The air doesn't matter. The article says that the 35nm gap between electrodes is less than the mean-free path of electrons in air. In other words, from the elec

The air doesn't matter. The article says that the 35nm gap between electrodes is less than the mean-free path of electrons in air. In other words, from the electron's perspective, it's the same as a vacuum since it doesn't (usually) encounter any air molecules when passing between the electrodes.