Experimental study at the nanometer scale of the gas breakdown in a controlled electrode gap.

The breakdown voltage (V_b) of gases can be reasonably estimated using Paschen's law, which is based on assumptions such as a perfectly uniform electric field, and infinite electrode size. This analytical approach has demonstrated remarkable capability in predicting V_b in numerous cases, by scaling it by the product of pressure and inter-electrode distance (p·d). This description is quite efficient and convenient over wide ranges of pressure and gap distance. However, the robustness of Paschen's law in predicting consistent values of V_b is severely compromised at gap distances shorter than typically 1 micrometer at atmospheric pressure. Several studies have provided experimental, theoretical, and simulation evidences highlighting these limitations. This raised significant concerns, both theoretical and practical, about the insulation properties of gases at short distances. This study focuses on experimentally investigating V_b of air in short electrode gaps, ranging from 100 nm to 6 µm. The electrode system consists of a silicon wafer coated with gold, connected to ground. The anode connected to high voltage is a sharp CuBe needle coated with gold, with 20 µm tip radius of curvature. The gap distance is controlled by a piezoelectric actuator. Ambient air is used at atmospheric pressure, allowing for comparisons with data from existing literature. Complementary experiments are also performed in a closed chamber allowing to vary the pressure from 10^-4 mbar to 3.0 bar, and control the gas purity and water content.