Carbon deposition on hematite ($\alpha$-Fe$_2$O$_3$) nanocubes by an annealing in the air: morphology study with grazing incidence small angle X-ray scattering (GISAXS)

TL;DR

This study uses GISAXS to analyze how annealing in air causes carbon deposition on hematite nanocubes, revealing morphology changes and providing a new method for in-situ nanoparticle surface characterization.

Contribution

It introduces a GISAXS-based approach to monitor carbon layer formation on hematite nanocubes during annealing in air.

Findings

Air annealing causes amorphous carbon coating on nanocubes.

GISAXS patterns reveal morphology changes due to carbon deposition.

Simulations accurately reproduce observed patterns, confirming core-shell structure.

Abstract

GISAXS has been used to study morphology change of $\alpha$-Fe$_2$O$_3$ nanocubes after annealing processes. A submonolayer of the nanocubes was deposited on a Si(100) substrate. While an annealing at 400 $^\circ$C in a vacuum does not change a GISAXS pattern from as-prepared nanocubes submonolayer, annealing in the air at the same temperature altered the GISAXS pattern significantly. SEM image showed that the air-annealed nanocubes were coated with thin layers which were identified as amorphous carbon layers based on Raman measurements. GISAXS simulations from morphologies of nanocube with 38 nm side-length and core-shell (nanocube-core and 7 nm thick carbon-shell) nicely reproduced measured patterns from the vacuum annealed and the air-annealed nanocubes, respectively. The current study provides new approach for in-situ characterization of carbon deposition on a uniform shape nanoparticle through monitoring of deposited carbon thickness.