An approach for fabrication of junctions with Langmuir–Blodgett films incorporated between molecular electrodes (original) (raw)
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Electrochemical properties of Langmuir—Blodgett films
Journal of Electroanalytical Chemistry, 1994
Electrochemical properties of thin films of electroactive materials formed on the electrode surface by the Langmuir-Blodgett (LB) technique are reviewed. The focus is on charge transfer materials which form electroconductive films (tetrathiafulvalene, tetracyanoquinodimethane, fullerenes, phthalocyanines, conjugated polymers etc.) and other LB redox materials such as porphyrins, ferrocenes, metal bipyridine complexes and viologens. Structure-property relationships in experimental voltammetry of LB films and their agreement with theoretical models are examined. Specially organized structures, formed by the LB technique, of different materials for the study of the mechanism of electron transfer and for possible application in molecular electronics are considered as well. Potential applications of the electroactive LB films in electrocatalysis, electrochromic displays, information storage devices and molecular electronic devices are envisaged.
Journal of the American Chemical Society, 1991
The Langmuir-Blodgett (L-B) technique is used to coat electrode surfaces with bifunctional monolayer films that are designed to carry out two functions: passivation and gating. We demonstrate that incorporation of ubiquinone (Q50) in otherwise passivating L-B monolayer films allows us to control access to the electrode surface via a controlled number of single molecule gate sites. The electrode passivation is accomplished with mixed octadecanethioVoctadecano1 (ClsSWC180H) monolayers, as described previously (Bilewicz, R.; Majda, M. Langmuir 1991,7,2794. Adetailed characterization ofthe passivating properties of these L-B monolayers is provided in view of the Amatore-Saveant-Tessier (A-S-T) theory (Amatore, C.; Saveant, J.-M.; Tessier, D. J. Electroanal. Chem. 1983,147,39). The incorporation of low levels (10-l2mol/cm2) of ubiquinone allows electroreduction of probe species such as Ru(NH&~+. At Q50 concentrations below moVcm2, these monolayers behave as a random array of individual, 5-A-radius disk microelectrodes each created by a single ubiquinone molecule. We postulate that a loose conformation of the ubiquinone's isoprenoid chain creates a channel that allows for a direct approach of Ru s3+ ions to the electrode surface. Electrochemical results are evaluated on the basis of A-S-T theory using direct comparison of the experimental and calculated cyclic voltammetric responses. Negative deviations in the observed voltammetric response compared with the theory at the Q50 concentrations higher than mol/cm2 are explained by postulating aggregation and loss of Q50 during L-B transfer. Abstract published in Advance A C S Abstracts, May 15, 1995. (1) Harrison, D. J.; Mallouk, T. E. inznterfacial Design and Chemical Sensing; Mallouk, T. E., Harrison, D. J., Eds.; ACS Symposium Series Experimental Section Materials. l-octadecanol (Aldrich, 99%) and l-octadecanethiol (Aldrich, 98%) were triply recrystallized from 100% ethanol. (23) Amatore, C.; SavBant, J.-M.; Tessier, D.
Chemistry of Materials, 2010
This paper describes the preparation of Langmuir-Blodgett (LB) films comprised of an oligomeric phenylene-ethynylene (OPE) derivative, 4-[4-(phenylethynyl)-phenylethynyl] benzoic acid (BPEBA). Analysis of the surface pressure and surface potential vs area per molecule isotherms reveal that good quality monolayer films can be formed at surface pressures of 15 mN/m. The monolayers were transferred onto solid substrates with a Z-type deposition and a transfer ratio of 1. Raman and surface-enhanced Raman spectroscopy (SERS) studies reveal that the films are physisorbed onto silver metal substrates. The morphology of the deposited films was analyzed by means of atomic force microscopy (AFM), revealing the formation of homogeneous layers free of three-dimensional defects. The optical and emissive properties of the LB films were determined, with significant blueshifted absorption spectra indicating the formation of two-dimensional H aggregates in the films. In addition, a significant Stokes shift in the excitation and emission spectra of the films is indicative of a distribution of molecular conformations around the long molecular axis in the solidlike monolayer environment. Scanning tunneling microscopy (STM) studies of single layer BPEBA LB films were performed. The tip-sample distance has been calibrated carefully to obtain I-V curves above the LB film. I-V curves are unexpectedly symmetrical in spite of the asymmetric contacts of the molecule with the tip and the substrate. Single molecule conductance for BPEBA has also been determined and the similarity of these results to I-V data for BPEBA incorporated in LB films indicates that lateral (intermolecular) conductance is negligible for electrical measurements using the STM configuration.
Use of electrochemical techniques to study the Langmuir–Blodgett films of redox active materials
Russian Chemical Reviews, 1997
The electrochemical properties of thin films of electroactive materials formed on the surface of an electrode by the Langmuir ± Blodgett (LB) technique are reviewed. Great attention has been paid to LB films of the charge-transfer materials which may form electroconductive films. This group includes tetrathiafulvalene, tetracyanoquinodimethane, dithiolate complexes of metals, fullerenes, phthalocyanines, conjugated polymers, etc. Also, LB films of other redox materials such as ferrocenes, metal bipyridine complexes, viologens and other electroactive LB films are comprehensively reviewed. Structure ± property relationships in the experimental voltammetry of LB films and their agreement with theoretical models are examined. Specially organized structures, formed by the LB technique, for the study of the mechanism of electron transfer are of special attention. Potential applications of electroactive LB films in electrocatalysis, electrochromic displays, information storage devices and molecular electronic devices are envisaged. The bibliography includes 163 references.
Beilstein Journal of Nanotechnology, 2015
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.
Preparation and conductivity of dithiolene complex Langmuir–Blodgett films
1999
The d.c. electrical property of the dithiolene complex, or bis(4-diethyannodithiobenzil)nickel (BDN) and stearyl alcohol (SA) mixed Langmuir±Blodgett ®lms was investigated. The conductivity of the LB ®lms as a function of the thickness of the ®lms and the ratio of BDN:SA as well as the current versus voltage (I±V) characteristics have been measured. The conductivity of the LB ®lms is about 3X5610 À10 S cm À1 which is less than the bulk conductivity of BDN, and the conductivity of the LB ®lms is strongly in¯uenced by BDN concentration. The I±V property of Al-LB ®lms is governed by the thickness of oxide layers at the LB ®lms with Al electrodes after Auger depth pro®ling analysis.