TEM analysis is carried out to study the structure and morphology of synthesized NPs. Fig. 4 shows TEM images of Au NPs
prepared using 5 ml of oil at room temperature (sample D). The
particles are mono dispersed and most of them are hexagonal with
an average length of 36 nm. Very few of the particles are spherical
and triangular in shape. The TEM image of sample C is given in
Fig. 5 which consists of a large number of anisotropic particles. This
is in agreement with its extended SPR band in UV–visible
spectrum. The NPs are hexagonal and triangular in shapes. Hexagonal particles have an average size of 37 nm and are dominant and
triangular particles are of average size 15 nm. In both cases SAED
pattern with bright circular rings can be indexed as (111), (200),
(220) and (311) reflections showing that the NPs are highly
crystalline [11,29,30]. NPs prepared at RT are more mono dispersed
and uniform in shape while at higher temperature, different
shaped like hexagonal, triangular and spherical particles were
formed. Thus the shape of NPs can be modulated by varying the
reaction temperature by which new possibilities can be developed
specifically for biological applications.