Structure of vicinal surfaces of alloys: Cu–Pd(17%)(1 1 5)

An even single step structure is observed by scanning tunneling microscopy for the Cu–Pd(17%)(1 1 5) surface in the chemically ordered phase. This is in contrast with the paired step structure of vicinals of (0 0 1) and (1 1 0) surfaces with higher average step–step distance of A 3B L1 2 alloys. The three possible structures for vicinal surfaces involving steps and subsurface antiphase boundaries (APBs) are compared. The observation of a paired step structure for Cu–Pd(17%)(1 1 11) and of a single step structure for (1 1 5) allows estimating the subsurface APB energy.