36 3 Surfaces in Nanomaterials
point where the two droplets touch each other, they coagulate. The coagulation
process concentrates the material of both drops in the larger drop. After coagulation, the continuing material transport leads again to the formation of the smaller
second droplet, which is nucleated at a discontinuity at the surface of the nanotube.
If there are no evaporation losses, this setup oscillates as long as it is connected
to a DC source.
It was possible to visualize this process in an electron microscope. A series of
figures displaying this process is presented in Figure 3.17.
In Figure 3.17, the carbon nanotube, the droplets and, most importantly, the
growth of the smaller particle at the expense of the larger one can be seen easily
Figure 3.16 Nanomotor based on
coagulation of metal droplets by surface
energy [8, 9]. The device consists of a
multiwall carbon nanotube and two droplets
of liquid metal, that is, indium. With an
electric field across the nanotube, metal
atoms are transported from the larger
droplet to the smaller one. Therefore, the
larger droplet shrinks and the smaller one
grows until both drops are touching. At this
moment, the droplets coagulate and the
process starts again with the material
transport from the large drop to a point,
where a new drop can be formed.
Metal droplet
+
Carbon nanotube
Transport of metal atoms
in the electric field
Touching parƟcles,
coagulaƟon starts
+
Growing droplet
Shrinking droplet
Figure 3.17 Oscillating system driven by
surface energy and electrical current [8].
These electron micrographs of a nanomotor
display the sequence of droplet growing
(micrographs a, b, and c) and after
coagulation (micrograph d). Indium atoms
are transported by electromigration at the
surface of a carbon nanotube [9].
(Reproduced by permission of Springer.)
100 nm
(a)
(b)
(c)
(d)
point where the two droplets touch each other, they coagulate. The coagulation
process concentrates the material of both drops in the larger drop. After coagulation, the continuing material transport leads again to the formation of the smaller
second droplet, which is nucleated at a discontinuity at the surface of the nanotube.
If there are no evaporation losses, this setup oscillates as long as it is connected
to a DC source.
It was possible to visualize this process in an electron microscope. A series of
figures displaying this process is presented in Figure 3.17.
In Figure 3.17, the carbon nanotube, the droplets and, most importantly, the
growth of the smaller particle at the expense of the larger one can be seen easily
Figure 3.16 Nanomotor based on
coagulation of metal droplets by surface
energy [8, 9]. The device consists of a
multiwall carbon nanotube and two droplets
of liquid metal, that is, indium. With an
electric field across the nanotube, metal
atoms are transported from the larger
droplet to the smaller one. Therefore, the
larger droplet shrinks and the smaller one
grows until both drops are touching. At this
moment, the droplets coagulate and the
process starts again with the material
transport from the large drop to a point,
where a new drop can be formed.
Metal droplet
+
Carbon nanotube
Transport of metal atoms
in the electric field
Touching parƟcles,
coagulaƟon starts
+
Growing droplet
Shrinking droplet
Figure 3.17 Oscillating system driven by
surface energy and electrical current [8].
These electron micrographs of a nanomotor
display the sequence of droplet growing
(micrographs a, b, and c) and after
coagulation (micrograph d). Indium atoms
are transported by electromigration at the
surface of a carbon nanotube [9].
(Reproduced by permission of Springer.)
100 nm
(a)
(b)
(c)
(d)