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首页> 外文期刊>Nanotechnology >On the relevance of the atomic-scale contact potential difference by mplitude-modulation and frequency-modulation Kelvin probe force microscopy
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On the relevance of the atomic-scale contact potential difference by mplitude-modulation and frequency-modulation Kelvin probe force microscopy

机译：振幅调制和频率开尔文探针力显微镜对原子级接触电势差的相关性

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The influence of short-range electrostatic forces on the measured local contact potential difference (CPD) by means of amplitude-modulation and frequency-modulation Kelvin probe force microscopy (AM- and FM-KPFM) is discussed on the base of numerical and analytical descriptions of both methods. The goal of this work is to help in interpreting recent experimental results reporting atomically resolved CPD images, in particular on bulk insulating samples. The discussion is carried out on the basis of spectroscopic curves. The expression of the bias-dependent electrostatic force is derived from a previous work and is estimated between a tip with simple geometry and the (001) facet of a perfect alkali halide single crystal. The force, with a short-range character, scales as a second-order polynomial function of the bias voltage. It is stated that the linear term is responsible for the occurrence of the atomic-scale CPD contrast, while the quadratic one, involving the sample polarization, accounts for the detected signal by the KPF methods. Nevertheless, analytical and numerical approaches stress the influence of the linear term on the measured CPD which intrinsically hinders the possibility to perform quantitative CPD measurements, but also makes the measured pseudo-CPD strongly deviating from the surface potential. Hence, in the short-range regime, AM- or FM-KPFM measurements neither reflect the CPD nor the local surface potential, but rather an effective value which is convoluted by the geometric parameters of the tip, the so-called local CPD. It is also stated that the local CPD measured by means of AM- or FM-KPFM differs when sub-nanometer vibration amplitudes of the cantilever are used. Otherwise, AM- and FM-KPFM easurements should be almost similar. At last, the influence of long-range, capacitive, lectrostatic forces is discussed in conjunction with the short-range ones. This allows us to draw conclusions regarding the distance dependence of the local CPD which then exhibits a resonant behavior as a function of the tip–surface separation. This phenomenon is expected to play a role in the KPFM imaging process.
机译：在数值和分析描述的基础上，讨论了短程静电力对通过振幅调制和频率调制的开尔文探针力显微镜（AM-和FM-KPFM）测量的局部接触电势差（CPD）的影响。这两种方法。这项工作的目的是帮助解释报告原子分辨CPD图像的最新实验结果，特别是在散装绝缘样品上。讨论是在光谱曲线的基础上进行的。取决于偏压的静电力的表达式是从先前的工作中得出的，并且是在具有简单几何形状的尖端与完美的碱金属卤化物单晶的（001）晶面之间进行估算的。具有短程特性的力按比例缩放为偏置电压的二阶多项式函数。据指出，线性项是导致原子级CPD对比发生的原因，而涉及样品极化的二次项则是通过KPF方法解释检测到的信号的原因。然而，分析和数值方法强调了线性项对被测CPD的影响，这固有地阻碍了进行定量CPD测量的可能性，但也使得被测伪CPD严重偏离表面电势。因此，在短距离范围内，AM或FM-KPFM测量既不反映CPD也不反映局部表面电势，而是反映了由尖端几何参数（即所谓的局部CPD）所盘绕的有效值。还指出，当使用悬臂的亚纳米振动幅度时，通过AM-或FM-KPFM测量的局部CPD是不同的。否则，AM和FM-KPFM的要求应该几乎相似。最后，结合短距离的影响，讨论了远距离的，电容性的，静电力的影响。这使我们可以得出有关局部CPD距离依赖性的结论，然后，该距离随尖端-表面间距的变化而表现出共振行为。预计该现象将在KPFM成像过程中起作用。

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