多鐵性鐵酸鉍(BiFeO3)具有相當高的尼爾(Nêel)和居禮(Curie)溫度，在應用元件上是非常具有發展潛力的。當鐵酸鉍(BiFeO3)長在鋁酸鑭(LAO)基板上時，由於受到基板壓縮應力的影響，此時鐵酸鉍(BiFeO3)會呈現出類長方晶(tetragonal-like)和類菱長晶(rhombohedral-like)的單斜晶(monoclinic)混相結構， 令人感興趣地是此二相可經由施加電場加以操控。在本篇論文探討的即為利用掃描探針顯微技術施加電場而達到操控此一具混相結構鐵酸鉍(BiFeO3)的目的。實驗分析是利用壓電力顯微鏡探討鐵酸鉍薄膜電域(domain)結構。由實驗結果可知，類長方晶(T-like)相鐵酸鉍電域(domain)結構的操控與施加電場的歷史路程有關，探針快軸方向決定了域壁(doamin wall)方向主要是沿著[110] 或 [1-10]，探針慢軸方向決定了電域(domain)的極性方向。相同地，探針快軸方向也控制了類菱長晶(R-like)相鐵酸鉍(BiFeO3)的生成，類菱長晶相(R-like)鐵酸鉍(BiFeO3)的生成傾向於與探針快軸方向垂直，且類菱長晶(R-like)相鐵酸鉍彎曲的方向亦與探針掃描方向(左往右掃或右往左掃)有關。本篇研究對於相變情況下提供了利用電場進行相調控的新方法。

Multiferroic BiFeO3 has high Curie and Nêel temperatures, which are capable for applications in new functional devices. As BiFeO3 grown on the LAO substrate, the compressive strain from the substrate will make the film composed by tetragonal(T)-like and rhombohedral(R)-like monoclinic phases. Interestingly, these two phases can be controlled by electric fields. In this study, we investigated the important parameters of phase transformation for the mix-phase BiFeO3 under writing voltages of scanning tips. The resultant domain structures were examined by the piezoresponse force microscopy (PFM). The obtained T-like domain structures depended on the written history. The direction of the fast scanning axis determined the domain wall orientation, mainly along [110] or [1-10], while the slow axis governed the direction of the polarization. Similarly, the fast axis also controlled the orientation of the R-like phase, with the tendency of the domain wall perpendicular to the probe-scanning direction. This study provided a new path way to control phase transformation by electric fields.

1. J. Seidel, L. W. Martin, Q. He, Q. Zhan, Y. H. Chu, A. Rother, M. E. Hawkridge, P. Maksymovych, P. Yu, M. Gajek, N. Balke, S. V. Kalinin, S. Gemming, F. Wang, G. Catalan, J. F. Scott, N. A. Spaldin, J. Orenstein and R. Ramesh, Nat Mater 8 (3), 229-234 (2009).
2. T. Zhao, A. Scholl, F. Zavaliche, K. Lee, M. Barry, A. Doran, M. P. Cruz, Y. H. Chu, C. Ederer, N. A. Spaldin, R. R. Das, D. M. Kim, S. H. Baek, C. B. Eom and R. Ramesh, Nat Mater 5 (10), 823-829 (2006).
3. S. Y. Yang, J. Seidel, S. J. Byrnes, P. Shafer, C. H. Yang, M. D. Rossell, P. Yu, Y. H. Chu, J. F. Scott, J. W. Ager, L. W. Martin and R. Ramesh, Nat Nano 5 (2), 143-147 (2010).
4. J. Wang, J. B. Neaton, H. Zheng, V. Nagarajan, S. B. Ogale, B. Liu, D. Viehland, V. Vaithyanathan, D. G. Schlom, U. V. Waghmare, N. A. Spaldin, K. M. Rabe, M. Wuttig and R. Ramesh, Science 299 (5613), 1719-1722 (2003).
5 R. J. Zeches, M. D. Rossell, J. X. Zhang, A. J. Hatt, Q. He, C. H. Yang, A. Kumar, C. H. Wang, A. Melville, C. Adamo, G. Sheng, Y. H. Chu, J. F. Ihlefeld, R. Erni, C. Ederer, V. Gopalan, L. Q. Chen, D. G. Schlom, N. A. Spaldin, L. W. Martin and R. Ramesh, Science 326 (5955), 977-980 (2009).
6 D. Mazumdar, V. Shelke, M. Iliev, S. Jesse, A. Kumar, S. V. Kalinin, A. P. Baddorf and A. Gupta, Nano Letters 10 (7), 2555-2561 (2010)
7 Q. He, Y. H. Chu, J. T. Heron, S. Y. Yang, W. I. Liang, C. Y. Kuo, H. J. Lin, P. Yu, C. W. Liang, R. J. Zeches, W. C. Kuo, J. Y. Juang, C. T. Chen, E. Arenholz, A. Scholl and R. Ramesh, Nat Commun 2, 225 (2011)
8 W. Eerenstein, N. D. Mathur and J. F. Scott, Nature 442, 17 (2006)
9 P. Shafer, F. Zavaliche, Y.-H. Chu, P.-L. Yang, M. P. Cruz and R. Ramesh, APPLIED PHYSICS LETTERS 90, 202909 (2007)
10 T. Tybell, P. Paruch, T. Giamarchi and J.-M. Triscone, Phys. Rev. Lett. 89, 9 (2002)
11 B. D. Cullity, S. R. Stock, Prentice Hall, New Jersey (2001)
12 Kenji Uchino. Ferroelectric Devices, Materials Engineering. Marcel Dekker, 2000
13 F. Zavaliche, P. Shafer, R. Ramesh, M. P. Cruz, R. R. Das, D. M. Kim, and C. B. Eom, App. Phys. Lett. , 87, 252902 (2005)
14 Ying-Hao Chu*, Lane W. Martin, Mikel B. Holcomb, and Ramamoorthy Ramesh Mater. Today.(2007)10,16
15 Claude Ederer* and Nicola A. Spaldin PHYSICAL REVIEW B 71, 060401(2005)
16 R. J. Zeches, M. D. Rossell, J. X. Zhang,A. J. Hatt, Q. He, C.-H. Yang, A. Kumar,C. H. Wang, A. Melville, C. Adamo, G. Sheng Y.-H. Chu, J. F. Ihlefeld, R. Erni C. Ederer, V. Gopalan, L. Q. Chen, D. G. Schlom, N. A. Spaldin, L. W. Martin, R.Ramesh SCIENCE VOL 326 13 NOVEMBER 2009
17 H. M. Christen, J. H. Nam, H. S. Kim, A. J. Hatt,and N. A. Spaldin PHYSICAL REVIEW B 83, 144107 (2011)
18 Zuhuang Chen , Zhenlin Luo,Chuanwei Huang,Yajun Qi,Ping Yang,Lu You,Chuansheng Hu ,Tom Wu ,Junling Wang ,Chen Gao , Thirumany Sritharan , and Lang Chen Adv. Funct. Mater. 2011, 21, 133–138
19 Q. He, Y. -H. Chu, J. T. Heron, S. Y. Yang, W. I. Liang, C.Y. Kuo, H. J. Lin, P. Yu, C. W. Liang, R. J. Zeches, W. C. Kuo, J. Y. Juang, C. T. Chen, E. Arenholz, A. Scholl & R. Ramesh Nature Commutications 1221 (2011)
20 N. Balke, S. Choudhury, S. Jesse, M. Huijben, Y. H. Chu, A. P. Baddorf, L. Q. Chen,R. Ramesh and S. V. Kalinin NATURE NANOTECHNOLOGY 293 VOL 4 DECEMBER 2009
21 Morris, V. J., Kirby, A. R., Gunning, A. P., “Atomic Force Microscopy for Biologists”, Imperial College Press: London, 1999
22 M. Alexe and A. Gruverman, “Nanoscale Characterisation of Ferroelectric Materials-Scanning Probe Microscopy Approach”, Springer, (2004)
23 Claude Ederer and Nicola A. Spaldin PHYSICAL REVIEW B 71, 060401 (2005)
24 Alison J. Hatt and Nicola A. Spaldin Phys. Rev. B 81, 054109 (2010)
25 Zuhuang Chen, Lu You, Chuanwei Huang, Yajun Qi, Junling Wang, Thirumany Sritharan,and Lang Chenb APPLIED PHYSICS LETTERS 96, 252903 (2010)
26 Yutaro Kitagawa(, Yuji Hiraoka, Takashi Honda, Taishi Ishikura, Hiroyuki Nakamura and Tsuyoshi Kimura NATURE MATERIALS VOL 9j OCTOBER 2010
27 H. Be´a,B. Dupe S. Fusil R. Mattana, E. Jacquet, B. Warot-Fonrose, F. Wilhelm, A. Rogalev, S. Petit,V. Cros, A. Anane, F. Petroff, K. Bouzehouane, G. Geneste, B. Dkhil, S. Lisenkov, I. Ponomareva, L. Bellaiche,M. Bibes,and A. Barthe PRL 102, 217603 (2009)
28 S. Lisenkov, D. Rahmedov and L. Bellaiche PRL 103, 047204 (2009)