Fig.2 Motion of a single screw dislocation of α-Fe in the presence and absence of hydrogen[27]: (a) bright-field transmission electron microscope image showing the pillar after a series of cyclic compression loading and unloading sessions. A mobile dislocation tagged as 1 in the boxed region is magnified and observed in Fig.2b, the white spots indicate the pinning points, (b) configurations of dislocation 1 at σmax in vacuum (N = 1) and in 2 Pa H2 (N = 2), (c) loading engineering stress σ and the digitally tracked projected glide distance δ of dislocation 1 in a typical load cycle are shown as a function of time. The critical stress for activating the dislocation (σc) and the maximum glide distance (δmax) are also indicated, (d, e) measured δmax and σc of dislocation 1 as a function of loading cycle number in vacuum (d) and in 2 Pa H2 (e). Errors for measurements of δmax and σc are ±1.4 nm and ±9.5 MPa, respectively. Error bars represent standard deviation. The tests in 2 Pa H2 were started after the pillar had been exposed to the 2 Pa H2 atmosphere for ~2 h. Scale bars, 100 nm
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