Feedback Panel

Allows the user to add the drive oscillation signal to the Z piezo voltage. This parameter is used to set up fluid cell oscillation in any Dimension system for Fluid TappingMode.

Range or Settings:

• Enabled—Enables Z Modulation. Drive oscillation signal (Drive Frequency) is added to Z piezo voltage. When Enabled, the Z Limit must be set ≤ 420V.
• Disabled—Disables the Z modulation (i.e., no additional signal is added to Z piezo voltage).

The desired Drive Amplitude and Drive Frequency voltages (Cantilever Tune) need to be set for Fluid TappingMode operation.

Selects the signal to be used for tip feedback according to the selected Microscope Mode parameter (Other panel). For Contact AFM, the choice defaults to Deflection; however, for TappingMode, you may select either TM Deflection or Amplitude. STM offers two choices of feedback: Linear and Log.

Range or Settings:

• TappingMode—Amplitude, TM Deflection- Phase (Forcemod only)
• Contact Mode—Deflection only
• STM—Linear, Log
  • Linear—The linear difference between the instantaneous tunneling current and the Setpoint current is used in the feedback calculation.
  • Log—The difference between the log of the instantaneous tunneling current and the log of the Setpoint current is used in the feedback calculation.

See also Optimizing the STM Feedback Parameters.

Controls the amount of integrated error signal used in the feedback calculation.

Range or Settings:

• 0 to 1024

Gain settings vary, depending upon the scanner used, the sample and scanner sensitivity.

Typical Integral Gain Ranges:

• Contact AFM and Forcemod—4.0 - 20.0
• TappingMode—0.4 - 2.0
• STM—0.3 - 5.0

See also Optimizing Integral and Proportional Gains.

Controls the amount of the proportional error signal used in the feedback calculation. The Proportional Gain term in the feedback calculation has equal gain at all frequencies; therefore, it has a dominating effect over the Integral Gain for high frequencies (scan rates).

Range or Settings:

• 0 to 1024 (Typical settings for the Proportional Gain parameter are 35-100% more than Integral Gain values).

The meaning of this parameter depends on the operating mode of the microscope as follows:

Amplitude Setpoint (TappingMode)—defines the amplitude of the cantilever oscillation signal to be maintained by the feedback loop. (Range: 0.00 to 10.00V)

Deflection Setpoint (Contact Mode)—Controls the deflection-signal level used as the constant desired voltage in the feedback loop. (Range: -12.00 to 12.00 V)

Current Setpoint (STM)—Controls the constant current maintained by the feedback loop. (Range: 0.0 to 100.0nA)

Selects the oscillation frequency applied to the piezoelectric crystal that vibrates the cantilever.

Range or Settings: 0.00 to 250MHz

The Center Frequency is adjusted with the Cantilever Tune command to find the resonance frequency of the cantilever. The maximum cantilever oscillation amplitude occurs at its resonant frequency. The software sets the Drive Frequency equal to the current Center frequency value when the OK button in the Cantilever Tune control panel is pressed.

Selects the amplitude of the drive voltage applied to the piezoelectric crystal that vibrates the cantilever.

Range or Settings: 0.00 to 20.00V

The Drive Amplitude is also adjusted with the Cantilever Tune command. Increasing the Drive Amplitude increases the cantilever-oscillation amplitude. The cantilever-oscillation amplitude is increased to an appropriate level with the Cantilever Tune command. In AutoTune, the Drive Amplitude automatically adjusts to get a cantilever oscillation (rms amplitude) equivalent to the user’s Target amplitude.

Controls the sign and magnitude of the bias voltage applied to the sample.

Range or Settings: -10.00 to 10.00V

When used with STM, typical settings for the Bias voltage parameter are 20 to 100mV for conductive samples and up to several volts with poorly conducting samples. Positive settings of the Bias voltage item correspond to negative current (electrons) tunneling from the tip into the sample on heads with the Bias applied to the Sample or Tip.

This voltage has no effect on the operation of the standard microscope, but is useful in custom applications.

Range or Settings: 10.00 to 10.00V.