Atomic Force Microscopy (AFM)

Atomic Force Microscopy (AFM)
Principle:

 

 

1. The molecular force is a strong function of the separation between two object
 
2. The force can be monitored by the deflection of a cantilever (100200mm long) which is in turn amplified by the deflection of a laser beam
3. Constant force is maintained by adjusting the z-position of the surface. A x-yscan will produce the morphology
 
Operation Modes of AFM
 
I. Contact mode

 

 

 

•Tip touching surface 
•Interaction force is repulsive (10-8-10-6N)
 
 
 
II. Tapping mode
•>10nm above surface, no contact 
•Cantilever set into vibration 
•Detect changes in the resonant frequency of cantilever 
•Feedback control of height

Applications of AFM

1. Imaging 
•Resolution ~nm 
•Topology 
•Able to image non-conducting materials e.g. polymer and biological samples
 
2. Force mapping
 
•To detect the variation of softness, elasticity and stickiness on sample surface 
•Useful for composite materials
 
3. Dip-Pen Nanolithography
4. Nanofabrication 
•Pattern molecules in high resolution 
•Functionalize surfaces with patterns of two or more components

Summary of STM and AFM Functions

Near-field Scanning Optical Microscope (NSOM)

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