Date post: | 20-Jan-2018 |
Category: |
Documents |
Upload: | clementine-nash |
View: | 217 times |
Download: | 0 times |
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 S1. 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 S3. 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 S7. 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