Since no catalyst is found at the tip of nanorods,
the growth can be understood based on vapor-solid
(VS) mechanism[7]. The nucleation site for the growth
of nanorods could be ZnO solid or ZnOx or Zn liquid
metal droplets. In our experiments, the source Zn
powder was heated directly up to the growth temperature
without supply of any oxygen. Hence, it
is likely that Zn liquid droplets are formed on the
substrate during the heating in an aligned manner,
which can promote the ZnO nucleation upon receiving
oxygen source.