vuv14, july 23, 2004 electronic structures of ca induced one-dimensional reconstructions on a...
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VUV14, July 23, 2004
Electronic structures of Ca induced one-dimensional reconstructions
on a Si(111) surface
Kazuyuki SakamotoDept. Phys., Tohoku University, Japan
H.M. Zhang, R.I.G. UhrbergIFM, Linköping University, Sweden
Outline1. Introduction2. Experimental details3. Results and discussion4.Conclusion
Outline1. Introduction2. Experimental details3. Results and discussion4.Conclusion
VUV14, July 23, 2004Introduction
1D (and quasi-1D) structures formed on semiconductor surfaces expected to show interesting physical phenomena
Ca/Si(111) surface (n×2) reconstructions (n=3, 5, 7, and 9) that culminates with a (2×1) phase at 0.5 ML. A.A. Baski et al., SS 476, 22 (2001), T. Sekiguchi et al., SS 493, 196 (2001), K. Sakamoto et al., PRB 66, 165319 (2002)
(3×2) phase (2×1) phase
honeycomb-chain channel (HCC) model π-bonded Seiwatz Si chains
S.C. Erwin and H.H. Weitering, R. Seiwatz, Surf. Sci. 2, 473 (1964) PRL 81, 2296 (1998)
intermediate phases; combinations of the HCC and Seiwatz models
the understanding of the surface band structures of the two end phases is essential to fully comprehended the electronic properties of
the Ca induced 1D and quasi-1D reconstructionsK. Sakamoto, H.M. Zhang, R.I.G. Uhrberg
VUV14, July 23, 2004
(3x2) surface semiconducting electronic characters
A.A. Baski et al., SS 476, 22 (2001), D.Y. Petrovykh et al., SS 512, 269 (2002), O. Gallus et al., Europhys. Lett. 60, 903 (2002), Y.K. Kim et al., PRB 68, 245312 (2003)
inconsistent resultsthese studies cover only a part of the surface Brillouin zone
(2x1) surface A.ABaski et al., SS 476, 22 (2001)
semiconducting electronic characters
surface band structure -> important input to the structure determination
Aim of this study
determination of the surface electronic structures of the Ca/Si(111)-(3x2) and (2x1) surfaces
Introduction
K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg
VUV14, July 23, 2004
• Si(111) n-type with a 1.1° miscut toward the [-1-12] directioncleaning followed the procedure described in APL 72, 948 (1998)check LEED, valence and Si 2p core-level spectrum
• Ca adsorption deposition onto a substrate kept at ~1000 K
beamline 33, MAX-I synchrotron radiation facility, Lund, Sweden
energy resolution: ~50 meV at h = 21.2 eV angular resolution: ±2°
base pressure: below 4×10-11 Torr
• measurements: 100 K
Experimental details
K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg
VUV14, July 23, 2004
no density of states at the Fermi level
semiconducting electronic structure
agree well with the earlier studies
Valence-band spectra measured using (a) h=21.2 eV and (b) 17 eV along the [-110] direction, and (c) spectra measured using h=21.2 eV along the [11-2] direction.
Results and discussion
K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg
VUV14, July 23, 2004
Band dispersion of the Ca/Si(111)-(3x2) surface
S1-S3 states follow a (3x1) periodicity instead of the (3x2) observed in LEED.
1 and 2:not observed in the earlier ARPES studies
same binding energy using different h direct bulk transition
no corresponding state around the point originate from an umklapp process
surface states
Results and discussion
K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg
VUV14, July 23, 2004
Surface state dispersions of the Ca/Si(111)-(3×2) surface. Solid gray lines are the theoretical surface state dispersions derived from the calculation for the Li/Si(111)-(3×1) surface taken from PRL 81, 2296 (1998).
A
C D
B A’
Results and discussion
S3; good agreement with S1+ S1+~ c+d 、 -bond between the c and d atoms hardly affected by the adsorbates S3; C + D
K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg
VUV14, July 23, 2004
Surface state dispersions of the Ca/Si(111)-(3x2) surface. Solid gray lines are the theoretical surface state dispersions derived from the calculation for the Li/Si(111)-(3x1) surface taken from PRL 81, 2296 (1998).
A
C D
B A’
Results and discussion
S2±~ a±b;cannot use the wave function of a and b atoms of a 1/3 ML HCC Assumption; (A±A’) ±B
HCC; stabilized by a donation of two electrons per (3×2) unit cell (A + A’) ~ A (A + A’) ± B ~ A ± B; same description as S2 ±
S1; A - B, S2; A + B
1 and 2; (A - A’) ± B (?)
K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg
VUV14, July 23, 2004
Valence-band spectra of the Ca/Si(111)-(2x1) surface
LEED pattern of the Ca/Si(111)-(2x1) surface
Band dispersion of the Ca/Si(111)-(2x1) surface
Results and discussion
K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg
VUV14, July 23, 2004
Surface state dispersions of the Ca/Si(111)-(2x1) surface. Solid gray lines are the theoretical surface state dispersions for the Si(111)-(2x1) surface taken from PRB 51, 4258 (1995) and the dashed lines are those taken from PRB 54, 1482 (1996).
dispersion behavior of S1 and S2
surface states of the Si(111)-(2x1) with a Seiwatz structure
situated just above and just below EF
supports the structural model proposed in the earlier studies
Results and discussion
K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg
VUV14, July 23, 2004
(3x2) surface
observation of six states in the gap and pocket of the bulk band projection the dispersion behavior of three of them agree well with
the surface states of a 1/3 ML HCC surface. S1; A - B, S2; A + B, S3; C + D
1 and 2; (A - A’) ± B (?)
(2x1) surface
observation of five states in the gap and pocket of the bulk band projection
S1 and S2 agrees well with the surface states of the Si(111)-(2x1) surface with a Seiwatz structure
A
C D
B A’
Conclusion
K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg
VUV14, July 23, 2004
K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg
Thank you very much for your attention!!