Jones Ecton, Mo, and Perez (JEMP)1 reported an experimental study of graphene under the electron-beam irradiation. In their Comment,1 JEMP reproduced our results for irradiated graphene,2 thus providing an independent confirmation for our visible (VIS) Raman spectroscopy data. JEMP then annealed an unspecified number of samples for 30 min, and observed a disappearance of D peak. Based on this observation alone, they speculated that graphene irradiation in vacuum (106Torr) for 2 min leads to its conversion to graphane, i.e., hydrogenated graphene. This hypothesis differs from our suggestion that mostly defects, residual carbon, and lattice disorder induced by irradiation are behind the observed Raman spectrum changes.2 In this reply we show that JEMP’s conclusion is based on wrong assumptions and is not supported by either the data provided in their Comment1 or available literature. Moreover, our ultraviolet (UV) Raman spectroscopy, electrical resistivity, and energy dispersive x-ray spectroscopy data show that JEMP hypothesis is not valid.

JEMP’s conjecture that 2 min electron-beam (e-beam) irradiation in vacuum leads to graphene’s transformation to graphane is based entirely on appearance of the disorder D peak, followed by its disappearance after annealing for 30 min at temperature T600K. No electrical resistivity or microscopy data were provided to support this claim. No explanation was given on where a sufficient amount of hydrogen required for graphene transformation to graphane would come in vacuum environment used for irradiation. For comparison, Elias et al.3 had to subject their graphene samples to 2 h of hydrogen-argon mixture with dc plasma to transform graphene to graphene. They needed 24 h of annealing at 750K to restore graphene’s metallic state. Ryu et al.4 had to coat graphene with 30 nm thick hydrogen silsesquioxane and irradiate it in order to generate hydrogen atoms needed for graphene transformation to graphane. Thus, the physics behind JEMP’s suggested hydrogenation is not clear.

In the discussion of disappearance of D peak after annealing JEMP make an assumption that the thermodynamics properties of two-dimensional (2D) graphene and three-dimensional (3D) graphite should be the same. JEMP further assume that only the high-temperature annealing (1300K) can be used for the lattice damage removal in graphite. Both these assumption are not valid. Thermodynamic and other properties of 2D and 3D systems are distinctively different. A recent investigation of graphene under soft x-ray irradiation conducted by Berkeley group5 has shown that graphene can be transformed to nanocrystalline form while bulk graphite does not undergo any modifications under the same radiation levels. The authors offered several possible mechanisms of sp2 bond-breaking in exfoliated graphene, which are absent in graphite.5 The low-energy e-beam irradiation is known6,7 to produce substantial damage, including bond breaking, in carbon nanotubes (in Ref. 7, 1 keV electrons with the dose up to 8×1017cm2 were used). In graphite, some of the radiation defects can be removed after low temperature treatment. For example, Niwase8 studied the irradiation-induced amorphization of graphite and reported that many defects were repaired at temperature 473K.

It is well known9 that UV Raman (excited at 325 nm or below) is sensitive to sp3 C–C and C–H bonds while visible Raman spectra are dominated by sp2 phase due to resonant enhancement even in graphane.3 As stated by Elias et al.,3 the majority of carbon bonds in hydrogenated graphene should acquire sp3 hybridization. We carried out detail UV Raman study of the samples described in our letter2 as well as of additional irradiated samples. Details of our UV Raman measurement procedures were reported elsewhere.10 We did not observe peaks characteristic for C–H bonds or C–C sp3 phase in any of our e-beam irradiated graphene samples (inset of Fig. 1). In addition, we performed detail energy dispersive x-ray spectroscopy investigation of all e-beam irradiated graphene samples. No traces of hydrogen were observed in the spectra while characteristic C, O (from the oxide layer) and Si (from the substrate) peaks were clearly seen.

JEMP’s hypothesis further implies that e-beam irradiated samples always return to the conducting state after annealing. The graphene samples described in our letter2 did not recover their current conducting ability after annealing at 600700K for more than 30 min. An extended study, completed by us well before Comment,1 indicates that the changes in irradiated graphene follow a more complex pattern than the one offered by JEMP. We established that if the e-beam dose is kept at minimum [before stage II (Ref. 2) is reached], graphene can be returned to the electrically conductive state by annealing. If the irradiation dose exceeds the threshold, irradiated graphene does not return to conductive state. In Fig. 1 we present data for new graphene samples irradiated in 106Torr vacuum (electron gun is kept at 6×1010Torr) with the constant beam current 0.15 nA, electron energies of 20 and 30 keV, and the radiation dose varying from 4.3×1014 to 9.3×1017e/cm2. The electrical current after a small irradiation dose (curve A) increases after annealing (B). Conduction is strongly inhibited after extended irradiation (C) and does not recover after annealing (D).

Finally, we point out at other deficiencies in Comment,1 which complicate data analysis. JEMP used high laser excitation intensity (6 mW), above of what is considered to be safe for graphene. Since the data accumulation time was not provided it is not clear if laser damage was a factor. Even moderate laser excitation (1 mW) for prolonged time can lead to C–C bond breaking and graphene transformation to nanocrystalline form.11 JEMP’s manuscript provided to us did not contain information on the excitation wavelength (we can only estimate it from the 2D peak position). For this reason, discussion of ID/IG ratio in the Comment does not have much meaning due to ratio’s dependence on the wavelength (see Fig. 2). JEMP’s indication that they based their conclusion about the number of atomic layers in the samples on the 2D-peak width instead of 2D-peak deconvolution, and the peak energy and symmetry analysis creates an ambiguity. Indeed, 2D band in their Fig. 2(a) (Ref. 1) appears to belong to multilayer rather than bilayer graphene.

In summary, we are pleased that our first report2 on e-beam irradiated graphene generated follow-up work. At the same time, we are of the opinion that JEMP,1 while successfully reproducing our Raman spectra, presented interpretation, which is purely speculative and not supported by the experimental data or theoretical considerations.

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