GB/T 40066-2021Nanotechnologies—Thickness measurement of graphene oxide—Atomic Force Microscopy (AFM) (English PDF)

3.1 Graphene oxide; GO

The chemically modified graphene obtained after oxidation and exfoliation of graphite has a base plane that has been strongly oxidized.

Note: Graphene oxide is a single-layer material with high oxygen content, usually characterized by the carbon-oxygen atomic ratio (related to the synthesis method, generally about 2.0). [GB/T 30544.13-2018, definition 3.1.2.13]

4.1 Principle

Lay the graphene oxide sample flat on the substrate, use AFM to characterize the surface morphology of the graphene oxide and the substrate, and then use the software to perform The line background is subtracted to obtain the contour line, and the height difference between the upper step and the lower step is measured, which is the thickness of the graphene oxide sample. Calculated height The poor methods are divided into 4.2 and 4.3.

4.2 Calculation Method One

The coordinates of each point of the upper and lower steps in the contour line are linearly fitted by the least square method, and two fitted straight lines (see Figure 1) and the pair are obtained. The corresponding fitting parameters a1, b1, a2, b2.Calculate the height difference H of the upper and lower steps by formula (1), which is the difference between the upper straight line and the lower straight line at point xT distance.

4.3 Calculation Method Two

The corresponding data on both sides of the steps formed by the graphene oxide and the substrate is converted into a height probability distribution histogram (see Figure 2), using Gaussian simulation The normal distribution curve is obtained together, and the difference of the x-coordinate between the height peaks on both sides is the thickness of the sample, and the thickness value is calculated by formula (2).

Note: The probability distribution histogram of the height data, where the black histogram represents the probability distribution of graphene oxide height, and the blue histogram represents the height of the substrate. The red line is the Gaussian fitting line obtained according to the formula in the figure. The upper and lower x are graphene oxide and the substrate obtained by Gaussian fitting The maximum value of the probability distribution of the height reached, the difference between the two is the sample thickness value.

9.1 Background deduction

Perform the background subtraction operation on the AFM original image of the selected sample (see Appendix A), and the height of the substrate baseline on both sides of the measured area can be obtained. Image with consistent degree (see Figure 3).

B.1 Experiment content

Example 2 of graphene oxide thickness measurement.

B.2 Sample preparation

Refer to A.2, A.3, A.4, A.5 for sample preparation, measurement steps, background subtraction, and contour selection process.

B.3 Data processing

Use the software analysis function to convert the height data on both sides of each selected step (base and sample) into height probability distributions. Rectangular graph, Gaussian fitting to get the maximum value of the probability distribution of the height of the base and the sample. Refer to the description of the analysis software used for specific processing methods. Recommended software Igor, Origin, Excel, etc.

Take the Igor software as an example, select the Histogram option in the Analysis menu bar, manually select Sourcewave and the corresponding outputwave; then set bins related parameters according to the data in Sourcewave, including the number of bins, the starting value of bins, and The width of the bin. The width of the bin is determined by the number of data in Sourcewave. Generally, the less the data, the smaller the bin value, so It can ensure the measurement of the thickness of a small area sample. The specific operations are as follows.

a) Import the base and sample height data respectively, see Figure B.1;

b) The height probability distribution analysis is shown in Figure B.2;

c) The height probability distribution fitting is shown in Figure B.3.