Femtosecond laser processing method for periodic ferrocobalt oxide single crystal stripe nanostructure

Abstract

The invention relates to a femtosecond laser processing method for a periodic ferrocobalt oxide single crystal stripe nanostructure, which comprises the following steps of: firstly, preparing a strontium titanate single crystal substrate, and depositing a single crystal epitaxial ferrocobalt oxide film (CFO) on the substrate through pulsed laser; and the included angle between the polarization direction of the femtosecond laser and the lattice orientation of the film is adjusted according to a preset crystallographic direction, so that the surface of the film is induced by the femtosecond laser to form a stripe-shaped periodic surface structure. The single crystal epitaxial cobalt ferrite film prepared by the method has a highly ordered nano structure, and the specific surface area and surface active sites of the material are remarkably improved, so that the application performance of the material in the fields of gas sensing and the like is enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-nano processing, and in particular to a femtosecond laser processing method for periodic cobalt iron oxide single crystal stripe nanostructures. Background Art

[0002] With the rapid development of nanotechnology, precise control of material surface structure has become crucial for improving material performance. Cobalt iron oxide (CoFe2O4, CFO), a spinel-structured magnetic oxide, exhibits promising applications in catalysis, gas sensing, and other fields due to its unique physicochemical properties. However, conventional methods for fabricating CFO single-crystal striped nanostructures have numerous limitations. For example, chemical synthesis methods struggle to precisely control the periodicity of the nanostripes. While physical methods such as electron beam lithography combined with etching offer high precision, they are expensive, complex, and inefficient. Furthermore, they struggle to maintain uniformity over large areas, limiting their application in large-scale industrial production and practical applications. Femtosecond laser technology, as an emerging processing method, boasts ultrashort pulse widths and high peak power. It can interact with materials in extremely short periods of time, enabling high-precision, non-thermal micro-nanofabrication, offering new possibilities for overcoming the limitations of conventional processing methods. Applying femtosecond laser processing to the fabrication of periodic CFO single-crystal striped nanostructures promises to overcome challenges in existing processes and achieve precise structural control.

[0003] Femtosecond laser processing technology, with its ultrashort pulse duration and extremely high peak power density, can produce periodic micro-nanostructures on the surface of materials, namely Laser-Induced Periodic Surface Structures (LIPSS). The formation mechanism of LIPSS involves processes such as multi-photon ionization, Coulomb explosion, shock wave propagation, plasma expansion and material removal generated by the interaction between laser and material. Due to the ultrashort pulse characteristics of femtosecond laser, these processes are regarded as "cold" processing, which effectively reduces the thermal effects. The formation of LIPSS gives the material surface rich physicochemical active sites, significantly improving the surface activity and application performance of the material. However, the formation mechanism of LIPSS is complex and extremely sensitive to laser parameters. Precise control of the formation and directional cutting of LIPSS has become a technical challenge in this field. Summary of the Invention

[0004] The present invention addresses the aforementioned shortcomings of the prior art by providing a femtosecond laser processing method for periodic cobalt iron oxide single crystal striped nanostructures. This method fabricates one-dimensional LIPSS on CFO, effectively expanding its surface area and enhancing gas sensing response. Compared with CFO with LIPSS facets along the {100} direction, CFO with LIPSS facets along the {110} direction further improves gas sensing performance, demonstrating that highly reactive facets play a key role in promoting surface reactivity and sensing sensitivity. This method offers the advantages of high efficiency, low cost, and the absence of a mask. The laser-induced LIPSS structure not only increases the material's specific surface area but also significantly enhances the detection sensitivity and response speed of ethanol gas by exposing highly reactive high-index facets.

[0005] The above-mentioned object of the present invention is achieved through the following technical solutions: A femtosecond laser processing method for periodic cobalt iron oxide single crystal striped nanostructures comprises the following steps: first, preparing a strontium titanate single crystal substrate, and pulsed laser deposition (PLD) of a single crystal epitaxial cobalt iron oxide thin film (CFO) on the substrate; and then adjusting the angle between the polarization direction of the femtosecond laser and the lattice orientation of the film according to a predetermined crystallographic direction, so as to utilize the femtosecond laser to induce the formation of a striped periodic surface structure on the surface of the film.

[0006] Furthermore, during the pulsed laser deposition process, a strontium titanate single crystal substrate of appropriate size is selected to ensure that its surface is clean and pollution-free, and a KrF excimer laser is used to pulse irradiate the CFO target in a high vacuum environment. Furthermore, during the pulsed laser deposition process, the laser energy density was controlled to be 1.3 J / cm², the growth gas pressure was 10 mTorr, and the number of pulses was 50,000.

[0007] Furthermore, during the pulsed laser deposition process, a KrF excimer laser is used to perform pulsed irradiation on the strontium titanate target in a high vacuum environment, and the distance between the strontium titanate target and the substrate is controlled to be 6 cm.

[0008] Furthermore, during the pulsed laser deposition process, the deposition thickness of the single crystal epitaxial cobalt iron oxide thin film is controlled to be 429 nm.

[0009] Furthermore, during the femtosecond laser induction process, the angle between the polarization direction of the femtosecond laser and the lattice orientation of the film is adjusted to 0° according to the

[100] crystallographic direction.

[0010] Alternatively, during the femtosecond laser induction process, the angle between the polarization direction of the femtosecond laser and the lattice orientation of the film is adjusted to 45° according to the

[110] crystallographic direction.

[0011] Furthermore, during the femtosecond laser induction process, the laser wavelength is controlled to be 1030 nm, the laser pulse width is 211 fs, and the repetition frequency is 100 kHz.

[0012] Furthermore, during the femtosecond laser induction process, the laser energy range is controlled to be 3-11 μJ, and the scanning speed range is 0.3-20 mm / s. The regulation of laser energy and scanning speed is a key parameter that directly affects the morphology and period of the laser-induced periodic surface structure (LIPSS).

[0013] Furthermore, during the femtosecond laser induction process, the focusing diameter of the femtosecond laser is controlled to be 20 μm.

[0014] In summary, the beneficial technical effects of the present invention are: 1. This invention achieves precise induction of the LIPSS structure on the surface of the CFO film and crystal plane-directional cutting by precisely controlling the parameters of the femtosecond laser, thereby obtaining a highly ordered single-crystal striped nanostructure; 2. By precisely controlling the orientation of LIPSS, the present invention achieves a one-dimensional nanostructure along high-index crystal planes, significantly increasing the material's specific surface area and surface active sites. This enables the film to possess significant surface oxygen adsorption capacity and provides more active sites, thereby enhancing its application in fields such as gas sensing. 3. The present invention is easy to operate and only requires adjusting the laser parameters and sample angle to achieve precise control of the CFO film surface structure; 4. The femtosecond laser processing technology of the present invention has high energy utilization efficiency and does not require complex chemical reagents, significantly reducing production costs. At the same time, the technology has high repeatability and stability, making it suitable for large-scale industrial production. 5. The single-crystal epitaxial cobalt iron oxide thin film produced by the present invention has an ordered single-crystal striped nanostructure. By exposing highly active high-index crystal planes, the specific surface area of the material is increased, which helps to improve the gas sensing response; 6. The single-crystal epitaxial cobalt iron oxide thin film prepared by the present invention has a highly ordered nanostructure, which significantly improves the specific surface area and surface active sites of the material, thereby enhancing its application performance in fields such as gas sensing; the method of the present invention has the advantages of simple operation, low cost, environmental friendliness and scalable production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic structural diagram of a femtosecond laser according to embodiment 2 of the present invention.

[0016] Figure 23 are SEM images of the single crystal epitaxial cobalt iron oxide thin films and periodic surface structures of Examples 2 and 3 of the present invention.

[0017] Figure 3 1 and 2 are XRD patterns of the single crystal epitaxial cobalt iron oxide thin films and periodic surface structures of Examples 2 and 3 of the present invention.

[0018] Figure 4 This is a high-magnification SEM image of the morphology evolution of the LIPSS nanostructure of the single-crystal epitaxial cobalt iron oxide thin film of Example 4 of the present invention. DETAILED DESCRIPTION

[0019] In order to make the technical means, creative features, objectives and functions achieved by the present invention clearer and easier to understand, the present invention is further explained below with reference to the accompanying drawings and specific implementation methods.

[0020] Example 1: A femtosecond laser processing method for a periodic cobalt iron oxide single crystal striped nanostructure disclosed in the present invention includes the following steps: first, preparing a strontium titanate single crystal substrate, and pulsed laser depositing (PLD) a single crystal epitaxial cobalt iron oxide thin film (CFO) on the substrate, and then adjusting the angle between the polarization direction of the femtosecond laser and the lattice orientation of the film according to a predetermined crystallographic direction, so as to utilize the femtosecond laser to induce the formation of a striped periodic surface structure (LIPSS) on the surface of the film.

[0021] Example 2: A femtosecond laser processing method for a periodic cobalt iron oxide single crystal stripe nanostructure disclosed in the present invention is different from Example 1 in that it includes the following steps: S1 prepares a strontium titanate single crystal substrate and pulsed laser deposits (PLD) a single crystal epitaxial cobalt iron oxide (CFO) thin film on the substrate. Pulsed laser deposition technology is considered one of the important methods for preparing single crystal epitaxial oxides. It has the advantages of highly controlled film growth, wide material applicability, high-quality film growth, controllable deposition rate, and direct growth without the need for catalysts. First, a strontium titanate single crystal substrate was selected as the base, ensuring that its surface was clean and free of contamination. In a high vacuum environment, a KrF excimer laser was used to pulse the strontium titanate target, with the distance between the strontium titanate target and the substrate controlled to be 4-8 cm. Secondly, by adjusting the laser energy, pulse frequency and deposition time, the growth rate and thickness of the film were controlled. The laser energy density was controlled to be 1.2-1.5 J / cm², the growth pressure was controlled to be 8-12 mTorr, the substrate temperature was controlled to be 600°C, and the pulse frequency was controlled to be 50,000 times. The deposition thickness of the single crystal epitaxial cobalt iron oxide film was 420-440 nm. S2 reference Figure 1The femtosecond laser used uses titanium-doped sapphire as the gain medium and uses the Kerr lens effect to achieve mode locking of the laser pulse in the cavity. In this way, the laser can output a continuous, periodic pulse sequence. The more modes the sapphire laser locks, the narrower the output pulse, and the laser can support a considerable number of longitudinal mode locking. The femtosecond laser used is produced by Light Conversion, model PH2-10. This laser can provide a wide range of output wavelengths, ranging from 515 to 1030 nm, and its pulse width is 221 fs. The adjustable repetition rate is between 50 and 200 kHz, and the highest pulse energy can reach 200 μJ. During the entire laser induction process, the laser wavelength was controlled at 1030nm, the laser pulse width was 211fs, and the repetition rate was 90-110kHz. The laser pulses emitted by the laser were first expanded and then guided by a scanning galvanometer, ultimately focusing in air on the surface of the CFO film, forming a focal spot approximately 10μm in size. The morphology and size of the LIPSS were optimized by adjusting the laser pulse energy and scanning speed. The laser beam had a focal diameter of 18-22μm, and precise control of the LIPSS period and depth was achieved by adjusting the laser pulse energy within the range of 3-11μJ and the scanning speed within the range of 0.3-20mm / s. All laser-related parameters and processing details, such as laser energy and scanning rate, were adjusted and set using EzCad and PH2 software. During the laser induction process, the orientation of LIPSS is precisely controlled by adjusting the relative angle between the polarization direction of the laser and the crystal orientation of the CFO film.

[0022] Example 3: A femtosecond laser processing method for a periodic cobalt iron oxide single crystal stripe nanostructure disclosed in the present invention is different from Example 2 in that the angle between the polarization direction of the femtosecond laser and the lattice orientation of the film is adjusted to 45° according to the

[110] crystallographic direction.

[0023] Figure 1 The schematic diagram of controlling the LIPSS direction by tuning the polarization of the femtosecond laser using the methods of Examples 2 and 3 is shown. The LIPSS microstructure formed is as follows: Figure 2 As shown in the figure, LIPSS nanostructures arranged at angles of 0° and 45° are specifically sliced along the

[100] and

[110] crystallographic directions to obtain CFO films with exposed crystal planes of {100} and {110}. By optimizing the parameters, the LIPSS structures along the {100} and {110} crystal planes are prepared, which are named CFO-{100}LIPSS and CFO-{110}LIPSS, respectively. The surface morphology and size of the LIPSS prepared in Examples 2-3 were characterized using a scanning electron microscope (SEM). Figure 2 The SEM analysis results were provided, showing that the period of the LIPSS structure was 131±15nm and the width was 85±15nm; the crystal structure of the film and LIPSS was analyzed by X-ray diffraction (XRD). Figure 3 XRD patterns of CFO films, CFO-{100}LIPSS, and CFO-{110}LIPSS are provided. XRD analysis reveals that only the (001) diffraction peaks of the CFO substrate and the (001) diffraction peaks of the strontium titanate (STO) substrate are identifiable, confirming the single-crystal epitaxial nature of the CFO films, CFO-{100}LIPSS, and CFO-{110}LIPSS.

[0024] Technical parameters such as Figure 4 As shown, by regulating the laser energy range of 3-11μJ and the scanning speed range of 0.3-20mm / s, LIPSS patterns with periodicity and high regularity were obtained. The direction of LIPSS is perpendicular to the polarization direction of the laser beam. The surface morphology and microstructure of LIPSS preparation were studied for the evolution of laser pulse energy and scanning speed. The formation of LIPSS is closely related to the laser pulse energy and scanning speed. When the laser pulse energy is 3μJ, LIPSS is formed at scanning speeds of 0.3mm / s and 1mm / s. When the scanning speed is increased to more than 10mm / s, no LIPSS pattern is obtained, indicating that there is a laser energy threshold for the formation of LIPSS. At a fixed scanning speed of 1mm / s, it is noted that the LIPSS width increases with the increase of laser pulse energy. At a fixed laser pulse energy of 7μJ, the LIPSS pattern becomes loosely arranged as the scanning speed increases from 0.3mm / s to 20mm / s.

[0025] Example 4: A femtosecond laser processing method for a periodic cobalt iron oxide single crystal stripe nanostructure disclosed in the present invention is different from Example 2 in that it includes the following steps: Comparative Example 1: A femtosecond laser processing method for periodic cobalt iron oxide single crystal striped nanostructures disclosed herein differs from Example 2 in that electron beam evaporation is used instead of pulsed laser deposition. When using PLD to prepare thin films, high-energy particle bombardment (~300 eV) promotes substrate surface activation, enabling epitaxial growth. The single crystal film (XRD half-width 0.12°) has a lattice orientation consistent with that of the STO substrate. However, when electron beam evaporation (EBE) is used instead of pulsed laser deposition, low-energy deposition (<1 eV) leads to insufficient particle mobility, forming a columnar polycrystalline structure and causing the LIPSS periodicity to disappear. PLD's high-energy particle deposition is the core process for obtaining single crystal films and directly affects the periodicity of LIPSS.

[0026] Comparative Example 2: A femtosecond laser processing method for a periodic cobalt iron oxide single crystal stripe nanostructure disclosed in the present invention. The difference from Example 2 is that silicon oxide is used instead of a strontium titanate single crystal substrate. The lattice / thermal matching of the strontium titanate single crystal substrate is a necessary condition for maintaining the integrity of the film layer and the uniformity of LIPSS. The thermal expansion coefficient difference of the strontium titanate single crystal substrate is Δα = 1.1×10⁻ 6 / K, the thermal stress can be ignored during annealing cooling; when using SiO2 substrate, the thermal expansion coefficient difference of SiO2 substrate is Δα=4.7×10⁻ 6 / K, the film layer is subjected to compressive stress during the cooling process, which will cause cracks at the edge of the film; the stress release causes the structure to break, and only incomplete stripes remain in the central area.

[0027] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A femtosecond laser processing method for periodic cobalt iron oxide single crystal stripe nanostructures, characterized by: The method comprises the following steps: first, preparing a strontium titanate single crystal substrate, and pulsed laser depositing (PLD) a single crystal epitaxial cobalt iron oxide (CFO) thin film on the substrate; and then adjusting the angle between the polarization direction of the femtosecond laser and the lattice orientation of the thin film according to a predetermined crystallographic direction, so as to utilize the femtosecond laser to induce the formation of a striped periodic surface structure on the surface of the thin film.

2. The femtosecond laser processing method for periodic cobalt iron oxide single crystal stripe nanostructures according to claim 1, characterized in that: During the pulsed laser deposition process, a strontium titanate single crystal substrate of appropriate size is selected to ensure that its surface is clean and pollution-free. In a high vacuum environment, a KrF excimer laser is used to perform pulsed irradiation on the CFO target.

3. The femtosecond laser processing method for periodic cobalt iron oxide single crystal stripe nanostructures according to claim 1, characterized in that: During the pulsed laser deposition process, the laser energy density is controlled to be 1.2-1.5 J / cm², the growth gas pressure is 8-12 mTorr, and the number of pulses is 50,000.

4. The femtosecond laser processing method for periodic cobalt iron oxide single crystal stripe nanostructures according to claim 3, characterized in that: During the pulsed laser deposition process, a KrF excimer laser is used to perform pulsed irradiation on a strontium titanate target in a high vacuum environment, and the distance between the strontium titanate target and the substrate is controlled to be 4-8 cm.

5. The femtosecond laser processing method for periodic cobalt iron oxide single crystal stripe nanostructures according to claim 1, characterized in that: During the pulsed laser deposition process, the deposition thickness of the single crystal epitaxial cobalt iron oxide thin film is controlled to be 420-440 nm.

6. The femtosecond laser processing method for periodic cobalt iron oxide single crystal stripe nanostructures according to claim 1, characterized in that: During the femtosecond laser induction process, the angle between the polarization direction of the femtosecond laser and the lattice orientation of the film is adjusted to 0° according to the [100] crystallographic direction.

7. The femtosecond laser processing method for periodic cobalt iron oxide single crystal stripe nanostructures according to claim 1, characterized in that: During the femtosecond laser induction process, the angle between the polarization direction of the femtosecond laser and the lattice orientation of the film is adjusted to 45° according to the [110] crystallographic direction.

8. The femtosecond laser processing method for periodic cobalt iron oxide single crystal stripe nanostructures according to claim 1, characterized in that: In the femtosecond laser induction process, the laser wavelength is controlled to be 1030 nm, the laser pulse width is 211 fs, and the repetition frequency is 90-110 kHz.

9. The femtosecond laser processing method for periodic cobalt iron oxide single crystal stripe nanostructures according to claim 8, characterized in that: During the femtosecond laser induction process, the laser energy is controlled within a range of 3 to 11 μJ, and the scanning speed is controlled within a range of 0.3 to 20 mm / s.

10. The femtosecond laser processing method for periodic cobalt iron oxide single crystal stripe nanostructures according to claim 9, characterized in that: During the femtosecond laser induction process, the focusing diameter of the femtosecond laser is controlled to be 18-22 μm.

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