Structural investigation of the quasi-one-dimensional reconstructions induced by Eu adsorption on a Si(111) surface

Abstract

The surface structures of the ͑quasi-͒one-dimensional reconstructions induced by the adsorption of Eu on Si͑111͒ have been investigated by low-energy electron diffraction ͑LEED͒ and high-resolution core-level photoelectron spectroscopy. Different phases were observed in LEED depending on the Eu coverage. The lowest coverage phase has a ͑3 ϫ 2͒ periodicity, and the highest coverage phase has a ͑2 ϫ 1͒ one. Of the intermediate phases, the LEED pattern of the so-called ͑5 ϫ 1͒ surface indicates that this surface has actually a ͑5 ϫ 4͒ periodicity. The Eu 4f core-level spectra show that the Eu coverages of the ͑3 ϫ 2͒, ͑5 ϫ 4͒, and ͑2 ϫ 1͒ phases are 1 / 6 monolayer ͑ML͒, 0.3 ML, and 0.5 ML, respectively, and that the valence state of the adsorbate is 2+ in all these three phases. In the Si 2p core-level spectra, three surface components were observed in both the lowest and highest coverage phases. By considering the energy shift and intensity of each surface component, we conclude that the structure of the ͑3 ϫ 2͒ phase is basically the same as that of the honeycomb-chain-channel model, and that the ͑2 ϫ 1͒ phase is formed by -bonded Seiwatz Si chains. Regarding the ͑5 ϫ 4͒ phase, two extra Si 2p surface components were observed together with the three components observed in the two end phases. Taking the energy shifts and intensities of the extra surface components into account, we propose a structural model of the ͑5 ϫ 4͒ phase.

Band structure ofTl/Ge(111)−(3×1): Angle-resolved photoemission and first-principles prediction of

“…The model also explains the HCC-͑3 ϫ 2͒ structures with 1/6 ML alkali-earth and rare-earth metals. [23][24][25][26][27][28][29] A comparison between the ͑3 ϫ n͒ ͑n =1,2͒ structures induced by monovalent and divalent metals leads to a simple rule that the optimal coverage of the adsorbed metal atoms is determined to fill the dangling bonds of the honeycomb chains. On the other hand, two probable adsorption sites of the metal atoms are proposed; the H 3 and T 4 sites, both being threefold symmetry sites on the ͑111͒ substrate of the diamond structure.…”

Ca-induced intermediate reconstructions on the Si(111) surface

“…As mentioned earlier Sakamoto et al 10,11 concluded that the ͑5 ϫ 2͒ and ͑5 ϫ 4͒ reconstructions are stable while ͑5 ϫ 1͒ is not. Using our theoretical method we can examine the relative stabilities of these reconstructions.…”

“…The 1/3 ML coverage of Ca, however, has been reported to produce a clear ͑5 ϫ 4͒ reconstruction. From an analysis of core-level photoemission spectra, Sakamoto et al 10 proposed two structural models for the Eu/ Si͑111͒-͑5 ϫ 4͒ surface with a coverage of 1/3 ML. In one model, called the H 3 model, each ͑5 ϫ 4͒ surface unit mesh contains four Eu atoms adsorbed on the T 4 site and two Eu atoms on the H 3 site.…”

“…[13][14][15] Miwa 13 performed ab initio calculations on the ͑3 ϫ 2͒, ͑3 ϫ 1͒, and ͑2 ϫ 1͒ reconstructions, and concluded that the ͑3 ϫ 1͒ reconstruction is not expected to occur even under Ca-rich conditions. His calculations also presented a qualitative picture for the core-level photoemission results obtained by Sakamoto et al 8 Sakamoto and co-workers 10,11 attempted to investigate the atomic geometry of the Ca/ Si͑111͒-͑5 ϫ 1͒ surface by using LEED and high-resolution core-level photoelectron spectroscopy. They concluded that the ͑5 ϫ 1͒ reconstruction, corresponding to 0.4 ML coverage of Ca, is not stable.…”

“…Of potential technological importance and scientific interest is the physics of metal adsorbed Si͑111͒ surfaces. On this surface quasi-1D structures have been fabricated by depositing group-I, group-II, and group-III elements with some examples of adsorbates being: noble metals ͑such as Au͒, 2 alkali metals ͑such as Li, Na, etc͒, 3 alkaline-earth metals ͑such as Ca, Mg, etc͒, [4][5][6][7][8][9][10][11] and In. 1,12 While only a few well established reconstructions are known to take place for the deposition of monovalent and trivalent metal adsorbates on Si͑111͒, it has been reported that a large number of reconstructions exist for divalent metal adsorbates.…”