Electronic Material Properties - und Geowissenschaften ...

Ta = 600 o C, held at Ta for a certain annealing time ta, and then cooled down to room
temperature. The samples were examined using a high-resolution scanning electron
microscope (HRSEM). The micrographs in Figure 2 illustrate two sequences of the
morphological transformation of (left) poly- and (right) single-crystalline cylindrical
gold wires caused by the Rayleigh instability. For both type of wires thickness
undulations are first developed along the wire axis leading to fragmentation.
Eventually, the fragments change to spheres. Figures 2a and 2e display the
morphology of the as-prepared poly- and single-crystalline wires prior to annealing.
The polycrystalline wires developed axial perturbations after one hour annealing (Fig.
2b), and the wires fragmented, and decayed partially into nanospheres after ta = 2 h
(Fig. 2c). Finally after ta = 2.5 h, the wires had been transformed completely into
chains of nanospheres (Fig. 2d). The decay of the single-crystalline wires is depicted
in Figures 2e-2h. The single-crystalline wires proved to be significantly more resistant
to Rayleigh instability compared to the polycrystalline ones. First radial perturbations
appeared after ta = 2.5 h, fragmentation was observed after ta = 3 h, and complete
decay into spheres occurred only after an annealing time of ta = 5 h.
200nm RT
(a)
(b)
(c)
(d)
2µm
5µm
2µm
500nm
t a =1h
t a =2h
t a =2.5h
200nm
(e)
200nm
(f)
RT
2µm t a =3.5h
(g)
(h)
5µm
t a =2.5h
t a =5h
Fig. 2: The HRSEM images show the stages of the decay of poly- (left), and single-crystalline
(right) gold nanowires of diameter 87 nm into nanospheres upon annealing for different times
ta at 600 o C.
In summary, the results that the nanowire crystallinity influences the Rayleigh
instability considerably. The single crystalline wires are found to be more resistant
against the Rayleigh instability than polycrystalline ones of the same thickness.
Acknowledgment:
The authors would like to thank Drs. T.W. Cornelius, R. Neumann (GSI), and A.G.
Balogh (Thin Films) for the fruitful collaboration.
- 93 -