The results show that CFTRinh-172 HAM-KPFM can get much higher spatial resolution and potential sensitivity even with a smaller V AC than that of FM-KPFM. The higher potential sensitivity of HAM-KPFM was explained as follows: the oscillation of the frequency shift at ω 1 in FM-KPFM and the oscillation of the amplitude at ω 2 in HAM-KPFM are both proportional to the gradient of the electrostatic force, whereas the quality

factor in UHV for the AFM system is approximately several tens of thousands greater, and learn more finally, that the minimum detectable electrostatic force in HAM-KPFM is smaller than in FM-KPFM according to Equations (1) and (2). Hence, the potential sensitivity in HAM-KPFM is higher than that in FM-KPFM. Further, lower crosstalk between topography and potential images in HAM-KPFM compared to that in FM-KPFM is due to the first and second resonance signals being separated from each other using low- and high-pass

filters in HAM-KPFM; on the other hand, the potential and topography signals are difficult to separate because the first resonance of the cantilever was oscillated in both measurements. In HAM-KPFM measurements, the high V AC effect was apparently removed because small BAY 63-2521 mw AC bias voltages were applied and the V CPD which compensated the CPD between tip and sample is 20 to 100 mV [11, 12], and this is of major importance for semiconducting samples for which voltages exceeding 100 mV may induce the band bending effect [21]. In some references, quasi-constant height mode was performed to eliminate the V AC influence

to the potential measurement [4]. Conclusions In summary, the potential sensitivity and crosstalk were compared in FM- and HAM-KPFM experimentally and theoretically. We demonstrated that the potential sensitivity in HAM-KPFM is higher than that in FM-KPFM theoretically. Then, we experimentally confirmed that SNRs of electrostatic force measurements, which determined the potential sensitivity in HAM-KPFM, are higher than that of FM-KPFM. Further, we applied the FM- and HAM-KPFM measurements to a Ge (001) surface under the same conditions, and atomic resolution in potential and topography images were obtained in HAM-KPFM, Dichloromethane dehalogenase whereas the atomic resolution was not visible in FM-KPFM. We attribute this to the higher sensitivity and lower crosstalk in HAM-KPFM compared to the FM-KPFM. Consequently, the HAM method proposed here is a useful tool for detecting the actual potential distribution on the surface. Acknowledgements This work was partially supported by the National Natural Science Foundation of China (NSFC) under grant no. 61274103, 91336110 and Grant-in-Aid for Scientific Research from the Japan Society of the Promotion of Science (JSPS). References 1. Nonnenmacher M, O’Boyle MP, Wickramasinghe HK: Kelvin probe force microscopy. Appl Phys Lett 1991, 58:2921–2923.CrossRef 2.