3 research outputs found
Vapor-Phase Molecular Doping of Graphene for High-Performance Transparent Electrodes
Doping is an essential process to engineer the conductivity and work-function of graphene for higher performance optoelectronic devices, which includes substitutional atomic doping by reactive gases, electrical/electrochemical doping by gate bias, and chemical doping by acids or reducing/oxidizing agents. Among these, the chemical doping has been widely used due to its simple process and high doping strength. However, it also has an instability problem in that the molecular dopants tend to gradually evaporate from the surface of graphene, leading to substantial decrease in doping effect with time. In particular, the instability problem is more serious for n-doped graphene because of undesirable reaction between dopants and oxygen or water in air. Here we report a simple method to tune the electrical properties of CVD graphene through n-doping by vaporized molecules at 70 °C, where the dopants in vapor phase are mildly adsorbed on graphene surface without direct contact with solution. To investigate the dependence on functional groups and molecular weights, we selected a series of ethylene amines as a model system, including ethylene diamine (EDA), diethylene triamine (DETA), and triethylene tetramine (TETA) with increasing number of amine groups showing different vapor pressures. We confirmed that the vapor-phase doping provides not only very high carrier concentration but also good long-term stability in air, which is particularly important for practical applications
Ultraclean Patterned Transfer of Single-Layer Graphene by Recyclable Pressure Sensitive Adhesive Films
We report an ultraclean, cost-effective,
and easily scalable method of transferring and patterning large-area
graphene using pressure sensitive adhesive films (PSAFs) at room temperature.
This simple transfer is enabled by the difference in wettability and
adhesion energy of graphene with respect to PSAF and a target substrate.
The PSAF-transferred graphene is found to be free from residues and
shows excellent charge carrier mobility as high as ∼17 700
cm<sup>2</sup>/V·s with less doping compared to the graphene
transferred by thermal release tape (TRT) or poly(methyl methacrylate)
(PMMA) as well as good uniformity over large areas. In addition, the
sheet resistance of graphene transferred by recycled PSAF does not
change considerably up to 4 times, which would be advantageous for
more cost-effective and environmentally friendly production of large-area
graphene films for practical applications
Simultaneous Etching and Doping by Cu-Stabilizing Agent for High-Performance Graphene-Based Transparent Electrodes
Cu etching is one of the key processes
to produce large-area graphene
through chemical vapor deposition (CVD), which is needed to remove
Cu catalysts and transfer graphene onto target substrates for further
applications. However, the Cu etching method has been much less studied
compared to doping or transfer processes despite its importance in
producing higher quality graphene films. The Cu etchant generally
includes a strong oxidizing agent that converts metallic Cu to Cu<sup>2+</sup> in a short period of time. Sometimes, the highly concentrated
Cu<sup>2+</sup> causes a side reaction leading to defect formation
on graphene, which needs to be suppressed for higher graphene quality.
Here we report that the addition of metal-chelating agents such as
benzimidazole (BI) to etching solution reduces the reactivity of Cu-etching
solution by forming a coordination compound between BI and Cu<sup>2+</sup>. The resulting graphene film prepared by Cu stabilizing
agent exhibits a sheet resistance as lows as ∼200 Ohm/sq without
additional doping processes. We also confirmed that such strong doping
effect is stable enough to last for more than 10 months under ambient
conditions due to the barrier properties of graphene covering the
BI dopants, in contrast to the poor stability of graphene additionally
doped by strong p-dopant such as HAuCl<sub>4</sub>. Thus, we expect
that this simultaneous doping and etching method would be very useful
for simple and high-throughput production of large-area graphene electrodes
with enhanced conductivity