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Science

Most Detailed Photos of an Atom Yet 229

Posted by timothy
from the one-downmanship dept.
BuzzSkyline writes "Ukrainian researchers have managed to take pictures of atoms that reveal structure of the electron clouds surrounding carbon nuclei in unprecedented detail. Although the images offer no surprises (they look much like the sketches of electron orbitals included in high school science texts), this is the first time that anyone has directly imaged atoms at this level, rather than inferring the structure of the orbitals from indirect measurements such as electron or X-ray interferometry."
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Most Detailed Photos of an Atom Yet

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  • Unscaled photo link (Score:5, Informative)

    by UPi (137083) on Tuesday September 15, 2009 @05:39AM (#29423873) Homepage

    The unscaled photo is here:

    http://insidescience.org/polopoly_fs/1.918!image/671260397.jpg [insidescience.org]

  • by Anonymous Coward on Tuesday September 15, 2009 @06:02AM (#29424003)

    "STMs and AFMs have been doing this since the very beginning"

    Niether of these directly measure electron density.
    STMs measures electrical conductivity, AFM measures surface accessibility, and depends mainly on electrostatic and Van Der Waals forces.

    This is the first technique to directly measure electron sensity

  • by Kupfernigk (1190345) on Tuesday September 15, 2009 @06:11AM (#29424027)
    Why? Because the "orbitals" are actually solutions of the Schroedinger Wave Equation. They are images or a probability distribution in abstract space. Electrons are not clouds or points, they are things we don't really understand but describe by means of quantum mechanics. So I am deeply suspicious of the picture, because there is no physical object of that shape to image.
  • by PvtVoid (1252388) on Tuesday September 15, 2009 @06:37AM (#29424137)

    Speaking as a chemist, could you explain what exactly this means? Up until this very moment I have been under the misguided notion that the nucleus of an atom was orbited by electrons within groups called "shells", and these worked very similarly to satellites around a planet.

    You're thinking of the Bohr model [wikipedia.org].

    So, could you in any way explain how we get from "think of it as a planet with many moons" to this or more importantly, what gives orbitals this shape?

    It's because the Schrodinger equation is a Laplacian [drexel.edu], and the hydrogen atom is a spherically symmetric problem [gsu.edu]. The natural basis for the Laplacian in spherical coordinates is spherical harmonics [wikipedia.org]. The shape you are seeing is the characteristic shape of different spherical harmonics, corresponding to the angular momentum of the electron.

  • by junglee_iitk (651040) on Tuesday September 15, 2009 @06:37AM (#29424139)

    It is anything but similar.
    * That article was about taking picture of big but fragile molecules, even though atoms have been pictures before with ease.
    * This article is about even detailed picture of atoms.

  • by S3D (745318) on Tuesday September 15, 2009 @06:42AM (#29424155)

    Up until this very moment I have been under the misguided notion that the nucleus of an atom was orbited by electrons within groups called "shells", and these worked very similarly to satellites around a planet.

    Think of a satellite randomly teleporting around the planet, leaving ghostly afterglow behind. The "glow" would have the shape of those shells. Or the "brightness" of the shell is the probability of existence of "satellite" in the point of space. What gives orbitals their shape is the Schrodinger equation.

  • by The_Duck271 (1494641) on Tuesday September 15, 2009 @06:45AM (#29424171)
    At atomic scales electrons cannot be thought of as points; instead they are smeared out probability distributions. They don't exist at any given point, there's a chance for a given electron to be found throughout a whole region of space, and the probability of finding it at any given point is given by a probability distribution. These probability distributions are called wave functions, and given an electron's wave function you can calculate the likelihood of getting different results when you take a measurement of the electron. It is a strange aspect of quantum mechanics that you can't calculate exactly what you will measure, you can only establish the probabilities of each possible outcome.

    Another aspect of quantum mechanics is that if you measure, say, the energy of an electron in an atom, you can only get one of a certain set of discrete values, and never any energy in between those values. The energy of the electron is quantized. In general, if you measure an electron's energy you have a certain probability to get a result corresponding to the first energy level, a probability to find it in the second energy level, and so on. This is also the case for some other things you can measure, like angular momentum.

    However, there are certain wave functions that correspond to exactly one value of energy; that is, if you have an electron with this wave function, you are guaranteed to get a certain energy value when you measure it. In fact, there is a special set of wave functions with the following three properties:
    • They each have a definite energy level.
    • They each have a definite total angular momentum around the nucleus.
    • They each have a definite angular momentum around the z axis.

    These wave functions are the atomic orbitals that are so important in chemistry. If you calculate the shapes of the wave functions that satisfy these properties, you get the shapes shown on the Wikipedia page. They are listed in a table indexed by the variables n, l, and m. n corresponds to the energy level, l corresponds to the total angular momentum, and m corresponds to the angular momentum around the z axis. For example, you can see that orbitals with high m (angular momentum around the z axis), like the ones on the very right of the Wikipedia table, are sort of flattened out by the centrifugal force from spinning fast around a vertical axis.

  • by Schiphol (1168667) on Tuesday September 15, 2009 @06:59AM (#29424225)
    Hey, individual orbitals are several orders of magnitude smaller than pentacene molecules.
  • by Richard Kirk (535523) on Tuesday September 15, 2009 @07:38AM (#29424405)

    They do look like the classical orbitals, don't they?

    However, there are some problems with interpreting the image as a photograph of an orbital. What the FEEM does is to charge up a very sharp point. The actual voltage may not be very big, but the local field strength depends on screening and curvature, so you can get very large electrostatic fields around sharp features, and if you get the balance right, electrons will leave the sharp points, zoom down the field lines, and get imaged. I remember seeing a sharp tungsten needle in a FEEM back in the seventies, and seeing the individual atoms. This sort of thing provided the first real evidence of a screw dislocation. You got a strange projection of the tip of the needle, as the electrostatic field tended to map the roughly spherical tip onto a flat plane.

    So what is happening here? Our field stripping an electron from the orbital. We are getting a map of the electron flows as focused by the electrostatic field. We calculate the trajectory back through the electrostatic field and guess some sort of map of emission. They must have stripped hundreds or thousands of orbital electrons from the same atom, and replaced them to get each image. However, if an orbital 'pokes out' of the atom, or forms a 'sharp feature' (inverted commas because they are wave functions, so these concepts are a bit hard to define) then we get a bright spot. The really cool bit is getting the atom to go back to the same hybridization state hundreds of times, so we got the two-lobed picture.

    It's dead clever. However, for my money, the atomic force probes are cooler as they can measure the fields without stripping the electrons. But, as the reviewer said, it takes all sorts...

  • Electrons act like both particles and waves, following the laws of quantum mechanics. They are not really like moons traveling around planets in a neat circle.

    I'm not a physicist but my understanding is that each element has a different number of electrons balancing the positive charge of the protons in the nucleus. These electrons form electron shells which are at different energy levels, and the shells are composed of a combination of atomic orbitals.

    Quantum physics says that one cannot know where an electron is until you measure it. The three-dimensional geometric shape of an orbital indicates where the probability is highest that the electron will be found, but it could be just about anywhere. Some orbitals are spherical but others are very different shapes.

    Here are some wikipedia links:

    Atomic Orbitals [wikipedia.org]
    Electron Configuration [wikipedia.org]
    Electron Shells [wikipedia.org]

  • by radtea (464814) on Tuesday September 15, 2009 @08:35AM (#29424743)

    Depends what you mean by real

    By "real" I mean things that obey the laws of non-contradiction and causality, which wavefunctions don't (which is why we see experimental violations of Bell's Inequalities.)

    So I see this argument over whether or not spherical harmonics are "real" kind of beside the point: they are a mathematically useful decomposition of a conceptual artefact that is already ontologically problematic.

  • by Anonymous Coward on Tuesday September 15, 2009 @08:36AM (#29424753)

    If I understand it correctly, what they've done is to "feed" the carbon atom with a stream of electrons (also known as a current...) and then the've imaged the pattern that forms as one electron after another is shot away from the atom to a phosphor surface.

  • by Anonymous Coward on Tuesday September 15, 2009 @10:52AM (#29426463)

    The article was extremely superficial when describing the actual experiment, but essentially a current was passed through a small chain of carbon atoms by applying a voltage across the chain. The current caused the the carbon atom at the tip to give off electrons to a phosphor screen. I would suppose that these "given off" electrons were integrated (summed) over time and this formed a pattern that reflected the shape of the probability distribution, i.e. orbital. Each electron that was "given off" constituted a sampling experiment regarding electron position, and the sum total of the samples would, over time, give rise to the orbital shape. In the case of an s orbital, electrons were given off in all radial directions. For the p orbital, certain angles gave off no electrons. This behavior corresponds to the quantum equations.

  • Pity this is AC (Score:5, Informative)

    by Kupfernigk (1190345) on Tuesday September 15, 2009 @11:07AM (#29426637)
    Thanks for responding. This could do with some mod points but I can't mod and post...so I'll respond. It's interesting to think about what is happening here. It's possibly unhelpful to refer in the same sentence to "current" and "electrons" but I know what you mean, though I would rephrase it a little to help my own understanding. The "current" did not cause the carbon atom to give off electrons; rather, the potential difference enabled some electrons to pass along the carbon chain until they left the tip, and the path of the emerging electrons was probabilitistically interfered with in a way that reflected the solution of the Schroedinger wave equation for the outer electrons of the end atom. That's a very interesting experiment. The benefit of using carbon atoms in a molecule is that the bond angle presumably locks the orientation of the P orbitals sufficiently to enable the experiment. So for many atoms it simply wouldn't work, and what we are seeing here is not an image per se but something more like the result of the Rutherford/Geiger/Marsden experiment. It looks like a significant experiment, but the summary is quite wrong as to what is being shown.
  • by locofungus (179280) on Tuesday September 15, 2009 @11:36AM (#29427027)

    No it doesn't because my post explicitly says that the wave function is a mathematical curiosity.

    My post does constantly confuse an electron with the probability function of finding it. But that's because that's the way electrons behave. If anything the probability function is more fundamental so it should be "You constantly confuse the probability function with a hypothetical billiard ball model of the electron"

    The wave function is a mathematical trick that just happens to allow us to calculate the probability distributions we observe. It has no known physical significance whatsoever.

    Tim.

  • by brian0918 (638904) <brian0918 AT gmail DOT com> on Tuesday September 15, 2009 @01:27PM (#29428555)

    You can turn down the beam current in the two slit experiment until you're talking about orders of magnitude less than one electron in the apparatus at any one time on average and you still get the diffraction pattern.

    That's not correct. See experiment and photos here [hitachi.com] (Figure 2). Single electrons produce single dots. It's only after you dump many electrons through that you get a pattern - that's simply because the electrons follow wave trajectories rather than the standard trajectory visualized from classical motion. In reality everything follows these same wave trajectories, it's just that for macroscopic objects, the individual oscillations of the individual particles cancel out.

    I don't know why it's any more conceptually obvious that a "variable" should be smeared out than an "electron" should be smeared out.

    The phrase "smeared out" conveys nothing, so it should be no surprise that it can be used for situations that are completely different.

  • Re:really? (Score:2, Informative)

    by easyTree (1042254) on Tuesday September 15, 2009 @06:09PM (#29432449)

    Did someone post the wrong image? Isn't this the winner of last year's "Least detailed photo of anything" contest? I'm pretty sure it is [insidescience.org].

  • by The_Duck271 (1494641) on Tuesday September 15, 2009 @07:30PM (#29433593)
    The z-axis is arbitrary; you just pick some direction and call it the z direction.
  • by pclminion (145572) on Wednesday September 16, 2009 @12:52AM (#29436217)

    or, we could simply call it a photograph and not worry about what detection and imaging techniques were used.

    I would kind of prefer that we limit the use of the word "photograph" to include images produced by illumination by photons. There's a reason that the imagery produced by electron microscopes are called "micrographs," not photographs. The images are produced by the irradiation of the specimen with electron waves, not photons.

  • by gribbly (39555) on Wednesday September 16, 2009 @04:26AM (#29437253)
    It *is* correct. GP said "less than one electron in the apparatus at any one time on average and you still get the diffraction pattern" which is right. Even if you only ever send one electron through it will be detected in a location consistent with the fringe pattern.

    From the link you included in your reply:

    "Although electrons were sent one by one, interference fringes could be observed."

    You say "Single electrons produce single dots. It's only after you dump many electrons through that you get a pattern" which I think is misleading at best. It suggests that the first electron could be found in a location consistent with classical mechanics. The reality is that from the very first dot you'll be seeing interference effects (this is the heart of the double slit experiment), although it's true it won't *look* like there's a pattern until you've accumulated many dots.

    Anyway, my point is that GP had it right.

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