Effect of Zr (IV) doping on the optical properties of sol–gel based nanostructured indium oxide films on glass

Zr (IV) doped indium oxide thin films (55 nm) were deposited onto pure silica glass by the sol–gel dip coating technique utilizing the precursors of 6 wt% equivalent oxide content. Three different Zr (IV) oxide (ZrO₂) dopant concentrations (5.0, 10.0 and 15.0 wt% w.r.t. total oxides) were chosen. XRD patterns suggested the films were of distinct cubic symmetry of In₂O₃. Nanostructured surface feature was revealed by FESEM images. Average cluster size decreased with increasing dopant concentration as evidenced from TEM study. Blue shift of band gap and UV cut off wavelength (lambda-50) occurred with increase in dopant concentration. The refractive index gradually increased with doping. Baking atmosphere plays an important role in tailoring the refractive index (RI) of the films and relatively high RI was obtained in the case of baking in pure oxygen. Presence of both free and bound excitons was detected by the photoluminescence (PL) study. The 5 wt% doped film exhibited relatively high PL intensity at 380 nm responsible for free exciton. The PL emissions gradually quenched with increase in dopant concentration. Similar behaviour was also observed when the film was baked in pure oxygen atmosphere.     

Fabrication of Ni electrode films by sintering Ni nanoparticle pastes: Compositional dependence of specific resistance and optimal composition

Ultra-thin nickel films are essential for the internal electrodes of the high density multi-layered ceramic capacitors (MLCCs) used in a variety of electronic devices. In this study, Ni electrode films were fabricated by sintering Ni nanoparticle pastes prepared by mechanically stirring mixtures of Ni nanoparticles (d = 40–150 nm), dispersant, binder, and solvent. Paste compositions were varied by using three solvents, two binders, one dispersant, and different amounts of nickel nanoparticles. In total 36 pastes and electrode films were prepared. The electrode film defects such as voids in films and exfoliation (film loss due to lack of adhesion to substrate) were noted, and film thicknesses and specific resistances (ρ) were measured. Voids were observed in all samples whereas exfoliations were observed only for several samples. Ni electrode film thicknesses and ρ values ranged from 2 to 7 μm and from 10⁻⁵ to 10⁻⁴ Ω cm, respectively, depending on paste composition. Based on considerations of ρ values, an optimal composition was determined. Of the three solvents and two binders used, terpineol and EC produced better quality films with lower ρ values and without exfoliation, suggesting that they are probably the most suitable for fabricating internal electrodes for high density MLCCs.     

Effect of cadmium oxide incorporation on the microstructural and optical properties of pulsed laser deposited nanostructured zinc oxide thin films

CdO doped (doping concentration 0, 1, 3 and 16 wt%) ZnO nanostructured thin films are grown on quartz substrate by pulsed laser deposition and the films are annealed at temperature 500 °C. The structural, morphological and optical properties of the annealed films are systematically studied using grazing incidence X-ray diffraction (GIXRD), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), atomic force microscopy (AFM), Micro-Raman spectra, UV–vis spectroscopy, photoluminescence spectra and open aperture z-scan. 1 wt% CdO doped ZnO films are annealed at different temperatures viz., 300, 400, 500, 600, 700 and 800 °C and the structural and optical properties of these films are also investigated. The XRD patterns suggest a hexagonal wurtzite structure for the films. The crystallite size, lattice constants, stress and lattice strain in the films are calculated. The presence of high-frequency E₂ mode and the longitudinal optical A₁ (LO) modes in the Raman spectra confirms the hexagonal wurtzite structure for the films. The presence of CdO in the doped films is confirmed from the EDX spectrum. SEM and AFM micrographs show that the films are uniform and the crystallites are in the nano-dimension. AFM picture suggests a porous network structure for 3% CdO doped film. The porosity and refractive indices of the films are calculated from the transmittance and reflectance spectra. Optical band gap energy is found to decrease in the CdO doped films as the CdO doping concentration increases. The PL spectra show emissions corresponding to the near band edge (NBE) ultra violet emission and deep level emission in the visible region. The 16CdZnO film shows an intense deep green PL emission. Non-linear optical measurements using the z-scan technique indicate that the saturable absorption (SA) behavior exhibited by undoped ZnO under green light excitation (532 nm) can be changed to reverse saturable absorption (RSA) with CdO doping. From numerical simulations the saturation intensity (I_s) and the effective two-photon absorption coefficient (β) are calculated for the undoped and CdO doped ZnO films.     

Physical and electrical properties of thin films produced by Low Energy Cluster Beam Deposition of mixed InxSb1−x clusters

We present a new gas-aggregation cluster source with two independent crucibles, one for indium and another one for antimony. This source was used to produce mixed In_xSb_1−x clusters in the nanometer range size (typically 4 nm), which were deposited at room temperature on amorphous carbon or glass substrates by low energy cluster beam deposition technique (LECBD). The film composition was analysed by energy dispersive X-ray (EDX) spectroscopy. The morphology and structure of the films were studied by transmission electron microscopy (conventional and high resolution) and selected area electron diffraction (SAED) at different compositions. Semiconducting InSb clusters could be produced by controlling the temperature of the two crucibles. The electrical properties of the films were studied at a film thickness of 20 nm. The conductivity versus temperature appeared to be thermally activated for all compositions.     

Tuning photoluminescence properties of ZnO nanorods via surface modification

Zinc oxide (ZnO) is a versatile material that has been used in photocatalysis, solar cells, chemical sensors, and piezoelectric transducers. All these are directly related to its surface properties. Here ZnO nanorod arrays were successfully synthesized by electrochemical deposition method, the surface of which was modified by dopamine, a robust anchor. Compared with pristine ZnO sample, the surface modification can greatly enhance the ultraviolet and visible-light photoluminescence. This is due to the formation of polydopamine on the nanorod surface, which may act as a dye that can be photoexcited. The resultant photogenerated electrons can inject into the conduction band of ZnO and take part in the luminescent process. These results may provide a foundation for real applications of ZnO nanomaterials in optoelectronic devices and, especially, for the applications in biological field as both the dopamine and ZnO are biocompatible materials.     

The influence of dispersing and stabilizing of indium tin oxide nanoparticles upon the characteristic properties of thin films

Stable suspensions of indium tin oxide nanoparticles were prepared by dispersing for 1 h in ethanol and stabilizing with 2-[2-(2-Methoxyethoxy)ethoxy]acetic acid. Particle size, morphology, and structure were characterized by a combination of dynamic light scattering, high resolution transmission electron microscopy, and X-ray diffraction. Spin coating of the stable suspensions resulted in densely packed films with a high transparency. Dispersing times exceeding 1 h led to a significant “overdispersing” effect, i.e. an increasing aggregate size of the suspensions was observed. Zeta-potential, pH, and X-ray photoelectron spectroscopy measurements were conducted to achieve a detailed understanding of the effect of “overdispersing”. With an increasing time of dispersion, i.e. with a decreasing stability of the suspensions, the thin films fabricated by spin coating displayed an increasing pore size distribution and surface roughness. In addition a strong decrease in transmittance and in conductivity was observed.     

Optical and electrical properties of ZnO nanoparticle thin films deposited on quartz by sparking process

ZnO nanoparticle thin films were deposited on quartz substrates by a novel sparking deposition which is a simple and cost-effective technique. The sparking off two zinc tips above the substrate was done repeatedly 50-200 times through a high voltage of 10 kV in air at atmospheric pressure. The film deposition rate by sparking process was approximately 1.0 nm/spark. The ZnO thin films were characterized by X-ray diffraction, Raman spectroscopy, UV-vis spectrophotometry, and ionoluminescence at room temperature. The two broad emission peaks centered at 483 nm (green emission) and 650 nm (orange-red emission) were varied after two-step annealing treatments at 400-800 °C. Moreover, the electrical resistivity of the films was likely to be proportional to the peak intensity of the orange-red emission.     

Preparation and visible-light-driven photoelectrocatalytic properties of boron-doped TiO2 nanotubes

In the present study, chemical vapour deposition (CVD) was applied to dope boron into TiO₂ nanotubes anodized Ti in C₂H₂O₄·2H₂O + NH₄F electrolyte with the goal of improving the photocatalytic (PC) activity under visible light. The undoped TiO₂ nanotubes had a highly self-organized structure. However, after doping through CVD, TiO₂ nanotubes suffered from an observable disintegration of morphological integrity. X-ray diffraction (XRD) results confirmed that annealing temperature had an influence on the phase structure and boron impurities could retard anatase–rutile phase transition. Diffuse reflectance absorption spectra (DRS) analysis indicated that B-doped samples displayed stronger absorption in both UV and visible range. B-doped TiO₂ nanotubes electrode annealed at 700 °C through CVD showed higher photoelectrocatalytic (PEC) efficiency in methyl orange (MO) degradation than that annealed at 400 °C and 550 °C. MO degradation was substantially enhanced with the increasing applied bias potential. Moreover, there was a synergetic effect between the electrochemical and photocatalytic processes, and the synergetic factor R reached 1.45. B-doped TiO₂ nanotubes electrode showed good stability after 10 times by repeating photoelectrocatalysis of MO.     

The attachment, modification and release of gold nanoparticles from a photolabile solid phase synthesis resin, a new methodology for nanoparticle surface modification

Gold nanoparticles were synthesis by a two-phase method (water/toluene) and attached to a solid phase synthesis (SPS) resins. The average diameter of the nanoparticles determined by TEM image analysis was 3.9 ± 0.3 nm. The SPS resin used was an o-nitrobenzyl based photolabile system. This was first loaded with Fmoc-Cys(Trt)-OH following standard PyBOP protocols. UV-Vis spectroscopy was used to monitor the reaction of the nanoparticle solution with the SPS resin. The bound nanoparticles were released from the SPS resin by exposure to UV light, (λ = 350 nm, intensity = 10 000 μW cm^− 2) and shown to reform a stable solution. The nanoparticles were further modified into clusters on the surface of the SPS resin by the addition of pentanedithiol or assembled into nanoparticle dimers by the addition of a 1,3-propanediamine post photolytic release.     

Numerical simulation of nanoparticle-generating electronegative plasmas in the PECVD of nanostructured silicon film

The results of numerical simulation of the equilibrium parameters of a low pressure nanopowder-generating discharge in silane for the plasma enhanced chemical vapor deposition (PECVD) of nanostructured silicon-based films are presented. It is shown that a low electron temperature and a low density of negative SiH₃⁻ ions are favorable for the PECVD process. This opens a possibility to predict the main parameters of the reactive plasma and plasma-nucleated nanoparticles, and hence, to control the quality of silicon nanofilms.     

On the formation mechanism of metal nanoparticle nanotubes

We have previously described nanoparticle nanotubes (NPNTs), i.e., tubular metallic nanostructures comprising coalesced nanoparticles (NPs), obtained by passing citrate-stabilized metal (Au, Ag, Pd) NP solutions through aminosilane-modified nanoporous alumina membranes. Here we show that the mechanism of NPNT formation involves two stages: (i) electrostatic binding of a monolayer of metal NPs to the amine groups on the membrane pore walls; and (ii) accumulation of NP multilayers and room-temperature coalescence to form solid nanotubes. Free-standing NPNTs are obtained by post-dissolution of the membrane template. An improved fabrication apparatus enabled evaluation of the role of drying and other preparation parameters on the NP coalescence and NPNT formation and structure. Intermittent drying during the NP accumulation stage is necessary for the formation of solid NPNTs, while a slow flow rate of the colloid solution through the membrane pores and reversal of the flow direction promote the formation of more uniform and longer NPNTs.     

The influence of the additives composition and concentration on the properties of SnOx thin films used in photocatalysis

The aim of this study is to investigate the influence of different organic additives on the surface properties of SnO_x thin films used for photocatalytic degradation of methylene blue. The films were obtained by anodic oxidation of tin substrate in electrolyte solutions containing green additives based on hydrophobic and hydrophilic maleic anhydride copolymers. The hydrophobic copolymer leads to the formation of thin films with increased specific area which generates a larger interfacial area between the layers and the dye solution. The consequence is an improvement in the photocatalytic efficiency: up to 16% compared to less than 5% for samples electrodeposited without polymer. The hydrophilic copolymer presence in the electrolyte solution leads to higher grain size and lower surface energy which significantly reduce the photocatalytic properties of the layers. The use of copolymers can be a tool for enhancing the surface roughness and film's wettability and thus the photodegradation efficiency.     

One-step chemical bath deposition and photocatalytic activity of Cu2O thin films with orientation and size controlled by a chelating agent

Nanocrystalline cuprous oxide (Cu₂O) thin films were prepared via a one-step chemical bath deposition (CBD) method. The effects of a chelating agent on the orientation, morphology, crystallite size, and photocatalytic activity of the thin films were carefully examined using X-ray diffractometry, scanning electron microscopy, and UV–vis spectrophotometry. The results confirmed that the crystallite size as well as the orientation of the films was dependent on the volume of trisodium citrate (TSC), demonstrating that the band gap ranged from 2.71 eV to 2.49 eV. The morphology and number density of the thin films also depended on the volume of TSC. In addition, the obtained Cu₂O thin films could degrade methyl orange (MO) efficiently in the presence of H₂O₂ under visible-light irradiation, and the mechanism for the enhanced photocatalytic activity of the Cu₂O thin films with the assistance of H₂O₂ was also explored in detail.     

Structural,electrical and photoluminescence properties of ZnO:Al network films grown on nanochannel Al2O3 substrates by direct current magnetron sputtering with an oblique target

ZnO:Al network films were grown on nanochannel Al₂O₃ substrates at 300 K by direct current magnetron sputtering with an oblique target. The film thicknesses are 60 nm, 160 nm and 190 nm. The holes of the network films diminish with increasing film thickness. For the 60-nm thick film, the network is formed by connecting grains. For the 160-nm and 190-nm thick films, however, the network is formed by connecting granules. The granules consist of many small grains. All the network films have a wurtzite structure. The 60-nm and 160-nm thick network films mainly have a [1 0 1] orientation in the film growth direction while the 190-nm thick network film grows with a random crystallographic orientation. A temperature dependence of the resistance within 160–300 K reveals that the network films exhibit a semiconducting behavior and their carrier transport mechanism is thermally activated band conduction. Room temperature photoluminescence spectra for wavelengths between 300 nm and 700 nm reveal a violet emission centered at 405 nm for the 60-nm thick network film and a blue emission centered at 470 nm for both the 160-nm and the 190-nm thick network films. Annealing decreases the resistivity of the network film.     

Assembly of foam and honeycomb films of a diblock copolymer doped with Au or Ag nanoparticles at the liquid/liquid interface and their catalytic properties

Composite thin films of poly(t-butyl methacrylate)-block-poly(2-vinyl pyridine) (PtBMA-b-P2VP) doped with silver or gold nanoclusters or nanoparticles were fabricated at the liquid/liquid interface between the polymer chloroform solution and AgNO₃ or HAuCl₄ aqueous solution. The formation of the thin films results from the adsorption of the polymer molecules at the interface, combination with the inorganic species in the water phases, and self-assembly of the composite molecules. Different from homo-P2VP and polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP) that self-assemble into foam film and honeycomb structure, respectively, two kinds of morphologies (foam and honeycomb structures) are formed simultaneously for PtBMA-b-P2VP, reflecting different assembling behaviors of these polymers at the interface. Silver or gold nanoclusters or nanoparticles were generated in the polymer films during the assembly process and further reduction of the combined precursors, which show high catalytic activity and durability for the reduction of 4-nitrophenol and other nitro-compounds.     

Preparation and characterization of CuO nanostructures on copper substrate as selective solar absorbers

Selective solar absorber coatings of copper oxide (CuO) on copper substrates are prepared by room temperature oxidation of copper at different alkaline conditions. The surface morphology and structural analyses of the CuO coatings are carried out by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and Raman spectroscopy techniques. XRD and Raman studies indicated the single phase nature and high crystallinity of the prepared CuO nanostructures. Different CuO nanostructures, viz., nanoneedles, nanofibers and nanoparticles are formed at different alkaline conditions. The influence of reaction time on morphology of the CuO nanostructures is also studied. The thermal emittance values of these nanostructured CuO samples are found to be in the range of 6–7% and their solar absorptances are ranged between 84 and 90%. The observed high solar selectivity values (>12.7) suggest that these coatings can be used as selective absorbers in solar thermal gadgets.     

Low temperature fabrication of barium titanate hybrid films and their dielectric properties

A method for incorporating BT nano-crystalline into barium titanate (BT) films is proposed for a low temperature fabrication of high dielectric constant films. BT nanoparticles were synthesized by hydrolysis of a BT complex alkoxide in 2-methoxyethanol (ME)/ethanol cosolvent. As the ME volume fraction in the cosolvent (ME fraction) increased from 0 to 100%, the particle and crystal sizes tended to increase from 13.4 to 30.2 nm and from 15.8 to 31.4 nm, respectively, and the particle dispersion in the solution became more improved. The BT particles were mixed with BT complex alkoxide dissolved in an ME/ethanol cosolvent for preparing a precursor solution that was then spin-coated on a Pt substrate and dried at 150 °C. The dielectric constant of the spin-coated BT hybrid film increased with an increase in the volume fraction of the BT particles in the film. The dissipation factor of the hybrid film tended to decrease with an increase in the ME fraction in the precursor solution. The hybrid film fabricated at a BT fraction of 30% and an ME fraction of 25% attained a dielectric constant as high as 94.5 with a surface roughness of 14.0 nm and a dissipation factor of 0.11.     

Effect of nanoparticle size on the onset temperature of surface melting

In this letter the onset temperature of surface premelting, T_sm, is determined in terms of the mean-field approximation. There are established relationships, describing the dependence of T_sm on a characteristic size of nanoparticles. It is shown that if a radius of a particle, r, exceeds 10 nm approximately, this dependence is weak. On the contrary, it is strong if the radius of a particle is less than 5 nm. The transition of surface layers into the quasi-liquid and pseudo-crystalline states is under consideration, too. A comparison of the proposed model with available experimental data and with molecular dynamics simulations is carried out.     

Hydrophilic plasticized biopolymers: Morphological influence on physical properties

Biopolymers such as amylose, when mixed with plasticizers have excellent potential in forming thin films for various food and packaging applications. In this study, the influences of moisture content, plasticizer type and content have been investigated on the physical tensile elongation and crystalline morphology of starch biopolymeric material. Biopolymeric samples prepared with starch and two types of plasticizer with different molecular weights, namely glycerol (M_wt = 92) and xylitol (M_wt = 152), were employed, which also have different numbers of hydroxyl (OH) groups (3 for glycerol and 5 for xylitol). A statistical design of experiments (DoE) was performed on the sample responses (i.e. tensile elongation and crystalline morphology) by varying the moisture content, plasticizer type as well as plasticizer content. Plasticizer type and degree of crystallinity have been found to be insignificantly related. However, the plasticizer content has shown a significant effect on both elongation and crystallinity. A clear B-type pattern (peak at 2θ = ∼ 20°) has been observed in most X-ray diffraction (XRD) results.