Fig. 4: Control of charging behaviour with different-material samples.
From: Adventitious carbon breaks symmetry in oxide contact electrification
a, Samples of four different oxides, with different composition, surface roughness and crystalline structure, are tested against each other. b, When measuring every pair combination with just our standard cleaning protocol, a perfect triboelectric series forms with alumina (Al2O3) at the top and silica (SiO2) at the bottom. c, For every pair combination, we bake the positively charging sample (sphere or plate) to reverse the charging polarity. d, The result is an ‘inverted’ triboelectric series with SiO2 at the top and Al2O3 at the bottom. These data illustrate that the ‘carbon effect’ competes with an underlying material effect. The latter is stronger if full carbon layers are present, whereas the former dominates if one surface is largely absent from carbon.
