KPFM Study on the Charge Sign Reversal during Nanoscale Triboelectric Charging Induced by a Worn Tip and Sample Pretreatment

Triboelectric charging is a sophisticated process; sometimes a charge sign reversal occurs due to a slight change in the property of the contact surfaces. Here, nanoscale triboelectric charging between an atomic force microscopy (AFM) tip and an SiO2 surface is performed in situ using a combination of contact-mode AFM and Kelvin probe force microscopy. It is revealed that the triboelectric charging process is enhanced by the increasing applied force at the tip-sample interface, while a larger force could result in tip damage and sample deformation. Subsequently, nanoscale triboelectric charging between the pretreated SiO2 surface and original/damaged tip is systematically investigated. The results show that the ethanol/acetone-rinsed SiO2 surface obtains negative charges on triboelectric charging with the original tip, while it gains positive charges when the tip is damaged. In addition, the ethanol/acetone ultrasonication process could further enhance the charge transfer at the tip-sample interface. As a comparison, the untreated sample always obtains negative charges no matter triboelectric charging with the damaged or original tip. A surface state model is proposed to explain the mechanism for the charge transfer at the tip-sample interface. These findings could facilitate the understanding of triboelectric charge sign reversal upon modification of contact surfaces.

Automated summary

Triboelectric charging is a complex process where the charge sign may reverse due to slight changes in contact surface properties. Experimental results show that increasing applied force at the tip-sample interface enhances the charge transfer process, but excessive force can lead to tip damage and sample deformation. Ethanol/acetone rinsed SiO2 surfaces acquire negative charges when in contact with an original tip, while damaged tips result in positive charges. Additionally, ultrasonication can further enhance charge transfer at the tip-sample interface.