Chemistry Reference
In-Depth Information
Figure 3.27. Schematic representation of the DPN technique. A water meniscus
forms between the AFM tip coated with alkanethiols and the gold substrate. The
size of the meniscus, which is controlled by relative humidity, affects the molecular
transport rate, the effective tip-substrate contact area, and DPN resolution.
of the organic layer (404 K) at fast heating rates (100 K min
−
1
). The samples be-
come opalescent after about 1 min at the final temperature, indicating defined light
diffraction behaviour as known from photonic crystal structures. Atomic force mi-
croscopy measurements reveal a morphology with well-defined periodic structures
of the order of 1.5
µ
m, which are shown in Fig. 3.26.
Scanning probe lithography
Dip-pen nanolithography
Controlled delivery of collections of molecules onto a substrate with nanometre
resolution can be achieved with the tip of an AFM. This positive printing mode
technique is called dip-pen nanolithography (DPN) and its working principle is
illustrated in Fig. 3.27. DPN uses an AFM tip as a
nanopencil
, a substrate as the
paper
and molecules with a chemical affinity for the substrate as the
ink
. Capillary
transport of molecules from the AFM tip to the solid substrate is used in DPN to
directly write patterns consisting of a relatively small collection of molecules in
submicrometre dimensions. The first example introducing the technique was the
transfer of octadecanethiol onto gold surfaces (Piner
et al.
, 1999).
