Nanoscale static voltage generation and its surface potential decay using scanning probe microscopy

Abstract

This work aims at the manipulation of nanoscopic voltage produced through uniform and non-uniform rubbing in neat unpolarised polymer polyvinylidene fluoride. A metal-insulator configuration is considered for the analysis. The decay of surface potential in such a configuration is also addressed in this work. The polarity of the voltage observed on the film depends on the work function of the metal electrode in contact as well as the electronegativity of polymeric material under study. Scanning probe microscopic techniques such as dynamic contact mode electrostatic force microscopy, scanning tunnelling microscopy are used for the investigation of specific electrostatic potential variation on polymer films. Effect of contact electrification leads to nanoscopic domains of voltage generation on the surface of the tribolayers. Electrostatic potential developed on the surface of unrubbed polymer film using modulated tip is in the range of 20-40 mV. The range of voltage generated increased from 20 to 125 mV in the case of rubbed polymer films. Charge retention is discussed through obtaining surface potential decay trend at various intervals. This also plays an important role in the generation of the voltage as well as the current. The above scenario has been demonstrated in both rubbed and unrubbed scenarios. Charge decay is observed to be gradually decreasing from 40 to 29.5 mV in unrubbed surface and 125 to 14 mV in rubbed surface for various time intervals. The obtained results suggest insignificance of triboelectric series on contact electrification between similar tribolayers.

α- & β-crystalline phases in polyvinylidene fluoride as tribo-piezo active layer for nanoenergy harvester

“…A positive gradient is observed due to the work function difference between the PVDF films and gold tip in EFM. 18 The EFM amplitude image after tapping shows a reduction in voltage gradient (to 10–20 mV) at films 1 and 2 indicated by colour contrast in Figure 4(b) (tapped PVDF films 1 and 2). This reduction is expected from the charge transfer occurring between the interfaces of films during the tapping process.…”

“…The dried electrodes were then used for spin coating using a spin coater SPIN 150 (APT GmBH, Am Klaepenberg) at 2000 r/min for 30 s. The thickness of our samples was optimized at various r/min for our previous work. 18 The thus coated samples of 1.5 µm thickness were post-baked at 160°C for 15 min to remove excess solvents in the film.…”

“…Electrical characterization of materials at nano regime is significant when mechanisms such as piezoelectric effect, triboelectric effect as well as ferroelectric effect are considered. Dynamic contact electrostatic force microscopy can be employed as an efficient technique to study the triboelectric, 18 ferroelectric as well as piezoelectric nature 19,20 of the films used in the nanoenergy harvester. Density functional theory (DFT) was carried out to explain the mechanism related to contact electrification from crystalline phases of PVDF material.…”