Thiis is right "从我的个人经验来看,在一定程度上增加积分增益是可以改善图像质量的,而比例增益似乎没有什么效果。不管怎样,根据图像来调节是没有错的。"
The gain value is for tip pixel Z height reference. If Gain value is high, the scanner will lift tip higher for next pixel and then down the tip for signal feedback (Deflection setting for contact mode, differentation for Tapping mode). So you can image
If Gain is too big, the scanner will lift too high for next pixel, when system hope to make feedback reasonably within pixel staying time (calaculted by scan rate and pixel numbers of a scan line-trace and retrace), this will make scanner unstable and generate oscillation.
If Gain is too slow, it is dangerous for tip to scratch surface becasue tip is lifted not high enough.
So gain must be setted reasonably. Basically integral gain dominate the feedback. If I Gain is in reasonable range, P Gain will not affect feedback too much. So P gain can be setted as I gain value.
You can use scope mode to check the feedback gain is reasonable, otherwise sometimes the wrong initial gain will wear tip. D3100 software also has a special engage auto gain adjutment. But no so many people can use it.The right manual operation way is
(1) Use reasonable inintial gain before engaging. The smoot surface use small gain. The rough surface use higher gain.This depend on on your surface feature.
(2) Ususally, use 1 um scan size for engaging. After engage, turn off slow scan axis and open scope mode.
(3) To reduce amplitude set point to make trace and retrace stable. It mean keep reduing set point will not change trace/retrace curve on scope mode image. This mean it is right amplitude set point for this scan line. If your surface is uniform surface, set point willbe use for whole image. If your surface has some special feature, such as bump or trench, you need to find a scan line cover these feature for set point adjustment. Otherwise the the set point and later gain value can not be used for whole image. Basically, SPM system is not so smart to change gain value automatically. If someone say yes, it is just for well know feature.
(4) After amplitude set point is ok. Adjust I gain from initial value. If trace and retrace scope is with oscillation, it mean the gain is too high. Please reduce I gain value. If there is no oscillation, you can increase I Gain value to see oscillation and then reduce I gain a little without oscillation. Then you will see trace and retrace will overlap perfectly. At least you can see trace and retrace is with sampe shape becasue sometimes retrace and retrace is not on perfect timing difference which can be adjust from scanner calibration value tunning.
(5) To let P gain value as I Gain.
Hope this can help you a little.
Thanks