Quantum Size Effect Driven Structure Modifications of Bi Films on Ni(111)

The quantum-size effect (QSE) driven growth of Bi film structures on Ni(111) was studied in situ using low energy electron microscopy and selective area low energy electron diffraction ($\mu \mathrm{LEED}$). Domains with a ($3\times 3$), $[\genfrac{}{}{0ex}{}{3}{1}\genfrac{}{}{0ex}{}{-1}{2}]$, and ($7\times 7$) film structure are found with a height of 3, 5, and 7 atomic layers, respectively. A comparison of $I/V\mathrm{\text{−}}\mu \mathrm{LEED}$ curves with tensor LEED calculations shows perfectly accommodated Fermi wavelengths, indicative that not only the quantized height, but also the film structure is driven by QSE.

Figure 1

LEEM image of a ($3\times 3$) domain and a [3-112] domain, both surrounded by the ($7\times 7$) wetting layer. The field of view (FoV) is $10\mu \mathrm{m}$, the electron energy is 20 eV, the substrate temperature is 474 K and the Bi coverage ${\theta }_{\mathrm{Bi}/\mathrm{Ni}}=0.66\mathrm{ML}$.

Figure 2

Quantum interference peaks in $I/V$-LEEM measurements as indicated by the arrows: two for the three atomic layer high ($3\times 3$) (top) and four for the five atomic layer high [3-112] Bi films on Ni(111) (bottom). Experimental curves (black) and best-fit (grey dashed) using the KP model. The Bragg peak at about 22 eV is indicated by $B$. For the used parameters see Table .

Figure 3

$\mu$-LEED images taken at 40.0 eV (a)–(c), and the corresponding real space unit cells (d)–(f) for the three different Bi film structures. Panels (a) and (d) show a ($7\times 7$) film structure with lattice constant 3.49 Å ($\theta =0.510\mathrm{ML}$), measured at 422 K. (b) and (e) show a ($3\times 3$) overlayer with lattice constant 3.74 Å ($\theta =0.444\mathrm{ML}$), and (c) and (f) show a [3-112] overlayer with a lattice constant 3.80 Å ($\theta =0.429\mathrm{ML}$), both measured at 474 K. For the real space images (d)–(f) green (dark gray) corresponds to (close to) threefold hollow, red (dark) to (near) on-top, yellow (light gray) to intermediate positions, where in all cases only the contact layer with the Ni(111) surface is drawn.