Measuring slow electrons is challenging, and understanding their behavior in solid materials is often trial and error. TU Wien has discovered new insights into these electrons by using fast electrons to generate slow electrons within the material. This new method, published in 'Physical Review Letters,' allows researchers to decipher previously inaccessible details.

Simultaneous Measurement of Two Electron Types

"We are interested in what the slow electrons do inside a material, for example inside a crystal or inside a living cell," said Prof. Wolfgang Werner from the Institute of Applied Physics at TU Wien. "To find out, you would actually have to build a mini-laboratory directly in the material to be able to measure directly on site. But that's not possible, of course."

Scientists can only measure electrons exiting the material, which doesn't reveal their origin within the material or their interactions. TU Wien's team tackled this by using fast electrons that penetrate and trigger various processes in the material. These fast electrons disturb the material's electrical charge balance, causing another electron to detach and travel slowly, sometimes escaping the material.

The key is measuring these electrons simultaneously: "On the one hand, we shoot an electron into the material and measure its energy when it leaves again. On the other hand, we also measure which slow electrons come out of the material at the same time." By combining this data, researchers can access previously inaccessible information.

Series of Collisions, Not a Cascade
The energy loss of fast electrons reveals their penetration depth, indicating where slow electrons were released. This data validates numerical theories on electron energy dissipation.

The findings were surprising. Previously, it was believed that fast electrons caused a cascade of electron displacements. Instead, the data showed that fast electrons undergo a series of collisions, retaining most of their energy, and releasing only one slow electron in each interaction.

"Our new method offers opportunities in very different areas," said Werner. "We can now finally investigate how the electrons release energy in their interaction with the material. It is precisely this energy that determines whether tumor cells can be destroyed in cancer therapy, for example, or whether the finest details of a semiconductor structure can be correctly formed in electron beam lithography."

Research Report:Energy Dissipation of Fast Electrons in Polymethylmethacrylate: Toward a Universal Curve for Electron-Beam Attenuation in Solids between ~ 0 - ? eV and Relativistic Energies

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