Time resolved and in-situ structural analysis of a ferroelectric thin film during polarization switching using synchrotron-based diffraction

提出了一种基于同步加速器的时间分辨衍射方法来表征压电薄膜。这就是为什么我们需要完成一个配备铁电测试系统的时间分辨衍射系统。本文介绍了用于铁电薄膜极化高速表征的磁电测试系统（Toyotechinca FCE-HS100D），并对其进行了改进，使其能够进行时间分辨和原位测量。我们成功地检测了外延Pb(Zr_<0.25>, Ti_<0.75>) O_3（PZT）和多晶BiFeO_3（BFO）等铁电薄膜的电致应变。电拉伸应变是由具有重复ns宽脉冲的外加电场引起的。此外，我们还通过衍射峰位移确定了压电常数。该装置使用射频信号作为Spring-8存储环的时钟，接收由508 MHz计数器形成的脉冲模式，并对样品施加脉冲电场。我们更多地使用脉冲模式作为触发器；因此，外加电场与入射x射线同步。样品采用金属有机化学气相沉积法在SrRuO_3薄膜上外延生长了750 nm厚的PZT薄膜。上面直径为100 μm的Pt电极排列在晶格中。一个探针接触到Pt入射x射线击中的上电极，而另一个探针接触到另一个上电极。我们在PZT薄膜中预先使用30 V的外加电压对齐极性方向；因此，极化（+Pr）仍然存在。我们围绕pzt004布拉格角进行Θ-2Θ扫描，并使用雪崩光电二极管探测器分别在0、10、20、30、40、50、55、60、70和75 V的固定电压下，记录了Θ和2Θ角的每种组合下衍射强度曲线作为时间的函数。单极矩形脉冲宽度为200 ns，周期为800 ns。每个角度的测量时间为100秒。使用的意外狭缝尺寸为15×15μm。我们观察到，004个主峰只有在外加电场打开时才会向低角度偏移。这表明（004）晶格平面沿表面法线的间距由于电致伸缩而延长。50 V时，主峰位移估计的脉冲电场感应应变Δd / d为0.0004；相应的，压电常数d_<33>为13 pm / v。此外，我们发现另一个峰值出现在较小的角度。从另一个峰移得到的d_<33>约为50 pm / v，这个值几乎与使用AFM测量得到的值相对应。我们还应用了时间分辨衍射方法来表征多晶BFO薄膜。施加电压分别为0、3、5、8、10、11和12 V，宽度为150 ns，周期为804 ns。（001）和（110）结构域的d_<33>值分别为27.8和26.4 pm / V。少

A synchrotron-based time-resolved diffraction method has been developed for characterizing a piezoelectric thin film. This was why we needed to complete a time-resolved diffraction system equipped with a ferroelectric test system. We introduced the fenoelectric test system(Toyotechinca FCE-HS100D) for high-speed characterization of polarization in a ferroelectric thin film and modified it for a time-resolved and in-situ measurement. We have succeeded in detection of electrostuction(electuc-field-induced strain) of ferroelectric thin films such as epitaxial Pb(Zr_<0.25>, Ti_<0.75>) O_3(PZT) and polycrystalline BiFeO_3(BFO) films. The electrostnctive strain was induced by an applied electric field having repeated ns-width pulses. In addition, we determined piezoelectric constants from diffraction peak shifts.The apparatus receives a pulse pattern formed by a 508 MHz counter using the RF signals as a clock of the Spring-8 storage ring and applies a pulse electric field to a sample. We use … More d the pulse pattern as a trigger ; accordingly the applied electric fields were synchronized with incident x-rays.A sample was a 750 nm-thick PZT film epitaxially grown on a SrRuO_3 thin film using metal organic chemical vapor deposition. Upper Pt electrodes with a diameter of 100 μm were arrayed in a lattice. One prober touched an upper electiode Pt incident x-rays hit, while the other touched another upper electrode. We aligned a polar direction in the PZT film using an applied voltage of 30 V in advance ; consequently, polarization(+Pr) remamed. We made a Θ-2Θ scan around the PZT 004 Bragg angle and recorded a diffraction- intensity profile as a function of time at each combination of Θ and 2Θ angle using an avalanche photo diode detector for a fixed voltage of 0, 10, 20 30 40 50, 55, 60, 70, and 75 V, respectively. The unipolar-rectangular-shape pulse width of 200 ns was repeatedly applied with a period of 800 ns. Measured time used at each angle was 100 s. An incident slit size used was 15×15μm.We observed that the 004 main peaks were shifted toward the lower angle only when the applied field was on. This indicates that the(004) lattice-plane spacing along the surface normal was lengthened because of electrostriction. The pulse electric-field induced strain Δd / d estimated from the main peak shift for 50 V was 0.0004 ; correspondingly, piezoelectric constant d_<33> was 13 pm / V. Furthermore, our finding is that the other peak appeared at a lower angle. d_<33> obtained from the other peak shift is ca. 50 pm / V. This value almost corresponds to that obtained using AFM measurements.We also applied the time-resolved diffraction method to characterizing a polycrystalline BFO thin film. The applied voltages were 0, 3, 5, 8, 10, 11, and 12 V with a 150 ns width and a 804 ns periodicity. Obtained d_<33> values for the(001) and(110) domain were 27.8 and 26.4 pm / V, respectively. Less