Mohamed Abu-bakr

Cracks develop during interaction with beam: surface layer under gold film is changing it's volume/shape due to induced beam damage and non-elastic gold layer produces cracks because it cannot adapt to a shape changes.

Thinner layer of gold should be better (always use as thin layer as you can), but again, no coating could be the best solution. Use the lowest accelerating voltage that produces enough contrast. 8 kV is a pretty high voltage, something like 1 kV should be much better.

I do not know what happens with "oil nanofluid" in an oven, but it looks like your specimens consists of nanotubes semi submerged in organic matrix. Almost smooth, low contrast. For specimens like this one thick gold coating may hide fine details. In addition some materials are very sensitive (don't know if yours can qualify as a one) and can change shape during spatter coating. On attached pictures you can see glue on Post-It notes without and with Au-Pd coating.

Cracks are due to damage (usually thermal damage) surface of your specimen can get during sputter coating or, more often, during interaction with electron beam. Very difficult to avoid.

By the way, Au is not really good for high magnifications. Pt or Au-Pd are better. But for In Lens mode no coating at all is the best.

Vladimir Dusevich

"but it looks like your specimens consists of nanotubes semi submerged in organic matrix"

This is actually true, I had to dry a very thin film of the nanofluid to see this image since I have tried to dry a droplet at first and I couldn't even identify any CNTs. However, I do think that the oven has nothing to do with this since it was successfully able to dry the thin film and CNTs were observable.

"Cracks are due to damage (usually thermal damage) surface of your specimen can get during sputter coating or, more often, during interaction with an electron beam. Very difficult to avoid. "

I don't think that the cracks were caused by interaction with the electron beam since the un-sputtered sample didn't show any cracks.

I will try to reduce the gold coating thickness and give it a try. I think this should reduce thermal damaging during sputtering and reveal more details if they are really hidden under a thick gold layer.

Thanks for your insights.

They are much appreciated.

hi

we experienced same type of Au morphology by sputtering process.

in my experiments with students we could show that Au morphology is afunction of sample distance and sputtering time. shorter sputtering time will lead to smoother morphology without cracks. clearly this should lead to thinner coating layers without own distinct surface morphology. d=50mm, t smaller than 20s we found as suitable parameter for our sputter coater. good vacuum conditions as a prerequisite generation conductable coatings on substrates.

best regards

Mohamed Abu-bakr

Cracks develop during interaction with beam: surface layer under gold film is changing it's volume/shape due to induced beam damage and non-elastic gold layer produces cracks because it cannot adapt to a shape changes.

Thinner layer of gold should be better (always use as thin layer as you can), but again, no coating could be the best solution. Use the lowest accelerating voltage that produces enough contrast. 8 kV is a pretty high voltage, something like 1 kV should be much better.

I don't know much about oils or CNTs but I have seen cracks like that when the gold spattering was too thick and it cracks just for surface tension during the deposition.

If your stub color is too goldish maybe you have too much gold that cover your features (even nanometers). In that case you could try exposing it for less time.