Electronic Material Properties - und Geowissenschaften ...

Texture investigations and field emission properties
of metallic nanowires
Florian Maurer, Joachim Brötz, and Hartmut Fueß
Due to their quasi one-dimensional geometry metallic nanowires possess high aspect
ratios, i.e. high ratio of length over diameter. High nanowire aspect ratios, as well as small
radii of curvature of the nanowire tips lead to an amplification of an externally applied
electric field [1] and thus increases the probability of a field emission current by tunnelling.
For field emission applications of vertically-aligned metallic nanowire ensembles it is
desirable to control the aspect ratio, as well as the radius of curvature. A suitable method
to fabricate high aspect nanowire ensembles (diameter a few ten nm, length a few ten µm)
with controllable geometric and structural properties is the polymer template technique [2]:
Nanoporous templates are produced by irradiating polymeric foils with accelerated heavy
ions. After chemical etching of the ion-induced damage tracks, the cylindrical pores of the
template are filled with metal by electrodeposition. The nanowire diameter is adjusted by
the time of etching the ion-induced tracks and its height is controlled during
electrodeposition by coulometry. The radius of curvature, i.e. the degree of single
crystallinity can be controlled by different electrodeposition parameters, e.g. temperature
or overvoltage. Different preferred growth orientations, i.e. textures, of the nanowires might
influence the field emission properties of metallic nanowires in terms of work function. Fig.
1 shows a scanning electron microscopy (SEM) image of a copper nanowire ensemble.
Fig. 1: SEM image of an ensemble with free-standing and vertically-aligned copper nanowires.
Strong textures in direction have been observed for numerous metallic fcc
nanowires under direct current (dc) deposition conditions [2, 3]. On the other hand, a
preferred growth direction of fcc nanowires in has been observed under alternating
current (ac) deposition conditions [3]. X-ray diffractograms of Au nanowire ensembles of
different textures are shown in Fig. 2.
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