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Approach (Vibrating Mode)

  • Select “Vibrating”
  • Ensure the Range Check is Complete (with green light) before approaching. DO range check with the probe somewhat close to the sample, so that you can see both sample and probe when range check is going on. During range check, the sample should translate around a square under the probe. If this does not happen, there is a problem.
  • Moving the probe towards the sample is achieved with the Manual Z motor control buttons, “Up” and “Down”. It is recommended to use a speed less than half the maximum in this control. The best way to tell if the probe is approaching your sample, is to focus on the sample, and move the probe down until it is NEARLY in focus.
  • Laser should already be aligned on probe, the place of the red dot on the photodetector is not very important. Ideally, TB should be in the middle of its range.
  • The “vibrating” option makes the “Tune Frequency” window active.
  • Use this window to find the resonant frequency of the probe, and set the correct amplitude:
  • You should know the range of possible values of the natural resonant frequency (Rf) of your probe, if not, look on the box. For AppNano ACT probes, it-s 200-400kHz.
  • Set “Lower” and “Upper” values accordingly to sweep this range. Note It won’t work if you have a “selected” value outside of the range.
  • An initial guess for the driving amplitude (“Amplitude Vpp”), would be 0.4. You need at least 1 step per KHz, so for the above case, set steps to 200.
  • Press “Sweep”
  • You should see a sharp positive peak in the amplitude trace somewhere in that range (fig 4a). Move the green (lower), blue (selected) and red (upper) lines to close in on the peak. DO this by putting the green line on the left og the peak, the blue on in the middle of it and the red one on the right of the peak. Reduce the number of steps. Typically 50 steps would be a good choice.
  • Repeat a sweep, with fewer steps (e.g. 50). Do this until the peak fills most to the windows as in figure 4b.



 FIGURE 4 Tune window: A: Initial tune; B: Tune at scale suitable for selecting operating conditions.


  •  When you can see the peak clearly as in figure 4b adjust the Driving Amplitude (Vpp) to achieve the desired peak amplitude in the window, for example 1.0V.
  • Now, the operating frequency should be chosen. Ideally, you will do this with the probe already close to the sample surface. If necessary, use “Down” button to achieve this, using the focus of the video microscope to help you get close.
  • This guide assumes you use software version 1.5.6. Other versions will be different in this part of the procedure.
  • Put the blue line on the highest point of the amplitude curve.
  • Click system tab. Look at the amplitude value, it should be oscillating a little in the decimal points. Note the value.
  • Go back to pre-scan window and move the blue line a little to the left. Check the amplitude value in system again. IF the amplitude increase, move a bit to the left again, and re-check. You want the amplitude to decrease by 2-5 % on moving left, compared to the maximum value. For example, if you have a maximum of 1.00V, look for a value of 0.95-0.98 V.
  • NOTE: This procedure is particularly confusing because of a bug in the software, which means the REAL amplitude curve is shifted to the left of the DISPLAYED amplitude curve by ca.100Hz.
  • Once you’ve done this, click “Lock Off”, which will turn to “Lock On”.
  • Amplitude value will no longer oscillate.
  • Ideally, you should start with a maximum amplitude between 1 and 1.2 V.
  • Before automated tip approach you should get the probe as close to the sample as possible, without risking damage to the probe.
  • Press “start” in the “automated tip approach” box.
  • The approach occurs step by step , in the “woodpecker” method (see [i])
  • Eventually, it should say feedback ON (green light).Ideally z drive should be in the centre of the range (0 V).
  •  If not in centre, press start again, and see if it goes to centre, if necessary try again.
 
  • If something goes wrong with approach, it's possible the procedure will press the tip HARD against the sample, so it's always a good idea to watch the video microscope while approach is occurring. If you see cantilever bending, STOP, and raise the tip.


[i] Atomic Force Microscopy, Eaton and West, Chapter 2.

 

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