Polarization rotation in copper doped zinc oxide (ZnO:Cu) thin films studied by Piezoresponse Force Microscopy (PFM) techniques

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• 作者：Juanxiu Xiao^a ; Tun Seng Herng^b ; Jun Ding^b ; Kaiyang Zeng^a ; ^{mpezk@nus.edu.sg" class="auth_mail" title="E-mail the corresponding author}
• 关键词：ZnO ; Cu thin films ; Piezoresponse Force Microscopy ; Polarization rotation ; Copper concentration ; Oxygen vacancy
• 刊名：Acta Materialia
• 出版年：2017
• 出版时间：15 January 2017
• 年：2017
• 卷：123
• 期：Complete
• 页码：394-403
• 全文大小：5687 K

文摘

In this study, the polarization rotation with approximately 180⁰, i.e., the phenomenon that polarization changes its angle by ∼180°, in copper doped ZnO (ZnO:Cu) films under an applied electrical field are characterized by using Piezoresponse Force Microscopy (PFM) based techniques. First, the Band Excitation PFM (BE-PFM) measurements show that the polarizations in ZnO:Cu sample prefer the upward direction when the copper concentration is higher (above 8 at.%). Second, it is found that the piezoresponse property is enhanced with increasing the copper concentration. Third, by conducting PFM in spectroscopy mode (PFS), it reveals that the anomalous hysteresis loops occurs at certain locations and can be tuned to symmetry by increasing the bias window. Furthermore, it is found the built-in field during the DC poling processes are contributed by the oxygen vacancy in the films. The PFS results from as-grown sample and samples annealed in air and vacuum also verify that the oxygen vacancy plays an important role in the polarization rotation. Finally, by using the switching spectroscopy PFM (SS-PFM) technique, it is confirmed that the local polarization rotation is mediated by copper concentration. The parameters determined from the PFS measurements, including positive and negative coercive bias, b=MathURL&_method=retrieve&_eid=1-s2.0-S1359645416308187&_mathId=si2.gif&_user=111111111&_pii=S1359645416308187&_rdoc=1&_issn=13596454&md5=24a8c3f821b1f74bf4fd162bf33ec3cc" title="Click to view the MathML source">Vb>pb> and b=MathURL&_method=retrieve&_eid=1-s2.0-S1359645416308187&_mathId=si3.gif&_user=111111111&_pii=S1359645416308187&_rdoc=1&_issn=13596454&md5=6046d34c4beaa3cfd72609e97e413d32" title="Click to view the MathML source">Vb>nb>, coercive bias, b=MathURL&_method=retrieve&_eid=1-s2.0-S1359645416308187&_mathId=si4.gif&_user=111111111&_pii=S1359645416308187&_rdoc=1&_issn=13596454&md5=3036611936a695c3fd2e8e804a6f3d7a" title="Click to view the MathML source">Eb>cb>, maximum and remanent switchable responses, b=MathURL&_method=retrieve&_eid=1-s2.0-S1359645416308187&_mathId=si5.gif&_user=111111111&_pii=S1359645416308187&_rdoc=1&_issn=13596454&md5=f06ca2d56a516413e5a66b4bde40a9f4" title="Click to view the MathML source">Rb>sb> and b=MathURL&_method=retrieve&_eid=1-s2.0-S1359645416308187&_mathId=si6.gif&_user=111111111&_pii=S1359645416308187&_rdoc=1&_issn=13596454&md5=faab0a545c466f7088c14fd06e430fd2" title="Click to view the MathML source">Rb>0b>, all increase with the copper concentration.