Kinetics study on the hydrogen atom-induced abstraction and associative desorption of deuterium adatoms from the Si(100) surface at 573 K

Abstract

Hydrogen atom-induced deuterium adatom abstraction has been studied on the Si͑100͒ surface from a desorption point of view. Abstraction of HD as well as collision-induced D 2 desorption are observed on the D/Si͑100͒ surface during H beam exposure at 573 K. For 1 ML D ad precoverage, about 30% of the desorbed D atoms are ejected as collision-induced D 2 desorption at the very beginning of H(g) exposure. It is found that the decay of the HD and D 2 rates are affected by the total coverage, HϩD . The decay rate of the HD rate is much lower in the low coverage regime than in the high coverage regime. The nominal cross section of the former is 2.3Ϯ1.0 Å 2 , while for the latter 7.2Ϯ0.5 Å 2 . The HD rate curves show that the abstraction obeys nearly first-order kinetics towards D coverage, D . On the other hand, the D 2 rate curves show that the collision-induced desorption obeys nearly fourth-order kinetics towards D . Such HD abstraction is also observed on an oxygen-deposited D/Si͑100͒ surface where the oxygen atoms are known to be incorporated between Si atoms. The observed decay rate of the HD rate is extremely low, with a cross section of 1.5Ϯ1.0 Å 2 . The reaction kinetics are well understood by adopting the kinetics model recently proposed by Flowers et al. ͓Surf. Sci. 396, 227 ͑1998͔͒. The abstraction of HD may be due to an Eley-Rideal mechanism rather than to a hot atom mechanism. Collision-induced D 2 desorption may take place upon encounter of two dideuteride species via an isomerization reaction at quasiequilibrium.

Rate equation analysis of hydrogen uptake on Si (100) surfaces

“…Equations ͑15͒ and ͑16͒ determine the relative coverages under the equilibrium condition 10 2 / 00 11 = 4Q 10 2 /Q 11 exp͑− 1 /kT͒ ͑ 17͒…”

“…Our H flux is 6.7ϫ 10 12 /cm 2 s with a ±30% error bar. After taking nearly unity sticking probability of H 25,27 into account, k s ͑= s for E a,s =0͒ is determined to be 0.01 ML/ s. 10 The values of HH and AID are available in Ref. 19, while the corresponding E a,HH and E a,AID are taken from Ref.…”

“…͑3͒-͑11͒ the rate of increase in the total H coverage ͑⌰: ͓ML͔͒ can be equated to the sum of adsorption and desorption rates. The fractional coverages are defined as 00 for ·Si-Si·, 11 for HSi-SiH, 10 for HSi-Si·, and 2 for HSiH. 16 Then, the rate equation is described as…”

“…It has been well established that H adatoms can be abstracted by H along not only a direct pathway but also an indirect pathway. 9,10 The indirect abstraction by H was distinguished from the direct abstraction by labeling adatoms with deuterium. The direct abstraction has been called ABS ͑: abstraction͒, and described as…”

“…So far, the abstraction reactions have been studied mainly from a kinetics point of view [9][10][11][12][13][14][15][16][17][18][19][20][21][22] rather than from a dynamics point of view. [23][24][25][26][27] Dinger, Lutterloh, and Küppers 9,20 reported that the reactions of Eqs.…”