Self-Doping of Ultrathin Insulating Films by Transition Metal Atoms

Abstract

Single magnetic Co atoms are deposited on atomically thin NaCl films on Au(111). Two different adsorption sites are revealed by high-resolution scanning tunneling microscopy (STM), i.e., at Na and at Cl locations. Using density functional based simulations of the STM images, we show that the Co atoms substitute with either a Na or Cl atom of the NaCl surface, resulting in cationic and anionic Co dopants with a high thermal stability. The dependence of the magnetic coupling between neighboring Co atoms on their separation is investigated via spatially resolved measurement of the local density of states.

Spontaneous doping of two-dimensional NaCl films with Cr atoms: aggregation and electronic structure

“…The Co dopants simply take the charge of the Na and Cl atoms they replace. 20 The occurrence of a charge transfer from the Cr dopant to the Au(111) support is also evidenced by the observed work function change of the NaCl/Au(111) film for high concentrations of Cr dopants, as described in the next section.…”

“…When Co atoms are deposited onto 2L NaCl, the two types of substitutional doping (Co Na and Co Cl ) are randomly distributed across the surface. 20 In the present work, the Cr dopant atoms show a very different and more interesting behavior: many Cr atoms are retrieved near the edge of the 2L NaCl islands, as illustrated in Fig. 1(a).…”

“…Similar phenomena have been described recently for the case of Cr and Mo impurities in MgO and CaO surfaces. 5,20,[35][36][37] Our calculations for Cr Na /NaCl(2L)/Au(111) show that the ground state corresponds to a Cr ion with four 3d electrons, i.e., the 4s 0 3d 4 configuration [see Fig. S4 in ESI †].…”

“…Very recently we reported an uncommon example of spontaneous doping of NaCl films by magnetic Co atoms. 20 In this paper, we investigate the behavior of Cr atoms deposited on bilayer (2L) NaCl/Au(111) films. While the tendency of the Cr atoms to spontaneously enter into the film is similar to what we found for Co, 20 the electronic structure of the Cr-doped NaCl films and the distribution of these transition metal impurities is very different from the Co case.…”

“…20 In this paper, we investigate the behavior of Cr atoms deposited on bilayer (2L) NaCl/Au(111) films. While the tendency of the Cr atoms to spontaneously enter into the film is similar to what we found for Co, 20 the electronic structure of the Cr-doped NaCl films and the distribution of these transition metal impurities is very different from the Co case. By comparing the results for our experimental STM/STS data and our density functional calculations, we find that there is an electron exchange of the Cr dopants with the Au support, which changes the electronic properties of the film.…”