Chemical Binding States Research Articles

Synchrotron-aided exploration of REE recovery from coal fly ashes within a Canadian context

Coal ashes in Canada have gained attention as a potential source for recovering rare earth elements (REE) from industrial waste. However, the complex chemical properties of coal ashes have made it difficult to determine the desirability, feasibility, and viability of REE recovery. To address this issue, this study systematically investigated distribution and structural information, speciation and chemical-binding state, and purity and extraction capacity of REE in multiple Canadian coal ashes (i.e., 2 fly ash and 1 bottom ash samples) through synchrotron-based X-ray fluorescence mapping and adsorption spectrum analyses, as well as high-resolution REE sequential extraction quantitation. The results showed that Y, Ce, and La were present in the glass phase of the bottom ash, and the distributions of these REE elements correlated with Ca. The XANES analysis revealed that the dominant form of REE in coal fly ash (CFA) was REE oxides, indicating a transformation during combustion, while Y2O3 and Y2(CO3)3 were the predominant Y species identified in CFA. The study found that there is no correlation between P and REEs, suggesting that REEs in CFA may exist as discrete particles rather than being associated with amorphous glass. The extractability of REEs in bottom ash samples was lower than that in fly ash samples. Additionally, the benefits of REE recovery were estimated to be USD 99.82 to 215.21 per ton of fly ash through life cycle analysis, indicating that REE recovery from fly ashes is a promising path to supplement the REE supply chain in Canada.

α-Bi2O3 tubular rods coated on Bi2O2CO3 nanosheets for high-performance asymmetric supercapacitor applications

Mixed phases of bismuth oxide nanostructures as an active electrode material in supercapacitor applications have recently gained huge research interest. In this study, the layered Bi2O2CO3 nanosheets and the secondary phase of α-Bi2O3 tubular rods named Bi2O2CO3/α-Bi2O3 heterostructure have been synthesized and utilized for supercapacitor applications. The crystal nature and microstructure of the Bi2O2CO3/α-Bi2O3 heterostructure were initially confirmed by powder X-ray diffraction (p-XRD), Raman, UV-Vis diffuse reflectance spectroscopy (UV-DRS, absorbance), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) studies. X-ray photoelectron spectroscopy (XPS) measurements have investigated the oxidation states and chemical binding energies. Regarding the electrochemical performances, the Bi2O2CO3/α-Bi2O3 heterostructure as electro-active material delivered a maximum specific capacitance (Cs) value of 635 F g−1 at the given current density value of 1 A g−1 in a conventional three-electrode mode. A coin cell type electrode has been fabricated using Bi2O2CO3/α-Bi2O3 heterostructure, resulting in an asymmetric supercapacitor device cell (ASC), which has a Cs of 112 F g− 1 (at 1 A g− 1) and a power density and energy density values of 515 W kg−1 and 22.5 Wh kg−1 respectively. The two supercapacitor electrodes in sequence effectively ignite the red-light-emitting diode (LED). Moreover, in the ASC type Bi2O2CO3 /α-Bi2O3 heterostructure, the specific capacitance value was slightly reduced to 12.3 % by 2000 cycles, showing favourable cyclic performance and stability during the electrochemical process. Based on the above-mentioned characterization, the appropriate electrochemical performances of Bi2O2CO3/α-Bi2O3 tubular rod heterostructures make them a promising candidate for future energy storage devices.

Effect of hydrogen on the chemical state, stoichiometry and density of amorphous Al2O3 films grown by thermal atomic layer deposition

Amorphous oxide thin films grown by thermal atomic layer deposition (ALD) typically contain high impurity concentrations of hydrogen, which affects both chemistry and structure and thereby the functional properties, such as the barrier properties in, for example, microelectronic and photovoltaic devices. This study discloses the effect of H incorporation in amorphous Al2O3 ALD oxide films on the local chemical binding states of Al, O and H, as well as the oxide density and stoichiometry, by a combined analytical approach using elastic recoil detection analysis, Rutherford backscattering spectroscopy and full chemical state analysis by dual‐source X‐ray photoelectron spectroscopy (XPS)/hard X‐ray photoelectron spectroscopy (HAXPES). The experimental findings are compared with crystalline anhydrous α‐Al2O3 and hydroxide α‐Al (OH)3 reference phases and further supported by molecular dynamic simulations. It is shown that H preferably forms covalent –OH hydroxyl bonds with O in the nearest‐neighbour coordination spheres of interstitial Al cations, which affects both the ligand electronic polarizability and the bond length of the randomly interconnected [AlOn] polyhedral building blocks in the amorphous ALD oxide films.

Correlation of the electronic structure and Li‐ion mobility with modulus and hardness in LiNi0.6Co0.2Mn0.2O2 cathodes by combined near edge X‐ray absorption finestructure spectroscopy, atomic force microscopy, and nanoindentation

AbstractThe electrochemical performance of cathode materials in Li‐ion batteries is reflected in macroscopic observables such as the capacity, the voltage, and the state of charge (SOC). However, the physical origin of performance parameters are atomistic processes that scale up to a macroscopic picture. Thus, revealing the function and failure of electrochemical devices requires a multiscale (and ‐time) approach using spectroscopic and microscopic techniques. In this work, we combine near‐edge X‐ray absorption fine structure spectroscopy (NEXAFS) to determine the chemical binding state of transition metals in LiNi0.6Co0.2Mn0.2O2 (NCM622), electrochemical strain microscopy to understand the Li‐ion mobility in such materials, and nanoindentation to relate the mechanical properties exhibited by the material to the chemical state and ion mobility. Strikingly, a clear correlation between the chemical binding, the mechanical properties, and the Li‐ion mobility is found. Thereby, the significant relation of chemo‐mechanical properties of NCM622 on a local and global scale is clearly demonstrated.

Surface modification of Ag-coated Cu particles using dicarboxylic acids to enhance the electrical conductivity of sintered films by suppressing dewetting in Ag shells

A resin-free paste containing 1.5 μm Cu@Ag particles was fabricated and used to form a film with excellent electrical conductivity even after a significantly high-speed sintering process. The particle surfaces were treated using three types of dicarboxylic acids, namely OA, SA, and PA, with carboxyl groups to suppress the dewetting behavior of Ag shells generated during thermal sintering. SEM, UV–vis, FT-IR, Raman spectroscopy, XPS, and TG-DTA analysis were performed to verify the morphological changes, chemical binding states (formation of an organo-metallic surface), and thermal behavior changes on the particle surfaces after surface treatment. The PA-modified particle surface exhibited a delayed dewetting behavior and the most suppressed oxidation degree. Furthermore, the paste containing the surface-modified particles exhibited a significantly low electrical resistivity (5.05 × 10−6 Ω·cm) after sintering for just 1 min at 300 °C under N2, which is an improvement of approximately three orders of magnitude over the original paste. Consequently, the surface treatment using effective dicarboxylic acid, which simultaneously inhibited Ag dewetting and suppressed Cu oxidation, improved Ag sintering between particles and enhanced the electrical properties of the sintered film.

Valence State Tuning of Gold Nanoparticles in the Dewetting Process: An X-ray Photoelectron Spectroscopy Study.

Gold nanoparticles (AuNPs) are commonly synthesized using the citrate reduction method, reducing Au3+ into Au1+ ions and facilitating the disproportionation of aurous species to Au atoms (Au0). This method results on citrate-capped AuNPs with valence single states Au0. Here, we report a methodology that allows obtaining AuNPs by the dewetting process with three different valence states (Au3+, Au1+, and Au0), which can be fine-tuned with ion bombardment. The chemical surface changes and binding state of the NPs were investigated using core-level X-ray photoelectron spectroscopy (XPS). This is achieved by recording high-resolution Au 4f XPS spectra as a function of ion dose exposure. The results obtained show a time-dependent tuning effect on the Au valence states using low-energy 200 V acceleration voltage Ar+ ion bombardment, and the valence state conversion kinetics involves the reduction from Au3+ and Au1+ to Au0. Proper control of the reduction in the valence states is critical in surface engineering for controlling catalytic reactions.

Plasma-enhanced atomic layer deposition of aluminum-indium oxide thin films and associated device applications

In this study, aluminum-indium oxide (AIO) semiconductors were fabricated by plasma-enhanced atomic layer deposition (ALD) using trimethyl (dimethylamino)propyl dimethyl indium and trimethylaluminum as the indium and aluminum precursors, respectively. The ALD supercycle consists of n indium oxide subcycles and one aluminum oxide subcycle, where n is 6, 9, 19, or 29. As the number of indium oxide subcycles decrease, the aluminum concentration in the AIO thin film increases and diminishes the thin film crystallinity. In addition, the chemical binding states of the AIO thin film also change with the number of indium oxide subcycles. AIO thin films made with a high number of indium oxide subcycles show stable aluminum oxide bonding and low oxygen related defects. In contrast, AIO thin films deposited with a small number of indium oxide subcycles form unstable AlOx, InOx, and oxygen related defects. The control of aluminum concentration in AIO thin films is essential to control the defect sites in the thin film. Finally, thin film transistors using AIO thin films are fabricated, demonstrating 2.16 V, 6.07 cm2/V s, and 1.50 V/decade with an optimized number of indium oxide subcycles.

Metallized polyimide films for biomedical applications: X‐ray photoelectron spectroscopy, surface tension, and blood compatibility studies

AbstractThe implications of nitrogen plasma exposure of a semi‐aromatic polyimide (PI) and a fully aromatic one, was studied in regard to gold adhesion for biomedical purposes. The hydrophobicity of the analyzed PI films, estimated by the contact angle method, was influenced by both plasma treatment and gold sputtering. Comparative evaluation of the chemical binding states and surface chemical composition was determined by X‐ray photoelectron spectroscopy (XPS) for pristine, plasma treated, and metallized PI films. The appearance of the polar functional groups upon plasma exposure facilitates binding of the gold on the PI surface. Hemocompatibility was theoretically evaluated based on surface tension data. The observed characteristics of the metallized samples could be useful for making components for blood contacting devices, such as blood pressure or blood glucose detection.

Interfacial control of SrTiO3/Si(0 0 1) epitaxy and its effect on physical and optical properties

The direct heteroepitaxy of strontium titanate (SrTiO3, STO) oxide on Si(001) substrate is an important step to integrate other functional perovskite oxides onto large scale wafers. In this study, we focused on the SrO interfacial layer in function of molecular oxygen gas exposure amount prior to the STO growth. The various formed interfaces showed large impact on the subsequent STO growth, including crystal quality and stoichiometry. The chemical binding states showed that the formation of thick SiOx interfacial layer was strongly correlated with the molecular oxygen exposure amount. More interestingly, the film stoichiometry is also strongly affected with overexposure, which resulted in optical properties degradation of the STO films. The STO optical constants, extracted from the spectroscopic ellipsometry (SE), exhibit obvious differences between crystalline and amorphous samples. Finally, post-deposition annealing was used to reduce the optical extinction, which is of primary importance for photonic applications.

XPS analysis of metallic trace contaminations on fused silica surfaces induced by classical optics manufacturing

Impurities on glass surfaces, such as metallic trace contaminations induced by manufacturing processes, can cause severely disturbing effects as for example, a reduction in laser resistance or optical performance. Both the amount and nature of such impurities was thus investigated in the present work. For this purpose, fused silica surfaces were produced by classical optics manufacturing consisting of cutting, grinding or lapping and polishing with different pad materials. After each production step, the amount and the chemical binding state of the trace contaminations of interest–calcium, cerium and sodium, originating from the used operating materials–were determined via X-ray photoelectron spectroscopy. It is shown that in the course of manufacturing the chemical bonds of these elements and its compounds are modified. The polished fused silica optics feature the trace elements sodium, cerium and calcium bound in the form of NaOH, Ce2O3 and CaF2. Such surfaces moreover feature the lowest grade of contamination in the range of 0.2–0.5 atom-%.

Photovoltaic Properties and Surface Analysis of Mixed (SnS2)x (CdS)1-x Thin Films by X-ray Photoelectron Spectroscopy (XPS)

Mixed thin films (SnS2)x(CdS)1-x with various x compositions (x=1, 0.8, 0.2, 0) have been synthesized by spray pyrolysis technique at a substrate temperature of 350°C. Cadmium chloride (CdCl2), Tin chloride (SnCl2), and thiourea (SC(NH2)2) were used as starting chemicals at different compositions. The chemical binding state of the deposited thin films was studied by X-ray photoelectron spectroscopy (XPS). XPS studies indicate the formation of the single phase of CdS and SnS2 thin films and mixed-phase (SnS2)x (CdS)1-x for x=0.8 and x=0.2. Four components of oxygen change in chemical states which are different in BE have been distinguished and studied in the O 1s spectrum. The optical expected absorption capacity and photocurrent (jph) depend on x concentration.

Effect of Surface Treatment on XPS Test of Graphene Films

Graphene was attended widely in recent years because of its excellent performance in electrical, mechanical, optical and magnetic applications. X-ray photoelectron spectroscopy (XPS) is commonly used tools for studying the chemical binding state, chemical modification, heteroatom dopants and quantitative chemical composition of graphene. In this work, XPS characterization of graphene films, obtained through reduction and then thermal treatment of graphene oxide films, was studied. The XPS of the graphene films are performed by direct testing, Ar+ etching, and direct peeling of the surface layer. The result shows that for graphene film, direct peeling is a simple and easy to use low-cost treatment, which can also be extended to XPS testing of other two-dimensional (2D) materials.

Nano-Grain Ni/ZrO2 Functional Gradient Coating Fabricated by Double Pulses Electrodeposition with Enhanced High Temperature Corrosion Performance

Functional gradient materials (FGM) have many excellent properties, and high-performance gradient coating exhibits good prospective application. In this paper, the nano-grain Ni/ZrO2 gradient coating was prepared by double pulse electrodeposition (BP). The surface morphology, crystal structure and electrochemical corrosion resistance of the nano-grain Ni/ZrO2 coating and Ni coating, annealed at different temperatures (400–800 °C), have been compared. In the vertical direction to the substrate surface, the content of ZrO2 increases from 0% to 34.99%. X-ray diffraction (XRD) revealed that the average crystal size of Ni/ZrO2 gradient coating gradually increases from 13.75 to 27.75 nm, and the crystal structure is a face-centered cubic (FCC). The main crystal orientation faces are (111) and (200), while the (200) face exhibited a stronger preferred orientation. Compared with the Ni coating by scanning electron microscopy, the surface morphology of double pulse fabricated Ni/ZrO2 gradient coating was revealed as being smoother, denser, and having fewer pores, and the crystal particle size distribution became narrow. X-ray photoelectron spectroscopy (XPS) shows that the chemical binding states of elements Ni and Zr have been altered. The binding energies of 2p3/2 and 2p1/2 for Ni have been increased, resulting in a higher electron donor state of Ni. The binding energy of 3d5/2 and 3d3/2 of Zr4+ in ZrO2 is decreased, thus becoming better electron acceptors. Chemical bonding has been formed at the Ni/ZrO2 interface. This study demonstrated that double pulse electrodeposition is a promising fabrication method for functional gradient coatings for high temperature applications.

Characteristics of etching residues on the upper sidewall after anisotropic plasma etching of silicon

Anisotropic Si nano-trench structures were fabricated using inductively coupled HBr + Cl2 plasmas for sidewall etching residue analysis. The sidewall etching residues formed inside the Si nano-trench patterns were analyzed via tilted X-ray photoelectron spectroscopy. The changes in the chemical composition and binding state of the etching residues formed on the Si nano-trench sidewalls were investigated with various gas mixing ratios in HBr + Cl2 plasma etching processes. The sidewall chemistry of the plasma-etched Si nano-trench patterns was examined at various take-off angles. SiO2 and suboxide groups (SixOy, x ≤ 2, y ≤ 3) were formed on the Si nano-trench sidewalls after the plasma etching. An increase in the chlorine content of the gas plasma resulted in the increased formation of SiO2 and suboxide residual groups on the Si nano-trench sidewalls. Additionally, the changes in the chemical states of the Si nano-trench sidewalls after a wet-cleaning process were examined using our designed experimental technique.

Ultrathin Ag2WO4-coated P-doped g-C3N4 nanosheets with remarkable photocatalytic performance for indomethacin degradation

As a metal-free photocatalyst, the photocatalytic activity of graphitic carbon nitride (g-C3N4) remains restricted due to an insufficient visible-light absorption capacity, the rapid recombination of photoinduced carriers, and low surface area. Consequently, P-doped g-C3N4 (PCN) was successfully prepared via a single -step thermal polymerization technique using phytic acid biomass and urea, which exhibited remarkable photocatalytic activity for the degradation of indometacin (IDM). The IDM degradation rate was 7.1 times greater than that of pristine g-C3N4 (CN). Furthermore, Ag2WO4 was loaded onto the surface of the PCN, which formed a Z-scheme heterostructure that promoted the separation of photogenerated carriers. According to analyses of the chemical binding states of PCN, P atoms replaced carbon atoms in the CN framework. According to electron localization function analysis, the low ELF values of P-N facilitated the transfer of photoelectrons. The results of active species scavenging experiments confirmed that superoxide radicals were the primary active species in the photocatalytic degradation system. Finally, the photocatalytic degradation pathways of IDM were predicted through the identification of by-products and IDM reaction sites.

Preparation, characterization and photocatalytic activity of nickel-substituted CoFe2O4: exploration of changes in the micro structural parameters and distribution of cations in the lattice

NixCo1−x Fe2O4 (x = 0.0, 0.3, 0.6 and 0.9) samples were prepared by sol-gel combustion method and were characterized by various analytical techniques. The tetrahedral (A) and octahedral (B) radius permits one to calculate the edge length and bond length of M–O at A and B sites. Cation distribution is used to calculate the ionic radius of tetrahedral and octahedral sites and oxygen positional parameter. We investigated the effects of Ni+2 substitutions on structural and electrochemical properties of CoFe2O4. Due to difference in the ionic radius of Ni2+ and Fe3+ for tetrahedral site and Co2+ and Fe3+ for octahedral site the changes are observed in the structural parameter like hopping length at tetrahedral (LA) site and octahedral (LB) and x-ray density. Ni0.6Co0.4 Fe2O4 shows lower charge transfer resistivity compared to other composition. UV-visible spectra of CoFe2O4, Ni0.3Co0.7Fe2O4, Ni0.6Co 0.4Fe2O4 and Ni 0.9Co 0.1Fe2O4 shows wide absorption and the calculated band gap values were found to be 2.59, 2.24, 2.17 and 2.41 eV respectively. The continue absorption implies active d-d transitions involving transition metals present in the composite. The PL spectra show lesser recombination of photogenerated charge carriers for Ni0.6Co 0.4Fe2O4 catalyst compared to other catalysts. Lower intensity peak represents the lower recombination rate. The chemical environment and elemental binding states of Co, Ni, Fe and O were confirmed by XPS analysis. Photocatalytic activity follows in the decreasing order Ni0.6Co0.4Fe2O4 > Ni0.9Co0.1 Fe2O4 > Ni0.3Co0.7 Fe2O4 > CoFe2O4. Superoxide, perhydroxy radical and hydroxyl free radicals are involved in the degradation of Alizarin Red S (ARS).

Effect of cobalt doping on the structural, optical and magnetic properties of sol-gel derived ZnS nanocrystalline thin films and ab initio studies

The effect of Co doping on the structural, optical and magnetic properties of sol-gel derived ZnS films was investigated for their dilute magnetic semiconducting behaviour. X-ray diffraction pattern shows nanocrystalline nature of the films. Raman spectroscopy was used to study the vibrational properties of the films and also to identify any kind of secondary phases. The surface morphology and roughness of the films was analysed through scanning electron microscopy and atomic force microscopy. The chemical binding state of Co in ZnS lattice was confirmed from the X-ray photoelectron spectroscopy. The optical band gap is found to be decreasing with the incorporation of Co in ZnS. The red emission ~1.7 eV ensures tetrahedral occupation of Co atoms in ZnS lattice. The observed room temperature ferromagnetism in Co:ZnS films is attributed to carrier induced magnetization as well as to the intrinsic defects. The origin of magnetism in Co:ZnS system was studied in terms of the spin-polarized electronic density of states obtained through the density functional theory.

X-RAY PHOTOELECTRON SPECTROSCOPIC STUDY ON HIGH-ELECTRON-MOBILITY GALLIUM AND HYDROGEN CO-DOPED ZINC OXIDE THIN FILMS

In this study, gallium and hydrogen co-doped ZnO (HGZO) thin films were investigated. The films were deposited by sputtering from Ga-doped ZnO (GZO) ceramic target in hydrogen and argon plasma. The as-deposited HGZO films possess enhanced electron mobility of 48.6 cm2/Vs as compared to that of 39.4 cm2/Vs of GZO films, sputtered from the same target. Because of insignificant variation in crystallinity, this improvement is attributed to roles of hydrogen in crystalline lattice structure of the films. X-ray photoelectron spectroscopy (XPS) is employed as an essential technique for quantitative analyses and chemical binding states of films constituent elements. The roles of hydrogen are clarified through the binding states of Zn 2p, O 1s and Ga 3d. Obtained results suggest that the films are deposited more effectively in hydrogen plasma. Some point defects such as oxygen vacancies (VO), dangling bonds can be passivated in form of H+VOHO and O–H bonds. As a result, the reduction of scattering centers is indicated as a reason for the mobility improvement of the HGZO films.

Photoluminescence properties of SrLaMgTaO6 double-perovskite thin film

We deposited epitaxial and polycrystalline SrLaMgTaO6 (SLMTO) thin films on SrTiO3 (001) and MgO (001) substrates, respectively, using pulsed laser deposition, and investigated the dependence of the structural and photoluminescence (PL) properties on the substrate. The X-ray diffraction patterns were examined to determine the growth behaviors of the SLMTO films on the SrTiO3 (001) and MgO (001) substrates. Under the same deposition conditions, the SLMTO films deposited on the SrTiO3 (001) substrate were aligned out of the substrate plane, whereas those on the MgO substrate exhibited polycrystalline growth. The PL spectra revealed that the SLMTO films exhibited significantly different visible light emissions. Further, X-ray photoelectron spectroscopy (XPS) analysis indicated differences in the chemical binding states of the TaO and MgO bonds on the surfaces of the thin film samples; these states play an important role in the visible light emission.

Using the light scattering properties of multi-textured AZO films on inverted hemisphere textured glass surface morphologies to improve the efficiency of silicon thin film solar cells

We report the light scattering characteristics of multi-textured aluminum-doped zinc oxide (AZO) thin films with high optical transmittance, haze ratio and step coverage for amorphous silicon thin film solar cells (a-Si TFSCs). Multi-textured AZO films were deposited on inverted hemisphere textured (IHT) glass surface morphologies. Multi-textured process was used to create modulated surface morphologies with micro and nano-features useful for the light scattering in visible as well as near-infrared wavelength region. Highly transparent IHT glass surface morphologies with high haze ratio were prepared by wet chemical etching of periodic glass substrates. Total transmittance of the IHT glass substrates showed higher average values (91.38–93.40%) as compared to that of bare glass (90.94%) in the visible wavelength region due to lower reflectance. Multi-textured AZO films showed higher rms roughness 100.479 nm, optical transmittance 82.60% and haze ratio 75.09% in the visible wavelength region. X-ray photoelectron spectroscopic analysis of multi-textured AZO thin films was used to study the atomic compositions and chemical binding states. Multi-textured AZO films with high transmittance and haze ratio were used as front transparent conductive oxide layers for the fabrication of a-Si TFSCs using an absorber layer thickness of 400 nm. Multi-textured AZO films deposited on the optimal textured glass surface morphologies yield the maximum performance of a-Si TFSCs as; Voc = 871 mV, Jsc = 16.55 mA/cm2, FF = 66.6% and η = 9.61%. An enhancement of photocurrent was noticed from 15.64 to 16.55 mA/cm2 for the a-Si TFSCs deposited on as deposit AZO to optimal textured AZO films.