Hello.
I'm curious about the transparency of Al thin film with sputtering method.
I made Aluminium(Al) thin film with sputtering method which has ~ 10nm thickness on a transparent substrate.
I see this Al thin film is transparent. Is this alright? or is there any problem in the Al thin film?
Ag thin film, Mg thin film I made is not transparent but, Al thin film is transparent.
I'm not sure the Al thin film is made properly.
Hi, metals have a finite absorption coefficient. Therefore, very thin layers are transparent up to a certain thickness, this thickness being proportional to the absorption coefficient of these materials. In case of aluminum, you can have two different effects. The first is the one mentioned just above. The second one is the fact that Al layers can oxidize in air. If you measure transmission in the vacuum chamber before opening it and after, you would be able to discriminate these two effects.
Hi,
Very thin metal layers when sputtered on glass show transparant behavior. Most metal layers should optically close at a thickness of 50-100 nm. It depends a lot on the deposition method and process. If you sputter at high pressures and low temperature, metals tend to grow in a columnar structure which tend to stay open while at lower sputter pressures and/or at higher temperatures you will get more microcrystalline/crystalline morphology and it will optically close much sooner.
Thank you, Peter Knapen! I have questions about your answer:
1) what is the meaning of "open" and "close" optically in your answer?
2) The high pressure means that the pressure is less vacuum level and the lower pressure means that the pressure is close to vacuum level, right?
Optically closed is: when you hold a glass in the direction of a light source .
you should not be able tot see through the deposited layer.
The lower and higher pressure is the operating pressure at which you deposit the layer with the help of Ar-gas, usually in the range of 5-15 mTorr.
Very thin metal films can be transparent in the usual sense - i.e. through this layer you can see the light and outlines of objects. A classic example is gold, which can be rolled mechanically into a transparent film (starting at a thickness less than 100 nm; with a green tint of passing light).
Hi, metals have a finite absorption coefficient. Therefore, very thin layers are transparent up to a certain thickness, this thickness being proportional to the absorption coefficient of these materials. In case of aluminum, you can have two different effects. The first is the one mentioned just above. The second one is the fact that Al layers can oxidize in air. If you measure transmission in the vacuum chamber before opening it and after, you would be able to discriminate these two effects.
Besides the Optical properties others have mentioned, it's important to know if you are expecting the metallic or conducting properties to be what you would expect for Al. Until the thickness reaches a critical amount of say ~1000nm, you should not expect conductive measurements that correspond to bulk metal.
There is something else to consider, too. Is your 10nm film continuous (2D) on your substrate and process deposition conditions, or it is still in island-like form(3D). I recall seeing Al islands when very thin (10nm-20nm) Al film is sputtered on clean Si surface at high temperature, > 400C. On thin Ti film sub-layer, however, Al film grows layer-by layer and is continuous. Continuity could make difference in optical appearance.
This is really getting interesting. I would like to ask others if they can explain why a layer such as Ti (how thick) would allow the film to grown more in layer mode. Perhaps it is a surface treatment changing the sticking coefficent, or it could be related to lattice matching. Interested to see what others think.
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