Covalent C-N Bond Formation through a Surface Catalyzed Thermal Cyclodehydrogenation.

The integration of substitutional dopants at predetermined positions along the hexagonal lattice of graphene-derived polycyclic aromatic hydrocarbons is a critical tool in the design of functional electronic materials. Here, we report the unusually mild thermally induced oxidative cyclodehydrogenation of dianthryl pyrazino[2,3-]quinoxalines to form the four covalent C-N bonds in tetraazateranthene on Au(111) and Ag(111) surfaces. Bond-resolved scanning probe microscopy, differential conductance spectroscopy, along with first-principles calculations unambiguously confirm the structural assignment.

Revealing the Local Electronic Structure of a Single-Layer Covalent Organic Framework through Electronic Decoupling.

Covalent organic frameworks (COFs) are molecule-based 2D and 3D materials that possess a wide range of mechanical and electronic properties. We have performed a joint experimental and theoretical study of the electronic structure of boroxine-linked COFs grown under ultrahigh vacuum conditions and characterized using scanning tunneling spectroscopy on Au(111) and hBN/Cu(111) substrates. Our results show that a single hBN layer electronically decouples the COF from the metallic substrate, thus suppressing substrate-induced broadening and revealing new features in the COF electronic local density of states (LDOS).

Orbital Character Effects in the Photon Energy and Polarization Dependence of Pure C Photoemission.

Recent direct experimental observation of multiple highly dispersive C valence bands has allowed for a detailed analysis of the unusual photoemission traits of these features through photon energy- and polarization-dependent measurements. Previously obscured dispersions and strong photoemission traits are now revealed by specific light polarizations. The observed intensity effects prove the locking in place of the C molecules at low temperatures and the existence of an orientational order imposed by the substrate chosen.

Synthesis of Polycyclic Aromatic Hydrocarbons by Phenyl Addition-Dehydrocyclization: The Third Way.

Polycyclic aromatic hydrocarbons (PAHs) represent the link between resonance-stabilized free radicals and carbonaceous nanoparticles generated in incomplete combustion processes and in circumstellar envelopes of carbon rich asymptotic giant branch (AGB) stars. Although these PAHs resemble building blocks of complex carbonaceous nanostructures, their fundamental formation mechanisms have remained elusive. By exploring these reaction mechanisms of the phenyl radical with biphenyl/naphthalene theoretically and experimentally, we provide compelling evidence on a novel phenyl-addition/dehydrocyclization (PAC) pathway leading to prototype PAHs: triphenylene and fluoranthene.

Identifying substitutional oxygen as a prolific point defect in monolayer transition metal dichalcogenides.

Chalcogen vacancies are generally considered to be the most common point defects in transition metal dichalcogenide (TMD) semiconductors because of their low formation energy in vacuum and their frequent observation in transmission electron microscopy studies. Consequently, unexpected optical, transport, and catalytic properties in 2D-TMDs have been attributed to in-gap states associated with chalcogen vacancies, even in the absence of direct experimental evidence. Here, we combine low-temperature non-contact atomic force microscopy, scanning tunneling microscopy and spectroscopy, and state-of-the-art ab initio density functional theory and GW calculations to determine both the atomic structure and electronic properties of an abundant chalcogen-site point defect common to MoSe and WS monolayers grown by molecular beam epitaxy and chemical vapor deposition, respectively.

Manipulating Topological Domain Boundaries in the Single-Layer Quantum Spin Hall Insulator 1T'-WSe.

We report the creation and manipulation of structural phase boundaries in the single-layer quantum spin Hall insulator 1T'WSe by means of scanning tunneling microscope tip pulses. We observe the formation of one-dimensional interfaces between topologically nontrivial 1T' domains having different rotational orientations, as well as induced interfaces between topologically nontrivial 1T' and topologically trivial 1H phases. Scanning tunneling spectroscopy measurements show that 1T'/1T' interface states are localized at domain boundaries, consistent with theoretically predicted unprotected interface modes that form dispersive bands in and around the energy gap of this quantum spin Hall insulator.

To Improve Outcomes, Health Systems Invest In Affordable Housing.

In Portland, Oregon, health care networks are helping expand access to stable housing and supportive services.

Gas phase synthesis of [4]-helicene.

A synthetic route to racemic helicenes via a vinylacetylene mediated gas phase chemistry involving elementary reactions with aryl radicals is presented. In contrast to traditional synthetic routes involving solution chemistry and ionic reaction intermediates, the gas phase synthesis involves a targeted ring annulation involving free radical intermediates. Exploiting the simplest helicene as a benchmark, we show that the gas phase reaction of the 4-phenanthrenyl radical ([CH]) with vinylacetylene (CH) yields [4]-helicene (CH) along with atomic hydrogen via a low-barrier mechanism through a resonance-stabilized free radical intermediate (CH).

Phonon Polariton-assisted Infrared Nanoimaging of Local Strain in Hexagonal Boron Nitride.

Strain plays an important role in condensed matter physics and materials science because it can strongly modify the mechanical, electrical, and optical properties of a material and even induce a structural phase transition. Strain effects are especially interesting in atomically thin two-dimensional (2D) materials, where unusually large strain can be achieved without breaking them. Measuring the strain distribution in 2D materials at the nanometer scale is therefore greatly important but is extremely challenging experimentally.

Simulating the Nanomechanical Response of Cyclooctatetraene Molecules on a Graphene Device.

We investigate the atomic and electronic structures of cyclooctatetraene (COT) molecules on graphene and analyze their dependence on external gate voltage using first-principles calculations. The external gate voltage is simulated by adding or removing electrons using density functional theory calculations. This allows us to investigate how changes in carrier density modify the molecular shape, orientation, adsorption site, diffusion barrier, and diffusion path.

Normative Concerns with High-Risk Pools.

Despite a significant amount of literature debating the efficiency of high-risk pools in health insurance, dramatically less has been written about their normative implications. The present article takes the route less traveled by setting aside the question of efficiency to argue that the use of high-risk pools creates some serious normative concerns. The article explores these concerns by dividing them on two fronts.

Consolidation Trends In California's Health Care System: Impacts On ACA Premiums And Outpatient Visit Prices.

California has heavily concentrated hospital, physician, and health insurance markets, but their current structure and functioning is not well understood. We assessed consolidation trends and performed an analysis of "hot spots"-markets that potentially warrant concern and scrutiny by regulators in terms of both horizontal concentration (such as hospital-hospital mergers) and vertical integration (hospitals' acquisition of physician practices). In 2016, seven counties were high on all six measures used in our hot-spot analysis (four horizontal concentration and two vertical integration measures), and five counties were high on five.

Confronting The Effects Of Climate Change On Health In California.

Vulnerable communities have been forced to address the deepening impact of severe weather events on residents' well-being.

One In Five Fewer Heart Attacks: Impact, Savings, And Sustainability In San Diego County Collaborative.

Before 2011 rates of hospitalization for heart attacks were about the same in San Diego County as they were in the rest of California. In 2011 a multistakeholder population health collaborative consisting of partners at the federal, state, and local levels launched Be There San Diego. The collaborative's goal was to reduce cardiovascular events through the spread of best practices aimed at improving control of hypertension, lipid levels, and blood sugar and through patient and medical community activation.

Observation of topologically protected states at crystalline phase boundaries in single-layer WSe.

Transition metal dichalcogenide materials are unique in the wide variety of structural and electronic phases they exhibit in the two-dimensional limit. Here we show how such polymorphic flexibility can be used to achieve topological states at highly ordered phase boundaries in a new quantum spin Hall insulator (QSHI), 1T'-WSe. We observe edge states at the crystallographically aligned interface between a quantum spin Hall insulating domain of 1T'-WSe and a semiconducting domain of 1H-WSe in contiguous single layers.

Topological band engineering of graphene nanoribbons.

Topological insulators are an emerging class of materials that host highly robust in-gap surface or interface states while maintaining an insulating bulk. Most advances in this field have focused on topological insulators and related topological crystalline insulators in two dimensions and three dimensions, but more recent theoretical work has predicted the existence of one-dimensional symmetry-protected topological phases in graphene nanoribbons (GNRs). The topological phase of these laterally confined, semiconducting strips of graphene is determined by their width, edge shape and terminating crystallographic unit cell and is characterized by a [Formula: see text] invariant (that is, an index of either 0 or 1, indicating two topological classes-similar to quasi-one-dimensional solitonic systems).

Super-Resolution Imaging of Clickable Graphene Nanoribbons Decorated with Fluorescent Dyes.

The functional integration of atomically defined graphene nanoribbons (GNRs) into single-ribbon electronic device architectures has been limited by access to nondestructive high-resolution imaging techniques that are both compatible with common supports such as Si or Si/SiO wafers and capable of resolving individual ribbons in dilute samples. Conventional techniques such as scanning probe (AFM, STM) or electron microscopy (SEM, TEM) have been restricted by requisite sample preparation techniques that are incompatible with lithographic device fabrication. Here we report the design and synthesis of ultralong (∼10 μm) cove-type GNRs (cGNRs) featuring azide groups along the edges that can serve as a universal handle for late-stage functionalization with terminal alkynes.

A Novel International Partnership for Actionable Evidence on Urban Health in Latin America: LAC-Urban Health and SALURBAL.

This article describes the origins and characteristics of an interdisciplinary multinational collaboration aimed at promoting and disseminating actionable evidence on the drivers of health in cities in Latin America and the Caribbean: The Network for Urban Health in Latin America and the Caribbean and the Wellcome Trust funded SALURBAL (Salud Urbana en América Latina, or Urban Health in Latin America) Project. Both initiatives have the goals of supporting urban policies that promote health and health equity in cities of the region while at the same time generating generalizable knowledge for urban areas across the globe. The processes, challenges, as well as the lessons learned to date in launching and implementing these collaborations, are described.

Hierarchical On-Surface Synthesis of Graphene Nanoribbon Heterojunctions.

Bottom-up graphene nanoribbon (GNR) heterojunctions are nanoscale strips of graphene whose electronic structure abruptly changes across a covalently bonded interface. Their rational design offers opportunities for profound technological advancements enabled by their extraordinary structural and electronic properties. Thus far, the most critical aspect of their synthesis, the control over sequence and position of heterojunctions along the length of a ribbon, has been plagued by randomness in monomer sequences emerging from step-growth copolymerization of distinct monomers.

Persistent Charge-Density-Wave Order in Single-Layer TaSe.

We present the electronic characterization of single-layer 1H-TaSe grown by molecular beam epitaxy using a combined angle-resolved photoemission spectroscopy, scanning tunneling microscopy/spectroscopy, and density functional theory calculations. We demonstrate that 3 × 3 charge-density-wave (CDW) order persists despite distinct changes in the low energy electronic structure highlighted by the reduction in the number of bands crossing the Fermi energy and the corresponding modification of Fermi surface topology. Enhanced spin-orbit coupling and lattice distortion in the single-layer play a crucial role in the formation of CDW order.

Local Electronic Structure of a Single-Layer Porphyrin-Containing Covalent Organic Framework.

We have characterized the local electronic structure of a porphyrin-containing single-layer covalent organic framework (COF) exhibiting a square lattice. The COF monolayer was obtained by the deposition of 2,5-dimethoxybenzene-1,4-dicarboxaldehyde (DMA) and 5,10,15,20-tetrakis(4-aminophenyl) porphyrin (TAPP) onto a Au(111) surface in ultrahigh vacuum followed by annealing to facilitate Schiff-base condensations between monomers. Scanning tunneling spectroscopy (STS) experiments conducted on isolated TAPP precursor molecules and the covalently linked COF networks yield similar transport (HOMO-LUMO) gaps of 1.