Al 2p Research Articles

Electronic structure and chemical bonding inTi2AlCinvestigated by soft x-ray emission spectroscopy

The electronic structure of the nanolaminated transition metal carbide Ti2AlC has been investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured Ti L, C K and Al L emission spectra are compared with calculated spectra using ab initio density-functional theory including dipole matrix elements. The detailed investigation of the electronic structure and chemical bonding provides increased understanding of the physical properties of this type of nanolaminates. Three different types of bond regions are identified; the relatively weak Ti 3d - Al 3p hybridization 1 eV below the Fermi level, and the Ti 3d - C 2p and Ti 3d - C 2s hybridizations which are stronger and deeper in energy are observed around 2.5 eV and 10 eV below the Fermi level, respectively. A strongly modified spectral shape of the 3s final states in comparison to pure Al is detected for the buried Al monolayers indirectly reflecting the Ti 3d - Al 3p hybridization. The differences between the electronic and crystal structures of Ti2AlC, Ti3AlC2 and TiC are discussed in relation to the number of Al layers per Ti layer in the two former systems and the corresponding change of the unusual materials properties.

Role of Ti in the reversible dehydrogenation of Ti-doped sodium alanate

The role of Ti in the reversible dehydrogenation of NaAlH4 has been the subject of debate for many years. The authors resolve this controversy by calculating the phase stability diagram of Na–Al–H–Ti and defect formation enthalpy of Ti doped NaAlH4 from first principles. The calculations show that Ti substitutes Al in NaAlH4 and forms a defect pair with interstitial H under H-rich and Al-poor conditions. However, the defect pair is not stable under H-poor and Al-rich conditions resulting in the formation of a Ti–Al intermetallic compound. The doped Ti reduces the Al–H bonding via additional Al 2p and Ti 3d hybridizations. The results give a picture why and how doped Ti acts to enhance hydrogen storage related solid phase transitions.

Growth and electronic structure of Mn on Al(1 1 1)

Growth and electronic structure of a 3d transition metal Mn on a free-electron-like metal Al(1 1 1) have been studied by photoelectron spectroscopy and low energy electron diffraction (LEED). A ( 3 × 3 ) R 30 ° LEED is observed at 6 ML Mn coverage, that is related to the α phase of bulk Mn. From the intensity of the adlayer and substrate core-level peaks and angle dependent studies, evidence of primarily layer by layer growth is observed. The Mn 2p core-level for 0.1 ML Mn coverage appears at 0.3 eV lower binding energy with respect to bulk Mn. With increasing Mn coverage, the Mn 2p binding energy increases. An extra component is observed at the lower binding energy side of the Al 2p spectra, that is related to interface alloying. The asymmetric line-shape of bulk-like Mn becomes symmetric for lower Mn coverages.

Auger electron emission in the interaction of slow Na + ions with Al surfaces

We present energy distributions of electrons emitted in the interaction of Na + ions with Al surfaces as a function of incident ion energy in the range 300–2000 eV. We discuss the Auger spectra of Sodium, which show several lines due to decay in vacuum of projectiles, singly and doubly excited in the 2p shell by electron promotion in close encounters with target atoms. Our results indicate that the double vacancy production is in close relation with the Al–2p electron excitation via an autoexcitation mechanism.

Superhard nanocomposite Ti–Al–Si–N films deposited by reactive unbalanced magnetron sputtering

Nanocomposite Ti–Al–Si–N films (Al content ranging from 0 to 16.7 at.% and Si from 0 to 11.8 at.%, respectively) were prepared on Si(1 0 0) substrates at 500 °C by reactive close-field unbalanced magnetron sputtering in an Ar–N 2 mixture. The chemical composition, bonding structure, surface morphology, microstructure, stress and mechanical properties of these films were systematically investigated by means of energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), X-ray diffraction (XRD), optical interference system and nanoindentation measurements. The XPS measurements reveal evolution of chemical composition and bonding structure of the deposited Ti–Al–Si–N films. The observed nonlinear peak shift of Ti 2p and N 1s indicates the bonding evolution of crystalline TiN. The spectra from Al 2p at 73.7 eV and Si 2p at 101.1 eV indicates the evolution of film composition from TiSiN to TiAlN with the incorporation of Al, and also implies that their chemical states are mainly in the form of SiN x and AlN, respectively. The (1 1 1) diffraction peak from the XRD θ–2 θ patterns shows a variation either on peak width or on peak position, indicating the variation of grain size and lattice constant. The calculated lattice constant reveals a mixture of different phases whose structures are similar to TiN. The nonlinear variation of grain size and lattice constant is considered due to the competition between two processes, i.e. Al addition and the underlying Si reduction. In order to further understand the microstructure evolution, the XRD spectra and corresponding calculations of the Ti–Al–Si–N films without heating during deposition are also shown for comparison. The effect of substrate heating is discussed. The present results show that the influence of Si and Al addition on the grain growth is different. The surface roughness of Ti–Al–Si–N films also exhibits a nonlinear variation, which is due to the variation of grain size and the competitive growth of different phases. The influence of stress on the hardness can be ignored due to its relatively low value (1–2 GPa) compared with the super-hardness of the films. All the quaternary Ti–Al–Si–N films show enhanced mechanical properties when compared with the nanocomposite Ti–Si–N and Ti–Al–N films deposited under the same condition. The best hardness, reaching superhard, is obtained for the Ti–Al–Si–N film with 7.5 at.% Al and 6 at.% Si. The combined effect of vacancy hardening and some of extrinsic hardening are considered responsible for the enhanced mechanical properties of Ti–Al–Si–N films.

X‐ray photoelectron, infrared, and Raman spectroscopy studies of novel submicrometric poly[(methacrylato)aluminum(III)

AbstractPoly[(methacrylato)aluminum(III)] was prepared by applying γ‐radiation to the corresponding aluminum(III) methacrylate monomer. Scanning electron microscopy images show pellets of ∼ 500 nm for the aluminum(III) methacrylate monomer, and submicrometric fibers‐made granules for the aluminum‐containing polymers. X‐ray photoelectron spectroscopy measurements reveal two peaks in the Al 2p core‐level spectra of the monomer and of the poly[(methacrylato)aluminum(III)], which means that two different coordination modes for the Al(III) ions might be present in these compounds. Infrared and Raman spectroscopy studies confirmed that the structure for this novel coordination polymer consists of hexa‐coordinated Al(III) ions linked by the carboxylate groups of methacrylate ligands, along with hydroxyl groups and coordinated water, in a combination of monodentate and bridging bidentate coordination modes. Hence, combination of spectroscopic methods is a helpful tool to get valuable information on the structure of nonmacrocrystalline coordination polymers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5212–5223, 2006

Composition and structure characterization of aluminum after laser ablation

The process of laser ablation of an aluminum surface with copper bromide laser (511 nm) was investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), with the laser fluence varying from 5.3 to 11.1 J/cm 2 and the laser beam scanning velocity from 20 to 100 mm/s. The experiments were done in two kinds of ambient atmosphere: air and argon. SEM analysis showed the porous structure of the laser treated surface and formation of micro- and nano-sized particles. The dimensions of the agglomerates formed were smaller in argon atmosphere. Upon irradiation in Ar atmosphere the aluminum nanoparticles were formed in a metal state and their surface was oxidized after exposure to O 2 in air. However, two mechanisms are possible in air, the first one being the same as under Ar and the second occurring direct in the plasma. The binding energies of the Al 2p (74.0 eV) and O 1s (531.4 eV) peaks and the O/Al ratio give information on the oxidation of the surface and presence of aluminum in Al 2O 3 and AlOOH. The oxide layer was porous, which was evidenced by SEM.

Core electron binding energy shifts of AlBr 3 and Al 2Br 6 vapor

The Al 2p and Br 3d inner-shell photoelectron spectra of aluminum tribromide monomer and dimer vapor were measured at 90 and 95 eV photon energy, respectively, to determine the core electron binding energies of the atoms in the two molecular species. While AlBr 3 has three identical Br atoms, Al 2Br 6 exhibits four terminal and two bridging Br atoms. The species are identified by their distinct valence photoelectron spectra. Comparison of the observed Al 2p 1/2 and Al 2p 3/2 electron binding energies of AlBr 3 with those of Al 2Br 6 shows that there is a chemical shift of (0.15 ± 0.03) eV to lower energy in the dimer. In Al 2Br 6, an assignment is proposed in which the Br 3d 3/2 and Br 3d 5/2 binding energies of terminal Br atoms are (1.18 ± 0.03) eV lower than those of bridging Br atoms. This assignment assumes that both types of Br atoms have similar cross-sections for ionization. With this result, the Br 3d 3/2 and Br 3d 5/2 binding energies of Br atoms in AlBr 3 are (0.81 ± 0.03) eV lower than those of bridging Br atoms of the dimer but (0.37 ± 0.03) eV higher than those of terminal Br atoms of the dimer. The obtained chemical shifts are considered in terms of the binding relations and electron density distributions in both molecules. Chemical shifts that are larger than a few hundred millielectron volts, as observed in the Al 2Br 6/AlBr 3 system, offer potential to study the dissociation dynamics of the dimer in a femtosecond visible or ultraviolet-pump/XUV-probe experiment.

Electronic structure of ternary ferromagnetic compounds MnAlGe and MnGaGe

Electronic band structures of ferromagnetic ternary compounds MnAlGe and MnGaGe have been studied by a self-consistent augmented–plane wave (APW) band structure calculation and a photoelectron spectroscopy. The calculated band structure shows that Mn 3d states are hybridized with Al 3p or Ga 4p states and Ge 4p states. A strong two-dimensional feature has been theoretically clarified in the Fermi surfaces especially for spin-down band. An itinerant character of Mn 3d electrons has been confirmed both theoretically and experimentally. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Reaction of the ground-state Al( 2P) with silane: Examination of the potential energy surfaces for complexation, insertion and interconversion

A route of formation of SiH 3AlH radical via insertion of the ground-state Al( 2P) into SiH 4 and subsequent rearrangements to various primary insertion product isomers including more stable SiH 2AlH 2 radical are predicted from the ab initio single-reference CCSD(T) and multi-reference MRMP2 calculations. For the insertion reaction, the lowest energy doublet ( 2A′) potential energy surface is studied within C s symmetry. Special attention is paid to the weakly bound Al⋯SiH 4 complexes formed in the initial stage of the reaction. The results presented are of relevance to recent matrix studies on reactivity of the Al/SiH 4 system.

A new nickel complex-templated layered aluminophosphate [Ni(C 4N 3H 13)(C 4N 3H 14)H 2O][Al 3P 4O 16

A new layered aluminophosphate [Ni(C 4N 3H 13)(C 4N 3H 14)H 2O][Al 3P 4O 16] has been prepared from a hydrothermal system Al( i-PrO) 3 Ni(OAc) 2 H 3PO 4 diethylenetriamine H 2O, and characterized by single-crystal X-ray diffraction, ICP, CHN and TG analyses. Its structure is built up from the alternation of AlO 4 and PO 3( O) tetrahedra to from 4.6.8-net sheets stacked in an ABAB sequence. The nickel complex Ni(C 4N 3H 13)(C 4N 3H 14)H 2O that is formed under hydrothermal conditions locates in the interlayer region and interacts with the inorganic sheets through H-bonds.

Chemical bonding and electronic structures of the Al2SiO5 polymorphs, andalusite, sillimanite, and kyanite: X-ray photoelectron- and electron energy loss spectroscopy studies

We have undertaken a detailed analysis of the X-ray photoelectron spectra obtained from the three polymorphs of Al2SiO5; andalusite, sillimanite, and kyanite. Comparison of the spectra was made based on the chemical bonding and structural differences in the Al- and Si-coordination within each polymorph. The spectra for Si(2p) for all three polymorphs are nearly identical, consistent with the fact that all the Si atoms are in 4-fold (tetrahedral) coordination, whereas the binding energies, peak shapes, and peak widths for Al(2p) vary depending on the type of polymorph. The upper-valence band for all three polymorphs is characterized by four main features derived from O(2p), Al(3s), Al(2p), Si(3s), and Si(3p), and the differences in their contributions are observed. The density of state of the Al2SiO5 polymorphs is relatively featureless compared to those observed from α-SiO2 and α-Al2O3, suggesting that the orbital overlaps span a greater range in energy. The observed band gap energy for Al2SiO5 (sillimanite) was ~9.1eV, a value in between those for α-SiO2 (~8.6eV) and α-Al2O3 (~9.6eV). The conduction band feature of Al2SiO5 was experimentally compared to those of α-SiO2 and α-Al2O3, and shown that it is indeed intermediate between the α-SiO2 and α-Al2O3 phases.

Characterization and catalytic activity of V 2O 5/Al 2O 3-TiO 2 for selective oxidation of 4-methylanisole

The vapour phase selective oxidation of 4-methylanisole to p-anisaldehyde and p-anisic acid was investigated over V 2O 5/Al 2O 3-TiO 2 catalysts containing various amounts of V 2O 5 (2–16 wt.%) in the temperature range 523–723 K under normal atmospheric pressure. The Al 2O 3-TiO 2 (1:1.3 mole ratio) binary oxide support was prepared by a homogenous coprecipitation method using urea as precipitating reagent. The V 2O 5/Al 2O 3-TiO 2 catalysts were prepared by a wet impregnation method from ammonium metavanadate dissolved in oxalic acid solution. The Al 2O 3-TiO 2 support and V 2O 5/Al 2O 3-TiO 2 catalysts were subjected to various calcination temperatures (773–1073 K) to understand the dispersion and thermal stability of catalysts and were characterized by means of X-ray diffraction, FT-infrared, X-ray photoelectron spectroscopy, O 2 chemisorption and BET surface area methods. The physicochemical characterization results reveal that the Al 2O 3-TiO 2 mixed oxide is homogeneous and thermally quite stable retaining titania-anatase phase up to 1073 K. The alumina-titania support also accommodates a monolayer equivalent of V 2O 5 in a highly dispersed state when calcined at 773 K. This observation is supported from XRD, FTIR and O 2 uptake results. The XPS studies reveal that titania, alumina and vanadia are in Ti(IV), Al(III) and V(V) oxidation states irrespective of calcination temperature employed. The O 1s, Ti 2p, Al 2p and V 2p photoelectron peaks of the V 2O 5/Al 2O 3-TiO 2 samples are highly sensitive to the calcination temperature as well as V 2O 5 coverage. The 16 wt.% V 2O 5/Al 2O 3-TiO 2 catalyst exhibits more conversion and more product selectivity to p-anisaldehyde when compared to other samples.

XPS characterisation of carbon‐coated alumina support

AbstractHybrid carbon–alumina supports, synthesised by pyrolysis of grafted 4,4′‐methylenebis‐(phenylisocyanate) moiety on the alumina surface, were characterised by X‐ray photoelectron spectroscopy. The recorded Al 2p and C 1s envelopes showed asymmetry that decreased with an increase in carbon loading. In all experimental Al 2p envelopes, the high‐energy individual components at 75.3–75.9 eV were present along with the low‐energy component at 74.0 eV typical for Al2O3. In the case of the C 1s envelope, the component around 284.3–284.4 eV and three high‐energy individual components at 285.9–286.0, 288.0–288.3 and 290.1–290.6 eV were observed. The presence of the high‐energy Al 2p components can be explained considering the occurrence of a steady‐state charging of the different parts of insulating alumina supports. The component around 284.3–284.4 eV in C 1s envelopes can be attributed to carbon, which constitutes the coating and, hence, ensures surface conductivity. The component around 285.9–286.0 eV is connected with carbon in carbonaceous surface species, which do not form the conducting layer on the alumina support. Carbonaceous surface species associated with CO, CO and OCO groups in carbon coating can be also identified due to the presence of corresponding components in XPS spectra at 285.9–286.0, 288.0–288.3 and 290.1–290.6 eV. Copyright © 2006 John Wiley & Sons, Ltd.

Electron Paramagnetic Resonance Study of the Mononuclear Al Species Formed in the Reaction of Al Atoms and Cyclopropylamine at 77 K in an Adamantane Matrix

Ground-state Al atoms have been reacted with cyclopropylamine (CpNH2) in an adamantane matrix at 77 K. The four paramagnetic species generated in the reaction have been studied by electron paramagnetic resonance (EPR) spectroscopy and their magnetic parameters extracted from the EPR spectra. The isotropic Al hyperfine interactions (hfis) for these radicals vary from 801 to 962 MHz and are consistent with values previously reported for structurally similar Al-centered radicals. The major species formed in the reaction has a highly anisotropic a tensor indicative of an Al-centered radical with a substantial amount of the unpaired spin density residing in the Al 3p orbital. In addition, there is EPR evidence that the insertion products, CpNH(AlH) and CpAlNH2, are formed in the reaction, suggesting that Al atoms can activate the N-H and C-N bonds of amines. It has been shown that a molecule of CpNH2 coordinates to CpNH(AlH), causing the Al, N and H hfi of the N-H insertion product to decrease. The values of the nuclear hfis calculated for the insertion products, using a density functional theory (DFT) method, are comparable to the experimental values.

Formation of Interfacial Layers in LaAlO3/Siliconduring Film Deposition

We have studied the interfacial reactions between amorphousLaAlO3 thin films and Si substrates, using high-resolutiontransmission electron microscopy and x-ray photoelectron spectroscopy.It has been shown that the interfacial layer between LaAlO3 filmand Si substrate is SiLaxAlyOz. The depthdistributions of La, Si and Al chemical states show that the ratio ofLa 4d3/2 to Al 2p of the interfacial layer remainsunchanged with the depth compared to that of the LaAlO3 film.Moreover, the Si content in the interfacial layer gradually decreaseswith increasing thickness of the interfacial layer. These resultsstrongly suggest that the Al element is not deficient in theinterfacial layer, as previously believed, and the formation of aSiLaxAlyOz interfacial layer is mainly due to thediffusion of Si from the substrate during the LaAlO3 filmdeposition. With the understanding of the interfacial layer formation,ones can control the interface characteristics to ensure the desiredperformances of devices using high-k oxides as gate dielectrics.

Effect of oxidation on the optical and surface properties of AlGaN

The chemical properties of Al x Ga 1− x N surfaces exposed to air for different time periods are investigated by atomic force microscopy (AFM), photoluminescence (PL) measurement and X-ray photoelectron spectroscopy (XPS). PL and AFM results show that Al x Ga 1− x N samples exhibit different surface characteristics for different air-exposure times and Al contents. The XPS spectra of the Al 2p and Ga 2p core levels indicate that the peaks shifted slightly, from an Al N to an Al O bond and from a Ga N to a Ga O bond. All of these results show that the epilayer surface contains a large amount of Ga and Al oxides.

The effect of the Mn constituent on the electronic structures ofAl70Pd22.5(Re1−xMnx)7.5 quasicrystals studied by x-ray absorption and photoemission spectroscopy

X-ray absorption near-edge fine structure (XANES) and valence-bandphotoelectron spectroscopy (PES) measurements were performed to elucidatethe effect of the Mn constituent on the electronic structures of icosahedral(i)-Al70Pd22.5(Re1−xMnx)7.5 quasicrystals(QCs). Pd and Re L3-edge and Al K-edge XANES spectra reveal that the unoccupied Pd 4d, Re 5dand Al 3p states are insensitive to the Mn doping. The valence-band PES andresonant photoemission analysis indicate a marked Mn 3d contribution within∼5 eV of the Fermi level, suggesting that the Mn doping increases the conductivity ofi-Al–Pd–Re–Mn QCs.

Structure and bonding of III/V compounds X 2Y 2, with X=B, Al, Ga, and Y=N, P, As

The geometries and electronic states of group III/V (13/15) X 2Y 2 compounds were investigated by B3LYP and MP2 calculations, using a 6-311+G(3df) basis set. Twelve different starting geometries for B 2N 2, B 2P 2, B 2As 2, Al 2N 2, Al 2P 2, Al 2As 2, Ga 2N 2, Ga 2P 2, and Ga 2As 2 were chosen for both singlet and triplet states. For aluminum and gallium compounds, the lowest energy structure was a rhombus in a 1A g ground state, having the group V atoms on the short diagonal. Al 2N 2 and Ga 2N 2 have a linear X–N–N–X Σ g − 3 state that lies only 0.05 and 0.08 eV, respectively, higher than the 1A g rhombus. B 2N 2 prefers a linear B–N–B–N arrangement in a triplet state ( 3Π), but a 3B 2 g rhombus, having the B atoms on the short diagonal, lies 0.14 eV (B3LYP) or 0.07 eV (MP2) higher. B 2P 2 and B 2As 2 were found to be most stable in a rhombus ( 3B 2 g) structure, with B on the short diagonal. Bonding in the rhombus and in linear symmetric structures is described.

Structure and bonding of tetramer clusters: Theoretical understanding of the aromaticity

The ground state geometries and energetics of charged ( Si 4 + 2 , Ge 4 + 2 , Si 2 Ge 2 + 2 , Si 3Al +, Si 3Ga + Ge 3Al +, and Ge 3Ga +) and neutral (Al 2Si 2, Al 2Ge 2, Ga 2Si 2, Ga 2Ge 2, Si 3Be, Si 3Mg, Ge 3Be, Ge 3Mg, Al 3P, Al 3As, Ga 3P, and Ga 3As) tetramer clusters have been performed using ab initio molecular-orbital calculations. Harmonic vibrational analysis has been performed to ensure the stability of the optimized geometries. From the comparison of the total energies between possible isomeric structures it is found that both homo- and hetero-atomic tetramer clusters favor planar configuration as the lowest energy structure. The aromatic character of these clusters has been analyzed based on planarity, electronic stability, Nuclear Independent Chemical Shift (NICS) Values and their molecular orbitals pictures. The extra electronic stability of these clusters towards donating or accepting of electrons is reflected in the calculated hardness, large ionization potential and low electron affinity. To check the chemical stability of these tetramer clusters further calculations have been carried out for the interactions of hydrogen atoms with few representative cluster like Si 4 + 2 , Al 4 − 2 and Al 2Si 2. Indeed, it is found that even after formation of four bonds with hydrogen atoms the planarity of these clusters retained and more interestingly, the delocalized π-electron cloud of the HOMO energy levels remained undisturbed.