In situ TEM oxidation study of Fe thin-film transformation to single-crystal magnetite nanoparticles

Leonardo Lari,Stephan Steinhauer,Vlado K Lazarov

doi:10.1007/s10853-020-04917-8

Abstract

In this work, we present an in situ transmission electron microscopy (TEM) study of Fe thin films to Fe nanoparticle formation and their oxidation to single-crystal magnetite nanoparticles. Amorphous Fe thin films were prepared by sputtering on TEM carbon grids. The thin Fe films were continuously heated in situ from room temperature to 700 °C under vacuum (4 × 10–4 Pa). With the increase in temperature, the continuity of the thin film starts breaking, and Fe nanoparticle nucleation centers are formed. At 600 °C, the thin film transforms into metallic Fe nanoparticles (NPs) with a small presence of different Fe oxide NPs. Further increase in the temperature to 700 °C resulted in the full oxidation of the NPs (i.e., no core–shell were found). Zero-loss energy filtered diffraction and HRTEM analysis of the lattice spacing reveals that all NPs have fully transformed into single-phase magnetite NPs. The structural study of the magnetite NPs shows that magnetite NPs are free of antiphase domain boundary defects. This work demonstrates that under low partial pressure of oxygen at elevated temperatures a complete oxidation of Fe NPs into magnetite single-crystal nanoparticles can be achieved.

Highlights

IntroductionThe study of iron oxide nanoparticles (NPs) has burgeoned during the last decades [1,2,3] due to their range of applications that include water purification [4], ferrofluids [5], hyperthermia treatments of tumors [6], chemical sensing [7, 8], magnetic resonance imaging contrast enhancement agents [9], and catalyst support [10,11,12]
In bulk ferrite (a-iron), carbon solubility is as low as \ 0.00005 wt% at room temperature which can increase up to 0.02 wt%, at about 720 °C, where Fe is supersaturated with C in the interstitial positions
In this work we studied the evolution of sputtered amorphous Fe thin films deposited on amorphous C as a function of temperature and low O2 pressure by using in situ transmission electron microscopy

Summary

Introduction

The study of iron oxide nanoparticles (NPs) has burgeoned during the last decades [1,2,3] due to their range of applications that include water purification [4], ferrofluids [5], hyperthermia treatments of tumors [6], chemical sensing [7, 8], magnetic resonance imaging contrast enhancement agents [9], and catalyst support [10,11,12] There are both chemical [13,14,15,16,17] and physical methods to produce iron oxide NPs [16, 18]. By performing in situ TEM studies, we were able to characterize the structural phase transformations from thin Fe film to single-crystal magnetite NPs

Methods

Results

Conclusion