[labnetwork] Should a pH Sensing Membrane be Conductive or Insulating?

[A. William (Bill) FLOUNDERS]

Mohamed Ghoneim,
Your gate insulator should be highly insulating.
You are attempting to monitor the degree of protonation of
surface hydroxyl groups as a function of solution pH.

I encourage you to review detailed principles of operation
and review articles from research group of Piet Bergveld. (1980 -2000).
I will continue conversation with you offline.

I repeat my regular proposal / request that labnet not host such detailed
research specific inquiries. I welcome ongoing discussion of our network.

Bill Flounders
UC Berkeley

On Wed, Jan 31, 2018 at 6:28 AM, Mohamed Ghoneim <
mohamed.t.ghoneim at gmail.com> wrote:

> When using EGFET pH sensing configuration (very similar to a metal/sensing
> membrane to collect ions from solution and generate voltage).....does the
> sensing thin film have to be conductive or insulating?
>
> Example Setup:
>
> [image: Inline image 1]
>
> I am using EGFET setup with commercial transistor that is connected to a
> Au electrode with a ZnO thin film (150 nm) on the part to be immersed in
> solution to sense the pH. I also use a reference electrode to set the
> offset voltage and bias the transistor.....does my ZnO thin film have to be
> conductive or insulating for reliable sensor performance?
>
> It is generally reported in literature that the preferred orientation of
> ZnO used for such purposes is (002) although few reported amorphous....but
> conductivity is not usually discussed. Since ZnO's conductivity is highly
> tunable, it would be very helpful if its conductivity matches the
> requirement for a good sensitivity and reliable measurements.
>
>
> All responses and discussions are appreciated...thanks in advance,
>
> Mohamed T. Ghoneim
> <https://scholar.google.com/citations?hl=en&user=-5mNcfYAAAAJ&view_op=list_works&sortby=pubdate>
> ,
> Postdoctoral Researcher
> MIT Media Lab, Building E-15, Fourth Floor, Room 443g.
> Website
> <https://sites.google.com/view/mtghoneim>
>
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