Peng et al. Nanoscale Research Letters 2012, 7:559 http://www.nanoscalereslett.com/content/7/1/559 conducting bridge associated with the migration of Au ions inside a defective ZnO film from cathode to anode via the conducting bridge during forward/reverse biases could be clearly observed by taking a series of consecu- tive TEM images, while the formed positions of the con- ducting bridge with a wide base and narrow neck is different from a typical formation of conducting bridge via the ECM mechanism. The difference can be ascribed to the different diffusivities of cations transported inside the dielectric layer, thereby significantly influencing the morphology of the conducting path. In addition, a broken region near the cathode after reset process was observed, while it will be reconnected after the set process, which provides a direct proof of the formation of the conducting bridge. The current TEM technique is quite unique and informative, which can be used to elu- cidate the dynamic processes in other devices in the future. Additional file Additional file 1: Electronic Supplementary Information (ESI). Contains Figure S1 and Figure S2. Competing interests The authors declare that they have no competing interests. Authors’ contributions CNP deposited the gold electrode and ZnO film for the in situ TEM sample, e-beam writer, and measured the RRAM property. CWW operated the in situ TEM instrument. TCC designed the in situ TEM sample. WYC carried out the SEM characterization. HWT grew the in situ sample of Si3N4 film. YCW etched and observed the in situ sample. WWW supported the knowledge and database of the in situ TEM. LJC supported the in situ TEM instrument. YLC organized the final version of the paper. All authors read and approved the final manuscript. Acknowledgments The research was supported by the National Science Council through grants no. NSC 101-2112-M-007-015-MY3 and NSC 101-2120-M-007-003, and National Tsing Hua University through grant no. 100N2024E1. YL Chueh greatly appreciates the use of the facility at CNMM, National Tsing Hua University, through grant no. 101N2744E1. Author details 1Department of Materials Science & Engineering, National Tsing Hua University, No. 101, Sec. 2, Kuang-Fu Rd., Hsinchu 30013, Taiwan. 2Department of Materials Science & Engineering, National Chiao-Tung University, No. 1001, University Rd., Hsinchu 30013, Taiwan. 3Center For Nanotechnology, Material Science, and Microsystem, National Tsing Hua University, No. 101, Sec. 2, Kuang-Fu Rd., Hsinchu 30013, Taiwan. Received: 9 August 2012 Accepted: 6 September 2012 Published: 8 October 2012 References 1. Cheng CH, Chin A, Yeh FS: Ultralow switching energy Ni/GeO/HfON/TaN RRAM. IEEE Electron Device Lett 2011, 32:366–368. 2. 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