CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 3
3.1.3.2 Atomic force microscopy
Atomic Force Microscope (AFM) is one of the important equipment in the field of material
science for surface investigation from micron to nano-meter range in ultrahigh vacuum, ambient
condition and liquid environment. The advantage of this microscope is that it is capable for
studying all types of surfaces such as conducting, semi-conducting and insulating of materials.
Major applications of atomic force microscope includes, (a) polymer crystallization studies, (b)
physical property measurement of thin films (c) failure analysis of integrated circuits, (d) presence
of phases in metals and alloys, (e) study of morphology of oxide films present on the surface, (f)
topographical variation due to process of corrosion, and (g) microscopic imaging of biological
specimens [65-69].
Atomic force microscope scans the surface in rastering pattern with the help of a probe to
obtain the information about the surface [70]. The schematic of an atomic force microscope is
shown in Fig. 2.4 [71]. It consists of (a) probe, (b) scanner (c) detection system, and (d) feedback
loop. The probe consists of a sharp tip made up of Si or Si 3 N 4 at the end of a cantilever which
scans the surface. The scanner which is made up piezo-ceramic elements and moves the tip in X,
Y and Z directions. The three dimensional movement of the tip is detected by the deflection of the
laser from the cantilever by photodiode. The feedback loop helps in detecting the force of
interaction between the tip and sample, and alters the tip-sample distance.
The basic modes of operation of AFM are; (a) contact mode, (b) semi-contact mode, and
(c) non-contact mode, respectively. In contact mode, tip scans the sample in close contact with the
surface, and is the most common mode of operation. In semi-contact mode, the tip oscillates near
the surface, and the reduction in amplitude of oscillation of cantilever is used to identify the
surface topography. In non-contact mode, tip measures the surface topography by sensing the van
der Walls force between tip and sample.