This method, called "inelastic electron tunneling spectroscopy," only gives an average reading on billions of molecules. Since the invention of the STM, scientists have searched for a way to do the same measurements on one molecule at a time. Stipe, Rezaei and Ho succeeded by using a specially made STM cooled to 8 degrees Kelvin minus degrees Celsius, or minus degrees Fahrenheit to minimize molecular motion, and working with acetylene C2H2 molecules bonded to a copper surface.
An STM consists of a needle so sharp that its tip can narrow to just one atom, suspended less than a billionth of a meter above the surface to be scanned. When a voltage is applied between the needle and the surface, a tiny electric current, called a "tunneling current," flows between the two. To form an image, the tip is moved back and forth across the surface and its height is adjusted so that the current remains constant. As such, an electron is partially particle-like and partially wave-like, but is really something more complex that is neither a simple wave nor a simple particle.
The electron is described by a probabilistic quantum wavefunction, which spreads out through space and vibrates, but in such a way that it still has certain discrete properties such as mass. When bound in a stable state in an atom, the electron wavefunction spreads out into a certain shape called an "orbital". The orbital does not contain the electron or describe the average location of a little hard electron orbiting around. Rather, the orbital is the electron. When bound in a stable state in an atom, an electron behaves mostly like an oscillating three-dimensional wave, i.
It's a bit like a vibrating guitar string. When you pluck a guitar string, you get the string shaking, which is what creates the sound. Scientifically, we would say that you have excited a standing wave in the string. The guitar string is not moving in the sense of shooting off to the other side of the room. In this sense, the guitar string is not moving at all, but remains clamped to the guitar. But the guitar string is moving in the sense that it is vibrating when you pluck it.
If you pick one spot on the plucked string and look at it closely, it is definitely moving from one location in space to another, back and forth repeatedly. By pulling the string, you transferred chemical energy in your arm to elastic energy in the stretched string. When you let go, the elastic energy was converted to motional energy kinetic energy as the string snapped back and started vibrating.
The total kinetic energy of the entire string averaged over time is zero, since the overall string is not going anywhere with respect to the guitar. An international research team of leading experts in electron spectroscopy led by Thomas Pichler at the University of Vienna, theoretical spectroscopy led by Francesco Mauri at La Sapienza University in Rome and electron microscopy led by Kazu Suenaga at the AIST Tsukuba in Japan, together with the Japanese company JEOL have presented an original method applying it to graphene nanostructures as model: "high resolution electron spectroscopy inside an electron microscope with enough sensitivity to measure even an atomic monolayer".
In this way they could for the first time determine all vibrational modes of freestanding graphene as well as the local extension of different vibrational modes in a graphene nanoribbon. This new method, which they called "large q mapping" opens entirely new possibilities to determine the spatial and momentum extension of phonons in all nanostructured as well as two dimensional advanced materials.
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