Selected Applications
Observation of Many-Body Exciton States using the attoCFM I
The image on the left shows a 3D map of the photoluminescence of a single InAs/
GaAs quantum dot in a charge-tunable device [1]. It was found that the coupling
between the semiconductor quantum dot states and the continuum of the Fermi
sea gives rise to new optical transitions, manifesting the formation of many-body exciton states. The experiments are an excellent proof for the stability
of the attoCFM as the measurements took more than 15 hours without the need
for re-alignment.
[1] N. A. J. M. Kleemans et al., Nature Physics 6, 534 - 538 (2010).
Addressing Strain and Doping in Isotopically
Labelled Graphene by In Situ Raman Mapping
Using an attoRAMAN confocal microscope insert installed in a 14 T cryomagnet,
temperature (10 – 300 K) and magnetic field induced changes of doping and
strain in single (1-LG) and double layer (2-LG) graphene, grown by chemical vapor
deposition and transferred on SiO2/Si substrate were investigated with a spatial
resolution of 500 nm [1,2]. Thanks to isotope labelling with 13C [3], the top (13C)
and bottom (12C) layer in 2-LG were addressed separately. In both the 1-LG and
the bottom layer of the 2-LG, which are in contact with the substrate, a significant amount of local strain is induced when varying the temperature. In contrast,
the influence of local strains on the top layer of the 2-LG is much smaller. The
strain evolution clearly reflects the thermal expansion of the substrate (Si).
Moreover, the strain release differs for the adhered and wrinkled graphene areas
considerably. The temperature dependence of the doping is clearly present in
both layers as demonstrated in the graphic panel by evolution of the normalized
peak intensity of the G mode for the top – 13C-G and bottom – 12C-G layer at selected temperatures (scale bar corresponds to 5 µm). The temperature dependence
of the doping suggests equalization of the captured charge in the 2-LG down to
low temperatures. The study thus implies that spatial distribution of doping and
especially the strain must be taken into account in all experiments on graphene
that include large temperature cycles.
[1] T. Verhagen, V. Vales, M. Kalbac and J. Vejpravova, Phys. Status Solidi B, 1–6 (2015) / DOI 10.1002/
pssb.201552223
[2] T. Verhagen, K. Drogowska, M. Kalbac and J. Vejpravova, submitted.
[3] O. Frank, L. Kavan, and M. Kalbac, Nanoscale 6, 6363 (2014).
attoDRY LAB
Dry Measurement Systems
attoCFM I+
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