Photosensitive Sol Research Articles

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.

Low-temperature sol–gel methods for the integration of crystalline metal oxide thin films in flexible electronics

The development of low-temperature sol–gel (solution) processes for the fabrication of crystalline metal oxide thin films has become a key objective in the emerging Flexible Electronics. To achieve this target, crystalline oxide films need to be deposited on flexible substrates, which have degradation temperatures below 350 °C (e.g., polymers or textile). This achievement would be a step towards improving the performance of the flexible device, making feasible applications now restrained (e.g. smart-skin, flexible-displays or solar-cells) and whose performance is associated to the functional properties of the crystalline oxide (e.g., ferroelectricity, pyroelectricity or piezoelectricity). However, this is a challenge because the crystallization of these oxides usually occurs at high temperatures, over 600 °C. This paper shows an overview to the solution strategies devised in our group for the low-temperature fabrication of crystalline metal oxide thin films, mostly ferroelectric perovskites (e.g., BiFeO3, PbTiO3 or Pb(Zr,Ti)O3). We have made use of UV-light as an alternative energy source to the thermal energy conventionally used to obtain the crystalline oxide. High photosensitive sol–gel solutions have been synthesized and the solution-deposited layers irradiated with UV-excimer lamps. A precise control of the photoreactions occurring during the irradiation of these layers has been carried out with the aim of advancing the formation of a high-densified, defect-free amorphous metal oxide film that easily can be converted into crystalline at temperatures compatible with the use of polymer substrates.Graphical An overview to the solution strategies devised in our group for the low-temperature fabrication of crystalline metal oxide thin films, mostly ferroelectric perovskites, is shown in this article. UV-light is used as an alternative energy source to the conventional thermal energy used to obtain crystalline oxide thin films. These solution strategies are based in the synthesis of high photosensitive sol–gel solutions and the irradiation of the solution-deposited layers with UV-excimer lamps under controlled irradiation atmospheres. A precise control of the photoreactions occurring in the system during the irradiation process has been carried out, with the aim of advancing the formation of high-densified, defect-free amorphous metal oxide films able to be converted into crystalline at temperatures compatible with the use of polymer substrates. This makes possible the integration of these advanced materials in the emerging Flexible Electronics.

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.

Improving the Holographic Recording Characteristics of a Water-Resistant Photosensitive Sol–Gel for Use in Volume Holographic Optical Elements

Continual improvements to holographic recording materials make the development of volume holographic optical elements increasingly more attainable for applications where highly efficient, lightweight diffractive optical elements can replace conventional optics. A fast-curing, water resistant photosensitive sol–gel capable of volume holographic recording has recently drawn attention for its extreme environmental and physical robustness, in particular its water/moisture and scratch resistance. However, to date, the refractive index modulation has been limited. While water-resistant properties are invaluable in the face of the weathering which many practical systems for outdoor applications will endure, high refractive index modulation is also important in order to facilitate high diffraction efficiency holograms recorded in relatively thin layers. Lower grating thickness ensures a large angular and wavelength range of operation-properties that are critical for many applications of holographic optical elements such as solar light harvesting, optical displays and illumination management. For any application where low-cost mass production is envisaged, sensitivity/writing speed is also a crucial factor. In this research, we studied the recording properties of these water-resistant photosensitive sol–gel layers at two different recording wavelengths (532 and 476 nm) and investigated methods for improving these properties. We report more than two-fold improvement of the refractive index modulation from 1.4×10−3 to 3.3×10−3 in layers of thickness ranging from 40–100 μm and more than an order of magnitude increase in photosensitivity/recording speed through better matching between recording wavelength and layer absorption, chemical alterations and thermal post-processing techniques.

Fabrication of TiO2: Nb array films and their enhanced electrochromic performance

In this work, Nb-doped TiO2 (NTO) array films were prepared on indium tin oxide (ITO) glasses via laser interferometry combined with the photosensitive sol–gel technique. The electrochromic properties of the NTO film with smooth surface and the one with array structure were compared. The results reveal that the both kinds of films have the property of selectively and independently spectral control over optical transmittance in the Visible (Vis) and near-infrared (NIR) regimes. Moreover, the NTO array film exhibits more superior electrochromic performance. The optical contrast of the NTO array film is 19.68% (in the NIR region) and 9.58% (in the Vis region) higher than that of the NTO film. The coloring time (tc) and bleaching time (tb) are tested to be 17 s and 3 s, which shortened 9 s and 4 s compared to NTO film. The enhanced electrochromism originates from the enhancement of the local surface plasmon resonance (LSPR) of the array.

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.

Microfabrication of VO2 Thin Films via a Photosensitive Sol-Gel Method

VO2 films are widely used in photoelectric switches, smart glasses, storage media, and terahertz communications. In these applications, microfabrication technology is a very important process for producing microdevices or even improving film properties. In this paper, a novel photoetching microfabrication method is proposed for VO2 thin films. First, a VO2 precursor sol with ultraviolet photosensitivity was prepared using vanadyl acetylacetonate as the raw material and anhydrous methanol as the solvent. The dip-coated VO2 gel film can be directly subjected to photolithography processing without coating additional photoresist by using the photosensitive sol. A fine pattern on the VO2 film with good phase-transition performance can be obtained after annealing in a nitrogen atmosphere at 550 °C for 1 h. This method can be used to prepare grating, microarray, and various other fine patterns with the remarkable advantages of a low cost and simplified process, and the as-obtained material performances are unaffected using the method. It is a potential alternative method for optics, electronics, and magnetics devices based on VO2 thin films.

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.

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.

Fabrication of large scale PS monolayer colloidal crystal film by using a novel secondary self-assembly method for nanoimprint technique

PS microspheres emulsions with different PS diameters of 207 and 378 nm were prepared by using an emulsifier-free polymerization method. A novel secondary self-assembly method which combined the spin coating and the lifting-up method was used to prepare the close-packed PS MCC films. During the process, the PS MCC film was firstly assembled on a glass substrate by a spin coating technique. Secondly, the obtained PS MCC film was transferred on the air-water interface by immersing the PS glass substrate in water using a dip-coater. Thirdly, the floating close-packed PS MCC films on the air-water interface was transferred to a new glass substrate by using a lifting-up method. During the spin-coating and the self-assembly process, some SDS solution was added in the PS films to improve the uniformity of the PS layer. Effects of the spin-coating speeds, the SDS solution concentration and the lifting-up rates on the morphology of PS MCC films have been discussed. Scanning electron microscopy was used to observe the morphological properties of the PS colloidal crystal films. Results indicate that a relatively close-packed and large scale PS MCC films can be obtained when the spinning speed is 2000 rpm for 60 s, the SDS solution concentration is 2 wt% and the lifting-up rate is 2 mm/min. Furthermore, the polydimethylsiloxane soft mold was replicated from the-fabricated PS MCC films and was then imprinted onto the photosensitive hybrid film under UV-irradiation and thus the micro-lens arrays built in the photosensitive hybrid sol–gel film were obtained.

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.

Facile micro-patterning of ferromagnetic CoFe2O4 films using a combined approach of sol–gel method and UV irradiation

CoFe2O4 photosensitive sol was prepared using iron nitrate and cobalt nitrate as precursors, acetyl acetone as a chelating agent, and ethanol as a solvent. CoFe2O4 photosensitive sol was used to fabricate smooth and micro-patterned CoFe2O4 films. The effects of UV irradiation on the crystallinity, surface morphology and ferromagnetic properties of CoFe2O4 films were investigated. For the film prepared using conventional sol-gel process, the crystallization of spinel CoFe2O4 phase was completely finished at ~ 600 ℃, and no intermediate phase was formed. However, when the sol-gel process was combined with UV irradiation, Fe2O3 and CoO intermediate phases were firstly generated, and then reacted to form CoFe2O4 phase. Facile micro-patterning of CoFe2O4 films can be realized using a combined approach of sol-gel method and UV irradiation without using any photoresist. The structure and functional properties of the CoFe2O4 film have not been affected during the patterning process, and its magnetic properties have also not been changed.

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.

X ray photoelectron spectroscopy (XPS) analysis of Photosensitive ZrO2 array

Based on organic zirconium source as the starting material, by adding chemical modifiers which are made up with photosensitive ZrO2 sol. A uniformed ZrO2 array dot was fabricated with a mean diameter of around 800 nm. By using UV-vis spectra and X-ray photoelectron spectroscopy analysis method, studies the photosensitive ZrO2 gel film of photochemical reaction process and the photosensitive mechanism, to determine the zirconium atom centered chelate structure, reaction formed by metal chelate Zr atom for the center, and to establish the molecular model of the chelate. And studied the ultraviolet light in the process of the variation of the XPS spectra, Zr3d5/2 to 184.9 eV corresponding to the binding energy of the as the combination of state peak gradually reduce; By combining with the status of Zr-O peak gradually increase; The strength of the peak is gradually decline. This suggests that in the process of ultraviolet light photo chemical reaction happened. This study is of great significance to the micro fabrication of ZrO2 array not only to the memory devices but also to the optical devices.

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.

Preparation of photosensitive sol and patterned tungsten oxide films by using 2,2-dipyridyl as a chemical modifier

A tungsten oxide gel film was prepared from a methanol solution containing W-chelate, which was synthesized by the chemical reaction between WCl6 and 2,2-dipyridyl. The UV spectra results indicated that the gel film had a UV photosensitive behavior. Using its property, a tungsten oxide gel pattern was fabricated by selective irradiation followed by leaching in organic solvents. Finally, an amorphous WO3 pattern was obtained after the heat treatment at 250 °C in O2 ambient for 120 min. The optical contrast (ΔT) at a wave band of 632.8 nm was about 43%.

졸-침투와 감광성 직접-패턴 기술을 이용하여 스크린인쇄된 Pb(Zr,Ti)O3후막의 하이브리드 제작

In this paper, we propose a fabrication technique for enhanced electrical properties of piezoelectric thick films with excellent patterning property using sol-infiltration and a direct-patterning process. To achieve the needs of high- density and direct-patterning at a low sintering temperature (< 850 °C), a photosensitive lead zirconate titanate (PZT) solution was infiltrated into a screen-printed thick film. The direct-patterned PZT films were clearly formed on a locally screen-printed thick film, using a photomask and UV light. Because UV light is scattered in the screen-printed thick film of a porous powder-based structure, there are needs to optimize the photosensitive PZT sol infiltration process for obtaining the enhanced properties of PZT thick film. By optimizing the concentration of the photosensitive PZT sol, UV irradiation time, and solvent developing time, the hybrid films prepared with 0.35 M of PZT sol, 4 min of UV irradiation and 15 sec solvent developing time, showed a very dense with a large grain size at a low sintering temperature of 800 °C. It also illustrated enhanced electrical properties (remnant polarization, Pr, and coercive field, Ec). The Pr value was over four times higher than those of the screen-printed films. These films integrated on silicon wafer substrate could give a potential of applications in micro-sensors and -actuators.

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.

Top-down patterning and self-assembly of flower-like gold arrays for surface enhanced Raman spectroscopy

A low-cost and controllable fabrication method of flower-like Au arrays has been developed by using photosensitive sol–gel and electrochemical reaction self-assembly strategy on a TiO2 patterned Si substrate. The effects of concentration of HAuCl4 solution and applied voltage have been investigated to tailor the growth of Au nanoflowers. At a proper applied voltage (12V) and concentration (0.005mM), fractal flower-like Au arrays is prepared and shows strong SERS effect. The concentration of detectable Rhodamine 6G can be down to 10−10M using the short data integration time (5s). These flower-like Au arrays with strong SERS effect could be used in biosensors and nanodevices with molecule-level detection.

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.