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Laser power electronic energy band structure of the new all-optical technology
Publisher:admin Add time:2018/6/7 Viewed:506
Scientists in Canada have unveiled a new technology for measuring the electronic band structure of solid materials. The new method does not require samples to be placed in a vacuum chamber and can detect large Numbers of samples, something that other technologies cannot. The team thinks its new method could work well in extreme research conditions, including diamond anvil under very high pressure.
Angular resolution emission spectroscopy (ARPES) is an important method for studying the electronic band structure of solid materials based on laser. The photons of the material from the sample have enough energy to eject electrons and measure the energy and momentum of the electrons they emit. The energy and momentum of the electrons within them are eliminated, and this information reveals the structure of their electron belts.
Surface science
Angular resolution emission spectroscopy (ARPES) has been widely used by physicists in material research, including semiconductor and superconductor materials, but the technology has some important limitations. Measurements must be made at a high vacuum (UHV) because the electrons emitted are dispersed and absorbed by the air. In addition, the ARPES only detect a thin layer of samples on the surface of the material because electrons cannot escape from deeper parts of the material.
Now, Paul Corkum and his colleagues, in the national institute of science and at the university of Ottawa, Canada's national research council, developed a new all-optical technology used to study the solid band structure, to overcome these problems.
The technique involves exposing the sample to intense pulses of laser light, but the photon energy is much lower than the energy of electrons ejected from the material. Associated with such a pulse has a very big electric field, this will lead to an electron in a quantum tunnel from the top of the valence band to the bottom of the electronic conduction band, so the hole in the electronic conduction band. Electrons and holes are driven by an electric field in the opposite direction to reach high momentum. The electric field itself is oscillating, and when the field changes direction, the electrons and the holes go back and forth. At this point, the electron recombines with the hole, sending out a photon escape material and being used for detection. The energy of a photon is equal to the gap between the valence band and the conduction band at the recombined point.
To measure the momentum of the electrons as they recombine, Corkum and his colleagues irradiated the samples with the same intensity pulses at the same time using darker, different color laser pulses. By measuring the intensity of the emitted light as a phase function between two laser pulses and the emitted light, the team could calculate the momentum of the electrons as they recombine to produce the emitted photons.
Chemical process
Electron-hole recombination process occurs very rapidly, and the combination with very short laser pulse means that the technology can be used to study the change in a very short period of time the band structure.
Corkum said the technology could prove particularly useful for studying materials under high pressure from diamond anvils, because diamonds are transparent to the laser pulses used to measure them. This method can be used to observe how the energy band structures of materials change during catalysis and other chemical processes, which cannot be studied in supervacuum. In the study, the material was subjected to a very high magnetic field, which may also deflect the ARPES electrons.

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