huangpanqi

Nature Electronics, Published online: 05 December 2022; doi:10.1038/s41928-022-00877-w

2D molybdenum compounds, by virtue of their high surface-to-volume ratio, unique electronic structure, and physicochemical properties, show great potential in electrocatalytic energy conversion applications. This review provides a comprehensive overview of the strategies for the synthesis and modulation of 2D molybdenum compounds and their applications in various electrocatalytic reactions that involve the cycles of water, carbon, and nitrogen.

Abstract

The development of advanced nanomaterials is urgent for electrocatalytic energy conversion applications. Recently, 2D nanomaterial-derived heterogeneous electrocatalysts have shown great promise for both fundamental research and practical applications owing to their extremely high surface-to-volume ratio and tunable geometric and electronic properties. Because of their unique electronic structure and physicochemical properties, molybdenum (Mo)-based 2D nanomaterials are emerging as one of the most attractive candidates among the nonprecious materials for electrocatalysts. This review provides a comprehensive overview of the recent advances in the synthesis and modulation of 2D Mo compounds for applications in electrocatalytic energy conversion. The categories based on different compositions and corresponding synthetic approaches of 2D Mo compounds are first introduced. Subsequently, various atomic/plane/synergistic engineering strategies, along with catalytic optimization in the electrochemical process that involves the cycles of water, carbon, and nitrogen, are discussed in detail. Finally, the current challenges and future opportunities for the development of 2D Mo-based electrocatalysts are proposed with the goal of shedding light on these promising 2D nanomaterials for electrocatalytic energy conversion.

Nature Chemistry, Published online: 21 November 2022; doi:10.1038/s41557-022-01085-x

A new type of second near-infrared (NIR-II) (1532 nm) light responsive upconversion nanoparticles with enhanced single-band red upconversion emission and controllable phase and size is designed by introducing Er³⁺ as sensitizer and utilizing Mn²⁺ as energy manipulator. Moreover, NIR-II light activated red upconversion bioimaging and photodynamic therapy are successfully achieved for the first time.

Abstract

Lanthanide based upconversion (UC) nanoprobes have emerged as promising agents for biological applications. Extending the excitation light to the second near-infrared (NIR-II), instead of the traditional 980/808 nm light, and realizing NIR-II responsive single-band red UC emission is highly demanded for bioimaging application, which has not yet been explored. Here, a new type of NIR-II (1532 nm) light responsive UC nanoparticles (UCNPs) with enhanced single-band red UC emission and controllable phase and size is designed by introducing Er³⁺ as sensitizer and utilizing Mn²⁺ as energy manipulator. Through tuning the content of Mn²⁺ in NaLnF₄:Er/Mn, the crystal phase, size, and emitting color are readily controlled, and the red-to-green (R/G) ratio is significantly increased from ≈20 to ≈300, leading to NIR-II responsive single band red emission via efficient energy transfer between Er³⁺ and Mn²⁺. In addition, the single band red emitting intensity can be further improved by coating shell to avoid the surface quenching effect. More importantly, NIR-II light activated red UC bioimaging and photodynamic therapy through loading photosensitizer of zinc phthalocyanine are successfully achieved for the first time. These findings provide a new strategy of designing NIR-II light responsive single-band red emissive UCNPs for biomedical applications.

Oxidation leads to the degradation of 2D MoTe₂ under in situ electron microscopy at low oxygen pressures, while 2D MoS₂ surface remains inert. The etching is facilitated by abundant oxygen at partial oxygen pressures above 1 × 10⁻⁷ torr. The atomic scale etching mechanism is revealed computationally. Hydrocarbon contamination, commonly found on surfaces, accelerates etching by over forty times.

Abstract

Oxidation is the main cause of degradation of many 2D materials, including transition metal dichalcogenides (TMDs), under ambient conditions. Some of the materials are more affected by oxidation than others. To elucidate the oxidation-induced degradation mechanisms in TMDs, the chemical effects in single layer MoS₂ and MoTe₂ are studied in situ in an electron microscope under controlled low-pressure oxygen environments at room temperature. MoTe₂ is found to be reactive to oxygen, leading to significant degradation above a pressure of 1 × 10⁻⁷ torr. Curiously, the common hydrocarbon contamination found on practically all surfaces accelerates the damage rate significantly, by up to a factor of forty. In contrast to MoTe₂, MoS₂ is found to be inert under oxygen environment, with all observed structural changes being caused by electron irradiation only, leading to well-defined pores with high proportion of molybdenum nanowire-terminated edges. Using density functional theory calculations, a further atomic-scale mechanism leading to the observed oxygen-related degradation in MoTe₂ is proposed, and the role of the carbon in the etching is explored. Together, the results provide an important insight into the oxygen-related deterioration of 2D materials under ambient conditions relevant in many fields.

npj 2D Materials and Applications, Published online: 15 November 2022; doi:10.1038/s41699-022-00360-2

Nature Communications, Published online: 17 November 2022; doi:10.1038/s41467-022-34690-y

Flexocatalysis in 2D centrosymmetric semiconductors is demonstrated for the first time via dynamic flexoelectric polarization, largely expanding the polarization-based mechanocatalysis from non-centrosymmetric materials into 2D centrosymmetric semiconductors. The flexocatalysis shows the distinguished performance comparable to the state-of-the-art piezocatalysis, with excellent stability and reproducibility. It opens the field of flexoelectric effect-based mechanochemistry in 2D centrosymmetric semiconductors.

Abstract

Catalysis is vitally important for chemical engineering, energy, and environment. It is critical to discover new mechanisms for efficient catalysis. For piezoelectric/pyroelectric/ferroelectric materials that have a non-centrosymmetric structure, interfacial polarization-induced redox reactions at surfaces leads to advanced mechanocatalysis. Here, the first flexocatalysis for 2D centrosymmetric semiconductors, such as MnO₂ nanosheets, is demonstrated largely expanding the polarization-based-mechanocatalysis to 2D centrosymmetric materials. Under ultrasonic excitation, the reactive species are created due to the strain-gradient-induced flexoelectric polarization in MnO₂ nanosheets composed nanoflowers. The organic pollutants (Methylene Blue et al.) can be effectively degraded within 5 min; the performance of the flexocatalysis is comparable to that of state-of-the-art piezocatalysis, with excellent stability and reproducibility. Moreover, the factors related to flexocatalysis such as material morphology, adsorption, mechanical vibration intensity, and temperature are explored, which give deep insights into the mechanocatalysis. This study opens the field of flexoelectric effect-based mechanochemistry in 2D centrosymmetric semiconductors.

The deterministic positioning of single-crystal plasmonic nanostructures into organized configurations represents a foundational capability for the advancement of wafer-based technologies. In this work, a benchtop nanofabrication route is presented for the formation of large-area arrays of gold nanotriangles. The route is unique in that it avoids colloid-to-substrate transfers, instead opting for the direct synthesis of nanotriangles on substrate surfaces.

Abstract

The advancement of nanoenabled wafer-based devices requires the establishment of core competencies related to the deterministic positioning of nanometric building blocks over large areas. Within this realm, plasmonic single-crystal gold nanotriangles represent one of the most attractive nanoscale components but where the formation of addressable arrays at scale has heretofore proven impracticable. Herein, a benchtop process is presented for the formation of large-area periodic arrays of gold nanotriangles. The devised growth pathway sees the formation of an array of defect-laden seeds using lithographic and vapor-phase assembly processes followed by their placement in a growth solution promoting planar growth and threefold symmetric side-faceting. The nanotriangles formed in this high-yield synthesis distinguish themselves in that they are epitaxially aligned with the underlying substrate, grown to thicknesses that are not readily obtainable in colloidal syntheses, and present atomically flat pristine surfaces exhibiting gold atoms with a close-packed structure. As such, they express crisp and unambiguous plasmonic modes and form photoactive surfaces with highly tunable and readily modeled plasmon resonances. The devised methods, hence, advance the integration of single-crystal gold nanotriangles into device platforms and provide an overall fabrication strategy that is adaptable to other nanomaterials.

Nature Electronics, Published online: 07 November 2022; doi:10.1038/s41928-022-00872-1

Emerging 2D metal oxides exhibit intriguing electronic and optical properties, which have great potential in emerging functional devices. Diverse structures and various synthesis methods open a new field of vision for device-fabrication-based 2D metal oxides. Their unique properties can bring new vigor and vitality into 2D material family.

Abstract

2D metal oxides have aroused increasing attention in the field of electronics and optoelectronics due to their intriguing physical properties. In this review, an overview of recent advances on synthesis of 2D metal oxides and their electronic applications is presented. First, the tunable physical properties of 2D metal oxides that relate to the structure (various oxidation-state forms, polymorphism, etc.), crystallinity and defects (anisotropy, point defects, and grain boundary), and thickness (quantum confinement effect, interfacial effect, etc.) are discussed. Then, advanced synthesis methods for 2D metal oxides besides mechanical exfoliation are introduced and classified into solution process, vapor-phase deposition, and native oxidation on a metal source. Later, the various roles of 2D metal oxides in widespread applications, i.e., transistors, inverters, photodetectors, piezotronics, memristors, and potential applications (solar cell, spintronics, and superconducting devices) are discussed. Finally, an outlook of existing challenges and future opportunities in 2D metal oxides is proposed.

Nature Nanotechnology, Published online: 31 October 2022; doi:10.1038/s41565-022-01237-7

The formation of ultrathin nanowires has thermodynamic advantages at low temperature. However, at low temperatures the monomers for nanocrystal growth are difficult to generate through precursor decomposition. In their Research Article (e202212251), Di Qiu, Yaping Du, and co-workers report an efficient growth process based on adding polyoxometalate clusters to the monomers. Fifteen types of rare earth oxide ultrathin nanowires were synthesized, all exhibiting polymer-like behavior due to the extremely high aspect ratio.

Low-temperature grown gallium arsenide (LT-GaAs) is one of the best photoconductive materials for detecting terahertz radiation. However, the large bandgap of LT-GaAs prevents its use with robust telecom lasers. This work presents a photoconductive LT-GaAs metasurface that uses the concept of perfect absorption to strongly enhance a very weak two-step optical absorption at 1.55 µm via midgap states, enabling sensitive terahertz detection.

Abstract

Superior ultrafast photoconductive properties make low temperature grown (LT) GaAs one of the best materials for photoconductive terahertz (THz) detection. However, the large bandgap of LT-GaAs limits its operation to gating at wavelengths shorter than 870 nm. Here, it is demonstrated for the first time that nanostructuring the LT-GaAs into a highly absorbing metasurface enables THz photoconductive detection with a pulsed laser at λ = 1.55 µm. The very weak sub-bandgap absorption mediated by midgap states in LT-GaAs is strongly enhanced using the concept of perfect absorption via degenerate critical coupling. Integrated with a THz antenna, the LT-GaAs metasurface enables high sensitivity THz detection with a high dynamic range of 60 dB and large bandwidth up to 4.5 THz. The LT-GaAs metasurface has the potential to serve as a universal ultrafast switching element for THz applications, enabling low-cost, turn-key THz systems for a variety of real-world applications.

Pt single-atom catalysts with novel and small-sized CrN nanoparticles as potential support is successfully prepared by atomic layer deposition method and exhibit superior activity and CO-tolerance toward hydrogen oxidation reaction, which is of great significance for the full utilization of low-cost H₂ with impurity CO in proton exchange membrane fuel cells.

Abstract

The large-scale application of proton exchange membrane fuel cells is currently hampered by high cost of commercial Pt catalysts and their susceptibility to poisoning by CO impurities in H₂ feed. In this context, the development of CO-tolerant electrocatalysts with high Pt atom utilization efficiency for hydrogen oxidation reaction (HOR) is of critical importance. Herein, Pt single atoms are successfully immobilized on chromium nitride nanoparticles by atomic layer deposition method, denoted as Pt SACs/CrN. Electrochemical tests establish Pt SACs/CrN to be a very efficient HOR catalyst, with a mass activity that is 5.7 times higher than commercial PtRu/C. Strikingly, the excellent performance of Pt SACs/CrN is maintained after introducing 1000 ppm of CO in H₂ feed. The excellent CO-tolerance of Pt SACs/CrN is related to weaker CO adsorption on Pt single atoms. This work provides guidelines for the design and construction of active and CO-tolerant catalysts for HOR.

A series of lanthanide(III)-Cu₄I₄ heterometallic organic frameworks (Ln-Cu₄I₄ MOFs)-based X-ray scintillators is developed by rationally assembling X-ray absorption centers ([Cu₄I₄] clusters) and luminescent chromophores (Ln(III) ions) in a specific manner. High-efficient excitation energy transfer from the cluster-based antenna to the Ln(III) ions enables Ln-Cu₄I₄ MOFs and their flexible film with excellent scintillation performance and high spatial resolution of 12.6 lp mm⁻¹.

Abstract

Scintillator-based X-ray imaging has attracted great attention from industrial quality inspection and security to medical diagnostics. Herein, a series of lanthanide(III)-Cu₄I₄ heterometallic organic frameworks (Ln-Cu₄I₄ MOFs)-based X-ray scintillators are developed by rationally assembling X-ray absorption centers ([Cu₄I₄] clusters) and luminescent chromophores (Ln(III) ions) in a specific manner. Under X-ray irradiation, the heavy inorganic units ([Cu₄I₄] clusters) absorb the X-ray energy to populate triplet excitons via halide-to-ligand charge transfer (XLCT) combined with the metal-to-ligand charge-transfer (MLCT) state (defined as the X/MLCT state), and then the ³X/MLCT excited state sensitizes Tb³⁺ for intense X-ray-excited luminescence via excitation energy transfer. The obtained Tb-Cu₄I₄ MOF scintillators exhibit high resistance to humidity and radiation, excellent linear response to X-ray dose rate, and high X-ray relative light yield of 29 379 ± 3000 photons MeV⁻¹. The relative light yield of Tb-Cu₄I₄ MOFs is ≈3 times higher than that of the control Tb(III) complex. X-ray imaging tests show that the Tb-Cu₄I₄ MOFs-based flexible scintillator film exhibits a high spatial resolution of 12.6 lp mm⁻¹. These findings not only provide a promising design strategy to develop lanthanide-MOF-based scintillators with excellent scintillation performance, but also exhibit high-resolution X-ray imaging for biological specimens and electronic chips.

2D superlattice materials combining the advantages of 2D materials and advanced composites provide tunable physical and chemical properties to meet diverse requirements in different applications. This review article summarizes the major fabrication methods for preparing 2D superlattice materials and reviews their applications in electrocatalysis involved in emerging energy devices.

Abstract

Exploring low-cost and high-efficient electrocatalyst is an exigent task in developing novel sustainable energy conversion systems, such as fuel cells and electrocatalytic fuel generations. 2D materials, specifically 2D superlattice materials focused here, featured highly accessible active areas, high density of active sites, and high compatibility with property-complementary materials to form heterostructures with desired synergetic effects, have demonstrated to be promising electrocatalysts for boosting the performance of sustainable energy conversion and storage devices. Nevertheless, the reaction kinetics, and in particular, the functional mechanisms of the 2D superlattice-based catalysts yet remain ambiguous. In this review, based on the recent progress of 2D superlattice materials in electrocatalysis applications, the rational design and fabrication of 2D superlattices are first summarized and the application of 2D superlattices in electrocatalysis is then specifically discussed. Finally, perspectives on the current challenges and the strategies for the future design of 2D superlattice materials are outlined. This review attempts to establish an intrinsic correlation between the 2D superlattice heterostructures and the catalytic properties, so as to provide some insights into developing high-performance electrocatalysts for next-generation sustainable energy conversion and storage.

A synergistic use of finite element simulations as a guide together with tellurization process by chemical vapor deposition allows to evidence the key role of tilt angle and distribution of Te vapor concentration gradient at the substrate position in the reactor to obtain molybdenum ditelluride few-layer nanosheets on large area growth and phase selectivity, namely pure 1T’ or 2H phase.

Abstract

Among transition metal dichalcogenides, molybdenum ditelluride (MoTe₂) holds significant attention due to its polymorphic nature including semiconducting, metallic, and topological semimetal phases. Considerable efforts are devoted to synthesizing MoTe₂ nanosheets to make them suitable for device integration in nanotechnologies and for fundamental investigations. In this respect, chemical vapor deposition (CVD) via tellurization of a pre-deposited Mo thin film is an easy and flexible way for synthesizing large scale MoTe₂ nanosheets. Here, the study report on the CVD of large-area (up to 4 cm × 1 cm) MoTe₂ nanosheets with pure 1T’ and 2H phase selection by design. Within the tellurization scheme, the vapor-solid reaction between the pre-deposited molybdenum film and tellurium vapor is studied thus optimizing the scalability and quality of the MoTe₂ nanosheets grown on SiO₂/Si substrates. It is demonstrated that the MoTe₂ structure and morphology are kinetically dictated by the tellurium concentration gradient on the reaction site with varying geometric configurations inside the CVD reactor. This study provides a pivot scheme for enabling scalable 1T’ and 2H-MoTe₂ integration in applications for novel micro- and nano-electronics, spintronics, photonics, and thermoelectric devices.

High-resolution multicolor patterning is achieved in a hybrid perovskite nanosheet, of which the linewidth can be down to ≈150 nm. A single perovskite nanosheet can not only gradually alter the color of the same pattern in a wide wavelength range, but also display different colors simultaneously. A perovskite photodetector with short channel length exhibits high responsivity.

Abstract

Ultrathin hybrid perovskites, with exotic properties and two-dimensional geometry, exhibit great potential in nanoscale optical and optoelectronic devices. However, it is still challenging for them to be compatible with high-resolution patterning technology toward miniaturization and integration applications, as they can be readily damaged by the organic solvents used in standard lithography processes. Here, a flexible three-step method is developed to make high-resolution multicolor patterning on hybrid perovskite, particularly achieved on a single nanosheet. The process includes first synthesis of precursor PbI₂, then e-beam lithography and final conversion to target perovskite. The patterns with linewidth around 150 nm can be achieved, which can be applied in miniature optoelectronic devices and high-resolution displays. As an example, the channel length of perovskite photodetectors can be down to 126 nm. Through deterministic vapor-phase anion exchange, a perovskite nanosheet can not only gradually alter the color of the same pattern in a wide wavelength range, but also display different colors simultaneously. The authors are optimistic that the method can be applied for unlimited perovskite types and device configurations for their high-integrated miniature applications.

Although research on low-dimensional nanomaterials has been booming for decades, more research is needed on how to utilize them to construct efficient information sensing, processing, and feedback devices. A review of recent representative studies on information sensing, processing, and feedback devices based on low-dimensional nanomaterials to provide a perspective on developing human–machine–thing natural interaction technologies is presented.

Abstract

A wide variety of low-dimensional nanomaterials with excellent properties can meet almost all the requirements of functional materials for information sensing, processing, and feedback devices. Low-dimensional nanomaterials are becoming the star of hope on the road to pursuing human–machine–thing natural interactions, benefiting from the breakthroughs in precise preparation, performance regulation, structural design, and device construction in recent years. This review summarizes several types of low-dimensional nanomaterials commonly used in human–machine–thing natural interactions and outlines the differences in properties and application areas of different materials. According to the sequence of information flow in the human–machine–thing interaction process, the representative research progress of low-dimensional nanomaterials-based information sensing, processing, and feedback devices is reviewed and the key roles played by low-dimensional nanomaterials are discussed. Finally, the development trends and existing challenges of low-dimensional nanomaterials in the field of human–machine–thing natural interaction technology are discussed.