New Model for Reconstructed Si(111) 7 × 7 Surface Superlattices

Structure-dependent Si(2/») surface core-level shifts and 2p photothreshold spectra which yield new surface geometry information are reported. For Si(100)-(2X 1), ~0.5 monolayer of surface atoms are found shifted to smaller binding energy (-0.5 eV) relative to the bulk; this rules out symmetric pairing models. Si(lll)-(7x 7) and Si(lll)-(2X 1) show different surface 2p core-level spectra (e.g., |-layer shifted -0.7 eV versus y layer shifted -0.4 eV), suggesting different geometries. Si(lll)-(ix 1)H exhibits first-layer (+0.26 eV) and second-layer (+0.15 eV) shifts.PACS numbers: 68.20.+ t, 79.60.£q Angle-integrated (~ 1.8 sr) photoelectron spectra were taken with a display-type spectrometer 8 with use of synchrotron radiation from the 240-MeV Tantalus-I storage ring. The Si(lll)-(2x 1) surface was prepared by cleaving in vacuum (mid-10 11 -Torr range); single domain cleaves were selected with no visible streaking of the LEED pattern (i.e., few steps). Exposing this surface to activated hydrogen resulted in a Si(lll)-(lx 1)H surface. The Si(100)-(2xl) and Si(lll)-(7x7) surfaces were prepared by very mild sputtering and by heating off the oxide film. Nearly intrinsic wafers were used (^10 Q, cm with large Debye screening lengths) with different dopings (p-type boron doped and n-type phosphor doped) to rule out band-bending effects. Fermi-level reference energies were obtained by measuring the Fermi edge of the Ta sample holder.Si(2p) core-level angle-integrated photoemission spectra for Si(100)~(2xl) are shown in Fig. 1 for two photon energies, hu= 108 and 130 eV. For hv= 130 eV, a shoulder is observed on the low-binding-energy side of the spin-orbit-split Zpi/2,3/2 doublet. This shoulder is very weak for hi; = 108 eV where the escape depth of the 2p photoelectrons is much longer than at the higher energy (final energy of =9eV above E F vs 31 eV). Exposure of this surface to oxygen or hydrogen quenches this surface-state level and introduces chemically shifted surface core levels on the high-binding-energy side of the bulk peak (not shown in Fig. 1). This rules out monochromator and spectrometer artifacts.We have decomposed the spectra in Fig. 1 into similarly shaped 2p l/2 and 2p 3 / 2 contributions (as shown by dashed lines) and have analyzed Si bulk and surface core-level features using a least squares fitting program with Lorentzian line shapes of equal width. From this, a spin-orbit splitting of A = 0.61 ±0.01 eV was determined with a (/>i/ 2 /p 3 / 2 ) branching ratio R that varied from 0.51 at hv^ 108 eV to 0.53 at /^=130 eV which is close to the statistical ratio of R = 0.5. This suggests that diffraction effects 9 are small.Spin-orbit-decomposed 2p 3 / 2 spectra for all Si surfaces studied are shown in Fig. 2 (solid lines). Together with surface-sensitive spectra at hv = 120 eV, we show one bulklike spectrum (hv = 108 eV) for the hydrogen-terminated Si(lll) surface. All energy scales have been referenced to the bulk Si 2p 3 / 2 core-level position as measured for hv = 108 eV. Using our 2p 3 j 2 binding ene...

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“…1,2,14 ' 15 We observe ~ £ monolayer of atoms with a -0.7 eV core-level shift [crosshatched in Fig. 2(b)].…”

Section: Si(100)-(2xi)-thismentioning

confidence: 94%

“…A recent model of the "rough" type (Ref. 15) proposes hexagonal islands of excess surface atoms. The island edge atoms should have greatly shifted core levels.…”

Section: Si(100)-(2xi)-thismentioning

confidence: 99%

Geometry-DependentSi(2p)Surface Core-Level Excitations for Si(111) and Si(100) Surfaces

et al. 1980

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“…The bulk energy bands of Ge and Si can be unfolded into an extended zone scheme and are then recognisably distortions of free-electron bands, though with a large energy gap on the Jones zone boundary (Heine and Jones 1969). From this point of view the electronic structure can be thought of as free-electron-like, perturbed by the (rather strong) ionic pseudopotentials; this scheme may even be applied to diamond (Phillips 1968). On the other hand, in the chemical bonding picture the group IV semiconductors and diamond are held together by local sp3 bonds-the local description should improve as the band gap increases.…”

Section: Surface States On Transition Metals: Conclusionmentioning

confidence: 99%

Surface electronic structure

Inglesfield

1982

Rep. Prog. Phys.

152

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The theory of the electronic structure of clean metal and semiconductor surfaces is reviewed, starting from an effective one-electron Schrodinger equation. Methods for solving the Schrodinger equation at surfaces are briefly described, and the effects of the surface on the electronic wavefunctions are discussed using simple models. The results of detailed calculations of the surface electronic structure of s-p bonded metals, transition metals and semiconductors are reviewed, with an emphasis on the effect of the local environment on the density of states. Properties like the work function and surface energy depend on the surface electronic structure, and their variation with material and surface is discussed; the surface energy contains an important contribution from the interaction between electrons, and this will be considered in some detail. The change in electronic structure compared with the bulk leads to changes in atomic structure, with surface reconstruction on semiconductor and some metal surfaces, and this is also discussed. The interplay between theory and experiment is very important in surface studies, and the theoretical surface energy bands reviewed in this article compare well with experimental photoemission results; this comparison has proved particularly useful for understanding surface reconstructions.

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“…The role of strains in surface physics has been recognized several years ago, as a new model for reconstructed Si(111) surface was proposed (see, for example, [47]). Meanwhile, recent experimental results have paid particular attention to the role of interface strains in heterostructure technology through their involvement in hetero-interface superstructures, in band structure shifts and in obtaining dislocation-free layers.…”

Section: Role Of Strains In Heteroepitaxy-induced Superstructuresmentioning

confidence: 99%

Elasticity-Based Approach of Interfaces: Application to Heteroepitaxy and Hetero-Systems

Masri¹,

Stauden²,

Pezoldt³

et al. 2001

phys. stat. sol. (a)

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In this paper, we discuss the validity of the S-correlated theory of misfit-induced interface superstructures (MIIS) and nucleation centers for misfit dislocation network (NCMDN) by comparing its results with (i) those obtained by a fully self-consistent numerical approach and (ii) available experimental results. Two main properties play an important role in the theory. The first one is the strain related S factor, which is the ratio of a linear function of the elastic constants over the material atomic density: this factor can be identified from the standard equations of the elasticity theory which, in our approach, represents the basic background. This implies a realistic lattice dynamics model which enables to interpret the velocity of longitudinal, transverse and shear vibrational waves in solids. The second property, n S , is a geometrical parameter related to the extension of MIIS and to the lattice spacing of misfit dislocation network (MDN). We then apply this theory to several hetero-systems and we demonstrate that it can be used to optimize heterointerfaces between host materials characterized by large lattice mismatch. P. Masri et al.: Elasticity-Based Approach of Interfaces: Application to Hetero-Systems Fig. 6. Schematic representation of the unit cell associated with the Al/Si (110) (3 Â 8) super-superstructure

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New Model for Reconstructed Si(111) 7 × 7 Surface Superlattices

Cited by 84 publications

References 22 publications

Geometry-DependentSi(2p)Surface Core-Level Excitations for Si(111) and Si(100) Surfaces

Geometry-DependentSi(2p)Surface Core-Level Excitations for Si(111) and Si(100) Surfaces

Surface electronic structure

Elasticity-Based Approach of Interfaces: Application to Heteroepitaxy and Hetero-Systems

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