Epitaxial graphene growth on silicon carbide
Graphene is one of the most promising nanomaterials for the future because of its various characteristics, like strong stiffness and high electric and thermal conductivity.
[3] In 1975, Bommel et al. then achieved to form monolayer graphite on the C-face as well as the Si-face of hexagonal SiC.
[4] [5] New insights in the electronic and physical properties of graphene like the Dirac nature of the charge carriers, half-integer quantum Hall effect or the observation of the 2D electron gas behaviour were first measured on multilayer graphene from de Heer et al. at the Georgia Institute of Technology in 2004.
[6][7] Still, the Nobel Prize in Physics ″for groundbreaking experiments regarding the two-dimensional material graphene″ in 2010 was awarded to Andre Geim and Konstantin Novoselov.
An official online document of the Royal Swedish Academy of Sciences about this awarding got under fire.
Walter de Heer mentions several objections about the work of Geim and Novoselov who apparently have measured on many-layer graphene, also called graphite, which has different electronic and mechanical properties.
[8] Emtsev et al. improved the whole procedure in 2009 by annealing the SiC-samples at high temperatures over 1650 °C in an argon environment to obtain morphologically superior graphene.
Due to the fact that the vapor pressure of carbon is negligible compared to the one of silicon, the Si atoms desorb at high temperatures and leave behind the carbon atoms which form graphitic layers, also called few-layer graphene (FLG).
Approximately three bilayers of SiC are necessary to set free enough carbon atoms needed for the formation of one graphene layer.
Using this technique, the resulting graphene consists of small grains with varying thickness (30–200 nm).
These grains occur due to morphological changes of the SiC surface under high temperatures.
On the other side, at relatively low temperatures, poor quality occurs due to the high sublimation rate.
[2] The growth procedure was improved to a more controllable technique by annealing the SiC-samples at high temperatures over 1650 °C in an argon environment.
On the SiC(0001) face, large-area single crystalline monolayer graphene with a low growth rate can be grown.
In this case, the graphene layer grows not directly on top of the substrate but on a complex
[15] This structure is non-conducting, rich of carbon and partially covalently bonded to the underlying SiC substrate and provides, therefore, a template for subsequent graphene growth and works as an electronic ″buffer layer″.
[15] Changing the growth parameters such as annealing temperature and time, the number of graphene layers on the SiC(0001) can be controlled .
[19] This buffer layer can be transformed into monolayer graphene by decoupling it from the SiC substrate using an intercalation process.
[14][21] Hite et al. however found out, that these islands are positioned at a lower level than the surrounding surface and referred them as graphene covered basins (GCBs).
[2] Growing graphene on the carbon-terminated face, every layer is rotated against the previous one with angles between 0° and 30° relative to the substrate.
Due to this, the symmetry between the atoms in the unit cell is not broken in multilayers and every layer has the electronic properties of an isolated monolayer of graphene.
[1] A fast method to evaluate the number of layers is using optical microscope in combination with contrast-enhancing techniques.
It is considered to surpass silicon in terms of key parameters like feature size, speed and power consumption and is therefore one of the most promising materials for future applications.
Using a two-inch 6H-SiC wafer as substrate, the graphene grown by thermal decomposition can be used to modulate a large energy pulse laser.
[24] The quantum Hall effect in epitaxial graphene can serve as a practical standard for electrical resistance.
