Defects, band bending and ionization rings in MoS2

Chalcogen vacancies in transition metal dichalcogenides are widely acknowledged as both donor dopants and as a source of disorder. The electronic structure of sulphur vacancies in MoS2 however is still controversial, with discrepancies in the literature pertaining to the origin of the in-gap features observed via scanning tunneling spectroscopy (STS) on single sulphur vacancies. Here we use a combination of scanning tunnelling microscopy (STM) and STS to study embedded sulphur vacancies in bulk MoS2 crystals. We observe spectroscopic features dispersing in real space and in energy, which we interpret as tip position- and bias-dependent ionization of the sulphur vacancy donor due to tip induced band bending (TIBB). The observations indicate that care must be taken in interpreting defect spectra as reflecting in-gap density of states, and may explain discrepancies in the literature.Comment: 7 pages, 5 figure

Non-Drude THz conductivity of graphene due to structural distortions

The remarkable electrical, optical and mechanical properties of graphene make it a desirable material for electronics, optoelectronics and quantum applications. A fundamental understanding of the electrical conductivity of graphene across a wide frequency range is required for the development of such technologies. In this study, we use terahertz (THz) time-domain spectroscopy to measure the complex dynamic conductivity of electrostatically gated graphene, in a broad $\sim$0.1 - 7 THz frequency range. The conductivity of doped graphene follows the conventional Drude model, and is predominantly governed by intraband processes. In contrast, undoped charge-neutral graphene exhibits a THz conductivity that significantly deviates from Drude-type models. Via quantum kinetic equations and density matrix theory, we show that this discrepancy can be explained by additional interband processes, that can be exacerbated by electron backscattering. We propose a mechanism where such backscattering -- which involves flipping of the electron pseudo-spin -- is mediated by the substantial vector scattering potentials that are associated with structural deformations of graphene. Our findings highlight the significant impact that structural distortions and resulting electrostatic vector scattering potentials can have on the THz conductivity of charge-neutral graphene. Our results emphasise the importance of the planar morphology of graphene for its broadband THz electronic response.Comment: 74 pages, 21 figure

Analysis of HCV Isolates Among the Li Ethnic in Hainan Island of South China Reveals Their HCV-6 Unique Evolution and a New Subtype

Background/Aims: Hainan Island has been inhabited by the “Li” aboriginal minority for centuries where the HCV genotype distribution patterns maybe remarkably different from other parts of China. We aimed to provide a better understanding of the infection with HCV genotype 6 among “Li” aboriginals on Hainan Island. Methods: Firstly, using RT-PCR and DNA sequencing to determined 517 partial HCV Core-E1(115 from Li Ethnic, 402 from Han Ethnic) and 8 full-length genomes from Li ethnic in Hainan Island successfully, and then using the phylogenetic tree to determine the HCV genotype distribution and analyze the evolution of them. Results: Phylogenetic tree analysis showed that the distribution pattern of HCV genotypes among the Han and Li ethnic population exhibits significant diferences: 6a was the most prevalent subtype in Han ethnic of Hainan Island followed by 1b, 3b, 2a, 3a, and 1a. All genomes from Li ethnic were classified into genotype 6, while 84 out of 115 (73%) could not be classified. Nine sequences (HN1350 et al.) from Li ethnic might be assigned to a new subtype 6xh as their p-distances ranged from 5.9∼9.7%. Furthermore, we sequenced and characterized full-length genomes for eight HCV-6 isolates which were all from Li ethnic in Hainan Island. Among these isolates, the HN1350 was classified as a new subtype: 6xh. Conclusion: Overall, we firstly defined a new subtype of genotype 6xh through partial and new full length genome. And we found a unique distribution pattern of HCV 6 in the Li tribe, which might provide a better way to understand the genetic diversity of HCV-6 and to investigate the phylogeny of HCV strains from Li tribe

Proceedings of the 29th EG-ICE International Workshop on Intelligent Computing in Engineering

This publication is the Proceedings of the 29th EG-ICE International Workshop on Intelligent Computing in Engineering from July 6-8, 2022. The EG-ICE International Workshop on Intelligent Computing in Engineering brings together international experts working on the interface between advanced computing and modern engineering challenges. Many engineering tasks require open-world resolution of challenges such as supporting multi-actor collaboration, coping with approximate models, providing effective engineer-computer interaction, search in multi-dimensional solution spaces, accommodating uncertainty, including specialist domain knowledge, performing sensor-data interpretation and dealing with incomplete knowledge. While results from computer science provide much initial support for resolution, adaptation is unavoidable and most importantly, feedback from addressing engineering challenges drives fundamental computer-science research. Competence and knowledge transfer goes both ways. &nbsp

Proceedings of the 29th EG-ICE International Workshop on Intelligent Computing in Engineering

This publication is the Proceedings of the 29th EG-ICE International Workshop on Intelligent Computing in Engineering from July 6-8, 2022. The EG-ICE International Workshop on Intelligent Computing in Engineering brings together international experts working on the interface between advanced computing and modern engineering challenges. Many engineering tasks require open-world resolution of challenges such as supporting multi-actor collaboration, coping with approximate models, providing effective engineer-computer interaction, search in multi-dimensional solution spaces, accommodating uncertainty, including specialist domain knowledge, performing sensor-data interpretation and dealing with incomplete knowledge. While results from computer science provide much initial support for resolution, adaptation is unavoidable and most importantly, feedback from addressing engineering challenges drives fundamental computer-science research. Competence and knowledge transfer goes both ways. &nbsp

A measurable refinement method of design and verification for micro-kernel operating systems in communication network

A secure operating system in the communication network can provide the stable working environment, which ensures that the user information is not stolen. The micro-kernel operating system in the communication network retains the core functions in the kernel, and unnecessary tasks are implemented by calling external processes. Due to the small amount of code, the micro-kernel architecture has high reliability and scalability. Taking the micro-kernel operating system in the communication network prototype VSOS as an example, we employ the objdump tool to disassemble the system source code and get the assembly layer code. On this basis, we apply the Isabelle/HOL, a formal verification tool, to model the system prototype. By referring to the mathematical model of finite automata and taking the process scheduling module as an example, the security verification based on the assembly language layer is developed. Based on the Hoare logic theory, each assembly statement of the module is verified in turn. The verification results show that the scheduling module of VSOS has good functional security, and also show the feasibility of the refinement framework

Highly Sensitive NO2 Gas Sensors Based on MoS2@MoO3 Magnetic Heterostructure

Recently, two-dimensional (2D) materials and their heterostructures have attracted con-siderable attention in gas sensing applications. In this work, we synthesized 2D MoS2-MoO3 heter-ostructures through post-sulfurization of α-MoO3 nanoribbons grown via vapor phase transport (VPT) and demonstrated highly sensitive NO2 gas sensors based on the hybrid heterostructures. The morphological, structural, and compositional properties of the MoS2-MoO3 hybrids were studied by a combination of advanced characterization techniques revealing a core-shell structure with the coexistence of 2H-MoS2 multilayers and intermediate molybdenum oxysulfides on the surface of α-MoO3. The MoS2@MoO3 hybrids also exhibit room-temperature ferromagnetism, revealed by vibrat-ing sample magnetometry (VSM), as a result of the sulfurization process. The MoS2@MoO3 gas sensors display a p-type-like response towards NO2 with a detection limit of 0.15 ppm at a working temperature of 125 °C, as well as superb selectivity and reversibility. This p-type-like sensing behavior is attributed to the heterointerface of MoS2-MoO3 where interfacial charge transfer leads to a p-type inversion layer in MoS2, and is enhanced by magnetic dipole interactions between the para-magnetic NO2 and the ferromagnetic sensing layer. Our study demonstrates the promising application of 2D molybdenum hybrid compounds in gas sensing applications with a unique combination of electronic and magnetic properties.</p

A DFT study of the surface charge transfer doping of diamond by chromium trioxide

In this study, a density functional theory method is employed to investigate the surface charge transfer doping of diamond by chromium trioxide (CrO3) with high electron affinity. Superior surface charge transfer of the hydrogenated diamond surface is demonstrated using CrO3 as an electron acceptor. The charge density difference and Bader charge analysis reveal that the electrons are transferred from the diamond surface to CrO3 molecule, leading to the formation of two-dimensional hole gas, and the holes left in the diamond surface increase the conductivity of the diamond surface. The analysis of electronic structure indicates that areal hole density as large as 9.85 × 1013cm−2 for CrO3-doped diamond surface can be achieved. Besides, the optical absorption near infrared region of the hydrogenated diamond surface is greatly enhanced upon CrO3 doping, which implies that this CrO3-doped diamond surface is a promising candidate for optoelectronic materials. The present study provides an in-depth theoretical understanding of the formation of two-dimensional hole gas on diamond surface induced by a new transition metal oxide, and predicts that the CrO3-doped diamond surface may have important implications in electronic and optoelectronic devices

Large-sized α-MoO3 layered single crystals for superior NO2 gas sensing

Molybdenum trioxide (MoO3) has attracted considerable research interest due to its unique structural and electronic properties. Herein, we report a monolithic and scalable NO2 gas sensor based on centimeter-sized single-crystalline α-MoO3 synthesized via vapor phase transport method. A combination of advanced characterization probes were utilized to study morphology, composition and crystalline structures of the as-synthesized crystals. At the optimal operating temperature of 100 °C, the centimeter-sized α-MoO3 single crystal based sensor shows an outstanding sensitivity towards NO2 with a limit of detection as low as 5 ppb, as well as superior selectivity and reversibility. The scalability and the intrinsic sensing response are further demonstrated by microscale sensor devices fabricated on individual exfoliated α-MoO3 nanoribbons. Our study presents promising opportunities to develop a high-performance gas sensing platform based on crystalline α-MoO3 to enable monolithic, scalable and integrable sensing technologies.</p

Is charge-transfer doping possible at the interfaces of monolayer VSe2 with MoO3 and K?

Being a metallic transition-metal dichalcogenide, monolayer vanadium diselenide (VSe2) exhibits many novel properties, such as charge density waves and magnetism. Its interfaces with other materials can potentially be used in device applications as well as for manipulating its intrinsic properties. Here, we present a scanning tunneling microscopy and synchrotron-based X-ray photoemission spectroscopy study of the surface charge-transfer doping using efficient electron-withdrawing and electron-donating materials, that is, molybdenum trioxide (MoO3) and potassium (K), on the molecular beam epitaxy-grown monolayer VSe2 on highly oriented pyrolytic graphite (HOPG). We demonstrate that monolayer VSe2 is immune to MoO3- and K-doping effects. However, at the monolayer edges where the local chemical reactivity is higher because of Se deficiency, MoO3 is seen to react with VSe2 to form molybdenum dioxide (MoO2) and vanadium dioxide (VO2). Compared to the obvious charge-transfer doping effects of MoO3 and K on HOPG, the electronic structure of monolayer VSe2 is barely perturbed. This is attributed to the large density of states at the Fermi level of monolayer VSe2 carrying the metallic character. This work provides new insights into the chemical and electronic properties of monolayer VSe2, important for future VSe2-based electronic device design.</p