Graphene is a single atomic layer of carbon with a hexagonal crystal structure. It has been examined heavily in the past ten years for its numerous unique material properties. With its near optical transparency, chemical inertness, high electrical and thermal conductivity, and high mechanical strength, graphene is seen as an extremely promising two-dimensional material for use in a wide range of applications, including optical displays, energy storage, and sensors1,2.
The ability to process the material without compromising its structural integrity is one challenge of working with graphene. With maximum applied powers of 10’s watts, plasma cleaners from Harrick Plasma are designed to impact surfaces on only an atomic level, so are perfect for treating graphene. Harrick Plasma explores the numerous ways researchers have applied plasma treatment to tune the numerous material properties of graphene.
Nitrogen Doping of Graphene
By utilizing nitrogen (N2) gas, plasma can be applied to incorporate N atoms into the graphene structure and so, alter its electronic properties. Due to its similar atomic size and favorable electron configuration to form strong covalent bonds with carbon, nitrogen is considered an ideal element for doping carbon materials3. The below papers detail applying N2 plasma to create N-doped graphene with semiconducting characteristics.
Wang et al. examined the modification of the intrinsic properties of graphene (as opposed to creating hybrid or composite graphene materials) to strengthen its performance in biosensing and electrocatalysis applications. They produced N-doped graphene with dopant concentrations of 0.11-1.35 at. % by controlling the N2 plasma treatment time.
A schematic was proposed based on TEM imaging, where N-doped graphene maintained a planar, two-dimensional structure, even after plasma treatment. It was suggested by the authors that N atoms substitute into the graphene lattice with the presence of periodic defect sites. This started a modification in the electronic band structure and so opened the energy bandgap to create semiconducting graphene.
More extensive assessment of the chemically-modified graphene was carried out through electrochemical measurements and fabrication of biosensor devices with the graphene as the electrode material. Wang et al. discovered that N-doped graphene showed excellent electrocatalytic activity for the decrease of H2O2 and high sensitivity and selectivity for glucose biosensing.
Yet, extended plasma exposures (>40 min) led to diminished electrocatalytic activity, indicating destruction of the graphene layer. Yanilmaz et al. investigated optimal plasma conditions to produce N-doped graphene for potential optical and electronic applications
In order to bind N to plasma-generated defects (step edges) without formation of excessive defects that can dismantle the planar, 2D structure of graphene, optimal process conditions were needed. Higher power and prolonged plasma treatment time (>30 min) destroyed the lattice structure and etched graphene without doping.
Effective doping was achieved at Medium RF power with 15 minute plasma treatment, where the resulting N-doped graphene was homogeneous across a 20 μm x 20 μm area. Theoretical calculations and experimental results suggested that periodic adsorption of N atoms happens on top of the C atoms rather than through N substitution within the graphene lattice.
Relevant Articles from Harrick Plasma Users
- Wang Y, Shao Y, Matson D, Li J and Lin Y. “Nitrogen-Doped Graphene and Its Application in Electrochemical Biosensing”. ACS Nano 2010 4(4): 1790-1798.
- Yanilmaz A, Tomak A, Akbali B, Bacaksiz C, Ozceri E, Ari O, Senger RT, Selamet Y and Zareie HM. “Nitrogen doping for facile and effective modification of graphene surfaces”. RSC Adv. 2017 7: 28383-28392.
- Allen MJ, Tung VC and Kaner RB. “Honeycomb Carbon: A Review of Graphene”. Chem. Rev. 2010 110(1): 132-145.
- Choi W, Lahiri I, Seelaboyina R and Kang YS. “Synthesis of Graphene and Its Applications: A Review”. Crit. Rev. Solid State 2010 35(1): 52-71.
- Wang H, Maiyalagan T and Wang X. “Review on Recent Progress in Nitrogen-Doped Graphene: Synthesis, Characterization, and Its Potential Applications”. ACS Catal. 2012 2: 781-794.
This information has been sourced, reviewed and adapted from materials provided by Harrick Plasma.
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