Ac240tm

All of the characterizations were conducted by the commercial scanning probe microscopy (MFP-3D, Asylum Research, USA). Both the surface morphology and stiffness images were carried out by AM-FM experiments in tapping mode using a tip (AC240TM, Olympus, Japan) with a force constant of 2 N·m⁻¹ and a resonance frequency of 70 kHz. Especially, the second eigenmode resonance frequency of the tip is 399.95 kHz. Before all characterization, the stiffness and inverse optical lever sensitivity of the cantilever were calibrated using Sader and thermal noise methods.
KPFM experiments were performed in tapping mode using a conductive probe (AC240TM, Olympus, Japan) with a force constant of 2 N·m⁻¹ and a resonance frequency of 70 kHz. During the KPFM scanning process, an AC voltage V_AC = 3 V was applied to the tip and the tip was lifted up 40 nm from the sample surface. Furthermore, in order to eliminate the affection of contaminants on surface potential, the sample was rinsed by acetone and deionized water three times before KPFM characterization. Other scanning parameters were also optimized for high quality images. All KPFM measurements were conducted under ambient environment.

The formed nanofiber mats of different PVDF/TPU blends ratios were analyzed using an atomic force microscopy (AFM) system MFP-3D (Asylum Research, High Wycombe, UK) with a single-frequency piezoresponse force microscope (PFM) contact mode at the Center of Advanced Materials (CAM), Qatar University, Doha, Qatar. In this characterization, the mechanical surface deformation had been measured under applied electric voltages. To excite the sample with the electric signal, a conductive tip with platinum-deposited cantilever AC240TM (Olympus, Tokyo, Japan) had been used. The tip, of 2 N/m spring constant and 70 kHz resonance frequency, was first calibrated using thermal GetRealTM mode to obtain an exact value of the spring constant and accurately convert the raw signal in (V) to picometer (pm) with applying voltage range from 1 V up to 10 V, and the subsequent surface roughness amplitude response was recorded and evaluated using Igor Pro 6.37 software (Wave Metrics, Portland, OR, USA).

First, Si probe was prepared by mechanically removing the Platinum (Pt) layer of the conductive probe (AC240TM from Olympus). More specifically, the probe was scanned on a sapphire film with a contact force of 600 nN for three cycles. The morphology of Si probe was characterized by Hitachi SU8020 with an acceleration voltage of 7 kV. Then a standardized focused ion beam (FIB) method was used to etch the channel region of the NTT (FEI Helios 600I), so that the cross-sectional view of the NTT can be characterized as shown in Supplementary Fig. 12. The measurement platform for the NTT was conducted in an MFP-3D AFM from Asylum Research at ambient environment with the relative humidity of 20–30%. In contact mode, the sensitivity of optical lever and spring constant of the cantilever are 197 nm V⁻¹ and 0.9 N m⁻¹, respectively. And the deflection of cantilever was set to be 0.005 V. Thus, the contact force was controlled as 1 nN during the process of nanoscale triboelectrification. The synchronous I_d–V_d output characteristics of the NTT were performed by using a Keithley 4200 A semiconductor characterization system. And the transfer characteristics were measured by using an SR570 low-noise current amplifier (Stanford Research System) and a programmable DC power supply (RIGOL DP832).