Linearity Correction

Most users will scan with the system set up for Closed LoopUses a position sensor to provide feedback on piezo movement in response to an applied voltage. feedback. However, if you are running applications in Open LoopFeedback is disabled to reduce noise and improve data resolution, useful for imaging very small features. Assumes that, once calibrated, the piezo will always move the same amount for a given voltage. that demand good linearity, the following procedure can be used to optimize the linearity correction parameters for individual scanners. As discussed previously, linearity correction is especially important for long-range scanners.

Adjust Mag0 and Arg

Set the mag0 and arg values while noting the scan beginning and ending.

Adjust Fast Mag0

	Mount a calibration reference in the SPM and begin imaging. This may consist of a generic (e.g., 10 μm silicon) reference, or a sample having features of known dimensions (e.g., grating, etc.).
	Turn the XY Closed Loop off in the Scan panel of the Scan Parameters List window (Expanded Mode):

	Verify that the Scan Angle is set to 0.00 degrees.
	Engage and begin scanning in Contact AFM mode.
	Optimize the image quality. Move the mouse cursor to the scan window, click the right mouse button and select Box then draw a box while depressing the left mouse button. Adjust the box until it is about one-third the size of the scan. Go to Calibrate > Scanner > X-Y... to open the open loop Scanner Calibration window. As parameters values are changed, the effects will be seen on the monitor.

Click the Image button in the Scanner Calibration window to make a measurement. Select Fast mag0, the first scanner parameter to modify. Move the zoom box to the start of the fast scan (on the left if the Line direction is set to Trace). Move and size the zoom box until the beginning third of the scan's features are exactly aligned with the zoom box.

NOTE: The beginning third of the scan is the standard for judging almost all of the linearity values. Ignore the set of features near the edges of the scan since these may be distorted slightly.

Move the zoom box to the end third of the scan. Align one side of the zoom box with desired features and observe how the other side aligns with the features under it. If the features are too large to fit an equal number inside the zoom box, decrease the Fast mag0 value. If the features are too small, increase the Fast mag0 value. Change Fast mag0 by about 0.1 to 0.3 units at a time. The entire scan axis is affected each time a parameter changes, so after every change, resize the zoom box at the beginning third of the scan and compare again with the end third.

Adjust Fast Arg

Once the beginning third of the scan is equal to the end third, check to see if the center needs adjusting. If the center features are too large for the box, decrease the Fast arg value. If the center features are too small, increase the Fast arg value. Change args by 0.2 to 0.5 units at a time. Changes affect the entire scan, so continue to resize the zoom box after each change. After an adjustment in Fast arg is made, Fast mag0 may need readjusting. Repeat Fast mag0 adjustment procedure until the rulings are evenly spaced across the Fast-axis

After setting Fast mag0 and Fast arg, insert the values for Slow mag0 and Slow arg. These values serve as close starting points before adjusting the slow linearities.

Adjust Slow Mag0

	Follow the same instructions as for Fast mag0.
	After a parameter change, wait until a new third of a scan begins before setting new parameters and resizing the zoom box.

NOTE: Setting the slow linearities requires a lot of time.

Move the resized box to the end of the scan and prepare to measure the end promptly.

NOTE: You may type in a new parameter value before the scan starts again.

NOTE: Be careful not to confuse scan top and bottom with beginning and ending, as the scan direction alternates.

	Adjust the zoom box to fit the beginning third of the scan and check against the end third.
	If the features of the end third are too large for the box, decrease the parameter. If the features are too small, increase the parameter.

NOTE: Compare only parts of the current scan, not the previous scan.

Adjust Slow Arg

	Follow the same instructions for Fast arg.
	Adjust the zoom box to fit the beginning and ending of the scan, then check the center.
	If the features in the center are too large, reduce the Slow arg value. If the features in the center are too small, increase the Slow arg value.
	After adjusting Slow arg values, check if Slow mag0 requires readjusting.
	Repeat the procedure for adjusting Slow mag0 until the rulings are evenly spaced along the slow axis.

Adjust Fast Mag1

Initial Adjustment

For initial adjustment, click OK to close the Scanner Calibration window.

NOTE: Selecting Cancel resets parameters to default values when the box is opened.

	Change the Scan size to 150 V.
	If the two scope traces do not overlap, Fast mag1 needs adjusting.
	On the Scan panel, select Slow Scan Axis. When tall features appear on the scope trace, press the keyboard right or left arrow key to switch the Slow Scan Axis to Disabled.
	Select Tools > Calibrate > X-Y... to open the Scanner Calibration box.
	Select Fast mag1.
	Change the value until the two traces align.

NOTE: The retrace line will shift to the right as the value is increased.

	Click OK to close the Scanner Calibration window.
	Set Slow scan axis back to Enabled.
	Select Image mode.

Fine Adjustment

Initial adjustment is usually adequate; however, if more precision is desired, use the following fine adjustment techniques to adjust Fast mag1.

	Use the same procedure for adjusting Fast Mag0.
	As before, set the Zoom box for the beginning of the scan and then check the ending. Because the scan is small, use a Zoom box up to one-half as large as the scan.
	If the end of the scan is larger than the beginning, reduce the Fast mag1 value. If the end is too small, increase the value of Fast mag1.

Adjust Slow Mag1

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