Comparative Study of Conventional and Quasi-Freestanding Epitaxial Graphenes Grown on 4H-SiC Substrate

Semiconductors - The structural and some other characteristics of quasi-freestanding single-layer graphene obtained by annealing of the buffer layer in the flow of hydrogen are studied in...     

Transport properties of graphene films grown by thermodestruction of SiC (0001) surface in argon medium

We present the results of investigations of the transport properties of graphene films obtained by thermodestruction of a 4H-SiC (0001) surface in argon. The charge-carrier concentration in the graphene layer was within 7 × 10¹¹–1 × 10¹² cm^–2, and the maximum mobility of electrons approached 6000 cm²/(V · s). The achieved parameters of mobility are close to theoretical values calculated for graphene films with intrinsic conductivity on the Si face of SiC at Т = 300 К in the absence of intercalated hydrogen.

     

Comparison of graphene films grown on 6H-SiC and 4H-SiC substrates

Abstract

Atomic force microscopy, Kelvin-probe microscopy and Raman spectroscopy have been used to examine graphene films grown by thermal decomposition of the Si face of semi-insulating substrates of 6H-SiC and 4H-SiC polytypes in the atmosphere of argon. It was demonstrated that the quality of graphene grown on substrates of various polytypes at identical technological growth regimes is about the same. A conclusion was made that the differences in crystal structure between 6H-SiC and 4H-SiC does not lead to significant dissimilarities in the mechanism of sublimation of silicon carbide components from the surface of a crystal and in that of graphene crystallization.     

Transformation of the buffer layer grown on 4H-SiC to single-layer graphene by ex situ hydrogen intercalation

Abstract

The buffer layer samples grown on the Si-face of the 4H- and 6H-SiC substrates were heated in a hydrogen flow at different temperatures (600–900?°C) and heating times (40–60?min) in order to obtain quasi-freestanding monolayer graphene. Their structural properties were characterized before and after heating by using the methods of Raman spectroscopy, atomic force microscopy, Kelvin probe force microscopy, and low-energy electron diffraction. The dependence of the degree of coverage of the sample with quasi-freestanding graphene and the number of defects in the resulting films on the heating temperature was studied. As a result of optimization of the technological parameters, it is shown that the highest quality of the resulting quasi-freestanding graphene can be achieved by using the following parameters: heating time of 40?minutes and temperature of 800?°C.     

Structural and Dynamical Properties of Short-Period GaN/AlN Superlattices: Experiment and Theory

Semiconductors - We report the results of systematic experimental and theoretical studies of structural and dynamical properties of short-period GaN/AlN superlattices. The multilayer structures...     

Raman Studies of Graphene Films Grown on 4H-SiC Subjected to Deposition of Ni

Semiconductors - Raman spectroscopy is used to evaluate the structural perfection of epitaxial graphene films before and after deposition of a Ni layer to their surface by magnetron sputtering. Two...     

Optical Estimation of the Carrier Concentration and the Value of Strain in Monolayer Graphene Grown on 4H-SiC

Semiconductors - Systematic studies of the effect of the electron concentration on the Raman spectra of single-layer graphene films have been carried out. The samples were grown by thermal...     

Boson Peak Related to Ga Nanoclusters in AlGaN Layers Grown by Plasma-Assisted Molecular Beam Epitaxy at Ga-Rich Conditions

Semiconductors - We report the results of systematic Raman spectroscopy studies of AlxGa1 –xN (x ~ 0.75) layers grown using plasma-assisted molecular beam epitaxy at various stoichiometric...     

Aluminosilicate-supported cobalt catalysts in the Fischer-Tropsch synthesis

Cobalt catalysts supported on SIRAL aluminosilicates have been prepared and tested in hydrocarbon synthesis from CO and H₂. It has been shown that the state of the cobalt metal on the catalyst surface is determined by both the cobalt content and the support nature, in particular, by the phase composition on its surface. The reaction rate on cobalt crystallites 3–6 nm in size is lower than that on 8–13-nm crystallites. It has been found that promotion with cerium oxide considerably increases the catalyst activity, although the selectivity for C⁵⁺ hydrocarbons slightly decreases.     

Surface morphology control of the SiC (0001) substrate during the graphene growth

Abstract

The dependence of surface morphology of the SiC(0001) substrate on the rate with which it is heated up to the temperature of graphene growth was studied by three techniques: atomic force microscopy, Raman spectroscopy and Kelvin probe force microscopy. The study was carried out for the rates of substrates heating ranging from 100?°C/min to 320?°C/min. As a result, it was found out that both the width of the terraces forming on the surface of SiC substrate and the uniformity of the graphene layers covering these terraces significantly depend on the applied rate of the heating. It was also shown that the most homogeneous monolayer graphene with the minimum of double-layers inclusions is formed if the rate of SiC heating is about 250?°C/min.