[HN Gopher] Home-Built Scanning Tunneling Microscope
___________________________________________________________________
Home-Built Scanning Tunneling Microscope
Author : _Microft
Score : 265 points
Date : 2021-04-08 16:45 UTC (6 hours ago)
(HTM) web link (dberard.com)
(TXT) w3m dump (dberard.com)
| leblancfg wrote:
| Can we add [2015] to the title?
| prennert wrote:
| His day-job is pretty mind-blowing, too. He basically works on
| combing DNA, by squashing it "into nanogrooves [that] are less
| than 50 nm"
|
| https://dberard.com/research/
|
| edit: added description of his work
| feralimal wrote:
| Yes, look at all that squashed DNA, lol.
|
| Seriously though, how do we know that is DNA? It just looks
| like wiggly worms.
|
| And the DNA pic is black and white, but the picture of graphite
| is in colour. How is it in colour? Is it 'enhanced' with
| photoshop or something?
| amelius wrote:
| DNA extraction is a routine procedure used to isolate DNA
| from the nucleus of cells.
|
| More here:
| https://www.sciencelearn.org.nz/resources/2036-dna-
| extractio...
| adge wrote:
| You can't actually "see" DNA itself because it is smaller
| than the wavelength of light. Those groves are 50nm and the
| wavelength of blue light is about 480nm.
|
| So how then are the images generated?
|
| It uses a technique called Fluorescence Microscopy:
| https://en.wikipedia.org/wiki/Fluorescence_microscope
|
| You essentially stick some special molecules on the DNA that
| absorb light in one frequency and then they emit light in
| another frequency. So you blast the molecules with light of
| one frequency and then use a dichroic mirror to filter that
| light out and you only see the emissions and thus you see
| where the DNA is, but you don't "see" the DNA itself.
|
| Like STM itself what we mean when we "see" something at those
| length scales is interesting. Scanning Tunnelling Microscopy
| is like a blind man reading braille - not really "seeing"
| anything but getting enough info to describe the picture.
|
| source: I used to work in the same lab as Dan. Hi Dan!
| feralimal2 wrote:
| This is a useful explanation - thanks!
|
| What does this mean to the value of what we are "seeing"?
|
| The example used before - that it is equivalent to a deaf
| man seeing a music visualisation - is apt. It is some sort
| of model, but not particularly close. It might still be
| useful, of course.
| snalty wrote:
| False colour is pretty much standard for many imaging
| techniques including STM.
| s0rce wrote:
| Its not even really false color, its just a look up table
| applied to the data, which is some equi-tunneling current
| or height map, don't know exactly how this is done, bit out
| of my field.
| jacquesm wrote:
| The tip is pointing down, so an increase in current would
| indicate a decrease in 'Z' coordinate of the sample
| surface.
| ahartmetz wrote:
| I worked with a simple STM in a lab exercise. At the beginning,
| we created a new, clean tip. Guess how we did that?...
|
| We cut a piece of ordinary steel wire diagonally with an ordinary
| wire cutter. Somehow we did it right - the first one worked. It
| was all somewhat fiddly and sometimes the image was noisy. But we
| did get images of atoms.
| jacquesm wrote:
| I think I'm going to build this with my kids. What better way to
| show them atoms than to actually make them build a microscope
| that shows you the things directly?
| biswaroop wrote:
| This is a wonderful idea. Children (and adults) learn best by
| doing. There's such a big difference between watching some tv
| show and making an actual experiment to see structures
| invisible to the naked eye. I know I would have been psyched to
| see atoms as a kid.
| feralimal wrote:
| I'm sure its a cool project.
|
| But its not showing things directly, is it? Its interpreting a
| frequency and converting that to an image. Is it really that
| different to a music visualiser?
| crispyambulance wrote:
| > But its not showing things directly, is it?
|
| I don't understand the downvotes. That's an honest
| fundamental question.
|
| It's not "showing things directly" because it can't. The
| limit of what you can see with light is proportional to the
| wavelength of the light (this is called the diffraction
| limit). For visible light and lens-based optics that's around
| 1/2 micron.
|
| The distance between the atoms in that graphite is ~3
| angstroms, that about 2000 times smaller than the diffraction
| limit for visible light.
|
| You CAN get atomic resolution with a transmission electron
| microscope. Instead of light it uses electrons and has a far
| finer diffraction limit that visible light. Instead of lenses
| it uses electrostatic deflection.
| jacquesm wrote:
| > I don't understand the downvotes.
|
| Because the comment is factually wrong. Because it tries to
| argue something in bad faith.
|
| > That's an honest fundamental question.
|
| But it wasn't a question, it was a statement, and a faulty
| one at that.
|
| Best case interpretation would require substituting
| 'current' for 'frequency' and even then it would be
| inaccurate because the current is a proxy for the
| Z-distance to the tip which is then used to convert to a 3D
| map, which in turn can be visualized.
|
| It is fairly obvious that this is an indirect process so
| clear the word 'directly' wasn't about 'seeing atoms' but
| all about the fact that you can make the observations
| yourself.
|
| Whether you are measuring a current or looking through an
| eyepiece both are observations. And looking at the
| resulting image is _also_ an observation.
|
| As opposed to reading about STMs and looking at pretty
| pictures online or in books.
|
| It's a shallow comment masquerading as an insightful one,
| the worst way to derail any conversation.
| feralimal2 wrote:
| The reason for the downvotes.... won't be popular to
| hear, but here it is.
|
| This forum apparently values the scientific outlook,
| which is purported to be a skeptical one. Do not commit
| to accepting whatever-it-is without evidence, right?
|
| But that unpopular, question opinions are so downvoted
| (which has the effect that replies cannot be posted until
| the next day when no one is watching) speaks volumes
| about how skeptical people really are. How much
| application of the scientific method do people actually
| use in their lives?
|
| What we really have in science, and society in general,
| is an echo chamber where lots of lip service is given to
| the scientific method but no one actually implements it
| personally. Then when someone like me comes along and
| critically reviews the presentation, it leaves people
| feeling uncomfortable as they realise just how much they
| have taken on trust.
|
| So, the answer is to downvote. Its not pretty but
| everyone can get back into the comfortable echo chamber.
| And in preventing unpopular skeptical opinions (ie
| maintaining the echo chamber) is what HN is here to
| facilitate.
| [deleted]
| argvargc wrote:
| The GP's "statement" contained three relevant sentences,
| two ending with question-marks. I learned from both your
| answer and its parent, furthering conversation, for me at
| least.
| jacquesm wrote:
| Directly as in: you do it yourself, without going through a
| bunch of intermediaries who will dazzle you with their pretty
| pictures, you yourself are the one observing the results.
|
| Of course a STM does not work with visible light so it's
| pretty damn obvious that any measurements will use some other
| mechanism, and will have to have their measurements converted
| into an image that we can see. But that does not mean we are
| not observing. As opposed to reading about someone else's
| observations.
|
| I take it you also believe that quasars have not been
| observed and ditto for the dark side of the moon?
| minitoar wrote:
| I mean, what is your brain doing if not that?
| feralimal wrote:
| You don't think there's a difference between what you see
| with your naked eye, and what is visualised for you by
| sensors and software?
| gryn wrote:
| do you think your eye is not a sensor ?
| feralimal wrote:
| Of course your eye is a sensor. As are all your senses.
| The difference is that the input it receives is
| unmediated by external sensors and software. Visualising
| atoms or DNA is fine, but it is an inferior source of
| information. By a long way.
|
| Imagine you were born deaf and couldn't hear music. But
| that someone showed you a music visualiser.
|
| Do you think if you were watching the output of that
| visualiser you would now know the music in some
| meaningful way?
| jacquesm wrote:
| Would it be possible for you to try at least to
| contribute to the discussion? This out of hand dismissal
| seems to be a bit of an issue for you, maybe try harder?
|
| https://news.ycombinator.com/item?id=26743591
| nightfly wrote:
| Sure, but digital cameras are still useful.
| s0rce wrote:
| Its a 2D map of the tip position which is a function of the
| tunneling current over a surface. Its not frequency.
| [deleted]
| edge17 wrote:
| Can someone ELI5 the vibration isolation [0] part of it? I kind
| of get what he's doing, but would appreciate some analogy if it
| makes sense to make an analogy.
|
| [0] https://dberard.com/home-built-stm/vibration-isolation/
| jacquesm wrote:
| In a nutshell: the vibrations that affect the imaging are
| pretty high frequency. So to get rid of them he has isolated
| his whole setup in such a way that if there is a vibration it
| will be _well_ under the lower cut-off frequency that is part
| of the measurements. So the whole apparatus may go up or down
| but that won 't affect the measurements. If the whole thing
| would not be isolated then the rumble from the tires of a
| passing car or a jet flying over would utterly ruin the
| measurements.
|
| Especially the vibration damping is nicely done, it is zero
| contact and has the effect of stopping any beginning
| oscillation in its tracks.
| terofle wrote:
| Imagine painting with a paintbrush while standing on a jumping
| castle with 5 jumping children.
|
| If you have no vibration isolation, it is nearly impossible to
| draw a very thin and straight line.
|
| (Maybe a bit exaggerated, the vibration analogy is a bit weaker
| in reality)
| sleavey wrote:
| Incidentally all of the techniques listed there are used for
| suspensions in LIGO, Virgo and other ground-based gravitational
| wave detectors, where the problem is the same: stop seismic
| noise from moving the object under test.
| kurthr wrote:
| CA3140 OpAmps also work well.
|
| The comments about 1pF feedback do speak to one of the challenges
| with feedback stability, where stray capacitance on the proto-
| board may or may not be present.
| analog31 wrote:
| Indeed, a 100-Meg feedback resistor is mostly a capacitor. You
| could think of it as an integrator with DC bias control. This
| is probably the best article I've seen about transimpedance
| amplifiers:
|
| https://electrooptical.net/static/oldsite/www/frontends/fron...
| jacquesm wrote:
| You could draw a pretty interesting graph of how the
| resistance/parasitic capacitance relationship governs which
| component is dominant at the high end of the resistance
| range.
| amelius wrote:
| Can you image non-conductive surfaces with this technique?
| ortusdux wrote:
| Best you can do is gold plate the object you would like to
| scan. Sputter coating is the preferred method.
|
| https://en.wikipedia.org/wiki/Scanning_electron_microscope#S...
| oasisbob wrote:
| That's for SEM. I've never heard of sputter coating used for
| STM.
| ortusdux wrote:
| You are right, I got those two methods mixed up. It looks
| like gold sputter coating would be a good solution for the
| home made tungsten STM tips mentioned in the link.
| Retric wrote:
| That's a SEM which is significantly lower resolution, but
| lets you zoom in and out across a huge range.
|
| STM on the other hand is for looking at individual atoms so
| coating a surface is just going to show that coating.
| https://en.wikipedia.org/wiki/Scanning_tunneling_microscope
| oasisbob wrote:
| Sort of?
|
| STM is frequently used to characterize adsorbed molecular
| monolayers on a graphite substrate.
|
| You're obviously depending on electron conduction to image the
| sample, but you can image all sorts of things which wouldn't be
| considered conductive as a bulk material.
| smitty1110 wrote:
| Nope, the technique for that is an Atomic Force Microscopy[1].
|
| 1: https://en.wikipedia.org/wiki/Atomic_force_microscopy
| alted wrote:
| And it turns out DIY atomic force microscopes are possible
| too! (e.g., [1]) It's probably less likely to get all the way
| to atomic resolution (0.01nm) like a scanning tunneling
| microscope, but atomic force microscopes can take many types
| of 1-to-1000nm-scale measurements and are often more
| practically useful.
|
| [1] https://hackaday.com/2014/04/29/a-diy-atomic-force-
| microscop...
| waiquoo wrote:
| OR helium ion microscopy, but that is not as widely available
| afaik
|
| 1:
| https://en.wikipedia.org/wiki/Scanning_helium_ion_microscope
| fit2rule wrote:
| This is an amazing project, in so many ways.
|
| My first thought is, the implant business has now got a problem.
| Soon enough, anyone and their pal will be able, finally, to
| validate their silicon at adequate scale.
| terofle wrote:
| This project is great.
|
| Last semester at university lab, our group tried to rebuild it in
| our lab.
|
| Through our spectacular fail, we learned how amazing this project
| actually is. It is harder than it seems.
|
| One can learn very much about piezo electronics, especially about
| OPamp circuits. And do not underrate the damping!
| jacquesm wrote:
| And the amplification circuitry, that's not trivial. I was
| actually surprised he got away with having the wiring out in
| the open without shielding it for EMI.
| FuriouslyAdrift wrote:
| In the section for "Electronics" is this line "I place a
| metal can over the STM during scanning to shield the tip and
| preamp. Without the shield, the images produced by the STM
| are dominated by 60 Hz noise pickup."
| jacquesm wrote:
| Ah! I totally missed that, thank you. I thought the
| pictures were of the scanner in operation, and that detail
| really confused me.
| lappa wrote:
| Similar project: http://e-basteln.de/other/stm/overview/
| dang wrote:
| Small past threads:
|
| _Home Built Scanning Tunneling Microscope Electronics_ -
| https://news.ycombinator.com/item?id=9752215 - June 2015 (9
| comments)
|
| _Home-Built Scanning Tunneling Microscope_ -
| https://news.ycombinator.com/item?id=8884085 - Jan 2015 (1
| comment)
| twobitshifter wrote:
| Ben Krasnow built his electron scanning microscope back in 2011.
| I never expected to see that one upped.
| https://benkrasnow.blogspot.com/2011/03/diy-scanning-electro...
| _Microft wrote:
| The scanning electron microscope project seems far more
| involved than this one. I submitted the SEM before this one by
| the way but it unfortunately did not catch on.
| oasisbob wrote:
| Homebrew STM is a pretty common and simple in principle. I used
| to have a chemistry prof who would guide a group of high
| schoolers through building an STM head each year.
|
| Homebrew SEM is probably much more difficult and rare.
___________________________________________________________________
(page generated 2021-04-08 23:00 UTC)