Limits...
Dopant morphology as the factor limiting graphene conductivity.

Hofmann M, Hsieh YP, Chang KW, Tsai HG, Chen TT - Sci Rep (2015)

Bottom Line: First the agglomeration of dopants into clusters provides a route to increase the graphene conductivity through formation of ordered scatterers.As the cluster grows, the charge transfer efficiency between graphene and additional dopants decreases due to emerging polarization effects.The presented results help identifying the range of beneficial doping density and guide the choice of suitable dopants for graphene's future applications.

View Article: PubMed Central - PubMed

Affiliation: Department of Material Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan.

ABSTRACT
Graphene's low intrinsic carrier concentration necessitates extrinsic doping to enhance its conductivity and improve its performance for application as electrodes or transparent conductors. Despite this importance limited knowledge of the doping process at application-relevant conditions exists. Employing in-situ carrier transport and Raman characterization of different dopants, we here explore the fundamental mechanisms limiting the effectiveness of doping at different doping levels. Three distinct transport regimes for increasing dopant concentration could be identified. First the agglomeration of dopants into clusters provides a route to increase the graphene conductivity through formation of ordered scatterers. As the cluster grows, the charge transfer efficiency between graphene and additional dopants decreases due to emerging polarization effects. Finally, large dopant clusters hinder the carrier motion and cause percolative transport that leads to an unexpected change of the Hall effect. The presented results help identifying the range of beneficial doping density and guide the choice of suitable dopants for graphene's future applications.

No MeSH data available.


Related in: MedlinePlus

Characterization of ozone adsorption: (a) (top) time evolution of Raman G-band position vs. ID/IG ratio (bottom) time evolution of adsorbate cluster dimension from EFM vs. according carrier concentration, (b) charge per adsorbate for increasing coverage.
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f3: Characterization of ozone adsorption: (a) (top) time evolution of Raman G-band position vs. ID/IG ratio (bottom) time evolution of adsorbate cluster dimension from EFM vs. according carrier concentration, (b) charge per adsorbate for increasing coverage.

Mentions: We characterize the effect of adsorbates on graphene’s transport properties by analyzing the defect related Raman ID/IG ratio and the G-Band position during ozone exposure (Fig. 3(a)). The ID/IG ratio is proportional to the adsorbate density (see Supporting Information for a detailed description) whereas Raman G-Band position increases with carrier density18. The observed initial proportionality between the parameters indicates a charge transfer between adsorbates and graphene as expected from doping. At intermediate exposure durations, however, the ID/IG ratio increases without a significant change in G-Band shift. This behavior is unexpected since charge transfer should occur as long as adsorption happens. The same behavior is observed when correlating the evolution of dopant morphology from EFM with electrical transport measurements. Figure 3(a) shows that the clusters keep growing even after the carrier concentration reaches equilibrium.


Dopant morphology as the factor limiting graphene conductivity.

Hofmann M, Hsieh YP, Chang KW, Tsai HG, Chen TT - Sci Rep (2015)

Characterization of ozone adsorption: (a) (top) time evolution of Raman G-band position vs. ID/IG ratio (bottom) time evolution of adsorbate cluster dimension from EFM vs. according carrier concentration, (b) charge per adsorbate for increasing coverage.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663794&req=5

f3: Characterization of ozone adsorption: (a) (top) time evolution of Raman G-band position vs. ID/IG ratio (bottom) time evolution of adsorbate cluster dimension from EFM vs. according carrier concentration, (b) charge per adsorbate for increasing coverage.
Mentions: We characterize the effect of adsorbates on graphene’s transport properties by analyzing the defect related Raman ID/IG ratio and the G-Band position during ozone exposure (Fig. 3(a)). The ID/IG ratio is proportional to the adsorbate density (see Supporting Information for a detailed description) whereas Raman G-Band position increases with carrier density18. The observed initial proportionality between the parameters indicates a charge transfer between adsorbates and graphene as expected from doping. At intermediate exposure durations, however, the ID/IG ratio increases without a significant change in G-Band shift. This behavior is unexpected since charge transfer should occur as long as adsorption happens. The same behavior is observed when correlating the evolution of dopant morphology from EFM with electrical transport measurements. Figure 3(a) shows that the clusters keep growing even after the carrier concentration reaches equilibrium.

Bottom Line: First the agglomeration of dopants into clusters provides a route to increase the graphene conductivity through formation of ordered scatterers.As the cluster grows, the charge transfer efficiency between graphene and additional dopants decreases due to emerging polarization effects.The presented results help identifying the range of beneficial doping density and guide the choice of suitable dopants for graphene's future applications.

View Article: PubMed Central - PubMed

Affiliation: Department of Material Science and Engineering, National Cheng Kung University, Tainan 70101, Taiwan.

ABSTRACT
Graphene's low intrinsic carrier concentration necessitates extrinsic doping to enhance its conductivity and improve its performance for application as electrodes or transparent conductors. Despite this importance limited knowledge of the doping process at application-relevant conditions exists. Employing in-situ carrier transport and Raman characterization of different dopants, we here explore the fundamental mechanisms limiting the effectiveness of doping at different doping levels. Three distinct transport regimes for increasing dopant concentration could be identified. First the agglomeration of dopants into clusters provides a route to increase the graphene conductivity through formation of ordered scatterers. As the cluster grows, the charge transfer efficiency between graphene and additional dopants decreases due to emerging polarization effects. Finally, large dopant clusters hinder the carrier motion and cause percolative transport that leads to an unexpected change of the Hall effect. The presented results help identifying the range of beneficial doping density and guide the choice of suitable dopants for graphene's future applications.

No MeSH data available.


Related in: MedlinePlus