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）观察了醋酸盐和三氟乙酸盐阴离子混合单层膜。得到的接触电位差（CPD）图显示了分子上的CPD变化。这种纳米尺度的对比在CPD图中不受悬臂振荡频率、悬臂振荡幅度以及在尖端和样品之间流动的隧道电流的扰动。结果表明，KPFM在纳米尺度上的CPD对比显示了真实的表面电位。研究发现，控制悬臂振荡幅度和研究样品表面的尖端诱导电荷是进一步精确CPD分析的必要条件。

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.