Electronic structures of Ca induced one-dimensional reconstructions on a Si(111) surface

1. Electronic structures of Ca induced one-dimensional reconstructions on a Si(111) surface Kazuyuki Sakamoto Dept. Phys., Tohoku University, Japan H.M. Zhang, R.I.G. Uhrberg IFM, Linköping University, Sweden Outline 1. Introduction 2. Experimental details 3. Results and discussion 4.Conclusion Outline 1. Introduction 2. Experimental details 3. Results and discussion 4.Conclusion

2. Introduction K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg 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) modelπ-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 reconstructions

3. Introduction Aim of this study determination of the surface electronic structures of the Ca/Si(111)-(3x2) and (2x1) surfaces K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg (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 results these studies cover only a part of the surface Brillouin zone (2x1) surfaceA.ABaski et al., SS 476, 22 (2001) semiconducting electronic characters surface band structure -> important input to the structure determination

4. Experimental details • beamline 33, MAX-I synchrotron radiation facility, Lund, Sweden • energy resolution: ~50 meV at hn= 21.2 eV • angular resolution: ±2° • base pressure: below 4×10-11 Torr • Si(111) n-type with a 1.1° miscut toward the [-1-12] direction • cleaning 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 • measurements: 100 K K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg

5. Results and discussion K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg no density of states atthe Fermi level semiconductingelectronic structure agree well with the earlier studies Valence-band spectra measured using (a) hn=21.2 eV and (b) 17 eV along the [-110] direction, and (c) spectra measured using hn=21.2 eV along the [11-2] direction.

6. Results and discussion K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg 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 Band dispersion of the Ca/Si(111)-(3x2) surface

7. Results and discussion A A’ B C D K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg S3; good agreement with S1+ S1+~c+d、 -bond between the c and d atoms  hardly affected by the adsorbates  S3; C+D 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).

8. Results and discussion A A’ B C D K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg 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 (?) 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).

9. Results and discussion LEED pattern of the Ca/Si(111)-(2x1) surface K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg Valence-band spectra of the Ca/Si(111)-(2x1) surface Band dispersion of the Ca/Si(111)-(2x1) surface

10. Results and discussion K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg dispersion behavior of S1 and S2 surface states of the Si(111)-(2x1) with a Seiwatz structure situated just above and just below EF 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). supports the structural model proposed in the earlier studies

11. Conclusion A A’ B C D K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg • (3x2) surface • observation ofsix statesin 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 offive statesin 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 aSeiwatz structure

12. K. Sakamoto, H.M. Zhang, R.I.G. Uhrberg Thank you very much for your attention!!