Diamond is known as a material with excellent
mechanical and thermal properties. Synthetic diamond coatings are often used for
drills or cutting blades. Synthetic diamond can also be used to work as an
electronic sensor to measure ultraviolet light or even magnetic fields! And the
latter is what we want to do on a stratospheric balloon. But where do these
sensing capabilities originate from?
Atoms, molecules, diamond lattices … are all
characterized by the states their electrons are in and what energy levels these
states have. States with the same energy levels are referred to as degenerate states.
When no external forces are present, these
energy levels are well defined and fixed. However, when an external force is
applied to a system, the energy levels can shift or even split in the case of
degenerate states. If a magnetic field is used as an external force, this
splitting is called Zeeman splitting
(Not to confuse with the clothing store http://www.zeeman.com)
By using a certain production method, it is
possible to introduce nitrogen vacancy defects within the diamond. A nitrogen
vacancy defect in diamond has three ground states, with two degenerate states
at a slightly higher energy level than the third state. If an electron from the
latter state gets excited, it will relax back to the ground state while sending
out red light. This phenomenon is known as photoluminescence. If in the other
case the electron gets excited from the slightly higher states (by first
exciting electrons from the lowest to the two degenerate states by microwaves),
it will also relax while sending out red light, but this time the light will be
less intense. This will show up as a dip when graphing the intensity against the frequency of the microwaves.
When a magnetic field is applied, the two degenerate states will split at the same
rate as the strength of the magnetic field. Now, two dips will show up in the
graph, one for each state. By exploiting this effect, the magnetic field can be
measured!
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