Answer:
A) The sketches for the required planes were drawn in the first attachment [1 2 1] and the second attachment [1 2 -4].
B) The closest distance between planes are d₁₂₁=a/√6 and d₁₂₋₄=a/√21 with lattice constant a.
C) Five posible directions that electrons can move on the surface of a [1 0 0] silicon crystal are: |0 0 1|, |0 1 3|, |0 1 1|, |0 3 1| and |0 0 1|.
Compleated question:
1. Miller Indices:
a. Sketch (on separate plots) the (121) and (12-4) planes for a face centered cubic crystal structure.
b. What are the closest distances between planes (called d₁₂₁ and d₁₂₋₄)?
c. List five possible directions (using the Miller Indices) the electron can move on the surface of a (100) silicon crystal.
Explanation:
A)To draw a plane in a face centered cubic lattice, you have to follow these instructions:
1- the cube has 3 main directions called "a", "b" and "c" (as shown in the first attachment) and the planes has 3 main coeficients shown as [l m n]
2- The coordinates of that plane are written as: π:[1/a₀ 1/b₀ 1/c₀] (if one of the coordinates is 0, for example [1 1 0], c₀ is ∞, therefore that plane never cross the direction c).
3- Identify the points a₀, b₀, and c₀ at the plane that crosses this main directions and point them in the cubic cell.
4- Join the points.
<u>In this case, for [1 2 1]:</u>
![l=1=1/a_0 \rightarrow a_0=1](https://tex.z-dn.net/?f=l%3D1%3D1%2Fa_0%20%5Crightarrow%20a_0%3D1)
![m=2=2/b_0 \rightarrow b_0=0.5](https://tex.z-dn.net/?f=m%3D2%3D2%2Fb_0%20%5Crightarrow%20b_0%3D0.5)
![n=1=1/c_0 \rightarrow c_0=1](https://tex.z-dn.net/?f=n%3D1%3D1%2Fc_0%20%5Crightarrow%20c_0%3D1)
<u>for </u>
<u>:</u>
![l=1=1/a_0 \rightarrow a_0=1](https://tex.z-dn.net/?f=l%3D1%3D1%2Fa_0%20%5Crightarrow%20a_0%3D1)
![m=2=2/b_0 \rightarrow b_0=0.5](https://tex.z-dn.net/?f=m%3D2%3D2%2Fb_0%20%5Crightarrow%20b_0%3D0.5)
![n=\overline{4}=-4/c_0 \rightarrow c_0=-0.25](https://tex.z-dn.net/?f=n%3D%5Coverline%7B4%7D%3D-4%2Fc_0%20%5Crightarrow%20c_0%3D-0.25)
B) The closest distance between planes with the same Miller indices can be calculated as:
With
,the distance is
with lattice constant a.
<u>In this case, for [1 2 1]:</u>
<u />
<u />
<u>for </u>
<u>:</u>
![d_{12\overline{4}}= \displaystyle \frac{a}{\sqrt{1^2+2^2+(-4)^2}}=\frac{a}{\sqrt{21}}=0.22a](https://tex.z-dn.net/?f=d_%7B12%5Coverline%7B4%7D%7D%3D%20%5Cdisplaystyle%20%5Cfrac%7Ba%7D%7B%5Csqrt%7B1%5E2%2B2%5E2%2B%28-4%29%5E2%7D%7D%3D%5Cfrac%7Ba%7D%7B%5Csqrt%7B21%7D%7D%3D0.22a)
C) The possible directions that electrons can move on a surface of a crystallographic plane are the directions contain in that plane that point in the direction between nuclei. In a silicon crystal, an fcc structure, in the plane [1 0 0], we can point in the directions between the nuclei in the vertex (0 0 0) and e nuclei in each other vertex. Also, we can point in the direction between the nuclei in the vertex (0 0 0) and e nuclei in the center of the face of the adjacent crystals above and sideways. Therefore:
dir₁=|0 0 1|
dir₂=|0 0.5 1.5|≡|0 1 3|
dir₃=|0 1 1|
dir₄=|0 1.5 0.5|≡|0 3 1|
dir₅=|0 0 1|