Narrow Results

This paper presents a comprehensive study of the optical properties of amorphous and crystalline MoO₃ thin films using spectroscopic ellipsometry. MoO₃ films were deposited on SiO₂/Si substrates with varying oxide thicknesses using the atomic layer deposition (ALD) method. The study utilized various optical oscillator models, including Lorentz, Tauc–Lorentz and Harmonic, to analyze the dielectric functions and identify midgap states resulting from oxygen deficiencies. The findings highlight significant differences in the optical properties between amorphous and crystalline MoO₃ films, demonstrating the impact of structural phases and substrate conditions. Specifically, amorphous films exhibited lower broadening and energy peaks compared to crystalline films, which showed distinct midgap states indicative of higher oxygen vacancy concentrations. These results enhance the understanding of the optical behavior of MoO₃ films and their potential applications in advanced optoelectronic devices.

This paper presents a brief review of nondestructive methods useful for the general purpose of characterizing nanostructure in layered materials using x-rays from synchrotron radiation. By way of examples, some practical applications of these methods to the study of layered systems of recent technological interest are demonstrated.

Thin film titanium/poly-para-xylylene nanocomposites with controlled Ti content are prepared by vacuum coevaporation and cocondensation of Ti and paracyclophane. The structure and chemical composition of as-deposited samples and the changes of electrical resistivity, which they undergo upon heating, are studied by atomic force microscopy, optical absorption spectroscopy, and the temperature coefficient of the electrical resistivity. It is shown that vacuum coevaporation results in the production of nanocomposite thin films with average Ti particle size of 10–50 nm. The inorganic phase is shown to be amorphous Ti for the samples with high metal content, whereas for the low-filled nanocomposites it consists of amorphous titanium oxide. Two types of kinetics of the nanocomposite oxidation process have been found and modeled by (i) inverse logarithmic and (ii) logarithmic functions depending on the metal content within the thin film. After a long preconditioning period in air the electrical conductivity of the thin film nanocomposites was carefully investigated by two-probe DC measurements. A strong correlation between the concentration of Ti in the thin films and the electrical conductivity dependency on temperature is found and modeled by a heterogeneous model of conductivity.

Trifluoropropyl-trichlorosilane reagents were used to tailor the surface chemistry of porous nano-structured thin films fabricated using glancing angle deposition (GLAD). GLAD produces high surface area films of isolated columnar structures and provides complete control over the film morphology. Here, the chemical tunability of these GLAD films was investigated using solution and vapor-phase surface functionalization methods. All films were characterized using scanning electron microscopy, X-ray photoelectron spectroscopy and advancing aqueous contact angle measurements. Our results indicate that the surface chemistry of the GLAD films was effectively changed after functionalization by either approaches. We also note that vapor-phase functionalization provides more consistent results and eliminates the need for organic solvents, making it an ideal method for tailoring the surface properties of GLAD films for specific applications.

Ferromagnetic nickel metal beads, fibers, and thin films have been successfully grown from salt solution by a stepwise hydrazine reduction route with and without surfactants. XRD analyses showed that nickel was grown in the metallic phase and no other phases such as nickel oxide were detected in the prepared samples. SEM investigations showed that bead-like structures that agglomerated in the form of cloth- or net-like structures of about 1 μm size that composed of needle-like nanoparticles have been synthesized without using a surfactant. Sharp decrease in size was observed when sodium dodecyl benzene sulphonate (SDBS) and/or polyethylene glycol (PEG) were used. Bead-like morphology of nickel nanostructures of < 150 nm were deposited in this case. Free-standing nickel thin film structures that composed of needle-like nanoparticles of about 50 nm size were deposited by a stepwise reduction. Nickel nanostructures of < 100 nm showed higher coercivity (Hc) value of 184.6,Oe and lower saturation magnetization (Ms) value of 13.29 emu/g. This might be due to the anisotropic shape and size effects. It is strongly believed that nickel nanoparticles are self-assembled through a dipolar–dipolar interaction due to the magnetic property.

The fimls of Pb_(1-x)Cd_(x)S have been prepared on glass substrates by chemical method. The optical study of transmission T(λ) and reflexion R(λ) spectra has enabled us to determine the compounds whose gap is close to 1.5 eV. The heterojunction is obtained by the chemical deposition of the Pb_(1-x)Cd_(x)S films grown on the p-type Silicon substrates (7 Ω cm). The preparation conditions of the ternary compound whose gap is 1.48 eV have been used to achieve the heterojunction Pb_(1-x)Cd_(x)S - n/Si - p, and we have studied the effect of thermal treatment on the prepared heterojunction. X-ray diffraction has been used to determine the variation of the crystalline parameter, the ratio of cadmium in the compound Pb_(1-x)Cd_(x)S and the dependence of the gap on the cadmium composition. C–V characteristics were examined to understand the average concentration of impurities in the compound Pb_(1-x)Cd_(x)S.

We have observed prominent change in the velocity of dislocation in thin films due to the proximity of free surfaces using molecular dynamics simulations. A simple model has been introduced and the numerical implementation of our model is in accord with the simulation results. Such surface effects have been attributed to the change in lattice resistance to dislocation motion.

Tin oxide thin films were prepared via spray pyrolysis method. The structural and morphological properties of SnO₂ thin films have been investigated using X-ray diffraction (XRD) and scanned electron microscope (SEM) analysis. The XRD pattern confirms the tetragonal rutile structure of SnO₂ with preferential orientation along (200) plane. SEM image reveals the nanocrystalline nature of the SnO₂ films. SnO₂ thin films were subjected to electrochemical tests to study the supercapacitor behavior. Maximum specific capacitance of 168 F/g at a scan rate of 25 mV/s was obtained using 0.5 M KOH as the electrolyte. This is the highest value ever reported for spray deposited tin oxide thin films.

A simple route involving the reaction between zinc powder and water under controlled pH and temperature was used to prepare ZnO nanorods (see Panchakarla et al.). Zinc oxide nanoparticles were prepared also using sol–gel method starting from zinc acetate precursor (as per Zang et al.). Thin films were prepare from both nanorods and nanoparticles by electrophoretic deposition (EPD) in aqueous media (see Dogan et al., Wang et al., Lommens et al., Tang et al. and Besra et al.). To have a uniform microstructure in the deposited films, the aqueous suspension was stabilized using an anionic surfactant. The effect of voltage and pH on the rate of electrophoretic deposition from nano zinc oxide colloid was studied in detail. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Atomic force microscopy (AFM) and UV-Vis Spectroscopy were used to characterize Zno thin films after sintering.

Multilayered structures of gold nanoparticles (AuNPs) embedded Zno films were prepared by sandwiching Au nanoparticles in between magnetron sputtered Zno films. More than 80% transmittance in visible region was observed for Zno film. For structures consisting of single and double layers of AuNPs, transmittance at ~600 nm was reduced to ~25% and ~6%, respectively. AuNPs embedded sandwiches showed a huge reduction in UV Photoluminescence that was prominent in pure Zno films, and was attributed to the interband absorption in Au.

This paper presents the growth of bismuth ferrite (Bi₂Fe₄O₉) thin film by radio frequency magnetron reactive sputtering on p-Si (100) substrate and the characterization of the grown thin film. The deposited thin film is characterized by X-ray diffraction (XRD), field emission scanning electron micrograph (FESEM), energy dispersive X-ray analysis (EDAX), dielectric measurements and vibrating sample magnetometer (VSM) analysis. The XRD study reveals the orthorhombic structure of the crystallites and the particle size is calculated as 45 nm. The FESEM result confirms that the film has smooth surface and uniform distribution of nanoclusters. The percentage of chemical compositions of the film is confirmed by EDAX measurement. The dielectric behavior of the film is examined in terms of the dielectric constant and the dielectric loss as a function of frequency. The magnetic behavior of the film is measured using VSM with the applied magnetic field of about 1 Tesla and the result shows the ferromagnetic behavior of the sample at room temperature.

TiO₂ powder was found to be polycrystalline with rutile system. TiO₂ films were deposited on quartz substrates by a sol–gel spin coating technique. X-ray diffraction and transmission electron microscope results have confirmed that the TiO₂ films have nanostructure nature. It is found the crystallite size increased with annealing temperature. The optical constants of nanostructured TiO₂ films were found to be independent of film thickness in the range from 100nm to 500nm. It is found that the optical constants and the dielectric constant of the thin films were all affected by annealing temperature. The existing allowed optical transitions in the as-deposited and annealed films were found to be direct and indirect transitions. Finally, the bandgaps of the as-deposited film were found to decrease with the annealing temperature.

ZnO thin films were deposited on quartz substrates by RF sputtering under argon, oxygen and nitrogen gas environment. The as deposited films showed hexagonal wurtzite structure with (002) orientation along c-axis. The mechanical properties of films with thickness ranging from 842nm to 1067nm and grain size 94–124nm were studied using nanoindentation technique. The Young’s modulus and hardness of the films were in the range 76–257GPa and 5–18GPa, respectively. Both parameters decreased with increase in indentation depth of the films. The spatial distribution of these parameters were strongly dependent on the gas environment used for film deposition.

Recent developments in the field of flexible electronics motivated the researchers to start working in verdict of new flexible substrate for replacing the existing rigid glass and flexible plastics. Flexible substrates offer significant rewards in terms of being able to fabricate flexible electronic devices that are robust, thinner, conformable, lighter and can be rolled away when needed. In this work, a new flexible and transparent substrate with the help of organic materials such as Polydimethylsiloxane (PDMS) and tetra ethoxy orthosilicate (TEOS) is synthesized. Transmittance of about 90–95% is acquired in the visible region (400–700nm) and the synthesized substrate shows better thermal characteristics and withstands temperature up to 200${}^{\circ }$C without any significant degradation. Characteristics such as transmittance ($T$), absorption ($A$), reflectance ($R$), refractive index ($n$) and extinction coefficient ($k$) are also reported.

Zinc oxide (ZnO) nanoparticles were synthesized by a simple solution route method using zinc acetate as the precursor and ethanol as the solvent. At a temperature of 60${}^{\circ }$C, a clear homogenous solution is heated to 100${}^{\circ }$C for ethanol evaporation. Then the obtained precursor powder is annealed at 600${}^{\circ }$C for the formation of ZnO nanocrystalline structure. Doped ZnO particle is also prepared by using aluminum nitrate nonahydrate to produce aluminum (Al)-doped nanoparticles using the same solution route method followed by annealing. Thin film fabrication is done by air evaporation method using the polymer polyvinyl alcohol (PVA). To analyze the optical and thermal properties for undoped and doped ZnO nanocrystalline thin film by precursor annealing, characterizations such as UV, FTIR, AFM, TGA/DTA, XRD, EDAX and Photoluminescence (PL) were also taken. It was evident that precursor annealing had great influence on thermal and optical properties of thin films while ZnO and AZO film showed low crystallinity and intensity than in the powder form. TGA/DTA suggests pre-annealing effect improves the thermal stability, which ensures that Al ZnO nanoparticle can withstand at high temperature too which is the crucial advantage in the semiconductor devices. UV spectroscopy confirmed the presence of ZnO nanoparticles in the thin film by an absorbance peak observed at 359nm with an energy bandgap of 3.4eV. A peak obtained at 301nm with an energy bandgap of 4.12eV shows a blue shift due to the presence of Al-doped ZnO nanoparticles. Both ZnO and AZO bandgap increased due to precursor annealing. In this research, PL spectrum is also studied in order to determine the optical property of the nanoparticle embedded thin film. From PL spectrum, it is observed that the intensity of the doped ZnO is much more enhanced as the dopant concentration is increased to 1wt.% and 2wt.% of Al in ZnO.

Zinc oxide (ZnO) thin films have been synthesized by thermally oxidizing the direct current magnetron sputtered zinc (Zn) films at 500${}^{\circ }$C for different annealing time periods (3–5h) in ambient air. Influence of annealing time on the structural, morphological, optical and electrical properties of ZnO films was studied using X-ray diffractometer, field emission-scanning electron microscopy (FE-SEM), UV–Vis spectrophotometer and two-probe method, respectively. ZnO films exhibited hexagonal crystal structure with (1 0 1) as preferential orientation plane, and the crystallite size of the films increased from 30nm to 83nm on increasing the annealing time. Pebble-like surface morphology was observed from the FE-SEM micrographs. Optical band gap of the films varied between 3eV and 3.5eV for different annealing times. Electrical resistance of the ZnO films was decreased with increase in the annealing time, which is due to the improvement in the crystallinity.

The copper telluride (Cu₂Te) thin film of thickness 240nm was coated on a microscopic glass substrate by thermal evaporation technique. The prepared films were annealed at 150${}^{\circ }$C and 250${}^{\circ }$C for 1h. The annealing effect on Cu₂Te thin films was examined with different characterization methods like X-ray Diffraction Spectroscopy (XRD), Scanning Electron Microscopy (SEM), Ultra Violet–Visible Spectroscopy (UV–VIS) and Photoluminescence (PL) Spectroscopy. The peak intensities of XRD spectra were increased while increasing annealing temperature from 150${}^{\circ }$C to 250${}^{\circ }$C. The improved crystallinity of the thin films was revealed. However, the prepared films are exposed complex structure with better compatibility. Moreover, the shift in band gap energy towards higher energies (blue shift) with increasing annealing temperature is observed from the optical studies.

The bandgaps of 1.187eV in non-irradiated nanostructured thin films of Cu(In,Ga)Se₂ (CIGSe) and of 1.182eV in those films irradiated with 10keV hydrogen ions were determined using optical transmission and reflection spectroscopy at 4.2K. The observed reduction in the bandgap is assigned to the formation of secondary antisite defect complexes inducing band tails of the density of states in the valence band.

The irradiation-induced effects in Cu(In,Ca)Se₂ thin films after irradiation with hydrogen ions with dose of $3\times 10^{15}$cm${}^{-2}$ and different energies in the range of 2.5–10keV were studied. Irradiated and nonirradiated thin films were investigated by low-temperature (4.2K) photoluminescence and photoluminescence excitation methods. The appearance of intense bands at $\sim 0.92$eV and 0.77eV in the photoluminescence spectra may be related to radiative recombination on the irradiation-induced defects with deep energy levels in the bandgap of Cu(In,Ca)Se₂ solid solutions. A possible nature of these defects and process of radiative recombination are discussed.

Nitrogen and ruthenium co-doped titania films synthesized by sol–gel technique exhibit high photocatalytic activity under both UV and visible light. Incorporation of nitrogen and ruthenium ions in titania lattice is proven by XPS. Both doping agents affected the structural properties of the films.