We have always speculated that applying a substrate bias during the silicon deposition “smooths” the film by creating a nicer film. With Graham’s help, I took a few AFM scans of films deposited at three different biases: 00, 05, and 50W. (a) 00 W: 0.337 nm RMS (b) 05 W: 0.145 nm RMS (c) 50…
We have already established that bias is an important parameter in controlling the morphology of 15 nm thick pnc-Si, but have yet to look at its effect on thicker films. This week, made a few 30 nm thick Si films with 02, 05, 25, and 50 W of substrate bias. I annealed these films at…
In this post, I will present my thoughts on the possible mechanisms of pore formation based on our most recent observations with the substrate bias experiments. As a precursor, I will discuss silicon crystallization since it is intimately related to the pore formation process. I will try to show that pore nucleation is driven by…
This is a continuation of the silicon substrate bias series. I have added several more data points to highlight the trend. Below are the TEM micrographs, pore distributions, average diameter/porosity/density plots. It would appear that the “optimal” bias is at 05W if we are using porosity as a metric. I also performed a short temperature…
I first wrote about quantifying the pore formation process using kinetic theory last year. In this post, I will develop my thoughts a bit more. In the literature, researchers oftentimes present charts, like the two shown below, describing the Arrhenius behavior of silicon crystallization (Sontheimer APL 95 2009). Figures 3 and 4 show the crystal…
I reported last week that a 15 nm silicon film deposited with 05 W substrate bias yielded a highly porous film. This week, I wanted to confirm this effect as well as compare it to films deposited at 10 W and 25 W (our baseline). We find that the 05 W is reproducible and the…
As a continuation of the substrate bias series, I deposited a 15 nm film with 05 W substrate bias and annealed at 1000 C. TEM shows that this condition generates a 13.4% porosity and a max pore size of ~40 nm! Here is a comparison of all the bias conditions tested thus far: I believe…
Last week, I reported on the the morphology of pnc-Si deposited with different substrate biases. We hypothesized that the reason for this was due to the different initial film stress of the as-deposited a-Si. Unfortunately, the pressure-displacement method does not allow us to measure amorphous films since it requires the membrane to be nearly flat…
We have always speculated that the substrate bias during the a-Si deposition had a strong effect on pore morphology of pnc-Si. Here, I looked at three 15 nm silicon films deposited with 00W, 25W, and 50W substrate bias. Recall, that the substrate bias applies rf energy to the substrate surface so that impinging Si atoms…
In an attempt to address the Nano Letters reviewer’s comment (show molecular separation, not just Au), I ran a simple experiment where I tried to pass BSA, Cyt. C, IgG, and β-galactosidase through carbonized membranes in the pressure cell. We have to be careful in calling this a “separation” since the two different species were never…