New Electron Microscope Shows Atoms in Color

Cornell's Duffield Hall has acquired a new electron microscope that is enabling scientists to see individual atoms in color for the very first time. While old electron microscopes can be compared to black and white cameras, this new scanning transmission electron microscope uses a new aberration-correction technology that is both more intense and allows for faster imaging speed. "The method also can show how atoms are bonded to one another in a crystal, because the bonding creates small shifts in the energy signatures. In earlier STEMs, many electrons from the beam, including those with changed energies, were scattered at wide angles by simple collisions with atoms. The new STEM includes magnetic lenses that collect emerging electrons over a wider angle. Previously, Silcox said, about 8 percent of the emerging electrons were collected, but the new detector collects about 80 percent, allowing more accurate readings of the small changes in energy levels that reveal bonding between atoms."

Not color, false color.

[oskay]

These atoms are color coded, not *seen* in color by the microscope.

Re:Not color, false color.

[kebes]

I'm not sure what the actual innovation is here.

Using false-color in an image is certainly not the innovation. What is innovative is their use of corrective optics to achieve much higher signal (100-fold increase compared to conventional techniques), and the integration of energy-loss spectroscopy. This means that for each pixel in the image, they can determine what kind of atom is being measured. So they can generate false-color maps of atomic identity. Most electron microscopes simply measure electron density: you can guess which element is which based on density, but there can be ambiguities. Some microscopes include detectors for determining what elements are present, but not with high spatial resolution. This new refinement allows precise maps where individual atoms can be both localized, and elementally identified.

The image they show is impressive when you consider that each blob of color is actually an individual atom, and that they've identified exactly what kind of atom is at each position. In this case they were using it to analyze interdiffusion of atoms at an interface. As nanotechnology becomes more and more 'real' you can imagine how useful it will be to image nano-objects with atomic resolution and elemental discrimination.

Re:Schrodinger's Fridge

[esocid]

I doubt that they still survive the process. Organic cells are destroyed due to the direct irradiation with electrons necessary to produce the "photograph" from the microscope. There are ways around this, such as only focusing the beam on a small part of a specimen or to use a deflection technique that minimally exposes the specimen and deflects the electron beam to the viewing stage. Others are preirradiating the specimens at low doses to stabilize them for increased irradiation. There are other complex techniques outside the realm of my understanding, but I think it still is really tough to preserve organic cells during electron microscopy.

Re:What do the electrons "reflect" off of?

[kebes]

Most of the space occupied by the atom is exactly that, space, nothing more. The electron cloud is a fuzzy region of probability, not a solid thing. The "side" of an atom must be defined by a force, not a particle?

You're right that an atom is mostly empty space, but that doesn't matter. An electron microscope works by shooting a beam of electrons at the sample, and measuring how many of those electrons are transmitted (this is called a TEM; an SEM works differently). The electrons that didn't go straight through the sample were scattered by the atoms of the material. Remember that electrons are charged: as the incident electrons travel through the atoms there will be very strong Coulomb forces. The incident electrons will be repelled by the electrons in the material. This interaction is 'long-range' by subatomic standards: even though the electrons themselves are vanishingly small, the Coulomb interaction distance is quite large.

To a first approximation, 'heavier' atoms (higher atomic number) will scatter electrons more strongly, since they have more electrons. On an electron micrograph, heavy atoms show up as dark (absorbed/scattered alot of electrons), whereas lighter atoms show up as being bright (most electrons were transmitted).

I'm glossing over many details, of course. The important thing to remember is that the incident charged electrons are interacting with the charged electron density surrounding the atoms in the material.

Re:Not color, false color.

[koolguy442]

Not to get too technical here, but each blob is actually a column of atoms, as the specimen is wedge-shaped and certainly more than one atomic layer thick.

Electron energy-loss spectroscopy (EELS) has been combined with STEM imaging for several years at least, allowing similar sorts of images to be synthesized. The major contribution of this work is that they've modified the optics so that, even at 0.5 angstrom beam widths (and hence pixel sizes), they still get enough signal to the EELS detector to allow for EELS mapping and spectra acquisition for each of those pixels, giving direct bonding information about the particular portions of atoms probed by the beam. That means that the researchers can tell the difference between titanium atomic columns at different locations within the crystal, depending on the other atoms surrounding them.

Well, I suppose I did end up getting too technical.

IAATEL (I am a transmission electron microscopist)

Re:What do the electrons "reflect" off of?

[Quadraginta]

The electron cloud is a fuzzy region of probability, not a solid thing.

Ah, the evil remnants of a flawed basic chemistry and/or atomic physics class.

Just FYI -- not that it relates to this article -- this is wrong. So far as we know, an electron is a point particle, and the electrons in an atom aren't any different from a free electron. They are a collection of little points located at various definite positions. There's no "fuzziness" and they aren't "smeared out" in any sense at all. The "fuzzy cloud" you see drawn around atoms is just the probability distribution of where the electrons are. It's only fuzzy for the same reason a photo of a bridge at night shows the car headlights all smeared out: the image you've chosen to construct averages over some very fast motion in which you're not interested.

It's amazing to me how often people end up so often misunderstanding [x,p] = ih, and how often teachers misstate its implications. It's not that you can't pinpoint the position of an electron exactly. It's that if you do, it then has a very indeterminate momentum, and you now have no clue where it will be in a few moments.