Photosensitive Sol Gel Method Research Articles

Micropatterning of LaCoO3 thin films through a novel photosensitive sol-gel lithography technique and their magnetic properties

This paper presents a study on the microstructure and magnetic properties of LaCoO3 (LCO) thin films, and also the micropatterning of LCO thin films using a novel photo-sensitive sol-gel lithography method. It is found that higher heat-treatment temperature can promote the healing of cracks and filling of pores, resulting in refining the grains, and improving the density of LCO film. The film treated at 850 °C has a larger nucleation energy, which makes the distribution of nucleation sites more uniform, promoting the healing of cracks and filling of pores, refining the grains, and improving the density of LCO film. LCO precursor sol, metal chelates with UV photosensitivity were synthesized by adding BzAcH photosensitizer. LCO micro-arrays with diameters of 50 μm, as well as other fine patterns with a minimum line width of about 2 μm were successfully prepared by a UV mask lithography technique. In contrast, our novel lithography method eliminates the need for photoresist, as the fine pattern is formed during the preparation of the LCO gel film, which is the advantages of our lithography method over traditional techniques.

Ferroelectric polarization of Pb0.92La0.08(Zr0.52Ti0.48)O3 modulating the electrical properties of YBa2Cu3O7−ẟ

Pb0.92La0.08(Zr0.52Ti0.48)O3/YBa2Cu3O7−ẟ (PLZT/YBCO) heterostructure was prepared via the photosensitive sol–gel method (P-SG) combined with pulsed laser deposition (PLD). Test results show that the preparation process of PLZT film does not significantly cause degradation of the superconductivity of underlying YBCO film, and the PLZT has good ferroelectric properties in the temperature range of 300–50 K. With decreasing temperature, ferroelectric domain formation and inversion become more difficult, which causes coercive field (Ec) of PLZT to increase. However, remanent polarization (Pr) remains almost constant with decreasing temperature. Furthermore, it is found that the critical transition temperature (Tc) of YBCO decreases and resistance of non-superconducting state of YBCO increases as positive electric field applied to PLZT increases, while Tc and the resistance of non-superconducting state of YBCO do not change when negative electric fields are applied. It is believed that polarization charges regulate Fermi level of PLZT, which results in the promotion (hindrance) of electron injection into YBCO for positive (negative) applied electric fields, thereby regulating Tc and the resistance of non-superconducting state of YBCO. When positive applied electric fields are removed, the superconducting properties of YBCO in PLZT/YBCO structure cannot be restored to their initial values due to the remanent polarization of PLZT.

Dielectric properties of SrTiO3/LaNiO3 composite structure prepared by “sol-gel” method

In this work, Pt/SrTiO3(STO)/LaNiO3(LNO) and Pt/STO/Pt structures were fabricated on Si substrates using sol–gel method. Dielectric tunability characteristics of these two structures are investigated over temperature range of 300–80 K. As temperature decreases, relative dielectric constant and tunability of STO films in both structures increase linearly, while loss tangent (tanẟ) decreases. STO prepared on LNO exhibits better crystallinity and dielectric tunability than that prepared on Pt. Furthermore, LNO top pole array with 0.2 mm diameter was prepared on STO/LNO using photosensitive sol–gel method, resulting in LNO/STO/LNO structure with symmetric electrode. Dielectric tunability tests reveal that, compared with Pt/STO/LNO structure, LNO/STO/LNO structure exhibits similar tunability, lower tanẟ, higher figure-of-merit (FOM) values, and better tunability symmetry. Relative dielectric constant, tunability (350 kV/cm), and FOM are approximately 391, 60%, and 142.6 at 80 K, respectively. Further analysis shows that because of Schottky barrier at Pt/STO interface, the FOM and tunability symmetry of Pt/STO/LNO structure are worse than those of LNO/STO/LNO structure. These results demonstrate that LNO electrode performs better than conventional inert metal electrodes.

Fine patterned YBCO films grown on flexible nickel–tungsten substrates by photosensitive sol–gel method

In recent years, efforts devoted to the study of processing technologies for flexible devices have been increasing significantly. The fabrication of YBa2Cu3O7-x (YBCO) fine patterns on flexible nickel–tungsten (NiW) substrates is beneficial for the application of flexible superconducting electronic devices. The most challenging task is the simultaneous achievement of fine patterning and biaxial epitaxial growth of YBCO films on NiW substrates. This work reports the application of the photosensitive sol–gel lithography in combination with an all chemical deposition process to prepare fine patterned YBCO films on NiW substrates using gadolinium-doped lanthanum zirconate (LGZO) films as buffer layers. High-quality patterned YBCO films were epitaxially grown on LGZO–buffered NiW substrates, and the well-continuous YBCO patterns on flexible substrates could withstand bending deformations. The superconductivity remains good after the mechanical bending deformation process. These results are useful as guidance for the application of flexible superconducting devices.

Synthesis and characterization of patterned La2/3Sr1/3MnO3 epitaxial thin films via the ultraviolet-visible spectrum assisted photosensitive sol-gel method

A La2/3Sr1/3MnO3 (LSMO) photosensitive sol was synthesized using La(NO3)3•6H2O, Sr(CH3COO)2•0.5H2O, and Mn(CH3COO)2•4H2O as starting materials and benzoylacetone (BzAc) as a chelating agent, and the corresponding gel films were casted on single crystal LaAlO3 (00l) substrates. The complexation mechanism between metal ions and the chelating agent was investigated via Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy. The results show that the Mn and La ions were chelated with BzAc, and the as-cast gel film shows photosensitivity to ultraviolet-visible light. Grating-patterned films were prepared by irradiating the gel films for 3 min using a two-beam interference process followed by rinsing in a solution of isopropyl alcohol and n-butyl alcohol (2:1 v/v) for 8 s. It was found that the irradiated portion of the gel film remained intact in the solvent, whereas the unirradiated portion was dissolved, producing the gratings. The shape of the gratings is highly periodic without broken wires or defects. After annealing at 750 °C, the patterned LSMO gel film turned into a c-axis orientated inorganic film. The patterned LSMO film exhibited a saturation magnetization value that is similar to that of the unpatterned LSMO film.

Fine patterned TiO2:Nb transparent conducting films prepared by a photochemical etching technique

Herein, microfabrication of a novel Nb-doped titanium dioxide (TNO) transparent conductive film is proposed using a photosensitive sol-gel method. The method employs a chemical modifier to coordinate Ti4+ in sol, followed by gel film preparation. The obtained Ti-coordinated chelate has a characteristic absorption peak at ca. 360 nm, which disappears after sufficient exposure to UV radiation. This feature is much similar to that of photoresist. Upon irradiated by UV light through a mask, the film can be dissolved in ethanol in order to obtain a fine-patterned surface. Finally, after annealing treatment at 450 °C Nb5+-doped TiO2 fine-patterned transparent conducting film is obtained. This photochemical lithographic technique integrates photochemical etching and filming process into one step, whilst effectively avoiding damage caused by conventional lithographic techniques (such as dry etching and wet etching) on the photoelectric properties of TNO film. Our methodology eliminates the need for photoresist, creating a simple process that is expected to be performed on large film area.

Enhanced electrochromic performances and patterning of Ni–Sn oxide films prepared by a photosensitive sol–gel method

A patterned NiO film with high electrochromic performance can be obtained by Sn4+ and SnO2 co-doping using a photosensitive sol–gel technique.

One step preparation of photosensitive Bi2Sr2CaCu2O8+x films and their fine patterns by a photosensitive sol–gel method

An acrylic acid-modified photosensitive sol–gel method is proposed to prepare Bi2Sr2CaCu2O8+x (Bi-2212) gel films and their fine patterns on LaAlO3 (LAO) single crystal substrates. An ultraviolet–visible absorption spectrum showed the UV characteristic absorption peak at around 270 ∼ 280 nm which originates from the π-π* electron transition of acrylic acid in metal complexes, and its intensity decreases as the UV irradiation time increases, indicating that Bi-2212 gel films are photosensitive. Based on the photosensitivity of Bi-2212 gel films, fine-patterned Bi-2212 gel films with the smallest resolution of 3 μm have been prepared. The prepared fine-patterned Bi-2212 superconducting films exhibit c-axis growth orientation and excellent superconducting properties.

Preparation of Bi2Sr2CaCu2O8+δ-YBa2Cu 3O7−δ Bilayer Films by Acetate Based Photosensitive Sol-Gel Method

Bi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Sr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> CaCu <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">8+δ</sub> (Bi-2212)/YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7-δ</sub> (YBCO) and YBCO/Bi-2212 heteroepitaxial bilayer films have been successfully prepared on LaAlO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (LAO) monocrystalline substrates by acetate based photosensitive Sol-Gel method. Two superconducting transition steps in the R-T curves of YBCO/Bi-2212 and Bi-2212/YBCO bilayer films were clearly observed. The first transition step has the superconducting critical transition temperature (Tc) of 90.1-90.8 K and the superconducting transition width (ΔTc) of 2-2.2 K, and these values correspond to the Tc and ΔTc values of YBCO single film. The second transition step has the Tc of 80-84 K and the ΔTc of 4.6-5.2 K, and these values correspond to the Tc and ΔTc values of Bi-2212 single film. XRD results showed that YBCO/Bi-2212 and Bi-2212/YBCO bilayer films grow heteroepitaxially with good in-plane and out-of-plane growth texture.

Non-UV activated superhydrophilicity of patterned Fe-doped TiO2 film for anti-fogging and photocatalysis

Fe3+-doped TiO2 films with the pattern surface were fabricated onto glass substrates by a facial photosensitive sol–gel method. The patterned TiO2 film has anatase crystallites and a micro- and nanometer-scale hill-to-valley hierarchical surface structure. The hydrophilicities of all TiO2 films stored in the dark for a long time were evaluated by measuring the water contact angle (CA) without being illuminated by ultraviolet (UV) light in advance. The results demonstrated that water droplets could quickly spread onto the surface of the patterned TiO2 film, resulting in a low CA. The patterned TiO2 film with the lowest period of 2 μm showed the lowest CA of 2° within 3 s. This indicated that the patterned TiO2 film had the good superhydrophilicity without any UV activation. The wetting behavior of the patterned TiO2 film followed the Cassie impregnating wetting regime, and the dynamic to hydrophilic state was attributed to the capillary effect. The patterned TiO2 film also had the non-UV induced anti-fogging performance and exhibited a good photocatalytic activity to decompose methyl orange pollutant.

Preparation of a porous NiO array-patterned film and its enhanced electrochromic performance

An array-patterned porous NiO film has been fabricated using a novel photochemical etching technology – a photosensitive sol–gel method.

Grating-patterned Bi0.85La0.15Fe0.95Mn0.05O3 epitaxial thin film prepared using photosensitive sol-gel method and its ferromagnetic and ferroelectric properties

Bi0.85La0.15Fe0.95Mn0.05O3 (BLFMO) gel films with benzoylacetone (BzAc) as a chelating reagent were fabricated on (00l) LaAlO3 (LAO) substrates using a photosensitive sol-gel method. The morphology, crystalline structure, electric and magnetic properties, and the grating-pattern of the films were investigated. The results showed that the epitaxial BLFMO films deposited on LAO single crystal substrates exhibit a higher degree of the c-axis orientation. The remnant polarization and saturation magnetization were found to be higher than those of the randomly oriented BLFMO films. Moreover, the gratings of the film with a period of 1 μm were obtained after exposure to two interference laser beams followed by leaching in ethanol. After treatment at 600 °C, the gel film turned into inorganic film gratings.

Patterning ZrO2 films surface: Superhydrophilic and superhydrophobic properties

A photosensitive sol-gel method was used to pattern the surface of ZrO2 film with a groove or a processus mastoideus structure. The surface roughness enhanced by the pattern structure had a strong effect on the ZrO2 film wettability. Compared to an un-patterned ZrO2 film, the patterned film showed a smaller static water contact angle (CA) and exhibited superhydrophilicity. Interestingly, the patterned ZrO2 film did not require the use of UV irradiation to induce the superhydrophilicity and exhibited an excellent anti-fogging behavior. The surface modification with a 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTCS) layer was found to induce the change in the wettability of the patterned ZrO2 films from superhydrophilicity to hydrophobicity/superhydrophobicity. The PFOTCS-modified ZrO2 film patterned with the processus mastoideus surface resulted in the highest CA value of 155° and the sliding angle (SA) value of about 7°, and almost did not change under UV irradiation or after being annealed below 350°C. The surface patterning by using a photosensitive sol-gel method was proved to be a practical approach to fabricate the ZrO2 film with superhydrophilic/superhydrophobic properties.

Facile fabrication of micro-patterned LSMO films with unchanged magnetic properties by photosensitive sol-gel method on LaAlO3 substrates

We propose here a facile and inexpensive photosensitive sol-gel method to fabricate micro-patterned La0.67Sr0.33MnO3(LSMO) films with c-axis orientation on (001) LaAlO3 (LAO) single crystal substrates. The photosensitive LSMO sol-gel was first prepared using methanol as solvent, strontium acetate, manganese acetate and lanthanum nitrate as precursors, and 2,2'-Bipyridyl (Bpy) as chelating modifier. The sol-gel was photosensitive and was used to fabricate micro-patterned LSMO films directly in the absence of any photoresist. The as-prepared micro-patterned films exhibited regular microarray structure with smooth surface and clear edge. We also investigated the magnetic properties of LSMO films on LAO substrates. The overlapping of the magnetic momentum vs. temperature (M-T) curves as well the overlapping in the magnetic hysteresis loops of the micro-patterned and un-patterned LSMO films suggests that the photosensitive sol-gel method would be a promising technique to fabricate micro-patterned LSMO films without disturbing the original structure and functional properties.

A facial approach combining photosensitive sol⿿gel with self-assembly method to fabricate superhydrophobic TiO2 films with patterned surface structure

Superhydrophobic TiO2 films with micro-patterned surface structure was prepared through a facial approach combining photosensitive sol⿿gel method with following surface modification by 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTCS). The patterned surface possessed quasi micro-lens array structure resembling processus mastoideus of lotus, leading to excellent hydrophobicity. The relationship between hydrophobic performance and the period of the micro-patterned TiO2 surface was investigated. The water contact angles (CAs) of micro-patterned TiO2 surface increased with the decrease of the periods, and the patterned surface with the lowest period of 0.83μm showed the highest CA of 163°. It suggests that this approach would offer an advantage to control the wettability properties of superhydrophobic surfaces by adjusting the fine pattern structure. Furthermore, the superhydrophobic state could be converted to the state of superhydrophilicity under ultraviolet (UV) illumination as a result of the photocatalytic decomposition of the PFOTCS monolayer on the micro-patterned TiO2 Surface.

Fabrication of undoped ZnO thin film via photosensitive sol–gel method and its applications for an electron transport layer of organic solar cells

We have investigated ZnO thin films prepared via photochemical reaction as the electron transport layer (ETL) of inverted organic solar cells (OSCs). Morphological and electrical properties of the ZnO thin films prepared by the photosensitive ZnO sol were studied according to the annealing temperature and their effects on the performance of the inverted poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester (P3HT:PCBM) OSCs was characterized. It was found that the optimal annealing temperature of the ZnO thin films was 330°C, and that devices with the ZnO ETL annealed at this temperature exhibited the largest short-circuit current density (Jsc) of 9.39mA/cm2, as well as the highest power conversion efficiency (PCE) of 2.31%, which can be attributed to enhanced electron transport and interfacial properties. Devices containing ZnO films formed at optimal annealing condition exhibited an open circuit voltage (Voc) of 0.60V and a fill factor (FF) of 41.0%. However, further increase of the annealing temperature led to degradation of the device performance, despite further improvements in electrical properties. We have found that marked increase in the surface roughness of the ZnO films occurred at temperatures above 350°C which could be detrimental to the OSCs characteristics due to a high contact resistance and a large leakage current.

Facile single-step fabrications of electrochromic WO3 micro-patterned films using the novel photosensitive sol–gel method

Fine-patterned WO3 film was prepared by a photosensitive sol–gel method utilizing tungsten chloride and benzoylacetone (BzAcH) as the starting material and chemical modifier respectively in ethanol. First, the photosensitive sol was obtained by a chelating reaction between tungsten ions and BzAcH. Then, through a single-step patterning process, a fine-patterned WO3 film was fabricated by a photochemical reaction between the chelated complexes and UV light. The structural properties of the films were characterized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The optical properties of the films tested in the electrochemical cell were determined by optical spectrophotometry in the visible range. The electrochromic properties were studied principally by the cyclic voltammetry (CV) technique.

In situ synthesis and characterization of fine-patterned La and Mn co-doped BiFeO3 film

La and Mn co-doped BiFeO3 (BLFMO) film was prepared by a photosensitive sol–gel method utilizing bismuth nitrate, lanthanum nitrate, manganese nitrate and ferric nitrate as starting materials. After a chelating reaction between benzoylacetone (BzAcH) and metallic ions, the precursor solution presented photosensitivity. Through a direct patterning process, a fine-patterned BLFMO film was obtained. The phase constituents, morphology, electric and magnetic properties of the as-prepared BLFMO film were characterized by X-ray diffractometer (XRD), Raman spectroscopy, scanning electron microscopy (SEM), ferroelectric testing unit, LCR Meter and vibrating sample magnetometer (VSM). The Mn dopant enhanced the saturation magnetization and remnant polarization of the BLFMO film.

Fabrication of surface: relief gratings and their laser induced damage resistance properties

This work demonstrates a promising method for fabricating ZrO2 surface–relief gratings by photosensitive sol–gel method combining with two-beam laser interference. UV-photosensitive ZrO2 resist with high resolution are prepared by using metal–chelate complexes as precursors. Two-beam laser interference lithography is carried out by a Kr ion laser with a wavelength of 350.7 nm and ZrO2 gratings with the minimum line-width of 150 nm are obtained. Laser induced damage resistance properties of ZrO2 gratings are investigated by a Q-switched solid state laser with the wavelength of 527 nm and the pulse width of 8.65 ns as the incident source. The results show that the LIDT of ZrO2 gratings on glass substrate heated at 600 °C is about 4.59 ± 0.06 J/cm2.

Fabrication of two-dimensional lattices by using photosensitive sol–gel and four-beam laser interference

This work demonstrates a promising method to fabricate 2D lattices by using photosensitive sol–gel method combining with four-beam of a 350.7 nm Kr ion laser interference. Photosensitive TiO 2 gel films with chelate complexes as precursors are fabricated. The characteristics of UV and IR spectra of the films and their variations in the process of laser irradiation are investigated. The results show that the gel films had an absorption peak at about 358 nm due to the formation of chelate complex. This peak gradually decreases with irradiation in time, which indicates the photosensitive properties of the TiO 2 films. A flexible four-beam interference system is proposed. Given incident angles 20.5° and 44.5°, the lattices with pitch of 700 nm and 326 nm are fabricated, respectively. The diffraction phenomenon of the 700 nm lattices is investigated by inverse method. The results are fully consistent with the 2D crystal diffraction theory.