Chemistry Reference
In-Depth Information
When an AFM tip coated with octadecanethiol is brought into contact with a
sample surface, the molecules flow from the tip to the sample by capillary action,
a process much like that of a dip pen (Fig. 3.27). Silicon nitride tips become
coated with octadecanethiol by dipping of the cantilever into a saturated solution
of octadecanethiol in CH
3
CN. The cantilever has to be blown dry with compressed
difluoroethane before being used. This elegant technique, which makes full use of
the capabilities of AFMs, can only be applied for the writing of large areas if an
efficient way of continuously providing solution to the tip is achieved.
Electrochemical nanopatterning
Electrochemical scanning probe lithography involves the operation of STMs and
conducting probe AFMs in the electrochemical operational mode. STMs and AFMs
offer the unique possibility to visualize simultaneously the topographical features
and the local electrical surface properties of the substrate. This mode has been
successfully applied for e.g., the local oxidation of inorganic semiconductors such
as silicon by applying probe voltage pulses of a few volts under controlled humidity
(Perez-Murano
et al.
, 1995). In this case nanometric dots and lines are routinely
obtained. The confinement of these electrochemical reactions in the nanometre-
scale range implies that the electrical current promoting these reactions flows only
in very limited regions between the probe apex and the substrates.
Smooth nanometre-scale insulating barriers on the (001) face of (TMTSF)
2
PF
6
single crystals have been obtained by means of an ambient-air operated conducting
probe AFM working in the oxidative mode (Schneegans
et al.
, 2001). At zero
bias there are no surface modifications in contrast to the surface modifications
achieved when the tip-substrate bias is applied. For positive substrate bias up to
+
4 V, smooth insulating lines are obtained, which increase in width for increasing
voltage potential.
The capabilities of scanning probe microscopes (SPMs) have not yet been fully
applied to MOMs!
