Fabrication Method and Application of Terahertz Wave Absorber with Adjustable Magnetic Response Frequency

Abstract

This invention provides a method for fabricating a terahertz wave absorber with adjustable magnetic response frequency. The method involves: cleaning, annealing, and polishing an aluminum sheet; anodizing using a two-step oxidation method; removing unoxidized aluminum substrates with a saturated CuCl2 solution; and then immersing the sheet in a 5% phosphoric acid solution at 30°C for pore expansion treatment to obtain UTAM (Underlying Tunneling Aluminum Electron Micrometer). This UTAM is then transferred to a single-crystal MgO(100) substrate. Using pulsed laser deposition, FePt material is ablated with a KrF excimer laser and then sprayed onto the UTAM, depositing pyramidal nanodots at the voids in the UTAM. The UTAM is then mechanically removed, followed by annealing to obtain a pyramidal L10-FePt array, which constitutes the terahertz wave absorber with adjustable magnetic response frequency. Applications are also provided for terahertz electromagnetic wave absorbing devices. This invention allows for the control of the resonant frequency by adjusting the geometry of the pyramidal L10-FePt and the spacing of the pyramidal L10-FePt array, which has significant application value in the development of terahertz devices.

Description

Technical Field

[0001] This invention belongs to the field of terahertz wave absorber technology, specifically relating to a method for preparing a terahertz wave absorber with adjustable magnetic response frequency and its application. Background Technology

[0002] Terahertz waves typically refer to electromagnetic waves with frequencies between 0.1 THz and 10 THz, representing the transition from microwaves to infrared waves. Terahertz waves possess unique properties not found in either microwave or infrared wavelengths, such as low energy, strong penetrability, and a wide spectrum, leading to their widespread applications in biology, communication, imaging, and materials diagnostics. In the terahertz band, natural materials exhibit relatively weak responses; most magnetic materials lose their magnetism above terahertz frequencies. This region is known as the terahertz gap. To address this, various periodic metamaterials have been designed to achieve terahertz responses. For example, Yen et al. designed open-cell resonant rings (SRRs) using Cu in 2004 and arranged multiple resonant rings into a periodic array, achieving a response near the 1 THz band [Science 303, 1494 (2004); DOI: 10.1126 / science.1094025]. However, artificial metamaterials face challenges in fabrication and processing costs, hindering practical production. Therefore, it is necessary to find other simple materials that can achieve magnetic responses in the terahertz band. In theory, permanent magnet materials with high magnetocrystalline anisotropy can also achieve magnetic responses in the terahertz frequency band, and their magnetic properties are more easily controlled artificially. Most traditional magnetic materials lose their magnetism above the terahertz frequency. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method for fabricating a terahertz wave absorber with adjustable magnetic response frequency and its application, which addresses the shortcomings of the prior art. The terahertz wave absorber with adjustable magnetic response frequency can achieve the control of resonant frequency by adjusting the size of the pyramid-shaped L10-FePt and the spacing of the pyramid-shaped L10-FePt array, and has significant application value in the development of terahertz devices.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a method for preparing a terahertz wave absorber with adjustable magnetic response frequency, the method being as follows:

[0005] S1. After cleaning, annealing and polishing, the polished aluminum sheet is anodized using a two-step oxidation method. Then, the unoxidized aluminum base is removed with a saturated CuCl2 solution. Finally, it is placed in a 5% phosphoric acid solution at 30°C for pore expansion treatment to obtain an ultrathin alumina mask with arrayed porous holes, named UTAM.

[0006] S2. The UTAM obtained in S1 is transferred to a single crystal MgO(100) substrate. The FePt material is ablated by a 248nm KrF excimer laser using pulsed laser deposition and then sprayed onto the UTAM. Pyramid-shaped nanodots are deposited in the voids of the UTAM to obtain UTAM with FePt material deposited on it.

[0007] The power density of the KrF excimer laser is 2 J / cm². 2 The laser irradiation frequency is 2Hz, and the working vacuum degree in the pulsed laser deposition method is 5×10⁻⁶. -5 Pa, target-substrate distance is 5cm, MgO substrate temperature is maintained at 600℃;

[0008] S3. The UTAM with FePt nanomaterials deposited in S2 is mechanically removed and annealed at 650℃ for 4 hours to obtain a pyramid-shaped L10-FePt array, which is a terahertz wave absorber with adjustable magnetic response frequency.

[0009] Preferably, the aluminum sheet in S1 has a purity of 99.999%.

[0010] Preferably, the aluminum sheet in S1 is a circular aluminum sheet with a diameter of 30 mm and a thickness of 0.22 mm.

[0011] Preferably, the cleaning method in S1 is as follows: the aluminum sheet is ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 10 minutes each.

[0012] Preferably, the annealing method in S1 is as follows: the cleaned aluminum sheet is annealed for 3 hours under vacuum conditions at 400°C.

[0013] Preferably, the polishing method in S1 is as follows: electrochemical polishing treatment at 15°C for 5 min, the polishing solution is a mixture of HClO4 and CH3CH2OH with a volume ratio of 1:4, the aluminum sheet is the anode, the graphite is the cathode, and an external voltage of 10V is applied.

[0014] Preferably, the two-step anodizing method in S1 is as follows: the polished aluminum sheet is oxidized for 4 hours at 40V in an oxalic acid solution at 17°C and a concentration of 0.3 mol / L, completing the first oxidation; then, the aluminum sheet after the first oxidation is immersed in a mixed solution of phosphoric acid and chromic acid at 60°C for 9 hours, then removed and placed in an oxalic acid solution at 40V in an oxalic acid solution at 17°C, completing the second oxidation; the mass fraction of phosphoric acid in the mixed solution of phosphoric acid and chromic acid is 6%, and the mass fraction of chromic acid is 1.8%.

[0015] Preferably, the hole enlargement process in S1 takes 120 minutes.

[0016] Preferably, the average pore size of the porous ultrathin alumina mask arranged in an array in S1 is 50 nm.

[0017] The present invention also provides the application of the tunable magnetic response frequency terahertz wave absorber prepared by the above-described preparation method, wherein the tunable magnetic response frequency terahertz wave absorber is used as a terahertz electromagnetic wave absorbing device.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. This invention uses L10-FePt with high magnetocrystalline anisotropy as the material and designs a pyramid-shaped L10-FePt. The three-dimensional pyramid structure has a significant impact on the magnetic properties of the material and has potential applications in perpendicular recording and terahertz wave fields. This invention can achieve the control of the resonant frequency by adjusting the geometric dimensions of the pyramid-shaped L10-FePt and the spacing of the pyramid-shaped L10-FePt array, which has significant application value in the development of terahertz devices.

[0020] 2. The L10-FePt material used in this invention has a magnetocrystalline anisotropy as high as 6.6 × 10⁻⁶. 6 J / m 3 The key factor in obtaining the terahertz frequency magnetic response is the change in the pyramid lattice spacing, which can effectively regulate the magnetic dipole interaction between FePt pyramid nanostructures, thereby controlling the terahertz magnetic response frequency.

[0021] 3. This invention achieves magnetic response at terahertz frequencies. Compared with existing technologies, the magnetic response frequency is ~GHz, and the magnetic response frequency is ~THz, exceeding the existing technologies by three orders of magnitude. This invention has good application prospects in the field of terahertz waves.

[0022] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a schematic diagram (a) of a single pyramid-shaped L10-FePt array in Embodiment 1 of the present invention and a dynamic magnetic susceptibility spectrum (b) of a pyramid-shaped L10-FePt array with different edge lengths.

[0024] Figure 2 This is a schematic diagram (a) of the pyramid-shaped L10-FePt array of Embodiment 1 of the present invention and a dynamic magnetic susceptibility spectrum (b) at different spacings. Detailed Implementation

[0025] Example 1

[0026] The method for fabricating a terahertz wave absorber with adjustable magnetic response frequency in this embodiment is as follows:

[0027] S1. After cleaning, annealing and polishing, aluminum sheets with a purity of 99.999% are anodized using a two-step oxidation method. Then, unoxidized aluminum substrates are removed with a saturated CuCl2 solution. Finally, the sheets are immersed in a 5% phosphoric acid solution at 30°C for 120 minutes to expand the pores, resulting in an array of porous ultrathin alumina masks, named UTAM. The average pore size of the array of porous ultrathin alumina masks is 50 nm, and the average spacing between two pores is 105 nm.

[0028] The aluminum sheet is a circular aluminum sheet with a diameter of 30 mm and a thickness of 0.22 mm;

[0029] The cleaning method is as follows: the aluminum sheet is ultrasonically cleaned in acetone, anhydrous ethanol, and deionized water for 10 minutes each in sequence;

[0030] The annealing method is as follows: the cleaned aluminum sheet is annealed under vacuum at 400℃ for 3 hours;

[0031] The polishing method is as follows: electrochemical polishing treatment at 15℃ for 5 min, wherein the polishing solution is a mixture of HClO4:CH3CH2OH with a volume ratio of 1:4, the aluminum sheet is the anode, the graphite is the cathode, and an external voltage of 10V is applied;

[0032] The two-step anodizing method is as follows: After polishing, the aluminum sheet is oxidized for 4 hours at 40V in a 0.3mol / L oxalic acid solution at 17℃ to complete the first oxidation. Then, the oxidized aluminum sheet is immersed in a mixed solution of phosphoric acid and chromic acid at 60℃ for 9 hours, removed, and then placed in a 0.3mol / L oxalic acid solution at 17℃ for 4 hours to complete the second oxidation. The mixed solution of phosphoric acid and chromic acid contains 6% phosphoric acid and 1.8% chromic acid by mass.

[0033] S2. The UTAM obtained in S1 is transferred onto a single-crystal MgO(100) substrate. Using pulsed laser deposition, FePt material is ablated with a 248nm KrF excimer laser and then sprayed onto the UTAM. Pyramid-shaped nanodots are deposited in the voids of the UTAM to obtain UTAM with FePt material deposited on it. The FePt target material used for pulsed laser deposition is provided by Zhongnuo New Materials Co., Ltd.

[0034] In this embodiment, as deposition proceeds, the pores in the top layer will close, resulting in a continuous reduction in pore size. This closing effect causes the top of the nanocone to gradually become pointed. Further evaporation of the material will block the pores, thus forming pyramid-shaped nanodots.

[0035] The power density of the KrF excimer laser is 2 J / cm². 2 The laser irradiation frequency is 2Hz, and the working vacuum degree in the pulsed laser deposition method is 5×10⁻⁶. -5 Pa, target-substrate distance is 5cm, and substrate temperature is maintained at 600℃;

[0036] S3. The UTAM with FePt material deposited in S2 is mechanically removed and annealed at 650℃ for 4 hours to obtain a pyramid-shaped L10-FePt array, which is a terahertz wave absorber with adjustable magnetic response frequency.

[0037] In this embodiment, the FePt alloy target is deposited on a single-crystal MgO substrate by pulsed laser evaporation. By controlling the temperature of the substrate and subsequent annealing, an L10 lattice structure is formed. L10-FePt has a face-centered tetragonal crystal structure, and FePt with this crystal structure exhibits strong magnetocrystalline anisotropy.

[0038] By adjusting the voltages of the two oxidation steps in step S1 of this embodiment to 40V, 60V, 80V, 100V, 120V, and 140V respectively, pyramid-shaped L10-FePt arrays with edge lengths of 50nm, 75nm, 100nm, 125nm, 150nm, and 175nm are obtained respectively.

[0039] like Figure 1 As shown, the resonant frequency of the pyramid-shaped L10-FePt decreases with increasing edge length (L), which may be related to the weakening of the demagnetizing field of large-size pyramid-shaped L10-FePt. With the edge length increasing from 50 nm to 175 nm, the resonant frequency of the first peak decreases from 0.308 THz to 0.302 THz, and the resonant frequency of the second peak decreases from 0.328 THz to 0.312 THz, showing significant changes. This can be applied to the production of terahertz electromagnetic wave absorbing devices and has scientific guiding significance for the manufacture of terahertz absorbing devices with tunable absorption frequencies.

[0040] (ii) Adjust the anodic oxidation voltage in step S1 of this embodiment to 6V, 10V and 14V respectively. At the same time, replace the electrolyte with sulfuric acid electrolyte and adjust the concentration. Control the oxidation time to obtain pyramid-shaped L10-FePt arrays with spacing of 4.0nm, 9.0nm and 14.0nm between adjacent pyramid-shaped L10-FePt, respectively. A single pyramid-shaped L10-FePt is used as a control.

[0041] like Figure 2 As shown, the resonant frequency of the pyramidal L10-FePt array increases with the increase of the spacing (S). The pyramidal L10-FePt model is similar to the dipole model; that is, the pyramidal L10-FePt generates stray fields on the outside that are opposite to the direction of the internal magnetic moment alignment. The intensity of the stray field weakens with increasing distance, while the effective field inside the pyramidal L10-FePt is the superposition of the stray field and the internal field. As the distance increases, the effective field increases, thus increasing the resonant frequency.

[0042] The terahertz wave absorber with adjustable magnetic response frequency prepared in this embodiment can be used as a terahertz electromagnetic wave absorbing device.

[0043] This embodiment uses L10-FePt with high magnetocrystalline anisotropy as the material and designs a pyramid-shaped L10-FePt. Unlike previous thin film and nanowire structures, the three-dimensional pyramid structure has a significant impact on the magnetic properties of the material and has potential applications in the fields of perpendicular recording and terahertz waves.

[0044] This invention can control the resonant frequency by adjusting the size of the pyramid-shaped L10-FePt and the spacing of the pyramid-shaped L10-FePt array, which has significant application value in the development of terahertz devices.

[0045] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A method for fabricating a terahertz wave absorber with adjustable magnetic response frequency, characterized in that, The method is as follows: S1. After cleaning, annealing and polishing, the polished aluminum sheet is anodized using a two-step oxidation method. Then, the unoxidized aluminum base is removed with a saturated CuCl2 solution. Finally, it is placed in a 5% phosphoric acid solution at 30°C for pore expansion treatment to obtain an ultra-thin alumina mask with arrayed porous holes, named UTAM. S2. The UTAM obtained in S1 is transferred to a single crystal MgO(100) substrate. The FePt material is ablated by a 248 nm KrF excimer laser using pulsed laser deposition and then sprayed onto the UTAM. Pyramid-shaped nanodots are deposited in the voids of the UTAM to obtain UTAM with FePt material deposited. The KrF excimer laser has a power density of 2 J / cm 2 , a laser irradiation frequency of 2 Hz, and a working vacuum degree of 5 x 10 -5 Pa in the pulsed laser deposition method, the target-substrate distance is 5 cm, and the MgO substrate temperature is maintained at 600 °C. S3. The UTAM with FePt nanomaterials deposited in S2 is mechanically removed and annealed at 650 °C for 4 hours to obtain a pyramid-shaped L10-FePt array, which is a terahertz wave absorber with adjustable magnetic response frequency. The annealing method in S1 is as follows: the cleaned aluminum sheet is placed in a vacuum chamber and annealed at 400 ℃ for 3 hours. The polishing method in S1 is as follows: electrochemical polishing treatment at 15℃ for 5 min, the polishing solution is a mixture of HClO4 and CH3CH2OH with a volume ratio of 1:4, the aluminum sheet is the anode, the graphite is the cathode, and an external voltage of 10V is applied. The two-step anodizing method in S1 is as follows: After polishing, the aluminum sheet is oxidized for 4 hours at 17°C in a 0.3 mol / L oxalic acid solution under a voltage of 40 V, completing the first oxidation step. Then, the oxidized aluminum sheet is immersed in a mixed solution of phosphoric acid and chromic acid at 60°C for 9 hours, removed, and placed in a 0.3 mol / L oxalic acid solution at 17°C under a voltage of 40 V for 4 hours, completing the second oxidation step. The mixed solution of phosphoric acid and chromic acid contains 6% phosphoric acid and 1.8% chromic acid by mass. The time for the hole expansion process in S1 is 120 min; The average pore size of the porous ultrathin alumina mask arranged in an array as described in S1 is 50 nm. The adjustable magnetic response frequency terahertz wave absorber is used as a terahertz electromagnetic wave absorbing device.

2. The method for fabricating a terahertz wave absorber with adjustable magnetic response frequency according to claim 1, characterized in that, The aluminum sheet described in S1 has a purity of 99.999%.

3. The method for fabricating a terahertz wave absorber with adjustable magnetic response frequency according to claim 1, characterized in that, The aluminum sheet mentioned in S1 is a circular aluminum sheet with a diameter of 30mm and a thickness of 0.22mm.

4. The method for fabricating a terahertz wave absorber with adjustable magnetic response frequency according to claim 1, characterized in that, The cleaning method in S1 is as follows: the aluminum sheet is ultrasonically cleaned in acetone, anhydrous ethanol and deionized water for 10 minutes each.

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