Cerium Oxide Thin Films Research Articles

DC-Voltage-Induced High Oxygen Permeation through a Lanthanum Silicate Electrolyte with a Cerium Oxide Thin Film

DC-Voltage-Induced High Oxygen Permeation through a Lanthanum Silicate Electrolyte with a Cerium Oxide Thin Film

Low-energy femtosecond pulsed laser deposition of cerium (IV) oxide thin films on silicon substrates

Cerium (IV) oxide (CeO2, ceria, or cerium dioxide) has been investigated for various applications due to its excellent physical and chemical properties. Since high-precision processing of such functional material can be conceived through pulsed laser deposition (PLD) with a low-energy, ultrashort pulsed laser, we report the low-energy (∼ 8.0 nJ) femtosecond PLD (fs-PLD) of CeO2 thin films on silicon (Si) substrates. The CeO2 thin films are deposited for 2.0 to 5.0 h at room temperature with background oxygen (O2) gas and then annealed at 1000 °C for 0.5 h in ambient air. The as-deposited CeO2 film is amorphous and featureless due to the low-energy laser pulse and room-temperature deposition but exhibits good stoichiometry due to the background gas. The film properties likewise improve with post-deposition annealing coupled with a longer deposition time. Despite the change in stoichiometry, the annealed CeO2 films exhibit improved reflectivity and enhanced crystallinity. Although other deposition parameters need to be optimized further and the film stoichiometry entails additional examination, our results show the viability of low-energy fs-PLD for the fabrication of CeO2 thin films and similar functional materials.

Study of a New Hydrogen Gas Sensor Synthesized With a Sputtered Cerium Oxide Thin Film and Evaporated Palladium Nanoparticles

A new hydrogen (H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) gas sensor, synthesized with a radio frequency (RF) sputtered cerium oxide (CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) thin film and rapid thermal evaporated palladium (Pd) nanoparticles (NPs), is fabricated and reported herein. The employed Pd NPs can effectively increase the surface area/volume ( S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</sub> /V) ratio and catalytic reactivity of Pd metal, thereby substantially enhancing the adsorption effect of hydrogen molecules on the device surface and improving the related sensing performance. Energy-dispersive X-ray spectroscopy (EDS), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to characterize the related properties of the studied device. Experimentally, a high sensing response of 120.2 under 1% H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /air gas at 350 °C with a relatively shorter response (recovery) time of 5 s (17 s) is obtained. The studied Pd NP/CeO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> -based sensor device shows wide operating ranges of temperature (200 °C-400 °C) and hydrogen concentration (10 ppm-1% H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /air). A thermodynamic analysis employed to study the surface coverage of hydrogen molecules is reported in this work. The studied sensor device also exhibits the advantages of a simple structure, easy fabrication process, and relatively low cost.

Investigation of dextran adsorption on polycrystalline cerium oxide surfaces

This study used non-reactive magnetron sputtered polycrystalline cerium oxide thin films as model substrates to mimic the surface morphology of cerium oxide nanoparticles. We investigated the interaction between dextran and polycrystalline cerium oxide surfaces by atomic force microscopy, X-ray photoelectron spectroscopy, and reflection-absorption infrared spectroscopy. A simplified sample preparation method probing solid-liquid interface was set up by conducting aqueous adsorption procedures in an argon-filled glove bag connected to an ultra-high vacuum chamber. We found that the adsorption of dextran from aqueous solution onto the polycrystalline cerium oxide surface leads to a mutual charge transfer between dextran and cerium ions, creating a surface accumulation of Ce3+. In the aqueous environment, dextran hydroxyl groups adsorbs on the polycrystalline cerium oxide surface competitively with the dissociated hydroxyl groups from water. By investigating glucose adsorbed onto polycrystalline ceria prepared by physical vapor deposition, we further confirmed the role of hydroxyl groups from polysaccharide during interaction with ceria. Thermal annealing of the dextran adsorbed polycrystalline cerium oxide surface results in desorption of weakly bonded dextran below 100 °C and decomposition of dextran above 100 °C.

Implication of Mn concentration on the properties of cerium oxide thin films

Uniform and adhesive Manganese doped cerium oxide (MDC) films are successfully deposited by Nebulizer Spray Pyrolysis (NSP) technique. The MDC films are characterized by XRD, FT-IR, UV-ViS, PL and I-V analysis. X-ray diffraction peaks reveal the single-phase polycrystalline cubic fluorite structure with preferential orientation along (2 0 0) direction. The broad bands observed at 695, 659, 538 and 517 cm-1 are due to the envelope of (Ce=O) symmetric, asymmetric terminal stretching and phonon band of metal oxide (Ce-O) network from FT-IR spectra. The transmittance decreases with Mn concentration due to the increase in scattering of photon by crystal defects created by doping and lower ionic size of Mn. The electrons in the outer orbits have travelled to the higher energy levels and have occupied vacant positions in energy bands. Some of the NBE emission and green emission peaks are vanished at higher doping level of Mn. The occurrence of a strong and broad blue emission peak at 15% for MDC films has been confirmed from emission spectra.

Fast switching characteristics of (111) oriented cerium oxide thin film-based metal-oxide semiconductor UV photodetector

This work presents the studies of cerium oxide (CeO2) thin films (TFs) with different thicknesses on Si substrates using the electron beam evaporation method for photodetector (PD) application in the UV region. The effect of thickness on the structural, morphological, and optoelectronic properties of the TF was comprehensively studied. The structure and crystallinity of the samples were characterized by x-ray diffraction and all TFs showed highly preferred orientation along the (111) plane. The crystallinity and structural parameters like crystallite size, lattice constant, microstrain and dislocation density were also calculated, and 200 nm film showed the best results. Field emission scanning electron microscopy revealed that the CeO2 TF was smoothly deposited on the substrate. The absorption enhanced with increased thickness and thereby, the bandgap energy decreased to 3.45 eV for 300 nm as compared to 3.65 eV for 100 nm thickness. The electrical performance also proved superior for thicker films with increased photocurrent accompanied by lower dark current. The 200 nm CeO2 TF device showed the fastest switching response with a rise time of 240 ms and a fall time of 152 ms at a bias voltage of −4 V with an on/off ratio of 13.59. Moreover, spectral responses were higher for 200 nm film, thus exhibiting good PD performance. It is believed that this work will be highly useful for use as a sensitive UV PD.

Effect of Zinc doping on structural, optical and morphological properties of spray deposited cerium oxide thin film for low level formaldehyde detection

Pure and doping with Zn material on CeO2 films were formed on the substrate at 250 °C and further it was annealing at 350 °C in the atmosphere for 2 h using spray pyrolysis technique. Noticeable variation in the crystallite size, porosity, band gap and room temperature sensing response was observed due to Zn-doping. The sensing studies namely response of resistivity, sensitivity and response-recovery characteristics of both films were compared at 32 °C. The appreciable sensing response was observed for doping with Zn ions into CeO2 film in formaldehyde at a lower detection (0.5 ppm) at 32 °C.

Investigation of cerium oxide thin film thickness using THz spectroscopy for non-destructive measurement

Through time of non-destructive measurement of individual layer of materials or paint layers at nano-scale, non-contact terahertz technique is a very good approach. In this research work, the cerium oxide (CeO2) thin film is deposited on sapphire (c-Al2O3) substrate having thickness of 430 µm by using RF magnetron sputtering technique. A terahertz pulses incident on the CeO2 film, layer of CeO2 interface with substrate. Some amount of incident pulse transmits and rest will reflect with respect to transmission mode and reflection mode, respectively. In the reflection mode, the time elapsed between the arrival and departure of cerium oxide layer is directly proportional to the thickness of the layer as a function of wavelength. The thickness of CeO2 is measured about 35.83 µm using terahertz spectroscopy. This study shows that terahertz spectroscopy is an experimental approach and possible to measure thickness of thin film for non-destructive measurement.

The role of substrate temperature on the performance of humidity sensors manufactured from cerium oxide thin films

Cerium oxide (CeO2) thin films as humidity sensors are obtained by pulsed laser deposition (PLD) grown on Si (100) substrate. CeO2 nanoparticles were taken as target materials for PLD technique. The effect of film deposition condition, such as deposition temperature on performance sensor, was explored. The substrate temperature ranges varied from 300 to 700 °C. The structural and surface morphologies were examined by X-ray diffractometer (XRD) and scanning electronic microscopy (SEM), respectively. The capacitance and resistance of the sensors were tested. The sensor utilizing CeO2 films exhibited high sensitivity, and the increase in humidity led to a gradual increase in sensitivity and decreased resistance. The sensor performance is highly dependent on morphology and surface, which in turn is affected by the change in electrical properties of the film.

Irradiation-induced reactions at the CeO2/SiO2/Si interface

The influence of high-energy (1.6 MeV) Ar2+ irradiation on the interfacial interaction between cerium oxide thin films (∼15 nm) with a SiO2/Si substrate is investigated using transmission electron microscopy, ultrahigh vacuum x-ray photoelectron spectroscopy (XPS), and a carbon monoxide (CO) oxidation catalytic reaction using ambient pressure XPS. The combination of these methods allows probing the dynamics of vacancy generation and its relation to chemical interactions at the CeO2/SiO2/Si interface. The results suggest that irradiation causes amorphization of some portion of CeO2 at the CeO2/SiO2/Si interface and creates oxygen vacancies due to the formation of Ce2O3 at room temperature. The subsequent ultra-high-vacuum annealing of irradiated films increases the concentration of Ce2O3 with the simultaneous growth of the SiO2 layer. Interactions with CO molecules result in an additional reduction of cerium and promote the transition of Ce2O3 to a silicate compound. Thermal annealing of thin films exposed to oxygen or carbon monoxide shows that the silicate phase is highly stabile even at 450 °C.

Microstructure, optical and dielectric properties of cerium oxide thin films prepared by pulsed laser deposition

Cerium oxide (CeO2) thin films were deposited on Pt (111)/Ti/SiO2/Si(100) substrates using pulsed laser deposition method at different temperatures such as, 300 K, 573 K and 873 K with 3 × 10−2 mbar oxygen partial pressure. The prepared films were systematically investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and electrical measurement system. XRD analysis clearly showed improved crystallinity of CeO2 films prepared at 573 and 873 K substrate temperatures. The AFM analysis indicated the uniform distribution of the nanocrystallites and dense structure with the roughness (RMS) of ~ 2.1–3.6 nm. The PL studies of the films showed a broad peak at ~ 366–368 nm, indicating the optical bandgap of 3.37–3.38 eV. The electrical property study showed minimum leakage current density of 2.0 × 10−7 A/cm2 at 873 K, which was measured at 100 kV and this value was much lower than that of the CeO2 film deposited at 300 K. The dielectric constants are increased and dielectric loss values decreased for the films with increasing substrate temperature.

TEM Investigations of Ion-Irradiated Cerium Oxide Thin Film

TEM Investigations of Ion-Irradiated Cerium Oxide Thin Film

Influence of the Cerium Oxide Thin Film Produc-Tion Methods on the Capacitance-Voltage Charac-Teristics of the Mis Structures

Thin films of cerium oxide are increasingly used in electronics. This interest is primarily due to the unique properties of cerium oxide: high dielectric constant; high dielectric strength; high refractive index; similarity to silicon in the crystal lattice parameter; thin film production methods are compatible with classical silicon MIS technology. The aim of this work is to establish a relationship between the electrophysical parameters of MIS structures and the technological method for producing thin dielectric films by analyzing the system of electric charges in a dielectric and at the insulator-semiconductor interface. The dependence of the electrophysical parameters of the MIS structure on the method for producing thin dielectric films is most clearly manifested in the capacitance – voltage (C – V) characteristics of these structures. This dependence is directly related to the system of electric charges in the insulator and at the insulator-semiconductor interface, which depends on the technological process of creating thin dielectric films on a semiconductor substrate.The system of charges at the insulator-semiconductor interface and near it is considered. It has been established that only the charge fixed in the dielectric influences the CV characteristics of such structures, since there are no other types of charges and / or their number is negligible. The article discusses methods for producing thin cerium oxide films that are compatible with classical silicon technology. It is shown that the capacitance-voltage characteristics (CV characteristics) of aluminum – cerium – silicon structures depend on the producing method of the dielectric film. To identify the presence of charge fixed in the dielectric, approximation of the CV characteristic was use in the voltage range corresponding to the depletion mode of the surface layer of the semiconductor. Since all experimental characteristics in the depletion mode of the surface layer of the semiconductor coincide with linear approximation, it should be assumed that the charge fixed in the dielectric is absent in the studied structures.It is established that the MIS structures obtained using the flash method are characterized by reversible changes in their flat-band voltage, due to a change in the charge value fixed in the dielectric, under the influence of external factors. The method of oxidation of a metal mirror makes it possible to obtain MIS structures with a charge fixed in a dielectric independent of external factors.Ref. 9, fig. 13.

Electrochemical activity of the polycrystalline cerium oxide films for hydrogen peroxide detection

Abstract Polycrystalline cerium oxide thin films (15 nm) deposited on a glassy carbon substrate were used as an electrode in a mediator-free, non-enzymatic electrochemical sensor for hydrogen peroxide. The electrode surface was characterized by X-ray photoelectron spectroscopy, resonant photoelectron spectroscopy, scanning electron microscopy and atomic force microscopy. The electrode sensitivity, detection limit and pH range of sensor stability were determined by applying electrochemical techniques: cyclic voltammetry and chronoamperometry. It was found that the sensor reactivity to H2O2 is directly related to the presence of electroactive cerium centres of 3+ character on the electrode surface. The Michaelis–Menten mechanism of catalase-like activity of ceria film is suggested as an explanation of the data and discussed. The results confirmed the sensing abilities of technologically well-accessible nanostructured cerium oxide films for hydrogen peroxide detection without using a mediator, i.e. the enzymatic properties of CeO2/GC electrode.

Skin protection against UV radiation using thin films of cerium oxide

In this work, we evaluated the efficiency of cerium oxide as sunscreen using titanium oxide as standard comparison material. Geant4 software was used to perform numerical simulation, we calculated the radiation dose that ultraviolet radiation deposits in a skin sample as a function of thin film thickness of the sunscreens. We found that in the interval between 5 and 15 nm of the thin film thickness and for wavelengths between 160 and 400 nm, cerium oxide has the potential to reduce the radiation dose more than 10% with respect to the same thickness band of titanium oxide. Using thin films of cerium oxide and titanium oxide with same thicknesses and greater than 45 nm, the difference in the attenuation of the radiation dose for both materials is less than 1%. The results lead us to propose cerium oxide as an alternative material to titanium oxide for the manufacture of sunscreens.

Quantitative analysis of gadolinium doped cerium oxide thin films via online-LASIL-ICP-OES

LASIL-ICP-OES is used to determine the stoichiometry of gadolinium doped cerium oxide thin films ranging from 220 to 14 nm with high accuracy and precision.

High growth-rate atomic layer deposition process of cerium oxide thin film for solid oxide fuel cell

Cerium oxide (CeO2) shows superior surface exchange, and therefore is widely used for the cathode interlayer coating material to reduce the activation loss in low temperature solid oxide fuel cell (LT-SOFC). Here, we report on the application of the high growth-rate atomic layer deposition (ALD) process of CeO2 thin films as cathodic interlayers for LT-SOFCs. We demonstrate that the maximum power density of the SOFC with pure CeO2 interlayer increases by 45% compared to the one without interlayer at 450 °C. More importantly, the performance degradation rate of the ALD CeO2 interlayered cell improves by 25 times compared to the cell without interlayer during 24 h operation at 450 °C.

Ordered phases of reduced ceria as inverse model catalysts

Inverse model catalysts represent valuable systems for studying metal-oxide interactions and finite size effects in heterogeneous catalysis. To maximize the potential of model catalytic studies, high level of control over model catalyst properties is desirable. Here we introduce experimental approaches for obtaining inverse ceria/copper model catalysts of well-defined crystallographic phases CeO2, ι-Ce7O12, CeO1.67, and c-Ce2O3 supported on Cu(1 1 1). The presented cerium oxide thin films are ultrathin (2 monolayers), discontinuous, and feature highly defined stoichiometry and crystallographic structure with characteristic (1 × 1), (√7×√7)R19°, (3 × 3), or (4 × 4) electron diffraction patterns. Compared to thicker films and bulk ceria, the prepared ultrathin cerium oxides exhibit a distinctly different dependence of the lattice constant on the stoichiometry, and show activation barrier preventing their complete oxidation. These phenomena illustrate that metal-oxide interactions and finite size effects strongly influence the behavior of the presented inverse model catalysts indicating their prospective use in disentangling complex functionalities of ceria/copper catalytic systems.

Structural, morphological and electrical characterization of ceria-based nanostructured thin films obtained by ultrasonic spray pyrolysis

In this work, the synthesis and the structural, morphological and electrical characterization of Ce1−xSmxO2−δ solid solution, with x=0, 0.10, 0.15, 0.20, 0.25 and 0.30mol, are reported. Nanocrystalline, homogeneous, and adherent samarium doped cerium oxide thin films were deposited onto glass (Pyrex®) substrates by a simple and cost effective ultrasonic spray pyrolysis system, at a low substrate temperature of 450°C and further annealing treatment at 500°C for 2h. For all the samples, X-ray diffraction results showed the formation of single phase and well crystalline thin films, with cubic fluorite type structure. Scanning electron microscopy analyses showed homogeneous surfaces for all the samples; from SEM micrographs crystallite sizes were found to be in the range 23–37nm. From atomic force microscopy, surface roughness in the range of 20–95nm was measured and the formation of smooth films with an average grain size of 45nm was observed. For the best sample in the solid solution, high oxygen ion conductivity of 1.71×10−1Scm−1, at 450°C, was determined by impedance spectroscopy, with an activation energy of 0.93eV. Results suggest that these films may have a potential application as electrolytes in intermediate temperature solid oxide fuel cells, IT-SOFC.

Atomic layer deposition of CeO2 using a heteroleptic cyclopentadienyl-amidinate precursor

Cerium oxide thin films were deposited on fused silica using atomic layer deposition (ALD). The novel Ce precursor, Ce(iPrCp)2(N-iPr-amd) [bis-isopropylcyclopentadienyl-di-isopropylacetamidinate-cerium] is a room-temperature liquid with good thermal stability and evaporates cleanly. Water vapor was used as the oxygen source. The growth characteristics and film properties of ALD CeO2 were investigated. A relatively broad ALD window of 165–285 °C resulted in a constant growth rate of 1.9 Å/cycle and good thickness uniformity. The films deposited at 240 °C were found to be polycrystalline with cubic structure without a preferential direction in as-deposited condition. However, films grown at 335 °C slightly favored a (200) preferred orientation. XPS analysis showed that films are free from contamination, and the Ce:O stoichiometry analysis revealed the existence of oxygen vacancies in the films with composition CeO1.74.