Layer LB Research Articles

Electrical properties of a calix[4]acid/amine Langmuir–Blodgett thin film

In this work the DC and AC characteristics for metal-LB film-metal structures deposited by a standard Langmuir–Blodgett film deposition technique are investigated. The conduction mechanism has been studied for a thin film structure in which a calix[4]arene substituted with carboxylic acid groups has been deposited alternately with a calix[4]arene molecule substituted with amine groups. This LB film structure shows a typical insulating behaviour for low voltage values and the Schottky effect becomes dominant when the voltage increases. The conductivity at low voltage values was found to be 1.34 × 10 −13 S cm −1. The height of the potential barrier was determined to be 1.65 eV for this alternate layer LB film system.

Preparation and characterization of Langmuir and Langmuir–Blodgett films from a pyridine-terminated stilbene

Langmuir and Langmuir–Blodgett films of a pyridine-terminated stilbene derivative, namely 4-hexyloxy-4′-[N-(4-pyridilmethylene)amine] stilbene (abbreviated as HPAS), have been fabricated and characterized at various surface pressures, with surface pressure and Brewster Angle Microscopy being used to map the different phases of the stilbene monolayer at the air–water interface. UV–vis reflection spectroscopy showed a strong blue shift of 48 and 93 nm of the reflection spectrum of the Langmuir film with respect to the spectrum of a solution of HPAS, which indicates that two dimensional H-aggregates are formed at the air–water interface. These structures represent a minimum free energy conformation for the system, as they are observed even before the compression process starts. The sequential transfer of monolayers of HPAS onto solid substrates results in a Y-type deposition. Single layer LB films transferred at several surface pressures onto mica substrates have been analyzed by means of atomic force microscopy, from which it can be concluded that 20 mN/m is an optimum surface pressure of transfer, giving well-ordered homogeneous films without three dimensional defects and a low surface roughness. The optical properties of the LB films have been determined, with significant blue-shifted absorption spectra suggesting that the two dimensional H-aggregates at the air–water interface are transferred undisturbed onto the solid substrates. In addition, absorption and emission spectra are indicative of a strongly coupled excitonic interaction between the HPAS H-aggregates. X-ray reflectivity (XRR) experiments yielded a film thickness consistent with one monolayer in which the molecules are tilted 73° with respect to the solid substrate.

Characterisation and gas sensing properties of tert-butyl silicon-[bis ethyloxy]-phthalocyanine LB films

An ultrathin Langmuir–Blodgett film of tert-butyl silicon-[bis ethyloxy]-phthalocyanine (tbPcSi(OC 2H 5) 2) has been investigated as an interesting candidate for the detection of nitrogen dioxide gas at a concentration of 5 ppm (by volume). Surface-pressure area isotherms reveal an area per molecule of around 80 Å 2 and that a compact ‘solid’ phase occurs in the region 10–30 mN m −1. Five layer LB films were deposited onto gold interdigitated electrodes on glass in order to facilitate I– V measurements and assess the conductometric sensing properties in response to 5 ppm NO 2. The I– V characteristic is Ohmic and yields a conductivity in the range 3.4 × 10 −6 to 5.9 × 10 −6 (Ω cm) −1 which is comparable to that obtained for other phthalocyanine monomers. Exposing the LB films to NO 2 results in an increase in current (for a 5 V bias) by a factor of 8 and a response time ( t 50) of approximately 200 s. Preliminary UV–vis spectroscopic investigations indicate that the film also responds optically.

Pyroelectric figure of merit for a calix [4] acid/amine alternate layer Langmuir–Blodgett film

In this work calix [4] acid (A) has been deposited alternately with calix [4] amine (B) using the LB film deposition technique to form a non-centrosymmetric ABABA… molecular architecture. Pyroelectric and dielectric electric measurements have been performed for a 31 layer calix [4] acid/amine alternate layer LB film. Pyroelectric coefficients for this LB film system have been obtained using a quasi-static measurement system. Dielectric measurements have been used to determine the dielectric constant and the dielectric loss tangent. The data obtained from pyroelectric and dielectric measurements have been used to calculate the figure of merit for these LB film systems which has a value of 2.56 μC m −2 K −1.

A study of pyroelectric and dielectric properties of alternate layer fluorodeconoylmonoitaconate Langmuir–Blodgett films

Abstract The pyroelectric effect of 1H, 1H1, 2H1, 2H- per fluorodeconoylmonoitaconate monomer/eicosylamine and 1H, 1H1, 2H1, 2H- per fluorodeconoylmonoitaconate polymer/eicosylamine alternate layer LB films has been studied in this work. The quasi-static method has been employed to measure the pyroelectric coefficients, dielectric constant and dielectric loss of these assemblies. Relatively high (for LB films) pyroelectric coefficients of 4.9 μC m−2 K−1 for the monomer/amine and 3.9 μC m−2 K−1 for the polymer/amine have been obtained.

Pyroelectric superlattices based on copolysiloxane/calix[8]arene alternate layer LB films

The pyroelectric effect in alternate layer LB superlattices incorporating interacting lamellae of carboxyl and amino moieties has been investigated. Three distinct systems have been studied, namely (a) a copolysiloxane carboxylic acid/aliphatic amine alternate multilayer, (b) a calix[8]arene carboxylic acid/calix[8]arene amine alternate multilayer, and (c) a hybrid system consisting of a copolysiloxane carboxylic acid/calix[8]arene amine multilayer. In all superlattices there occurs proton transfer between acid and amine moieties leading to a temperature-dependent electric polarisation which is reinforced by added contributions from dipolar reorientation effects. This paper describes how the pyroelectric coefficient can be enhanced by utilising a hybrid alternate layer LB film superlattice containing a 50:50 copolysiloxane substituted with polar aromatic side-chains terminated with carboxyl groups, which is co-deposited with a calix[8]arene molecular basket substituted with primary amine groups. The pyroelectric activity of the copolysiloxane acid/calix[8]arene amine system is substantially higher and stable over a wider temperature range than either of the other two superlattices, giving a pyroelectric coefficient of 10.2 μC m −2 K −1 at 25°C.

The preparation and conductivity of LB films of a novel polymer electrolyte and its complexes with sodium triflate and eicosylamine

Surface pressure-repeat unit area isotherms of a novel helical polyether bearing -C 16H 33 side chains (C16O5), its two-component complex with NaCF 3SO 3 and its three-component complex with C 20H 41NH 2 are described. The areas per molecular repeat unit following addition of salt by uptake from the aqueous phase and by addition in a pre-prepared three-component mixture follow the sequence C16O5<C16O5:NaCF 3SO 3 (subphase)<C16O5:NaCF 3SO 3 (premixed)<C16O5:NaCF 3SO 3:C 20H 41NH 2, where the amine was added by the alternate layer LB technique. Grazing incidence IR confirms the presence of salt in the LB films (20 layers; 10 C16O5:NaCF 3SO 3/10 C 20H 41NH 2) and the formation of a single-phase three-component complex is supported by DSC of bulk materials. Ionic conductivities of the three-component systems, measured normal to the LB layers, show that the pre-prepared sample has the highest conductivity and demonstrates temperature independent conductivity (10 −7 S/cm) over the range ambient to approx. 80°C.

Semiconducting Langmuir-Blodgett films of new Triazolephthalocyanines

Semiconducting Langmuir-Blodgett films of Phthalocyanine analogues 1 and 2 have been prepared. These compounds orient vertically on the Langmuir and Langmuir-Blodgett layers. Six layer LB films show a conductivity around 10 −4 Ω −1 cm −1. Resistance temperature dependence experiments have been performed. The resistance behaviour of the samples is rational with a semiconductor.

Langmuir-Blodgett films of linear polysiloxanes incorporating aromatic side-chains: structure-property relationships

Four aromatic acid side-chain polymers on two different polysiloxane backbones, namely poly(hydrogen-methylsiloxane) homopolymer and poly(hydrogenmethylsiloxane-dimethylsiloxane) copolymer, have been synthesised and characterised. Two different ω-(4-alkoxyphenyl)alkanoic acid side-groups have been studied whose primary spacer groups (the alkyl chain that separates the siloxane backbone from the oxyphenyl group) are -(CH 2) 8- and -(CH 2) 4- and whose secondary spacer groups (the alkyl chain that separates the oxyphenyl group from the carboxylic acid group) are both -(CH 2) 2-. All of these compounds form stable Langmuir films on a pure water subphase and can be co-deposited with monomeric eicosylamine (CH 3(CH 2) 19NH 2) to form alternate layer ABABA… superlattices. Such assemblies exhibit the pyroelectric effect. Indeed, one such alternate layer LB film containing monolayers of the polysiloxane copolymer backbone substituted with aromatic side-chains has yielded one of the highest quasi-static pyroelectric coefficients ever reported for LB films. Its value of 4.6 microC m −2 K −1 is a factor of 3 greater than the coefficient measured for a similar polysiloxane copolymer/eicosylamine multilayer in which the siloxane backbone is substituted with purely aliphatic acid side-groups. Therefore the presence of a molecular dipole (oxyphenyl) within each side-chain, in addition to the ionic dipole that arises from proton transfer between acid and amine groups in adjacent monolayers, has led to a dramatically improved pyroelectric response.

A Two-Legged Spacer Molecule for Alternate Layer LB Film Deposition with Optically Nonlinear Dyes

ABSTRACTSecond harmonic generation from Langmuir-Blodgett films of E-N-octadecyl-4-(2-(4-dimethylaminophenyl)ethenyl)pyridinium iodide (a hemicyanine) interleaved with 4, 4'-dioctadecyl-3, 5, 3', 5'-tetramethyldipyrrylmethene hydrobromide (spacer) increases quadratically with the number of active layers, the second-order nonlinear optical susceptibility of film structures comprising from 1 to 150 bilayers being 70 pm/V. The synthesis and nonlinear optical properties are reported.