**4. Nanolithography on various substrates**

In some reported experiments, a commercial scanning probe microscope (Solver P47H, NT-MDT Company), operated in AFM contact and noncontact modes, equipped with (NSG11) and (DCP20) cantilevers were used to perform the lithography of desired surfaces (Sadegh Hassani et al., 2008a; 2008b; 2010). The NSG11 cantilever made of silicon nitride had a rectangular shape, and its length, width and thickness were 100 ± 15 m, 35 ± 3 µm and 1.7– 2.3 m, respectively. Its normal bending constant measured by supplier was 11.5 nN/nm. Another cantilever which was used in this process was DCP20 Cantilever made of diamond with the length, width and thickness of 90±5m, 60±3m and 1.7-2.3m, respectively. The normal bending constant measured by supplier was 48 nN/nm.

These two types of cantilever were selected to reach deformation of different types of surfaces and also for obtaining good images of scratches. These experiments were designed to fabricate scratches on the various surfaces with the different rigidity.

The lithography process was executed with the use of lithography menu supported by the microscope software. The AFM tip was brought into contact with the sample surface using the smallest force possible to minimize any undesired surface modification. An image of surface was prepared in order to choose a suitable surface free of defects for lithography; then the nanolithography process was executed under various specific and controlled conditions to analyze the effect of lithography important factors on the shape of scratches.

For studying force effect, the force was increased by applying a higher voltage to the piezoscanner in order to reach the cantilever deflection (Z) corresponding to the force (F) range where plastic deformation of polymeric surface occurred. (Santinacci et al., 2003; Notargiacomo et al., 1999; Sadegh Hassani et al., 2008 b). Scratches were made in Y direction on various substrates in different conditions (Sadegh Hassani et al., 2008a; 2008b; 2010), so in this way the influences of applied normal force, scanning velocity, time of applying pressure and number of scratching cycles were investigated. Finally surface was scanned by atomic force microscope in non-contact mode to observe and evaluate the shape and depths of scratches. If the contact mode had been chosen to image the scratches, the surface of substrates would have probably been damaged.

### **4.1 Nanolithography on PMMA thin films**

Sadegh Hassani et al. (2008a; 2008b; 2010) reported lithography performance on PMMA thin films. In this regard, soft thin films of PMMA polymer on the silicon and glass substrates were prepared. For making PMMA (LG-IH830) thin film on silicon and glass substrates, these substrates were washed and sonicated in acetone/ethanol (50-50 % vol.) for 15 minutes at room temperature. Then a very small amount of diluted PMMA/CHCl3 solution was coated over the silicon and glass surfaces using spin coater with 6000 rpm for 30 seconds. The coated substrates were dried in an oven at 130 °C for 30 minutes. The thickness of these coated layers was ~150 nm, measured by atomic force microscope.

Nanolithography Study Using Scanning Probe Microscope 463

substrate topography, the scratch depth may appear smaller by AFM imaging than their

Fig. 3. (a-e) Surface profiles for scratched PMMA film (Sadegh Hassani et al., 2008a) (N= 10 cycles, T=25 ms, V=140 nm/s and F is equal to (a) 2350 nN, (b) 2700 nN, (c) 3050 nN, (d)

actual size (Sadegh Hassani et al., 2008a).

3400 nN and (e) 3510 nN).

In order to choose suitable area for nanolithography process, the topography images and the roughness of the surfaces of PMMA thin films were investigated with the AFM (Sadegh Hassani et al., 2008a). It was reported (Notargiacomo et al., 1999) that "a high value of the surface roughness could produce unwanted features and inhomogeneous results during patterning". At the first step, it was necessary to evaluate the substrate surface after cleaning. In Figure 2 the evolution of the topography images and profiles of the silicon surface after cleaning and PMMA thin films are presented. It is seen that the roughness of PMMA thin film is low and its surface profile is appropriate for lithography. An accurate study was performed on the samples in order to find the optimum patterning conditions for the PMMA film.

Fig. 2. The evolution of the topography images and profiles of (a & b) silicon surface after cleaning and (c & d) PMMA thin film (Sadegh Hassani et al., 2008a).

For PMMA coated on silicon substrate, scratches were performed using the NSG 11 tip. The main factor in pattern formation was the magnitude of the force applied to the sample. The influence of the applied normal force on the scratches created on the PMMA film coated the silicon substrate had been investigated. In Figure 3 (a-e) some of surface profiles of nanoscratches are presented, which are formed with the constant scanning velocity of 140 nm/s, number of scratching cycle of 10 within 25 ms at various forces (2350, 2700, 3050, 3400, and 3510 nN).

These profiles indicate that the increase of applied normal force, leads to the deeper scratches. The scratches are V-shape; however protrusions are visible along some of the scratches indicating the presence of permanent deformation. It was found that the optimum value for applied normal force was about 3050 nN. The scratch made by this force is shown in Figure 4. In Figure 5, the scratch depths are plotted as a function of the applied normal force. As expected, the scratch size increases with increasing the force load. The depth varies from 4 to 32 nm by increasing force load from 1300 to 3510 nN. However, Notargiacomo et al. claimed (1999) that as the applied force increases, curved cuts ("tails") become visible at the ends of the lines. It has to be mentioned that due to the convolution effect of the tip and

In order to choose suitable area for nanolithography process, the topography images and the roughness of the surfaces of PMMA thin films were investigated with the AFM (Sadegh Hassani et al., 2008a). It was reported (Notargiacomo et al., 1999) that "a high value of the surface roughness could produce unwanted features and inhomogeneous results during patterning". At the first step, it was necessary to evaluate the substrate surface after cleaning. In Figure 2 the evolution of the topography images and profiles of the silicon surface after cleaning and PMMA thin films are presented. It is seen that the roughness of PMMA thin film is low and its surface profile is appropriate for lithography. An accurate study was performed on the samples in order to find the optimum patterning conditions for

Fig. 2. The evolution of the topography images and profiles of (a & b) silicon surface after

For PMMA coated on silicon substrate, scratches were performed using the NSG 11 tip. The main factor in pattern formation was the magnitude of the force applied to the sample. The influence of the applied normal force on the scratches created on the PMMA film coated the silicon substrate had been investigated. In Figure 3 (a-e) some of surface profiles of nanoscratches are presented, which are formed with the constant scanning velocity of 140 nm/s, number of scratching cycle of 10 within 25 ms at various forces (2350, 2700, 3050,

These profiles indicate that the increase of applied normal force, leads to the deeper scratches. The scratches are V-shape; however protrusions are visible along some of the scratches indicating the presence of permanent deformation. It was found that the optimum value for applied normal force was about 3050 nN. The scratch made by this force is shown in Figure 4. In Figure 5, the scratch depths are plotted as a function of the applied normal force. As expected, the scratch size increases with increasing the force load. The depth varies from 4 to 32 nm by increasing force load from 1300 to 3510 nN. However, Notargiacomo et al. claimed (1999) that as the applied force increases, curved cuts ("tails") become visible at the ends of the lines. It has to be mentioned that due to the convolution effect of the tip and

cleaning and (c & d) PMMA thin film (Sadegh Hassani et al., 2008a).

the PMMA film.

3400, and 3510 nN).

substrate topography, the scratch depth may appear smaller by AFM imaging than their actual size (Sadegh Hassani et al., 2008a).

Fig. 3. (a-e) Surface profiles for scratched PMMA film (Sadegh Hassani et al., 2008a) (N= 10 cycles, T=25 ms, V=140 nm/s and F is equal to (a) 2350 nN, (b) 2700 nN, (c) 3050 nN, (d) 3400 nN and (e) 3510 nN).

Nanolithography Study Using Scanning Probe Microscope 465

Fig. 6. Dependence of scratches depth, created on PMMA/glass (Sadegh Hassani et al., 2010), with the applied normal force while scanning velocity, number of scratching cycle

Fig. 7. Topography image of the scratch created on PMMA/glass (Sadegh Hassani et al., 2010), while the applied normal force, scanning velocity, number of scratching cycle and

The influence of the number of scratching cycles was also investigated by scratching experiments. In Figure 8 dependence of the scratch depth to the number of cycles (N = 1, 5, 10, 15, 20, 25, and 30) in a constant applied normal force of 2350nN, scanning velocity of 140 nm/s in 25 ms is presented. This figure shows that the depth varies from 4 to 30 nm by increasing the number of cycles. As expected, the depths of scratches increase with N linearly. This linear relationship between depth and number of cycles confirms layer-by-layer removal mechanism (Sadegh Hassani et al., 2008a). This result is in agreement with that of obtained by Santinacci

time of applying pressure were 3000 nN, 140 nm/s, 10 and 25 ms, respectively.

and coworkers (2003) for performing nanolithography on p-Si (100) substrate.

and time of applying pressure were 140 nm/s, 10 and 25 ms, respectively.

Fig. 4. Topography images of the scratch performed on the PMMA /silicon (Sadegh Hassani et al., 2008a; 2008b; 2010) at N= 10 cycles, T=25 ms, V=140 nm/s and F= 3050 nN. (a) Two dimensional image and (b) Three dimensional image

Fig. 5. Dependence of the scratch depth, created on PMMA/silicon, to the applied normal force (Sadegh Hassani et al., 2008a; 2008b; 2010). (The time of applying pressure, number of scratching cycle and scanning velocity are 25 ms, 10 and 140 nm/s, respectively.)

For PMMA coated glass substrate, scratches were performed with exerting various normal forces using NSG 11 tip. In Figure 6, the groove depths are plotted as a function of the applied normal force for PMMA on glass substrate. The most uniform scratches were achieved by applying 3,000 nN force load, while scanning velocity, number of scratching cycle and time of applying pressure were 1400 Å/s, 10 and 25 ms, respectively. Topography image of this scratch is shown in Figure 7. The uniformity of scratches on PMMA coated on silicon and glass is comparable. However, the depth of scratch on the PMMA/glass at the same conditions is more than that of on the PMMA/silicon.

Fig. 4. Topography images of the scratch performed on the PMMA /silicon (Sadegh Hassani et al., 2008a; 2008b; 2010) at N= 10 cycles, T=25 ms, V=140 nm/s and F= 3050 nN. (a) Two

Fig. 5. Dependence of the scratch depth, created on PMMA/silicon, to the applied normal force (Sadegh Hassani et al., 2008a; 2008b; 2010). (The time of applying pressure, number of

For PMMA coated glass substrate, scratches were performed with exerting various normal forces using NSG 11 tip. In Figure 6, the groove depths are plotted as a function of the applied normal force for PMMA on glass substrate. The most uniform scratches were achieved by applying 3,000 nN force load, while scanning velocity, number of scratching cycle and time of applying pressure were 1400 Å/s, 10 and 25 ms, respectively. Topography image of this scratch is shown in Figure 7. The uniformity of scratches on PMMA coated on silicon and glass is comparable. However, the depth of scratch on the PMMA/glass at the

scratching cycle and scanning velocity are 25 ms, 10 and 140 nm/s, respectively.)

same conditions is more than that of on the PMMA/silicon.

dimensional image and (b) Three dimensional image

Fig. 6. Dependence of scratches depth, created on PMMA/glass (Sadegh Hassani et al., 2010), with the applied normal force while scanning velocity, number of scratching cycle and time of applying pressure were 140 nm/s, 10 and 25 ms, respectively.

Fig. 7. Topography image of the scratch created on PMMA/glass (Sadegh Hassani et al., 2010), while the applied normal force, scanning velocity, number of scratching cycle and time of applying pressure were 3000 nN, 140 nm/s, 10 and 25 ms, respectively.

The influence of the number of scratching cycles was also investigated by scratching experiments. In Figure 8 dependence of the scratch depth to the number of cycles (N = 1, 5, 10, 15, 20, 25, and 30) in a constant applied normal force of 2350nN, scanning velocity of 140 nm/s in 25 ms is presented. This figure shows that the depth varies from 4 to 30 nm by increasing the number of cycles. As expected, the depths of scratches increase with N linearly. This linear relationship between depth and number of cycles confirms layer-by-layer removal mechanism (Sadegh Hassani et al., 2008a). This result is in agreement with that of obtained by Santinacci and coworkers (2003) for performing nanolithography on p-Si (100) substrate.

Nanolithography Study Using Scanning Probe Microscope 467

Fig. 10. The indentation depth created on PMMA/Si as a function of the time of applying pressure (Sadegh Hassani et al., 2008a; 2008b) (The applied normal force, scanning velocity

This experiment was performed on the polyethylene (PE) substrate (Sadegh Hassani et al., 2008b; 2010). Polyethylene surface was cleaned by washing and sonicating in acetone-ethanol (50-50%Vol.) for 15 minutes at room temperature. This substrate was more inflexible than PMMA thin layer, so performing any modification over PE needed more rigid cantilever tip. The results verified this comment. Scratches were just made by maximum amount of force load, which was equal to 4 N for NSG11 cantilever tip that was the threshold of force for modifying the PE substrate. The investigation of force effect on the PE substrate was continued by DCP20 cantilever with diamond tip. The force load created by this tip was sufficient to

Fig. 11. Dependence of scratches depth with the applied normal force on the PE substrate (Sadegh Hassani et al., 2008b; 2010), while scanning velocity, number of scratching cycle and

and number of cycle are 2350 nN, 140 nm/s and 10, respectively.)

make modification on the PE substrate because of higher spring constant.

time of applying pressure are 140 nm/s, 20 and 50 ms, respectively.

**4.2 Nanolithography on polyethylene substrate** 

Fig. 8. Dependence of scratch depth created on PMMA/Si to the number of cycles (Sadegh Hassani et al., 2008a; 2008b) (The applied normal force, scanning velocity and time of applying pressure are 2350 nN, 140 nm/s, and 25 ms, respectively.)

The influence of the scanning velocity on the lithography pattern, taken at a normal force of 2350 nN is presented in Figure 9. As it is shown in this figure, the depth varies from 24 to 8 nm by decreasing scanning velocity from 140 to 540 nm/s. It is observed that the increase of the scanning velocity induces a decrease in the scratch depth. Thus, slower scans seem to generate higher pressure and as a result deeper scratch pattern are obtained. However, it could not be determined whether the depth decreases linearly or exponentially with the increase of the scanning velocity (see Fig. 9). To analyze the time effect, nanoindentations are performed on the PMMA surface. The indentation depth created on PMMA/Si depth as a function of time of applying pressure using constant force is presented in Figure 10. It can be seen that by increasing the time of applying pressure, indentation depth is increased. In the other words, the plastic deformation on the PMMA film is time dependent. In this case, to accumulate the tip-induced stress, dilation changes such as defects created or absorbed near the vicinity of the deformed region on the surface occur. This effect leads to an additional plastic deformation of the film.

Fig. 9. The influence of the scanning velocity on the depth of the lithographed pattern created on PMMA/Si (Sadegh Hassani et al., 2008a) (The applied normal force, time of applying pressure and number of cycle are 3125 nN, 25 ms and 10, respectively.)

Fig. 8. Dependence of scratch depth created on PMMA/Si to the number of cycles (Sadegh Hassani et al., 2008a; 2008b) (The applied normal force, scanning velocity and time of

The influence of the scanning velocity on the lithography pattern, taken at a normal force of 2350 nN is presented in Figure 9. As it is shown in this figure, the depth varies from 24 to 8 nm by decreasing scanning velocity from 140 to 540 nm/s. It is observed that the increase of the scanning velocity induces a decrease in the scratch depth. Thus, slower scans seem to generate higher pressure and as a result deeper scratch pattern are obtained. However, it could not be determined whether the depth decreases linearly or exponentially with the increase of the scanning velocity (see Fig. 9). To analyze the time effect, nanoindentations are performed on the PMMA surface. The indentation depth created on PMMA/Si depth as a function of time of applying pressure using constant force is presented in Figure 10. It can be seen that by increasing the time of applying pressure, indentation depth is increased. In the other words, the plastic deformation on the PMMA film is time dependent. In this case, to accumulate the tip-induced stress, dilation changes such as defects created or absorbed near the vicinity of the deformed region on the surface occur. This effect leads to an

Fig. 9. The influence of the scanning velocity on the depth of the lithographed pattern created on PMMA/Si (Sadegh Hassani et al., 2008a) (The applied normal force, time of applying pressure and number of cycle are 3125 nN, 25 ms and 10, respectively.)

applying pressure are 2350 nN, 140 nm/s, and 25 ms, respectively.)

additional plastic deformation of the film.

Fig. 10. The indentation depth created on PMMA/Si as a function of the time of applying pressure (Sadegh Hassani et al., 2008a; 2008b) (The applied normal force, scanning velocity and number of cycle are 2350 nN, 140 nm/s and 10, respectively.)

#### **4.2 Nanolithography on polyethylene substrate**

This experiment was performed on the polyethylene (PE) substrate (Sadegh Hassani et al., 2008b; 2010). Polyethylene surface was cleaned by washing and sonicating in acetone-ethanol (50-50%Vol.) for 15 minutes at room temperature. This substrate was more inflexible than PMMA thin layer, so performing any modification over PE needed more rigid cantilever tip. The results verified this comment. Scratches were just made by maximum amount of force load, which was equal to 4 N for NSG11 cantilever tip that was the threshold of force for modifying the PE substrate. The investigation of force effect on the PE substrate was continued by DCP20 cantilever with diamond tip. The force load created by this tip was sufficient to make modification on the PE substrate because of higher spring constant.

Fig. 11. Dependence of scratches depth with the applied normal force on the PE substrate (Sadegh Hassani et al., 2008b; 2010), while scanning velocity, number of scratching cycle and time of applying pressure are 140 nm/s, 20 and 50 ms, respectively.

Nanolithography Study Using Scanning Probe Microscope 469

According to Figures 12 and 13, repeatability of results for PE substrate is less than PMMA layer. It refers to roughness and flexibility of PMMA thin film. In the other words, making scratch over very uniform and flexible PMMA thin layer is much more successful than PE

This experiment was performed on the HOPG substrate as a completely hard surface and by exerting applied normal force ranging from 5.5 to 50.5 N (Sadegh Hassani et al., 2010). Moreover, in comparison with PMMA thin films and polyethylene substrate, the scanning velocity for performing nanolithography on HOPG surface had to be increased which would led to wearing tip very fast. However, the time of applying pressure on HOPG was much less than those applied on PMMA thin films and polyethylene substrate. Hence, after some trial experiments, 10000 nm /s was chosen for scanning velocity on HOPG substrate at 1 ms. HOPG surface was cleaned using double-sided tape and removing one layer of it. The results of this experiment are obtained by DCP20 cantilever and are presented in Figure 14. Because HOPG surface was very uniform with very low roughness, shape of made scratches were completely V-form. Topography image and cross section of one of the scratches performed on the HOPG is shown in Figure 15. Meanwhile, increase of applied normal force caused cumulating of material at the start and end point of the grooves. This deformity occurred because of cantilever bending at the start point of moving tip through the surface

Fig. 14. Dependence of scratches depth to the applied normal force executed by DCP20 cantilever on the HOPG (Sadegh Hassani et al., 2010) substrate, while scanning velocity, number of scratching cycle and time of applying pressure are 10000 nm /s, 1 and 1 ms,

substrate.

**4.3 Nanolithography on HOPG** 

(Wendel et al., 1996).

respectively.

A topography image of nanoscratche made on the PE showed that the best quality of scratch was obtained by applying of a 4N force load. The obtained results showed that the uniformity of the scratches reduced by increasing the force load. Accumulation the vicinity of scratches was occurred, because increasing the applied force induced additional plastic deformation. Figure 11 shows the linear increase of scratches depth on the PE substrate as a function of applied normal force. Meanwhile, increase of applied force caused cumulating of material at the start and end point of the grooves. This deformity was occurred because of cantilever bending at the start point of moving tip through the surface (Notargiacomo et al., 1999; Sadegh Hassani et al., 2088b).

In Figures 12 and 13, the indentation depths are plotted as a function of the time of applying pressure and number of cycles for PE substrate, respectively. Figure 12 shows that the dependence of depth to time is not quite linear. This result was also reported by Santinacci et al. (2005). Figure 13 shows the linear increase of scratches depth with number of cycles, as expected (Santinacci et al., 2003; Santinacci et al., 2005; Sundararajan & Bhushan, 1998).

Fig. 12. Indentation depth dependence to time of applying pressure for PE substrate (Sadegh Hassani et al., 2008b), while applied normal force, scanning velocity and number of scratching cycle are 4N, 140 nm/s, 10, respectively.

Fig. 13. Indentation depth dependence to number of scratching cycle for PE substrate (Sadegh Hassani et al., 2008b), while applied normal force, scanning velocity and time of applying pressure are 4N, 140 nm/s, 25 ms, respectively.

According to Figures 12 and 13, repeatability of results for PE substrate is less than PMMA layer. It refers to roughness and flexibility of PMMA thin film. In the other words, making scratch over very uniform and flexible PMMA thin layer is much more successful than PE substrate.

#### **4.3 Nanolithography on HOPG**

468 Recent Advances in Nanofabrication Techniques and Applications

A topography image of nanoscratche made on the PE showed that the best quality of scratch was obtained by applying of a 4N force load. The obtained results showed that the uniformity of the scratches reduced by increasing the force load. Accumulation the vicinity of scratches was occurred, because increasing the applied force induced additional plastic deformation. Figure 11 shows the linear increase of scratches depth on the PE substrate as a function of applied normal force. Meanwhile, increase of applied force caused cumulating of material at the start and end point of the grooves. This deformity was occurred because of cantilever bending at the start point of moving tip through the surface (Notargiacomo et al.,

In Figures 12 and 13, the indentation depths are plotted as a function of the time of applying pressure and number of cycles for PE substrate, respectively. Figure 12 shows that the dependence of depth to time is not quite linear. This result was also reported by Santinacci et al. (2005). Figure 13 shows the linear increase of scratches depth with number of cycles, as expected (Santinacci et al., 2003; Santinacci et al., 2005; Sundararajan & Bhushan, 1998).

Fig. 12. Indentation depth dependence to time of applying pressure for PE substrate (Sadegh

Hassani et al., 2008b), while applied normal force, scanning velocity and number of

Fig. 13. Indentation depth dependence to number of scratching cycle for PE substrate (Sadegh Hassani et al., 2008b), while applied normal force, scanning velocity and time of

scratching cycle are 4N, 140 nm/s, 10, respectively.

applying pressure are 4N, 140 nm/s, 25 ms, respectively.

1999; Sadegh Hassani et al., 2088b).

This experiment was performed on the HOPG substrate as a completely hard surface and by exerting applied normal force ranging from 5.5 to 50.5 N (Sadegh Hassani et al., 2010). Moreover, in comparison with PMMA thin films and polyethylene substrate, the scanning velocity for performing nanolithography on HOPG surface had to be increased which would led to wearing tip very fast. However, the time of applying pressure on HOPG was much less than those applied on PMMA thin films and polyethylene substrate. Hence, after some trial experiments, 10000 nm /s was chosen for scanning velocity on HOPG substrate at 1 ms. HOPG surface was cleaned using double-sided tape and removing one layer of it. The results of this experiment are obtained by DCP20 cantilever and are presented in Figure 14. Because HOPG surface was very uniform with very low roughness, shape of made scratches were completely V-form. Topography image and cross section of one of the scratches performed on the HOPG is shown in Figure 15. Meanwhile, increase of applied normal force caused cumulating of material at the start and end point of the grooves. This deformity occurred because of cantilever bending at the start point of moving tip through the surface (Wendel et al., 1996).

Fig. 14. Dependence of scratches depth to the applied normal force executed by DCP20 cantilever on the HOPG (Sadegh Hassani et al., 2010) substrate, while scanning velocity, number of scratching cycle and time of applying pressure are 10000 nm /s, 1 and 1 ms, respectively.

Nanolithography Study Using Scanning Probe Microscope 471

required. It must be mentioned that the minimum necessary force to modify the PE surface is about 4 N that can be achieved by NSG11 tip and with maximum force load. Therefore, for investigation of the effect of higher forces, DCP20 tip is used for PE substrate. The experimental results show that depth of the lithography pattern increased with the increase of the applied normal force with a linear trend for all of the applied substrates. The increase of applied normal force caused accumulating of material at the start and end point of the grooves. This deformity occurred because of cantilever bending at the start point of the tip

It is presented that the increase of the scanning velocity induces a decrease in the scratch depth. Thus, slower scans seem to generate higher pressure and as a result, deeper scratch pattern are obtained. However, it could not be determined whether the depth decreases

The increase of the lithography depth with the loading time suggests that the plastic deformation on PMMA layer is time dependent. However, the results show that the dependence of depth to the loading time is not quite linear. By the tip-induced stress, dilation changes such as defects created or absorbed near the vicinity of the deformed region on the surface might occur, which would lead to an additional plastic deformation of

It is shown that the depth of the lithography mark increases with the increase of the number of scratching cycle. The depths of scratches increase linearly with the number of scratching cycle. Finally, due to the convolution effect of the tip and substrate topography, the scratch depth

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Fig. 15. Two and three-dimensional topography images and cross-section of one of the scratches performed on the HOPG (Sadegh Hassani et al., 2010) , while scanning velocity, number of scratching cycle, time of applying pressure and applied normal force are 10000 nm /s, 1, 1 ms and 50.4 N, respectively.
