The new technique observes the movement of electrons to an accuracy of atto seconds

European researchers have just developed a new technique that allows the study of the motion of electrons in solids with precision within a short time to attoseconds (10-16s). With this technique, the team was able to accurately measure the time the electron moved to the surface of the sample when they were excited by laser light.

Can now accurately record the electron shift time in solids?

Experiments on emission spectra have shown that electrons from the conduction band are shifted at twice the rate of electrons in the valence band.

" Semi-classical " atomic theory Bohr predicted that electrons take a period of 150 attoseconds when moving in orbit (for electrons of Hydrogen atoms). The actual atomic nucleus moves a lot slower, which means that the atto-second spectrometer can be used to study the properties when the basic atom freezes for a while.

While atto-second spectroscopic techniques for atomic gases are carried out, similar experiments performed on solids are limited by femtosecond time resolution (10-14s). And recently, the team of Ferenc Krausz and colleagues at the Max Planck Institute for Quantum Optics in Garching (Germany), and physicists from a number of other Universities in Germany, Austria and Spain has successfully developed a method that allows the recording of the atto of the electron emitted from the surface of a solid.

This new technique uses the ultra ultraviolet (XUV) to excite the sample to emit electrons according to the mechanism of the photoelectric effect. At the same time a much longer pulse of infrared light is reflected on the surface of the sample. When the electrons bounce off the surface of the sample, it will be accelerated by the infrared light towards the sensor that recognizes the " shift time" (time-of-flight - TOF) placed above the sample. This device allows electronic electronic travel time recording to an accuracy of atto seconds.

Figure 1. The principle diagram of the new technique (Nature 449 1029).

The team demonstrated the effectiveness of this technique by studying the electron shift time that bounces off the surface of a sample of tungsten crystals when absorbing photons of light XUV. They discovered that the electron escaped from the material in two separate groups of about 110 attoseconds . By recording the kinetic energy of the electron in each group, Krausz and his colleagues concluded that the first exit group was electrons from the conduction band, and then the electrons in the bound state (on group f).

According to the results of the group's study, there is a delay of about 20 attoseconds due to excited bonding electrons that can travel longer through tungsten samples compared to excited electrons from the conduction band, and therefore inter-electrons are like coming from a deeper position from within the sample. Approximately 90 attoseconds remaining corresponds to the kinetic difference between the bonding electron and the conduction electron (created by absorbing a photon XUV).

Figure 2. Evidence of the shifting delay of two electron groups: electron emission from the conduction band (red graph) and electron from the 4f link area (blue graph) (Nature 449 1029) .

The atto-second time resolution is actually a shift limit of an electron operating in electronic components. Therefore, in principle, tiny electronic circuits of only a few atoms can open and close the current with frequencies up to petahertz (1015 Hz), which means that at a million times faster compared to current processors. However, at the present time, there is little knowledge of how an electron moves in such electronic circuits - and that is why Krausz's team believes their technology can Very useful for developing future electronic components.

(See the article for more details in Nature 449 1029 ).

The Doctrine of Independence