Sol-gel Spin-coating Technique Research Articles

Investigation of the Structural, Optical and Electrical Properties of Gadolinium-Doped Zinc Oxide Films Prepared by Sol-Gel Method

Thin films of undoped and gadolinium-doped zinc oxide (Gd-doped ZnO) with different Gd concentration (1-8 at. %) were deposited onto a glass substrate by sol–gel spin-coating technique. X-ray diffraction (XRD, Bruker D8 Advance) studies confirmed the nature of the films as polycrystalline, with typical hexagonal wurtzite structure. The film also showed variation in crystallite size and change in relative intensities, upon different Gd concentrations. Besides, the influence of Gd concentration on the optical transmittance of ZnO films was studied using ultraviolet-visible spectrophotometer (UV-Vis, Shimadzu UV 1800) in the wavelength range 300-800 nm. The optical transmittance of all films is higher than ~95% in the visible region, and doped films become more transparent. The electrical resistance was measured by two point probe (Keithley-2400). The resistance decrease with increasing Gd concentration up to 2 at.% and it increased for further increase Gd concentrations.

NiO films grown epitaxially on MgO substrates by sol–gel method

NiO films were grown epitaxially on MgO (100) substrates by a sol–gel spin-coating technique using a solution of nickel acetate tetrahydrate in 2-methoxyethanol stabilized by monoethanolamine. X-ray diffraction, high-resolution transmission electron microscopy, and selected-area electron diffraction analyses indicated that the NiO films grew epitaxially on the MgO substrates. X-ray reciprocal space maps around the asymmetric 311 diffraction point revealed that the NiO films were in a partially strained state, with the lattice parameter contracted along the direction normal to the surface and expanded along the direction parallel to the surface in each film, caused by a lattice mismatch between NiO and MgO. Strain relaxation was gradually enhanced as the film thickness increased. In addition, the Poisson's ratio of NiO was estimated to be about 0.22 from the lattice parameter changes, which is somewhat lower than the value predicted from the elastic constants of NiO.

Nanocrystalline Cu2O/p-Si solar light-responsive Schottky photodiode

Nanocrystalline of Cu2O thin film was synthesized by sol–gel spin-coating technique. The spectrophotometric characteristics of transmission and reflection were studied for the film deposited on glass substrate. The optical absorption measurements near the absorption edge indicate that the absorption mechanism is due to allowed direct transition with energy gap value of 2.09 eV. The current–voltage characteristics of Al/Cu2O/p-Si/Al diode were studied under dark and various light intensities in the range 20–100 mW/cm2. The main diode parameters such as barrier height, ideality factor, series resistance were calculated from the analysis of current–voltage characteristics and studied under various illumination intensities. Moreover, the results indicate that the diode has a high photoresponsivity and the photocurrent increases with increasing light intensity which supports the availability of the diode for photosensor applications. The capacitance and conductance characteristics indicate that the diode highly depends on both voltage and frequency. Higher increase in the capacitance under low frequency as well as the presence of a characteristic peak in the capacitance–frequency characteristics indicates the presence of interface states. Moreover, the stronger parameters of the diode performance such as series resistance and interface states were extracted from the capacitance–voltage–frequency and conductance–voltage–frequency characteristics.

Low Temperature Annealed Zinc Oxide Nanostructured Thin Film-Based Transducers: Characterization for Sensing Applications.

The performance of sensing surfaces highly relies on nanostructures to enhance their sensitivity and specificity. Herein, nanostructured zinc oxide (ZnO) thin films of various thicknesses were coated on glass and p-type silicon substrates using a sol-gel spin-coating technique. The deposited films were characterized for morphological, structural, and optoelectronic properties by high-resolution measurements. X-ray diffraction analyses revealed that the deposited films have a c-axis orientation and display peaks that refer to ZnO, which exhibits a hexagonal structure with a preferable plane orientation (002). The thicknesses of ZnO thin films prepared using 1, 3, 5, and 7 cycles were measured to be 40, 60, 100, and 200 nm, respectively. The increment in grain size of the thin film from 21 to 52 nm was noticed, when its thickness was increased from 40 to 200 nm, whereas the band gap value decreased from 3.282 to 3.268 eV. Band gap value of ZnO thin film with thickness of 200 nm at pH ranging from 2 to 10 reduces from 3.263eV to 3.200 eV. Furthermore, to evaluate the transducing capacity of the ZnO nanostructure, the refractive index, optoelectric constant, and bulk modulus were analyzed and correlated. The highest thickness (200 nm) of ZnO film, embedded with an interdigitated electrode that behaves as a pH-sensing electrode, could sense pH variations in the range of 2-10. It showed a highly sensitive response of 444 μAmM-1cm-2 with a linear regression of R2 =0.9304. The measured sensitivity of the developed device for pH per unit is 3.72μA/pH.

Preparation of Transparent-Type Plasmonic Sensors By the Sol-Gel Process and Electrodeposition

Surface-enhanced Raman scattering spectroscopy (SERS)1 is a powerful method for molecular-level characterization of various surfaces and interfaces, featuring high detection ability compared to normal Raman spectroscopy. We have developed plasmonic sensors for the SERS, which could achieve very high enhancement effect, and succeeded to analyze extremely small amount of materials2. The plasmonic sensor has a patterned nanostructure with concentric circular grooves so as to have high electric field at its center. The sensors are made of metals such as Ag, Au, and Cu, which are active for the plasmonic enhancement. In the present study, we proposed a new type of the sensor, “transparent” plasmonic sensor, which enables the measurements of various types of specimens, regardless of the substrate materials. In order to fabricate these sensors, we applied a sol-gel process to form SiO2 films and the formation of Au–Ag nanodot patterns embedded in the sol–gel SiO2 films using electrodeposition. We also evaluated the performance of the fabricated sensors. The transparent-type plasmonic sensors were fabricated by the following process. Indium tin oxide (ITO) was sputtered on a glass substrate. SiO2 thin films were prepared by the sol-gel spin-coating technique on the ITO-glass surface, using tetraethoxysilane as the precursor material and polyethylene glycol (PEG) as a thickener. Polydimethylsiloxane (PDMS), which exists as fine needles, was used as a template. The template, consisting of fine PDMS needles, was pressed into the SiO2 thin film and then heated, thus forming and transferring nanodot patterns into the film. The residual SiO2 film on the ITO was removed by reactive ion etching (RIE). Then, Au–Ag films were electrodeposited at −0.7 V vs. Ag/AgCl on the SiO2 nanodot patterns. Electrodeposition and electrochemical measurements were performed with an electrochemical analyzer (HZ-7000, Hokuto Denko). The surface morphology was observed by scanning electron microscopy with a field-emission source (FE-SEM, S-4800, Hitachi High-Technologies Corp.) and focused ion beam–scanning electron microscopy (FIB-SEM, NB-5000, Hitachi). SERS measurements were performed using Raman microscopy (Nanofinder 30, Tokyo Instruments, Inc.). 30-nm-depth nanodot patterns in sol-gel SiO2 films were confirmed using PDMS template. And, after the removal of the residual SiO2 film on the ITO, we could embed the Au-Ag films in the nanodot patterns by electrodeposition. And, we evaluate the behavior of PEG in the sol-gel SiO2 process. By 350 °C annealing, it was confirmed that the Raman peak of PEG disappeared and then the use of PEG in sol-gel SiO2 process didn’t affect the property of transparent-type plasmonic sensors. Using these sensors, we evaluated the outermost surfaces of electrodeposited Cu films and the behavior of organic additives in electrodeposition to confirm the ability of transparent-type plasmonic sensor. From the examination, the status of oxidation of Cu and a small amount of organic additives was detected. It was confirmed that the developed transparent-type plasmonic sensors worked well. We have developed a process to prepare transparent-type plasmonic sensors which were constituted from Au–Ag nanodot patterns embedded in sol–gel SiO2 films. From these results, it is clear that these developed plasmonic sensors are effective for the in situ analysis and detection of the interfaces between solids and liquids in water or electrolyte. Acknowledgments This research was partially supported by "Nanotechnology Network Project", "Development of Systems and Technology for Advanced Measurement and Analysis", and "Grant-in-Aid for Scientific Research, 23656470 and 25630041” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

Growth and Characterization of Aln Thin Film Deposited by Sol-Gel Spin Coating Techniques

This study signifies the growth and characterization of aluminium nitride (AlN) thin film deposited on the atmospheric plasma treated n-type silicon [n-Si (100)]. Basically, the low cost spin coating technique which emphasized the production of a thin and uniform film on a flat substrate through a dilute solution is adopted. For the precursor preparation, the main ingredient of aluminium nitrate hydrate is dissolved with an organic solvent. The nitridation process is carried out on the deposited coating at 1100 °C for 1 hour. The surface morphology and structural properties of the thin film were investigated by field-emission scanning electron microscope, atomic force microscopy energy, dispersive X-ray spectroscopy and X-ray diffraction; while the optical properties of the deposited thin film was determined by using Fourier transform infrared spectrometer. All the results revealed that AlN thin film was successfully deposited on n-Si (100) substrate.

Morphological and Optical Properties of Different Mg Percentage of ZnO/Mg Thin Films Prepared by Sol-Gel Spin-Coating and Immersion Method

We have successfully demonstrated ZnO/Mg thin films on Mg seeded-template by using sol-gel spin-coating and immersion technique. By increasing weight percentage of Mg, zinc particles become agglomerate and displayed flower formed as displayed in FESEM characterization. It was observed that the morphology of the zinc particles on Mg seeded-template change from inconsistently distribution for 1 and 3 % into cluster flower-like of zinc particles for 5 and 7 % weight percentage of Mg. The optical properties of the ZnO/Mg thin films were examined by UV-Vis spectroscopy and the Tauc plot methods was used to estimate the optical band gap. The study reveals that, 7 % weight percentage of Mg was recorded as the highest transmittance which is more than 60 % in visible wavelength compared to others. With the rise weight percentage of Mg, the transmittance of the thin films was increased except for 5 %. This gradually downgraded to below 60 % of transmission most probably due to the grain size that becomes bigger. The optical band gap can be tuned by using different Mg percentage to the ZnO/Mg thin films.

Photovoltaic Properties of Dye-Sensitized Solar Cells Using Novel Aligned ZnO Nanorod Arrays on Sn-Doped ZnO Seeded Catalyst with Different Aspect Ratio

The Sn-doped ZnO thin films were deposited on glass and ITO by sol gel Spin Coating technique. The Structural and electrical properties of Sn-doped ZnO thin films were studied and discussed. The Sn-doped ZnO thin film particle sizes were decreased whenever the doping concentration increased. Besides that, the resistivity 7.7 x 102 Ω.cm was obtained at 2 at.% Sn-doped thin films and aligned ZnO nanorod arrays with large surface area were grown on 2 at.% Sn-doped ZnO film. Therefore, dye sensitized solar cell at 2.0 at.% Sn-doped ZnO thin films with aligned ZnO Nanorod arrays have improved in the photocurrent density and conversion efficiency.

Preparation of a Novel Zinc Zirconate Nanocomposite Coated on Glass for Removal of a Textile Dye (Reactive Brilliant Red X8B) From Water

In the present work, zinc zirconate nanocomposite (ZZN) thin film was coated on glass surface by sol-gel spin-coating technique via zirconium acetylacetonate, zinc acetate, monoethanolamine, and 1,3-propanediol. The product was characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive analysis of X-ray, and UV-vis spectroscopy. XRD data confirmed the formation of nanostructure zinc zirconate (ZnZrO3) layer. The photocatalytic activity of the ZZN thin film was estimated on the degradation and mineralization of Reactive Brilliant Red textile dye under metal halide lamp irradiation. Effects of some parameters such as pH of solution, irradiation time, cycles of use and initial dye concentration were studied and obtained results demonstrated that the degradation efficiency was affected by initial concentration of the dye. Total organic carbon of aqueous dye solution after 180 min irradiation showed 95% decrease in carbon.

Printed Barium Strontium Titanate capacitors on silicon

In this paper, we show that Barium Strontium Titanate (BST) films can be prepared by inkjet printing of sol–gel precursors on platinized silicon substrate. Moreover, a functional variable capacitor working in the GHz range has been made without any lithography or etching steps. Finally, this technology requires 40 times less precursors than the standard sol–gel spin-coating technique.

Effect of molarity of TiO2 seeded-template to the growth of ZnO nanostructures

ZnO nanostructures were deposited by solution-immersion method on TiO2 layers by sol-gel spin-coating technique. Seven layers of TiO2 were coated on glass substrates at different molarities, followed by annealing treatment and solution-immersion process in aqueous solution containing 1:1 ratio of 0.05 M of zinc nitrate hexahydrate (Zn(NO3)2.6H2O) and hexamethylenetetramine (HMTA) (C6H12N4). FESEM images confirmed that ZnO nanostructures grown on TiO2 seeded-template are in needle-like shape with smaller tip can be observed. Photoluminescence (PL) spectroscopy showed that as the molarity of TiO2 seeded- template increase, the intensity of PL emission at UV region decrease. UV emission peak for 0.10 M and 0.25 M are higher compared to UV emission peak film of 0.50 M and 1.00 M, which are too low. Meanwhile, the UV absorption properties of the nanostructured thin film for 0.25 M of TiO2 seeded-template was higher compared to other thin films.

Structure and properties of the Mn doped CeO2 thin film grown on LaAlO3 (0 0 1) via a modified sol–gel spin-coating technique

Here we report Mn doped cerium oxide films prepared on the LaAlO3 (001) substrate via an ethylene glycol modified sol–gel spin coating technique and evaluation of their properties as diluted magnetic semiconductors. Cerium oxide was selected because of its high dielectric constant and fluorite cubic structure, matching the silicon and lanthanum aluminate based electronic devices. The concentration of the Mn ions was varied from 1 to 13at.% and the influence of this concentration on the structure, surface morphology, optical and magnetic properties of these films was studied using scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy, ellipsometric spectroscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and magnetic measurements. The incorporation of 7at.% of Mn ions was found to provide formation of exceptionally smooth films, demonstrating the highest saturation magnetization of 1.75μB/Mn and the coercive field of 487 Gauss. These properties are assigned to the conversion of Ce4+ to Ce3+ upon incorporation of Mn ions into the CeO2 structure and the oxidation of Mn2+ to Mn4+, creating two oxygen vacancies to preserve the cubic structure of cerium oxide and promoting ferromagnetism.

Characterization of Cuprous Oxide Thin Films Prepared by Sol-Gel Spin Coating Technique with Different Additives

Cuprous oxide (Cu2O) thin films were formed onto indium tin oxide (ITO) coated glass substrate by sol-gel spin coating technique using different additives namely polyethylene glycol and ethylene glycol. It was found that the organic additives added had an important influenced on the formation mechanism of Cu2O films and lead to different microstructures and optical properties. The films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and ultraviolet-visible spectroscopy (UV-Vis). Based on the FESEM micrographs the grain size of film prepared by polyethylene glycol has smallest grain of about 83 nm with irregular shape. The highest optical absorbance film was obtained by the addition of polyethylene glycol.

Preparation and characterization of sol–gel-derived n-ZnO thin film for Schottky diode application

n-ZnO film has been formed on p-Si substrate using sol–gel spin-coating technique. For structural, optical and morphological characterization, the XRD pattern, SEM images and EDX spectra of the n-ZnO film have been obtained. The optical band gap of n-ZnO has been calculated as 3.29 eV. A Schottky diode application of the film has been performed by evaporation of Au on n-ZnO film. It has been seen that the device has exhibited good rectifying behavior. The current–voltage (I–V) and capacitance–voltage (C–V) measurement of the device has been taken as a function of the frequency, at room temperature. Using I–V curve, the ideality factor and barrier height (Φb) of n-ZnO have been calculated as 1.93 and 0.80 eV, respectively. (Φb) (C–V) has been found 0.86 eV, at 500 kHz frequency.

Structural, optical and ferroelectric behavior of pure BiFeO3 thin films synthesized by the sol–gel method

In this paper, BiFeO3 (BFO) thin films were synthesized by the sol–gel spin-coating technique followed by annealing at different temperatures. The effect of annealing temperature on structural, optical, dielectric and ferroelectric properties of BFO thin film has been investigated. Single phase polycrystalline BFO films are confirmed by X-ray diffraction patterns. A strong dependence of grain size and shape on annealing temperature was observed. The optical energy band gap values found decrease from 2.42 to 2.27 eV with raise annealing temperature from 500–600 °C, respectively. The film annealed at 500 °C showed a well saturated polarization–electric field loop. The remnant polarization and saturation polarization values are decreased with increasing annealing temperature. The anomaly in temperature dependent dielectric permittivity was observed at magnetic transition point.

Multiferroic BiFeO3 thin films: Structural and magnetic characterization

BiFeO3 (BFO) film has been deposited on indium tin oxide (ITO) substrate by a simple sol–gel spin-coating technique. The crystal phase composition, surface morphology, topography and magnetization measurements of the BFO thin film were investigated using grazing incidence X-ray diffraction (GIXRD), scanning electronic microscope (SEM), atomic force microscope and vibrating sample magnetometer, respectively. GIXRD analysis revealed that the film was fully crystallized and no impure phase was observed. Cross-section SEM results indicated that compact and homogeneous BFO thin film was deposited on ITO with a thickness of about 180nm. Moreover, most of A and E-symmetry normal modes of R3c BFO were assigned by Raman spectroscopy. We report here that the pure phase BFO film shows ferromagnetism at room temperature with remarkably high saturation magnetization of 63kAm−1. Our results are discussed mainly in correlation with the condition of processing technique and destruction of the spiral spin cycloid at interface layers and grain boundaries.

Free Growth of Iron Oxide Nanostructures by Sol-Gel Spin Coating Technique—Structural and Magnetic Properties

The study of on iron oxide, especially magnetite Fe 3 O 4 , in the form of thin films and nanostructures, is interesting due to its wide applications in data storage, biomedical, and spintronic devices. Seven different sols are synthesized with varying concentration from 1.8 to 0.6 mM using the sol-gel technique. The concentration of 1.4 mM results in a pure phase whereas others show mixed magnetite and maghemite phases. In addition, changes in film preferred orientation from (400) to (220) planes are responsible for changing the ferromagnetic behavior of films to ferrimagnetic with increased saturation magnetization. Free growth of iron oxide nanostructures, including nanoneedles and nanobrushes, are observed in scanning electron microscope images.

Spectroscopic properties of Rhodamine B entrapped in hybrid porous nanolayers at high dye concentration

The preparation procedure and characterization of Rhodamine B entrapped in zirconia, silica and mixed silica–zirconia nanolayers is described. The nanolayers were produced by the sol–gel spin-coating technique. The pronounced effect of the dye concentration on the absorption and fluorescence spectra as well as on time-resolved fluorescence spectra was found. The results show that the aggregation of Rhodamine B is stronger in silica based matrices compared to zirconia nanolayers. Time-resolved emission spectra at highest Rhodamine B concentration show that the dye aggregates are fluorescent.

Bioactive hybrid coatings of poly(ε-caprolactone)–silica xerogel on titanium for biomedical applications

Poly(ε-caprolactone)–silica xerogel (PCL–SiO2) hybrid coatings were successfully prepared on the surface of titanium (Ti) plates via a sol–gel spin-coating technique. The influences of the SiO2 content on the phase composition, surface morphology, wettability and in vitro bioactivity of the coatings were investigated. The results showed that silica xerogel was homogeneously hybridized with PCL when the SiO2 content was less than 30%, forming hybrid coatings with a quite smooth and dense surface. Moreover, the PCL-30% SiO2 hybrid coatings exhibited a significant improvement in hydrophilicity and apatite-forming ability as compared to the pure PCL coatings, thus potentially serving as a good candidate to improve the biological performance of the Ti implants.

Elliptical concave microlens arrays built in the photosensitive TiO2/ormosils hybrid films

Photosensitive TiO2/organically modified silane hybrid thin films were prepared by a low-temperature sol–gel spin-coating technique. Optical and structural properties of the hybrid films with different titanium contents were characterized by prism coupling technique, UV–visible spectroscopy, Fourier transform infrared spectroscopy, and thermal gravimetric analysis. Advantages for fabrication of elliptical concave micro-lens arrays (MLAs) based on the as-prepared hybrid films were demonstrated by combining polydimethylsiloxane soft mold with a UV-cured imprint technique. Results indicate that the as-prepared hybrid films have great applicability for the fabrication of photonic components, and the fabrication technique provides a simple and cost-effective way for the fabrication of the sol–gel elliptical concave MLAs.