1. 1.Oxidation effects of 2D-materials

2. Why is this important? 2D materials are a promising technology
Fundamental knowledge
Oxygen alters electrical properties
Production steps with oxygen

3. Two main groups Transition Metal DiChalcogenides (TMDCs)
MX2 - (M = Mo, Nb, Hf) – (X = S, Se, Te)
Semiconductivity and even superconductivity in some
Band gap allows for use in FETs and many other applications
Oxidation decreases conductivity
Graphene
Started the adventure for 2D-materials
Two dimensional carbon in honeycomb structure
When oxidized it becomes graphene oxide (GO)
Might want to oxidize it

4. Effects of oxygen on TMDCs
MoS2 has indirect band gap of 1.23eV in bulk
Direct band gap of 1.8eV as a monolayer
Vacancies causes ‘doping’
The Chalcogen is most likely to be vacant (except SnS)
n-doped
Oxygen removes gap states

5. Effects of oxygen on TMDCs
MoS2 has indirect band gap of 1.23eV in bulk
Direct band gap of 1.8eV as a monolayer
Vacancies causes ‘doping’
The Chalcogen is most likely to be vacant (except SnS)
n-doped
Oxygen removes gap states

6. Effects of oxygen on TMDCs
MoS2 has indirect band gap of 1.23eV in bulk
Direct band gap of 1.8eV as a monolayer
Vacancies causes ‘doping’
The Chalcogen is most likely to be vacant (except SnS)
n-doped
Oxygen removes gap states

7. Oxygen reactivity O2, H2O, O* and OH-
DFT - ΔG(p,T) = ΔH(p,T)-TΔS, T = 0k
Chemical potential
Vacancies increase reactivity
MX2 + H2O -> MX2(O) + H2
MX2 + O2 -> MX2(O) + ½ O2
MX2 + O* -> MX2(O)

8. Healing and prevention
The use of strongly reducing agents such as H2S, H2Se, H2Te can heal oxidation
It is better to prevent oxidation
A full recovery is thought impossible

9. Effects of oxygen on graphene
Graphene oxide
Creates tuneable band gap
Becomes hydrophillic
Flake size can also be tuned
Makes it usefull for electronics as a material for electronics, clean energy devices, biology and medicine

10. How do we make it happen?
Modified Hummers method – NaNO3, KMnO4 and H2SO4
Hummers method creates a high amount of defects
Functional groups
Rapid thermal annealing used to reduce graphene oxide

11. Final words Still many things to be researched Production Prevention
Application
Fundamental physics and chemistry
The effects of oxidation depends on the material
The interested listener could check out black posphorus (posphene)
Thank you.,. Ü

12. Sources - J. Mater. Chem. A, 2019,7, 4291-4312
Phys. Chem. Chem. Phys., 2019,21,
Procedia Engineering, 2017, 184,