Rapid identification of graphene flakes: alumina does it better

Abstract

We report a systematic investigation of the colour contrast (CC) of graphene (one, two and three layers) on 50, 72 and 80 nm thick Al(2)O(3)/Si(100) and 100 and 300 nm thick SiO(2)/Si(100). The CC is determined by the analysis of optical microscopy images taken under white light illumination. A corresponding assignment of graphene in the single-layer, double-layer and trilayer phases is made using micro-Raman spectroscopy. A quantitative evaluation allows us to conclude that the colour contrast between 72 nm alumina and graphene is significantly larger than that between 300 nm silicon oxide and graphene (by factors of 2.2, 2.0 and 3.3 for the single-layer, double-layer and trilayer graphene flakes respectively). Moreover, data indicate that, to increase visibility, the use of a red or a green light is preferable.

Synthesis of few-layer graphene by lamp ablation

“…We also noted a decrease in the FWHM for the 2D band of approximately 15% further indicating the formation of multilayer graphene from the graphite precursor. The I 2D /I G ratio for our graphene products has been observed by previous research groups and corresponds to approximately 3-5 layers [10,11]. The shape of the 2D band for the graphene we generated is also close to that of other reports, which corresponds to approximately 4-5 layers [9,12].…”

Mechanical exfoliation and layer number identification of single crystal monoclinic CrCl3

“…In that work it is evidenced how the most remarkable spectral differences are detected with low-temperature (10 K) polarised micro-Raman set-ups and manifest themselves in significant layer dependent changes of the relative spectral weight rather than in significant frequency shifts. It is evident then, from our layer dependent measurements, that, at variance with other two dimensional materials, like for example graphene [30], or MoS 2 A c c e p t e d M a n u s c r i p t A c c e p t e d M a n u s c r i p t [23], where non polarised RT micro-Raman spectroscopy clearly assign a layer dependent spectral finger print to the 2D material, this is not the case for CrCl 3 and likely other CrX 3 systems. We ultimately assign this occurrence to the very weak interlayer coupling in these materials.…”

“…Noteworthy, as displayed in the inset of Figure 5 (i), this corresponds to a notable 20% (13%) relative increase of the contrast for the monolayer (bilayer) flakes. As already stressed in the literature [23,30]. The theoretical framework to quantitatively explain the oxide thickness and layer number dependent variation of the optical contrast is given by the Fresnel equations as discussed and reported in SI.…”

Purification/annealing of graphene with 100-MeV Ag ion irradiation

“…It is expected that the intensity ratio I 2D / I G would increase at higher fluence when the number of layers decreases [35,37,50], but at the same time due to higher defect density, the ratio I 2D / I G decreases much more rapidly [51]. Therefore, overall effect is decreased in I 2D / I G ratio as shown in Figure 4.…”