Cerium Oxide Thin Films Research Articles

Direct liquid injection chemical vapor deposition of platinum doped cerium oxide thin films

Thin films of Pt-doped CeO2 were grown by direct liquid injection chemical vapor deposition on silicon wafer covered by native oxide at 400°C using Ce(IV) alkoxide and organoplatinum(IV) as precursors. X-ray photoelectron spectra evidenced that the platinum oxidation state is linked to the deposition way. For platinum deposited on top of cerium oxide thin films previously grown, metallic platinum particles were obtained. Cerium and platinum codeposition allowed obtaining a Pt0 and Pt2+ mixture with the Pt2+ to Pt ratio strongly dependent on the platinum flow rate during the deposition. Indeed, the lower the platinum precursor flow rate is, the higher the Pt2+ to Pt ratio is. Moreover, surface and cross-sectional morphologies obtained by scanning electron microscopy evidenced porous layers in any case.

The influence of the technological parameters on the ionic conductivity of samarium doped ceria thin films

Sm 0,20 Ce 0,80 O 2 powder was used for the formation of samarium doped cerium oxide (SDC) thin films using e-beam. Surface area of powder was 34.9 m 2 /g and particle size – 0.3-0.5 μm. Thin films were deposited using physical vapor deposition system on SiO 2 and Alloy 600 substrates. 2 A/s – 16 A/s growth rate and 20 °C – 600 °C substrate temperature were used during the deposition. Ionic conductivity investigation revealed that the maximum ionic conductivity (1.67 S/m) has the thin film deposited on 300 °C temperature substrate using 4 A/s growth rate. Minimum ionic conductivity (0.26 S/m) has thin film which was deposited on 20 °C temperature substrate using 8 A/s growth rate. Vacancy activation energies vary in 0.87 eV – 0.97 eV range. Furthermore the calculations of crystallite size revealed that crystallite size increases with increasing substrate temperature: from 7.50 nm to 46.23 nm on SiO 2 substrate and from 9.30 nm to 44.62 nm on Alloy 600 substrate. Molar concentration of samarium in initial evaporated material is 19.38 mol% and varies from 11.37 mol% to 21 mol% in formed thin films depending on technological parameters. DOI: http://dx.doi.org/10.5755/j01.ms.21.1.5700

Altering properties of cerium oxide thin films by Rh doping

Ceria containing highly dispersed ions of rhodium is a promising material for catalytic applications. The Rh–CeOx thin films with different concentrations of rhodium were deposited by RF magnetron sputtering and were studied by soft and hard X-ray photoelectron spectroscopies, Temperature programmed reaction and X-ray powder diffraction techniques. The sputtered films consist of rhodium–cerium mixed oxide where cerium exhibits a mixed valency of Ce4+ and Ce3+ and rhodium occurs in two oxidation states, Rh3+ and Rhn+. We show that the concentration of rhodium has a great influence on the chemical composition, structure and reducibility of the Rh–CeOx thin films. The films with low concentrations of rhodium are polycrystalline, while the films with higher amount of Rh dopants are amorphous. The morphology of the films strongly influences the mobility of oxygen in the material. Therefore, varying the concentration of rhodium in Rh–CeOx thin films leads to preparing materials with different properties.

Effect of rf power on the properties of magnetron sputtered CeO2 thin films

Cerium oxide (CeO2) thin films were prepared by rf magnetron sputtering (PVD) technique onto glass substrates at a pressure of 3 × 10−4 mbar of Ar+ atmosphere. The thickness of deposited CeO2 films ranges from 380 to 590 nm. X-ray diffraction studies on the films showed that the films are polycrystalline in nature. The crystallite size (D), dislocation density (δ) and micro-strain (e) were evaluated from XRD patterns. The obtained micro-strain and dislocation density of the films were found to be ~10−3 and ~1016 lines/m2 respectively, along with a marginal increase in crystallite size from ~6 to ~9 nm. The experimental diffraction values of the films agreed with the standard values. The optical properties of cerium oxide films were studied in the wavelength range 325–900 nm. Optical absorption, extinction coefficients, refractive index and optical conductivity were evaluated from optical measurements. The films are found to be highly transparent in visible region and exhibits low reflectance in the ultraviolet region. The optical band gap of the films was found to decrease from 3.53 to 3.45 eV, with the increase of film thickness. The defects were found to increase with the increase of rf power. Emission bands like UV, weak blue, blue, blue–green and green bands were observed from PL spectra of CeO2 thin films. Raman active mode (F2g) of CeO2 thin films was observed at 466 cm−1 and films deposited at higher rf power show increased line width as well as peak intensity in Raman spectra. Rf power induced formations of flower like morphology were observed in SEM images. The surface roughness of CeO2 thin films was increased from 2.9 to 7.7 nm with the increase of rf power as ascertained from AFM images and the results are discussed.

Hydrothermal Synthesis and UV Irradiation Shielding Performances of Nanometer Cerium (IV) Oxide Thin Films

Abstract The cerium oxide films with high refractive index and good UV irradiation shielding performance were synthesized on the glass substrates by a hydrothermal method using Ce(NO 3 ) 3 ·6H 2 O and CO(NH 2 ) 2 as raw materials. The films and the powders prepared at the same time were characterized by SEM, XRD, FT-IR, ellipsometer and UV-vis. The influences of original Ce(III) concentration and urea dosage on cerium oxide films were researched. The results show that the films are smooth and the particles are small at low Ce(III) concentration and urea dose. The sediments are cerium oxide and Ce(CO 3 ) 2 O·H 2 O crystal, and silicon of substrate is involved in hydrothermal reaction. Meanwhile, the film refractive indexes are affected by film compact and chemical composition. Both of absorbance and absorption wavelength edge become big with increasing of Ce(III) concentration and urea dose, and the main influence factors are the film thickness and composite semiconductors. The optimal Ce(III) concentration is 0.008 mol/L, and the optimal urea dosage is 0.06 g.

Growth and composition of nanostructured and nanoporous cerium oxide thin films on a graphite foil.

The morphology and composition of CeOx films prepared by r.f. magnetron sputtering on a graphite foil have been investigated mainly by using microscopy methods. This study presents the formation of nanocrystalline layers with porous structure due to the modification of a carbon support and the formation of cerium carbide crystallites as a result of the deposition process. Chemical analyses of the layers with different thicknesses performed by energy dispersive X-ray spectroscopy, electron energy loss spectroscopy and X-ray photoelectron spectroscopy have pointed to the reduction of the cerium oxide layers. In the deposited layers, cerium was present in mixed Ce(3+) and Ce(4+) valence. Ce(3+) species were located mainly at the graphite foil-CeOx interface and the chemical state of cerium was gradually changing to Ce(4+) going to the layer surface. It became more stoichiometric in the case of thicker layers except for the surface region, where the presence of Ce(3+) was associated with oxygen vacancies on the surface of cerium oxide grains. The degree of cerium oxide reduction is discussed in the context of particle size.

Structure and photoluminescent properties of (200)-oriented Eu-doped CeO2 thin films fabricated on fused silica substrates by chemical solution deposition

(200)-oriented Eu-doped cerium oxide thin films were fabricated, on fused silica substrates by a chemical solution deposition method. The thin films obtained were characterized by X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and photoluminescence measurements. Ce with valence state 4+ is confirmed to be predominant in Eu-doped CeO2 thin films. All the thin films were dense and crack-free, and showed bright orange-red emissions under ultraviolet light excitation, originated from the 5D0→7F1 and 5D0→7F2 transitions of Eu3+ ions. Structure distortions induced by Eu-doping affected the light emission of electric dipole transition 5D0→7F2. The strongest photoluminescent intensity was observed in the thin films with a Eu-doping content x of 0.08, indicating the existence of concentration quenching effect of photoluminescence. Lifetime study of photoluminescence indicated that the decrease of lifetime was originated from augmented pathway for deactivating excited Eu3+ ions. Our study suggests that Eu3+-doped CeO2 thin films have potential applications in optoelectronic devices.

Structural and electrical study of samarium doped cerium oxide thin films prepared by e-beam evaporation

Samarium doped cerium oxide (Sm0.15Ce0.85O1.925, SDC) thin films were grown on the Alloy 600 (Fe–Ni–Cr) and optical quartz (SiO2) substrates using e-beam deposition technique. Formed SDC thin films were characterized using different X-ray diffraction (XRD) techniques, scanning electron microscope (SEM), energy-dispersive spectrometry (EDS) and impedance spectroscopy. The deposition rate of formed SDC thin films was changed from 2Å/s to 16Å/s.XRD analysis shows that all thin films have a cubic (FCC) structure and repeat the crystallographic orientation of the initial powders evaporated with different deposition rate and on different substrates. The crystallite size increases from 7.7nm to 10.3nm and from 7.2nm to 9.2nm on Alloy 600 substrate and optical quartz (SiO2) substrate respectively as the thin film deposition rate increases. SEM images indicate a dense and homogeneous structure of all formed SDC thin films.The ionic conductivity depends on thin films density and blocking factor. The best ionic conductivity (σg=1.34Sm−1 and σgb=2.29Sm−1 at 873K temperature, activation energy ΔEg=0.91eV and ΔEgb=0.99eV) was achieved for SDC thin films formed at 4Å/s deposition rate. It was found that the highest density (5.25g/cm3) and the lowest relaxation time in grain (τg =9.83×10−7s), and the lowest blocking factor (0.39) is in SDC thin films formed at 4Å/s deposition rate. The deposition rate influences the stoichiometry of the formed SDC thin ceramic films.

CeO2 thin film as a low-temperature formaldehyde sensor in mixed vapour environment

Nanostructured cerium oxide thin film was deposited onto the glass substrate under optimized condition using spray-pyrolysis technique. X-ray diffraction result indicates polycrystalline nature of the film with fluorite-type face-centered-cubic structure. The atomic force micrograph indicates the presence of nanocrystallites over the film surface. The vapour sensing characteristics of the annealed film were studied by chemiresistive method for various concentrations of formaldehyde vapour at room temperature (~ 30 °C). For 0.5 ppm of formaldehyde vapour, the film shows a response and recovery time of 36 and 1 s, respectively. The vapour sensing properties of the cerium oxide film in mixed environment were studied and reported.

Momentum transfer driven textural changes of CeO2 thin films

The influence of the target erosion depth on the film texture was investigated during DC reactive magnetron sputter deposition of CeO2 thin films. Three fluxes towards the substrate surface (the relative negative oxygen ion flux, the material flux, and the energy flux) were measured and related to the ongoing erosion of a cerium target. As the deposition rate increased for more eroded targets, both the energy flux and the negative ion flux decreased. Cerium oxide thin films that were deposited at different target erosion states, exhibited a change in preferential crystalline orientation from [200] to [111]. This textural change cannot be explained in terms of the energy per arriving atom concept. Instead, it is shown that the momentum of the high energetic negative ions is an essential condition to clarify the witnessed trends.

Effect of solvent and substrate temperature on morphology of cerium oxide thin films by simple nebuliser spray pyrolysis technique

Cerium oxide thin films are coated on glass substrates by nebuliser spray pyrolysis technique. The crystallographic structures, surface morphology, optical properties and I–V characteristics have been studied as a function of solvent and substrate temperature (300–500°C). X-ray diffraction was used to estimate crystallographic texture, grain size, strain and lattice constant. All films exhibit cubic fluorite structure with different preferred orientations depending on the preparation conditions. Photoluminescence spectra revealed the presence of violet and blue emissions in the visible region. The calculated band gap energy is found to be in the range 3·0 to 3·6 eV. Spherical and lamellar shaped particles with crystallite size 10–41 nm are found in the film surface. X-ray photoelectron spectroscopy analysis confirms the highly non-stoichiometric nature of the films with dominant occurrence of Ce4+ (CeO2) and subsidiary occurrence of Ce3+ (Ce2O3).

Consequence of source material on the surface properties of nebulizer spray coated cerium oxide thin films

Cerium oxide thin films are coated on glass substrates by nebulizing spray pyrolysis technique using cerium nitrate and cerium chloride as a source material. Their crystallographic structures, surface morphology, optical properties and I–V characteristics are analyzed as a function of substrate temperature (300–500 °C). XRD is used to estimate the crystallographic texture, crystalline size, strain and lattice constant. All films exhibit a cubic fluorite structure with different preferred orientation depending on the preparation conditions. All the films exhibit dense, smooth and crack-free spherical nanostructures with some uneven surfaces in the range 400 nm. PL analysis indicates the presence of indigo and blue emission in the visible region centered at ∼425 and ∼467 nm respectively. UV-ViS spectra revealed that the films are transparent (70%) in the visible region. Optical parameters like refractive index, optical conductivity and band gap are calculated for different Ts. XPS analysis revealed the existence of Ce, O and C in the films. It demonstrates the prevalent occurrence of Ce4+ rather than Ce3+. I–V characteristics confirm the semiconducting behavior of cerium oxide thin films due to its linear response to applied voltage.

Nanostructured cerium oxide thin films by nebulized spray pyrolysis (NSP) technique: Impact of surfactants on the structural, optical and compositional properties

Cerium oxide thin films are deposited on glass substrates with different surfactants by nebulized spray pyrolysis technique. Their crystallographic structures, surface morphology, optical properties and I–V characteristics are analyzed as a function of surfactants. All films exhibit cubic fluorite structure with preferred orientations along (111) and (200) direction depending upon preparation conditions with an average grain size 37nm. Fourier Transform-Infra Red analysis confirmed the presence of terminal stretching (Ce=O) and phonon band (Ce–O) of the metal oxide network. The intensity of carbonation bands is diminished with the addition of amine groups. The films exhibit dense, smooth and crack-free tiny particles composed of closed chains, golf-ball, hollow spherical and slap shaped nanostructures with an average size 180nm. It also exhibits nicely separated well-outlined cones and spheres with rounded apex having an average roughness 121nm. Optical spectra reveal that the films are transparent (70%) in the visible region. Optical parameters like refractive index, optical conductivity and band gap are calculated for different surfactants. Photo Luminescence analysis indicates the presence of blue and green emission peaks in the visible region centered around ~425 and ~467nm attributed to the persistence of electron–phonon interaction between Ce4f and O2p bands. X-ray Photoelectron Spectroscopy analysis reveals the existence of Ce, O, Na and C atoms in the prepared films. It also brings out the dominant occurrence of Ce4+ rather than Ce3+ in the films. It is ensured that the rare earth compounds having unpaired electrons can give raise an extra satellite peak (923.5eV) due to photoelectron energy gain or loss assigned to finger print of CeO2 phase. The electrical conductivities are in the range 7.20×10−7 to 1.21×10−4S/cm for different surfactants.

Determination of Non-Stoichiometry in Mixed Conducting Oxide Thin Films of Arbitrary Chemistry

The dependence of oxygen non-stoichiometry on oxygen partial pressure and temperature is critical to many of the applications of non-stoichiometric oxides in electrochemical energy conversion processes. It has been increasingly recognized that electrochemical methods, in particular, AC impedance spectroscopy, can be used to evaluate this non-stoichiometry. The method is particularly useful for determining the properties of thin films, for which conventional thermogravimetric methods are inapplicable. To date, analysis of the ACIS data to extract non-stoichiometry values has relied on application of various simplifying assumptions for the thermodynamic behavior, limiting the approach to oxides with ideal solution behavior. In this work, we determine the oxygen non-stoichiometry of cerium oxide, which displays non-ideal behavior under certain thermodynamic conditions. The chemical capacitance of single crystal, epitaxial thin films of cerium oxide deposited on yttria stabilized zirconia substrates is measured and related to the oxygen non-stoichiometry using thermodynamic principles. This work will demonstrate the validity of the chemical capacitance measurements to reliably extract non-stoichiometry of a generalized oxide system.

Influences of the main anodic electroplating parameters on cerium oxide films

Abstract Cerium oxide thin films were fabricated onto 316 L stainless steel via a potentiostatically anodic electrodeposition approach in the solutions containing cerium(III) nitrate (0.05 M), ammonia acetate (0.1 M) and ethanol (10% V/V). The electrochemical behaviors and deposition parameters (applied potential, bath temperature, dissolving O 2 and bath pH) have been investigated. Results show that, the electrochemical oxidation of Ce 3+ goes through one electrochemical step, which is under charge transfer control. The optimum applied potential for film deposition is 0.8 V. Bath temperature plays a significant effect on the deposition rate, composition (different colors of the film) and surface morphology of the deposits. Due to the hydrolysis of Ce 3+ , cerous hydroxide is facility to form when the bath temperature is higher than 60 °C. The electroplating bath pH is another key role for the anodic deposition of cerium oxide thin films, and the best bath pH is around 6.20. N 2 or O 2 purged into the bath will result in film porosities and O 2 favors cerium oxide particles and film generation.

Structural, morphological and optical properties of spray deposited Mn-doped CeO2 thin films

Cerium oxide and manganese (Mn) doped cerium oxide thin films on glass substrates were prepared by home built spray pyrolysis system. The effect of Mn doping on the structural, morphological and optical properties of CeO2 films were studied. It was found that both the undoped and doped CeO2 films were polycrystalline in nature but the preferential orientation and grain size changed upon doping. Atomic force micrograph showed a complete changeover of surface morphology from spherical to flake upon doping. A water contact angle result displayed the hydrophobic nature of the doped CeO2 film. Optical properties indicated an increase in band-gap and a decrease in transmittance upon doping owing to Moss–Burstein effect and inverse Moss–Burstein effects. Other optical properties such as refractive index, extinction coefficient and dielectric constant as a function of doping were analysed and reported.

HAXPES study of CeOx thin film–silicon oxide interface

Investigation of cerium oxide thin film deposition on silicon and silicon oxide is important due to many possible applications of cerium oxide based micro-systems in electronics and catalysis. rf-Magnetron sputtering is technologically the most suitable method of preparation of such systems. Mechanism of film growth is strongly influenced by interaction of Ce atoms with the substrate and their oxidation by oxygen containing rf plasma. We show using hard X-ray photoelectron spectroscopy with high information depth that cerium is reducing silicon oxide by forming complex silicate phase at the interface with Ce in the 3+ state. For this reason composition of very thin films of cerium oxide is strongly influenced by thin film–substrate interaction. A coating of the silicon oxide substrate by an intermediate thin carbon film provides conductive substrate for electrocatalytic applications and decreases the silicon oxide substrates–cerium oxide interaction essentially.

Preparation of Magnetron Sputtered Thin Cerium Oxide Films with a Large Surface on Silicon Substrates Using Carbonaceous Interlayers

The study focuses on preparation of thin cerium oxide films with a porous structure prepared by rf magnetron sputtering on a silicon wafer substrate using amorphous carbon (a-C) and nitrogenated amorphous carbon films (CNx) as an interlayer. We show that the structure and morphology of the deposited layers depend on the oxygen concentration in working gas used for cerium oxide deposition. Considerable erosion of the carbonaceous interlayer accompanied by the formation of highly porous carbon/cerium oxide bilayer systems is reported. Etching of the carbon interlayer with oxygen species occurring simultaneously with cerium oxide film growth is considered to be the driving force for this effect resulting in the formation of nanostructured cerium oxide films with large surface. In this regard, results of oxygen plasma treatment of a-C and CNx films are presented. Gradual material erosion with increasing duration of plasma impact accompanied by modification of the surface roughness is reported for both types of films. The CNx films were found to be much less resistant to oxygen etching than the a-C film.

The Composition-Dependent Color Evolution of Anodic Electrodeposited Cerium Oxide Thin Film

Cerium oxide thin films with various colors were deposited onto 316L stainless steel using anodic electrodeposition approach. The correlation between color, composition and deposition time has been established. Results show that the film color evolves from golden yellow (1.5 h), purple (3 h), blue (5 h), gray-green (7 h) and turns back to yellow (12 h) again, and all these colored films are stable in the ambient conditions. The film color is related to both the contents of Ce(III) and hydroxide species in the films. The relative content of Ce(III) increases from 21.19% to 27.57% with increasing the deposition time from 1.5 h to 7 h, and then decreases to 22.93% for the film deposited at 12 h. The content of hydroxide species shows the same variation trend as Ce(III) with the deposition time.

High permittivity cerium oxide thin films on AlGaN/GaN heterostructures

Cerium oxide (CeO2) thin films have been grown by metal-organic chemical vapor deposition on AlGaN/GaN heterostructures and their insulating properties as gate dielectric layer have been explored. The deposited thin films have been found to be textured on the GaN based heterostructures and exhibited a permittivity of 26. This high permittivity value and large band gap are certainly advantageous with respect to other reported materials for the metal insulator semiconductor high electron mobility transistor application. The reduced leakage current density clearly suggests that these CeO2 films are very promising as gate dielectric for AlGaN/GaN transistors low power consumption technology.