Abstract
Transmission X-ray microscopy is employed to detect nanoscale valence changes in resistive switching SrTiO3 thin film devices. By recording Ti L-edge spectra of samples in different resistive states, we could show that some spots with slightly distorted structure and a small reduction to Ti3+ are already present in the virgin films. In the ON-state, these spots are further reduced to Ti3+ to different degrees while the remaining film persists in the Ti4+ configuration. These observations are consistent with a self-accelerating reduction within pre-reduced extended growth defects.
Highlights
In recent years resistive switching in transition metal oxides received a lot of research interest due to the proposed application as resistive random access memory (RRAM).[1,2,3]
In material systems which are classified as valence change materials (VCM) the resistive switching process is usually attributed to the diffusion of oxygen vacancies driven by the applied voltage and an associated valence change of the transition metal cations
For NEXAFS-transmission X-ray microscopy (TXM) experiments photon transparent samples with a thickness below 100 nm are irradiated by photons in the soft X-ray regime
Summary
On a virgin pad the Ti L-edge spectra of the homogeneous film as well as the growth defect reveal the typical absorption characteristic of a Ti4+ configuration in STO in good agreement with literature[21,22] (see Fig. 2(b)). The observed broadening of the eg lines could be a signature of a slightly reduced long range order within the growth defect while the local structure is still dominated by the Ti4+ configuration in perovskite lattice geometry.[23,24] on some defects a small shift
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