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Get to the point!. CD stamper. AlGaN/GaN quantum well waveguide. surface atoms on Si single crystal. polymer growth. AFM - atomic force microscopy. A 'new' view of structure (1986).

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CD stamper

AlGaN/GaN quantum well waveguide

surface atoms on Si single crystal

polymer growth

AFM - atomic force microscopy

A 'new' view of structure (1986)

See Vocabulary of Surface Crystallography, Journal of Applied Physics 35, 1306 (1964), by Elizabeth A. Wood


laser

diode

photodiode

mirror

Si3N4tip

sample

AFM - atomic force microscopy

How does the microscope work?

Tip scans sample

Up and down movement of tip recorded by position sensing photodiode


laser

diode

photodiode

mirror

Si3N4tip

sample

AFM - atomic force microscopy

How does the microscope work?

Tip scans sample

Up and down movement of tip recorded by position sensing photodiode


laser

diode

photodiode

mirror

Si3N4tip

sample

AFM - atomic force microscopy

How does the microscope work?

Two modes of operation


Tip: 5-20 nm radius, 10-25 m high, on 50-400 m cantilever beam

AFM - atomic force microscopy

How does the microscope work?

Contact mode - short-range interactions (Å) - interatomic forces


AFM - atomic force microscopy

How does the microscope work?

Contact mode - short-range interactions (Å) - interatomic forces

Tip: 5-20 nm radius, 10-25 m high, on 50-400 m cantilever beam

Cantilever: low stiffness - can't deform surface

Tip contacts surface

Tip scans surface: either tip or specimen moved by piezoelectric positioning system over x and y

Detector system can measure deflections in nm range


AFM - atomic force microscopy

How does the microscope work?

Contact mode - short-range interactions (Å) - interatomic forces

Two ways - 'constant force' ……. feedback system

moves tip in z direction to keep force

constant

'constant height'……. no feedback system -

usually used when surface roughness small

higher scan speeds possible


AFM - atomic force microscopy

How does the microscope work?

Tapping mode - long-range forces - van der Waals,

electrostatic, magnetic

Tip vibrates (105 Hz) close to specimen surface (50-150 Å) with amplitude 10-100 nm

May at times lightly contact surface

Suitable for soft materials


Amplitude

Tip height

AFM - atomic force microscopy

How does the microscope work?

Tapping mode

Tip vibrates (105 Hz) close to specimen surface (50-150 Å) with amplitude 10-100 nm

May at times lightly contact surface

When near or on surface, oscillation is damped - tip z position corrected so that vibration amplitude stays constant


AFM - atomic force microscopy

From force-distance plot, can get:

range & magnitude of attractive & repulsive forces

elastic modulus & adhesion energy


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