X-ray Photoelectron Spectroscopy Investigation Research Articles

Thermal atomic layer etching of CoO using acetylacetone and ozone: Evidence for changes in oxidation state and crystal structure during sequential exposures

Thermal atomic layer etching (ALE) of CoO was demonstrated using sequential exposures of acetylacetone (Hacac) and ozone (O3). During the surface reactions, Hacac can remove CoO according to: CoO + 2Hacac → Co(acac)2 + H2O. Ozone was employed to eliminate carbon residue resulting from Hacac adsorption. In situ spectroscopic ellipsometry observed a linear decrease in CoO film thickness versus Hacac and O3 exposures with an etch rate of 0.43 Å/cycle at 250 °C. The surface of the CoO film was also observed to undergo changes in oxidation state and crystal structure with each reactant exposure. Ex situ grazing incidence X-ray diffraction (GIXRD) studies revealed that the initial h-CoO thin films were oxidized to c-Co3O4 by O3. Subsequently, the GIXRD analysis showed that the c-Co3O4 thin films were reduced to c-CoO by Hacac. X-ray photoelectron spectroscopy investigations confirmed the oxidation state of the various cobalt oxides. Quadrupole mass spectrometry measurements observed Co(acac)2 etch products during Hacac exposures on Co3O4 and CoO powder. Atomic force microscopy measurements also monitored a reduction in surface roughness during CoO ALE. These studies reveal that alternating changes in oxidation state and crystal structure occur during the sequential Hacac and O3 exposures that define CoO thermal ALE.

Memristive effect in niobium oxide thin films obtained by the pulsed laser deposition

NbOx thin films demonstrating the analog resistive switching characteristics in planar geometry were fabricated by the droplet-free pulsed laser deposition from Nb metal targets. The memristive properties of the films were controlled by tuning the oxygen pressure from 0.7 to 8 Pa and the wavelength of the ablative laser (λ = 248 nm or λ = 532 nm). The stoichiometry of the NbOx films was controlled by the X-ray photoelectron spectroscopy, optical and electrical investigations. Variation of the film thickness from 20 to 50 nm affects the resistive switching characteristics. The 20 nm NbO2 films obtained at the oxygen pressure of 1.3 Pa show a volatile memristive switching with a memory window of ON/OFF resistances ∼ 101 after 500 direct current cycles at an operating voltage of 4.5 V. The 30 nm Nb2O5 films fabricated at the oxygen pressure of 4 Pa, showed a gradual increase in device conductivity with successive positive voltage sweeps with an amplitude of +5 V, which is characteristic of non-volatile memristive switching. Thus, the use of NbOx memristive films of different compositions and crystallinity degree will allow creating neuromorphic systems based on the same material by controlling the memristive behavior by the laser synthesis conditions.

Hydrothermal Fabrication of GO Decorated Dy2WO6-ZnO Ternary Nanocomposites: An Efficient Photocatalyst for the Degradation of Organic Dye

Environmental and human health are seriously threatened by organic dye pollution. Many efforts have been made to find effective and safe methods of eliminating these contaminants. To mitigate these effects, the hydrothermal method was used to effectively generate a ternary kind of Dy2WO6-ZnO embedded in graphene oxide (DWZG) nanocomposites, which were used to degrade the pollutant. Powder X-ray diffraction (XRD) investigation confirms the crystalline character of the as-prepared DWZG nanocomposite. The Dy2WO6-ZnO composition on the graphene oxide (GO) layer is shaped like a combination of algae (Dy2WO6) and clusters (ZnO), as shown by scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) investigation revealed the composition of elements and oxidation state of C, Dy, O, W and Zn elements. Methylene blue (MB) was chosen as the organic dye target for photocatalytic degradation using the produced nanocomposites. MB is degraded with a photocatalytic efficiency of 98.2% in about 30 min using a DWZG catalyst. Based on the result of the research entitled “Reactive Oxidative Species,” the primary reactive species involved in the MB degradation are photo-generated •OH and O2•− radicals. The recycle test was also successful in evaluating the catalysts’ long-term viability as well as their reusability.

Salen-based porous aromatic frameworks with multi-active sites as anode materials for lithium-ion batteries

Porous organic polymers are considered as excellent candidates for the electrode materials in rechargeable battery due to their desirable properties including porosity, customizable structure, and intrinsic chemical stability. Herein a Salen-based porous aromatic framework (Zn/Salen-PAF) is synthesized through a metal directed method and further used as efficient anode materialfor lithium-ion battery. Attributing to the stable functional skeleton, Zn/Salen-PAF delivers a reversible capacity of 631 mAh·g−1 at 50 mA·g−1, a high-rate capability of 157 mAh·g−1 at 20.0 A·g−1 and a long-term cycling capacity of 218 mAh·g−1 at 5.0 A·g−1 even after 2000 cycles. Compared to the Salen-PAF without metal ions, Zn/Salen-PAF possesses better electrical conductivity and more active sites. X-ray photoelectron spectroscopy (XPS) investigation indicates that the coordination of Zn2+ with N2O2 unit not only improves the conjugation of the framework but also contributes to the in situ cross-sectional oxidation of the ligand during reaction, which results in the electron redistribution of oxygen atom and the formation of CO bonds.

XPS determination of the uranium valences in U3O8

Uranium oxides are tightly related to the whole nuclear fuel cycle in the nuclear industry. However, the understanding of the chemical states in mixed valence uranium oxides remains scattered and deserves more exploration. The current study aims to recognize the valences of uranium in U3O8 by a simple X-ray photoelectron spectroscopy (XPS) investigation. U3O8 mixed with TiO2 was photocatalytically reduced under UV or X-ray irradiation, and the chemical states were in-situ determined by XPS. Under UV irradiation, the shoulder peaks at 380.9 eV (U 4f7/2) and 392.7 eV (U 4f5/2) gradually increased, and an enhancement in intensity was also observed at 399.6 eV, which is the characteristic of U(V) satellite. Therefore, it was proved that the shoulder peak originated from U(V), and U3O8 consists of U(V) and U(VI). Under the irradiation by X-ray, the main lines of U 4f shifted lower by ∼0.8 eV, and a new satellite at ∼397.6 eV appeared and grew with increasing irradiation time, proving the generation of U(IV). This in turn verified that the shoulder peaks in primary U3O8 should be U(V) rather than U(IV). Therefore, it was confirmed by the current study that there are two-U(V) and one-U(VI) in each U3O8 unit cell.

Pressureless manufacturing of high purity Ti3AlC2 MAX phase material: Synthesis and characterisation

The reported study involves the synthesis of high purity layered ternary carbide Ti3AlC2 MAX phase material by mixing the TiH2, Al and TiC powders in a planetary ball mill followed by two step pressureless sintering in flowing Argon (Ar) atmosphere. XRD and Raman analysis confirms the presence of Ti3AlC2 phase without impurities of Al2O3 and TiC. The morphology studies using SEM confirms the lamellar structure of Ti3AlC2 and EDS measurements shows atomic percentage of Ti, Al and C are in compliance with the XRD phase analysis. X-ray Photoelectron spectroscopy investigations confirm the Ti–C bond. Core level XPS data of Al2p peak show a negative shift indicating electrostatic bonding of Al in Ti3AlC2. Ti2p and C1s core level spectra show the bonding of Mn+1Xn i.e TiC bond. TG-DSC results revealed approximately 7% increase in weight. Ti3AlC2 phase follows an endothermic pattern and does not undergo decomposition upto 1400 °C in vacuum environment. From XRD analysis at different temperatures, it was seen that Al2O3 and TiCx peaks started to form along with Ti3AlC2 at 1000 °C because of selective oxidation of Al into Al2O3. Thus, this study provides a beneficial approach to synthesis of high-purity Ti3AlC2 materials and understanding the thermal behaviour of Ti3AlC2 for high temperature applications.

Adsorption and X-ray photoelectron spectroscopy investigation of bisphosphonates on titania and hydroxyapatite surfaces

This study investigates the adsorption of bisphosphonates (BPs) on TiO2, hydroxyapatite (HA), and TiO2+HA composite surfaces. We first examined the adsorption of these molecules on titania particles and explored the influence of UV irradiation through adsorption curves. Our findings indicate that surface irradiation leads to an increase in the adsorbed BP content due to enhanced BP deprotonation and hydroxyl group generation. Additionally, we evaluated the adsorption of BPs on the TiO2, HA, and TiO2+HA surfaces primarily through X-ray photoelectron spectroscopy (XPS). Our results suggest that BPs adsorb onto TiO2 via a condensation reaction between the BPs and titania surfaces, while phosphate and Ca2+ ions coordinate onto HA surfaces. All functionalized films exhibit a water contact angle of zero. Atomic force microscopy (AFM) measurements show that BP adsorption had less impact on titania topography than HA topography, and mixed films demonstrated behavior similar to that of titania films.

Irradiation-enhanced Interactions at UO2/Al2O3/Al Interfaces

Combustion synthesis is used to prepare thin UO2 films on aluminum alloy substrates. This simple preparation method involves electrospraying uranyl nitrate + acetylacetone + 2-methoxyethanol solution on the substrate, followed by a short annealing at 350 or 550 °C. The irradiation of films with a 40Ar2+ ion beam (energy of 1.7 MeV and fluences of 7.7 × 1016 and 1.3 × 1017 ions/cm2) is conducted to investigate irradiation-induced restructuring processes. High-resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) investigations show that the annealing temperature significantly influences the crystallinity and stability of materials during irradiation. A small amount of Mg in the alloy substrate diffuses into the amorphous Al2O3 interfacial layer between the film and the substrate. Local thermal spikes from the incoming ions facilitate the irradiation-induced mixing of immiscible Al2O3 and UO2 for the materials prepared at 350 °C. This mass diffusion produces relatively large cavities at the interface. Selective diffusion of a more significant amount of Mg for the materials prepared at 550 °C suppresses the mixing of the Al2O3 interlayer with the film but forms MgyU1–yO2±x solid solutions during irradiation. Local thermal heating triggers the precipitation of a discontinuous crystalline MgO layer close to the film surface. The enhanced and selective diffusion of Mg into the film makes the materials prepared at 550 °C more robust and mechanically stable than those prepared at 350 °C.

Impedance Spectroscopy on Hafnium Oxide‐Based Memristive Devices

AbstractMemristive devices for neuromorphic computing have been attracting ever growing attention over the last couple of years. In neuromorphic electronics, memristive devices with multi‐level resistance states are required to accurately reproduce synaptic weights. Here, a memristive device based on a multilayer oxide system (Nb/NbOx/Al2O3/HfO2/Au), which features a filamentary‐free, homogenous interfacial resistive switching mechanism, is investigated. To gain a deeper insight into the switching mechanism, impedance spectroscopy (ImpSpec), X‐ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) are exploited. While this work focuses on the analysis of impedance and current‐voltage characteristics, XPS and TEM investigations can be found in a companion paper (Zahari et al.). In the course of this investigation, potentiodynamic impedance spectroscopy (PD‐ImpSpec) and time resolved impedance spectroscopy (TR‐ImpSpec) in combination with transient analysis are used. Evidence is presented of switching kinetics at voltages above 2.1 V directly related to changes in Schottky barrier resistance. These switching kinetics can in turn be interpreted by the charging and discharging of double positively charged oxygen vacancies ≈ 0.9 eV. The results of the impedance analysis are translated into a more general model for memristive devices to map the physical processes during switching.

High Poisonous Cd Ions Removal by Ru-ZnO-g-C3N4 Nanocomposite: Description and Adsorption Mechanism

Ru-ZnO-g-C3N4 nanocomposite was made using a straightforward ultrasonication method and evaluated for its potential to remove Cd ions from aqueous environments. X-ray diffraction analysis confirms composite production with an average crystalline size of 6.61 nm, while transmission electron microscopy results indicate nanosheet-like nanomaterials with uniform elements distribution. Measurements of N2 adsorption–desorption reveal the creation of a mesoporous structure with a BET surface area of approximately 257 m2/g. Fourier converted infrared reveals vibrational modes for O-H, amino groups, triazine, and Ru-ZnO. In contrast, X-ray photoelectron spectroscopy investigation reveals the presence of the elements Ru, Zn, O, N, and C. Ru-ZnO-g-C3N4 nanocomposite has remarkable adsorption efficiency for aqueous Cd ions, achieving 475.5 mg/g in 18 min. This study reveals that the Ru-ZnO-g-C3N4 nanocomposite may be used as an effective and reusable adsorbent for removing Cd ions during wastewater treatment and, possibly, for eliminating other toxic metal ions.

Synergistic Reductive Electrolysis Mixture Additive-Based Dual-Cell Configuration: An Effective Approach for High-Performance Aqueous Aluminum–Air Battery

Neutral aqueous electrolyte-based aluminum–air (Al–air) batteries have managed to gather significant attention because of their characteristic safety and cost effectiveness. However, the formation of the passivation layer [Al(OH)3] on the aluminum anode inhibits the long-term shelf life of the battery. Herein, a novel strategy to overturn the passivation by altering the aluminum/electrolyte interface is proposed. Incorporation of synergistic reductive electrolysis mixture additives (Tiron + NaNO3) can significantly reduce the passivation of the aluminum anode. The efficacy of the Tiron + NaNO3 synergistic mixture additive has been systematically examined using half-cell and full-cell with different concentrations of the additives in 0.5% NaCl. Furthermore, dual cell performance was investigated with optimum concentration (0.005 M Tiron + 0.005 M NaNO3) of the additive in 0.5% NaCl as the anolyte and different concentrations of H2SO4 as the catholyte. It is found that the resulting pumpless dual cell battery comprising neutral electrolyte with 0.005 M Tiron + 0.005 M NaNO3 mixture additive as the anolyte and 1 M H2SO4 as the catholyte demonstrated a remarkable cell potential of 1.14 V at a current density of 1 mA g–1, which is closer to the theoretical value. Morphological investigations using optical microscopy studies and X-ray photoelectron spectroscopic investigations also confirmed that the Tiron + NaNO3 additive is effective in preventing the discharge product on both anode and cathode surfaces and thus resulting in enhanced battery performance.

BiOBr Surface-Functionalized Halide Double-Perovskite Films for Slow Ion Migration and Improved Stability

Surface-tailored lead-free halide double-perovskite (Cs2AgBiX6) thin films are utilized for ion migration studies. A thin surface layer of BiOBr/Cl is grown via intentional annealing of the halide films in ambient conditions. Herein, we physically stacked the two films, viz., Cs2AgBiBr6 and Cs2AgBiCl6, to thermally activate the halide ion migration at different temperatures (room temperature (RT)-150 °C). While annealing, the films' color changes from orange to pale yellow and transparent brown to yellow as a result of the migration of Br- ions from Cs2AgBiBr6 to Cs2AgBiCl6 and Cl- ions from Cs2AgBiCl6 to Cs2AgBiBr6, respectively. Annealing helps in homogenizing the halide ions throughout the films, consequently leading to a mixed phase, i.e., Cs2AgBiClxBr6-x/Cs2AgBiBrxCl6-x (x = 0 to 6) formation. The movement of ions is understood by absorption studies performed at regular time intervals. These investigations reveal a redshift (from 366 to 386 nm) and a blueshift (from 435 to 386 nm) in absorption spectra, indicating the migration of Br- and Cl- toward Cs2AgBiCl6 and Cs2AgBiBr6, respectively. The films characterized using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) reveal the presence of a peak at 2θ = 10.90° and binding energy of 158.1 eV, respectively, corresponding to the formation of Bi-O bonds at the film surface. Also, XRD studies show a lower 2θ shift of the diffraction peak in the case of Cs2AgBiCl6 films and a higher 2θ shift in the case of Cs2AgBiB6 films, which further confirms the migration of Cl- and Br- from one film to the other. XPS investigations confirm the compositional change with a gradual increment in the concentration of Br-/Cl- with an increase in heating time for Cs2AgBiCl6/Cs2AgBiBr6 films. All these studies confirm thermal diffusion of halide ions in double-perovskite films. Further, from the exponential decay of the absorption spectra, the rate constant for halide (Br) ion diffusion is calculated, which shows an increment from 1.7 × 10-6 s-1 at RT to 12.1 × 10-3 s-1 at 150 °C. The temperature-dependent rate constant follows Arrhenius behavior and renders an activation energy of 0.42 eV (0.35 eV) for bromide (chloride) ion mobility. A larger estimated value as compared to the reported values for Cs2AgBiBr6 wafers (∼0.20 eV) reveals a slow mobility of halide ions in thin films of Cs2AgBiBr6/Cl6. The formation of a BiOBr passivation layer at the surface of Cs2AgBiBr6 thin film might be one of the plausible causes of the slow anion diffusion in the present work. Slow ion migration is an indication that the films are stable and of high-quality.

Role of SiCl4 addition in CH3F/O2 based chemistry for Si3N4 etching selectively to SiO2, SiCO, and Si

Dry etching of amorphous silicon nitride (Si3N4) selectively toward silicon dioxide (SiO2), silicon oxicarbide (SiCO), and crystalline silicon (c-Si) in an inductive coupled plasma reactor using CHF3/O2/He chemistry with SiCl4 addition is studied. Plasma exposure of c-Si, SiO2, and SiCO leads to an oxifluoride deposition. The deposition rate is the same for all these materials and increases linearly with the amount of SiCl4 added. On the other hand, Si3N4 etching is observed at very small amount of SiCl4 added (2 SCCM), while oxide deposition takes place at higher SiCl4 flow (10 SCCM). Quasi-in situ angle resolved x-ray photoelectron spectroscopy investigation shows oxifluoride SiOxFy deposition on c-Si and SiCO, while a thin F-rich reactive layer is observed on Si3N4. The oxidation of the Si3N4 surface with O2 plasma prior to CHF3/O2/He with small SiCl4 addition plasma treatment showed that the oxidation state plays a significant role in the etching/deposition equilibrium. In addition, it is found that oxifluoride deposition on Si3N4 is driven by ion energy, with deposition observed at 0 V substrate bias voltage, while etching is observed for values higher than 150 V. All these results show that a competition takes place between silicon oxifluoride deposition and etching, depending on the substrate material, surface oxidation, and ion energy. Based on the additional optical emission spectroscopy data, we proposed insights to explain the different etching and deposition behaviors observed. It is focused on the crucial role of ion energy and the nitrogen presence in Si3N4 leading to the formation of CN and HCN, helping to get a thinner reactive layer and to evacuate etch by-products on Si3N4 while an oxifluoride buildup on the other materials takes place.

Synthesis, characterization and activity of CeO2 supported Cu-Mg bimetallic catalysts for CO2 to methanol

Cerium oxide was synthesized by thermal method using cerium carbonate hydrate and utilized as a catalysts support. Precipitation method was employed to deposit copper and magnesium oxides on the surface of cerium oxide. The synthesized Cu-Mg/CeO2 catalysts were characterized by different analytical techniques. FTIR studies confirmed the incorporation of copper and magnesium oxides on cerium oxide surface. Field Emission Scanning Electron Microscope (FESEM) revealed uniform distribution of both metal oxides on cerium oxide support. Nitrogen adsorption-desorption studies recorded surface profile of CeO2 loaded Cu-Mg bimetallic catalysts. The X-ray photoelectron spectroscopy (XPS) revealed existence of Cu and Mg metals in the form of Cu2+ and Mg2+ on CeO2 surface. Furthermore, the role of Ce was apprehended by XPS investigations in terms of methanol synthesis rate. Activities studied of the synthesized catalysts revealed the promoting role of Cu-Mg composition with highest activity of 71 g.meth/kg.cat.h was recorded for 4Cu-6Mg/CeO2 catalysts. The efficiency of CeO2 based Cu-Mg bimetallic catalysts was established by the comparative data from the literature in terms of methanol synthesis rate.

X-ray photoelectron spectroscopic investigation of atomic-layer-deposited spinel Li4Ti5O12: Calcination under reducing atmosphere

Across all material candidates used as anodes in lithium-ion batteries, lithium titanate (Li4Ti5O12) (LTO) is an excellent replacement for conventional electrode materials, such as graphite or silicon. Compares to commercial graphite anodes, LTO offers a higher charging rate and safer operation, and compares to silicon, it undergoes almost no volume expansion during intercalation of lithium ions into the crystal lattice, so-called zero-strain material. However, the LTO performance still suffers from low conductivity due to the oxidation of titanium (Ti) in spinel-LTO and low ionic kinetics diffusion while cycling, which largely limits its application in solid-state batteries. Modifying the LTO lattice or crystal structure is one way to mitigate this problem. This study shows the coexistence of two main components, Ti4+ and Ti3+, in the crystal structure of LTO developed with a modified atomic layer deposition. The X-ray photoelectron spectroscopy analysis shows calcination under reducing gas, introduces Ti3+ and oxygen vacancies into the Li4Ti5O12 crystal, which can affect the electronic conductivity of LTO. Furthermore, we show how different substrates acting as diffusion barriers affect the film properties.

Mechanochemical Synthesis of Bi2VO5.5 for Improved Photocatalytic Dye Degradation.

A single-phase Bi2VO5.5 powder is formed effectively through a mechanochemical ball milling approach at 650 °C in 5h and its photocatalytic performance on methylene blue dye is explored. X-ray diffraction and Raman spectroscopy analytical instruments are utilized to confirm the phase formation. The evident presence of irregular-shaped grains is affirmed using a scanning electron microscope. To ascertain the chemical condition of the components present, the Bi2VO5.5 powdered sample undergo an X-Ray photoelectron spectroscopy investigation. The sample is analyzed using a time-dependent photocurrent to discern its charge carrier transportation behavior. A photocatalytic study using Bi2VO5.5 powder produced through the mechanochemical ball milling method has not been explored till now. The efficacy of the ball-milled Bi2VO5.5 powder to attain enhanced photocatalytic efficiency which hasn't been investigated till now, is explored. The ball-milled Bi2VO5.5 sample achieved 70% degradation efficiency when performing the photocatalysis investigation. The photocatalytic dye degradation discerns pseudo-first-order kinetics and achieves a notable k value of 0.00636 min-1. The scavenger test indicates that h+ radicals are the prominent active species during the photocatalysis experiment. The germination index is determined by conducting a phytotoxicity test with the use of Vigna radiata seeds. Here ball-milled Bi2VO5.5 powder attains enhanced dye degradation efficiency.

Modulation of Structural, Electronic, and Optical Properties of Titanium Nitride Thin Films by Regulated In Situ Oxidation

Epitaxial titanium nitride (TiN) and titanium oxynitride (TiON) thin films have been grown on sapphire substrates using a pulsed laser deposition (PLD) method in high-vacuum conditions (base pressure <3 × 10-6 T). This vacuum contains enough residual oxygen to allow a time-independent gas phase oxidation of the ablated species as well as a time-dependent regulated surface oxidation of TiN to TiON films. The time-dependent surface oxidation is controlled by means of film deposition time that, in turn, is controlled by changing the number of laser pulses impinging on the polycrystalline TiN target at a constant repetition rate. By changing the number of laser pulses from 150 to 5000, unoxidized (or negligibly oxidized) and oxidized TiN films have been obtained with the thickness in the range of four unit cells to 70 unit cells of TiN/TiON. X-ray photoelectron spectroscopy (XPS) investigations reveal higher oxygen content in TiON films prepared with a larger number of laser pulses. The oxidation of TiN films is achieved by precisely controlling the time of deposition, which affects the surface diffusion of oxygen to the TiN film lattice. The lattice constants of the TiON films obtained by x-ray diffraction (XRD) increase with the oxygen content in the film, as predicted by molecular dynamics (MD) simulations. The lattice constant increase is explained based on a larger electrostatic repulsive force due to unbalanced local charges in the vicinity of Ti vacancies and substitutional O. The bandgap of TiN and TiON films, measured using UV-visible spectroscopy, has an asymmetric V-shaped variation as a function of the number of pulses. The bandgap variation following the lower number of laser pulses (150-750) of the V-shaped curve is explained using the quantum confinement effect, while the bandgap variation following the higher number of laser pulses (1000-5000) is associated with the modification in the band structure due to hybridization of O2p and N2p energy levels.

Study of Defect-Induced Chemical Modifications in Spinel Zinc-Ferrites Nanostructures by In-Depth XPS Investigation

Spinel zinc ferrite nanomaterials with exceptional physiochemical properties are potential candidates for various applications in the energy and environmental fields. Their properties can be tailored using several methods to widen their applications. The chemical combustion approach was followed to prepare the spinel zinc ferrite nanomaterials, which were then subjected to thermal treatment at a fixed temperature. Thermal heat treatment at a fixed temperature was used to evaluate the phase and morphological characteristics of the prepared spinel zinc−ferrite nanocomposites. Various techniques were employed to examine the samples, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS and X-ray−induced Auger electron spectroscopy were used to extensively examine the surface characteristics of the zinc−ferrite. To study the actual chemical states of the synthesized spinel zinc ferrite nanomaterials and the defects created during the thermal treatment, an extensive investigation of the kinetic energy of the X-ray−induced Zn L3M45M45 and Fe L3M45M45 was conducted. Finally, a detailed analysis of the Wagner plot using the modified Auger parameter was performed to verify the exact chemical states of Zn and Fe. Thus, the findings of the investigation show that XPS is a promising and powerful technique to study the composition and chemical states of spinel zinc ferrites, providing an understanding of changes in their properties for functional applications.

Methodological approach to the chloramphenicol adsorption by acid-leached halloysites: Preparation, characterization, performance and mechanism

Adsorptive removal was found to be an environmentally friendly and effective approach to treat emerging contaminants such as chloramphenicol (CAP), an antibiotic widely used to care for human and animal diseases, which after using is discharged into the environment, disrupting thus ecosystems and inducing microbial resistance. In this study, we systematically investigated the effect of sulfuric acid treatment on the physico-chemical and adsorptive properties of halloysite with the objective of combining the results of acid-leached halloysite characterization, CAP adsorption and spectroscopic investigation to propose a coherent mechanism of the CAP−acid-leached halloysite interaction. After preparation, the acid-leached samples were characterized by X-ray diffraction analysis (XRD), X-ray fluorescence (XRF), N2 adsorption–desorption, Transmission electron microscopy (TEM), zetametry, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS), and used in CAP adsorption. The specific surface area increased significantly from 63 for H to a maximum of 240 m2 g−1 for the H2SO4-leached sample with 10 M concentration (H-10M). An amount of CAP adsorbed by the best adsorbent, H-10M, of 197.2 was found compared to 92.5 mg g−1 for H. The experimental isotherms were suitably fitted by the Langmuir-Freundlich equation. Thermodynamic parameters suggested physical, spontaneous, and endothermic adsorption. H-10M was easily desorbed by methanol whose involvement was explained by FTIR, and maintained its adsorption capacity for three cycles. By combining the results of the characterization, adsorption parameters such as the influence of pH, affinity, and thermodynamic data, and the FTIR and XPS (X-ray photoelectron spectroscopy) investigations between CAP and H-10M, a mechanism has been proposed which involves two interactions: a hydrophobic interaction taking place between −Si–O–Si− species and CAP aromatic ring and hydrogen bonding which occurs between the oxygen of the carbonyl group and the hydrogen of silanols (SiO–H). This integrated methodological approach has significant implications for the effective understanding and prediction of the environmental fate of these emergent contaminants in wastewater.

Effect of substrate temperature on properties of AlN buffer layer grown by remote plasma ALD

Aluminum nitride (AlN) thin film has considerable properties, which makes it advantages for a variety of applications. AlN films were prepared by remote plasma atomic layer deposition (RP-ALD) with the growth temperature of 100 to 450 °C. The properties of AlN films with various growth temperatures were studied systematically. In addition, AlN/GaN layers deposited on sapphire (Al2O3) substrates were also investigated. The AlN/GaN interfaces and AlN/Al2O3 interfaces characteristics were analyzed. The optical property of GaN films prepared on sapphire substrates with and without AlN buffer layer were identified by photoluminescence measurement. The experiment result shows that crystal AlN films became to present at 250 °C with a hexagonal wurtzite structure. X-ray photoelectron spectroscopy investigation shows that AlN films contain Al-O, Al-O-N complexes and Al-Al metallic aluminum bonds except the main Al-N bond confirmed by high resolution Al 2p and N 1 s spectra. High-resolution transmission electron microscopy measurement reveals sharp interfaces of AlN/Al2O3 and AlN/GaN. The obtained lowest lattice mismatch of AlN/Al2O3 and AlN/GaN are 11.0% and 2.1%, respectively. Photoluminescence measurement further confirms that AlN buffer layer enhances the quality of GaN grown on sapphire substrates. High quality AlN/GaN layers prepared by RP-ALD provides a promising pathway towards high quality GaN-based devices.