PHYSICAL REVIEW B 67, 153307(2003)

1. PHYSICAL REVIEW B 67, 153307(2003) Model for C defect on Si(100) : The dissociative adsorption of a single water molecule on two adjacent dimers M. Z. Hossain, Y. Yamashita, K. Mukai, and J. Yoshinobu* The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8521, Japan Received 10 February 2003 ; published 30 April 2003 mujiny NANO LAB.

2. Dimer A defect B defect C defect I N T R O D U C T I O N C defect 1. The intrinsic vacancy model ; - R.J. Hamers and U.K. Kohler, J. Vac. Sci. Technol. A 7, 2854 (1989) = Metallic 2.The subsurface impurity model : Boron 3. The extrinsic adsorbate model : two water molecules

3. E X P E R I M E N T • Si(100) : boron doped, resistivity 0.1cm phosphorous doped, resistivity 0.05cm • PBase ~ 1.5 ⅹ 10-8 Pa • flashing at 1500K • Defect 1%↓ • Water(Pulse-valve doser)

4. R E S U L T S A N D D I S C U S S I O N S 1. C defect at RT occupied states Unoccupied states • Unoccupied states : Bean shape protrusion, depression • Occupied states : two odd atoms appear much brighter than the dimers on the clean terrace at low bias Agreement with the previous work ! !

5. R E S U L T S A N D D I S C U S S I O N S 2. C defect at 80K • The asymmetric teardrop shape : 4 type • Perpendicular mirror plane : U, U’ and D, D’ ( direction) • Parallel mirror plane : U, D and U’, D’ ( direction) Zoomed in imaged (D’) U U’ Unoccupied states D D’ Enantiomorphic protrusions

6. Cross-shaped depressions + : missed upper atom - : slightly depressed upper atom Perpendicular mirror plane : Y, Y’ → Z, Z’ ? Parallel mirror plane : Y’, Z’ They have determined that missed upper atom and the tail of the asymmetric teardrop protrusion lie on the same dimer site. R E S U L T S A N D D I S C U S S I O N S occupied states

7. R E S U L T S A N D D I S C U S S I O N S 3. The origin of C defect ??? • Water adsorption on the Si(100) surface • The concentration of the C defect increased from 0.75% to 1.85% at 80K • The number of the C defect incresed at RT • C defects are caused by water adsorption Agreement with the previous work ! ! 4. Water dissociates on the Si(100) surface • IR and EELS • Water dissociates and Si-H and Si-OH species are formed • Theoretical calculations → no energy barrier for the dissociative adsorption • Water molecule initially interacts with the low atoms of buckled dimer and dissociated • OH → lower atom • H → upper atom • Same dimer : both occupied and unoccupied state STM image are the depression • Two adjacent dimers : C defect → same dimer or adjacent two dimers in a row

8. R E S U L T S A N D D I S C U S S I O N S 5. Water dissociation of two adjacent dimers • Tow unreacted atoms should still remain at the same side • Depressed side at RT : OH and H reacted sites • At low tem.(80K) the dangling bond on the OH reacted dimer is found brighter than that on the H reacted dimer → the asymmetric teardrop protrusion 6. Four different configurations • The preferential adsorption of OH on the down dimer atom • Missed and slightly depressed upper atoms → see fig. • OH reacted dimer becomes nonbuckled H-reacted atom Unreacted atom of OH reacted dimer

9. R E S U L T S A N D D I S C U S S I O N S 7. Nishizawa et al. : Model of C defect • Neither explain the STM images(two pairs of enantiomorphic protrusions) nor the metallic properties • Metallic properties ??? the unreacted atoms of free dangling bond in the C defect • The reactivity of these free dangling bonds : CO and O2 are preferentially adsorbed near the C defect on Si(100) at low tem.

10. C O N C L U S I O N • Two pairs of enantiomorphic protrusions of C defect • Single water molecule • The dissociated H and OH species adsorb on the same side of two adjacent dimers • Four different local configuration