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how to get Atomic Imaging with Multimode in verison8 software

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lujie posted on Tue, Aug 23 2011 11:59 PM

I try to mapping some atomic resolution imaging in contact mode with E scanner  and Multimode.

I am following steps in Tech. Support Bulletin No. (NBSB-0042) Atomic Imaging with Nanoscope Multimode System and start with mica sample in liquid.

However, this note just mentioned how to set up  the high/low  pass filter parameter for V5 and V6 and i could not find this for new software V8. I do not get any information from the height image  in  high scan rate.  The tip i am using is normal NP serial.

Do anyone has the update note for that or any experience on how to play these parameters in V8? 

Thanks!

Lujie

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Answered (Verified) Hartmut replied on Wed, Aug 31 2011 12:15 PM
Verified by lujie

Hi Lujie,

probe should be ok (it is a quite soft cantilever). However, you might consider the short, thin type (0.32N/m), which is shorter and hence more sensitive.

As discussed, skip trying to get a good height signal at first. Try to find the atomic periodicity first in deflection and friction signals. Use small I gain, zero P gain, amd play with setpoint, scan angle, and scan rate.

You can see, if the drift has come down, when the z-position after engagement (visible as voltage close to the green piezo monitor bar) stays at a more or less constant value. As well a constant vertical photodiode signal in disengaged stage is a hint of good conditions (because, if the laser heats up the cantilever, it will bend due to the bimetal effect, which changes the vertical photodiode reading). One needs to wait till a) the photodiode signals are constant over time, and b) after engagement, the z-position in feedback stays constant.

My recommendation is, to set up everything (aligned laser, prepared sample), engage once, scan a few lines (with 10nm scan size), then withdraw once, after that wait over night (instrument fully left operational, nothing switched off). Next morning recenter the photodiode check over a few minutes, how the signals change, if they are ok., engage again and try. But still check after engagement, how the piezo z-position changes. If there is a significant change of more than 0.1V over a minute after you have scanned the frist few frames, you need to wait longer (just keep on scanning and wait).

How long this takes depends on the lab conditions. In a good environment, it might need less than an hour after cold start. You might consider to use some protection against airflow etc. Make sure, that you have a good vibration isolation.

Usually, I don't change the lowpass filter. As explained, if you don't see a periodicity, a filter will not be helpful.

Regards,

Hartmut.

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Ang Li replied on Wed, Aug 24 2011 2:46 AM

Hi, I guess you should start with imaging in air instead of in liquid. The note is also for in air but not for in liquid. There should be little difference between different software versions.

LA

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Suggested by Ang Li

Hi Lujie,

E-scanner and a Multimode are a good choice for atomic resolution trials.

However, there can be many reasons, why you don't get it - starting from badly peeled or not very well fixed sample (particularly with mica, which is a layered material, where layers easily can slip against each other), insufficient vibrational and acoustic isolation in a drifty and noisy environment, cantilever clamped floppily etc. etc.

It is not so uncommon, that atomic resolution is not so easily seen in the height signal. It might be easier to be recognized in deflection or even friction channels (where you can work with lower gains, or even fully in constant height mode). It is preferrable, to minimize any limit as much as possible (z limit, deflection limit). This means, z-piezo and as well photodiode signals needs to be quite well in the center, that the low limits can be used. As well, drift should have come to a minimum, which might require some waiting time (depending on environment).

Theoretically, it works better with shorter cantilevers. However, my best experiences in air I had with a Microlever Type A in air (others might recommend other levers).

It works as well in liquid, whereas higher forces (and stiffer/shorter contact levers) are necessary due to lack of capillary forces. But better try first in air like Ang has suggested. 

Typically, you start seeing atomic rows after some time (they keep their lateral periodicity in nm, when you change scan size at the same scan rate). After lateral drift has come down, you will see are more or less clean lattice. Often the right choice of scan angle (scanning against the drift) will make the difference.

As far as I know, in version 8 you can only set low pass filter cutoffs for deflection and friction (visible in the expanded view). To be active at all, they need to be enabled under "other" (which is the standard setting). They should not be necessary to be changed (if you don't see any atomic periodicity, a further filter won't make it better, in contrast: sometimes less filtering reveals more signal and better information).

Hope, some of these remarks are helpful.

Good luck,

Hartmut.

 

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lujie replied on Wed, Aug 31 2011 3:08 AM

Hi, Ang and Hartmut,

Thanks for your helpful comments.

I tried some imaging in air recently but still cannot get any signal on height channel. The tip I am using is NP-10 serial with the spring constant 0.12N/m one. Does this tip proper for this kind of image taking? As you mentioned that it will take some time for coming down the drift, how long it usually takes? So there is no need to change the low filter value when imaging in atomic resolution? As this is mentioned in that note.

Many thanks!

Lujie

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Answered (Verified) Hartmut replied on Wed, Aug 31 2011 12:15 PM
Verified by lujie

Hi Lujie,

probe should be ok (it is a quite soft cantilever). However, you might consider the short, thin type (0.32N/m), which is shorter and hence more sensitive.

As discussed, skip trying to get a good height signal at first. Try to find the atomic periodicity first in deflection and friction signals. Use small I gain, zero P gain, amd play with setpoint, scan angle, and scan rate.

You can see, if the drift has come down, when the z-position after engagement (visible as voltage close to the green piezo monitor bar) stays at a more or less constant value. As well a constant vertical photodiode signal in disengaged stage is a hint of good conditions (because, if the laser heats up the cantilever, it will bend due to the bimetal effect, which changes the vertical photodiode reading). One needs to wait till a) the photodiode signals are constant over time, and b) after engagement, the z-position in feedback stays constant.

My recommendation is, to set up everything (aligned laser, prepared sample), engage once, scan a few lines (with 10nm scan size), then withdraw once, after that wait over night (instrument fully left operational, nothing switched off). Next morning recenter the photodiode check over a few minutes, how the signals change, if they are ok., engage again and try. But still check after engagement, how the piezo z-position changes. If there is a significant change of more than 0.1V over a minute after you have scanned the frist few frames, you need to wait longer (just keep on scanning and wait).

How long this takes depends on the lab conditions. In a good environment, it might need less than an hour after cold start. You might consider to use some protection against airflow etc. Make sure, that you have a good vibration isolation.

Usually, I don't change the lowpass filter. As explained, if you don't see a periodicity, a filter will not be helpful.

Regards,

Hartmut.

  • | Post Points: 13
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Points 135
lujie replied on Wed, Aug 31 2011 6:14 PM

Thanks for your supportive information, Hartmut, I will try  to do it again.

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