Hi James,
Visual appearance can be very deceiving. I can do a run or two and
some testing, no problem. I have found pure aluminum to be as high as
90% and sometimes 91%. I usually get a better coating by pumping down
to about 1X10-6 Torr before coating. I have seen coatings done with
1X10-3 Torr.
With silver, its very important to have fine overcoats for
protection. I always finish off with amorphous(non crystalline)
materials such as SiO2 or SiO.
In talking with others, I have found that the smoothest aluminum
coats are done at room temperature. The reason I use chromium is
because its the universal thin-films bonding material. It requires
special materials to strip it. Most acids won't touch it.
Our machines have very rapid cycle times. Pump down is about 15
minutes. We may be coming into a number of powerful roughing pumps at
very low prices from Boeing Surplus in Seattle. I'll let you know
about them. These are capable of 4X10-4 Torr.
We run our Cryos at about 10 Kelvin.
Al M
--- In VacuumX@..., "James Lerch" <jlerch1@t...> wrote:
Hi Al,
Looks like you have some seriously nice 'Toys' there! :)
I have a few questions if I may,
Any pictures? Especially ones documenting the E-beam layout,
distance from source to target, number of sources, Chamber details,
etc..
Can you tell us some more about this optical thickness monitoring
method? (links are fine, just curious about the theory behind it..)
If you ever have some free time, might you consider evaporating
some of my 'secret sauce' (aka Reynolds Wrap, ~100nm thick) onto a
surface and measure its reflectivity for me? Since I'm pretty much
financially stuck with Tungsten thermal sources (there cheap!) I'm
left to play with only single layer coatings. So far my 'secret
source' (an alloy of Al, Fe, SI) physically appears superior to pure
Al in many ways (good adhesion, very few pinholes (often none), and
significantly more resistant to scratch/sleeks during intentionally
torturous cleanings), however I have often wondered about its
reflectivity... (it looks shiny :)
Protected Silver, WOW! That's a visible wavelength dream come
true :)
Thanks,
James Lerch
(My telescope construction,testing, and
coating site)
----- Original Message -----
From: sloanpk2000
To: VacuumX@...
Sent: Monday, March 31, 2003 9:54 AM
Subject: [VacuumX] New Member - Al M Sirius Optics
Hi,
This is an imteresting group. I have been involved in thin films
for
about 20 years.
We have 3 E-beam systems, utilizing cryo-pumps for deep vaccum.
Other
equipment includes spectrometers, photometers, and
spectralradiometers. We use crystal monitoring for thickness
monitoring. We are now placing and optical monitoring system for
improved accuracy. The E-beam power supplies are 2 10KV an 1
14KV
system. We feed these power supplies with 3 phase 220V at 100Amp.
Two
of them are air-cooled. The 14KV system is water cooled.
I usually design and make interference filters. This weekend, I
coated 12 mirrors from 6" to 10" in size and about 50 diagonals.
I found an interesting combo of layers that I really like. It
starts
with about 20nm of Chromium, followed by 130nm of Aluminum and
finished with 4 layers of Tantalum Pentoxide(Ta2O50) and SiO2 for
enhancement and protection. I get about 94% reflectivity with
this
combo. I find that very few people use Ta2O5.
I found that the thin Chromium layer all, but eliminates
pinholing.
The Ta2O5 is an extremely adherent material and combines very
well
with SiO2. I have silver mirrors that I coated the same way. I
have
one mirror in my MN56 that is over 3 years old and is still like
brand new. The reflectivity of that mirror is about 97%.
Al M
