Tuned optical properties of in-situ synthesized m-nitroaniline doped Ag/PVA nano-composites

Meta-nitroaniline (m-NA) doped silver/poly(vinylalcohol) (Ag/PVA) nanocomposites are prepared via in-situ reduction of silver salt by employing hydrazine hydrate (HH) in order to study the effect of the NLO active m-NA on the optical properties of nanoparticles of silver in the colloidal as well as self supported film form. Reduction of silver salt in aqueous alcoholic PVA with HH is done first followed by doping of the reaction mixture with m-NA. The UV-Visible absorption spectra show peak at about 400 nm for Ag nanoparticles due to surface plasmon resonance phenomenon, which gets blue shifted with the change in m-NA concentration. The Second Harmonic Generation (SHG) studies show improvement in intensity with increasing m-NA concentration up to a saturation point (approximately 2.52 wt% with respect to PVA). Further increase in m-NA concentration leads to decrease in SHG intensity. The solutions and the films are characterized by photoluminescence (PL), FTIR spectroscopy, XRD, SEM, TEM, and thermal analysis. m-NA doped composites showed better PL efficiency. SEM of the nanocomposite film shows uniform distribution of particles within the film. The particle size as shown by TEM is found to be less than 10 nm.     

Synthesis of silver/poly (diallyldimethylammonium chloride) hybride nanocomposite

This paper presents a method for the preparation of silver nano-particles in poly (diallyldimethylammonium chloride) (PDDA) using N,N-dimethylformamide (DMF) as a medium has been performed successfully. A golden solution in its UV–vis absorption spectrum showed surface plasmon resonance absorption bands between 410 and 425 nm in solutions and at about 461 nm in a transparent film. The Ag/PDDA nano-composite was characterized by X-ray diffraction (XRD) measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier-transform-infrared spectroscopy (FT-IR) and thermo-gravimetric analysis (TGA). XRD showed the fcc crystal structure of the bulk Ag with particles of <22 nm in size similar to that is observed by TEM and PDDA is crucial to the formation of such silver nano-composite. SEM indicated uniform distribution of particles in the film. TGA confirmed enhanced thermal stability of the polymer.     

Annealing effect on the structural and optical properties of embedded Au nanoparticles in silicon suboxide films

Au/SiO_x nanocomposite films have been fabricated by co-sputtering Au wires and SiO₂ target using an RF magnetron co-sputtering system before the thermal annealing process at different temperatures. The structural and optical properties of the samples were characterized using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), optical transmission, and reflection spectroscopy. XPS analysis confirms that the as-prepared SiO_x films are silicon-rich suboxide films. FESEM images reveal that with an increase in annealing temperature, the embedded Au NPs tend to diffuse toward the surface of the SiO_x films. In IR spectra, the intensity of the Si-O-Si absorption band increases with the annealing temperature. Optical spectra reveal that the position and intensity of the surface plasmon resonance (SPR) peak are dominated by the effect of the inter-particle distance and size of the Au NPs embedded in the SiO_x films, respectively. The SPR absorption peak shows the blue-shift from 672 to 600 nm with an increase in annealing temperature. The growth of silica nanowires (SiO_x NWs) is observed in the film prepared on a c-Si substrate instead of a quartz substrate and annealed at temperatures of 1000 °C.     

Structural and optical properties of thermally evaporated zinc phthalocyanine thin films

Thermally evaporated zinc phthalocyanine (ZnPc) films in the as deposited condition were identified to be as-amorphous. It undergoes structural transformation upon annealing up to 613 K. The optical properties and spectral behavior of as deposited and annealed thin films of ZnPc were studied using spectrophotometric measurements of the transmissivity and reflectivity at normal incidence of light in the wavelength range 200–2500 nm. The refractive index, n, and absorption index, k, were calculated and it was found that they are independent of film thickness in the thickness range 205–530 nm. Annealing at 613 K increases absorbance of films by 5–6 times in comparison with absorbance of as deposited ones and shifts peak positions of all bands towards low energy side of spectra except the peak position of N-band is shifted towards high energy side of spectra. The absorption spectra in the UV–VIS. region has been analyzed in terms of both molecular orbital and band theories. Indirect allowed transitions near the onset and fundamental absorption edges were observed. The energy at the onset was obtained and equals to 1.45 and 1.51 eV for as deposited and annealed films, respectively. The fundamental energy gap was obtained and equals to 2.94 and 2.88 eV for as deposited and annealed films, respectively. The absorption spectra shows four absorption bands. The oscillator strength, f, the electric dipole strength, q², the molar extinction coefficient, ζ_molar, were calculated for as deposited and annealed ZnPc thin films.     

Metal oxide nano-particles for improved electrochromic and lithium-ion battery technologies

Hot-wire chemical vapor deposition (HWCVD) has been employed as an economically scalable method for the deposition of crystalline tungsten oxide nano-rods and nano-particles. Under optimal synthesis conditions, only crystalline WO₃ nano-structures with a smallest dimension of ∼10-50 nm are observed with extensive transmission electron microscopy (TEM) analyses. The incorporation of these particles into porous films led to profound advancement in state-of-the-art electrochromic (EC) technologies. HWCVD has also been employed to produce crystalline molybdenum oxide nano-rods, particles and tubes at high density. TEM analyses show that the smallest dimension of these nano-structures is ∼5-30 nm. XRD and Raman analyses reveal that the materials are highly crystalline and consist of Mo, MoO₂ and MoO₃ phases. It is also possible to fabricate large-area porous films containing these MoO_x nano-structures. Furthermore, these films have been tested as the negative electrode in lithium-ion batteries, and a surprisingly high, reversible capacity has been observed.     

Effect of rapid thermal annealing time on Au/SiOx film prepared by hot wire assisted plasma enhanced chemical vapour deposition technique

In this study, nanocomposite material consisting of silicon suboxide (SiO_x) film embedded with gold nanoparticles (Au NPs) was synthesized using hybrid technique combining hot wire evaporation and plasma enhanced chemical vapour deposition (PECVD) method. As prepared Au/SiO_x films were rapid thermal annealed at constant temperature of 800 °C for different annealing times from 30 to 120 s. The use of tungsten filament for Au evaporation allowed the effective reduction of the silicon content. Depth profiling analysis confirmed the embedded in structure of Au/SiO_x film. FESEM, UV/VIS/NIR and PL spectroscopy were utilized to study the structural and optical properties of annealed Au/SiO_x film for different times. Embedded Au NPs diffused towards the surface of SiO_x film agglomerate and increased in size with an increase in annealing time. Localized surface plasmon resonance (LSPR) peak induced by Au NPs in SiO_x, which is dependent on annealing time, was clearly observed in optical spectra. Intensity and position of the PL peak located at 580 nm experienced a decrease and red-shift, as annealing time increased.     

Optical nonlinearities of BaTiO3 matrix-embedded Au nanoparticles

Composite thin films Au/BaTiO₃ comprising nanometer-sized gold particles embedded in BaTiO₃ matrices were synthesized on MgO(1 0 0) substrates by co-depositing Au and BaTiO₃ targets using pulsed laser deposition technique. The nanostructure of the films and the size distributions of the Au particles were analyzed by high-resolution transmission electron microscopy. Crystal lattice fringes from the Au nanocrystals and BaTiO₃ matrices were observed. The nonlinear optical properties of the Au/BaTiO₃ films were measured using z-scan method at the wavelength of 532 nm with a laser duration of 10 ns. The nonlinear refractive index n₂ and the nonlinear absorption coefficient β were determined to be 2.72 × 10⁻⁶ esu and −1.1 × l0⁻⁶ m/W, respectively.     

Synthesis,structure, and optical properties of Au–TiO2 composite thin films

Titanium dioxide (TiO₂) films with varying concentrations of gold particles were synthesized using pulsed DC magnetron sputtering, with the intent to develop infrared reflecting films for use on cars and planes to reduce solar heat load. Under our deposition conditions, the films are smooth (RMS roughness on the order of 1.0–2.0 nm) and consist of rutile TiO₂ with embedded gold. The average gold particle diameter on the sample surface was found to change from 60 to 200 nm as the volume fraction of gold in the films increased from 1.9 to 4.3% (3.5 to 7.9 mol% Au). The maximum reflectance of these films in the infrared region (800–2500 nm) is > 50%, compared with 30% for pure TiO₂. The Maxwell–Garnett equation does not model the reflectance data very well, due to the relatively large gold particle size. Instead, by assuming that the contribution of gold particles to the reflectance response is proportional to their projected areal fraction in an effective medium approximation, we were able to fit the observed reflectance data quite well.     

Observation on growth process of gold Y- and phi-shaped nanoparticles in solutions

The morphological evolution of gold (Au) nanoparticles is demonstrated via TEM and UV-vis spectroscopy in a real-time basis. Y-shaped and phi-shaped Au nanoparticles were prepared by a seed mediated method at 0 degrees C. The evolution of shape ranging from spheres to Y- and phi-shapes was characterized by UV-vis spectroscopy. For the spherical particles, the corresponding transverse plasmon absorption (540 nm) was observed at the initial growth stage. As further growth proceeded, new peaks appeared at ca. 620 nm and ca. 700-1000 nm, which was to the characteristic peak of Y-shaped and phi-shaped nanoparticles, respectively. In addition, all intermediate steps were observed in the morphology change by TEM. At the initial step, spherical particles with 20 nm size were generated and the particles were gradually evolved from tiny triangular shape or I-shape to Y- and phi-shape. In this study, the growth mechanism of Au nanoparticles was investigated by the characterization of optical properties as well as morphologies with respect to reaction time.     

Preparation and characterization of gold nanocrystals on NaCl(100) surfaces as labels for the dynamical x-ray tracking technique

We report on the fabrication of single crystalline gold nanocrystals of sizes between 10 nm and 25 nm. Gold was deposited under ultra high vacuum conditions on a freshly-cleaved NaCl(001) surface by means of the Molecular Beam Epitaxy technique. The preparation parameters substrate temperature and average thickness of the deposited gold were studied systematically. After the preparation, the crystals were characterized by means of different techniques, such as Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), X-Ray Diffractometry (XRD) and Laue Diffractometry.Measurements of the deposited cluster size, as measured by AFM, and the crystal size, as measured by XRD exhibited similar results at substrate temperatures between approx. 200 °C and 250 °C, indicating a high amount of single gold crystals. TEM images of gold crystals, made after the gold crystals had been dissolved in an aqueous 3-[(3-cholamidopropyl)dimethyl-ammonio]propane solution, support these results.Further, an effect of the substrate temperature during the deposition on the orientation of the gold crystals with respect to the NaCl(001) surface was observed. XRD measurements reveal a perpendicular texture of Au(111) parallel to NaCl(001) at approximately 310 °C. The second detected texture:Au(001)||NaCl(001) (in plane) and Au[100]||NaCl[100] (perpendicular) was observed over the complete studied temperature range (180 °C-330 °C).     

Broadband optical absorption enhancement in Au-coated ZnO nanotips

The enhancement of broadband optical absorption in zinc oxide (ZnO) nanotip (NT) arrays coated with evaporated gold (Au) on fluorine-doped SnO2 (FTO)/glass by a simple hydrothermal growth and subsequent Au evaporation is reported. As the core of ZnO NT arrays is gradually coated with evaporated Au, the reflectance is slightly increased at lambda > approximately 800 nm while the transmittance is decreased at lambda approximately 400-1800 nm. For both FTO/glass and ZnO NT arrays on FTO/glass, the coating of Au improves the light absorption due to the antireflective geometry compared to the flat Au films and the absorptance is also enhanced by increasing the nominal thickness of Au with evaporation time. For the ZnO NT arrays with an Au evaporated for 600 s at 0.5 A/s, a high absorptance of >72% is achieved over the wavelength range of 250-2000 nm, indicating a significant increase due to the enhanced antireflection property as well as the increased surface area compared to the Au-coated FTO/glass without ZnO NT arrays.     

Investigation of self-assembly growth and thermal stability of Au nano-particles on atomic-layer-deposited Al2O3 film

在原子层淀积的Al₂O₃薄膜表面自组装生长Au纳米颗粒,研究了Au纳米颗粒的自组装过程和热稳定性. 结果表明,原子层淀积的Al₂O₃薄膜表面很容易吸附氨丙基三甲基硅烷(APTMS), 有利于Au纳米颗粒的自组装, 生长出的Au纳米颗粒尺寸为5--8 nm, 密度约为4×10¹¹cm^-2. 在300℃氮气中退火使Au纳米颗粒的尺寸增大, 但是没有改变APTMS的吸附状态和Au的化学组成. 当退火温度提高到450℃时, Au纳米颗粒发生明显的团聚, 且分布变得极不均匀.     

Au-MgF2复合纳米颗粒薄膜的制备和微结构

用射频磁控共溅射法制备了Au体积分数分别为6%、15%、25%、40%、50%和60%的Au-MgF2复合纳米颗粒薄膜.用X射线衍射、透射电镜、X射线光电子能谱对薄膜的微结构和组分进行了测试分析,分析结果表明:制备的Au-MgF2复合纳米颗粒薄膜由fcc-Au晶态纳米微粒镶嵌于主要为非晶态的MgF2陶瓷基体中构成,当Au体积百分含量由15%增至60%时,其平均晶粒尺寸由5.1nm增大到21.2 nm,晶格常数由0.399 84nm增大到0.407 43nm;随Au体积百分含量由6%增至50%,其颗粒平均粒径则由9.8nm增至21.4 nm.名义组分为vol.60%Au-MgF2样品中Au的体积百分含量约为62.6%,与设计值基本一致.     

Energy dependent saturable and reverse saturable absorption in cube-like polyaniline/polymethyl methacrylate film

Solid films of cube-like polyaniline synthesized by inverse microemulsion polymerization method have been fabricated in a transparent PMMA host by an in situ free radical polymerization technique, and are characterized by spectroscopic and microscopic techniques. The nonlinear optical properties are studied by open aperture Z-scan technique employing 5 ns (532 nm) and 100 fs (800 nm) laser pulses. At the relatively lower laser pulse energy of 5 μJ, the film shows saturable absorption both in the nanosecond and femtosecond excitation domains. An interesting switchover from saturable absorption to reverse saturable absorption is observed at 532 nm when the energy of the nanosecond laser pulses is increased. The nonlinear absorption coefficient increases with increase in polyaniline concentration, with low optical limiting threshold, as required for a good optical limiter.     

Ion-beam sputtering and nanostructures of noble metals

Using the technique of ion-beam sputtering on gold (Au) and silver (Ag) metal films, metal nanoclusters vis-à-vis nanostructure materials are synthesized on silica glass substrates. Analyses of Rutherford backscattering spectra of Ar⁺-ion irradiated films confirm the ion-beam sputtering of metal films. Exponential decrease of experimentally measured areal density of Au atoms with the increase of ion doses has been elucidated. Optical absorption spectroscopy results reveal the formation of metal nanoclusters on the glass substrates. Red shift of the surface-plasmon resonance position due to the sputtering induced size reduction of Au nanoclusters on the silica substrates has been explained. Size reduction in this case is further corroborated with the scanning electron microscopy results.     

Synthesis of anisotropic gold nanoparticles in a water-soluble polymer

Anisotropic gold nanoparticles have been synthesized by a UV irradiation technique through the interaction of HAuCl₄ and a stabilizing agent, poly (vinyl pyrrolidone) (PVP). The effect of irradiation time on the size and shape of gold nanoparticles was investigated by UV-visible spectroscopy and Transmission Electron Microscopy (TEM). The absorption spectra of all samples show a broad band with the characteristic surface plasmon resonance (SPR) peak visible at around 530 nm. The presence of an additional low intensity absorption peak at a longer wavelength suggests the presence of non-spherical nanoparticles. The TEM measurements show evidence of particle shapes such as spheres, hexagons, decahedrons and truncated triangles as the reaction proceeded from 5 min to 24 h. The variation in particle shape is probably due to the effect of the reduced gold to PVP ratio as the reaction proceeds.     

Optical and photoluminescent properties of sol-gel Al-doped ZnO thin films

Al-doped zinc oxide (AZO) thin films have been prepared via a sol-gel process. Optical and photoluminescent properties of the AZO films have been investigated. The UV absorption edge was blue shifted with increasing Al doping concentration. Efficient green–yellow emission was obtained after annealing at 850 °C. For the 850 °C-annealed samples, the green peak was red shifted from 518 to 565 nm as the Al doping concentration increased from 0 to 2.0 at.%. In addition, violet emission in the range of 400–450 nm was observed in the 850 °C-annealed AZO films. The possible origins responsible for these emission bands have been discussed.     

Influence of the deposition conditions on the optical absorption of Ag-SiO2 nanocermet thin films

We report a study of the influence of the deposition conditions on the morphological parameters (shapes, size distribution and ordering) of Ag nanoclusters embedded in SiO2, deposited by different techniques of co-sputtering or multilayer deposition. The influence of the substrate temperature on the nucleation and growth process is also studied. The different cluster morphologies determined by various complementary techniques (transmission electron microscopy, scanning electron microscopy, atomic force microscopy) are then correlated with the optical absorption, showing that the fabrication process is the key factor to control the position, shape and width of the surface plasmon resonance peaks and to achieve the desired optical properties. Films deposited by co-sputtering from 2 targets on a substrate heated at 440 °C show a very narrow absorption peak at 370 nm corresponding to the plasma resonance in near spherical silver particles. In multilayered films, the absorption peak is shifted from 340 to 480 nm with a larger half-band width. In cermet films co-sputtered from composite target on a rotating substrate, two absorption peaks are observed due to the more elongated shape of the metal nanoparticles. The experimental results are analysed in the frame of the Maxwell Garnett theory.     

Nanostructure characterization of polymer-stabilized gold nanoparticles and nanofilms derived from green synthesis

The fabrication and characterization of gold (Au) nanostructured materials draws significant attention because of their distinctive properties and their technological applications. The first objective of this study is to fabricate polymer-stabilized Au nanoparticles and nanofilms (PAN) through a cost effective and green synthetic methodology. In this study, the gold trication (Au³⁺) can be spontaneously converted into metallic gold atom using a non-toxic reductant (ascorbic acid). The ultrafine Au clusters were formed and stabilized through metallic bonds in the colloidal suspension, which was then deposited on a micro-glass or polymer-bead substrate to prepare thin films. It was found that ascorbic acid was the best reducing agent due to its rapid rate, spontaneity of reaction, and its non-toxic nature. In order to prevent aggregation of the nanoparticles, a dispersing agent (gum Arabic) was used. The second objective of this study was to analyze the PAN using a number of state-of-the-art instrumentation techniques and analytical approaches, such as X-ray powder diffraction (XRD), atomic force microscopy (AFM), scanning and transmission electron microscopy (SEM and TEM), ultraviolet–visible (UV–Vis) spectroscopy, and ZetaPALS. These techniques were applied to evaluate specific properties of the PAN, such as characterization of its crystalline phase, surface topology, characteristic plasmon, particle size distribution, and stability. From this study, it can be concluded that the ultrafine Au nanoparticles and uniform films were obtained using the green chemistry method. The ultrafine Au particles are highly stabilized and monodispersed as demonstrated by their high absolute value of zeta potential.     

Synthesis,characterization, and catalytic application of Au/ZnO nanocomposites prepared by coprecipitation

In this study, Au/ZnO nanocomposites of different gold contents (0.8, 2.5, and 9%) and specific surface areas (from 41 to 51 m²/g) were synthesized via a coprecipitation method. The pure ZnO was obtained at the same experimental conditions. The samples were characterized by XRD, SEM, TEM, HRTEM, and XPS. The influence of gold nanoparticles (Au-NPs) loading on the catalytic activity of Au/ZnO nanocomposite was studied in the model reaction of CO oxidation. Spherical shape and homogeneous distribution of Au-NPs were observed in all samples prepared. The average size of Au-NPs in the obtained catalysts are almost the same (about 4 nm) allowing the studied effect to be manifested. The decrease of intrinsic catalytic activity of the coprecipitated Au/ZnO nanocomposites follows the sequence 2.5, 9, and 0.8% Au, as corresponding to the decrease of relative surface content of Au-NPs. It could be suggested that the catalytic activity is noticeably influenced by the distribution of Au-NPs between the bulk and surface of catalysts.