Synthesis of Iron Oxide Nanostructures via Carbothermal Reaction of Fe Microspheres Generated by Infrared Pulsed Laser Ablation

Abstract

Iron oxide nanostructures were synthesized using the carbothermal reaction of Fe microspheres generated by infrared pulsed laser ablation. The Fe microspheres were successfully deposited on Si(100) substrates by laser ablation of the Fe metal target using Nd:YAG pulsed laser operating at λ = 1064 nm. By varying the deposition time (number of pulses), Fe microspheres can be prepared with sizes ranging from 400 nm to 10 µm. Carbothermal reaction of these microspheres at high temperatures results in the self-assembly of iron oxide nanostructures, which grow radially outward from the Fe surface. Nanoflakes appear to grow on small Fe microspheres, whereas nanowires with lengths up to 4.0 μm formed on the large Fe microspheres. Composition analyses indicate that the Fe microspheres were covered with an Fe₃O₄ thin layer, which converted into Fe₂O₃ nanowires under carbothermal reactions. The apparent radial or outward growth of Fe₂O₃ nanowires was attributed to the compressive stresses generated across the Fe/Fe₃O₄/Fe₂O₃ interfaces during the carbothermal heat treatment, which provides the chemical driving force for Fe diffusion. Based on these results, plausible thermodynamic and kinetic considerations of the driving force for the growth of Fe₂O₃ nanostructures were discussed.

1. Introduction

Nanomaterials offer a new way of designing structural, functional, and electronic devices on the nanometer scale. These nanostructures show exceptional and dimension-dependent properties that are not readily observed in their bulk form and which can be exploited for biological and molecular applications [1,2,3,4,5]. In particular, Fe₂O₃ (iron oxide) nanostructures have been intensively studied because of their unique electrical and magnetic properties while maintaining their chemical compatibility with biological tissues for possible biological applications [1,2,3,4,5,6]. Their use extend to recording, ultrahigh density memory storage, and targeted drug delivery, including water splitting for energy applications [4,5,6]. Several techniques have been reported for the growth and preparation of iron oxide nanostructures, which aim at finding simple ways of controlling the morphology, size, and growth direction of these nanostructures for enhanced functionality. Most studied preparation techniques include hydrothermal synthesis [3,4], sol-gel techniques [5], thermal oxidation [6,7], electric arc gas discharge [8], and the pulsed laser deposition (PLD) method [9,10,11]. Common to all these methods, metal catalysts, such as Au (template), are necessary to assist in the production of nanostructures, which partially limits the controllability of the features, size, and functionality of the nanostructures.

The PLD method offers flexibility in the growth of thin films, including the size of nanoparticles, composition, and phase, by controlling the laser excitation source (wavelength), substrate temperature, oxygen partial pressure, and target composition [12,13]. The PLD techniques have been successfully applied to prepare different oxide materials, such as superconductors [14,15,16,17,18], magnetic materials [19,20], perovskite cathodes, and barrier layers for solid oxide fuel cells [21,22,23,24,25], including perovskite thin-film solar cells [26,27]. In particular, the preparation of nanostructure thin films, such as Au-TiO₂ [28,29], and nanostructure multilayered perovskite cathodes [30] under different PLD growth conditions were explored. These materials in nanostructured thin film forms showed a significant enhancement of the catalytic activities as compared to their bulk counterparts. As in the case of the laser-assisted growth of one-dimensional (1D) nanostructures, such as nanowires [31,32], gas-based lasers operating in the ultraviolet wavelength (UV) were commonly utilized. However, the cost of the gas sources limits their practical application as well as the apparent deviation of the composition of the grown layer, which has a complex stoichiometry (more than three elements), thus necessitating the use of an alternative laser source for PLD assisted growth [33,34].

One possible candidate for the excitation source for PLD is the Nd:YAG laser. It is all solid-state, thus requiring no toxic and expensive gas, is easy to maintain, and is environmentally friendly. The Nd:YAG laser is also highly tunable, which can be operated from its fundamental harmonic of λ = 1064 nm (infrared) to its fourth harmonic at λ = 266 nm (UV). Hence, the Nd:YAG laser is a promising excitation source for a safe and low-cost PLD process. The use of the fourth harmonics (λ = 266 nm) of the Nd:YAG for coated conductor thin film was demonstrated and showed comparable electrical properties with UV gas-based lasers [35]. Previously, we reported the use of the fundamental harmonic (λ = 1064 nm) of the Nd:YAG laser for the preparation of high-temperature superconducting thin film materials. The initial morphology of the as-prepared samples is spheroidal, which crystallize and form a relatively smooth and flat film layer after high-temperature post-annealing (>850 °C) [36,37,38,39,40]. This spheroidal feature of the ablated species was observed for all types of oxide materials we investigated, suggesting that the ablated materials from the target are molten when they arrive on the substrate. Since the substrate is kept at room temperature, the ablated particles solidify on the substrate layer upon cooling. Chemical analysis of the ablated species together with time-resolved optical emission spectroscopy of the laser produced plasma during infrared pulsed laser ablation showed a strong tendency of the spheroidal particles to maintain the stoichiometry of the target [37,38]. We extended the idea of using the Nd:YAG laser operating at λ = 1064 nm as the excitation source for the formation of nanoparticles on a Si(100) substrate coupled with the carbothermal reaction process to synthesize iron oxide nanostructures. The objective of this work is two-fold: (1) Synthesis of iron oxide nanostructures by carbothermal oxidation of Fe microspheres generated by infrared pulsed laser ablation, demonstrating the formation of iron oxide nanostructures without the need of catalysts (or self-assembly); (2) discussion of the plausible mechanism for the self-assembly of iron oxide nanostructures in terms of thermodynamics and kinetic processes.

2. Materials and Methods

The experiment consists of two parts: (1) Preparation of Fe microspheres by infrared ablation of Fe metal, and (2) carbothermal oxidation of Fe microspheres to generate the iron oxide nanostructures as shown in Figure 1. For the Fe microsphere preparation, a high power tunable Q-switch Nd:YAG pulsed laser (Quanta-Ray Pro Spectra Physics, Santa Clara, CA, USA) operating at the fundamental wavelength, λ = 1064 nm, with an 8 ns pulse duration, was used to ablate a rotating Fe metal target (99.9%, Kurt J. Lesker Company, Jefferson Hills, PA, USA) with a Si(100) substrate placed 30 mm away from target as shown in Figure 1a. The ablation was performed at a laser fluence of 4.32 J/cm² at a 10 Hz repetition rate. The deposition chamber was continuously evacuated to reach a pressure of 10⁻² mbar. During the ablation process, no substrate heating and no background gas was employed. Herein, the deposition time was varied from 35 min (21,000 pulses) to 75 min (45,000 pulses) to control the density and size of nanoparticles on the Si(100) substrate. Since the substrate is kept at room temperature, the condensation of iron nanoparticles and microclusters aggregate on the Si substrate as spheroids, similar to our previous reports [37,38]. To grow the iron oxide nanowires/nanoflakes, the Fe microspheres were heat treated in a carbon-rich environment, as schematically shown in Figure 1b. Herein, the Si wafer with Fe microspheres was placed in a ceramic crucible containing 5.0 g of 99.99% activated carbon powders. The heat treatment was carried out in a box combustion furnace at temperatures between 750 to 800 °C for 145 min. To systematically evaluate the microstructural features and the composition of the Fe microspheres and Fe₂O₃ nanostructures, scanning electron microscopy coupled with energy dispersive x-ray spectroscopy (SEM-EDS, Hitachi S-3400N, Tokyo, Japan) was performed. Fourier transform infrared transmission spectroscopy (FTIR, Bio-Rad FTS-40A spectrometer (Cambridge, MA, USA) with KBr as the reference) was used to further confirm the iron oxide phase after thermal oxidation in the carbon-rich environment.

3. Results

Figure 2 shows the SEM micrographs of Fe microspheres generated by infrared laser ablation using the Nd:YAG laser. To control the size and density of the Fe microspheres, the deposition time was varied while keeping other deposition parameters fixed. Analysis of the SEM image reveals that the particle size density increases from 1.80 × 10³ to 3.70 × 10³ per µm² after fixing the deposition time to 75 min. The Fe particles are randomly distributed on the Si substrate with sizes ranging from 400 nm to 10 µm. Some Fe microspheres are smaller in size (~100 nm to 1.2 µm) at a shorter deposition time (35 min or 21,000 pulses, Figure 2a,b), whereas increasing the deposition time to 75 min (45,000 pulses) showed that large Fe microspheres up to 10 µm in diameter can be generated. At longer deposition times, the microspheres appear to coalesce together on the substrate (Figure 2c,d). The control of the microsphere density and size is possible by adjusting the laser pulses. However, the diameter of the particles has a tendency to saturate as evidenced by the distorted shape of the grains. It is possible that nanoparticles aggregated and further deposited on the microspheres as shown in Figure 2c,d. By changing the other PLD deposition conditions, such as the deposition pressure, substrate temperature, and target-to-substrate distance, it is possible to further tune the size, density, and morphological features of the grains [28,29,37]. It is interesting to note that the oxidation of the arriving particles can occur during the ablation process due to the minute amount of oxygen or during the cool down inside the growth chamber. This suggests that the Fe microspheres may have been covered with an oxide layer (oxidized) after the ablation process.

It can be seen that the characteristic feature of the surface particulates derived using infrared pulsed laser ablation is spherical or microspherical. This is because the nanoparticles, as well as the micron-sized droplets, are simultaneously generated by laser ablation. In general, to produce a thin film by PLD, the preparation condition is adjusted to decrease or suppress the droplets. More importantly, since no heat is induced on the site of arrival (usually by substrate heating), the droplets solidify, taking on a thermodynamically favored shape that in all the reported cases is spherical [36,37,38]. Previous studies also reveal that the ablation of a sintered target by an Nd:YAG laser operating at the infrared wavelength (λ = 1064 nm) produces ablation species consisting of molten-like spheroidal particles with stoichiometry resembling that of the target [36,37,38]. Longer wavelengths result in deeper target penetration, which causes subsurface evaporation and block-by-block ejection of larger clusters, which we observed as spheroids in the substrate [12,37,38,40]. Whereas, shorter wavelengths offer a higher photon energy, which is more suitable for efficient vaporization and ionization of the solid sample, resulting in atomized material delivery on a nearby substrate [12,33]. In particular, we reported UV pulsed laser ablation of iridate targets showing iridate nanoparticles (average size ~50 nm) on unheated MgO single crystal substrates [41]. The iridate nanoparticles are spheroidal with an apparent tendency to increase its particle density with increasing laser fluence [40]. The formation of large ZnO microspheres (sizes of more than 30 μm) was successfully synthesized using very high laser fluences up to 440 J/cm² (which is 10³ higher than conventional laser density used in PLD) [41]. However, undesired severe target fragmentation was observed at this range of laser fluence. The systematic variation of the deposition conditions to create different features of iron microstructures is out of the scope of this work and is suggested for future studies.

Figure 3 shows the Fe microspheres (D = 10 µm) after carbothermal heat treatment at (a,b) 750 °C and (c,b) 800 °C for 145 min. It can be observed that iron oxide nanostructures grew radially outward from the surface of Fe microspheres. At 750 °C, iron oxide nanowires grew outward from the surface of Fe microspheres. The iron oxide nanostructures’ diameters, D, vary from 500 nm (nanoflakes) to 2 µm (nanowires) as shown in Figure 3a. Nanosize pores on the surface of Fe microspheres are also evident at 750 °C (Figure 3a,b). On the other hand, carbothermal treatment at 800 °C decreases the size of the Fe microspheres, but results in longer nanowires extending up to L = 4.0 µm with a large aspect ratio (L/D = 44) as shown in Figure 3c. This suggests that increasing the carbothermal temperature assists in the growth of iron oxide nanowires. Pores are also present on the surface as well as some nanoflakes growing adjacent to the nanowires as shown in Figure 3d. A representative SEM micrograph of small microspheres (D = 1.8 µm) prepared at shorter laser pulses is also shown for comparison (Figure 3e). Nanoflakes appear to dominate the surface with no apparent growth of nanowires. The difference in the morphology of the iron oxide nanostructure indicates that the growth of nanowires sensitively changes with the size of the Fe microspheres. This suggests that large (>10.0 µm) microspheres are necessary to provide a sufficient supply of Fe during the carbothermal process for the growth of iron oxide nanowires. To illustrate the role of the carbon-rich environment in the self-assembly of iron oxide nanostructures, a reference Fe microsphere was oxidized in air (or without carbon) as shown in Figure 3f. It is clear from this result that the oxidation in air (or the trace amount of CO₂ in air) is insufficient to generate iron oxide nanowires, indicating that high vapor pressure carbon (or high density of carbon gaseous species) is critical for the synthesis of iron oxide nanostructures. The mechanistic growth of iron oxides under the carbothermal route will be discussed later. It is interesting to note that by changing the size/temperature, the resulting dimensions of the nanowires can be tuned, suggesting a flexibility of the infrared pulsed laser ablation assisted carbothermal growth of nanostructures. As the diameter of the wire decreases, the number of surfaces greatly increases. Hence, the large surface-to-volume ratio of the nanowire is expected to increase the number of active surfaces, which alters the physiochemical properties of the nanowires. A large aspect ratio is highly ideal for improving the sensitivity of the nanowires for real-time monitoring for sensor applications [1,2,3,4,5,6,7]. As a prospective future work, the micromanipulation and harvesting of iron oxide nanowires using the cantilevers of an atomic force microscope should be performed to isolate iron oxide nanowires for possible electronic applications (which our group has successfully demonstrated in the case of hydrothermally prepared ZnO nanowires exhibiting highly suitable scintillation properties, see [42,43]).

Figure 4a shows the cross-sectional SEM image of iron oxide nanowires radially growing from the surface of Fe microspheres, which can extend up to 10 µm in length. The nanowires have a sharp tip with well-defined edges (290 nm in length) as shown in Figure 4b. The diameter of the iron oxide nanowires is typically around 440 nm. To elucidate the phase of the iron oxide nanowire generated by infrared pulsed laser ablation with the carbothermal technique, representative FTIR transmittance spectroscopy was performed as shown in Figure 4c. The FTIR spectra show absorbance peaks at 457.0 and 667.0 cm⁻¹ as indicated in the figure. The characteristic absorption bands of the Fe₂O₃ phase are at 460 cm⁻¹ (transverse-optical mode, TO) and 537 cm⁻¹ (longitudinal-optical mode, LO). The FTIR spectra of the iron oxide nanostructure showed a small phase shift (3.0 cm⁻¹) in the TO mode and (5.0 cm⁻¹) LO mode as compared to the reported values of the TO and LO for Fe₂O₃ [44,45]. Representative EDS spectrum with a semi-quantitative analysis of Fe and O of the iron oxide nanostructure is shown in Figure 4d. The EDS confirmed that the nanowires contain both Fe and O in approximately a 2:3 ratio, indicating the formation of Fe₂O₃, which is consistent with the FTIR results. Hence, the iron oxide nanostructure formed can be assigned to the Fe₂O₃ phase. A trace amount of C was detected from the carbon used in the coating of the sample. Si was also detected since EDS may include some information from the substrate because of the penetration of the electron beam.

4. Discussion

To describe the plausible growth mechanism of Fe₂O₃ nanostructures under the carbothermal reaction, the following chemical reactions are considered. The reaction of carbon and Fe with oxygen in air proceeds as follows:

C (s) + O₂ (g) → CO₂ (g)

(1)

whereas:

3 Fe (s) + 2 O₂ (g) → Fe₃O₄

(2)

Based on our results, the Fe₃O₄ appears to be in the intermediate phase of the nanoparticles or may be present in the walls of the microspheres and may react with carbon dioxide, forming Fe₂O₃ in the process:

2 Fe₃O₄ (s) + CO₂ (g) = 3 Fe₂O₃ + CO (g)

(3)

Alternatively, Fe₃O₄ may react with CO (g) following the reduction process:

Fe₃O₄ (s) + CO (g) = 3 FeO (s) + CO₂ (g)

(4)

FeO (s) + CO (g) = Fe (s) + CO₂ (g)

(5)

Note that gasification of solid carbon can also occur under large amounts of CO₂ gas via [46]:

C(s) + CO₂ (g) = 2CO (g)

(6)

Hence, it possible that Equations (3) and (4) may occur simultaneously. The cycle proceeds until a sufficient supply of Fe is available to form Fe₂O₃ nanostructures, which in this case can be inferred from the change of the highly smooth surface of Fe microspheres to a rough porous like surface after the carbothermal reaction. In the case of the two stable oxide phases of Fe₃O₄ and Fe₂O₃, we can hypothesize that the surface contains two layers. The Fe₂O₃ may form at the outmost layer and subsurface of the less oxidized oxide phase containing Fe₃O₄. The ratio of these phases depends on the availability of Fe species present in bulk. It is highly improbable that Fe and C affect the Fe₃O₄-Fe₂O₃ layer and the reduction of Fe₃O₄ at the surface once both phases are established during the reaction. These reaction steps suggest that both supplies of Fe and carbon species are critically important to producing the Fe₂O₃ nanostructures. In other words, the availability of both Fe and C are the rate-limiting steps. In the absence of a sufficient carbon supply (low carbon vapor pressure), Fe₃O₄ may form around the walls of iron microspheres, which is consistent with our observation (Figure 3e) [47], and ceases to be converted to Fe₂O₃. Previously, we reported the spectroscopic analysis of the Fe layer on Si(100) carbothermally heat treated at 800 °C [47]. Raman spectroscopy reveals that the iron oxide nanostructures after carbothermal heat treatment were predominantly the Fe₂O₃ phase. A significantly broad Fe₃O₄ peak was also detected with respect to the literature value [48], suggesting that remnant Fe₃O₄ may be present in the sample, which did not fully convert to the Fe₂O₃ phase. The large shift in the observed Fe₃O₄ peak suggests that the Fe₃O₄ layer is less crystalline and more strained on the Fe microsphere than the highly faceted Fe₂O₃ nanowires. Based on the SEM analysis, the initially smooth surface of the Fe microspheres transformed into a rough and porous-like structure, which is a characteristic feature of the Fe₃O₄ film after thermal oxidation [46]. We take this to indicate that the walls of Fe microspheres contain a thin layer of Fe₃O₄. Kinetically, the solid–solid reaction is expected to be much slower compared to gas–solid. Hence, the driving force for Fe₂O₃ formation is the availability of carbon gas species surrounding the iron oxide nanoparticles [49].

To plausibly describe the apparent radial or outward growth of Fe₂O₃ nanowires on the surface of Fe microspheres generated by infrared pulsed laser ablation, we propose that compressive stresses are generated across the iron oxide interfaces during carbothermal processes, leading to the formation of iron nanostructures, as schematically shown in Figure 5. The atomic flux can be described using Fick’s second law of diffusion [50] via:

$$J=cB\Delta \mathsf{\mu }$$

(7)

where c is the concentration of the diffusion species (Fe), B is the mobility, and $\Delta \mathsf{\mu }$ is the chemical potential gradient. The chemical potential gradient can be expressed in terms of the gradient of the hydrostatic pressure [51], σ, and can serve as the driving force, which can be written as:

$$J=\frac{cDV}{{\mathrm{k}}_{\mathrm{B}}T}\Delta \mathsf{\sigma }$$

(8)

where the mobility, B, can be expressed as a factor of the diffusion coefficient, D, and the atomic (V) volume per unit of Boltzmann’s constant, k_B, and the absolute temperature, T. The atomic flux is then directed from a more compressive/less tensile area to a less compressive/more tensile area. When Fe spheroids are heated in a carbon-rich environment, as described in the chemical reactions above, two thermodynamically stable oxide layers are formed, namely, Fe₃O₄ to Fe₂O₃ [49]. Since the molar volumes were in the order of Fe, or FeO < Fe₃O₄ < Fe₂O₃, hydrostatic stresses are generated across the interface. In this process of formation, Fe ions migrate from the Fe microsphere to the surface via bulk diffusion, leaving pores in the process. Fe ions can reach the Fe₃O₄/Fe₂O₃ via grain boundary diffusion. The Fe₃O₄ maybe in the transient state, transforming into Fe₂O₃ in the presence of a carbon-rich environment. The fast migration of Fe via surface diffusion can further promote the length of Fe₂O₃ nanowires. Hence, the migration of Fe ions via different diffusion pathways across the surface provides a continuous supply for the growth of the Fe₂O₃ nanowires. In this sense, larger sizes of Fe microspheres provide a larger volume for the mass transport of Fe ions. Large Fe microspheres (>10.0 µm) generate nanowires whereas small Fe microsphere result in the formation of nanoflakes. Our result is similar to the growth of CuO nanowires by hydrostatic stresses induced by the formation of different molar species of Cu across the Cu/Si interface under heat treatment [51]. The driving force for the growth of CuO nanowires was attributed to the stresses induced in the samples during annealing in air. Cu flux, which tends to migrate to some specific sites through surface and grain boundaries, provides for the growth of CuO nanowires [51]. The stress gradient determines the direction of Fe₂O₃.

The sufficient presence of CO₂ during heat treatment (or a carbon rich-environment) allows for the simultaneous reaction and reduction of Fe species, which is essential for the self-assembly of Fe₂O₃ nanostructures. Oxidation in air of the Fe microsphere did not produce an Fe₂O₃ nanostructure, indicating that the supply of both Fe and carbon are the rate-limiting steps for the growth of Fe₂O₃ nanostructures. Various stages of the growth formation of iron oxide nanostructures are schematically shown in Figure 5. Herein, Fe may diffuse from the bulk (microsphere) to the surface and may react with the oxygen and or carbon forming intermediate phase, Fe₃O₄ (stage 1 to stage 2). Fe ions may further diffuse at the Fe₃O₄/Fe₂O₃ interface via the grain boundary, whereas Fe may be transported through the nanowires via surface diffusion (stage 3). The diffusion of Fe ions through the nanowires was also reported to occur during the thermal oxidation of Fe metal at 600 °C, resulting in the growth of Fe₂O₃ nanowires [52], which is consistent with our results. In fact, the diffusivity of Fe ions is enhanced at high-temperatures (as in our case, which is 800 °C). Hence, the length of iron oxide nanowires strongly depends on the diffusion of Fe through the iron oxide interface. However, for growth to proceed, a carbon-rich environment is necessary as described in the chemical reactions presented in Equations (3)–(5). This is an important consideration in controlling the type of iron oxide nanostructure. Another possible growth route is via diffusion assisted seed crystal growth, however, the evidence suggests the contrary. As shown in Figure 3f, although Fe (seed) is present, the Fe/air interface did not produce iron oxide nanowires. However, under the carbothermal reaction route, the self-assembly of iron oxide nanowires occurred. The size and length of these nanowires are kinetically and thermodynamically controlled by the diffusion of Fe and the availability of carbon in air. It is important to note that in most surface-diffusion induced growth of nanowires, such as ZnO, the nanowires are prepared with small Au clusters on GaN substrates [53,54] and/or in Zn acetate seeds on amorphous substrates, where the diffusion of Zn ions controls the length of the nanowires [55]. A thorough discussion on the growth of ZnO nanowires from Zn-based seeds can be found in [55]. However, iron oxide nanowires were observed to grow on the surface of microspheres even without a catalyst as long as a sufficient amount of carbon was present, which was supplied by heating the activated carbon at high temperatures. The influence of the strain in the iron oxide nanostructure may also be explored in future works by changing the type of oxide substrate.

5. Summary

In summary, the formation of iron oxide nanostructures was successfully demonstrated using combined infrared pulsed laser ablation and carbothermal heat treatment of Fe microspheres. Results show that iron oxide nanowires and nanoflakes can be synthesized without the need of a catalyst. The iron oxide nanostructures grew radially outward from the Fe microspheres, suggesting a possible growth via self-assembly. Chemical and morphological analyses indicate that the synthesized iron oxide nanostructures can be attributed to the Fe₂O₃ phase. The plausible growth mechanism of iron oxide nanowires was described in terms of the chemical driving force for the diffusion of Fe species through the microsphere, as well as Fe₃O₄/Fe₂O₃ interfaces, which are both thermodynamically and kinetically controlled by the amounts of Fe and carbon gaseous species. The features of the nanoparticles can be easily tuned by simply adjusting the number of laser pulses or depositions during infrared pulsed laser ablation. The features of the iron oxide nanostructure (nanoflakes or nanowires) appeared to strongly depend on the size of the Fe microspheres. We also demonstrated that a sufficient amount of carbon during the heat treatment of Fe microspheres is necessary to generate iron oxide nanowires. An investigation of the electrical and magnetic properties of Fe₂O₃ is recommended for future work. It is interesting to note that the iron oxide nanostructures from infrared pulsed laser ablation result in the growth of Fe₂O₃ nanowires with a high aspect ratio. Iron oxide nanostructures with a high aspect ratio are highly suitable for bioengineering applications. Hence, this method is highly advantageous in fabricating iron oxide nanostructures with a high aspect ratio. It is important to point out that the use of an all solid-state laser, such as the Nd:YAG pulsed laser, allows for the controllable synthesis of nanostructure materials. It is envisioned that infrared laser ablation in combination with carbothermal heat-treatment could be a viable method to grow other nanostructured functional materials.