Thickness effect on electrical properties of Pb(Zr0.52Ti0.48)O3 thick films embedded with ZnO nanowhiskers prepared by a hybrid sol-gel route

Silicon-based lead zirconate titanate thick films embedded with zinc oxide nanowhiskers (ZnO_w-PZT) were prepared by a hybrid sol-gel route. ZnO_w-PZT films with thickness from 1.5 μm to 4 μm are perovskite structure and have smooth surface without any cracks. As the thickness increases, the remanent polarization and dielectric constant increase, but the coercive field and tetragonality decrease. Compared with PZT films, the ZnO_w-PZT film has the close tetragonality and electrical properties which are different from those of bulk PZT-based ceramic doped with ZnO powder. The thickness dependences of the ferroelectric and dielectric properties are attributed to the relaxation of internal stress.     

Monomolecular enzyme films stabilized by amphiphilic polyelectrolytes for biosensor devices

This paper describes the use of new amphiphilic polyelectrolytes for protein immobilization. Monomolecular films of glucose oxidase (GO) and monoamine oxidase (MAO) stabilized by amphiphilic polyelectrolytes (polyethyleneimine and poly-4-vinylpyridine derivatives modified by lauryl chains) were formed on a water surface in a Langmuir-Blodgett trough. The compressed films containing the enzymes were transferred onto the surface of a polypropylene membrane of a Clark electrode according to the Langmuir-Schaefer method. The analytical responses of the resulting biosensors were linear over the range 1–10 mM of glucose and 8–100 μM of tyramine. Furthermore, direct functional coupling of GO and ferrocenecarboxylic acid in multilayer films stabilized by amphiphilic polyelectrolytes was demonstrated. The amperometric response of such a sensor was linear over the range 1–20 mM of glucose. The dependence of the kinetic parameters of the enzymes on the amphiphilic polyelectrolyte structures is discussed.     

Effects of sol infiltration on the screen-printed lead zirconate titanate thick films

Ferroelectric PZT(60/40) thick films were fabricated by the screen-printing method and the PZT precursor solution was spin-coated on the thick films to obtain a densification. Structural and electrical properties of the thick films with the treatment of sol coating were investigated. The lattice constant of PZT thick films was 0.4073 nm and there is no dependence on the number of sol coatings. The thickness of PZT films obtained by one screen-printing was approximately 16 μm. The relative dielectric constant increased and dielectric loss decreased with the increase in the number of sol coatings, and the values of the 15-coated PZT-15 film were 369 and 2.16% at 1 kHz, respectively. The remanent polarization, coercive field, and breakdown strength of the PZT-15 thick film were 23.2 μC/cm², 18.03 kV/cm and 78 kV/cm, respectively.     

Langmuir-Blodgett films from polyaniline/ruthenium complexes as modified electrodes for detection of dopamine

Langmuir-Blodgett (LB) films from mixtures of polyaniline (PANI) and the ruthenium complex mer-[RuCl₃(dppb)(py)] (dppb=PPh₂(CH₂)₄PPh₂; py=pyridine) (Rupy) were used to modify electrodes and to detect dopamine (DA). The electrochemical response has been used as the principle of detection in order to exploit the molecular-level interaction between PANI and Rupy in the LB films. Cyclic voltammograms were performed in a potential range where the Rupy complex is not electroactive and the response is dominated by the interconversion between the oxidation states leucoemeraldine and emeraldine of PANI. In the presence of DA a further redox pair appears at approximately 230 and 0 mV, associated with oxidation/reduction of DA to dopaminequinone. The current increased linearly in the range between 4.0×10⁻⁵ and 1.2×10⁻³ mol/l. The detection limit for DA concentrations for the 21-layer LB film from PANI/Rupy was 4.0×10⁻⁵ mol/l, which is sufficient to detect DA in a pharmaceutical product. The modified electrode based on PANI/Rupy LB films is selective to DA, particularly because the oxidation potential for DA is lowered, in comparison to a bare indium-tin-oxide electrode. The presence of ascorbic acid, which is an important interferent for DA, could be detected when its concentration was three times that of DA.     

Physico-chemical and electrical properties of InSe films

Thin films of InSe were obtained by vacuum evaporation of polycrystalline material onto well cleaned glass substrates. After deposition on a cold substrate the samples were placed in a vacuum-sealed Pyrex tube for the annealing process. Physico-chemical and electrical properties of the InSe layers have been investigated. RBS and X-ray diffraction measurements showed that the InSe phase could be obtained. Electrical properties of the InSe layers are studied for different annealing temperatures. Conductivity measurements show that the behaviour of the films is sensitive to their thermal environment. The conductivity is controlled by grain boundaries.     

Spreading behavior of polymerizable monolayers of acrylamides with double alkyl chains and polymerization of the LB films

The spreading behavior of N,N'-dialkylacrylamide (dAAs) monomers on a water surface is investigated by measurement of surface pressure-area isotherms as a function of alkyl chain length and temperature. The monolayers of dAAs can be classified into three types. (I) N,N'-dioctadecylacrylamide (dODA) shows a rapid increase in surface pressure indicating formation of a rigid condensed monolayer; (II) the isotherm of N,N'-dihexadecylacrylamide (dHDA) has a plateau region in surface pressure corresponding to a phase transition from a expanded form to a condensed form, which corresponds to gel-liquid crystal phase transition often observed in biomembranes; and (III) the dialkylacrylamides with alkyl chain length shorter than the hexadecyl group form expanded monolayers with no condensed monolayer at any temperature. The similar three kinds of monolayers are also observed in the isotherms for dHDA monolayer as a function of temperature. It is found that two carbon elongation in double alkyl chains causes the same effect on the monolayer induced by about 10 °C cooling. Under various conditions, only liquid condensed monolayers are transferred on to a solid support, yielding the monomer LB films, practically, of dODA at any temperature and dHDA at low temperature. The polymerization of those LB films by UV irradiation was ascertained by the electronic absorption spectra.     

Dynamic scaling function of polarization hysteresis in ferroelectric thin films

The scaling behavior of the polarization hysteresis dispersion in a mode spin-like system based on the three-dimensional (Φ²)² model with O(N) symmetry in the limit N → ∞, upon applying of the time-varying electric field, is investigated. We perform a simple analysis on the dynamic relaxation of the polarization and propose a scaling function in order to describe the scalability of the hysteresis dispersions over a wide range of field magnitude. The applicability of this scaling function is demonstrated by a consistent fitting to the experimental data on several types of ferroelectric thin films.     

Resistive hysteresis in BiFeO3 thin films

Capacitor-like Au/BiFeO₃/SrRuO₃ thin film with (1 1 1) orientation was grown on the SrTiO₃ (1 1 1) substrate by radio frequency magnetic sputtering. It shows a resistive switching behavior, where a stable hysteresis in current–voltage curve was well developed by applying an optimum voltage at room temperature, and it reached the saturation at a bias voltage of 8 V. The Child's law in V_max → 0 direction and the interface-limited Fowler–Nordheim tunneling in 0 → V_max direction, together with the polarization reversal in the BiFeO₃ barrier, are shown to involve in the observed resistive hysteresis.     

Effect of Nb2O5 seed layer on electrical properties of alkaline niobate based ferroelectric thin films

K_0.5Na_0.5NbO₃ and K_0.5Na_0.5Nb_0.995V_0.005O₃ ferroelectric thin films were prepared by a chemical solution deposition method. The Nb₂O₅ seed layer was introduced to investigate the electrical properties of the films. Crystalline structures and microstructures were analyzed by X-ray diffraction and scanning electron microscope at room temperature. The electrical properties were studied both for the films with and without Nb₂O₅ seed layer. It is found that the films' quality was modified by adding the seed layer, and the V-doping also plays an important role in improving the films quality. The ferroelectric and dielectric properties of the films were obviously enhanced by adding the seed layer, especially for the V-doped film. These results may be due to the better crystallization and microstructure of the films.     

All-organic polymer-dispersed liquid crystal light-valves integrated with electroactive anthraquinone-2-sulfonate-doped polypyrrole thin films as driving electrodes

All-organic PDLC (polymer-dispersed liquid crystal) light-valves using all-polymer conductive substrates containing thin films of polypyrrole doped with anthraquinone-2-sulfonate (AQSA⁻) as the driving electrodes were fabricated in this study. The all-polymer conductive substrates were prepared under ambient conditions by in situ depositing polypyrrole thin films on blank flexible poly(ethylene terephthalate), or PET, substrates from aqueous media in which oxidative polymerization of pyrrole was taking place. The obtained flexible all-polymer conductive substrates were semi-transparent with cohesive coatings of AQSA⁻-doped polypyrrole thin films (thickness ∼55 nm). The all-polymer flexible conductive substrates had sheet resistivity ∼40 kΩ □ ⁻¹and T% transparency against air ∼78% at 600 nm. The light-valves fabricated using the above all-polymer conductive substrates showed ∼50% transparency against air at 600 nm when 4 V μm⁻¹ electric field was applied.     

Structural and electrical properties of Ag films sputter-deposited on HCl-doped and undoped polyaniline substrates

Ag films were sputter-deposited on HCl-doped polyaniline (HCl-PANI) and undoped polyaniline (PANI) substrates at 300 K. The 50 nm- and 200 nm-thick Ag films grown on HCl-PANI substrates convert respectively to the AgCl film and the AgCl–Ag composite film because Cl ions in the HCl-PANI substrate diffuse into the Ag films and the chemical reaction of Ag atoms with Cl ions occurs. The AgCl and AgCl–Ag composite films are porous. The Ag film grown on PANI substrate has a dense structure and its grain size increases with increasing film thickness. The conductance of the film grown on the PANI substrate does not change markedly with aging time. For the Ag film grown on the HCl-PANI substrate, however, the conductance decreases significantly with increasing aging time. After the aging time reached a threshold value, the conductance does not change with the aging time. The threshold time increases with increasing film thickness. The reaction controlled process dominates the formation of AgCl film on the HCl-PANI substrate.     

Direct current electrical conduction mechanism in plasma polymerized thin films of tetraethylorthosilicate

The plasma polymerized tetraethylorthosilicate (PPTEOS) thin films were deposited on to glass substrates at room temperature by a parallel plate capacitively coupled glow discharge reactor. The current density-voltage (J-V) characteristics of PPTEOS thin films of different thicknesses have been observed at different temperatures in the voltage region from 0.2 to 15 V. In the J-V curves two slopes were observed — one in the lower voltage region and another in the higher voltage region. The voltage dependence of current density at the higher voltage region indicates that the mechanism of conduction in PPTEOS thin films is space charge limited conduction. The carrier mobility, the free carrier density and the total trap density have been calculated out to be about 2.80 × 10^− 15m²V^− 1s^− 1, 1.50 × 10²²m^− 3 and 4.16 × 10³³m^− 3 respectively from the observed data. The activation energies are estimated to be about 0.13 ± 0.05 and 0.46 ± 0.07 eV in the lower and higher temperature regions respectively for an applied voltage of 2 V and 0.09 ± 0.03 and 0.43 ± 0.10 eV in the lower and higher temperature regions respectively for an applied voltage of 14 V. The conduction in PPTEOS may be dominated by hopping of carriers between the localized states at the low temperature and thermally excited carriers from energy levels within the band gap in the vicinity of high temperature.     

Structure and electrical properties of bismuth thin films prepared by flash evaporation method

Polycrystalline Bi thin films with thickness in the range 40-160 nm have been successfully deposited on glass substrates at 453 K by flash evaporation method for the first time. XRD and FE-SEM were performed to characterize their structure and surface morphology respectively. Electrical resistivity measurement was carried out in the temperature range 300-350 K. Hall coefficient, electron concentration and mobility were measured at 300 K. A distinctly oscillatory behavior has been observed for the electrical properties of the Bi thin films.     

Thin films of liquid crystal fumarates and a related acrylate

Five fumarate esters and one acrylate ester have been synthesized and their properties examined. Four of them can be deposited as multilayers by evaporation in vacuo, and three of this group behave as thermotropic smectic liquid crystals. We have attempted to stabilize the homeotropic smectic phase by polymerizing the film using UV light. In two cases we have been successful and have produced films which are resistant to prolonged heating in THF. We infer that these materials are both polymerized and cross linked. They retain their regular layer structure after polymerization, a behaviour which we have demonstrated by X-ray diffraction. We have also attempted to form Langmuir-Blodgett multilayers with these compounds and in four cases have been successful.     

Monoparticulate films of polyaniline

Monoparticulate films were prepared from colloidal polyaniline (PANI) via the Langmuir-Blodgett (LB) technique. An aqueous dispersion of PANI obtained by aniline polymerization in the presence of polyvinyl alcohol was spread at the air-water interface in a LB trough. The floating films were transferred by the vertical lifting method to Si wafer or glass substrates. The films were very stable and could not be removed during immersion in aqueous solutions for at least several months. The color of dry monoparticulate PANI films was violet independently of the color adapted upon immersion in aqueous media at different pH. We suggest that not only the wavelength of the absorbed light, but also that of the scattered light, has an effect on the color of PANI.     

Effect of the electrode structure on the electrical properties of alkoxide derived ferroelectric thin film

Effect of the thermal expansion coefficient of electrode on the electrical properties in lead zirconate titanate (PZT) with morphotropic phase boundary (Pb(Zr_0.53,Ti_0.47)O₃: MPB) composition film was demonstrated in this paper. The lanthanum nickel oxide (LaNiO₃: LNO) and lanthanum strontium cobalt oxide ((La_0.5,Sr_0.5)CoO₃: LSCO) was deposited by chemical solution deposition (CSD) as bottom electrode on Si wafer. Highly (100)-oriented LSCO layers were successfully prepared by CSD on Si wafer using (100)-oriented LNO layers as seeding layer for the crystal orientation control. As a result, (100) and (001) oriented PZT film was also successfully prepared on LSCO/LNO/Si stacking structure. The obtained dielectric and ferroelectric properties changed according to the thermal stress which was influenced by the bottom electrode thickness.     

On the structural and electrical characteristics of zinc oxide thin films

ZnO thin films with thickness d = 100 nm were deposited by radio frequency magnetron sputtering onto glass substrate from different targets. The structural analyses of the films indicate they are polycrystalline and have a wurtzite (hexagonal) structure. Crystallites are preferentially oriented with (002) plane parallel to the substrate surface and the samples have low values for surface roughness, between 1.7 nm and 2.7 nm. The mechanism of electrical conduction in the studied films is strongly influenced by this polycrystalline structure and we used Van der Pauw method to analyze these properties. Electrical studies indicate that the ZnO thin films are n-type. For the cooling process, thermal activation energy of electrical conduction of the samples can vary from 1.22 eV to 1.07 eV (for the ZnO layer obtained from for metallic Zn target) and from 0.90 eV to 0.63 eV (for the ZnO layer obtained from ZnO target), respectively. The influence of deposition arrangement and oxidation conditions on the structural and electrical properties of the ZnO films was investigated in detail.     

Nanostructure, electrical and optical properties of p-type hydrogenated nanocrystalline silicon films

In this paper, p-type hydrogenated nanocrystalline (nc-Si:H) films were prepared on corning 7059 glass by plasma-enhanced chemical vapor deposition (PECVD) system. The films were deposited with radio frequency (RF) (13.56 MHz) power and direct current (DC) biases stimulation conditions. Borane (B₂H₆) was a doping agent, and the flow ratio η of B₂H₆ component to silane (SiH₄) was varied in the experimental. Films’ surface morphology was investigated with atomic force microscopy (AFM); Raman spectroscopy, X-ray diffraction (XRD) was performed to study the crystalline volume fraction X_c and crystalline size d in films. The electrical and optical properties were gained by Keithly 617 programmable electrometer and ultraviolet-visible (UV-vis) transmission spectra, respectively. It was found that: there are on the film surface many faulty grains, which formed spike-like clusters; increasing the flow ratio η, crystalline volume fraction X_c decreased from 40.4% to 32.0% and crystalline size d decreased from 4.7 to 2.7 nm; the optical band gap E_g^opt increased from 2.16 to 2.4 eV. The electrical properties of p-type nc-Si:H films are affected by annealing treatment and the reaction pressure.     

Electrical manifestation of dielectric non-centrosymmetry using Langmuir-Blodgett multilayers of ω-tricosenoic acid

Centrosymmetric (Y-type) and non-centrosymmetric (Z-type) Langmuir-Blodgett (LB) multilayers of ω-tricosenoic acid have been deposited as part of an M¦LB¦M structure and the electrical characteristics measured. The symmetry of the LB film was manifested in the electrical properties of the junction, with the behaviour of centrosymmetric LB films being independent of the applied bias sense and non-centrosymmetric LB films possessing a distinct bias sense dependence.