4. Operating mechanism

Compared with the expected 1.8-fold increase in resistivity, we can observe a much more marked reduction in electrical resistivity. At 10% hydrogen, it can be divided by 4 for our resistive-type sensors, and is virtually zero for our switch-type sensors. Thus, the amplitude of variation, like its direction, is clearly distinct from what is normally observed with the hydrogen resistive sensors described so far. An intimate mechanism of operation must be put forward to explain the behavior of our palladium nanowire-based devices.

The mechanism we propose to explain this inverse response is described in figure 7 and is based on in situ AFM observations: prior to any exposure to hydrogen, our sensors...