Prada Stefano, Giordano Livia, Pacchioni Gianfranco
Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, 20125 Milano, Italy.
J Phys Condens Matter. 2014 Aug 6;26(31):315004. doi: 10.1088/0953-8984/26/31/315004. Epub 2014 Jun 17.
Transition metal atoms incorporated into insulating materials (oxides in particular) can deeply modify their adsorption properties. In particular, charge transfer to adsorbed species can be induced by the presence of substitutional dopants, which introduce new electronic states in the band gap of the host crystal. Here we show, by means of density functional theory calculations, that Nb represents an excellent dopant to turn the rather inactive CaO(100) surface into an electron-rich support. The charge transfer ability of the doped material is shown by comparing the adsorption properties of the electronegative Au atoms on pure and Nb-doped CaO. While in the first case the CaO-Au bonding is relatively weak and the Au atom is essentially neutral, in the Nb-doped system a much stronger adhesion is found due to a net charge transfer from the Nb dopant and to the formation of a gold anion. This mechanism occurs also for Nb in high oxidation states. Nb is thus an excellent modifier of the calcium oxide properties.
掺入绝缘材料（特别是氧化物）中的过渡金属原子可以深刻改变其吸附特性。特别是，替代掺杂剂的存在可诱导向吸附物种的电荷转移，这在主体晶体的带隙中引入了新的电子态。在此，我们通过密度泛函理论计算表明，Nb是一种出色的掺杂剂，可将相当惰性的CaO(100)表面转变为富电子载体。通过比较电负性Au原子在纯CaO和Nb掺杂CaO上的吸附特性，展示了掺杂材料的电荷转移能力。在第一种情况下，CaO-Au键相对较弱，Au原子基本呈中性，而在Nb掺杂体系中，由于Nb掺杂剂的净电荷转移以及金阴离子的形成，发现了更强的附着力。这种机制在高氧化态的Nb中也会发生。因此，Nb是氧化钙性质的出色改性剂。
