Conducting LB Films Research Articles

Metal ion adsorption to conducting organic langmuir-blodgett films

The interactions between conducting LB films and different transition-metal ions (Ni 2+, Cd 2+, Cu 2+, and Zn 2+) have been investigated. The conducting LB films are obtained by mixing bis(ethylenedioxy)tetrathiafulvalene molecule with fatty acid (FA) [H. Ohnuki, T. Noda, M. Izumi, T. Imakubo, R. Kato, Phys. Rev. B 55 (1997) R10225, H. Ohnuki, B. Desbat, M. Giffard, M. Izumi, T. Imakubo, G. Mabon, P. Delhaes, J. Phys. Chem. 105 (2001) 4921]. Characterization of LB films was investigated by infrared absorption and X-ray diffraction techniques. The DC resistivity was increased after immersion of the film in aqueous MCl 2 ( M = Cd, Cu, and Zn) solution with concentration of 2.5 × 10 −4 M. The carboxylate modes were initially absent but could be seen after the film was immersed in the solution.

Incorporation of Glucose Oxidase into Conducting Organic Langmuir-Blodgett Films

Conducting organic Langmuir-Blodgett films (LB) were prepared and their ability to immobilize a protein molecule was discussed. The conducting LB films are obtained by mixing bis-ethylenedioxy-tetrathiafulvalene (BO) molecule with fatty acid (FA). As an enzyme, glucose oxidase (GOD) was immobilized on the conducting LB film. Molecular orientations and other characterization of GOD-LB complexes were investigated by infrared absorption technique. To discuss the use of the conducting LB films for fabricating a glucose sensor, we investigate the change of the FT-IR in GOD-LB complexes after injection of glucose. GOD is absorbed in the LB films and maintains its bioactivity and sensitivity. The present technique with highly ordered conducting LB films is to be used as a suitable platform for immobilization of the enzyme for sensor architecture.

Conducting organic Langmuir–Blodgett films as chemical sensors

A glucose sensor was designed by immobilizing glucose oxidase (GOD) in a conducting organic Langmuir–Blodgett film (LB). GOD–LB complexes were characterized by infrared absorption. The rate of change in the dc conductivity for GOD–LB complexes is ranging from −13.4 to 7.9% after immersion in 3 × 10 −2 mol/l glucose for 2 min. GOD possibly absorbs in the LB films and maintains its bioactivity and sensitivity. The present technique with highly ordered conducting LB films is to be used as a suitable platform for immobilization of the enzyme for sensor architecture.

Effect of UV irradiation on conducting LB films of BEDO-TTF and stearic acid

We report the effect of Uv irradiation on the conducting LB films made of BEDO-TTF and stearic acid. The de electrical resistance of these films increases strongly versus time of irradiation: live orders of magnitude after continuous irradiation for 3 hour. FT-IR spectra also reveal changes from metallic behavior to semiconductive one. X-ray diffraction profile shows a disorder of the film structure. The irreversible transformation of metal to non-metal is due to a loss of the long range order needed for a metallic conduction in the film plane.

Electronic property of the conducting LB film of BEDO-TTF and stearic acid in high magnetic field

The transverse magnetoresistance was measured up to 15 T in the metallic LB films of BEDO-TTF and stearic acid. The negative magnetoresistance shows the existence of the weak localizaion in two-dimensional electronic system (2DES) in these LB films. The magnetoresistance increased linearly with the magnetic field above 3 T , and then exhibited a specific curve associated with 2DES.

New TTF derivatives with pyridine groups: synthesis, electrochemical studies, crystal structure and formation of conducting LB films

Electron donors with two and four pyridine groups 1– 6 were synthesized and characterized. Their oxidation potentials were determined with cyclic voltammetry. A 3D supramolecular complex was formed between 3 and c hlor a nilic acid (CA), and the crystal structure of this neutral complex was determined. Conducting LB films with room temperature conductivity up to 1.1×10 −3 S cm −1 were prepared from electron donors 1 and 4.

Structural Control of Alkylammonium-Au(dmit)2 LB Films

The structure of conductive LB films based on dioctadecyldimethylammonium-Au(dmit)2 (2C18-Au(dmit)2) is studied by introducing into a parameter, “waiting time”, which is defined as the time between the application of spreading solvent and the onset of compression. The π-A isotherms and the Brewster angle microscopy suggest that 2C18-Au(dmit)2 complex forms multi-layered films on the water surface, whereas, the in-plane conductivity of the LB films after anodic oxidation increases with increasing the “waiting time”.

Structure and Properties of Highly Conductive Langmuir-Blodgett Films Based on Dialkyldimethylammonium-metal(dmit)2

Structure and electrical properties of conductive LB films based on dioctadecyldimethylammonium-Au(dmit)2 (2C18-Au) are studied. UV/visible polarized absorption spectra suggest that the longer axis of Au(dmit)2 is appreciably tilted against the film plane. Both of the as-deposited and electrochemically oxidized LB films give sharp X-ray diffraction peaks at 2θ = 3.15° indicating a d-spacing of 2.8 nm. The in-plane conductivity of the film is semiconductor-like with an activation energy of 0.05 eV.

SYNTHESIS AND PROPERTIES OF NEW BISDITHIOLENE METAL COMPLEXES OF THE 1,3-DITHIOLE-2-THIONE-4,5-DITHIOLATE (DMIT) LIGAND

Two series of integer or non-integer oxidation-state metal complexes of the multi-sulfur donor ligand 1,3-dithiole-2-thione-4,5-dithiolate (DMIT) with Cd (II). Hg (II), Sn (II), Mn (II). Fe (II), Co (II). or Bi (III) have been prepared as tetraalkylammonium salts. The compounds are characterized by elemental analysis, 1H NMR spectra, Fourier Transform IR spectra, and UV-Vis spectral analysis. The electrochemical properties of the complexes are also studied by cyclic voltammogram and conductivity measurements on the compressed pellets. A highly conducting LB film is constructed from one of the complexes cetylpyridinium-Cd(dmit)2.

A novel strategy to prepare conducting LB films based on TTF derivatives

A new method is described for the preparation of conducting Langmuir-Blodgett films based on tetrathialfulvalene (TTF) derivatives without long alkyl chain substitution. The mixed molecular system of behenic acid (BA) and oxygen-substituted TTF-type donor molecules such as 4,5-ethylenedioxy-4′,5′-ethylenedithio-tetrathiafulvalene (EOET) or bis-ethylenedioxy-tetrathiafulvalene (BO) provides a stable bilayer film at the air/water interface. In the LB films prepared by Y-type deposition, the donor molecules form mixed-valence dimers such as D + D 0, without secondary treatments. The maximum conductivities of the LB films reached 1.0S cm −1 (EOET + BA) and 25 S cm −1 (BO + BA) at room temperature. The surface pressure/area isotherms and Fourier transform infra-red spectra are also reported with regard to, respectively, film formation on the water surface and the mixed-valence dimer state under different molar ratios of the donors to B A.

Attenuation of surface acoustic waves by conducting Langmuir-Blodgett films of charge-transfer complexes (C 16H 33-TCNQ) 0.4-(C 17H 35-DMTTF) 0.6

The d.c. conductivity and attenuation of surface acoustic waves (SAW) have been measured in conducting LB films prepared by the vertical dipping method as a function of temperature. The large attenuation of SAW by the film is due to the electric field coupling loss in the film. The a.c. conductivity calculated from the attenuation data is compared with the d.c. conductivity

Thin film organic channel field effect transistor

Accumulation Field effect transistors based on undoped, conducting Langmuir-Blodgett films have been successfully made. They exhibit reasonably high field induced drain current modulation. In the voltage range explored, the onset of drain current saturation is observed. A model accounting for the electrical behaviour of these FET's is presented, which gives access to several material characteristics impossible to obtain by direct measurements on the conducting LB films.

Semiconducting Langmuir–Blodgett films of non-amphiphilic ethylenedithio–tetrathiafulvalene derivatives bearing pyridine and pyridinium substituents

Compounds 1 and 2 form stable Langmuir–Blodgett films which after iodine doping are semiconducting (σrt= 10–3 S cm–1), demonstrating that the attachment of long alkyl chains is not a prerequisite for the formation of conducting LB films of tetrathiafulvalene (TTF)-based charge-transfer complexes.

Physical properties of a mixed conducting Langmuir-Blodgett film based on tetrathiafulvalene derivative with or without iodine oxidation

A tetrathiafulvalene derivative — tetrabenzylthiotetrathiafulvalene (TBT-TTF) — is a new material for a conducting Langmuir-Blodgett film. A 1:1 molar mixture with stearic acid was built up to obtain a conducting LB film. The conductivities of this mixed LB film were calculated from experimental results before and after iodine oxidation. To understand the increase in conductivity after iodine oxidation, the IR electronic absorption spectra and X-ray diffraction were investigated. The IR results suggest that the system undergoes continuous free chemical reactions after iodine oxidation. TBT-TTF forms the radical cation dimers associated with I 3 −. Finally, interaction of this new charge transfer complex (TBT-TTF) x (I 3 −) 1− x ( x < 1), gives rise to a new conducting LB film with the highest conductivity (4.7 × 10 −2 S cm −1). However, the conducting phase is unstable. The LB film can be oxidized repeatedly by iodine vapour. This is a possible application for gas sensors. The result of X-ray diffraction demonstrates that the molecular reorganization occurs because of tri-iodine chains in the bilayer.

Surface potential studies of monolayers of surfactant donor and acceptor molecules

The surface potential technique was used for investigation of donor, acceptor and mixed monolayers, containing molecules suitable for deposition of conducting LB films. It is shown that the donor and acceptor monolayers are neutral at the air-water interface. Big positive values of surface potential in the case of donor molecules are explained by peculiarities of dipole depolarization near the surface of the water and by charge transfer salt formation with water-soluble impurities. The dipole moment arising due to charge transfer between donor and acceptor molecules in mixed monolayers is parallel to the layer plane. Other details of charge transfer complexes or salt formation in the mixed monolayers are discussed.

Doped (conducting) and undoped (semi-insulating) LB films: application to gas sensing

The present paper deals with the use of semi-insulating and conducting LB films as conductimetric sensors. The response of such sensors consists in conductivity changes induced by gas exposure. Examples collected in the literature are presented and show that the LB technique is very convenient for making continuous ultrathin organic materials exhibiting detection properties towards toxic gases (NO 2, PH 3,…). Very interesting results have been obtained using mixed LB films even if the conducting properties of the resulting material and the detection mechanism are not well understood. Some multifunctional materials are required exhibiting conduction properties for transduction and ‘recognition properties’ for selective detection. With that goal, the LB technique associated with organic chemistry provides undeniable advantages.

Prototype of a phosphine sensor based on a conducting LB film

Prototype of a phosphine sensor based on a conducting LB film

Atomic force microscopic study on the molecular arrangement of highly conductive LB films of metal(DMIT) 2

The atomic force microscope (AFM) was used to obtain the images of the LB film of tridecylmethylammonium-Au(dmit) 2 complex mixed with icosanoic acid. A single-layered sample of the as-deposited LB film revealed a heterogeneous structure with very thin plate-like crystallites of the order of μm distributed in the film surface. The height of the crystalline was about 18 nm measured from the planar region in which a monolayer of icosanoic acid was assumed to be present. This thickness corresponded to a stacking of ca. 10 molecules of Au(dmit) 2 with each of the molecular plane almost parallel to the film surface, taking into account the molecular arrangement in a single crystal. No epitaxial deposition was observed for a multilayered sample, which was shown by the almost random stacking of the plate-like crystallites. The AFM image changed with the electrochemical oxidation that was necessary to make the film conductive. The blurring of the outline of the plate-like crystallites was observed, suggesting a structural change of the crystallites accompanied by the electrochemical oxidation.

ESR analysis of columnar structure in conductive LB films of TCNO salts with alkylpyridinium and its derivatives

The temperature dependent spin susceptibility of the LB films of a TCNQ salt with an alkylpyridinium was found to be explained by the random-exchange Heisenberg antiferromagnetic chain model, indicating the development of 1D spin chains in the system. The ESR spectra of the films at the X and K bands show clear out-of-plane anisotropy. The analysis of these line shapes using the spectrum simulation method reveals that the linewidth anisotropy is dominated by the exchange-narrowed secular dipolar width peculiar to quasi-1D spin systems. This result provides further evidence for the development of the 1D columnar structure of TCNQ molecules, and suggests that the chain axis lies in the film plane. In addition, the analysis yields the orientation of TCNQ molecules, which is consistent with the formation of the columnar structure.

Molecular Systems of Photoactive and Conductive LB Films

Abstract Photoactive and conductive Langmuir-Blodgett films are described utilizing cyclodextrin derivatives, TCNQ radical salts, metal-dmit complexes and fullerenes to form 0,1,2, and 3-dimensional molecular systems.