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Ryan’s MFP-3D Procedural Operation ‘Manualette’ Version 10 (v080501; Igor 6.03A); ©2008 6.16 A B C D Figure 6.1.12: Q gain and repulsive imaging: A) post auto tune- no Q gain; B)almost ringing; C) ringing; D) freakout. If all else fails, the tip could be too blunt (recall larger surface areas promote attractive mode- see Table 6.1.4)- CHANGE THE TIP; or the sample could possess charge that needs to be quelled/ dissipated using a ‘Static Master’ (see Figure 6.1.12). TROUBLESHOOTING- If you are still having trouble with mode hopping, it could be due to the sample - here are a couple things that may be contributing to it- 1) If you are experiencing difficulty keeping the tip in repulsive mode, perhaps the tip is too dull (see Table 6.1). If you are re-using the tip, this is a strong likely hood. 2) Surface charges- use the Static Master device to dissipate the charge. Place the Static Master in the vicinity of the sample (see Figure 6.1.13). Sometimes the glass slide the sample is glued to is the culprit of the excess charge- in these cases, mounting the sample on a magnetic puck and placing it on a metal sample holder can help quell this charge. Static master Figure 6.1.13: Placing static master near sample to dissipate charge.
Ryan’s MFP-3D Procedural Operation ‘Manualette’ Version 10 (v080501; Igor 6.03A); ©2008 6.17 3) the Q gain needs to be increased slightly- See above and Ssection 6.1.4B for a description of increasing the Q gain and performing subsequent Manual tunes to confirm no ringing is occurring (i.e., Figure 6.1. 154). 4) The tip could be sticking to the sample- Keith Jones (AR apps scientist) has found that a Pt coated Si cantilever can sometimes work well with ‘sticky’ samples. We use Electrilevers (Olympus AC 240s coated with Pt), but if you have access to a sputterer, perhaps you can make your own. Try 3 nm of an adhesion layer such as Ir, Cr, Ti; and 5 to 10 nm of Pt. 6.1.4B: ATTRACTIVE MODE IMAGING: Hints to get a good attractive mode image- Imaging in attractive mode is great for soft samples that shouldn’t be perturbed as much in repulsive mode, however can sometimes be tricky when you actually want it to occurhere are some simple steps to help keep the tip in attractive mode: In the Tune tab of the Main panel- Set the Target Amplitude to 1V; this will have to be adjusted (decreased) later, but for the initial Auto tune, it will give the cantilever enough amplitude to have a successful Auto tune. A B Set the Target Percent to +10 to +20%; this will set the Drive frequency on the right side of the cantilever’s resonant peak- a position more likely to keep the tip in attractive mode while imaging. Click the ‘Auto Tune’ button. This will sweep the piezo frequency and find the Drive Frequency based on the setvar parameters just entered. A plot similar to Figure 6.1.154A should be seen. C ▪ This will give a good starting point for the next step- Slightly increase the Q gain from 0.00 to 0.01. Click the ‘One Tune’ button. Notice the FWHM value of the new resonant peak will decrease. These values are also calculated and displayed in the Auto Tune plot (Figure 6.1.3). Repeat this process until the resonant peak & Phase start to show ringing (Figure 6.1.154B). Figure 6.1.14: Attractive mode drive frequency and amplitude selection with an Olympus AC 240 Si cantilever. A) after auto tune; B) increase Q Gain until Phase and Drive has ringing; C) Decrease Q gain until ringing disappears Now decrease the Q gain until this ringing ceases in the Drive or Phase plots (Figure 6.1.14C). Lastly, click the ‘Center Phase’ button to center the inflection point of the phase signal with the resonant peak of the cantilever.
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