(155g) Visualizing Oxidation Mechanisms in Few-Layered Black Phosphorus Via in Situ Transmission Electron Microscopy
AIChE Annual Meeting
2021
2021 Annual Meeting
Materials Engineering and Sciences Division
Two-Dimensional Materials and Thin Films
Monday, November 8, 2021 - 2:40pm to 3:00pm
Layered two-dimensional (2D) black phosphorus (BP) exhibits novel semiconducting properties including a
tunable bandgap and high electron mobility. However, the poor stability of BP in ambient environment severely
limits potential for application in future electronic and optoelectronic devices. While passivation or
encapsulation of BP using inert materials/polymers has emerged as a plausible solution, a detailed
fundamental understanding of BP’s reaction with oxygen is imperative to rationally advance its use in
applications. Here, we use in situ environmental transmission electron microscopy to elucidate atomistic
structural changes in mechanically exfoliated few-layered BP during exposure to varying partial pressures of
oxygen. An amorphous oxide layer is seen on the actively etching BP edges, and the thickness of this layer
increases with increasing oxygen partial pressure, indicating that oxidation proceeds via initial formation of
amorphous PxOy species which sublime to result in the etching of the BP crystal. We observe that while few layered
BP is stable under the 80 kV electron beam (e-beam) in vacuum, the lattice oxidizes and degrades at
room temperature in the presence of oxygen only in the region under the e-beam. The oxidative etch rate also
increases with increasing e-beam dosage, suggesting the presence of an energy barrier for the oxidation
reaction. Preferential oxidative etching along the [0 0 1] and [0 0 1] crystallographic directions is observed, in
good agreement with density functional theory calculations showing favorable thermodynamic stability of the
oxidized BP (0 0 1) planes compared to the (1 0 0) planes. We expect the atomistic insights and fundamental
understanding obtained here to aid in the development of novel approaches to integrate BP in future
applications.
tunable bandgap and high electron mobility. However, the poor stability of BP in ambient environment severely
limits potential for application in future electronic and optoelectronic devices. While passivation or
encapsulation of BP using inert materials/polymers has emerged as a plausible solution, a detailed
fundamental understanding of BP’s reaction with oxygen is imperative to rationally advance its use in
applications. Here, we use in situ environmental transmission electron microscopy to elucidate atomistic
structural changes in mechanically exfoliated few-layered BP during exposure to varying partial pressures of
oxygen. An amorphous oxide layer is seen on the actively etching BP edges, and the thickness of this layer
increases with increasing oxygen partial pressure, indicating that oxidation proceeds via initial formation of
amorphous PxOy species which sublime to result in the etching of the BP crystal. We observe that while few layered
BP is stable under the 80 kV electron beam (e-beam) in vacuum, the lattice oxidizes and degrades at
room temperature in the presence of oxygen only in the region under the e-beam. The oxidative etch rate also
increases with increasing e-beam dosage, suggesting the presence of an energy barrier for the oxidation
reaction. Preferential oxidative etching along the [0 0 1] and [0 0 1] crystallographic directions is observed, in
good agreement with density functional theory calculations showing favorable thermodynamic stability of the
oxidized BP (0 0 1) planes compared to the (1 0 0) planes. We expect the atomistic insights and fundamental
understanding obtained here to aid in the development of novel approaches to integrate BP in future
applications.
References:
Naclerio et al. ACS Appl. Mater. Interfaces 2020, 12, 13, 15844-15854, DOI:10.1021/acsami.9b21116