a) Assume that the growth of the solidification front of a pure metal is limited by...

 

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a) Assume that the growth of the solidification front of a pure metal is limited by heat conduction. In the following cases, when do you expect to observe dendrite structures to form? Why? Also, explain briefly how dendrites form? Tm Solid | Liquid T m Solid | Liquid x i b) Consider a situation where you are growing a thin film on a substrate using pulsed laser deposition. In this process, you use a short pulse (-10-30 ns) laser to ablate a material and can control the number of pulses per second. Assume that I will do the growth at 1 Hz pulse rate (only one pulse per second) and the incoming flux of atoms is of sub-monolayer atomic density (the coverage you can get for a pulse is only a fraction of the atomic density on the surface of the substrate, hence 2D growth is dominant). Let us assume that the lattice constant of the film and the substrate are ~4 . Assume that I use a substrate with a miscut of 1 to the (001) face of the crystal and the surface diffusivity of incoming flux is 10-10 cm/s at 700C along this face irrespective of the miscut. Which is the dominant growth mechanism among (a) step flow growth or (b) layer-by-layer growth for this case? Why? Can you name two parameters you can control to change the growth mode from one to another? a) Assume that the growth of the solidification front of a pure metal is limited by heat conduction. In the following cases, when do you expect to observe dendrite structures to form? Why? Also, explain briefly how dendrites form? Tm Solid | Liquid T m Solid | Liquid x i b) Consider a situation where you are growing a thin film on a substrate using pulsed laser deposition. In this process, you use a short pulse (-10-30 ns) laser to ablate a material and can control the number of pulses per second. Assume that I will do the growth at 1 Hz pulse rate (only one pulse per second) and the incoming flux of atoms is of sub-monolayer atomic density (the coverage you can get for a pulse is only a fraction of the atomic density on the surface of the substrate, hence 2D growth is dominant). Let us assume that the lattice constant of the film and the substrate are ~4 . Assume that I use a substrate with a miscut of 1 to the (001) face of the crystal and the surface diffusivity of incoming flux is 10-10 cm/s at 700C along this face irrespective of the miscut. Which is the dominant growth mechanism among (a) step flow growth or (b) layer-by-layer growth for this case? Why? Can you name two parameters you can control to change the growth mode from one to another?

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a Dendrite Formation Dendrite formation occurs when the solidification front is limited by heat conduction Heres why Undercooling When a pure metal co... View the full answer