UV-A Treatment of ZrO2 Thin Films Fabricated by Environmental Friendlier Water-Based Solution Processing: Structural and Optical Studies

An environmentally friendlier solution processing has been introduced to fabricate zirconium oxide (ZrO2) films on quartz substrates, using spin coating of simple water-based solution. The films cured with UV-A = 330 nm for different times (40, 80, 120 min) were investigated for structural and optical properties and compared with thermally annealed film (at 350 °C). XRD and Raman spectroscopy showed amorphous structure in all the samples with no significant phase transformation with UV-A exposure. AFM microscopy showed smooth and crack free films with surface roughness ≤2 nm that reduced with UV-A exposure. Ultraviolet-visible (UV–Vis) spectroscopy demonstrated optical transmittance ≥88% and energy band gap variations as 4.52–4.70 eV. Optical constants were found from spectroscopic ellipsometry (SE). The refractive index (n) values, measured at 470 nm increased from 1.73 to 2.74 as the UV-A exposure prolonged indicating densification and decreasing porosity of the films. The extinction coefficient k decreased from 0.32 to 0.19 indicating reduced optical losses in the films under the UV-A exposure. The photoluminescence (PL) spectra exhibited more pronounced UV emissions which grew intense with UV-A exposure thereby improving the film quality. It is concluded that UV-A irradiation can significantly enhance the optical properties of ZrO2 films with minimal changes induced in the structure as compared to thermally treated film. Moreover, the present work indicates that water-based solution processing has the potential to produce high-quality ZrO2 films for low cost and environmental friendlier technologies. The work also highlights the use of UV-A radiations as an alternate to high temperature thermal annealing for improved quality.

Effect of Post-Annealing Treatment on the Morphological and Optical Properties of ZnO Thin Film Fabricated by Spraying Deposition Method

<p class="AbstractText">This work investigated the effect of post-annealing treatment on the fabrication of zinc oxide (ZnO) thin film by spraying deposition method. Based on SEM analysis, the annealed ZnO thin film at 400˚C presented better uniformity as compared to the non-annealed film. Further measurement by UV-Vis revealed that the lowest optical band gap energy (<em>E_g</em>) (3.22 eV) was achieved by 400˚C sample. These results confirmed that post-annealing treatment enhanced the optical and morphological properties of the fabricated ZnO thin film.</p>

Structural, Morphological, Optical, Luminescent and Magnetic Properties of Nanostructured ZnO Thin Film

ZnO thin film deposited on the glass substrate at various substrate temperature by spray technique using perfume atomizer. The deposited ZnO thin films are annealed at 450ºC. The deposited films are highly transparent and adhered to the substrate. The structure and microstructural, morphological, compositional, optical and luminescent characteristics were studied by X-ray diffraction (XRD), Raman, Field emission scanning electron microscope (FE-SEM with EDX), Atomic force microscope (AFM), Ultra violet visible spectrophotometer (UV-Vis) and photoluminescence spectroscopic techniques. The crystalline nature of annealed film were confirmed from XRD and the shows preferred orientation along (1 0 1) plane. At higher substrate temperature, reorientation of planes was seen. The spherical shaped grains are observed from morphological studies. The roughness of ZnO film, one of the key parameter obtained from AFM, increases with substrate temperature. The high transparency of about 80% in visible region are obtained for ZnO film with band gap ranging from 3.24 – 3.19 eV. The presence of defects in ZnO films are identified from PL bands. The electronic vibrations in ZnO film were understood from Raman spectra. The weak ferromagnetic behavior at room temperature is observed and exchange interactions stemming from oxygen vacancy produce BMP and subject to RTFM in ZnO.

Crystallization of Optically Thick Amorphous Silicon Films by Near-IR Femtosecond Laser Processing

We demonstrated efficient crystallization of amorphous Si films induced by their direct irradiation with near-IR femtosecond laser pulses coming at sub-MHz repetition rate. Comprehensive analysis of morphology and composition of the laser-annealed film by atomic-force microscopy, Fourier-transform IR, Raman and energy dispersive X-ray spectroscopy as well as numerical modeling of optical spectra confirmed efficient crystallization of amorphous Si and high-quality of the obtained films opening pathway for applications in thin-film solar cells, transistors and displays.

Epitaxy from a Periodic Y–O Monolayer: Growth of Single-Crystal Hexagonal YAlO3 Perovskite

The role of an atomic-layer thick periodic Y–O array in inducing the epitaxial growth of single-crystal hexagonal YAlO3 perovskite (H-YAP) films was studied using high-angle annular dark-field and annular bright-field scanning transmission electron microscopy in conjunction with a spherical aberration-corrected probe and in situ reflection high-energy electron diffraction. We observed the Y–O array at the interface of amorphous atomic layer deposition (ALD) sub-nano-laminated (snl) Al2O3/Y2O3 multilayers and GaAs(111)A, with the first film deposition being three cycles of ALD-Y2O3. This thin array was a seed layer for growing the H-YAP from the ALD snl multilayers with 900 °C rapid thermal annealing (RTA). The annealed film only contained H-YAP with an excellent crystallinity and an atomically sharp interface with the substrate. The initial Y–O array became the bottom layer of H-YAP, bonding with Ga, the top layer of GaAs. Using a similar ALD snl multilayer, but with the first film deposition of three ALD-Al2O3 cycles, there was no observation of a periodic atomic array at the interface. RTA of the sample to 900 °C resulted in a non-uniform film, mixing amorphous regions and island-like H-YAP domains. The results indicate that the epitaxial H-YAP was induced from the atomic-layer thick periodic Y–O array, rather than from GaAs(111)A.

Investigation of Optical and Dielectric Constants of Benzobis(thiazole)- based Copolymer Films

Introduction: Copolymer PBB-T with benzo[1,2-d:4,5-d']bis(thiazole) (BBT) as the accepting unit and benzodithiophene (BDT) as the donor unit is a promising candidate for highperformance non-fullerene polymer solar cells (PSCs). So far optical and dielectric constants of the PBB-T are not fully known. Method: PBB-T was synthesized and thin films of PBB-T were prepared. By using the Kramers-Kronig relations and the transmission spectra of the PBB-T films, the optical and dielectric constants, including in absorption coefficient (α(λ)), extinction coefficient (κ(λ)), refractive index (n(λ)), dielectric constant (ε1(λ),ε2(λ)), band gap (Eg) and mobility of the PBB-T films were calculated and analyzed. Result: At 500 nm, α, κ, n, ε1 and ε2 are 1.65×105 cm-1, 0.46, 1.8163, 3.0 and 1.65 respectively. Eg is 2.111 eV. The hole mobility of PBB-T are 2.41×10-5 cm2 V-1 s-1 and 1.71×10-4 cm2 V-1 s-1 for the as-cast film and for the solvent vapor annealed film respectively. The results show that these optical and dielectric constants of the PBB-T films are almost independent on the thicknesses of the films, indicating our results are reliable. The features of the optical and dielectric constants show the PBB-T films are very promising candidates for high-performance non-fullerene PSCs and potential cut-off filter only permitting red and near-infrared light passing. Conclusion: These results are significant for designing optoelectronic devices related to the PBBT thin films.

Effect of Temperature on Structural and Optical Properties of Methyl-Ammonium Bismuth Iodide Thin Films

Organic–Inorganic perovskites are promising materials for an alternative to silicon technology for cost-effective performance of photovoltaic’s (PVs). Lead-based hybrid perovskite has lower stability and high toxicity. The bismuth-based hybrid perovskite, Methyl Ammonium Bismuth Iodide (MABI) could be as an alternative to the lead-based system. In the present work, we present the structural and optical studies on hybrid MABI perovskite thin films synthesized at different temperature. Bandgap analyzed from UV-Vis absorption spectroscopy have shown the formation of MABI complex in thin films prepared from the single step spin coating and dip coating method. Further, the MABI formation confirmed by Raman analysis. Optical and structural properties obtained are comparable to earlier reported theoretical studies. The roughness of highly stable annealed film was analyzed by non-contact tapping mode atomic force microscopy.

Influence of annealing temperature on the sensitivity of nickel oxide nanosheet films in humidity sensing applications

Nickel oxide (NiO) nanosheet films were successfully grown onto NiO seed-coated glass substrates at different annealing temperatures for humidity sensing applications. NiO seed layers and NiO nanosheet films were prepared using a sol-gel spin coating and sonicated sol-gel immersion techniques, respectively. The properties of NiO nanosheet films at as-deposited, 300 ℃, and 500 ℃-annealed were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), ultraviolet-visible (UV-vis) spectroscopy, and humidity sensor measurement system. The XRD patterns demonstrate that the grown NiO films have crystalline cubic structures at temperature of 300 ℃ and 500 ℃. The FESEM images show that the large porous nanosheet network spread over the layers as the annealing temperature increased. The UV-vis spectra revealed that all the nanosheet films have the average transmittance below than 50% in the visible region, with absorption edges ~ 350 nm. The optical band gap energy was evaluated in ranges of 3.39 to 3.61 eV. From the obtained humidity sensing results, it shows that 500 ℃-annealed film exhibited the best sensitivity of 257, as well as the slowest response time, and the fastest recovery time compared with others.

Preparation of UV-Curable Low Surface Energy Polyurethane Acrylate/Fluorinated Siloxane Resin Hybrid Coating with Enhanced Surface and Abrasion Resistance Properties

Low surface energy coatings have gained considerable attention due to their superior surface hydrophobic properties. However, their abrasion resistance and sustainability of surface hydrophobicity are still not very satisfactory and need to be improved. In this work, a series of utraviolet (UV)-curable fluorosiloxane copolymers were synthesized and used as reactive additives to prepare polyurethane acrylate coatings with low surface energy. The effect of the addition of the fluorinated graft copolymers on the mechanical durability and surface hydrophobicity of the UV-cured hybrid films during the friction-annealing treatment cycles was investigated. The results show that introducing fluorosiloxane additives can greatly enhance surface hydrophobicity of the hybrid film. With addition of 2 wt.% fluorosiloxane copolymers, the water contact angle (WCA) value of the hybrid film was almost tripled compared to that of the pristine PU film, increasing from 58° to 144°. The hybrid film also showed enhanced abrasion resistance and could withstand up to about 60 times of friction under a pressure of 20 kPa. The microstructure formed in the annealed film was found to contribute much to achieve better surface hydrophobicity. The polyurethane acrylate/fluorinated siloxane resin hybrid film prepared in this study exhibits excellent potential for applications in the low surface energy field.

Photocatalytic Properties of Thermally Annealed Films of Titanium Butoxide-=SUP=-*-=/SUP=-

We show that titanium dioxide particles capable of Reactive oxygen species generation can be produced in titanium butoxide films by annealing them at 500oC. Optimal conditions for the films deposition by a modified Langmuir-Blodgett technique were selected basing on the film uniformity examined by optical and electron microscopy. The photocatalytic activity of the annealed film was tested using RNO sensor bleaching.