Which type of capping layer can be used as a protective layer to avoid the oxidation of metallic thin films?
I think it depends on what you want to do with the metal itself. If you add another more noble metal on the film you want to protect, then you possibly will not be able to use any optical (UV-Vis-range) technique to look at your underlying metal, as most of the visible light will be reflected from the capping layer. So if you intend to do some Magneto-Optical-Kerr-Effect-measurements (MOKE), then a transparent layer would be more favourable compared to a Gold or Platinum capping. Here in fact a thin oxide layer of another metal (e.g. Al2O3 or TiO2) may be useful, and even the oxidized metal itself can be useful if the oxide protects the metal (i.e. it acts as passivating oxide). A ceramic material such as Si3N4 as proposed by Vibhu may be better also.
But again, it depends on what you want to do with the metal film! Best regards, Dirk
depends on the metal type. You can nitride the surface. Oxygen needs to diffuse through the capping layer. so you want capping layer with very high bond energy and tightly packed scheme.
Nitridation will work great for most of the cases.
if you dont want to nitride then deposit other metal nitride (for eg Si3N4) or carbide (like SiC) film insitu or in a different chamber (without taking out in atmosphere) to protect your surface.
Many people also use other metal layers to protect the thin metal layer beneath. W would be your friend there. You can find more alternatives by looking at electron affinities
I think it depends on what you want to do with the metal itself. If you add another more noble metal on the film you want to protect, then you possibly will not be able to use any optical (UV-Vis-range) technique to look at your underlying metal, as most of the visible light will be reflected from the capping layer. So if you intend to do some Magneto-Optical-Kerr-Effect-measurements (MOKE), then a transparent layer would be more favourable compared to a Gold or Platinum capping. Here in fact a thin oxide layer of another metal (e.g. Al2O3 or TiO2) may be useful, and even the oxidized metal itself can be useful if the oxide protects the metal (i.e. it acts as passivating oxide). A ceramic material such as Si3N4 as proposed by Vibhu may be better also.
But again, it depends on what you want to do with the metal film! Best regards, Dirk
thank you for your valuable information, i want to do the magnetic anisotropy and MOKE studies of Rare-Earth transition metallic thin films, so i need to coat the capping layer on these thin films as these films have highly oxidization nature. For that i want to know what type of capping layer is suitable for these studies and how much thickness is sufficient to overcome the oxidation and to avoid the effect of capping layer from the film properties.
For MOKE measurements Pt or Au capping layer 3-5 nm thick is very good, as I mentioned earlier. However, you need to be aware that by the coverage of the sample you introduce a new interface which may contribute to magnetic anisotropy: e.g. additional surface anisotropy or alloying at the interface. Thinner magnetic layer the effect stronger. This effect may be substantial when a magnetic layer thickness is equal to a few nanometers. E. g. for a Co layer 2 nm thick magnetization reorientation depends on type of a capping layer. However, in a case of RE it should not be very strong.
@Andrzej, these are exactly the issues I wanted to address - and thus I would prefer a transparent oxide for capping purposes. But you are right, if you consider the influence of the capping layer on the MOKE, than you may also use a more noble metal as capping ... Enjoy your week - ends
Dirk
@ Dirk, certainly Pt and Au capping is not universal and ideal. In some cases these metals are not transparent enough. We met some limitations while preparing samples for depth-resolved XMCD measurements. And another story is spin perturbation by a cap layer (in general) if one performs spin resolved measurement. Thanks, and nice time for you.
For capping our rare-earth nitride films we use GaN or AlN, these are optically transparent and do a good job of protecting the reactive film underneath.
I am also working with rare earth thin (but not so thin, as they have 700nm thick) films. Im using Ti as a capping layer (Im not focused on MOKE experiments), although Im not completly sure this is the best option to prevent oxidation.
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