While carrying out PFM for my polymer films, I observed that while taking butterfly curves and phase plots; if during analysis it is sample biased and tip biased we are getting a marginal difference in values. Also, there is a specific inversion of 180deg. in phase plot.
Is this related to my sample? What can be the reason behind this?
Kindly help!
Thank you
Dear Akanksha Adaval , Please specify more about which PFM methods you used (Contact resonance, DART PFM...) and what kind of polymers as well as sample preparation techniques you used (is it thin film, nanofibers or bulk film..). The phase inversion of 180 in PFM, if not taken carefully, can be induced by many artifacts such as topography cross-talk or electrostatic effects.
Best regards,
Cuong Nguyen Thai I was using contact mode for the analysis. The samples are solution casted thin films with thickness in the range of 30-50 micrometer.
Dear Akanksha Adaval , thank you for your information. Normally, PFM will be carried out using contact mode but you will need contact resonance mode, such as DART, to enhance your signal-to-noise.
As for the sample, I think a 30-50 micrometer sample might be too thick. Probably you will get a weak response signal even for polymers with large piezoelectric response such as PVDF. Otherwise you will have to apply a really high AC voltages, which poses the risk of increased electrostatic effect.
It could be easier and safer to reduce the thickness of your sample.
Best regards,
Phase-response curves
With the notion of phase defined, we now examine how a perturbation shifts the phase of the oscillator. In Figure 12A , we show the voltage time course for the Morris-Lecar system in the oscillating regime. At a fixed time, say t, after the voltage peak, we apply a brief depolarizing current pulse. This shifts the time of the next peak (Figure 12A) and this shift remains for all time (the solid curve is the perturbed oscillation and the dashed is the unperturbed - in this case the time for the next peak is shortened). If the time of the next peak is shortened from the natural time, we say that the stimulus has advanced the phase. If the time of the next peak is lengthened then we have delayed the phase. Let 📷 denote the time of the next peak. The phase shift is 📷, and 📷 depends on the time t or the phase 📷 at which the stimulus is applied. Thus, we can define a phase shift 📷. The graph of this function is called the phase response curve (PRC) for the oscillator. If 📷 is positive then the perturbation advances the phase and the peak will occur sooner. On the other hand, if 📷 is negative then the phase is delayed and the next peak will occur later. We can easily compute this function numerically and the same idea can be used to analyze an experimental system. Moreover, this curve can be used as a rough approximation of how the oscillator will be affected by repeated perturbation (periodic forcing) with the same current pulse. More complete descriptions and numerous examples of phase models
Cuong Nguyen Thai Thank you for the answer!
Actually, I am getting pretty good results without any electrostatic interference or noise for my samples. I just wanted to know the difference in results originating from sample biasing and tip biasing.
Dear Akanksha Adaval , it's quiet relieved that you can achieve good results without electrostatic contributions.
When you tried sample bias, the dipole of your sample will be reversed into opposite direction compared with in case of tip bias. That's why you will get the total inversion of the phase. The amplitude, which measure the local intensity of the dipole, will remain the same for two cases.
I hope this helps.
Best regards,
Cuong Nguyen Thai Thank you for the explanation!
Can you please explain in depth how the dipole reversal occurs during sample biasing? I am relatively new to this field.
Also, while sample biasing the obtained amplitude value is higher as compared to when tip biased, can you explain the probable reason for that?
Dear Akanksha Adaval ,
If you are new to this field, it will be better to start with some articles review written by experts of the field. Some of them are:
1. Collins, L., Liu, Y., Ovchinnikova, O. S. & Proksch, R. Quantitative Electromechanical Atomic Force Microscopy. ACS Nano 13, 8055–8066 (2019)
2. Kim, B., Seol, D., Lee, S., Lee, H. N. & Kim, Y. Ferroelectric-like hysteresis loop originated from non-ferroelectric effects. Appl. Phys. Lett. 109, 102901 (2016)
3. Kwon, O., Seol, D., Qiao, H. & Kim, Y. Recent Progress in the Nanoscale Evaluation of Piezoelectric and Ferroelectric Properties via Scanning Probe Microscopy. Adv. Sci. 7, (2020)
4. Qiao, H., Seol, D., Sun, C. & Kim, Y. Electrostatic contribution to hysteresis loop in piezoresponse force microscopy. Appl. Phys. Lett. 114, (2019).
5. Qiao, H., Kwon, O. & Kim, Y. Electrostatic effect on off-field ferroelectric hysteresis loop in piezoresponse force microscopy. arXiv vol. 116 172901 (2020)
From my experience, one possible reason for not obtaining the same amplitude value could be the effect of electrostatic effect. As you read the above articles, you can see that there are many factors that can result in ferroelectric-liked hysteresis curves. Therefore, one addition thing you can do is to subsequently pole your sample using negative and positive DC bias and then do the PFM mapping as many people have done with PVDF films.
Best regards,
Cuong Nguyen Thai Thank you for all your help! Really appreciate it!
- Badges
- Science topic