The Experts below are selected from a list of 2319 Experts worldwide ranked by ideXlab platform
J.w. Rogers - One of the best experts on this subject based on the ideXlab platform.
-
Initial stages of AlN thin‐film growth on alumina using trimethylamine Alane and ammonia precursors
Journal of Applied Physics, 1994Co-Authors: D. C. Bertolet, Herng Liu, J.w. RogersAbstract:A novel precursor combination, trimethylamine Alane (TMAA) and ammonia (NH3), has been investigated for the low‐temperature chemical vapor‐deposition of AlN thin films. The initial stages of AlN growth on alumina powder substrates were studied by Fourier transform infrared spectroscopy and x‐ray photoelectron spectroscopy. Upon exposure of TMAA to the alumina surface at 300 K, infrared data show the presence of molecular trimethylamine Alane on the surface. NH3 reacts with the TMAA derivatized surface at 300 K, removing all of the trimethylamine, and leaving a four‐coordinate ‐NH2‐ species bound to aluminum in extended networks. Concurrently, the population of Alane on the surface is greatly reduced as a result of reaction with NH3 to form ‐NH2‐ and liberate H2. Subsequent exposure of TMAA leads to reaction with the surface ‐NH2‐ species and the further adsorption of TMAA. These reactions continue to propagate following additional alternating exposures of NH3 and TMAA, although with decreasing efficiency....
-
initial stages of aln thin film growth on alumina using trimethylamine Alane and ammonia precursors
Journal of Applied Physics, 1994Co-Authors: D. C. Bertolet, Herng Liu, J.w. RogersAbstract:A novel precursor combination, trimethylamine Alane (TMAA) and ammonia (NH3), has been investigated for the low‐temperature chemical vapor‐deposition of AlN thin films. The initial stages of AlN growth on alumina powder substrates were studied by Fourier transform infrared spectroscopy and x‐ray photoelectron spectroscopy. Upon exposure of TMAA to the alumina surface at 300 K, infrared data show the presence of molecular trimethylamine Alane on the surface. NH3 reacts with the TMAA derivatized surface at 300 K, removing all of the trimethylamine, and leaving a four‐coordinate ‐NH2‐ species bound to aluminum in extended networks. Concurrently, the population of Alane on the surface is greatly reduced as a result of reaction with NH3 to form ‐NH2‐ and liberate H2. Subsequent exposure of TMAA leads to reaction with the surface ‐NH2‐ species and the further adsorption of TMAA. These reactions continue to propagate following additional alternating exposures of NH3 and TMAA, although with decreasing efficiency....
Jason Graetz - One of the best experts on this subject based on the ideXlab platform.
-
Effect of Titanium Doping of Al(111) Surfaces on Alane Formation Mobility, and Desorption
The Journal of Physical Chemistry C, 2011Co-Authors: Irinder S. Chopra, Jason Graetz, Santanu Chaudhuri, Jean François Veyan, Yves J. ChabalAbstract:Alanes are critical intermediates in hydrogen storage reactions for mass transport during the formation of complex metal hydrides. Titanium has been shown to promote hydrogen desorption and hydrogenation, but its role as a catalyst is not clear. Combining surface infrared (IR) spectroscopy and density functional theory (DFT), the role of Ti is explored during the interaction of atomic hydrogen with Ti-doped Al(111) surfaces. Titanium is found to reduce the formation of large Alanes, due to a decrease of hydrogen mobility and to trapping of small Alanes on Ti sites, thus hindering oligomerization. For high doping levels ({approx}0.27 ML Ti) on Al(111), only chemisorbed AlH{sub 3} is observed on Ti sites, with no evidence for large Alanes. Titanium also dramatically lowers the desorption temperature of large Alanes from 290 to 190 K, due to a more restricted translational motion of these Alanes.
-
thermochemistry of Alane complexes for hydrogen storage a theoretical and experimental investigation
Journal of Physical Chemistry C, 2011Co-Authors: Bryan M. Wong, David Lacina, Jason Graetz, Ida M. B. Nielsen, Mark D. AllendorfAbstract:Knowledge of the relative stabilities of Alane (AlH(3)) complexes with electron donors is essential for identifying hydrogen storage materials for vehicular applications that can be regenerated by off-board methods; however, almost no thermodynamic data are available to make this assessment. To fill this gap, we employed the G4(MP2) method to determine heats of formation, entropies, and Gibbs free energies of formation for 38 Alane complexes with NH(3-n)R(n) (R = Me, Et; n = 0-3), pyridine, pyrazine, triethylenediamine (TEDA), quinuclidine, OH(2-n)R(n) (R = Me, Et; n = 0-2), dioxane, and tetrahydrofuran (THF). Monomer, bis, and selected dimer complex geometries were considered. Using these data, we computed the thermodynamics of the key formation and dehydrogenation reactions that would occur during hydrogen delivery and Alane regeneration, from which trends in complex stability were identified. These predictions were tested by synthesizing six amine-Alane complexes involving trimethylamine, triethylamine, dimethylethylamine, TEDA, quinuclidine, and hexamine and obtaining upper limits of ΔG° for their formation from metallic aluminum. Combining these computational and experimental results, we establish a criterion for complex stability relevant to hydrogen storage that can be used to assess potential ligands prior to attempting synthesis of the Alane complex. On the basis of this, we conclude that only a subset of the tertiary amine complexes considered and none of the ether complexes can be successfully formed by direct reaction with aluminum and regenerated in an Alane-based hydrogen storage system.
-
Thermochemistry of Alane Complexes for Hydrogen Storage: A Theoretical and Experimental Comparison
The journal of physical chemistry. C Nanomaterials and interfaces, 2011Co-Authors: Bryan M. Wong, David Lacina, Jason Graetz, Ida M. B. Nielsen, Mark D. AllendorfAbstract:Knowledge of the relative stabilities of Alane (AlH3) complexes with electron donors is essential for identifying hydrogen storage materials for vehicular applications that can be regenerated by off-board methods; however, almost no thermodynamic data are available to make this assessment. To fill this gap, we employed the G4(MP2) method to determine heats of formation, entropies, and Gibbs free energies of formation for thirty-eight Alane complexes with NH3-nRn (R = Me, Et; n = 0-3), pyridine, pyrazine, triethylenediamine (TEDA), quinuclidine, OH2-nRn (R = Me, Et; n = 0-2), dioxane, and tetrahydrofuran (THF). Monomer, bis, and selected dimer complex geometries were considered. Using these data, we computed the thermodynamics of the key formation and dehydrogenation reactions that would occur during hydrogen delivery and Alane regeneration, from which trends in complex stability were identified. These predictions were tested by synthesizing six amine-Alane complexes involving trimethylamine, triethylamine, dimethylethylamine, TEDA, quinuclidine, and hexamine, and obtaining upper limits of delta G for their formation from metallic aluminum. Combining these computational and experimental results, we establish a criterion for complex stability relevant to hydrogen storage that can be used to assess potential ligands prior to attempting synthesis of the Alane complex. Based on this, we conclude that only a subset of the tertiary amine complexes considered and none of the ether complexes can be successfully formed by direct reaction with aluminum and regenerated in an Alane-based hydrogen storage system.
-
The reversible synthesis of bis(quinuclidine) Alane
Journal of Alloys and Compounds, 2011Co-Authors: David Lacina, James J. Reilly, J.r. Johnson, James Wegrzyn, Jason GraetzAbstract:Abstract Aluminum hydride is a material that is well known for its high gravimetric and volumetric hydrogen densities and thus is an attractive hydrogen storage compound; however, it is thermodynamically unstable at room temperature requiring 7 × 103 bar pressure to reform the hydride from Al and H2. An alternate method of AlH3 formation is possible using a reversible organometallic synthesis employing catalyzed Al powder, H2, and quinuclidine, or another tertiary amine, as an intermediate step. Additionally, many tertiary amines are known to react directly with AlH3 to form adducts. Previous work indicates that two polymorphs of quinuclidine Alane exist, formed using an irreversible process that requires expensive starting materials (e.g. LiAlH4). The conditions of reversible adduct formation are detailed herein, as well as an analysis of quinuclidine Alane by Fourier transform infrared spectroscopy and X-ray diffraction.
-
Regeneration of aluminium hydride using dimethylethylamine
Energy & Environmental Science, 2010Co-Authors: David Lacina, James J. Reilly, James Wegrzyn, Yusuf Celebi, Jason GraetzAbstract:Aluminium hydride is a compound that is well known for its high gravimetric and volumetric hydrogen densities and favorable hydrogen storage properties. Tertiary amine–aluminium hydride complexes have gained interest due to their application as chemical reducing agents and in aluminium thin-film deposition. Various complexes of these amine Alane compounds have been created and studied previously, but these compounds were not formed directly using pressurized hydrogen. Here, we demonstrate the direct reaction of catalyzed aluminium, a tertiary amine, and hydrogen in a common solvent proceeds to form an amine Alane adduct at moderate pressures and temperatures. A complex of aluminium hydride has been formed with dimethylethylamine by this technique. A vibrational analysis of the product of these reactions by Raman and infrared spectroscopy is presented, including experimental and theoretical data. The results clarify the molecular and vibrational structure of amine Alane complexes formed by direct hydrogenation and are compared with previously determined experimental information. In addition, we demonstrate a new method for the formation of triethylamine Alane using the direct hydrogenation of dimethylethylamine and catalyzed aluminium followed by transamination with triethylamine. Finally, we propose a new low energy method to regenerate AlH3 from catalyzed aluminium and hydrogen gas.
D. C. Bertolet - One of the best experts on this subject based on the ideXlab platform.
-
Initial stages of AlN thin‐film growth on alumina using trimethylamine Alane and ammonia precursors
Journal of Applied Physics, 1994Co-Authors: D. C. Bertolet, Herng Liu, J.w. RogersAbstract:A novel precursor combination, trimethylamine Alane (TMAA) and ammonia (NH3), has been investigated for the low‐temperature chemical vapor‐deposition of AlN thin films. The initial stages of AlN growth on alumina powder substrates were studied by Fourier transform infrared spectroscopy and x‐ray photoelectron spectroscopy. Upon exposure of TMAA to the alumina surface at 300 K, infrared data show the presence of molecular trimethylamine Alane on the surface. NH3 reacts with the TMAA derivatized surface at 300 K, removing all of the trimethylamine, and leaving a four‐coordinate ‐NH2‐ species bound to aluminum in extended networks. Concurrently, the population of Alane on the surface is greatly reduced as a result of reaction with NH3 to form ‐NH2‐ and liberate H2. Subsequent exposure of TMAA leads to reaction with the surface ‐NH2‐ species and the further adsorption of TMAA. These reactions continue to propagate following additional alternating exposures of NH3 and TMAA, although with decreasing efficiency....
-
initial stages of aln thin film growth on alumina using trimethylamine Alane and ammonia precursors
Journal of Applied Physics, 1994Co-Authors: D. C. Bertolet, Herng Liu, J.w. RogersAbstract:A novel precursor combination, trimethylamine Alane (TMAA) and ammonia (NH3), has been investigated for the low‐temperature chemical vapor‐deposition of AlN thin films. The initial stages of AlN growth on alumina powder substrates were studied by Fourier transform infrared spectroscopy and x‐ray photoelectron spectroscopy. Upon exposure of TMAA to the alumina surface at 300 K, infrared data show the presence of molecular trimethylamine Alane on the surface. NH3 reacts with the TMAA derivatized surface at 300 K, removing all of the trimethylamine, and leaving a four‐coordinate ‐NH2‐ species bound to aluminum in extended networks. Concurrently, the population of Alane on the surface is greatly reduced as a result of reaction with NH3 to form ‐NH2‐ and liberate H2. Subsequent exposure of TMAA leads to reaction with the surface ‐NH2‐ species and the further adsorption of TMAA. These reactions continue to propagate following additional alternating exposures of NH3 and TMAA, although with decreasing efficiency....
M. E. Gross - One of the best experts on this subject based on the ideXlab platform.
-
Aluminum thin film growth by the thermal decomposition of triethylamine Alane
Surface Science, 1991Co-Authors: L.h. Dubois, M. E. Gross, B. R. Zegarski, Ralph G. NuzzoAbstract:Abstract Triethylamine Alane (TEAA) decomposes on an Al(111) single crystal surface at temperatures above ∼310 K to yield pure aluminum thin films, liberating hydrogen and triethylamine into the gas phase. Aluminum deposition is epitaxial and clean (no carbon or nitrogen containing species are observed by Auger electron spectroscopy). The film growth rate is limited by the rate of the recombinative desorption of hydrogen from the surface. These results are compared to similar data from experiments on the surface-mediated thermal decomposition of trimethylamine Alane.
-
Liquid source metalorganic chemical vapor deposition of aluminum from triethylamine Alane
Journal of Applied Physics, 1991Co-Authors: M. E. Gross, K.p. Cheung, C. G. Fleming, L. A. HeimbrookAbstract:Low‐pressure metalorganic chemical vapor deposition (MOCVD) of aluminum using triethylamine Alane (TEAA) is reported. This liquid source combines the chemical advantages of adduct precursors such as solid trimethylamine Alane (TMAA), with the processing and handling advantages of liquid precursors such as triisobutyl aluminum (TIBA). High‐purity Al films were deposited on TiN and thin in situ evaporated Cu and Ti films, which serve as activators for nucleation of Al. The electrical resistivities of the Al films on TiN were close to the 3 μΩ cm of sputtered Al. In the case of depositions on Cu, the Cu diffuses readily into the Al and serves to improve the electromigration resistance of the latter. The Al deposition rates using TEAA are 2–4 times those using TIBA at 250 °C, although the TEAA process is not fully optimized at this point and further work is needed to improve the film morphologies.
Minh Tho Nguyen - One of the best experts on this subject based on the ideXlab platform.
-
Hydrogen Release from Ammonia Alane-Based Materials: Formation of Cyclotrialazane and Alazine
The Journal of Physical Chemistry C, 2015Co-Authors: Vinh Son Nguyen, D. Majumdar, Jerzy Leszczynski, Minh Tho NguyenAbstract:In previous papers (Nguyen et al. J. Phys. Chem. C 2008, 112, 5662–5667 and J. Phys. Chem. C 2009, 113, 18914–18926), formation of H2 molecules from ammonia Alane monomer (AAl) and dimers (AAl)2 was shown to be facilitated by the addition of one or more Alane or ammonia molecules that can play the role of efficient bifunctional catalyst. Ammonia Alane emerges as a good starting compound for building up materials for chemical hydrogen storage (CHS). Further exploration of the products based on the H2 release from ammonia Alane were carried out using coupled-cluster theory computations together with the aug-cc-pVTZ basis set (based on MP2/aug-cc-pVDZ optimized geometries). Our ab initio MO calculations for the first time led to the identification of cyclotrialazane [(H2AlNH2)3], alazine [(HAlNH)3], and its oligomer [H2Al(HNAlH)2NH2] that are produced along the multistep dehydrogenation processes from the reactions of ammonia Alane and AlH3NH2AlH2NH3. The formation of alazine (homologue of borazine) as the f...
-
Hydrogen release from systems containing phosphine, borane, Alane and gAlane: A mechanistic study
Chemical Physics Letters, 2013Co-Authors: Vinh Son Nguyen, D. Majumdar, Jerzy Leszczynski, Minh Tho NguyenAbstract:Abstract The H 2 release mechanism from phosphine borane and phosphine Alane was investigated using quantum chemical methods (MP2/aug-cc-pVTZ geometry optimization and coupled-cluster energies were obtained through complete basis set extrapolation, CCSD(T)/CBS). The effect of catalysts borane, Alane and gAlane on the processes was also explored. As the energy barriers for the release of H 2 from BH 3 PH 3 and AlH 3 PH 3 are much higher than the B–P and Al–P bond energies, the presence of inherent catalysts can reduce substantially such energy barriers (using BH 3 for BH 3 PH 3, while AlH 3 and GaH 3 for AlH 3 PH 3 ), and these systems could be useful as probable hydrogen source.
-
the effect of the nh2 substituent on nh3 hydrazine as an alternative for ammonia in hydrogen release in the presence of boranes and Alanes
Physical Chemistry Chemical Physics, 2009Co-Authors: Minh Tho Nguyen, Myrna H. Matus, Nguyen Vinhson, Saartje Swinnen, David A. DixonAbstract:Potential energy surfaces for H2 release from hydrazine interacting with borane, Alane, diborane, diAlane and borane–Alane were constructed from MP2/aVTZ geometries and zero point energies with single point energies at the CCSD(T)/aug-cc-pVTZ level. With one borane or Alane molecule, the energy barrier for H2-loss of ∼38 or 30 kcal mol−1 does not compete with the B–N or Al–N bond cleavage (∼30 or ∼28 kcal mol−1). The second borane or Alane molecule can play the role of a bifunctional catalyst. The barrier energy for H2-elimination is reduced from 38 to 23 kcal mol−1, or 30 to 20 kcal mol−1 in the presence of diborane or diAlane, respectively. The mixed borane–Alane dimer reduces the barrier energy for H2 release from hydrazine to ∼17 kcal mol−1. A systematic comparison with the reaction pathways from ammonia borane shows that hydrazine could be an alternative for ammonia in producing borane amine derivatives. The results show a significant effect of the NH2 substituent on the relevant thermodynamics. The B–N dative bond energy of 31 kcal mol−1 in NH2NH2BH3 is ∼5 kcal mol−1 larger than that of the parent BH3NH3. The higher thermodynamic stability could allow hydrazine–borane to be used as a material for certain energetic H2 storage applications.
-
Calculations suggest facile hydrogen release from water using boranes and Alanes as catalysts
Chemical Physics Letters, 2009Co-Authors: Saartje Swinnen, Vinh Son Nguyen, Shogo Sakai, Minh Tho NguyenAbstract:Abstract Producing H 2 from water is a very challenging task. Using quantum chemical calculations with the MP2 and CCSD(T) methods and the aug-cc-pVnZ basis sets (extrapolated to CBS), we investigated the possibilities of B 2 H 6 , AlH 3 , Al 2 H 6 and AlH 3 BH 3 to act as catalysts in the reactions that split water. Hydrogen production from H 2 O is greatly accelerated in the presence of Alane, diAlane or borane–Alane in such a way that reaction H 2 O + Al 2 H 6 is a nearly spontaneous process. The main catalytic effect of AlH 3 arises from the occurrence of a strong dihydrogen bond of the type Al–H δ− – δ+ H–O within a cyclic transition structure.
-
Theoretical Study of the Hydrogen Release from Ammonia Alane and the Catalytic Effect of Alane
The Journal of Physical Chemistry C, 2008Co-Authors: Vinh Son Nguyen, Minh Tho Nguyen, Myrna H. Matus, Vu Thi Ngan, David A. DixonAbstract:Electronic structure calculations at the CCSD(T) level with the aug-cc-pVnZ and aug-cc-pV(n+d)Z basis sets (n = D, T, and Q) were employed to construct the potential energy surfaces for H2 release from ammonia Alane without and with the presence of Alane (AlH3). In the AlH3NH3 monomer, although the energy barrier for H2 loss of ∼29 kcal/mol is comparable with the energy for Al−N bond cleavage (∼27 kcal/mol), kinetics calculations show that only the latter is important at 298 K. The calculated results demonstrate that Alane can play the role of an efficient bifunctional catalyst for H2 release from ammonia Alane. The transition state for H2 production from AlH3NH3 + AlH3 is located 4.3 kcal/mol lower in energy than the separated reactants and 18.7 kcal/mol above the complex AlH3NH3···AlH3. A systematic comparison with the reaction pathways for H2 loss from ammonia borane (BH3NH3) with AlH3 or BH3 as the catalyst shows that Alane is a better catalyst than borane. The predicted kinetic rate constants for hyd...
