Figure 8

(a) Representation of positioned laser reduction on one side of a graphene oxide (GO) fiber. The black region corresponds to the laser-induced G region along the brown GO fiber. (b) Photomicrograph of the top surface of the asymmetric graphene/GO (G/GO) fiber. Scale bar, 50 μm. (c) Photograph of the G/GO fiber walker within the narrow slit between two glass slides on the ratchet paper. (d) The initial state of the G/GO fiber walker, which is manually bent slightly in advance to provide a standing pose. (e, f) A series of photographs of the G/GO fiber walker crawling on the ratchet paper in response to the ‘on’ and ‘off’ states of applied moisture. The G side of G/GO fiber is placed downward. Relative humidity (RH; ‘on’ state)=80%, RH (‘off’ state)=25%. Scale bars in (c, d), 1 cm. Reproduced with permission. Copyright 2013 from Cheng et al.⁶³