Department of Applied Physics, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
Nanotechnology. 2013 Jun 7;24(22):225701. doi: 10.1088/0957-4484/24/22/225701. Epub 2013 Apr 30.
The effect of stray capacitance on potential measurements was investigated using Kelvin probe force microscopy (KPFM) at room temperature under ultra-high vacuum (UHV). The stray capacitance effect was explored in three modes, including frequency modulation (FM), amplitude modulation (AM) and heterodyne amplitude modulation (heterodyne AM). We showed theoretically that the distance-dependence of the modulated electrostatic force in AM-KPFM is significantly weaker than in FM- and heterodyne AM-KPFMs and that the stray capacitance of the cantilever, which seriously influences the potential measurements in AM-KPFM, was almost completely eliminated in FM- and heterodyne AM-KPFMs. We experimentally confirmed that the contact potential difference (CPD) in AM-KPFM, which compensates the electrostatic force between the tip and the surface, was significantly larger than in FM- and heterodyne AM-KPFMs due to the stray capacitance effect. We also compared the atomic scale corrugations in the local contact potential difference (LCPD) among the three modes on the surface of Si(111)-7 × 7 finding that the LCPD corrugation in AM-KPFM was significantly weaker than in FM- and heterodyne AM-KPFMs under low AC bias voltage conditions. The very weak LCPD corrugation in AM-KPFM was attributed to the artefact induced by topographic feedback.
在室温下的超高真空 (UHV) 环境中，使用开尔文探针力显微镜 (KPFM) 研究了杂散电容对电位测量的影响。在三种模式下探索了杂散电容效应，包括调频 (FM)、调幅 (AM) 和外差调幅 (heterodyne AM)。我们从理论上表明，在 AM-KPFM 中，调制静电力的距离依赖性明显弱于 FM 和外差 AM-KPFM，并且严重影响 AM-KPFM 中电位测量的悬臂杂散电容在 FM 和外差 AM-KPFM 中几乎完全消除。我们通过实验证实，由于杂散电容的影响，在 AM-KPFM 中补偿尖端和表面之间的静电力的接触电位差 (CPD) 明显大于 FM 和外差 AM-KPFM。我们还比较了三种模式下 Si(111)-7×7 表面的局部接触电位差 (LCPD) 的原子级起伏，发现 AM-KPFM 中的 LCPD 起伏在低交流偏压条件下明显弱于 FM 和外差 AM-KPFM。AM-KPFM 中非常弱的 LCPD 起伏归因于形貌反馈引起的伪影。
