Do you simply take the positive value? Or is the 0 point an arbitrary position and you need to add the positive value and absolute of the negative value? (Ex. The minimum detectable value is -2 nm and the feature height is 3 nm. Is the feature 3 nm or 5 nm?)
Since AFM measures only relative heights and not the absolute thickness, you can add/subtract to/from your zero value whatever you want, you just shouldn't multiply the scale with anything. The zero height setting was recently discussed here:
https://www.researchgate.net/post/How_to_set_zero_height_in_AFM_images_of_deposited_films
Dear Bin Jeremiah Duenas Barba,
The feature height will be approx. 5nm. You have to add the minimum and maximum detectable height by the AFM tip to get the actual height.
Also, the raw image may have electrical noises which can alter the actual feature height data. Therefore, it is always better to use a post processing software for the AFM images and then from the rendered (processed) image, by drawing a line profile (over the surface features) you can determine the actual feature height.
Regards
Sumita
@Barba, the AFM height image is basically determined by the Z controller. The z-axis value typically indicates the position of the Z controller. Usually, the center position of the Z controller is not callibrated to 0 Volts. Hence, the position of the Z controller while we start the scan is at a random position either more than 0 Volts or less than that. This is reflected as a positive or negative height in an AFM height image.
For this reason, it's ok to calculate the relative positions as mentioned by others!
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