TEOS and pnc-Si Discoloration Assay

Over the last week, I’ve run a discoloration assay similar to one run a while back (Barrett’s post here). It was demonstrated in a subsequent paper (Agrawal2010) that annealing the pnc-Si films prevents discoloration of the membrane, which he tied to the nanomembrane remaining intact. I was given a few chips from the recent TEOS lot, and the wafer which we sent to Kevin Webb last week. I was trying to confirm the same results that Barrett achieved, assuming that the discoloration indicates the membrane dissolving.

Procedure

1. Select 5 TEM grids from each treatment, placed in 24 well plates, flatside up. The samples had intact membranes wherever possible, but it was difficult to get any for the TEOS 1000C treatment.

2. Sterilization by 70% ethanol for 1 hr.

3. Pipette out ethanol, dry in 70C oven 30min.

4. Photograph Day Zero sample.

5. Fill wells with 400 uL of DMEM + 10% FBS media. One well at the end of each row was filled with media as a control (I was also looking out for fungus).

6. Incubate 24 well plates at 37C , 5% CO2

7. A single sample was removed from each treatment at 5 different times, by aspirating the media, removing the sample with tweezers, and rinsing in ethanol for ~15-30 seconds. A few were rinsed longer, due to dropping the samples in the rinse bath.

8. The samples were placed on gelpacks and dried in the 70C oven.

9. Samples were photographed after the 5th timepoint.

 

Results

We see the same results in the Kevin annealed vs Unannealed treatment that Barrett found: The unannealed variety discolors over the course of 48 hours and looks like bulk Silicon, whereas the annealed portion persists a while longer. For some reason, the first sample on Kevin Annealed completely discolored well before any of the other samples. It is possible, though unlikely, that I switched the samples accidentally at the day 1 timepoint. I don’t have an explantation for what this sample would be otherwise. Are there other factors here at work that work to discolor the membrane? A day 0 sample of some of the treatments would have been nice to do, but I simply forgot to take a sample before giving the wafers back to Tucker.

It’s interesting to see the TEOS 1000C sample not discolor at all, but the TEOS 600C gradually lighten. Jamie suggested that maybe the samples are absorbing the pH indicator dye in the media. We could repeat this run in a different media, EMEM, and see if the same discoloration occurs. Photos of the media at time 0 and 117hrs show that the media didn’t change color.

 

If anyone wants to see the raw samples, I’ve left them on my desk in the 3rd floor office.