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Uniform Atomic Layer Deposition of Al 2 O 3 on Graphene by Reversible Hydrogen Plasma Functionalization

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ABSTRACT

A novelmethod to form ultrathin, uniform Al2O3 layerson graphene using reversible hydrogen plasma functionalizationfollowed by atomic layer deposition (ALD) is presented. ALD on pristinegraphene is known to be a challenge due to the absence of danglingbonds, leading to nonuniform film coverage. We show that hydrogenplasma functionalization of graphene leads to uniform ALD of closedAl2O3 films down to 8 nm in thickness. Hallmeasurements and Raman spectroscopy reveal that the hydrogen plasmafunctionalization is reversible upon Al2O3 ALDand subsequent annealing at 400 °C and in this way does not deterioratethe graphene’s charge carrier mobility. This is in contrastwith oxygen plasma functionalization, which can lead to a uniform5 nm thick closed film, but which is not reversible and leads to areduction of the charge carrier mobility. Density functional theory(DFT) calculations attribute the uniform growth on both H2 and O2 plasma functionalized graphene to the enhancedadsorption of trimethylaluminum (TMA) on these surfaces. A DFT analysisof the possible reaction pathways for TMA precursor adsorption onhydrogenated graphene predicts a binding mechanism that cleans offthe hydrogen functionalities from the surface, which explains theobserved reversibility of the hydrogen plasma functionalization uponAl2O3 ALD.

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Schematic overviewof the energetically most favorable TMA chemisorptionmechanisms on pristine and functionalized graphene based on the PBE-D3-levelcalculations.
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fig8: Schematic overviewof the energetically most favorable TMA chemisorptionmechanisms on pristine and functionalized graphene based on the PBE-D3-levelcalculations.

Mentions: Considering the varietyin the reaction mechanisms employed forthe dissociative binding of TMA on diverse graphene surfaces, an overviewis given in Figure 8. The most plausible pathway for hydrogenated graphene that combinesH2 and CH4 release mechanisms is predicted toclean the hydrogen functionalities off the surface (typically threehydrogens per bound TMA molecule). In contrast, on the GO surfaces,the oxygen adatoms are predicted to stay on the graphene surface onall feasible pathways. This is the likely reason for the observedreversibility of the H2 plasma treatment after Al2O3 ALD as opposed to O2 plasma treaded graphene(see Figure 4).


Uniform Atomic Layer Deposition of Al 2 O 3 on Graphene by Reversible Hydrogen Plasma Functionalization
Schematic overviewof the energetically most favorable TMA chemisorptionmechanisms on pristine and functionalized graphene based on the PBE-D3-levelcalculations.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5384478&req=5

fig8: Schematic overviewof the energetically most favorable TMA chemisorptionmechanisms on pristine and functionalized graphene based on the PBE-D3-levelcalculations.
Mentions: Considering the varietyin the reaction mechanisms employed forthe dissociative binding of TMA on diverse graphene surfaces, an overviewis given in Figure 8. The most plausible pathway for hydrogenated graphene that combinesH2 and CH4 release mechanisms is predicted toclean the hydrogen functionalities off the surface (typically threehydrogens per bound TMA molecule). In contrast, on the GO surfaces,the oxygen adatoms are predicted to stay on the graphene surface onall feasible pathways. This is the likely reason for the observedreversibility of the H2 plasma treatment after Al2O3 ALD as opposed to O2 plasma treaded graphene(see Figure 4).

View Article: PubMed Central - PubMed

ABSTRACT

A novelmethod to form ultrathin, uniform Al2O3 layerson graphene using reversible hydrogen plasma functionalizationfollowed by atomic layer deposition (ALD) is presented. ALD on pristinegraphene is known to be a challenge due to the absence of danglingbonds, leading to nonuniform film coverage. We show that hydrogenplasma functionalization of graphene leads to uniform ALD of closedAl2O3 films down to 8 nm in thickness. Hallmeasurements and Raman spectroscopy reveal that the hydrogen plasmafunctionalization is reversible upon Al2O3 ALDand subsequent annealing at 400 °C and in this way does not deterioratethe graphene’s charge carrier mobility. This is in contrastwith oxygen plasma functionalization, which can lead to a uniform5 nm thick closed film, but which is not reversible and leads to areduction of the charge carrier mobility. Density functional theory(DFT) calculations attribute the uniform growth on both H2 and O2 plasma functionalized graphene to the enhancedadsorption of trimethylaluminum (TMA) on these surfaces. A DFT analysisof the possible reaction pathways for TMA precursor adsorption onhydrogenated graphene predicts a binding mechanism that cleans offthe hydrogen functionalities from the surface, which explains theobserved reversibility of the hydrogen plasma functionalization uponAl2O3 ALD.

No MeSH data available.