Couche électronique | EPFL Graph Search

vignette vignette|Modèle de Bohr d'un atome à trois couches électroniques. En chimie et en physique atomique, une couche électronique d'un atome est l'ensemble des orbitales atomiques partageant un même nombre quantique principal n ; les orbitales partageant en plus un même nombre quantique azimutal ℓ forment une sous-couche électronique. Les termes couche et sous-couche sont hérités de la théorie des quanta du début du , et notamment des développements théoriques introduits par Arnold Sommerfeld autour du modèle de Bohr, qui expliquaient la structure fine des raies spectrales de l'atome d'hydrogène et des ions hydrogénoïdes par la quantification des niveaux d'énergie des électrons autour des noyaux atomiques en fonction de nombres quantiques. Les couches électroniques sont identifiées par leur nombre quantique n, valant 1, 2, 3 ou, historiquement, par les lettres K, L, M utilisées en spectroscopie des rayons X. Elles correspondent à une énergi

Evolution of open many-electron systems

Aric Gliesche

Starting from the quantum statistical master equation derived in [1] we show how the connection to the semi-classical Boltzmann equation (SCBE) can be established and how irreversibility is related to the problem of separability of quantum mechanics. Our principle goal is to find a sound theoretical basis for the description of the evolution of an electron gas in the intermediate regime between pure classical behavior and pure quantum behavior. We investigate the evolution of one-particle properties in a weakly interacting N-electron system confined to a finite spatial region in a near-equilibrium situation that is weakly coupled to a statistical environment. The equations for the reduced n-particle density matrices, with n < N are hierarchically coupled through two-particle interactions. In order to elucidate the role of this type of coupling and of the inter-particle correlations generated by the interaction, we examine first the particular situation where energy transfer between the N-electron system and the statistical environment is negligible, but where the system has a finite memory. We then formulate the general master equation that describes the evolution of the coarse grained one-particle density matrix of an interacting confined electron gas including energy transfer with one or more bath subsystems, which is called the quantum Boltzmann equation (QBE). The connection with phase space is established by expressing the one-particle states in terms of the overcomplete basis of coherent states, which are localized in phase space. In this way we obtain the QBE in phase space. After performing an additional coarse-graining procedure in phase space, and assuming that the interaction of the electron gas and the bath subsystems is local in real space, we obtain the semi-classical Boltzmann equation. The validity range of the classical description, which introduces local dynamics in phase space is discussed.

EPFL2007

Effect of the pn junction engineering on Si microwire-array solar cells

Anna Dalmau Mallorquí, Franz Michael Epple, Anna Fontcuberta i Morral

We report on the impact of the doping concentration design on the performance of silicon microwire arrays as photovoltaic devices. We have fabricated arrays with different p- and n-doping profiles and thicknesses, obtaining mean efficiencies as high as 9.7% under AM 1.5G solar illumination. The results reveal the importance of scaling the microwire diameter with the depletion width resulting from doping concentrations. The doping of the core should be kept low in order to reduce bulk recombination. Furthermore, the thickness of the n-shell should be kept as thin as possible to limit the emitter losses.

Wiley-VCH Verlag Berlin2012

Electronic Structure and Solvation of Copper and Silver Ions: A Theoretical Picture of a Model Aqueous Redox Reaction

Leonardo Bernasconi, Ivano Tavernelli

Electronic states and solvation of Cu and Ag aqua ions are investigated by comparing the Cu2+ + e- -> Cu+ and Ag2+ + e- -> Ag+ redox reactions using d. functional-based computational methods. The coordination no. of aq. Cu2+ is found to fluctuate between 5 and 6 and reduces to 2 for Cu+, which forms a tightly bound linear dihydrate. Redn. of Ag2+ changes the coordination no. from 5 to 4. The energetics of the oxidn. reactions is analyzed by comparing vertical ionization potentials, relaxation energies, and vertical electron affinities. The model is validated by a computation of the free energy of the full redox reaction Ag2+ + Cu+ -> Ag+ + Cu2+. Investigation of the one-electron states shows that the redox active frontier orbitals are confined to the energy gap between occupied and empty states of the pure solvent and localized on the metal ion hydration complex. The effect of solvent fluctuations on the electronic states is highlighted in a computation of the UV absorption spectrum of Cu+ and Ag+. [on SciFinder (R)]

2004

Evolution of open many-electron systems

Aric Gliesche

EPFL2007