Identification of the origin of nanoscale image contrast in contact potential difference maps given by a Kelvin probe force microscope

用开尔文探针力显微镜(KPFM)观察了醋酸根和三氟乙酸根的混合单分子膜。得到的接触电势差(CPD)图显示了分子上接触电势的变化。CPD图中这种纳米尺度的对比度与悬臂振荡频率、悬臂振荡幅度和针尖与样品之间的隧穿电流的扰动无关。结果表明，KPFM的纳米级CPD对比度具有真实的表面电势。研究发现，悬臂梁振动幅度的控制和样品表面针尖感应电荷的研究对于进一步精确的CPD分析是必要的。

Mixed monolayers of acetate and trifluoroacetate anions were examined by a Kelvin probe force microscope(KPFM). Obtained contact potential difference(CPD) maps showed the CPD change on the molecules. Such nanometer scale contrast in the CPD map was independent of the perturbation of cantilever oscillation frequency, cantilever oscillation amplitude, and tunneling current flowing between the tip and sample. The results proved that the nanometer scale CPD contrast by the KPFM shows true surface potential. It was found that the control of the cantilever oscillation amplitude and the investigation of tip-induced charges on the sample surface are necessary for further precise CPD analysis.