Optical and electrical transport properties of polyaniline–silver nanocomposite

Polyaniline–silver nanocomposite has been synthesized successfully by the chemical oxidative polymerization of aniline with ammonium peroxydisulphate as an initiator in presence of negatively charged silver nanoparticles. Silver nanoparticles are prepared by standard citrate reduction method. TEM, SEM, XRD, FTIR, TGA, DSC, optical absorption and photoluminescence studies are done for the morphological, structural, thermal and optical characterization of the polyaniline nanocomposite. From the TEM and SEM image, it is observed that nanoparticles are well dispersed in the polyaniline matrix. XRD pattern shows that polyaniline is amorphous, but peaks present in XRD pattern in polymer nanocomposites are for silver nanoparticles. TGA and DSC results show that polyaniline silver nanocomposite is more crystalline and more thermally stable. A surface plasmon absorption band is obtained from the optical absorption at 380 nm, which indicates that silver nanoparticles are present in the polyaniline matrix. The optical band gap of nanocomposite decreases with increasing content of silver nanoparticles. An enhancement in photoluminescence has been observed in polyaniline–silver nanocomposite than that in pure polyaniline. The electrical conductivity of polyaniline–silver nanocomposite increases with increase in silver nanoparticle content than that of pure polyaniline. This is a simple way by which optical and electrical properties of polyaniline may be enhanced by doping with suitable nanoparticles.     

Plasmon properties of silver spherical nanoparticles and films

The effects of the geometrical shape of silver nanoparticles and the electronic configurations of Ag atom in the ground and excited states on the plasmon characteristics of nanoparticles are considered. A relationship between the static polarizability of silver and gold atoms and the plasmon energies of nanoparticles is found. The ΔE excitation energy of a silver atom that corresponds to the 4d ¹⁰5s(² S _1/2) → 4d ¹⁰5p(² P _1/2 and ² P _3/2) transition is shown to determine the plasmon energy of thin silver films. In the case of spherical silver nanoparticles in aqueous solution, the size effect—namely, the correlation between λ_pl wavelengths of plasmon transitions and d diameters of nanoparticles—is discovered. With the increase in the diameter of nanoparticles, the plasmon transition peaks are red shifted. In the range of d = 9–120 nm, λ_pl values are shown to change from 370 to 440 nm. The resonance splitting of plasmon bands determined by the mixed valence states of silver atoms is predicted.     

Microstructure and optical absorption properties of Au-dispersed CoO thin films

Au nanoparticles dispersed cobalt monoxide (CoO) composite films were fabricated via a chemical solution approach combined with a spin-coating processing. Au particles were spherical approximately and uniformly dispersed in the amorphous CoO matrix. The mean diameters of Au particles in the Au/CoO thin films with 40 mol% Au are about 30 nm. The optical absorption peaks due to the surface plasmon resonance (SPR) of Au particles were observed in the UV-vis absorption spectra in the wavelength range of 550-650 nm. The SPR peaks exhibit a red shift and intensify with increasing Au content from 10 to 40 mol%, but show a blue shift and weaken from 40 to 60 mol%. The band gap E_g decreases with increasing Au contents from 10 to 40 mol% but increases by further increasing Au content.     

Optical properties of nanostructured thin films containing noble metal clusters: AuN, (Au0.5Ag0.5)N and AgN

The optical properties of nanocomposite thin films of gold, silver and bimetallic silver-gold clusters embedded in a porous alumina matrix have been investigated in the size range 2–6.7 nm. The metallic particles are produced by laser vaporization of either an Au_0.5Ag_0.5 alloy or a pure metal target whereas the dielectric matrix is evaporated by an electron gun. Samples involving a low metal concentration have been characterized by several complementary techniques in order to determine their composition, morphology and cluster size distribution. The mixed particles have the same stoichiometry as the target rod. Optical absorption spectra exhibit a surface plasmon resonance whose position is shifting with cluster mean size, giving evidence of finite size effects. Theoretical calculations in the framework of Time-Dependent-Local-Density-Approximation (TDLDA), taking into account an inner skin of ineffective screening and the porosity of the matrix, are consistent with observed size evolutions of the Mie frequency in each type of sample.     

The effect of Au/Ag ratios on surface composition and optical properties of co-sputtered alloy nanoparticles in Au–Ag:SiO2 thin films

Gold–silver alloy nanoparticles with various Au concentrations in sputtered SiO₂ thin films were synthesized by using RF reactive magnetron co-sputtering and then heat-treated in reducing Ar + H₂ atmosphere at different temperatures. The UV–visible absorption spectra of the bimetallic systems confirmed the formation of alloy nanoparticles. The optical absorption of the Au–Ag alloy nanoparticles exhibited only one plasmon resonance absorption peak located at 450 nm between the absorption bands of pure Au and Ag nanoparticles at 400 and 520 nm, respectively, for the thin films annealed at 800 °C. The maximum absorption wavelength of the surface plasmon band showed a red shift with increasing Au content. XPS results indicated that the alloys were in metallic state, and they had a greater tendency to lose electrons as compared to their corresponding monometallic state. Moreover, the positive and negative shift of the Au(4f) core-level binding energies was observed for low and high Au concentration, respectively. Also a negative shift of the Ag(3d) binding energies was increased by increasing Au concentration. Diffusion of the particles toward the surface by increasing the temperature has also been illustrated by AFM images. Based on AFM observations, we have found that the particle size reduced from 35 to 20 nm by increasing the annealing temperature from 600 to 800 °C, while particle size increased by increasing Au concentration in films. In addition, lateral force microscopy (LFM) analysis showed that the alloy particles were uniformly distributed on the surface.     

Why superconducting transition of polycrystalline β-ET2I3 in surface conducting films is observed below 8 K?

An onset of the superconducting transition in surface conducting films of polycarbonate with β-ET₂I₃ (ET: bis (ethylenodithio)tetrathiafulvalene) is observed at temperature(5–6 K) lower than that for single crystals (8 K). It is shown using X-ray diffraction technique that the interlayer spacing d in β-ET₂I₃ microcrystals in polymer film decreases stronger with temperature than in crystals without polymer. This is considered as an important factor suppressing the transition to superconductivity. It is assumed that stronger dependence d(T) in β-ET₂I₃ in polymer films is related to the stress induced by the shrinkage of the polymer matrix.     

One-pot synthesis of highly stable silver nanoparticles-conducting polymer nanocomposite and its catalytic application

Herein, we report the preparation of highly stable Ag_nano–PEDOT nanocomposite by one-pot fashion in acidic condition using 3,4-ethylenedioxythiophene (EDOT) as a reductant and polystyrene sulfonate (PSS^?) as a dopant for PEDOT as well as particle stabilizer for silver nanoparticles (AgNPs). The above nanocomposite denoted as Ag_nano–PEDOT/PSS^? nanocomposite. The formation of AgNPs with concomitant EDOT oxidation was followed by UV–visible (UV–vis) spectroscopy at different time intervals. Ag_nano–PEDOT/PSS^? nanocomposite shows absorption bands at 380 and above 700 nm, which correspond to surface plasmon resonance (SPR) peak of AgNPs and oxidized PEDOT, respectively. Ag_nano–PEDOT/PSS^? nanocomposite was characterized by infrared (IR) spectroscopy, transmission electron microscopy (TEM), and XRD. TEM study reveals that AgNPs are distributed uniformly around PEDOT polymer with an average particle size diameter of 10–15 nm. In addition, Ag_nano–PEDOT/PSS^? nanocomposite was tested for the catalytic reduction of 4-nitrophenol. For comparing stability, we were also synthesized AgNPs in the absence of PSS^? (denoted as Ag_nano–PEDOT) using EDOT as reductant. UV–vis spectrum of Ag_nano–PEDOT nanocomposite revealed that AgNPs prepared in the absence of PSS^? was not stable.     

(Au,Ag,Cu)/SiO_2二元金属单分散复合薄膜非线性光吸收性的Mie理论模拟

采用修正的Mie理论模拟计算了(Ag, Cu)/SiO₂, (Au, Cu)/SiO₂和(Ag, Au)/SiO₂二元单质金属纳米颗粒分散体系的理论吸收光谱. 研究发现, 二元金属纳米颗粒分别以单质金属形式存在时, 吸收光谱分别在2个波段处出现表面等离子共振吸收峰, 二元金属的相对含量影响吸收峰的峰强, 与峰位无关. 理论模拟吸收光谱与前人实验结果符合良好.     

Enhanced optical modulation due to SPR in gold nanoparticles embedded WO3 thin films

Surface plasmon resonance (SPR) phenomenon of metal-dielectric composite thin films formed by embedding the noble metal nanoparticles in a dielectric matrix offers a high degree of flexibility and enables many applications such as surface enhanced spectroscopes, numerous biological and chemical sensing fields. A remarkable enhancement in optical modulation after embedding the gold nanoparticles in a reticulated mesh like matrix of WO₃ thin films was observed. WO₃ films were prepared onto the conducting ITO coated glass substrates by a novel pulsed spray pyrolysis technique (PSPT). A reticulated mesh like morphology of WO₃ was achieved by optimizing the deposition parameters of PSPT and the gold nanoparticles were embedded in the WO₃ matrix by a drop casting method. Enhancements in electrochromic properties of WO₃ in terms of optical modulation (ΔOD), coloration efficiency (η) and response times (t_c and t_b) were attributed to the assistance of SPR in gold nanoparticles during coloration and electric field induced quenching of SPR during bleaching.     

The effect of the microstructure and the surface topography on the electrical properties of thin Ag films deposited by high power pulsed magnetron sputtering

In this work thin silver (Ag) films are grown employing high power pulsed magnetron sputtering (HPPMS) for various pulse on/off time configurations, as well as by dc magnetron sputtering (dcMS), for reference. It is shown that the increase of the pulse off-time from 450 μs to 3450 μs, while the pulse on-time is kept constant at 50 μs, results in an increase of the peak target current (I_Tp) from 3 A to 22 A. The increase of I_Tp is accompanied by an increase of the ion flux towards the growing film. This is particularly pronounced for I_Tp > 11 A. The microstructure, the surface topography and the electrical properties of Ag films grown at I_Tp = 11 A, I_Tp = 22 A and by dcMS are investigated, as a function of the film thickness d. It is shown that for d > 20 nm the electrical resistivity of films sputtered at I_Tp = 22 A is similar to that of films grown by dcMS. Slightly higher values are measured for films grown at I_Tp = 11 A. It is found that in this thickness range the film conductivity is strongly affected by the vertical grain size and the scattering of the charged carriers at the film interfaces. For d < 15 nm the resistivity of films deposited at I_Tp = 22 A is substantially lower as compared to that of films grown by dcMS. Films deposited at I_Tp = 11 A exhibit also in this case a higher conductivity. In this thickness regime the electronic transport and, thus the conductivity are profoundly determined by the surface topography and the film density.     

Electrical properties of TiO2-filled polyimide nanocomposite films prepared via an in situ polymerization process

To fully understand the reliable electrical properties of the nanocomposite films, their physical and chemical behaviors as well as dielectric properties were analyzed. Polyimide/TiO₂ (PI/TiO₂) nanocomposite films were prepared using in situ dispersion polymerization process. Influences of frequency, temperature and the nano-TiO₂ particles loading concentration on dielectric permittivities of the PI/TiO₂ nanocomposite films were studied. The dielectric relaxation behavior of the PI/TiO₂ nanocomposite films has been investigated with dielectric relaxation spectrum. It was found that interfacial polarization, namely Maxwell–Wagner–Sillars, existed in the PI/TiO₂ nanocomposite films with different loading concentration of the nano-TiO₂ particles. Dielectric permittivities of the PI/TiO₂ nanocomposite films fluctuation with temperature (?50–150 °C) were attributed to the mobility and thermal expansion of the polymer matrix, for which the Cole–Davidson model, or modified Cole–Cole model, was brought to account.     

Synthesis and third order optical nonlinearity studies of the donor–acceptor conjugated polymer,poly(2-[3,4-didodecyloxy-5-(1,3,4-oxadiazol-2-yl)thiophen-2-yl]-5-phenyl-1,3,4-oxadiazole) and a polymer/TiO2 nanocomposite

A donor–acceptor conjugated polymer (PDOThPOD) containing 3,4-didodecyloxythiophene and (1,3,4-oxadiazolyl)benzene units is synthesized by using precursor polyhydrazide route. Cyclic voltammetry studies reveal that the polymer possesses a low-lying LUMO energy level (?3.57 eV). A nanocomposite of polymer PDOThPOD and nano TiO₂ is also prepared. The linear optical properties of PDOThPOD and the nanocomposite are studied using UV–vis absorption spectroscopy and fluorescence emission spectroscopy. z-scan technique is used to study the third order nonlinear optical properties of the polymer and nanocomposite films. Both polymer and nanocomposite films show a strong optical limiting behavior. The value of nonlinear absorption coefficient (β) is found to be of the order of 10^?7 m/W, indicating that these materials are potentially suited for fabricating optical limiters.     

Conducting polymer embedded with nanoferrite and titanium dioxide nanoparticles for microwave absorption

The present paper deals with the synthesis of conducting ferrimagnetic polyaniline nanocomposite embedded with γ-Fe₂O₃ (9–12 nm) and titanium dioxide (70–90 nm) nanoparticles via a micro-emulsion polymerization. The microwave absorption properties of nanocomposite in 12.4–18 GHz (Ku-band) frequency range shows shielding effectiveness due to absorption (SE_A) value of ?45 dB, which is much higher than polyaniline composite with iron oxide and polyaniline–TiO₂ composites. The higher EMI shielding is mainly arising due to combined effect of γ-Fe₂O₃ and TiO₂ that leads to more dielectric and magnetic losses which consequently contributed to higher values of shielding effectiveness. XRD analysis of the nanocomposite reveals the incorporation of nanoparticles in the conducting polymer matrix while the thermal gravimetric analysis (TGA) demonstrates that the nanocomposite is stable up to 250 °C.     

Optical properties of thermally evaporated Bi2Se3 thin films treated with AgNO3 solution

Bismuth selenide (Bi₂Se₃) thin films have been prepared onto clean glass substrates by the thermal evaporation technique. The deposited films were then immersed in silver nitrate solution for different periods of time, followed by annealing in Argon atmosphere at 473 K for 1 h, to obtain Ag/Bi₂Se₃ samples. The prepared films have been examined by X-ray and transmission electron microscopy for structural determination. The optical transmission and reflection spectra of the deposited films have been recorded within the wavelength range 400-2500 nm. The variation of the optical parameters of the prepared films, such as refractive index, n, and the optical band gap, E_g as a function of the immersion duration times has been determined. The refractive index dispersion in the transmission and low absorption region is adequately described by the well-known Sellmeier dispersion relation, whereby the values of the oscillator strength, oscillator position, the high-frequency dielectric constant, ε_∞ as well as the carrier concentration to the effective mass ratio, N/m* were calculated as a function of the immersion duration time.     

Sol-gel derived Li-Mg co-doped ZnO films: Preparation and characterization via XRD, XPS, FESEM

Li-Mg co-doped ZnO films have been deposited onto glass substrates by sol-gel spin coating method. The structural and morphological properties of the films were characterized by X-ray diffractometer (XRD), X-ray photo-electron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). The XRD spectra indicated that the films have polycrystalline nature. The crystallite size values decreased with the increasing Mg content. The chemical composition of the Li-Mg co-doped ZnO films were confirmed by XPS. Additionally, XPS results clearly showed the existence of Mg as a doping element into ZnO crystal lattice. The surface morphology of the films was found to depend on the concentration of Mg in the ZnO:Li. The absorption band edge values of the films were calculated and these values of the films increased with increasing Mg concentration. The refractive index dispersion curves of the films obeyed the single-oscillator model. The dispersion parameters such as E_o (single-oscillator energy) and E_d (dispersive energy) of the films were determined and increase with Mg content.     

Modulation of field emission properties of DLC films with the incorporation of nanocrystalline silver nanoparticles by CVD technique

Composite films containing Ag nanoparticles embedded in diamond-like carbon (DLC) matrix were deposited on glass substrates by using capacitively coupled plasma (CCP) r.f. chemical vapour deposition technique (CVD). Amount of silver incorporation was controlled by the amount of argon in the argon and methane mixture in the plasma. Field emission properties of these films are reported here. Films became sp² rich with increased incorporation of silver nanoparticles in the DLC matrix. Field enhancement factor increased significantly for films with higher silver content in the DLC matrix. Work function (?) values obtained from the Fowler-Nordheim model varied between 0.04 and 0.10 eV while the field factor (β) varied between 336 and 2759. The critical field was found to vary between 10 and 100 V/μm.     

Microstructural control of Cr–Si–N films by a hybrid arc ion plating and magnetron sputtering process

The microstructural evolution of Cr–Si–N films deposited by a hybrid arc ion plating and magnetron sputtering process was investigated by varying the sputtering power of Si target and substrate bias voltage. Detailed nanocomposite microstructures of the films were studied by high-resolution transmission electron microscopy. The results indicated that the incorporation of Si into the growing CrN films at 0 V led to the formation of a nanocomposite containing CrN nanocolumns embedded in amorphous SiN_x matrix or near-amorphous microstructure. For the films having a Si content of ～10 at.% and ～15 at.%, a negative bias voltage of ?50 V resulted in the aggregation of nanocolumns in the amorphous matrix. Further increase of negative bias voltage to ?250 V led to the formation of a three-dimensional CrN/a-SiN_x nanocomposite microstructure. The mechanism of microstructure evolution is discussed by considering the thermodynamic and kinetic factors.     

Charge transport mechanism and the effect of poling on the current-voltage characteristics of conducting polyaniline–BaTiO3 composites

Conducting polyaniline–barium titinate (PANI–BaTiO₃) composites have been synthesized by `in situ' deposition technique by placing the fine grade powder of BaTiO₃ (prepared by conventional sol–gel technique) in the polymerization reaction mixture of aniline — finally yielding the Polyaniline–BaTiO₃ composites. The charge transport process in these composites have been studied by sandwiching the pellets of these composites between the silver and platinum electrodes. It presumably suggests presence of a nonlinear space charge controlled charge transport process. Also, a large hysteresis in the I–V characteristics of these composites has been observed which also supports the space charge controlled conduction. The samples were poled by applying a constant voltage for a fixed time and the I–V characteristics were traced before and after poling. Some striking differences have been observed in the I–V characteristics before and after poling. These have been explained on the basis of creation of an internal electric field due to poling which in turn opposes the externally applied electric field.     

Preparation and oxidation behaviour of electrodeposited Ni–CeO2 nanocomposite coatings

Ni–CeO₂ nanocomposite coatings with different CeO₂ contents were prepared by codeposition of Ni and CeO₂ nanoparticles with an average particle size of 7 nm onto pure Ni surfaces from a nickel sulfate. The CeO₂ nanoparticles were dispersed in the electrodeposited nanocrystalline Ni grains (with a size range of 10–30 nm). The isothermal oxidation behaviours of Ni–CeO₂ nanocomposite coatings with two different CeO₂ particles contents and the electrodeposited pure Ni coating were comparatively investigated in order to elucidate the effect of CeO₂ at different temperatures and also CeO₂ contents on the oxidation behaviour of Ni–CeO₂ nanocomposite coatings. The results show that the as-codeposited Ni–CeO₂ nanocomposite coatings have a superior oxidation resistance compared with the electrodeposited pure Ni coating at 800 °C due to the codeposited CeO₂ nanoparticles blocking the outward diffusion of nickel along the grain boundaries. However, the effects of CeO₂ particles on the oxidation resistance significantly decrease at 1050 °C and 1150 °C due to the outward-volume diffusion of nickel controlling the oxidation growth mechanism, and the content of CeO₂ has little influence on the oxidation.     

Optical dispersion and electronic transition characterizations of spin coated polyaniline thin films

Optical properties of polyaniline, PANI thin films of different thicknesses ranged from 200 to 310 nm prepared by spin coating were characterized by using spectrophotometric measurements of transmittance and reflectance in the spectral range of 200–2500 nm. The optical constants namely refractive index (n) and the absorption index (k) were calculated by using a special computer program. The absorption spectra in the UV–vis region were analyzed in terms of both molecular orbital and band theories. The region shows two absorption bands, namely the Q-band and the Soret (B) band. Some of the important spectral parameters, namely the optical absorption coefficient (α), molar extinction coefficient (?_molar), oscillator strength (f) and electric dipole strength (q²) were evaluated. The analysis of the spectral behavior of the absorption coefficient α in the absorption region revealed two direct allowed transitions corresponding to the onset and the fundamental energy gaps. The refractive index n showed an anomalous dispersion in the absorption region as well as normal dispersion in the transparent region. The dispersion of the refractive index in PANI films was analyzed using the concept of the single oscillator. Within this concept the oscillator energy (E₀), the dispersion energy (E_d), the high frequency and the dielectric constant (?_∞) as well as the lattice dielectric constant (?_L) were evaluated. Discussion of the obtained results and their comparison with the previously published data were also given.