One-step preparation method of annular plasmon focusing structure on surface of metal material

Abstract

The invention provides a one-step preparation method of an annular plasmon focusing structure on the surface of a metal material. The method comprises the following steps that firstly, a single metal particle is placed on the surface of a substrate material, then the surface of the substrate is vertically irradiated through laser, and therefore the annular structure with the specific diameter and period is generated on the surface of the material. The diameter and the period of the annular structure can be controlled by regulating and controlling the size of the metal particles. The prepared annular structure can effectively converge a plasmon field, and can be applied to the fields of plasmon lenses, near-field optical devices, high-sensitivity biosensors and the like.

Description

Technical Field

[0001] This invention relates to the technology for preparing and controlling periodic structures on the surface of metallic materials, specifically a one-step method for preparing a ring-shaped plasma element focusing structure on the surface of a metallic material. Background Technology

[0002] Laser-induced periodic structures on material surfaces (LIPSS) are subwavelength periodic structures formed on material surfaces by the interaction of laser and matter. Their formation mechanism is primarily attributed to the interference effect between the incident laser and the electromagnetic field scattered from the material surface. This interference leads to a periodic energy distribution on the material surface, inducing non-uniform ablation or phase transition, ultimately forming a periodic undulating structure. In existing technologies, the morphology of LIPSS can be influenced to some extent by adjusting laser parameters, but the determinism of periodicity and spatial arrangement remains insufficient, making it difficult to meet the requirements of surface plasmon polariton (SPP) devices for precise spatial modulation and process repeatability. Summary of the Invention

[0003] This invention proposes a one-step method for preparing a ring-shaped plasma element focusing structure on the surface of a metallic material.

[0004] The technical solution to achieve the objective of this invention is as follows: a one-step method for preparing a ring-shaped plasma element focusing structure on a metal material surface. A single metal particle is placed on the surface of the metal material, and vertical laser irradiation is applied. Under the influence of the metal particle, a periodic optical field enhancement is generated on the surface of the metal material. When the local electric field intensity exceeds the etching threshold of the metal material, the periodic optical field enhancement region selectively induces the formation of a laser-induced periodic surface structure on the metal material surface. By controlling the size of the metal particle, periodic surface structures with different diameters and periods can be obtained on the metal material surface. This structure can effectively control the plasma element field distribution, achieving localized enhancement and focusing of the electromagnetic field.

[0005] Preferably, the metal particle is a single particle.

[0006] Preferably, the metal particles are any one of spheres, cylinders, cubes, and square pyramids.

[0007] Preferably, the diameter of the spherical metal particles ranges from 80 nm to 650 nm, the diameter and height of the bottom surface of the cylindrical metal particles range from 80 nm to 700 nm, the edge length of the cubic metal particles ranges from 80 nm to 700 nm, and the edge length of the square pyramidal metal particles ranges from 80 nm to 600 nm.

[0008] Preferably, the metal substrate and the metal particulate material are any combination of iron, copper, silver, gold, chromium or platinum.

[0009] Preferably, the polarization state of the etching laser is circularly polarized or radially polarized.

[0010] Preferably, the etching laser is an ultraviolet light with a wavelength of 350 nm-360 nm.

[0011] Preferably, the etching laser energy density ranges from 20.4 mJ / cm² to 278.4 mJ / cm², and the number of laser pulses ranges from 40N to 150N.

[0012] Compared with existing technologies, the significant advantages of this invention are as follows: By pre-arranging metal particles on the surface of a metal material, the distribution pattern of laser energy on the material surface is controlled by the metal particles, forming a ring-shaped energy distribution pattern related to the particle size. When the local energy density exceeds the material ablation threshold, a ring structure can be induced to form at a predetermined location, overcoming the limitation of random distribution of structural morphology in traditional LIPSS technology. By controlling the size of the metal particles, the diameter and period of the prepared ring structure can be controlled, thereby achieving active control of the focusing effect of surface plasmons.

[0013] Furthermore, the metal particles required for this invention can be prepared using standardized chemical synthesis processes or by directly purchasing commercially available products. Particles obtained through both methods exhibit good compositional consistency and dimensional accuracy, ensuring the reliability and repeatability of experimental results.

[0014] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the arrangement of metal particles on the substrate surface.

[0016] Figure 2 The energy distribution on the substrate surface induced by irradiation with circularly polarized and radially polarized etching lasers at a wavelength of 355 nm is shown.

[0017] Figure 3 This shows the relationship between the particle diameter and the inner ring diameter D and ring spacing d of the SPP focused structure generated by etching under 355 nm laser irradiation.

[0018] Figure 4 For based on Figure 2 (a) The SPP focusing structure prepared when the particle diameter is 350 nm.

[0019] Figure 5 For based on Figure 4 Energy distribution on the substrate surface of the focusing structure, where Figure 5 (a), (b), and (c) are two-dimensional electric field energy distribution diagrams of SPP excited and focused by linearly polarized 355nm, 632nm, and 1064nm lasers, respectively. Figure 5 (d) shows the variation of the electric field energy peak over a wide spectral range of focusing wavelength from 200 nm to 2000 nm. Figure 5 (e) shows the electric field energy distribution curves of the internal central region of the etched structure without grooves with different ring numbers in the XOZ section.

[0020] Figure 6 For based on Figure 2 (c) Focusing effect of SPP focused structures etched by particles of different diameters under radial polarization laser irradiation at a wavelength of 355 nm, wherein... Figure 6 (a) shows the electric field energy distribution curves in the XOZ section of the internal central region of the etched structure without grooves, corresponding to particles of different diameters. Figure 6 (b) is the curve showing the change of peak electric field energy with the size of the etched particles. Detailed Implementation

[0021] A one-step method for fabricating a ring-shaped plasmonic focusing structure on a metallic material surface. A single metal particle is placed on the surface of a metallic substrate. When a circularly polarized or radially polarized laser is perpendicularly irradiated onto the substrate containing the metal particle, a periodic optical field enhancement is generated. The structure is formed in regions where the enhanced periodic optical field intensity exceeds the material etching threshold. By controlling the size of the metal particle, ring-shaped structures with different diameters and periods can be obtained on the material surface. This structure can effectively control the plasmonic field distribution, achieving localized enhancement and focusing of the electromagnetic field. The specific steps are as follows:

[0022] Metal particles are arranged on the surface of a metal material, and the size of the particles is controlled.

[0023] Furthermore, the metal particles are single particles, and their morphology includes, but is not limited to, various geometric shapes such as spheres, cylinders, cubes, and square pyramids.

[0024] Furthermore, the diameter of the spherical metal particles ranges from 80 nm to 650 nm, the diameter and height of the bottom surface of the cylindrical metal particles range from 80 nm to 700 nm, the edge length of the cubic metal particles ranges from 80 nm to 700 nm, and the edge length of the square pyramidal metal particles ranges from 80 nm to 600 nm.

[0025] For SPP wavelength, its value is related to the dielectric constant of the material, and the calculation formula is:

[0026]

[0027] in, It is the dielectric constant of the material. It is the dielectric constant of the environment, which is air. .

[0028] The period of a LIPSS corresponds to the wavelength of the surface plasmonic element, and the calculation formula is as follows:

[0029]

[0030] in, For the period of LIPSS, The incident etching laser wavelength, Let be the laser incident angle. Therefore, when the laser is incident perpendicularly, the wavelength of the SPP is numerically equal to the period of the LIPSS. Specifically, when the incident etching laser wavelength is 355 nm, and the material is iron with a dielectric constant of , the etching process is successful. = -1.7996 + 9.1233i, the period of LIPSS is calculated to be 352.8nm.

[0031] In specific implementation cases, the arrangement of metal particles is as follows: Figure 1 As shown, a is the diameter of the metal particle, E is the laser polarization direction, and the etching laser wavelength is 355 nm.

[0032] Furthermore, under circularly polarized light irradiation, the material surface will exhibit phenomena such as... Figure 2 The electric field energy distribution is shown in (a). Under radially polarized light irradiation, the electric field energy distribution is as follows: Figure 2 As shown in (c), it can be clearly observed that the material surface generates periodic light field enhancements under the influence of metal particles. When the local electric field intensity exceeds the material etching threshold, these periodically enhanced regions selectively induce the formation of laser-induced periodic surface structures (LIPSS) on the material surface.

[0033] Under circularly polarized light irradiation, when the diameter of the metal particles increases from 80 nm to 650 nm, the inner ring diameter D of the induced ring structure increases from 811 nm to 3146 nm; Figure 2 (b) Performing a Fourier transform yields the period of the ring structure, half of which is the ring spacing d. Increasing from 169 nm to 178 nm approaches half of the theoretical LIPSS period, as shown below. Figure 3 As shown, the relative change is 5.3%. Furthermore, when the particle diameter is less than 100 nm, the light field enhancement effect does not reach the etching threshold, so this region is considered a structureless region.

[0034] Under radially polarized light irradiation, the material surface also exhibits similar phenomena. Figure 2 (c) shows the periodic energy distribution, and the electric field intensity distribution on the XOZ cross section is as follows: Figure 2As shown in (d), when the diameter of the metal particles increases from 80 nm to 650 nm, the inner ring diameter D of the induced ring structure first decreases and then increases in the region with a particle diameter of 100 nm to 200 nm, while in the range of 250 nm to 650 nm, it increases from 1744 nm to 2476 nm. After a non-monotonic change, the ring spacing d also approaches half of the theoretical LIPSS period, as shown in (d). Figure 3 As shown.

[0035] Furthermore, in order to obtain periodic rings of the same width under both polarized light conditions, a [missing information] was selected. Figure 3 The parameters corresponding to the intersection of the interring spacing curves of the circularly polarized light and the radially polarized light are obtained by irradiating a metal particle with a diameter of 350 nm. The resulting SPP focusing structure is as follows. Figure 4 As shown, its inner ring diameter D is 1788 nm and the ring spacing d is 173.5 nm.

[0036] This invention controls the diameter and period of the annular stripes by adjusting the diameter of the metal particles, thereby achieving the regulation of the inner ring diameter and the ring spacing of the focusing structure.

[0037] Example 1:

[0038] The following example illustrates the technical solution of this invention by describing the construction of a surface SPP focusing structure based on iron metal particles on an iron substrate using circularly polarized etching laser.

[0039] (1) Provide a single-sided polished iron material substrate with a size of 1mm × 1mm × 0.5mm.

[0040] (2) Arrange a spherical iron metal particle with a diameter a of 350 nm on the surface of the iron substrate, such as Figure 1 As shown.

[0041] (3) A circularly polarized laser with an etching wavelength of 355 nm is used to vertically irradiate the surface of an iron substrate on which metal particles are arranged.

[0042] (4) After irradiation, the metal particles are removed, and multiple ring-shaped periodic etching structures can be obtained on the iron substrate surface. The inner ring diameter D is 1788 nm. Taking the inner ring diameter as the starting point, a 2 μm range is selected and Fourier transform is performed on it, resulting in a period of 347 nm. Figure 2 As shown in (c), the ring spacing d is 173.5 nm, the etching depth is 70 nm, and the number of rings is 6, as follows. Figure 2 As shown in (a) and (b).

[0043] (5) The etched annular structure constitutes the SPP focusing structure. By adjusting the size of the metal particles, the width of the focusing structure can be further controlled, such as... Figure 3 As shown.

[0044] (6) The prepared SPP focusing structure is as follows Figure 4 As shown, its geometric parameters are: total thickness δ of the focusing structure is 200 nm, etching depth δ1 is 70 nm, unetched thickness δ2 is 130 nm, inner ring diameter D is 1788 nm, ring spacing d is 173.5 nm, ring width is also 173.5 nm, and the number of rings is 6.

[0045] (7) The prepared SPP focusing structure was irradiated with linearly polarized light at a wavelength of 355 nm, and its electromagnetic field energy distribution is as follows. Figure 5 As shown in (a), the red dashed line represents the boundary of the annular groove, forming two focusing centers inside the groove. A concave feature exists between the two focusing centers. The electric field energy distribution of the XOZ cross-section in the internal central region without the groove is as follows: Figure 5 As shown in (e), the electric field intensity moves radially outward from the focal center, exhibiting a sinusoidal oscillation pattern, with its oscillation amplitude decreasing as the distance increases.

[0046] (8) Further, by adjusting the laser wavelength range to 200-2000 nm, Figure 5 (a), (b), and (c) show the two-dimensional electric field energy distribution formed by exciting SPP with linearly polarized light at wavelengths of 355 nm, 632 nm, and 1064 nm, respectively. At 355 nm, close to the laser wavelength used for etching, the electric field energy is strongest at the center of both focal points. As the wavelength increases to 632 nm, the focusing ability weakens, and the electric field energy decreases significantly. At 1064 nm, the electric field energy further decreases, and the focusing effect is weakest. The peak electric field energy at the focal point is shown in the diagram for the entire wavelength range of 200–2000 nm. Figure 5 As shown in (d), it exhibits a clear non-monotonic variation trend, reaching a global maximum value near 355 nm. This wavelength is highly matched with the plasmon resonance characteristics of the structure surface, thus achieving the optimal field enhancement effect.

[0047] (9) By changing the number of rings in the focusing structure, under linearly polarized light with a wavelength of 355 nm from the focused SPP, it can be seen that the number of rings increases monotonically with increasing number, such as... Figure 5 As shown in (e).

[0048] Example 2:

[0049] The following example illustrates the technical solution of this invention by describing the construction of a surface SPP focused structure based on iron metal particles on an iron substrate using radially polarized etching laser.

[0050] (1) Provide a single-sided polished iron material substrate with a size of 1mm × 1mm × 0.5mm.

[0051] (2) Arrange a spherical iron metal particle with a diameter a of 350 nm on the surface of the iron substrate, such as Figure 1 As shown.

[0052] (3) A radially polarized laser with an etching wavelength of 355 nm is used to vertically irradiate the surface of an iron substrate on which metal particles are arranged.

[0053] (4) After irradiation, the metal particles are removed, and multiple ring-shaped periodic etching structures can be obtained on the iron substrate surface. The inner ring diameter D is 1829.2 nm. Taking the inner ring diameter as the starting point, a 2 μm range is selected and Fourier transform is performed on it, resulting in a period of 347 nm. Figure 3 As shown in the diagram, the ring spacing d is 173.5 nm, the etching depth is 70 nm, and the number of rings is 6. Figure 2 As shown in (c) and (d).

[0054] (5) The etched annular structure constitutes the SPP focusing structure. By adjusting the size of the metal particles, the width of the focusing structure can be further controlled, such as... Figure 3 As shown.

[0055] (6) When SPP focusing structures with different inner ring diameters D and ring spacing d corresponding to different metal particle diameters are irradiated with linearly polarized light at a wavelength of 355 nm, the electromagnetic field energy distribution at the bottom of the structure exhibits obvious modulation characteristics. The electric field energy distribution of the XOZ cross section in the internal central region without grooves is as follows: Figure 6 As shown in (a), the relationship between the peak electric field intensity and the particle diameter is as follows: Figure 6 As shown in (b), when the particle diameter is 350 nm, the induced SPP focusing structure produces the greatest focusing effect, with its electric field peak reaching 2.14 V / m; while when the particle diameter is 100 nm, the electric field peak drops to 1.14 V / m, and the aggregation effect is the weakest.

Claims

1. A one-step method for preparing a ring-shaped plasma element focusing structure on the surface of a metallic material, characterized in that, A single metal particle is placed on the surface of a metal material and vertically irradiated with a laser. Under the influence of the metal particle, the surface of the metal material generates a periodic light field enhancement. When the local electric field intensity exceeds the etching threshold of the metal material, the periodic light field enhancement region selectively induces the formation of a laser-induced periodic surface structure on the surface of the metal material. By controlling the size of the metal particle, periodic surface structures with different diameters and periods can be obtained on the surface of the metal material.

2. The one-step preparation method of the annular plasma element focusing structure on the surface of a metallic material according to claim 1, characterized in that, The metal particle is a single particle.

3. The one-step preparation method of the annular plasma element focusing structure on the surface of a metallic material according to claim 1, characterized in that, The metal particles are any one of spherical, cylindrical, cubic, and square pyramidal shapes.

4. The one-step preparation method of the annular plasma element focusing structure on the surface of a metallic material according to claim 3, characterized in that, The diameter of spherical metal particles ranges from 80 nm to 650 nm, the diameter and height of the bottom surface of cylindrical metal particles range from 80 nm to 700 nm, the edge length of cubic metal particles ranges from 80 nm to 700 nm, and the edge length of square pyramidal metal particles ranges from 80 nm to 600 nm.

5. The one-step preparation method of the annular plasma element focusing structure on the surface of a metallic material according to claim 3, characterized in that, The metal substrate and the metal particulate material are any combination of iron, copper, silver, gold, chromium or platinum.

6. The one-step preparation method of the annular plasma element focusing structure on the surface of a metallic material according to claim 1, characterized in that, The polarization state of the laser is either circularly polarized or radially polarized.

7. The one-step preparation method of the annular plasma focusing structure on the surface of a metallic material according to claim 1, characterized in that, The etching laser is an ultraviolet light with a wavelength of 350 nm-360 nm.

8. The one-step preparation method of the annular plasma element focusing structure on the surface of a metallic material according to claim 1, characterized in that, The etching laser energy density ranges from 20.4 mJ / cm² to 278.4 mJ / cm².

9. The one-step preparation method of the annular plasma element focusing structure on the surface of a metallic material according to claim 1, characterized in that, The number of etching laser pulses ranges from 40N to 150N.

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