A. Lapiccirella

Hydrogen (and muonium) in crystalline silicon: static properties and diffusion mechanisms

A two-channel model is first proposed which accounts for the two activation energies lately observed for hydrogen diffusion in c-Si. A unified understanding of the hydrogen and muonium static properties and of their thermally activated processes is given. This is obtained in terms of a stable state at a near bond centre site, of a metastable state at the tetrahedral site and of energy barrier arguments. These results have been obtained in a cluster approach by a Hartree-Fock analysis of the hydrogen potential energy surface.

Molecular cluster studies of the crystal growth process in mbe and mo-mbe: i. structure and thermodynamics of gas phase reactants [as2, as4, ga(ch3)3]

Abstract The structure and thermodynamics of some gas phase molecular reactants [As 2 , As 4 , Ga(CH 3 ) 3 ] used in MBE (molecular beam epitaxy) and MO-MBE (metal-organic molecular beam epitaxy) has been studied by Hartree-Fock-Roothaan molecular-orbitals linear-combination-of-atomic-orbitals self-consistent-field (HFR-MO-LCAO-SCF) ab initio methods. A first attempt to simulate the sticking of a gallium atom at the (100) surface of GaAs has also been made.

On Bureaucratic Behavior

Bureaucracy is by its inherent nature inefficient. This fact is due to the structure of the governance in a democratic system: the bureaucrats respond to the political apparatus and they do not respond directly to the citizens who elect the above quoted political apparatus. Bureaucracies, as Von Mises argues, supply services that cannot be bought or sold for a per unit price. Consequently, bureaucracies cannot be governed by a profit objective or economic calculation. In the absence of a profit objective bureaucracies are centrally governed by auto referential rules. Not working on the basis of the free sinallagma exchange, bureaucracies are basically an instrument to deny the freedom of choice of the citizen with whom bureaucracy does not have a direct relationship. The bureaucrats as individuals are governed, as all other human beings, by the maximization of their own utility and in doing so they are not controlled by their true stakeholder, the citizen. “Civil Servant”, a term often referred to bureaucrats, is one of the most hypocritical way of saying that can be found in political economy: the bureaucrats certainly serve themselves and their own interests in a very “educated”(civil) manner but, not being controlled directly by their natural clients- the citizens-, they are allowed by a colluded political apparatus, whose unique interest is that of being re-elected, to maximize their own utility, an end that very often does not coincide with the maximization of the citizens’ utility.

A note on the force field treatment of an amorphous silicon model

The diffraction function for amorphous silicon, computed for a Continuous Random Network is calculated and compared with experiment.

An SCF-Xα-SW cluster study on the electronic structure of a-Si and a-SiH

Abstract SCF-Xα-SW calculations have been performed on a Si 16 H 22 disordered cluster built according to the CRN theory. The computed electronic structure has been analysed and compared with several experimental optical and photo-electronic results obtained for a-Si and a-SiH.

A note about the structure ofπ 2 SiHSiH

SummaryIt has been computed the potential-energy curve ofπ2 SiH, as a function of the silicon hydrogen bond distance, by means ofab initio HFR-MO-LCAD-SCF-CI method. It has been investigated, in particular, the influence of different basis sets on the computed structural and vibrational properties of above-quoted molecule.RiassuntoSi è effettuato il calcolo della curva di energia potenziale dello statoπ2 di SiH in funzione della distanza di legame silicio-idrogeno per mezzo di metodiab initio HFR-MO-LCAD-SCF-CI. In particolare si è studiata l’influenza che hanno diversi insiemi di funzioni di base sul calcolo delle proprietà strutturali e vibrazionali della molecola in questione.

Dangling Bonds Reconstruction at the Core of a 90° Partial Dislocation in Silicon: A Theoretical Study

The energetics of bond reconstruction at the core of a 90° partial dislocation in silicon has been studied by means of HFR-MO-LCAO-SCF computations on Si5H10, Si9H18 and SilOH18 model molecular clusters’. These studies show the reconstructed geometry to be the most favourable one.