**5.1. SEM experiments**

**4.3. HR-TEM experiments**

scopy using Pimenta formula (2).

lattice on graphene **Figure 20(c)**.

**Figure 21.** TGA curves of the CNOs (Gas: argon, *T* = 50–1200°C).

**4.4. TGA experiments**

in the furnace.

94%.

The products obtained by ablating the pure graphite target using conditions for CNOs synthesis in **Table 1**, look like well-defined nano-onions, both individual and clustered through a matrix of amorphous carbon. As can be seen in **Figure 20(a)** the diameter is between 10 and 25 nm which is in good agreement with the dimensions obtained from micro-Raman spectro-

304 Applications of Laser Ablation - Thin Film Deposition, Nanomaterial Synthesis and Surface Modification

**Figure 20.** (a) CNOs clustered; (b) CNOs profile perpendicular to shells (c) CNOs profile along of the shell.

If we measure the graphitic interlayer distance of the CNOs from perpendicular direction to shells profile we found 0.35 nm in great agreement with the graphene monolayer thickness (**Figure 20(b)**). On the other hand if we analyze the profile in along of shell we found the distance between two consecutive atoms to be 0.24 nm, in good agreement with the atomic

In order to measure the purity of obtained CNOs we perform thermo-gravimetric analysis (TGA) as can be seen in **Figure 21**. The percentage of weight lost has been measured using a constant heating rate of 5°C/min under a 20 mL/min Ar flux that limited the oxygen content

The mass loss between 350 and 600°C was assigned to the oxidation of the CNOs and is about

High quality graphene sheets obtained by laser ablation in our reactor are shown in **Figure 22**. As can be seen the amorphous carbon content is small. We observe in **Figure 22** that by ablating the target under conditions for graphene product we obtain totally different material comparing with SWCNTs images from **Figure 10** and CNOs images from **Figure 19**.

**Figure 22.** SEM images of graphene sheets.
