Scanner, Probe, and Sample Preparation

Silicon nitride (SiN) substrates are used for SPM operation in Contact Mode AFM. SiN substrates consist of a cantilever integrated with a sharp tip on the end. For Contact Mode AFM imaging, the cantilever must be soft enough to deflect very small forces and have a high enough resonant frequency to avoid vibrational instabilities.

1. Install a SiN probe onto an AFM probe holder (see Prepare and Load the Probe Holder for more detailed instructions).
2. Mount the probe holder with installed probe onto the scanner tube of the Dimension Icon SPM scanner (see Install the Probe Holder on the SPM Scanner for more detailed instructions).
3. Align the laser using the laser control knobs (see Align the Laser for more detailed instructions).
4. Verify the laser beam is positioned on the back of the cantilever, with a spot visible in the Dimension Icon scanner filter screen and a SUM signalThe sum of all four photodetector quadrants (A+B+C+D); indicates how much laser power is reaching the detector. Reflective cantilevers have a higher SUM signal than non-reflective cantilevers. The first step of aligning the laser is to ensure that there is sufficient SUM signal measured from the detector. of 4–6 V.
5. Adjust the photodetector so that the red dot moves toward the center of the Dimension Icon scanner filter screen using the two photodetector adjustment knobs located on the side of the Dimension Icon scanner (see Adjust the Photodetector).
6. Verify that the red dot is centered and elliptical in shape in the Dimension Icon scanner filter screen.
7. Set the Vertical Deflection such that when the system reaches the setpointOperator-selected threshold used as the target of the feedback control loop. voltage, the laser spot will have moved to the 0 V vertical position on the photodetector. For example, for a 1 V setpoint, set the Vertical Deflection to –1 V. The selection of a setpoint voltage is dependent upon your sample type and probe selection.
8. Adjust the Vertical Deflection such that when the system reaches the Deflection Setpoint, the laser spot will have moved to the 0 V vertical position on the photodetector. Two methods are available:
   • Method 1:

   The most straightforward approach is to center the photodetector at 0 V Vertical Deflection before engaging on the sample, and upon engage the tip is pushed into the sample with enough force to deflect the cantilever until the Vertical Deflection matches the Deflection Setpoint.

   • Method 2 (recommended):

   Since the photodetector is most linear at the center of its range, the method 1 is not optimal. An alternate approach enables the AFM to scan with the Vertical Deflection at the centered (0 V) on the photodetector:

   1. Set the Deflection Setpoint to 0 V.
   2. Determine the desired degree of deflection you wish the cantilever to reach upon contact with the sample. This will depend on your probe type and degree of sample softness. The contact force can be determined either experimentally, through experience, or using the Contact Mode Force Calibration procedure. For example, for a soft sample and a SiN probe, you may want to use a low force of 0.5 V.
   3. Offset the Vertical Deflection on the photodetector such that when the desired degree of deflection is obtained the system will reach the Deflection Setpoint. For in the example give in b (above), set the Vertical Deflection to –0.5 V.

Previous Step:

1. Set Up the Experiment

Next Steps:

3. Locate the Probe Tip
4. Focus Surface
5. Check Initial Scan Parameters
6. Engage and Scan

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