Growth of a flat Mn monolayer on Ag(001)

We have carefully investigated the possibility of preparing a well-ordered p(1×1) two-dimensional Mn monolayer on Ag(001) by means of photoelectron diffraction. It is found that a flat monolayer (ML) with a good degree of perfection is actually achieved by deposition at low rates (typically 0.1--0.2 ML/min) on a substrate held at 80 K. Substrate temperatures higher than ~130K invariably result in the exchange of Mn adatoms with Ag and the formation of a surface alloy. Valence-band photoemission indicates a giant atomiclike magnetic moment in the flat monolayer, essentially the same as in dilute Ag-based Mn alloys. Most interestingly, low-energy electron diffraction reveals a very sharp p(1×1) chemical cell pattern with weak but sizable (1/2,1/2) extra spots visible up to about 100 eV and attributed to in-plane c(2×2) antiferromagnetic order.