44 research outputs found
Understanding resonant charge transport through weakly coupled single-molecule junctions
Off-resonant charge transport through molecular junctions has been
extensively studied since the advent of single-molecule electronics and it is
now well understood within the framework of the non-interacting Landauer
approach. Conversely, gaining a qualitative and quantitative understanding of
the resonant transport regime has proven more elusive. Here, we study resonant
charge transport through graphene-based zinc-porphyrin junctions. We
experimentally demonstrate an inadequacy of the non-interacting Landauer theory
as well as the conventional single-mode Franck-Condon model. Instead, we model
the overall charge transport as a sequence of non-adiabatic electron transfers,
the rates of which depend on both outer and inner-sphere vibrational
interactions. We show that the transport properties of our molecular junctions
are determined by a combination of electron-electron and electron-vibrational
coupling, and are sensitive to the interactions with the wider local
environment. Furthermore, we assess the importance of nuclear tunnelling and
examine the suitability of semi-classical Marcus theory as a description of
charge transport in molecular devices.Comment: version accepted in Nature Communications; SI available at
https://researchportal.hw.ac.uk/en/publications/understanding-resonant-charge-transport-through-weakly-coupled-s
Marked isotopic variability within and between the Amazon River and marine dissolved black carbon pools
Riverine dissolved organic carbon (DOC) contains charcoal byproducts, termed black carbon (BC). To determine the significance of BC as a sink of atmospheric CO2 and reconcile budgets, the sources and fate of this large, slow-cycling and elusive carbon pool must be constrained. The Amazon River is a significant part of global BC cycling because it exports an order of magnitude more DOC, and thus dissolved BC (DBC), than any other river. We report spatially resolved DBC quantity and radiocarbon (Î14C) measurements, paired with molecular-level characterization of dissolved organic matter from the Amazon River and tributaries during low discharge. The proportion of BC-like polycyclic aromatic structures decreases downstream, but marked spatial variability in abundance and Î14C values of DBC molecular markers imply dynamic sources and cycling in a manner that is incongruent with bulk DOC. We estimate a flux from the Amazon River of 1.9â2.7 Tg DBC yrâ1 that is composed of predominately young DBC, suggesting that loss processes of modern DBC are important
Understanding resonant charge transport through weakly coupled single-molecule junctions
Off-resonant charge transport through molecular junctions has been
extensively studied since the advent of single-molecule electronics and it is
now well understood within the framework of the non-interacting Landauer
approach. Conversely, gaining a qualitative and quantitative understanding of
the resonant transport regime has proven more elusive. Here, we study resonant
charge transport through graphene-based zinc-porphyrin junctions. We
experimentally demonstrate an inadequacy of the non-interacting Landauer theory
as well as the conventional single-mode Franck-Condon model. Instead, we model
the overall charge transport as a sequence of non-adiabatic electron transfers,
the rates of which depend on both outer and inner-sphere vibrational
interactions. We show that the transport properties of our molecular junctions
are determined by a combination of electron-electron and electron-vibrational
coupling, and are sensitive to the interactions with the wider local
environment. Furthermore, we assess the importance of nuclear tunnelling and
examine the suitability of semi-classical Marcus theory as a description of
charge transport in molecular devices.Comment: version accepted in Nature Communications; SI available at
https://researchportal.hw.ac.uk/en/publications/understanding-resonant-charge-transport-through-weakly-coupled-s
Breast cancer management pathways during the COVID-19 pandemic: outcomes from the UK âAlert Level 4â phase of the B-MaP-C study
Abstract: Background: The B-MaP-C study aimed to determine alterations to breast cancer (BC) management during the peak transmission period of the UK COVID-19 pandemic and the potential impact of these treatment decisions. Methods: This was a national cohort study of patients with early BC undergoing multidisciplinary team (MDT)-guided treatment recommendations during the pandemic, designated âstandardâ or âCOVID-alteredâ, in the preoperative, operative and post-operative setting. Findings: Of 3776 patients (from 64 UK units) in the study, 2246 (59%) had âCOVID-alteredâ management. âBridgingâ endocrine therapy was used (n = 951) where theatre capacity was reduced. There was increasing access to COVID-19 low-risk theatres during the study period (59%). In line with national guidance, immediate breast reconstruction was avoided (n = 299). Where adjuvant chemotherapy was omitted (n = 81), the median benefit was only 3% (IQR 2â9%) using âNHS Predictâ. There was the rapid adoption of new evidence-based hypofractionated radiotherapy (n = 781, from 46 units). Only 14 patients (1%) tested positive for SARS-CoV-2 during their treatment journey. Conclusions: The majority of âCOVID-alteredâ management decisions were largely in line with pre-COVID evidence-based guidelines, implying that breast cancer survival outcomes are unlikely to be negatively impacted by the pandemic. However, in this study, the potential impact of delays to BC presentation or diagnosis remains unknown
Reorganization energy upon charging a single molecule on an insulator measured by atomic force microscopy
Direct Visualization of Individual Aromatic Compound Structures in Low Molecular Weight Marine Dissolved Organic Carbon
Dissolved organic carbon (DOC) is the largest pool of exchangeable organic carbon in the ocean. However, less than 10% of DOC has been molecularly characterized in the deep ocean to understand DOC's recalcitrance. Here we analyze the radiocarbon ( C) depleted, and presumably refractory, low molecular weight (LMW) DOC from the North Central Pacific using atomic force microscopy to produce the first atomic-resolution images of individual LMW DOC molecules. We evaluate surface and deep LMW DOC chemical structures in the context of their relative persistence and recalcitrance. Atomic force microscopy resolved planar structures with features similar to polycyclic aromatic compounds and carboxylic-rich alicyclic structures with less than five aromatic carbon rings. These compounds comprise 8% and 20% of the measurable molecules investigated in the surface and deep, respectively. Resolving the structures of individual DOC molecules represents a step forward in molecular characterization of DOC and in understanding its long-term stability. 1
Molecular Chessboard Assemblies Sorted by Site-Specific Interactions of Out-of-Plane dâOrbitals with a Semimetal Template
We
show that highly ordered two-dimensional (2D) chessboard arrays
consisting of a periodic arrangement of two different molecules can
be obtained by self-assembly of unsubstituted metalâphthalocyanines
(metal-Pcs) on a suitable substrate serving as the template. Specifically,
CuPc + MnPc and CuPc + CoPc mixtures sort into highly ordered Cu/Mn
and Cu/Co chessboard arrays on the square p(10 Ă 10) reconstruction
of bismuth on Cu(100). Such created bimolecular chessboard assemblies
emerge from the site-specific interactions between the central transition-metal
ions and the periodically reconstructed substrate. This work provides
a conceptually new approach to induce 2D chessboard patterns in that
no functionalization of the molecules is needed
Configuring electronic states in an atomically precise array of quantum boxes
FAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOA 2D array of electronically coupled quantum boxes is fabricated by means of onâsurface selfâassembly assuring ultimate precision of each box. The quantum states embedded in the boxes are configured by adsorbates, whose occupancy is controlled with atomic precision. The electronic interbox coupling can be maintained or significantly reduced by proper arrangement of empty and filled boxes.122837573763FAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULOFAPESP - FUNDAĂĂO DE AMPARO Ă PESQUISA DO ESTADO DE SĂO PAULO2013/04855-0The authors would like to acknowledge financial support from the Swiss Nanoscience Institute (SNI), Swiss National Science Foundation (Grants Nos. 200020â149713 and 206021â121461), the Spanish Ministry of Economy (Grant No. MAT2013â46593âC6â4âP), the Basque Government (Grant No. IT621â13), the SĂŁo Paulo Research Foundation (Grant No. 2013/04855â0), Swiss Government Excellence Scholarship Program, Netherlands Organization for Scientific Research NWO (Chemical Sciences, VIDIâGrant No. 700.10.424), the European Research Council (ERCâ2012âStG 307760âSURFPRO), University of Basel, University of Heidelberg, Linköping University, University of Groningen, Paul Scherrer Institute, and the Japan Science and Technology Agency (JST) âPrecursory Research for Embryonic Science and Technology (PRESTO)â for a project of âMolecular technology and creation of new function.â The authors sincerely thank Marco Martina and RĂ©my Pawlak for support during the measurements