I have observed that, on annealing in oxygen, one of my ferrite thin films changes color from yellowish brown to black. Visibly I could see that the film was peeled from the substrate at few places. On doing XRD I found that the annealed film showed lattice parameter changes of about 0.23 Angstrom.
The film ideally has a pseudocubic structure (before annealing in oxygen). When I fitted the XRD data of annealed film using powderX I found few peaks corresponding to hexagonal structure (my material in bulk form exists in different structural polymorphs depending on oxygen stoichiometry). There are no impurity peaks corresponding to constituent oxides. The annealed film is wearing off very quickly.
As far as I can understand from your description, it is normal to observe this kind of behavior. Changing the structure (which means you are also changing the lattice parameter) leads to internal stresses at the interface, causing the loss of adhesion and finally what you observe is the film to peel-off from the substrate. All you have to do in order to support your observation is to find out which crystallographic direction is preferred on the deposition, find the lattice constant for this direction and compare it with the substrate lattice constant. Over a certain threshold, internal stresses lead to detachment of the film.
Normal.. What material is it.. How has it been deposited..
Sound to go in a nice research topic.. Starting condition, end conditions, some effects in between.. Keep on analysing what is going on.
It is barium ferrite...I deposited it using Pulsed Laser Deposition system. deposition temperature was 700 degree Celsius. The film was annealed at 900 degree Celsius. It showed huge increase in ferromagnetism on annealing but the problem is the sample weared off...I wanted to report this result but the problem is lack of proof to support my observation...
can you do the insitu XRD? checking the phase (microstructure changes) during the annealing? but do not only the theta-2theta, but some stress determination too.
observing the structure change with time, or the onset of one diffusion or so is exciting.
all of things goes on..
if you can repeat the experim ent 2 or 3 times.. you do not have to have a peeled-off sample to show.. publish if you think it is worth it.
i am not good at these materials and temperatures..
As far as I can understand from your description, it is normal to observe this kind of behavior. Changing the structure (which means you are also changing the lattice parameter) leads to internal stresses at the interface, causing the loss of adhesion and finally what you observe is the film to peel-off from the substrate. All you have to do in order to support your observation is to find out which crystallographic direction is preferred on the deposition, find the lattice constant for this direction and compare it with the substrate lattice constant. Over a certain threshold, internal stresses lead to detachment of the film.
dear lukas...I don't have insitu XRD. I have used a tube furnace to annealing my samples. I have done this experiment twice and both time the film just peeled off. Another observation was that Titanium doping somehow resulted in holding the film on the substrate. The XRD data of Ti doped samples fitted well with hexagonal structure.
Dear Gregory,
My substrate was single crystal SrTiO3 (100). Though I couldn't do phi scan but the powder XRD of the film grown showed peaks in along (100) direction which means it is highly oriented in (100) direction. The lattice mismatch is 2.3%..
What i feel there is a mismatch between the thermal expansion coefficient.... check it ....
If possible find the buffer layer which can be ....adjust the TEC of both substrate and film....or alternative solution is increase the surface roughness of your substrate......
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