Oxide Nanocrystalline Thin Films Research Articles

Acetone Sensors Based on Al-Coated and Ni-Doped Copper Oxide Nanocrystalline Thin Films.

Acetone detection is of significant importance in various industries, from cosmetics to pharmaceuticals, bioengineering, and paints. Sensor manufacturing involves the use of different semiconductor materials as well as different metals for doping and functionalization, allowing them to achieve advanced or unique properties in different sensor applications. In the healthcare field, these sensors play a crucial role in the non-invasive diagnosis of various diseases, offering a potential way to monitor metabolic conditions by analyzing respiration. This article presents the synthesis method, using chemical solutions and rapid thermal annealing technology, to obtain Al-functionalized and Ni-doped copper oxide (Al/CuO:Ni) nanostructured thin films for biosensors. The nanocrystalline thin films are subjected to a thorough characterization, with examination of the morphological properties by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analysis. The results reveal notable changes in the surface morphology and structure following different treatments, providing insight into the mechanism of function and selectivity of these nanostructures for gases and volatile compounds. The study highlights the high selectivity of developed Al/CuO:Ni nanostructures towards acetone vapors at different concentrations from 1 ppm to 1000 ppm. Gas sensitivity is evaluated over a range of operating temperatures, indicating optimum performance at 300 °C and 350 °C with the maximum sensor signal (S) response obtained being 45% and 50%, respectively, to 50 ppm gas concentration. This work shows the high potential of developed technology for obtaining Al/CuO:Ni nanostructured thin films as next-generation materials for improving the sensitivity and selectivity of acetone sensors for practical applications as breath detectors in biomedical diagnostics, in particular for diabetes monitoring. It also emphasizes the importance of these sensors in ensuring industrial safety by preventing adverse health and environmental effects of exposure to acetone.

Combustion synthesis of Eu2O3 nanomaterials with tunable phase composition and morphology

Combustion reactions in europium nitrate – acetylacetone – 2-methoxyethanol solutions and gels were investigated to produce europium (III) oxide (Eu2O3) nanocrystalline materials and thin films. Thermal analyses of solutions indicated that the 2-methoxyethanol solvent also acts as a fuel in the absence of acetylacetone. Adding acetylacetone increases the overall heat of the reaction. Thermal analysis results revealed that the slow oxidation of unburned hydrocarbon residues follows the primary combustion reaction. Time-temperature profile measurements of the bulk combustion synthesis process in air and nitrogen atmospheres enabled the extraction of the maximum reaction temperature and the heating and cooling rates in the combustion zone. Several direct correlations exist between measured combustion parameters and the phase composition of the products. Combustion in air results in mixed-phase cubic and monoclinic nanocrystalline Eu2O3. Increasing the acetylacetone concentration in solutions increases the synthesis temperature and decreases the quantity of cubic Eu2O3. The reaction of solutions in a nitrogen atmosphere or diluted with Eu2O3 provides control of the product phase composition and reduces the quantity of the monoclinic phase. Transmission electron microscopy imaging shows that the Eu2O3 end products are highly porous aggregates of nanocrystalline particles. Electrospraying of reactive solutions onto different substrates followed by short annealing makes the preparation of Eu2O3 materials with diverse morphologies possible.

Phase transformation and enhanced blue photoluminescence of zirconium oxide poly-crystalline thin film induced by Ni ion beam irradiation

Swift heavy ions (SHI) irradiation of Nickel (Ni) beam with different ions fluence bring the modifications in the functional properties of radio frequency (RF) grown zirconium oxide (ZrO2) nanocrystalline thin films. X-ray diffraction analysis affirms the monoclinic to tetragonal phase transformation and diminishing of peak at higher fluence 1 × 1014 and 2 × 1014 ions/cm2 induced by electronic excitation caused by SHI. Zirconium oxide thin films exhibit the same thickness (195 nm) of virgin and irradiated samples and whereas the nanocrystalline thin films have the elemental composition in proper stoichiometry (1:2) as analyzed by rutherford backscattering spectroscopy (RBS). Photoluminescence measurements confirm the blue emission of virgin and irradiated sample recorded at excitation wavelength 270 to 310 nm. The intensity of obtained emission bands varies with fluence which is interpreted in terms of generation and annihilation of defect centers. The characteristic Ag and Bg Raman modes of monoclinic and tetragonal ZrO2 are obtained at different positions. Moreover, the nanocrystalline ZrO2 thin films exhibits the most prominent absorption phenomenon in the visible range and the irradiation cause significant decrease in band gap to 3.69 eV compare to the virgin ZrO2 sample (3.86 eV). XPS analysis indicates the shifting of the core levels Zr 3d and O 1s towards higher binding energy and spin—orbit splitting of different states. The findings in this research justify that the irradiated thin films can be a potential candidate for designing of new materials, intense radiation environments, nuclear reactors, nuclear waste systems, clean energy sources.

Characterization and device application of indium doped ZnO homojunction prepared by RF magnetron sputtering

Undoped and Indium doped Zinc Oxide (IZO) nanocrystalline thin films were synthesized via RF magnetron sputtering techniques using home-made cold pressed powder targets. The morphology, crystal structure, elemental analyses were studied using FESEM, AFM, XRD, EDS and XPS techniques. All the films showed hexagonal wurtzite structure, and revealed appreciable variations in (100), (002) and (101) peak intensities with indium doping. The incorporation of In into the ZnO films was confirmed by both EDS and XPS measurements. XPS and Photoluminescence (PL) studies of doped films demonstrated significant reduction of oxygen vacancies (Vo) after incorporation of indium in ZnO lattice at substitutional sites. PL spectra showed convoluted peaks, which correspond to band to band transitions and defect level emissions. The optical studies showed high transmittance of over 90% in the UV–vis region and exhibited the absorption edge near 380 nm. The band gap energy of the films increased from 3.27 eV to 3.42 eV, with In content. In addition, typical rectifying I–V characteristics of SZO/IZO homojunction layers were demonstrated.

Nanomechanical characterization of titanium incorporated gallium oxide nanocrystalline thin films

The effect of titanium (Ti) incorporation on the crystal structure and mechanical properties of nanocrystalline gallium oxide (Ga2O3) films (Ga-Ti-O) is reported. Ti content was varied from 0 to ∼5 at% in the cosputter-deposited Ga-Ti-O films. The sputtering power applied to the Ti target was varied in the range of 0–100 W, while the sputtering power to Ga2O3 was maintained at 100 W, to produce Ga-Ti-O films with variable Ti contents (0–5 at%). The Ti incorporation-induced effects were significant on the structural and mechanical properties. X-ray diffraction analysis indicated that structural transformation occurred with the increase in Ti content. The effect of Ti and associated microstructural changes are significant on the hardness (H) and elastic modulus (Er). The H values increased continuously from 25 to 30 GPa as a function of Ti up to 1.5 at%, after which a decreasing trend was observed. The Ga-Ti-O films exhibited excellent mechanical characteristics: H ∼30 GPa, Er ∼310 GPa, H/Er ∼0.14, and H3/Er2 ∼0.4 GPa, which are higher compared to those of intrinsic β-Ga2O3. On the basis of these results, a structure-composition-mechanical property correlation in Ga-Ti-O films is established.

Investigation of sensing properties of sol–gel processed 4 at%Sb:SnO2/TiO2 thin films

In this work we investigate the gas and photo sensing properties of the antimony doped tin oxide and titanium oxide (4 at%Sb:SnO2/TiO2) nanocrystalline thin films deposited by sol–gel dip-coating. Photoconductivity measurements are carried out under solar light spectra irradiation at different powers. These results show a photo sensitivity of the films in a lateral junction due to interfacial defects. Gas sensitivity was studied at different pressures, and higher conductivity is presented at lower pressure compared to oxygen-rich atmosphere. It occurs due to absence of oxygen adsorption on the semiconductors surface. TiO2 films are also investigated concerning its properties to gas sensing under photo-excitation with InGaN LED light source with wavelength centered in 450 nm. The decay of photo-induced current evaluated under O2 and vacuum atmospheres shows that the sample illumination may contribute to higher gas-sensitivity. This measurement allows determining the charge carrier capture energy, that is related to trapping dominated by distinct defects in each atmosphere.

Fabrication of Cu2O nanocrystalline thin films photosensor prepared by RF sputtering technique

Cuprous oxide (Cu2O) nanocrystalline thin films were prepared on two types of substrates known as crystalline silicon and amorphous glass, by radio frequency reactive magnetron sputtering method. Scanning electron microscopy images confirmed that Cu2O particles covered the entire surface of both substrates with smoothing distribution. The root mean square surface roughness for the prepared Cu2O thin films on glass and Si (111) substrates is 4.16, and 3.36nm, respectively. Meanwhile, X-ray diffraction results demonstrated that the two phases of Cu2O and CuO were produced on Si (111) and glass substrates. The optical bandgap of Cu2O thin films synthesised on glass substrate is 2.42eV. Furthermore, the prepared Cu2O nanocrystalline thin films have showed low reflectance value in the visible spectrum. Metal-Semiconductor-Metal photodetector based Cu2O nanocrystalline thin films deposited onto Si (111) was fabricated using aluminium and platinum, with the current-voltage and photoresponse characteristic investigated under various applied bias voltages. The fabricated Metal-Semiconductor-Metal (M-S-M) photodetector had shown 126% sensitivity in the presence of 10mW/cm2 of 490nm light with 1.0V bias, displaying 90 and 100ms response and recovery times, respectively. These findings have demonstrated the suitability of M-S-M Cu2O photodetector as an affordable photosensor in the future.

Direct, functional relationship between structural and optical properties in titanium-incorporated gallium oxide nanocrystalline thin films

We present an approach to design Ga2O3-based materials with tunable optical properties. In the Ti-doped Ga2O3 model system, where the Ti content (x) was varied up to ∼5 at. %, Ti induced significant effects on the structural and optical properties. Single-phase β-Ga2O3 formation occurs for a lower Ti content (≤1.5 at. %); however, composite-oxide (Ga2O3-TiO2) formation occurs for a higher Ti content. While band gap reduction (Eg ∼ 0.9 eV) coupled with refractive index (n) enhancement occurs, indicating the electronic-structure modification, with Ti incorporation, the changes are dominant only in the Ga2O3-TiO2-composite. A direct, functional Ti(x)-Eg-n relationship was found, which suggests that tailoring the optical quality and performance of Ga-Ti-O is possible by tuning the Ti content and structure.

Morphology, composition, structure and optical properties of CuO/Cu2O thin films prepared by RF sputtering method

In this paper, copper oxide (CuO/Cu2O) nanocrystalline thin films were deposited by radio frequency (RF) magnetron sputtering system at 75 W and 100 W. The surface, optical, composition and structural properties of obtaining samples were characterized by using atomic force microscopy (AFM), UV–Vis spectrophotometer, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). The optical band gaps of produced films were calculated as 2.05 eV and 1.83 eV for 75 W and 100 W. The layer’s thicknesses were measured as 20 nm and 50 nm using a Filmetrics F20. FESEM images of the samples prove the AFM images change and also show homogeneity of thin films and variation relative to power change, thus revealed the surface of samples disturb in homogen mode. EDX results denote presence of Cu and O elements inside the deposited samples.

Studies of aluminum oxide thin films deposited by laser ablation technique

This paper presents the structural and optical investigations of the aluminum oxide nanocrystalline thin films. Investigated films were fabricated by laser ablation technique in high vacuum onto quartz substrates. The films were deposited at two different temperatures of the substrates equal to room temperature and 900K. X-ray Diffraction spectra proved nanocrystalline character and the corundum phase of the film regardless on the substrate temperature during the deposition process. Values of the refractive indices, extinction and absorption coefficients were calculated by using Transmission and Reflection Spectroscopy in the UV–VIS–NIR range of the wavelength. Coupling Prism Method was used for films thickness estimations. Experimental measurements and theoretical calculations of the Third Harmonic Generation were also reported. Obtained results show that the lattice strain may affect obtained values of the third order nonlinear optical susceptibility.

Improved electrochromic performance in sprayed WO3 thin films upon Sb doping

We report for the first time improved electrochromic properties of tungsten oxide (WO3) nanocrystalline thin films upon Sb doping. The Sb-doped WO3 films were deposited by cost effective spray pyrolysis technique. The structural and morphological studies of the as-deposited films have been carried out by grazing incidence X-ray diffraction (GIXRD) and field emission scanning electron microscopy (FESEM). XRD analyses reveal polycrystalline monoclinic nature of the as-deposited films. The electrochromic behaviours of the films have been studied in an electrochemical analyzer using a three-electrode electrochemical cell, and 0.01 M H2SO4 solution (aqueous) as electrolyte. The charge storage capacity, electrochemical stability and reversibility of the films as well as H+ ion diffusion coefficient in the films during coloration/decoloration process improve upon Sb doping and are optimal for 20 at% Sb dopant concentration.

Oriented Zinc Oxide Nanocrystalline Thin Films Grown from Sol-Gel Solution

Zinc oxide (ZnO) is a wide band gap (~3.37 eV) semiconductor. Thin film ZnO has many attractive applications in optoelectronics and sensors. Recently, nanostructured ZnO (e.g. ZnO quantum dot) has been demonstrated as a hyperbolic material; its dielectric function has opposite signs along different crystal axes within the mid-infrared, making it an interesting material for metamaterials and nanophotonics. Conventional sputtering deposition usually leads to the formation of polycrystalline ZnO films with randomly oriented grains and rough surface. This work demonstrated a solution-based process to grow ZnO thin films with highly oriented nanocrystals. Low-temperature plasmas were employed to modulate the microstructure and optical properties of the films. Such highly anisotropic nanostructured transparent semiconductor films may lead to interesting material properties in developing new optoelectronic devices.

Defect engineered d ferromagnetism in tin-doped indium oxide nanostructures and nanocrystalline thin-films

Origin of unexpected defect engineered room-temperature ferromagnetism observed in tin-doped indium oxide (ITO) nanostructures (Nanowires, Nano-combs) and nanocrystalline thin films fabricated by pulsed laser deposition has been investigated. It is found that the ITO nanostructures prepared under argon environment exhibit strongest ferromagnetic signature as compared to that nanocrystalline thin films grown at oxygen. The evidence of singly ionized oxygen vacancy (V0+) defects, obtained from various spectroscopic measurements, suggests that such V0+ defects are mainly responsible for the intrinsic ferromagnetic ordering. The exchange interaction of the defects provides extensive opportunity to tune the room-temperature d0 ferromagnetism and optical properties of ITOs.

Structural, optical and dispersion energy parameters of nickel oxide nanocrystalline thin films prepared by electron beam deposition technique

In the present paper, we report on the structure and optical properties of non-annealed nickel oxides (NiO) nanocrystalline semiconductor thin films synthesized by electron beam deposition technique. The structure parameters of the as-deposited NiO nanocrystalline thin films are extracted from the X-ray powder diffraction (XRD) spectra and shows that the as-deposited films crystallize in the form of cubic NaCl structure with average lattice constant equal to 4.1797 Å and average lattice volume 73.018 (Å)3. In addition, the crystallite size (D) is found to increase from 15 nm to 24 nm with increasing film thickness from 151 nm to 343 nm. In a wide wavelength range, the optical parameters (absorption coefficient, refractive index and refractive index dispersion) of the nanocrystalline NiO thin films have been calculated from transmission and reflection spectra. The variation of the factors (αhν)2 and (αhν)0.5 as a function of photon energy identifying the optical transitions as direct transition with energy Egdir≈ 3.849 eV and indirect transition with energy Egindir≈ 2.924 eV and phonon energy of order 212 meV, respectively. In the same wavelength range, the variation of the refractive index show normal dispersion behavior with single oscillator model Eo and Ed parameters obtained as 3.082 eV and 10.47 eV, respectively. The coordination number of the NiO nanocrystalline thin film is identified as 3.36. In addition, the lattice oscillator strength El, lattice dielectric constant εl, ratio of free carrier density to free carrier effective mass (N/m∗) and plasma frequency (ωp) are extracted as 0.31 eV, 5.408, 1.043 × 1047 g−1 cm−3, 5.492 × 10+14 s−1, respectively. Also, the molar and volume refractions Rm, Vm and molar polarizability αm, are also calculated and found to be 3.082 cm3/mol, 11.20 cm3/mol, 2.49(A∘)3, respectively. Finally, the Urbach energy Eu is also calculated and found to be 0.38 eV.

Effect of precursors on the microstructural, optical, electrical and electrochromic properties of WO3 nanocrystalline thin films

Spray-deposited tungsten oxide (WO3) nanocrystalline thin films were investigated by X-ray diffraction, Raman spectroscopy, scanning electron mi- croscopy and atomic force microscopy in order to study the precursor induced changes in their structural and morpho- logical properties. The crystallite size and the root mean square surface roughness have been found to be minimum for the WO3 thin films prepared using ammonium tung- state. The optical and spectral studies of the films were carried out using UV-visible spectroscopy and photolu- minescence spectroscopy. Electrical transport properties of the films were studied by measuring the film resistivity as a function of temperature. Electrochromic studies of the WO3 films were carried out from cyclic voltammetry, chronocoulometry and chronoamperometry measurements. The films grown using ammonium tungstate exhibit high electrochromic reversibility (*91 %) and large charge storage capacity. The cyclic voltammograms of the films do not change even after 50 scan cycles, confirming the electrochromic stability in the WO3 films. Overall, the film prepared using ammonium tungstate may be a suitable candidate for electrochromic devices.

Tin-Incorporation Induced Changes in the Microstructural, Optical, and Electrical Behavior of Tungsten Oxide Nanocrystalline Thin Films Grown Via Spray Pyrolysis

Undoped and Sn-doped WO3 thin films were grown on cleaned glass substrates by chemical spray pyrolysis, using ammonium tungstate (NH4)(2)WO4 as the host precursor and tin chloride (SnCl4 center dot 5H(2)O) as the source of dopant. The XRD spectra confirm the monoclinic structure with a sharp narrow peak along (200) direction along with other peaks of low relative intensities for all the samples. On Sn doping, the films exhibit reduced crystallinity relative to the undoped film. The standard deviation for relative peak intensity with dopant concentration shows enhancement in heterogeneous nucleation growth. As evident from SEM images, on Sn doping, appearance of island-like structure (i.e., cluster of primary crystallites at few places) takes place. The transmittance has been found to decrease in all the Sn-doped films. The optical band gap has been calculated for both direct and indirect transitions. On Sn doping, the direct band gap shows a red shift and becomes 2.89 eV at 2 at.% doping. Two distinct peaks, one blue emission at 408 nm and other green emission at 533 nm, have been found in the PL spectra. Electrical conductivity has been found to increase with Sn doping.

Growth and Characterization of Iron Oxide Nanocrystalline Thin Films via Sol-Gel Dip Coating Method

In this paper, iron (III) oxide thin films are deposited on glass substrate via sol-gel dip coating by increasing withdrawal speeds in the range 100-250 mms <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> . Prepared thin films were characterized by UV-VIS spectrophotometer, spectroscopic ellipsometry (SE), X-ray diffraction (XRD), scanning electron microscope (SEM), vibrating sample magnetometer (VSM) and Fourier transform infrared (FTIR) spectroscopy. UV-VIS spectrum and SE show decrease in bandgap energy from 2.8 to 1.6 eV with increased withdrawal speed. FTIR results indicate formation of α-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (hematite) phase of iron oxide with preferred orientation along (104) plane. From SEM studies, it is observed that the developed α-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films are nanocrystalline with small grain size. The surface of α-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> films is smooth and homogenous, which also supports the XRD results. VSM results show that α-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> thin films have ferromagnetic behavior.

Correlation between phase and optical properties of yttrium-doped hafnium oxide nanocrystalline thin films

Yttrium-doped hafnium oxide (YDH) nanocrystalline films were produced by sputter-deposition at a substrate temperature of 400°C. The deposition was made onto Si (100) and optical grade quartz substrates with variable deposition time to produce YDH films in a wide range of thickness, dYDH∼25nm to 1.1μm. The effect of dYDH on the crystal structure, surface/interface morphology and optical properties of YDH films was investigated. X-ray diffraction analyses revealed the formation of monoclinic phase for relatively thin films (<150nm). The evolution towards stabilized cubic phase with increasing dYDH is observed. The scanning electron microscopy results indicate the dense, columnar structure of YDH films as a function of dYDH. Spectrophotometry analyses indicate that the grown YDH films are transparent. The band gap was found to be ∼5.60eV for monoclinic YDH films while distinct separation and an increase in band gap to ∼6.03eV is evident with increasing dYDH and formation cubic YDH films. A correlation between growth conditions, phase evolution, and optical properties of the YDH nanocrystalline films is established.

Swift heavy ion induced topography changes of Tin oxide thin films

Monodisperse tin oxide nanocrystalline thin films are grown on silicon substrates by electron beam evaporation method followed by 100MeV silver ion bombardment with varying ion fluence from 5×1011 ionscm−2 to 1×1013 ionscm−2 at constant ion flux. Enhancement of crystallinity of thin films with fluence is observed from glancing angle X-ray diffraction studies. Morphological studies by atomic force microscopy reveal the changes in grain size from 25nm to 44nm with variation in ion fluence. The effect of initial surface roughness and adatom mobility on topography is reported. In this work correlation between ion beam induced defect concentration with topography and grain size distribution is emphasized.

On the Mechanism of Electrical Conduction in Cobalt-Doped Zinc Oxide Nanocrystalline Thin Films

ZnO and Co-doped ZnO thin films (3 and 11 at. %) were grown on glass substrates by spin coating method and structurally investigated by X-ray diffraction, X-ray photoelectron spectroscopy and UV–vis absorption spectroscopy. It was established that Co enters into ZnO wurtzite lattice by substitution. The electrical conductivity of undoped and Co-doped ZnO nanocrystalline thin films was measured in the temperature range of 300–425 K. The electrical conduction mechanism of the films is explained on the basis of the multiphonon assisted hopping model with a weak electron–phonon coupling. We found that the conductivity first increases with incorporation in ZnO structure of an amount of 3 at. % Co but then it decreases when the amount of Co is increased to 11 at. %. This situation is well explained by the fluctuation in the hopping rate.