Cerium Deposition Research Articles

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.

Rational Development of Guanidinate and Amidinate Based Cerium and Ytterbium Complexes as Atomic Layer Deposition Precursors: Synthesis, Modeling, and Application.

Owing to the limited availability of suitable precursors for vapor phase deposition of rare‐earth containing thin‐film materials, new or improved precursors are sought after. In this study, we explored new precursors for atomic layer deposition (ALD) of cerium (Ce) and ytterbium (Yb) containing thin films. A series of homoleptic tris‐guanidinate and tris‐amidinate complexes of cerium (Ce) and ytterbium (Yb) were synthesized and thoroughly characterized. The C‐substituents on the N‐C‐N backbone (Me, NMe2, NEt2, where Me=methyl, Et=ethyl) and the N‐substituents from symmetrical iso‐propyl (iPr) to asymmetrical tertiary‐butyl (tBu) and Et were systematically varied to study the influence of the substituents on the physicochemical properties of the resulting compounds. Single crystal structures of [Ce(dpdmg)3] 1 and [Yb(dpdmg)3] 6 (dpdmg=N,N'‐diisopropyl‐2‐dimethylamido‐guanidinate) highlight a monomeric nature in the solid‐state with a distorted trigonal prismatic geometry. The thermogravimetric analysis shows that the complexes are volatile and emphasize that increasing asymmetry in the complexes lowers their melting points while reducing their thermal stability. Density functional theory (DFT) was used to study the reactivity of amidinates and guanidinates of Ce and Yb complexes towards oxygen (O2) and water (H2O). Signified by the DFT calculations, the guanidinates show an increased reactivity toward water compared to the amidinate complexes. Furthermore, the Ce complexes are more reactive compared to the Yb complexes, indicating even a reactivity towards oxygen potentially exploitable for ALD purposes. As a representative precursor, the highly reactive [Ce(dpdmg)3] 1 was used for proof‐of‐principle ALD depositions of CeO2 thin films using water as co‐reactant. The self‐limited ALD growth process could be confirmed at 160 °C with polycrystalline cubic CeO2 films formed on Si(100) substrates. This study confirms that moving towards nitrogen‐coordinated rare‐earth complexes bearing the guanidinate and amidinate ligands can indeed be very appealing in terms of new precursors for ALD of rare earth based materials.

The synergistic effect of cerium acetate and sodium sulphate on corrosion inhibition of AA2024-T3 at various temperatures

The present work examines the corrosion inhibition of aluminium alloy 2024-T3 immersed in NaCl+Ce(OAc)3 and NaCl+Ce(OAc)3+Na2SO4 solutions to evaluate the synergetic effect between cerium and sulphate ions at various temperatures (5 °C, 25 °C and 50 °C). The electrochemical properties were studied using short-term potentiodynamic measurements and long-term electrochemical impedance measurements. The surface topography, morphology and composition of cerium deposits formed on the alloy surface after two days of immersion were evaluated using scanning electron microscopy combined with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The results revealed an efficient long-term (up to 8 weeks) corrosion inhibition in NaCl+Ce(OAc)3 that was superior in the NaCl+Ce(OAc)3+Na2SO4 solution, especially at lower temperatures (5 °C > 25 °C > 50 °C). The composition of the Ce-based film varied with the temperature and the presence of Na2SO4, resulting in different mixtures of Ce(III) and Ce(IV) species. The synergistic effect of cerium and sulphate ions on corrosion inhibition was reflected by a higher degree of cerium oxidation from Ce3+ to Ce4+ at a low temperature and the incorporation of sulphates into the formed film, which protected the surface from the corrosion medium more efficiently.

Electrochemical study of reduction Ce(III) ions and production of high purity metallic cerium by electrorefining in fused LiCl-KCl eutectic

Abstract The electrode reactions of the Ce3+/Ce couple in molten LiCl–KCl eutectic in the temperature range 723–823 K on solid Mo electrodes were investigated by electrochemical techniques. The mechanism of deposition of metallic cerium has been established. It was found that the cathode reaction is irreversible and proceeds in one stage. The apparent standard Gibbs energy of CeCl3 formation from the elements was calculated. The values of enthalpy and entropy were equal: ΔH* = − 1000.2 kJ/mol, ΔS* = 166.0 J/mol·K. The conditions of high-purity cerium production have been studied. The chemical structure of cathode deposits as well as the surfaces of the crucible were investigated by XRD, ICP and SEM-EDS methods. It was established that the best results for purification of the cathode product from impurities were achieved in the range 40–60 mA/cm2 using a two-stage electrolysis. The amounts of the main impurities in the final product were 0.005 wt% Al, 0.0021 wt% Fe, and 0.003 wt% Si. The total purity of metallic cerium after cleaning was increased up to 99.971 wt% if a vitreous carbon crucible was used.

Fabrication of miniature 141Ce sources by chemical deposition towards possible use in the performance evaluation of gamma cameras - A feasibility study

141Ce sources were fabricated for quality assurance of gamma cameras. The fabrication process consisted of electro-deposition of Ni on a Cu sphere in 0.01 N H2SO4 containing 30 mg/mL H3BO3 and 50 μg of NiSO4·7H2O at pH 2–3 followed by deposition of 141Ce on it. > 95% deposition of 141Ce on substrate could be achieved at pH 5. Source core was loaded in custom-made Al holder. Autoradiography confirmed uniform activity distribution. SEM and EDS analyses confirmed deposition of Cerium on substrate.

Role of Oxidative Stress and Apoptosis in the Hepatic Toxicity Induced by Cerium Oxide Nanoparticles Following Intratracheal Instillation in Male Sprague-Dawley Rats

Inhaled cerium oxide (CeO₂) nanoparticles have been shown to be capable of translocation to the liver where they can cause dose dependent toxic effects. Herein, we investigate if the deposition of cerium in the liver is linked to increased oxidative stress and cellular apoptosis. Specific pathogen free male Sprague-Dawley rats were instilled with either vehicle (saline) or CeO₂ nanoparticles (7.0 mg/kg) and euthanized 1, 3, 14, 28, 56, or 90 days post exposure.

On the Role of pre-treatment of Aluminum Substrate on Deposition of Cerium Based Conversion Layers and Their Corrosion-Protective Ability

On the Role of pre-treatment of Aluminum Substrate on Deposition of Cerium Based Conversion Layers and Their Corrosion-Protective Ability

Synthesis and in vitro characterization of cerium oxide mixed calcium oxy fluoro borophosphate bioactive glasses by means of spectroscopic studies

The main objective of this study is to achieve Ce substituted hydroxy apatite (HAp) deposition on the surface of the bio-active glasses which is more affective in antibacterial activity. Calcium oxy fluoro borophosphate glasses (with BaO as modifier) doped with different concentrations of Ce2O3 were prepared by melt quenching techniques. In vitro bioactivity studies were performed by soaking the samples in simulated body fluid (SBF) for about 30 days. The XRD and SEM studies have revealed the deposition of cerium substituted crystalline HAp coating on the surface of the post immersed glasses. The formation of HAp layer is further confirmed by IR and Raman spectral studies. The possible site preference of cerium ions in the HAp layer has been discussed using the results of above mentioned studies. The information regarding dependence of the magnitude of HAp layer developed on the concentration of Ce2O3 dopant is obtained by degradation studies viz., weight loss of the samples and the variation of pH of the residual solutions. The analysis of the results of degradability together with X-ray diffraction (XRD), Infrared (IR), Raman and optical absorption spectra indicated the increasing magnitude of Ce-HAp with the concentration of Ce2O3. Some of the characterization studies have also pointed out the co-presence of Ce ions in Ce4+ oxidation state along with Ce3+ state in the glass samples. The simultaneous presence of cerium ions in these two states in the crystalline HAp layer is predicted to be more useful in promoting the antibacterial activity of the glasses.

Study of selective deposition mechanism of cerium-based conversion coating on Rheo-HPDC aluminium-silicon alloys

Cerium-based conversion coatings were deposited on Rheo-High Pressure Die Cast (HPDC) Al-Si alloys by immersion in cerium nitrate aqueous solutions. Rheocast Al-Si alloys have a heterogeneous microstructure and present a challenge for the conversion treatment. Different parameters were studied to optimize the conversion coating, and NaCl or H2O2 were also added to the solution to modify or accelerate the deposition process. The mechanism of the coating formation was studied by means of focused ion beam milling (FIB) assisted SEM. The results show that applying cerium-based conversion coating to Al-Si alloys, is possible and a preferential deposition is obtained due to the presence of iron-rich intermetallic particles inside the eutectic region. The formation mechanism of selectively deposited cerium-based conversion coating includes dissolution of aluminium matrix, selective dissolution of aluminium from the noble intermetallic particles, oxidation of iron from the intermetallic particles, and the deposition of cerium hydroxide/oxide layer. The results reveal that the improvement in corrosion resistance in the presence of selectively deposited cerium-based conversion coating is more significant compared to the homogenous coating deposited from the conversion solution containing H2O2.

Synthesis of organosiloxane-coated SiO2/CeO2 with multilayered hierarchical structure and its application in optical diffusers

In this study, a simple, convenient and green approach for the preparation of organosiloxane-coated SiO2/CeO2 (SiO2/CeO2/poly(VTMS)) with multilayered hierarchical structure is demonstrated by consecutive surface cerium deposition and organosiloxane grafting on the bare silica spheres. The results of the UV–Vis spectrum and photoluminescence analysis suggest that the fillers may be potentially applied in UV absorbers and bioimaging materials. Moreover, the optical diffusers based on the multilayered spheres can be prepared via a solvent-free UV curing process and exhibit enhanced properties like suitable light transmittance, good diffusion capacity and low-incident angle dependence, which are critical for the optical diffusers. In addition, when the concentration of the fillers was 15 wt%, the optical diffusers presented superior light-diffusing properties among all the as-prepared samples. Thus, the films based on the SiO2/CeO2/poly(VTMS) with multilayered hierarchical structure may open up new possibilities in applications as multifunctional light diffusion films in liquid crystal displays.

Deposition and Characterization of Cerium-Based Conversion Coating on HPDC Low Si Content Aluminum Alloy

Cerium-based conversion coatings were deposited on high pressure die cast (HPDC) Al-Si alloys using an immersion method. Hydrogen peroxide and sodium chloride were added to the conversion solution to accelerate the coating formation and to understand its formation mechanism. These studies showed that the deposition of cerium hydroxide/oxide conversion layer starts from iron-rich intermetallic particles, which are located inside the eutectic region and then the coating growth continues to cover the entire alloy surface. This phenomenon passivates the active interfaces between iron-rich intermetallic particles and/or the eutectic silicon phase and the aluminum matrix, which are prone to localized corrosion in chloride ions containing environments. Accordingly, values of the total impedance in EIS measurements significantly increased for the treated substrates. Morphologies of the conversion coatings and the oxidation state of cerium compounds were found to be dependent on the composition of the solution and the presence of chloride ions and/or hydrogen peroxide. Aluminum alloy with higher silicon content showed a more active surface during immersion in the conversion solution. This makes it more difficult to be treated using aggressive conversion solutions.

Preparation of Thin Melanin-Type Films by Surface-Controlled Oxidation.

The preparation of thin melanin films suitable for applications is challenging. In this work, we present a new alternative approach to thin melanin-type films using oxidative multilayers prepared by the sequential layer-by-layer deposition of cerium(IV) and inorganic polyphosphate. The interfacial reaction between cerium(IV) in the multilayer and 5,6-dihydroxyindole (DHI) in the adjacent aqueous solution leads to the formation of a thin uniform film. The oxidation of DHI by cerium(IV) proceeds via known melanin intermediates. We have characterized the formed DHI-melanin films using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-vis spectroscopy, and spectroelectrochemistry. When a five-bilayer oxidative multilayer is used, the film is uniform with a thickness of ca. 10 nm. Its chemical composition, as determined using XPS, is typical for melanin. It is also redox active, and its oxidation occurs in two steps, which can be assigned to semiquinone and quinone formation within the indole structural motif. Oxidative multilayers can also oxidize dopamine, but the reaction stops at the dopamine quinone stage because of the limited amount of the multilayer-based oxidizing agent. However, dopamine oxidation by Ce(IV) was studied also in solution by UV-vis spectroscopy and mass spectrometry in order to verify the reaction mechanism and the final product. In solution, the oxidation of dopamine by cerium shows that the indole ring formation takes place already at low pH and that the mass spectrum of the final product is practically identical with that of commercial melanin. Therefore, layer-by-layer formed oxidative multilayers can be used to deposit functional melanin-type thin films on arbitrary substrates by a surface-controlled reaction.

Growth of cerium tungstate epitaxial layers: influence of temperature

Thin films of cerium tungstate prepared in situ by cerium deposition in oxygen atmosphere onto the W(100) single‐crystal were investigated by means of photoelectron spectroscopy and low‐energy electron diffraction (LEED). The studied temperature range was 173–1073 K. It was found that the temperature necessary for the oriented growth of Ce6WO12(100) was 673 K, and at higher temperatures, the LEED pattern improved. Photoemission data revealed the partial formation of CeO2 on the surface at preparation temperatures below 473 K due to limited diffusion of tungsten atoms from the substrate. Copyright © 2015 John Wiley & Sons, Ltd.

Synthesis and application of CeO2–NiO loaded TiO2 nanofiber as novel catalyst for hydrogen production from sodium borohydride hydrolysis

A simple electrospinning technique was used to fabricate cerium–nickel loaded titanium nanofibers for efficient use in catalytic applications for hydrogen production. The prepared nanofibers were characterized by the SEM (scanning electron microscopy), EDX (energy dispersive X-ray spectrometer), FTIR (fourier transform infrared spectroscopy), XRD (X-ray diffraction), BET (Brunauer–Emmett–Teller) technique and TEM (transmission electron microscopy). The SEM and TEM analyses showed that fabricated nanofibers were defect-free and had well deposition of cerium and nickel. The BET analysis concluded that cerium–nickel loaded titanium oxide nanofiber showed greater surface area and high porosity than other nanofiber compositions. The experimental results showed that addition of cerium with nickel enhanced the catalytic activity significantly, but excessive cerium-loading had a negative effect on sodium borohydride hydrolysis. Activation energy of cerium–nickel loaded titanium oxide nanofiber was comparatively lesser than nickel-loaded titanium oxide nanofiber. It was evident that cerium had a beneficial effect in the catalytic activity for hydrogen production. Furthermore, it is very convenient to recover the catalyst at the end of reactions; the solid catalyst left could be readily reused for the next consecutive cycles.

RHEED and XPS study of cerium interaction with SnO2 (110) surface

Abstract Interaction of cerium with thin epitaxial film of tin dioxide with (110) surface orientation was investigated by methods of X-ray Photoelectron Spectroscopy (XPS) and Reflection High Energy Electron Diffraction (RHEED). Strong interaction of cerium and tin leads to cerium diffusion into the tin dioxide bulk and formation of tin–cerium mixed oxide indicated by highly non-stoichiometric cerium oxide Ce 3d core level spectrum. This process is more pronounced with higher temperature during the deposition of cerium. With higher amount of deposited cerium, the tin dioxide substrate is gradually saturated with cerium atoms and the cerium atoms start to create 3D epitaxial clusters of cerium oxide with the (100) and (111) crystallographic planes parallel to the surface. The clusters show a higher oxidation state than the cerium atoms located in the tin oxide bulk. Oxygen required for the creation of these clusters comes from the tin dioxide substrate, which is partially reduced to metallic tin in this process. At the end of the experiment, we obtained a multilayer system consisting of layers of partially reduced tin dioxide, tin–cerium mixed oxide and top layer of partially reduced epitaxial grains of cerium oxide.

Electrochemical formation process and phase control of Mg-Li-Ce alloys in molten chlorides

An electrochemical approach for the preparation of Mg-Li-Ce alloys by co-reduction of Mg, Li and Ce on a molybdenum electrode in KCl-LiCl-MgCl2-CeCl3 melts at 873 K was investigated. Cyclic voltammograms (CVs) and square wave voltammograms indicated that the underpotential deposition (UPD) of cerium on pre-deposited magnesium led to the formation of Mg-Ce alloys at electrode potentials around −1.87 V. The order of electrode reactions was as follows: discharge of Mg(II) to Mg-metal, UPD of Ce on the surface of pre-deposited Mg with formation of Mg-Ce alloys, discharge of Ce(III) to Ce-metal and after that the discharge of Li+ with the deposition of Mg-Li-Ce alloys, which was investigated by CVs, chronoamperometry, chronopotentiometry and open circuit chronopotentiometry. X-ray diffraction (XRD) illuminated that Mg-Li-Ce alloys with different phases were obtained via galvanostatic electrolysis by different current densities. The microstructures of Mg-Li-Ce alloys were characterized by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. The analysis of energy dispersive spectrometry (EDS) showed that Ce existed at grain boundaries to restrain the grain growth. The compositions and the average grain sizes of Mg-Li-Ce alloys could be obtained controllably corresponding with the phase structures of the XRD patterns.

Dissolution properties of cerium dibutylphosphate corrosion inhibitors

The corrosion inhibitor cerium dibutylphosphate, Ce(dbp)3, prevents corrosion by cerium and dbp deposition at the alkaline cathode and acidic anode respectively. The pH dependent Ce(dbp)3 solubility seems to play an essential role in the inhibition degree. We found that Ce(dbp)3 scarcely dissolves in water with a ̃1 mM solubility limit between pH 2 and 9, whereas at pH 1, we found ̃3 mM due to protonation of dbp, and for pH >9, the cerium precipitated as Ce(OH)3. We believe that the Ce(dbp)3 dissolution process is an important aspect for understanding its release from coatings and thus the corrosion inhibition. In case of a pressed Ce(dbp)3 tablet, its dissolution is dominated by transport of dissolved Ce(dbp)3 across a stagnant diffusion layer. The chemical bond strength between cerium and dbp is a major factor in their transport. The infrared spectrum of Ce(dbp)3 powder revealed a covalent-like bond, while the molar conductivity showed complete dissociation, so Ce(dbp)3 transports in water as separate ions.

Preparation and morphology of nano-size ceria by a stripping precipitation using oxalic acid as a precipitating agent

The precursors organic cerium deposits were obtained by a stripping precipitation method from cerium-loaded P507 organic phase using oxalic acid as a precipitating agent and nano-sized ceria particles were prepared by calcining the precursors at 500 °C. The morphologies, phase structure of the precursors and ceria particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TG-DSC) and infrared spectroscopy analysis (FTIR). The results indicated that the concentration of oxalic acid had a little impact on the morphology of the precursors, which was blocky-shape Ce2(C2O4)3·10H2O with a monoclinic lattice structure. With the volume ratio of organic phase and oxalic acid aqueous solution (aqueous phase) varied from 1:3 to 1:6, the morphologies of the precursors Ce2(C2O4)3·10H2O precipitates gradually changed from inhomogeneous blocky-shape to uniform spherical particles. The precursors could be turned to CeO2 crystal particles with a fluorite structure by calcining, and the products ceria particles were similar in the size and morphology to the precursors.

Influence of oxidizing ability of the medium on the growth of lanthanide layers on galvanized steel

Protection mechanisms offered to galvanized steel by lanthanide salts in a 0.1 M NaCl solution were investigated by using electrochemical techniques such as polarization curves, electrochemical impedance spectroscopy (EIS), scanning vibrating electrode technique (SVET) and surface analysis such as scanning electron microscope (SEM) and glow discharge optical emission spectrometry (GDOES). The role of the oxidizing ability of the medium was studied by changing the aeration conditions: aerated, saturated, deaerated and acid deaerated solutions. In aerated solution, the cerium deposition quickly offers an inhibition of the oxygen reduction. Current density cartographies (SVET) are consistent with surface analysis and other electrochemical techniques.

A route to continuous ultra-thin cerium oxide films on Cu(1 1 1)

The growth and morphology of ultra-thin CeO 2(1 1 1) films on a Cu(1 1 1) substrate were investigated by means of low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). The films were grown by physical vapor deposition of cerium in an oxygen atmosphere at different sample temperatures. The preparation procedure is based on a modification of a previous method suggested by Matolin and co-workers [1], involving growth at elevated temperature (520 K). Here, LEED shows good long range ordering with a “(1.5 × 1.5)” superstructure, but STM reveals a three-dimensional growth mode (Vollmer–Weber) with formation of a closed film only at larger thickness. Using a kinetically limited growth process by reactive deposition at low sample temperatures (100 K) and subsequent annealing, we show that closed layers of ceria with atomically flat terraces can be prepared even in the regime of ultra-thin films (1.5 ML). Closed and atomically flat ceria films of larger thickness (3 ML) are obtained by applying a multistep preparation procedure, in which successive ceria layers are homoepitaxially grown on this initial film. The resulting overlayers show strong similarities with the morphology of CeO 2(1 1 1) single crystal surfaces, suggesting the possibility to model bulk ceria by thin film systems.