Aluminum Dimer Research Articles

Density functional theory study of the reaction mechanism of aluminum nitride synthesis by sol–gel method

In recent years, aluminum nitride has undergone significant advancements and has found extensive application in optoelectronic and microelectronic devices due to its remarkable physicochemical properties. The quality of aluminum nitride powder plays a critical role in determining device performance, thus making the synthesis of high-quality powder a prominent area of research. The sol–gel method is a widely used approach for producing superior powders. In this study, we investigated the ammonolysis-polymerization mechanism of tris(dimethylamino)aluminum monomer and dimer using Gaussian16 software at the B3LYP-D3BJ/6-311G(d,p) level. Our objective was to provide theoretical guidance for the experimental synthesis of aluminum nitride powders using the sol–gel method. Our findings demonstrate that the ammonolysis reaction of tris(dimethylamino)aluminum dimer proceeds through six spontaneous steps. The two calculated polymerization steps also exhibit spontaneous behavior. All reactions demonstrate rapid occurrence, suggesting the theoretical feasibility of the ammonolysis-polymerization reaction of tris(dimethylamino)-aluminum dimer for synthesizing aluminum nitride.

Molybdenum Oxide Functional Passivation of Aluminum Dimers for Enhancing Optical-Field and Environmental Stability

In this contribution, we present an experimental and numerical study on the coating of Al plasmonic nanostructures through a conformal layer of high-refractive-index molybdenum oxide. The investigated structures are closely coupled nanodisks where we observe that the effect of the thin coating is to help gap narrowing down to the sub-5-nm range, where a large electromagnetic field enhancement and confinement can be achieved. The solution represents an alternative to more complex and challenging lithographic approaches, and results are also advantageous for enhancing the long-term stability of aluminum nanostructures.

Ab initio characterization of the aluminum dimer in its X and A electronic states.

The potential energy functions of the aluminum dimer, Al2 , in its lowest-energy electronic states, X and A have been determined from ab initio calculations using the multi-reference averaged coupled-pair functional method in conjunction with the correlation-consistent basis sets up to septuple-zeta quality. The core-electron correlation, scalar relativistic, and spin-orbit effects were taken into account. The vibration-rotation energy levels for both the states of Al2 were calculated to near the "spectroscopic" accuracy. The state was unequivocally confirmed to be the electronic ground state of Al2 , and the electronic term value of the state was predicted to be 247 cm-1 . The energies and intensities of direct electronic-vibration transitions X ↔A were predicted.

Synthesis, spectroscopy, and crystallography of mononuclear, five-coordinate aluminum complexes that act as cyclic ester polymerization initiators

Three ketoimines with pendant quinolyl moieties and a series of five-coordinate ketoiminate aluminum complexes were prepared and characterized spectroscopically and crystallographically. The synthesis of the ketoimines completed a series of ten regioisomers for which the product ratio varied between the product resulting from quinoline addition adjacent to the alkyl/aryl group or adjacent to the trifluoromethyl substituent. Quantitation of the ketoimine regioisomer ratios with 19F NMR demonstrated the role of steric encumbrance in the nucleophilic attack mechanistic step of the Schiff base condensation reaction and was further supported by linear free energy relationships with the Charton steric parameter and DFT calculations. Eight five-coordinate aluminum complexes were prepared in 57–92% yield from ketoimines and tris(2,6-dimethylphenoxide) aluminum dimer and characterized with 1H, 13C, 19F, and 27Al nuclear magnetic resonance spectroscopy, UV–visible absorbance spectroscopy, elemental analysis, and single-crystal X-ray crystallography. These mononuclear complexes differ from previously reported aluminum ion-pair complexes due to the symmetric cleavage of tris-dimethylphenoxide aluminum dimer by THF and were shown to have distorted trigonal bipyramidal coordination geometries (τ5 = 0.73–0.89). In a preliminary study, the aluminum complexes were demonstrated to be effective initiators for ring-opening polymerization of ε-caprolactone (εCL) to poly-caprolactone (PCL) and l-lactide (LA) to poly-lactic acid (PLA), reaching 77–99% conversion in 2 h for εCL and 10 h for LA at 100 °C.

Near-field enhancement in oxidized close gap aluminum dimers

Aluminum bowtie nanoantennas represent a possibility to confine and enhance electromagnetic (EM) field at optical frequencies in subwavelength regions by using an abundant and inexpensive metal. The native oxidation process of this metal is often viewed as a limitation for its application in plasmonics. Here, we show that in close gap configurations, the high refractive index of the native aluminum oxide helps in squeezing the plasmonic mode in extremely reduced size volumes, providing a higher EM near-field confinement and enhancement in the bowtie antenna gaps than achieved in the pure aluminum counterpart.Hence, the study provides new perspectives in the use of such a plasmonic antenna geometry within this aluminum system, which can be useful for improving plasmonics-enabled effects such as surface-enhanced Raman scattering- and light–matter interaction in strong coupling regime.

Adhesion‐Engineering‐Enabled “Sketch and Peel” Lithography for Aluminum Plasmonic Nanogaps

AbstractAluminum is one of the most significant plasmonic materials for its advantage of low cost, natural abundance, as well as the ultraviolet optical response. However, it is still very challengeable for the fabrication of aluminum plasmonic nanogaps, which greatly limits the applications of aluminum plasmonics considering the essential role of nanogaps for electric field enhancement. Here, the reliable patterning of aluminum plasmonic nanogaps employing a modified “Sketch and Peel” lithography strategy is demonstrated. By introducing a self‐assembled monolayer to engineer the surface energy of the substrate, the adhesiveness of the aluminum film outside outline template is significantly decreased to implement the selective peeling process. Besides, the near‐infrared Fano resonance in the periodic aluminum heptamers has been first revealed by enabling the strong electric field and plasmon coupling in the aluminum nanostructures with 10 nm scale nanogaps. In addition, surface‐enhanced Raman spectroscopy and infrared spectroscopy are also illustrated in the rationally designed aluminum dimers. The present work provides a robust method to obtain aluminum plasmonic nanogaps, which may play an important role on the practical applications of aluminum plasmonics, such as surface‐enhanced vibration spectroscopy and nonlinear optics.

Photofragment imaging and electronic spectroscopy of Al2.

A combination of photodissociation spectroscopy, ion imaging, and high-level theory is employed to refine the bond strength of the aluminum dimer cation (Al2+) and elucidate the electronic structure and photodissociation dynamics between 38 500 and 42 000 cm-1. Above 40 400 cm-1, structured photodissociation is observed from an extremely anharmonic excited state, which calculations identify as the double minimum G 2Σ+u state. The photodissociation spectrum of the G 2Σ+u ← X 2Σ+g transition in Al2+ gives an average vibrational spacing of 170 cm-1 for the G 2Σ+u state and ν0 = 172 cm-1 for the ground state. Photofragment images of G 2Σ+u ← X 2Σ+g transitions indicate that once the Al (4P) + Al+ (1S) product channel is energetically accessible, it dominates the lower energy, spin-allowed pathways despite being spin-forbidden. This is explained by a proposed competition between radiative and non-radiative decay pathways from the G 2Σ+u state. The photofragment images also yield D0 (Al+-Al) = 136.6 ± 1.8 kJ/mol, the most precise measurement to date, highlighting the improved resolution achieved from imaging at near-threshold energies. Additionally, combining D0 (Al+-Al) with IE (Al) and IE (Al2) gives an improved neutral D0 (Al-Al) = 136.9 ± 1.8 kJ/mol.

Synthesis and structures of aluminum ion-pair complexes that act as L- and racemic-lactide ring opening polymerization initiators

Seven aluminum ion-pair complexes (1–7) were synthesized by reaction of NNO Schiff base ketoimines with differing substituents with tris(2,6-dimethylphenoxy) aluminum dimer in an inert atmosphere glovebox at room temperature. The complexes were characterized with 1H, 13C, and 19F nuclear magnetic resonance spectroscopy, absorbance spectroscopy, and elemental analysis. Furthermore, the dinuclear nature of the complexes was elucidated with single crystal X-ray crystallography and 27Al NMR. The ion-pair complexes consisted of a bis-ligating homoleptic ketoiminate with octahedral coordination as an aluminum cation complex and a tetrahedral aluminum anion complex of 2,6-dimethylphenoxide. Each ion-pair was used to initiate the ring opening polymerization (ROP) of L- and rac-lactide to poly-lactic acid (PLA) in toluene at 100 °C at a 100:1 [LA]:[ion-pair] ratio. Proton NMR spectra showed percentage conversions of monomer to polymer of 96–99% in 18 h. The isolated polymeric materials were determined to have moderate molecular weights with low to moderate polydispersity index values using gel permeation chromatography. The bis-ligated aluminum cation and tetraphenoxide aluminate anions of 1 were isolated into separate compounds (8 and 9) with unreactive counter ions, and each yielded low molecular weight PLA under the polymerization conditions. Thus, lactide polymerization appeared to require both ion-pair components to yield the moderately high molecular weight PLA, and this was investigated spectroscopically.

Polarization-Resolved Plasmon-Modulated Emissions of Quantum Dots Coupled to Aluminum Dimers with Sub-20 nm Gaps

An aluminum dimer nanoantenna with nanogaps is an ideal platform for enhancing light–matter interaction at the nanoscale for the UV–vis spectrum, but its realization has been hindered by the surface oxidation of aluminum nanostructures, aluminum interband loss, and practical limitations in lithographic patterning. Here, we have overcome these problems and demonstrated the successful fabrication of an aluminum dimer antenna with a ∼10 nm gap, which to the best of our knowledge marks the smallest features of an Al nanoantenna. We present the first in-depth study of strongly polarization-dependent emissions of colloidal quantum dots coupled with Al dimers and elucidate the individual contributions of the excitation intensity, quantum yield, and extraction efficiency enhancements from numerical and experimental perspectives. We estimate the Purcell effect corresponding to a single Al-dimer antenna as ∼104 by taking into account the ensemble averaging effect and the distributions in emitter dipole orientations...

Reassessment of the Four-Point Approach to the Electron-Transfer Marcus-Hush Theory.

The Marcus–Hush theory has been successfully applied to describe and predict the activation barriers and hence the electron-transfer (ET) rates in several physicochemical and biological systems. This theory assumes that in the ET reaction, the geometry of the free Gibbs energy landscape is parabolic, with equal curvature near the local minimum for both reactants and products. In spite of its achievements, more realistic models have included the assumption of the two parabolas having not the same curvature. This situation is analyzed by the Nelsen’s four-point method. As a benchmark to compare the Marcus–Hush approximation to a precise calculation of the excitation energy, we studied the non-ET process of the electronic excitation of the aluminum dimer that has two local minima (3∑g– and 3∏u electronic states) and allows to obtain analytically the Marcus–Hush nonsymmetric parameters. We appraise the ability of the Marcus–Hush formula to approximate the analytical results by using several averages of the two reorganization energies associated with the forward and backward transitions and analyze the error. It is observed that the geometric average minimizes the relative error and that the analytical case is recovered. The main results of this paper are obtained by the application of the Nelsen’s four-point method to compute the reorganization energies of a large set of potential π-conjugated molecules proposed for organic photovoltaic devices using the above-mentioned averages for the Marcus–Hush formula. The activation energies obtained with the geometric average are significantly larger for some donor–acceptor pairs in comparison with the previously employed arithmetic average, their differences being suitable for experimental testing.

Interaction of aluminum dimer with defective graphene

In the present work, density functional theory (DFT) calculations using cluster and slab models were performed in order to study the adsorption of Al dimer on a monovacancy of graphene. With cluster models, two different approaches were considered for the exchange and correlation functional; namely, the Perdew, Burke and Ernzerhof (PBE) and the Becke, 3-parameter, Lee–Yang–Parr (B3LYP) functionals. Under the slab approximation only PBE was employed. The geometry where two Al atoms are simultaneously adsorbed on both sides of a monovacancy (H3–H3) is the most stable thermodynamically, followed by the structure in which one Al atom resides over the center of a vacancy and the other makes a bridge between two carbon atoms (H3-B). The magnitude of the Al2 adsorption energy is larger than that of an adsorbed Al atom. While the ground states for both free Al2 and isolated defective graphene is predicted to be a triplet, that corresponding to the dimer adsorbed on the monovacancy is calculated to be a singlet. Charge population analysis has shown that a significant electron transfer from Al to the substrate of about 2e is produced. The corresponding density of states (DOS) obtained with periodic conditions indicate that the Al2/defective graphene system at the H3-B geometry with a doping level of about 3% has a nearly zero band gap with almost no states at the Fermi level, unlike the situation where only one Al atom is adsorbed on the monovacancy which present a metal-like behavior.

Stable spin states of boron, aluminum and silicon dimers in a self-consistent GW calculation

Some small clusters, in particular dimers (diatomic molecules), composed of nonmagnetic atoms exhibit intrinsic spin magnetic moments. In this paper, we discuss the most stable spin state of boron, aluminum and silicon dimers. In order to treat the dynamically screened exchange interaction between electrons correctly, we adopt the self-consistent GW approximation in many-body perturbation theory. We find that the energy gain of the triplet ground state from the singlet excited state as a reference is mainly caused by the dynamically screened exchange interaction, although other contributions to the total energy do not have the same tendency between the triplet and singlet states. We also explicitly show the resulting quasiparticle energy spectra which can be compared with the photoemission and inverse photoemission spectroscopy measurements.

Aluminum and Indium Plasmonic Nanoantennas in the Ultraviolet

We use classical electrodynamics calculations to investigate the versatility and capability of aluminum and indium dimers with small gaps as ultraviolet plasmonic nanoantennas, focusing on the particle size and wavelength range that gives optimum near-field enhancement. We find that Al and In are highly capable plasmonic materials in the ultraviolet, even with the incorporation of Al2O3 shells on the Al spheres; however, Al is strongly influenced by quadrupole modes while In is not. Al is the optimal material in the deep-UV, while In is ideal in the near-UV and near-visible spectral regions. Unlike Au and Ag, Al and In are most effective with the lowest refractive index background media possible, with vacuum being ideal. Ag outperforms both Al and In red of ∼320 nm, but optimal surface-enhanced Raman spectroscopy enhancement factors are still substantial for Al and In, with peak |E|4 values (for dimers in vacuum with a 1 nm gap) determined to be: Al, 2.0 × 109 (at 204 nm); In, 1.2 × 109 (at 359 nm); Al/Al...

The Complexation of AlIII, PbII, and CuIIMetal Ions by Esculetin: A Spectroscopic and Theoretical Approach

UV-visible absorption spectroscopy combined with quantum chemical calculations and, notably, Time-Dependent Density Functional Theory were used to probe the structure of metal complexes with esculetin in dilute aqueous solution, at pH = 5. For the 1:1 complex formation, the studied metal ions can be classified according to their complexing power: aluminum(III) > copper(II) > lead(II). For the three complexes, a chelate is formed with the fully deprotonated catechol moiety and an absorption band is observed at the same wavelength. In all cases, a pronounced ionic character is calculated for metal-ligand bonds. However, the complexes differ in their coordination sphere. Copper and lead are bound to two water molecules leading to a square plane geometry and a hemidirected complex, respectively, whereas aluminum atom has an octahedral environment involving three water molecules and a hydroxide ion. For Al(III) only, a 2:1 complex is observed, and the involvement of an aluminum dimer was evidenced.

Optimal Basis Functions for Siegert Resonance State Representation in Al2Electronic Predissociation

We compare the relative usefulness of common basis functions and numerical integration methods in representing complex resonance state encountered in the molecular scattering problem of aluminum dimer electronic predissociation. Specifically, the basis set size and computing CPU times are monitored in order to find the minimum requirement for ensuring the modest accuracy of calculated resonance energies (0.1 ) for more than 100 resonance states. The combination of the so-called one-dimensional box eigenfunctions and energy-dependent boundary functions are found to be most efficient if integration is done using the basis set quadrature rules.

Aluminum alkoxide complexes from highly substituted 3,4-epoxy alcohols: An NMR and computational study

The organoaluminum mediated epoxide ring opening of epoxy alcohols is a key step in the oxirane-based approach for polypropionate synthesis. However, this reaction has shown unanticipated regioselectivities when applied to 2-methyl-3,4-epoxy alcohols. In order to gain mechanistic insight into the factors controlling the epoxide ring opening process, diastereomeric 2-methyl-3,4-epoxy alcohols were reacted with triethylaluminum in order to identify the aluminum complexes formed by these systems. Different epoxide–aluminum complexes were calculated using ab initio HF/[13s7p/11s5p] and B3PW91/6-31G** gauge-including atomic orbital (GIAO) methods and compared to the experimental NMR data. The calculated and experimental data correlates with the aluminum dimer complex (TIPSOCH2CH(OAlEt2)CH(CH)3CHCH(O)(AlEt3))2 (VIII) for the systems favoring the nucleophilic attack at the external C4 epoxide carbon, while an unusual trialuminum species TIPSOCH2CH(OAlEt2)CH(CH)3CHCH(O)(AlEt3)2 (X) is consistent with the systems favoring the internal C3 attack. The 27Al NMR data established the tetracoordinated nature of the aluminum metal in all alkoxy aluminum intermediates, while the 13C NMR data provided insight into the aluminum-oxygen coordination. The formation of the complexes was dictated by the stereochemical disposition of the substituents. These complexes are different from the generally accepted bidentate intermediates proposed for 2,3-epoxy alcohols and simpler 3,4-epoxy alcohols. Copyright © 2012 John Wiley & Sons, Ltd.

The decay of ion bunches in the self-bunching mode

The properties of ion bunches stored in an electrostatic ion beam trap (EIBT) have been investigated using the Cryogenic Trap for Fast ion beams (CTF). The extremely high vacuum used rendered the main ion loss mechanism, namely collisions with the rest gas, negligible. Aluminum dimer anions were photo-detached by a pulsed laser to measure the longitudinal ion distribution in the bunch, which for the first time revealed the presence of a dc ion beam component co-existing with the oscillating ion bunch after several hundreds of revolutions. Bunches stabilized by the so-called self-bunching mode of operation have been observed for times as long as 12 s (a factor of 100 longer than previous room-temperature experiments) using N+2 and Al−2 bunches at 6–7.1 keV beam energies after which the bunch abruptly decayed. The decay of the bunch was observed to be intensity dependent and is well reproduced by a model that includes the expansion of the bunch along the beam axis, intrabeam scattering and collisional losses between the bunch and the dc component. Radio-frequency bunching of the ions resulted in the extension of the bunch observation time to 600 s, placing upper limits on all other EIBT ion bunch and trap losses as well as supporting the newly developed decay model and EIBT-adapted bunch dynamics.

Hydrogen dissociation on small aluminum clusters

Transition states and reaction paths for a hydrogen molecule dissociating on small aluminum clusters have been calculated using density functional theory. The two lowest spin states have been taken into account for all the Al(n) clusters considered, with n=2-6. The aluminum dimer, which shows a (3)Π(u) electronic ground state, has also been studied at the coupled cluster and configuration interaction level for comparison and to check the accuracy of single determinant calculations in this special case, where two degenerate configurations should be taken into account. The calculated reaction barriers give an explanation of the experimentally observed reactivity of hydrogen on Al clusters of different size [Cox et al., J. Chem. Phys. 84, 4651 (1986)] and reproduce the high observed reactivity of the Al(6) cluster. The electronic structure of the Al(n)-H(2) systems was also systematically investigated in order to determine the role played by interactions of specific molecular orbitals for different nuclear arrangements. Singlet Al(n) clusters (with n even) exhibit the lowest barriers to H(2) dissociation because their highest doubly occupied molecular orbitals allow for a more favorable interaction with the antibonding σ(u) molecular orbital of H(2).

Half-Sandwich Structure of Cyclopentadienyl Dialuminum [Al2(η5-C5H5)] from Pulsed-Field Ionization Electron Spectroscopy and ab Initio Calculations

Cyclopentadienyl dialuminum [Al2Cp, Cp = C5H5] was prepared in a pulsed laser ablation cluster beam source and identified with a time-of-flight photoionization mass spectrometer. The high-resolution electron spectrum of this complex was obtained using pulsed-field ionization zero electron kinetic energy (ZEKE) photoelectron spectroscopy. Three isomeric structures with two Al atoms residing on the same or opposite sites of the Cp plane were predicted by second-order Møller-Plesset perturbation theory. A half-sandwich structure with an aluminum dimer perpendicular to the Cp plane was identified by the experiment. The ground electronic states of the neutral and ionized species are 2A' ' in Cs symmetry and 1A1 in C5v symmetry, respectively. In both the neutral and ionic states, one of the Al2 atoms binds with five carbons, and the metal-ligand bonding consists of orbital and electrostatic contributions. Ionization of the 2A' ' neutral state enhances the metal-ligand bonding but weakens the metal-metal interaction.

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.