book of abstracts - IM2NP

A B S T R A C T S TUESDAY, JUNE 29 N A N O S E A 2 0 1 0
2 – Abstract
To study the Ge overgrowth on Mn5Ge3, we first grow a 25 nm thick Mn5Ge3 layer on Ge(111) substrates
by depositing Mn at room temperature followed by a thermal annealing at ~450 °C. The surface
reconstruction prior to Ge deposition is a (√3x√3)R30, characteristic of Mn5Ge3. During Ge deposition, we
have found via RHEED that the (√3x√3)R30 reconstruction persists up to a thickness of 10 nm for a Ge
growth temperature of 250 °C and can be larger than 200 nm for a growth carried out at 450 °C. This
indicates that Mn has segregated on the Ge growing surface and the segregation length depends on the
growth temperature. Figures 1 and 2 represent two typical TEM images obtained after depositionof 60 nm of
Ge on a 25 nm thick Mn5Ge3 layer at 250 and 450 °C, respectively. These images reveal that the Ge
deposition has greatly modified the underneath Mn5Ge3 layer. For a Ge deposition carried out at 250 °C, the
underneath Mn5Ge3 layer is still present but some defects inside the layer have appeared and the interfaces
of Mn5Ge3 with both Ge substrate and Ge overgrowth become rough. For Ge growth at 450 °C, the initial
Mn5Ge3 layer has been destroyed, a part of Mn diffuses into the Ge substrate forming Mn5Ge3 clusters, the
other part segregates on top of the growing surface, reacts with deposited Ge to form a Mn5Ge3 layer. As a
consequent, the thickness of the remaining Mn5Ge3 layer on the top surface is about 17 nm, compared to the
initial thickness of 25 nm.
3 – Conclusion
The Mn segregation pathways and reaction with deposited Ge at various substrate temperatures have been
experimentally evidenced. We have combined numerous techniques, structural characterizations via
RHEED, TEM, SIMS along with magnetic characterizations by means of VSM, to investigate this
phenomenon. The mechanisms of Mn segregation will be discussed by considering the surface energy and
the solubility of Mn in Ge.
Fig. 1: TEM image of a sample obtained after deposition of 60 nm of Ge on a 25 nm thick Mn5Ge3 layer at 250 °C.
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