W. Richard Bowen and Nidal Hilal 4

264 9. APPLICATION OF ATOMIC FORCE MICROSCOPy
may be positioned adjacent to the cantilever holder. For the multimode
system, a light intensified high-speed camera (an APX I2 intensified
head) was employed due to illumination restrictions. Photomicrographic
studies using the XE-120 (optical head system) are readily achieved as
the optical head system permits peripheral access.
The selection of a suitable microscope assembly is determined principally
by the minimum attainable distance between lens and colloid
probe; therefore ultralong working distance (ULWD) lenses were used
(with supplementary lenses) as shown in Figure 9.9.
Separation of the surfaces is achieved either by raising the probe (conventional
force–distance) or by lowering the sample substrate using a
piezoceramic actuator. The Explorer is especially suited to the latter as it
may be positioned above an independent piezoceramic stack.
Figure 9.10 shows filamentatious behaviour of a viscoelastic polymer
(the V-shaped cantilever is 85 µm long). The fluid is stretched between
FIguRE 9.9 The high-speed optical microscopy system incorporating (1) APX Fastcam
high-speed camera, (2) extension tube, (3) supplementary macrolens magnification and
motorised focus, (4) light source and (5) ULWD microscope lens.
FIguRE 9.10 Formation of microscale viscoelastic liquid filament formed between a
V-shaped cantilever and a reflective silica substrate.