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Burning Graphene Layer-by-Layer.

Ermakov VA, Alaferdov AV, Vaz AR, Perim E, Autreto PA, Paupitz R, Galvao DS, Moshkalev SA - Sci Rep (2015)

Bottom Line: In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates.Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification.The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material.

View Article: PubMed Central - PubMed

Affiliation: Center for Semiconductor Components, State University of Campinas, CP 6101, Campinas, SP, 13083-870, Brazil.

ABSTRACT
Graphene, in single layer or multi-layer forms, holds great promise for future electronics and high-temperature applications. Resistance to oxidation, an important property for high-temperature applications, has not yet been extensively investigated. Controlled thinning of multi-layer graphene (MLG), e.g., by plasma or laser processing is another challenge, since the existing methods produce non-uniform thinning or introduce undesirable defects in the basal plane. We report here that heating to extremely high temperatures (exceeding 2000 K) and controllable layer-by-layer burning (thinning) can be achieved by low-power laser processing of suspended high-quality MLG in air in "cold-wall" reactor configuration. In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates. Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification. The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material.

No MeSH data available.


Related in: MedlinePlus

(I) Arrhenius plot for the temperature dependences of etching rates (1–3 – present study, 4,5 – other works): 1 – in-plane (suspended platelets), 2 – cross-plane (suspended platelets), 3 – cross-plane (supported platelets), 4 – in-plane (supported), 5 – cross-plane (supported); experimental data from other works: a19, b35, c36, d37, e38, f39, g40. In-plane etching represents the MLG flake etching along the basal plane (lateral size reduction), while cross-plane etching represents the etching in direction normal to the basal plane (thinning). (II) Raman intensities for G and D bands for suspended (bottom) and supported (top) graphene flakes during the laser exposure. The absence of the D peak in the suspended flakes spectra throughout the whole etching process demonstrates the high quality of the samples. In the case of supported flake the permanently increasing intensity of the D peak is a consequence of strong cross-plane etching and formation of hole.
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f2: (I) Arrhenius plot for the temperature dependences of etching rates (1–3 – present study, 4,5 – other works): 1 – in-plane (suspended platelets), 2 – cross-plane (suspended platelets), 3 – cross-plane (supported platelets), 4 – in-plane (supported), 5 – cross-plane (supported); experimental data from other works: a19, b35, c36, d37, e38, f39, g40. In-plane etching represents the MLG flake etching along the basal plane (lateral size reduction), while cross-plane etching represents the etching in direction normal to the basal plane (thinning). (II) Raman intensities for G and D bands for suspended (bottom) and supported (top) graphene flakes during the laser exposure. The absence of the D peak in the suspended flakes spectra throughout the whole etching process demonstrates the high quality of the samples. In the case of supported flake the permanently increasing intensity of the D peak is a consequence of strong cross-plane etching and formation of hole.

Mentions: Note that for the hot-wall reactor configuration, high-energy oxygen atoms have been pointed out as responsible for formation of defects (vacancies) in graphitic sheets303132, triggering the etching process. Nitrogen contribution to graphene etching is assumed to be much smaller, compared to those from oxygen31. In order to better understand the mechanisms of uniform thinning of suspended multi-layer graphene in our experiments, we have also performed extensive reactive molecular dynamics (MD) simulations of graphitic layers oxidation and gasification. To describe essential features of the experiments, we created a computational model in which a heated tri-layer graphene sample was exposed to an atmosphere composed of atomic oxygen. To mimic the cold-wall reactor experimental conditions, periodic boundary conditions were considered. In this way, the MD simulation results are contrasted below with the experimental ones. All molecular dynamics simulations were carried out using the ReaxFF force field what can effectively describe chemical reactions, in special combustion. This force field has been already applied with success for understanding of graphene oxidation33 process and materials in extreme environments34. Experimental data on etching rates within the basal plane (in-plane) and along the direction normal to the basal plane (cross-plane), measured in the present study and in other works19353637383940, are presented in Fig. 2. Data from literature are related to oxidation of graphitic samples (graphene or graphite) in furnaces (i.e., under conditions of hot-wall reactors), mostly for in-plane etch rate, whereas the cross-plane etch rate is expected to be much smaller. Thicknesses of suspended samples before and after laser irradiation were estimated here using tilted SEM images, and the temperatures of samples were estimated in-situ from the Raman spectra (see Methods for details).


Burning Graphene Layer-by-Layer.

Ermakov VA, Alaferdov AV, Vaz AR, Perim E, Autreto PA, Paupitz R, Galvao DS, Moshkalev SA - Sci Rep (2015)

(I) Arrhenius plot for the temperature dependences of etching rates (1–3 – present study, 4,5 – other works): 1 – in-plane (suspended platelets), 2 – cross-plane (suspended platelets), 3 – cross-plane (supported platelets), 4 – in-plane (supported), 5 – cross-plane (supported); experimental data from other works: a19, b35, c36, d37, e38, f39, g40. In-plane etching represents the MLG flake etching along the basal plane (lateral size reduction), while cross-plane etching represents the etching in direction normal to the basal plane (thinning). (II) Raman intensities for G and D bands for suspended (bottom) and supported (top) graphene flakes during the laser exposure. The absence of the D peak in the suspended flakes spectra throughout the whole etching process demonstrates the high quality of the samples. In the case of supported flake the permanently increasing intensity of the D peak is a consequence of strong cross-plane etching and formation of hole.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4477407&req=5

f2: (I) Arrhenius plot for the temperature dependences of etching rates (1–3 – present study, 4,5 – other works): 1 – in-plane (suspended platelets), 2 – cross-plane (suspended platelets), 3 – cross-plane (supported platelets), 4 – in-plane (supported), 5 – cross-plane (supported); experimental data from other works: a19, b35, c36, d37, e38, f39, g40. In-plane etching represents the MLG flake etching along the basal plane (lateral size reduction), while cross-plane etching represents the etching in direction normal to the basal plane (thinning). (II) Raman intensities for G and D bands for suspended (bottom) and supported (top) graphene flakes during the laser exposure. The absence of the D peak in the suspended flakes spectra throughout the whole etching process demonstrates the high quality of the samples. In the case of supported flake the permanently increasing intensity of the D peak is a consequence of strong cross-plane etching and formation of hole.
Mentions: Note that for the hot-wall reactor configuration, high-energy oxygen atoms have been pointed out as responsible for formation of defects (vacancies) in graphitic sheets303132, triggering the etching process. Nitrogen contribution to graphene etching is assumed to be much smaller, compared to those from oxygen31. In order to better understand the mechanisms of uniform thinning of suspended multi-layer graphene in our experiments, we have also performed extensive reactive molecular dynamics (MD) simulations of graphitic layers oxidation and gasification. To describe essential features of the experiments, we created a computational model in which a heated tri-layer graphene sample was exposed to an atmosphere composed of atomic oxygen. To mimic the cold-wall reactor experimental conditions, periodic boundary conditions were considered. In this way, the MD simulation results are contrasted below with the experimental ones. All molecular dynamics simulations were carried out using the ReaxFF force field what can effectively describe chemical reactions, in special combustion. This force field has been already applied with success for understanding of graphene oxidation33 process and materials in extreme environments34. Experimental data on etching rates within the basal plane (in-plane) and along the direction normal to the basal plane (cross-plane), measured in the present study and in other works19353637383940, are presented in Fig. 2. Data from literature are related to oxidation of graphitic samples (graphene or graphite) in furnaces (i.e., under conditions of hot-wall reactors), mostly for in-plane etch rate, whereas the cross-plane etch rate is expected to be much smaller. Thicknesses of suspended samples before and after laser irradiation were estimated here using tilted SEM images, and the temperatures of samples were estimated in-situ from the Raman spectra (see Methods for details).

Bottom Line: In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates.Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification.The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material.

View Article: PubMed Central - PubMed

Affiliation: Center for Semiconductor Components, State University of Campinas, CP 6101, Campinas, SP, 13083-870, Brazil.

ABSTRACT
Graphene, in single layer or multi-layer forms, holds great promise for future electronics and high-temperature applications. Resistance to oxidation, an important property for high-temperature applications, has not yet been extensively investigated. Controlled thinning of multi-layer graphene (MLG), e.g., by plasma or laser processing is another challenge, since the existing methods produce non-uniform thinning or introduce undesirable defects in the basal plane. We report here that heating to extremely high temperatures (exceeding 2000 K) and controllable layer-by-layer burning (thinning) can be achieved by low-power laser processing of suspended high-quality MLG in air in "cold-wall" reactor configuration. In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates. Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification. The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material.

No MeSH data available.


Related in: MedlinePlus