Australian Overturns 15 Years of Nano-Science Doctrine 79
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."
Great.......but now what? (Score:4, Insightful)
In the mean time, can someone possibly provide examples of any popular theories or situations that this discovery may have thrown off? I just want something more substance than "it changed a lot".
Re:Seeing the future doesn't work (Score:1)
Re:Great.......but now what? (Score:2, Interesting)
The most exciting thing I can see using AFM is using it in Micro-electro mechanical systems (MEMS), which are pretty much just printed onto a chip like your ordinary integrated circuit. I just want to know: will this help or hinder AFM devices?
Re:Great.......but now what? (Score:2, Interesting)
its got to help, right? i mean, the flaw is a flaw in the sense that they were using an un-optimised detector, now ths guy has just said how a different shape will increase performance. I dont know how much i believe him though... i mean, the guy does design and ship these things around the world (see last paragraph of the article), and if he plays his cards right, he will have every user buying tips from HIM this year :-/ me thinks it might be a $$$ scam. but lets hope not, because developments like this (if true) can only help us all out in the long run.
anyone know what these 'well known mechanical principles' are? i cant see a detialed enough paper on those... if they are 'classical' principles, then this guy is talking out of his arse, as classical mechanics breaks down at this scale. but he is a mathematician, not an engineer, so he will know better (i hope); not knocking engineers or anything... its just you dont get taught quantum mechanics in an engineering profession, but applied mathematicians definitely do.
Re:Great.......but now what? (Score:5, Informative)
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:Great.......but now what? (Score:2, Interesting)
ok, cool, then this may be a very real observation by the ozzy dude... but, how come orignal users of the device found better results with the V-shape than with a flat top?
Re:Great.......but now what? (Score:2, Informative)
The reason that it's important is that, like many other industries that produce objects with precision tolerances, we "tweaked" our entire mastering process to match what the AFM told us would provide disks with the best electrical characteristics. I often wondered why we ended up having to tweak, mold, test, repeat until we found the right process. I certainly didn't suspect the instrument of pointing us in the wrong direction.
I just hope they figure out a way to change the tips in the DI AFM's! What a pain.....
Re:Great.......but now what? (Score:1)
That'll teach me to not use the preview button.....
Re:Great.......but now what? (Score:1)
I'm sure there are other examples of where engineers got so buried into the complexities of a problem that they overlooked a basic assumption.
Re:Great.......but now what? (Score:5, Informative)
With AFM, the finger is a little beam with a probe (often times a carbon nanotube) hanging down, running along the surface. On the top of the beam there is a mirror that reflects a laser beam onto a detector. As the surface height increases, the tip moves up, forcing the beam to flex just a little bit. This flex changes the mirror and thus the laser beam reflects to a different part of the detector. Raster scan a sample, and you get an x,y, and now z (height) value, so you have a 3d image of the sample.
If I read this correctly, the discovery is that the shape of beam that holds the tip, which is currently a V shape, works better when it is flat. The V-shape makes a beam stronger, and less likely to twist...or at least it was thought to. Intuitively, this makes sense. Fold a rectangular piece of paper into a V along the long axis. It seems stronger and more stable than if you just hold the unfolded paper out. Apparently, though, this is not the case with AFM cantilevers. Why this is the case is not mentioned, nor do I have any idea.
The reason this was not discovered is likely many reasons. First, it is obvious that a V-shape is stronger and more stable. That this is an incorrect assumption was probably not really even considered. It's as if you were building a computer, and everyone knows that a faster processor makes a faster computer. So you use the fasted one you can find. Except, in this certain circumstance a slower processor works better.
As for the effect of this, it really likely does not invalidate many experiments. It is a technical issue, not a new theory. It just means that you were not getting as much information as you could have from your machine.
-Ted
Re:Great.......but now what? (Score:1)
Ahh (Score:5, Funny)
Re:Ahh (Score:1, Offtopic)
Re:Cantilevers on the internet? (Score:2, Informative)
is the actual quote. Dont know where you got internet from.
Godamnit :/ (Score:4, Funny)
Good thing? (Score:5, Funny)
Hope noone at my company realises this.
Re:Good thing? (Score:1)
Cheers
Stor
Well-known (Score:5, Informative)
Re:Well-known (Score:5, Informative)
(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:Well-known (Score:3, Insightful)
Re:Well-known (Score:2)
The most interesting use is for lateral force microscopy (LFM) where the torsion on the tip from scanning can be detected thru extra sensors, and the relative frictions at the nanoscale surfaces can be compared - somewhat important to have a high vacuum though, as there is an inherent meniscus formed from water on the surface of all objects. Traditionally LFM would not give as good results with a v-tip, but perhaps this paper coming out disproves that.
Re:Well-known (Score:2)
Nothing is harder than seeing the obvious. At least until it
If you explore everything that doesn't quite make sense, you're quickly lost in an (infinite?) depth-first tree search.
O.T. Mathematics is easy. Everything else is vastly more complicated.
Most nano-science won't work anyway... (Score:4, Funny)
Recall that standard supersymmetry work with strings in 11 space dimensions on Yang-Calbai manifolds. At sizes below 15 angstroem you'll effects from these 11 dimensions. Especially has the wave equation non-trivial, non-analytic solutions and Hygens' principle fails (due to the topology of the Yang-Calbai manifolds, recall that the 5th deRham cohomology group is non-trivial).
So you'll get the effect of string resonance - strings are coupled together the 3rd order Laplace equation which overrules strong and weak interaction. This means that control of dynamical systems below the 15 angstroem barrier is impossible - you'll always get 5th order resonance which collapses the control Lie-algebra.
So all these nifty little nano-machines won't work, they'll be just little protein blob wiggling around and doing nothing useful.
As an example see this example [arxiv.org].
woosh (Score:5, Funny)
Re:Most nano-science won't work anyway... (Score:1, Offtopic)
Re:Most nano-science won't work anyway... (Score:3, Informative)
"If modern string theory is true then most nano science applications will fail to work."
Note your use of the word "if." While the numbers on string theory work quite well on paper, there has yet to be experimental proof one way or the other. You can't say for sure it wouldn't work because nobody knows for sure if the rules we know are the correct rules.
Re:Most nano-science won't work anyway... (Score:1)
http://math.ucr.edu/home/baez/bogdanov/
You wish! (Score:2)
What atomic resolution? (Score:1)
In order to resolve individual atoms you still need STM and even then obtaining good atomic resolution images requires a lot of work, luck and know-how.
Re:What atomic resolution? (Score:1)
The AFM is fantastic in that it addresses a range of length scales that are quite useful in today's technology applications/devices (~50nm to several microns); it works every time and gives much better resolution than the SEM.
Making an AFM microscope shouldn't be that hard (Score:1, Interesting)
All you need is a laser ,sensors, tip, tip holder(lever).
Why should these microscopes cost alot ??
Re:Making an AFM microscope shouldn't be that hard (Score:2, Interesting)
Repeat after me: the smaller the volume of production, the higher the unit cost.
Re:Making an AFM microscope shouldn't be that hard (Score:4, Informative)
This is because an STM tip can just be a pointy piece of wire, snipped off with pliers, and still give decent results some of the time. Also, there are easy techniques for making sharper STM tips yourself, such as electrochemical etching, which in this case is a very simple, easy-to-do-at-home process.
i read somewhere (Score:1)
Re:Making an AFM microscope shouldn't be that hard (Score:4, Interesting)
Re:Making an AFM microscope shouldn't be that hard (Score:5, Informative)
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.
Re:Making an AFM microscope shouldn't be that hard (Score:1)
I guess dealing with atoms at room temp will always be difficult.
Re:Making an AFM microscope shouldn't be that hard (Score:1)
Well perhaps, but that's because it's on a bigger scale, with more complex structures. Imaging a crystal surface or individual atoms (eh, need an STM or a TEM here) won't be quite as "interesting" to you in an "artistic" or "cool" sense, but is of equal scientific "beauty" and importance.
Re:That He's Australian Is Important...How...? (Score:2)
I suppose that if you live in the US, then the "default" would be to assume American if not specified. Doesn't seem unreasonable to me.
Re:That He's Australian Is Important...How...? (Score:1)
What headline would you suggest?
"Skip nerd pisses Yank nerds off. Woot!"
Now it needs to be proven empirically (Score:5, Insightful)
(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:Now it needs to be proven empirically (Score:2, Informative)
What you need to remember/know is that certain crystal faces are more resilliant to etching than others. For example, if the 111 plane etched faster than the 100 plane, etc.
However, I don't think that tips are created this way, as etching isn't the most accurate of things to do. A different way to do it would be to etch a small "hole" into SiO2, and then deposit Si onto it via evaporation. As the hole closes because of Si building up on the top surface, the bottom of the hole sees less and less buildup of Si. This in turn creates a point (cone) until the top closes off. The cone that is created is then atomically sharp. This is a much better tip than one that is created from harsh etching.
Re:Now it needs to be proven empirically (Score:1)
That the shape of a cantilever beam changes the angle of twist (the number of degrees that the end twists through) of the beam due to an applied torque is a well known mechanical/civil engineering fact. Basically a beams angle of twist (all else being equal) is inversely proportional to something called the polar moment of interia, which is just the distance of each differential piece of the beam shape from some central point squared and added up for all differential pieces. For the same order of magnitude size of a V shape versus say a flat shape there is no question in my mind that the V shape would twist more under the same torque. In this case the torque could be provided by the force differing in direction or magnitude on each side of the cantilever.
I have no experience working with AFM so I do not know whether the torsion is significant enough to change measurements.
So there... it definitely does not need to be verified experimentally since this fact is well known amongst engineers. Just consult any sophomore level text on mechanics of materials.
What's the problem with twist? (Score:4, Informative)
Does somebody know why twist is a problem? I tried to look up the RevSciInstr article, but couldn't find it.
Yeah... but they work (Score:4, Interesting)
V-shaped cantilevers work fine. People can obtain atomic resolution with them. What more could you want?
I have used both straight and V-shaped. If there is a difference in performance, the difference is mostly likely very small and over-shadowed by other factors.
Not Just Incorrect Measurements (Score:3, Interesting)
hmm.. (Score:1)
Re:hmm.. (Score:2)