MgF2 grain size as a function of temperature

ByGreg Madejski

Summary

Surface roughness is believed to impact the SERS effect. Rougher surfaces tend to produce more SERS activity. We can manipulate the npMgF2 surface by changing the deposition temperature, in the form of changing the grain nucleation, shifting the overall grain size and roughness. I performed TEM tomography and segmentation to pull out distributions of MgF2 grains and found that the average grain size appeared to be minimized at 250C.

Tilt Stacks

1148 NPN coated with 50 nm of MgF2 at 150C. -10 to +36 deg.
1148 NPN coated with 50 nm of MgF2 at 250C. -14 to +14 deg.
1148 NPN coated with 50 nm of MgF2 at 250C. -14 to 0 deg.

Tomograms

1148 NPN coated with 50 nm of MgF2 at 150C. Tomogram sho
1148 NPN coated with 50 nm of MgF2 at 250C. Tomogram shows
1148 NPN coated with 50 nm of MgF2 at 350C. Tomogram

Analysis

If I use Weka segmentation on the image stacks, I get probability maps of these structures.

350C Weka segmentation

 

350C probability plot

 

350C MgF2 grains threshold.

I used the pore processing software to cleanup the images and pull out individual particles. There is some variability in adjusting thresholds, which propagates into the changing the grain size, but the adjustments I made were consistent across the images. I used Majority, Erode and Dilate (1x), Majority to clean images.

Histograms

Top = 150C, Middle = 250C, Bottom = 350C. There is a minimum in average grain size for 250C. 150C and 350C distributions look similar. Here the Pore Equivalent Diameter is equivalent to the equivalent grain diameter.

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