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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.

No MeSH data available.


Hydrogen plasma reversibility for a graphenesample exposed for35 s to H2 plasma and annealed at 200 and 400 °C.a) Raman spectra and b) mobility determined from Hall measurementsafter the different processing steps. The pristine graphene samplewas annealed at 400 °C before the Hall measurement to excludethe influence of annealing effects on the mobility.
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fig6: Hydrogen plasma reversibility for a graphenesample exposed for35 s to H2 plasma and annealed at 200 and 400 °C.a) Raman spectra and b) mobility determined from Hall measurementsafter the different processing steps. The pristine graphene samplewas annealed at 400 °C before the Hall measurement to excludethe influence of annealing effects on the mobility.

Mentions: The additional improvement of the mobility observedafter Al2O3 ALD and annealing for the H2 treatedsample compared to the pristine graphene sample (152% vs 140%) couldbe caused by the removal of polymer residues from the graphene surfaceduring the plasma exposure. To investigate this possible cleaningeffect, a graphene sample, which was first annealed at 400 °C,was hydrogenated and subsequently annealed at 200 °C for 2 hand 400 °C for 2 h without performing Al2O3 ALD (Figure 6). Ramanspectroscopy (Figure 6a) shows that after annealing at 400 °C the graphene is recoveredto its original state without functionalization. Figure 6b shows that this is accompaniedby an increase in the mobility to 134% of its original value. Thisindicates that the H2 plasma indeed removes polymer residualsfrom the surface and explains the additional improvement observedcompared to pristine graphene.


Uniform Atomic Layer Deposition of Al 2 O 3 on Graphene by Reversible Hydrogen Plasma Functionalization
Hydrogen plasma reversibility for a graphenesample exposed for35 s to H2 plasma and annealed at 200 and 400 °C.a) Raman spectra and b) mobility determined from Hall measurementsafter the different processing steps. The pristine graphene samplewas annealed at 400 °C before the Hall measurement to excludethe influence of annealing effects on the mobility.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5384478&req=5

fig6: Hydrogen plasma reversibility for a graphenesample exposed for35 s to H2 plasma and annealed at 200 and 400 °C.a) Raman spectra and b) mobility determined from Hall measurementsafter the different processing steps. The pristine graphene samplewas annealed at 400 °C before the Hall measurement to excludethe influence of annealing effects on the mobility.
Mentions: The additional improvement of the mobility observedafter Al2O3 ALD and annealing for the H2 treatedsample compared to the pristine graphene sample (152% vs 140%) couldbe caused by the removal of polymer residues from the graphene surfaceduring the plasma exposure. To investigate this possible cleaningeffect, a graphene sample, which was first annealed at 400 °C,was hydrogenated and subsequently annealed at 200 °C for 2 hand 400 °C for 2 h without performing Al2O3 ALD (Figure 6). Ramanspectroscopy (Figure 6a) shows that after annealing at 400 °C the graphene is recoveredto its original state without functionalization. Figure 6b shows that this is accompaniedby an increase in the mobility to 134% of its original value. Thisindicates that the H2 plasma indeed removes polymer residualsfrom the surface and explains the additional improvement observedcompared to pristine graphene.

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.