Electron spectrometer deciphers quantum mechanical effects

Filled with an inert gas, the pressure chamber contains light-guiding hollow-core fibers. The gas and the light interact with each other. As a result, the optical spectrum widens and the pulses become shorter (30 fs). Credit: Fraunhofer IOF, Walter Oppel

Electronic circuits are miniaturized to such an extent that quantum mechanical effects become noticeable. Using photoelectron spectrometers, solid-state physicists and material developers can discover more about such electron-based processes. Fraunhofer researchers have helped revolutionize this technology with a new spectrometer that works in the megahertz range.

Our vision is limited to the macroscopic world. If we look at an object, we merely see its surface. At the nanoscale, things would appear very different. This is a world of atoms, electrons and electron bands, in which the laws of quantum mechanics hold sway. Investigating these tiniest building blocks of matter more closely is a very interesting avenue for solid-state physicists and material developers – such as those who work on electronic circuits, which are so miniaturized in some cases that quantum mechanical effects become noticeable.

Photoelectron spectroscopy opens a window on atoms together with their energy states and their electrons. The principle can be described as follows: Using a laser, you shoot high-energy photons (particles of light) onto the surface of the solid-state object to be investigated – an electronic circuit, for instance. The high-energy light knocks electrons out of the atomic bond. Depending on how deep the electrons are located in the atom – or more precisely, what energy band they are in – they reach the detector at a sooner or later time. Analyzing the time it takes electrons to reach the detector, material developers can draw inferences about the energy states of the electron bands and the structure of the atomic bonds in the solid. Just like in a race, all the electrons must start at the same time – otherwise, the race cannot be analyzed. This kind of simultaneous start can be achieved only by using a pulsed laser beam. Put simply: You shoot the laser onto the surface, look at what has been released – and shoot again. Usually, the lasers work in the kilohertz range, which means they emit a few thousand laser light pulses per second.

The problem is that if you set too many electrons free simultaneously with a pulse, they repel each other – making it impossible to measure them. So you turn down the power of the laser. To be able to nevertheless measure enough electrons for a reliable sample, you need to arrange for suitably long measurement times. But sometimes this is not feasible, as the samples and beam source parameters cannot be kept sufficiently stable over such a long period. Slashing measurement times from five hours to ten seconds.

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Images courtesy of phys.org