Al 3p States Research Articles

Nitrogen flow rate dependent atomic coordination, phonon vibration and surface analysis of DC magnetron sputtered nitrogen rich-AlN thin films

In this work, the effect on crystallite orientation, surface morphology, fractal geometry, structural coordination and electronic environment of DC magnetron sputtered AlN films were investigated. X-ray diffraction results disclosed that the c-axis orientation of AlN films increased with the preferred wurtzite hexagonal structure above 17% N2 flow. X-ray reflectivity data confirmed AlN film density increased with increasing N2 flow and was found to be 3.18 g/cm3 for 40% N2. The transition of electrons from N 1s to 2p states hybridized with Al 3p states because of π* resonance was obtained from X-ray absorption spectroscopy of the N K-edge. The semi-empirical coordination geometry of nitrogen atoms has been studied by deconvolution of N K-edge. The surface composition of AlN films at 40% N2 consists of 32.08, 51.94 and 15.97 at.% Al, N and O respectively. Blue-shifting of A1(LO) and E1(LO) modes in the Raman spectra at phonon energies 800 and 1051 cm−1 respectively was most likely due to the presence of oxygen bonds in the AlN films.

The prediction of Al2Cu/Cu interfacial structure and properties: A first-principles study

The interfacial structure is critical in the practical application of layered materials. To comprehend the interfacial bonding of Cu/Al layered composites more deeply, the interface binding properties at the Al2Cu(110)/Cu(111) interface were investigated using first-principles calculations. In this work, four different interface models are considered. Among them, the AlA terminal, one of the four terminals on the surface of Al2Cu(110), exhibited the best stability among the Al2Cu/Cu interfaces, with the maximum adhesion work (3.094 J/m2) and the lowest interfacial energy. The Cu-3d and Al-3p states at its interface exhibit hybridization. Electronic analysis has shown that the covalent and metallic bonds between the Al and Cu atoms at the interface are the main sources of the interfacial bonding. The results discussed above offer critical recommendations for enhancing the interfacial stability and strength of Cu/Al layered composites.

Structural, elastic, electronic, and optical properties of NaAlSi3O8 and Al4[Si4O10](OH)8 from first-principles calculations

Based on the first-principles calculations, this paper investigates the structural, elastic, electronic, and optical properties of albite and kaolinite, respectively. It is determined that both of them show structural stability, mechanical stability, and brittleness by calculating formation enthalpy, phonon dispersion, elastic, and mechanically relevant properties. Both materials are insulators with an indirect bandgap. By calculating the TDOS and PDOS, the main characteristics of the electronic structure of NaAlSi3O8 come from O-2p and Si-3p states, O-2p, and Al-3p states hybridization, similar to Al4[Si4O10](OH)8. The covalence of Si-O bonds in NaAlSi3O8 is greater than Al-O bonds, and the covalent property sequence of Si-O bands in NaAlSi3O8 is Si2-O3 > Si1-O4 > Si2-O2 > Si1-O8 > Si1-O6 > Si3-O2 > Si3-O4. The optical anisotropy of NaAlSi3O8 and Al4[Si4O10](OH)8 is analyzed. First-principles density functional theory (DFT) calculation was carried out by the CASTEP computer program. The GGA-PW91 exchange-correlation was used. The energy convergence tolerance, the maximum force, and the maximum displacement were set in the calculation.

Investigating the β-Mg17Al12 Alloy under Pressure Using First-Principles Methods: Structure, Elastic Properties, and Mechanical Properties

Calculations of first principles were employed to explore the elastic constants of the β-Mg17Al12 intermetallic complex under pressure, along with several related physical parameters, including the bulk modulus, the shear modulus, Young’s modulus, Poisson’s ratio, and the anisotropy index. The volume of the β-Mg17Al12 crystal in the ground state was V0 = 1180.353 Å3, and the lattice parameter was 10.57 Å. This is in agreement with the available results in the literature, which indicate that the calculations were correct. The three independent elastic constants, C11, C12, and C44, increased with increasing pressure. The bulk modulus B, shear modulus G, and Young’s modulus E increased with increasing pressure, indicating that the bulk deformation resistance, shear deformation resistance, and stiffness of the β-Mg17Al12 phase increased with increasing pressure. The phase had a B/G > 1.75 and a Poisson’s ratio of ν > 0.26 and increased with pressure, indicating that the β-Mg17Al12 crystals were ductile and that the ductility increased with pressure. The Cauchy pressure C12–C44 increased with increasing pressure. The anisotropy coefficients A(100) and A(110) deviated further from 1, and the anisotropy increased. The electronic structure calculations showed that the total density of the states (TDOS) was achieved mainly by the Mg-3p and Al-3p states, and the total density of states moved toward the higher energy regions under pressure, with enhanced interatomic bonding, leading to an increase in the elastic constants and ultimately to an increase in each physical property with increasing pressure.

Insight into the role of atomic interaction and ionic radius in Al doped BiFeO3: Structural, electronic, and optical properties

Chemical doped multiferroic BiFeO3 has received much research interest from both fundamental and applications due to enhanced magnetism, reduced leakage current, increased piezoelectric effect and novel optical responds. Here, we report on a theoretical investigation of structural, electronic and optical properties of Al doped BiFeO3 using density functional theory. The calculated results show that doping of Al atoms with a smaller ionic radius at the A(Bi)-site resulted in a more significant change compared to the B(Fe)-site. It confirms that the smaller ionic radius and interatomic interaction are important factors contributing to the change of atomic structure. The calculated DOS reveals that Al contributes significantly to the reduction of the energy band gap where Al 3p states are occupied in the valence band and the conduction band. This study sheds light on the Al doped BiFeO3, paving the way for the development of novel materials with excellent multiferroic and solar properties.

Ab initio and thermodynamic picture of Al adsorption of AlN(0001) surface – Role of bond creation and electron transition contributions

The role of bond creation and electron transition contribution were investigated in thermodynamic picture of adsorption obtained from intensive ab initio density functional theory (DFT) calculations. It was shown that electron transitions may reduce the overall energy gain from Al adsorption at AlN(0001) surface by 50%. Accordingly properties of AlN polar N-terminated AlN(0001) surface such as crystallographic structure, the type and energy of the surface states, the band profiles close to the surface were obtained. At the clean surface Al is adsorbed with the energy gain of 9.6 eV at H3 site creating bonds using two Al3p states by the overlap with the neighboring surface N atoms. The excess electrons are transferred to surface N broken bond states. At the critical coverage θAl-cr=14ML all these states are occupied, therefore for higher Al coverage the electrons are transferred to Al3pz states. As their energy is higher by 2.5 eV, the adsorption energy gain is dropped to 4.089 eV, i.e. about 50%. For higher coverage Al adatoms are shifted to bridge and on-top configurations reducing the electron transfer and increasing energy gain by 2.5 eV for full coverage of Al adatoms located in the on-top positions. The temperature dependent pressure-coverage diagram was obtained showing the two stable regions. The first, up to 0.25 ML Al (θAl≤14ML) with Al adatoms located in H3 positions, correspond to extremely low Al pressure, below 10−13 bar at 2500 K. The second region, at pAl>2.18×10-5bar, is stable for high coverage, i.e. for θAl>0.999ML (at 2500 K) with Al adatoms located in the on-top positions. For the pressures between, i.e. 1.80×10-12bar<pAl<2.18×10-5bar, nonuniform coverage is stable, composed to these two phases. Finally at the coverage close to 1 ML, Langmuir entropic singularity in chemical potential was detected, corresponding to dramatic increase of the pressure over single Al layer which leads to transition to multiple Al layers and bulk Al.

First-principles prediction of enhancing graphene/Al interface bonding strength by graphene doping strategy

In this research work, first-principles calculation method is performed to investigate the effects of atomic doping in graphene on the graphene/Al interface bonding properties. It is found that the bonding strength of Al(1 1 1)/perfect graphene/Al(1 1 1) interface is extremely weak (only 0.063 J/m2) due to the limited charge redistribution on the interface. The atomic doping (including N-doping, B-doping and B-N co-doping) in graphene could obviously enhance the Al(1 1 1)/graphene/Al(1 1 1) interface bonding strength with more than ten times, the improvement effect increases with the enhancement of doping concentration and the N-B co-doping in graphene has the best improvement effect at the same doping concentration. The reason why the N-doping or B-doping in graphene could obviously enhance the interface bonding strength is that the doped atom could cause the pronounced hybridization between a more delocalized Al-3p states and the 2p states of both the doped atoms and their neighboring C atoms. For the N-B co-doping case, more specifically, the strong interaction between the doped-N and doped-B atoms could weaken the interactions of their neighboring C atoms, resulting in the further enhancement of interaction between interfacial Al atoms and C atoms neighboring the doped atom. This study could provide an efficient way of modifying the graphene/Al interface to improve the mechanical properties of graphene/Al composites.

Band structures and optical properties of Ag and Al co-doped ZnO by experimental and theoretic calculation

Crystal structures, band structures, density of states (DOS), optical properties including dielectric function, absorption, loss function, refractive index, reflectivity and photoluminescence (PL) emission are investigated by combining experimental results with theoretic calculation. Results indicated that crystal quality of ZnO is improved after Al and Ag doping. In addition, compared with Al-doped and Ag-doped ZnO, Ag-Al co-doped ZnO have smaller bandgap. It imply that Ag-Al co-doping can adjust the bandgap more flexibly, and then change the electronic structure and optical properties. At the same time, Al-3p and Ag-5s states have stronger interaction in Ag-Al co-doped ZnO, which makes the conduction band wider, so the DOS further moves toward lower energy. For Ag-doped ZnO, a very narrow peak at around 0.21 eV is observed in dielectric function spectra, which is associated with the electron transition between Ag-4d states and partially filled valence band. PL spectra of pure ZnO shows a broad blue emission band at 421 nm, and its intensity increases and the full-width at half maximum (FWHM) decreases after Al and Ag doping. Interestingly, emission band red shifts toward green waveband as Al and Ag is co-doped in ZnO.

Anisotropic elasticity, electronic structure and thermodynamic properties of Al-Fe-Si intermetallic compounds from first principles calculations

In this paper, structural stability, elastic properties, electronic structure and thermodynamic properties of Al-Fe-Si compounds are systematically investigated by first-principles calculations. The negative formation enthalpy indicates that all Al-Fe-Si compounds are thermodynamically stable, and the Al-Fe-Si compounds are determined to be mechanically stable by the stability criteria. The bulk, shear and Young's moduli as well as Poisson's ratio of Al-Fe-Si compounds are also calculated. The results show that Al2Fe3Si3 has the highest shear modulus and Young's modulus, which leads to stronger shear deformation resistance and stiffness. The elastic anisotropy and shear anisotropic factors of Al-Fe-Si compounds are analyzed in this study, and the anisotropy of Al3Fe2Si3 is the greatest among them. Al3Fe2Si3 and Al2Fe3Si4 show metallic character and Al2Fe3Si3 is classified as direct band gap semiconductors. The DOS of Al-Fe-Si compounds are found mainly from Al 3p, Si 3p and Fe 4d states and the Fe-Al/Si bonding is much stronger than that of Al-Si. According to the results, Al2Fe3Si3 has the highest Debye temperature, indicating strong chemical bonding and higher thermal conductivity, which are consistent with the results of Young's modulus and minimum thermal conductivity.

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.

Atomic structure, stability and electronic properties of S(Al2CuMg)/Al interface: A first-principles study

Interfacial models of Al2CuMg/Al were investigated by first-principles calculations based on density functional theory. Two types of Al2CuMg(001)/Al(021) interface structures were investigated in consideration of two different terminations for Al2CuMg(001) surface (Al-terminated and CuMg-terminated). The interaction of interfaces was analyzed by the optimized atomic structures. The ideal work of adhesion (Wad) of the Al2CuMg(001)/Al(021) interfaces was also calculated. The results show that the interface model with CuMg-terminated is more stable than that of Al-terminated. It is also demonstrated from the values of interfacial energy (γint) that the CuMg-terminated interface is more thermodynamically stable. The calculated electronic properties, including charge density distribution and density of states, reveal that there is a significant hybridization among the interfacial Cu 3d, Mg 3p and Al 3p states. It is the main reason why CuMg-terminated interface is more stable.

A comparative study of NbAl3 and Nb3Al intermetallic compounds under pressure

The effects of pressure on the structural, electronic and mechanical properties of tetragonal NbAl3 and cubic Nb3Al have been investigated using first-principles density functional theory approach within the generalized gradient approximation. The calculated structural parameters of two compounds were in good agreement with previous theoretical and experimental data, which linearly decreased with the increasing pressure. The electronic properties of two compounds under pressure have been analyzed. The enhanced covalence under pressure was found due to the increased hybridization between Nb-4d and Al-3p states. The independent elastic constants and mechanical properties have been calculated under pressure. We found that the pressure had a very important influence on mechanical properties. Finally, the ductile/brittle character and mechanical stability of two compounds have been discussed.

Electronic structure of FeAl alloy studied by resonant photoemission spectroscopy and Ab initio calculations

Resonant photoemission spectroscopy has been used to investigate the character of Fe 3d states in FeAl alloy. Fe 3d states have two different character, first is of itinerant nature located very close to the Fermi level, and second, is of less itinerant (relatively localized character), located beyond ∼2 eV below the Fermi level. These distinct states are clearly distinguishable in the resonant photoemission data. Comparison between the results obtained from experiments and first principle based electronic structure calculations show that the origin of the itinerant character of the Fe 3d states is due to the ordered B2 structure, whereas the relatively less itinerant (localized) Fe 3d states are from the disorders present in the sample. The exchange splitting of the Fe 3s core level peak confirms the presence of local moment in this system. It is found that the itinerant electrons arise due to the hybridization between Fe 3d and Al 3s and 3p states. Presence of hybridization is observed as a shift in the Al 2p core-level spectra as well as in the X-ray near edge absorption spectra towards lower binding energy. Our photoemission results are thus explained by the co-existence of ordered and disordered phases in the system.

Energetics and electronic structure of UAl4 with point defects

UAl4 ideal and defect structures were studied within the framework of the Density Functional Theory. The structural and magnetic ordering of UAl4 in paramagnetic, ferromagnetic, and antiferromagnetic states have been investigated, within the collinear and non-collinear spin approximation, using the GGA model, as embedded in the program package VASP. An antiferromagnetic (01¯1) layer structure with spins aligned to the [010] direction was found to be energetically preferred. The analysis of density of states and bonding charge density point out that the bonding mechanism consists primarily of band mixing between the U 5f and Al 3p states. Supercells were built from UAl4 unit cells with the established magnetic structure. For those supercells we calculated the energy of formation of vacancies and antisite defects taking into account the existence of three distinct aluminum sites. Point defect formation energies, local lattice relaxations, as well as the defect induced magnetic ordering and electronic density redistribution, are discussed. It is shown that antiferromagnetism is locally broken. Al antisites and U antisites in Al 4e Wyckoff positions are the constitutional point defects in Al-rich and U-rich oI20 UAl4, respectively. In this way we have presented here the first set of data which makes it possible to discuss and quantify the point defects concentrations in the experimental composition range for existence of this uranium aluminide.

Synthesis, Crystal and Electronic Structure of the Quaternary Magnetic EuTAl4Si2 (T = Rh and Ir) Compounds

Single crystals of the quaternary europium compounds EuRhAl4Si2 and EuIrAl4Si2 were synthesized by using the Al-Si binary eutectic as a flux. The structure of the two quaternary compounds has been refined by single crystal X-ray diffraction. Both compounds are stoichiometric and adopt an ordered derivative of the ternary KCu4S3 structure type (tetragonal tP8, P4/mmm). The two compounds reported here represent the first example of a quaternary and truly stoichiometric 1:1:4:2 phase crystallizing with this structure type. In light of our present results, the structure of the BaMg4Si3 compound given in literature as representing a new prototype is actually isotypic with the KCu4S3 structure. Local spin density approximation including the Hubbard U parameter (LSDA + U) calculations show that Eu ions are in the divalent state, with a significant hybridization between the Eu 5d, Rh (Ir) 4d (5d), Si 3p and Al 3p states. Magnetic susceptibility measured along the [001] direction confirms the divalent nature of the Eu ions in EuRhAl4Si2 and EuIrAl4Si2, which order magnetically near ∼11 and ∼15 K, respectively.

Effect of oxygen vacancy and Al-doping on the electronic and optical properties in SnO2

The electronic and optical properties of Al-doped SnO2 without and with O vacancies are investigated by means of first-principles calculations. Our results indicate that Al-doped SnO2 is of p-type conductivity character and its band gap decreases compared with undoped SnO2. The accompanied oxygen vacancies can introduce localized gap states below the bottom of the conduction band and lead to the conductivity character translating to n-type from p-type in Al-doped SnO2. The localized gap states are contributed by the hybridizing of Sn 5s, 5p, O 2p, and Al 3p states and the density of these states becomes much stronger with oxygen vacancies increasing. Meanwhile, Fermi level shifts upward, showing a stronger n-type conductive character. With respect to the optical properties, Al-doped SnO2 has a weak absorption peak at about 2.73eV in the visible region, while the presence of oxygen vacancies reinforces the absorption in the visible light region.

Atomic and electronic structure of amorphous Al–Zr alloy films

Amorphous Al73Zr27 alloy film, grown and then subjected to heat treatments at 400 and700 °C,was studied using a combination of x-ray diffraction and soft x-ray spectroscopic techniques. The AlL2, 3 and Al K x-ray absorption spectroscopy (XAS) and AlL2, 3 x-ray emission spectroscopy (XES) used allowed probing the unoccupied and occupied Al3s, d states and unoccupied Al 3p states in the sample studied. An irreversibletransition from amorphous alloy to a mixture of polycrystalline alloy and amorphousalloy, and then to an amorphous oxide phase was observed. After the annealing at400 °C theAl L2, 3 spectra obtained by XAS could be explained as sums of spectra from amorphousAl73Zr27 alloy and (poly)crystalline Al. This indicates that the sample consists of a mixture of Al-richcrystalline and Zr-enhanced amorphous alloys, as compared to the stoichiometry of the as-depositedAl73Zr27 sample, and that the electronic wavefunctions in the crystalline and amorphous regions canbe considered to be confined within the respective regions. The relative amounts of Alatoms were found to be around 1:3 in the crystalline and amorphous phases,respectively, as deduced from the analysis of changes in the electronic structure using AlL2, 3 XAS data. The interpretation was confirmed by the Al K XAS and AlL2, 3 XES. Upon furtherannealing at 700 °C the polycrystalline phase transformed into amorphous oxide, while the amorphous alloyphase underwent gradual oxidation. The important finding was that the greater part of thesample remained in the amorphous state throughout the temperature regimesdescribed.

Theoretical study of structural, electronic, lattice dynamical and dielectric properties of SrAl 2O 4

We investigate the structural, electronic, lattice dynamical, and dielectric properties of SrAl 2O 4 within density-function theory. The crystal structure is fully relaxed, and the structural parameters are found to be well consistent with the experimental data. The first pressure derivatives of the bulk modulus are predicted to be 2.5 and 4.3 for local density approximation (LDA) and generalized gradient approximation (GGA), respectively. The electronic band structure shows that the valence band maximum is comprised of O 2p states and a small amount of Al 3s and 3p states, and the conduction band minimum is comprised of Sr 5s and a small amount of O 2p, Al 3s and Al 3p states. The phonon frequencies at the center of the Brillouin zone and the dielectric permittivity tensors are calculated using density-function perturbation theory. The electronic ( ɛ ∞) and static ( ɛ 0) dielectric permittivity tensors are theoretically predicted by the calculations with both LDA and GGA formalisms. The results show that the electronic dielectric permittivity is isotropic, while the static dielectric permittivity exhibits to be somewhat anisotropic due to the dominant ionic contributions in static dielectric permittivity.

Study by optical emission spectroscopy of a physical vapour deposition process for the synthesis of complex AlCuFe(B) coatings

abstract Article history:Received 18 May 2010Accepted in revised form 18 May 2010Available online 23 May 2010Keywords:PVDQuasicrystalOptical emission spectroscopy We investigate the formation of complex Al Cu metallic phases by magnetron dc sputtering of elementaltargets followed by low temperature annealing. We show that all stable low temperature phases of the Al Cusystem can be grown this way and suggest that some of these phases could be used as an interfacial layer toimprove the adhesion of quasicrystalline AlCuFe coatings on metal substrate. Then we introduce opticalemission spectroscopy as a tool to monitor the composition of thin lms obtained by sputtering Al 63 Cu 25 Fe 12 and Al 59.5 Cu 25.3 Fe 12.2 B 3 targets. This method should improve the synthesis of complex metallic alloy phasesas new coating materials of industrial interest.© 2010 Elsevier B.V. All rights reserved. 1. IntroductionQuasicrystals are solids with long-range order but no translationperiodicity, exhibiting non-crystallographic rotational axis like ve-fold or tenfold symmetries[1]. They usually form in relatively narrowregions of binary or ternary phase diagrams. Their structural andchemical complexity is frequently associated with unique physicalproperties not encountered in simple metallic systems. Following thediscovery of quasicrystals by Shechtman et al., there has been anintense renewal of interest for binary Al-transition metal(s) systemscontaining complex metallic alloys (CMA) with very large unit cellsand exhibiting local cluster features similar to those found inquasicrystalline phases[2 10]. It was found that both quasicrystalsand CMA possess speci c properties like low friction, poor wettingand good corrosion resistance which are of interest to develop newcoating materials[11 14]. Those surface properties are related totheir peculiar electronic structure characterized by a low density of Al3p states at the Fermi level, usually associated with a poor metallicbehavior. In particular, experiments show that their surface energy isrelatively low compared to normal metallic systems which makes thedeposition of CMA and quasicrystals on metallic substrates verychallenging[14,15].Strategies can be developed to circumvent the poor adhesion ofthese alloys on metallic substrates for example by using an interfaciallayer such as to obtain a gradient of properties between the substrateand the surface[16].Resortingto PVD processes to deposit both the buffer layer and thequasicrystal is a technologically reliable method as already describedby several groups[17 20]. A crucial point in such PVD processes is thecontrol of the chemical composition of the deposit, due to the limitedcompositional ranges of quasicrystalline and CMA phases. In thisarticle, we present a study of the synthesis of new coatings containingCMAphasesintheAl Cusystembyreactivediffusioninthesolidstatebetween bilayers deposited by dc magnetron sputtering. The aim is todevelop an interfacial layer to improve the adhesion between aquasicrystalline Al Cu Fe thin lm and a metal substrate. Then, wedescribe some rst results on the possibility to follow the compositionof thin lms in the Al Cu Fe system by optical emission spectroscopy.This possibility is particularly interesting to check any drift with timein the deposition process.2. Experimental detailsThe Al/Cu and Al/Cu/Fe multilayers can be grown by dc magnetronsputtering using the experimental set-up shown inFig. 1. The basepressure in the sputtering system is 1.10

The mechanism of Al donor defects in (Zn, Co)O:Al: a view from resonant x-rayspectroscopies

We studied the effect of Al doping inZn0.94Co0.05Al0.01O nano-powders from the electronic structure point of view by applying x-ray absorptionspectroscopy and resonant inelastic x-ray scattering at the oxygen K- and Co L-edges. Theintensity of the pre-edge structure of the O-K XAS spectra is enhanced following theintroduction of the Al defect. Multiple scattering calculations demonstrate it can beaccounted for by the gain of the hybridization strength between O 2p and Al 3p (and/orCo 3d) states. The consensus on the hybridization strength is reached by combining Co-LXAS and RIXS investigations and multiplet calculations. It reveals different spatialsubstitutions of Al doping can alter the number of shared oxygen atoms between the Coand Al tetrahedrons. These shared ligands are responsible for the Al 3p and Co 3dstate hybridization strength as well as the ferromagnetism of the ground state.The magnetic difference is better understood to be governed by various sharedoxygen atoms rather than the distance between the Al defect and Co impurities.