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[Display omitted] Two-dimensional (2D) van der Waals (vdW) heterostructures offer new platforms for exploring novel physics and diverse applications ranging from electronics and photonics to optoelectronics at the nanoscale. The studies to date have largely focused on transition-metal dichalcogenides (TMDCs) based samples prepared by mechanical exfoliation method, therefore it is of significant interests to study high-quality vdW heterostructures using novel materials prepared by a versatile method. Here, we report a two-step vapor phase growth process for the creation of high-quality vdW heterostructures based on perovskites and TMDCs, such as 2D Cs 3 Bi 2 I 9 /MoSe 2 , with a large lattice mismatch. Supported by experimental and theoretical investigations, we discover that the Cs 3 Bi 2 I 9 /MoSe 2 vdW heterostructure possesses hybrid band alignments consisting of type-I and type-II heterojunctions because of the existence of defect energy levels in Cs 3 Bi 2 I 9. More importantly, we demonstrate that the type-II heterojunction in the Cs 3 Bi 2 I 9 /MoSe 2 vdW heterostructure not only shows a higher interlayer exciton density, but also exhibits a longer interlayer exciton lifetime than traditional 2D TMDCs based type-II heterostructures. We attribute this phenomenon to the reduced overlap of electron and hole wavefunctions caused by the large lattice mismatch. Our work demonstrates that it is possible to directly grow high-quality vdW heterostructures based on entirely different materials which provide promising platforms for exploring novel physics and cutting-edge applications, such as optoelectronics, valleytronics, and high-temperature superfluidity. [ABSTRACT FROM AUTHOR]

[Display omitted] Vacancy engineering of 2H-transition metal dichalcogenides (2H-TMDs) has recently attracted great attention due to its potential to fine-tune the phonon and opto-electric properties of these materials. From a mechanical perspective, this symmetry-breaking process typically reduces the overall crack resistance of the material and adversely affects its reliability. However, vacancies can trigger the formation of heterogeneous phases that synergistically improve fracture properties. In this study, using MoSe 2 as an example, we characterize the types and density of vacancies that can emerge under electron irradiation and quantify their effect on fracture. Molecular dynamic (MD) simulations, employing a re-parameterized Tersoff potential capable of accurately capturing bond dissociation and structural phase changes, reveal that isolated transition metal monovacancies or chalcogenide divacancies tend to arrest the crack tip and hence enhance the monolayer toughness. In contrast, isolated chalcogenide monovacancies do not significantly affect toughness. The investigation further reveals that selenium vacancy lines, formed by high electron dose rates, alter the crack propagating direction and lead to multiple crack kinking. Using atomic displacements and virial stresses together with a continuum mapping, displacement, strain, and stress fields are computed to extract mechanistic information, e.g., conditions for crack kinking and size effects in fracture events. The study also reveals the potential of specific defect patterns, "vacancy engineering," to improve the toughness of 2H-TMDs materials. [ABSTRACT FROM AUTHOR]

Different aspects of CO 2 capture addressed in this review. [Display omitted] The separation and sequestration of anthropogenic CO 2 is one of the most effective steps to counter global warming by curtailing the excess CO 2 levels in the atmosphere. However, to achieve the global climate change targets, in addition to the capture of CO 2 from the point sources, complementary carbon-negative technologies that capture CO 2 directly from the atmosphere are also necessary. The most crucial aspect of any CO 2 capture technology is the selection of a suitable sorbent, which is the most efficient in a specific temperature, pressure, and moisture range. The urgent nature of the CO 2 crisis has led to overwhelming contributions from researchers globally in terms of different sorbents, measurement techniques, reactors, and processes. Additionally, to develop a commercially viable CO 2 capture technology, a detailed and holistic techno-economic analysis is also vital. In this review, we have documented the recent progress on CO 2 capture studies using different solid sorbents under various operational conditions, along with the methodologies and reactors used for these studies. Furthermore, this review presents a detailed account of the industrial status of various existing CO 2 capture technologies, including direct air capture and its techno-economic prospects. This review aims to provide a bird's eye view of the status of CO 2 capture research with a particular emphasis on the most recent developments in this field. [ABSTRACT FROM AUTHOR]

[Display omitted] Reliable transfer processes that enable manipulation of two-dimensional (2D) materials, e.g., transition metal dichalcogenides (TMDCs) and MXenes, from one substrate to another has been a necessity for successful device fabrication. With both mechanical exfoliation and chemical vapor deposition (CVD) widely used, a versatile, clean, deterministic, and yet simple transfer technique is highly needed. To address such need, we developed a transfer method that takes advantage of wettability contrast between interfaces without the use of sacrificial layers or chemical processes. More importantly, a setup was developed to carry out this transfer method with high sample selectivity and fine control of the position and orientation of transferred TMDC crystals, a feature required for fabrication of the devices based on vertical 2D heterostructures. Using both exfoliated and CVD grown materials and subsequent atomic force microscopy (AFM), photoluminescence (PL), confocal Raman and tip enhanced Raman spectroscopy (TERS) characterization, we ascertained the quality of interfaces resulting from the transfer process while preserving excellent 2D material integrity. PL and TERS maps revealed nanometer-scale heterogeneities in the interfaces of fabricated heterostructures, which should enable further perfection of the transfer technique. TERS/TEPL information were employed to identify areas suitable for nanodevice fabrication, making the reported transfer and characterization methods ideal for making high quality assembly of 2D heterostructure more accessible, which should facilitate exploration of vertical 2D heterostructures for applications in electronics, batteries, solar cells, and twistronics. [ABSTRACT FROM AUTHOR]

[Display omitted] Two-dimensional (2D) materials are at the forefront of current materials research due to their exciting and unique properties. 2D tellurides are emerging materials which are yet to be fully explored. To provide an overview of this emergent field, in this review, we discuss the structure, properties, synthesis methods, and applications of selected 2D tellurides, with stoichiometry of M x Te y , and M x N y Te z , (M, N are metal atoms). We present a summary of the latest advances in modeling, experimental synthesis, and characterization of 2D tellurides. Additionally, stress and strain-induced tunability of the physical properties have been reviewed, with a focus on the application of 2D tellurides in electronic, optoelectronic, and magnetic devices. We have discussed many emergent quantum properties of these materials. Finally, we conclude with a perspective on the future of 2D metal tellurides. [ABSTRACT FROM AUTHOR]

Monoelemental two-dimensional (2D) materials has attracted significant attention due to their exciting electro-mechanical properties and extreme thinness. Here we report the existence of piezoelectricity in atomically thin monoelemental α-Tellurium films. Theoretical and experimental exploration demonstrate the existence of through thickness piezoelectricity due to the Born effective charges, similar to traditional perovskite piezoelectric structures. [Display omitted] Monoelemental two-dimensional (2D) materials have attracted significant attention due to their exciting electro-mechanical properties and extreme thinness. However, most of these materials have stable centro-symmetric structures due to same electronegativities of all atoms and lack interesting properties such as piezoelectricity and ferroelectricity. Here we report the existence of piezoelectricity in atomically thin monoelemental α-Tellurium films. DFT calculations reveal that monoelemental few layer α-Tellurene is electrostrictive. However, group theory analysis shows that α-Tellurene belongs to piezoelectric C2 group due to negligible asymmetry and has high anomalous Born effective charges, similar to the traditional perovskite piezoelectric structures. Experimental exploration demonstrates the existence of through thickness piezoelectricity. With single and dual AC resonance tracking piezoelectric force microscopy, piezoelectric coefficient (d 33) up to 1 pm/V is observed for the Te ultrathin films. Moderate layer dependent piezoelectricity observed in α-Te films makes it a promising candidate for the realization of atomically thin piezoelectric devices. [ABSTRACT FROM AUTHOR]

Interfaces are often crucial determinants of the physicochemical properties of a material. As a result, the rational production and engineering of heterogeneities, and the resulting interfaces, can enhance the functionality of a material system. This is especially true of two dimensional (2D) materials, which are only a few atoms thick and thus sensitive to small perturbations of their surroundings. As a result, 2D materials and their heterostructures have been recently modified to function as catalysts, photodetectors, chemical sensors, memory, logic devices, single photon emitters, and more. In this review, we summarize the current understanding of functional interfaces in few-layered chalcogenide 2D systems, and address the following topics: The classification of interfaces by dimensionality and electronic structure, methods of creating 2D interfaces, characterization techniques and related challenges, applications of interfacial engineering in 2D systems, and finally a perspective on the future of this rapidly advancing field of study. [ABSTRACT FROM AUTHOR]

Efficient exfoliation of layered materials has attracted considerable attention in various applications due to their superior photoelectric, physical and chemical properties. Here, we report a universal, rapid approach to prepare the two-dimensional (2D) nanosheets and zero-dimensional (0D) quantum dots (QDs) using a simple cryo-mediation liquid phase exfoliation of layered materials (graphite, MoS 2 , WS 2). The QDs decorated nanosheets 0D/2D homostructure can be subsequently formed by the self-assembly of the as-exfoliated QDs and nanosheets. The unique structural properties of the mono- or few-layer mesoporous nanosheets interspersed with QDs can expose abundant active edge sites as well as improve the conductivity, which exhibits excellent activity and stability towards electrocatalytic hydrogen evolution reaction (HER). This work offers a powerful methodology to prepare 2D homostructures from a variety of layered materials. [ABSTRACT FROM AUTHOR]

The emerging non-noble metal two-dimensional (2D) catalyst, such as MoS 2 , for the hydrogen evolution reaction (HER) is known to have an inert basal plane unless being converted to a metastable metallic phase or defect engineered. In order to take advantage of the majority of the material in such layered catalysts, fast screening of 2D catalysts with superior basal plane activity is imperative. A local electrochemical measurement method assisted by the e-beam lithography patterning was developed and applied to quantify the activity of basal planes of different layered transition metal dichalcogenides (TMDs) toward HER. This local measurement offers a robust platform to discover active TMDs fast and precisely. The construction of HER volcano plot leads to the discovery of superior basal plane active group VB metal disulfides, especially 3R-NbS 2. Interestingly, the trends found in the volcano plot imply distinctive differences in the mechanism of TMD catalysts compared to their metal counterparts. The intensive hydrogen evolution reaction in-between the basal planes drives self-nanostructuring in morphology of 3R-NbS 2. The increase in the effective surface area, and decrease in the electron-transfer resistance across the substrate and basal plane interface induced by the self-nanostructuring in turn enhances the HER performance of 3R-NbS 2. The 3R-NbS 2 clearly stands out among non-noble metal catalysts for HER. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Although quantum dots (QDs) based on two dimensional (2D) materials have manifested fascinating properties and promising applications in a wide range of fields, a low cost and non-tedious approach for the preparation of atomically thick 2D QDs with high yield remains elusive. Herein, for the first time, we demonstrate a reflux pretreatment-mediated sonication approach to produce a series of ultrathin 2D QDs (e.g., graphene, TiS 2 , MoS 2 , MoSe 2 , WSe 2 , NbS 2 , SnS 2 , and h-BN QDs) from their bulk counterparts. The solvent molecules, confined in the channels of layered materials during reflux, assist the delamination and fracture of 2D sheets in the process of bath sonication. The resulting 2D QDs exhibited uniform lateral size distribution of 2–7 nm and a mean thickness of 0.8–1 nm, almost identical to the monolayer thickness of layered materials. To demonstrate the unique property of these 2D QDs, the optical limiting activity was studied using open aperture z-scan technique. TiS 2 QDs exhibited appreciable nonlinear optical limiting, reaching 50% by a tapered and sharp absorption at input laser fluence of 4.24 GW/cm2. [ABSTRACT FROM AUTHOR]

Biological materials are multifunctional performing more than one function in a perfect synergy. These materials are built from fairly simple and limited components at ambient conditions. Such judicious designs have proven elusive for synthetic materials. Here, we demonstrate a multifunctional phase change ( pc ) composite from simple building blocks, which exhibits high stiffness and optical transmittance control. We show an increase of more than one order of magnitude in stiffness when we embed paraffin wax spheres into an elastomer matrix, polydimethylsiloxane (PDMS) in a dynamic compression test. High stiffness is mainly influenced by presence of microcrystals within the wax. We further show fast temperature-controlled optical switching of the composite for an unlimited number of cycles without any noticeable mechanical degradation. Through experimental and finite element method, we show high energy absorption capability of pc-composite . Based on these properties, the pc-composite could be used as an effective coating on glasses for cars and windows. This simple approach to multi-functionality is exciting and could pave way for designs of other multifunctional materials at the macro-scale. [ABSTRACT FROM AUTHOR]

Chronic diseases are becoming more prevalent, and the complexities of managing patients continue to escalate, since their care must be balanced between the home and clinical settings. Diabetes is the most advanced example, where self-monitoring has been shown to be necessary. Glucometers are point-of-care (POC) devices that have become standard platforms at home and clinical settings. Similarly, many other POC biosensors have also been developed. Enzymes are often used in these sensors because of their specificity and the reaction products can be electrochemically transduced for the measurement. When enzymes are immobilized to an electronically active substrate, enzymatic reactions can be transduced by direct electron transport. This paper describes an approach for the development of graphene-based POC devices. This includes modifying enzymes for improved performance, developing methods to bind them to the graphene surface, incorporation of the functionalized graphene on a field-effect transistor (FET), and integration into a microfluidic device suitable for home use. This paper describes an approach for the development of a graphene-based POC biosensor platform using glucose as an example of target molecule. [ABSTRACT FROM AUTHOR]