Atomic Scale Insights into the Early Stages of Metal Oxidation: A Scanning Tunneling Microscopy and Spectroscopy Study of Cobalt Oxidation

Abstract

Understanding the mechanisms driving the early stages of oxidation of metallic surfaces is of fundamental importance in fields such as nanocatalysis, electrochemistry, and nanoelectronics. In this work, the early stages of oxidation of ultrathin Co films deposited on the Fe(001)-p(1 × 1)O surface have been investigated by means of Auger electron spectroscopy, scanning tunneling microscopy, and scanning tunneling spectroscopy. The oxidation is initiated by homogeneous oxide nucleation over the atomically flat Co terraces, inducing the development of a smooth oxide wetting layer when the islands coalesce. Atomically resolved images reveal that the oxide wetting layer is highly defective, possibly due to the presence of oxygen vacancies. Constant current scanning tunneling microscopy images acquired in different tunneling conditions, as well as scanning tunneling spectroscopy, reveal the distinct electronic properties of the oxide nuclei with respect to the chemisorbed phase. The fundamental band gap develops since the early stages of oxide nucleation. Moreover, spectroscopic curves acquired in the near-field-emission regime reveal a significant lowering of the sample work function induced by the oxide development. Our results represent a remarkable case in which metal oxidation can be studied at the atomic-scale level.

Epitaxial growth of thermally stable cobalt films on Au(111)

“…These STM investigations clearly show the necessity of sample annealing up to 575 K to produce high quality Co films on Au(111) with large atomically flat terraces. While similar changes in surface morphology were also reported for ultrathin ferromagnetic films grown on different single crystalline surfaces such as Ru(0001) [41] and Fe(001) [42], our results show that this thermal activation procedure can also be extended to bulk-like ferromagnetic films.…”

Structural Dynamics of Ultrathin Cobalt Oxide Nanoislands under Potential Control

“…A more detailed explanation of the tunneling mechanism is given in Chapter 3, Supporting Information. This behavior was observed, for example, for CoO islands on Ag(100) [ 25 ] and Pt(111), [ 26 ] for a thin CoO layer on Fe(001), [ 27 ] and for NiO on Ag(100). [ 24 ] In contrast to the BL, the apparent height of the DL features is independent of the bias voltage.…”

Magnetic anisotropy at the buried CoO/Fe interface

“…17 In particular, the CoO/Fe(001) interface has been a workbench for many investigations related to AF/FM systems with reactive interfaces, ranging from the exchange bias mechanism, 14,18 to the influence of structure and stoichiometry on the magnetic properties, 19 to the realization of peculiar magnetic configurations, like vortices. 20 Very recently, we have demonstrated that it is possible to prepare a CoO/Fe(001) interface characterized by the absence of any Fe oxide, 21,22 which is a quite unique feature with respect to the common experimental situations. 10,19,23 This result has been accomplished by exploiting an ultra-thin Co buffer layer with a bct cubic structure.…”