# Structural and Plasmonic Evolution in Mixed-Dimensionality Bismuth/Graphene Heterostructures

## TL;DR

This paper studies how bismuth nanostructures form on graphene and how their structure and plasmonic properties evolve with temperature and electron beam exposure.

## Contribution

The study reveals new insights into the structural and plasmonic evolution of bismuth/graphene heterostructures using high-resolution electron microscopy.

## Key findings

- Bismuth deposited at room temperature forms β-Bi crystals and nanorods with specific orientations relative to graphene.
- Higher temperature depositions produce amorphous bismuth nanoparticles that crystallize under the electron beam.
- Plasmonic features of bismuth nanoparticles are linked to their crystallization state.

## Abstract

Mixed-dimensionality
heterostructures of low-dimensional
bismuth
(Bi) with two-dimensional (2D) graphene are of interest in a variety
of application fields ranging from nanoelectronics, next-generation
batteries, and (photo)­catalysis to plasmonics. We here explore the
evolution of the morphology and structure of low-dimensional Bi/graphene
heterostructures by high-resolution (scanning) transmission electron
microscopy ((S)­TEM). To this end, we deposit low-dimensional Bi nanostructures
onto suspended monolayer graphene membranes via physical vapor deposition
(PVD). This enables us to study intrinsic Bi–graphene interactions,
in contrast to prior work that utilized Bi on supported graphene.
We find that Bi deposited onto room temperature graphene consists
of grains formed by irregularly shaped β-Bi crystals with a
β-Bi[001]⊥graphene(001) texture and β-Bi nanorods
with a β-Bi[2–21]⊥graphene(001) texture. Importantly,
both texture types show rotational van der Waals epitaxy with the
supporting graphene. The room temperature depositions grow via an
initial amorphous β-Bi[2–21]-like state into a closed
film of β-Bi structure. For higher graphene temperatures of
150 to 250 °C during deposition, we find the formation of amorphous
Bi nanoparticles (NPs) at much reduced coverage due to Bi reverse
desorption at these temperatures. While the room temperature deposited
Bi films remain static under the electron beam in (S)­TEM, the amorphous
Bi NPs from higher temperature depositions exhibit electron beam induced in situ crystallization in TEM. In parallel to observing
their structural evolution during this crystallization, this also
enables us to probe the evolution of plasmonic features of Bi NPs
via (valence) electron energy loss spectroscopy ((V)­EELS), suggesting
a link between crystallization state and Bi NP surface plasmon (SP)
energy.