An evaporator is used to deposit aluminum. The aluminum charge is maintained at

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An evaporator is used to deposit aluminum. The aluminum charge is maintained at a uni- form temperature of 1100 degree C. If the evaporator planetary has a radius of 40 cm and the diameter of the crucible is 5 cm, what is the deposition rate of aluminum? If the chamber also has a back- ground pressure of 10^-6 torr of water vapor and the water vapor is assumed to be at room temparature, determine the ratio of the arrival rates of the aluminum atoms and the water molecules. The mass density of solid aluminum is 2.7 gm/cm^3 (2700 kg/m^3). Solution According to Figure 12.2, at 1100 degree C the vapor pressure of aluminum is about 1 * 10^3 torr. The area of the crucible is 19.6 cm^2. The atomic mass of aluminum is 27. Using Equation 12.8 with MKS units, R = 8.45 * 10^-6 * 3.59 * 10^-3 * 9.8 X 10^-4 R = 2.9 X 10^-11 =17.8 The arrival rate of aluminum atoms is just the growth rate times the number density of aluminum or J_Al=R* =1.78*10^18 According to Equation 10.10 and 12.2, the arrival rate of the water (atomic mass 18) is J_H_2O= =4.8*10^18

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