In our beginner’s guide to AFM we focused on the mechanics of setting up the AFM and your sample. Now that you’re more of a pro with how an AFM works, the next step in developing your skills is much more about mindset and asking questions.
Here are 5 more top tips for effective AFM imaging, brought to you by one of the masters of AFM Prof. Mervyn Miles….
1) Play around – have fun!
The first thing you need to be aware of is that the road to AFM mastery requires patience, more so than any other microscopy because of the variables. Actually, that’s half the fun though (remember, this is about mindset). You need to think about and fiddle with all of those variables – e.g. what’s the model of your tip? What happens when you reduce the force? What’s the best set point you can get away with?
With a new sample, once you’ve found the best conditions to image it, you need to go back again and check that if you apply all the same variables you get the same outcome. For example check the contact with the surface, lift off and come back again – does it look the same?
Remember you don’t want an average when you want to see something on a molecular level. Try looking at the same molecule under different conditions. Do different things at the same time, combined.
2) Use your common sense
Quite simply ask - Does it make sense?
Think about your sample. How soft is it? Are you going to compress it or pick bits up? Are you wearing the tip out as you scan? How is the image changing? Does it scale the right way? Does speed affect it?
3) Check your vision
In particular you need to ensure you are not ‘joining up dots’ that are actually just the noise in the background. As human beings we’re programmed to find and see patterns, so you need to sanity check what you think you’re seeing. Change the scan direction through 90 degrees. Look at the trace and retrace signals. If you have a chip with lots of different probes, try a different stiffness of probe. Have a couple of windows open so you can compare your images.
Don’t forget to check you’ve set the dimensions correctly; ensure there are enough pixels for the size of sample you’re looking at.
4) Take risks
There’s a real ‘Do or be damned spirit’ required when you’re working with AFM. As a beginner that can feel pretty scary of course but once you feel more confident with the machine it’s worth remembering that the rule book isn’t that well written yet.
For example, if you’re working with a High Speed AFM, turn the speed right up on your sample. It might be that if you go fast enough your sample can handle it and return you the images you need, whereas a gradual increase might damage or destroy the sample. You need to think about your sample not in its own right so much as a sample ‘in confined conditions’. Then you need to think about the speed, force and energy you’re putting into it and how that might affect it.
5) If in doubt – ask a(nother) physicist
Talking the problem through with a physicist (whether you are one yourself or not) can be enormously helpful. Sometimes you’re so close to the work you’re doing you can’t quite get a handle on what else you could be doing or what might need to be done differently.
If you’re not a physicist there’s a real value to be had from combining your knowledge of your sample and the kind of outcomes you’re expecting or hoping to see with their knowledge of how the AFM may be acting and interacting with your sample.
Whilst patience and a ‘try and try again’ attitude are essential characteristics to foster in your work with AFM, sometimes stopping and chatting to someone else can be the difference between getting results and spending many frustrating hours in the lab.
And a final top tip - If it’s working – just keep going! Whatever time it is, whatever else might be happening in your life, because if you’re on a roll with results you don’t want to risk that tomorrow it won’t work in the way it is right now!
If you liked this blog post you might also like An interview with Professor Mervyn Miles , 5 top tips for effective AFM imaging: a beginners guide and From one AFM user to another…
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