Coulomb staircases and quantum size effects in tunnelling spectroscopy on ligand-stabilized metal clusters

TLDR: In this article, the authors describe scanning tunnelling spectroscopy results on the ligand-stabilized metal cluster Pt309Phen36*O30 (where Phen is phenanthrolin) at 4.2 K.

Abstract: We describe scanning tunnelling spectroscopy results on the ligand-stabilized metal cluster Pt309Phen36*O30 (where Phen is phenanthrolin) at 4.2 K. If the STM tip is positioned above a single cluster, clear charging effects are observed, varying from a reduction of the current around zero bias (Coulomb blockade) to a stepwise increase of the current as a function of bias voltage (Coulomb staircase). In addition to the regular Coulomb staircase with steps in the current at equal voltage spacing, we observed also staircases whit additional structure. This additional structure can be explained in terms of quantum levels in the cluster.

Figures

Fig. 1 . - Tunnel characteristics on two different P t 3oi) clusters, which both show charging effects. Curve a) only shows a reduction of the current around zero bias (Coulomb blockade). Curve b) shows a Coulomb staircase. The measurement temperature is 4.2 K. The upper curve in b) shows a theoretical curve (offset by 40 pA). The fit parameters for this curve are C\ = 1.2 aF, C2 = 0.8 aF, Ri = 4 GH, i ?2 = 0.2 Gil, Qo = —0.3, and the temperature T = 4.2 K.