Electron diffraction


by quietrain
Tags: diffraction, electron
quietrain
quietrain is offline
#1
Mar12-10, 05:55 AM
P: 651
ok, i did a lab and found values of the diameter of the electron rings after diffraction from a graphite. i also have the voltage that i accelerate the electrons to hit the graphite.

so to find the distance between adjacent planes of graphite carbon "d", we use bragg's diffraction law right? 2dsin(theta) = n(lamda)

but the problem is what if i need to find the interatomic distance "a" between the carbon atoms on the same plane. is there some sort of equation or law i can use to find this distance from the experiment data that i obtained above? i don't seem to recall any.

and also, am i right to say, the outer diffraction ring is caused by the diffraction between atoms of the same plane (interatomic) whereas the inner diffraction ring is caused by the diffraction between layers of atoms "d" given by bragg's law?

thanks a ton!
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quietrain
quietrain is offline
#2
Mar14-10, 03:44 AM
P: 651
maybe i rephrase my question

ok, we use bragg's law to determine the spacing d between LAYERS of graphite

but how do we determine the interatomic spacing A between the individual Carbon atoms for each plane of individual graphite?

anyone knows?
Modey3
Modey3 is offline
#3
Mar14-10, 06:42 PM
P: 136
quietrain,

Graphite is pretty simple when it comes to determining the structure-factor. I won't solve the problem for you, but try to represent graphite in terms of a orthorhombic unit-cell with a multi-atom basis. Find the structure-factor based on that symmetry. There is no easy "plug and chug" answer for this problem. Your going to need to do some work!

modey3

quietrain
quietrain is offline
#4
Mar15-10, 05:52 AM
P: 651

Electron diffraction


er i know the bond angles are 120 and the interatomic distance is around 0.142nm. but how do i get the interatomic distance from an experiment? i only have values for voltage, and the electron ring diffraction diameter only?

so with this 2 variables, i can find the interplanar distance d using bragg's law. but what about the interatomic distance? can i find it from just those 2 variables?
Modey3
Modey3 is offline
#5
Mar15-10, 08:49 AM
P: 136
quietrain,

You will need to use more than just one diffraction ring to determine the inter-atomic distance. That's why you need to determine the structure-factor.

modey3
quietrain
quietrain is offline
#6
Mar16-10, 02:02 AM
P: 651
oh ya... i have 2 radius of diffraction rings... one bigger than the other... but i dont understand why there are two?

what is the structure? i only know that graphite is hexagonal in shape, so they have bond angles of 120?

but how does that allow me to find the interatomic distance?


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