Australian Overturns 15 Years of Nano-Science Doctrine

Roland Piquepaille writes "Dr John Sader, from the University of Melbourne, discovered a design flaw in a key component of the Atomic Force Microscope (AFM). He 'used established mechanical principles to prove that the popular V-shaped cantilever inadvertently degrades the performance of the instrument, and delivers none of its intended benefits.' This finding may reshape the industry by proposing a single new standard and because the AFM 'has been the instrument of choice for three dimensional measurements at the atomic scale, since its invention in 1986.' Check this column for more details and an AFM diagram or read the original University of Melbourne's article. You also can visit the 'How AFM works' page."

Comments

Ahh

[Timesprout]

But if an Australian overturns something does that not mean its actually the right way up ?

Good thing?

[JohnnyKlunk]

Since the Aussie police have raided all the Universities and removed MP3/DivX collections they've had to turn their attention to work.
Hope noone at my company realises this.

woosh

[Cyno01]

*passes hand over head*

Now it needs to be proven empirically

[cerulean]

It's very intriguing that a mathematician has been able to mathematically prove that V-shaped cantilevers are worse for Atomic Force Microscopy.If the proof is so conclusive, however, it would have been nice for them to wait until they'd fabricated some straight-beam cantilever AFM tips, so that they could do a nice thorough study proving that they get better performance using them for actual data.

(It shouldn't be any more difficult, and it might be a little easier, even, to make straight beam cantilever tips than to make V-shaped ones. This is because the cantilever part of the tip is typically made by some sort of photochemical etching, and a straight beam is certainly a simpler shape to etch.)

Anyway, even with recent advancements in tip design technology atomic force microscopy is still rather inexact when it comes to getting good results consistently. As much as they try to design good tips, you'll never really know if you'll get good images from it until you mount it in the AFM and actually use it. I've certainly heard of grad students who will find a good tip (through trial and error) and become very protective of it (which is hard to do because they're extremely delicate), just because getting good results from Atomic Force Microscopy can often be tricky business, and a tip that you know is good is a great advantage.

Re:Well-known

[brarrr]

Thats not really true...

(I just tried to access the april issue of review of scientific instruments and it is not yet online, so I don't know the math behind his findings)

But no, the flaw is not well known, and no, most people haven't dumped v-shaped for nanotubes, you're confusing a few things.

One measurement technique in AFMs involves attaching a carbon nanotube to the tip of a cantilever (a v-shaped one, as thats what is available). This gives much greater resolutions (tube diameter is ~10nm) vs tip of cantilever diameter ~25nm. HOWEVER, when you do that, you can only scan very slowly, and cannot scan surfaces with steep topographies. Otherwise the nanotubes will just knock off the tip of the cantilevers.

Also, getting the tube on the tip is a hit or miss process, and rarely repeatable with the same length/angle/etc - and usually held on using electrostatic forces.

I haven't read anything about AFMs in a year or so, but this is what I remember from when I was involved with them.

Now I'm on to bigger things (ducks)

Re:Great.......but now what?

[Thurn und Taxis]

The cantilever arms, which are what differ between the V-shaped and the straight-beam cantilever arms, have characteristic dimensions on the scale of micrometers. That's six orders of magnitude larger than the atomic scale, so classical mechanical principles work just fine.

I don't have access to the paper yet, but I think the difference is fairly intuitive. To twist the tip of a V-shaped cantilever, you mostly just have to bend the center of one arm upward and the center of the other arm downward. To twist the tip of a straight-beam cantilever, though, you have to twist the whole beam. Most thin beams will bend much more easily than they'll twist (try it with a twig), so the V-shaped cantilever will twist more easily. Pretty intuitive, really, once you know the answer.

I wonder how much of a difference this really makes in the measurements, though, and whether the V-shaped cantilevers have other advantages that counteract this torsion problem. Newer AFMs use quadrature photodiodes, so it should be possible to measure the torsion of the tip and find out.

Re:Making an AFM microscope shouldn't be that hard

[today]

I've been working on the software for these types of instruments since 1991. Making something that resolves atoms at room temperature is quite a daunting task. In electronics, just the basic Johnson Noise of resistors becomes significant when trying to resolve such tiny measurements. On top of that, the thermal drift of the metal in your instrument which moves your measuring device relative to what your measuring is enough to prevent you from seeing atoms. Then you also have to worry about digital noise generated by your processors radiating into the sensor electronics over ground and power leads.

To make a commerically viable AFM, you need a lot of smart people from several different fields. But even then, these people have to have a few years of building this sort of instrumentation under their belt. It is not easy at all. And the machining costs alone will always dictate a high price for these instruments.

-todd-

PS - Although atoms get a lot of press, I think the most interesting uses of AFM are in biology and hard drive research. These certainly produce the more spectacular looking images.