High frequency study of electropolymerised conducting polypyrrole thin film

The polypyrrole (PPY) thin films were synthesized by electropolymerisation in potassium nitrate solution. The substrate used was stainless steel. DC conductivity, microwave reflection, microwave conductivity and microwave dielectric constant of the conducting PPY thin films are reported. DC conductivity was between 1.6 × 10⁻² S/cm and 42.3 × 10⁻² S/cm. Microwave conductivity was between 10 S/cm and 160 S/cm. The ?′ generally decreases as frequency increases similarly ?″ also decreases with increases in frequency. The measurements have been carried over the frequency range 8.2-12 GHz. These polypyrrole thin films were characterized by FTIR. The polypyrrole thin film increases the reflectivity of the stainless steel.     

From silver nanoparticles to thin films: Evolution of microstructure and electrical conduction on glass substrates

Silver nanoparticles embedded in a dielectric matrix are investigated for their potential as broadband-absorbing optical sensor materials. This contribution focuses on the electrical properties of silver nanoparticles on glass substrates at various morphological stages. The electrical current through thin films, consisting of silver nanoparticles, was characterized as a function of film thickness. Three distinct conductivity zones were observed. Two relatively flat zones (“dielectric” for very thin films and “metallic” for films thicker than 300-400 Å) are separated by a sharp transition zone where percolation dominates. The dielectric zone is characterized by isolated particle islands with the electrical conduction dominated by a thermally activated tunneling process. The transition zone is dominated by interconnected silver nanoclusters—a small increase of the film thickness results in a large increase of the electrical conductivity. The metallic conductivity zone dominates for thicknesses above 300-400 Å.     

Electrical conductivity and dielectric properties of SiO<Subscript>2</Subscript> nanoparticles dispersed in conducting polymer matrix

Electrical and dielectric properties of conducting polypyrrole–wide band gap silica (PPY–SiO₂) nanocomposites have been investigated as a function of temperature and frequency for different concentrations of polypyrrole. The average grain size of the nanocomposites is in the range of 40–80 nm. Impedance spectra reveal two distorted semicircles corresponding to grain and grain boundary effects. The magnitude of conductivity and its temperature variation are significantly different from polypyrrole and silica. A very large dielectric constant of about 4800 at 30 kHz and at room temperature has been observed for the highest concentration of silica. Inhomogeneous behavior of nanocomposites gives rise to high dielectric constant.     

Dielectric property of CaCu3Ti4O12 thin film grown on Nb-doped SrTiO3(100) single crystal

Thin film of CaCu₃Ti₄O₁₂ (CCTO) has been deposited on Nb-doped SrTiO₃(100) single crystal using pulsed laser deposition. The dielectric constant and AC conductivity of CCTO film in the metal–insulator–metal capacitor configuration over a wide temperature (80 to 500 K) and frequency (100 Hz to 1 MHz) range have been measured. The small dielectric dispersion with frequency observed in the lower temperature region (<300 K) indicates the presence of small defects in the deposited CCTO thin film. The frequency-dependent AC conductivity at lower temperature indicates the hopping conduction. The dielectric dispersion data has been analyzed in the light of both conductivity relaxation and Debye type relaxation with a distribution of relaxation times. Origin of dielectric dispersion is attributed to the distribution of barrier heights such that some charge carriers are confined between long-range potential wells associated with defects and give rise to dipolar polarization, while those carriers which do not encounter long-range potential well give rise to DC conductivity.     

Electronic transport mechanisms in tetraphenyleprophyrin thin films

Thermally-evaporated thin films of tetraphenylporphyrin, TPP, with thickness range from (175 to 735) nm had been prepared. Annealing temperatures ranging from (273–473) K do not influence the amorphous structure of these films. The influence of environmental conditions: film thickness, temperature and frequency on the electrical properties of TPP thin films had been reported. It was found that dc conductivity increases with increasing temperature and film thickness. The extrinsic conduction mechanism is operating in temperature range of (293–380) K with activation energy of 0.13 eV. The intrinsic one is in temperatures >380 K via phonon assisted hopping of small polaron with activation energy of 0.855 eV. The ac electrical conductivity and dielectric relaxation in the temperature range (293–473) K and in frequency range (0.1–100) kHz had been also studied. It had been shown that theoretical curves generated from correlated barrier hopping (CBH) model gives the best fitting with experimental results. Analysis of these results proved that conduction occurs at low temperatures (300–370) K by phonon assisted hopping between localized states and it is performed by single polaron hopping process at higher temperatures. The temperature and frequency dependence of both the real and imaginary parts of dielectric constant had been reported.     

Improving the electrical conductivity of CuCrO2 thin film by N doping

N-doped CuCrO₂ thin films were prepared by using radio frequency magnetron sputtering technique. The XRD and XPS measurements were used to confirm the existence of the N acceptors in CuCrO₂ thin films. Hall measurements show the p-type conduction for all films. The electrical conductivity increases rapidly with the increase in N doping concentration, and the maximum of the electrical conductivity of 17 S cm⁻¹ is achieved for the film deposited with 30 vol.% N₂O, which is about three orders of magnitude higher than that of the undoped CuCrO₂ thin film. Upon increasing the doping concentrations the band gaps of N-doped CuCrO₂ thin films increase due to the Burstein-Moss shift.     

Dependence of the optical properties of UHV deposited silver thin films on the deposition parameters and their relation to the nanostructure of the films

Silver films were deposited on glass substrates under different deposition conditions, i.e. different film thicknesses, deposition rates and deposition angles. Their optical properties were measured by spectrophotometry in the spectral range of 185–3300 nm. The Kramers–Kronig method was used to analyze the reflectivity curves of the silver films to obtain their optical constants. The influence of substrate temperature on the microstructure of thin metallic films, the structure zone model (SZM), is well established, whereas there has been some previous work on the influence of film thickness and morphology, deposition rate and deposition angle on the microstructure and morphology of thin films. An effective medium approximation (EMA) analysis was used to establish the relationship between the atomic force microscopy results, SZM predictions and EMA results, and hence the optical properties of silver thin films. The predictions of the Drude free-electron theory are compared with experimental results for dielectric functions of Ag films produced under different deposition conditions. The real part of the dielectric constant increases with film thickness and decreases with increasing deposition rate and with increasing incidence angle, whereas the imaginary part of the dielectric constant decreases with increasing film thickness and deposition rate and with decreasing incidence angle over the whole energy range measured, including the interaband and interband regions.     

High frequency impedance spectroscopy study on Gd-doped CeO<Subscript>2</Subscript> thin films

The gadolinia-doped ceria (GDC) thin films were deposited by pulsed laser deposition. Samples with special geometry were prepared which allowed us to characterize GDC film in across-plane direction. The electrical properties of the films were investigated by means of impedance spectroscopy in the frequency range of 10 Hz to 10 GHz and 380–600 K temperature interval. The data analysis was performed by using appropriate equivalent circuit. The equivalent circuit modeled thin GDC film itself, platinum metal connections (traces) in the dielectric medium of sapphire substrate and interfaces between the film and platinum electrodes. Hence, several factors influenced the impedance spectra, namely the properties of substrate, the oxygen-ion transport in the film, ion blocking at the interface between the film and the electrode, and metal traces. The electrical properties of GDC thin films were compared with these of bulk ceramics and showed similar conductivity and dielectric permittivity values. The study also revealed that measurement data at electrical field frequencies of up to 10 GHz were particularly important to correctly estimate electrical properties of GDC thin films, because at high temperatures the electric response of GDC film shifts to high frequencies (higher than 1 MHz at 600 K). The thin film sample preparation for high frequency measurements and fitting of impedance data by using relatively simple equivalent circuit model is presented.     

The conductivity and dielectric studies of solid polymer electrolytes based on poly (acrylamide-co-acrylic acid) doped with sodium iodide

Solid polymer electrolyte thin films based on polyacrylamide-co-acrylic acid (PAAC) doped with sodium iodide (NaI) with different ratios of polymer and salt added with fixed amount of additive of propylene carbonate (PC) were prepared by using solution casting method. The PC was added to the mixture of the solution to provide more flexibility to the polymer film by increasing the plasticity of the thin film membrane. The conductivity and dielectric studies were carried out on these thin films to understand the ion transport properties of the polymer electrolytes. The highest conductivity obtained was 1.88?×?10^?5 S cm^?1 for the 30% NaI salt-doped polymer electrolyte system at room temperature. The temperature-dependent conductivity agrees with Arrhenius relationship which shows that hopping mechanism of ions in the polymer matrix. The dielectric properties especially the loss tangent used to analyze the segmental relaxation of the polymer chain as more concentration of salt was incorporated. The electric modulus was studied to understand the electrical relaxation processes to overcome electrode polarization effect.     

Coupling of surface plasma oscillations in thin periodically corrugated silver films

We investigated surface plasma oscillations (SPO's) in a layer system of thin dielectric films with a periodically corrugated surface coated by a silver film. SPO's at both surfaces of the silver film could be excited by light. We observed coupling of the two SPO's through the thin film via the periodicity of the surface and as a consequence a discontinuity in the dispersion relations of the SPO.     

Synthesis and characterization of silver-polypyrrole film composite

In this work, we report the chemical polymerization of pyrrole to obtain thin film of polypyrrole (PPy) hydrochloride deposited onto the electrode of the quartz crystal microbalance (QCM). The film in the base form was exposed to a solution of AgNO₃. Electroless reduction for silver ions by the PPy film took place and silver particles were adsorbed onto the film surface. The silver particles content at the PPy films were analyzed by QCM and the results showed that the concentrations of silver uptakes increase as the original AgNO₃ solution increases. The morphology of the surface of the PPy film and the silver-PPy film composite were studied by the scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDX). They showed that the obtained silver particles have spherical, cubic and tetrahedral structures. X-ray diffraction (XRD) and Fourier transformed infra-red spectroscopy (FTIR) were used to characterize the structure of the powder composite. This work reveals the capability of PPy film coating on QCM in sensing and removing silver from several environmental samples.     

Cerium oxide nanoparticles protect primary mouse bone marrow stromal cells from apoptosis induced by oxidative stress

The sintering of a silver (Ag) nanoparticle film by laser beam irradiation was studied using a CW DPSS laser. The laser sintering of the Ag nanoparticle thin film gave a transparent conductive film with a thickness of ca. 10 nm, whereas a thin film sintered by conventional heat treatment using an electronic furnace was an insulator because of the formation of isolated silver grains during the slow heating process. The laser sintering of the Ag nanoparticle thin film gave a unique conductive network structure due to the rapid heating and quenching process caused by laser beam scanning. The influences of the laser sintering conditions such as laser scan speed on the conductivity and the transparency were studied. With the increase of scan speed from 0.50 to 5.00 mm/s, the surface resistivity remarkably decreased from 4.45 × 10⁸ to 6.30 Ω/sq. The addition of copper (Cu) nanoparticles to silver thin film was also studied to improve the homogeneity of the film and the conductivity due to the interaction between the oxidized surface of Cu nanoparticle and a glass substrate. By adding 5 wt% Cu nanoparticles to the Ag thin film, the surface resistivity improved to 2.40 Ω/sq.     

氮化硅纳米薄膜非平衡热导率实验研究

3ω实验方法是一种可以对薄膜热导率进行瞬时测量的方法。根据3ω方法测试原理,搭建了薄膜导热系数测试平台,并且分别测试低频率段和高频段薄膜与基底的温升以及薄膜热导率。测试结果表明:Si3N4薄膜的热导率随温度的升高而增大;高频段下,热导率受频率影响大,误差大;在低频段下薄膜热导率与频率变化基本无关;基于电子与声子的局部热平衡运输方程假设,S i3N4薄膜的热导率具有极度非平衡性;通过比较电阻、热导率与温度的关系可以看出加热器的尺寸大小会影响薄膜的热导率,最佳加热器的宽度选用20μm左右。     

Electrical conductivity and dielectric properties of β-BaB<Subscript>2</Subscript>O<Subscript>4</Subscript> crystal in the temperature range 90–300 K

The electrical conductivity σ and dielectric properties (?, tanδ) of β-BaB₂O₄ were studied in the temperature range 90–300 K. The quantities σ, ?, and tanδ were measured at frequencies of 0.1, 1, and 10 kHz and 1 MHz. The dielectric permittivity and electrical conductivity were found to grow with increasing temperature at all frequencies. The permittivity decreases and the electrical conductivity increases (by several orders of magnitude) with increasing frequency. Maxima were observed in the σ=f(T) and tanδ=f(T) curves for all frequencies; the maxima shift toward higher temperatures with increasing frequency.     

Proton and electron conduction in polymer intercalated vanadium pentoxide xerogel

A comprehensive proton and electron conduction in vanadium pentoxide xerogel-conducting polymer nanocomposites are analyzed by the impedance spectroscopy. The complex impedance plots are used to estimate the proton and electron conductivity. Both protonic and electronic conductivities follow Arrhenius type behavior with temperature. Protonic conductivity increases with the increase of intercalated conducting polypyrrole. The highly ordered conducting polypyrrole (PPY) molecule enhances the diffusion of H₃O⁺ ions into the host lattice. Broad dielectric loss peaks are found in a wide range of frequency domain (KHz–MHz). The intercalated water within the oxide network of vanadium pentoxide remains supercooled up to lowest measured temperature 137 K.     

Modeling absorption spectrum and saturation intensity of ZnO nano-colloid

In this work, the complex magnitude of the dielectric constant of a thin film of ZnO nano-particles has been obtained in the range of visible spectrum. Using this spectrum, the UV–visible absorptive spectrum of ZnO spherical nano-colloid is obtained using Mie theory. The absorption spectrum of ZnO nano-colloid has been related to the optical properties of the prepared thin film with a simulation model based on the Mie theory and the findings are corroborated by fitting with the experimental results. Based on this curve fitting, the volume fraction of nanoparticles in the nano-colloid is obtained and the diameter (and the Bohr radius) of the molecules contributing in a nanoparticle crystal structure has been obtained. In this paper, frequency dependence of the optical properties coefficients and also local field considerations are applied. Finally the precise magnitude of saturation intensity of ZnO nano-colloid is measured.     

Deposition of hexagonal boron nitride thin films on silver nanoparticle substrates and surface enhanced infrared absorption

Silver nanoparticle thin films with different average particle diameters are grown on silicon substrates. Boron nitride thin films are then deposited on the silver nanoparticle interlayers by radio frequency （RF） magnetron sputtering. The boron nitride thin films are characterized by Fourier transform infrared spectra. The average particle diameters of silver nanoparticle thin films are 126.6, 78.4, and 178.8 nm. The results show that the sizes of the silver nanoparticles have effects on the intensities of infrared spectra of boron nitride thin films. An enhanced infrared absorption is detected for boron nitride thin film grown on silver nanoparticle thin film. This result is helpful to study the growth mechanism of boron nitride thin film.     

Dielectric relaxation in LaSrCo1−x Al x O4 ceramics

Dielectric properties of LaSrCo_1−x Al _x O₄ (x=0, 0.1, 0.3, and 0.5) ceramics were investigated in a broad frequency and temperature range. The AC conductivity decreased with the increasing Al concentration. Dielectric constant increased at lower frequency and decreased at higher frequency when the Al concentration increased from 0.1 to 0.3, then it decreased at all frequencies as the x value was 0.5. While the dielectric loss decreased first and then increased with the increasing Al concentration. There was one dielectric relaxation in the curve of temperature dependence of dielectric properties of LaSrCo_0.7Al_0.3O₄ ceramics. The nonadiabatic small polaronic hopping process should contribute to the dielectric relaxation in the present ceramics. The AC conductivity increased in about one order of magnitude after annealing the sample in the oxygen atmosphere, and this should be attributed to the appearance of interstitial oxygen in the annealed sample.     

掺杂聚吡咯薄膜的金属电导

用电化学方法制备了以BF₄^-,HSO₄^-和ClO₄^-掺杂的聚吡咯薄膜,其电导率和电导率的温度依赖性分别用标准四探针法和电压端短路法VSC(Voltage Shorted compaction)测试。实验结果表明:由标准四探针法所得到的电导率的温度依赖性呈现典型的半导体特性。由于掺杂聚吡咯薄膜的形态是块状物的堆砌,四探针法所得电导率及其温度依赖性由块与块之间的接触电阻所限制,并 关键词：     

Effect of the film thickness on the impedance behavior of sol–gel Ba0.6Sr0.4TiO3 thin films

Perovskite Ba_0.6Sr_0.4TiO₃ sol–gel thin films with different thicknesses are fabricated as MFM configuration to study the effect of the film thickness on the dielectric relaxation phenomenon and the ionic transport mechanism. The frequency dependent impedance, electric modulus, permittivity and AC conductivity have been investigated in this context. Z? plane for all the tested samples shows two regions, corresponding to the bulk mechanism and the distribution of the grain boundaries–electrodes process. Electric modulus versus frequency plots reveal non-Debye relaxation peaks. The observed decrease in both the impedance and permittivity with the increase in film thickness is attributed to the grain size effect. The frequency dependent conductivity plots show three regions of conduction processes, i.e. low-frequency region due to DC conduction, mid-frequency region due to translational hopping motion and high-frequency region due to localized hopping and/or reorientational motion.