Question

Diffusion Mechanisms - Nonsteady State Diffusion - Copy Learning Goal: To learn how the diffusion rate changes in dynamic conditions where the diffusion profile changes with time, and how in some cases it can be modeled easily In steady stadision, the concentration Cis a function only of position (not of time). When usion is nonsteady Cis a function of position and time, Oix Nonsteady state diffusion in one direction can be modeled using Fick's Second Law -D where is the concentration and is the diffusion coefficient Fick's Second Law is a second order differential equation. To solve we need a domain, an initial condition, and boundary conditions. The domain region of the that we are interested in. The initial condition is a known concentration profile at the starting time for every point on the is that is in the domain. The boundary conditions specity ether the concentration or the concerto gradient at the end of the domain The diffusion coefficient is treated as a constant in this equation. However, it can vary significantly with temperature. The relationship between the diffusion coefficient and temperature is D (T) = where Do and Ea are parameters that depend on the host and diffusing species D. exp . Part A - General nonsteady diffusion Consider the diagram below, which shows an initial concentration profie Cut0) of some atomic species in a host material. This could be the concentration protte of phosphorous that was on implanted into silicon at two different energies (causing the two local maxima in the profile this were the case, the concentration of phosphorous would be much less than 1% of the icon hostatoms. At which of the four points will the concentration increase as a result of the flux? Depth in material Check all that apply. View Available Hints) point A point 0 point a point Submit

Answer 1

Part - A Correct Prowes - and option:- Point B! Here, As depth very from A to Be - the concentsation de deesoare) For B to a concentention I insesse For to D Concentration to Celecrease last Bi- here, Co=0.20% = 2.00% +2 24 hours a= 2mm - 0.56% Al) Now, cas-lo a 9-eef (ano) 0.56 - 0.20 2 – 0.20 ent)