Pipsa Hirva

Theoretical studies on the growth mechanisms of silicon thin films by atomic layer epitaxy

Abstract Atomic layer epitaxy (ALE) is an efficient method for growing high quality thin films. The method is based on alternating chemisorption reactions on the surface. In the present work we have used quantum chemical methods to study the chemisorption processes on the reconstructed Si(100) surface and to elucidate possible mechanisms for the ALE growth of silicon thin films. Silanes, chlorosilanes, hydrogen and chlorine were considered as adsorbates. Two different types of mechanisms were considered: radical mechanisms and molecular mechanisms. Chemisorption of the reactants to the reconstructed Si(100) surface was generally found favourable. The main obstacle for the ALE growth seems to be the difficulty of releasing HCl from the surface.

Modeling the interaction of amine bases on isolated and geminal hydroxyl groups on silica

In the present work different silica surface sites have been studied with quantum chemical methods. Hydrogen bonding of amines with the silica surfaces has been modeled with ammonia and pyridine adsorption. The results indicate that on partially dehydroxylated silica surfaces the geminal hydroxyl groups provide the more stable adsorption sites.

Molecular valence calculations: second row elements

Abstract The recently developed stepwise approximate method for the calculation of the valence electronic structure of molecules has been extended for the second row elements. The steps of the approximations have been tested separately and their contributions to the valence orbital energies and the total energies of atoms have been presented. Molecular test calculations for optimized geometries include the hydride molecules NaH, MgH 2 , AlH 3 , SiH 4 , PH 3 , H 2 S and HCl.

MOLECULAR VALENCE CALCULATIONS FOR THIRD ROW, MAIN GROUP ELEMENTS (K-KR)

Abstract In this work the previously developed valence method based on stepwise density matrix approximations has been extended for third row, main group elements (K-Kr). All the approximations have been tested separately in atomic calculations and their contributions to the valence total energies have been presented. Molecular test calculations have been carried out for third row hydrides and chlorides.