Optical Fingerprints of Si Honeycomb Chains and Atomic Gold Wires on the Si(111)-(5×2)-Au Surface

Abstract

The intensively studied Si(111)-(5 Â 2)-Au surface is reexamined using reflectance anisotropy spectroscopy and density functional theory simulations. We identify distinctive spectral features relating directly to local structural motifs such as Si honeycomb chains and atomic gold wires that are commonly found on Au-reconstructed vicinal Si(111) surfaces. Optical signatures of chain dimerization, responsible for the observed (Â 2) periodicity, are identified. The optical response, together with STM simulations and first-principles total-energy calculations, exclude the new structure proposed very recently based on the reflection high-energy electron diffraction technique analysis of Abukawa and Nishigaya [Phys. Rev. Lett. 110, 036102 (2013)] and provide strong support for the Si honeycomb chain with the triple Au chain model of Erwin et al. [Phys. Rev. B 80, 155409 (2009)]. This is a promising approach for screening possible models of complex anisotropic surface structures. DOI: 10.1103/PhysRevLett.111.087401 PACS numbers: 78.68.+m, 73.20.Àr, 78.20.Bh The Si(111)-(5 Â 2)-Au surface has been the subject of long and intensive experimental and theoretical study, due to its potential for applications in nanoelectronics and its prototypical nature for studying self-assembly and properties of one-dimensional quantum structures [1,2]. On the experimental side, this includes STM [3][4][5], reflection high-energy electron diffraction (RHEED) [6], LEED [7], photoemission [8][9][10], and optical spectroscopy [11,12]; theoretical works generally focus on surface energies, electronic structure, and STM simulations [13][14][15][16]. Nonetheless, its structure remains controversial. Significant inconsistencies arose when even the most promising structures, all of which feature a Si honeycomb chain [17], were compared with experimental data [5].The recalibration in 2009 [18] of the Au coverage from 0.4 monolayers (ML) to 0.6 ML prompted a reevaluation of the Si(111)-(5Â2)-Au atomic structure. In particular, an exhaustive theoretical-experimental study by Erwin-Barke-Himpsel [16] (henceforth, EBH) proposed a three-chain model that largely resolved the remaining discrepancies in the STM and photoemission data [5]. However, a recent RHEED study by Abukawa and Nishigaya [6] (henceforth, AN) predicted a completely new structure, which appears consistent with Y-shaped structures found in STM [3,5]. Most notably, the model does not contain Si honeycomb chains.Independent evaluation of competing structural models is provided by reflectance anisotropy spectroscopy (RAS) [19]. The technique probes both filled and empty surface and interface states while discriminating against the bulk response of cubic materials and hence is particularly sensitive to the local surface and interface atomic structure. Moreover, RAS simulation has now evolved to a level capable of producing impressive agreement with experiment, revealing sensitivity to subtle structural phenomena, such as dimer composition [20] [26] in interface systems. Adsorbaterecon...

Titration of submonolayer Au growth on Si(111)

“…Still, their model was recently questioned in a paper by Hogan. 22 All these groups constrain themselves to structures with a precise coverage of 0.6 ML of Au. However, in the experimental literature there is no consensus on this value.…”

Identification of the Au Coverage and Structure of theAu/Si(111)−(5×2)Surface

“…The AN model has the same Au and Si coverages as the EBH model but quite distinct structural features: It has no Si honeycomb chain, and the Au chain contains four Au rows rather than three. More recently, however, the AN model was excluded by Hogan et al [27]: The AN model was energetically and microscopically unfavored in DFT calculations, and their analysis of previous reflectance anisotropy spectroscopy data [18] strongly supported the presence of Si honeycomb chains, thereby being in favor of the EBH model.…”

“…Its atomic structure, however, is not yet solved in spite of extensive experimental studies [8][9][10][11][12][13][14][15][16][17][18][19] and density functional theory (DFT) calculations [20][21][22][23][24][25]. This long-standing surface science problem is thus considered a touchstone of our ability to look into the structure of complex surface/nano systems at truly atomic scale.In particular, the structural debate was recently reignited by two conflicting reports [26,27]. Figure 1(a) shows the best structural model so far, proposed by a combined theoretical-experimental study of Erwin, Barke, and Himpsel (hereafter, EBH) in 2009 [25].…”

“…In particular, the structural debate was recently reignited by two conflicting reports [26,27]. Figure 1(a) shows the best structural model so far, proposed by a combined theoretical-experimental study of Erwin, Barke, and Himpsel (hereafter, EBH) in 2009 [25].…”

Modeling 1D structures on semiconductor surfaces: synergy of theory and experiment

“…Indium atoms on Si(111) form NWs with a metallic character, [30][31][32][33][34][35][36][37] but also on high-index surfaces, such as Si(557), atomic wires are observed. 38 This is similar to Au, which preferentially forms chains on the high-index surfaces like Si(553) 17,20,[39][40][41] and Si(557) 20,25,40,[42][43][44][45][46] . Also Pb on Si(557) gives rise to conducting NWs, with quasi-1D states below a critical temperature of 78K; above this critical temperature the two dimensional (2D) coupling of the NWs makes the Pb chains 2D conducting.…”