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Hi,
I want to reduce the imaging forces to about 50-100pN. How could I realise this in both contact and tapping mode?
In contact mode, is it appropriate to adjust the setpoint until certain value that the forces are in the ranges above?
In tapping mode, how could I adjust the drive amplitude to ~1nm, by reducing targeting tapping amplitude or setpoint? When I reduce the targeting tapping amplitude, I found that the engage is difficult. So I reduce the setpoint to about 0.2V (cannot reduce further). I have taken a force curve while in tapping mode and now I know the slope is about 50. Therefore, the amplitude is 0.2V/50=4 nm. Is the operation correct? Can it reduce the forces in tapping mode?
Thanks a lot.
Zhuoyang
Hi Zhuoyang,
In contact mode it is indeed as you say. Once in feedback one can reduce the imaging force until the cantilever alsmost pulls off the surface. For practical reasons you probably want to reduce uintil the cantilever pulls off and then go back into contact and stay with a setpoint a bit above the pull off point. Operating here might not be so easy as the cantilever can indeed loose contact with the surface. This is why you may want to scan slower than you are used to. Another well known method is to actually image in fluids as this will reduce the adhesion force and thus the total force on your tip/sample.
The forces in tapping mode are basically how much energy you are disspipating meaning a function of drive amplitude and setpoint (Bruker application note #133 has a very rough estimate about that in the appendix). Even though very amplitude tapping mode indeed offers low interaction force on the vast majority of samples one probably has to increase the drive, and thus the forces, again due to strong adhesive forces. A good start for you might be to use and 'input gain" on your tapping control of "20" and a target amplitude of no more than 3V and start from there. Does your controller have an 'IO-MOD+" board or the "IO-L" board?
Best,
Stefan
Hi Stefan,
Thanks for your answer. Our Nanodrive controller has an "IO-MOD+" board.
For the IOMOD-+ when using an TESPA or OTESPA tip I suggest using an input gain of 20 and a target amplitude of around 3V.
I couldn't find the application note #133 in the Bruker Media-Application notes. Could you please send me one copy? My email address is luzhuoyang@gmail.com. Thank you very much!