24. Continue moving the spot in the same direction. As we continue moving, the spot should reappear on the paper (Figure 36.7B) and again give diffraction (Figure 36.7C).
    
    
25. Bring back the laser spot between two legs and move it towards the tip of the cantilever (Figure 36.7D).
    
    
26. Focusing on the cantilever is suggested by almost completely obscured spot on the paper screen.
    
    
27. The spot on the Lucite block should look like an ‘X’ (Figure 36.7E). This happens when the laser beam is right on the tip of the cantilever.
    
    
28. Insert the Photodiode detector into the detector groove by sliding it into the groove (Figure 36.6I).
    
    
29. Plug the detector’s connector into the correct slot present on the head base plate.
    
    
30. Check the ‘Amplitude’, ‘Deflection’, and ‘LFM’ values in the instrument controller. The deflection value should be zero or close to zero (Preferably within ±0.7).
    
    
31. Fix the mica on the metallic disc provided with the instrument using a double-adhesive tape (Figure 36.6J).
    
    
32. Fix the circular ‘Sample plate’ on the sample stage holder and place the metallic disc having mica piece at the centre of the plate. The disk is held in place by a magnet present in the sample plate (Figure 36.6J).
    
    
33. Place, without tilting, the sample plate into the screws present beneath the base of the microscope’s head base plate (Figure 36.6K, 36.6L). A magnet present on the sample plate secures its position.
    
    
34. Bring the sample close to the cantilever tip using coarse adjustment screw.
    
    
35. Start the software, PicoScan.
    
    
36. Go to the ‘Preferences’ and set the ‘Scanner type’. An AFM can have multiple scanners; select the appropriate option. In this experiment, we shall be using large scanner compatible with the Agilent AFM system.
    
    
37. Go to the ‘Mode’ and select AC–AFM.
    
    
38. A dialogue box appears that shows that the AC mode controller is online i.e. connected.
    
    
39. Go to the SPS tab and select the ‘AC Mode’ frequency plot.
    
    
40. Provide the frequency range for oscillation. It is better to cover the entire frequency range specified by the manufacturer for a particular cantilever slot.
    
    
41. Click Sweep/Connect button present in the ‘AC Mode Control’ dialogue box.
    
    
42. A graph between amplitude and the frequency is generated.
    
    
43. Select the frequency slightly lower than the resonance frequency.
    
    
44. Go to ‘View’ menu.

a. In the ‘Buffer Assignment’ window, add a buffer by clicking the + button. Buffer means the type of data required, such as topography, amplitude, etc.

b. In the ‘Servo Control’ window, set the Force Setpoint to 0 V and set the ‘Integral Gain’ and ‘Proportional Gain’ to 0.6 and 0.3, respectively.

c. In the ‘Scan and Approach Control’ window, set the ‘Stop’ at 0.9 V and set the motor speed for probe approach and withdraw.