You are here: NanoScope Software 8.15 User Guide > Offline Commands > Force Curve and Ramping Analysis > Force Volume

Force Volume Display and Interpretation

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.

Force Volume Display Procedure

  1. Display individual force curves by first opening the file and then selecting the Single radio button from the Force Curve Mode selection dialog. Click the left mouse button on a specific pixel in either the Height image or the Slice image to display the associated Force Curve in the Force Plots region (see Figure 1).
NOTE: The pixels in the Height image and the Slice image are marked with white crosses.

 

  1. The Z value of the Slice is displayed in the force volume image as a red vertical cursor at that particular Z value. Adjust the red cursor in the Force Plot region to find the position in the Slice image that shows good contrast.

 

Figure 1: Initial Offline Force Volume View

 

  1. Selecting the Multiple radio button from the Force Curve Mode selection dialog will display several force curves in the Force Plots region. Click the Height or the Slice image in 2 areas with different contrast to display the associated force curve in the Force Plots region. Superimpose multiple force curves by selecting multiple pixels. Click on the Clear All button in the Force Curve Mode selection dialog to erase the force plots region. The source of the contrast in the Slice image should now be depicted in the Force Plot region.

 

Figure 2: Selecting Appropriate Z Display

 

  1. Selecting the range radio button from the Force Curve Mode selection dialog will display all of the force curves in a selected box in the Force Plots region. To draw a box, place the cursor in the Height or Slice image, click the left mouse button and drag the box to the desired size. The Force Plots region will be automatically updated with the data for the chosen area.
  2. Individual force curves can be analyzed separately from the height and volume data; select Save Curves and the standard force curve analysis view is saved and can be opened from the Browse window. Once modified and analyzed, select File > Save to save the image and modified force curve. If multiple force curves are displayed, clicking Save Curves saves each curve as its own standard Force Curve file.

 

Figure 3: Using the Range Box

 

Force Volume Interface

 

Table 1:   Force Curve Mode Selections & Buttons

ParameterDescription
SingleDisplays the associated force curve for the selected pixel chosen in the Height or Slice image.
MultipleDisplays several force curves in the force plots region for the selected pixels chosen in the Height and Slice image.
RangeDisplays several force curves in the force plots region for the selected area chosen in the Height and Slice image.
Select AllPlots all Force Curves in the Force Plots region.
Clear AllErases the Force Curves shown in the Force Plots region.
Save CurvesSaves each Force Curve as its own standard Force Curve file that can be opened separately.

 

Table 2:   Force Volume Parameters

ParameterDescription
Z displayThe Z display parameter determines the Z position of the Slice to be displayed in the Slice image. The Z display can be set in two ways. The first is to enter the desired Z value of the slice in the control panel. The second is to use the mouse to change the horizontal position (that is, the Z position) of the cursor in the force plot region. For example, a Z display of 30 nm causes the force volume image region to depict forces on the tip when it is at a Z position of 30 nm above the piezoelectric actuator position at the Trig threshold. The Z display parameter may be thought of as defining bands of force at fixed distances from the sample surface.
Z directionThe Z direction parameter determines which portion of the force curve, Extend or Retract, is shown in the Slice image. For example, if adhesion forces are probed, then the Retract portion is used.
Center plotWhen Center Plot is On, any additional Force Curves added to the Force Plot will be translated vertically so that the leftmost data points in the curve are Zero. If Center Plot is Off, added Force Curves are not translated.
UnitsChoose: Volts or Metric

 

www.bruker.com Bruker, Inc.
www.brukerafmprobes.com 112 Robin Hill Rd.
http://nanoscaleworld.bruker-axs.com Santa Barbara, CA 93117
   
  Customer Support: (800) 873-9750
  Copyright 2010, 2011. All Rights Reserved.