# The Attachment of Carbon Nanotubes to Atomic Force Microscopy Tips Using the Pick-Up Method
## 3 Results
### CNT Attachment to Contact Mode Probe Using the Pick-Up Method and High-Force Imaging  
Figure 4 shows tapping mode AFM images of the attachment process using high-force imaging and the pick-up method for a Bruker NP contact mode (Bruker Corporation, Billerica, MA, USA) with spring constant equal to 0.28 N/m [73]. Figure 4a shows that the image was very unstable which is due to the low spring constant of the contact mode cantilever causing the tip to adhere too strongly for the feedback to maintain stable imaging. The nominal diameter of these tips is 40 nm which is relatively large compared to standard tapping mode probes. However, in Figure 4a high force imaging was used and sections of the image show CNTs resolved which indicates CNT attachment is occurring. When CNT attachment was assumed to have taken place, which was confirmed by the AVD curve in Figure 5, then the probe was moved to a different location on the sample and a stable AFM image in tapping mode was achieved (refer to Figure 4b). Stable tapping mode imaging with a contact mode probe is more likely after CNT attachment as the diameter of the CNT will be much less than the nominal diameter for the tip, thus reducing adhesion. Additionally, the stiffness of the CNT may add additional stability to the imaging process, provided the amplitude set-point is above 70-80% of the free cantilever amplitude. This is important as it demonstrates that modified high force imaging can facilitate CNT attachment to contact mode probes using the pick-up method. Therefore, since contact mode probes have spring constants 0.1-0.01 of the spring constant of standard tapping mode probes they can image soft materials with significantly reduced imaging force. This is the first time this technique has been used to attach CNTs to low spring constant contact mode probes. Figure 3: SEM images of CNTs attached to AFM tips. The scale bars in each image are (**a**) 200 nm, (**b**) 500 nm, (**c**) 200 nm, (**d**) 200 nm, (**e**) 200 nm and (**f**) 200 nm. It can be seen in (**f**) that the electron beam moved the CNT from a relatively straight position, given by the dotted line, to a bent position. CNT Attachment to Two Tapping Mode Probes Simultaneously Using the Pick-Up Method and High-Force Imaging  
The pick-up method using high-force tapping mode imaging was applied to 1930-00 dlevers (Bruker Corporation, Billerica, MA, USA) which has two tapping mode AFM probes of the same length located on the same ship, with the nominal parameters described in Table 1. The methodology described in Section 2.3 was applied to these probes to demonstrate that the pick-up technique can be used to attach CNTs to more than 1 AFM probe simultaneously. An example of data indicating CNT attachment is shown in Figure 6a,b. This figure shows AVD curves acquired using 1930-00 dLever-C and 1930-00 dLever-D probes located on the same chip respectively. These AVD curves display distinctive buckling signatures indicating that CNT attachment has been achieved. Figure 4: (**a**) exhibits unstable imaging expected due to the low spring constant of the contact mode probe (0.28 N/m). High force imaging was used to attach a CNT to the AFM tip as can be seen in in sections of the image where CNTs are visible. (**b**) shows that CNT attachment was achieved due to a stable tapping mode image of the CNT surface. The height colour scale for images is 6 nm. Figure 5: Shows an AVD curve for the contact mode probe used to acquire the AFM images in Figure 4a,b. The buckling signature typical for CNT attachment can observed. To verify that the CNT attachment to both probes is stable tapping mode AFM images were acquired on the CNT covered substrate and are shown in Figure 7a,b. In approximately 50% of attempts simultaneous CNT attachment was achieved demonstrating that the pick-up method, facilitated by high-force imaging, is capable of attachment to multiple AFM probes.