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Most Detailed Photos of an Atom Yet

Posted by timothy on 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."

8 of 229 comments (clear)

  1. Unscaled photo link by UPi · · Score: 5, Informative

    The unscaled photo is here:

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

  2. It makes me very suspicious indeed. by Kupfernigk · · Score: 4, Informative

    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.

    --
    From scarped cliff or quarried stone she cries "A thousand types are gone, I care for nothing, no not one."
    1. Re:It makes me very suspicious indeed. by Anonymous Coward · · Score: 5, Informative

      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.

  3. Re:Speaking as a chemist by PvtVoid · · Score: 5, Informative

    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.

    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, and the hydrogen atom is a spherically symmetric problem. The natural basis for the Laplacian in spherical coordinates is spherical harmonics. The shape you are seeing is the characteristic shape of different spherical harmonics, corresponding to the angular momentum of the electron.

  4. Re:Speaking as a chemist by The_Duck271 · · Score: 5, Informative
    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.

  5. Not quite a of an electron in an orbital by Richard+Kirk · · Score: 5, Informative

    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...

  6. Pity this is AC by Kupfernigk · · Score: 5, Informative

    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.

    --
    From scarped cliff or quarried stone she cries "A thousand types are gone, I care for nothing, no not one."
  7. Re:Speaking as a chemist by brian0918 · · Score: 4, Informative

    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 (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.