论文标题
一种简单的基于KPFM的无静电地形测量方法：SIO $ _2 $的MOS $ _2 $的情况
A simple KPFM-based approach for electrostatic-free topographic measurements: the case of MoS$_2$ on SiO$_2$
论文作者
论文摘要
据报道，开尔文探针力显微镜的简单实现，即在没有静电力的任何组件的情况下，可以录制地形图像。我们的方法基于在数据立方体模式下操作的近环Z-光谱镜检查。尖端样本距离随时间的函数的曲线记录到2D网格上。专用电路持有KPFM补偿偏置，随后在光谱采集中定义明确的时间窗口中切断了调制电压。地形图像是从光谱曲线的矩阵重新计算的。这种方法应用于通过化学蒸气沉积在氧化硅底物上生长的过渡金属二盐元素（TMD）单层。此外，我们还可以通过录制一系列图像来进行适当的堆叠高度估计，以减少偏置调制幅度的值。两种方法的输出均显示完全一致。结果说明了在超高真空下非接触式AFM的工作条件下，由于tip表面电容呈梯度的变化，即使KPFM控制器无效，因此由于尖端表面电容呈梯度的变化，堆叠的高度值也可以显着高估。我们表明，只有在使用调制偏置幅度降低以其严格的最小值或甚至更好的情况下，没有任何调制偏置，就可以安全地评估TMD的原子层数量。最后，光谱数据表明，与非对静电景观相比，TMD/氧化物界面处的缺陷可能对静电景观产生反直觉影响，从而导致常规的NC-AFM/KPFM显然降低了测量的堆叠高度。因此，事实证明，无静电Z成像是评估在氧化物上生长的原子薄的TMD层缺陷的有前途的工具
A simple implementation of Kelvin probe force microscopy is reported that enables recording topographic images in the absence of any component of the electrostatic force. Our approach is based on a close loop z-spectroscopy operated in data cube mode. Curves of the tip-sample distance as a function of time are recorded onto a 2D grid. A dedicated circuit holds the KPFM compensation bias and subsequently cut off the modulation voltage during well-defined time-windows within the spectroscopic acquisition. Topographic images are recalculated from the matrix of spectroscopic curves. This approach is applied to the case of transition metal dichalcogenides (TMD) monolayers grown by chemical vapour deposition on silicon oxide substrates. In addition, we check to what extent a proper stacking height estimation can also be performed by recording series of images for decreasing values of the bias modulation amplitude. The outputs of both approaches are shown to be fully consistent. The results exemplify how in the operating conditions of non-contact AFM under ultra-high vacuum, the stacking height values can dramatically be overestimated due to variations in the tip-surface capacitive gradient, even though the KPFM controller nullifies the potential difference. We show that the number of atomic layers of a TMD can be safely assessed, only if the KPFM measurement is performed with a modulated bias amplitude reduced at its strict minimum or, even better, without any modulated bias. Last, the spectroscopic data reveal that defects at the TMD/oxide interface can have a counterintuitive impact on the electrostatic landscape, resulting in an apparent decrease of the measured stacking height by conventional nc-AFM/KPFM compared to non-defective sample areas. Hence, electrostatic free z-imaging proves to be a promising tool to assess the existence of defects in atomically thin TMD layers grown on oxides
