Electron Transfer in Nanoscale Contact Electrification: Effect of Temperature in the Metal–Dielectric Case

Abstract

The phenomenon of contact electrification (CE) has been known for thousands of years, but the nature of the charge carriers and their transfer mechanisms are still under debate. Here, the CE and triboelectric charging process are studied for a metal–dielectric case at different thermal conditions by using atomic force microscopy and Kelvin probe force microscopy. The charge transfer process at the nanoscale is found to follow the modified thermionic‐emission model. In particular, the focus here is on the effect of a temperature difference between two contacting materials on the CE. It is revealed that hotter solids tend to receive positive triboelectric charges, while cooler solids tend to be negatively charged, which suggests that the temperature‐difference‐induced charge transfer can be attributed to the thermionic‐emission effect, in which the electrons are thermally excited and transfer from a hotter surface to a cooler one. Further, a thermionic‐emission band‐structure model is proposed to describe the electron transfer between two solids at different temperatures. The findings also suggest that CE can occur between two identical materials owing to the existence of a local temperature difference arising from the nanoscale rubbing of surfaces with different curvatures/roughness.

The Overlapped Electron‐Cloud Model for Electron Transfer in Contact Electrification

“…The OEC model was further tested when a temperature difference was established between the tip and sample. In the experiments, the sample temperature was maintained at 313 K and tip temperature were varied from 313 to 433 K (the details for the temperature control were described in our previous studies) . The effects of the temperature difference on the phase shift of the tapping tip are shown in Figure S3 (Supporting Information).…”

“…The conductive tip used here was Multi75E‐G (BudgetSensors, Bulgaria; Pt‐coated; tip radius: 25 nm; spring constant: 3 Nm −1 ). In the temperature effect experiments, the sample temperature and the tip temperature were controlled by the sample heater and the tip heater, respectively (the details of the temperature experiments were described somewhere else) . In the tapping mode charging experiments, the interaction region between the tip and sample was controlled by setting the free amplitude and set tapping amplitude of the tip in the scanning.…”

“…When an insulator is involved, the charge carriers are suspected to be ions, since there are no free electrons on the insulator surface . However, recent studies about temperature effect and photon excitation effect revealed that the charge carriers in metal‐insulator and dielectric‐dielectric CE are also electrons. Based on these experimental results, an overlapped electron‐cloud (OEC) model is proposed to explain the electron transfer for all types of CE phenomena for general materials, including insulators .…”

“…In fact, external stimuli are often applied at the interface of two contact solids to control the CE. For example, a temperature difference and/or an electric field at the interface of two materials were demonstrated can affect the CE significantly. These two stimuli were both suggested to affect the CE by changing the energy of the electrons trapped in the surface states of the materials.…”

Unraveling Temperature‐Dependent Contact Electrification between Sliding‐Mode Triboelectric Pairs

“…Also, although the Q SC rapidly decayed at higher test temperatures for the contact–separation mode Ti–SiO 2 TENGs, the sliding mode TENG was capable of generating even a small amount of transferred charge (0.05 nC) before decay took over at the highest tested temperature (563 K). In addition to Q SC , surface charge density is also a satisfactory variable in investigating temperature effects on TENGs, and a recent study using and tapping mode AFM has found that triboelectric charge decay follows the thermionic emission model at nanoscale . It would be of great interest to continue this line of research by using contact scanning mode AFM to mirror a sliding mode TENG.…”