Currently working on this project: Alexander Littig
, Andreas Nielsen
Figure 1: Schematic illustration of the formation for CdSe NWs by SLS methodology.
(NWs) have been prepared in solution by the Solution-Liquid-Solid (SLS)
method where low melting point metal such as bismuth (Bi) nanoparticle
is used as catalysts (figure 1). We focused on CdE (E = Se, Te, S)
structure which is used as prototype material of the II-VI group
structures. The CdE NWs can be synthesized by different types of
precursors. For instance, we have generated the NWs by using either the
soluble molecular precursors or pre-formed CdE nanoclusters as
single-source precursors. Varying the parameters of the approaches,
homostructure NWs with different sizes are prepared (figure 2).
Moreover, the complicated heterostructure NWs such as core-shell, block
NWs are capable to be prepared by using the combination of molecular
and cluster precursors (figure 1). These core-shell NWs (e.g. CdSe/CdS
NWs) and block NWs (e.g. CdSe/CdTe NWs) can play the very important
role for further optical and electrical devices.
Figure 2: Left a, b) the TEM images of CdSe NWs; c, d) the TEM images of CdTe NWs.
Right a) the TEM image of CdSe/CdTe block NW, b) element mapping of block NW;
c,d) TEM images of CdSe/CdS core-shell NWs.
Spectroscopy of semiconductor nanowires
Currently working on this project: Dino Behn
, Aina Reich
single NWs is illuminated, it shows, similar to nanocrystals, a
behavior. This means that the fluorescence intensity is not constant
the bulk material but changes between different intensities over time
Figure 4: Blinking in a single CdSe
blinking is thought to be correlated to the charge of the NW, hence
about the charge state could contribute to a better understanding of
blinking phenomenon. An EFM (an AFM that probes electrostatic forces)
employed to measure the charge state of the nanowire under various
Figure 5: Fluorescence, AFM, and EFM image of the same nanowire.
Due to the fact of thermal broadening it is
at room temperature not possible to resolve in photoluminescence
the different transitions which could occur in a single nanowire. For
reason the normal photoluminescence signal of a nanowire is a broad
peak as it
is shown in figure 6.
Figure 6: Photoluminescence of a single nanowire. Left: Room temperature; Right: Low temperature.
To relate these peaks to the different
transitions in the semiconductor nanowire we achieve time dependent
photoluminescence measurements (Figure 8).
The measured Lifetimes give us information about what is
the charge carriers in the nanowire.
Figure 8: Time dependent photoluminescence measurement of a nanowire at low