CeO2 Thin Films Research Articles

First-principles quantum analysis of structural, optoelectronic, and thermophysical properties of Co/Ni doped ceria Ce1−xTmxO2 (Tm=Co, Ni) for solar cell applications

The properties of CeO2 thin films, such as their memory store capabilities, visual transparency, chemical and thermal durability, adjustable energy band topologies, and high oxygen storage capacity have captured the attention of scientists. The energy band dispersions for Ce1−xTmxO2 (Tm = Co, Ni; x = 12.5%) are calculated to get insight into the characteristics of the materials under investigation. The anticipated energy bandgaps for Ce1−xCoxO2 and Ce1−xNixO2 are 2.6 and 2.7 eV, respectively, in the spin ↑ channel. However, both compounds show metallic character in inspin ↓ channel. The phenomena of photon absorption/dispersion by the host materials can be elucidated using dielectric function εω of Ce1−xTmxO2 (Tm = Co, Ni; x = 12.5%). Significant photon absorption can be noted in UV and IR regions for Ce1−xTmxO2 (Tm = Co, Ni; x = 12.5%) in spin ↑ and spin ↓ channels, respectively. Ce1−xTmxO2 (Tm = Co, Ni; x = 12.5%) exhibits a minimal photon reflection, approximately 15%. Ce1−xNixO2 shows excellent thermoelectric characteristics as its ZT value is high (1.8 at 1000K) compared to Ce1−xCoxO2. Based on their thermodynamic properties, Ce1−xTmxO2 (Tm = Co, Ni; x = 12.5%) are thermodynamically stable compounds.

Influence of Post-Annealing Treatment on Some Physical Properties of Cerium Oxide Thin Films Prepared by the Sol–Gel Method

In this study, thin films of Cerium Oxide CeO2 were fabricated using the sol–gel technique and deposited onto a glass substrate. The annealing process was carried out at various temperatures ranging from 200 to 600 °C to investigate the structural, morphological, and optical properties of the films and their interrelations. X-ray diffraction (XRD) patterns revealed the crystalline nature of the prepared films, with film quality exhibiting enhancement with increasing annealing temperature. The average crystallite size, dislocation density, microstrain, and lattice constant were determined from XRD patterns. Higher annealing temperatures were found to increase the crystallite size values from 4.71 to 15.33 nm and decrease the dislocation density and microstrain of the unit cell. Scanning electron microscope (SEM) images illustrated the uniformity of the films, presenting a spheroid shape. Optical properties such as transmittance, absorbance, reflectance, the direct band gap, extinction coefficients, the refractive index, and optical conductivity were assessed using optical measurements. The direct optical band gap of the CeO2 film was observed to decrease from 3.99 to 3.75 eV with increasing film thickness. Using the Wemple and DiDomenico (WDD) single-oscillator model, dispersion energy parameters were calculated based on the refractive index. The nonlinear optical properties of the CeO2 thin films were evaluated using these dispersion energy parameters. The improvement of optical parameters holds significance in standardizing CeO2 thin films for various optoelectronic applications.

Exploring the ammonia gas sensing properties of Gd doped CeO2 thin films deposited by spray pyrolysis method

The present study investigates the synthesis and characterization of Gd-doped CeO2 thin films using a simple nebulizer spray pyrolysis method for ammonia sensing application. The films were prepared with varying Gd concentrations from 1 to 5 wt%. The structural, morphological, and optical properties of the samples were analyzed to examine the effect of Gd doping on physical parameters, and the results show that the 4 wt% Gd doped sample exhibits the highest crystallite size, uniform particle size distribution, and a smaller optical band gap. Additionally, the presence of defects and oxygen vacancies in the host lattice is enhanced in this sample. The gas sensing properties of the 4 wt% Gd doped CeO2 exhibits a gas responsivity of 731 %, rise time of 10.4 s, and fall time of 9.2 s indicating that the fabricated thin film sensor was found to be ideal for room temperature gas sensing application. Overall, the study demonstrates that the 4 wt% Gd doped CeO2 thin film is a promising candidate for commercial gas sensor applications.

Realization of CO2 gas sensors and broadband photodetectors using metal/high-k CeO2/p-Si heterojunction

Realization of high-k dielectric oxide material-based devices such as photodetectors (PDs)/gas sensors fabricated on silicon substrate seems to be the utmost promising as a cost-effective approach to use in next generation optoelectronic field. We have explored metal/CeO2/p-Si heterojunction to construct as a broadband (BB) PD and CO2 gas sensor device. The effect of post-annealing procedure on photodetection and CO2 gas sensing characteristics were correlated using AFM, XRD, XPS, Raman and UV–Vis studies. At 0 V bias, the fabricated as-deposited Au/CeO2/p-Si PD device exhibits outstanding performance with enhanced responsivity of 85 AW−1 (at 910 nm), detectivity of 1.36×1015 Jones (at 850 nm), EQE of 1.3×104 % (at 850 nm), faster rise and fall times of 124 ms and 107 ms (at 900 nm). On the other hand, the photodetection characteristic parameters were slightly deteriorated as a function of annealing with respect to the as-deposited device. One of the causes for this fact was attributed to the increase in rms surface roughness (AFM) and decrease in absorbance of CeO2 thin film (UV–Vis). Additionally, Ag/CeO2/p-Si heterojunction was studied as a CO2 gas sensor and evaluated response/recovery times as a function of CO2 gas concentration. Sensing responses of CeO2 as-deposited, CeO2-400, CeO2-500, CeO2-600 and CeO2-700 °C were around 58, 60, 62, 81 and 90 %, respectively, when exposed to 200 ppm of CO2. Thus, we validate that the prospect of integrating enhanced performance in BB PDs and CO2 gas sensors using metal/CeO2/p-Si heterojunction could serve as a basic building block in near future optoelectronic applications. Furthermore, the effect of post-annealing temperature on the morphological, structural, BB photodetection and CO2 gas sensing properties were discussed in detail.

Effect of temperature on polaronic transport in CeO2 thin-film.

The outstanding catalytic property of cerium oxide (CeO2) strongly depends on the polaron formation due to the oxygen vacancy (V̈O) defect and Ce4+ to Ce3+ transformation. Temperature plays an important role in the case of polaron generation in CeO2 and highly influences its electrical transport properties. Therefore, a much needed attention is required for detailed understanding of the effect of temperature on polaron formation and oxygen vacancy migration to get an idea about the improvement in the redox property of ceria. In this work, we have probed the generation of polarons in CeO2 thin-film deposited on a silicon (Si) substrate using the resonance photoemission spectroscopy (RPES) study. The RPES data show an increase in polaron density at the substrate-film interface of the thermally annealed film, indicating the formation of an interfacial Ce2O3 layer, which is, indeed, a phase change from the cubic to hexagonal structure. This leads to a modified electronic band structure, which has an impact on the capacitance-voltage (C-V) characteristics. This result nicely correlates the microscopic property of polarons and the macroscopic transport property of ceria.

Tuning of interface quality of Al/CeO2/Si device by post-annealing of sol-gel grown high-k CeO2 layers

A comprehensive study has been done on the influence of post-deposition annealing temperature on high-k cerium oxide (CeO2) layer grown on n-type silicon (Si) substrate and its resultant interface states have been studied for Al/CeO2/Si metal-oxide-semiconductor (MOS) devices. The high-k CeO2 thin films were deposited by spin-coating and sintered at different annealing temperatures (Ta) in the range of 400–900 °C. The parameters such as fixed charge density (Qeff), dielectric constant (k) of the layers, flat-band voltage (VFB), interface defect density (Dit), etc., of the MOS device were evaluated from CV and I-V measurements. A minimum value of flat band shift (∼0.05 V) with lower Qeff (−4.81 × 1011 C/cm2) have been achieved for the Ta of 600 °C. The k and Dit were evaluated to be 22 and 1.29 × 1012 cm−2, respectively at the Ta of 600 °C. In addition, the CV measurements showed a very small hysteresis and very low frequency dispersion for the Ta of 600 °C sample. Energy distribution of defect states was evaluated and it was maximum towards the bottom of the conduction band. This shows that the 600 °C is the optimum annealing temperature, which results in high quality interface, and the electron affinity of the corresponding CeO2 layers was found to be 3.29 eV as evaluated from ultraviolet photoelectron spectroscopy (UPS). Further, a maximum value of minority carrier lifetime (147 μs) has been achieved for the samples annealed at Ta of 400 °C, indicating that the post-annealing temperature plays a significant role on the properties of CeO2 films deposited by sol-gel process. Thus, the present study demonstrates the possibility of sol-gel grown high k-CeO2 layers suitable for MOS like devices.

Comparing the Effect of In2O3 and Eu2O3 Impurities on the Structural and Optical Properties of Cerium Oxide

This work compares the changes in optical and structural properties of cerium oxide (CeO2) when doped with different concentrations (3%,5%,7%, and 9%) of two oxides, In2O3 and Eu2O3. X-ray diffraction and spectrophotometry were employed in the visible, ultraviolet, and near-infrared regions. The findings demonstrated that CeO2 doped with In2O3 and Eu2O3 thin films were polycrystalline and had a cubic structure. The crystal size increased from 20.5 to 32.15 when Eu2O3 doping ratio increased from 0% to 7% and then decreased to 28.46 nm at 9%. While the crystal size showed an increase from 20.5 to 21.42 nm with the increase of the In2O3 doping ratio, while the lattice constant measured for cubic CeO2 changed opposite to that. The optical measurement showed that Eu2O3 and In2O3 doped CeO2 thin films have a direct band gap with allowed transition with 3.0 eV for the undoped CeO2. The band gap energy changed in a non-regular manner with the increase of the doping ratio of both oxides. The minimum band gap energy was 1.2 eV obtained for 7% Eu2O3 doped CeO2 thin film, and the minimum band gap energy was 1.4 eV obtained for 9% In2O3 doped CeO2. These results qualify them for use as absorbers in solar cell applications.

Comparative studies on the structural, optical and electrochemical properties of Gd, Nd and In-doped CeO2 nanostructured thin films

Cerium oxide nanostructured thin films, as well as their variants doped with Gadolinium (Gd), Neodymium (Nd) and Indium (In), were successfully deposited onto both glass and ITO substrates using the spray pyrolysis method. Their structural, morphological, optical, and electrochemical properties were then experimentally studied. X-ray diffraction (XRD) has confirmed the generation of a single-phase polycrystalline cubic fluorite structure of CeO2. The crystallite size and microstrain of the thin films were found to depend on the type of doping element. Red-shift, peak broadening, and asymmetry in the Raman mode (F2g), as well as a red-shifted energy gap, were confirmed through Raman spectroscopy and UV–Vis–NIR analyses. SEM images reveal nanograin formation in all the films, while EDS analysis confirms the presence of the elements. The electrochemical measurements indicate that doping CeO2 with Gd, Nd, and In enhances its electrochemical properties. Furthermore, the doped CeO2 thin films maintain full transparency during the intercalation and deintercalation of Li + ions. Such pivotal findings broaden the potential applications of this oxide, particularly in supercapacitors and electrochromic devices.

Investigation of the large-signal electromechanical behavior of ferroelectric HfO2–CeO2 thin films prepared by chemical solution deposition

Investigation of the large-signal electromechanical behavior of ferroelectric HfO2–CeO2 thin films prepared by chemical solution deposition

Synthesis and Characterization of Cerium Oxide Thin Films Fabricated via the Facile Doctor Blade Method

In this study, we present an in-depth investigation of cerium oxide (CeO2) thin films synthesized using the doctor blade approach, with polyethylene glycol employed as a binder. A comprehensive characterization employing X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-visible spectroscopy, and atomic force microscopy (AFM) has been conducted to elucidate the structural, chemical, and morphological attributes of the fabricated films. The XRD analysis reveals distinctive wide diffraction peaks indicative of a face-centered cubic CeO2 crystalline structure existing in a singular phase. The morphological analysis using AFM delineates a mean square roughness of 34.54 nm, providing valuable insights into the surface topography of the CeO2 thin films. Additionally, the direct correlation between the material’s band gap, determined as 1.92 eV through UV-visible spectroscopy, and its nanostructural features is established using spectroscopic ellipsometry in conjunction with AFM studies. This approach offers a unique perspective on the optical characteristics of CeO2 films, enhancing our understanding of their nanostructures and facilitating the optimization of their performance for energy applications. Furthermore, the synergistic utilization of scanning electron microscopy (SEM) and spectroscopic ellipsometry contributes to a comprehensive understanding of the growth modes and surface characteristics of the thin films. The integration of these advanced techniques not only refines the fabrication process but also provides crucial insights into the intricate interplay between morphology and optical properties, crucial for optimizing thin films for various applications.

Optical and microstructural characterization of Er3+ doped epitaxial cerium oxide on silicon

Rare-earth ion dopants in solid-state hosts are ideal candidates for quantum communication technologies, such as quantum memories, due to the intrinsic spin–photon interface of the rare-earth ion combined with the integration methods available in the solid state. Erbium-doped cerium oxide (Er:CeO2) is a particularly promising host material platform for such a quantum memory, as it combines the telecom-wavelength (∼1.5μm) 4f–4f transition of erbium, a predicted long electron spin coherence time when embedded in CeO2, and a small lattice mismatch with silicon. In this work, we report on the epitaxial growth of Er:CeO2 thin films on silicon using molecular beam epitaxy, with controlled erbium concentration between 2 and 130 parts per million (ppm). We carry out a detailed microstructural study to verify the CeO2 host structure and characterize the spin and optical properties of the embedded Er3+ ions as a function of doping density. In as-grown Er:CeO2 in the 2–3 ppm regime, we identify an EPR linewidth of 245(1) MHz, an optical inhomogeneous linewidth of 9.5(2) GHz, an optical excited state lifetime of 3.5(1) ms, and a spectral diffusion-limited homogeneous linewidth as narrow as 4.8(3) MHz. We test the annealing of Er:CeO2 films up to 900 °C, which yields narrowing of the inhomogeneous linewidth by 20% and extension of the excited state lifetime by 40%.

Synthesis and characterization of Nd-doped CeO2 thin films grown by spray pyrolysis method: Structural, optical and electrochemical properties

In the present research, we successfully synthesized thin films of Cerium Oxide (CeO2) and Neodymium (Nd) doped CeO2 on both glass and ITO substrates using the chemical spray pyrolysis method. Their structural, morphological, optical and electrochemical properties were experimentally studied. X-ray diffraction analyses showed that all the layers exhibited the cubic fluorite phase characteristic of CeO2. Raman spectroscopy reveals a downward F2g band shift in all Nd3+-doped CeO2 films due to oxygen vacancies. The asymmetry and broadening of the Raman modes arise from the injection of Nd3+ ions in CeO2 thin films, which leads to variations in the presence of Ce3+ and oxygen vacancies. Additionally, the morphology of the films changes with different levels of Nd-doping. The UV–Vis-NIR spectra obtained in the wavelength scale between 300 nm and 1800 nm showed a noticeable reduction in the band gap from 3.46 eV to 3.30 eV. The cyclic voltammetry (CV) results indicate that the addition of Nd improves the ion storage capacities (ISC) of the cerium oxide thin film. Even after the intercalation/deintercalation of lithium ions, the doped cerium oxide thin films remain fully transparent. These significant findings broaden the potential applications of this oxide, particularly for electrochromic devices.

Efficient catalytic activity of NiO and CeO2 films in benzoic acid removal using ozone.

This research focuses on the synthesis of NiO and CeO2 thin films using spray pyrolysis for the removal of benzoic acid using ozone as an oxidant. The results indicate that the addition of CeO2 films significantly enhances the mineralization of benzoic acid, achieving a rate of over 80% as the CeO2 films react with ozone to produce strong oxidant species, such as hydroxyl radicals, superoxide radicals, and singlet oxygen as demonstrated by the presence of quenchers in the reaction system. The difference in catalytic activity between NiO and CeO2 films was analyzed via XPS technique; specifically, hydroxyl oxygen groups in the CeO2 film were greater in number than those in the NiO film, thus benefitting catalytic oxidation as these species are considered active oxidation sites. The effects of nozzle-substrate distances and deposition time during the synthesis of the films on benzoic acid removal efficiency were also explored. Based on XRD characterization, it was established that the NiO and CeO2 films were polycrystalline with a cubic structure. NiO spherical nanoparticles were well-distributed on the substrate surface, while some pin holes and overgrown clusters were observed in the CeO2 films according to the SEM results. The stability of the CeO2 films after five consecutive cycles confirms their reusability. The retrieval of films is easy because it does not require additional separation methods, unlike the catalyst in powder form. The obtained results indicate that the CeO2 films have potential application in pollutant removal from water through catalytic ozonation.

Ultra-high vacuum compatible reactor for model catalyst study of ammonia synthesis at ambient pressure

A high sensitivity reactor was developed to study slow reactions, such as ammonia synthesis over low surface area model catalysts at 1 bar and up to 550 °C. The reactor is connected to an ultra-high vacuum system with a transferable sample design, which allows for cleaning, preparation, and spectroscopic characterization of samples before and after the reaction without exposure to any contaminated environment, such as air. A quasi-closed small volume (250 µl) quartz glass reaction cell is integrated through a capillary with a quartz glass sniffer tube connected to a mass spectrometer. The capillary reduces the 1 bar pressure in the cell to 10−7 mbar in the sniffer tube and mass spectrometer chamber. A quartz fiber-guided laser is used to heat up the sample, and the temperature can be regulated by the proportional–integral–derivative controlled laser power output for fast reaction kinetics research. Proof of principle ammonia synthesis experiments in this reactor at 1 bar, 350–500 °C on Fe(111) single crystal and mass-selected Ru clusters supported on CeO2 thin film yield kinetic parameters that agree very well to those reported in the literature.

Crack formation and optical properties in 175 MeV Au13+ ion beam irradiated CeO2 thin films

CeO2 thin films have been deposited on fused silica substrates using RF-sputtering technique. 175 MeV Au13+ ions beam with two different fluences, 1 × 1012 ions/cm2 and 5 × 1012 ions/cm2, have been applied to modify the structural, surface and optical properties of CeO2 thin films. X-ray diffraction (XRD), atomic force microscopy (AFM), UV–visible absorption and photoluminescence (PL) measurements have been performed to investigate the 175 MeV Au13+ ion-irradiation induced changes in CeO2 thin films. The irradiated films show the formation of nanocrystalline granulizes on the film surface. The mud like cracks have been evolved at the ion-fluence of 5 × 1012 ion/cm2. The modifications in the optical and structural properties and the formation of cracks have been studied under the light of 175 MeV Au13+ ion irradiation and energy loss process into CeO2 lattice.

Anti-reflective effect of CeO2 thin films produced by sol-gel method on crystalline silicon solar cells

Anti-reflective effect of CeO2 thin films produced by sol-gel method on crystalline silicon solar cells

Structural, and magnetic studies of a novel homemade spray pyrolysis synthesized Fe-doped CeO2 thin films

Thin film samples of pure CeO2 and Fe-doped CeO2 were prepared via a homemade spray pyrolysis set-up with an aim to explore its suitability for use as functional materials in spintronics applications. Compressed air was used as a carrier gas to spray deposit the films on preheated glass substrate at an optimum temperature of 400 °C. Structural analysis using X-ray diffraction confirm the single-phase formation of CeO2 for pure and Fe-doped samples. Field emission electron microscope images illustrate the fairly uniform deposition of thin films with nanocrystalline nature. Energy dispersive X-ray analysis confirm the near stoichiometry of doped Ce1-xFexO2 (x = 0, 0.05, 0.1) samples. Magnetic behavior of the samples were studied using Vibrating Sample Magnetometer which show a dominant diamagnetic behavior for both Fe-doped and pure CeO2 thin films. Insufficient number of oxygen vacancies produced during the deposition of thin films is expected to the cause for the absence of ferromagnetic ordering at room temperature.

Temperature-dependent optical dispersion spectra for a single CeO2 thin-film layer in UV–vis and its reflection and transmission in the IR region

CeO2 is a rare-earth refractory material with high refractive index, high thermal stability and infrared transparency; this knowledge can be utilized to develop practical thin films for high temperature thermophotovoltaics (TPVs) and thermal barrier coatings (TBCs). Here, we report ellipsometric measurements of a CeO2 thin film in the wavelength range 210 nm–2500 nm from room temperature to 500 ∘C. Because most previous spectroscopic studies of CeO2 evaluated its optical properties only at room temperature, our findings provide insights into the potential impacts of temperature change on the aforementioned applications, induced by the changes in its electronic structure. We also provide the reflectance and transmittance measurements of the same CeO2 thin film at room temperature using Fourier transform infrared (FTIR) spectroscopy. This knowledge can be leveraged to develop TPV and TBC designs. Finally, we used a software package called Stanford Stratified Structure Solver (S4) to simulate the angle-dependent reflectance spectrum. The optical properties of CeO2 films measured by ellipsometry are used as inputs to predict reflectance spectra. Comparison of the experimental FTIR reflectance with simulated reflectance in S4 shows strong agreement at three different angles.

Enhanced hydrophobicity of CeO2 thin films: Role of the morphology, adsorbed species and crystallography

In order to guarantee the long-term efficiency of hydrophobic materials in real-world situations, it is necessary that their surfaces are highly resistant to scratching, fouling and misting. Furthermore, for the specific applications, e.g. in photovoltaic systems, the water-repelling material must necessarily have a large bandage, such that it does not absorb light in the spectral range which is utilized by the underlying photovoltaic cell. One especially promising candidate for this and many other technologically important applications is cerium dioxide (CeO2, ceria). In the current study, we propose the production framework for the manufacturing of CeO2-based thin films with tunable wetting behavior. For obtaining the coatings with various hydrophobicity, ceria is deposited on the substrates with different roughness via reactive magnetron sputtering, with consequent treatment of the films in vapor of different hydrocarbons. By systematic study using the XRD, SEM, XPS and water contact angle (WCA) instruments, we found that surface texturization, different plains at the surface of the films as well as the adsorbed organic molecules all strongly influence on wettability of the CeO2 thin films. In addition, comparison of WCAs for ceria and silicon oxide SiOx is performed. The higher wettability for the former points out the essential role of the surface material despite presence of hydrocarbons. It is demonstrated that by purposeful controlling for all the parameters – surface texturization, the top material and its crystallography, and adsorbed organic molecules – one can reach superhydrophobic state of the surface.

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