Annealing effects on structure of the graphene directly synthesized on Si(100)


Project no.: 09.3.3-LMT-K-712-15-0076

Project description:

2D nanomaterial graphene is at the top of the significant interest due to the giant electron and hole mobility, charge carrier multiplication, energy band engineering and quantum interference, flexibility, optical transparency, chemical inertness
One of the main limitations preventing the wider application of graphene in semiconductor device technology is a complex graphene transfer procedure that is part of catalyst assisted graphene deposition. In this technology graphene is synthesized on catalytic Cu or Ni foils by chemical vapor deposition (CVD). Afterward, the long process follows of graphene transfer onto the targeted semiconductor or dielectric substrates. During that process, graphene can be contaminated by different adsorbents [5]. The transfer causes wrinkles or ripples on the surface of graphene.
Among a wide range of possible applications, graphene is also being used in the manufacture of a variety of ultra-fast electronic devices and ultra-sensitive photosensors. Graphene is grown on Cu or Ni foil or extrafoliated. The long process of transferring graphene to the surface of a semiconductor or dielectric is followed. In such a case, control of the graphene layer or graphene-semiconductor contact properties becomes complicated. Recently it was demonstrated that direct synthesis of graphene on semiconducting or dielectric substrates can be performed by using plasma enhanced chemical vapor deposition. However, development of this technology is in the very beginning. The graphene synthesized in this way has a high density of structural defects. These defects, in turn, reduce the mobility of charge carriers in graphene and increase the resistivity of graphene.
In this study experiments on graphene heating will be done to reduce the density of defects in directly synthesized graphene. Raman scattering spectroscopy and reflection spectra will be used to investigate the influence of heating on the structure of the samples and the thickness of the graphene layers.
The aim of the project is to investigate the influence of heating on the structure of graphene grown directly on Si (100) by microwave plasma enhanced chemical vapor deposition by using various synthesis process conditions.

Project funding:

Project is funded by EU Structural Funds according to the 2014–2020 Operational Programme for the European Union Funds’ Investments priority “Development of scientific competence of researchers, other researchers, students through practical scientific activities” under Measure No. 09.3.3-LMT-K-712.

Project results:

After the investigation of directly synthesized graphene samples before and after annealing in argon environment, there was no apparent ID/IG ratio change, although there was a clear appearance of shoulder D’ peak as the annealing temperature rises (ID/IG ratio increase with increased defects density). This is often described as formation of wrinkles in graphene sheets or introduction of impurities. There were also no distinct changes in I2D/IG ratio after (in almost all cases I2D/IG ~ 0.5). However, the biggest difference in peak intensities after annealing in argon environment is seen around 800 ?, where D and G band intensities are small and there is also a big reduction of 2D peak intensity, which indicates rather poor graphene quality and possible introduction of strain due to negative (graphene) and positive (silicon) thermal expansion coefficient mismatch. Annealing at nitrogen and vacuum environments gives a decrease of ID/IG ratio near 300 ?, which could indicate the decrease of defects. Furthermore, there is also an increase of ID/IG ratio in the case of annealing in nitrogen environment at 400 ? and this particular behavior of ID/IG is in agreement with other authors works. After annealing in vacuum and nitrogen I2D/IG does not show apparent change and thus could supposedly mean that the quality of graphene was not reduced. Reflection in all cases is seen as more or less the same in all visible spectrum range and thus, prevents us from making any assumptions about peculiar structural changes in our samples.

Period of project implementation: 2019-07-01 - 2019-08-30

Project coordinator: Kaunas University of Technology

Šarūnas Meškinis

2019 - 2019

Institute of Materials Science, Research Laboratory of Vacuum and Plasma Processes