Jiuxiang Dai

Publication date: December 2021

Source: Materials Today, Volume 51

Author(s): Laurie Winkless

npj 2D Materials and Applications, Published online: 18 November 2021; doi:10.1038/s41699-021-00265-6

Unidirectional Kondo scattering in layered NbS₂

Nature Nanotechnology, Published online: 18 November 2021; doi:10.1038/s41565-021-01020-0

Dense, short hydrophobic nanochannels have been restacked from two-dimensional quantum sheets to achieve both high areal and volumetric capacitance in thick electrodes under ultrahigh rates.

Nature Communications, Published online: 19 November 2021; doi:10.1038/s41467-021-27033-w

Single-photon emitters in 2D semiconductors hold promise for quantum applications, but usually operate in the 500-800 nm wavelength range. Here, the authors report site-controlled creation of quantum emitters in the telecommunication wavelength window by coupling 2D MoTe2 to strain inducing nano-pillar arrays.

The saturation magnetization of LaMnO₃ (LMO) films is enhanced by 56% after releasing from substrates, and is significantly increased by 92% with bending films to a curvature of 1 mm⁻¹. This enhancement of the ferromagnetism is attributed to the strengthened Mn–O–Mn super-exchange interactions from the augmented characteristics of the unconventional P2₁/n structure of LMO films.

Abstract

A variety of novel phenomena and functionalities emerge from lowering the dimensionality of materials and enriching the degrees of freedom in modulation. In this work, it is found that the saturation magnetization of LaMnO₃ (LMO) films is largely enhanced by 56% after releasing from a brand-new phase of tetragonal strontium aluminate buffer layer, and is significantly increased by 92% with bending films to a curvature of 1 mm⁻¹ using a water-assisted direct-transferring method. Meanwhile, the Curie temperature of LMO films has been improved by 13 K. High-resolution spherical aberration-corrected scanning transmission electron microscopy and first-principles calculations unambiguously demonstrate that the enhanced ferromagnetism is attributed to the strengthened Mn–O–Mn super-exchange interactions from the augmented characteristics of the unconventional P2₁/n structure caused by the out-of-plane lattice shrinking after strain releasing and increased flexure degree of freestanding LMO films. This work paves a way to achieve large-scale and crack-and-wrinkle-free freestanding films of oxides with largely improved functionalities.

Nature Communications, Published online: 18 November 2021; doi:10.1038/s41467-021-27041-w

The interfaces between ferromagnets and superconductors receive many attentions due to emergent relativistic spin-orbit coupling. Here, the authors provide possible evidence for spin triplet Andreev reflection at the interface between a van der Waals ferromagnet Fe0.29TaS2 and a s-wave superconductor NbN.

The contradictory energy gap (E _G) values (≈0.05 and ≈0.5 eV) are reported for bulk PdSe₂. Here, it is quantitatively estimated that the E _G of bulk PdSe₂ is ≈0.3 eV based on the maximum depletion width (W _Dm)–acceptor density (N _A) relationship.

Abstract

2D PdSe₂, a Group 10 noble metal dichalcogenide, has been reported to have a strong thickness-dependent bandgap energy, ranging from ≈1.6 eV (monolayer) to ≈0.05 eV (bulk) and a high photoresponsivity for bulk samples in the far infrared wavelength range of 10.6 μm. However, a middle bandgap of ≈0.5 eV has been contradictorily reported for bulk PdSe₂ via optical absorption measurements. In this study, detailed electrical transport measurements are conducted to solve this contradiction. The key difference between narrow gap and middle gap semiconductors is the contribution of a depletion layer to the transfer characteristics. Hall measurements reveal intrinsic p-type carrier densities of ≈1.9 × 10¹⁸ cm⁻³ at 300 K and the contribution of the depletion layer to the transfer characteristics for bulk PdSe₂, suggesting a middle bandgap. Moreover, the maximum depletion width (W _Dm) is determined from top- and back-gate coupling in dual gate transistors to be ≈17–18 nm. Based on the W _Dm – acceptor density diagram, the bandgap of bulk PdSe₂ is quantitatively estimated to be ≈0.3 eV. Although this is not a desirable result from the viewpoint of far infrared material, it helps us to correctly understand the mechanism for the photoresponse of PdSe₂.

Nanoporous Graphene Transistors

Bottom-up synthesis has recently enabled the fabrication of nanoporous graphene with atomically precise pores and consequent uniform band gap. In article number 2103798, Jeffrey Bokor and co-workers use this strategy to turn molecules into nanoporous graphene, which is subsequently transferred to devices and turned into field-effect transistors. The switching performance is high and correlates with the degree of structural perfection.

Author(s): Dilip Bhoi, Jun Gouchi, Naoka Hiraoka, Yufeng Zhang, Norio Ogita, Takumi Hasegawa, Kentaro Kitagawa, Hidenori Takagi, Kee Hoon Kim, and Yoshiya Uwatoko

A complex interplay of different energy scales involving Coulomb repulsion, spin-orbit coupling, and Hund’s coupling energy in 2D van der Waals (vdW) material produces a novel emerging physical state. For instance, ferromagnetism in vdW charge transfer insulator CrGeTe3 provides a promising platform...

[Phys. Rev. Lett. 127, 217203] Published Wed Nov 17, 2021

Nature, Published online: 17 November 2021; doi:10.1038/s41586-021-03949-7

Two-dimensional transition metal dichalcogenide diodes with defect-free van der Waals contacts allows minimization of the extrinsic interfacial disorder-dominated recombination and access to the intrinsic excitonic behaviour in two-dimensional semiconductor devices.

Nature, Published online: 17 November 2021; doi:10.1038/s41586-021-03979-1

This Review discusses the exciton physics of transition metal dichalcogenides, focusing on moiré patterns and exciton many-body physics, and outlines future research directions in the field.

An integrated optical noncontact controlling system (ONCS) based on PtTe _x /Si optoelectronic heterojunction array was designed by recognizing shadow-induced spatiotemporal sequence changes in heterojunction array photocurrents, which provides a new perspective for constructing high-performance noncontact interaction systems.

Abstract

Noncontact interaction systems have attracted considerable research attention in recent years because of convenient operation, sterility, and injury prevention. However, the insufficient sensing distance and weak robustness of noncontact interaction systems for complex environments limit their practical applications. Here, we designed an integrated optical noncontact controlling system (ONCS) based on PtTe _x /Si optoelectronic heterojunction array. Broadband sensitive photoresponse is realized at zero bias voltage, with excellent detectivity and responsivity, boosting the noncontact sensing distance to at least 150 mm. Consequently, the system can perform noncontact detection, encoding, and control by recognizing shadow-induced spatiotemporal sequence changes in heterojunction array photocurrents. As a proof of concept, different interactive functions have been demonstrated with good accuracy and robustness by encoding finger movement above the ONCS. This study provides a new perspective for constructing high-performance noncontact interaction systems.

Metastable amorphous oxides/single-crystalline semiconductor nanosheets assemble into 3D shapes via reconfiguration of the atomic structure of the oxide during heat treatment. For heating parameters leading to densification of the amorphous film, axial forces (F ₁, F ₂) and a torque (M) drive bending of the nanosheet perpendicularly to its surface. The mechanism allows fabrication of strained superlattices and strain-engineering of complex oxides.

Abstract

Reconfiguration of amorphous complex oxides provides a readily controllable source of stress that can be leveraged in nanoscale assembly to access a broad range of 3D geometries and hybrid materials. An amorphous SrTiO₃ layer on a Si:B/Si_{1− x} Ge _x :B heterostructure is reconfigured at the atomic scale upon heating, exhibiting a change in volume of ≈2% and accompanying biaxial stress. The Si:B/Si_{1− x} Ge _x :B bilayer is fabricated by molecular beam epitaxy, followed by sputter deposition of SrTiO₃ at room temperature. The processes yield a hybrid oxide/semiconductor nanomembrane. Upon release from the substrate, the nanomembrane rolls up and has a curvature determined by the stress in the epitaxially grown Si:B/Si_{1− x} Ge _x :B heterostructure. Heating to 600 °C leads to a decrease of the radius of curvature consistent with the development of a large compressive biaxial stress during the reconfiguration of SrTiO₃. The control of stresses via post-deposition processing provides a new route to the assembly of complex-oxide-based heterostructures in 3D geometry. The reconfiguration of metastable mechanical stressors enables i) synthesis of various types of strained superlattice structures that cannot be fabricated by direct growth and ii) technologies based on strain engineering of complex oxides via highly scalable lithographic processes and on large-area semiconductor substrates.

Nature Communications, Published online: 17 November 2021; doi:10.1038/s41467-021-26804-9

Achieving high output power and low noise integrated lasers is a major challenge. Here the authors experimentally demonstrate integrated lasers from a Si/SiN heterogeneous platform that shows Hertz-level linewidth, paving the way toward fully integrating low-noise silicon nitride photonics in volume using real devices for lasing.