Forums
Bruker Media
Community Media
Bruker AFM Probes
SPM Digest
Application Notes
NanoTheater
Website
中文
Brochures & Datasheets
Publications
Probes Catalog
Events
Manuals & Documentation
Presentations
Guide to AFM Modes
News
Journal Club
Webinars & Video
Nanovations
Other
Hi,
I try to improve our MM V AFM tapping operation in liquid. We normally use SNL-C (0.24N/m) cantilvers with a normal liquid cell (MTFML) in buffer solution (e.g. PBS). In literature I always find the lever/driving amplitude ratio is >1 for the same setup. In my case the ratio lies around 0.5-0.2 (e.g. 800mV driving amplitude results in 200-300mV lever amplitude). Even very close to the surface. To eliminate the possibility of a setup-problem I would like to ask if this is a normal...
Thx very much,
Raphi
Hi Raphi,
You are using the same AFM probe (SNL-C) that we use for the majority of TappingMode in fluid applications. For fluid imaging we typically target a free amplitude of 300-500 nm depending on your sample. For this probe, 800 nm is not that uncommon of a drive amplitude to use to get these amount of free amplitude. The important thing is that you do not lose too much of this amplitude once your probe is near the surface. Is the resonance frequency you are using around 8 kHz? If you lose a lot of amplitude near the surface (do a surface tune to see) then you may need to try increasing the drive amplitude even more (I usually do not like to go higher than 1500 mV with the MM fluid holder). If you find you cannot get enough amplitude at higher drives you can try using another frequency - some people like using the peak out around 16 kHz. You may also want to check the clip on the fluid holder. If the clip does not hold the probe substrate tightly in the pocket then you will not get efficient drive coupling and hence have low tapping amplitudes.
Hope this helps. Good luck!
Best,
Andrea
Hi Andrea,
thx for your answer. The resonance frequency is always around 6.9-7.1 kHz. I never got a peak around 8...
Do you use a special set of tapping engage parameters?
Best, Raphi
I agree to Andrea's suggestions. I would also rec
I think my previous didn’t go through, so let’s try again…
Hi Raphael,
Actually I am not so surprised to hear that when you tune, you don’t see any peak between 8 and 12 kHz since you have to make it appear: just increase the drive amplitude until you start seeing the peak. It doesn’t have to be a very sharp peak (for this, you would have to increase the DA a lot!) but it should not be too shouldered too. Then move the drive frequency slightly to the left of the peak top (I guess you know why this is required).
Then to me the most critical parameter is the ration setpoint (Amplitude setpoint / Free amplitude of oscillation) which should be between 0.2 and 0.99 (if you go higher, the phase image will be the same as the amplitude image!). This really depends on what type of information you are interested in. If you are interested in volume properties (elasticity, viscosity), 0.5 is a good option. If you want to get a nice topo image on a delicate sample, stay in light tapping conditions (0.9 or higher).
Good luck,
Alex.
Thank you all for your responses!
I am really not sure if everything is working correctly in my setup. I just do not see any peak between 8 and 12kHz. It works with a frequency around 6-7kHz, maybe I should stick to this peak.
Attached you will find a frequency sweep with SNL-C cantilever close to the surface <1um. There is no additional peak when I increase the drive amplitude by a factor of 2 or 3.
It's okay if you see a peak at 6-7 kHz rather than 8 kHz. I've actually found the position can vary between ~6-12 kHz depending on the probe and the probe holder itself.
Thanks for including the screenshot of the frequency sweep in your post. That definitely helps. I'll assume that this is an off-surface sweep (tip withdrawn). You seem to have multiple peaks in the sweep which means that in addition to your cantilever resonance peak, you are getting some mechanical excitation as well (creating the additional peaks). This could indicate that something is loose - like the clip holding the probe, as I mentioned before. I would check that. As well as the bracket in the MM head that clamps down on the probe holder itself. If this is not holding the probe holder tightly then it can cause these additional peaks.
Do you happen to know if this is a relatively new fluid probe holder? The substrate thickness on the SNL probes is thinner than the older style (D)NP-S probes. The clip on the older probe holders are best suited for holding the older style probes and do not hold the thinner SNL probes very tightly. Newer probe holders (purchased in the past year or so) are optimized for holding the thinner SNL probes. If this is the case then we should get you in contact with our Service Group here in Santa Barbara (1-800-873-9750 or AFMSupport@bruker-nano.com) and they help you to resolve this issue.