I can't comment on the adhesion, but a single-layer AR coating of NaF
(or MgF2 or cryolite) may do the trick. Depends on what wavelength (or
range of wavelengths) for which you want to attenuate the wavelength.

The amount of light that's reflected from a surface (at normal
incidence) is given by
R = [(n1 - n2)/(n1 + n2)]^2

for quartz (n = 1.54) in air (n=1), R=0.045. That is, about 4.5% of the
incident light is reflected.

Ideally, you'd want to put down an AR coating with a refractive index =
[n(air)*n(substrate)]^(1/2). For this system, n(coating)=1.24.
Practically speaking, one uses solid fluorides with n around 1.33.

If the coating is MgF2 (n = 1.38), R = (2.5% - 0.3%) = 2.2%. The
reflectivity has been halved.

The thickness of the coating needs to be one quarter of the wavelength
of the incident light, taking into account the change in wavelength when
it goes into the higher n material (thickness=lambda/n/4). For green
light and an MgF2 coating, the thickness = 550 nm/1.38/4 = ~100nm.

Adding additional coatings of varying n can reduce your reflectivity
even further. Check out an optics text for this.

Also, see this glossary page:
http://www.mellesgriot.com/glossary/wordlist/glossarydetails.asp?wID=90

To put it down, I'd use e-beam evaporation onto a heated (300 C)
substrate. It'll go down very fast (<1 min for 100nm at ~10^-5 mbar).

Chris

On Friday, May 10, 2002, at 07:01  pm, Ali Razavi wrote:

>    I plan to deposit Aluminium fingers on quartz wafers to make
> reflection gratings. I also need to limit the aperture size. For this
> purpose I need to deposit another layer such that
>   1. it attaches both to quartz and to aluminium
>   2. it does not reflect light
>   I was wondering what kind of material/process I can use. Any
> refernce in this regard?
>   Thanks,
>   Ali
--
Christopher F. Blanford
Inorganic Chemistry Laboratory, South Parks Road, Oxford, OX1 3QR, UK
Phone: (44)/(0)-1865-282603; Fax: (44)/(0)-1865-272690
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