Limits...
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

Experimental setup and SEM images for:suspended (a) and supported (b) multi-layer graphene (MLG) samples heated up by a focused laser beam. The corresponding SEM images correspond to samples before (top) and after (bottom) laser exposures, respectively. Suspended MLG samples are uniformly thinned, while supported MLG samples are etched non-uniformly, forming holes down to the substrate at the laser spot (0.5 μm in diam.). Scale bars –1 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4477407&req=5

f1: Experimental setup and SEM images for:suspended (a) and supported (b) multi-layer graphene (MLG) samples heated up by a focused laser beam. The corresponding SEM images correspond to samples before (top) and after (bottom) laser exposures, respectively. Suspended MLG samples are uniformly thinned, while supported MLG samples are etched non-uniformly, forming holes down to the substrate at the laser spot (0.5 μm in diam.). Scale bars –1 μm.

Mentions: Experimental configurations for laser heating of suspended and supported nanoplatelets are shown schematically in Fig. 1a,b, respectively. Suspended samples were obtained by deposition from MLG-containing solutions over commercial amorphous holey carbon grids used in transmission electron microscopy (TEM). The scanning electron microscope (SEM) images of samples before and after heating experiments are also shown. The results are remarkably different for suspended and supported samples. Suspended platelets (Fig. 1(a)) are etched mostly in-plane, resulting in a gradual and uniform thinning while the sample shape (lateral dimensions) is basically maintained. The laser heating experiments were performed using a confocal Raman spectrometer configuration, allowing for simultaneous monitoring of the characteristic Raman bands (e.g., G and D bands15). In particular, the frequency downshift of G band (alternatively, the ratio of anti-Stokes/Stokes components of the G band) is widely used for graphene temperature measurements, while the ratio of D/G bands intensities characterizes the material quality (i.e., presence of defects within the basal planes)29. When elevated laser power (>1 mW) was used, complete burning of the samples was observed to happen within a few seconds (usually, together with the supporting holey carbon grids), and we were able to observe the exact moment of the sample disappearance through the backscattered Raman signal. Gradual decrease of the Raman signal was observable for sample thicknesses smaller than 10 nm allowing avoiding the complete sample burning in order to obtain extremely thin (possibly, a few-layer) samples. In contrast, for samples supported over oxidized silicon substrates (Fig. 1(b)), there is a significant non-uniform cross-plane etching, eventually creating holes at the laser focus point with the diameter of near 0.5 μm. These holes can be etched through dozens of graphene layers (leaving just a few layers at the substrate, as the remaining graphene layers absorb a small fraction of the incident light and thus cannot be heated up to high temperatures25). Also, it was necessary to use higher laser powers (up to 10 mW) in order to etch supported samples.


Burning Graphene Layer-by-Layer.

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

Experimental setup and SEM images for:suspended (a) and supported (b) multi-layer graphene (MLG) samples heated up by a focused laser beam. The corresponding SEM images correspond to samples before (top) and after (bottom) laser exposures, respectively. Suspended MLG samples are uniformly thinned, while supported MLG samples are etched non-uniformly, forming holes down to the substrate at the laser spot (0.5 μm in diam.). Scale bars –1 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f1: Experimental setup and SEM images for:suspended (a) and supported (b) multi-layer graphene (MLG) samples heated up by a focused laser beam. The corresponding SEM images correspond to samples before (top) and after (bottom) laser exposures, respectively. Suspended MLG samples are uniformly thinned, while supported MLG samples are etched non-uniformly, forming holes down to the substrate at the laser spot (0.5 μm in diam.). Scale bars –1 μm.
Mentions: Experimental configurations for laser heating of suspended and supported nanoplatelets are shown schematically in Fig. 1a,b, respectively. Suspended samples were obtained by deposition from MLG-containing solutions over commercial amorphous holey carbon grids used in transmission electron microscopy (TEM). The scanning electron microscope (SEM) images of samples before and after heating experiments are also shown. The results are remarkably different for suspended and supported samples. Suspended platelets (Fig. 1(a)) are etched mostly in-plane, resulting in a gradual and uniform thinning while the sample shape (lateral dimensions) is basically maintained. The laser heating experiments were performed using a confocal Raman spectrometer configuration, allowing for simultaneous monitoring of the characteristic Raman bands (e.g., G and D bands15). In particular, the frequency downshift of G band (alternatively, the ratio of anti-Stokes/Stokes components of the G band) is widely used for graphene temperature measurements, while the ratio of D/G bands intensities characterizes the material quality (i.e., presence of defects within the basal planes)29. When elevated laser power (>1 mW) was used, complete burning of the samples was observed to happen within a few seconds (usually, together with the supporting holey carbon grids), and we were able to observe the exact moment of the sample disappearance through the backscattered Raman signal. Gradual decrease of the Raman signal was observable for sample thicknesses smaller than 10 nm allowing avoiding the complete sample burning in order to obtain extremely thin (possibly, a few-layer) samples. In contrast, for samples supported over oxidized silicon substrates (Fig. 1(b)), there is a significant non-uniform cross-plane etching, eventually creating holes at the laser focus point with the diameter of near 0.5 μm. These holes can be etched through dozens of graphene layers (leaving just a few layers at the substrate, as the remaining graphene layers absorb a small fraction of the incident light and thus cannot be heated up to high temperatures25). Also, it was necessary to use higher laser powers (up to 10 mW) in order to etch supported samples.

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