The pulsed laser ablation of solid in liquids media (PLAL) process for synthesizing titanium carbide (TiC) nanoparticles was performed using a typical experimental setup for this method [2] [6] , as described in Figure 1. A Nd:YAG pulsed laser (EXPLA) operating at its fundamental emission line (1064 nm), with a pulse width of 150 ps, a per-pulse laser energy of 30 mJ, and a 10 Hz repetition rate, was focused down with a 30 cm lens on the surface of a solid carbon target (Kurt Lesker, 99.999% pure) while immersed in 20 ml of pure acetone (Sigma Aldrich) for 10 minutes. The ablation process allowed the obtaining of a carbon nanostructure-based colloidal solution. In the second step, a pure Ti solid target (Kurt Lesker, 99.9999% pure) was immersed in the described carbon colloid, inducing the ablation process for 10 minutes under the same irradiation parameters. The obtained colloid then contained C and Ti nanostructures, and due to the reactive process, TiC and core/shell Ti/C structures were formed, as shown below. For comparison, the ablation process of the pure Ti target immersed in acetone was also performed.

Structural characterization of the as-prepared nanoparticles was performed using scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS), transmission electron microscopy (TEM), and high-resolution

transmission electron microscopy (HRTEM). Raman spectroscopy was also used to provide a complete analysis. The structural analysis was conducted only for the Ti-ablated sample in the C-enriched acetone ambient.

SEM-EDS analysis was performed using a JOEL-JSM IT-100 microscope operating in high vacuum with an acceleration voltage of 20 kV. EDS allowed for the determination of the elemental composition of the products obtained, as well as their percentages. For TEM characterization, 0.05 g of each sample was placed on Cu-grids coated with carbon, and three drops of the solution were evaporated on the grid to leave behind the TiC nanoparticles. TEM and HRTEM measurements were carried out using a JEOL-2010 electron microscope at an accelerating voltage of 200 kV.

Raman analysis was conducted using a Raman Horiba Jobin Yvon equipment model XPLORA-PLUS equipped with a laser with a wavelength of 780 nm as an excitation source, with a nominal power of 0.2 mW. The laser beam was focused on the samples with a 50× objective, which also served to collect the scattered light and direct it to a charge-coupled device (CCD) camera. Analysis was performed over a range of 300 - 2300 cm⁻¹ to identify the corresponding Raman peaks.

Figure 1 shows the dark-brown solution obtained after the pulsed laser ablation process, which contains both C- and TiC-nanoparticles, due to the synthesis process described in section 2.1. A SEM micrograph is displayed in Figure 2. The material collected for SEM analysis was obtained from the bottom of the container after full acetone evaporation, and it was collected by scraping material

with a spatula. Figure 2 shows a topographic picture of the ablated Ti in the presence of colloidal carbon sample with a ×1200 amplification. The micrograph shows an apparently solid structure with a size over 50 µm covered by irregular grey structures and white granular sphere agglomerates whose size can be estimated to be around 0.5 µm diameter. In addition to the topographic information from SEM, coupled EDS analysis is described above.

For EDS analysis, the selected area identified with the green rectangle in Figure 2 was used. From the analysis, it was found that the largest amount of material obtained is carbon, as shown in Figure 3(a) and Table 1. In atomic percentages, 58.83% is occupied by carbon, while titanium accounts for 10.28%. Oxygen was found to be 27.74%, and its presence can be attributed to a great extent to the fact that the ablation and analysis processes were not isolated. Likewise, in the dissociation process due to the laser-interaction, hydroxyl groups are found in acetone, from which oxygen can be released. Additionally, a smaller quantity of polluting elements such as silicon and sodium were recorded, which were attributed to the vial that contained the material, as the vial was scraped with a spatula during the process to obtain it. It is necessary to note a particular contaminant, chlorine, with a percentage of 1.82%, which makes it significant and abundant. This particular contaminant can be attributed to the drying process, where cleaning with chlorine was constant, so its vapor could have reached the samples and contaminated them significantly.

As mentioned earlier, SEM-EDS can obtain images with elemental maps so that the distribution of each element can be presented with different colors. The analysis was conducted on titanium and carbon. In the case of carbon, the area where it is found was assigned with green color, while titanium is red, as observed in Figure 3(b) and Figure 3(c). It can be observed that the agglomerates with a lighter tone are registered in the image, and this abundance of the metal can be corroborated with the composition spectrum of Figure 3(a). These results indicate the presence of both carbon and titanium as products of the fragmented material and in the agglomerates, as expected. From the images, we can get an idea of the structures formed. Within the Ti-ablated material and due to the amount of carbon and titanium, it is expected to find both TiC and Ti-C core-shell nanoparticles.

In Figure 4, micrographs obtained from TEM characterization reveal the presence of both large and small nanoparticles. The larger nanostructures appear to be nearly perfect spheres of varying sizes. Figure 4(a) and Figure 4(b) depict two distinct nanoparticles with diameters of 50 nm and 100 nm, respectively. This size is also observed in Figure 4(c) and Figure 4(d), where particles less than 40 nm can be observed in Figure 4(c) and a not well-shaped structure, along with another particle whose size is less than 40 nm, can be seen in Figure 4(d). These nanostructures appear to be surrounded by smaller nanoparticles,

measuring just a few nanometers in size. According to reports on the production of C nanoparticles using the PLAL route, the synthesis process leads to the production of nanoparticles measuring less than 10 nm [6] . Therefore, these structures can be identified as entirely carbon nanostructures resulting from the previous C-enrichment process.

Zooming in on the nanoparticle in Figure 4(c) reveals that the nanostructures are embedded within a matrix, as depicted in Figure 5(e) and Figure 5(f), with 20 nm and 10 nm scales, respectively. The appearance of the particle is similar to that of core-shell nanostructures. As shown in these figures, the nanoparticles have a spherical section with a surrounding layer or shell (identified by the non-continuous orange line), which has a thickness of approximately 12 nm (indicated by the yellow line). Based on their observable features, the core is presumed to be composed of amorphous carbon, as will be demonstrated below through Raman analysis.

High-resolution TEM (HRTEM) images, as shown in Figure 5, allow for the observation of crystallographic planes of the produced nanoscale structures. The GATAN Digital Micrograph software was used to examine these planes and determine the distance between them. Micrographs with a 5 nm scale, shown in Figures 5(a)-(c), reveal the crystallographic planes of Ti in its Hexagonal Close-Packed (HCP) structure [23] . The most important plane, (1 1 1), corresponding to the titanium carbide structure in its face-centered cubic (FCC) crystalline phase [24] , was identified in Figure 5(b). Additionally, the (0 0 2) plane, corresponding to graphite planes, was identified in Figure 5(d) [25] . However, no atomic planes were observed in the shell structure proposed as the carbon

shell, beyond the area where Ti and TiC planes were found (see orange line). This observation confirms the possibility of proposing the production of Ti-C core-shell or even TiC-C nanostructures. However, to strictly confirm this proposal, further characterization using XPS or XRD techniques is necessary, which is beyond the scope of the present work. Figure 5 shows the atomic plane analysis, which strictly corresponds to TiC in the core part, while the amorphous structure is for amorphous carbon. The non-continuous dark pattern in the structure suggests that the C-shell structure may not be completely homogeneous, which has been previously reported in Cu-C core-shell nanostructures [26] . Besides that, a previous study reported the production of MoC-Graphite core-shell nanostructures in a carbon-enriched ambient [27] , which is similar to what is being reported here and supports our proposed core-shellproduced nanostructure. This effect was also observed as descriptive evidence for the formation of Fe₃O₄/Ag core-shell nanoparticles [28] .

Figure 6 displays the Raman spectrum of the produced nanostructures. The Raman shift related to the carbon signal has been fitted with four Lorentzian peaks, enabling identification of the main Raman peaks of the produced nanostructures. The G band, located at approximately 1590 cm⁻¹, corresponds to the E_2g vibrational mode and represents the stretching vibration of the sp²-type hybridized carbon bonds in the graphite structure. Therefore, this band is indicative of the degree of crystallinity, unlike the D band [25] . The D band, located around 1378 cm⁻¹, is directly associated with the degree of structural disorder in graphite due to the loss of symmetry. This can be attributed to the stretching

vibration in the sp² and sp³-type hybridized bonds of the carbon atoms. In simpler terms, it is due to amorphous carbon. As observed in the registered intensity, amorphous carbon is the most abundant compound in the substance [19] [27] . Two additional Raman peaks were recorded that are not usually reported for TiC-based nanomaterials and could be due to the C-enrichment process. The first band, assigned as T band, was identified at approximately 1170 cm⁻¹ and is related to the presence of C-C bindings. The second band, at 1865 cm⁻¹, is a Raman peak overtone called M or D’ + TA and is also related to the presence of C=C carbon bindings [29] . The high intensity of the D-band is associated with the presence of defects, disorder, or structural imperfections in the carbon lattice, which agrees with the amorphous shell observed in Figure 5 TEM micrographs.

The small, not very intense bands recorded around 300 and 600 cm⁻¹ in Figure 6, corresponding to the vibrational modes of non-stoichiometric TiC, is of particular interest, as it strictly confirms the presence of the produced TiC nanostructures. Stoichiometric TiC does not present Raman signals [30] [31] . The Raman signals recorded at 390 and 605 cm⁻¹ identify the TiC nanostructures. However, they have low Raman intensity, which confirms that the bulk of the material target is stoichiometric TiC.

In addition, the ID/IG ratio, which is the ratio between Raman peak intensities, was calculated from the Raman results and found to be 1.52. This ratio was obtained from the raw data of the Raman equipment (719.581/473.152), and considered the photons reaching the detector. It is widely recognized that an increase in the ID/IG ratio corresponds to an increase in structural disorder or defect density in carbon materials. Higher values of ID/IG indicate the presence of defects, such as edge defects and vacancies, which occur in the case of amorphous graphite that lacks a regular crystalline structure [32] .