Structure,morphology, photocatalytic and antibacterial activities of ZnO thin films prepared by sol–gel dip-coating method

ZnO thin films were deposited on soda lime glass substrates by the sol–gel dip-coating method with variations of the initial Zn²⁺ concentrations. Various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) were used to investigate the effects of the initial Zn²⁺ concentrations on the structure, and surface morphology and topography of the prepared films. All prepared ZnO thin films showed a high transparency of over 88% in the visible region. The particle size increased with an increased initial Zn²⁺ concentration. This also reduced the surface denseness and the energy band gap of the ZnO thin films. All the prepared films showed photocatalytic properties through photodegradation of the methylene blue (MB) dye. The ZnO thin film prepared from the 0.1 M Zn²⁺ concentration showed the greatest efficiency as it had the highest surface area because of its greatest surface roughness. Furthermore, the prepared ZnO thin film showed antibacterial activities against the Escherichia coli bacterium.     

Surface morphology and optoelectronic studies of sol–gel derived nanostructured CdO thin films: heat treatment effect

Morphological dependence of the optoelectronic properties of sol–gel derived CdO thin films annealed at different temperatures in air has been studied. After preparing, the films were investigated by studying their structural, morphological, d.c. electrical and optical properties. X-ray diffraction results suggest that the samples are polycrystalline and the crystallinity of them enhanced with annealing temperature. The average grain size is in the range of 12–34?nm. The root mean square roughness of the films was increased from 3.09 to 6.43?nm with annealing temperature. It was observed that the electro-optical characteristics of the films were strongly affected by surface roughness. As morphology and structure changed due to heat treatment, the carrier concentration was varied from 1.13?×?10¹⁹ to 3.10?×?10^19?cm^?3 with annealing temperature and the mobility increased from less than 7 to 44.8?cm² V^?1 s^?1. It was found that the transmittance and the band gap decreased as annealing temperature increased. The optical constants of the film were studied and the dispersion of the refractive index was discussed in terms of the Wemple–DiDomenico single oscillator model. The real and imaginary parts of the dielectric constant of the films were also determined. The volume energy loss increases more than the surface energy loss at their particular peaks.     

Optical constants of thermally evaporated Se–Sb–Te films using only their transmission spectra

Amorphous Se_82 ? xTe₁₈Sb_x thin films with different compositions (x = 0, 3, 6 and 9 at.%) were deposited onto glass substrates by thermal evaporation. The transmission spectra, T(λ), of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. Based on the use of the maxima and minima of the interference fringes, a straightforward analysis proposed by Swanepoel has been applied to derive the optical constants and the film thickness. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model. Tauc relation for the allowed non-direct transition describes the optical transition in the studied films. With increasing antimony content the refractive index increases while the optical band gap decreases. The optical band gap decreases from 1.62 to 1.26 eV with increasing antimony content from 0 to 9 at.%. The chemical-bond approach has been applied successfully to interpret the decrease of the optical gap with increasing antimony content.     

X-ray absorption spectroscopy study of thermally annealed Cu–Al–O thin films

Cu–Al–O thin films are deposited on (0001) sapphire substrates by radio-frequency sputtering using an Al–Cu mosaic target. The Cu/Al atomic ratio of as-deposited Cu–Al–O films is measured to be 1.1. After deposition, the Cu–Al–O films are annealed at 600, 800, and 1000 °C, respectively, for 1 h in a N₂ atmosphere. The film crystal structure, electronic structure, valence band, and electrical properties are studied. The as-deposited films are amorphous and films annealed at 600 °C contain the crystallized CuO phase; the structure becomes crystallized CuAlO₂ after annealing at 800 °C and 1000 °C. The 800 °C annealed film grows along the (00l) plane. The crystallization decreases with the growth of the (012) and (018) planes for films annealed at 1000 °C. The resistivity values of the 800 °C and 1000 °C annealed films were measured as 1.07 Ω-cm and 864.01 Ω-cm, respectively. The lower resistivity of the 800 °C annealed film is attributed to preferred (00l) growth orientation and a reduction of the energy band gap.     

Investigation of morphology, a.c. electrical and optical properties of nanostructured thin film of polypyrrole–bromoaluminium phthalocyanine

In this research, nanocomposite polypyrrole (PPy) + 30 % bromoaluminium phthalocyanine (BrAlPc) was prepared in our laboratory. Optical absorption and field emission scanning electron microscopy characterized the thin films. The powder of nanocomposite was characterized by X-ray diffraction. The nanocomposite PPy + 30 % BrAlPc thin film deposited on pre-cleaned glass substrate with a thickness of 100 nm, which was deposited in a high vacuum device of electron-beam gun in the pressure of 10^?5 mbar. The capacitance and the dissipation factor were measured in a.c. electrical and in the range of 10²–10⁵ Hz frequency and 303–413 K temperatures. The nanoparticles are spherical in shape with an average size about 25–37 nm. Their UV–Vis spectra of the nanocomposite (PPy + 30 % BrAlPc) is typically described by two strong Q and Soret bands 600–700 and 300–400 nm. The results showed a sharp diffraction peak appeared in 2θ = 8.72 (d = 10.1296 Å) and grian size D = 8.991 nm. The results can be described by the theory of Goswami–Goswami for sandwich devices.     

Synthesis, characterization and electrical properties of nanostructured LaAlO3 by sol–gel auto combustion method

Semiconductive nanostructured LaAlO₃ was synthesized by sol–gel auto combustion method using inorganic reagents as La (NO₃)₃·6H₂O, Al (NO₃)₃·9H₂O and glycine as a fuel. Structural characterization of prepared sample was characterized by X-ray diffraction technique (XRD), and Fourier transforms infrared spectroscopy (FTIR). The morphology of the particle was found by scanning electron microscopy while elemental composition by energy dispersive X-ray spectroscopy and transmission electron microscopy (TEM) was used to study the nanostructure of the material. XRD pattern reveals the formation of single phase orthorhombic structure without any other phase formation. The system LaAlO₃ show porous morphology. Particle size obtained from TEM analysis was found to be ~40 nm. The FTIR spectra showed the characteristic of two strong absorption bands at 656 and 442 cm^?1 corresponding to metal–oxygen bond vibrations for the perovskite structure compound. Superhydrophilic nature of LaAlO₃ was investigated at room temperature by sessile drop technique. The electrical properties of the compound showed that LaAlO₃ exhibits conducting behavior.     

Optical properties of nanostructured ruthenium dioxide thin films via sol–gel approach

High purity ruthenium dioxide (RuO₂) nanoparticles with the average size is about 9 nm in diameter are readily synthesized through a low cost sol–gel method. RuO₂ thin films have been deposited on SiO₂ substrates by sol–gel spin coating techniques at room temperature, followed by annealing at 500 °C for 2 h. The result of X-ray diffraction indicates that the RuO₂ nanoparticles are well crystallized with a rutile tetragonal structure. Morphological of RuO₂ films were characterized using atomic force microscopy (AFM), transmission electron microscopy and high resolution transmission electron microscopy. The AFM images confirmed a spherical-shape nanoparticles with diameter of 9 nm and surface roughness of 12 nm of the films. The optical absorption studies showed the presence of direct band transition with band gap equal to 1.87 eV. Refractive index and dielectric properties of the films were estimated from optical measurements. Room temperature photoluminescence of RuO₂ film showed an emission band at 432 nm.     

Fabrication and characteristics of La,Cd and Sn doped BST thin films by sol–gel method

Ba_1−x Sr _x TiO₃ (BST) thin films doped with La, Cd and Sn were prepared by sol–gel method on the Pt/Ti/SiO₂/Si substrate. X-ray diffraction analysis and atomic force microscopy showed that dopant La and Cd causes decreased grain size of BST thin films obviously, and Sn-doped BST thin films was similar to BST films in grain size. La and Cd doped decreased the tunability of BST thin films and Sn doped increased it, which may be explained by stress, electronegativity and oxygen vacancies factors. All the doped BST thin films improved the leakage current characteristic.     

Preparation and characterization of pyrolytically deposited (Co–V–O and Cr–V–O) thin films

The metal acetylacetonates of vanadium, cobalt and chromium were prepared from commercial reagents. The corresponding metal acetylacetonates were mixed in desired ratio and deposited on soda lime glass substrate by metal organic chemical vapor deposition technique. Mixed oxides thin films with atomic composition Co_0.31V_1.37O₅ and Cr_0.5V₂O₅ were obtained. A combination of Rutherford backscattering spectroscopy and energy-dispersive X-ray fluorescence was used for the transition element identification and atomic compositional study of the thin films. The thickness of the Co–V–O and Cr–V–O thin films was 166 and 127 nm, respectively. The optical spectra of the films were obtained using a Pye Unicam SP8-400 spectrophotometer in the ultraviolet/visible region. The result of the spectral analyses gave the optical bandgap energy of the materials. The temperature dependence of the electrical resistivity measured using the Van der Pauw method indicated that the materials are semiconducting. Their activation energy was obtained from plots of the natural logarithm of conductivity vs. the reciprocal of temperature. The sign of the thermopower shows that both materials are p-type semiconductors.     

Structure and morphology of electroless Ni–P deposits

Abstract

The high-voltage electron microscope has been used to study the structure and morphology of electroless Ni–P deposits of varying phosphorus contents. Except for low (<3 wt-%) phosphorus contents the deposits are amorphous. The crystallization processes depend on a number of variables, including thickness and phosphorus content of the deposit and presence or otherwise of an iron substrate. These processes include epitaxial crystallization of Ni_2.55P, spherulitic (or dendritic) crystallization of Ni_2.55P and Ni₃P, precipitation of nickel particles, and structures arising from interdiffusion between nickel, phosphorus, and the substrate.

MST/660     

Electrical transport properties of as evaporated and annealed amorphous GexSe1−x thin films

D.C. conductivity measurements were made on evaporated and annealed amorphous Ge_xSe_1−x thin films as a function of temperature (80–330K) and composition (x = 1.0, 0.9, 0.7, 0.5, 0.3, 0.1). It was observed that for Ge-rich films (x = 1.0, 0.9, 0.7) the conduction in the high temperature region takes place due to thermally assisted tunneling of charge carriers in localized states at the band edges and at low temperatures conduction is due to variable range hopping in localized states near the Fermi level. For Se-rich films (x=0.5, 0.3, 0.1) the conduction is intrinsic in the entire temperature range of measurements. It was observed that annealing reduces the density of states at the Fermi level. At the highest annealing temperature films become polycrystalline.     

Homogeneous and polymorphic transformations to ordered intermetallics in nanostructured Au–Cu multilayer thin films

Journal of Materials Science - Atomic arrangements in the nanostructured grains and interfaces of thermally evaporated Au/Cu multilayer thin films on polycrystalline Si substrate have been explored...     

Spectroscopic,microscopic, and electrical characterization of nanostructured SnO2:Co thin films prepared by sol–gel spin coating technique

Cobalt doped SnO₂ thin films were prepared by sol–gel spin coating technique and influence of dopant concentration on structural, morphological and optical properties of thin films were investigated by XRD, XPS, FTIR, SEM, AFM, PL, UV–vis, and Hall effect measurement. All samples have a tetragonal rutile structure and the grain size decreases with increasing the doping concentration. XPS results clearly showed the presence of Co²⁺ ions into the SnO₂. The SEM and AFM images reveal that the morphology of samples was affected by dopant. Conductivity type of the films changes from n-type to p-type with increasing Co-dopant above 3 mol% and electrical resistivity increases with increasing Co content. The optical band gap gradually decreases with improved cobalt concentration from 3.91 eV to 3.70 eV. The PL measurements revealed the decrease in intensity of blue emission lines and increase in green emission when content of Co is enhanced in the thin films.     

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.     

The effect of Ca,Sr, and Ba substitutions on the morphology and electrical resistivity of La1 − xAxCu0.5O3 thin films

Thin La_{1 − x}A_xCu_0.5Mn_0.5O₃ (A = Ca, Sr, Ba; x = 0.1, 0.2, 0.3) films were deposited on polycrystalline Al₂O₃ substrates using the sol-gel technique. It was found that the phase composition was not greatly affected by the substituting elements, but, the film morphology strongly depended on the type and concentration of alkali earth elements. Films containing Ca were most porous with significant cracks while Sr substitution lead to inhomogeneous films of large surface area. The introduction of Ba produced dense films and the formation of inhomogeneous packages of crystallites on the surface. The relative dependence of electrical resistivity on temperature was similar for all films in the temperature range 25–600 °C and exhibited semiconducting behaviour with an almost linear slope in the range 25–80 °C. The results permit comparison with films prepared by others using vacuum techniques.     

Growth and optical properties of Sn–Si nanocomposite thin films

The growth and optical properties of nanocomposite thin films comprising of nanocrystalline Sn and Si are reported. The nanocomposite films are produced by thermal annealing of bilayers of Sn and Si deposited on borosilicate glass substrates at various temperatures from 300 to 500 °C for 1 h in air. X-ray diffraction reveals that the as-deposited bilayers consist of nanocrystalline Sn films with a crystallite size of 30 nm, while the Si thin films are amorphous. There is onset of crystallinity in Si on annealing to 300 °C with the appearance of the (111) peak of the diamond cubic structure. The crystallite size of Si increases from 5 to 18 nm, whereas the Sn crystallite size decreases with increase in annealing temperature. Significantly, there is no evidence for any Sn–Si compound, and therefore it is concluded that the films are nanocomposites of Sn and Si. Measured spectral transmittance curves show that the films have high optical absorption in the as-deposited form which decreases on annealing to 300 °C. The films show almost 80 % transmission in the visible-near infrared region when the annealing temperature is increased to 500 °C. There is concomitant decrease in refractive index from 4.0, at 1750 nm, for the as-deposited film, to 1.88 for the film annealed at 500 °C. The optical band gap of the films increases on annealing (from 1.8 to ~2.9 eV at 500 °C). The Sn-Si nanocomposites have high refractive index, large band gap, and low optical absorption, and can therefore be used in many optical applications.     

Effects of RF magnetron sputtering power density on NTC characteristics of Mn–Co–Ni thin films

Thin film NTCR (negative temperature coefficient resistance), based on Mn–Co–Ni oxide, was prepared by reactive RF magnetron sputtering with various sputtering power density (0.95–3.82 W/cm²). The crystalline structure and surface morphology of the NTC thin film were analyzed by XRD and AFM. The NTC characteristics, as a function of sputtering power density, were investigated. The values of B, α ₂₅ and R ₂₅ were in the range of 3,740–3,847 K, ?4.328 to ?4.207 %/K and 8.7–2,082.5 KΩ, respectively. With the increasing power density, the standard resistance (R ₂₅ ) decreased and the consistency of R₂₅ increased. Thin film NTCR with stable B value (3,740 K), low R ₂₅ (10⁴ Ω) and excellent consistency could be fabricated in mass production with about 3.82 W/cm² sputtering power density.     

Deposition potential dependence of composition, microstructure, and surface morphology of electrodeposited Ni–Cu alloy films

Composition, microstructure, and surface morphology of Ni–Cu alloy films electrodeposited at different deposition potentials have been investigated. The microstructural analysis carried out by using X-ray diffraction (XRD) confirmed that all Ni–Cu films are polycrystalline in nature and possess face-centered cubic structure. XRD analysis also revealed that the (111) peak of the Ni–Cu alloy films splits into two as Cu-rich and Ni-rich peaks and the peak intensities change depending on the deposition potential and hence the film composition. Compositional analysis of Ni–Cu films carried out by energy dispersive X-ray spectroscopy showed that Ni content within the films increases as the deposition potential becomes more negative. The morphological analysis performed by using a scanning electron microscopy and an atomic force microscopy revealed that the surface morphology changes significantly with applied deposition potential. Furthermore, a direct correlation is observed between the surface roughness and lattice strain.