VUV14, July 23, 2004 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

VUV14, July 23, 2004 Introduction 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, (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 reconstructions K. 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, (2003) inconsistent results these 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] direction cleaningfollowed the procedure described in APL 72, 948 (1998) checkLEED, 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× 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 S 1 -S 3 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 S 3 ; good agreement with S 1 + S 1 + ~  c +  d 、  -bond between the c and d atoms  hardly affected by the adsorbates  S 3 ;  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 S 2 ± ~  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 S 2 ± S 1 ;  A -  B, S 2 ;  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 S 1 and S 2 surface states of the Si(111)-(2x1) with a Seiwatz structure situated just above and just below E F 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. S 1 ;  A -  B, S 2 ;  A +  B, S 3 ;  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!!