h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Entry: Scanning Probe Microscopes - A637076
Author: Hell - U171578

This entry is a part of an entry complex on microscopy. It can perfectly stand alone.

I am aware of the University, nevertheless I prefer to submit this to peer review. The links will have to be added after the (potential) inclusion to the guide.

HELL

Phew! This saves me writing this one - just as well really. I think this is a very good introduction to the field, and should get into the guide no problem. some comments...

The IBM logo, and some nifty other stuff, can be found at http://www.almaden.ibm.com/vis/stm/gallery.html

Invention of AFM was about 1986, at least that's when the first papers were published.

"AFMs are a sort of an extension of STMs". Ummm, that's not how I would put it. Same scanning system, yes, but completely different detection principle (mechanical vs. electronic. Let's leave Tunneling AFM out of this for the moment)

Footnote 1 - strictly, the *surface* density of states (ooh, get him...)

Detection of AFM bending - there are a slew of different techniques here. I think capacitance is fairly uncommon these days. I would mention interferometry here, as this is fairly common on home-built systems.

Size of AFM tips. Most tips tend to be roughly pyramidal, so you only get down to nm dimensions at the end. For instance, Nanosensors etched Si tips are about 12 microns high, about the same across the base and have a tip radius between 20 to 10 nm (at least, the ones I've looked at normally are). Most general purpose AFM tips are about this size, although I reckon the tips will get smaller as more sensitive instruments are developed.

Carbon nanotube tips. They might be rigid for their size, but in AFM terms they can be pretty flexible. This is a good thing, as it make them very robust. You can bend a nanotube around 90 degrees and it will spring back no problem.

I think you have got tapping mode mixed up with force spectroscopy. In tapping mode, the probe oscillates vertically, and 'taps' the surface. This reduces the force exerted on the surface so you can image nasty squigy stuff (polymers, cells etc.) Force spectroscopy is when you vary the probe-surface distance and see how the force on the probe changes, which, as you say, can be used to measure how sticky a surface is etc.

NSOM I would be tempted to leave out altogether. If you get this entry in then you (or someone else) can write a more detailed entry on NSOM. Not that it is badly written (it isn't) but I feel it would be better served as a seperate article.

(which reminds me, must get move on with MFM article)

Thanks jamie, again. I have re-written the tapping mode part, added the suggested link, corrected footnotes and wrote more about the tip size.

Question: Would you mind getting co-credited for this entry?

( ) Yes
( ) No
( ) I don't care

About NSOM: Until someone writes something about NSOM I think it's better to leave this part in for the sake of completeness. Afterwards, when the NSOM entry exists, this one might be subjected to an update HQ procedure. On the other hand, no-one would really miss NSOM (oops...) so it might be perfectly left out... On yet another hand, it's in there already, so, why not leave it?

Thanks a lot,

HELL

If you want to credit me - sure, be my guest This is looking pretty good now. I'll go through a a bunch of small problems now...

A very sensitive and very sharp tip (the probe) is finely scanned over the surface of an object, or - actually - the object finely scanned under the probing tip (remember the old vinyl-record players)

First paragraph. I'd replace "or - actually - the object finely scanned" with "or the object is finely scanned".

Second paragraph. I'd change it about a bit to read "The scanning method is what all techniques have in common, and can be performed with an accuracy of some hundred picometres (that's about the width of one atom) thanks to the development of very precise positioning motors (piezo-motors) and high-precision positioning accuracy (using various techniques). Therefore, in most cases the resolution of an SPM is not limited by the scanning system."

Now in the AFM bit you actually describe mention the cantilever detection system twice - in footnote 2 and also two paragraphs down. (Actually, I have a feeling I should have noticed this before). Would it be better to move the stuff in footnote 2 down to the paragraph, and thus have it all in the one place?

AFM in practice - this reads well now

NSOM - not restricted to solid surfaces? Well yes, but AFM and STM can be performed in liquid enviroments as well. Or do you mean that NSOM can be used to scan an area of liquid that does not have a solid surface under it? I can see that you could do this, but I'm not sure what information you could get doing this. Then again, I do not know that much about NSOM, so feel free to ignore anything I say on the subject

I'll incorporate your suggestions tomorrow, jamie. I'm sure It will read a lot better in the way aou suggest.

About NSOM: Yes, that's exactly what I meant: Bulk liquid.

See you,

HELL

You'll be pleased to know that I recommended this entry and it has now gone into the Editorial Process for future inclusion in the Edited Guide. When it does get into the Edited Guide, the editors will email to let you know, but please bear in mind it can take a while for entries to go through the process. Please see this for more details.

http://www.bbc.co.uk/dna/h2g2/alabaster/SubEditors-ProcessSubEditors-Process.

Woo-hoo



H