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I hope you have eliminated the evaporation source and process
themselves as the sources of problem. Mg deposition is very tricky
because it is very reactive. <br>
<br>
The particles are probably contaminants that are present on the
substrate/wafer before evaporation. Two possibilities for the
rings: The rings are present around the particle before deposition
and are from the same source of contamination. They manifest
vividly after deposition. Other origin for the rings is
out-gassing or decomposition of the particle. Shadowing by the
particle can also cause some rings. The substrate (elemental such
as silicon or oxide such as SiO2 or Al2O3) can play a role in this
too. Varying thermal treatment without breaking the vacuum may help
to understand this. Look up literature on reactions with substrate
and condensation phenomena in ultra-thin films in JVST and APL.
Substate processes can modify film structure (Very interesting
effect is described here: <a
href="http://apl.aip.org/resource/1/applab/v93/i21/p213304_s1?view=fulltext&display=print&bypassSSO=1">http://apl.aip.org/resource/1/applab/v93/i21/p213304_s1?view=fulltext&display=print&bypassSSO=1</a>
) But the "rings" strongly suggest contamination. <br>
<br>
There is one way to be perfect and infinite ways to be imperfect.
Contamination is an imperfection in the process. It is not
something that happens universally. Hence it is difficult to
explain what is happening based on your brief comment. Someone has
to audit your complete process (not just the evaporation)
thoroughly. You will also have to do some experimentation and
analytical work to resolve this. <br>
<br>
Good luck....<br>
<pre class="moz-signature" cols="72">Pramod C Karulkar Ph. D.
Home 2*5*3* 3*0*3 0*4*1*8
6024 33rd Street Ct NW
Gig Harbor WA 98335</pre>
<div class="moz-cite-prefix">On 7/16/2013 3:33 PM, Iyer, Nandini
wrote:<br>
</div>
<blockquote
cite="mid:91625D20BE5AA24FB206AAAC6EF156176B871B@ex06.net.ucsf.edu"
type="cite">
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<div style="direction: ltr;font-family: Tahoma;color:
#000000;font-size: 10pt;">Hi,<br>
<br>
Recently, we have noticed some unusual spots on our evaporated
Mg film (~10um). It consists of a contaminating particle and a
ring shaped discolouration around the particle. We suspect that
the contaminant may be Mg particles deposited during evaporation
but we are not certain about this. Does anyone have any theories
about what could be happening?<br>
<br>
Thank you.<br>
<br>
Nandini<br>
</div>
<br>
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<br>
<pre class="moz-signature" cols="72">--
Pramod C Karulkar Ph. D.
Home 2*5*3* 3*0*3 0*4*1*8
6024 33rd Street Ct NW
Gig Harbor WA 98335 </pre>
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