Hello,

I have seen sputtered Cr on an ordinary sputtering machine, and it
looks rough, very rough. What roughness are you getting Scott? How did
you measure it? Maybe there are ways to obtain wery smooth thin Cr
films. They may require special sputtering or evaporating machines,
but I think there are alternatives.

Evaporation of thin gold indeed forms crystalline grains. There should
be no problem with it if your layer is thin enough since it will be
totally transparent to electron beam. I have already found this in a
paper where SiO2 was coated with gold and believe me, it looks nice. I
can send you the reference.

Jason you may also check if your PDMS sample is well connected to the
ground. This helped me alot while doing images on SiO2 without any
coating.

Jason, if you want you can send me a sample. I will try to find some
PDMS around, and see how this takes place in a SEM FEG.

Scott I work with people who are expericenced with SEM and have
already used gold for coating insulating substrates. They are part of
what you call "electron microscopy community".

Best wishes,
Cristian

On 8/17/05, Scott Walck  wrote:
> I didn't respond to this because I just don't know what a PDMS structure
> is or the material.  It sound like it must be a polymeric material from
> the response that I saw below. Even if it is not, I would like to make a
> few comments on high resolution SEM imaging.
>
> Imaging should be done at relatively low accelerating voltages for best
> results.  This gives you the surface detail because the signal is
> originating close to the surface.  If a field emission inlens or
> semi-inlens detector is available, then very good work can be done at
> 1kV accelerating voltage or less without coating the sample.  Even with
> these types of SEM's, though, it is common to put a high resolution
> sputtered coating on the sample.  It is generally accepted by the
> electron microscopy community that an ion sputtered Cr coating gives the
> best resolution because the grain size is very small.  You do have to
> have a special coater to coat a sample with any topography with a
> continuous, uniform film that is less than 1 nm thick.  My company makes
> such a high resolution coater.  Because Cr oxidizes over a relatively
> short period, people have gone to Ir and W coatings.  These coatings
> also have fine grain structure and can be coated with less than 1 nm of
> a continuous and uniform coating but do not oxidize as readily.
> Sublimed Os coatings are an alternative fine grain size coating that has
> been used successfully.  If the grain size of the coating is not fine
> enough, then at magnifications in the microscope, you can see the grain
> structure of the coating and it can interfere with the structure that
> you are trying to determine.
>
> The response that was given below is incorrect for a high resolution SEM
> coating application.  First, 2 nm of gold is too thick.  Evaporated gold
> also has very large crystalline grains and forms islands that are not
> continuous on polymeric materials.
>
> In the original posting, the painting is typically silver or carbon
> paint that is applied around the edges of the area of interest and helps
> make a good contact from the coated region to the microscope stage.  The
> drying time was done to avoid the ougassing of solvents.  This painting
> is not done over the area of interest.