CeO2 Thin Films Research Articles

Improvement of optoelectronic properties of in doped CeO2 thin films for photodiode applications

Improvement of optoelectronic properties of in doped CeO2 thin films for photodiode applications

Fabrication of Gd2O3-doped CeO2 thin films through DC reactive sputtering and their application in solid oxide fuel cells

Fabrication of Gd2O3-doped CeO2 thin films through DC reactive sputtering and their application in solid oxide fuel cells

Engineering of Grain Boundaries in CeO2 Enabling Tailorable Resistive Switching Properties

AbstractDefect engineering in valence change memories aimed at tuning the concentration and transport of oxygen vacancies are studied extensively, however mostly focusing on contribution from individual extended defects such as single dislocations and grain boundaries. In this work, the impact of engineering large numbers of grain boundaries on resistive switching mechanisms and performances is investigated. Three different grain morphologies, that is, “random network,” “columnar scaffold,” and “island‐like,” are realized in CeO2 thin films. The devices with the three grain morphologies demonstrate vastly different resistive switching behaviors. The best overall resistive switching performance is shown in the devices with “columnar scaffold” morphology, where the vertical grain boundaries extending through the film facilitate the generation of oxygen vacancies as well as their migration under external bias. The observation of both interfacial and filamentary switching modes only in the devices with a “columnar scaffold” morphology further confirms the contribution from grain boundaries. In contrast, the “random network” or “island‐like” structures result in excessive or insufficient oxygen vacancy concentration migration paths. The research provides design guidelines for grain boundary engineering of oxide‐based resistive switching materials to tune the resistive switching performances for memory and neuromorphic computing applications.

Solution-Route Inkjet Fabrication of CeO2 Thin Films with Tunable Microstructure.

We report the fabrication and characterization of solution-route CeO2 thin films with a tunable porosity and microstructure. Films were deposited by means of inkjet printing technique using 0.2 M, 0.4 M and 0.6 M concentration inks prepared from Ce(NO3)3·6H2O precursor. Printing was performed at two different temperatures of 60 °C and 300 °C to study the variation in structure. Printing parameters were adjusted for the consecutive deposition of layers, resulting in ≈140 nm and ≈185 nm thick single layers for 60 °C and 300 °C printing temperatures, respectively. We compared the microstructure of printed films for different concentrations, printing temperatures, solvents and substrates. The formation of the cubic fluorite structure of the printed films was confirmed via XRD characterization. We suggest this technique as an advanced method for high-quality film fabrication with a controlled microstructure and with a minimal waste of materials. Through adjusting printing parameters, both dense and porous films can be produced for use in different applications.

Structural, optical, and magnetic properties of Co‐doped CeO2 thin films prepared by radio‐frequency magnetron sputtering

Co‐doped CeO2 (Ce1‐xCoxO2, x = 0, 0.03, and 0.06) thin films were prepared by radio‐frequency magnetron sputtering. The structural, optical, and magnetic properties of these films were characterized by X‐ray diffraction (XRD), Raman spectroscopy (Raman), atomic force microscopy (AFM), Fourier transform‐infrared spectroscopy (FT‐IR), spectroscopic ellipsometry (SE), and superconducting quantum interference magnetometer (SQUID). XRD and Raman studies revealed that all the films exhibited single phase of cubic fluorite structure, with highly (111) preferred orientation. No Co and Co‐related oxide was detected. Compared with undoped CeO2 films, the defect concentration of Co‐doped films increases. AFM images displayed that the film surface morphology is dependent on the Co‐doped content. The vibrational band assignment of undoped and Co‐doped CeO2 films was analyzed by FT‐IR. The energy dispersion optical constants (the refractive index n and the extinction coefficient k) of Ce1‐xCoxO2 thin films were obtained by analyzing the SE spectra in the ultraviolet and visible‐near infrared (UV–NIR) region (0.5–5.9 eV). The optical band gap energies Eg for these films were determined. The Eg values of the Ce1‐xCoxO2 thin films are 3.35, 3.27, and 3.25 eV, and the n values at wavelength of 632 nm are about 2.35, 2.38, and 2.42 for Co‐doped content x = 0, 0.03, and 0.06, respectively. SQUID measurements show that Co‐doped CeO2 films exhibit room temperature ferromagnetism, and the saturation magnetization (Ms) is 0.0051 and 0.0098 emμ/cm3 with the Co doping content x = 0.03 and 0.06, respectively. The ferromagnetism of Co‐doped CeO2 films belong to the intrinsic magnetism of the films.

Structural, electronic and optical study of Zr:CeO2 thin films by computational and experimental approach

Transition metal oxide shows some exceptional optical and electronic properties explore in recent investigations. In this context, the current study presents first principal and experimental investigations of pure and Zr doped CeO2 thin films. The simulations were performed using density functional theory based Wien2k-code with PBE-GGA approximation. The uniform and well-distributed granular thin films were grown for experimental investigations. The simulations and experimental results show a good resemblance in outcomes. The density of states predicts the p-d hybridization between Ce and O atoms while band structure reduce with Zr incorporation in CeO2 structure. Crystallographic analysis reveals the presence of crystalline cubic phase with space-group 225-F-m3m in thin films. Experimentally observed bandgap follows the reducing trend with Zr incorporation as predicted by simulations data and found as 2.38 eV for pure CeO2 and 1.51 eV for 6.25% Zr doping content. Optical parameters were recorded as a function of photon energy which strongly influenced by Zr concentration. The sharp increase in optical absorption and real part of dielectric constant in Zr containing composition makes these materials more efficient and favorable for photovoltaic and optoelectronic applications.

Impact of Molarity on the Structural, Morphological and Optical Properties of CeO2 Thin Films Prepared by Spray Pyrolysis Technique

Impact of Molarity on the Structural, Morphological and Optical Properties of CeO2 Thin Films Prepared by Spray Pyrolysis Technique

Metal-organic decomposed cerium oxide thin film in mixed ambient at different temperatures for MOS capacitor

Post-deposition annealing of CeO2 thin films in nitrogen/oxygen/nitrogen ambient from 400 until 1000 °C successfully transformed the films from oxygen poor to oxygen-rich state, in which an excess of oxygen was detected at higher temperatures as the oxygen interstitials. The adsorbed nitrogen attaching to oxygen vacancies in the CeO2 thin films would inhibit further oxidation of the films, and thus controlling the film thickness in addition to expanding the lattice. The increase of temperature has enhanced adsorption and diffusion of nitrogen and oxygen, decreasing the attachment of nitrogen to the oxygen vacancies. The dissociated nitrogen would reside as dangling bonds that caused a difficulty in controlling the oxidation and hence interfacial layer growth was expected. An exaggerated film growth dominated by interfacial layer happened at the highest temperature, surpassing the CeO2 layer thickness. The lowest interface trap density was attained but a degradation in the current-voltage characteristic happened due to the presence of excess oxygen and nitrogen as the scattering center for the incoming electrons during forward bias operation. A better performance was achieved by the film annealed at 800 °C via the demonstration of the lowest leakage current level, surpassing other films. Detailed explanation was discussed in this work.

Cerium oxide thin films: synthesis, characterization, photocatalytic activity and influence on microbial growth

The resistance of surfaces to biofouling remains a significant advantage for optical devices working in natural conditions, increasing their lifetime and reducing maintenance costs. This paper reports on the functionalities of transparent CeO2 thin films with thicknesses between 25 and 600 nm deposited by reactive magnetron sputtering on the glass substrate. The CeO2 photocatalytic performance exhibited an efficiency of 30% on imidacloprid degradation under 6 h of UV radiation and increased linearly with the irradiation time, suggesting a complete degradation within 48 h. The films did not alter the growth rate of the green algae Chlorella vulgaris after 72 h short-term exposure. The tested CeO2 films proved to efficiently inhibit with high efficiency the Staphylococcus aureus biofilms and planktonic growth (reducing the counts of bacterial cells by 2 to 8 logs), demonstrating the promising potential of these materials for obtaining antimicrobial and antibiofilm surfaces, with broad applications for the biomedical, ecological and industrial fields.

Spectroscopic ellipsometry study of Mn doped CeO2 thin films prepared by radio-frequency magnetron sputtering

Mn doped CeO2 (Ce1-xMnxO2, x=0, 0.03, 0.06) thin films were deposited on Si (100) substrates by radio-frequency magnetron sputtering. X-ray diffraction and Raman analysis indicates that the films are cubic fluorite crystal structure with a preferred orientation along (111), which is the same as that of pure CeO2. Atomic force microscopy reveals that the film surface morphology is dependent on the Mn doped content. The influence of Mn doped content on the optical properties was studied by spectroscopic ellipsometry (SE) in the UV-NIR region (210∼2500 nm). The energy dispersion optical constants (the refractive index n and the extinction coefficient k) of Ce1-xMnxO2 thin films were obtained by analyzing the SE spectra. Under the assumption of a direct band-to-band transition, the optical band gap energies Eg for these films were determined. The values of n, k and Eg are functions of the Mn doped contents. The results showed that the Eg values of the Ce1-xMnxO2 thin films are 3.22, 3.32 and 3.35 eV, and the n values at wavelength of 632 nm are about 2.29, 2.38 and 2.49 for Mn doped content x=0, 0.03 and 0.06, respectively. The values of n and Eg increases linearly with increasing Mn doped content.

Tailoring of defects dependent magnetic properties of swift heavy ion irradiated CeO2 for spintronics application

The present investigation reports the swift heavy ion induced effects on cerium oxide (CeO2) thin films. These thin films were deposited on Si (111) substrates by the electron-beam evaporation method and irradiated by a 100 MeV O7+ ion beam with different ion fluences. X-ray diffraction analysis of these films confirms the stable fluorite phase of CeO2 even after the higher fluence of irradiations. Raman measurement also supports the presence of the F2g phase of CeO2 and the presence of defect states. The Gaussian deconvolution of photoluminescence (PL) spectra reveals various defect-associated peaks. The broad peaks in the PL spectra are associated with oxygen vacancies and are red-shifted (494–520 nm) with ion fluences. The surface morphological images show the modification in the surface roughness with ion irradiation and the re-growth of smaller circular-formed nanoparticles on the surface is observed at the fluence of 5 × 1011 ions/cm2. Magnetic measurements show an enhancement in magnetic ordering with ion irradiation. All the samples demonstrate room temperature ferromagnetism with magnetic saturation (Ms) up to 14.57 emu/cm3. The saturation magnetization in irradiated thin films is directly correlated to the area under the peak of defect-associated PL emission. The mechanism such as the oxygen vacancy-based F-center exchange model is considered to understand the enhancement of ferromagnetism in ion irradiated CeO2 thin films. Some popular theoretical models are also employed to determine various magnetic parameters.

Synergistic interactions between water and the metal/oxide interface in CO oxidation on Pt/CeO2 model catalysts

The significance of catalytic active interfacial sites in metal supported on metal oxide systems has been well established in prototypical CO oxidation reactions. Here, we investigate the role of water molecules in the CO oxidation reaction using Pt nanoparticles (Pt NPs) supported by a two-dimensional (2D) cerium oxide thin-film. The 2D model CeO2 thin films were fabricated using the e-beam evaporation technique and a monolayer of Pt nanoparticles deposited on CeO2 thin films by the Langmuir-Blodgett (LB) method. The well-defined reaction conditions, such as humid and dry conditions, were achieved using an ultra-high vacuum (UHV) batch chamber. Interestingly, we found a strong metal-support interaction (SMSI) in the Pt/CeO2 catalyst under dry reaction conditions, which was increased further by the presence of water molecules. However, water had a detrimental effect on a Pt thin-film model catalyst under humid reaction conditions. By altering the partial pressures of water molecules and CO, the reaction mechanism was established under humid conditions. The current results demonstrate that hydroxyl intermediates from water molecules provide an alternative pathway to the Pt/CeO2 catalyst, resulting in increased overall turnover rates. These findings shed light on the synergistic interplay of water and metal-oxide interfaces.

The Influence of CeO2 Concentration on Some Physical Properties of Y2O3 Thin Films

Thin films of pure yttrium oxide (Y2O3) and doped with cerium oxide (CeO2) were prepared by the chemical spray pyrolysis(CSP)method. The structural, optical and electrical properties of the prepared films were investigated. The analysis of X-ray diffraction (XRD) thin films revealed that the undoped and doped Y2O3 were amorphous with a broad hump around 27o and narrow humps around 48o and 62o for all samples. Except for the Y2O3:6wt.%CeO2 thin film, all had signal preferential orientation along the (100) plane at 2θ=12.71o which belongs to CeO2, Field emission scanning electron microscopic (FE-SEM) images confirmed the formation of the nanosized particles which resembles circles and others revealed rods and balls shape. UV-Vis spectra study showed peak absorption at a wavelength of 305 nm, with blue shift due to quantum confinement, and this also happened for the doped films, with direct energy band gaps. The photoluminescence spectra (PL) of undoped Y2O3 and doped thin films showed an emission peak at 365 nm at the same wavelength of all the prepared samples with a slight difference. All prepared films show three activation energies except Y2O3:6wt.%CeO2 film has two activation energies. From I-V characteristic curves, the prepared films have Schottky behavior except Y2O3:6wt.%CeO2 film, which displayed ohmic behavior. Y2O3:6wt.%CeO2 fabricated device revealed good photosensitivity for VIS and IR wavelength.

Ammonia sensing characteristics of a cerium oxide thin film coated with platinum nanoparticles

This paper reports on ammonia (NH3) sensing characteristics of a new semiconducting metal oxide (SMO) sensor. employing a cerium oxide (CeO2) thin film and platinum (Pt) nanoparticles (NPs) as a sensing layer. The thickness of CeO2 thin film is 30 nm and the particle size of Pt NPs is about 4–6 nm. Based on the enhanced surface area/volume (SA/V) ratio and catalytic ability of Pt metal, the sensing behaviors are efficiently improved owing to the smaller Pt NPs. A high sensing response of 5.81 under 1000 ppm NH3/air gas and a low detectable content of 1 ppm NH3/air are acquired at 275 ℃. In addition, a relatively fast sensing action with the response (recovery) times of 15 s (85 s) and 6 s (25 s) are observed upon exposure to 1000 and 1 ppm NH3/air gas, respectively, at 300 ℃. The Langmuir isotherm is used to study the related surface coverage under introduced ammonia gas. The proposed Pt NP/CeO2 sensor shows prominent stability for long-term operation without intentional passivation treatment. The proposed sensor device’s benefits include a simple device structure, relatively easy manufacturing, a wide sensing range of ammonia gas content (1–1000 ppm NH3/air), and lower cost.

Oxygen vacancies and defects tailored microstructural, optical and electrochemical properties of Gd doped CeO2 nanocrystalline thin films

In this study, the authors present a pure and Gadolinium (Gd) doped CeO2 nanostructures, successfully elaborated onto the glass and Indium Tin Oxide (ITO) coated glass substrates under optimized parameters. A spray pyrolysis method was used at a temperature of 450 °C, with simultaneous incorporation of Gd at various concentrations (0, 2, 4, 6, 8 at. %) as a dopant. Different techniques for characterization were used to study the Gd impact on the microstructural, the morphological, the optical and the electrochemical behaviors of the CeO2 material. The XRD patterns shows that Gd3+ ions are inserted at the Ce4+ ion sites in the cubic fluorite structure network of CeO2 nanocrystals (NCs). Raman spectroscopy and UV–Vis–NIR have been utilized to study the defect structure and optical behaviors in these NCs. Broadening and Peak asymmetry of Raman active mode are attributed to the existence of Ce3+ and oxygen vacancy, which have been changed with addition of Gd3+ ions in CeO2 NCs. The results of UV–Vis–NIR spectroscopy show the variations of the optical gap energy with fluencies of Gd3+ due to the variations of particles sizes of NCs. Cyclic voltammetry results show that the ion storage capacities (ISC) of CeO2 thin films are increased with Gd doping. This research paper reports on the fluencies of Gd doping in CeO2 nanocrystals, to understand the role of oxygen vacancies and the impact they have on the tailoring of the microstructural, optical and electrochemical behaviors of doped CeO2 nanocrystals for multiple applications such as, catalysts, oxygen transportation, ultraviolet fuel cells, and electrochromic devices etc.

Influence of Ag+ ions on the physical properties of spray coated CeO2 thin films and photo-response of p-Si/n-SDC junction diodes

Two-layer optoelectronic devices like p-n junction diode have attracted much attention due to their modern fast switching, optical detection, and sensing applications. In this work, we have fabricated a p-Si/n-SDC junction diode with higher photocurrent by preparing pure and Silver doped CeO2 (SDC) thin-film through facile spray pyrolysis. A monophase cubic fluorite crystal structure was confirmed by XRD analysis. FE-SEM micrographs showed noticeable grain growth after doping the Silver (Ag) in CeO2 film. UV-Vis. study revealed a sharp absorption peak at 340 nm for 6 wt. % of SDC film. The conductivity of SDC films was found to improve while increasing the doping level of Ag. The p-Si/n-SDC junction diode exhibited a higher photocurrent under an illumination environment, conforming to the fabricated diode's photo-conducting behavior. Compared with the p-Si/n-CeO2 diode, the SDC diode recorded a higher ON-OFF response as expected.

Inherent characteristics of ultra-photosensitive Al/Cu–CeO2/p-Si metal oxide semiconductor diodes

An ultrahigh photosensitive diode was developed using a Cu-doped CeO2thin film through spray pyrolysis processing, which has made a unique contribution in the field of optoelectronic device fabrication process.

Solid solubility and charge compensation/exchange mechanisms in Ga- or Mn-Doped CeO2 thin films on 3D printed biomedical titanium alloy

CeO2 films doped with 0–9 mol% Ga/Mn were fabricated by spin coating on 3D-printed Ti6Al4V, calcined at 650 °C for 2 h, and characterised by TEM, FESEM, 3D laser scanning confocal microscopy, GAXRD, and XPS. The results depend on the roles of several factors: (1) Sol-gel precursor viscosity affected pore filling and surface coverage. (2) Lattice contraction and resultant intervalence charge transfer increased the Ce3+ concentration as a minority effect. (3) Substitutional solid solubility and associated redox charge compensation controlled the defect equilibria, which highlight the majority role of this solid solubility mechanism in decreasing the Ce3+ concentration. (4) Electronegativity played a negligible role in affecting the valences but was important in initiating intervalence charge transfer. (5) Multivalence charge transfer combined electron exchanges between film matrix, dopants, and Ti substrate. The present work provides a foundation to interpret the effects of extrinsic effects from both dopant and substrate on the properties of films.

Thermal behaviour of Cu and Au nanoparticles grown on CeO2 thin films

Bimetallic catalysts are often more active and/or selective than their monometallic counterparts. The behaviour of such catalysts is frequently strongly dependent on the molar ratio of the two elements as well as nanoparticle size and the interaction with the support material. X-ray photoelectron spectroscopy (XPS) is an excellent surface analytical technique for probing the electronic properties of catalytic systems. When a mixture of pure and alloyed particles is present, it is more difficult to extract information from XPS given that it is a spatial averaging technique. Recently, the technique of medium energy ion scattering (MEIS) has been exploited to investigate the depth-dependent composition of nanoparticles on planar surfaces. Herein, we combine the two techniques to investigate the nature of Cu and Au nanoparticles deposited onto ultrathin CeO2 films on Si(111) examining their morphology and chemical composition as a function of annealing temperature for samples that have been maintained in an ultrahigh vacuum environment and exposed to air. The Cu/Au/CeO2/Si(111) is chosen as a model system in order to provide insight into how the catalytic properties of Cu/Au/CeO2 depend on the presence of discrete Cu and Au particles versus fully intermixed Cu/Au systems.

Influence of manganese rate on structural, optical and electrochemical properties of CeO2 thin films deposited by spray pyrolysis: Supercapacitor applications

The present work aimed to investigate the electrochemical properties of ITO substrates in propylene carbonate (PC) with 0.5 mol/L lithium perchlorate (LiClO4) medium in the presence of elaborated thin films of cerium dioxide pure and doped with manganese at varying percentages. Ce1–xMnxO2 (x = 0 wt%, 2 wt%, 4 wt% and 6 wt%) were successfully deposited by the spray pyrolysis (SP) technique on the glass substrate and ITO at 450 °C. The effects of manganese (Mn) doped thin films Ce1–xMnxO2 were studied and investigated by using different analyses namely X-ray diffraction (XRD) analysis, Raman spectroscopy method, UV–Vis spectrophotometer technique, atomic force microscopy (AFM) analysis and electrochemical properties. XRD data obtained present a polycrystalline with a face-centred cubic structure of fluorite type. Raman results of undoped and Mn doped thin films show two peaks at 465 and 600 cm−1, due to the formation of extrinsic oxygen vacancies by the incorporation of Mn into Ce1–xMnxO2 matrix. Energy dispersive spectroscopy (EDS) data show the presence of Ce, O, and Mn elements in the elaborated films. The AFM results reveal that the surface roughness decreases with increasing Mn rate. Further, band gap energy of thin films decreases with increasing in Mn rate due to the formation of defect state between valence and conduction band. The storage capacity of the elaborated Ce1–xMnxO2/ITO/PC + LiClO4 electrode reaches a maximum of 1.997 mF in the presence of 6 wt% of Mn.