Hot electron effects and electric field scaling near the metal-insulator transition in multilayer MoS2

The layered transition metal dichalcogenides have emerged as valuable platforms to study the challenging problem of metal-insulator transition in two dimensions. It was demonstrated that multilayer MoS2 exhibits clearly distinctive metallic and insulating behaviors in conductivity in response to both temperature and the electric field. Here, we report on the scaling analyses of conductivity for the electric field in addition to the temperature, which is performed with the consideration of electron-electron interactions for multilayer MoS2. Based on the analysis of hot electron effects in the electric field, we find that scaling for the electric field is relevant for the metallic phase in the high-field regime, enabling one to extract the dynamical critical exponent z close to 1. This result supports that the metal-insulator transition in multilayer MoS2 is a true quantum critical phenomenon, in which strong interactions induce the transition. ©2020 American Physical Society11sciescopu

Infrared phases of 3D class R theories

We study the IR phases of 3D class R theories associated with closed non-hyperbolic 3-manifolds. Non-hyperbolic 3-manifolds can be obtained by performing Dehn fillings on 1-cusped hyperbolic 3-manifolds along exceptional slopes. In 3D-3D correspondence, the ‘exceptional’ Dehn filling corresponds to the gauging of an SU(2) flavor symmetry in a superconformal field theory associated with a 1-cusped 3-manifold with ‘small’ Chern-Simons levels. With several explicit examples, we analyze various interesting non-perturbative IR phenomena (such as spontaneous SUSY breaking, generation of mass gap and supersymmetry enhancement) from the ‘exceptional’ gaugings. Interestingly, distinguished features of the IR phases can be captured by simple topological properties of non-hyperbolic 3-manifolds. We also find that 3D class R theories associated with certain classes of atoroidal non-hyperbolic 3-manifolds always exhibit supersymmetry enhancement at low energy and actually flow to 3D rank-0 N= 4 SCFTs with trivial vacuum moduli space

Scalable Production of Highly-Sensitive Nanosensors Based on Graphene Functionalized with a Designed G Protein-Coupled Receptor

We have developed a novel, all-electronic biosensor for opioids that consists of an engineered mu opioid receptor protein, with high binding affinity for opioids, chemically bonded to a graphene field-effect transistor to read out ligand binding. A variant of the receptor protein that provided chemical recognition was computationally redesigned to enhance its solubility and stability in an aqueous environment. A shadow mask process was developed to fabricate arrays of hundreds of graphene transistors with average mobility of ~1500 cm2 V-1 s-1 and yield exceeding 98%. The biosensor exhibits high sensitivity and selectivity for the target naltrexone, an opioid receptor antagonist, with a detection limit of 10 pg/mL.Comment: Nano Letters 201

Misorientation-angle-dependent electrical transport across molybdenum disulfide grain boundaries

Grain boundaries in monolayer transition metal dichalcogenides have unique atomic defect structures and band dispersion relations that depend on the inter-domain misorientation angle. Here, we explore misorientation angle-dependent electrical transport at grain boundaries in monolayer MoS2 by correlating the atomic defect structures of measured devices analysed with transmission electron microscopy and first-principles calculations. Transmission electron microscopy indicates that grain boundaries are primarily composed of 5–7 dislocation cores with periodicity and additional complex defects formed at high angles, obeying the classical low-angle theory for angles <22°. The inter-domain mobility is minimized for angles <9° and increases nonlinearly by two orders of magnitude before saturating at ∼16 cm2 V−1 s−1 around misorientation angle≈20°. This trend is explained via grain-boundary electrostatic barriers estimated from density functional calculations and experimental tunnelling barrier heights, which are ≈0.5 eV at low angles and ≈0.15 eV at high angles (≥20°)

New insight into the material parameter B to understand the enhanced thermoelectric performance of Mg2Sn1−x−yGexSby

Historically, a material parameter B incorporating weighted mobility and lattice thermal conductivity has guided the exploration of novel thermoelectric materials. However, the conventional definition of B neglects the bipolar effect which can dramatically change the thermoelectric energy conversion efficiency at high temperatures. In this paper, a generalized material parameter B* is derived, which connects weighted mobility, lattice thermal conductivity, and the band gap. Based on the new parameter B*, we explain the successful tuning of the electron and phonon transport in Mg[subscript 2]S[subscript n1−x−y]Ge[subscript x]Sb[subscript y], with an improved ZT value from 0.6 in Mg[subscript 2]Sn[subscript 0.99]Sb[subscript 0.01] to 1.4 in Mg[subscript 2]Sn[subscript 0.73]Ge[subscript 0.25]Sb[subscript 0.02]. We uncover that the Ge alloying approach simultaneously improves all the key variables in the material parameter B*, with an ∼25% enhancement in the weighted mobility, ∼27% band gap widening, and ∼50% reduction in the lattice thermal conductivity. We show that a higher generalized parameter B* leads to a higher optimized ZT in Mg[subscript 2]Sn[subscript 0.73]Ge[subscript 0.25]Sb[subscript 0.02], and some common thermoelectric materials. The new parameter B* provides a better characterization of material's thermoelectric transport, particularly at high temperatures, and therefore can facilitate the search for good thermoelectric materials.United States. Department of Energy. Office of Science. Solid-State Solar Thermal Energy Conversion Center (Award DE-SC0001299/DE-FG02-09ER46577

Analysis of vapor barrier experiments to evaluate their effectiveness as a means to mitigate HF concentrations: final report

CER88-89RNM-DEN-SHS-TS-TZT-GW-1.Prepared for Exxon Research and Engineering Company.On behalf of An Industry Cooperative HF Mitigation Program, Vapor Barrier Subcommittee.Includes bibliographical references (pages 153-159).July 1988 (Revised February, 1989).Accidental releases of Hydrogen Fluoride (HF) can result in initially dense, highly reactive and corrosive gas clouds. These clouds will typically contain a mixture of gases, aerosols and droplets which can be transported significant distances before lower hazard levels of HF concentration are reached. Containment fences or vapor barriers have been proposed as a means to hold-up or delay cloud expansion, elevate the plume downwind of the barriers, and enhance cloud dilution. Previous related field and laboratory experiments have been analyzed to estimate the effectiveness of barrier devices. The experiments were examined to determine their relevance to Hydrogen Fluoride spill scenarios. Wind tunnel and field data were compared where possible to validate the laboratory experiments. Barrier influence on peak concentrations, cloud arrival time, peak concentration arrival time, and cloud departure time were determined. These data were used to develop entrainment models to incorporate into integral and depth averaged numerical models. The models were then run to examine barrier performance for a typical Hydrogen Fluoride spill for a wide range of vapor barrier heights, spill sizes, meteorological conditions and release configurations. Finally the results of the data analysis and numerical sensitivity study were interpreted and expressed in a form useful to evaluate the efficacy of vapor barrier mitigation devices