Structure Of Thin Films Research Articles

Controlling the structure and composition of SnO2-based thin film with reactive sputtering to improve the sensitivity of semiconductor CO2 sensor

The sensitivity of SnO2 thin film-based CO2 gas sensors was enhanced by controlling the surface structure employing reactive sputtering during the deposition process to carefully adjust the oxygen partial pressure to modify the surface structure of the SnO2 films. This process increased the sensitivity, primarily due to larger surface area and improved gas adsorption capabilities. Furthermore, the effect of heterojunctions between p-type SnO and n-type SnO2 on the sensitivity was investigated using a model diagram. Both theoretical analysis and experimental data consistently demonstrated that the number of heterojunction interfaces contributes significantly to the sensitivity of SnO-SnO2 heterojunction gas sensors. These findings highlight the effectiveness of controlling the surface structure and composition ratio of thin films through reactive sputtering to enhance sensitivity. This study offers valuable insights for optimizing SnO2 thin-film-based gas sensors for CO2 detection.

Finite element simulation and experiment of residual stress evolution in MEMS structures

The MEMS device structure is usually formed by the combination of thick film and thin film deposition of many different materials, and the residual stress generated in the process of integration/superposition of different materials has a significant impact on the performance and reliability of the device.In this study, a test structure of a multilayer thin film was designed and processed. Based on this, finite element modeling analysis and reliability experiment, analyze the evolution of residual stress and construct the corresponding theoretical analysis model. The finite element modeling analysis can characterize the evolution and distribution laws of residual stress. The reliability experiment is mainly by carrying out the temperature shock experiment, and measuring the resistance value, resonance frequency and the surface morphology of the device, so as to better reflect the change of residual stress. Through this study, the resonant frequency and surface morphology of the device can reflect the residual stress of the device, which provides help for the test and analysis of the residual stress. To a certain extent, it can help reduce the harm caused by the residual stress in the design and manufacturing process, and improve the performance and reliability of MEMS devices.

Investigation of gamma induced effects on the properties of gamma irradiated Ce2S3 thin films

Nanostructure cerium sulphide (Ce2S3) thin films were prepared using successive ionic layer adsorption and reaction (SILAR). The properties of the prepared samples were investigated as a function of gamma rays’ doses of 0, 250, 500, and 1000Gy, respectively. The X-ray diffraction (XRD) results suggest an orthorhombic phase structure for Ce2S3 thin films and the crystallinity is enhanced with increasing gamma-ray doses. The irradiated thin films exhibit a variation in the energy band gap associated with the quantum confinement effect with larger grain size. This simple strategy of modifying properties of Ce2S3 thin films by the incident gamma rays can be an attractive way to investigate this material for dosimetry and radiation detection.

MORPHOLOGICAL, OPTICAL PROPERTIES AND ELECTRONIC STRUCTURE OF ZnO THIN FILMS DOPED WITH ALUMINUM

This paper presents the results of investigation of aluminum-doped zinc oxide thin films obtained by radio-frequency magnetron deposition on a glass substrate. It was shown by energy dispersion X-ray spectroscopy that the average aluminum content in the thin films was 0.2–0.8 at.%. An increase in the average grain size with increasing aluminum concentration was shown, and column-like growth of the films was established using microscopic images. Investigation of the electronic structure showed a redistribution of intensity in the O 1s spectrum with aluminum doping. The valence band spectra were also obtained, and theoretical calculations were performed within the framework of density functional theory to better understanding the results. Using a spectrophotometer, the transparency of the films obtained after aluminum doping was shown to increase. With the help of the Tauc method, the band gap was determined to be 3.41 eV, while DFT calculations showed a band gap of 1.25 eV.

Magneto-Conductive and Magnetic Properties in La<sub>1-<i>x</i></sub>Sr<i><sub>x</sub></i>MnO<sub>3 </sub>Thin Films on a-SiO<sub>2</sub> Substrates Produced by Metal Organic Decomposition Method

We have studied magneto-conductive and magnetic properties of La1-xSrxMnO3 (LSMO) thin films on a-SiO2 substrates produced by the metal organic decomposition (MOD) method. LSMO thin films for x = 0, 0.15 and 0.3 have been produced in a pure O2 gas atmosphere. Although LaMnO3 (LMO) single crystal is an antiferromagnetic insulator (AFI), LMO thin films we have produced show ferromagnetic metal (FM) properties for suitable heat treatment conditions. We consider that the excess of O2- ions in LMO thin films produced in a pure O2 gas atmosphere induces the strong hole self-doping into those and the LMO thin films change from AFI to FM. Whereas, the ordinary hole doping is also occurred in LSMO thin films at x > 0. Thus, the carrier doping for LSMO thin films at x > 0 is caused by the hole self-doping by O2- ions and the ordinary hole doping by the replacement of La3+ ions by Sr2+ ones. To investigate the crystallographic and surface structures of the LSMO thin films, X-ray diffraction and SEM measurements have been performed, respectively. From the X-ray diffraction measurement, we have found that all LSMO thin films have perovskite structure and are polycrystalline. From the SEM measurement, we have seen that the LSMO thin films are formed of the aggregation of LSMO fine particles. Electrical resistivities (ERs) and magneto-resistivity (MR) ratios of the LSMO thin films have been measured on the temperature dependence (4K-300K). From MR ratio measurements, the coercive forces of them have been obtained as a function of temperature, and the Curie temperatures have been estimated from the temperature dependences of the coercive forces. We have discussed the origin of the magneto-conductive and magnetic properties of LSMO thin films.

Highly oriented epitaxial Cu2O (011) thin film grown on MgO (001) substrate by dynamic aurora PLD method

The epitaxial Cu2O films are grown on MgO (001) substrates by the dynamic aurora pulsed laser deposition (PLD) method. The structure and epitaxial growth of the as-prepared thin films at different substrate temperatures (25 °C to 600 °C) were investigated. The thin film prepared at room temperature (RT, 25 °C) exhibits (111) plane of monoclinic CuO phase with poor crystallinity. The thin films deposited at 200 °C to 600 °C show single-phase cubic Cu2O with good crystallinity. The highly oriented epitaxial Cu2O thin film on the MgO substrate is achieved at low temperatures of 200 °C by applying an induced electromagnetic field during thin film growth. The quality and crystallinity of epitaxial Cu2O thin films remarkably improved with increasing temperature from 200 °C to 600 °C and all these thin films exhibited an out-of-plane epitaxial relationship of Cu2O (011) ‖ MgO (001). The CuO thin film grown on MgO substrate at RT shows a single domain structure, as observed by RHEED. In constrast, Cu2O films grown at 200 °C to 600 °C exhibit two different kinds of domain structure with corresponding in-plane epitaxial relationship of Cu2O [100] ‖ MgO [110] and Cu2O [100] ‖ MgO [11¯0]. This report reveals, for the first time, the feasibility of epitaxial growth of highly oriented Cu2O (011) thin film achieved at the low temperature of 200 °C by the dynamic aurora PLD method. The quality of epitaxial Cu2O (011) is significantly enhanced with increasing substrate temperature from 200 °C to 600 °C.

The Effect of Sputtering Target Density on the Crystal and Electronic Structure of Epitaxial BaTiO3 Thin Films

Barium titanate (BaTiO3) is a promising material for silicon-integrated photonics due to its large electro-optical coefficients, low loss, high refractive index, and fast response speed. Several deposition methods have been employed to synthesize BaTiO3 films. Magnetron sputtering is one of these methods, which offers specific advantages for growing large-scale films. However, there is a scarcity of studies investigating the effect of sputtering target density on the quality of BaTiO3 films. Therefore, this study aims to uncover the effect of sputtering targets on the crystal and electronic structures of epitaxial BaTiO3 thin films. Two BaTiO3 ceramic targets were sintered at different densities by altering the sintering temperatures. The crystal structure and chemical composition of the targets were then characterized using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Subsequently, BaTiO3 epitaxial films were grown by magnetron sputtering using these two targets. The crystal and electronic structures of the BaTiO3 films were analyzed using high-resolution X-ray diffraction, X-ray photoemission spectroscopy, atomic force microscopy, and spectroscopic ellipsometry. Notably, the BaTiO3 films grown with high-density targets show superior quality but contain oxygen vacancies, whereas those films synthesized with low-density targets display high surface roughness. These findings provide insights into the effect of sputtering target density on the crystal and electronic structures of epitaxial BaTiO3 thin films.

Planar defects in α-Ga2O3 thin films produced by HVPE

The defect structure of α-phase gallium oxide thin films was investigated using transmission electron microscopy (TEM). Epitaxial Ga2O3 films were grown via halide vapor-phase epitaxy on c-plane sapphire substrates. TEM analysis revealed a high density of extended planar defects within the films, primarily located along prismatic planes of {112¯0} type. Displacement vectors were determined using the invisibility criterion for stacking faults. The study encompassed both planar and cross-sectional views of the films. It is hypothesized that these defects form due to the motion of edge partial dislocations with the 13⟨11¯00⟩ Burgers vector. Various mechanisms of their formation have been explored.

Effect of annealing temperature on the structure and dielectric characterization of ITO thin films on a boro-float substrate prepared by radio frequency sputtering

Effect of annealing temperature on the structure and dielectric characterization of ITO thin films on a boro-float substrate prepared by radio frequency sputtering

MXene/AlGaN van der Waals heterojunction self-powered photodetectors for deep ultraviolet communication

Self-powered deep ultraviolet (DUV) photodetectors (PDs) have attracted considerable attention in environmental, industrial, and military fields because of their power-independent and environmentally sensitive photodetection. However, DUV PDs based on traditional thin film structures are limited by the low intrinsic mobility of aluminum-gallium nitride (AlGaN) and the large barrier width of the heterogeneous structure, which makes it difficult to achieve efficient spontaneous separation, resulting in lower responsiveness and a slow response speed. Herein, a 2D/3D DUV PD based on the MXene, niobium carbide (Nb2CTx)/AlGaN van der Waals heterojunctions (vdWHs) has been proposed. The as-prepared DUV PDs revealed self-powered properties with a high responsivity of 101.85 mA W−1, as well as a fast response (rise/decay time of 21/22 ms) under 254 nm DUV illumination, thanks to the excellent electrical conductivity and tunable work function of the MXene. It also showed a large linear dynamic range of 70 dB under −2 V bias because of the strong DUV absorption of MXene/AlGaN vdWH, and the enhanced carrier mobility under high illumination density. This study presents an easy processing route to fabricate high-performance self-powered DUV PDs based on MXene/AlGaN vdWHs for DUV communication.

Simultaneous Intra- and Intermolecular Singlet Fission in Bipentacene Macrocycle Aggregates.

Singlet fission (SF) is a process where a singlet state splits into two triplet states, which is essential for enhancing optoelectronic devices. Macrocyclic structures allow for precise control of chromophore orientation and facilitate singlet fission in solutions. However, the behavior of these structures in thin films, crucial for solid-state device optimization, remains underexplored. This study examines the aggregation and singlet fission processes of bipentacene macrocycles (BPc) in thin films using molecular dynamics simulations and electronic structure calculations. Findings indicate that BPc aggregates more rapidly with less chloroform, aligning parallel to the substrate. Intramolecular singlet fission (iSF) rates are rarely changed during evaporation, but the efficiency of intermolecular singlet fission (xSF) improves due to the increase in packing domains, suggesting that orderly crystal domains are not necessary for device efficiency. This opens avenues for varied device designs and traditional solution-based methods for optimal device development.

Characterization of acid-modified polyvinyl alcohol and its application to barrier-coated paper for eco-friendly food packaging

Polyvinyl alcohol(PVA) can be used as a barrier film against gases such as oxygen because of its dense thin-film structure formed by hydrogen bonding; however, its poor water/moisture resistance and low water vapor barrier properties limit its application in food packaging. Herein, oxalic acid-modified PVA(POA) was prepared and crosslinked with Ca2+ to develop a PVA coating solution with improved water resistance for application on paper-based food packaging materials. The crosslinking reaction to improve the water resistance of conventional PVA requires a long reaction time, and preparing a coating solution with crosslinked PVA is virtually impossible. However, the newly developed PVA coating solution may be suitable for the paper-coating industry because crosslinking proceeds simultaneously with drying after coating. Furthermore, in eco-friendly processes using water as a solvent, multilayer-coating is not possible with conventional PVA, whereas the developed coating is resistant to water-soluble processes through crosslinking and can be stacked on top of each other. The Ca2+-crosslinked POA layer exhibited excellent oxygen and water vapor barrier properties through an additional acrylic emulsion coating resulting in OTR and WVTR of 0.13 mL/m2·day and 0.82 g/m2·day. To evaluate recyclability of the coated paper, alkali dissociation and recyclability tests were conducted, and the results showed a repulpability rate of 99.7%, indicating that the paper pulp can be recycled. Biodegradability tests under lab-scale simulated industrial composting conditions showed 91.8% biodegradability, confirming eco-friendliness of the coated paper. Those multifunctional properties of the developed multicoated paper make it excellent additions to paper packaging, particularly for food packaging applications.

Thickness-related variation in the structure, morphology and optical characteristics of nickel thin films for neutral density filtering

In this paper we fabricate neutral density filter (NDF) for the visible region on the Borosilicate glass substrate at room tempreature. E-Beam coating unit is used for fabrication of Nickel thin film on the Borosilicate glass substrate under high vacuum. XRD measurement examined the amorphous growth of thin film at low thickness (t = 10 nm) while higher thickness supported crystalline growth. The Crystallite size (D) and lattice strain ( ϵ ) is decreasing with increasing the thickness. Microstructural investigation by atomic force microscope (AFM) revealed that surface roughness is decreasing with increasing of thickness i.e. From 0.018 to 0.008 nm. The decreasing of roughness prevents scattering loss in neutral density filter. Optical transmittance spectra are obtained using UV–visible spectrophotometer. Nickel 70 nm thickness is an optimum thickness to achieve high optical density (OD = 2.5) but neutrality is poor for higher thickness of filter. Hence the spectral variation of thin filters in our case 10 nm has least spectral variation (ΔOD = 0.11) for stable and durable NDF.

The Topological Hall Effect in CoGd Films Controlled by Hydrogen Migration under Gate Voltage

AbstractThe topological Hall effect (THE) presents hump signals in the Hall resistance versus magnetic field hysteresis loop, showing promise for future spintronics due to its robust chiral magnetic textures. Here, it is shown that solid‐state protonic gating can control possible topological magnetic structures in CoGd thin films. Injecting H+ leads to sizable hump signals in the film. Magneto‐optical Kerr microscopy shows that induced hump signals in transporting measurements do not scale with magnetization, supporting topological magnetism. Successive hydrogen ion extraction completely erases the effect. Thus, topological magnetism manipulations are reversible, nonvolatile, and effective. Ab inito calculations and effective chiral spin models demonstrate that hydrogen injection remarkably enhances the Dzyaloshinskii–Moriya interaction over fourfold, stabilizing chiral structures contributing to the large THE. These findings reveal the vital role of hydrogen ions in topological magnetism and suggest that amorphous ferrimagnetic CoGd thin films are outstanding platforms for realizing controllable topological spintronics at room temperature.

Effect of Fe doping on crystalline phase, structure and photocatalytic properties of TiO2 thin films

Undoped and Fe-doped TiO2 thin films were fabricated on Si substrates using sol-gel method. XRD and Rietveld refinement results show the anatase to rutile transition in the system. SEM and AFM spectra demonstrate that the generation of agglomeration phenomena after Fe doping provides the nucleation point for the phase transition, and the difference in the Gibbs free energies of the two phases provides the driving force for the phase transition. XPS measurements verify that the formation of oxides after Fe doping contributes to the surface thermodynamic equilibrium and the possibility of the surface atomic rearrangements during the anatase to rutile phase transition. The energy band diagram illustrates at the level of electronic structure that the phase transition raises the position of the conduction band minimum of the film and the oxide of Fe that is formed becomes the charge complex center. Finally, the results of degradation of methylene blue solution under simulated visible light irradiation show that Fe doping reduces the photocatalytic ability of TiO2 films. The corresponding mechanism is proposed to explain the photocatalytic activity by which Fe3+ of larger radius replaces Ti4+ to promote the transition of the film from anatase to rutile and to act as a charge complex center.

Bulk and interface spin-orbit torques in Pt/Co/MgO thin film structures

Bulk and interface spin-orbit torques in Pt/Co/MgO thin film structures

Nitrogen doped single layer graphene for CZTS-based thin film solar cells

CdS thin films are commonly utilized as a buffer layer in chalcopyrite thin-film solar cells. However, due to the toxic nature of Cadmium (Cd), ongoing efforts are being directed towards exploring alternative options. In this contribution, doped graphene film with remarkable optical and electrical properties has been introduced for the first time as an alternative buffer layer, replacing CdS in CZTS thin-film solar cell application. In this study, nitrogen-doped graphene (N-doped graphene) film was utilized as a substitute buffer layer in the CZTS thin-film solar cell structure, replacing the conventional CdS thin film. For comparative analysis, CZTS/N-doped graphene and CZTS/CdS traditional solar cell structures were fabricated and separately characterized. The CZTS thin films produced were examined through EDX, XRD, SEM, Raman, optical transmission and PL spectroscopy measurements. According to performed analyses, the Cu-poor and Zn-rich kesterite CZTS thin films exhibited a uniform and dense polycrystalline microstructure as observed in surface and cross-sectional SEM images. XRD spectra of the kesterite CZTS thin film displayed predominant peaks corresponding to the (112), (220/204), and (312/116) diffraction planes of the kesterite CZTS phase. Raman spectra showed a dominant peak at ∼336 cm−1 associated with the kesterite CZTS phase. PL emission spectra indicated transitions from the conduction band to defect levels. The CVD-grown doped graphene film exhibited a 3.43 I2D/IG ratio and a 25 cm−1 FWHM of the 2D peak, indicating a single-layer graphene according to Raman analysis. Permanent nitrogen doping with a 2% atomic concentration was confirmed by XPS measurement. The optical transmission measurement of the single layer doped graphene film showed a 95% transmittance value. Nitrogen doping was contributed to decrease the sheet resistance of the graphene film. The Glass/Mo/CZTS/N-doped graphene/i-ZnO/ITO/Al solar cell displayed a VOC of 0.267 V, JSC of 24.6 mA/cm2, FF of 36.46, and η of 2.37%, showing higher FF and Jsc values but lower conversion efficiency compared to the Glass/Mo/CZTS/CdS/i-ZnO/ITO/Al traditional solar cell structure. Hence, the superior working function and transparency properties position the N-doped graphene film as a competitive buffer layer for use in CZTS-based thin-film solar cells.

Effect of Mesoporous Silica as a Solid Precursor on the Properties of Silicon Oxycarbide Thin Films via Hot Filament Chemical Vapor Deposition

AbstractThis study investigates the impact of mesoporous silica tablets on the synthesis and properties of silicon oxycarbide thin films produced via Hot Filament Chemical Vapor Deposition. Results reveal significant variations in composition and cluster morphology, influenced by the introduction of mesoporous silica tablets. The study demonstrates controlled deposition, consistent synthesis, and the substantial impact of mesoporous silica tablets on the composition, structure, and optical properties of thin films. These findings offer new possibilities for tailor design applications in electronics, optics, and sensors.

Crystalline Structure and Optical Properties of Cobalt Nickel Oxide Thin Films Deposited with a Pulsed Hollow-Cathode Discharge in an Ar+O2 Gas Mixture

Cobalt nickel oxide films are deposited on Si(111) or fluorine-doped tin-oxide-coated (FTO) glass substrates employing a pulsed hollow-cathode discharge. The hollow cathode is operated with argon gas flowing through the nozzle and with O2 gas admitted to the vacuum chamber. Three different cathode compositions (Co20Ni80, Co50Ni50, and Co80Ni20) are investigated. Deposited and annealed thin films are characterized by X-ray diffraction, infrared (Raman) spectroscopy, and ellipsometry. As-deposited films consist of a single mixed cobalt nickel oxide phase. Upon annealing at 600 °C, the mixed cobalt nickel oxide phase separates into two cystalline sub-phases which consist of cubic NiO and cubic Co3O4. Annealed films are investigated by spectroscopic ellipsometry and the optical bandgaps are determined.

Improving Surface Structures of Al-Doped Zinc Oxide Thin Films to Apply in CO Gas-Sensing Property by Designing Processes Through RF Magnetron Sputtering

Improving Surface Structures of Al-Doped Zinc Oxide Thin Films to Apply in CO Gas-Sensing Property by Designing Processes Through RF Magnetron Sputtering