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I am looking for a material witch is easy to deposit in thin films and which changes its solubility if a electric potential is applied.

Do you know of any such materials ?

EDIT: This is for what I need it. I have a Si Substrate on which there is sputtered SiO2. Then I have the material (to be found) and then a Si on top. Some parts of the Si are connected electronically to the bottom Si and create a electric potential. The orange material underneath the top "electrodes" should be removed. The aim is to remove the "orange" material underneath the top "electrodes" but keep it where the Si is not connected to the bottom electrode.

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How could you do this ?

EDIT2: please Igore the spelling error in the bottom electrode. It should be "connected"

EDIT3: based on Alchimista's answer: enter image description here enter image description here

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  • $\begingroup$ That is an incredibly broad question. Have you tried any literature research before? If so, include it, if not, do it, then include it. $\endgroup$ – Martin - マーチン Dec 19 '17 at 10:35
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    $\begingroup$ This is a very interesting question. $\endgroup$ – henry Dec 19 '17 at 10:45
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    $\begingroup$ Solubility in what? Can deposition solvent / electrolytic solvent / any third solvent be different? If you want a fixed insoluble film I know many ( especially if electrochemistry count as deposition techniques) $\endgroup$ – Alchimista Dec 19 '17 at 12:11
  • $\begingroup$ @Alchimista By applying a electric potential it should be able to remove the material from the substrate. Preferably the electric potential should be small. $\endgroup$ – james Dec 19 '17 at 12:30
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    $\begingroup$ I am in app. Just a smartphone here. What I do not understand if why to place a material then remove it. Anyway I was thinking of electrochemistry that won't work in compact dry configuration. No to mention that Si is not very robust as electrode $\endgroup$ – Alchimista Dec 19 '17 at 13:13
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This is a tentative that perhaps does not fit with restrictions posed by the setup of the question, but does offer an example of a class of materials whose solubility (integrity, to be more precise) is easily altered by an electrochemical process.

A number of conjugated polymers can be deposited atop an electrode by A: electrochemical polymerisation ( this resulting in a film of the polymer in a more or less conductive state ) or

B: as pristine material if available and soluble in some solvent ( spin coating, dipping, dr blading. ..).

The state of the polymer can be electrochemically controlled by the applied potential. ( however the complete neutralisation to its insulating/semiconducting state is generally difficult ).

Overoxidation of these films results in chemical damage associated with removal of the material, directly or by subsequent washing.

3-methylthiophene and poly(3-hexylthiophene) are well known examples for an electrochemical depositable polymer and for a polymer which can be directly cast from its solutions.

In both cases the poly(3-alkylthiophene) (P3AT) film is insoluble in polar solvents and electrolyte solutions. Applying an electrochemical potentially higher than, say, 2 V, overoxidize it damaging the skeleton to such an extent that the material fall out the electrode and / or can be washed out.

Specifically to the question: only case B is viable.

Looking at the figure in the Q, bottom, the orange part will be consisting of neutral P3AT.

Resolution will be not too precise as overoxidation will take place at the edge of the electrode, too.

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  • $\begingroup$ Thank you very much!! Is my drawing in the answer correct ? How would you deposit P3AT onto the wafer: Can you do it with spin coating, sputtering PECVD or anything similar ? What electrolyte would you suggest ? Where should the positive and where the neagtive potential be applied ? $\endgroup$ – james Dec 20 '17 at 13:59
  • $\begingroup$ I would go by spin coating. Yes your drawing is correct just a reference electrode would be necessary to control the process. In principle you could let flow current and destroy the material in contact with the electrode. A controlled potential and moderate current will help you no to dope the adiacent material and clean everything. you would likely need the help of somebody with a minimal knowledge of electrochemistry as well as a setup. Plus test of the behaviour on electrodes similar but different from your final stuff. I said poly3hexylthiophene as readily available commercially. $\endgroup$ – Alchimista Dec 20 '17 at 15:52
  • $\begingroup$ It is not that the material will migrate to the counterelctrode but rather it will be oxidized to an extent disrupting not only the pi system but the sigma skeleton too. Ergo low mechanical properties / enhanced solubility. Just for a more chemically precise picture. $\endgroup$ – Alchimista Dec 20 '17 at 16:05
  • $\begingroup$ Thank you so much ! This is really helpful. May I ask what electrolyte you would suggest for the process ? One thing that is still not clear to me is what to do after the oxidization has taken place ? Should I dissolve P3AT in a specific solvent ? $\endgroup$ – james Dec 20 '17 at 18:22
  • $\begingroup$ (I also changed the last picture) $\endgroup$ – james Dec 20 '17 at 18:49
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Check out this question:

Do indigo and leuco-indigo have fully conjugated pi systems?

Leucoindigo is a soluble, colorless compound which can be oxidized to dark blue indigo, which is insoluble. Such oxidation is accomplished electrolytically through anodic polarization (or reversed through cathodic polarization). You get a color change too.

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  • $\begingroup$ Thanks for your answer. I am not so familiar with oxidisation, therefore would you mind to further elaborate your answers. Especially how it should be done for this question. The best would be, if you give me a step by step answer, such that I can clearly follow what you think. Thank you very much! $\endgroup$ – james Dec 20 '17 at 15:13
  • $\begingroup$ Also PANI in one of its various forms might help. The problem in answering is that one should fully know what you are aimed to. .....Thus A is correct but it will let you remove the material where the electrode is not connected. $\endgroup$ – Alchimista Dec 20 '17 at 15:55
  • $\begingroup$ @Alchimist The elcectrode which are not connected should stay. $\endgroup$ – james Dec 20 '17 at 16:12
  • $\begingroup$ Yes therefore it is tricky. Look at my answer and try that. It seems you need help from every one somehow familiar with el chem and some tests. It really depends on your final expectations. $\endgroup$ – Alchimista Dec 20 '17 at 16:15

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