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Science

Australian Overturns 15 Years of Nano-Science Doctrine 79

Posted by CowboyNeal from the back-to-the-drawing-board dept.
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."
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Australian Overturns 15 Years of Nano-Science Doctrine More

Australian Overturns 15 Years of Nano-Science Doctrine

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  • Great.......but now what? (Score:4, Insightful)

    by Omikr0n ( 656115 ) on Saturday March 08, 2003 @02:16PM (#5467724)
    Okay I just read the articles and as much as I'd like to understand it, most of it just seems way over my head. But from the minimal information I can understand, it seems that such a flaw shouldn't have been overlooked for this many years. Why did we just discover it now? Perhaps it will become more clear for me after next semester.

    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".

    • As far as I know, AFM is good for minute things and it is becoming even more important with the development of nanodrives like IBM's Millipede project. If the design is flawed, does that mean that there will be improvements or that AFM will stop progressing? If there will be improvements from this, it sounds like a good thing. I wonder if this could do anything to help AFM observe and manipulate objects at smaller scales.

      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?

      • I just want to know: will this help or hinder AFM devices?

        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)

          by Thurn und Taxis ( 411165 ) on Saturday March 08, 2003 @03:37PM (#5468107) Homepage
          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.
          • That's six orders of magnitude larger than the atomic scale

            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?

    • I don't know about theories and discoveries, but I can tell you for a fact that that a lot of industries use it for Quality Assurance testing. I know we did at the CD plant that I worked at. The AFM was much better than the old electron microscope we used to use.

      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.....
    • I think they just made some wrong assumptions. Intuitively, a V-shape would seem stronger, but the physics at such a small scale are very different. Perhaps it's such a simple assumption that no one bothered to analyze it.

      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)

      by tfoss ( 203340 ) on Saturday March 08, 2003 @06:05PM (#5468750)
      AFM is basically dragging a pointer over a surface, and using a laser and fancy equipment to measure how much the pointer moves up down. This up and down motion is an indication of the height of the surface. In a way, it is very much like using your fingers to read braille. You run your fingers over a surface, and where the dots are raised, your nerves notice it, fire and you feel height.

      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

  • Ahh (Score:5, Funny)

    by Timesprout ( 579035 ) on Saturday March 08, 2003 @02:19PM (#5467738)
    But if an Australian overturns something does that not mean its actually the right way up ?

    • Re:Ahh (Score:1, Offtopic)

      by $$$$$exyGal ( 638164 )
      Here's some more information about Australia:
      Lisa: Bart, water will only go the other way in the Southern hemisphere.
      Bart: What the hell is the "Southern hemisphere"?
      Lisa: [sighs] Haven't you ever looked at your globe?
      Lisa: [pointing] See, the Southern hemisphere is made up of everything below the equa -- [stops, sees Bart looking blankly] -- this line.
      Bart: Hmm. [spins globe] So down there in, say, Argentina, or...[reads logo] Rand McNally, all their water runs backwards?
      Lisa: Uh huh. In fact, in Rand McNally, they wear hats on their feet and hamburgers eat people.
      Bart: Cool!

  • Godamnit :/ (Score:4, Funny)

    by dark-br ( 473115 ) on Saturday March 08, 2003 @02:25PM (#5467767) Homepage
    Ill be sending my refund form right now!

  • Good thing? (Score:5, Funny)

    by JohnnyKlunk ( 568221 ) on Saturday March 08, 2003 @02:27PM (#5467777)
    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.

  • Well-known (Score:5, Informative)

    by Bowling Moses ( 591924 ) on Saturday March 08, 2003 @02:33PM (#5467804) Journal
    I don't do AFM, but my labmate has. He said that this flaw was well-known, and that most people dumped the v-shaped cantilevers in favor of nanotubes (I think) or straight cantilevers. Cool thing he said was that to get a tip, very popular was the gunk that piles up after you clean an electron microscope. One man's trash is another's treasure, I suppose.

    • Re:Well-known (Score:5, Informative)

      by brarrr ( 99867 ) on Saturday March 08, 2003 @02:56PM (#5467909) Journal
      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:Well-known (Score:3, Insightful)

        by Bowling Moses ( 591924 )
        Blarg. Yeah I got a little confused as to what the nanotube's for. My labmate went back to the old-fashioned straight beam kind--the deal was that they just noticed the old cantilevers worked a little better and went about their experiments thinking it was just an oddity with their equipment. Amazing how close you can be to something important and just...not...quite...get it.
        • I forgot to add that many people do still use the rectangular tips quite frequently.

          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.
        • Amazing how close you can be to something important and just...not...quite...get it.
          Nothing is harder than seeing the obvious. At least until it ...is... obvious.
          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)

    by Krapangor ( 533950 ) on Saturday March 08, 2003 @02:34PM (#5467809) Homepage
    If modern string theory is true then most nano science applications will fail to work.
    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].

  • What atomic resolution? (Score:1)

    by Anonymous Coward
    AFT does not yield atomic resolution!

    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.

    • The AFM yields atomic resolution in the z-direction (the height), so you're not completely correct here. In the lateral direction, however, you'll be imaging the shape of the tip for anything less than lateral features of less than ~50nm (tip-radius*2) due to tip-convolution effects.

      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.
  • Trying to make an Atomic force microscope seems should be easier than constructing an electron microscope.

    All you need is a laser ,sensors, tip, tip holder(lever).

    Why should these microscopes cost alot ??

    • Yes, the microscope is cheap. It's making the really tiny lathes and milling machines cost all the money. You try building a lathe chuck one atom at a time, especially as you need to build in lots of carefully planned dislocations to make it rigid..

      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)

      by cerulean ( 99519 ) on Saturday March 08, 2003 @02:57PM (#5467919) Homepage
      The tips are very delicate, and so far, they only seem to be made by photochemical etching. This is in contrast to Scanning Tunneling Electron micrscopes, which you can (and people do [ustc.edu.cn]) make out of reasonably cheap parts.

      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.

    • Re:Making an AFM microscope shouldn't be that hard (Score:5, Informative)

      by today ( 27810 ) on Saturday March 08, 2003 @06:24PM (#5468837) Homepage
      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 [bldrdoc.gov] 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.
      • i have seen an IBM article about millipede that uses this technology to increase densities on hard drives by a great deal.

        I guess dealing with atoms at room temp will always be difficult.

      • 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

        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.

  • Now it needs to be proven empirically (Score:5, Insightful)

    by cerulean ( 99519 ) on Saturday March 08, 2003 @02:51PM (#5467893) Homepage
    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.
    • 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.

      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.

    • 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)

    by photonic ( 584757 ) on Saturday March 08, 2003 @03:20PM (#5468024)
    I happened to play with an AFM for an introductory lab course some years ago. What i remember is that by bouncing laser-light of the tip onto a 4-quadrant detector you could detect both the deflection and the twist of the tip. By scanning the tip sideways you get a twist depending on the local 'sticky-ness' of the sample, which could give some extra information about the sample.

    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)

    by helix_r ( 134185 ) on Saturday March 08, 2003 @03:23PM (#5468034)

    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)

    by agg123456789 ( 593765 ) on Saturday March 08, 2003 @04:54PM (#5468481)
    AFMs are being used to do alot more than measure nowadays. This summer I worked on Dip-Pen Nanolithography which uses an AFM like a fountian pen of sorts. It's pretty cool stuff, and if that cantilever is off (the piece which holds the "nub" of the pen) then all of the work done could be rendered incorrect... DPN Information [nwu.edu]

  • hmm.. (Score:1)

    by C21 ( 643569 )
    It's great they're pointing out FLAWS in nanotechnology, but I wish they'd get going on more outlandish product development...like "porno star in a can", just spray it on your bed and bingo...
    • Would you rather find out about the flaws *now*, or discover that the flaw caused a defective porno-star-in-a-can that had teeth in inappropriate places?

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