# Silver (111) surface structure, and is bulk structure body-center or face-center cubic?

I'd like to understand the atomic arrangement is on a silver (111) surface.

Step 1 would be to find out the bulk crystal structure.

Wikipedia lists silver as face-center cubic (fcc) here and here and the page Silver: crystal structures also shows fcc and links to Lin-gun Liu and W. A. Bassett, J. Appl. Phys., 1973, 44, 1475:

But the page Ag(111) and Ag/Si(111): similarities and differences begins

The crystal structure of silver is body-centred cubic (Figure 4.4a), and so the Ag(111) plane exhibits a close-packed, hexagonal structure (Figure 4.4b). Ag is a stable transition metal, and one of the few metals found abundantly in nature as a pure native element. This stability is due to its relative inertness, and the Ag(111) close-packed surface has the lowest energy of its high-symmetry surfaces.

While this page tells me that the silver (111) surface will be a close-packed hexagonal arrangement, I am uncertain I can trust this because it begins by stating that silver is bcc and Wikipedia tells me silver is fcc.

Figure 4.4: (a) Schematic model of the silver body-centred cubic structure, showing the (111) cleavage plane. (b) Model of the close-packed Ag(111) surface, with the principal directions indicated.

Question(s):

1. Is bulk silver bcc or fcc?
2. What is the structure of the silver (111) surface?
• – uhoh
Jun 10, 2019 at 3:52
• Silver is most definitely fcc (face centered cubic). Now, what the surface looks like as a clean surface is down to the surface reconstruction (which your companion question is getting at). Jun 10, 2019 at 12:44

It's been two years, it seems I can finally answer my own question.

Is bulk silver bcc or fcc?

Per Wikipedia's Silver and @JonCuster's comment its structure is face-centered cubic.

What is the structure of the silver (111) surface?

This has two parts;

1. What does a mathematical fcc lattice look like if you slice it along a (111) plane?
2. What happens to atoms on a real Ag(111) surface; do they stay put or do they move around into an energy minimizing surface reconstruction the way Au(111) and Si(111) famously do?

1. What does a mathematical fcc lattice look like if you slice it along a (111) plane?

If you stand an fcc structure up on one corner and look from the side, then you see the atoms fall on three planes, and the arrangement in each plane is hexagonal with each atom touched by six coplanar atoms. Each plane is offset so the atoms of one fit into the voids in the layers above and below.

The fcc(111) planes are arranged in an ABCABC fashion. From one corner (in the "A" plane) the three adjacent corners and sides make the next "B" plane. The opposite corner is also "A" and the three adjacent corners and sides can be called "C".

above left: same image as abo e but with "A", "B", and "C" circled in red, green and blue. right fcc structure tipped on one corner showing ABCA planes, from https://www.chemtube3d.com/ccp-cubic-close-packing/ click for larger

above: Screen shots from slide 8 of 5/22/2013 L. Viciu| ACII| close packed structures click for larger

1. What happens to atoms on a real Ag(111) surface; do they stay put or do they move around into an energy minimizing surface reconstruction?

While Au(111) reconstructs into a very elegant $$23 \times \sqrt{3}$$ super cell that can have three possible rotations and these join up into a herringbone pattern, the Ag(111) surface remains flat, almost exactly like it was a (111) plane in the bulk. There is a very slight readjustment of the atomic locations for energy minimization, the inter-plane spacing slightly expand, but there is no reconstruction.

This flat hexagonal metal surface can then be used as a "workbench" or template on which to grow a wide variety of materials.