Figure 4. Effect of 800 nm height step on the dynamics of a Janus microswimmer.

(a) An active Janus particle approaching a step; after direct contact with the step, it reorients until its propulsion axis is parallel to the step. R=2.5 μm, h_step=800 nm, 2.5%vol. H₂O₂. (b) Numerically calculated steady-state distribution c(r) of reaction products around half catalyst-covered Janus sphere as a function of the step distance and the cap orientation with respect to the step. The colour map shows c(r) at the surfaces of the particle and substrate; c(r) is in units of c₀ (see Methods). Scale bar, 5 μm.