Force Volume

NanoScope Force Volume (FV) imaging with the atomic force microscope (AFM) combines force measurement with topographic imaging. Typical AFM images depict the topography of a surface by measuring the action of a feedback loop to maintain a constant tip/sample interaction as the tip is scanned across the surface. The force volume data set combines nearly simultaneously measured topographic and force information into a single data set allowing the microscopist to test for correlations between forces and surface features.

Theory

A single force curve records the force on the tip as it approaches and retracts from a point on the sample surface. When the Force reaches a user specified "trigger" value, the system records the height for that pixel and the tip retracts. Force volume imaging associates each (X,Y) position with a force curve in Z for some selected range. By plotting these values along X and Y coordinates, you may view stratified layers of force at various Z-axis heights above the sample surface. The value at a point (X,Y,Z) in the volume is the deflection (force) of the cantilever at that position in space. The height image is composed of the relative Z positions of the trigger points.

A force volume data set can be used to map in two or three dimensions the interaction forces between a sample and the AFM probe tip. Possible applications include studies of elasticity, adhesion, electrostatics and magnetics. Force volume imaging enables the measurement of forces at various Z-positions and at thousands of (X,Y) positions during a single image scan.

Varieties of Force Volume Imaging

The type of force image captured from a surface depends on how the SPM is set up. For example:

• If an magnetic force microscopy (MFM) image is being captured, force volume imaging (phase) allows the detection of long-range magnetic forces otherwise difficult to detect.
• For ordinary contact AFM, the use of force volume imaging (deflection) allows the user to see otherwise invisible electrostatic forces.

Sample Preparation

Samples intended for force volume imaging require no special preparation. Force volume imaging can be done in both air and fluid environments.

Interpretable force volume images depend on an appropriate probe selection. A stiff cantilever may provide better control when measuring strong forces and is less prone to entrapment by surface tension; however, a stiff cantilever does not respond to small forces. A flexible cantilever is more sensitive to small forces and is less harmful to delicate samples. Too pliant a probe, in responding to myriad small forces, generates noise, and may jump to contact if large attractive forces act. Refer to the Bruker probes website, www.brukerafmprobes.com, for an illustrated survey of probe options.

Next:

A Force Volume Imaging "Jump Start"

Force Volume Procedures

Detailed Force Volume Procedure

Nanomechanical Property Mapping

Sample Force Volume Parameter Settings

Force Volume Troubleshooting

Force Volume Glossary

Force Volume Image File Format

Open topic with navigation