Citation for published item:wil nD h vid gF nd elEyw ediD yd y eF nd yerthelD w rieEghristine nd w rqu¡ esEqonz¡ lezD nti go nd frookeD i h rd tF nd fry eD w rtin F nd ge D il r nd perrerD t ime nd rigginsD imon tF nd v m ertD golin tF nd vowD ul tF nd solt w nriqueD h vid nd w rtinD nti go nd xi holsD i h rd tF nd hw rz herD lther nd q r ¡ % E u¡ rezD ¡ % tor wF @PHITA 9 olvent dependen e of the single mole ule ondu t n e of oligoyneE sed mole ul r wiresF9D tourn l of physi l hemistry gFD IPH @PWAF ppF ISTTTEISTURF Further information on publisher's website:This document is the Accepted Manuscript version of a Published Work that appeared in nal form in The Journal of Physical Chemistry C, copyright c American Chemical Society after peer review and technical editing by the publisher. To access the nal edited and published work see http://dx.doi.org/10.1021/acs.jpcc.5b08877. Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details.

Using a scanning tunnelling microscope break-junction technique, we produce 4,4'-bipyridine (44BP) single-molecule junctions with Ni and Au contacts. Electrochemical control is used to prevent Ni oxidation, and to modulate the conductance of the devices via non-redox gating -the first time this has been shown using non-Au contacts. Remarkably the conductance and gain of the resulting Ni-44BP-Ni electrochemical transistors is significantly higher than analogous Au-based devices. Ab-initio calculations reveal that this behaviour arises because charge transport is mediated by spin-polarized Ni d -electrons, which hybridize strongly with molecular orbitals to form a 'spinterface'.Our results highlight the important role of the contact material for single-molecule devices, and show that it can be varied to provide control of charge and spin transport. KeywordsSingle-molecule, Break-junction, Electrochemical gating, Spintronics, Density functional theory, Metal-molecule interface Main TextSingle-molecule transistor behaviour can be achieved using a gate electrode to control the energy levels of a molecule bridging two metallic electrodes. 1 This gate can be provided electrochemically using the double layer potential existing at the metal-electrolyte interface (Fig. 1a). An electrochemical gate avoids the complex fabrication of solid-state threeterminal molecular devices, can operate in room temperature liquid environments, and can produce high gate efficiencies thanks to the large electric fields which are achievable. There has been significant interest in redox active molecules such as viologens as candidates for electrochemical transistors, 2-4 however the gating of non-redox molecules has only recently been demonstrated using Au electrodes by Li et al. 5 with 4,4'-bipyridine (44BP) molecules,

In recent years, economic, political and social pressures to adopt sustainable work practices have led to a renewed emphasis on developing effective waste minimisation measures for major construction projects. This research explored the efficacy of measures used for minimising waste in high profile UK‐based projects. The case studies revealed a diverse range of waste strategies, the broader applicability of which was then explored via a questionnaire survey of waste minimisation specialists. The most effective measures were deemed to be those that fostered “waste minimisation partnerships” throughout the supply chain. Questions remain, however, as to whether the industry is culturally prepared for the collaborative relationships necessary to engender radical improvements in waste minimisation performance.

Oligoynes are archetypical molecular wires due to their 1-D chain of conjugated carbon atoms and ability to transmit charge over long distances by coherent tunneling. However, the stability of the oligoyne can be an issue. Here we address this problem by two stabilization methods, namely sterically shielding endgroups, and rotaxination to produce an insulated molecular wire. We demonstrate the threading of a hexayne within a macrocycle to form a rotaxane and report measurements of the electrical conductance of this single supramolecular assembly within an STM break junction. The macrocycle is retained around the hexayne through the use of 3,5-diphenylpyridine stoppers at both ends of the molecular wire, which also serve as chemisorption contacts to the gold electrodes of the junction. Molecular conductance was measured for both the supramolecular assembly and also for the molecular wire in the absence of the macrocycle. The threaded macrocycle, which at room temperature is mobile along the length of the hexayne between the stoppers, has only a minimal impact on the conductance. However, the probability of molecular junction formation in a given break junction formation cycle is notably lower with the rotaxane. In seeking to understand the conductance behavior, the electronic properties of these molecular assemblies and the electrical behavior of the junctions have been investigated by using DFT-based computational methods.

We demonstrate here a new concept for a metal-molecule-semiconductor nanodevice employing Au and GaAs contacts that acts as a photodiode. Current-voltage traces for such junctions are recorded using a STM, and the "blinking" or "I(t)" method is used to record electrical behavior at the single-molecule level in the dark and under illumination, with both low and highly doped GaAs samples and with two different types of molecular bridge: nonconjugated pentanedithiol and the more conjugated 1,4-phenylene(dimethanethiol). Junctions with highly doped GaAs show poor rectification in the dark and a low photocurrent, while junctions with low doped GaAs show particularly high rectification ratios in the dark (>10 for a 1.5 V bias potential) and a high photocurrent in reverse bias. In low doped GaAs, the greater thickness of the depletion layer not only reduces the reverse bias leakage current, but also increases the volume that contributes to the photocurrent, an effect amplified by the point contact geometry of the junction. Furthermore, since photogenerated holes tunnel to the metal electrode assisted by the HOMO of the molecular bridge, the choice of the latter has a strong influence on both the steady state and transient metal-molecule-semiconductor photodiode response. The control of junction current via photogenerated charge carriers adds new functionality to single-molecule nanodevices.

In most single- or few-molecule devices, the contact electrodes are simple ohmic resistors. Here we describe a new type of single-molecule device in which metal and semiconductor contact electrodes impart a function, namely, current rectification, which is then modified by a molecule bridging the gap. We study junctions with the structure Au STM tip/X/n-GaAs substrate, where "X" is either a simple alkanedithiol or a conjugated unit bearing thiol/methylthiol contacts, and we detect current jumps corresponding to the attachment and detachment of single molecules. From the magnitudes of the current jumps we can deduce values for the conductance decay constant with molecule length that agree well with values determined from Au/molecule/Au junctions. The ability to impart functionality to a single-molecule device through the properties of the contacts as well as through the properties of the molecule represents a significant extension of the single-molecule electronics "tool-box".

One of the principal aims of single-molecule electronics is to create practical devices out of individual molecules. Such devices are expected to play a particularly important role as novel sensors thanks to their response to wide ranging external stimuli. Here we show that the conductance of a molecular junction can depend on two independent stimuli simultaneously. Using a scanning tunnelling microscope break-junction technique (STM-BJ), we found that the conductance of 4,4'-vinylenedipyridine (44VDP) molecular junctions with Ni contacts depends on both the electrochemically applied gate voltage and the pH of the environment. Hence, not only can the Ni|44VDP|Ni junction function as a pH-sensitive switch, but the value of the pH at which switching takes place can be tuned electrically. Furthermore, through the simultaneous control of pH and potential the STM-BJ technique delivers unique insight into the acid-base reaction, including the observation of discrete proton transfers to and from a single molecule.

In recent years, the use of non-metallic electrodes for the fabrication of single-molecule junctions has developed into an elegant way to impart new properties to nanodevices. Integration of molecular junctions in a semiconducting platform would also speed technological deployment, as it would take advantage of established industrial infrastructures. In a previous proof-of-concept paper, we used simple α,ω-dithiol self-assembled monolayers on a gallium arsenide (GaAs) substrate to fabricate molecular Schottky diodes with a STM. In the devices, we were also able to detect the contribution of a single-molecule to the overall charge transport. The prepared devices can also be used as photodiodes, as GaAs is a III-V direct bandgap (1.42 eV at room temperature) semiconductor, and it efficiently absorbs visible light to generate a photocurrent. In this contribution, we demonstrate that fine control can be exerted on the electrical behaviour of a metal-molecule-GaAs junction by systematically altering the nature of the molecular bridge, the type and doping density of the semiconductor and the light intensity and wavelength. Molecular orbital energy alignment dominates the charge transport properties, resulting in strongly rectifying junctions prepared with saturated bridges (e.g. alkanedithiols), with increasingly ohmic characteristics as the degree of saturation is reduced through the introduction of conjugated moieties. The effects we observed are local, and may be observed with electrodes of only a few tens of nanometres in size, hence paving the way to the use of semiconducting nanoelectrodes to probe molecular properties. Perspectives of these new developments for single molecule semiconductor electrochemistry are also discussed.