Nanoengineering of Tin Monosulfide (SnS)‐Based Structures for Emerging Applications

Self-powered SnSx/TiO2 photodetectors (PDs) with dual-band binary response and the applications in imaging and light-encrypted logic gates

In this work, we report the design and fabrication of self-powered binary response PDs based on II-type heterostructures consisting of SnSx nanoflakes (NFs) and rutile TiO2 nanorod arrays (NRs). The TiO2 NRs effectively block light with wavelengths below 400 nm from reaching SnSx. Under 385 nm light, the photoelectrons in TiO2 recombine with holes in SnSx at the interface due to the energy band bending, resulting in a positive photocurrent. Under 410 nm light, the photoelectrons in SnSx and the photogenerated holes in TiO2 accumulate at the interface, overcoming the interfacial potential barriers induced by the higher Fermi levels of SnSx and inducing a negative photocurrent. Based on the bipolar response, the dual-band imaging capability without external filters and the light-encrypted OR, AND, and NOT logic gates using a single device are demonstrated. This work provides a blueprint for the development of multifunctional self-powered PDs that can simplify system architecture, reduce the energy consumption, and improve accuracy for applications, such as visual systems, light-controlled logic circuits, and encrypted optical communications.

2D Monolayer Catalysts: Towards Efficient Water Splitting and Green Hydrogen Production

A viable alternative to non-renewable hydrocarbon fuels is hydrogen gas, created using a safe, environmentally friendly process like water splitting. An important role in water-splitting applications is played by the development of two-dimensional (2D) layered transition metal chalcogenides (TMDCs), transition metal carbides (MXenes), graphene-derived 2D layered nanomaterials, phosphorene, and hexagonal boron nitride. Advanced synthesis methods and characterization instruments enabled an effective application for improved electrocatalytic water splitting and sustainable hydrogen production. Enhancing active sites, modifying the phase and electronic structure, adding conductive elements like transition metals, forming heterostructures, altering the defect state, etc., can improve the catalytic activity of 2D stacked hybrid monolayer nanomaterials. The majority of global research and development is focused on finding safer substitutes for petrochemical fuels, and this review summarizes recent advancements in the field of 2D monolayer nanomaterials in water splitting for industrial-scale green hydrogen production and fuel cell applications.

Determining the Out-of-Plane Longitudinal Sound Speed in GeS by Broadband Time-Domain Brillouin Scattering

Over the past decade, two-dimensional (2D) layered semiconducting materials, with their distinctive structures and unique physicochemical properties, have attracted attention for potential applications in photonics and optoelectronics. In this study, we utilized time-domain broadband Brillouin scattering on a single germanium monosulfide (GeS) crystal to determine the out-of-plane longitudinal sound speed, evaluated at vL = (4035 ± 200) m/s. The reported results demonstrate the effectiveness of this nondestructive, all-optical technique for measuring the elastic properties in fragile 2D layered materials and provide the value of the out-of-plane compressive elastic constant, C = (69 ± 7) GPa.

Emerging Xene-Based Single-Atom Catalysts: Theory, Synthesis, and Catalytic Applications

In recent years, the emergence of novel 2D monoelemental materials (Xenes), e.g., graphdiyne, borophene, phosphorene, antimonene, bismuthene, and stanene, has exhibited unprecedented potentials for their versatile applications as well as addressing new discoveries in fundamental science. Owing to their unique physicochemical, optical, and electronic properties, emerging Xenes have been regarded as promising candidates in the community of single-atom catalysts (SACs) as single-atom active sites or support matrixes for significant improvement in intrinsic activity and selectivity. In order to comprehensively understand the relationships between the structure and property of Xene-based SACs, this review represents a comprehensive summary from theoretical predictions to experimental investigations. Firstly, theoretical calculations regarding both the anchoring of Xene-based single-atom active sites on versatile support matrixes and doping/substituting heteroatoms at Xene-based support matrixes are briefly summarized. Secondly, controlled synthesis and precise characterization are presented for Xene-based SACs. Finally, current challenges and future opportunities for the development of Xene-based SACs are highlighted.

Vapor growth of V-doped MoS2 monolayers with enhanced B-exciton emission and broad spectral response

Dynamically engineering the optical and electrical properties in two-dimensional (2D) materials is of great significance for designing the related functions and applications. The introduction of foreign-atoms has previously been proven to be a feasible way to tune the band structure and related properties of 3D materials; however, this approach still remains to be explored in 2D materials. Here, we systematically demonstrate the growth of vanadium-doped molybdenum disulfide (V-doped MoS2) monolayers via an alkali metal-assisted chemical vapor deposition method. Scanning transmission electron microscopy demonstrated that V atoms substituted the Mo atoms and became uniformly distributed in the MoS2 monolayers. This was also confirmed by Raman and X-ray photoelectron spectroscopy. Power-dependent photoluminescence spectra clearly revealed the enhanced B-exciton emission characteristics in the V-doped MoS2 monolayers (with low doping concentration). Most importantly, through temperature-dependent study, we observed efficient valley scattering of the B-exciton, greatly enhancing its emission intensity. Carrier transport experiments indicated that typical p-type conduction gradually arisen and was enhanced with increasing V composition in the V-doped MoS2, where a clear n-type behavior transited first to ambipolar and then to lightly p-type charge carrier transport. In addition, visible to infrared wide-band photodetectors based on V-doped MoS2 monolayers (with low doping concentration) were demonstrated. The V-doped MoS2 monolayers with distinct B-exciton emission, enhanced p-type conduction and broad spectral response can provide new platforms for probing new physics and offer novel materials for optoelectronic applications.

Ultrafast Hole Migration at the p-n Heterojunction of One-Dimensional SnS Nanorods and Zero-Dimensional CdS Quantum Dots

The p-n heterojunctions fabricated from one-dimensional (1D) p-type tin sulfide nanorods (SnS NRs) decorated with n-type zero-dimensional (0D) cadmium sulfide quantum dots (CdS QDs) have gained significant research attention in energy storage devices. Herein, we have successfully synthesized a 1D/0D SnS@CdS heterostructure (HS) using a hot injection method. Structural and morphological studies clearly suggest that CdS QDs are uniformly anchored on the surface of SnS NRs, resulting in intimate contact between two components. The photoluminescence (PL) study revealed the transfer of photoexcited holes from CdS QDs to SnS NRs, which was further confirmed by transient absorption (TA) studies. TA measurements demonstrate the hole transfer from the valence band of CdS QDs to SnS NRs and delocalization of electrons between the conduction band of SnS NRs and CdS QDs in SnS@CdS HS, resulting in efficient charge separation across the p-n heterojunction. These findings will open up a new paradigm for improving the efficiency of optoelectronic devices.

High-Pressure Synthesis of Single-Crystalline SnS Nanoribbons

Two-dimensional tin monosulfide (SnS) is attractive for the development of electronic and optoelectronic devices with anisotropic characteristics. However, its shape-controlled synthesis with an atomic thickness and high quality remains challenging. Here, we show that highly crystalline SnS nanoribbons can be produced via high-pressure (0.5 GPa) and thermal treatment (400 °C). These SnS nanoribbons have a length of several tens of micrometers and a thickness down to 5.8 nm, giving an average aspect ratio of ∼30.6. The crystal orientation along the zigzag direction and the in-plane structural anisotropy of the SnS nanoribbons are identified by transmission electron microscopy and polarized Raman spectroscopy, respectively. An ionic liquid-gated field-effect transistor fabricated using the SnS nanoribbon exhibits an on/off current ratio of >103 and a field-effect mobility of ∼0.7 cm2 V-1 s-1. This work provides a unique way to achieve one-dimensional growth of SnS.

Lead Monoxide Nanostructures for Nanophotonics: A Review

Black-phosphorus-analog lead monoxide (PbO), as a new emerging 2D material, has rapidly gained popularity in recent years due to its unique optical and electronic properties. Recently, both theoretical prediction and experimental confirmation have revealed that PbO exhibits excellent semiconductor properties, including a tunable bandgap, high carrier mobility, and excellent photoresponse performance, which is undoubtedly of great interest to explore its practical application in a variety of fields, especially in nanophotonics. In this minireview, we firstly summarize the synthesis of PbO nanostructures with different dimensionalities, then highlight the recent progress in the optoelectronics/photonics applications based on PbO nanostructures, and present some personal insights on the current challenges and future opportunities in this research area. It is anticipated that this minireview can pave the way to fundamental research on functional black-phosphorus-analog PbO-nanostructure-based devices to meet the growing demands for next-generation systems.

Recent Progress in Interface Engineering of Nanostructures for Photoelectrochemical Energy Harvesting Applications

With rapid and continuous consumption of nonrenewable energy, solar energy can be utilized to meet the energy requirement and mitigate environmental issues in the future. To attain a sustainable society with an energy mix predominately dependent on solar energy, photoelectrochemical (PEC) device, in which semiconductor nanostructure-based photocatalysts play important roles, is considered to be one of the most promising candidates to realize the sufficient utilization of solar energy in a low-cost, green, and environmentally friendly manner. Interface engineering of semiconductor nanostructures has been qualified in the efficient improvement of PEC performances including three basic steps, i.e., light absorption, charge transfer/separation, and surface catalytic reaction. In this review, recently developed interface engineering of semiconductor nanostructures for direct and high-efficiency conversion of sunlight into available forms (e.g., chemical fuels and electric power) are summarized in terms of their atomic constitution and morphology, electronic structure and promising potential for PEC applications. Extensive efforts toward the development of high-performance PEC applications (e.g., PEC water splitting, PEC photodetection, PEC catalysis, PEC degradation and PEC biosensors) are also presented and appraised. Last but not least, a brief summary and personal insights on the challenges and future directions in the community of next-generation PEC devices are also provided.

Phase-Controllable Growth of Air-Stable SnS Nanostructures for High-Performance Photodetectors with Ultralow Dark Current

The epitaxial growth of low-dimensional tin chalcogenides SnX (X = S, Se) with a controlled crystal phase is of particular interest since it can be utilized to tune optoelectronic properties and exploit potential applications. However, it still remains a great challenge to synthesize SnX nanostructures with the same composition but different crystal phases and morphologies. Herein, we report a phase-controlled growth of SnS nanostructures via physical vapor deposition on mica substrates. The phase transition from α-SnS (Pbnm) nanosheets to β-SnS (Cmcm) nanowires can be tailored by the reduction of growth temperature and precursor concentration, which originates from a delicate competition between SnS-mica interfacial coupling and phase cohesive energy. The phase transition from the α to β phase not only greatly improves the ambient stability of SnS nanostructures but also leads to the band gap reduction from 1.03 to 0.93 eV, which is responsible for fabricated β-SnS devices with an ultralow dark current of 21 pA at 1 V, an ultrafast response speed of ≤14 μs, and broadband spectra response from the visible to near-infrared range under ambient condition. A maximum detectivity of the β-SnS photodetector arrives at 2.01 × 108 Jones, which is about 1 or 2 orders of magnitude larger than that of α-SnS devices. This work provides a new strategy for the phase-controlled growth of SnX nanomaterials for the development of highly stable and high-performance optoelectronic devices.

Emerging Xene-Related Nanostructures for Versatile Applications

Investigations into semiconductor nanomaterials from both an academic and industrial point of view are of great significance [...].

Functional MXene-Based Materials for Next-Generation Rechargeable Batteries

MXenes are seen as an exceptional candidate to reshape the future of energy with their viable surface chemistry, ultrathin 2D structure, and excellent electronic conductivity. The extensive research efforts bring about rapid expansion of the MXene families with enriched functionalities, which significantly boost performance of the existing energy-storage devices. In this review, the strategies that are developed to functionalize the MXene-based materials, including tailoring their microstructure by ions/molecules/polymers-initiated interaction or self-assembly, surface/interface engineering with dopants or functional groups, constructing heterostructures from MXenes with various materials, and transforming them into a series of derivatives inheriting the merits of the MXene precursors are highlighted. Their applications in emerging battery technologies are demonstrated and discussed. With delicate functionalization and structural engineering, MXene-based electrode materials exhibit improved specific capacity and rate capability, and their presence further suppresses and even eliminates dendrite formation on the metal anodes, which lengthens the lifespan of the rechargeable batteries. Meanwhile, MXenes serve as additives for electrolytes, separators, and current collectors. Finally, some future directions worth of exploration to address the remaining challenging issues of MXene-based materials and achieve the next-generation high-power and low-cost rechargeable batteries are proposed.

Towards preventing exfoliation glaucoma by targeting and removing fibrillar aggregates associated with exfoliation syndrome

Exfoliation syndrome presents as an accumulation of insoluble fibrillar aggregates that commonly correlates with age and causes ocular complications, most notably open-angle glaucoma. Despite advances in understanding the pathogenesis and risk factors associated with exfoliation syndrome, there has been no significant progress in curative pharmacotherapy of this disease. It is thought that the ability to target the fibrillar aggregates associated with exfoliation may offer a new therapeutic approach, facilitating their direct removal from affected tissues. Phage display techniques yielded two peptides (LPSYNLHPHVPP, IPLLNPGSMQLS) that could differentiate between exfoliative and non-affected regions of the human lens capsule. These peptides were conjugated to magnetic particles using click chemistry to investigate their ability in targeting and removing exfoliation materials from the anterior human lens capsule. The behavior of the fibrillar materials upon binding to these magnetic particles was assessed using magnetic pins and rotating magnetic fields of various strengths. Ex vivo studies showed that the magnetic particle-peptide conjugates could generate enough mechanical force to remove large aggregates of exfoliation materials from the lens capsule when exposed to a low-frequency rotating magnetic field (5000 G, 20 Hz). Biocompatibility of targeting peptides with and without conjugated magnetic particles was confirmed using MTT cell toxicity assay, live/dead cell viability assay, and DNA fragmentation studies on primary cultured human trabecular meshwork cells. This is a novel, minimally invasive, therapeutic approach for the treatment of exfoliation glaucoma via the targeting and removal of exfoliation materials that could be applied to all tissues within the anterior segment of the eye.

Two-Dimensional Selenium Nanosheet-Based Sponges with Superior Hydrophobicity and Excellent Photothermal Performance

Photothermally assisted superhydrophobic materials play an important role in a variety of applications, such as oil purification, waste oil collection, and solar desalination, due to their facile fabrication, low-cost, flexibility, and tunable thermal conversion. However, the current widely used superhydrophobic sponges with photothermal properties are usually impaired by a high loading content of photothermal agents (e.g., gold or silver nanoparticles, carbon nanotubes), low photothermal efficiency, and require harmful processes for modification. Here, a one-pot, simple composite consisting of two-dimensional (2D) selenium (Se) nanosheets (NSs) and commercially used melamine sponge (MS) is rationally designed and successfully fabricated by a facile dip-coating method via physical adsorption between 2D Se NSs and MS. The loading content of 2D Se NSs on the skeleton of the MS can be well controlled by dipping cycle. The results demonstrate that after the modification of 2D Se NSs on the MS, the wettability transition from hydrophilicity to hydrophobicity can be easily achieved, even at a very low loading of 2D Se NSs, and the highly stable photothermal conversion of the as-fabricated composites can be realized with a maximum temperature of 111 ± 3.2 °C due to the excellent photothermal effect of 2D Se NSs. It is anticipated that this composite will afford new design strategies for multifunctional porous structures for versatile applications, such as high-performance solar desalination and photothermal sterilization.

Size-tunable bismuth quantum dots for self-powered photodetectors under ambient conditions

Although black phosphorus analogue, bismuthene, has been extensively investigated in recent years, yet the investigation into the photoelectronic devices is still in its infancy. In this contribution, uniform zero-dimensional (0D) bismuth (Bi) quantum dots (QDs) with different sizes were successfully synthesized by a simple solvothermal method. The as-synthesized 0D Bi QDs serve as working electrode materials by a direct deposition for photoelectrochemical (PEC)-type photodetection. The PEC results demonstrate that the as-fabricated 0D Bi QD-based electrode not only possess suitable self-powered broadband photoresponse, but also displays excellent photodetection performance. Under simulated light, the photocurrent density and photoresponsivity of the as-fabricated 0D Bi QD-based electrode can reach 2690 nA cm^-2, and 22.0μA W^-1, respectively. In addition, the as-prepared Bi QDs with the average diameter of 17 nm exhibit the best PEC photoresponse behavior in the studied size range of Bi QDs, mainly ascribed to the synergistic effect of suitable band gap and accessible active sites. It is anticipated that the uniform Bi QDs can be served as building blocks for a variety of photoelectronic devices, further expanding the application prospects of bismuthene, and can provide in-depth acknowledge on the performance optimization of monoelement Bi-based optical devices.

Infrared Light Emission Devices Based on Two-Dimensional Materials

Two-dimensional (2D) materials have garnered considerable attention due to their advantageous properties, including tunable bandgap, prominent carrier mobility, tunable response and absorption spectral band, and so forth. The above-mentioned properties ensure that 2D materials hold great promise for various high-performance infrared (IR) applications, such as night vision, remote sensing, surveillance, target acquisition, optical communication, etc. Thus, it is of great significance to acquire better insight into IR applications based on 2D materials. In this review, we summarize the recent progress of 2D materials in IR light emission device applications. First, we introduce the background and motivation of the review, then the 2D materials suitable for IR light emission are presented, followed by a comprehensive review of 2D-material-based spontaneous emission and laser applications. Finally, further development directions and challenges are summarized. We believe that milestone investigations of 2D-material-based IR light emission applications will emerge soon, which are beneficial for 2D-material-based nano-device commercialization.