Crossections of Au-MgF2-Partially Etched NPN stacks

ByGreg Madejski

This post is a continuation of the work in Partial Etch RIE Blows out NPN Pores and MgF2 Nanomembrane Fabrication on partially etched NPN substrates. We believe the underlying NPN template influences the shape of our SERS active nanostructures and therefore the SERS properties. In this post, we’ll take a look at some of the structures resulting from partially etching the NPN template, thinning and broadening the template, which will change the shape of the structures that are fabricated upon them.

 

 

After the fabrication, each of these membranes were fractured and then coated with 8-9 nm of platinum. I will probably use less next time, as it was occluding my crossections.

 

Native 1236 NPN template + MgF2 + Au (No etch)

 

 

3 layer stack, Designed 50 nm Au, 50 nm MgF2, 50 nm NPN.

 

Colorized Image. Gold (yellow – 57 nm wide), MgF2 (Blue – 52 nm wide) and NPN (Purple – not etched 46 nm).

 

 

Channels through all three layers are small.

 

Channels through all three layers are small

 

10s etch 1236 NPN + MgF2 + Au

10 s etch viewed from the back. Fractures through the NPN are pretty straight, not conical.

 

Colorized 10 s etch

20s etch 1236 NPN + MgF2 + Au

We’re not certain to what degree does the partial etched membrane have conical features.

 

20s etch. The NPN template is thinning. and we can see that the gold has some interesting pointed shapes when peeled away.
20 s colorized

 

30s etch 1236 NPN + Au

Since the much thinned NPN template cannot survive the MgF2 evaporation stress, we coat gold on the thinned NPN directly.
30 s etch. Thinned NPN reveals gold volcanoes.
30 s etch colorized.
Scraping up the gold in the bulk region shows that volcanoes are formed with some porosity. Internally, they may be more pinched than the shape of the volcano indicates.

 

40 s etch 1236 NPN + Au

 

40 s etch. Viewed from the backside, it is clear that the features of the NPN have changed, as more pores have merged together. Thin bits of gold are viewable through the pores, as it comprises most of the film thickness.

 

40 s colorized

 

Aerial Image shows a contiguous membrane into the freestanding region (darker).

Similar Posts