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I am curious if anyone has used a Witec 1st generation analog Pulsed Force Microscopy box with a Nanoscope 3 or 3a, and what comments and observations you had with this?
I am presently trying to set up an Analog Witec PFM with a Nanoscope 3 system ( non A ) and despite the std Witec (37pin cabled ) DI interface not being (formally) supported by Witec with the Nanoscope 3 non A, I suspect the 1st Gen Witec PFM can be made to work with the Nanoscope 3(nonA) using BNC cables with an SBOB or modifying the Z Board in the Nano3 to sum the PFM Zmod signal to the low voltage Z signal prior to HV amplification ( with gain / attenuation set properly on the modification- a summing amp - summing std Z low voltage signal + the PFM Z modulation prior to the Apex HV amp ).
At least I hope it should be able to be made to work with one channel of either Stiffness OR adhesion when running Pulsed Force mode despite Witec indicating the 3(non A) not being supported.
Clearly with fewer A/D's a Nano3 (non A ) it cannot support Stiffness and Adhesion concurrently, but that is not a concern of mine ( I can afford the added time of sequential images run switching between Adhesion and Stiffness ). Even if I only get peak force imaging that will still be ok...( without adhesion or stiffness on a Nano3 non A )
Also I am curious about the PFM Peak Force mode of the Witec analog PFM with a Nanoscope 3 / 3 A, specifically just for topography imaging.
Can it enable reduced imaging forces with fewer adhesion artifacts as a poor man's ScanAsyst, if operated with lowest (but non adaptive - ie constant ) Peak Force for Z servo tracking signal?
Specifically might ScanAsyst tips ( soft and sharp ) run comparable magic of lowest forces with highest fidelity ? Just with a Witec PFM and Nanoscope 3? ( granted adaptive forces will not be possible, but PFM's slapping pulsed mode with soft sharp tips I suspect will do most of the work needed without high speed real time digitizing of the entire Scan Asyst force curve - ie the oscilloscope diagnostic from the PFM signal I suspect is quite instructive for setting up Peak Force tuning / setpoint?
I am curious what some folks who have used the analog Witec PFM with a Nanoscope 3 or 3a have to say about these questions?
Thanks
Mark,
First off, using the analog Witec version would not the a "poor man's ScanAsyst" as you refer to it but rather some incomplete version of PeakForce Tapping. ScanAsyst is the automation algorithm that uses PeakForce Tapping to get low force and hassle free imaging. ScanAsyst also does not provide you with nanomechanical properties like energy dissipation, identation depth, adhesion and stiffness. That is another computation heavy module that we refer to as the QNM package. That package is of course based on PeakForce tapping as the underlying imaging mode.
Having that said, I have used the old analog Witec box on a variety of systems in the past and I do not see a reason why you should not be able get it to work on a Nanoscope 3. Being analog, the oscillator will be prone to some drift and typically operates around 300 Hz if I remember correctly whereas we currently run PeakForce Tapping at 1Khz and 2 kHz respectively. The (analog) Witec electronics also do not perform any significant signal clean-up of the deflection signal in order to subtract spurious background signals to extract the peak force (setpoint). One of the results will be that the minimal force you can realistically work is still approximately 50x higher than using our digital PeakForce tapping implementation. These and other significant differences warranted the new name PeakForce tapping. Again, you will get it to work but do not expect PeakForce Tapping quality performance.
Cheers,
Stefan
Stephan,
Thanks for the clarifications. This is quite helpful. Do you have any info as to how to properly wire the analog PFM from witec to implement it with SBOB ( if needed ) and Z board modifications for the NS3 (non A ) ? ( and diagrams from your old work ).
Witec was initially ( ?wrongly ) indicating the NS3(non-A) would have difficulty accepting the Witec Zmod signal ( true there will need to be a board mod?), but if the Z board modification is made to the NS3 I suspect functionally it is nominally the same as the NS3A as I think they share Z Boards revs in the controllers ( with the exception of # of saved channels in the Aux boards which are different )
There might be some other subtleties in function ( I know the front panel interconnect board is different, and the Aux board cable is different NS3 to NS3a, but else much is largely the same ?
I do rmember that the Witec literature indicates they can operate up to a 1 Khz maybe a little more. The analog instability you note is noteworthy as I remember in frequency stability tapping mode's success ( in its time ) in part was due to a stable DDS generator. I will have to monitor frequency stability on the analog PFM, just to see if it is drifty and by how much.
When you refer to signal cleanup, what specifically is done ( referencing a numerically computed baseline or ratioing to SUM, what else might there be ?
I believe your 50x number, it is quite likely and credible. I am curious how this relates to say a Tapping force using same cantilever - NS5 Peak Force, analog witec Peak Force and say Tapping, in best corners each? how might they compare relatively one against the other? ( ie part of this is can the Witec use a scanasyst type tip to any benefit for lower force than conventional tapping and still get a decent image?
Thanks for your kind patience. I am trying to start a commercial imaging lab on a tight budget.
Mark
Hi Mark,
It is more than 6 years since I touched a Witec unit last. It is however not that difficult. You need to inject the oscillation signal to the AFM z-piezo. If I remember Witec had two different Oscilaltion modules and depending on that you might have to use a resitor in-line or not (should be easy to figure out). I leave the location of the addition of the signal to the z-piezo up to you. Keep in mind what final z-movement you want and check the voltage range from the Pulsed-Force box. This should help. You then have interupt the deflection signal and use it as an input for the PFM box. This may involve soldering on the NS3 controller. The output of the PFM box should then be fed in back into the NSIII as this is the new feedback signal. (This is from my memory. Consult your PFM documentation and your Nanoscope schematics before doing ANY changes to the NS3 controller).
Unfortunately, I can not elaborate what we do to the signal to clean it up. You might understand that.
I doubt that the Witec PFM will get any lower force than a carefully carried out Tapping Mode setup. Using the same cantilever, especially a soft one is also not really a good comparison as soft levers are not that preferable for a lot of Tapping Mode operations. One reason is that they tend to snap onto the surface and thus require a quite large amplitude to get them off again. This amplitude will of course limit your imaging force. Thus, in general, you may want to use a rather stiff lever for tapping mode operation. You can also use phase feedback rather than amplitude feedback to get better sensitivity although you have to be a bit more careful selecting the operating conditions. This way you can use a rather small tip amplitude. In PeakForce Tapping this not really an issue.