The initial stage of the fast electrical breakdown of an air gap with a pin-to-plane electrode geometry is studied on a nanosecond time scale using multi-frame laser probing with an exposure time of 70 ps and spatial resolution as high as 3–4 μ m. We find that the gap breakdown is associated with the fast (≲1 ns) formation of a micron-sized (∼10 μ m) cathode spot that appears as a plasma with an electron density of n e ≈ 10 19 cm − 3 . The spot is then transformed into a spark channel having an electron density of n e ∼ 10 19 – 10 20 cm − 3 . Within ∼1 ns after the breakdown the dynamics of the highly ionized near-cathode plasma governs the current capacity of the discharge gap as well as the current rise rate.

We report on the results of studying quasi-two-dimensional nanostructures synthesized here in the form of semiconducting CdSe nanoplatelets with a characteristic longitudinal size of 20–70 nm and a...