Phase Formation Behavior in Ultrathin Iron Oxide

A multi-level memristor based on atomic layer deposition of iron oxide

This work reports the fabrication of memristive devices based on iron oxide (Fe₂O₃) thin films grown by atomic layer deposition (ALD) using ferrocene as iron precursor and ozone as oxidant. An excellent control of the ALD process was achieved by using an experimental procedure based on a sequence of micro-pulses, which provided long residence time and homogeneous diffusion of precursors, allowing ALD of thin films with smooth morphology and crystallinity which was found to increase with layer thickness, at temperatures as low as 250 °C. The resistive switching of symmetric Pt/Fe₂O₃/Pt thin film devices exhibited bipolar mode with good stability and endurance. Multi-level switching was achieved via current and voltage control. It was proved that the ON state regime can be tuned by changing the current compliance while the OFF state can be changed to intermediate levels by decreasing the maximum voltage during RESET. The structural analysis of the switched oxide layer revealed the presence of nano-sized crystalline domains corresponding to different iron oxide phases, suggesting that Joule heating effects during I-V cycling are responsible for a crystallization process of the pristine amorphous layer.

Optical quantum confinement and photocatalytic properties in two-, one- and zero-dimensional nanostructures

Low-dimensional nanomaterials have been explored extensively in the last decades, partly fuelled by the new possibilities for tuning and controlling their electronic properties. In a broader perspective within catalysis, two-, one- and zero-dimensional (2D, 1D and 0D) inorganic nanomaterials represent a bridge between the selectivity of molecular catalysts and the high performance and stability of inorganic catalysts. As a consequence of the low dimensions, higher surface areas are obtained but also introduce new physics and increased tuneability of the electronic states in the nanostructured system. Herein, we derive the commonly used equations for optical transitions and carrier confinement in semiconductors and discuss their effect on the optical and photocatalytic properties of direct band and indirect band gap materials. In particular, the physical properties of the optical and photocatalytic properties of Fe₂O₃ and ZnO will be used to exemplify the effects of the low dimensionality. Carrier confinement effects with changes in the density of states, band gap/shift of band edges will be outlined together with their effects on the tuneability of the material and their wider application as photocatalytic materials.