Imaging Tips - Imaging Tips These sections offer...

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Imaging Tips These sections offer suggestions on setting system parameters to optimize image quality. Servo Settings (Gains, Setpoint ) Scan Settings (Speed, Resolution) Tips for the Servo Dialog Box Settings Setpoint and Gain settings are very tip-sample dependent and will change with tip type, scan speed, scan size and surface topography. These suggestions give some general guidelines for working with the settings in the Servo dialog box. Setting Integral and Proportional Gains The I and P gains dictate how quickly the feedback system reacts to changes in deflection. The I gain setting has a much greater effect on imaging than the P gain. When the gains are set too high, the system will overcompensate to correct changes in tip deflection which will lead to “ringing” at the leading and trailing edges of features. When the gains are too low, the system will not adjust the tip quickly enough for that scan speed, blurring the topography. To adjust the I and P Gains, observe both Topography and the servo input signal (Deflection or Amplitude) in the Realtime Images window. Look for rapid response and quick settling in the Topography data and oscillations in the Servo Input signal to help fine tune the Gain settings. - Observing Trace and Retrace scans in the Topography image can indicate how well the tip is tracking the surface while scanning. Adjust the Gains and Scan Speed so that the tip tracks the surface the same in both scan directions. - Image quality is more sensitive to I Gain and P Gain . - The I and P Gains are multiplied by the Input Gain on the Advanced Tab , and by the Servo Gain Multiplier in Scanner Setup . The following procedure is a useful way to adjust the gains: 1. Begin imaging with I Gain and P Gain set fairly low (0.50-1.00). 2. Slowly increase the I Gain to increase the contrast and detail of the image. 3. Increase the I Gain until oscillations appear in the scan lines, then decrease until the oscillations cease. 4. Adjust the P Gain to increase image quality. P Gain is typically larger than I Gain, almost 2X or more depending on conditions. Gain settings of 5 - 10% are typical, though some iteration will most often be required to optimize the gains for a particular sample, Setpoint and scan Speed. Adjusting the Setpoint
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- In STM Mode the Setpoint should usually be between 0.1 and 1.0 nA, depending on conditions. Note that increasing the Setpoint value decreases the tip-sample separation distance. - In AFM Mode, the Setpoint should be set to zero and the Photodiode Detector should be adjusted to read between -2 to -5 (depending on the amount of force you would like the cantilever to exert on the sample) before engaging the sample. Increasing the Setpoint value once the sample is engaged increases the applied force between the tip and sample. - In ACAFM Mode, the Setpoint should be a percentage of the free amplitude of the cantilever.
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Imaging Tips - Imaging Tips These sections offer...

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