Dear Shashi Kant , thanks for sharing this question with the RG community.

Let us assume that you want a mirror which blocks completely the pass of light (visible light). In my own experience you would need a film thicker than 150 nm, otherwise the mirror will be a partial mirror (some light will pass through). For security you can deposit a thicker layer, say 200 or 300 nm thick.

In my experiments I never used a bonding layer. Aluminum is fairly attached to the glass surface (soda-lime glass, BK7) and also to several polymers (PET, PDMS, PMMA, etc). Of course the substrate must be cleanead following the common cleaning processes.

The RF sputtering parameters do not just depend on the RF power, several other aspects are important as well, such as base pressure (chamber vacuum), the sort of sputtering atoms used, their presure while sputtering is also important, the deposition rate, RF power and temperature are also variables to take into account.

This aspect has been already clearly explained previosly here, please, see for example:

https://www.researchgate.net/post/What_are_the_factors_for_Aluminum_thin_film_depostion_when_Rf_sputtering_is_used

For more detailed descriptions you might be interested in reading some classic publication, such as:

Article “Aluminum films deposited by RF sputtering“

Apart from direct internet searches you could give a try to the RG´s searching option, it will provide useful informations in most cases.

One last note, that could be or not important for your work. Aluminum surface will be readily oxidised when exposed to the air, in few hours it will be completely covered by a thin layer of Al2O3, but as the oxide layer get thicker it becomes more and more impermeable to O2 and when it reaches a thickness of around 4 nm it stops growing.

Hope this helps. Good luck with your work and my best wishes!

Shashi Kant , There is a really cool spectral reflectance calculator from filmetrics

https://www.filmetrics.com/reflectance-calculator. this allows you to very the thickness and you can observe the resulting spectral reflectance.

As previously mentioned, as long as the transmittance is minimum, then you should have a good reflective surface.

I've sputtered Al on glass for most of my PhD and I never used an adhesion layer. What I would do though is prior to sputtering aluminum, I would do a piranha clean in 4:1 sulfuric acid and hydrogen peroxide to clean the glass. I would then do the deposition.

As Manuel Gómez stated the deposition parameters such as rate, pressure, and substrate temp will affect parameters such as film microstructure and will likely have implications on reflectance.

Good Luck,

Adam

The filmetrics reflectance calculator is indeed great, easy to use and fast. Thanks Adam Weidling for bring it to my mind and for sharing it here!

Dear Sir,

what is the bonding layer? What do you mean by "stable mirror"?

I agree with Manuel Gomez but need to add that the Al quality (mainly purity as determined by ESA/XPS )should be very high, close to 100%. Experince is that oxygen in the Al is causing discoloration and also poor stability to the NaOH and other tests. But there seems to be more to it as I found different NaOH stabilities depending on the underlying materials. I could not clarify this in the past.