Seminars Archive

Deposition of metal atoms and clusters on two-dimensional insulators

Abstract
Metal clusters are normally produced and deposited on solid surfaces. The interaction of a cluster with the support (usually an oxide) is fundamental as it determines its final shape and physico-chemical properties. Particularly interesting is the case of the deposition of metal atoms and clusters on ultra-thin films of insulating materials grown on a metal surface. Thanks to the reduced dimensionality insulators at the nanoscale provide new opportunities for the design of innovative materials [1]. Here we discuss three examples. (1) Gold atoms and clusters deposited on MgO/Ag(100) ultrathin films show the occurrence of charging effects via direct electron tunnelling through the oxide layer, an effect which is not observed on thick films or bulk oxides and which results in the formation of 2D gold particles [2]. (2) Also Ni clusters deposited on MgO/Ag(100) monolayer films assume a 2D shape but the phenomenon however has a different origin. Here excess oxygen present at the interface diffuses across the MgO films and oxidize the 3D Ni clusters leading to 2D NixOy aggregates [3]. (3) The last example is that of the deposition of transition metal atoms like Co or Cr on two-layer NaCl/Au(111) films [4-8] and two-layer MgO/Ag(100) films [7]. Cr and Co atoms spontaneously replace Na and Cl ions in the NaCl films changing the electronic and magnetic properties of the system (spontaneous doping). This effect is peculiar of NaCl and does not occur on MgO/Ag(100) films. The nature of the adsorbed species is thus strongly dependent on the nature of the supporting material. [1] G. Pacchioni, “Two-dimensional oxides: multifunctional materials for advanced technologies”, Chemistry a European Journal, 18, 10144-10158 (2012). [2] G. Pacchioni, H. J. Freund, Chemical Reviews, 113, 4035-4072 (2013). [3] M. Smerieri, J. Pal, L. Savio, L. Vattuone, R. Ferrando, S. Tosoni, L. Giordano, G. Pacchioni, M. Rocca, “Spontaneous Oxidation of Ni Nanoclusters on MgO Monolayers Induced by Segregation of Interfacial Oxygen”, J. of Physical Chemistry Letters, 6, 3104-3109 (2015) [4] Z. Li, H.-Y. T. Chen, K. Schouteden, K. Lauwaet, L. Giordano, M. I. Trioni, E. Janssens, V. Iancu, C. Van Haesendonck, P. Lievens, G. Pacchioni, “Self-doping of ultrathin insulating films by transition metal atoms”, Physical Review Letters, 112, 026102 (2014). [5] H.-Y. T. Chen, L. Giordano, G. Pacchioni, “Adsorption properties of two-dimensional NaCl: a DFT study of the interaction of Co, Ag, and Au atoms with NaCl/Au(111) ultrathin films”, J. of Physical Chemistry C, 118, 12353-12363 (2014). [6] Z. Li, H.-Y. T. Chen, K. Schouteden, E. Janssens, C. Van Haesendonck, P. Lievens, G. Pacchioni, “Spontaneous doping of two-dimensional NaCl films with Cr atoms: aggregation and electronic structure”, Nanoscale, 7, 2366-2373 (2015). [7] H.-Y. T. Chen, G. Pacchioni, "Properties of two-dimensional insulators: a DFT study of Co adsorption on NaCl and MgO ultrathin films", Physical Chemistry Chemical Physics, 16, 21838-21845 (2014). [8] Z. Li, H.-Y. T. Chen, K. Schouteden, K. Lauwaet, E. Janssens, C. Van Haesendonck, G. Pacchioni, P. Lievens, “Lateral manipulation of atomic vacancies in ultrathin insulating films”, ACS Nano, 9, 5318-5325 (2015).