Atomic Force Microscopy: characterization of surface topography

Andrius Martinavičius

AFM schematically

Most AFMs use a laser beam deflection system, introduced by Meyer and Amer.

The atomic force microscope senses force in nano-contacts at the nano-Newton level

AFM Cantilevers and Tips

Diamond-coated AFM tip FIB Sharp Tip

Gold-coated Si3N4

Tip

Pyramidal, tetrahedral, or

conical tips are the most common tip

shapes

AFM -Tips

Pie

zo

Substrate

P

Substrate

Pie

zo

Substrate

Pie

zo

Substrate

Pie

zo

Substrate

Pie

zo

Substrate

Pie

zo

Substrate

Pie

zo

Substrate

Pie

zo

Substrate

Pie

zo

Substrate

Pie

zo

Substrate

Pie

zo

Substrate

Pie

zo

Substrate

Pie

zo

Substrate

P

Substrate

Jump to Contact

Jump off contact

Hysteresis

Jump to Contact

Jump off Contact

Deflection-DisplacementCharacteristics

AFM-Tip Approaching and Retracting

Deflection as a function of the distance

Contact Region Non-Contact Region

Stable Contact Unstable

Very stablevery damagingshear forces

Too unstablebut would be less damaging

force-distance characteristics

Non-Contact and Contact modes

In contact mode, also known as repulsive mode, an AFM tip makes soft “physical contact” with the surface.

The cantilever is oscillated above the surface of the sample at such a distance that we are in the attractive regime.

Tapping Mode

A cantilever with attached tip

is oscillated at its resonant

frequency and scanned

across the sample surface.

Tip touches sample for a very

short time.

The amplitude of the

oscillations changes when

the tip scans over bumps or

depressions on a surface.

Contact Mode Non-contact Mode Tapping Mode

AFM Modes

1 micron

1 micron

Tapping Mode vs. Contact Mode AFM

Contact mode

2 microns

Tapping mode

2 microns

Some examples

DNQ151-1VH

A is total roughness

Ra is average roughness

Rq is root-mean-square average roughness

Some roughness parameters

Rp is the height of the highest peak

Rv is the depth of the deepest valley

Rt is the sum of these two - total roughness

Some examples

Average roughness

The average roughness is the area between the roughness profile and its mean line

Digital expression

Root-Mean-Square Roughness

Integral expression

Digital expression

Some examples

Thank You for attention