Synthetic two-dimensional (2D) materials have no bulk counterparts and typically exist as single atomic layers due to substrate-stabilized growth. Multilayer formation, although broadly sought for ...structure and property tuning, has not yet been achieved in the case of synthetic 2D boron: that is, borophene
. Here, we experimentally demonstrate the synthesis of an atomically well-defined borophene polymorph beyond the single-atomic-layer (SL) limit. The structure of this bilayer (BL) borophene is consistent with two covalently bonded α-phase layers (termed BL-α borophene) as evidenced from bond-resolved scanning tunnelling microscopy, non-contact atomic force microscopy and density functional theory calculations. While the electronic density of states near the Fermi level of BL-α borophene is similar to SL borophene polymorphs, field-emission resonance spectroscopy reveals distinct interfacial charge transfer doping and a heightened local work function exceeding 5 eV. The extension of borophene polymorphs beyond the SL limit significantly expands the phase space for boron-based nanomaterials.
Research on in‐plane and vertically‐stacked heterostructures of graphene and hexagonal boron nitride (h‐BN) have attracted intense attentions for energy band engineering and device performance ...optimization of graphene. In this review article, recent advances in the controlled syntheses, interfacial structures, and electronic properties, as well as novel device constructions of h‐BN and graphene heterostructures are highlighted. Firstly, diverse synthesis approaches for in‐plane h‐BN and graphene (h‐BN‐G) heterostructures are reviewed, and their applications in nanoelectronics are briefly introduced. Moreover, the interfacial structures and electronic properties of h‐BN‐G heterojunctions are discussed, and a zigzag type interface is found to preferentially evolve at the linking edge of the two structural analogues. Secondly, several synthetic routes for the vertically‐stacked graphene/h‐BN (G/h‐BN) heterostructures are also reviewed. The role of h‐BN as perfect dielectric layers in promoting the device performance of graphene is presented. Finally, future research directions in the synthesis and application of such heterostructures are discussed.
In‐plane and vertically stacked heterostructures of graphene and hexagonal boron nitride have attracted intense attention for energy band engineering and device performance optimization of graphene. The synthesis and interfacial properties of both in‐plane (h‐BN‐G) and vertically stacked (G/h‐BN) heterostructures, which should evoke further investigations of the related novel properties, as well as their versatile applications in various aspects, are discussed.
Synthetic two-dimensional polymorphs of boron, or borophene, have attracted attention because of their anisotropic metallicity, correlated-electron phenomena, and diverse superlattice structures. ...Although borophene heterostructures have been realized, ordered chemical modification of borophene has not yet been reported. Here, we synthesize "borophane" polymorphs by hydrogenating borophene with atomic hydrogen in ultrahigh vacuum. Through atomic-scale imaging, spectroscopy, and first-principles calculations, the most prevalent borophane polymorph is shown to possess a combination of two-center-two-electron boron-hydrogen and three-center-two-electron boron-hydrogen-boron bonds. Borophane polymorphs are metallic with modified local work functions and can be reversibly returned to pristine borophene through thermal desorption of hydrogen. Hydrogenation also provides chemical passivation because borophane reduces oxidation rates by more than two orders of magnitude after ambient exposure.
The purpose of this study is to examine the relationship between renewable energy sources and economic growth of the South Asian Association for regional cooperation (SAARC) countries. This study ...uses three main renewable energy sources, namely geothermal, hydro, and wind.This study collects data set from SAARC countries from 1995 to 2018 and applies a fixed effect test and panel vector error correction model (PVECM) for data analysis. The overall results show that all three renewable energy sources have a positive significant impact on economic development among SAARC countries’ economies. Moreover, hydropower renewable energy has more effects and influences on economic growth as compared to the other two individual sources of renewable energy.
The reproduction of social relationships in a rural tourism destination is examined through a micro-sociological lens that explores residents’ everyday interactions. Interaction ritual theory is ...adopted as the theoretical foundation. Zhinan, a mountainous village in Hangzhou, China, which initiated tourism in 2014, is the study site. Two rounds of focus groups and interviews were conducted with village residents. Qualitative inquiry shows that, under the influence of tourism, residents’ daily interactions consist of three interaction rituals, that is, rural living rituals, tourism operation rituals, and event and festival rituals. Due to the distinct ingredients, these rituals unfold differentially and engage different social actors. They complement each other in the co-construction of rural social relationships that have symbolic, emotional, collective, and normative connotations. This study provides in-depth, contextualized understandings of rural residents’ interactions and relationships, and draws practical implications for sustainable development of rural tourism destinations.
Mass production of graphene powders affording high quality and environmental benignancy serves as a prerequisite for the practical usage of graphene in multiple energy storage applications. Herein, ...we exploit a salt-templated CVD approach to harness the direct synthesis of nitrogen-doped graphene (NG) nanosheets and related ink dispersions in a scalable, safe, efficient, and green fashion. Thus-fabricated NG accompanying large productivity, excellent electrical conductivity, and favorable solution processability possesses implications in printable energy storage devices. With the NG-based ink in hand, self-standing 3D architectures with programmable patterns can be directly printed over a myriad of substrates. Accordingly, both electrode preparation for flexible supercapacitors and separator modification in Li–S batteries can be enabled via printing by employing our NG-based composite inks. This work thus represents a practical route for mass production of graphene inks with cost-effectiveness and eco-friendliness for emerging energy storage technology.
Graphene/hexagonal boron nitride (h-BN) vertical heterostructures have recently revealed unusual physical properties and new phenomena, such as commensurate-incommensurate transition and fractional ...quantum hall states featured with Hofstadter's butterfly. Graphene-based devices on h-BN substrate also exhibit high performance owing to the atomically flat surface of h-BN and its lack of charged impurities. To have a clean interface between the graphene and h-BN for better device performance, direct growth of large-area graphene/h-BN heterostructures is of great importance. Here we report the direct growth of large-area graphene/h-BN vertical heterostructures by a co-segregation method. By one-step annealing sandwiched growth substrates (Ni(C)/(B, N)-source/Ni) in vacuum, wafer-scale graphene/h-BN films can be directly formed on the metal surface. The as-grown vertically stacked graphene/h-BN structures are demonstrated by various morphology and spectroscopic characterizations. This co-segregation approach opens up a new pathway for large-batch production of graphene/h-BN heterostructures and would also be extended to the synthesis of other van der Waals heterostructures.
Graphitic nitrogen-doped graphene is an excellent platform to study scattering processes of massless Dirac Fermions by charged impurities, in which high mobility can be preserved due to the absence ...of lattice defects through direct substitution of carbon atoms in the graphene lattice by nitrogen atoms. In this work, we report on electrical and magnetotransport measurements of high-quality graphitic nitrogen-doped graphene. We show that the substitutional nitrogen dopants in graphene introduce atomically sharp scatters for electrons but long-range Coulomb scatters for holes and, thus, graphitic nitrogen-doped graphene exhibits clear electron–hole asymmetry in transport properties. Dominant scattering processes of charge carriers in graphitic nitrogen-doped graphene are analyzed. It is shown that the electron–hole asymmetry originates from a distinct difference in intervalley scattering of electrons and holes. We have also carried out the magnetotransport measurements of graphitic nitrogen-doped graphene at different temperatures and the temperature dependences of intervalley scattering, intravalley scattering, and phase coherent scattering rates are extracted and discussed. Our results provide an evidence for the electron–hole asymmetry in the intervalley scattering induced by substitutional nitrogen dopants in graphene and shine a light on versatile and potential applications of graphitic nitrogen-doped graphene in electronic and valleytronic devices.
Small tourism firms (STFs) established and operated by local families can be an engine of sustainable rural tourism. This paper stresses the intimate intertwining of family and business in rural STFs ...and conceptualizes their entrepreneurial success as a combination of business performance and family well-being. Integrating the resource-based view and network embeddedness theory, relationships among the STF owners’ dual social networks (family and industry networks), entrepreneurial resource acquisition, and entrepreneurial success are proposed and tested with a sample of 276 STFs in rural China. The empirical analyses reveal that (1) compared with tangible and knowledge-based resources, the owners’ acquisition of psychic resources has the strongest effect on entrepreneurial success; and (2) although industry networks provide more diverse access to entrepreneurial resources, family networks are superior in facilitating psychic resource acquisition, thus are especially important to the entrepreneurial success of rural STFs. Theoretical and practical implications are discussed.
Two dimensional (2D) materials-based plasmon-free surface-enhanced Raman scattering (SERS) is an emerging field in nondestructive analysis. However, impeded by the low density of state (DOS), an ...inferior detection sensitivity is frequently encountered due to the low enhancement factor of most 2D materials. Metallic transition-metal dichalcogenides (TMDs) could be ideal plasmon-free SERS substrates because of their abundant DOS near the Fermi level. However, the absence of controllable synthesis of metallic 2D TMDs has hindered their study as SERS substrates. Here, we realize controllable synthesis of ultrathin metallic 2D niobium disulfide (NbS2) (<2.5 nm) with large domain size (>160 μm). We have explored the SERS performance of as-obtained NbS2, which shows a detection limit down to 10–14 mol·L–1. The enhancement mechanism was studied in depth by density functional theory, which suggested a strong correlation between the SERS performance and DOS near the Fermi level. NbS2 features the most abundant DOS and strongest binding energy with probe molecules as compared with other 2D materials such as graphene, 1T-phase MoS2, and 2H-phase MoS2. The large DOS increases the intermolecular charge transfer probability and thus induces prominent Raman enhancement. To extend the results to practical applications, the resulting NbS2-based plasmon-free SERS substrates were applied for distinguishing different types of red wines.
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