Triazatriangulene as Binding Group for Molecular Electronics (original) (raw)
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RSC Adv., 2014
Why do use thiols in Molecular Electronics? They stink, oxidize readily, poison catalysts, and often require nontrivial protection/deprotection chemistry. In this communication we demonstrate the fabrication of tunneling junctions formed by contacting self-assembled monolayers (SAMs) of terminal alkynes on silver and gold substrates. The SAMs form spontaneously upon exposure of the substrates to ethanolic solutions of the alkynes. Characterization by vibrational spectroscopy, XPS, and contact angles shows that the packing of the SAMs is nearly identical to those formed from equivalent thiols. Electrical characterization of the junctions revealed virtually no differences between SAMs on gold and silver, yielding β Au = 1.17 ± 0.04 n −1 C , J 0 = (2.836 ± 0.001) × 10 3 A/cm 2 for Au, and β Ag = 1.23 ± 0.09 n −1 C , J 0 = (4.722 ± 0.002) × 10 3 A/cm 2 for Ag. These values are in excellent agreement with junctions formed from alkanethiols of the same lengths as the alkynes, suggesting that there is no functional difference between thiols and alkynes as anchoring groups for SAMs. Yet alkynes are synthetically versatile, do not poison catalysts, are not odorous, and do not spontaneously oxidize, which are all attractive features for use in Molecular Electronics. The strong, selective binding of organothiols to gold and other noble metals is widely exploited in Molecular Electronics (ME) to bind molecules to one or both electrodes in a device. Bottom-up tunneling junctions rely almost exclusively on self-assembled monolayers (SAMs) of thiols to define the gap between the electrodes. 1 Alkanethiols, in particular, are favored because they reproducibly form dense monolayers in a variety of conditions and tolerate a wide variety of head groups. The key feature of SAMs of thiols is the simultaneous strength and reversibility of the metal-thiol bond, † Electronic Supplementary Information (ESI) available: [details of any supplementary information available should be included here].
Optical and transport studies of single molecule tunnel junctions based on self-assembled monolayers
Solid State Communications, 2005
We have fabricated a variety of novel molecular tunnel junctions based on selfassembled-monolayers (SAM) of two-component solid-state mixtures of molecular wires (1,4 methane benzene-dithiol; Me-BDT with two thiol anchoring groups), and molecular insulator spacers (1-pentanethiol; PT with one thiol anchoring group) at different concentration ratios, r of wires/spacers, which were sandwiched between two metallic electrodes such as gold and cobalt. FTIR spectroscopy and surface titration were used, respectively to verify the formation of covalent bonds with the electrodes, and obtain the number of active molecular wires in the device. The electrical transport properties of the SAM devices were studied as a function of (i) r-value, (ii) temperatures, and (iii) different electrodes, via the conductance and differential conductance spectra. The measurements were used to analyze the Me-BDT density of states near the electrode Fermi level, and the properties of the interface barriers. We measured the Me-BDT single molecule resistance at low bias and gold electrodes to be 6x10 9 Ohm. We also determine the energy difference, ∆ between the Me-BDT HOMO level and the gold Fermi level to be about 1.8 eV. In addition we also found that the temperature dependence of the SAM devices with r < 10 -4 is much weaker than that of the pure PT device (or r = 0), showing a small interface barrier.
Single-molecule electrical studies on a 7 nm long molecular wire
Chemical Communications, 2006
A self-assembled arylene-ethynylene molecular wire with a rigid 7 nm long backbone exhibits symmetrical current-voltage (I-V) characteristics and a single-molecule current of 0.35 ¡ 0.05 nA at 0.3 V; these data are supported by theoretical calculations.
Adventures in molecular electronics: how to attach wires to molecules
Applied Surface Science, 2003
Films of both methoxy-terminated alkanethiols and a molecular wire candidate on Au{1 1 1} substrates were exposed to a variety of transition and alkali earth metals (Al, Au, Ag, Ca, Cr, Fe, Cu, Mg, Ti). The results show that aggressively reacting metals, such as Ti, destroy the organic monolayer and metals of intermediate reactivity, e.g. Cu, react at the termini and also penetrate the monolayer and react with the substrate. The results of these investigations provide a basis by which future construction of molecular devices based on desired chemical reactivity may proceed.
Atomically Wired Molecular Junctions: Connecting a Single Organic Molecule by Chains of Metal Atoms
Using a break junction technique, we find a clear signature for the formation of conducting hybrid junctions composed of a single organic molecule (benzene, naphthalene, or anthracene) connected to chains of platinum atoms. The hybrid junctions exhibit metallic-like conductance (∼0.1−1G 0 ), which is rather insensitive to further elongation by additional atoms. At low bias voltage the hybrid junctions can be elongated significantly beyond the length of the bare atomic chains. Ab initio calculations reveal that benzene based hybrid junctions have a significant binding energy and high structural flexibility that may contribute to the survival of the hybrid junction during the elongation process. The fabrication of hybrid junctions opens the way for combining the different properties of atomic chains and organic molecules to realize a new class of atomic scale interfaces.
Conjugated Thiol Linker for Enhanced Electrical Conduction of Gold−Molecule Contacts
The Journal of Physical Chemistry B, 2005
Single-molecule electrical conduction studies are used to evaluate how the molecular linking unit influences the tunneling efficiency in metal-molecule-metal (m-M-m) junctions. This work uses conducting-probe atomic force microscopy (CP-AFM) to compare the molecular conduction of two π-bonded molecules: one with a single thiol linker, and another with a conjugated double thiol linker at both ends of the molecules. The results demonstrate that the molecule with conjugated double thiol linkers displays higher conduction in gold-molecule-gold junctions than nonconjugated single thiol-gold contacts.
Making electrical contacts to molecular monolayers
Nanotechnology, 2002
Electrical contacts between a metal probe and molecular monolayers have been characterized using conducting atomic force microscopy in an inert environment and in a voltage range that yields reversible current-voltage data. The current through alkanethiol monolayers depends on the contact force in a way that is accounted for by the change of chain-to-chain tunnelling with film thickness. The electronic decay constant, β N , was obtained from measurements as a function of chain length at constant force and bias, yielding β N = 0.8 ± 0.2 per methylene over a ±3 V range. Current-voltage curves are difficult to reconcile with this almost constant value. Very different results are obtained when a gold tip contacts a 1,8-octanedithiol film. Notably, the current-voltage curves are often independent of contact force. Thus the contact may play a critical role both in the nature of charge transport and the shape of the current-voltage curve.
Journal of the American Chemical Society, 2000
Thiolate self-assembled monolayers (SAMs) on metal surfaces have been explored recently to address the assembly and connection issue in molecular electronics. In these systems, the molecule-metal contact is detrimental to electron transport. This is manifested not only in contact resistance, but also in the nature of the molecular device, which depends on the extent of wave function mixing between the molecule and the metal surface. We probe interfacial electronic structure, particularly unoccupied electronic states, in thiolate SAMs on Cu(111) using laser two-photon photoemission spectroscopy, in conjunction with ab initio calculations of model molecules. We find that the interfacial electronic structure is dominated by two virtual orbitals localized to the thiolate anchor and strongly coupled to the metal substrate. The shapes and energies of these interfacial σ*-like orbitals are independent of the nature of the hydrocarbon group (conjugated aromatics or saturated alkyls). As low-lying acceptor orbitals, they may play important roles in electron transport through self-assembled molecular wires.
Insulated molecular wires: inhibiting orthogonal contacts in metal complex based molecular junctions
Nanoscale, 2017
Metal complexes are receiving increased attention as molecular wires in fundamental studies of the transport properties of metal|molecule|metal junctions. In this context we report the single-molecule conductance of a systematic series of d(8) square-planar platinum(ii) trans-bis(alkynyl) complexes with terminal trimethylsilylethynyl (C[triple bond, length as m-dash]CSiMe3) contacting groups, e.g. trans-Pt{C[triple bond, length as m-dash]CC6H4C[triple bond, length as m-dash]CSiMe3}2(PR3)2 (R = Ph or Et), using a combination of scanning tunneling microscopy (STM) experiments in solution and theoretical calculations using density functional theory and non-equilibrium Green's function formalism. The measured conductance values of the complexes (ca. 3-5 × 10(-5)G0) are commensurate with similarly structured all-organic oligo(phenylene ethynylene) and oligo(yne) compounds. Based on conductance and break-off distance data, we demonstrate that a PPh3 supporting ligand in the platinum c...