Bi2O3 Thin Films Research Articles

Highly oriented as-grown beta-phase bismuth oxide for optical MEMS

AbstractReactive sputtering of bismuth has been used to form highly oriented beta-phase Bi2O3 thin films at 120 °C. Notably, the films consist of nearly vertical ~ 50 nm diameter nano-filaments of highly aligned β phase pure bismuth oxide. The optical characteristics of the films include a direct optical bandgap of 3.95 eV at 300 K and nearly negligible optical absorption in the wavelength range from 500 to 3000 nm. Nanoindentation experiments show that the mechanical characteristics of the films include reduced modulus and hardness values of 90 and 4.5 GPa, respectively. As fabricated, the films exhibit tensile stress which in combination with a relatively high refractive index value in the range of 2.4–2.5 makes the realized Bi2O3 films structurally and optically suitable for fabrication of optical microelectromechanical (MEMS) devices with applications in the visible to mid-infrared wavelength region, such as MEMS-based Fabry–Pérot microspectrometers, which is demonstrated through simulations. Graphical Abstract

Introducing Bi2S3 Interlayer to Synergistically Modify Mo Back Contact and Regulate Bulk Defects in Kesterite Solar Cells.

A suitable interlayer between the Mo back electrode and kesterite absorber layer has been proven to have a positive effect on limiting the bulk defects of the absorber by the constitute diffusion. Here, a thin Bi2S3 layer is used as the back-interface intermediate layer for the first time, this innovative approach allows for simultaneous modification of the back contact and reduction of bulk defects, resulting in improving the power conversion efficiency of the kesterite device from 9.66% to 11.8%. The evaporated Bi2O3 thin films turn into the Bi2S3 interlayers after sintering the Cu2ZnSnS4 precursor thin films. The Bi2S3 interlayer can inhibit the decomposition reaction of back contact and suppress the formation of the secondary phases. It can also optimize the Fermi level offset and promote the separation of the photoinduced carriers, resulting from its characteristic of high work function. Besides, a small part of the Bi element can diffuse into Cu2ZnSn(S, Se)4 film and induce the crystal growth and restrain Zn-related defects, which is attributed to forming the low melting-point liquid BiSex phase during the high-temperature selenization process. The conclusions highlight the bifunction of the thin Bi2S3 intermediate layer, which can provide a new approach to improve the photoelectric conversion efficiency of kesterite solar cells.

Structural investigations, enhanced dielectric and electrical characteristics of iron-doped Bi2O3 thin films designed for high-frequency applications

Structural investigations, enhanced dielectric and electrical characteristics of iron-doped Bi2O3 thin films designed for high-frequency applications

Defect-enabled room-temperature acetone gas sensors based on Zn-doped cauliflower-like bismuth oxide

Metal oxide-based gas sensors have promising advantages, such as low cost and high sensitivities, but the high working temperature (150°C–300 °C) hinders their practical applications. Herein, this study demonstrated a Zinc (Zn)-doped approach to achieve defect-enabled room-temperature acetone gas sensors based on bismuth oxide (Bi2O3) thin film. Through a simple chemical bath deposition method, the varying substitutional doping of zinc (2 wt% to 8 wt%) can induce the morphological transformation of Bi2O3 nanosheets to a cauliflower-like nanostructure, leading to enhanced surface area and active sites. The incorporation of Zn ions can result in oxygen vacancies in the Bi2O3 lattice and the rising of the depletion layer, facilitating the interaction toward acetone molecules at ambient temperatures, leading to an increment of response ∼6. The Zn-doped cauliflower-like Bi2O3 electrode exhibits a superior sensing performance of acetone gas with a low detection limit of 1 ppm and high stability over 90 days. This work underscores the potential of controlled doping of Zn for oxygen vacancy-riched Bi2O3 thin film as a promising room-temperature acetone gas sensor, offering new avenues for the detection of hazardous gases with improved sensitivity.

N,S-modified ZnO and Bi2O3 thin films supported on titanium mesh as photoanodes

The effect of S doping on the physicochemical and photoelectrochemical properties of ZnO and Bi2O3 films has been studied. Two procedures were used for the synthesis of S-ZnO and S-Bi2O3 thin films on Ti mesh, obtaining lamellar shape nanocrystals for S-ZnO film. The presence of TiO2 anatase phase and wurtzite (ZnO and S-ZnO film) and TiO2 anatase and α-Bi2O3 (Bi2O3 and S- Bi2O3) was observed. The inclusion of sulfur and nitrogen atoms as part of the lattice of the films was evidenced by XPS analysis.

Development of spray pyrolysis-synthesised Bi2O3 thin films for photocatalytic applications

The deposition of Bi2O3 thin films and the photocatalytic efficiency of the obtained films.

The Role of Annealing Treatment on Crystallographic, Optical, and Electrical Features of Bi2O3 Thin Films Prepared Using Reactive Plasma Sputtering Technology

Bismuth oxide (Bi2O3) has attracted considerable research interest in test thin films made utilizing the reactive plasma sputtering (RPS) technology-assisted annealing treatment, allowing the development of diverse BixOx thin films. SEM, phase X-ray diffraction patterns, UV-Vis spectrometers, and D.C. two-probes are used to identify the crystallographic structure and assess the films’ optical-electrical properties. The XRD examination showed that forming Bi2O3 films with an amorphous to multiphase crystalline structure for sputtering time of 40 min was due to soda glass substrate temperature at a range of 30–35°C. Thin films of Bi2O3 crystal structures improved with annealing heat treatment at 200, 300, 400, and 500°C. Yet the formation of crystalline phase (β-Bi2O3 with δ-Bi2O3) Bi2O3 nanostructures occurred at higher temperatures. SEM images showed transparent particles highly affected by annealing temperatures. The nanostructures were about 102–510 nm long, and the diameter was 50–100 nm. The Bi2O3 film optical band gaps and nanostructures ranged from 2.75 to 3.05 eV. The annealing temperature differences affected the crystallite sizes, optical band gaps, and surface roughness. The findings showed that these differences caused the phase transition in Bi2O3 structures. The electrical calculation revealed that the electrical conductivity improved with annealing temperatures of 150–250°C while declining with temperature (300–500)°C with typical semiconductor films.

Effect of substrate temperature on the properties of Bi2O3 thin films grown by sol-gel spray coating

Bi2O3 thin films have been successfully deposited on glass substrate by sol-gel spray coating technique at different temperatures between 150 °C and 550 °C using bismuth nitrate pentahydrate as raw material. Thin films were then annealed at a temperature of 350 °C. This study aims to analyze the effect of substrate temperature on the structural, morphological, topological, and optical properties by X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and UV–Vis Spectroscopy. The diffraction peak position of XRD showed that the as-obtained Bi2O3 thin films were crystalline and different substrate temperatures played a key role in the phase transition β→δ-Bi2O3. The morphology and topology of Bi2O3 show different results which are highly influenced by substrate temperatures whereas Bi2O3 thin film at 450 °C has the highest value of surface roughness. The skewness and kurtosis were also investigated. The optical study showed the band gap energy values of the as-obtained Bi2O3 thin film varied at different substrate temperatures between 2.35 eV and 2.78 eV.

Preparation of Ti-Doped ZnO/Bi2O3 Nanofilm Heterojunction and Analysis of Microstructure and Photoelectric Properties

Ti-doped ZnO (TZO) and Bi2O3 thin films were designed and deposited by magnetron sputtering successively on ITO glass substrate to form a Ti-doped ZnO/Bi2O3 (TZO/Bi2O3) heterojunction. Microstructure and photoelectric properties of TZO, Bi2O3, and TZO/Bi2O3 films were tested and characterized. The results showed that TZO film with a hexagonal wurtzite structure was preferentially grown along the crystal plane (002), had a good crystallization state, and was an N-type semiconductor film with high transmittance (90%) and low resistivity (4.68 × 10−3 Ω·cm). However, the Bi2O3 film sputtered in an oxygen-containing atmosphere and was a polycrystalline film that was preferentially grown along the crystal plane (111). It had a lower crystallization quality than TZO film and was a P-type semiconductor film with low transmittance (68%) and high resistance (1.71 × 102 Ω·cm). The I–V curve of TZO/Bi2O3 composite films showed that it had an obvious heterojunction rectification effect, which indicates that the PN heterojunction successfully formed in TZO/Bi2O3 films.

Structural and optical properties of Zn doped Bi2O3 thin films prepared by chemical route with effect of bath temperatures

The present work attempts to synthesize Zn doped Bismuth Oxide thin films deposited effectively on to micro glass substrates at different bath temperatures by Chemical Bath Route. The films were characterized by XRD, SEM, EDAX and optical analysis. XRD analysis reveals that all the films belong to monoclinic in polycrystalline structure with preferred orientation along (012). The optical energy gap values of Zn doped Bi2O3 thin films were in the range 2.21- 2.81 eV which depend on deposition temperatures. Zn - Bi2O3 thin films can be used in photo voltaic cells, gas sensors, optical coatings, flat-panel displays, micro electronics, light emitting diodes, batteries, super capacitors and fuel cell industries.

Selective formation of crystal polymorphs in Er3+-doped Bi2O3 thin films and their photoluminescence properties

The process conditions for selectively forming crystal polymorphs in Er3+-doped Bi2O3 films deposited on Si, SiO2, and C-plane sapphire substrates were systematically investigated. Bi2O3:Er films were deposited at either room temperature or 300 °C and subsequently post annealed to promote crystallization. The critical factor controlling the crystal polymorphs was Er content. When the Er content was less than 1.5 at.%, only α-Bi2O3 phase nucleated upon post annealing. Deposition at 300 °C somewhat lowered the oxidization state, under which β-Bi2O3 structure appeared at lower temperatures and α-Bi2O3 structure appeared at higher temperatures. When the films were doped with over 2 at.% Er3+ ions, the excess Er2O3 stabilized the δ-Bi2O3 structure as the lowest temperature phase. The universal phase transition scheme with increasing annealing temperature was δ-Bi2O3 → β-Bi2O3 → α-Bi2O3. The δ → β transition proceeded through splitting each diffraction peak of δ-Bi2O3 into two components of β-Bi2O3, indicating a correlation between the structures of β-Bi2O3 and δ-Bi2O3. The γ-Bi2O3 phase appeared only in films on Si(100) substrates and after vacuum annealing, suggesting the formation of sillenite (Bi12SiO20). Deposition on C-plane sapphire by using H2O as the oxygen source gas produced a highly (111)-oriented δ-Bi2O3 structure, whereas deposition with O2 yielded a randomly oriented δ-Bi2O3 structure. At Er content exceeding 4 at.%, δ-Bi2O3 was the primary phase in the films on SiO2. The photoluminescence (PL) activity of dopant Er3+ under excitation at a wavelength of 532 nm strongly depended on the crystal polymorphs. α-Bi2O3:Er exhibited intense and stable PL spectra consisting of eight Stark splitting lines. PL from γ-Bi2O3:Er exhibited much weaker two emission lines. δ-Bi2O3:Er and β-Bi2O3:Er films were not emission-active at all. However, δ-Bi2O3:Er film on SiO2 with an Er content of 4 at.% exhibited an intense and broad emission at 1530 and 1560 nm.

Facile synthesis of flower-like Bi2O3 as an efficient electrode for high performance asymmetric supercapacitor

Herein, we report a facile, economic, efficient and binder-free strategy to synthesize a flower-like Bi2O3 thin films on flexible stainless steel mesh (FSSM) substrates by rotational chemical bath deposition (R-CBD) approach. The flower-like Bi2O3/FSSM exhibits a monoclinic α-Bi2O3 phase demonstrating the mesoporous nature with a 58.69 m2 g−1 specific surface area. The Bi2O3/FSSM electrode exhibits specific capacitance of 421.76 F g−1 and specific capacity of 674.8 C g−1 at 10 mA cm−2 current density, remarkable cycle stability (60% up to 1000 cycles), and high energy density (149.95 Wh kg−1) with power density (963.85 W kg−1) in 6 M KOH electrolyte. The results indicate that the 6 M KOH is optimized concentration for Bi2O3/FSSM electrodes. An aqueous asymmetric supercapacitor (ASC) device is fabricated by activated carbon (AC) as cathode and Bi2O3/FSSM as an anode. The assembled Bi2O3||AC ASC device exhibits a specific capacitance of 36.37 F g−1 at a current density of 1 mA cm−2 with the energy density (ED) of 18.24 Wh kg−1 at a power density (PD) of 1008.67 W kg−1 and 83.67% capacitance retention after 1000 cycles at the current density of 2 mA cm−2. The derived Bi2O3/FSSM served as a binder-free electrode that provides potential application for electrochemical energy storage devices.

Er3+-catalyzed interdiffusion of elements across the interface between Bi2O3 film and SiO2 substrate resulting in host-material-specific photoluminescence spectra of Er3+

Er3+-doped Bi2O3 thin films were sputter-deposited on SiO2 substrates under various process conditions. After post annealing in an O2 atmosphere, near-infrared photoluminescence (PL) spectra from Er3+ ions in specific product oxides were observed. For sufficiently oxidized Bi2O3:Er films with Er contents less than 1.5 at%, α-Bi2O3:Er having a monoclinic structure nucleated with negligible intermixing of the elements across the interface. Its PL spectra exhibited Er3+ luminescence signals consisting of eight Stark splitting peaks. Deposition at temperatures higher than 400 °C and/or with high Er content produced a somewhat reduced Bi2O3 network. Post annealing triggered diffusion of Si into the film as well as diffusion of Bi and Er into the SiO2 substrate, creating Bi2O3 −SiO2 −Er2O3 compound oxides. The original film body crystallized into a δ-Bi2O3 structure, which was stabilized by the presence of a large amount of Er. The emission-active product at Er contents of 2 at% was Bi2O3:Er−SiO2 (Bi2SiO5:Er), which exhibited four-line emission spectra and the intensity was lower than that of α-Bi2O3:Er. For Er3+ contents higher than 4 at%, interdiffusion of Si and O atoms was enhanced and SiOx:Er domains were created in the Bi2O3:Er film. Intense and broad emission peaks at 1530 and 1560 nm were observed in the PL spectra. The emission-active species in the Bi2O3 −SiO2 −Er2O3 compound oxide will be either Er3+ doped in the strongly disordered δ-Bi2O3 lattice involving oxygen deficiencies or Er3+ attached to SiOx domains formed inside the δ-Bi2O3 network.

Structural analysis, FTIR study and optical characteristics of graphene doped Bi2O3 thin film prepared by modified sol–gel technique

Bismuth oxide(Bi2O3) and Graphene doped bismuth oxide thin films were synthesized using modified Sol-gel technique at a temperature about 180–220 °C in a cost effective procedure. In this experiment, self synthesized graphene was used as dopant. The effect of graphene doping on the microstructure and crystalline nature of bismuth oxide were studied after the samples had been subjected to XRD. The prepared graphene was found to be in hexagonal crystal structure and the bismuth oxide was monoclinic in structure. A increase in lattice parameters and decrease in crystallite size and an increase in microstrain and dislocation density was also resulted in this work for graphene doped bismuth oxide (Bi2O3). A detailed structure study from rietveld refinement was carried out in terms of atomic position of various partipating atom, their bond angles and lengths. Finally, a simulated structure was also generated for Bi2O3 and graphene doped Bi2O3. Obtained bandgap of doped Bi2O3 was low. Also the optical properties like refractive index, SELF, interband transition strength etc. were studied.

Crystal-phase-specific near-infrared photoluminescence from Er3+-doped Bi2O3 thin films

Er3+-doped Bi2O3 films were sputter deposited on Si(100) substrates at room temperature with H2O vapor as an oxygen source gas. Crystal phases appearing after postannealing in an O2 atmosphere included single-phases of α-Bi2O3, γ-Bi2O3, and δ-Bi2O3, as well as a mixed phase of α-Bi2O3 and γ-Bi2O3. Selection of the crystal phase was possible in terms of H2O pressure and postannealing temperature. Photoluminescence spectra from Er3+ ions excited at a laser wavelength of 532 nm revealed distinct spectral features specific to the crystal phases. A clear crystal-field splitting feature consisting of eight emission lines was observed in PL spectra from sufficiently oxidized α-Bi2O3:Er films, indicating that Er3+ ions occupied low-symmetry C2v sites of Bi3+. The optimum annealing temperature for optical activation of Er3+ ions was between 400 and 450 °C. The emission intensity of α-Bi2O3:Er deposited with H2O was seven times higher than that of α-Bi2O3:Er deposited with O2 probably because larger numbers of Er3+ could substitute Bi3+ sites under reduced condition. Increasing deposition temperature lowered the emission intensity due to the loss of OH and H species from the as-deposited films. The emission spectra of γ-Bi2O3:Er were featureless and its emission intensity was one order of magnitude lower than that of α-Bi2O3:Er. The low-temperature phase of δ-Bi2O3:Er turned out to be entirely emission inactive. Reactions at the interface between the Bi2O3 film and the Si substrate were promoted upon postannealing at 500 °C. The resulting Bi2SiO5:Er exhibited a weak emission spectrum with four emission lines, which reflected occupation at tetragonal Bi3+ sites in the (Bi2O2)2− layers.

A study on strain and density in graphene-induced Bi2O3 thin film

A study on strain and density in graphene-induced Bi2O3 thin film

Synthesis and characterization of 2-D La-doped Bi2O3 for photocatalytic degradation of organic dye and pesticide

Photocatalytic degradation of organic dye by AOP's is an effective method to minimize water pollution. The semiconducting materials have a larger bandgap and difficult to fabricate in the form of 2 D-films. Here we report a simple method for the effective fabrication of undoped and La-doped Bi2O3 thin films by a chemical solution deposition method. The incorporation of lanthanum dopant was successfully done and confirmed with the help of SEM, EDAX, XRD, and other advanced characterization techniques. A brilliant flower-like morphology and incorporation of La ions in Bi2O3 lattice helped the fabricated doped thin film for efficient degradation of carbol fuchsin (CF) organic dye, and Chlorpyrifos (CPS) organic pesticide under 120 min of stimulating light source irradiation. Detailed deposition effect on morphology is discussed. The narrowing of bandgap (2.85 eV) in the doped thin film as compared to undoped Bi2O3 film (3.01 eV) resulted in efficient degradation of CF up to 89% with a rate constant of 0.520 min−1 and CPS to 67% with 0.366 min−1. The scavenger addition confirmed ●OH as the major ROS and, metabolites formed during the degradation are identified by LC-MC analysis of degraded samples of both CF and CPS. The reusability study confirmed the efficiency of films up to multiple catalytic cycles. The work confirmed La-Bi2O3 film was effective for the degradation of moieties from a separate class of organic framework.

Synthesis and photocatalytic performance of Bi2O3 thin films obtained in a homemade spin coater

This paper describes the deposition of Bi2O3 thin films by spin-coating in a homemade apparatus and their application as photocatalyst in dye photodegradation under UV radiation. For substrate fixation in the spin coating equipment, we developed an alternative method named fit-in method, where the substrate is directlly fixed in a polytetrafluorethylene (PTFE) polymer base used as a sample holder. The Bi2O3 precursor resin was obtained according to the polymeric precursor method and deposited on glass substrates by a dynamic system operating at 4000 RPM, varying the number of added drops (10 or 20), followed by a calcination step to promote oxide crystallization. The thin films were characterized by X-ray diffratometry (XRD), scanning electronic microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), and sessile drop method (SDM). The photocatalytic efficiency of Bi2O3 thin films was evaluated by the photodegradation of Rhodamine B (RhB) under UV radiation. The as-obtained Bi2O3 thin films presented high performance in RhB dye removal from aqueous solution and stability during five cycles of reuse, regardless of deposition conditions, which is considered the main feature of a thin film used as a photocatalyst.

Characterization of Bi2O3 thin films for doping photoluminescent Er3+ ions

Undoped and Er3+-doped Bi2O3 thin films were sputter-deposited on Si(100) substrates. Sufficiently oxidized Bi2O3 films with refractive indices between 2.17−2.23 were obtained at a wavelength of 633 nm; these values are comparable to those of bulk Bi2O3 crystals. While the film composition was stable for deposition temperatures between room temperature (RT) and 450 °C, the refractive index steeply decreased above 450 °C and reached 1.4 at 600 °C. The lowering of the optical transmittance spectra indicated aggregation of metallic Bi and darkening of the film. All films exhibited X-ray diffraction patterns of α-Bi2O3. The direct and indirect bandgap energies derived from the Tauc plots were 3.4–3.7 eV and 1.9–2.5 eV, respectively, depending on the O2 flow rate and deposition temperature. Upon excitation of Er3+-doped Bi2O3 films at 532 nm, Er3+ emissions peaking at 1537 and 1541 nm appeared, and the photoluminescence spectra included fine structures reflecting crystal-field splitting. Resonant excitation of Er3+ 4f levels and indirect excitation via the defect levels of Bi2O3 followed by energy transfer to Er3+ contributed to the emission. The films deposited at RT with Er concentrations of 2 at.% had the emission intensity of Er3+, but concentration quenching strongly suppressed the Er3+ emission because the doped Er3+ ions stayed inside the Bi2O3 crystals. At deposition temperatures above 400 °C, the concentration quenching was mitigated possibly because out-diffusion of Er3+ ions reduced the effective number of Er3+ ions in the Bi2O3 crystalline domains.

Coverage Layer Phase Composition-Dependent Photoactivity of One-Dimensional TiO2-Bi2O3 Composites.

TiO2–Bi2O3 composite rods were synthesized by combining hydrothermal growth of rutile TiO2 rod templates and sputtering deposition of Bi2O3 thin films. The TiO2–Bi2O3 composite rods with β-Bi2O3 phase and α/β-Bi2O3 dual-phase decoration layers were designed, respectively, via in situ radio-frequency magnetron sputtering growth and post-annealing procedures in ambient air. The crystal structure, surface morphology, and photo-absorption performances of the pristine TiO2 rods decorated with various Bi2O3 phases were investigated. The crystal structure analysis reveals that the crystalline TiO2–Bi2O3 rods contained β-Bi2O3 and α/β-Bi2O3 crystallites were separately formed on the TiO2 rod templates with different synthesis approaches. The morphology analysis demonstrates that the β-Bi2O3 coverage layer on the crystalline rutile TiO2 rods showed flat layer morphology; however, the surface morphology of the α/β-Bi2O3 dual-phase coverage layer on the TiO2 rods exhibited a sheet-like feature. The results of photocatalytic decomposition towards methyl orange dyes show that the substantially improved photoactivity of the rutile TiO2 rods was achieved by decorating a thin sheet-like α/β-Bi2O3 coverage layer. The effectively photoinduced charge separation efficiency in the stepped energy band configuration in the composite rods made from the TiO2 and α/β-Bi2O3 explained their markedly improved photoactivity. The TiO2-α/β-Bi2O3 composite rods are promising for use as photocatalysts and photoelectrodes.