Piezoresponse force microscopy and surface effects of perovskite ferroelectric nanostructures
Piezoresponse force microscopy and surface effects of perovskite ferroelectric nanostructures
复制标题
钙钛矿铁电纳米结构的压电响应力显微镜和表面效应
DOI：
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
F. Peter
中科院分区：
文献类型：
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作者：
F. Peter
随着铁电非易失性存储器的小型化，自发极化和位移电流如何随尺寸缩放的问题出现了。压电响应力显微镜（PFM）是研究这些性能的首选方法。尽管这种方法取得了巨大的成功，但对比度形成机制的许多方面尚未被理解。这项工作的目的是铁电纳米结构的PFM测量的内在和外在的贡献进行了系统的调查。X射线光电子能谱和PFM测量证实，在环境条件下，钙钛矿铁电体被吸附物覆盖。在PFM中，这导致施加到样品上的电场严重减少，并使压电响应衰减高达一个数量级。高真空热处理成功地减少了吸附物的量和影响，并基本上恢复了压电响应。由于悬臂梁的几何形状，平面内响应的光放大比平面外响应大约20倍。这种大的光学放大使得面内压电响应测量非常有吸引力。然而，在c-axs取向的薄膜中，由于尖端下方的径向电位分布，根本不应检测到面内压电响应。测量和模拟表明，只要径向对称性被打破，可以检测到一个平面内的响应。这可能是由于不对称的悬臂、材料参数的局部变化或不平坦的表面。特别是在铁电纳米岛的斜坡上，形貌对面内PFM信号有显著的影响。由于径向电势分布的对称性破缺和尖端下方材料的不平衡量，即使在c轴取向的晶粒的周边处也发生面内响应的显著增强。由于悬臂梁的几何形状，这种增强仅限于平行于悬臂梁轴线的晶粒的斜率。然而，由于机械串扰，在平面外测量中，在垂直于光轴的斜率上也可以观察到增强。另一种串扰来源于悬臂相对于四扇区光电二极管的未对准。在这种情况下，明显的面内响应取代面外信号，并且在某些横向力显微镜配置中，这甚至可能导致面内信号影响原子力显微镜的z反馈回路。提出了一种新的机械补偿方案来消除这种串扰。与其他成像测量技术类似，PFM建议非常直观地访问所采集的数据。在这个意义上说，目前的工作解决了新的关键方面的测量技术，强调在吸附物的存在下的尖端样品相互作用。
With the advancing miniaturization of ferroelectric, non-volatile memories, the question arises how the spontaneous polarization and the displacement current scale with size. Piezoresponse Force Microscopy (PFM) is the method of choice to study these properties. Notwithstanding the huge success of this method, many aspects of the contrast formation mechanisms are not yet understood. The aim of this work is a systematic investigation of the intrinsic and extrinsic contributions to PFM measurements of ferroelectric nanostructures. X-Ray Photoelectron Spectroscopy and PFM measurements confirm that perovskite ferroelectrics are covered by adsorbates under ambient conditions. In PFM this leads to a severe reduction of the electric field applied to the sample and attenuates the piezoresponse by up to one order of magnitude. Heat treatment in high vacuum is successfully employed to lessen the amount and impact of adsorbates and to substantially recover the piezoresponse. Due to the cantilever geometry the optical amplification for the in-plane response is about 20 times larger than for the out-of-plane response. This large optical amplification makes the in-plane piezoresponse measurements highly attractive. However, in c-ax s oriented thin films no in-plane piezoresponse should be detected at all due to the radial potential distribution underneath the tip. Measurements and simulations are presented showing that an in-plane response can be detected whenever the radial symmetry is broken. This can be due to an asymmetric cantilever, local variations of material parameters or an uneven surface. Especially on the slopes of ferroelectric nanoislands, the topography has a significant influence on the in-plane PFM signal. As a result of the broken symmetry of the radial potential distribution and the unbalanced amount of material underneath the tip a significant enhancement of the in-plane response occurs at the perimeter even of c-axis oriented grains. Due to the cantilever geometry, this enhancement is restricted to slopes of the grain parallel to the axis of the cantilever. However, the enhancement may also be observed on the slopes perpendicular to the cantilever-axis in out-of-plane measurements as a result of a mechanical crosstalk. Another kind of crosstalk originates from a misalignment of the cantilever with respect to the four sector photo diode. In this case the pronounced in-plane response supersedes the outof-plane signal and in some lateral force microscopy configurations this may even result in the in-plane signal impacting the z-feedback-loop of the Atomic Force Microscope. A novel mechanical compensation scheme is suggested to eliminate this crosstalk. Similar to other imaging measurement techniques, PFM suggests a very intuitive access to the acquired data. In this sense the present work addresses new critical aspects of the measurement technique with an emphasis on the tip-sample interaction in the presence of adsorbates.
影响因子：
4
作者：
Sugimura, H;Ishida, Y;Nakagiri, N
通讯作者：
Nakagiri, N