Jiuxiang Dai

2D metal-organic framework (MOF) with matching 2D morphology, excellent stability performance, and outstanding optoelectronic performance is grown on the MXene surface through heterojunction-engineering to suppress the direct contact of reactive molecules without affecting the original advantages of MXene. The photoelectric dual gain MXene@MOF heterojunction is confirmed. This work offers a forward-looking strategy for the design of interface materials with excellent photoelectric performance.

Abstract

MXene is widely used in the construction of optoelectronic interfaces due to its excellent properties. However, the hydrophilicity and metastable surface of MXene lead to its oxidation behavior, resulting in the degradation of its various properties, which seriously limits its practical application. In this work, a 2D metal-organic framework (2D MOF) with matching 2D morphology, excellent stability performance, and outstanding optoelectronic performance is grown in situ on the MXene surface through heterojunction engineering to suppress the direct contact between reactive molecules and the inner layer material without affecting the original advantages of MXene. The photoelectric dual gain MXene@MOF heterojunction is confirmed. As a photoelectric material, its properties are highly suitable for the demand of interface sensitization layer materials of surface plasmon resonance (SPR). Therefore, using SPR as a platform for the application of this interface material, the performance of MXene@MOF and its potential mechanism to enhance SPR are analyzed in depth using experiments combined with simulation calculations (FDTD/DFT). Finally, the MXene@MOF/peptides-SPR sensor is constructed for rapid and sensitive detection of the cancer marker exosomes to explore its potential in practical applications. This work offers a forward-looking strategy for the design of interface materials with excellent photoelectric performance.

Nature Materials, Published online: 28 December 2023; doi:10.1038/s41563-023-01757-0

Inspired by the observed coherent interface between hexagonal α-Fe2O3 and tetragonal fluorine-doped SnO2, an oxygen sublattice-matching paradigm is proposed to grow textured films on lattice-mismatched substrates. Through assessing the similarity of Voronoi cells for sublattices, this approach offers opportunities to synthesize (semi)coherent heterostructures and textured films.

The subthreshold swing (SS) serves as the key performance parameter for high-speed and low-power electronics. Boltzmann distribution limits the SS to 60 mV dec⁻¹ in conventional field effect transistors. Here, in a state-of-the-art device architecture, ultralow SS across the five decades of drain current is achieved by utilizing efficient Dirac contacts and ultrafast negative-capacitance transition in layered ferroelectric gate insulator.

Abstract

Negative capacitance gives rise to subthreshold swing (SS) below the fundamental limit by efficient modulation of surface potential in transistors. While negative-capacitance transition is reported in polycrystalline Pb(Zr_0.2Ti_0.8)O₃ (PZT) and HfZrO₂ (HZO) thin-films in few microseconds timescale, low SS is not persistent over a wide range of drain current when used instead of conventional dielectrics. In this work, the clear nano-second negative transition states in 2D single-crystal CuInP₂S₆ (CIPS) flakes have been demonstrated by an alternative fast-transient measurement technique. Further, integrating this ultrafast NC transition with the localized density of states of Dirac contacts and controlled charge transfer in the CIPS/channel (MoS₂/graphene) a state-of-the-art device architecture, negative capacitance Dirac source drain field effect transistor (FET) is introduced. This yields an ultralow SS of 4.8 mV dec⁻¹ with an average sub-10 SS across five decades with on-off ratio exceeding 10⁷, by simultaneous improvement of transport and body factors in monolayer MoS₂-based FET, outperforming all previous reports. This approach could pave the way to achieve ultralow-SS FETs for future high-speed and low-power electronics.

This report proposes a device exhibiting remarkable multiple functionalities with tunable detection and emission operation according to the different applied biases to the heterojunction, covering an extremely wide range of wavelengths from DUV to NIR regions. This study further employes them in various optoelectronic systems, demonstrating outstanding applications in multicolor imaging, filterless color discrimination, and DUV/NIR visualization.

Abstract

Low-dimensional semiconductor nanostructures, particularly in the form of nanowire configurations with large surface-to-volume-ratio, offer intriguing optoelectronic properties for the advancement of integrated photonic technologies. Here, a bias-controlled, superior dual-functional broadband light detecting/emitting diode enabled by constructing the aluminum-gallium-nitride-based nanowire on the silicon-platform is reported. Strikingly, the diode exhibits a stable and high responsivity (R) of over 200 mAW⁻¹ covering an extremely wide operation band under reverse bias conditions, ranging from deep ultraviolet (DUV: 254 nm) to near-infrared (NIR: 1000 nm) spectrum region. While at zero bias, it still possesses superior DUV light selectivity with a high off-rejection ratio of 106. When it comes to the operation of the light-emitting mode under forward bias, it can achieve large spectral changes from UV to red simply by coating colloid quantum dots on the nanowires. Based on the multifunctional features of the diodes, this study further employs them in various optoelectronic systems, demonstrating outstanding applications in multicolor imaging, filterless color discrimination, and DUV/NIR visualization. Such highly responsive broadband photodetector with a tunable emitter enabled by III–V nanowire on silicon provides a new avenue toward the realization of integrated photonics and holds great promise for future applications in communication, sensing, imaging, and visualization.

Defects in amorphous oxide films and heterostructures affect the performance ofmicroelectronic devices, thin-film transistors, and electrocatalysis. In this perspective, the experimental and theoretical evidence of the effects of oxygen deficiency in amorphous oxide films and the validity of the analogy between the structure and properties of point defects in amorphous and crystalline oxides are critically discussed.

Abstract

Understanding defects in amorphous oxide films and heterostructures is vital to improving performance of microelectronic devices, thin-film transistors, and electrocatalysis. However, to what extent the structure and properties of point defects in amorphous solids are similar to those in the crystalline phase are still debated. The validity of this analogy and the experimental and theoretical evidence of the effects of oxygen deficiency in amorphous oxide films are critically discussed. The authors start with the meaning and significance of defect models, such as “oxygen vacancy” in crystalline oxides, and then introduce experimental and computational methods used to study intrinsic defects in amorphous oxides and discuss their limitations and challenges. To test the validity of existing defect models, ab initio molecular dynamics is used with a non-local density functional to model the structure and electronic properties of oxygen-deficient amorphous alumina. Unlike some previous studies, the formation of deep defect states in the bandgap caused by the oxygen deficiency is found. Apart from atomistic structures analogous to crystal vacancies, the formation of more stable defect states characterized by the bond formation between under-coordinated Al ions is shown. The limitations of such defect models and how they may be overcome in simulations are discussed.

Combined in situ Raman spectroscopy with XAS, this work reveals that ^*OO species generated through the O–O coupling of adsorbed oxygen species directly from water is the key intermediate for OER, and weakening its adsoprtion will greatly boost OER performance.

Abstract

Developing efficient oxygen evolution reaction (OER) electrocatalysts can greatly advance the commercialization of proton exchange membrane (PEM) water electrolysis. However, the unclear and disputed reaction mechanism and structure-activity relationship of OER pose significant obstacles. Herein, the active site and intermediate for OER on AuIr nanoalloys are simultaneously identified and correlated with the activity, through the integration of in situ shell-isolated nanoparticle-enhanced Raman spectroscopy and X-ray absorption spectroscopy. The AuIr nanoalloys display excellent OER performance with an overpotential of only 246 mV to achieve 10 mA cm⁻² and long-term stability under strong acidic conditions. Direct spectroscopic evidence demonstrates that ^*OO adsorbed on IrO_x sites is the key intermediate for OER, and it is generated through the O–O coupling of adsorbed oxygen species directly from water, providing clear support for the adsorbate evolution mechanism. Moreover, the Raman information of the ^*OO intermediate can serve as a universal “in situ descriptor” that can be obtained both experimentally and theoretically to accelerate the catalyst design. It unveils that weakening the interactions of ^*OO on the catalysts and facilitating its desorption would boost the OER performance. This work deepens the mechanistic understandings on OER and provides insightful guidance for the design of more efficient OER catalysts.

Both wavelength-tunable coloration and light intensity-tunable photoluminescence are independently and reliably manipulated in the thin polymer-based film. A rewritable dual-responsive encryption display that has the benefit of direct and intuitive identification of encrypted information by the human eye is presented, enabling high information security and anti-counterfeiting.

Abstract

Optical encryption using coloration and photoluminescent (PL) materials can provide highly secure data protection with direct and intuitive identification of encrypted information. Encryption capable of independently controlling wavelength-tunable coloration as well as variable light intensity PL is not adequately demonstrated yet. Herein, a rewritable PL and structural color (SC) display suitable for dual-responsive optical encryption developed with a stimuli-responsive SC of a block copolymer (BCP) photonic crystal (PC) with alternating in-plane lamellae, of which a variety of 3D and 2D perovskite nanocrystals is preferentially self-assembled with characteristic PL, is presented. The SC of a BCP PC is controlled in the visible range with different perovskite precursor doping times. The perovskite nanocrystals developed in the BCP PC are highly luminescent, with a PL quantum yield of ≈33.7%, yielding environmentally stable SC and PL dual-mode displays. The independently programmed SC and PL information is erasable and rewritable. Dual-responsive optical encryption is demonstrated, in which true Morse code information is deciphered only when the information encoded by SCs is properly combined with PL information. Numerous combinations of SC and PL realize high security level of data anticounterfeiting. This dual-mode encryption display offers novel optical encryption with high information security and anti-counterfeiting.

Highlights

• A Cr₅Te₈@expanded graphite heterostructure is fabricated by chemical vapor deposition, exhibiting remarkable microwave absorption performance with a minimum reflection loss of up to − 57.6 dB at a thin thickness of only 1.4 mm under a low filling rate of 10%.

• Density functional theory calculations deeply reveal the polarization loss mechanism triggered by heterogeneous interfaces.

• The heterostructure coating displays a remarkable radar cross section reduction of 31.9 dB m², demonstrating a great electromagnetic microwave scattering ability and radar stealth capability.

Freestanding slender fluid filaments of a ferroelectric nematic liquid crystal are observed and studied. They are stabilized either by bound charges formed due to polarization splay or by external voltage applied between suspending wires. The slenderness ratio can exceed 100. Without external electric fields, the fluid ferroelectric filament becomes unstable in time due to ionic screening of the bound charges.

Abstract

Freestanding slender fluid filaments of room-temperature ferroelectric nematic liquid crystals are described. They are stabilized either by internal electric fields of bound charges formed due to polarization splay or by external voltage applied between suspending wires. The phenomenon is similar to those observed in dielectric fluids, such as deionized water, except that in ferroelectric nematic materials the voltages required are three orders of magnitudes smaller and the aspect ratio is much higher. The observed ferroelectric fluid threads are not only unique and novel but also offer measurements of basic physical quantities, such as the ferroelectric polarization and viscosity. Ferroelectric nematic fluid threads may have practical applications in nano-fluidic micron-size logic devices, switches, and relays.

Guided-growth of surface topographies in soft materials like liquid crystal polymers is achieved by harnessing the smectic ordering during the formation of electrohydrodynamic patterns. Coupled with the advanced tools for controlling liquid crystal alignment, intricate surface topographies can be produced in liquid crystal polymer films starting from relatively simple designs.

Abstract

The guided-growth strategy has been widely explored and proved its efficacy in fabricating surface micro/nanostructures in a variety of systems. However, soft materials like polymers are much less investigated partly due to the lack of strong internal driving mechanisms. Herein, the possibility of utilizing liquid crystal (LC) ordering of smectic liquid crystal polymers (LCPs) to induce guided growth of surface topography during the formation of electrohydrodynamic (EHD) patterns is demonstrated. In a two-stage growth, regular stripes are first found to selectively emerge from the homogeneously aligned region of an initially flat LCP film, and then extend neatly along the normal direction of the boundary line between homogeneous and homeotropic alignments. The stripes can maintain their directions for quite a distance before deviating. Coupled with the advanced tools for controlling LC alignment, intricate surface topographies can be produced in LCP films starting from relatively simple designs. The regularity of grown pattern is determined by the LC ordering of the polymer material, and influenced by conditions of EHD growth. The proposed approach provides new opportunities to employ LCPs in optical and electrical applications.

A novel approach is reported to facilely prepare graphene nanoribbons (GNRs) through the simple annealing of single-walled carbon nanotubes (SWCNTs) on Cu(111). The surface-catalyzed unzipping of SWCNTs occurs along a longitudinal line which directly contacts with Cu(111), affording straight GNRs. The structural evolution process is characterized by low-temperature scanning tunneling microscopy with atom resolution.

Abstract

Graphene nanoribbons (GNRs) are promising in nanoelectronics for their quasi-1D structures with tunable bandgaps. The methods for controllable fabrication of high-quality GNRs are still limited. Here a way to generate sub-5-nm GNRs by annealing single-walled carbon nanotubes (SWCNTs) on Cu(111) is demonstrated. The structural evolution process is characterized by low-temperature scanning tunneling microscopy. Substrate-dependent measurements on Au(111) and Ru(0001) reveal that the intermediate strong SWCNT-surface interaction plays a pivotal role in the formation of GNRs.

The antimony selenide (Sb₂Se₃) films achieve the transition from (hk0) to (hk1) plane on the contact substrate of digenite (Cu₉S₅) films. The ordered arrangement of chained Sb₄Se₆ appears as (211), (221), (101), (151), (301), and (410) crystal plane by post-annealing treatment. The different crystal growth in the Sb₂Se₃ films leads to flake- and flower-like morphologies on the surface.

Abstract

Antimony selenide (Sb₂Se₃) is a promising semiconductor for photodetector applications due to its unique photovoltaic properties. Achieving optimal carrier transport in (001)-Sb₂Se₃ by the material of contacting substrate requires in-depth study. In this paper, the induced growth of Sb₂Se₃ films from (hk0) to (hk1) planes is achieved on digenite (Cu₉S₅) films by post-annealing treatment. The flake-like and flower-like morphologies on the surface of Sb₂Se₃ films are caused by different thicknesses of the Cu₉S₅ films, which are related to the (hk0) and (hk1) planes of Sb₂Se₃ surface. The epitaxial growth of Sb₂Se₃ films on (105)-Cu₉S₅ surfaces exhibits thickness dependence. The results inform research into the controlled induced growth of low-dimensional materials. The device of Sb₂Se₃/Cu₉S₅/Si has good broadband response (visible to near-infrared), self-powered characteristics, and stability. As the crystalline quality of the Sb₂Se₃ film increases along the (hk1) plane, the carrier transport is enhanced correspondingly. Under the 980 nm light irradiation, the device has an excellent switching ratio of 2 × 10⁴ at 0 bias, with responsivity, detectivity, and response time up to 17 µA W⁻¹, 1.48 × 10⁷ Jones, and 355/490 µs, respectively. This suggests that Sb₂Se₃ is suitable for self-powered photodetectors and related optical and optoelectronic devices.

Cu on amorphous CeO_x facilitates H₂O splitting to generate abundant *H, which is combined with *NO intermediate produced by deoxygenation and hydrogenation of adsorbed NO₃ ⁻ to form ammonia via hydrogen spillover mechanism.

Abstract

The electrochemical nitrate reduction reaction (NO₃RR) is an environment-friendly and promising alternative to the conventional Haber–Bosch ammonia synthesis process, which is a complex process of proton-coupled electron transfer. Hereon, the amorphous CeO_x support introduced to construct Cu/a-CeO_x heterostructure is prepared to provide sufficient *H and synergistically catalyze the NO₃RR. Cu/a-CeO_x achieves a maximum ammonia yield of 1.52 mmol h⁻¹ mg_cat ⁻¹. In the flow cell, the NH₃ yield reaches 17.93 mmol h⁻¹ mg_cat ⁻¹ at 1 A cm⁻², which exceeds most of the state-of-the-art catalysts. In situ X-ray diffraction (XRD) and in situ Raman observe that the catalyst undergoes structural reconfiguration under operating conditions, thus confirming that Cu₂O is not the true active center in the catalytic process. Furthermore, in situ characterizations and density functional theory (DFT) calculations demonstrate that the amorphous CeO_x in Cu/a-CeO_x modulates the electronic structure of Cu and overcomes the higher potential barrier required for the decomposition of water on Cu, which greatly facilitates the hydrolysis process and provides a higher H-coverage rate for the hydrogenation of NO₃ ⁻, realizing a dynamic equilibrium between the production and consumption of active hydrogen. This component design strategy centered on the amorphous structure opens up a new pathway for the electrochemical NO₃RR.

Via unzipping and zipping processes, an ultrathin two-dimensional layered carbosilicate is obtained by hydrothermal treatment. In a one-pot reaction, CNT and bulk silica are unzipped by the reaction of iron and water, followed by iron zipping the unzipped species to form the carbosilicate. The unprecedent phenomenon brings us new insight on synergistic chemistry, stimulating the discovery of new structures and materials.

Abstract

A key task in today's inorganic synthetic chemistry is to develop effective reactions, routes, and associated techniques aiming to create new functional materials with specifically desired multilevel structures and properties. Herein, we report an ultrathin two-dimensional layered composite of graphene ribbon and silicate via a simple and scalable one-pot reaction, which leads to the creation of a novel carbon-metal-silicate hybrid family: carbosilicate. The graphene ribbon is in situ formed by unzipping carbon nanotubes, while the ultrathin silicate is in situ obtained from bulk silica or commercial glass; transition metals (Fe or Ni) oxidized by water act as bridging agent, covalently bonding the two structures. The unprecedented structure combines the superior properties of the silicate and the nanocarbon, which triggers some specific novel properties. All processes during synthesis are complementary to each other. The associated synergistic chemistry could stimulate the discovery of a large class of more interesting, functionalized structures and materials.

Nature Materials, Published online: 22 December 2023; doi:10.1038/s41563-023-01776-x

A fast-switching thermal transistor