Nanoscope 5 controller

The size distribution of the GO flakes was measured by atomic force microscopy (AFM) on a Multimode 8 microscope with a Nano Scope 5 controller with peakforce tapping (Bruker, MA, USA). The GO dispersion (10 µg mL⁻¹) was dropped onto a clean mica surface and dried in a desiccator overnight at room temperature. Then the GO flakes were measured using a silicon tip (tapping mode) with nominal resonance frequency of 320 kHz and nominal force constant of 42 N m⁻¹. Thermogravimetric analysis (TGA) was performed for the GO on a STA 449F3 Jupiter@ instrument (NETSCH, Deutschland, Germany), employing a heating rate of 110 °C mim⁻¹ (from 25 to 750 °C) with a synthetic air flow of 50 mL min⁻¹. X-ray diffraction analysis (XRD) to structurally characterise the GO was performed on an Advanced Eco D8 XDR instrument (Bruker, MA, USA), using a Cu Kα1 radiation (λ: 1.5406 Å) at 40 kV in the range of 2θ = 5–90°. For surface chemistry analysis, the GO was characterised using attenuated total reflection Fourier infrared spectroscopy (ATR-FTIR, Nicolet^™, Thermo Scientific, MA, USA); and X-ray photoelectron spectroscopy (XPS, K-alpha, Thermo Scientific, MA, USA), applying a pass energy of 200 eV and 50 eV to obtain the survey and high-resolution spectra, respectively. Raman confocal spectroscopy was employed for structural defects characterisation in GO with laser 532 nm (Horiba^®, Kyoto, Japan).

Quantitative nanomechanical analysis of the samples was conducted using a MultiMode 8 with a NanoScope V controller equipped with a J-type scanner (Bruker, Billerica, MA, USA), using the PeakForce QNM mode. PFQNM is based on the Peak Force Tapping mode, wherein the material property mapping is based on the individual force vs. the separation curves obtained from each tap (Figure 1a) [41 (link)]. Each force curve represents a deflection of the probe lever relative to the change in the z-axis piezo position (Figure 1b). The shift in deflection is caused by differences in the interaction between the tip and the sample surface. The force curve is logged for each map pixel of the scanned image, which provides the mapping of all the investigated properties in a single scan line.
Each scan was performed with a 1 Hz rate and a scan size of 512 × 512 points, which is equivalent to a 262,144 force vs. separation curves. For each of the tested samples, scans of three noncontiguous areas of 10 × 10 μm were collected. Measurements were conducted at room temperature and 40% relative humidity. The z-range was set on 300 nm.