6.152J/3.155J So flux of atoms hitting surface per unit time k T DImensional analysts: (force/area- en/vol ) p- vol =n——=Jmv Numerically,-35×l02 Tom)(atos/ sec) This gives a flux 1 monolayer (ML) arriving per sec at 10-6 Torr 6.152J3.155J Wed, Sept. 10, 2003 Diffusivity ooO Recall for solids: Debye 101351 For gas, no energy barrier, just collisions. recall 2=- kT much weaker T-dep than In solld 6.152J3.155J Wed, Sept. 10, 20036.152J/3.155J 6.152J/3.155J 7 So flux of atoms hitting surface per unit time area # / vol. vx Jx = nvx 2 = n 2 2kT pm ideal gas p 2pmkT = Jx Di i l l i l p = Ekin Vol = n mv 2 2 = Jmv Numerically, Jx = 3.5 ¥1022 p(Torr) MT(g / mole ⋅K) (atoms /cm 2 sec) This gives a flux 1 monolayer (ML) arriving per sec at 10-6 Torr l = kB T 2pd 2 p Compare: Wed., Sept. 10, 2003 mens ona ana ys s: (force/area = en/vo .): Diffusivity DG D0 exp - È DG˘ Recall for solids: D = Í˙ Î kT ˚ Debye n 1013 s-1 For gas, no energy barrier, just collisions. dC n Jgas gas = D @ D dx l lvx Dgas ª nv 2 x (cm2 2 /s) kT recall l = 2pd 2 p v \D x µ T much weaker T-dep. than in so gas µT lid 3/ 2 6.152J/3.155J Wed., Sept. 10, 2003 8 4