Formation Of Ce Research Articles

Effect of cerium on the primary carbides and inclusions in electroslag remelted M35 high speed steel

To restrain the formation of primary carbides in M35 high speed steel, the present work investigated the effect of cerium on the microstructure, primary carbides and inclusions in electroslag remelted M35 high speed steel based on experimental characterizations and thermodynamic calculations. The primary carbides in M35 high speed steel are M2C-type carbides with orthorhombic crystal structure and MC-type carbides with FCC crystal structure. M2C-type carbides are the dominant carbides, whose precipitation is prior to the MC-type carbides. With adding cerium content to 0.0230wt%, the evolutionary process of inclusions is: MgO∙Al2O3→Ce2O3, CeAlO3 and Ce2O2S→Ce2O3, Ce2O2S and Ce2O3 core surrounded by Ce–As–P layer. Adding cerium content from 0 to 0.0230wt% causes the secondary dendrite arm spacing to decrease from 36.8 μm to 29.4 μm, as the heterogeneous nucleation of Ce2O3, Ce2O2S and CeAlO3 inclusions, as well as the effect of dissolved cerium including the increase in the constitutional undercooling and the drag on the migration of liquid–solid interface. Ce2O3, Ce2O2S and CeAlO3 are the less effective heterogeneous nucleation cores for M2C-type and MC-type primary carbides precipitation than MgO∙Al2O3 inclusions, which is conducive to the decrease in the area fraction of primary carbides with adding 0.0067wt% cerium. Further increasing cerium content to 0.0230wt%, the formation of Ce–As–P inclusions surrounding Ce2O3 promotes the precipitation of M2C-type primary carbides, causing the increase in the area fraction of primary carbides.

Remarkably efficient Pt/CeO2–Al2O3 catalyst for catalytic hydrodeiodination of monoiodoacetic acid: Synergistic effect of Al2O3 and CeO2

Monoiodoacetic acid (MIAA) is one of the highly toxic halogenated disinfection by-products, which is formed during water disinfection processes. Catalytic hydrogenation with supported noble metal catalyst is a green and effective technique for the transformation of halogenated pollutant, but its activity still needs to be identified. In this study, Pt nanoparticles were supported on CeO2 modified γ-Al2O3 (Pt/CeO2–Al2O3) by chemical deposition method and the synergistic effect of Al2O3 and CeO2 on catalytic hydrodeiodination (HDI) of MIAA was systematically studied. Characterizations revealed that Pt dispersion could be improved by the introduced CeO2 through the formation of Ce–O–Pt bond and MIAA adsorption could be facilitated by high Zeta potential of Al2O3 component. Furthermore, optimal Ptn+/Pt0 could be obtained by adjusting CeO2 deposition amount on Al2O3, which could effectively facilitate the activation of C–I bond. Therefore, Pt/CeO2–Al2O3 exhibited remarkable catalytic activities and TOF values compared with those of Pt/CeO2 and Pt/Al2O3. Through detailed kinetic experiments and characterization, the extraordinary catalytic performance of Pt/CeO2–Al2O3 can be attributed to the abundant Pt sites as well as the synergistic effect between CeO2 and Al2O3.

Graphitic carbon nitride (g-C3N4) as a super support for Mn–Ce based NH3-SCR catalyst: Improvement of catalytic performance and H2O/SO2 tolerance for NOx removal

Low temperature NH3 selective catalytic reduction (NH3-SCR) technology is an efficient and economical strategy for NOx removal. In this study, Mn–Ce oxides supported on graphitic carbon nitride (g-C3N4) was applied to the NH3-SCR of NOx at low temperature compared with Mn–Ce oxides supported on commercial TiO2, γ-Al2O3, and montmorillonite (MNT). The NOx conversion and H2O/SO2 tolerance of 8% Mn–Ce/g–C3N4–300 were superior to those of 8% Mn–Ce/TiO2-300, 8% Mn–Ce/γ-Al2O3-300 and 8% Mn–Ce/MNT-300 in the temperature window of 100–300 °C, and more than 95% NOx conversion could be obtained within the whole temperature range. According to the experimental and characteriazation results, the superior low temperature NH3-SCR performance of 8% Mn–Ce/g–C3N4–300 could be attributed to the formation of Ce–O–Mn solid solution structure, the higher concentrations of the surface elements, the optimun low-temperature reduction behavior, the largest amount of total acid sites, the highest (Mn4++Mn3+)/(Mn4++Mn3++Mn2+) and (Ce3+)/(Ce3++Ce4+) ratios, and the modest Oα/(Oα+Oβ) ratio.

New synthetic [LREE (LREE = La, Ce, Pr, Sm), Pb]-phosphate phases

Abstract Search for inexpensive and efficient methods of critical raw materials recovery is of great importance across the world due to growing demand for green technologies. Formation and detailed characterization of new Pb- and Light Rare Earth Elements (LREE)-containing phosphates, compared to already described Pb- or LREE-containing phosphates, was described in this work. These phases were precipitated at experimental conditions similar to these used in a newly proposed coprecipitation route for REE recovery from aqueous solutions. The formation of La, Ce, Pr and Sm phosphates from aqueous solutions proceeded differently in the presence of Pb than in its absence. No rhabdophane group minerals, (REE,Ca,Th)(PO4)·nH2O were formed, which were the product of crystallization in the absence of Pb, as evidenced by the PXRD analysis of the control LREE phosphates. Instead, a new, distinct phase was formed, which is neither a ‘phosphoschultenite’, PbHPO4, with La, Ce, Pr or Sm substitution nor a rhabdophane with Pb substitution. This showed that PbHPO4 structure did not accept isomorphic substitutions of LREE elements and rhabdophane structures are reluctant to accept Pb substitutions. At the same time, the formation of a hitherto unknown crystalline phase was found to be a mixed (LREE,Pb)-phosphate. A lower pH caused higher crystallinity of phases, as confirmed by SEM and PXRD. FTIR spectroscopy showed the hydrous nature of the obtained phases, which was additionally confirmed by thermal analysis. Decreasing pH of the reaction solution resulted in a higher crystalline water content. Moreover, La-bearing phases contained more chemically bound water than other phases. A combined EDS analysis and ICP-OES led to the chemical composition of new Pb phases with La, Ce, Pr and Sm that can be expressed as La2Pb3(PO4)4·3.5H2O, Ce2Pb3(PO4)4·3.3H2O, Pr2Pb3(PO4)4·3.1H2O and Sm2Pb3(PO4)4·3.3H2O, respectively. These results give a better understanding of potential novel recovery pathways of REE from phosphate mineral sources or wastes.

Heterostructures of polyaniline and Ce–ZnO nanomaterial coated flexible PET thin films for LPG gas sensing at standard environment

The n-type Ce doped ZnO (Ce–ZnO) and p-type polyaniline (PANI) heterojunction were successfully synthesized via simple chemical solution method for sensing liquefied petroleum gas (LPG) at standard environment. The morphology and structures of as-prepared Ce–ZnO & PANI nanoparticles were analyzed by numerous kinds of techniques. Ce–ZnO & PANI nanoparticles were mixed with n-methylpyrrolidone (NMP) which is coated over the gold coated PET electrode by doctor blade method and dried overnight at 60 °C to form p-n junction. The as-formed p-n junction is to be driven with the help of 1.5 V potential at ambient temperature. X-ray photoelectron spectroscopy results of Ce–ZnO nanoparticles confirmed the existence of Ce4+ and the improved amount of both chemisorbed oxygen and oxygen vacancy after the formation of Ce–ZnO heterojunction. The maximum response of 80% was realized for hollow Ce–ZnO/PANI sensor at 100 ppm. The proposed material is a novel candidate to detect the LPG even at low (30) ppm and this study reveals the possibility of developing a potentially inexpensive hollow Ce–ZnO/PANI sensor for sensing LPG efficiently.

What would a human-centred ‘social’ Circular Economy look like? Drawing from Max-Neef's Human-Scale Development proposal

The Circular Economy (“CE”) has emerged as a concept to radically transform how resources are used and managed, with promise to solve the ecological turmoil of the prevailing linear economy. Circularity has since been framed as an important concept to contribute to achieving sustainable development. Thus, the CE is increasingly being adopted as key a strategy by various stakeholders, including large corporations and political institutions. Despite seemingly high interest and growing uptake demonstrated by an influx of new business models and policy guidance, there is concern amongst scholars that current interpretations fail to consider the social impacts and implications of this circular shift. There is a notable lack of theoretical contribution to address this void, and without robust theorising this can be an obstacle to effective and transformative practice. This research contributes to addressing this problematic shortcoming by utilising an existing development framework to identify a theoretically grounded direction for the formation of an alternative Social CE. We use the key features of Max-Neef's Human Scale Development (“H-SD”) proposal to illustrate how reframing the CE to take account of this perspective can provide a basis for articulating and developing a compelling social narrative. We argue that human needs satisfaction should be both the objective of a Social CE, but also embedded into the means as to how it is achieved. Grassroots initiatives that enable self-reliant communities should balance the current disproportionate influence wielded by powerful institutions and businesses. Equilibrium is required between different components and actors, including between humans and the environment, which ultimately represents a version of circularity that adheres to the limits of the biosphere.

Dual-purpose nickel-iron layered double hydroxides by controlled lanthanide and phosphide incorporation for promoting overall water splitting efficiency

Developing non-noble metal and binder-free bifunctional electrocatalysts is of paramount importance but challenging for simultaneously promoting oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) processes. In the work, we introduce the dual-purpose utilization of nickel-iron layered double hydroxides (LDH) by a lanthanide and phosphide incorporation strategy for highly efficient overall water splitting (OWS). The screening of lanthanides effect shows that the lanthanide dopants (Ce, La and Nd) greatly contribute to the layer lattice distortion of LDH host structure and strong electronic interaction with Fe2+ species, leading to the increment of OER active species content of α-Ni(OH)2 phase and Fe3+. Specially, the formation of Ce3+/4+ reversible redox species can significantly promote charge transfer efficiency, thus corporately attributing to the excellent OER activity (η10 = 207 mV) and durability (300 mA·cm−2 for 200 h). On the other hand, we found that with further phosphide anions engineering, the HER Volmer step is accelerated in lanthanide and phosphide co-doped LDH, as compared to the solely phosphide doped LDH. The present of co-doped lanthanide can modify the adsorption energy of hydrogen intermediates and the Ce3+/4+ reversible redox species also facilitate the formation of HER active Ni2P phase, resulting in the lowest η10 value of 134 mV. The dual-purpose configuration of the Ce LDH // Ce LDH-P electrodes, provides low OWS potentials of 1.638 and 1.839 V to reach current densities of 10 and 100 mA·cm−2, respectively. These findings could introduce a new way to integrate nonprecious-metal bifunctional electrocatalysts into an efficient OWS system.

Origins of p-Doping and Nonradiative Recombination in CsSnI3.

It is commonly believed that the spontaneous p-doping in Sn-based perovskites is caused by Sn vacancies. By performing rigorous first-principles calculations for a prototypical Sn-based perovskite CsSnI3 , we reveal that, in fact, the defects dominating p-doping are Cs vacancies. The reason that adding extra Sn2+ could reduce p-doping is that Cs and Sn present the same changing trend in terms of chemical potentials, and thus inhibiting the formation of Sn vacancies will also limit the formation of Cs vacancies. Moreover, we show that I vacancies are the dominant nonradiative recombination centers, and can result in sizable nonradiative losses, which explains why the experimentally measured carrier lifetime is only a few nanoseconds even if p-doping is suppressed. This work provides new insights into the origins of p-doping and nonradiative recombination in CsSnI3 , and suggests that minimizing the formation of Cs and I vacancies is critical to realizing the best device performance.

Origins of p‐Doping and Nonradiative Recombination in CsSnI3

AbstractIt is commonly believed that the spontaneous p‐doping in Sn‐based perovskites is caused by Sn vacancies. By performing rigorous first‐principles calculations for a prototypical Sn‐based perovskite CsSnI3, we reveal that, in fact, the defects dominating p‐doping are Cs vacancies. The reason that adding extra Sn2+ could reduce p‐doping is that Cs and Sn present the same changing trend in terms of chemical potentials, and thus inhibiting the formation of Sn vacancies will also limit the formation of Cs vacancies. Moreover, we show that I vacancies are the dominant nonradiative recombination centers, and can result in sizable nonradiative losses, which explains why the experimentally measured carrier lifetime is only a few nanoseconds even if p‐doping is suppressed. This work provides new insights into the origins of p‐doping and nonradiative recombination in CsSnI3, and suggests that minimizing the formation of Cs and I vacancies is critical to realizing the best device performance.

Multiple interfaces from nano-sized Pt on bimetal oxides of CeO2 and MnO2 promote complete degradation of o-xylene in a room-temperature operated plasma-catalytic reactor

Pt/CeO2/β-MnO2 catalyst with multiple interfaces (Pt and CeO2, Pt and MnO2, CeO2 and MnO2, and Pt sandwiched by CeO2 and MnO2) was developed by supporting nano-sized Pt on CeO2-loaded MnO2 for o-xylene degradation in a room-temperature operated plasma catalytic reactor. It was found that 100 % o-xylene conversion and 88 % CO2 selectivity can be achieved using Pt/CeO2/β-MnO2 catalyst. Characterization results revealed that the best performance of Pt/CeO2/β-MnO2 is due to the highest ratios of Ce3+/Cetotal, Pt0/Pttotal, and Oads/Ototal, while the lowest ratio of Mn3+/Mntotal. Pt and CeO2 on β-MnO2 have synergistic effect on the formation of Ce3+ and Pt0, which can promote the generation of oxygen vacancies and surface reactive oxygen species. The relationship between structure factors and reaction activities has been correlated, the Ce3+/Cetotal ratio can be used as the descriptor to reveal the plasma catalytic activity.

Enhancing mechanical properties of Mg-Gd-Y-Zn alloys via microalloying with Ce and La

This study investigated the microstructure and mechanical properties of Mg-1Gd-1Y-1Zn (at.%) alloys containing designed amounts of Ce or La. The Mg<sub>5</sub>(Gd,Zn) phase formed in the as-cast Mg-Gd-Y-Zn-Ce/La alloys and disappeared after a homogenization treatment at 500°C for 24 h. The addition of Ce and La resulted in the formation of Ce(Mg,Zn)<sub>12</sub> and La(Mg,Zn)<sub>12</sub> phases, respectively. Except for that, the Ce or La addition had no significant effect on the morphology, volume fraction, and type of the long-period stacking ordered (LPSO) phases in the Mg-Gd-Y-Zn alloy. The grain size decreased with increasing microalloying content because the heavy Ce and La atoms impeded atomic migration across the boundaries. The solute drag effect led to the formation of the rare earth texture in the extruded Mg-Gd-Y-Zn-Ce/La alloys, whose extent decreased with increasing microalloying content. The mechanical strength was improved by the addition of Ce or La at the sacrifice of ductility. In particular, La exhibited a stronger reinforcement ability than Ce when it was added to the Mg-Gd-Y-Zn alloys. Among the investigated chemical compositions, the Mg-1Gd-1Y-1Zn-0.3La alloy exhibited the highest strength because it had the finest grains, the highest volume fraction of the second phase, and the weakest texture intensity. Furthermore, the alloys showed an unusual yield asymmetry due to the difference in the deformation mode of the LPSO phase.

Tuning the hard magnetic properties of nanocrystalline Ce-Fe-B alloys by Ho substitution

• Paramagnetic CeFe 2 phase is suppressed by Ho substitution. • Ho tends to enter into 2:14:1 phase in melt-spun Ce-Fe-B alloy. • Coercivity of Ce-Fe-B alloy is greatly enhanced with Ho substitution. • Ho-substituted Ce-Fe-B alloy has better thermal stability. To improve the performance of Ce-based magnets and take full advantages of heavy rare earth (RE) element of Holmium, Ce-Fe-B alloys with different Ho substitutions were prepared by melt spinning. Their phase constitution and magnetic properties have been systematically studied. Ho can enter into the main phase to form (Ce,Ho) 2 Fe 14 B phase, and the introduction of Ho can suppress the formation of CeFe 2 phase in the (Ce 1- x Ho x ) 14 Fe 80 B 6 alloys. Partial Ho substitution can tune the magnetic properties of RE-rich (Ce 1- x Ho x ) 14 Fe 80 B 6 alloys and single-phase (Ce 1- x Ho x ) 12 Fe 82 B 6 alloys. For RE-rich (Ce 1- x Ho x ) 14 Fe 80 B 6 alloys, the intrinsic coercivity H cj , Curie temperature T c and thermal stability are greatly improved by Ho substitution. H cj reaches a high value of 1317.7 kA/m at x = 0.5. For single phase alloy, ( BH ) max greatly increases from 18.7 kJ/m 3 to 56.1 kJ/m 3 when x increases from 0 to 0.3. The microstructure observation of (Ce 0.7 Ho 0.3 ) 14 Fe 80 B 6 alloy indicates the formation of (Ce,Ho) 2 Fe 14 B and RE-rich phases, and Ho prefers to enter 2:14:1 phase than Ce. This work suggests the possibility of developing cost-effective permanent magnets based on Ce and Ho elements.

Effect of CeO2 doping on high temperature oxidation resistance of YSZ TBCs

In the present work, YSZ TBCs and 10 wt% CeO2-doped YSZ thermal barrier coatings (CeYSZ TBCs) were prepared via atmospheric plasma spraying(APS) respectively, whereupon high temperature oxidation experiment was carried out at 1100 °C to compare the high temperature oxidation behavior and mechanism of the two TBCs. The results showed that the doping of CeO2 reduced the porosity of YSZ TBCs by 23%, resulting in smaller oxidation weight gain and lower TGO growth rates for CeYSZ TBCs. Besides, the TGO generated in CeYSZ TBCs was obviously thinner and there were fewer defects inside it. For YSZ TBCs, as the oxidation process proceeded, Al, Cr, Co and Ni elements in the bonding coating were oxidized successively to form loose and porous spinel type oxides (CS), which was apt to cause the spalling failure of TBCs. While, the Al2O3 layer of the TGO generated in CeYSZ TBCs ruptured later than that in YSZ TBCs, which delayed the oxidation of Cr, Co, and Ni elements and the formation of CS accordingly. Therefore, CeO2 doping can effectively improve the high temperature oxidation resistance of YSZ TBCs.

Cerium metal oxidation studied by IR reflection-absorption and Raman scattering spectroscopies

Oxidation of cerium metal is a complex process which is strongly affected by the presence of water vapor in the oxidative atmosphere. Here, we explore, by means of infrared reflection-absorption spectroscopy (IRRAS) and Raman scattering spectroscopies, thin oxide films, formed on cerium metal during oxidation, under dry vs ambient (humid) air conditions (∼0.2% and ∼50% relative humidities, respectively) and compare them with a thin film of CeO2 deposited on a Si substrate. Complementary analysis of the thin films using x-ray diffraction and focused ion beam-scanning electron microscopy enables the correlation between their structure and spectroscopic characterizations. The initial oxidation of cerium metal results in the formation of highly sub-stoichiometric CeO2−x . Under dry air conditions, a major fraction of that oxide reacts with oxygen to form CeO∼2, which is spectroscopically detected by Raman scattering F 2g symmetry mode and by IRAAS F 1u symmetry mode, splitted into doubly-degenerate transverse optic and mono-degenerate longitudinally optic (LO) modes. In contrast, under ambient (humid) conditions, the oxide formed is more heterogenous, as the reaction of CeO2−x diverges towards the dominant formation of Ce(OH)3. Prior to the spectral emergence of Ce(OH)3, hydrogen ions incorporate into the highly sub-stoichiometric oxide, as manifested by Ce–H local vibrational mode detected in the Raman spectrum. The spectroscopic response of the thin oxide layer thus formed is more complex; particularly noted is the absence of the LO mode. It is attributed to the high density of microstructural and compositional defects in the oxide layer, which results in a heterogenous dielectric nature of the thin film, far from being representable by a single phase of CeO∼2.

Influence of the Alkali-promoted phase transformation in monazite for selective recovery of rare-oxides using deep eutectic solvents

• High temperature formation of Ce 1 - x Ln x O 2 - x / 2 solid solutions has been demonstrated. • Electrochemical activity of pure rare earth oxides in the DES Ethaline has been proven. • 23.85% Nd 2 O 3 in a 0.1 mol/L glucose solution in Ethaline was dissolved. • No dissolution was reported for pure CeO 2 , La 2 O 3 and PrO 2 /Pr 2 O 3 . • Dissolution of Ce 1 - x Ln x O 2 - x / 2 formed in roasting was not possible because of its inert behaviour. The physico-chemical changes occurring during the high-temperature phase transformation of monazite in the presence of Na 2 CO 3 at 1000 °C for 2 h duration at monazite: Na 2 CO 3 ratios between 1.0 and 5.0, were investigated. The formation of sodium lanthanide phosphates was prevalent above a monazite:alkali ratio of 2, however, below this ratio, the dephosphorization of monazite as Na 3 PO 4 and Ce 1 - x Ln x O 2 - x / 2 solid solutions occur offering unique selectivity for rare-earth oxide separation from the mineral matrix. Cyclic voltammetry of pure CeO 2 , La 2 O 3 , Nd 2 O 3 , and PrO 2 /Pr 2 O 3 was carried out in the deep eutectic solvent Ethaline (1:2 mixture of choline chloride and ethylene glycol) proving the electrochemical activity of these oxides. Electrodissolution of pure oxides and water-leached monazite after high-temperature reaction with a ratio of 1:1 was carried out in a 0.1 mol/L glucose solution in Ethaline showing a preferential solubility of 23.85% for pure Nd 2 O 3 . In contrast, pure oxides of CeO 2 , La 2 O 3 and PrO 2 /Pr 2 O 3 were found to be insoluble. We also observed that electrodissolution of the water leached monazite was not possible because of the inert behaviour of Ce 1 - x Ln x O 2 - x / 2 solid solutions. Avoiding cerium oxidation during the high-temperature process will lead to a method for further selectivity for rare-earth oxide processing using staged electro-chemical winning of oxides.

Structural, vibrational and luminescence properties of solid solution based on the (1-x/2) Ce2(WO4)3 + (x/2) Sm2(WO4)3 system

A series of 14 polycrystalline cerium samarium tungstates belonging to the system [(1-x/2).Ce2(WO4)3 + x/2 Sm2(WO4)3] was synthesized by a coprecipitation method followed by thermal treatment at 1000 °C. The polycrystalline samples were characterized by X-ray diffraction, scanning electron microscopy and Raman spectroscopy. Their crystal structure was subjected to Rietveld refinement calculations and quasi-linear variation of cell parameters was observed, suggesting the formation of a solid solution Ce(2-x)Smx(WO4)3 (0 ≤ x ≤ 2). Raman spectroscopy was used to confirm the formation of the disordered solid solution. The analyses of Bragg peak and Raman emission profiles allowed evidencing the formation of structural defects. Scanning electron microscopy images show relatively well crystallized grains. Photoluminescence experiments were performed under polychromatic X-ray excitation delivered by copper source. The characteristic luminescence of Ce3+ cations was not observed whatever the composition x. The resulting emissions were ascribed to Sm3+ cations associated with additional emission from structural defects. Chromaticity diagrams show that color coordinates vary with Sm composition and structural defects in the orange-red range.

Preparation, structure and luminescence properties of Ce3+ activated translucent glass ceramics containing garnet microcrystals

Glass ceramics containing Ce3+ doped garnet microcrystals were prepared from the spontaneous crystallization of SiO2-Al2O3-Y2O3-MgO-BaO-CeF3 glass melt. The formation of Ce3+:(Y,Mg)3(Al,Si)5O12 grains in the glass matrix were investigated by X-ray diffraction, scanning electron microscope and photoluminescence spectra. The transmittance of samples improves with higher melting temperature or increasing BaO/MgO ratio, while the Ce3+: 5d → 4f emission intensity weakens monotonously. Besides, the transmittance declines sharply after being heat treated above 950°C, which is originated from the schistose BaAl2Si2O8 microcrystals in the glass matrix. The optimized sample with composition of 40SiO2-16Al2O3-8Y2O3-24BaO-12MgO-0.3CeF3 was chosen to construct a white LED device, which yields bright white light with luminous efficiency of 23.6 lm/W, correlated color temperature of 5260 K and Ra of 85.5. It indicates that the investigated glass ceramics can be a promising color converter for white LEDs.

Photo-oxidative degradation of polyacids derived ceria nanoparticle modulation for chemical mechanical polishing

The effects of photo-oxidative degradation of polyacids at various concentrations and with different durations of ultraviolet (UV) irradiation on the photo-reduction of ceria nanoparticles were investigated. The effect of UV-treated ceria on the performance of chemical mechanical polishing (CMP) for the dielectric layer was also evaluated. When the polyacids were exposed to UV light, they underwent photo-oxidation with consumption of the dissolved oxygen in slurry. UV-treated ceria particles formed oxygen vacancies by absorbing photon energy, resulting in increased Ce3+ ions concentration on the surface, and when the oxygen level of the solution was lowered by the photo-oxidation of polymers, the formation of Ce3+ ions was promoted from 14.2 to 36.5%. Furthermore, chain scissions of polymers occurred during the oxidation process, and polyacids with lower molecular weights were found to be effective in ceria particle dispersion in terms of the decrease in the mean diameter and size distribution maintaining under 0.1 of polydispersity index. With increasing polyacid concentration and UV irradiation time, the Ce3+ concentration and the dispersity of ceria both increased due to the photo-oxidative degradation of the polymer; this enhanced the CMP performance in terms of 87% improved material removal rate and 48% lowered wafer surface roughness.

Fabrication of Novel Chitosan–Hydroxyapatite Nanostructured Thin Films for Biomedical Applications

In this study, we develop chitosan–hydroxyapatite (CS–HAp) composite layers that were deposited on Si substrates in radio frequency (RF) magnetron sputtering discharge in argon gas. The composition and structure of CS–HAp composite layers were investigated by analytical techniques, such as Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), metallographic microscopy (MM), and atomic force microscopy (AFM). On the other hand, in the present study the second order derivative of FT-IR–ATR spectra, for compositional analyses of CS–HAp, were used. The SEM, MM, and AFM data have shown the formation of CS–HAp composite layers. The surface of CS–HAp composite layers showed uniform growth (at an Ar gas working pressure of p = 2 × 10−3 mbar). The surface of the CS–HAp composites coatings became more nanostructured, becoming granular as the gas pressure increased from 5 × 10−3 to 1.2 × 10−2 mbar. However, our studies revealed that the surface morphology of the CS–HAp composite layers varies with the Ar gas working pressure. At the same time, optical properties are slightly influenced by Ar pressure. Their unique physicochemical properties make them suitable for various applications in the biomedical field, if we consider the already proven antimicrobial properties of chitosan. The antifungal properties and the capacity of the CS–HAp composite layers to inhibit the development of fungal biofilms were also demonstrated using the Candida albicans ATCC 10231 (C. albicans) fungal strain.

Development of a novel wet cleaning solution for Post-CMP SiO2 and Si3N4 films

After CMP, the removal of ceria nanoparticle residues is difficult due to the formation of Ce–O–Si chemical bonds on the SiO2 film surface. After STI CMP, several post-CMP cleaning processes are performed, including the application of PVA brushing and megasonic technologies using conventional cleaning solutions such as SC1, SC2, and SPM. However, more effective post-CMP cleaning technologies are still needed for the fabrication of advanced integrated circuit devices. In this study, we developed a novel post-CMP cleaning solution consisting of tetramethylammonium hydroxide (TMAH), ethylenediaminetetraacetic acid (EDTA), and Disponil to replace existing cleaning solutions. In its non-diluted form, this cleaning solution removed 99.5% of residual particles and 98.3% of ceria residue on an SiO2 film surface, as well as 98.5% of residual particles and 98.1% of ceria residue on an Si3N4 film surface, respectively. At 5 × dilution, it removed 97.8% of residual particles and 97.0% of ceria residue on the SiO2 film surface, as well as 97.8% of residual particles and 96.3% of ceria residue on the Si3N4 film surface, respectively. The effectiveness of this cleaning solution for residual ceria nanoparticles is highly comparable to SC1 and SPM conventional cleaning solutions, even though it is used at a relatively low temperature with less etching. Additionally, AFM of the surface topography showed fewer particles and better surface roughness compared with SC1 and SPM cleaning. Thus, this approach can be used to remove ceria nanoparticles from polished SiO2 and Si3N4 films through increased wettability, slight dissolving of the film, and extremely enhanced repulsive force.