Analytical conditions for Si

[Richard Walshaw]

Hi All

Just a quickie - i am setting up to do some machine monitoring using a long run of repeat acquisitions on Si "metal".
I'm not sure which beam conditions to use, to save me time can someone let me know if pure Si is beam sensitive ?

Regards

Richard

[JohnF]

Richard

Depends what you mean by "sensitive"...what exactly are your operating conditions? Are you sitting on one spot? Moving the specimen? What are you trying exactly to do? With a W? LaB6? FE probe?

Without moving, you probably build up a contamination spot and eventually counts will drop due to that, I would guess.

[John Donovan]

Just a quickie - i am setting up to do some machine monitoring using a long run of repeat acquisitions on Si "metal".
I'm not sure which beam conditions to use, to save me time can someone let me know if pure Si is beam sensitive ?

Hi Richard,
This reminds me of the beam sensitivity issue in SiO2 glass versus SiO2 quartz as seen in the image attached below. What's weird (in a way) is that SiO2 crystal (quartz) is much more sensitive to beam damage than SiO2 glass. I guess the glass SiO2 molecules are already disorganized!

To return to your question, normally we don't think of Si metal as beam sensitive, though there may be some trace dopant (boron) migration issues in semiconductor grade Si which I have not investigated. However I can tell you this:

I *have* seen beam damage in pure Si metal after the sample was re-polished with colloidial silica. After a few seconds of polishing the carbon contamination disappeared but some little tiny beam damage marks became visible in a grid pattern where my standardization had been performed.

I believe this is from the chemical etching aspect of the colloidial silica polish which will attack the more structurally damaged areas preferentially.

I will also note as an aside that I often see that the carbon coating is particularly difficult to remove from our Si standards- I wonder if the carbon bonds especially well to the Si surface?  I often find little "leftover" patches of carbon coat on our Si metal after colloidial silica polishing, but not on our other metal standards.

[Richard Walshaw]

Thanks Guys

Sorry i was thin on information. I was setting up to make repeat spot analyses of pure silicon using a rectangular grid of points so the beam was jumping to a new position for every repeat. i did this on our tungsten machine at 15kV.
i was unsure about the beam sensitivity of the material and was stuck for time so i just made an executive decision and treated it like a feldspar to be safe (10nA, 2um defocus).  The results were fine for what i wanted to do (looking for drift in intensities over the course of a weekend). If i do this again i will turn the power up a little (not all the way up to 11 though!)

Cheerio

Richard

[jon_wade]

Hi rich

Si metal is a common standard for us weird experimental folk.  i regularly calibrate on Si metal (or whatever it is in there - I have a bunch of Si wafers I 'borrowed'  if you need a bit) and analyse for Si in metals as a trace.

its not beam sensitive as such but you may want to check count rates to ensure you don't have any dead time issues.

cheers!
Jon

[D.]

I will also note as an aside that I often see that the carbon coating is particularly difficult to remove from our Si standards- I wonder if the carbon bonds especially well to the Si surface?  I often find little "leftover" patches of carbon coat on our Si metal after colloidial silica polishing, but not on our other metal standards.

John,

Do you polish all your standards with colloidal silica?

Cheers,
Deon.

[Probeman]

I will also note as an aside that I often see that the carbon coating is particularly difficult to remove from our Si standards- I wonder if the carbon bonds especially well to the Si surface?  I often find little "leftover" patches of carbon coat on our Si metal after colloidial silica polishing, but not on our other metal standards.

John,

Do you polish all your standards with colloidal silica?

Cheers,
Deon.

Hi Deon,
I do- well my lab manager Julie usually does.  We do a lot of materials characterization so we tend to repolish our standards after coating our standards simultaneously with our samples for example.

But I should add that our standard mounts are mounted in acrylic rounds with Petropoxy epoxy so there are no cracks or crevices to catch oil or polishing compounds, and that makes them extremely easy to clean as seen here:

http://probesoftware.com/smf/index.php?topic=172.msg1436#msg1436

john

[D.]

John,

Do you polish all your standards with colloidal silica?

Cheers,
Deon.

Hi Deon,
I do- well my lab manager Julie usually does.  We do a lot of materials characterization so we tend to repolish our standards after coating our standards simultaneously with our samples for example.

But I should add that our standard mounts are mounted in acrylic rounds with Petropoxy epoxy so there are no cracks or crevices to catch oil or polishing compounds, and that makes them extremely easy to clean as seen here:

http://probesoftware.com/smf/index.php?topic=172.msg1436#msg1436

john

I was toying with that idea, so it's good to hear some affirmation 

Thanks,
Deon.