Mechanism of formation and electronic structure of semiconducting ZnSb nanoclusters electrodeposited from an ionic liquid

Abstract

Electrocrystallization of Sb and the compound semiconductor ZnSb has been investigated by in situ SPM methods at the electrified ionic liquid/Au(1 1 1) interface at an elevated temperature of 50 °C for the first time employing the ionic liquid ZnCl 2–[C 4mim] +Cl − (45:55). Prior to the underpotential deposition (UPD) process of Sb, ZnCl 3 − anions adsorb on the gold surface at the open-circuit potential (OCP). An ordered region – showing the characteristic of a Moiré-like pattern – coexists with a disordered region indicative of an interfacial phase transition. When the potential is reduced to −0.40 V versus Pt/Pt(II), 2D electrocrystallization of Sb starts showing a typical 3 × 3 structure of the first monolayer. Further decreasing the potential to −0.5 V a second layer of Sb islands occurs. Stepping the potential from the UPD region to −0.60 V, the OPD of Sb sets in showing randomly dispersed clusters of homogeneous size. Near the ZnSb deposition potential, at ∼−0.95 V, a nearly homogeneous distribution of clusters of spherical shape with diameters up to 15 nm is found. Their corresponding STS curves exhibit an obvious semiconducting behaviour with a gap-energy of ∼0.6 ± 0.2 eV. Experiments at deposition conditions on the Sb-rich or Zn-rich side relative to the ZnSb deposition potential show an obvious doping effect – in the case of Zn excess – which is revealed by the corresponding normalized conductance (NC) spectra.