Quantifying Image Charge Effects in Molecular Tunnel Junctions Based on Self-Assembled Monolayers of Substituted Oligophenylene Ethynylene Dithiols.

A number of factors contribute to orbital energy alignment with respect to the Fermi level in molecular tunnel junctions. Here, we report a combined experimental and theoretical effort to quantify the effect of metal image potentials on the highest occupied molecular orbital to Fermi level offset, εh, for molecular junctions based on self-assembled monolayers (SAMs) of oligophenylene ethynylene dithiols (OPX) on Au. Our experimental approach involves the use of both transport and photoelectron spectroscopy to extract the offsets, εhtrans and εhUPS, respectively. We take the difference in these quantities to be the image potential energy eVimage. In the theoretical approach, we use density functional theory (DFT) to calculate directly eVimage between positive charge on an OPX molecule and the negative image charge in the Au. Both approaches yield eVimage ∼ -0.1 eV per metal contact, meaning that the total image potential energy is ∼-0.2 eV for an assembled junction with two Au contacts. Thus, we find that the total image potential energy is 25-30% of the total offset εh, which means that image charge effects are significant in OPX junctions. Our methods should be generally applicable to understanding image charge effects as a function of molecular size, for example, in a variety of SAM-based junctions.

Looking Through the COVID-19 Window of Opportunity: Future Scenarios Arising From the COVID-19 Pandemic Across Five Case Study Sites.

The COVID-19 pandemic has caused (and continues to cause) severe disruption in global and local economies and has forced countries, societies, and individuals to adapt quickly to the unprecedented and unpredictable situations. Despite the obvious negative consequences of the pandemic, many have called for efforts to identify transformative opportunities for sustainable development throughout this disorderly time. In the present paper, we explore such potential opportunities in the context of an interdisciplinary, international research project, which is focusing on sustainable marine management in biosphere reserves and marine parks in Southeast Asia. During a virtual workshop conducted as part of the GCRF (Government's Global Challenges Research Fund) Blue Communities Project, future scenarios were developed depicting the potential effects of the COVID-19 pandemic on five case study sites. All of these sites are in areas of internationally recognized outstanding ecological value (Taka Bonerate Kepulauan-Selayar Biosphere Reserve, Indonesia; Tun Mustapha Park, Sabah, Malaysia; Palawan Biosphere Reserve, Philippines; North Devon Biosphere Reserve, United Kingdom; Cu Lao Cham-Hoi An Biosphere Reserve, Vietnam). At the macro-level, economies, governance structures, and societal norms are undergoing big changes. At the micro-level, the livelihoods, lifestyles, and backyards of local residents have to adapt. Collaboratively, we explored how COVID-19 posed challenges in our five case study sites, but we also focused on the potential COVID-19-related windows of opportunity for future sustainable development. Opportunities could be identified in all three pillars of sustainable development: the environment, the society, and the economy. Although remarkable similarities can be found across all five sites, we conclude that there cannot be a "one-size-fits-all" solution to turn the tide toward achieving sustainable development. Just as before the pandemic, sustainable development starts with engaging with and understanding local environments, challenges, and situations; building on local knowledge; and developing tailor-made solutions for the communities in situ.

Charge injection and transport properties of large area organic junctions based on aryl thin films covalently attached to a multilayer graphene electrode.

The quantum interaction between molecules and electrode materials at molecule/electrode interfaces is a major ingredient in the electron transport properties of organic junctions. Driven by the coupling strength between the two materials, it results mainly in the broadening and energy shift of the interacting molecular orbitals. Using new electrode materials, such as the recently developed semi-conducting two-dimensional nanomaterials, has become a significant advancement in the field of molecular/organic electronics that opens new possibilities for controlling the interfacial electronic properties and thus the charge injection properties. In this article, we report the use of atomically thin two-dimensional multilayer graphene films as the base electrode in organic junctions with a vertical architecture. The interfacial electronic structure dominated by the covalent bonding between bis-thienyl benzene diazonium-based molecules and the multilayer graphene electrode has been probed by ultraviolet photoelectron spectroscopy and the results are compared with those obtained on junctions with standard Au electrodes. Room temperature injection properties of such interfaces have also been explored by electron transport measurements. We find that, despite strong variations of the density of states, the Fermi energy and the injection barriers, both organic junctions with Au base electrodes and multilayer graphene base electrodes show similar electronic responses. We explain this observation by the strong orbital coupling occurring at the bottom electrode/bis-thienyl benzene molecule interface and by the pinning of the hybridized molecular orbitals.