Wednesday, January 2, 2019

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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