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  • 1.
    Arhammar, C.
    et al.
    Sandvik Coromant, Sweden .
    Silvearv, F.
    Luleå University of Technology, Sweden .
    Bergman, A.
    Uppsala University, Sweden .
    Norgren, S.
    Sandvik Coromant, Sweden Uppsala University, Sweden .
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Ahuja, R.
    Uppsala University, Sweden .
    A theoretical study of possible point defects incorporated into alpha-alumina deposited by chemical vapor deposition2013In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 133, no 2, p. 1433-Article in journal (Refereed)
    Abstract [en]

    The energetics and electronic structure of carbon, chlorine, hydrogen, and sulfur in alpha-Al2O3 was investigated by first principles and thermodynamical calculations. These species are present in the gas phase during the synthesis of alpha-Al2O3 by chemical vapor deposition (CVD) but little is known of their solubility in this compound. The heat of formation from standard reference states of the elements varying the chemical potential of each element was calculated. An attempt to model the actual conditions in the CVD process was made, using the species and solid compounds present in a common CVD process as reference states. Our calculations suggest that sulfur from the catalyzing agent H2S will not solve in alpha-Al2O3 during deposition by CVD. It is found that the neutral chlorine and hydrogen interstitial defects display the lowest heat of formation, 281 and 280 kJ/mol, respectively, at the modeled CVD conditions. This energy is too high in order for neutral defects to form during CVD of alpha-Al2O3 at any significant amounts. The charged defects and their compensation were studied. Carbon substituting oxygen is found to be energetically favored under the modeled CVD conditions, considering carbon dioxide as competing species to solid solubility in alpha-Al2O3 at an energy of -128 kJ/mol. However, care needs to be taken when choosing the possible competing carbon-containing phases. Compensation of carbon substituting for oxygen by oxygen vacancies takes place at 110 kJ/mol from standard reference states, graphite, fcc-Al and O-2. The carbon solubility in Al2O3 is difficult to measure with standard analysis techniques such as X-ray diffraction and energy dispersive X-ray spectroscopy, but several stable compounds in the Al-C-O are available in the literature.

  • 2.
    Danielsson, Örjan
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Sukkaew, Pitsiri
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Physical Chemistry. Linköping University, The Institute of Technology.
    Kordina, Olof
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Shortcomings of CVD modeling of SiC today2013In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 132, no 11, p. 1398-Article in journal (Refereed)
    Abstract [en]

    The active, epitaxial layers of silicon carbide (SiC) devices are grown by chemical vapor deposition (CVD), at temperatures above 1,600 °C, using silane and light hydrocarbons as precursors, diluted in hydrogen. A better understanding of the epitaxial growth process of SiC by CVD is crucial to improve CVD tools and optimize growth conditions. Through computational fluid dynamic (CFD) simulations, the process may be studied in great detail, giving insight to both flow characteristics, temperature gradients and distributions, and gas mixture composition and species concentrations throughout the whole CVD reactor. In this paper, some of the important parts where improvements are very much needed for accurate CFD simulations of the SiC CVD process to be accomplished are pointed out. First, the thermochemical properties of 30 species that are thought to be part of the gas-phase chemistry in the SiC CVD process are calculated by means of quantum-chemical computations based on ab initio theory and density functional theory. It is shown that completely different results are obtained in the CFD simulations, depending on which data are used for some molecules, and that this may lead to erroneous conclusions of the importance of certain species. Second, three different models for the gas-phase chemistry are compared, using three different hydrocarbon precursors. It is shown that the predicted gas-phase composition varies largely, depending on which model is used. Third, the surface reactions leading to the actual deposition are discussed. We suggest that hydrocarbon molecules in fact have a much higher surface reactivity with the SiC surface than previously accepted values.

  • 3.
    Eriksson, Emma S. E.
    et al.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Erdtman, Edvin
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, Faculty of Science & Engineering.
    Eriksson, Leif A.
    Department of Chemistry and Molecular Biology, University of Gothenburg.
    Permeability of 5-aminolevulinic acid oxime derivatives in lipid membranes2016In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 135, no 1, p. 1-9Article in journal (Refereed)
    Abstract [en]

    The endogenous molecule 5-aminolevulinic acid (5ALA) and its methyl ester (Me-5ALA) have been used as prodrugs in photodynamic treatment of actinic keratosis and superficial non-melanoma skin cancers for over a decade. Recently, a novel set of 5ALA derivatives based on introducing a hydrolyzable oxime functionality was proposed and shown to generate considerably stronger onset of the photoactive molecule protoporphyrin IX (PpIX) in the cells. In the current work, we employ molecular dynamics simulation techniques to explore whether the higher intercellular concentration of PpIX caused by the oxime derivatives is related to enhanced membrane permeability, or whether other factors contribute to this. It is concluded that the oximes show overall similar accumulation at the membrane headgroup regions as the conventional derivatives and that the transmembrane permeabilities are in general close to that of 5ALA. The highest permeability of all compounds explored is found for Me-5ALA, which correlates with a considerably lower fee energy barrier at the hydrophobic bilayer center. The high PpIX concentration must hence be sought in other factors, where slow hydrolysis of the oxime functionality is a plausible reason, enabling stronger buildup of PpIX over time.

  • 4.
    Finzel, Kati
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    About the atomic shell structure in real space and the Pauli exclusion principle2016In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 135, no 6, p. 148-Article in journal (Refereed)
    Abstract [en]

    It is shown that any set of eigenfunctions (1s, 2s) of a bare Coulomb Hamiltonian exhibit the same atomic shell structure pattern for the real-space indicator a(1), which is defined as the ratio between the positive kinetic energy density and the electron density. Since this model Hamiltonian excludes all effects due to the electron-electron repulsion, the appearance of the atomic shell structure is attributed to the Pauli exclusion principle that arises from the requirements for a fermionic wavefunction. Since the derivation is independent of the nuclear charge and the energy of the system, reversely imposing proper atomic shell structure behavior in the design of kinetic energy functionals mimics the Pauli exclusion principle during a variational process.

  • 5.
    Finzel, Kati
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Reinvestigation of the ideal atomic shell structure and its application in orbital-free density functional theory2016In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 135, no 4, p. 87-Article in journal (Refereed)
    Abstract [en]

    It is shown how to determine the ideal shell radii solely as a function of the nuclear charge. With the help of those ideal shell radii, an approximation to the Pauli potential for atoms in their groundstate can be constructed. The so-called SSB-ideal potential (shell structure-based) yields self-consistent orbital-free electron densities with proper atomic shell structure from Hohenberg-Kohn variational principle.

  • 6.
    Finzel, Kati
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Ayers, Paul W.
    McMaster University, Canada.
    Functional constructions with specified functional derivatives2016In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 135, no 12, article id 255Article in journal (Refereed)
    Abstract [en]

    A bifunctional construction depending on a specified density-potential pair and an approximate guiding electron density functional is presented. The proposed bifunctional construction properly transforms under homogeneous coordinate scaling and yields the specified functional derivative, which determines the electron density. Whereas the method is general and applicable to all functional types, it will prove especially helpful in the context of orbital-free density functional theory, where most existing approximate density functionals predict inaccurate potentials.

  • 7.
    Kalered, Emil
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Pedersen, Henrik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Janzén, Erik
    Linköping University, Department of Physics, Chemistry and Biology, Semiconductor Materials. Linköping University, The Institute of Technology.
    Ojamäe, Lars
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Adsorption and surface diffusion of silicon growth species in silicon carbide chemical vapour deposition processes studied by quantum-chemical computations2013In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 132, no 12Article in journal (Refereed)
    Abstract [en]

    The effect chlorine addition to the gas mixture has on the surface chemistry in the chemical vapour deposition (CVD) process for silicon carbide (SiC) epitaxial layers is studied by quantum-chemical calculations of the adsorption and diffusion of SiH2 and SiCl2 on the (000-1) 4H–SiC surface. SiH2 was found to bind more strongly to the surface than SiCl2 by approximately 100 kJ mol−1 and to have a 50 kJ mol−1 lower energy barrier for diffusion on the fully hydrogen-terminated surface. On a bare SiC surface, without hydrogen termination, the SiCl2 molecule has a somewhat lower energy barrier for diffusion. SiCl2 is found to require a higher activation energy for desorption once chemisorbed, compared to the SiH2 molecule. Gibbs free energy calculations also indicate that the SiC surface may not be fully hydrogen terminated at CVD conditions since missing neighbouring pair of surface hydrogens is found to be a likely type of defect on a hydrogen-terminated SiC surface.

  • 8.
    Pedersen, Henrik
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Chemistry. Linköping University, The Institute of Technology.
    Elliott, Simon D.
    National University of Ireland University of Coll Cork, Ireland .
    Studying chemical vapor deposition processes with theoretical chemistry2014In: Theoretical Chemistry accounts, ISSN 1432-881X, E-ISSN 1432-2234, Vol. 133, no 5, p. 1476-Article in journal (Refereed)
    Abstract [en]

    In a chemical vapor deposition (CVD) process, a thin film of some material is deposited onto a surface via the chemical reactions of gaseous molecules that contain the atoms needed for the film material. These chemical reactions take place on the surface and in many cases also in the gas phase. To fully understand the chemistry in the process and thereby also have the best starting point for optimizing the process, theoretical chemical modeling is an invaluable tool for providing atomic-scale detail on surface and gas phase chemistry. This overview briefly introduces to the non-expert the main concepts, history and application of CVD, including the pulsed CVD variant known as atomic layer deposition, and put into perspective the use of theoretical chemistry in modeling these processes.

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