Al-O Bonds Research Articles

Stability of Indium Gallium Zinc Aluminum Oxide Thin-Film Transistors with Treatment Processes

The indium-gallium-zinc-aluminum-oxide (IGZAO) channel layer of the bottom-gate-type thin-film transistors (TFTs) was deposited on indium tin oxide-coated glass substrates using a magnetron radio frequency co-sputtering system with dual targets of indium gallium zinc oxide and Al. The 3 s orbital of Al cations provided an extra transport pathway and widened the bottom of the conduction band, thus increasing the electron mobility in the IGZAO films. The Al-O bonds could sustain the stability of oxygen of the IGZAO films. The IGZAO TFTs were processed by O2 plasma and post-annealing treatments. Hysteresis analysis was carried out in order to study the stability of the resulting IGZAO TFTs, the positive bias temperature stress (PBTS) performance, and the hot carrier effect were also measured. For the IGZAO TFTs, the threshold voltage shift of the PBTS performance and the hot carrier effect were 0.1 V and 0.06 V, respectively. Overall, the IGZAO TFTs exhibited good stability in this study.

First-principles-based simulation of interlayer water and alkali metal ions in weathered biotite.

We performed first-principles-based simulations of weathered biotites (WBs) including alkali metal ions to investigate the adsorption states of interlayer cations and the cation/water distribution in their interlayer. Our simulations suggest that the inclusion of Fe3+ ions in octahedral sheets of WBs alters significantly the vibrational states, the adsorption states of alkali ions, and the cation/water distribution in our WBs. The Al-O bond cleavage suggested to occur in Fe3+-rich regions of WBs upon the H2O adsorption on Al3+ in tetrahedral sheets enhances greatly the dipole moment of adsorbed H2O molecules, thus enhancing the preference for aggregating inner-sphere complexes of heavy alkali ions particularly Cs+.

The physical mechanism on the threshold voltage temperature stability improvement for GaN HEMTs with pre-fluorination argon treatment

In this paper, a normally-off AlGaN/GaN MIS-HEMT with improved threshold voltage (VTH) thermal stability is reported with investigations on its physical mechanism. The normally-off operation of the device is achieved from novel short argon plasma treatment (APT) prior to the fluorine plasma treatment (FPT) on Al2O3 gate dielectrics. For the MIS-HEMT with FPT only, its VTH drops from 4.2 V at room temperature to 0.5 V at 200 °C. Alternatively, for the device with APT-then-FPT process, its VTH can retain at 2.5 V at 200 °C due to the increased amount of deep-level traps that do not emit electrons at 200 °C. This thermally stable VTH makes this device suitable for high power applications. The depth profile of the F atoms in Al2O3, measured by the secondary ion mass spectroscopy, reveals a significant increase in the F concentration when APT is conducted prior to FPT. The X-ray photoelectron spectroscopy (XPS) analysis on the plasma-treated Al2O3 surfaces observes higher composition of Al-F bonds if APT was applied before FPT. The enhanced breaking of Al-O bonds due to Ar bombardment assisted in the increased incorporation of F radicals at the surface during the subsequent FPT process. The Schrödinger equation of Al2OxFy cells, with the same Al-F compositions as obtained from XPS, was solved by Gaussian 09 molecular simulations to extract electron state distribution as a function of energy. The simulation results show creation of the deeper trap states in the Al2O3 bandgap when APT is used before FPT. Finally, the trap distribution extracted from the simulations is verified by the gate-stress experimental characterization to confirm the physical mechanism described.

Molecular dynamics investigation on structural and transport properties of Na3AlF6–Al2O3 molten salt

To study the effect of Al2O3 concentration on the local structure and transport properties of Na3AlF6–Al2O3 molten salt, molecular dynamics (MD) simulations with the Coulomb–Buckingham potential model were carried out. MD simulation results show [AlF4]−, [AlF5]2− and [AlF6]3− groups coexist in Na3AlF6–Al2O3 molten salt and [AlF6]3− ions are the dominant species at low Al2O3 concentration of 1–2wt%. The percentages of [AlF4]−, [AlF5]2− and [AlF6]3− groups are approximately equal at 3wt% Al2O3 and [AlF4]− ions become the major species at 4wt% Al2O3. O atoms mainly exist in the form of bridge Ob up to 90%, worsening the fluidity and transport properties of Na3AlF6–Al2O3 molten salt. According to quantum chemical calculations, AlF and AlO bonds in the [Al2OF6]2− groups have ionic characters as well as partial covalent characters due to the hybridization of F, O-2p and Al-3s (3p) orbitals, while NaF and FF bonds are ionic. The orders of particle's diffusion ability follow as Na+>F−>Al3+>O2–. In addition, Al2O3 acts as bridges connecting ionic structure networks and more Al2O3 can increase the polymerization degree of the local structure in Na3AlF6–Al2O3 molten salt, and the viscosity increase and ionic conductivity reduce accordingly.

A novel surfactant 2-amino-6-decanamidohexanoic acid: Flotation performance and adsorption mechanism to diaspore

In this paper, a novel surfactant, 2-amino-6-decanamidohexanoic acid (AHA-10) was synthesized and used as a collector for flotation separation of diaspore and aluminosilicate minerals. The adsorption mechanism of AHA-10 onto diaspore was also evaluated by FTIR spectra, zeta potential, XPS and solution chemistry. The flotation results demonstrated that AHA-10 exhibited superior collecting power to diaspore and good selectivity against kaolinite and illite, and could effectively recover diaspore from bauxite ores contained aluminosilicate minerals at pH around 10. The analyses of FTIR spectra, zeta potential and solution chemistry inferred that at pH around 10, AHA-10 might chemisorb on diaspore surfaces by formation of AlO and AlN bonds. AHA-10’s unique properties, such as characteristic bond model to Al atoms on diaspore surfaces, double hydrophobic groups and intermolecular hydrogen bonds between neighboring AHA-10 molecules coated on diaspore surfaces, rendering a weakening surface energy and enhancing hydrophobicity of diaspore particles.

Ab Initio Investigation of O-H Dissociation from the Al-OH2 Complex Using Molecular Dynamics and Neural Network Fitting.

The dissociation dynamics of the O-H bond in Al-OH2 is investigated on an approximated ab initio potential energy surface (PES). By adopting a dynamic sampling method, we obtain a database of 92 834 configurations. The potential energy for each point is calculated using MP2/6-311G (3df, 2p) calculations; then, a 60-neuron feed-forward neural network is utilized to fit the data to construct an analytic PES. The root-mean-square error (rmse) for the training set is reported as 0.0036 eV, while the rmse for the independent testing set is 0.0034 eV. Such excellent fitting accuracy indeed confirms the reliability of the constructed PES. Subsequently, quasi-classical molecular dynamics (MD) trajectories are performed on the constructed PES at various levels of vibrational excitation in the range of 1.03 to 2.23 eV to investigate the probability of O-H bond dissociation. The results indicate a linear relationship between reaction probability and internal energy, from which we can determine the minimum activation internal energy required for the dissociation as 0.62 eV. Moreover, the O-H bond rupture is shown to be highly correlated with the formation of Al-O bond.

Diameter monodispersity of imogolite-like nanotube: a density functional theory study

The diameter monodispersity and the surface charge distribution of three imogolite-like nanotubes (not substituted (IMO), substituted by NH2 (IMO-NH2), substituted by F (IMO-F) are investigated using self-consistent periodic density functional theory, and the phenomenon of the monodispersity is explained qualitatively in terms of bond length. We assume that the axial length of the nanotube is constant and confirm it; the energetic minimum axial lengths of the three nanotubes increase in the sequence IMO_NH2 IMO IMO_F, and are respectively 8.61, 8.62 and 8.66 . Then the energies for different nanotubes and lamellar structures are calculated. A series of strain energy curves of IMO, IMO_NH2 and IMO_F are plotted based on calculations, and the results show that the energetic minimum diameters of these three nanotubes increase in the sequence of IMO IMO_NH2 IMO_F, and are respectively N= 9, 10 and 11. In order to explain the diameter monodispersity, we have calculated the bond lengths of SiO, AlO and AlOH three nanotubes and plotted the curves of length against diameter. Results show that the monodispersity can be attributed to the interaction between the energy increase resulting from the stretching of the SiO, AlO bonds in the inner wall, and the energy decreases caused by the shortening of the AlOH bond in the outer wall. In a word, with the increase of tube diameter, the SiO and AlO bonds increase while the AlOH bond decreases monotonically. Additionally, we have also calculated the Mulliken charge distributions of the three nanotubes with different diameter and analysed their surface charges. On this basis, we summarize the effect of diameter on surface charge. Results show that the main positive charges are accumulating on the outer surface while the negative charges are located on the inner region, and the outer surface charge increases gradually with the increase of the diameter of the nanotubes. The study indicates that the internal surface functional group has an effect on the axial length, diameter and surface charge of the imogolite-like nanotubes. We can control the nanotube diameter and surface charge distribution by changing different functional substitutes in the inner surface; it is significant in the molecular design and application of imogolite-like materials.

Photoluminescence And Decay Properties Of Sm3+ And Dy3+ In SrAl4O7 Phosphor

In this study, Sm 3+ - and Dy 3 -doped SrAl4O7 phosphors were synthesized by combustion method. X-ray diffraction (XRD) measurement confirmed the monoclinic crystal structure of SrAl4O7. Sr-O and Al-O bonds were identified by Fourier transform infrared (FTIR) spectroscopy. Under 352 nm excitation, the SrAl4O7: Dy 3+ phosphor shown emission bands at 475 nm (blue) and 574 nm (yellow) that are due to 4 F9/2→ 6 H15/2, 6 H13/2 transitions, respectively. Photoluminescence spectra (PL) of SrAl4O7: Sm 3+ phosphor has shown bright orange red emission at 598 nm with an excitation wavelength of 405 nm. The decay curve of Sm 3+ and Dy 3+ single doped SrAl4O7 phosphors were well fitted to a bi-exponential function. The obtained results show that the prepared phosphors may be applicable in the field of eco-friendly solid state lighting technology. Copyright © 2015 VBRI Press.

Quantitative study for surface properties of AlGaN epi-layers by ARXPS

The surface chemical properties of Al x Ga 1-x N (x=0.35, 0.47, 0.60) epi-layers grown on c-plane sapphire substrates by metal-organic chemical vapor deposition (MOCVD) were quantitatively characterized by angle-resolved X-ray photoelectron spectroscopy (ARXPS). The results suggested that the Ga Auger peak for the Al x Ga 1-x N epi-layers was greatly suppressed with increasing Al composition since the amount of N-Ga bonds were dramatically decreased. Moreover, more Al-O bonds were found near the surfaces of the Al x Ga 1-x N epi-layers with relatively high Al composition due to the large chemical affinity of aluminum to oxygen. In addition, the Al composition in the Al x Ga 1-x N epi-layers was showed to be non-uniform because Al atom has higher oxidizability and lower mobility than Ga atom, especially for the Al x Ga 1-x N epi-layers with relatively high Al composition. Our work should be very helpful to further investigation of the surface properties for making Al-containing III-nitrides optoelectronic devices.

Facile Aluminum Reduction Synthesis of Blue TiO2 with Oxygen Deficiency for Lithium-Ion Batteries.

An ultrafacile aluminum reduction method is reported herein for the preparation of blue TiO2 nanoparticles (donated as Al-TiO2 , anatase phase) with abundant oxygen deficiency for lithium-ion batteries. Under aluminum reduction, the morphology of the TiO2 nanosheets changes from well-defined rectangular into uniform round or oval nanoparticles and the particle size also decreases from 60 to 31 nm, which can aggressively accelerate the lithium-ion diffusion. Electron paramagnetic resonance (EPR) and positron annihilation lifetime spectroscopy (PALS) results reveal that plentiful oxygen deficiencies relative to the Ti(3+) species were generated in blue Al-TiO2 ; this effectively enhances the electron conductivity of the TiO2 . X-ray photoelectron spectrometry (XPS) analysis indicates that a small peak is observed for the Al-O bond, which probably plays a very important role in the stabilization of the oxygen deficiencies/Ti(3+) species. As a result, the blue Al-TiO2 possesses significantly higher capacity, better rate performance, and a longer cycle life than the white pure TiO2 . Such improvements can be attributed to the decreased particle size, as well as the existence of the oxygen deficiencies/Ti(3+) species.

Density-functional theory investigation of Al pitting corrosion in electrolyte containing chloride ions

The behavior of chloride ions (Cl−) and oxygen species (the oxygen atom, O or molecular oxygen, O2) on Al(111) surface has been studied by density functional theory calculations in order to deepen the molecular understanding of fundamental processes leading to pitting of aluminum (Al). The adsorption behavior of individual species, Cl−, O atom and O2 was determined first. Subsequently, three possible scenarios in different pitting stages were modeled exploring the repassivation and dissolution of Al in neutral electrolyte containing Cl−. In scenario i, it was found that Cl− can hardly destroy even an O-monolayer on Al(111) surface, however may lead to the elongation of AlO bond and the weakened binding between the first Al layer and subsequent Al layers. Both O2 and Cl− were simultaneously introduced onto Al(111) in scenario ii. The result showed a weakened AlO interaction and an intensive hybridization peak at −0.18 Ha between Al-3p with Cl-3p suggesting insufficient repassivation behavior of Al under this condition. Finally, scenario iii mimicked different local environmental conditions in pits formed on Al. At low coverage of Cl−, chloride ions had little effect on surface relaxation. The interaction among chloride ions and Al surface became stronger as Cl− coverage increased. Surface Al atoms dissolved gradually and substructures such as AlCl3 and Al2Cl5 formed when the coverage was larger than 2/3 ML of a monolayer.

Structure, molecular simulation, and release of a spirin from intercalated Zn–Al-layered double hydroxides

Aspirin or acetylsalicylic acid (AA), a non-steroidal anti-inflammatory drug, is intercalated into Zn–Al-layered double hydroxides (ZnAl-LDHs) by co-precipitation and reconstruction methods. The composition, structure, and morphology of the intercalated products as well as their release behavior are determined experimentally and theoretically by Material Studio 5.5. Experimental results disclose the strong interaction between the LDHs sheets and AA in the intercalated ZnAl-LDHs produced by co-precipitation and slow release of AA from the intercalated ZnAl-LDHs in both phosphate buffered saline (PBS) and borate buffered saline (BBS) solutions. The percentage of AA released from the ZnAl-LDHs prepared by both methods in PBS (96.87% and 98.12%) are much more than those in BBS (68.59% and 81.22%) implying that both H4BO4− and H2PO4− can exchange with AA in the ZnAl-LDHs. After AA is released to PBS, ZnAl-LDHs break into small pieces. The experimental results are explained theoretically based on the calculation of the bonding energy between the anions and LDHs sheets as well as the AlO bond length change in the LDHs sheets.

Theoretical prediction on mechanical and thermal properties of a promising thermal barrier material: Y4Al2O9

The mechanical and thermal properties of Y4Al2O9 were predicted using a combination of first-principles and chemical bond theory (CBT) calculations. Density functional theory (DFT) computations were performed for the structural, mechanical, and thermal properties, and the results were confirmed by chemical bond theory. Based on the calculated equilibrium crystal structure, heterogeneous bonding nature has been revealed, i.e., Al-O bonds are stronger than Y-O bonds. Low second-order elastic constants c44, c55, and c66 demonstrate the low shear deformation resistance. Low G/B ratio suggests that Y4Al2O9 is a damage tolerant ceramic. Y4Al2O9 shows anisotropy in elastic behavior based on the discussion of direction dependence of Young's modulus. The hardness is predicted to be 10.2 GPa from calculated elastic moduli. The thermal expansion coefficient (TEC) calculated by chemical bond theory is 7.51×10 6 K 1 . In addition, the minimum thermal conductivity of Y4Al2O9 is estimated to be 1.13 W·m 1 ·K 1 , and the thermal conductivity decreases with

Impact of post-deposition annealing on interfacial chemical bonding states between AlGaN and ZrO2 grown by atomic layer deposition

The effect of post-deposition annealing on chemical bonding states at interface between Al0.5Ga0.5N and ZrO2 grown by atomic layer deposition (ALD) is studied by angle-resolved x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. It has been found that both of Al-O/Al 2p and Ga-O/Ga 3d area ratio decrease at annealing temperatures lower than 500 °C, which could be attributed to “clean up” effect of ALD-ZrO2 on AlGaN. Compared to Ga spectra, a much larger decrease in Al-O/Al 2p ratio at a smaller take-off angle θ is observed, which indicates higher effectiveness of the passivation of Al-O bond than Ga-O bond through “clean up” effect near the interface. However, degradation of ZrO2/AlGaN interface quality due to re-oxidation at higher annealing temperature (>500 °C) is also found. The XPS spectra clearly reveal that Al atoms at ZrO2/AlGaN interface are easier to get oxidized as compared with Ga atoms.

A DFT study of atomic geometry and electronic structures for oxidized Al0.25Ga0.75N (0 0 1) (2 × 2) reconstruction surfaces

In order to study formation energies, atomic geometry, electronic structures, and surface states of oxidized Al0.25Ga0.75N (001) (2×2) reconstruction surfaces, models of Al0.25Ga0.75N (001) (2×2) reconstruction surfaces with different coverages of oxygen atoms were built, and first-principles calculations were performed based on density functional theory (DFT). The results of these calculations show that formation energy of the oxidized Al0.25Ga0.75N (001) (2×2) reconstruction surfaces decreases as the increasing of O coverage under O-rich conditions. O atom prefers to locate on the top of GaGa and GaAl dimers. After relaxation, the length values of GaO and AlO bonds are 1.856Å and 1.853Å, respectively. With smaller electronegativity values, Ga and Al atoms donate electrons to O atom, and the dangling bonds of Ga and Al atoms on the surface were occupied. At Fermi level, the partial density of states (PDOS) of Ga and Al atoms on the topmost surface decrease significantly after Ga and Al atoms bond with O atoms, showing that surface states disappear. O atoms adsorption or replacement on Al0.25Ga0.75N (001) (2×2) reconstruction surface induces charge redistribution, which in turn forms Ga(Al)O dipoles oriented to O atoms. With Ga(Al)O dipoles, work functions of oxidized surfaces are larger than that of clean surface, and the work function increases as O coverage increases.

Interaction of Al with O2 exposed Mo2BC

A Mo2BC(040) surface was exposed to O2. The gas interaction was investigated using ab initio molecular dynamics and X-ray photoelectron spectroscopy (XPS) of air exposed surfaces. The calculations suggest that the most dominating physical mechanism is dissociative O2 adsorption whereby MoO, OMoO and Mo2CO bond formation is observed. To validate these results, Mo2BC thin films were synthesized utilizing high power pulsed magnetron sputtering and air exposed surfaces were probed by XPS. MoO2 and MoO3 bond formation is observed and is consistent with here obtained ab initio data. Additionally, the interfacial interactions of O2 exposed Mo2BC(040) surface with an Al nonamer is studied with ab initio molecular dynamics to describe on the atomic scale the interaction between this surface and Al to mimic the interface present during cold forming processes of Al based alloys. The Al nonamer was disrupted and Al forms chemical bonds with oxygen contained in the O2 exposed Mo2BC(040) surface. Based on the comparison of here calculated adsorption energy with literature data, AlAl bonds are shown to be significantly weaker than the AlO bonds formed across the interface. Hence, AlAl bond rupture is expected for a mechanically loaded interface. Therefore the adhesion of a residual Al on the native oxide layer is predicted. This is consistent with experimental observations. The data presented here may also be relevant for other oxygen containing surfaces in a contact with Al or Al based alloys for example during forming operations.

High stability mechanisms of quinary indium gallium zinc aluminum oxide multicomponent oxide films and thin film transistors

Quinary indium gallium zinc aluminum oxide (IGZAO) multicomponent oxide films were deposited using indium gallium zinc oxide (IGZO) target and Al target by radio frequency magnetron cosputtering system. An extra carrier transport pathway could be provided by the 3 s orbitals of Al cations to improve the electrical properties of the IGZO films, and the oxygen instability could be stabilized by the strong Al-O bonds in the IGZAO films. The electron concentration change and the electron mobility change of the IGZAO films for aging time of 10 days under an air environment at 40 °C and 75% humidity were 20.1% and 2.4%, respectively. The experimental results verified the performance stability of the IGZAO films. Compared with the thin film transistors (TFTs) using conventional IGZO channel layer, in conducting the stability of TFTs with IGZAO channel layer, the transconductance gm change, threshold voltage VT change, and the subthreshold swing S value change under the same aging condition were improved to 7.9%, 10.5%, and 14.8%, respectively. Furthermore, the stable performances of the IGZAO TFTs were also verified by the positive gate bias stress. In this research, the quinary IGZAO multicomponent oxide films and that applied in TFTs were the first studied in the literature.

Reduction mechanism for Eu ions in Al2O3-containing glasses by heat treatment in H2 gas.

Superior functional glasses doped with rare-earth ions have been prepared by controlling the valence states of rare-earth ions. However, recent work has revealed unresolved questions about the controlling mechanism of rare-earth ions' valence states. To address these questions, oxide glasses with and without Al2O3 and doped with Eu(3+) ions were prepared by a melting process; then, the valence states of Eu(3+) ions were investigated during heating under a hydrogen environment. The Eu(3+) ions were reduced to Eu(2+) only in the glass containing Al(3+) ions; the reduction occurred in the center of the glass over a short heating period. It was discovered that the reduction of Eu(3+) ions concurrently occurred with the formation of OH bonds which were bound with Al(3+) ions. Considering this and the data for the H2 gas diffusion through the glass, we conclude that diffusing H2 gas molecules react with Al-O(-) bonds surrounding Eu(3+) ions to form AlOH bonds and reduce Eu(3+) ions to Eu(2+) via the extracted electrons. When H2 reacts with a glass structure, that hydrogen has transformed into -OH bonds and the hydrogen concentration in the glass decreases. In order to make up the lost hydrogen, more hydrogen molecules can enter into the glass, resulting in the fast reduction of Eu(3+) ions in the center of the glass.

AlN-AlN Layer Bonding and Its Thermal Characteristics

Homogeneous bonding was successfully demonstrated on 150 mm Si wafers by face-to-face direct dielectric bonding of clean and smooth aluminum nitride (AlN) layers. Characterization result from XPS confirms the layer composition and reveals that approximately 5 nm of the layer surface was partially oxidized during processing. After activation, substoichiometric nitrogen bound to aluminum, Al-O and Al-OH bonds were found at the thin film surface. The as-bonded wafer pairs are nearly void and particle free with a high bonding strength of 1527.8 ± 272.2 mJ/m2, enabling them to withstand the subsequent process steps. In addition, experimental results have indicated that the AlN-AlN bonded wafers can achieve a 23 and 16% improvement respectively in terms of heat dissipation compared with those using SiO2 and Al2O3 as the bonding layer. It is concluded that this AlN-AlN bonded wafer pairs can exhibit a better heat dissipation capability than other bonded counterparts.

Excited electronic state decomposition mechanisms of clusters of dimethylnitramine and aluminum

In this report, electronically non-adiabatic decomposition pathways of clusters of dimethylnitramine and aluminum (DMNA-Al and DMNA-Al2) are discussed in comparison to isolated dimethylnitramine (DMNA). Electronically excited state processes of DMNA-Al and DMNA-Al2 are explored using the complete active space self-consistent field (CASSCF) and the restricted active space self-consistent field (RASSCF) theories, respectively. Similar to the nitro-nitrite isomerization reaction pathway of DMNA, DMNA-Aln clusters also exhibit isomerization pathway. However, it involves several other steps, such as, first Al-O bond dissociation, then N-N bond dissociation followed by isomerization and finally NO elimination. Furthermore, DMNA-Aln clusters exhibit overall exothermic decomposition reaction pathway and isolated DMNA shows overall endothermic reaction channel. In the electronically non-adiabatic decomposition mechanism of DMNA-Al cluster, it is predicted that NO elimination is followed by the nitro-nitrite isomerization as the primary decomposition channel.