[labnetwork] Cleaning the Surface of ZnO

[Mac Hathaway]

Hi Mohamed,

I don't know about the details of ZnO for pH sensing, but just an fyi, 
ALD ZnO is particularly pure, and can be deposited at a range of 
temperatures, which might allow your to modulate your sensing/stability 
response.  The stoichiometry for ALD films can be expected to be very 
precise, and stable over a range of deposition temperatures.  ALD is 
available at Harvard CNS.

For resistivity of the deposited film, we have found that an anneal 
helps to stabilize the film.  This might also help to stabilize your pH 
response in your sputtered film.  From what I know about reactively 
sputtered oxides, their stoichiometry is pretty sensitive to process 
conditions, which would presumably lead to sample-to-sample variability 
in your pH measurements.


Mac

Mac Hathaway

Senior Process and Systems Engineer

Harvard Center for Nanoscale Systems

11 Oxford St.

Cambridge, MA02138

617-495-9012


On 1/29/2018 10:31 AM, Mohamed Ghoneim wrote:
> Dear All,
>
> I am sputtering ZnO thin films for pH sensing. Getting repeatable and 
> stable results is a challenge that I though first has to do with 
> chemical fouling and other selectivity issues but based on the 
> literature these issues are there for ZnO but usually do not affect 
> the reliability of measurements to a great extent. I am more concerned 
> now about the crystallinity and stoichiometry effects and as well as 
> surface cleaning techniques to make sure I do not have contaminants on 
> the surface that significantly affects the surface chemistry.
> These are the XRD results of the films (x-axis is 2Theta and the blue 
> (XYZ) are for ZnO:
> Inline image 1
> These are the XPS results of the films (the blue one is the 
> as-deposited ZnO and the red one is after some tests in buffer solutions):
> Inline image 2
>
> Can you please share thoughts about the effect of (a) Crystalline 
> Structure and (b) Stoichiometry (or elemental composition) of ZnO thin 
> film on its pH sensing capabilities and how it affects the surface 
> integrity in terms of: 1- Sensitivity 2- Repeatability 3- Stability of 
> the Measurments.
> All thoughts, comments are highly appreciated,
> Thanks in advance and wish you a great day!
>
>
> Mohamed T. Ghoneim 
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__scholar.google.com_citations-3Fhl-3Den-26user-3D-2D5mNcfYAAAAJ-26view-5Fop-3Dlist-5Fworks-26sortby-3Dpubdate&d=DwMFaQ&c=WO-RGvefibhHBZq3fL85hQ&r=TEMLD8-VsxCGtcVzmvpT5GFNSczskEKHzW6aYlttmIY&m=bVSGBkFEqsSawg8pHJO_jnQJeur_F7n5vs7oe4cALzU&s=WJcNu45WUbGNqMM8-c7UzH3tLW2FC5LJhwFT8-lyQZE&e=>, 
>
> Postdoctoral Researcher
> MIT Media Lab, Building E-15, Fourth Floor, Room 443g.
> Website
> <https://urldefense.proofpoint.com/v2/url?u=https-3A__sites.google.com_view_mtghoneim&d=DwMFaQ&c=WO-RGvefibhHBZq3fL85hQ&r=TEMLD8-VsxCGtcVzmvpT5GFNSczskEKHzW6aYlttmIY&m=bVSGBkFEqsSawg8pHJO_jnQJeur_F7n5vs7oe4cALzU&s=-57KMBniKU-tS8awvWypKA3mktsoIBITMHCkn08uJUs&e=>
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