# Se Nanowire Crystal Formation via Oxidation of 2D HfSe2: A Solid-State, In Situ Reaction Coupling for Heterogeneous Integration Technologies

## TL;DR

This paper describes a new method to create selenium nanowires by oxidizing 2D HfSe2 at low temperatures without using wet chemistry.

## Contribution

A solid-state, in situ oxidation method for forming Se nanowires from 2D HfSe2 is introduced.

## Key findings

- Se nanowires with diameters from 45 nm to 1.9 μm and lengths up to 43 μm are formed via HfSe2 oxidation.
- The process involves amorphous Se segregation and subsequent crystallization into trigonal nanowires.
- Reaction kinetics and mechanisms are analyzed for integration into heterogeneous technologies.

## Abstract

Effective heterogeneous
integration of low-dimensional
nanomaterials
in applications ranging from quantum electronics to biomedical devices
requires a detailed understanding of different formation and interfacing
reactions and the ability to synergize these processes. We report
the formation of 1D Se nanowires via low-temperature (30–150
°C) atmospheric oxidation of 2D HfSe2 crystals. The
localized, surface-bound process starting from exfoliated HfSe2 flakes on a SiO2/Si wafer support does not involve
wet chemistry and allows us to implement optical operando reaction
screening and explore the relevant parameter space and underpinning
mechanisms. Hf oxidation frees Se at the buried hafnia–HfSe2 interface, which segregates as amorphous Se, forming aggregates,
blisters, and interfacial films. We show that upon diffusion to the
stack surface, this Se can crystallize into trigonal Se nanowires
with diameters ranging from ∼45 nm to 1.9 μm and lengths
up to 43 μm depending on temperature and process time. We discuss
the coupled reaction kinetics and pathways for application-relevant
integrated process designs and connect diverse literature on the oxidation
of transition metal dichalcogenides, Se polymerization and crystallization
studies, and prior synthetic strategies for producing Se nanowires.