A 0.2-mm-thick wafer of silicon is treated so that a uniform concentration gradient of antimony is produced. One surface contains 1 Sb atom per 108 Si atoms and the other surface contains 500 Sb atoms per 108 Si atoms. The lattice parameter for Si is 5.4307 Å (Appendix A). Calculate the concentration gradient in (a) at% Sb per cm; and (b) Sb atoms cm ? cm3 .

- 0.0249% Sb/cm

Explanation:

Given that:

One surface contains 1 Sb atom per  10⁸  Si atoms and the other surface contains 500 Sb atoms per  10⁸ Si atoms.

The concentration gradient in atomic percent (%) Sb  per cm can be calculated as follows:

The difference in concentration =

The distance = 0.2-mm = 0.02 cm

Now, the concentration of silicon at one surface containing  1 Sb atom per 10⁸ silicon atoms and at the outer surface that has 500 Sb atom per   10⁸ silicon atoms can be calculated as follows:

= - 0.0249% Sb/cm

b) The concentration of Sb in atom/cm³ for the surface of 1 Sb atoms can be calculated by using the formula:

Lattice parameter = 5.4307 Å;  To cm ; we have

=

=

The concentration of Sb in atom/cm³ for the surface of 500 Sb can be calculated as follows:

   =  

   =

Finally, to calculate the concentration gradient

- lead + phosphoric acid = hydrogen + lead(ii) phosphate

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.