A reassessment of impact crater degradation by climatic processes on early Mars

Crater degradation on Mars is a key to understand erosion through time. Strongly eroded craters in the highlands are interpreted to be the result of enhanced erosion rate during the Noachian epoch. While fluvial valleys climatic meaning and duration are still difficult to define (strongly warmer climate or episodic activity under slightly warmer climate), the enhanced Noachian craters degradation favors a prolonged erosion with high erosion rates. Most data used for classification and understanding of these craters were done using Viking data by photoclinometry. We choose here to use MOLA data in two Noachian regions to study the evolution of this degradation in time: North Hellas and Southern Margaritifer Terra

Diffusion of Mn interstitials in (Ga,Mn)As epitaxial layers

Magnetic properties of thin (Ga,Mn)As layers improve during annealing by out-diffusion of interstitial Mn ions to a free surface. Out-diffused Mn atoms participate in the growth of a Mn-rich surface layer and a saturation of this layer causes an inhibition of the out-diffusion. We combine high-resolution x-ray diffraction with x-ray absorption spectroscopy and a numerical solution of the diffusion problem for the study of the out-diffusion of Mn interstitials during a sequence of annealing steps. Our data demonstrate that the out-diffusion of the interstitials is substantially affected by the internal electric field caused by an inhomogeneous distribution of charges in the (Ga,Mn)As layer.Comment: 11 pages, 5 figure