Abstract The investigation of clean Cu 3Au(100) with 180° low-energy ion scattering and detection of neutrals (NICISS) shows that the surface is terminated at room temperature with the Au-rich plane. The clean surface exhibits a LEED c(2 × 2) superstructure and has been imaged by scanning tunneling microscopy (STM) in ultrahigh vacuum with atomic resolution. The measured different grey scale heights in the unit cell can be attributed to the position of Au and Cu atoms, respectively. Adsorption of atomic nitrogen starts with the formation of islands. From the NICISS data it has been concluded that after saturation with O or N the surface is terminated with the Cu plane. On the basis of STM and direct recoil spectroscopy (DRS) the fourfold hollow site above Cu atoms has been deduced for both adsorbates.