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

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)

Dimer A defect

B defect C defect = Metallic

2.The subsurface impurity model : Boron

3. The extrinsic adsorbate model : two water molecules

C defect

• Si(100) : boron doped, resistivity 0.1cm phosphorous doped, resistivity 0.05cm

• PBase ~ 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

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 terr

ace at low bias

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’)

]110[__

]101[_

U U’

D D’Enantiomorphic protrusions

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 teardr

op 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

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

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 t

hat 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 do

wn dimer atom

• Missed and slightly depressed upper atoms → see fig.

• OH reacted dimer becomes nonbuckled

H-reacted atom

Unreacted atom of OH reacted dimer

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.

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