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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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DFT-predicted structures of the lowest-energy(left) physisorbedand (right) chemisorbed species and their relative energies from theTMA adsorption on pristine graphene, oxygenated graphene (i.e., grapheneoxide, GO), and hydrogenated graphene (HG).
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fig7: DFT-predicted structures of the lowest-energy(left) physisorbedand (right) chemisorbed species and their relative energies from theTMA adsorption on pristine graphene, oxygenated graphene (i.e., grapheneoxide, GO), and hydrogenated graphene (HG).

Mentions: The results ofTMA physisorption and chemisorption on the differentgraphene model systems are compiled in Table 1, whereas the corresponding minimum-energystructures of the physisorbed and chemisorbed species for the mostrelevant pathways are shown in Figure 7. A complete overview of all considered reaction pathwayscan be found in the Supporting Information (Figure S4).


Uniform Atomic Layer Deposition of Al 2 O 3 on Graphene by Reversible Hydrogen Plasma Functionalization
DFT-predicted structures of the lowest-energy(left) physisorbedand (right) chemisorbed species and their relative energies from theTMA adsorption on pristine graphene, oxygenated graphene (i.e., grapheneoxide, GO), and hydrogenated graphene (HG).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5384478&req=5

fig7: DFT-predicted structures of the lowest-energy(left) physisorbedand (right) chemisorbed species and their relative energies from theTMA adsorption on pristine graphene, oxygenated graphene (i.e., grapheneoxide, GO), and hydrogenated graphene (HG).
Mentions: The results ofTMA physisorption and chemisorption on the differentgraphene model systems are compiled in Table 1, whereas the corresponding minimum-energystructures of the physisorbed and chemisorbed species for the mostrelevant pathways are shown in Figure 7. A complete overview of all considered reaction pathwayscan be found in the Supporting Information (Figure S4).

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.