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SSRM Ramping and R-V Spectra

NanoScope software permits “IV” measurements (current, I, as a function of voltage, V) in a specified location on the sample. Typically the SPM tip is placed at the center of an image where an IV-spectrum is captured. By applying X and Y Offsets, the tip may be moved to other locations.

Perform an IV Measurement

  1. Click the Ramp icon to open the Ramp Parameter list, shown in Figure 1. Ramp parameters are summarized in .

Figure 1: The Ramp Parameter list window

Parameter Use with SSRM
Ramp Output

Select an SSRM parameter to ramp:

  • Z (for standard force curve measurements)
  • DC Test Bias
  • DC Sample Bias
Ramp Begin, Ramp End The beginning and end points of a ramp.
Ramp Rate All ramps are begin-end-begin cycles. Ramp Rate refers to one complete cycle.
Forward velocity, Reverse velocity The ramp value from beginning to end, or end to beginning.
X Offset, Y Offset Moves the probe tip to a different location.
Number of samples The number of sample points per ramp (minimum 16, maximum 64,000 for low, < 0.31 Hz, Ramp Rates).
Plot Units Metric or Volts
Feedback Type

Ensures that the deflection feedback is ON during ramping.

Settings:

  • Ramp enables feedback after each ramp cycle (start-end feedback).
  • Cycle enables feedback after each ramp cycle (start-end-start-feedback).
  • Pixel enables feedback after every sample point of the ramp. This is useful for slow ramps with few sample points.
Feedback Counts Select 50 for proper feedback.
Feedback Value Select 0 V.
Dark ramp Enable or Disable. Refer to Dark Lift for details.
Refer to Dark ramp delay Time after laser is turned on.

Table 1: SSRM: Ramp Controls Parameters in the Ramp Parameter list window

NOTE: Ramp Rate, Forward Velocity and Reverse Velocity are interdependent. Changing a velocity affects the overall Ramp Rate, and vice versa.
 
  1. Select the parameter you wish to ramp for Ramp Output.
  2. Select desired values for the other parameters in the Ramp Parameter List window.
  3. To view RV-spectra, set Data Type to Resistance (V) for Channel 1, Channel 2 or Channel 3.
  4. Start or stop ramping by clicking the associated toolbar button (see Figure 2). 

Figure 2: Toolbar Buttons: Start, Stop and Capture Ramp Curves

 
  • Start Continuous Ramping icon: begins repeated cycling. The measurement continues until you click the Stop Ramping icon (see Figure 2). 
  • The voltage ramp stops at whatever value is applied at the time the Stop Ramping button is clicked. To stop multiple voltage ramps at a specific voltage, switch to the Single Ramp Cycle icon before pressing the Stop Ramping button; this adds a single ramp to the multiple ramps and leaves the bias voltage at V-start.
  • Single Ramp icon: starts a single ramp at the Ramp Begin voltage value, increases or decreases the voltage until the Ramp End value is reached, then ramps back to the Ramp Begin level.
  • Stop Ramp icon: ends the ramping process.
  • Auto Ramp icon: starts an array of multiple RV-spectra (see Multiple RV-Spectra).
  • Capture icon: saves the spectrum acquired during a measurement.
  1. Capture ramping curves using the standard Capture commands or toolbar buttons.

Trigger Mode Function and Operation

Trigger Mode enables limiting the current passing through a sample to protect it. See the Ramp > Mode panel (see Figure 3) for trigger parameters. Table 2 describes trigger parameter functions.

Figure 3: The TUNA Ramp Mode panel

Parameter Use with SSRM
Trigger Mode Triggering is either Off, Absolute or Relative. For IV-spectra select Absolute to turn the trigger on (see following caution).
Data Type For RV-Spectra, select Resistance (V)for triggering on the resistance (voltage).
Trigger threshold This sets the trigger value.
Trigger direction See Trigger Direction
Start mode

Start mode allows you to switch between the various force modes without returning to image mode.

Range or Settings:

  • Calibrate—Produces standard force plots. Includes the ability to continuously cycle the tip up and down.
  • Step—Produces standard force plots, with added control to step the tip towards the surface.
  • Motor step—Tip is stepped towards surface using the motor.
Z step size The change in tip height per step when using force step.
Surface delay

Specifies a delay when the tip reaches the point closest to the sample.

Range or Settings:

  • 0 to 3600 seconds
 
Retracted delay

Similar to Surface delay, this value specifies the duration of the delay when the piezo is at the top of the cycle (farthest away from the sample).

Range or Settings:

  • 0 to 3600 seconds
 
XY Move Tip Pos

Three options are available for moving, in XY, from one point to another:

  • Surface — Move on surface with Z feedback on.
  • Lift — Move with the probe tip at lift height.
  • Retract — Retracts the probe before moving

Table 2: TUNA: Mode Panel Parameters

CAUTION: Trigger Mode must be set to Absolute when performing SSRM RV-spectra. Ignore parameters which share the same control panels but are relevant only to force curves.

Trigger Direction

Triggering requires specifying the Trigger Direction.

 
  1. If the Ramp Begin value is larger than the Ramp End value (i.e., the ramp voltage as a function of time, V(t), has a negative slope), select Negative for Trigger Direction (see Figure 4).
  2. If the Ramp Begin value is smaller than the Ramp End value (i.e., the ramp voltage as a function of time, V(t), has a positive slope), select Positive for Trigger Direction (see Figure 5).

Figure 4: TUNA, SSRM: Negative Trigger Direction for VStart > VEnd

Figure 5: TUNA, SSRM: Positive Trigger Direction for VStart < VEnd

Delaying Ramps

The Mode panel offers two more parameters that are used to independently add delay times at the end of a start-end ramp, or at the end of a complete start-end-start cycle (see Figure 6).

Figure 6: TUNA, SSRM: Delaying Ramps

NOTE: Delay times are not included in the Ramp Rate parameter.
NOTE: When switching from one start/end value to another, Ramp Rate is kept at a constant value. Forward and Reverse Velocity automatically adjust to maintain Ramp Rate.

 

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