Crystalline Films Research Articles

Effect of Al doping on the structural, optical and photocatalytic properties of sol-gel spin-coated NiO thin films

Nanostructured NiO thin films are renowned for their catalytic activity and potential for degradation of industrial effluents. In this study, Al-doped NiO (Ni1-xAlxO with x = 0, 0.02, 0.04, 0.06, and 0.08) thin films were synthesized by sol–gel spin coating, and the influence of Al doping on their physical properties, surface morphology, optical band gap, and photo-catalytic performance was investigated. X-ray diffraction (XRD) analysis confirmed the high crystallinity of the thin films and revealed a pronounced doping effect on parameters such as crystallite size, microstrain, and dislocation density. Scanning electron microscopy (SEM) revealed the formation of spherical nanoparticles with particle sizes ranging from 26 nm to 11 nm. The elemental composition was verified through energy-dispersive x-ray (EDX) analysis. The optical bandgap of the prepared films was determined through UV-visible spectroscopy. The Ni0.98Al0.02O films exhibited the lowest PL intensity, indicating a reduced recombination rate. To assess the photo-degradation capability of the prepared thin film catalysts, industrial effluent Indigo Carmine was employed as a test compound. The Ni0.98Al0.02O sample demonstrated the highest degradation efficiency, achieving about 96% degradation within 2 h of UV–vis light irradiation. Furthermore, the degradation followed pseudo-first-order kinetics.

Atomic and electronic structures of the [formula omitted]-FeSi2/Si(001) interface

The atomistic interface structure between β-FeSi2 and Si substrate was investigated by cross-sectional scanning transmission electron microscopy and density functional theory calculations (DFT). A high quality single crystalline β-FeSi2 film was epitaxialy grown on Si(001) substrate. We demonstrate that the β-FeSi2(100) plane is bonded to the Si(001) plane with two Si dimers per unit cell. With such interface structure, DFT band calculations reveal that metallic electronic states are localized at the interface. This finding implies the presence of two dimensional electronic states at the interface of β-FeSi2/Si(001), which may have potential applications in silicon-based electronic devices.

Mechanical and electrical properties of α-MoO3 belts under strain for flexible electronics applications

This study investigated a straightforward and cost-effective method for synthesizing α-MoO3 belts and evaluated their potential as substrates for flexible electronic devices. Transparent α-MoO3 belts, featuring millimeter-scale side lengths and micrometer-scale thicknesses, were produced through a one-step sintering process using metallic molybdenum powder. When affixed to stretchable substrates, the α-MoO3 belts demonstrated robust mechanical stability under continuous and sustained tensile strain in the longitudinal direction. The belts exhibited a transmittance exceeding 68 % in the visible and near-infrared light regions. The current between gold dots on belts fixed to a stretchable polydimethylsiloxane substrate increased with the application of tensile strain. Furthermore, a CoFe2O4 thin film deposited at elevated temperature onto an α-MoO3 belt exhibited significant magnetic anisotropy. These findings introduce a novel and efficient approach for fabricating highly crystalline thin films on stretchable and bendable substrates using α-MoO3 belts.

Effect of spin coating speeds on electrical and optical characteristic of perovskite SrTiO3 thin films prepared by sol-gel method

The perovskite strontium titanate (SrTiO3/STO) was prepared by the sol-gel process, and the STO thin film was deposited onto a glass substrate by the spin coating method. Effect of different spin coating speeds on the thickness, structural, optical, and electrical properties of the STO thin films was discussed. Five STO films with various spin coating parameters of 2000, 4000, 6000, 8000, and 10000 RPM were prepared. Thickness profilometer tests have shown that the thickness of the STO film changes from 802 nm at 10000 RPM to 1321 nm at 2000 RPM spin coating speed. The prepared STO films morphology was examined by scanning electron microscope. X-ray diffraction measurements have shown that crystalline STO films have been produced with a cubic perovskite structure. The optical properties of the prepared STO films were investigated using an ultraviolet visible spectrophotometer, and the results indicated that the STO film at 8000 and 4000 RPM spin speed show the lowest and the maximum optical band gap (2.83 and 2.90 eV, respectively). All STO films have absorption coefficient values higher than 103 cm−1. The prepared STO thin films had a refractive index between 2.40 and 2.42. The electrical characteristics of the prepared STO films were investigated using the four-point probe method, and it was found that as the spin coating speed increased from 2000 to 8000 RPM, the resistivity of the STO films reduced from 6.629∗1010 to 3.009∗1010 Ω. Moreover, the STO film at 8000 RPM spin speed has the best electrical conductivity (3.301∗10−5 S m−1).

Photoluminescence and Raman spectroscopy of Ce3+ doped Y3Al5O12 single crystalline films grown onto Y3Al5O12 and Lu3Al5O12 substrates

Raman spectroscopy, high spectral resolution luminescence, and X-ray diffraction techniques were employed to study two Ce3+ doped Y3Al5O12 single crystalline films grown by liquid phase epitaxy method onto Y3Al5O12 and Lu3Al5O12 single crystal substrates. Optical spectra were obtained with a micrometer step along the cross-sections of epitaxial structures, allowing excellent differentiation of the film, the transition layer, and the substrate of each sample. X-ray measurements demonstrate the mismatch between the lattice constants of the Y3Al5O12:Ce3+ film and its Lu3Al5O12 substrate, an effect related to different compositions. Consequently, the film grown onto Lu3Al5O12 exhibits higher residual stresses than its counterpart grown onto Y3Al5O12. This was confirmed by a mutual comparison of the Raman bands positions of the films. The luminescence spectra of both samples consist mainly of cerium 5d-4f emission, the intensity of which allows for additional study of epitaxial cross section and estimation of the size of transition layer.

Functionalized sp2 Carbon-Conjugated Covalent Organic Frameworks for Interfacial Modulation of Inverted Perovskite Solar Cells.

Interfacial modulation utilizing functional materials is proven to be crucial for obtaining high photovoltaic performance in lead halide perovskite solar cells (PSCs). This study investigates, for the first time, the utilization of a pyrene-based sp2 carbon-conjugated covalent organic framework (sp2c-COF) as an interfacial layer in inverted PSCs. Functionalized with cyano (-CN) Lewis base groups, the sp2c-COF exhibits a dual effect, simultaneously passivating both the NiOx and the perovskite layers. Detailed characterization results highlight the role of sp2c-COF in reducing the Ni3+ defect density in NiOx films and forming Lewis acid-base adducts with undercoordinated Pb2+ on the perovskite surfaces, thereby inhibiting interfacial redox reactions and suppressing non-radiative recombination. Moreover, sp2c-COF leads to improved crystallinity of perovskite films. Benefiting from the synergistic effects, sp2c-COF-modified devices delivered a champion efficiency of 17.64%. These findings underscore the potential of sp2c-COF as a functional interface material for PSCs, offering enhanced efficiency and stability. The study contributes to advancing the understanding and application of covalent organic frameworks in photovoltaic technologies.

Unveiling the role of Cs ion in perovskite phase formation during solid–vapor reactions

The preparation of perovskite solar cells (PSCs) using a solid–vapor reaction has shown great potential due to its scalability and lack of organic solvent. The phase formation process in the solid–vapor reaction is crucial for the crystallization of perovskite films. Previous studies mainly introduced Cs into the solid–vapor reaction, but insufficient attention was paid to the role of Cs in purifying the phase formation path during the crystallization process. In this study, we investigated the effect of Cs on the phase formation process in the solid–vapor reaction and found that Cs can decrease the crystallinity of lead halide films, induce a purified phase formation process to prevent the formation of δ-phase and other impurity phases, regulate the crystallization rate of perovskite, and produce high-quality, low-defect perovskite films. The result was achieving a champion power conversion efficiency (PCE) of 21.54 % for a small area (0.148 cm2) and 18.65 % for larger mini-modules (5 × 5 cm2). Furthermore, the devices maintained over 80 % of their initial efficiencies after 450 h of continuous operation under AM 1.5 G irradiation. This work underscores the importance of purified phase formation paths in solid–vapor reactions for outstanding crystal quality in high-performance perovskite solar cells.

Tuning the thermodynamic ordering of strongly correlated protons in ice by angstrom-scale interface modification

The static and dynamic behaviour of strongly correlated many-body protons in nanoscale hydrogen-bond networks plays crucial roles in a wide range of physicochemical, biological and geological phenomena in nature. However, because of the difficulty of probing and manipulating the proton configuration in nanomaterials, controlling the cooperative behaviour of many-body protons remains challenging. By combining proton-order sensitive nonlinear optical spectroscopy and well-defined interface modification at molecular/atomic scale, we demonstrate the possibility of extensively tuning the emergent physical properties of strongly correlated protons beyond the thermodynamic constraints of bulk hydrogen bonds. Focusing on heteroepitaxially grown crystalline ice films as a model of a strongly correlated and frustrated proton system, we show that the emergence and disappearance of a high-Tc proton order on the nano- to mesoscale is readily switched by angstrom-scale interface engineering. These results pave a way to designing and controlling emergent properties of correlated proton systems.

Multiphoton‐And SHG‐Active Pyrimidine‐Based Liquid Crystalline Thin Films Toward 3D Optical Data Storage

AbstractAn original asymmetric achiral pyrimidine core molecule, with long carbon chains on one side and a coumarin fragment on the other, is designed. This advanced molecular structure enabled the spontaneous emergence of crystalline and liquid crystalline thin films with strong 2nd harmonic generation (SHG) without any corona polishing process or tedious deposition techniques. Moreover, pin‐pointed multiphoton absorption in the liquid crystalline phase effectively switches off the SHG signal locally and permanently, underlining its interest in 3D data storage. This prototypical material, which can be fully addressed by NLO processes, multiphoton writing, and SHG reading, paves the way for the development of efficient flexible materials for 3D optical data storage.

Polycaprolactone-based electrospun films incorporating sage extract: From active food packaging application to accelerated biodegradation by Pseudomonas

Polycaprolactone films incorporating sage extract (SE), developed by electrospinning and annealing, were tested as active, fast-degradable food contact materials. First, a release test with food simulants showed the films’ ability to release phenolics. This beneficial property was highlighted in the films’ application as pads for preventing raspberry quality deterioration. The highest SE containing film (20 %) demonstrated the highest preserving potential, suppressing raspberry spoilage, breakdown of soluble solids, maintaining color, and increasing phenolics content. Secondly, the degradation under natural environment conditions and conditions accelerating the degradation of the films was evaluated. Complete films’ bio-disintegration in compost occurred within three months, being catalyzed to four weeks by adding Pseudomonas aeruginosa, regardless of the SE incorporation. Visual appearance, light, scanning electron, and atomic force microscopy indicated an inhomogeneous surface degradation mechanism depended on the morphology of the films. Analysis of the structural properties and crystallinity showed that both amorphous and crystalline film regions were affected by biodegradation. The developed films as packaging materials can be beneficial from an economic and environmental point of view, as they can extend the shelf-life of fresh fruit, prevent the generation of food waste, reduce the accumulation of discarded packaging materials, protect the environment, and contribute to sustainable development.

Effect of substrate temperature on the growth mechanism of FeSe superconducting films

Abstract Among all the iron-based superconductors (IBSs), Fe-chalcogenides (Fe-Ch) possess the advan tages of simple structure, non-toxicity, low anisotropy and the potential for high-field applications.One of the most effective methods for preparing Fe-Ch films is pulsed laser deposition (PLD). However, high quality film growth is challenged by the significant volatility difference between the iron
and chalcogens (S, Se, Te), which affects stoichiometric transfer from target to substrate and subsequently impacts superconductivity. Currently, there is limited research on the correlation between the growth mechanism and preparation conditions of Fe-Ch films, particularly in explaining chalcogen volatility during deposition. Technically, PLD offers various adjustable parameters, among
which the substrate temperature (Ts) is the most critical one affecting film quality. It governs particle behavior on the substrate including adsorption, diffusion, bonding reactions, crystallization processes while also strongly affecting volatilization rates. In this study, we fabricated a series of FeSe films using PLD at different Ts ranging from 25 ℃ to 750 ℃.We reveal in detail the impact of
competitive processes between Se volatilization and reactive crystallization of Fe/Se on film quality. The optimal film was obtained at Ts=500 ℃ with a composition ratio of Fe1.01Se. We also investigate the correlations between Ts and film crystallinity, surface morphology, along with their influence on superconductivity. Additionally, the pinning mechanism in FeSe film grown at the
optimal Ts was briefly analyzed. Our results provide reliable experimental evidence regarding the growth mechanism of FeSe films while revealing comprehensive insights into how Ts affects both film quality and performance.

Systematic approach for high piezoelectric AlN deposition

Aluminum nitride (AlN) is a wide band gap semiconductor with interesting piezoelectric properties for many applications, including micromechanical systems (MEMS), acoustic wave sensors or energy harvesting devices. The influence of DC reactive magnetron sputtering (DCRMS) deposition parameters on the structural, crystalline, and piezoelectric properties of AlN thin films are presented. The systematic approach of Design of Experiments (DoE) has been used to evaluate the role of magnetron power, nitrogen and argon flows on the deposition process and the film properties. Magnetron power and argon flow have resulted to be the parameters causing the most significant effects on the deposition rate. AlN films have been deposited with a high crystal quality, showing low values of FWHM (0.28) and c-axis orientation parallel oriented respect to the growth direction, as evidenced by X-ray diffraction (XRD) analysis and high-resolution transmission electron microscopy (HRTEM). These samples also showed a high piezoelectric coefficient (d33) of 5 pC/N for AlN thin films. This work highlights the importance of deposition parameters on the properties of the film and the important role that DoE play for its optimization with a minimum number of depositions.

Hybrid Aromatic Fluoro Amine‐Modified SnO2 Electron Transport Layers in Perovskite Solar Cells for Enhanced Efficiency and Stability

SnO2 is a widely used electron‐transporting layer (ETL) in perovskite solar cells. Despite the high compatibility with the perovskite absorber layers, the presence of traps at the perovskite|SnO2 interface results in performance losses; hence, their modification to improve the performance and stability of perovskite solar cells (PSCs) is therefore important. Herein, the SnO2 ETL is enhanced by incorporating a bifunctional aromatic amino fluorine molecule into the SnO2 precursor solution. The fluorine molecule is found to partially substitute the Sn and alter the energy levels while the aniline group aids in regulating the nucleation/growth rate of the perovskite crystalline films. Herein, a hole transporting material‐free carbon‐based PSCs (CPSCs) is fabricated. It is found that perovskite absorber layers deposited on these modified SnO2 hybrid layers have higher optoelectronic quality, resulting in enhanced photovoltaic performance, device stability, and reduced hysteresis in CPSCs. Devices made with the modified hybrid SnO2 layers exhibit power conversion efficiencies of 15.6% significantly better than unmodified SnO2 with 13.5%. CPSCs with these modified SnO2 films also exhibit remarkable retention of 88.7% of their initial PCE for a shelf‐life period (ISOS‐D1I) exceeding 1200 h.

Epitaxial growth and characterization of copper gallate (CuGa2O4) thin films by pulsed laser deposition

High-quality crystalline copper gallate (CuGa2O4) thin films were grown on c-plane sapphire substrates using the pulsed laser deposition (PLD) technique by optimizing the growth parameters (i.e., temperature, oxygen chamber pressure, and laser energy density). The obtained XRD patterns validated that the preferred orientation of the crystalline CuGa2O4 thin film is along the [111] direction, and the crystallinity of the films improved with increasing substrate temperature while maintaining a constant O2 pressure, as assessed by measuring the full width at half maximum (FWHM) of the prominent (222) plane. Reducing the oxygen pressure leads to the emergence of β-Ga2O3 peaks rather than the CuGa2O4 peaks due to the incomplete oxidation of copper (Cu). Subsequent XRD phi (φ) scans revealed a sixfold rotational symmetry of CuGa2O4 and a 30° epitaxial relationship between the film and the sapphire substrate. X-ray photoelectron spectroscopy (XPS) spectra confirmed the presence of Cu1+, Cu2+, and Ga3+ oxidation states in the films. Increasing laser energy density resulted in the complete oxidation of Cu and an increase in the film thickness from 51.8 nm to 183.4 nm. The direct bandgap of CuGa2O4 films was determined to be approximately 4.50 eV by analyzing the UV–Vis absorbance spectra using the Tauc equation. The refractive index was found to be approximately 2.05 ± 0.01 based on the spectroscopic ellipsometry data. While the impact of increasing laser energy density was negligible on the parameters such as crystal structure, rotational symmetry, oxidation states of gallium (Ga), oxygen (O), bandgap, and refractive index of CuGa2O4 thin film, notable alterations in the oxidation state of Cu and film thickness were observed. The surface roughness (Rrms) measured from AFM images showed a strong correlation with the values derived from ellipsometry analysis.

Appropriate flame-spraying treatment exacerbates thermal oxidative degradation of residual polyethylene films

In dryland farming, plastic film mulching can significantly increase crop yields, but the resulting residues impair soil health. Heretofore, only few studies had examined how heat treatment facilitates the rapid degradation of polyethylene (PE) residual films. Herein, we characterized the variations in micro-morphology, functional groups, and crystallinity of PE residual films after moderate heat exposure using a self-made flame-spraying equipment. The results revealed that solid residues (SR) obtained from flame-spraying showed a gravimetric weight loss of 9.39 %–15.35 % compared with untreated PE residual films (UPF). Scanning electron microscope equipped with energy dispersive X-ray spectroscopy revealed considerable pits, cracks, and visible roughness in appearance and an increase in the oxygen-to‐carbon (O/C) atomic ratio. Fourier-transform infrared spectroscopy identified characteristic oxygen-containing functional groups and double bonds. X-ray diffraction showed that flame-spraying treatments did not alter the crystal form of polymer, but increased the crystallinity. Higher flame-spraying temperatures resulted in larger oxygen-containing bond indices and lower crystallinity, suggesting a more severe decomposition of PE residual film. The possible volatile gaseous products at different reaction temperatures were predicted using thermogravimetric analysis coupled with Fourier transform infrared spectroscopy (TG-FTIR). Degradation of the PE residual film started at 220 °C, and concentrated release of major products such as long-chain aliphatic hydrocarbons, ketones, and CO2, occurred in the temperature range of 340 °C–440 °C. These results highlighted the effectiveness of the moderate flame-spraying method in accelerating rapid decomposition of residual films, and a flame-spraying temperature range of 220 °C–340 °C should be recommended to avoid potential environmental risks induced by the release of large quantities of degradation products. This study will contribute to enhance our understanding of the thermal oxidative degradation behavior of PE waste and provide a scientific basis for the rapid and clean establishment of PE residual films mitigation in agricultural fields.

Nanomechanical Crystalline AlN Resonators with High Quality Factors for Quantum Optoelectromechanics.

High-quality factor (Qm) mechanical resonators are crucial for applications where low noise and long coherence time are required, as mirror suspensions, quantum cavity optomechanical devices, or nanomechanical sensors. Tensile strain in the material enables the use of dissipation dilution and strain engineering techniques, which increase the mechanical quality factor. These techniques have been employed for high-Qm mechanical resonators made from amorphous materials and, recently, from crystalline materials such as InGaP, SiC, and Si. A strained crystalline film exhibiting substantial piezoelectricity expands the capability of high-Qm nanomechanical resonators to directly utilize electronic degrees of freedom. In this work, nanomechanical resonators with Qm up to 2.9 × 107 made from tensile-strained 290 nm-thick AlN are realized. AlN is an epitaxially-grown crystalline material offering strong piezoelectricity. Nanomechanical resonators that exploit dissipation dilution and strain engineering to reach a Qm × fm-product approaching 1013 Hz at room temperature are demonstrated. A novel resonator geometry is realized, triangline, whose shape follows the Al-N bonds and offers a central pad patterned with a photonic crystal. This allows to reach an optical reflectivity above 80% for efficient coupling to out-of-plane light. The presented results pave the way for quantum optoelectromechanical devices at room temperature based on tensile-strainedAlN.

Formamidinium lead iodide perovskite photovoltaics with MoS2 quantum dots

We present the formation of a composite film made out of formamidinium lead iodide (FAPI) and molybdenum disulphide quantum dots (MoS2 QDs) and propose a corresponding photovoltaic device architecture based on a ‘type-I’ alignment of the two materials’ electronic energy levels. The introduction of the MoS2 QDs has not compromised the overall crystallinity of the FAPI film and the composite absorber has shown improved stability. We report on the benefits of this composite film and energy band arrangement as the photogenerated carriers in MoS2 QDs, both positive and negative, are injected into the FAPI host matrix, resulting in an increased current density of 24.19 mA cm−2 compared to a current density of 19.83 mA cm−2 for the control device with FAPI only. The corresponding photoconversion efficiency increases from 12.6 to 15.0%. We also show that inclusion of MoS2 QDs in FAPI films resulted in a notable improvement in the fill factor and open-circuit voltage of the solar cells. Most importantly, MoS2 QDs enhanced the film stability by reducing defect formation and acting as passivating agents that minimize recombination losses and improve charge carrier transport. Our results suggest that a composite film in a type-I device architecture can introduce benefits for both future developments in perovskite solar cells and effectively tackling the longstanding challenges of carrier transport in QDs solar cells.

Optimization of molar concentrations for enhanced crystallinity and bandgap tuning of ZrO2 thin films via spray pyrolysis for advanced optical applications

In this study, Zirconium oxide (ZrO2) thin films were synthesized on glass substrates at 400°C using the Spray Pyrolysis method, due to its simplicity, cost-effectiveness, and precise control. The films were prepared at varying molar concentrations (0.1, 0.15, and 0.2 M) and analyzed for their structural, optical, and morphological properties. X-ray diffraction (XRD) confirmed that all films exhibited a tetragonal crystalline structure with a preferred orientation along the (101) plane. The crystallite size, calculated using the Scherrer equation, reached a maximum of 27.26 nm at 0.2 M concentration, indicating improved crystallinity with higher concentration. Optical studies revealed a decrease in transmittance and an increase in absorbance in the visible region as the concentration increased, accompanied by a reduction in the optical band gap from 3.84 to 3.57 eV and an increase in Urbach energy. Scanning Electron Microscopy (SEM) images showed that the films had a dense and smooth morphology, while Energy Dispersive X-ray (EDX) analysis confirmed the elemental presence of zirconium and oxygen in the films.

Deposition of highly crystalline AlScN thin films using synchronized high-power impulse magnetron sputtering: From combinatorial screening to piezoelectric devices

Deposition of highly crystalline AlScN thin films using synchronized high-power impulse magnetron sputtering: From combinatorial screening to piezoelectric devices

Analog and digital resistive switching in W/TiO2/ITO devices: the impact of crystallinity and Indium diffusion

The resistance-switching memristor with capabilities of information storage and brain-inspired computing has prime importance in recent research. In this study, the impact of crystallinity and Indium diffusion on the existence of analog and digital resistive switching in a W/TiO2/ITO device has been reported. The memristor devices are fabricated by depositing titania films by sol–gel and spin-coating techniques. The films annealed at 250 °C and 400 °C were characterized using x-ray diffraction, Raman spectroscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy (XPS). The characteristic anatase phase started appearing after annealing at 400 °C, whereas the 250 °C annealed sample was in the amorphous state. The electrical characterization revealed significant differences in the switching characteristics of amorphous and crystalline samples, especially in the switching interface, compliance properties, and current conduction mechanism. The grain boundary assisted oxygen vacancy migration, and the diffusion of indium ions from the ITO bottom electrode helped the crystalline sample to show highly stable and reproducible resistive switching compared to amorphous film. The XPS studies confirmed the indium ion diffusion in the crystalline sample. The oxygen vacancy-induced barrier modulation and conductive filament formation caused characteristic switching in amorphous and crystalline samples, respectively. Schottky emission in the amorphous film and SCLC mechanism in the crystalline film confirmed the experimental results. This study provides a distinctive viewpoint and an innovative strategy for developing multifunctional resistive switching devices.