Ceria Samples Research Articles

N2 as an Efficient IR Probe Molecule for the Investigation of Ceria-Containing Materials.

Ceria and ceria-based catalysts are very important in redox and acid-base catalysis. Nanoceria have also been found to be important in biomedical applications. To design efficient materials, it is necessary to thoroughly understand the surface chemistry of ceria, and one of the techniques that provides such information about the surface is the vibrational spectroscopy of probe molecules. Although the most commonly used probe is CO, it has some disadvantages when applied to ceria and ceria-based catalysts. CO can easily reduce the material, forming carbonate-like species, and can be disproportionate, thus modifying the surface. Here, we offer a pioneering study of the adsorption of 15N2 at 100 K, demonstrating that dinitrogen can be more advantageous than CO when studying ceria-based materials. As an inert gas, N2 is not able to oxidize or reduce cerium cations and does not form any surface anionic species able to modify the surface. It is infrared and transparent, and thus there is no need to subtract the gas phase spectrum, something that often increases the noise level. Being a weaker base than CO, N2 has a negligible induction effect. By using stoichiometric nano-shaped ceria samples, we concluded that 15N2 can distinguish between surface Ce4+ sites on different, low index planes; with cations on the {110} facets and on some of the edges, Ce4+-15N2 species with IR bands at 2258-2257 cm-1 are formed. Bridging species, where one of the N atoms from the molecule interacts with two Ce4+ cations, are formed on the {100} facets (2253-2252 cm-1), while the interaction with the {111} facets is very weak and does not lead to the formation of measurable amounts of complexes. All species are formed by electrostatic interaction and disappear during evacuation at 100 K. In addition, N2 provides more accurate information than CO on the acidity of the different OH groups because it does not change the binding mode of the hydroxyls.

The effect of morphological and textural properties of ceria on its adsorption affinity towards CO2

The adsorption of CO2 on both commercial and prepared porous ceria samples was investigated. The two samples exhibited distinctive variations in morphology and texture. The porous sample, characterized by a sponge-like morphology and high surface area, demonstrated a superior affinity for CO2 compared to the non-porous sample with a plate-like structure. Additionally, at elevated temperatures, the adsorption capacity of both samples decreased; however, the porous ceria sample continued to adsorb more CO2 than the commercial sample. Furthermore, the reusability of the porous ceria sample was examined, revealing a more favorable adsorption behavior compared to the commercial sample, and notably, it exhibited this performance without necessitating any thermal treatment.

Ceria-Catalyzed Hydrolytic Cleavage of Sulfonamides.

Nanoceria is a promising nanomaterial for the catalytic hydrolysis of a wide variety of substances. In this study, it was experimentally demonstrated for the first time that CeO2 nanostructures show extraordinary reactivity toward sulfonamide drugs (sulfadimethoxine, sulfamerazine, and sulfapyridine) in aqueous solution without any illumination, activation, or pH adjustment. Hydrolytic cleavage of various bonds, including S-N, C-N, and C-S, was proposed as the main reaction mechanism and was indicated by the formation of various reaction products, namely, sulfanilic acid, sulfanilamide, and aniline, which were identified by HPLC-DAD, LC-MS/MS, and NMR spectroscopy. The kinetics and efficiency of the ceria-catalyzed hydrolytic cleavage were dependent on the structure of the sulfonamide molecule and physicochemical properties of Nanoceria prepared by three different precipitation methods. However, in general, all three ceria samples were able to cleave SA drugs tested, proving the robust and unique surface reactivity toward these compounds inherent to cerium dioxide. The demonstrated reactivity of CeO2 to molecules containing sulfonamide or even sulfonyl (and similar) functional groups may be significant for both heterogeneous catalysis and environmentally important degradation reactions.

A comparative study about the influence of nitrogen doping and oxygen vacancies on the photocatalytic performance of ceria

Aimed to evaluate the influence of nitrogen doping on the photocatalytic performance of ceria, three ceria samples, including nitrogen doped, rich oxygen vacancies contained and contrastive ceria were prepared from the decomposition of CeCO3OH under varied atmospheres. The physico-chemical characterizations and photocatalytic properties towards methylene blue (MB) and tetracycline (TC) of the obtained ceria were comparatively discussed in detail. Nitrogen-doped CeO2 exhibited significantly superior photocatalytic activities compared to CeO2 with rich oxygen vacancies for MB and TC photodegradation, which is mainly attributed to the significantly enhanced separation of photo-generated carriers (e−/h+). Density Functional Theory (DFT) simulation suggests that the introduced impurity states of N-doped CeO2 advance the formation and separation of e−/h+. Moreover, the electrons are simultaneously excited from N 2p and O 2p, which further elevates the carrier concentration on the nitrogen-doped CeO2, and promotes the effect of e− during the photodegradation. The obtained results offer powerful evidences for the significant enhancement on photocatalytic performances of nitrogen doped CeO2.

One-pot auto-combustion synthesis, characterization, and photocatalytic performance of cobalt doped porous ceria nanoparticles

The three-dimensional porous ceria (CeO2) nanostructures and cobalt (Co) doped porous ceria with different cobalt contents (1 %, 2.5 %, 5 %, and 10 % wt%) were prepared by using the auto-combustion technique. Several characterization techniques, including ICP elemental analysis, XRD, DR UV-Vis, SEM, and TEM, were utilized to describe the fabricated products. The findings confirmed the incorporation of cobalt ions into the ceria framework. Furthermore, the light absorption property of cobalt-doped porous ceria samples was observed to be red-shifted, with the calculated bandgap decreasing from 3 to 2.1 eV for neat porous ceria and 10 % Co doped ceria, respectively. The photocatalytic efficiency of cobalt-doped porous CeO2 was investigated in the decolourization of methyl green dye by utilizing visible light illumination. The photocatalytic data obtained revealed a remarkable increase in activity that is nearly three times greater than the un-doped ceria sample. Furthermore, the best performed cobalt-doped ceria sample was reusable until the fourth consecutive reaction without treatment.

Electrochemical Impedance Spectroscopy Integrated with Environmental Transmission Electron Microscopy.

The concept of combining electrical impedance spectroscopy (EIS) with environmental transmission electron microscopy (ETEM) is demonstrated by testing a specially designed micro gadolinia-doped ceria (CGO) sample in reactive gasses (O2 and H2 /H2 O), at elevated temperatures (room temperature-800 °C) and with applied electrical potentials. The EIS-TEM method provides structural and compositional information with direct correlation to the electrochemical performance. It is demonstrated that reliable EIS measurements can be achieved in the TEM for a sample with nanoscale dimensions. Specifically, the ionic and electronic conductivity, the surface exchange resistivity, and the volume-specific chemical capacitance are in good agreement with results from more standardized electrochemical tests on macroscopic samples. CGO is chosen as a test material due to its relevance for solid oxide electrochemical reactions where its electrochemical performance depends on temperature and gas environment. As expected, the results show increased conductivity and lower surface exchange resistance in H2 /H2 O gas mixtures where the oxygen partial pressure is low compared to experiments in pure O2 . The developed EIS-TEM platform is an important tool in promoting the understanding of nanoscale processes for green energy technologies, e.g., solid oxide electrolysis/fuel cells, batteries, thermoelectric devices, etc.

Investigation of Cu-doped ceria through a combined spectroscopic approach: Involvement of different catalytic sites in CO oxidation

Copper-ceria mixed oxides are widely considered promising catalysts for oxidation reactions, especially when the participation of lattice oxygen is required. However, the mechanistic understanding of these catalytic systems is still incomplete, due to their considerable complexity. In fact, copper doping of ceria results in the formation of a significant number of different interacting sites in continuous evolution during the catalytic processes. In the present study, pure and Cu-doped ceria samples were deeply investigated through combined spectroscopic techniques, i.e. XPS, EPR, and in situ FTIR and Raman spectroscopy. Through this systematic approach, the copper sites and lattice defects responsible for the enhanced CO oxidation activity of doped ceria were elucidated. Superficial Cu+ species and small Cu0 clusters promote the adsorption of CO at low temperature, while isolated Cu2+ monomers and dimers well-dispersed in the ceria matrix foster lattice oxygen mobility, involving the sub-surface in the redox phenomena. Consequently, the structure of Cu-doped ceria undergoes substantial modifications throughout CO oxidation in the absence of O2, with the formation of oxygen vacancy clusters. Anyway, these changes are reversible, and structural reorganization in the presence of O2 can occur even at room temperature. The excellent performance of Cu-doped ceria eventually stems from the effective cooperation among the different catalytic sites in the mixed oxide.

Ceria nanomaterials containing ytterbium: low and high concentration - luminescence analyzed in the near infrared region.

Lanthanide based ceria nanomaterials are important practical materials due to the redox properties that are useful in the avenues pertaining to technology and life sciences. Sub 10 nm spherical and highly monodisperse Ce1-xYbxO2-y (0.04 ≤ x ≤ 0.22) nanoparticles were synthesized by thermal decomposition, annealed separately at 773 K and 1273 K for 2 hours and characterized. Elemental mapping for Yb3+ doped ceria nanoparticles shows homogeneous distribution of Yb3+ atoms in the ceria with low Yb3+ content annealed at 773 K and 1273 K for 2 hours. However, clusters are observed for 773 K annealed ceria samples with high concentration of Yb3+. These clusters are not detected in 1273 K annealed nanomaterials. Introducing small amounts of Yb3+ ions into the ceria lattice as spectroscopic probes can provide detailed information about the atomic structure and local environments allowing the monitoring of small structural changes, such as clustering. The emission spectra observed at room temperature and at 4 K have a manifold of bands that corresponds to the 2F5/2 → 2F7/2 transition of Yb3+ ions. Some small shifts are observed in the Stark splitting pattern depending on the sample and the annealing conditions. The deconvolution by PARAFAC analysis yielded luminescence decay kinetics as well as the associated luminescence spectra of three species for each of the low Yb3+ doped ceria samples annealed at 773 K and one species for the 1273 K annealed samples. However, the ceria samples with high concentration of Yb3+ annealed at the two temperatures showed only one species with lower decay times as compared to the low Yb3+ doped ceria samples.

Chemical expansion of CeO2−δ and Ce0.8Zr0.2O2−δ thin films determined by laser Doppler vibrometry at high temperatures and different oxygen partial pressures

The chemical expansion of ceria (CeO2−δ) and ceria-zirconia (Ce0.8Zr0.2O2−δ, CZO80) thin films is investigated by high-temperature laser Doppler vibrometry (LDV) at temperatures from 600 to 950 °C. The films are deposited on single-crystalline 8 mol-% yttria-stabilized zirconia substrates, which act as pumping cells to adjust oxygen non-stoichiometry in the thin films. Oxygen deficiency causes film expansion, leading to mechanical strain that bends the sample. The total displacement, i.e., the sum of bending and film-thickness change, is determined contact-less by LDV. A differential laser Doppler vibrometer (D-LDV) is realized to enable measurements on a very long time scale, which is necessary due to the long equilibrium times of the ceramic films. These displacements are compared to those acquired with a commercial single-point laser Doppler vibrometer (SP-LDV) for motions above 1 Hz. Here, both devices yield similar results. CZO80 films are found to bend a substrate much more than ceria films under similar experimental conditions. A model describing the displacement of the sample is derived from the Stoney model and applied to calculate deflections using literature data. The displacements at the center of the CZO80 sample measured with the SP-LDV increase from 0.18 nm at 10 Hz and 600 °C to 32.7 nm at 0.1 Hz and 800 °C. For ceria, the displacements range from 1.6 nm (10 Hz, 800 °C) to 79.4 nm (0.1 Hz, 900 °C). The D-LDV enables the detection of quasi-static displacements at very low frequencies. The ceria sample exhibits 218 nm at 0.001 Hz and 800 °C.

Capturing CO2 by ceria and ceria-zirconia nanomaterials of different origin.

Ceria and ceria-zirconia nanomaterials of different origin were studied in order to elucidate the role of their structural and textural characteristics in controlling the performance towards CO2 capture. Two commercial cerias and two home-prepared samples, CeO2 and CeO2-ZrO2 (75% CeO2) mixed oxide, were investigated. The samples were characterized by a number of analytical techniques including XRD, TEM, N2-adsorption, XPS, H2-TPR, Raman and FTIR spectroscopy. Static and dynamic CO2 adsorption experiments were applied to assess the CO2 capture performance. The type of surface species formed and their thermal stability were evaluated by in situ FTIR spectroscopy and CO2-TPD analysis. The two commercial ceria samples possessed similar structural and textural characteristics, formed the same types of carbonate-like surface species upon CO2 adsorption and, consequently, demonstrated almost identical CO2 capture performance under both static and dynamic conditions. The thermal stability of the adsorbed species increased in the order bidentate (B) carbonates, hydrogen carbonates (HC) and tridentate carbonates (T-III, T-II, T-I). Reduction of CeO2 increased the relative amount of the most strongly bonded T-I tridentate carbonates. Preadsorbed water led to hydroxylation and enhanced formation of hydrogen carbonates. Although the synthesized CeO2 sample had a higher surface area (by 30%) it showed a disadvantageous long mass transfer zone in the CO2-adsorption breakthrough curves. Because of its complex pore structure, this sample probably experiences severe intraparticle CO2 diffusion resistance. Having the same surface area as the synthesized CeO2, the mixed CeO2-ZrO2 oxide exhibited the highest CO2 capture capacity of 136 μmol g-1 under dynamic conditions. This was related to the highest concentration of CO2 adsorption sites (including defects) on this sample. The CeO2-ZrO2 system showed the lowest sensitivity to the presence of water vapor in the gas stream due to the lack of dissociative water adsorption on this material.

Visible light active Ni2+ doped CeO2 nanoparticles for the removal of methylene blue dye from water

The treatment of organic dye pollutants in water, by photocatalysis is getting much attention nowadays. In the present study, a series of visible light active Ni2+ doped ceria (CeO2) photocatalysts were synthesized by combining sol-gel and hydrothermal methods. X-ray diffraction patterns of the Ni2+ doped and undoped ceria nanoparticles represent a cubic fluorite structure. The thermal stability of the photocatalysts has been confirmed from thermogravimetric analysis (TGA) and the X-ray photoelectron spectroscopy (XPS) analysis confirms the effective doping of Ni2+ in ceria. Surface morphology and particle size were determined by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analysis. Compared to undoped ceria, Ni2+ doped ceria samples showed strong visible range absorption, among them, 5 wt % Ni2+ doped ceria exhibits the highest absorption. The photocatalytic activity of the samples was evaluated under direct sunlight, using methylene blue dye as a model system. 5 wt % Ni2+ doped ceria had the maximum photocatalytic activity, with 85.83% degradation efficiency.

Facile fabrication of efficient Pr2Ce2O7 ceramic nanostructure for enhanced photocatalytic performances under solar light

The design and synthesis of high-performance catalytic compounds for the decomposition and removal of wastewater containing hazardous contaminants are substantial for water remediation. Here, we report the efficient preparation of A 2 Ce 2 O 7 (A = Bi, Dy, and Pr) nanostructures and cerium dioxide nanoparticles utilizing barberry extract as an environmentally friendly reactant and their application as natural-based nanocatalysts to decompose and eliminate hazardous contaminants in an aqueous medium. The features of the produced oxide nanostructures were checked utilizing various techniques. The activity of the fabricated photocatalytic nanostructures was evaluated in the decomposition of Acid Red 14 contaminants under visible light. The outcomes revealed that the kind of trivalent element introduced meaningfully affects the dimension, architecture, optical properties, porosity, and catalytic performance of the ceria sample. Compared to other nanocatalysts, porous Pr 2 Ce 2 O 7 nanostructures exhibited enhanced photodegradation yield for decomposing Acid Red 14 (99.2%). The porous Pr 2 Ce 2 O 7 sample also demonstrated stable performance after ten cycles. Photo-generated holes and hydroxyls are the leading species accounting for Acid Red 14 decomposition. Furthermore, the decomposition kinetics of Acid Red 14 followed the pseudo-first-order kinetics.

Tuning the selectivity of cerium oxide for ethanol dehydration to ethylene

Ethylene is a prized raw material in the chemical industry, as well as a valued monomer to produce important commodities. At present, ethylene is mainly produced via the cracking of hydrocarbons, but there is an increasing interest in exploiting renewable biomass-derived feedstocks. The catalytic dehydration of bioethanol is a sustainable alternative route to produce ethylene. Ceria-based catalysts are active for ethanol dehydration to ethylene at low-temperature, but their selectivity is limited by the undesired formation of acetaldehyde. Partially reduced ceria can promote the dehydration of primary alcohols into alkenes over their dehydrogenation to aldehydes. This work provides computational insight into the role of surface oxygen vacancies in the selectivity of ceria. Based on this, it is proposed that the selectivity of ceria toward ethylene can be tuned by substituting Ce4+ with La3+ cations. This is tested using both density functional theory (DFT) calculations and temperature-programmed desorption (TPD) experiments to quantify the impact of doping ceria with lanthanum on the production of ethylene and acetaldehyde. The La-doped ceria sample is found to be more active and selective. This insight can guide the rational design of new ceria-based catalysts for an ethanol dehydration reaction with high selectivity to ethylene.

Influences of CeO2 morphology on enhanced performance of electro-Fenton for wastewater treatment

As a kind of rare-earth oxide, CeO2 has been considered as a great potential material for its abundant oxygen vacancies and catalysis activity in wastewater treatment. In this study, three ceria samples with different morphological structure were prepared, and their effect on contaminates degradation in electro-Fenton (E-Fenton) system was investigated. It is found that the morphology of CeO2 has great influence on promoting the performance of E-Fenton process. The rod-like CeO2 (R–CeO2) induced E-Fenton system shows higher azo dye X3B removal and mineralization rates than cubs (C–CeO2) and octahedrons (O–CeO2), and the degradation kinetic rate constants are 0.28, 0.169 and 0.181 min−1 respectively, already surpass that of the blank one (0.120 min−1). The H2O2 generation capacity of R–CeO2 induced E-Fenton system is also superior to the others, and the corresponding Faraday current efficiency even increases to 166.2% at 2.5 min. Characterizations by scanning-transmission electron microscopy (STEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), Raman spectroscopy were conducted to disclose the mystery behind this phenomenon. The results indicate that the difference of surface oxygen vacancy density in different shaped CeO2 acts as a magic driving force for the accelerated oxygen reduction, and then leads to the enhanced degradation efficiency of E-Fenton system. This work provides a new insight into the development and application of rare-earth elements based catalyst in E-Fenton technology.

High Temperature Corrosion Stability of Ceramic Materials for Magnetohydrodynamic Generators

Abstract Corrosion by alkali metals and their compounds poses a significant challenge to the long-term material stability and service life for both metal alloys and ceramics at high operating temperatures. Chemical reactivity between alkali metals and materials underlie numerous industry challenges ranging from fireside corrosion in biomass-fired boilers to reaction with silica-based refractory ceramics in glass furnaces. The problem is particularly significant in magnetohydrodynamic (MHD) generators, where potassium or cesium compounds are introduced to improve the electrical conductivity of the working fluid. Thus, resistance to attack by alkali metal vapor is an important consideration in the selection and fabrication of ceramic electrodes and insulators for MHD generators. We evaluated several refractory ceramics to assess phase stability and known reactions with potassium and its compounds at high temperatures (T > 1,200 °C). Refractory ceramics were tested for potassium vapor corrosion using a modified ASTM standard test method with in situ monitoring of gas composition. Unlike other materials, the magnesia (MgO) and ceria (CeO2) samples did not exhibit corrosion, and no phase or mass changes were observed. This indicates that CeO2 and MgO could exhibit long lifetimes as plasma facing components in MHD generators. Ultimately, this development provides valuable data in evaluating critical materials performance issues that can attest to the viability of high temperature direct fired MHD generator applications.

Properties and Potential Applications of Manganese‐doped Ceria Gained by Mechanochemical Synthesis

AbstractManganese doped nanosized ceria samples were prepared by mechanochemical synthesis. Characterization was done using X‐ray diffraction (XRD), UV‐Vis diffuse reflectance spectroscopy (UV‐Vis DRS), X‐ray photoelectron spectroscopy (XPS) and others. Different conditions of synthesis were tried. Beside cerium carbonate, cerium chloride and amorphous phase remain in the product. Cerium carbonate decomposes around 250 °C, while the decomposition process centered at 330 °C was attributed to cerium chloride decomposition. Along with ceria, birnessite occurs in doped samples after thermal treatment and washing. Ceria lattice constant is reduced from 5.405 Å for pure sample to 5.401 Å for the 30 % doped sample as a consequence of manganese entrance in the ceria lattice. Ceria bandgap is significantly reduced with doping. Particle size was far greater than crystallite size due to a strong tendency toward agglomeration. All prepared powders proved to be efficient catalysts for toluene oxidation with the 30 % doped sample being the most promising.

SYNTHESIS OF CERIA NANOPARTICLES: EFFECT OF ALCOHOL/WATER RATIO ON THE MORPHOLOGY AND CRYSTAL STRUCTURE

In this study, ceria nanoparticles were synthesized via one of the simplest methods, which is the precipitation method. The effects of three different ethanol/DI water ratios (i.e. 1:1; 1:4; 0:1) and post-heat treatments (i.e. drying only and drying + calcination) on the crystal structure and morphology of the ceria nanoparticles have been investigated. The characterization of the ceria nanoparticles was conducted using X-Ray Diffractometer (XRD) for the crystal structure and Transmission Electron Microscopy (TEM) for the morphology. From XRD analysis results, the comparison of the highest XRD intensity peaks (at 2θ = 28.6°) of the ceria nanoparticles samples showed that all the ceria nanoparticles samples with drying + calcination treatment were higher than the ones with drying treatment only. Additionally, the XRD peaks were analyzed using a well-known Scherrer’s equation to determine the average crystallite size of the ceria nanoparticles. It was found that the ceria nanoparticles sample prepared using the ethanol/DI water ratio of 1:1 (i.e. Ceria-C1) had the biggest average crystallite size (i.e. 14 nm). Nevertheless, the TEM analysis showed that Ceria-C1 showed better morphology and dispersion compared to other Ceria samples and also clearly exhibited sphere-like nanoparticles. This finding can be associated with the dispersion stability analysis, which showed that the suspension of Ceria-C1 shows a little bit better dispersion compared to other Ceria samples.

Structural, morphological and optical properties of Ni-doped CeO2 nanospheres prepared by surfactant free co-precipitation technique

A high qualitative material is indeed depends on the technique utilized during its preparation as well as its composition. This is because particles do interact to form agglomerates, and in consequence, produce particles with deteriorated quality. In this study, ceria and Ni doped ceria nanospheres (NSs) were prepared using a surfactant free precipitation and co-precipitation techniques, respectively. The prepared samples were characterized using XRD, SEM, EDX, UV-VIS and FTIR. XRD pattern of the undoped ceria confirms the formation of a fluorite cubic structure of ceria and the absence of additional phase in the XRD patterns of the doped ceria samples implies that the ceria cubic structure is retained. FE-SEM analysis revealed that samples possess spherical morphology. Both the average crystallite sizes and the average particle diameters of the samples were found to occur within nano-range. UV-Vis analysis reveals that samples demonstrated excellent optical properties. The optical band gap of the undoped ceria was found to increase with doping 3% and 5% Ni, which could be due to Burstein- Moss effect. However, doping 1% Ni was found to reduce the optical band gap of the undoped ceria, which could be associated with the reduction of the average crystallite size and therefore, is regarded as the optimum dopant. EDX analysis confirms the presence of the cerium, oxygen as well as the expected doping concentrations of the Ni precursor. FTIR analysis shows the presence of O-H stretching vibrations in all samples. Therefore, these nanostructures with such enhanced properties could be utilized as potential materials in a number of electronic and catalytic applications.

Measuring Diffusion Coefficients of the Ceria Phase in a Dual-Phase Oxygen Permeation Membrane Using a Combined Polarization - Kelvin Probe Force Microscopy Method

Dual-phase membranes with FeCo2O4 or its iron-rich pendant Fe2CoO4 and Gd-doped ceria as an oxygen ion conductor have already been successfully applied as oxygen permeation membranes with high permeability in the temperature range above 800 °C [1-3]. Apart from Gd-doped ceria, Sm-doped ceria also can be an interesting alternative in this kind of composite due to its high ionic conductivity [4].As especially ceria or ceria-based composites have gained more and more interest for low-temperature applications, e.g. as catalyst materials, current research efforts are aiming to improve the composition and microstructure of such dual-phase membranes for application in a membrane reactor at considerably lower temperatures (below 600 °C) to perform partial oxidation reactions. For temperatures between 600-1200 °C the defect chemistry of these materials is well established, but experimental data for low temperature charge transport are limited and not fully understood, yet.Kelvin Probe Force Microscopy (KPFM) is an Atomic Force Microscopy (AFM)-based measurement method which can measure the local surface potential (or from the physics view: the Volta potential) of the sample [5, 6]. The surface potential is a measure for local changes of the defect chemistry, as it is directly related to the local Fermi niveau [7]. The implications of local oxidation and reduction at low temperatures for charge carrier mobility in pure ceria, and especially in dual-phase materials, are not very well understood so far, but KPFM can be used to measure the surface potential difference directly at the polarized contact area as well as to map the time-dependent relaxation process of the introduced gradient, also giving information about the local surface potential distribution, lateral extent of the gradient, variations of the shape of the gradient etc. [8, 9].In the present study, single ceria grains in a dual-phase Ce0.8Sm0.2O2-δ + FeCo2O4 oxygen permeation membrane were polarized at room temperature in ambient air using a Pt-coated AFM tip and a large silver paste back contact. Subsequently, the introduced defect concentration gradient (which is visible as a gradient of the surface potential) and the relaxation process over time was monitored by KPFM.By comparing the measurement results to previously acquired data of single phase ceria samples with different doping concentrations and crystallinity, we were able to show that by this technique, chemical diffusion coefficients of a single phase in a composite material are accessible. Acknowledgements: The work was funded by the German Research Foundation - project #387282673. Literature: Ramasamy, M.; Baumann, S.; Palisaitis, J.; Schulze‐Küppers, F.; Balaguer, M.; Kim, D.; Meulenberg, W. A.; Mayer, J.; Bhave, R.; Guillon, O. J Amer Ceram Soc 2016, 99 (1), 349-355.Ramasamy, M.; Persoon, E. S.; Baumann, S.; Schroeder, M.; Schulze-Küppers, F.; Görtz, D.; Bhave, R.; Bram, M.; Meulenberg, W. A. Journal of membrane science 2017, 544, 278-286.Lin, Y.; Fang, S.; Su, D.; Brinkman, K. S.; Chen, F. Nature Comm 2015, 6 (1), 1-9.Mori, T.; Drennan, J.; Lee, J.-H.; Li, J.-G.; Ikegami, T. Solid State Ionics 2002, 154-155, 461-466.Örnek, C.; Leygraf, C.; Pan, J. Corr Eng Sci Tech 2019, 54 (3), 185-198.Melitz, W.; Shen, J.; Kummel, A. C.; Lee, S. Surf Sci Rep 2011, 66 (1), 1-27.Zhang, Z.; Yates, J. T. Chem Rev 2012, 112 (10), 5520-5551.Neuhaus, K.; Schulze-Küppers, F.; Baumann, S.; Ulbrich, G.; Lerch, M.; Wiemhöfer, H.-D. Solid State Ionics 2016, 288, 325-330.Lee, W.; Lee, M.; Kim, Y.-B.; Prinz, F. B. Nanotechnology 2009, 20 (44), 445706.

Investigations on the mechanism of silica particle removal during the Cu buff cleaning process

A new buff cleaning method to remove particles remaining on the Cu surface after chemical mechanical polishing was developed. Because the van der Waals force is the dominant adhesion force when silica particles are attached to a blanket Cu film, an alkaline solution or hot water was previously recommended to increase the lifting force and weaken the van der Waals force, thereby improving the cleaning efficiency by 92.58% and 92.71%, respectively. In this study, the temperature effects on physical and chemical bonding were thoroughly compared for silica and ceria samples. Soft pads are recommended to improve the particle removal efficiency and prevent scratching the Cu surface during the buff process. Almost all of the particles were dislodged and scratching was successfully prevented after optimization. This work elucidates the mechanisms of particle adhesion and removal in Cu buff cleaning from the standpoints of force and energy, thus optimizing Cu buff cleaning and achieving an ideal cleaning efficiency.