I am trying to do EBSD characterization of graphene samples. Is ion beam milling (FIB) the best way to get good indexing?
Thanks in advance
Hi Rahul,
Can you give some details? You have graphene film on the some polycrystalline substrate? If not, what you expect to see? FIB is good for sample preparation for EBSD, but maybe not for graphene
Hi Evgeny,
Thank you very much for your response. It is a graphene film on copper substrate.
Graphene is single nano layer normally to my understanding. If it is more than one layer then it acts as Graphite. If you have deposited Graphene on Cu foil using CVD method, you don't need any preparation method, you can check my EBSD data. Other option is you can use T-EBSD method (refer below link for details of method).
http://www.oxford-instruments.com/businesses/nanotechnology/nanoanalysis/t-ebsd.
It is not eassy to index Graphene because of the following
1) it is single atomic layer, so beam will penetrate through the surface.
2) if you have more than 10 layer of graphene, the peak becomes similar to that of graphite. So hard to differentiate between graphene and graphite using diffraction techniques. In this case Raman spectroscope works well.
These are two main issues, to index graphene using EBSD.
If it is really single layer graphene it would surprize me to see any EBSD pattern. For diffraction you need a crystal which is a periodic arrangement of atoms or molecules in 3D. You can certainly get some image for a 2D periodicity but as far as I know there is no system available which can simulate or index these patterns (however they will look like). From this follows, if your patterns look like Kikuchi patterns it is not graphene but graphite.
FIB preparation is per se not good for EBSD since it will definitely generate radiation defects. Whether they are disturbing depends on the operation conditions but also from the material. You can destroy a crystal structure with Ga ions, but this you can also get with electrons already (e.g. for zeolites). There it is very likely the local heating which kills the crystalline arrangement.
TKD is good for small grains. The information depth is practically identical for TKD and EBSD. Therefore, for good patterns the common recommendation are thicknesses about 80nm and more. Thinner layers do not have the periodicity in 3D in order to generate a interference pattern for all directions. The patterns become extremely blurred and are hard to index. Therefore, TKD is good for an increased spatial resolution because of no or comparatively small sample tilt...and the lower spread of electrons below the surface. But please keep in mind that a big spread means that the respective electrons loose energy so that these electrons cannot interfere anymore to the formed signal which displays practically only electrons close to the acceleration energy (about 500V lower only). This means, highly or multiple-scattered electrons don't contribute to the visible Kikuchi pattern at all and disappear with their signal in the background which is removed.
The thickness of samples i have analysed are about 50 microns in thickness. Graphene is deposited on polychromatic Cu ribbon using CVD at 1000 degrees. Graphene is deposited only on one surface. The beam power we normally use between 15-20KV (+/- 5KV). Due to this high power, the beam penetrates deeper and it is almost not possible to index graphene because they are usually one or few atom thickness. By placing graphene deposited surface down face (i.e. towards detector) can we use T-EBSD method to detect graphene or not?.
The grain size of CU are not more than 100 micro meter.
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