Structure determination of the ordered 3×3R30° phase of Ni2Si and Ni2Ge surface alloys on Ni(111) via low-energy electron diffraction

Abstract

a b s t r a c tThe ð ffiffiffi 3 p  ffiffiffi 3 p ÞR30 structures of 2-D nickel silicide and nickel germanide surface alloys on Ni(111) were investigated using quantitative low-energy electron diffraction analysis. The unit cells of the determined silicide and germanide structures contain two Ni atoms and one Si or Ge atom, corresponding to the chemical compositions Ni 2 Si and Ni 2 Ge, respectively. Both the Si and Ge atoms adopt substitutional face-centered cubic hollow sites to sit on the Ni(111) substrates, and the alloy surfaces exhibit a slight corrugation. The Ni\ \Si and Ni \ \Ge distances were 2.44 and 2.56 Å, respectively, and corresponded well to their respective empirical radii. It was also found that the Ni atoms in the second and third layers moved toward the Si or Ge atom sites from their bulk crystal positions. These results indicate rather strong interactions of the Ni atoms with both the Si and Ge atoms at the surface, leading to trapping of the Si and Ge atoms at the substitutional sites without diffusion into the bulk.

Formation of two-dimensional silicide on Ni(100) surface

“…As for the Ni(111) surface, on the other hand, a 3 3-R30°structure with 1/3 ML Si has been reported. [25][26][27] In this case, there is no exactly coincident bulk counterpart, but the ( 210) face of orthorhombic δ-Ni 2 Si (Co 2 Si structure) has a similar atomic configuration to the 3 3-R30°structure, although the corresponding bulk structure is not completely flat but somewhat undulating. As for the surface silicide, the unit cell of the ( 210) face of δ-Ni 2 Si is −5.3% on the c-axis and +4.4% on the ¯+ a b 2 -axis.…”

“…Indeed, only a few reports discussing the structure and reaction of silicidation on metal surfaces have been published. [25][26][27][28][29][30][31] It was reported that 2 × 2 and 3 3 -R30°structures are formed by exposing a Ni(111) surface to silane at high temperatures. 25) In a later study, it was found that a one-third monolayer of Si is involved in the 3 3 -R30°structure, indicating the formation of 2-D Ni 2 Si.…”

“…26) Detailed atomic structures of the 2 × 2 and 3 3-R30°s tructures were determined by low-energy electron diffraction (LEED). 27,28) Moreover, on a Ni(100) surface implanted with Si ions and subsequently annealed, epitaxial Ni 3 Si was revealed by transmission electron microscopy and Rutherford backscattering spectroscopy (RBS). 29) In addition to those reports, we recently reported 2-D silicides on a Ni(110) surface, in which p(1 × 2), c(2 × 2), and c(4 × 2) structures coexist in half-monolayer Si on the Ni(110) surface.…”

First-principles Study of Si-embedded Ni(100) Surfaces

“…In a later study [5], one-third monolayer of Si was found to form the √3 × √3-R30 ° structure, which indicated the formation of a two-dimensional (2D) Ni 2 Si layer. The detailed atomic structures of the 2 × 2 and √3 × √3-R30 ° structures were determined by low energy electron diffraction (LEED) [6,7]. In addition, the Ni(100) surface implanted with Si ions and subsequently annealed was studied by transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS), and epitaxial Ni 3 Si was shown [8].…”

Alloyed surfaces: New substrates for graphene growth

“…) symmetry with respect to the underlying Ni(111) (1 × 1) phase, and the effective formation of the surface alloy, with Sn substituting surface Ni atom. The subject was recently re-examined by Rahman et al [23], which have demonstrated that the same ordered structure can be obtained depositing silicon and germanium on-top the Ni(111) surface followed by thermal annealing at 650 K. Structural analysis revealed a XNi 2 (X=Si, Ge) stoichiometry of the surface, in agreement with XPS [13]. Interestingly, the alloyed phases are rather stable: for example the √ 3 reconstruction of SnNi 2 is still present up to temperature of about 1000K [22] (850K for Ge(Si)Ni 2 [23]).…”