2D materials.