# AFM Characterization of Track-Etched Membranes:
## 5 Experimental Results and Discussion  
When studying samples by the AFM method, it is necessary to select the optimal scanning modes to avoid the appearance of various artifacts (blurring, noise) (Figure 3). As the scanning statistics show, such artifacts arise when the feedback coefficient is incorrectly selected, the probe is too close to the samples, and the scanning speed is too high. Figure 3: AFM images of the same section of the TM and of a single pore (inset) with non-optimal scanning parameters (**a**) and with optimal scanning parameters (**b**). To obtain information on the distributions of the pores parameters, the scanning scale of 20 \(\times\) 20 \(\upmu\)m was used, with a step size of \(\sim\)78 nm (resolution 256 \(\times\) 256 points) and a scanning frequency of 0.5 Hz. The optimum scanning parameters were found to avoid undesirable artifacts in AFM images like blurring and noise (see Figure 3a). When the parameters of single pores were investigated, the measurements were carried out using a smaller scan scale (from 5 to 10 \(\upmu\)m) with the resolution of 512 \(\times\) 512 points, with the same scanning frequency. To determine the positions of the centers \(\{X_{c}\), \(Y_{c}\}\) and diameters \(D\) of the pores on the AFM images, we used a special software, which works in a semi-automatic mode by approximation of measured pores profiles with 2D-Gaussian (Figure 4a). Figure 4b shows the distribution of the measured pore diameters \(P_{\text{D}}\) and marks the range of \"true\" pore diameters (green area in the center), i.e., pores that are not considered defective according to their deviation from the mean value. Moreover, this criterion made it possible to exclude defective pores if the distance between their centers was comparable to their sizes. Such pores are indicated in Figure 4a by the white square in their centers. The results obtained for PP TM are shown in Figure 5a-d. The images of 1951 pores were analyzed. The average value of the pore diameter was approximately 182.6 nm (at RMS about 66 nm). We determined that 16% of the pores were defective. Further, the data for the remaining 1641 pores were analyzed. The average value of the minimum distance between PP pores was approximately 697.9 nm. The average pore density was around 0.6 \(\times\) 10\({}^{8}\) pores/cm\({}^{2}\). Similar measurements were performed for PETP- and PC-based TM. The obtained pore parameters are shown in Table 1. The results obtained for PETP are shown in Figure 5e-h, and those for PC are shown in Figure 5i-l.  
Figure 4: AFM image of the surface of a PETP TM with marked positions (squares) and calculated pore sizes (dashes) (**a**). Histogram of pore diameters distribution, where the green zone in the center denotes the area of diameters \(D\) for “good” pores, and the red zones at the edges indicate defective pores (**b**). The red line shows the result of approximating the obtained distribution by the Gaussian function (with standard deviation of \(\sigma=215\) nm). The analysis of the AFM images of the TM samples using the developed procedure made it possible to conclude that the pore orientation had no preferred direction and to obtain the characteristic values of pore density. We developed a technique for processing AFM images which can also be used for processing images obtained by the SEM method. An important advantage of the AFM technique over the SEM method is the ability to obtain three-dimensional data and the