Mars og Marsaktiviteter - nye projekter under opsejling

Mars Simulerings Laboratoriet på Aarhus Universitet har bidraget med vigtig viden i forbindelse med Mars-missionerne, og der er også udsigt til, at igangværende projekter kommer i betragtning til NASAs og ESAs Mars-ekspeditioner i 2007 og 2011

Unusual charge states and lattice sites of Fe in Al x Ga1-x N:Mn

Charge states and lattice sites of Fe ions in virgin and Mn-doped Al x Ga1-x N samples were investigated using Fe-57 emission Mossbauer spectroscopy following radioactive Mn-57(+) ion implantation at ISOLDE, CERN. In the undoped Al x Ga1-x N, Fe2+ on Al/Ga sites associated with nitrogen vacancies and Fe3+ on substitutional Al/Ga sites are identified. With Mn doping, the contribution of Fe3+ is considerably reduced and replaced instead by a corresponding emergence of a single-line-like component consistent with Fe4+ on Al/Ga sites. Density functional theory calculations confirm the Fe4+ charge state as stabilised by the presence of substitutional Mn2+ in its vicinity. The completely filled spin up orbitals in Mn2+ (3d(5)) are expected to enhance magnetic exchange interactions. The population of the Fe4+ state is less pronounced at high Al concentration in Al x Ga1-x N:Mn, a behaviour attributable to hybridisation effects of 3d states to the semiconductor bands which weakens with increasing (decreasing) Al (Ga) content. Our results demonstrate that co-doping promotes the co-existence of unusual charge states of Fe4+ and Mn2+, whereas their trivalent charge states prevail with either transition metal incorporated independently in III-nitrides. Co-doping thus opens up a new avenue for tailoring novel magnetic properties in doped semiconductors.This work was supported by the European Union Seventh Framework through ENSAR (Contract No. 262010) and the German BMBF under Contract Nos. 05K13TSA and 05K16PGA. The work was funded by the Austrian Science Fund (FWF) through Projects No. P26830 and No. P31423. H Masenda, K Bharuth-Ram, and D Naidoo acknowledge support from the South African National Research Foundation and the Department of Science and Innovation within the SA-CERN programme. H Masenda also acknowledges support from the Alexander von Humboldt (AvH) Foundation. B Qi, H P Gislason and S lafsson acknowledge support from the Icelandic Research Fund. I Unzueta thanks the support of (MINECO/FEDER) and the Basque Government for the Grants RTI2018-094683-B-C5 (4, 5) and IT-1005-16, respectively