Surface electronic structures of the Eu-induced Si(111)-(3×2)and -(2×1)reconstructions

Abstract

The electronic structures of the Eu/ Si͑111͒-͑3 ϫ 2͒ and ͑2 ϫ 1͒ surfaces have been investigated by angleresolved photoelectron spectroscopy. On the ͑3 ϫ 2͒ surface, we identify six surface states in the gap and a pocket of the bulk band projection. Among the five surface states observed in the bulk band gap, the dispersions of three of them agree well with those of the surface states of monovalent atom adsorbed Si͑111͒-͑3 ϫ 1͒ surfaces. The dispersions of the two other surface states observed in the band gap agree well with those observed on the Ca/ Si͑111͒-͑3 ϫ 2͒ surface, which has basically the same structure as that of monovalent atom adsorbed Si͑111͒-͑3 ϫ 1͒ surfaces. Taking these results into account, we conclude that the five surface states observed in the band gap originate from the orbitals of Si atoms that form a honeycomb-chain-channel structure. In the case of the ͑2 ϫ 1͒ surface, two semiconducting states are observed in the bulk band gap. The difference in binding energy of these two states at the ⌫ point agrees well with that of the surface states obtained theoretically for a clean Si͑111͒-͑2 ϫ 1͒ surface with a Seiwatz structure, and the dispersion of the upper state shows good agreement with the corresponding theoretical surface state. These observations indicate that the two surface states in the band gap originate from Si atoms that form a Seiwatz chain. The present results support the structures of the Eu/ Si͑111͒-͑3 ϫ 2͒ and ͑2 ϫ 1͒ surfaces proposed in the literature.

Surface electronic structures of the Eu- and Ca-induced so-calledSi(111)−(5×1)reconstructions

“…1͑b͒. 9,[11][12][13][14]18,21,24 The observation of two surface states, which originate from Si atoms that form a Seiwatz chain, on both the Eu-and Ca-induced ͑2 ϫ 1͒ phases 18,21,24 supports the structural model.…”

“…1͑a͔͒. [8][9][10][11]14,[18][19][20][21][22] The surface electronic structures of the Eu-and Ca-induced ͑3 ϫ 2͒ phases resemble closely not only each other, but also the surface electronic structure of a Liinduced Si͑111͒-͑3 ϫ 1͒ HCC surface, [18][19][20][21][22] and support indirectly the proposed structural model. Regarding the highestcoverage phase, the basic atomic structures of both the Euand Ca-induced ͑2 ϫ 1͒ phases have been proposed to follow the Seiwatz structure 23 illustrated by the model in Fig.…”

“…[7][8][9][10][11] The Ca/ Si͑111͒ surface has been reported to form quasi-1D and 1D reconstructions that are quite similar to those formed by Eu. [12][13][14] Of these reconstructions, the atomic structure of the lowest-coverage ͑3 ϫ 2͒ phase has been proposed to be basically the same as that of the honeycomb-chain-channel ͑HCC͒ model [15][16][17] for both the Eu-and Ca-induced phases ͓Fig.…”

“…11.͔ However, no strong evidence has been reported regarding the atomic structure of this intermediate phase, and the determination of the surface electronic structure of this phase is an important input to the structure determination. Moreover, the determination of the electronic structure of the so-called ͑5 ϫ 1͒ phase is essential to fully understanding the physical properties of divalent-atom-induced quasi-1D reconstructions.…”

Structural investigation of the Ca/Si(111)-(3*2) surface using photoelectron diffraction

“…This kind of Si(111)-(3×1) surface has been reported to be formed by various adsorbates, e.g., alkali metals (AM's), alkaline-earth metals (AEM's), rare-earth metals (Eu, Sm and Yb), and Ag with a coverage of either 1/3 monolayer (ML) or 1/6 ML. Although some of the adsorbates actually show different diffraction patterns (Ag shows a (6×1) pattern [3][4][5][6], and Ca [7,8], Eu and Yb [9,10] show a (3×2) pattern) all reconstructed surfaces are widely believed to have a quite similar structure based on the similarity of the low-energy electron diffraction (LEED) I-V curves [11,12], scanning-tunnelingmicroscopy (STM) images [13][14][15][16][17], and surface core-level shift measurements [3,8,[17][18][19][20]. That is, the basic structures of all these surfaces follow the honeycomb-chainchannel (HCC) model [21][22][23], which was originally proposed for 1/3 ML monovalent atom induced Si(111)-(3×1) reconstructions, and the difference in diffraction pattern is proposed to originate from the different adsorption sites of the metal atoms.…”