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 NANO LAB. mujiny

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

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

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 Agreement with the previous work ! ! Unoccupied states occupied 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

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

6. R E S U L T S A N D D I S C U S S I O N S occupied states 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.

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 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 5. Water dissociation of two adjacent dimers 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 1. Two pairs of enantiomorphic protrusions of C defect 2. Single water molecule 3. The dissociated H and OH species adsorb on the same side of two adjacent dimers 4. Four different local configuration