Probing the structural transition from buffer layer to quasifreestanding monolayer graphene by Raman spectroscopy

2019 ◽  
Vol 99 (4) ◽  
Author(s):  
S. Wundrack ◽  
D. Momeni Pakdehi ◽  
P. Schädlich ◽  
F. Speck ◽  
K. Pierz ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Buffer Layer ◽  
Structural Transition ◽  
Monolayer Graphene

scholarly journals Critical View on Buffer Layer Formation and Monolayer Graphene Properties in High-Temperature Sublimation

2021 ◽  
Vol 11 (4) ◽  
pp. 1891
Author(s):  
Vallery Stanishev ◽  
Nerijus Armakavicius ◽  
Chamseddine Bouhafs ◽  
Camilla Coletti ◽  
Philipp Kühne ◽  
...  
Keyword(s):  
High Temperature ◽  
Charge Carrier ◽  
Buffer Layer ◽  
Free Charge Carrier ◽  
Monolayer Graphene ◽  
Free Charge ◽  
Layer Formation ◽  
Free Hole ◽  
Sublimation Growth ◽  
Insulating Substrates

In this work we have critically reviewed the processes in high-temperature sublimation growth of graphene in Ar atmosphere using closed graphite crucible. Special focus is put on buffer layer formation and free charge carrier properties of monolayer graphene and quasi-freestanding monolayer graphene on 4H–SiC. We show that by introducing Ar at higher temperatures, TAr, one can shift the formation of the buffer layer to higher temperatures for both n-type and semi-insulating substrates. A scenario explaining the observed suppressed formation of buffer layer at higher TAr is proposed and discussed. Increased TAr is also shown to reduce the sp3 hybridization content and defect densities in the buffer layer on n-type conductive substrates. Growth on semi-insulating substrates results in ordered buffer layer with significantly improved structural properties, for which TAr plays only a minor role. The free charge density and mobility parameters of monolayer graphene and quasi-freestanding monolayer graphene with different TAr and different environmental treatment conditions are determined by contactless terahertz optical Hall effect. An efficient annealing of donors on and near the SiC surface is suggested to take place for intrinsic monolayer graphene grown at 2000 ∘C, and which is found to be independent of TAr. Higher TAr leads to higher free charge carrier mobility parameters in both intrinsically n-type and ambient p-type doped monolayer graphene. TAr is also found to have a profound effect on the free hole parameters of quasi-freestanding monolayer graphene. These findings are discussed in view of interface and buffer layer properties in order to construct a comprehensive picture of high-temperature sublimation growth and provide guidance for growth parameters optimization depending on the targeted graphene application.

Raman Spectroscopy of Epitaxial Si/Si1-xGe, xHeterostructures

1998 ◽  
Vol 533 ◽  
Author(s):  
Ran Liu ◽  
Stefan Zollner ◽  
Ming Liaw ◽  
David O'meara ◽  
Nigel Cave
Keyword(s):  
Raman Spectroscopy ◽  
Thermal Treatment ◽  
Raman Scattering ◽  
Buffer Layer ◽  
Excellent Agreement ◽  
Lattice Mismatch ◽  
Theoretical Curve ◽  
Sum Rule ◽  
Si Substrates ◽  
Strain Coefficient

AbstractRaman scattering studies were carried out on epi Si/Si1-xGex (x = 0.1 to 0.3) heterostructures consisting of a thin Si cap layer (100 - 400 A˚), a grade-down Si1-xGex layer, a constant Si1-xGex, buffer layer and a grade-up graded Si1-xGex layer on (100) oriented Si substrates. Different Ge composition, Si1-xGex layer thicknesses and thermal treatment were used to achieve different relaxation in the Si1-xGex layers. It has been revealed that, to a very good approximation, the absolute strains in the cap Si and constant Si1-xGex layers follow a simple sum-rule that is imposed by the lattice mismatch between unstrained Si and completely relaxed Si1-x Gex. This sum rule can be used to determine the Ge composition and stresses in both cap Si and constant Si1-xGex layers. Excellent agreement was found between the theoretical curve obtained with LO phonon strain coefficient b=−930cm−1 and the experimental total strain for all samples, regardless of the degree of the relaxation of the grade-up Si1-xGex layer.

Simple and environment-friendly method for graphene synthesis by using ultrasound.

2021 ◽  
Vol 17 ◽  
Author(s):  
Irena Markovska ◽  
Dimitar Georgiev ◽  
Fila Yovkova ◽  
Miroslav Abrashev
Keyword(s):  
Electrical Conductivity ◽  
Raman Spectroscopy ◽  
Monolayer Graphene ◽  
Conductivity Measurements ◽  
Environment Friendly ◽  
Complex Processes ◽  
Graphene Synthesis ◽  
Pure Graphite ◽  
Ft Ir ◽  
Electrodes For Supercapacitors

Background: This paper proposes a technology for the production of monolayer graphene by an easy, accessible, and non-toxic method. Methods: For the preparation of graphene, a combination of chemical and physical (ultrasonic) treatment of the original graphite precursor (purity >99%) was applied. The precursor of graphite is placed in a beaker with a solution of KOH or H2SO4. The mixtures were homogenized well and sonicated for 4h. The applied ultrasound has a power of 120 W, frequency 40 kHz. Due to the effects of ultrasound, complex processes take place in the solutions, which leads to the formation of superfine graphene. Better results were obtained at samples treated with 2n H2SO4. The physicochemical properties of the resulting graphene were characterized mainly by Raman spectroscopy, FT-IR, TEM, SEM, and electrical conductivity measurements. Results: Our research was focused mainly on the field of nanotechnology, in particular on the synthesis of graphene, which could be used as a coating on electrodes for supercapacitors. In this connection, three series of samples were developed in which the pristine graphite was treated with 2n H2SO4, 4n H2SO4, and 6n H2SO4, respectively, and their electrical properties were measured. Conclusion: The obtained graphene shows electrical resistivity 2-3 times lower than that of the precursor of pure graphite.

scholarly journals Self-preservation and structural transition of gas hydrates during dissociation below the ice point: an in situ study using Raman spectroscopy

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Jin-Rong Zhong ◽  
Xin-Yang Zeng ◽  
Feng-He Zhou ◽  
Qi-Dong Ran ◽  
Chang-Yu Sun ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Gas Hydrates ◽  
Structural Transition ◽  
In Situ Study

scholarly journals The strength of mechanically-exfoliated monolayer graphene deformed on a rigid polymer substrate

Nanoscale ◽  
2019 ◽  
Vol 11 (30) ◽  
pp. 14339-14353 ◽  
Author(s):  
Xin Zhao ◽  
Dimitrios G. Papageorgiou ◽  
Liyan Zhu ◽  
Feng Ding ◽  
Robert J. Young
Keyword(s):  
Raman Spectroscopy ◽  
Systematic Investigation ◽  
Polymer Substrate ◽  
Monolayer Graphene ◽  
Rigid Polymer

A systematic investigation of the strength of monolayer graphene via the application of Raman spectroscopy is presented, revealing that the strength of the flakes decreases with increasing flake width, due to the presence of defects.

Graphene Layers on Silicon Carbide Studied by Raman Spectroscopy

2008 ◽  
Vol 600-603 ◽  
pp. 567-570 ◽  
Author(s):  
Jonas Röhrl ◽  
Martin Hundhausen ◽  
Konstantin V. Emtsev ◽  
Thomas Seyller ◽  
Lothar Ley
Keyword(s):  
Silicon Carbide ◽  
Raman Spectroscopy ◽  
Light Scattering ◽  
Graphene Layer ◽  
Monolayer Graphene ◽  
Spectroscopy Study ◽  
Graphene Layers ◽  
Layer Graphene ◽  
Micro Raman Spectroscopy ◽  
Few Layer Graphene

We present a micro-Raman spectroscopy study on single- and few layer graphene (FLG) grown on the silicon terminated surface of 6H-silicon carbide (SiC). On the basis of the 2D-line (light scattering from two phonons close to the K-point in the Brillouin zone) we distinguish graphene mono- from bilayers or few layer graphene. Monolayers have a 2D-line consisting of only one component, whereas more than one component is observed for thicker graphene layers. Compared to the graphite the monolayer graphene lines are shifted to higher frequencies. We tentatively ascribe the corresponding phonon hardening to strain in the first graphene layer.

Monolayer graphene films through nickel catalyzed transformation of fullerol and graphene quantum dots: a Raman spectroscopy study

2014 ◽  
Vol T162 ◽  
pp. 014030 ◽  
Author(s):  
J R Prekodravac ◽  
S P Jovanović ◽  
I D Holclajtner-Antunović ◽  
D B Peruško ◽  
V B Pavlović ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Raman Spectroscopy ◽  
Graphene Quantum Dots ◽  
Monolayer Graphene ◽  
Spectroscopy Study ◽  
Graphene Films
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