Temperature control of the growth of iron oxide nanoislands on Fe(001)

The control of atomically flat interfaces between iron (Fe) and insulating oxide films, such as the Fe/MgO(001) interface, is crucial for tunnel-magnetoresistance (TMR) devices. However, the realization of an ideal atomically flat and clean interface is rather difficult since iron easily binds to impurities such as oxygen. Atomic step defects and iron oxide at the interface could reduce TMR. In this study, the oxidization of an atomically flat and clean Fe(001)-whisker single crystal at different substrate and annealing temperatures was investigated with an ultrahigh-vacuum scanning tunneling microscope (STM). Annealing up to a temperature of 850 K was required to obtain ordered and atomically flat Fe(001)-p(1×1)O terraces after the oxidization with the coexistence of Fe–O nanoislands (∼1 nm in height, ∼50 nm in size). We found that the growth of such nanoislands, which enhances interface roughness, strongly depends on the substrate temperature (T$_S$) during the oxidization. A T$_S$ lower than 300 K reduces the coverage by the nanoislands to less than 10%.