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Feedback Parameters

Peak Force Setpoint

The setpoint for peak force. If the deflection sensitivity is calibrated, the force (in Newtons) will be displayed.

When the ScanAsyst Setup is On, Peak Force Setpoint is automatically controlled by NanoScope software. Under some conditions, you may desire to control the Peak Force Setpoint manually. A Peak Force Setpoint that is too high can either damage the sample or wear the tip. It is generally desirable to reduce the Peak Force Setpoint to as small a value as is possible. However, in order to achieve accurate Elastic modulus measurement, sufficient sample deformation is needed. If the deformation is less than 2nm, increase the Peak Force Setpoint to achieve sufficient sample deformation.

NOTE: When performing Auto Config operations with a small Peak Force Setpoint (less than ~20 mV), the tip may drift out of contact with the surface and will be unable to return and track the surface. It is therefore recommended using a relatively large Peak Force Setpoint while performing Auto Config operations and reducing the Peak Force Setpoint later if necessary.

Feedback Gain

The gain of the Peak Force Tapping feedback control loop.

NOTE: Both Peak Force Setpoint and Feedback Gain are dynamically and automatically controlled when ScanAsyst Auto Control is set to On.
NOTE: A Feedback Gain that is too large will cause oscillation of the system and increase noise, while too small a Feedback Gain will result in poor sample tracking.

Low Pass Deflection Bandwidth

The low pass filter is used to reduce deflection noise. Lower bandwidths will reduce noise but will distort the force curve and introduce errors in quantitative nanomechanical property measurements.

Range and Settings: 10 kHz–65.56 kHz (Default value: 40 kHz).

ScanAsyst Setup

Range and Settings:

  • Never: Does not allow ScanAsyst Auto Control.
  • Allow: Allows ScanAsyst Auto Control.
NOTE: Show All, discussed in the NanoScope Software Version 8 User Guide, must be enabled to view and edit this parameter.

ScanAsyst Noise Threshold

ScanAsyst Noise Threshold is linked to the Feedback Gain and is used to tune it. Larger ScanAsyst Noise Thresholds will result in better sample tracking but increased oscillation noise. Lower ScanAsyst Noise Thresholds will result in a cleaner image but the sample tracking will suffer.

Range and Settings: 0.5 nm is appropriate for most samples while 1 nm is appropriate for rough samples and 0.05 nm may be appropriate for very flat samples.

NOTE: When ScanAsyst Auto Z Limit control is turned On, the ScanAsyst Noise Threshold parameter is automatically set by the program and cannot be changed.

ScanAsyst Auto Config Frames

At the end of every N frames, an Auto Config operation is performed.

Range and Settings: 0–100. If ScanAsyst Auto Config Frames = 0, periodic Auto Config operations are not performed.

ScanAsyst Auto Control

Range and Settings:

  • Off: Turns ScanAsyst Auto Control Off.
  • On: Turns ScanAsyst Auto Control On.
  • Individual: Allows individual control of ScanAsyst Auto Gain, ScanAsyst Auto Setpoint, ScanAsyst Auto Scan Rate and ScanAsyst Auto Z Limit.

ScanAsyst Auto Gain

ScanAsyst Auto Gain allows NanoScope to dynamically control Feedback Gain.

Range and Settings:

  • Off: Turns ScanAsyst Auto Gain Off.
  • On: Turns ScanAsyst Auto Gain On.

ScanAsyst Auto Setpoint

ScanAsyst Auto Setpoint allows NanoScope to dynamically control the Peak Force Setpoint.

Range and Settings:

  • Off: Turns ScanAsyst Auto Setpoint Off.
  • On: Turns ScanAsyst Auto Setpoint On.
NOTE: This option is very useful for users who want to change the Peak Force Setpoint manually to achieve adequate deformation on the sample while leaving ScanAsyst Auto Gain On.

ScanAsyst Scan Auto Scan Rate

ScanAsyst Scan Auto Scan Rate allows NanoScope to control the Scan Rate.

Range and Settings:

  • Off: Turns ScanAsyst Scan Auto Scan Rate Off.
  • On: Turns ScanAsyst Scan Auto Scan Rate On.

ScanAsyst Auto Z Limit

ScanAsyst Auto Z Limit allows NanoScope to control the Z Limit. The ScanAsyst Auto Z Limit function will detect if the surface is sufficiently smooth to allow reduction of the Z Limit and thus avoid bit noise in the Height and Height Sensor channel. This will be effective after a whole frame of the image is scanned. If the Z Limit needs to be reduced, the ScanAsyst Noise Threshold will automatically be reduced to 0.15 times the original ScanAsyst Noise Threshold to reduce the oscillation noise for smooth samples.

Range and Settings:

  • Off: Turns ScanAsyst Auto Z Limit Off.
  • On: Turns ScanAsyst Auto Z Limit On.

 

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