GROWTH OF A FLAT MN MONOLAYER ON AG(001)

We have carefully investigated the possibility of preparing a well-ord ered p(1 X 1) two-dimensional Mn monolayer on Ag(001) by means of phot oelectron diffraction. It is found that a flat monolayer (ML) with a g ood degree of perfection is actually achieved by deposition at low rat es (typically 0.1-0.2 ML/min) on a substrate held at 80 K. Substrate t emperatures higher than similar to 130 K invariably result in the exch ange of Mn adatoms with Ag and the formation of a surface alloy. Valen ce-band photoemission indicates a giant atomiclike magnetic moment in the hat monolayer, essentially the same as in dilute Ag-based Mn alloy s. Most interestingly, low-energy electron diffraction reveals a very sharp p(1 X 1) chemical cell pattern with weak but sizable (1/2,1/2) e xtra spots visible up to about 100 eV and attributed to in-plane c(2 X 2) antiferromagnetic order.