Imaging Ferroelectric Domains and Domain Walls Using Charge Gradient Microscopy: Role of Screening Charges
Imaging Ferroelectric Domains and Domain Walls Using Charge Gradient Microscopy: Role of Screening Charges
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DOI：
10.1021/acsnano.5b07551
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发表时间：
2016-02-01
期刊：
影响因子：
17.1
通讯作者：
Roelofs, Andreas
中科院分区：
文献类型：
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作者：
Tong, Sheng;Jung, Il Woong;Roelofs, Andreas
先进的扫描探针显微镜(SPM)为利用磁区和磁区壁作为有源元件的下一代铁性器件开辟了可能性。然而，目前的SPM缺乏结合屏蔽电荷的传输来动态监测磁区和磁区壁的运动的能力，从而降低了磁区和磁区壁的总静电能量。电荷梯度显微镜(CGM)是克服这些缺点的有力候选者，因为它可以高速地映射磁区和磁区壁，并机械地去除屏蔽电荷。然而，由于静电相互作用的复杂性，CGM信号的潜在机制还没有完全被理解。在这里，我们设计了一种半导体金属CGM针尖，它可以通过简单地改变扫描方向来分离和量化铁电畴和畴壁信号。我们的研究表明，磁区壁信号是由于极化电荷的空间变化引起的，而磁区信号则是由于CGM尖端的屏蔽电荷的持续移除和供应。此外，我们还观察到来自上下磁区的不对称的CGM磁畴电流，这是由于正负束缚电荷的脱键能和屏蔽电荷量的不同所致。我们相信，我们的发现可以帮助设计具有高空间分辨率的CGM，并导致信息存储和能量收集设备的突破。
Advanced scanning probe microscopies (SPMs) open up the possibilities of the next-generation ferroic devices that utilize both domains and domain walls as active elements. However, current SPMs lack the capability of dynamically monitoring the motion of domains and domain walls in conjunction with the transport of the screening charges that lower the total electrostatic energy of both domains and domain walls. Charge gradient microscopy (CGM) is a strong candidate to overcome these shortcomings because it can map domains and domain walls at high speed and mechanically remove the screening charges. Yet the underlying mechanism of the CGM signals is not fully understood due to the complexity of the electrostatic interactions. Here, we designed a semiconductor metal CGM tip, which can separate and quantify the ferroelectric domain and domain wall signals by simply changing its scanning direction. Our investigation reveals that the domain wall signals are due to the spatial change of polarization charges, while the domain signals are due to continuous removal and supply of screening charges at the CGM tip. In addition, we observed asymmetric CGM domain currents from the up and down domains, which are originated from the different debonding energies and the amount of the screening charges on positive and negative bound charges. We believe that our findings can help design CGM with high spatial resolution and lead to breakthroughs in information storage and energy-harvesting devices.