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4 H. Jeong, O. Kim, J. Kim, J. Hwang, J.-E. Kim, J. Lee, T. Yoon,
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the thickness decreasing from 80 to 40 nm, with all about ꢁ2.3 V.
This phenomenon is also consistent with the conclusion that the
transition voltage is determined by the energy barrier between
the work function of the ITO bottom electrode and the HOMO
level of P(Azo)x(St)y.
5 H. Li, Q. Xu, N. Li, R. Sun, J. Ge, J. Lu, H. Gu and F. Yan, J. Am.
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6 Q. Ling, D. Liaw, C. Zhu, D. Chan, E. Kang and K. Neoh, Prog.
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Conclusions
7 W. Lee, T. Kurosawa, S. Lin, T. Higashihara, M. Ueda and W. Chen,
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8 C. Liu and W. Chen, Polym. Chem., 2011, 2, 2169.
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10 D. Kim, Y.-G. Ko, J. Choi, K. Kim, W. Kwon, J. Jung, T.-H. Yoon
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11 Y. Ma, X. Cao, G. Li, Y. Wen, Y. Yang, J. Wang, S. Du, l. Yang,
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13 C. Liu, T. Kurosawa, A. Yu, T. Higashihara, M. Ueda and W. Chen,
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16 B. Cho, T. Kim, M. Choe, G. Wang, S. Song and T. Lee, Org.
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In summary, we have demonstrated that uniform P(Azo)x(St)y
nanofilms prepared by simple spin-coating can be successfully
utilized in a novel nonvolatile nano memory device. This device
exhibited WORM behavior with high ON/OFF ratios up to 104.
It was found that the switching threshold voltage varied almost
linearly with the functional moiety content, which was attributed
to the reduced energy barrier between the HOMO of copolymer
nanofilm and the ITO work function. The mechanism of the
WORM behavior was further elucidated from the molecular
simulations of electron density from the HOMO to LUMO
surfaces, and the obviously electron density shifting from donor
to acceptor side indicates that the charge separated state could
remain permanently and wouldn’t revert to its original state even
after applying a reverse voltage scan. Overall, the nano memory
devices fabricated with P(Azo)x(St)y copolymers have potential
applications in the future.
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Acknowledgements
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This work was supported by the Chinese Natural Science
Foundation (NSFC 21076134, 21176164), the Natural Science
Foundation of Jiangsu Province (BK2010208), and the Doctoral
Program of Higher Education of China (Grant no.
20113201130003), and a project funded by the Priority Academic
Program Development (PAPD) of Jiangsu Higher Education
Institutions.
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This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 19957–19963 | 19963