XPS studies of NaCl deposited on Cu(100) and Ni/Cu(100) surfaces

Abstract

The interaction of vapor-deposited NaCl with Cu(100), 1 ML Ni/Cu(100) and 3 ML Ni/Cu(100) has been investigated by X-ray photoelectron spectroscopy and X-ray-induced Auger electron spectroscopy. Five types of deposited NaCl are found by resolving Na KLL Auger peaks: two types of isolated species, two-dimensional NaCl islands and two types of three-dimensional NaCl islands. These peaks are characterized by spectral changes during the increase in the NaCl coverage and after heating of the surfaces using Auger parameters for sodium. The Auger parameters for the isolated NaCl are close to that of Na metal, implying a large extra-atomic relaxation in the photoelectron process and less polarization in NaCl. Owing to a weak interaction of NaCl with Cu(100) three-dimensional growth is favored over the two-dimensional and isolated ones in the submonolayer region. The covering of the Cu(100) with 1 ML and 3 ML Ni atoms strengthens the interaction of NaCl with the surfaces and leads to a stabilization of the isolated species and two-dimensional islands. Preadsorbed oxygen prevents the deposited NaCl at submonolayer coverage from growing as 3D islands by strong electrostatic interaction with the Na ions.