b) List two types of vacuum pumps that could be used to operate at this pressure
ID: 715449 • Letter: B
Question
b) List two types of vacuum pumps that could be used to operate at this pressure range. Problem 2: Sticking Coefficient Monolayer graphene is being deposited by chemical vapor deposition onto copper foil in an isothermal quartz tube reactor. The inlet gas consists of an 0.1% mixture of methane (CH4) in H2 and the chamber pressure and temperature are held constant at 10 Torr and 800°C, respectively. 2 The density of carbon atoms in graphene is 3.95x1015 atoms/cm2 and the thickness of a monolayer is 3.45 A 2 a) Calculate the partial pressure of CH4 in the gas phase. b) Under these conditions, it takes 30 minutes to grow 1 monolayer of graphene. What fraction of the carbon atoms in the CH4 molecules impinging on the copper surfaces end up incorporated into the monolayer? This can be considered as the "sticking coefficient. Assume the H2 leaves as a gas. b) When the deposition temperature is increased to 1000°C, the sticking coefficient increased to 1x10. Suggest one or two possible reasons for the increase in sticking coefficient (and therefore monolayer growth rate) with increasing temperature. (A sentence or two is all that is needed.) rfice Problem 3: Gas Transport through Orifice You are interested in using a vacuum system with the geometry shown at the right for a deposition process. A 0 2 m with a numning speed (S1) of 17 P2Explanation / Answer
Given:
Ptotal = 10 Torr = 0.0131579 atm
T= 800 °C = 1073.15 K
(a) Partial pressure of methane, P1 = Ptotal * [(0.1% methane)/100]
= 0.0131579 atm * [0.1/100]
= 0.000013159 atm
(b) Sticking coefficient, S0 = Pa/ [Pa+ Pd]
Where Pa= probability that molecule will adsorb to the surface
Pd= probability that molecule will desorb from the surface
(c) One of the possibility as to why sticking co-efficient increases with increase in temperature is the result of condensation mechanism. As temperature increases, there could be an enhancement in the kinetics of this process. This can happen by increasing the case of methane copper interaction or by weakening the hydrogen methane interaction in the surface layer and increasing the probability of replacement of a hydrogen atom by a methane.
Another possible reason for this increase is the increase in surface mobility as temperature increases.
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