Al 2p Research Articles

Floc structure and membrane fouling affected by sodium alginate interaction with Al species as model organic pollutants

Membrane filtration combined with pre-coagulation has advantages in advanced wastewater treatment. As a model of a microbial polysaccharide, research on the effect of sodium alginate (SA) on alum hydrolysis has been rare; therefore, it is necessary to gain insight into the interface interaction between SA molecules and Al species, and the role SA plays during floc formation. In this study, the interaction mechanism between SA and Al species has been investigated, by evaluating the effect of SA on floc characteristics and membrane fouling during coagulation–ultrafiltration with different Al species coagulants (AlCl3 and preformed Al13). Al 2p X-ray photoelectron spectroscopy (XPS) confirmed that the complexation of ligands and Al species strongly affects the reaction pathways for Al hydrolysis and the final nature of the flocs, as Al13 can be decomposed into octahedral precipitates when SA is added. The presence of SA can affect floc properties, which have important impacts on the characteristics of the cake layer and membrane fouling. Due to the bridging ability of SA, the floc strength increased by about 50% using Ala, which was much better than preformed Al13, with a percentage increase of only about 6%. Moreover, the recovery factor of HA-flocs was decreased from 96% to 43% with SA addition of 0.5 mg/L. It was concluded that SA can affect the characteristics of the cake layer and membrane fouling through participating in the formation of primary flocs and altering the Al hydrolysis pathway.

First-principles X-ray photoelectron spectroscopy binding energy shift calculation for boron and aluminum defects in 3C-silicon carbide

We systematically investigated the core-level X-ray photoelectron spectroscopy (XPS) binding energy shifts of B 1s and Al 2p and formation energies for defects including boron and aluminum in 3C-silicon carbide (SiC) by first-principles calculation. We analyzed the relation between the XPS binding energy shift and defect states and found that the defects with localized electrons in the band gap or energy gap in the valence band have larger XPS relaxation energies (XPSREs) than those without localized electrons. In contrast, spread electrons and electrons localized away from the core hole hardly affect the XPSREs. Further, we analyzed the dependence on crystal matrices, that is, elemental and compound semiconductors, on XPS spectra by comparing the XPS spectra of Si and 3C-SiC. Although the variation of the local potential in 3C-SiC is larger than that in Si, the variations of their relaxation energies are comparable.

Synthesis of new Ln4(Al2O6F2)O2 (Ln = Sm, Eu, Gd) phases with a cuspidine-related structure.

The first fluorination of the cuspidine-related phases of Ln4(Al2O7□)O2 (where Ln = Sm, Eu, Gd) is reported. A low-temperature reaction with poly(vinyl-idene difluoride) lead to the fluorine being substituted in place of oxygen and inserted into the vacant position between the dialuminate groups. X-ray photoelectron spectroscopy shows the presence of the F 1s photoelectron together with an increase in Al 2p and rare-earth 4d binding energies supporting F incorporation. Energy-dispersive X-ray spectroscopy analyses are consistent with the formula Ln4(Al2O6F2)O2, confirming that substitution of one oxygen by two fluoride atoms has been achieved. Rietveld refinements show an expansion in the cell upon fluorination and confirm that the incorporation of fluoride in the Ln4(Al2O7□)O2 structure results in changes in Al coordination from four to five. Thus, the isolated tetrahedral dialuminate Al2O7 groups are converted to chains of distorted square-based pyramids. These structural results are also discussed based on Raman spectra.

Differential charging effects from impurities in pyrolytic graphite

This work reports differential charging effects in samples of pyrolytic graphite. Despite being considered a nuisance in XPS analyses, differential charging effects can be exploited for the identification and quantification of chemical species in heterogeneous materials. In this case, charging effects were useful to identify impurities at the surface of pyrolytic graphite. For these impurities, the analysis of the O 1s, Si 2p, and Al 2p core levels allowed distinguishing the contributions of SiO2 and Al2O3 from those of silicone/alumino-silicate oxides. Though both groups of compounds are insulators, a splitting of the above peaks was induced by the use of the flood gun device of the spectrometer when the samples were mounted on a conductive metallic sample holder. The shape and relative concentration of the chemical species ascribed to the split peaks served as a basis for the decomposition of the corresponding O 1s, Si 2p, and Al 2p peaks registered over a ceramic sample holder. The latter allowed for inducing a well controlled differential charging of the samples that led to the identification of true chemical shifts, i.e. those ascribed to variations on the chemical environment of the elements. A qualitative model for describing the observed charging effects was postulated. The model was based on an analogy between electrical circuits and the geometrical configuration of the impurity particles intercalated within the graphite particles.

X-ray photoelectron spectroscopy and Raman microscopy of a ferroan platinum crystal from the Kondyor Massif, Russian Far East

X-ray Photoelectron Spectroscopy was used to study a ferroan platinum crystal from the Kondyor Massif, Russian Far East. Prior to the X-ray Photoelectron Spectroscopic analyses, the nature of the crystal was confirmed by X-ray diffraction. The survey scan showed mainly the presence of Pt and Fe, with smaller amounts of O and Si. The high resolutions spectra of the Pt 4f and Fe 2p showed 18.3 atom% Fe in the crystal, which puts the composition on the lower boundary for ferroan platinum and confirms earlier analyses using other methods such as Scanning Electron Microscopy-Energy Dispersive X-ray analysis/microprobe. The binding energy of the Pt 4f5/2 was 74.0 eV and Pt 4f7/2 70.5 eV, while the Fe 2p3/2 for metallic Fe was observed at 707.2 eV. The Fe 2p3/2 for metallic Fe was significantly sharper than that of Fe 2p3/2 at 710.7 eV associated with surface material. The Raman spectrum was dominated by the Pt–Pt stretching mode at 253 cm−1. Changed orientation resulted in the observation of two bands at 127 and 139 cm−1, interpreted as being due to stretching modes of two Pt–Pt bonds with the third bond to Fe and Pt fixed. The presence of Ca-Fe-Al-Mg-Si-O on the surface was probably associated with the presence of a clinopyroxene. These minerals can be expected since the crystal came originally from a clinopyroxenite-dunite matrix. The spectra showed a variety of interferences, e.g. Al 2p with Pt 4f, Mg 2p with Fe 3p, and Ca 2p1/2 with Mg Auger, making exact determinations of the ratios of these elements difficult.

Physical and chemical characterization of Chinese maize stalk leaf ash: Calcining temperature and aqueous solution

This study focused on the physical and chemical characterization of Chinese maize stalk leaf ash (MSLA) calcined at 500, 700, and 850 °C and MSLA residual leaching in aqueous solutions. The grain size distribution, chemical composition, and microstructure of MSLA were investigated using a laser Mastersizer, X-ray fluorescence, and scanning electron microscopy. The ash samples obtained before and after dissolving were analyzed using X-ray powder diffraction and X-ray photoelectron spectroscopy to identify the present minerals and observe the 2p atomic orbit of surface silicon and aluminum (Si 2p and Al 2p) transformation behaviors. The zeta potential and pH values of hybrid solutions were tested for various dissolving times. Silica was the predominant component observed in the MSLA. As dissolving time increased, the pH value gradually decreased, and the zeta potentials first slightly decreased and then remarkably increased. Quartz was identified in the MSLA. Another polymorphous crystalline form of silica, cristobalite, only appeared in the 850 °C sample. The binding energies of Si 2p and Al 2p shifted, which transformed the XPS peaks after the thermal and aqueous solution treatment of MSLA. These findings can be utilized to study the application potential of MSLA in cementing systems.

Investigation of Improvement of Electronic Properties and Ductility of RuAl2 Semiconducting Material by Boron Doping Using First-Principles Calculations

The occupation mechanism and influence of B doping on the electronic and mechanical properties of RuAl2 semiconducting compound have been investigated using first-principles calculations. Four possible B doping sites are considered. The results show that B-doped RuAl2 is thermodynamically stable. In particular, B element prefers to occupy B(4) site in comparison with other sites. Importantly, B doping improves the electronic properties of RuAl2 by shifting the Al 3p and Ru 4d states from the Fermi level (EF) to the valence band. Although B doping weakens the resistance to volume and shear deformation as well as the elastic stiffness of RuAl2, it improves the ductility due to the formation of Ru-B and Al-B bonds. Therefore, it can be concluded that B is a favorable doping element to improve the electronic properties and ductility of RuAl2 semiconducting compound.

Atomistic origins of Guinier-Preston zone formation and morphology in Al-Cu and Al-Ag alloys from first principles

Using first-principles computations we provide comprehensive energetics at zero Kelvin of Guinier-Preston zone (GPZ) formation and topologies of GPZs in two classical Al binaries: Al-Cu and Al-Ag. Without a priori geometric and morphological assumptions, we conclusively show that GPZs in Al-Cu prefer a planar arrangement of {100} layers while GPZs in Al-Ag consist of clusters with {111} facets. We expand the model to 34 additional elements from the fourth and the fifth rows of the periodic table. The morphologies can be entirely related to directional nature and hybridization of Al 3s and 3p orbitals in the presence of secondary elements.

Improved interfacial properties of thermal atomic layer deposited AlN on GaN

The interfacial properties of atomic layer deposited AlN on n-GaN substrate were investigated. Capacitance–voltage (CV) characteristics showed that the sample with a 24 nm thick AlN had lower interface state density than the sample with a 7.4 nm thick AlN. Analysis on the X-ray photoelectron spectroscopy (XPS) spectra showed the better AlN formation near the AlN/GaN interface with a 24 nm thick AlN. The dominant peak shift to lower binding energy in the Al 2p core level spectra was observed with increasing the AlN thickness, which could be due to the strain relaxation resulted from the lattice mismatch between AlN and GaN.

Properties of AlN Thin Films on p-Ge Deposited by Thermal Atomic Layer Deposition

The electrical and interfacial properties of atomic layer deposited AlN on p-Ge were investigated. A very large capacitance–voltage (C–V) hysteresis at 1 MHz was observed, resulted from the presence of high density of slow traps that is associated with the GeO volatilization. Nonetheless, well-behaved C–V characteristics with minimal frequency dispersion and the absence of bumps near the flat-band voltage were obtained except 1 MHz, implying that the AlN passivation occurred near the AlN/Ge interface. Parallel conductance values showed that both slow and fast states were located within a narrow energy range. X-ray photoelectron spectroscopy (XPS) spectra revealed that large amount of oxygen atoms are present near the AlN/Ge interface. Above the AlN critical thickness, the strong Al–Al bond in the Al 2p spectra was observed, which could be explained by the strain relaxation due to the lattice mismatch between AlN and Ge.

Growth and characterization of co-sputtered aluminum-gallium oxide thin films on sapphire substrates

Aluminum gallium oxide (AGO) films were deposited on c-plane sapphire by co-sputtering of Al and Ga2O3 targets at a substrate temperature of 600 °C, and then annealed at 900 °C to enhance their crystal quality. The effect of DC power (0, 5, 10, 30, 50 and 70 W) for Al target on the structural, optical and compositional characteristics of AGO films were investigated. After annealing, the films prepared at the DC powers of 0–50 W for Al target all exhibited the single crystalline structure with the (−201) plane family. The annealed film grown at the DC power of 10 W possessed the highest crystal quality than the others. With increasing the DC power from 0 to 70 W, the Al composition of AGO film increased from 0 to 6.08 at.%, while its bandgap increased from 4.89 to 5.19 eV. X-ray photoelectron spectroscopy studies indicate the intensity of Ga 2p3/2 peak (1117.9 eV) for the AGO film decreases, whereas the intensity of Al 2p peak (74.6 eV) increases with increasing the DC power. The metal-semiconductor-metal photodetector with the annealed AGO film deposited at the DC power of 10 W possesses the largest photocurrent of 5.7 × 10−9 A and the on/off current ratio (Ion/Ioff) of 1.5 × 104 (@2 V and 230 nm). The better optoelectronic performance of this device was attributed that the AGO film (DC power: 10 W) had a higher crystal quality, the O/(Al+Ga) ratio close to the optimum value of 1.5. Our results present the AGO films can be successfully prepared via sputtering technique, which are highly potential for deep-ultraviolet applications.

Morphological and Structural Properties of CVD Deposited Titanium Aluminium Nitride (TiAlN) Thin Films

Titanium aluminium nitride (TiAlN) thin film coatings were synthesized via Atmospheric pressure chemical vapour deposition (APCVD) at various deposition temperature using titanium di-oxide (TiO2) powder, Al powder (99% pure) and N2 gas. The thin films were characterized by scanning electron microscopy (SEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) for analysing the morphological, vibrational and compositional characteristics of the deposited film. SEM images showed successful deposition of TiAlN thin film over Si wafers. Raman peaks revealed the optical phonon bands of the coated thin film within a range of 214.6-335.1 cm-1and 552.63-815.23 cm-1 for acoustic and optic range respectively at different processing temperatures. XPS spectra clearly showed the presence of different phases like Ti-N, Ti-O-N, Al2O3, N-Al, TiO2 Al-O in Ti (2p), Al (2p) and N (1s) orbitals, which is in a good agreement with past work.

Direct evaluation of electrical dipole moment and oxygen density ratio at high-k dielectrics/SiO2 interface by X-ray photoelectron spectroscopy analysis

The electrical dipole moment at an ultrathin high-k (HfO2, Al2O3, TiO2, Y2O3, and SrO)/SiO2 interface and its correlation with the oxygen density ratio at the interface have been directly evaluated by X-ray photoelectron spectroscopy (XPS) under monochromatized Al Kα radiation. The electrical dipole moment at the high-k/SiO2 interface has been measured from the change in the cut-off energy of secondary photoelectrons. Moreover, the oxygen density ratio at the interface between high-k and SiO2 has been estimated from cation core-line signals, such as Hf 4f, Al 2p, Y 3d, Ti 2p, Sr 3d, and Si 2p. We have experimentally clarified the relationship between the measured electrical dipole moment and the oxygen density ratio at the high-k/SiO2 interface.

Dependence of electron impact differential cross sections on the ionic charge to radius ratio for the Al3+(2p) and Be2+(1s) ions.

The triple differential cross sections (TDCSs) have been obtained for the electron impact ionization of ionic targets, Al3+(2p) and Be2+(1s), having nearly the same ratio of ionic charge to radius. In the first of this kind of study, the trends of cross sections have been found to match to a greater extent despite ionization taking place from the ionic targets having considerable difference in nuclear charges as well as the ionization taking place from different types of orbitals, p-orbital and s-orbital. The trends of TDCSs have not been found to agree considerably for the neutral Al (3p) and Be (2s) targets.

The origin of the heterogeneous distribution of bismuth in aluminosilicate laser glasses

AbstractAs one kind of novel and burgeoning laser materials, bismuth‐doped silicate glasses have aroused increasing attention for the super broadband near‐infrared (NIR) emission. However, the large optical scattering loss, resulting from optical heterogeneity in glass color and refractive index, limits their further applications in telecommunication system. Thus, it is urgent to uncover the essence of heterogeneity in Bi‐doped silicate glasses and subsequently improve glass optical performance. It will give us some hint to homogenize the glass component and Bi active centers so as to boost the development of Bi‐based glass materials. Here, taking 1 typical Bi‐doped calcium aluminosilicate glass as an example, we revealed the origin of the optical heterogeneities in glass color and refractive index through the NIR emission spectra, electron probe microanalyzer (EPMA) of elements and X‐ray photoelectron spectroscopy (XPS) of Bi 4f5/2, Bi 4f7/2, and Al 2p. The inhomogeneous distribution of Bi and aluminum components is responsible for the heterogeneity in this glass system. In addition, we found that tetrahedral coordinated aluminum favors the existence of Bi NIR centers, consequently resulting in enhanced Bi NIR emissions. Furthermore, based on our results and the role of Al3+ in glass network, we demonstrate the homogenizing of glass component by finely tuning glass composition. This work will enrich the understanding of Bi‐doped laser glass and provide a guideline for the design of component‐derived Bi‐doped silicate glasses and fibers with efficient NIR emission and high optical quality.

Versatile technique for assessing thickness of 2D layered materials by XPS

X-ray photoelectron spectroscopy (XPS) has been utilized as a versatile method for thickness characterization of various two-dimensional (2D) films. Accurate thickness can be measured simultaneously while acquiring XPS data for chemical characterization of 2D films having thickness up to approximately 10 nm. For validating the developed technique, thicknesses of few-layer graphene (FLG), MoS2 and amorphous boron nitride (a-BN) layer, produced by microwave plasma chemical vapor deposition (MPCVD), plasma enhanced chemical vapor deposition (PECVD), and pulsed laser deposition (PLD) respectively, were accurately measured. The intensity ratio between photoemission peaks recorded for the films (C 1s, Mo 3d, B 1s) and the substrates (Cu 2p, Al 2p, Si 2p) is the primary input parameter for thickness calculation, in addition to the atomic densities of the substrate and the film, and the corresponding electron attenuation length (EAL). The XPS data was used with a proposed model for thickness calculations, which was verified by cross-sectional transmission electron microscope (TEM) measurement of thickness for all the films. The XPS method determines thickness values averaged over an analysis area which is orders of magnitude larger than the typical area in cross-sectional TEM imaging, hence provides an advanced approach for thickness measurement over large areas of 2D materials. The study confirms that the versatile XPS method allows rapid and reliable assessment of the 2D material thickness and this method can facilitate in tailoring growth conditions for producing very thin 2D materials effectively over a large area. Furthermore, the XPS measurement for a typical 2D material is non-destructive and does not require special sample preparation. Therefore, after XPS analysis, exactly the same sample can undergo further processing or utilization.

Self-Assembly of Metal Oxide Nanoparticles in Liquid Metal toward Nucleation Control for Graphene Single-Crystal Arrays

Summary We have achieved the spontaneous assembly of alumina nanoparticles on a liquid metal surface and further synthesized a very-large-scale graphene single-crystal array. The effective electrical field established as a result of the electrical charge of the alumina nanoparticles in the liquid metal ensures the ordered self-assembly of the alumina islands and lays the foundation for precise spatial control of graphene nucleation, leading to the formation of graphene single-crystal arrays. In addition, controlling the density of the alumina in the liquid metal can precisely tune the periodicity of the arrays. This simple strategy, which is unlike the usual solid/aqueous solution system, opens up new territory for nanoparticle assembly. Focusing on the origin of the nanoparticle interaction that drives the self-assembly of ordered structure in the liquid metal system is a promising avenue for triggering more interesting applications.

First stages of oxide growth on Al(1 1 0) and core-level shifts from density functional theory calculations

The formation of islands of O-atoms is the dominant mode of growth of the oxide in the first stages of oxidation of Al(1 1 1). It is however unknown if a similar mechanism exists for other low index surfaces of Al. We performed a density functional theory (DFT) and ab initio molecular dynamics investigation of the first stages of the oxidation of Al(1 1 0) using two distinct models: a homogeneous surface disposition of O-atoms; and a model where the O-atoms are close-spaced forming clusters or islands. We investigated the surface reactions with oxygen up to a coverage of 2 ML and found that for both models the adsorption energy per dissociating O2(g) becomes more negative with increasing coverage. Our results show that for coverages up to 1.25 ML the oxide forms clusters or islands while for coverages higher than 1.5 ML the oxide covers the surface homogeneously. This is because the O-atoms bind preferably to neighboring sites even at the minimum coverage. With increasing coverage, the clusters of O start to form stripes along the [1 1¯ 0] direction. The work function (ϕ) of the surface decreases when going from bare Al(1 1 0) to up to 1 ML coverage of O-atoms, but for coverages of 1.25 ML and higher, ϕ increases. The Al 2p surface core level shifts (SCLS) shift towards higher binding energies with increasing surface coverage of O-atoms and start to approach the values of Al 2p in Al2O3 already at a coverage of 2ML. A relation between the SCLS and the coordination number of Al to O-atoms was made. The Al 2p SCLS increases with increasing coordination to O-atoms, for single, twofold and three-fourfold coordinated cations. For the O-atoms that terminate the surface at the short-bridge sites, the SCLS of O 1s, is largely affected by the proximity to other O-atoms. These results demonstrate that the cooperative effects between surface bound O-atoms have important roles in the mechanism of growth of the oxide at Al(1 1 0), and similarly to what happens for Al(1 1 1), the initial oxidation of Al(1 1 0) proceeds via the formation of islands of O-atoms.

Interfacial Chemistry Study of GaN by Trimethylaluminum-Only Cycles and X-ray Photoelectron Spectroscopy

The interfacial chemistry of n-type Ga-face GaN during atomic layer deposition of Al2O3 is studied by preceding the deposition process with several trimethylaluminum(TMA)-only cycles to clarify the impact of this precursor on the Al2O3/GaN interface. X-ray photoelectron spectroscopy analysis shows that the TMA precursor can react with the surface gallium oxide (GaOx) and convert the latter into aluminum oxide (AlOx), in accordance to past reports. However, the extent of conversion is limited as the reaction between TMA and GaOx is saturated after the first few TMA-only cycles. On the other hand, we found that the Ga/N ratio (GaN stoichiometry) is increased with the number of TMA-only cycles. At the same time, the Al-N bond peak appears in the Al 2p core-level spectrum, and its intensity also increases with the number of TMA-only cycles. The latter points to the formation of an Al-N layer, which may be attributed to Al ions from the TMA metal precursor penetrating the AlOx/GaOx layer and reacting with the underlying GaN. The reaction results in a loss of N from Ga bonding sites, and the increase of the Ga/N ratio. The resultant AlN layer protects the underlying GaN from oxidation and forms a high-quality interface with the Al2O3.

Microstructure and mechanical properties of Al–Si eutectic alloy modified with Al–3P master alloy

The fraction of primary Si and primary α–Al in Al–Si eutectic alloy were largest after modification at 740°C when a certain amount of Al–3P was added. The fraction of primary Si and primary α–Al in Al–Si eutectic alloy first increased and then decreased with increasing amount of Al–3P. The fraction of primary Si and primary α–Al in the Al–Si eutectic alloy was largest when the added amount of Al–3P modifier was 0.4wt.%. The fraction of primary Si and primary α–Al decreased with further increased Al–3P modifier. The size of the primary Si decreased continuously. Compared to the unmodified Al–Si eutectic alloy, the tensile strength and elongation of the alloy modified with 0.4wt.% Al–3P at 740°C increased by 7% and 74%, respectively.