Flexible Sol-Gel—Processed Y2O3 RRAM Devices Obtained via UV/Ozone-Assisted Photochemical Annealing Process

Flexible indium tin oxide (ITO)/Y₂O₃/Ag resistive random access memory (RRAM) devices were successfully fabricated using a thermal-energy-free ultraviolet (UV)/ozone-assisted photochemical annealing process. Using the UV/ozone-assisted photochemical process, the organic residue can be eliminated, and thinner and smother Y₂O₃ films than those formed using other methods can be fabricated. The flexible UV/ozone-assisted photochemical annealing process-based ITO/Y₂O₃/Ag RRAM devices exhibited the properties of conventional bipolar RRAM without any forming process. Furthermore, the pure and amorphous-phase Y₂O₃ films formed via this process showed a decreased leakage current and an increased high-resistance status (HRS) compared with the films formed using other methods. Therefore, RRAM devices can be realized on plastic substrates using a thermal-energy-free UV/ozone-assisted photochemical annealing process. The fabricated devices exhibited a resistive window (ratio of HRS/low-resistance status (LRS)) of >10⁴, with the HRS and LRS values remaining almost the same (i.e., limited deterioration occurred) for 10⁴ s and up to 10² programming/erasing operation cycles.     

Red Y2O3:Eu-Based Electroluminescent Device Prepared by Atomic Layer Deposition for Transparent Display Applications

Y₂O_3:Eu is a promising red-emitting phosphor owing to its high luminance efficiency, chemical stability, and non-toxicity. Although Y₂O₃:Eu thin films can be prepared by various deposition methods, most of them require high processing temperatures in order to obtain a crystalline structure. In this work, we report on the fabrication of red Y₂O₃:Eu thin film phosphors and multilayer structure Y₂O₃:Eu-based electroluminescent devices by atomic layer deposition at 300 °C. The structural and optical properties of the phosphor films were investigated using X-ray diffraction and photoluminescence measurements, respectively, whereas the performance of the fabricated device was evaluated using electroluminescence measurements. X-ray diffraction measurements show a polycrystalline structure of the films whereas photoluminescence shows emission above 570 nm. Red electroluminescent devices with a luminance up to 40 cd/m² at a driving frequency of 1 kHz and an efficiency of 0.28 Lm/W were achieved.     

Influence of Tin Doped TiO2 Nanorods on Dye Sensitized Solar Cells

The one-step hydrothermal method was used to synthesize Sn-doped TiO₂ (Sn-TiO₂) thin films, in which the variation in Sn content ranged from 0 to 7-wt % and, further, its influence on the performance of a dye-sensitized solar cell (DSSC) photoanode was studied. The deposited samples were analyzed by X-ray diffraction (XRD) and Raman spectroscopy, which confirmed the existence of the rutile phase of the synthesized samples with crystallite size ranges in between 20.1 to 22.3 nm. In addition, the bare and Sn-TiO₂ thin films showed nanorod morphology. A reduction in the optical band gap from 2.78 to 2.62 eV was observed with increasing Sn content. The X-ray photoelectron spectroscopy (XPS) analysis confirmed Sn⁴⁺ was successfully replaced at the Ti⁴⁺ site. The 3-wt % Sn-TiO₂ based DSSC showed the optimum efficiency of 4.01%, which was superior to 0.87% of bare and other doping concentrations of Sn-TiO₂ based DSSCs. The present work reflects Sn-TiO₂ as an advancing material with excellent capabilities, which can be used in photovoltaic energy conversion devices.     

Fabrication of Multiferroic Co-Substituted BiFeO3 Epitaxial Films on SrTiO3 (100) Substrates by Radio Frequency Magnetron Sputtering

The 10 at.% Co-substituted BiFeO₃ films (of thickness 50 nm) were successfully prepared by radio frequency (r.f.) magnetron sputtering on SrTiO₃ (100) substrates with epitaxial relationships of [001](001)Co-BiFeO₃//[001](001)SrTiO₃. In this study, a single phase Co-substituted BiFeO₃ epitaxial film was fabricated by r.f. magnetron sputtering. Sputtering conditions such as Ar, O₂ gas pressure, annealing temperature, annealing atmosphere, and sputtering power were systematically changed. It was observed that a low Ar gas pressure and low sputtering power is necessary to suppress the formation of the secondary phases of BiO_x. The Co-substituted BiFeO₃ films were crystalized with post-annealing at 600 °C in air. The process window for single phase films is narrower than that for pure BiFeO₃ epitaxial films. By substituting Fe with Co in BiFeO₃, the magnetization at room temperature increased to 20 emu/cm³. This result suggests that Co-substituted BiFeO₃ films can be used in spin-filter devices.     

Inkjet-Printed Electron Transport Layers for Perovskite Solar Cells

Inkjet printing emerged as an alternative deposition method to spin coating in the field of perovskite solar cells (PSCs) with the potential of scalable, low-cost, and no-waste manufacturing. In this study, the materials TiO₂, SrTiO₃, and SnO₂ were inkjet-printed as electron transport layers (ETLs), and the PSC performance based on these ETLs was optimized by adjusting the ink preparation methods and printing processes. For the mesoporous ETLs inkjet-printed from TiO₂ and SrTiO₃ nanoparticle inks, the selection of solvents for dispersing nanoparticles was found to be important and a cosolvent system is beneficial for the film formation. Meanwhile, to overcome the low current density and severe hysteresis in SrTiO₃-based devices, mixed mesoporous SrTiO₃/TiO₂ ETLs were also investigated. In addition, inkjet-printed SnO₂ thin films were fabricated by using a cosolvent system and the effect of the SnO₂ ink concentrations on the device performance was investigated. In comparison with PSCs based on TiO₂ and SrTiO₃ ETLs, the SnO₂-based devices offer an optimal power conversion efficiency (PCE) of 17.37% in combination with a low hysteresis. This work expands the range of suitable ETL materials for inkjet-printed PSCs and promotes the commercial applications of inkjet printing techniques in PSC manufacturing.     

Thermal Annealing Effects of V2O5 Thin Film as an Ionic Storage Layer for Electrochromic Application

A vanadium pentoxide (V₂O₅) thin film with thermal annealing as an ionic storage layer for electrochromic devices is presented in our study. The V₂O₅ thin film was deposited on an ITO glass substrate by an RF magnetron sputtering. The electrochromic properties of the film were evaluated after various thermal annealing temperatures. The structural analysis of the film was observed by X-ray diffraction (XRD), field emission electron microscopy (FE-SEM), and atomic force microscopy (AFM). The structure of the V₂O₅ thin film transformed from an amorphous to polycrystalline structure with directions of (110) and (020) after 400 °C thermal annealing. The electrochromic properties of the film improved compared with the unannealed V₂O₅ thin film. We obtained a charge capacity of 97.9 mC/cm² with a transparent difference ΔT value of 31% and coloration efficiency of 6.3 cm²/C after 400 °C thermal annealing. The improvement was due to the polycrystalline orthorhombic structure formation of V₂O₅ film by the rearrangement of atoms from thermal energy. Its laminate structure facilitates Li⁺ ion intercalation and increases charge capacity and transparent difference.     

Fabrication of CIS Absorber Layers with Different Thicknesses Using A Non-Vacuum Spray Coating Method

In this study, a new thin-film deposition process, spray coating method (SPM), was investigated to deposit the high-densified CuInSe₂ absorber layers. The spray coating method developed in this study was a non-vacuum process, based on dispersed nano-scale CuInSe₂ precursor and could offer a simple, inexpensive, and alternative formation technology for CuInSe₂ absorber layers. After spraying on Mo/glass substrates, the CuInSe₂ thin films were annealed at 550 °C by changing the annealing time from 5 min to 30 min in a selenization furnace, using N₂ as atmosphere. When the CuInSe₂ thin films were annealed, without extra Se or H₂Se gas used as the compensation source during the annealing process. The aim of this project was to investigate the influence of annealing time on the densification and crystallization of the CuInSe₂ absorber layers to optimize the quality for cost effective solar cell production. The thickness of the CuInSe₂ absorber layers could be controlled as the volume of used dispersed CuInSe₂-isopropyl alcohol solution was controlled. In this work, X-ray diffraction patterns, field emission scanning electron microscopy, and Hall parameter measurements were performed in order to verify the quality of the CuInSe₂ absorber layers obtained by the Spray Coating Method.     

MoO3 Thickness,Thermal Annealing and Solvent Annealing Effects on Inverted and Direct Polymer Photovoltaic Solar Cells

Several parameters of the fabrication process of inverted polymer bulk heterojunction solar cells based on titanium oxide as an electron selective layer and molybdenum oxide as a hole selective layer were tested in order to achieve efficient organic photovoltaic solar cells. Thermal annealing treatment is a common process to achieve optimum morphology, but it proved to be damageable for the performance of this kind of inverted solar cells. We demonstrate using Auger analysis combined with argon etching that diffusion of species occurs from the MoO₃/Ag top layers into the active layer upon thermal annealing. In order to achieve efficient devices, the morphology of the bulk heterojunction was then manipulated using the solvent annealing technique as an alternative to thermal annealing. The influence of the MoO₃ thickness was studied on inverted, as well as direct, structure. It appeared that only 1 nm-thick MoO₃ is enough to exhibit highly efficient devices (PCE = 3.8%) and that increasing the thickness up to 15 nm does not change the device performance.     

Tuning Stoichiometry and Structure of Pd-WO3−x Thin Films for Hydrogen Gas Sensing by High-Power Impulse Magnetron Sputtering

By tuning the deposition parameters of reactive high-power impulse magnetron sputtering, specifically the pulse length, we were able to prepare WO_3−x films with various stoichiometry and structure. Subsequently, the films were annealed in air at moderate temperature (350 °C). We demonstrate that the stoichiometry of the as-deposited films influences considerably the type of crystalline phase formed in the annealed films. The appropriate sub-stoichiometry of the films (approx. WO_2.76) enabled crystallization of the monoclinic phase during the annealing. This phase is favorable for hydrogen sensing applications. To characterize the sensory behavior of the films, the tungsten oxide films were decorated by Pd nanoparticles before annealing and were assembled as a conductometric gas sensor. The sensory response of the films that crystallized in the monoclinic structure was proven to be superior to that of the films containing other phases.     

Effect of Annealing Temperature and Oxygen Flow in the Properties of Ion Beam Sputtered SnO2?x Thin Films

Tin oxide (SnO_2−x) thin films were prepared under various flow ratios of O₂/(O₂ + Ar) on unheated glass substrate using the ion beam sputtering (IBS) deposition technique. This work studied the effects of the flow ratio of O₂/(O₂ + Ar), chamber pressures and post-annealing treatment on the physical properties of SnO₂ thin films. It was found that annealing affects the crystal quality of the films as seen from both X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. In addition, the surface RMS roughness was measured with atomic force microscopy (AFM). Auger electron spectroscopy (AES) analysis was used to obtain the changes of elemental distribution between tin and oxygen atomic concentration. The electrical property is discussed with attention to the structure factor.     

Thin Film Mixed Matrix Hollow Fiber Membrane Fabricated by Incorporation of Amine Functionalized Metal-Organic Framework for CO2/N2 Separation

Membrane separation technology can used to capture carbon dioxide from flue gas. However, plenty of research has been focused on the flat sheet mixed matrix membrane rather than the mixed matrix thin film hollow fiber membranes. In this work, mixed matrix thin film hollow fiber membranes were fabricated by incorporating amine functionalized UiO-66 nanoparticles into the Pebax^® 2533 thin selective layer on the polypropylene (PP) hollow fiber supports via dip-coating process. The attenuated total reflection-Fourier transform infrared (ATR-FTIR), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) mapping analysis, and thermal analysis (TGA-DTA) were used to characterize the synthesized UiO-66-NH₂ nanoparticles. The morphology, surface chemistry, and the gas separation performance of the fabricated Pebax^® 2533-UiO-66-NH₂/PP mixed matrix thin film hollow fiber membranes were characterized by using SEM, ATR-FTIR, and gas permeance measurements, respectively. It was found that the surface morphology of the prepared membranes was influenced by the incorporation of UiO-66 nanoparticles. The CO₂ permeance increased along with an increase of UiO-66 nanoparticles content in the prepared membranes, while the CO₂/N₂ ideal gas selectively firstly increased then decreased due to the aggregation of UiO-66 nanoparticles. The Pebax^® 2533-UiO-66-NH₂/PP mixed matrix thin film hollow fiber membranes containing 10 wt% UiO-66 nanoparticles exhibited the CO₂ permeance of 26 GPU and CO₂/N₂ selectivity of 37.     

Biocompatibility and Surface Properties of TiO2 Thin Films Deposited by DC Magnetron Sputtering

We present the study of the biocompatibility and surface properties of titanium dioxide (TiO₂) thin films deposited by direct current magnetron sputtering. These films are deposited on a quartz substrate at room temperature and annealed with different temperatures (100, 300, 500, 800 and 1100 °C). The biocompatibility of the TiO₂ thin films is analyzed using primary cultures of dorsal root ganglion (DRG) of Wistar rats, whose neurons are incubated on the TiO₂ thin films and on a control substrate during 18 to 24 h. These neurons are activated by electrical stimuli and its ionic currents and action potential activity recorded. Through X-ray diffraction (XRD), the surface of TiO₂ thin films showed a good quality, homogeneity and roughness. The XRD results showed the anatase to rutile phase transition in TiO₂ thin films at temperatures between 500 and 1100 °C. This phase had a grain size from 15 to 38 nm, which allowed a suitable structural and crystal phase stability of the TiO₂ thin films for low and high temperature. The biocompatibility experiments of these films indicated that they were appropriated for culture of living neurons which displayed normal electrical behavior.     

Drop–Dry Deposition of Ni(OH)2 Precursors for Fabrication of NiO Thin Films

Drop–dry deposition (DDD) is a method of depositing thin films by heating and drying the deposition solution dropped on a substrate. We prepared Ni(OH)₂ precursor thin films by DDD and annealed them in air to prepare NiO thin films. The appropriate deposition conditions were found by changing the number of drop–dry cycles and the concentrations of chemicals in the solution, and the Ni(OH)₂ precursor film with a thickness of 0.3 μm and optical transmittance of more than 95% was successfully deposited. Raman and X-ray diffraction measurements were performed, and it was found that the NiO film was successfully fabricated after annealing at 400 °C. The p-type conductivity of the annealed film was confirmed by photoelectrochemical measurements. In addition, we prepared n-type ZnO by electrochemical deposition on NiO thin films. The current–voltage measurement results show that the ZnO/NiO heterojunction had rectification properties.     

Impact of Annealing on Magnetic Properties and Structure of Co40Fe40W20 Thin Films on Si(100) Substrate

Co₄₀Fe₄₀W₂₀ monolayers of different thicknesses were deposited on Si(100) substrates by DC magnetron sputtering, with Co₄₀Fe₄₀W₂₀ thicknesses from 10 to 50 nm. Co₄₀Fe₄₀W₂₀ thin films were annealed at three conditions (as-deposited, 250 °C, and 350 °C) for 1 h. The structural and magnetic properties were then examined by X-ray diffraction (XRD), low-frequency alternative-current magnetic susceptibility (χ_ac), and an alternating-gradient magnetometer (AGM). The XRD results showed that the CoFe (110) peak was located at 2θ = 44.6°, but the metal oxide peaks appeared at 2θ = 38.3, 47.6, 54.5, and 56.3°, corresponding to Fe₂O₃ (320), WO₃ (002), Co₂O₃ (422), and Co₂O₃ (511), respectively. The saturation magnetization (Ms) was calculated from the slope of the magnetization (M) versus the CoFeW thickness. The Ms values calculated in this manner were 648, 876, 874, and 801 emu/cm³ at the as-deposited condition and post-annealing conditions at 250, 350, and 400 °C, respectively. The maximum M_S was about 874 emu/cm³ at a thickness of 50 nm following annealing at 350 °C. It indicated that the M_S and the χ_ac values rose as the CoFeW thin films’ thickness increased. Owing to the thermal disturbance, the M_S and χ_ac values of CoFeW thin films after annealing at 350 °C were comparatively higher than at other annealing temperatures. More importantly, the Co₄₀Fe₄₀W₂₀ films exhibited a good thermal stability. Therefore, replacing the magnetic layer with a CoFeW film improves thermal stability and is beneficial for electrode and strain gauge applications.     

Annealing Effect on the Characteristics of Co40Fe40W10B10 Thin Films on Si(100) Substrate

This research explores the behavior of Co₄₀Fe₄₀W₁₀B₁₀ when it is sputtered onto Si(100) substrates with a thickness (t_f) ranging from 10 nm to 100 nm, and then altered by an annealing process at temperatures of 200 °C, 250 °C, 300 °C, and 350 °C, respectively. The crystal structure and grain size of Co₄₀Fe₄₀W₁₀B₁₀ films with different thicknesses and annealing temperatures are observed and estimated by an X-ray diffractometer pattern (XRD) and full-width at half maximum (FWHM). The XRD of annealing Co₄₀Fe₄₀W₁₀B₁₀ films at 200 °C exhibited an amorphous status due to insufficient heating drive force. Moreover, the thicknesses and annealing temperatures of body-centered cubic (BCC) CoFe (110) peaks were detected when annealing at 250 °C with thicknesses ranging from 80 nm to 100 nm, annealing at 300 °C with thicknesses ranging from 50 nm to 100 nm, and annealing at 350 °C with thicknesses ranging from 10 nm to 100 nm. The FWHM of CoFe (110) decreased and the grain size increased when the thickness and annealing temperature increased. The CoFe (110) peak revealed magnetocrystalline anisotropy, which was related to strong low-frequency alternative-current magnetic susceptibility (χ_ac) and induced an increasing trend in saturation magnetization (Ms) as the thickness and annealing temperature increased. The contact angles of all Co₄₀Fe₄₀W₁₀B₁₀ films were less than 90°, indicating the hydrophilic nature of Co₄₀Fe₄₀W₁₀B₁₀ films. Furthermore, the surface energy of Co₄₀Fe₄₀W₁₀B₁₀ presented an increased trend as the thickness and annealing temperature increased. According to the results, the optimal conditions are a thickness of 100 nm and an annealing temperature of 350 °C, owing to high χ_ac, large Ms, and strong adhesion; this indicates that annealing Co₄₀Fe₄₀W₁₀B₁₀ at 350 °C and with a thickness of 100 nm exhibits good thermal stability and can become a free or pinned layer in a magnetic tunneling junction (MTJ) application.     

Closed-Surface Multifunctional Antireflective Coating Made from SiO2 with TiO2 Nanocomposites

An SiO₂-TiO₂ closed-surface antireflective coating was fabricated by the one-dipping method. TiO₂ nanoparticles were mixed with a nanocomposited silica sol, which was composed of acid-catalyzed nanosilica networks and silica hollow nanospheres (HNs). The microstructure of the sol-gel was characterized by transmission electron microscopy. The silica HNs were approximately 40–50 nm in diameter with a shell thickness of approximately 8–10 nm. The branched-chain structure resulting from acidic hydrolysis grew on these silica HNs, and TiO₂ was distributed inside this network. The surface morphology of the coating was measured by field emission scanning electron microscopy and atomic force microscopy. After optimization, transmittance of up to 94.03% was obtained on photovoltaic (PV) glass with a single side coated by this antireflective coating, whose refractive index was around 1.30. The short-circuit current gain of PV module was around 2.14–2.32%, as shown by the current-voltage (IV) curve measurements and external quantum efficiency (EQE) tests. This thin film also exhibited high photocatalytic activity. Due to the lack of voids on its surface, the antireflective coating in this study possessed excellent long-term reliability and robustness in both high-moisture and high-temperature environments. Combined with its self-cleaning function, this antireflective coating has great potential to be implemented in windows and photovoltaic modules.     

The ZnO-In2O3 Oxide System as a Material for Low-Temperature Deposition of Transparent Electrodes

The development of optoelectronic devices based on flexible organic substrates substantially decreases the possible process temperatures during all stages of device manufacturing. This makes it urgent to search for new transparent conducting oxide (TCO) materials, cheaper than traditional indium-tin oxide (ITO), for the low-temperature deposition of transparent electrodes, a necessary component of most optoelectronic devices. The article presents the results of a vertically integrated study aimed at the low-temperature production of TCO thin films based on a zinc-indium oxide (ZIO) system with acceptable functional characteristics. First, dense and conducting ceramic targets based on the (100-x) mol% (ZnO) + x mol% (In₂O₃) system (x = 0.5, 1.5, 2.5, 5.0, and 10.0) were synthesized by the spark plasma sintering method. The dependences of the microstructure and phase composition of the ZIO ceramic targets on the In₂O₃ content have been studied by powder X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy methods. Then, a set of ZIO thin films with different Zn/In ratios were obtained on unheated glass substrates by direct current (dc) magnetron sputtering of the sintered targets. Complex studies of microstructure, electrical and optical properties of the deposited films have revealed the presence of an optimal doping level (5 mol% In₂O₃) of the ZIO target at which the deposited TCO films, in terms of the combination of their electrical and optical properties, become comparable to the widely used expensive ITO.     

Fabrication of Transparent Mg(OH)2 Thin Films by Drop-Dry Deposition

Magnesium hydroxide (Mg(OH)₂) thin films were deposited by the drop-dry deposition (DDD) method using an aqueous solution containing Mg(NO₃)₂ and NaOH. DDD was performed by dropping the solution on a substrate, heating-drying, and rinsing in water. Effects of different deposition conditions on the surface morphology and optical properties of Mg(OH)₂ thin films were researched. Films with a thickness of 1−2 μm were successfully deposited, and the Raman peaks of Mg(OH)₂ were observed for them. Their transmittance in the visible range was 95% or more, and the bandgap was about 5.8 eV. It was found that the thin films have resistivity of the order of 10⁵ Ωcm. Thus, the transparent and semiconducting Mg(OH)₂ thin films were successfully prepared by DDD.     

Intrinsic Properties of Multi-Layer TiO2/V2O5/TiO2 Coatings Prepared via E-Beam Evaporation

Nanocomposite multi-layer TiO₂/V₂O₅/TiO₂ thin films were prepared via electron-beam evaporation using high-purity targets (TiO₂ and V₂O₅ purity > 99.9%) at substrate temperatures of 270 °C (TiO₂) and 25 °C (V₂O₅) under a partial pressure of oxygen of 2 × 10⁻⁴ mbar to maintain the stoichiometry. Rutherford backscattering spectrometry was used to confirm the layer structure and the optimal stoichiometry of the thin films, with a particle size of 20 to 40 nm. The thin films showed an optical transmittance of ~78% in the visible region and a reflectance of ~90% in the infrared. A decrease in transmittance was observed due to the greater cumulative thickness of the three layers and multiple reflections at the interface of the layers. The optical bandgap of the TiO₂ mono-layer was ~3.49 eV, whereas that of the multi-layer TiO₂/V₂O₅/TiO₂ reached ~3.51 eV. The increase in the optical bandgap was due to the inter-diffusion of the layers at an elevated substrate temperature during the deposition. The intrinsic, structural, and morphological features of the TiO₂/V₂O₅/TiO₂ thin films suggest their efficient use as a solar water heater system.     

Mechanical Properties of Cu2O Thin Films by Nanoindentation

In this study, the structural and nanomechanical properties of Cu₂O thin films are investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and nanoindentation techniques. The Cu₂O thin films are deposited on the glass substrates with the various growth temperatures of 150, 250 and 350 °C by using radio frequency magnetron sputtering. The XRD results show that Cu₂O thin films are predominant (111)-oriented, indicating a well ordered microstructure. In addition, the hardness and Young’s modulus of Cu₂O thin films are measured by using a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) option. Results indicated that the hardness and Young’s modulus of Cu₂O thin films decreased as the growth temperature increased from 150 to 350 °C. Furthermore, the relationship between the hardness and films grain size appears to closely follow the Hall-Petch equation.