Jiuxiang Dai

Publication date: October 2022

Source: Progress in Materials Science, Volume 130

Author(s): Bo Li, Yue Luo, Yufeng Zheng, Xiangmei Liu, Lei Tan, Shuilin Wu

A protocol to fabricate highly efficient organic light-emitting diodes that use an intrinsically stretchable 2D-contact electrode topped with graphene is reported. As a benefit of the fast carrier mobility with complete 2D contact with the organic material and the tunable work function of the 2D-contact stretchable electro (TCSE), the limited charge injection of the widely used silver-nanowire-based stretchable electrode is solved.

Abstract

Intrinsically stretchable organic light-emitting diodes (ISOLEDs) are becoming essential components of wearable electronics. However, the efficiencies of ISOLEDs have been highly inferior compared with their rigid counterparts, which is due to the lack of ideal stretchable electrode materials that can overcome the poor charge injection at 1D metallic nanowire/organic interfaces. Herein, highly efficient ISOLEDs that use graphene-based 2D-contact stretchable electrodes (TCSEs) that incorporate a graphene layer on top of embedded metallic nanowires are demonstrated. The graphene layer modifies the work function, promotes charge spreading, and impedes inward diffusion of oxygen and moisture. The work function (WF) of 3.57 eV is achieved by forming a strong interfacial dipole after deposition of a newly designed conjugated polyelectrolyte with crown ether and anionic sulfonate groups on TCSE; this is the lowest value ever reported among ISOLEDs, which overcomes the existing problem of very poor electron injection in ISOLEDs. Subsequent pressure-controlled lamination yields a highly efficient fluorescent ISOLED with an unprecedently high current efficiency of 20.3 cd A⁻¹, which even exceeds that of an otherwise-identical rigid counterpart. Lastly, a 3 inch five-by-five passive matrix ISOLED is demonstrated using convex stretching. This work can provide a rational protocol for designing intrinsically stretchable high-efficiency optoelectronic devices with favorable interfacial electronic structures.

Nature Communications, Published online: 14 June 2022; doi:10.1038/s41467-022-29976-0

Light: Science & Applications, Published online: 13 June 2022; doi:10.1038/s41377-022-00857-x

Nature Electronics, Published online: 13 June 2022; doi:10.1038/s41928-022-00778-y

Light: Science & Applications, Published online: 14 June 2022; doi:10.1038/s41377-022-00875-9

Defect-rich MoS₂ QDs are obtained via a mild biomineralization-assisted bottom-up strategy to show enhanced photoluminescence and reactive oxygen species (ROS) generation due to great defect/active sites elevation.

Abstract

Transition metal dichalcogenide (TMD) quantum dots (QDs) with defects have attracted interesting chemistry due to the contribution of vacancies to their unique optical, physical, catalytic, and electrical properties. Engineering defined defects into molybdenum sulfide (MoS₂) QDs is challenging. Herein, by applying a mild biomineralization-assisted bottom-up strategy, blue photoluminescent MoS₂ QDs (B-QDs) with a high density of defects are fabricated. The two-stage synthesis begins with a bottom-up synthesis of original MoS₂ QDs (O-QDs) through chemical reactions of Mo and sulfide ions, followed by alkaline etching that creates high sulfur-vacancy defects to eventually form B-QDs. Alkaline etching significantly increases the photoluminescence (PL) and photo-oxidation. An increase in defect density is shown to bring about increased active sites and decreased bandgap energy; which is further validated with density functional theory calculations. There is strengthened binding affinity between QDs and O₂ due to lower gap energy (∆E _ST) between S₁ and T₁, accompanied with improved intersystem crossing (ISC) efficiency. Lowered gap energy contributes to assist e⁻–h⁺ pair formation and the strengthened binding affinity between QDs and ³O₂. Defect engineering unravels another dimension of material properties control and can bring fresh new applications to otherwise well characterized TMD nanomaterials.

Abstract

Artificial synaptic devices hold great potential in building neuromorphic computers. Due to the unique morphological features, two-dimensional organic semiconductors at the monolayer limit show interesting properties when acting as the active layers for organic field-effect transistors. Here, organic synaptic transistors are prepared with 1,4-bis ((5′-hexyl-2,2′-bithiophen-5-yl) ethyl) benzene (HTEB) monolayer molecular crystals. Functions similar to biological synapses, including excitatory postsynaptic current (EPSC), pair-pulse facilitation, and short/long-term memory, have been realized. The synaptic device achieves the minimum power consumption of 4.29 fJ at low drain voltage of −0.01 V. Moreover, the HTEB synaptic device exhibits excellent long-term memory with 10⁹ s EPSC estimated retention time. Brain-like functions such as dynamic learning-forgetting process and visual noise reduction are demonstrated by nine devices. The unique morphological features of the monolayer molecular semiconductors help to reveal the device working mechanism, and the synaptic behaviors of the devices can be attributed to oxygen induced energy level. This work shows the potential of artificial neuroelectronic devices based on organic monolayer molecular crystals.

Eu₂P₂S₆ exhibits excellent NLO properties, including a phase-matchable second-harmonic generation (SHG) response ≈0.9×AgGaS₂@2.1 μm, and a high laser-induced damage threshold of 3.4×AgGaS₂. Eu₂P₂S₆ is the first NLO-active rare-earth-based chalcogenophosphate.

Abstract

Metal chalcogenophosphates are receiving increasing interest, specifically as promising infrared nonlinear optical (NLO) candidates. Here, a rare-earth chalcogenophosphate Eu₂P₂S₆ crystallizing in the monoclinic noncentrosymmetric space group Pn was synthesized using a high-temperature solid-state method. Its structure features isolated [P₂S₆]⁴⁻ dimer, and two types of EuS₈ bicapped triangular prisms. Eu₂P₂S₆ exhibits a phase-matchable second-harmonic generation (SHG) response ≈0.9×AgGaS₂@2.1 μm, and high laser-induced damage threshold of 3.4×AgGaS₂, representing the first rare-earth NLO chalcogenophosphate. The theoretical calculation result suggests that the SHG response is ascribed to the synergetic contribution of [P₂S₆]⁴⁻ dimers and EuS₈ bicapped triangular prisms. This work provides not only a promising high-performance infrared NLO material, but also opens the avenue for exploring rare-earth chalcogenophosphates as potential IR NLO materials.

A new synthesis method is proposed to achieve horizontally self-standing Bi₂O₂Se nanoplates on SiO₂/Si substrates by abrupt adjustment of the growing pressure during the growth. In contrast to flat Bi₂O₂Se nanoplates grown on mica, they display improved photoresponse performance, indicating a new potential in high-quality 2D electronic nanostructures with optimal optoelectronic functionality.

Abstract

Air-stable 2D Bi₂O₂Se material with high carrier mobility appears as a promising semiconductor platform for future micro/nanoelectronics and optoelectronics. Like most 2D materials, Bi₂O₂Se 2D nanostructures normally form on atomically flat mica substrates, in which undesirable defects and structural damage from the subsequent transfer process will largely degrade their photoelectronic performance. Here, a new synthesis route involving successive kinetic and thermodynamic processes is proposed to achieve horizontally self-standing Bi₂O₂Se nanostructures on SiO₂/Si substrates. Fewer defects and avoidance of transfer procedure involving corrosive solvents ensure the integrity of the intrinsic lattice and band structures in Bi₂O₂Se nanostructures. In contrast to flat structures grown on mica, it displays reduced dark current and improved photoresponse performance (on–off ratio, photoresponsivity, response time, and detectivity). These results indicate a new potential in high-quality 2D electronic nanostructures with optimal optoelectronic functionality.

In this work, the vanadium nitride support as an example was investigated to reveal the role of nitrogen chemistry for anchoring behavior for single platinum-group metal atoms. As a proof-of-concept for hydrogen generation, the platinum-based single-atom catalyst shows an onset overpotential of 43.7 mV and a mass activity of 22.55 A mg⁻¹ _Pt, superior to commercial platinum/carbon catalysts.

Abstract

Single-atom catalysts (SACs) with a maximum atom utilization efficiency have received growing attention in heterogeneous catalysis. The supporting substrate that provides atomic-dispersed anchoring sites and the local electronic environment in these catalysts is crucial to their activity and stability. Here, inspired by N-doped graphene substrate, the role of N is explored in transition metal nitrides for anchoring single metal atoms toward single-atom catalysis. A pore-rich metallic vanadium nitride (VN) nanosheet is fabricated as one supporting-substrate example, whose surface features abundant unsaturated N sites with lower binding energy than that of widely used N-doped graphene. Impressively, it is found that this support can anchor nearly all platinum-group single atoms (e.g., platinum, palladium, iridium, and ruthenium), and even be extendable to multiple SACs, i.e., binary (Pt/Pd) and ternary (Pt/Pd/Ir). As a proof-of-concept application for hydrogen production, Pt-based SAC (Pt₁-VN) performs excellently, exhibiting a mass activity up to 22.55 A mg⁻¹ _Pt at 0.05 V and a high turnover frequency value close to 0.350 H₂ s⁻¹, superior to commercial platinum/carbon catalyst. The catalyst's durability can be further improved by using binary (Pt₁Pd₁-VN) SAC. This work provides inexpensive and durable nitride-based support, giving a possible pathway for universally constructing platinum-group SACs.

npj 2D Materials and Applications, Published online: 09 June 2022; doi:10.1038/s41699-022-00316-6

Graphene is an atomically thin material for which all atoms are exposed to the interfaces that need to be studied using a nondestructive and sensitive technique. In this review, it is summarized and discussed how to characterize these interfaces by synchrotron radiation techniques to understand the structure and property evolution of graphene.

Abstract

Recently, many breakthroughs have been made in graphene research, allowing scientists to explore and understand the material world from a two-dimensional (2D) perspective. The interface issue of graphene is the most important, because all of its atoms are exposed to the interface for this atomically thin material. The 2D nature necessitates a sensitive and non-destructive interface probe to detect the structure and properties. Synchrotron radiation (SR) characterization techniques, with the ultra-high resolution and extremely wide energy range, have been utilized with increasing frequency to explore the challenging interface sciences. In this review, these interface characterization techniques based on SR and how they monitor the structure evolution of graphene in different interfaces such as graphene–substrate and graphene–graphene interface are first introduced. Graphene's layer number, interlayer spacing, and stacking order are governed by these interfaces, determining the final properties. Then, the property detection and modulation in different interfaces of graphene are also discussed. Finally, the current challenges and outlook on the future development for SR techniques to characterize graphene interface are presented.

An efficient approach is developed to produce 2D non-van der Waals (vdW) transition-metal chalcogenide (TMC) (V₃S₄) layers by topological conversion of vanadium-based MAX phase. By harnessing the unique topological conversion, 2D non-vdW ultrathin layers with vacancy-enriched structure, and high electrical conductivity are achieved, exhibiting good electrochemical performance for zinc storage. The protocol can also produce a large number of non-vdW TMC layers.

Abstract

Although 2D non-van der Waals (vdW) layers show many intriguing physical and chemical properties as well as wide applications in the fields of electronics, catalysis, and energy storage, they still lack efficient synthetic approaches owing to their three-dimensionally bonded structures. Here, a facile approach to produce 2D non-vdW transition-metal chalcogenide (TMC) layers based on the conversion of vanadium-based MAX phase (V₂GeC) at high temperatures in hydrogen sulfide gas is developed. Associated with the etching of the germanium layers from the MAX phase, the vanadium layers are transformed into 2D non-vdW V₃S₄ layers. This originates from the self-intercalation of ordered V atoms within the vdW space of intermediated vdW vanadium disulfide layers during the conversion reaction. Owing to the ultrathin character, highly exposed active surface, and unique vacancy-enriched structure, the resultant 2D non-vdW V₃S₄ layers deliver a high reversible capacity of 341 mAh g⁻¹, good rate capabilities, and long-term cycling performance for zinc storage.

Abstract

In recent years, few-layer or even monolayer ferromagnetic materials have drawn a great deal of attention due to the promising integration of two-dimensional (2D) magnets into next-generation spintronic devices. The SrRuO₃ monolayer is a rare example of stable 2D magnetism under ambient conditions, but only weak ferromagnetism or antiferromagnetism has been found. The bi-atomic layer SrRuO₃ as another environmentally inert 2D magnetic system has been paid less attention heretofore. Here we study both the bi-atomic layer and monolayer SrRuO₃ in (SrRuO₃)_n/(SrTiO₃)_m (n = 1, 2) superlattices in which the SrTiO₃ serves as a non-magnetic and insulating space layer. Although the monolayer exhibits arguably weak ferromagnetism, we find that the bi-atomic layer exhibits exceedingly strong ferromagnetism with a T_c of 125 K and a saturation magnetization of 1.2 µ_B/Ru, demonstrated by both superconducting quantum interference device (SQUID) magnetometry and element-specific X-ray circular dichroism. Moreover, in the bi-atomic layer SrRuO₃, we demonstrate that random fluctuations and orbital reconstructions inevitably occurring in the 2D limit are critical to the electrical transport, but are much less critical to the ferromagnetism. Our study demonstrates that the bi-atomic layer SrRuO₃ is an exceedingly strong 2D ferromagnetic oxide which has great potentials for applications of ultracompact spintronic devices.

Abstract

Moiré superlattices are formed by a lattice mismatch or twist angle in two-dimensional materials, which can generate periodical moiré potentials leading to strong changes in the band structure, resulting in new quantum phenomena. However, the experimental engineering of in-situ deformation of moiré heterostructures remains deficient. Here, we demonstrate a dynamic local deformation of the twisted heterostructures using a diamond anvil cell (DAC), enabling in-situ dynamic modulation of moiré potential in twisted WS₂—WSe₂ heterostructures at room temperature. Deformation of the twisted heterostructure increases the moiré potential, causing a red shift of the moiré exciton resonance, and observed the red shift of the intralayer exciton resonance up to 16.3 meV (less than 1.1 GPa). The blue shift of the interlayer excitons of twisted WS₂—WSe₂ heterostructures shows an evident transition of the pressure sensitive exciton, induced by the dominant effect of modifying the band structure on optical properties. Combined with the spectral changes of pressurized Raman, which further demonstrated that the DAC can efficiently regulate the interlayer coupling. Our results offer an effective strategy for in-situ dynamic modulation of moiré potential, providing a promising platform for the development of novel quantum devices.

Nature Electronics, Published online: 09 June 2022; doi:10.1038/s41928-022-00777-z