From an organometallic monolayer to an organic monolayer covered by metal nanoislands: A simple thermal protocol for the fabrication of the top contact electrode in molecular electronic devices

et al.In this contribution, a novel method for practical uses in the fabrication of the top contact electrode in a metal/organic monolayer/metal device is presented. The procedure involves the thermally induced decomposition of an organometallic compound, abbreviated as the TIDOC method. Monolayers incorporating the metal organic compounds (MOCs) [[4-{(4-carboxy)ethynyl}phenyl]ethynyl]-(triphenylphosphine)-gold, 1, or [1-isocyano-4-methoxybenzene]-[4-amino-phenylethynyl]-gold, 2, were annealed at moderate temperatures (1: 150 °C for 2h and 2: 100 °C for 2 h), resulting in cleavage of the Au-P or Au-C bond and reduction of Au(I) to Au(0) as metallic gold nanoparticles (GNPs). These particles are distributed on the surface of the film resulting in formation of metal/molecule/GNP sandwich structures. Electrical properties of these nascent devices were determined by recording I¿V curves with a conductive-AFM. The I¿V curves collected from these metal/organic monolayer/GNPs sandwich structures are typical of metal-molecule-metal junctions, with no low resistance traces characteristic of metallic short circuits observed over a wide range of set-point forces. The TIDOC method is therefore an effective procedure for the fabrication of molecular junctions for the emerging area of molecular electronics.Peer Reviewe

An Explicit Scheme for Incorporating Ambipolar Diffusion in a Magnetohydrodynamics Code

We describe a method for incorporating ambipolar diffusion in the strong coupling approximation into a multidimensional magnetohydrodynamics code based on the total variation diminishing scheme. Contributions from ambipolar diffusion terms are included by explicit finite difference operators in a fully unsplit way, maintaining second order accuracy. The divergence-free condition of magnetic fields is exactly ensured at all times by a flux-interpolated constrained transport scheme. The super time stepping method is used to accelerate the timestep in high resolution calculations and/or in strong ambipolar diffusion. We perform two test problems, the steady-state oblique C-type shocks and the decay of Alfv\'en waves, confirming the accuracy and robustness of our numerical approach. Results from the simulations of the compressible MHD turbulence with ambipolar diffusion show the flexibility of our method as well as its ability to follow complex MHD flows in the presence of ambipolar diffusion. These simulations show that the dissipation rate of MHD turbulence is strongly affected by the strength of ambipolar diffusion.Comment: 25 pages, 5 figures, ApJS accepte

Potential-Modulated Ion Distributions in the Back-to-Back Electrical Double Layers at a Polarised Liquid|Liquid Interface Regulate the Kinetics of Interfacial Electron Transfer

Biphasic interfacial electron transfer (IET) reactions at polarisable liquid|liquid (L|L) interfaces underpin new approaches to electrosynthesis, redox electrocatalysis, bioelectrochemistry and artificial photosynthesis. Herein, using cyclic and alternating current voltammetry, we demonstrate that under certain experimental conditions, the biphasic 2-electron O2 reduction reaction can proceed by single-step IET between a reductant in the organic phase, decamethylferrocene, and interfacial protons in the presence of O2. Using this biphasic system, we demonstrate that the applied interfacial Galvani potential difference ΔwoØ provides no direct driving force to realise a thermodynamically uphill biphasic IET reaction in the mixed solvent region. We show that the onset potential for a biphasic single-step IET reaction does not correlate with the thermodynamically predicted standard Galvani IET potential and is instead closely correlated with the potential of zero charge at a polarised L|L interface. We outline that the applied ΔwoØ required to modulate the interfacial ion distributions, and thus kinetics of IET, must be optimised to ensure that the aqueous and organic redox species are present in substantial concentrations at the L|L interface simultaneously in order to react.M.D.S. acknowledges funding from Science Foundation Ireland (SFI) under grant no. 13/SIRG/2137 and the European Research Council through a Starting Grant (agreement no. 716792). A.G.-Q. acknowledges funding received from an Irish Research Council (IRC) Government of Ireland Postdoctoral Fellowship Award (grant number GOIPD/2018/252) and a Marie Skłodowska-Curie Postdoctoral Fellowship (Grant Number MSCA-IF-EF-ST 2020/101018277)

Fabricación del electrodo superior en dispositivos moleculares mediante la formación de enlaces covalentes σ C-Au

Resumen del póster presentado a la 6ª Jornada de Jóvenes Investigadores en Física y Química de Aragón celebrada en Zaragoza el 20 de noviembre de 2014.-- et al.Peer reviewe

Electrical characterization of single molecule and Langmuir-Blodgett monomolecular films of a pyridine-terminated oligo(phenylene-ethynylene) derivative

Monolayer Langmuir–Blodgett (LB) films of 1,4-bis(pyridin-4-ylethynyl)benzene (1) together with the “STM touch-to-contact” method have been used to study the nature of metal–monolayer–metal junctions in which the pyridyl group provides the contact at both molecule–surface interfaces. Surface pressure vs area per molecule isotherms and Brewster angle microscopy images indicate that 1 forms true monolayers at the air–water interface. LB films of 1 were fabricated by deposition of the Langmuir films onto solid supports resulting in monolayers with surface coverage of 0.98 × 10−9 mol·cm−2. The morphology of the LB films that incorporate compound 1 was studied using atomic force microscopy (AFM). AFM images indicate the formation of homogeneous, monomolecular films at a surface pressure of transference of 16 mN·m−1. The UV–vis spectra of the Langmuir and LB films reveal that 1 forms two dimensional J-aggregates. Scanning tunneling microscopy (STM), in particular the “STM touch-to-contact” method, was used to determine the electrical properties of LB films of 1. From these STM studies symmetrical I–V curves were obtained. A junction conductance of 5.17 × 10−5 G 0 results from the analysis of the pseudolinear (ohmic) region of the I–V curves. This value is higher than that of the conductance values of LB films of phenylene-ethynylene derivatives contacted by amines, thiols, carboxylate, trimethylsilylethynyl or acetylide groups. In addition, the single molecule I–V curve of 1 determined using the I(s) method is in good agreement with the I–V curve obtained for the LB film, and both curves fit well with the Simmons model. Together, these results not only indicate that the mechanism of transport through these metal–molecule–metal junctions is non-resonant tunneling, but that lateral interactions between molecules within the LB film do not strongly influence the molecule conductance. The results presented here complement earlier studies of single molecule conductance of 1 using STM-BJ methods, and support the growing evidence that the pyridyl group is an efficient and effective anchoring group in sandwiched metal–monolayer–metal junctions prepared under a number of different conditions.S. M., M. C. L, and P. C. are grateful for financial assistance from Ministerio de Economía y Competitividad from Spain in the framework of project CTQ2012-33198 and support from DGA and Fondos Feder for funding the Platon research group. S. M. also thanks his JIUZ-2013-CIE-05 grant. S. M and P. C. are grateful for the award of the CTQ2013-50187-EXP grant. P. J. L. thanks EPSRC for funding and also gratefully acknowledges support from the Australian Research Council (DP 140100855) and the award of the Future Fellowship (FT120100073). R. J. N. and S. J. H. thank EPSRC for funding (grant EP/H035184/1 and EP/K007785/1).Peer Reviewe

Tetrakis(ferrocenylethynyl)ethene:synthesis, spectro)electrochemical and quantum chemical characterisation

Tetrakis(ferrocenylethynyl)ethene (1) has been prepared in four steps from ethynyl ferrocene (2). In a dichloromethane solution containing 10–1 M NBu4[PF6], only a single oxidation process is observed by cyclic voltammetry, corresponding to the independent oxidation of the four ferrocenyl moieties. However, in dichloromethane containing 10–1 M NBu4[BArF4] electrolyte, where [BArF4]– is the weakly associating anion [B{C6H3(CF3)2-3,5}4]–, four distinct oxidation processes are resolved, although further spectroelectrochemical investigation revealed essentially no through bond interaction between the individual ferrocenyl moieties. Quantum chemical treatment of 1 identified several energetic minima corresponding to different relative orientations of the ferrocenyl moieties and the plane of the all-carbon bridging fragment. Further computational investigation of the corresponding monocation [1]+ supported the notion of charge localisation with no evidence for significant through bond electronic interactions

Aromatic Features in AGN: Star-Forming Infrared Luminosity Function of AGN Host Galaxies

We describe observations of aromatic features at 7.7 and 11.3 um in AGN of three types including PG, 2MASS and 3CR objects. The feature has been demonstrated to originate predominantly from star formation. Based on the aromatic-derived star forming luminosity, we find that the far-IR emission of AGN can be dominated by either star formation or nuclear emission; the average contribution from star formation is around 25% at 70 and 160 um. The star-forming infrared luminosity functions of the three types of AGN are flatter than that of field galaxies, implying nuclear activity and star formation tend to be enhanced together. The star-forming luminosity function is also a function of the strength of nuclear activity from normal galaxies to the bright quasars, with luminosity functions becoming flatter for more intense nuclear activity. Different types of AGN show different distributions in the level of star formation activity, with 2MASS> PG> 3CR star formation rates.Comment: Accepted for publication in ApJ, 24 pages, 13 figure

Electrically transmissive alkyne-anchored monolayers on gold

Well-ordered, tightly-packed (surface coverage 0.97 × 10−9 mol cm−2) monolayer films of 1,4-bis((4-ethynylphenyl)ethynyl)benzene (1) on gold are prepared via a simple self-assembly process, taking advantage of the ready formation of alkynyl C–Au σ-bonds. Electrochemical measurements using [Ru(NH3)6]3+, [Fe(CN)6]3−, and ferrocenylmethanol [Fe(η5-C5H4CH2OH)(η5-C5H5)] redox probes indicate that the alkynyl C–Au contacted monolayer of 1 presents a relatively low barrier for electron transfer. This contrasts with monolayer films on gold of other oligo(phenylene ethynylene) derivatives of comparable length and surface coverage, but with different contacting groups. Additionally, a low voltage transition (Vtrans = 0.51 V) from direct tunneling (rectangular barrier) to field emission (triangular barrier) is observed. This low transition voltage points to a low tunneling barrier, which is consistent with the facile electron transport observed through the C–Au contacted self-assembled monolayer of 1.P. C. and J. L. S. are grateful for financial assistance from Ministerio de Economia y Competitividad from Spain and fondos FEDER in the framework of projects MAT2016-78257-R and CTQ2015-70174-P, respectively. J. L. S. also acknowledges the funded project Hierarchical Self Assembly of Polymeric Soft Systems, “SASSYPOL”, from the 7th Framework Programme (CEE, Ref-607602). L. H., S. M., J. L. S, and P. C. acknowledge support from DGA/Fondos FEDER (construyendo Europa desde Aragón) for funding PLATON (E31_17R) and CLIP (E47_17R) research groups. R. J. N. thanks EPSRC for funding (EP/M029522/1, EP/K007785/1, EP/M014169/1 and EP/M005046/1), and P. J. L. also gratefully acknowledges support from the Australian Research Council (FT120100073; DP140100855).Peer reviewe

Electrical stimulation of renal nerves for modulating urine glucose excretion in rats

Abstract Background The role of the kidney in glucose homeostasis has gained global interest. Kidneys are innervated by renal nerves, and renal denervation animal models have shown improved glucose regulation. We hypothesized that stimulation of renal nerves at kilohertz frequencies, which can block propagation of action potentials, would increase urine glucose excretion. Conversely, we hypothesized that low frequency stimulation, which has been shown to increase renal nerve activity, would decrease urine glucose excretion. Methods We performed non-survival experiments on male rats under thiobutabarbital anesthesia. A cuff electrode was placed around the left renal artery, encircling the renal nerves. Ureters were cannulated bilaterally to obtain urine samples from each kidney independently for comparison. Renal nerves were stimulated at kilohertz frequencies (1–50 kHz) or low frequencies (2–5 Hz), with intravenous administration of a glucose bolus shortly into the 25–40-min stimulation period. Urine samples were collected at 5–10-min intervals, and colorimetric assays were used to quantify glucose excretion and concentration between stimulated and non-stimulated kidneys. A Kruskal-Wallis test was performed across all stimulation frequencies (α = 0.05), followed by a post-hoc Wilcoxon rank sum test with Bonferroni correction (α = 0.005). Results For kilohertz frequency trials, the stimulated kidney yielded a higher average total urine glucose excretion at 33 kHz (+ 24.5%; n = 9) than 1 kHz (− 5.9%; n = 6) and 50 kHz (+ 2.3%; n = 14). In low frequency stimulation trials, 5 Hz stimulation led to a lower average total urine glucose excretion (− 40.4%; n = 6) than 2 Hz (− 27.2%; n = 5). The average total urine glucose excretion between 33 kHz and 5 Hz was statistically significant (p < 0.005). Similar outcomes were observed for urine flow rate, which may suggest an associated response. No trends or statistical significance were observed for urine glucose concentrations. Conclusion To our knowledge, this is the first study to investigate electrical stimulation of renal nerves to modulate urine glucose excretion. Our experimental results show that stimulation of renal nerves may modulate urine glucose excretion, however, this response may be associated with urine flow rate. Future work is needed to examine the underlying mechanisms and identify approaches for enhancing regulation of glucose excretion.https://deepblue.lib.umich.edu/bitstream/2027.42/143868/1/42234_2018_Article_8.pd

Electrical characterization of single molecule and Langmuir–Blodgett monomolecular films of a pyridine-terminated oligo(phenylene-ethynylene) derivative

Monolayer Langmuir–Blodgett (LB) films of 1,4-bis(pyridin-4-ylethynyl)benzene (1) together with the “STM touch-to-contact” method have been used to study the nature of metal–monolayer–metal junctions in which the pyridyl group provides the contact at both molecule–surface interfaces. Surface pressure vs area per molecule isotherms and Brewster angle microscopy images indicate that 1 forms true monolayers at the air–water interface. LB films of 1 were fabricated by deposition of the Langmuir films onto solid supports resulting in monolayers with surface coverage of 0.98 × 10-9 mol·cm-2. The morphology of the LB films that incorporate compound 1 was studied using atomic force microscopy (AFM). AFM images indicate the formation of homogeneous, monomolecular films at a surface pressure of transference of 16 mN·m-1. The UV–vis spectra of the Langmuir and LB films reveal that 1 forms two dimensional J-aggregates. Scanning tunneling microscopy (STM), in particular the “STM touch-to-contact” method, was used to determine the electrical properties of LB films of 1. From these STM studies symmetrical I–V curves were obtained. A junction conductance of 5.17 × 10-5 G0 results from the analysis of the pseudolinear (ohmic) region of the I–V curves. This value is higher than that of the conductance values of LB films of phenylene-ethynylene derivatives contacted by amines, thiols, carboxylate, trimethylsilylethynyl or acetylide groups. In addition, the single molecule I–V curve of 1 determined using the I(s) method is in good agreement with the I–V curve obtained for the LB film, and both curves fit well with the Simmons model. Together, these results not only indicate that the mechanism of transport through these metal–molecule–metal junctions is non-reso- nant tunneling, but that lateral interactions between molecules within the LB film do not strongly influence the molecule conduc- tance. The results presented here complement earlier studies of single molecule conductance of 1 using STM-BJ methods, and support the growing evidence that the pyridyl group is an efficient and effective anchoring group in sandwiched metal–monolayer–metal junctions prepared under a number of different conditions