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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.


XPSspectra of the core level C 1s of a) pristine graphene (aftertransfer to SiO2), b) graphene after a 30 s O2 plasma treatment, and c) graphene after a 35 s H2 plasmatreatment at a pressure of 50 mTorr and a plasma power of 100 W.
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fig1: XPSspectra of the core level C 1s of a) pristine graphene (aftertransfer to SiO2), b) graphene after a 30 s O2 plasma treatment, and c) graphene after a 35 s H2 plasmatreatment at a pressure of 50 mTorr and a plasma power of 100 W.

Mentions: The XPS measurements of the C 1s spectra ofgraphene after a 30 s O2 plasma treatment and a 35 s H2 plasma treatment are shown in Figure 1. As a reference the spectrum of pristinegraphene after transfer to 90 nm SiO2 and 400 °C annealis also shown in Figure 1. The main peak contributing to the C 1s spectrum of pristine graphene(Figure 1a) is locatedat 284.4 eV and originates from the sp2 bonding of the carbon atoms. The weak peak at 286.4 eV correspondsto C–O bonding. These C–O bonds are commonly seen onthe graphene basal plane and originate from grain boundaries or defectssites38,39 or are the result of polymer residues remainingon the graphene after its transfer to SiO2 and annealing.40 In addition, two plasmon loss features observedat 290.4 and 293.2 eV are caused by the interaction of the photoelectronwith free electrons present in the graphene.41


Uniform Atomic Layer Deposition of Al 2 O 3 on Graphene by Reversible Hydrogen Plasma Functionalization
XPSspectra of the core level C 1s of a) pristine graphene (aftertransfer to SiO2), b) graphene after a 30 s O2 plasma treatment, and c) graphene after a 35 s H2 plasmatreatment at a pressure of 50 mTorr and a plasma power of 100 W.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC5384478&req=5

fig1: XPSspectra of the core level C 1s of a) pristine graphene (aftertransfer to SiO2), b) graphene after a 30 s O2 plasma treatment, and c) graphene after a 35 s H2 plasmatreatment at a pressure of 50 mTorr and a plasma power of 100 W.
Mentions: The XPS measurements of the C 1s spectra ofgraphene after a 30 s O2 plasma treatment and a 35 s H2 plasma treatment are shown in Figure 1. As a reference the spectrum of pristinegraphene after transfer to 90 nm SiO2 and 400 °C annealis also shown in Figure 1. The main peak contributing to the C 1s spectrum of pristine graphene(Figure 1a) is locatedat 284.4 eV and originates from the sp2 bonding of the carbon atoms. The weak peak at 286.4 eV correspondsto C–O bonding. These C–O bonds are commonly seen onthe graphene basal plane and originate from grain boundaries or defectssites38,39 or are the result of polymer residues remainingon the graphene after its transfer to SiO2 and annealing.40 In addition, two plasmon loss features observedat 290.4 and 293.2 eV are caused by the interaction of the photoelectronwith free electrons present in the graphene.41

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.