I have been doing SECM approach curves a million times on a substrate (semiconductor) at different locations but it seems like I always have got the same problems.
1) The tip of the electrode was damaged as a result from the contact between the tip and the substrate. How do I get the SECM tip to be as close to the substrate as possible in order to get a feedback without damaging it. if it's too far from the substrate, the feedback will be low (or no feedback at all), if you get too close, the SECM tip will be damaged. I have used a microscope to see that my SECM tip had not made contact with the substrate but I would not get the feedback. I would get a flat current.
2) When the SECM tip had approached the substrate (consider that the substrate is not flat and might be tilted a little bit, thus, the offset would not be the same at all locations). The feedback was really high up to 1500 nA. Probably because the electroactive radii of the SECM tip had made contact with the substrate. Is it possible to stop the movement of the tip as soon as the feedback we got went up to 6 - 15 nA, considering that the tip might touch the substrate if the SECM movement was not stopped (and damaging the SECM tip even more)?
3) The steady state current while doing the SECM was really high up to 6 - 11 nA compared to steady state current obtained when regular shape electrode was used (not truncated). Is it because the RG was so small?
4) The steady state current was not stable.
Could you help me with these problems please?
First of all, I would like to say thank you for your replies.
The mediator that I am using is 1 mM potassium hexachloroiridate (III) with 0.5 M KCl considering that it is a very stable and an outer-sphere redox system.
The micropositioner that I am using right now does not receive commands from the electroanalytical software that I am using. It also does not respond to stop command which had made it more difficult to run the experiment. But I could give command the micropositioner to stop before it touches the surface of the sample (2 micrometer-ish). The micropositioner that I am using is a homemade micropositioner from Physik instrument run by a software called PI Mikromove and the electroanalytical software that I am using is NOVA.
I managed to make my SECM tip to be really small with the RG of about 3. would it be helpful if I make it bigger but not more than RG 10? so that I can still fit the data with the theoretical current. because having a really small RG made it hard to tell if the surface of the tip is really flat and has no cracks.
Two sides of the sample was clamped by means of a rubber pad in order to hold it in place but this does not guarantee that the sample is laid flat at the bottom of the cell. But the tilt might have been just a small order of magnitude.
Alright. Thank you so much. I will try the method that you have suggested first and get back to you guys. Hopefully the issues will be resolved soon.
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