Figure 2.

Motion of (a) positive, (b) quasi-neutral, and (c) negative particles using a p-doped Si/Pt pump in 1% H₂O₂. Positive particles stick on the Pt disk. The black color of the disk is due to the accumulation of particles. The quasi-neutral P⁰ particles move toward the platinum disk. After having crossed the Si–Pt border, they are pushed upward. The figures are the superposition of 45 images recorded with the optical microscope every 0.2 s. (d) Average radial velocity (V_r) of P⁺ and P⁰ particles as a function of the radial component in H₂O₂. The yellow area represents the area of the platinum disk. The diameter of the disk is 50 μm. The velocity plot for P⁺ particles is based on the averaged data of eight devices and 28 particles. The plot for P⁰ tracers has been obtained by processing three devices and 19 particles.