[Ifeffit] Substrate material question

[Chris Glover]

Paul,

A further idea along the thin Si path could be to use SOI (Silicon on 
Insulator) wafers - high quality wafers suitable even for Ge MBE 
applications.  This then makes the growth process and handling easy. The 
trick is to then etch through the SiO2 layer with HF (from the sides) 
whilst applying a suitable mask... sounds nasty but is actually quite 
easy.  Furthermore, if you are after 50-100um thick substrates, that 
thickness (with say 10% uniformity) can be easily obtained by post growth 
mechanical polishing.  One thing you may have to consider is possible 
diffraction effects for the thicker films.  Im not sure that your 1/e loss 
is really going to be a problem for you if you can prepare samples with a 
reasonable edge jump..... that sort of equates to measuring the As edge in 
transmission from a 10um thick GaAs film.  Ive played with 10um Silicon 
before in a 2" wafer - I tried used it as a widgee (SP?) board between my 
fingers, and it was certainly intact when it left my hands.

SiN 'windows' (ie SiN grown on Si, with a 'hole' in the middle with the Si 
removed) are also another alternative (these have been used for UHV metal 
depositions in for eg surface magnetism).  Might be tricky to figure out 
the exact curvature though.

What about a Be substrate / window - they oxidise easily but this might not 
matter; might be a bit stiff though.

Mylar?

I guess the end choice depends on your growth conditions / requirements

Chris.

At 09:58 AM 28/04/2004 +0900, you wrote:
>   I have still not decided on the final substrate material, but I have a 
> couple of samples coming from Dupont of polyimide (same composition as 
> Kapton) material called vespel.  It is essentially inert as one would 
> expect (like Kapton), but due to differences in manufacture I understand 
> it is hydroscopic.  From this I assume that the reaction for making 
> Kapton is diffusion limited and Vespel is essentially a "polycrystalline" 
> -- in the sense there are grains between which water can absorb -- form 
> of Kapton.  The energy in question is 11.6 keV (the Ge edge).  Si is an 
> interesting idea but the loss for a 200 micron thick substrate is 
> essentially 1/e.  It is certainly worth considering for higher energies 
> though!  The 1/e value for polyimide is about 3500 microns in contrast, 
> while the 1/e value for MgO is about 300.  As in my experiment I want to 
> create biaxial stress in a thin film on the substrate, I worry that the 
> stress/strain curves for MgO are too stiff.  On the other hand, thin Si 
> is a real possibility (darn, Si technology is everywhere!).  I like the 
> Si idea and might try that in parallel.  Has anyone tried using thinned 
> Si wafers (Virginia Technology ? sells mechanically thinned wafers I 
> think -- I saw them at a MRS booth a long time ago).  How fragile are the 
> wafers?
>
>
>On 2004/04/28, at 0:32, Jeff Terry wrote:
>
>>Hi Matt,
>>
>>Both items are good to know. I didn't realize that the laminated kapton 
>>structures still had good heat resistance.
>>
>>Jeff
>>
>>
>>On Apr 27, 2004, at 10:22 AM, Matt Newville wrote:
>>
>>>Hi Paul,
>>>
>>>I think you can get polyimide thicker than 175 microns. It may not
>>>go as Kapton, but maybe as Cirlex or Torlon or something else.  I
>>>think goodfellow.com carries these in millimeter thick sheets and
>>>rods, and that they're still radiation and heat resistant.
>>>Goodfellow tends to be pricey, but has excellent information on
>>>thermal and mechanical properties.
>>>
>>>Using MgO, sapphire, or even diamond might be reasonable too.
>>>
>>>--Matt
>>>
>>>PS: I have a working build of PGPLOT with all of Aquaterm, X11,
>>>     Postscript, and Png devices on Mac OS X.  I'm still tweaking
>>>     the makefile so that it links directly to the png objects to
>>>     avoid possible conflicts with dynamic png and zlib libraries,
>>>     but I should have a working ifeffit binary using this in a
>>>     matter of days, and then be ready to tweak horae's Makefile.PL
>>>     so that horae_update works.
>>>
>>>
>>>_______________________________________________
>>>Ifeffit mailing list
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>>
>Dr. Paul Fons
>Senior Researcher
>National Institute for Advanced Industrial Science & Technology
>METI
>Center for Applied Near-Field Optics Research (CANFOR)
>AIST Central 4, Higashi 1-1-1
>Tsukuba, Ibaraki JAPAN 305-8568
>
>tel. +81-298-61-5636
>fax. +81-298-61-2939
>
>email: paul-fons at aist.go.jp
>
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