Tunable narrow-band chiral metamaterial surface based on silicon and germanium antimony tellurium composite nanostructure

Abstract

The invention discloses a tunable narrow-band chiral metasurface based on a silicon and germanium-antimony-tellurium composite nanostructure. The tunable narrow-band chiral metasurface comprises a substrate and a silicon and germanium-antimony-tellurium composite chiral metasurface formed on the surface of the substrate, the surface of the silicon and germanium-antimony-tellurium composite chiral super-structure comprises a plurality of silicon and germanium-antimony-tellurium composite chiral nano-structures which are periodically arranged, and each chiral nano-structure is composed of two rectangular nano-rods which are vertically connected and is in an L shape; the silicon and germanium-antimony-tellurium composite chiral nanostructure is a germanium-antimony-tellurium and silicon double-layer chiral nanostructure from bottom to top. The silicon and germanium-antimony-tellurium composite chiral super-structure surface disclosed by the invention can realize narrow-band circular dichroism response in an infrared band, and the wavelength of the narrow-band circular dichroism response can be dynamically adjusted through germanium-antimony-tellurium phase change.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metasurface devices, and particularly relates to a tunable narrow-band chiral metasurface based on silicon and germanium antimony tellurium composite nanostructures. BACKGROUND

[0002] Chirality refers to the lack of mirror symmetry of an object, and its mirror image cannot coincide with it by rotation or translation. In nature, chiral substances are very common. When left-handed circularly polarized light and right-handed circularly polarized light are incident on a chiral substance, their transmission, reflection or absorption shows different responses, which is called circular dichroism. However, the optical response of chiral substances in nature is very weak, and the circular dichroism phenomenon is not obvious. The emergence of metasurfaces greatly solves this dilemma. It not only can control the amplitude, phase and polarization of electromagnetic waves, but also can significantly enhance the optical chiral response of artificially prepared chiral metasurfaces compared with biological molecules, so that it can be detected and utilized. Chiral metasurfaces can significantly enhance circular dichroism by designing mirror-symmetry-free metal or dielectric nanostructures and using resonance effects in the structures. In recent years, chiral quasi-continuous domain bound states have attracted widespread attention, which exhibit a relatively narrow linewidth in circular dichroism, i.e. a high quality factor. Based on chiral quasi-continuous domain bound states in metasurfaces, circularly polarized lasers, circularly polarized nonlinear enhancement and chiral molecule sensing have been achieved.

[0003] Although chiral metasurfaces have been widely studied, most of the devices lack the ability of dynamic regulation and are difficult to apply to practice. In order to realize a dynamically tunable chiral metasurface, a chiral metasurface can be combined with a tunable material, and the physical properties of the tunable material can be changed by light control, temperature control or electric control to dynamically regulate circular dichroism. In the prior art, many works have used graphene, liquid crystals, vanadium dioxide and other tunable materials to design dynamically tunable metasurfaces. Germanium antimony tellurium, as a reversible and stable phase change material, and a large change in refractive index before and after phase change, has also been widely studied. At room temperature, germanium antimony tellurium is in an amorphous state, which exhibits low absorption loss in the infrared band. When the temperature gradually rises to a certain threshold (usually around 160°C), germanium antimony tellurium will change to a crystalline state, at which time the absorption loss of germanium antimony tellurium increases, and the refractive index also increases. At present, some works have integrated germanium antimony tellurium on chiral metal metasurfaces to achieve dynamic regulation of circular dichroism. However, most of the previous works combined germanium antimony tellurium with chiral metal structures, and due to the ohmic loss of the metal, the quality factor of the circular dichroism response is relatively low. Although the chiral quasi-continuous domain bound state of the dielectric metasurface can achieve a high-quality factor circular dichroism response, few works have combined the chiral quasi-continuous domain bound state with germanium antimony tellurium to achieve a dynamically tunable narrow-band chiral metasurface. SUMMARY

[0004] To solve the above problems, the application provides a silicon and germanium antimony tellurium composite nanostructure tunable narrowband chiral metasurface, which can realize narrowband circular dichroism response in the infrared waveband, and the wavelength of the narrowband circular dichroism response can be dynamically adjusted through germanium antimony tellurium phase transition.

[0005] The specific technical solutions are as follows:

[0006] The application discloses a silicon and germanium antimony tellurium composite nanostructure tunable narrowband chiral metasurface, which comprises a substrate and a silicon and germanium antimony tellurium composite chiral metasurface formed on the surface of the substrate; the silicon and germanium antimony tellurium composite chiral metasurface comprises a plurality of periodically arranged silicon and germanium antimony tellurium composite chiral nanostructures, each chiral nanostructure is composed of two vertically connected rectangular nanorods and has an "L" shape; the silicon and germanium antimony tellurium composite chiral nanostructure is a germanium antimony tellurium and silicon double-layer chiral nanostructure from bottom to top. The working wavelength of the chiral metasurface can be dynamically adjusted through germanium antimony tellurium phase transition.

[0007] Preferably, the long side of the transverse rectangular nanorod of the silicon and germanium antimony tellurium composite chiral nanostructure is 800-1200 nm, and the short side is 400-700 nm.

[0008] Preferably, the long side of the longitudinal rectangular nanorod of the silicon and germanium antimony tellurium composite chiral nanostructure is 700-900 nm, and the short side is 400-700 nm.

[0009] Preferably, the thickness of the germanium antimony tellurium and silicon double-layer structure of the silicon and germanium antimony tellurium composite chiral nanostructure is 50-100 nm from bottom to top, and 500-700 nm.

[0010] Preferably, the period of the silicon and germanium antimony tellurium composite chiral nanostructure is 1600-2200 nm.

[0011] Preferably, the substrate is a dielectric material with low absorption loss in the infrared waveband, for example, glass, silicon, aluminum oxide, barium fluoride, etc.

[0012] In actual use of the chiral metasurface, the germanium antimony tellurium phase transition can be excited through heat, electricity and light, and the working wavelength of the chiral metasurface can be dynamically adjusted.

[0013] The tunable narrow-band chiral metasurface based on the silicon and germanium antimony tellurium composite nanostructure can be prepared by the following method: first, a germanium antimony tellurium and silicon double-layer film is plated on the substrate from bottom to top through a magnetron sputtering technology; then, an electron beam glue is spin-coated on the film, and the electron beam glue is etched into a periodic nanostructure by an electron beam etching technology; then, the film not covered by the electron beam glue is removed by a reactive ion beam etching; finally, the remaining electron beam glue is removed to obtain a periodic silicon and germanium antimony tellurium composite nanostructure.

[0014] The tunable narrow-band chiral metasurface based on the silicon and germanium antimony tellurium composite nanostructure breaks the in-plane inversion symmetry and mirror symmetry, and has a chiral quasi-continuous domain bound state with a high quality factor. Under circularly polarized light incidence, the left-handed circularly polarized light and the right-handed circularly polarized light have different transmittances, that is, circular dichroism is generated, and the spectral line width is relatively narrow. Meanwhile, the germanium antimony tellurium in the chiral metasurface can change the refractive index through phase transition, so that the working wavelength of the circular dichroism response also changes. Therefore, by combining the chiral quasi-continuous domain bound state and the phase transition property of the germanium antimony tellurium, the tunable narrow-band chiral metasurface can be realized.

[0015] The present application has the following beneficial effects:

[0016] (1) The present application provides a design idea for realizing a tunable narrow-band chiral metasurface by using a silicon and germanium antimony tellurium composite nanostructure. The narrow-band circular dichroism is realized by exciting a chiral quasi-continuous domain bound state, and the working wavelength of the circular dichroism response is dynamically adjusted by using the phase transition of the germanium antimony tellurium.

[0017] (2) Compared with the previous method of designing multiple chiral metasurfaces with different geometric parameters to realize circular dichroism responses at different wavelengths, the present application only needs to design one silicon and germanium antimony tellurium composite chiral metasurface, and the working wavelength of the circular dichroism response is adjusted by controlling the phase transition of the germanium antimony tellurium.

[0018] (3) Compared with the previous method of combining germanium antimony tellurium with chiral metal structures to realize dynamic adjustment of circular dichroism, the present application does not contain metal materials, and the excitation of a chiral quasi-continuous domain bound state realizes a circular dichroism response with a narrower line width. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 : The schematic diagram of the silicon and germanium antimony tellurium composite nanostructure in one period unit, including a silicon layer 1, a germanium antimony tellurium layer 2 and a substrate layer 3. Wherein, L1 is the long side length of the transverse rectangular nanorod, W1 is the short side length of the transverse rectangular nanorod; L2 is the long side length of the longitudinal rectangular nanorod, W2 is the short side length of the longitudinal rectangular nanorod; h1 and h2 are the thicknesses of silicon and germanium antimony tellurium respectively, Px is the period along the x direction, and Py is the period along the y direction.

[0020] Figure 2 (a) the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the amorphous phase; (b) the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the semi-crystalline phase; (c) the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the crystalline phase; (d) the difference between the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the amorphous phase, i.e. circular dichroism; (e) the difference between the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the semi-crystalline phase, i.e. circular dichroism; (f) the difference between the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the crystalline phase, i.e. circular dichroism. Wherein the length of the long side of the transverse rectangular nanorod L1 is 900 nm, the length of the short side of the transverse rectangular nanorod W1 is 500 nm, the length of the long side of the longitudinal rectangular nanorod L2 is 700 nm, the length of the short side of the longitudinal rectangular nanorod W2 is 500 nm, the thicknesses of the medium silicon and germanium antimony tellurium h1 and h2 are 550 nm and 60 nm respectively, the period Px along the x direction is 1700 nm, and the period Py along the y direction is 1700 nm.

[0021] Figure 3 (a) the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the amorphous phase; (b) the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the semi-crystalline phase; (c) the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the crystalline phase; (d) the difference between the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the amorphous phase, i.e. circular dichroism; (e) the difference between the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the semi-crystalline phase, i.e. circular dichroism; (f) the difference between the transmittance of left-handed circularly polarized light and right-handed circularly polarized light of the crystalline phase, i.e. circular dichroism. Wherein the length of the long side of the transverse rectangular nanorod L1 is 1080 nm, the length of the short side of the transverse rectangular nanorod W1 is 600 nm, the length of the long side of the longitudinal rectangular nanorod L2 is 840 nm, the length of the short side of the longitudinal rectangular nanorod W2 is 600 nm, the thicknesses of the medium silicon and germanium antimony tellurium h1 and h2 are 660 nm and 72 nm respectively, the period Px along the x direction is 2040 nm, and the period Py along the y direction is 2040 nm. DETAILED DESCRIPTION

[0022] The application will be further explained in conjunction with the accompanying drawings and specific embodiments.

[0023] Example 1 discloses a tunable narrow-band chiral metasurface based on silicon and germanium antimony tellurium composite nanostructure, which combines Figure 1The silicon-germanium-antimony-tellurium composite nanostructure shown is located within a single periodic unit. The long side length L1 of the transverse rectangular nanorods is 900 nm, the short side length W1 is 500 nm, the long side length L2 of the longitudinal rectangular nanorods is 700 nm, and the short side length W2 is 500 nm. The thicknesses h1 and h2 of the silicon and germanium-antimony-tellurium dielectrics are 550 nm and 60 nm, respectively. The period Px along the x-direction is 1700 nm, the period Py along the y-direction is 1700 nm, and the substrate is glass.

[0024] Figure 2 (a) The transmittance of left-handed and right-handed circularly polarized light simulated in the germanium-antimony-tellurium structure in the amorphous phase is given. We can see a narrow resonance at a wavelength of 2528 nm, where the transmittance of left-handed circularly polarized light reaches 0.90, while the transmittance of right-handed circularly polarized light is 0.11. Therefore, there is a significant difference in transmittance between left-handed and right-handed circularly polarized light at 2528 nm. Circular dichroism can be obtained by calculating the difference in transmittance between left-handed and right-handed circularly polarized light, such as... Figure 2 As shown in (d), we can see a resonance peak at 2528 nm, with a circular dichroism value of 0.79 and a full width at half maximum (FWHM) of 16 nm. We also calculated the transmittance of this structure when germanium-antimony-tellurium is transformed into a semi-crystalline phase, as shown in (d). Figure 2 As shown in (b). At this point, due to the increased refractive index of germanium-antimony-tellurium, the transmission peak of the left-handed circularly polarized light we are interested in shifts to 2570 nm. Simultaneously, due to the increased absorption loss of germanium-antimony-tellurium, the peak value decreases to 0.77. The transmittance of the right-handed circularly polarized light at the same wavelength is 0.10, and the difference in transmittance between the two is still significant. Figure 2 (e) It is known that there is a resonance peak at 2570 nm, with a circular dichroism value of 0.67 and a full width at half maximum (FWHM) of 24 nm. We also calculated the transmittance of left-handed and right-handed circularly polarized light of this structure when germanium-antimony-tellurium is completely transformed into the crystalline phase, as shown below. Figure 2 As shown in (c), the resonant wavelength of interest shifts to 2658 nm. This is because when germanium-antimony-tellurium is completely transformed into its crystalline phase, the refractive index of germanium-antimony-tellurium further increases, leading to a further redshift of the peak wavelength. Simultaneously, the absorption loss of germanium-antimony-tellurium also increases, thus reducing the peak value to 0.71 nm. Figure 2 (f) shows that the circular dichroism value at 2658 nm is 0.64, and the full width at half maximum (FWHM) of the resonance peak is 31 nm. Therefore, when germanium-antimony-tellurium transforms from an amorphous phase to a crystalline phase, the operating wavelength of the chiral metasurface changes from 2528 nm to 2658 nm, thus realizing a chiral metasurface with dynamically adjustable operating wavelength.

[0025] Example 2: In the silicon and germanium-antimony-tellurium composite nanostructure, the long side length L1 of the transverse rectangular nanorod is 1080 nm, the short side length W1 of the transverse rectangular nanorod is 600 nm, the long side length L2 of the longitudinal rectangular nanorod is 840 nm, the short side length W2 of the longitudinal rectangular nanorod is 600 nm, the thickness h1 and h2 of the dielectric silicon and germanium-antimony-tellurium are 660 nm and 72 nm respectively, the period Px along the x-direction is 2040 nm, the period Py along the y-direction is 2040 nm, and the substrate is glass.

[0026] Figure 3 (a) The simulated transmittance results of germanium-antimony-tellurium in the amorphous phase for left-handed and right-handed circularly polarized light. A narrow resonance peak can be observed at a wavelength of 3024 nm, with the peak value of left-handed circularly polarized light reaching 0.89, which is significantly different from the transmittance of right-handed circularly polarized light at the same wavelength. Figure 3 In (d), the circular dichroism value at that wavelength is 0.78, and the full width at half maximum (FWHM) is 19 nm. We also calculated the transmittance of the structure when germanium-antimony-tellurium transforms into a semi-crystalline phase, such as... Figure 3 As shown in (b). At this point, the peak value of the transmission peak of the left-handed circularly polarized light we are interested in drops to 0.74, while the transmittance of the right-handed circularly polarized light at the same wavelength is 0.11. The two still maintain a large difference, corresponding to... Figure 3 (e) has a circular dichroism value of 0.63 and a full width at half maximum (FWHM) of 30 nm. Simultaneously, due to the increased refractive index of germanium-antimony-tellurium, a redshift occurs in the resonant wavelength, shifting the target resonant peak from 3024 nm to 3075 nm. Furthermore, the absorption loss of germanium-antimony-tellurium also increases, resulting in a decrease in the transmission peak value. When germanium-antimony-tellurium is completely transformed into a crystalline phase, the transmittance of the structure to circularly polarized light is as follows: Figure 3 As shown in (c), due to the further increase in the refractive index of germanium-antimony-tellurium, the resonant wavelength continues to redshift to 3171 nm. Simultaneously, the absorption loss continues to increase, causing the peak value of the transmission peak of left-handed circularly polarized light to drop to approximately 0.66, corresponding to... Figure 3 (f) The circular dichroism value is 0.60 and the full width at half maximum (FWHM) of the resonance peak is 39 nm. That is, as germanium, antimony, and tellurium gradually transform from the amorphous phase to the crystalline phase, the working wavelength of the chiral metasurface changes from 3024 nm to 3171 nm, realizing a tunable chiral metasurface.

[0027] In summary, this invention proposes to realize a tunable narrowband chiral metasurface using a silicon-germanium-antimony-tellurium composite nanostructure. By adjusting the geometric parameters of the structure, the silicon-germanium-antimony-tellurium composite nanostructure can achieve a narrowband chiral metasurface with tunable operating wavelength in the infrared band. When germanium-antimony-tellurium transforms from an amorphous phase to a crystalline phase, the operating wavelength of the narrowband chiral metasurface also changes accordingly. It should also be noted that the combinations of geometric parameters for the silicon-germanium-antimony-tellurium composite chiral metasurface given in the two embodiments above are only two combinations of those proposed in this invention; other combinations of parameters are also possible. Tunable narrowband chiral metasurfaces can also be realized when other parameters are selected; the only difference is that the operating wavelength of the narrowband chiral metasurface changes.

[0028] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A tunable narrowband chiral metasurface based on a silicon-germanium-antimony-tellurium composite nanostructure, characterized in that, The invention includes a substrate and a silicon-germanium-antimony-tellurium composite chiral metasurface formed on the substrate surface. The silicon-germanium-antimony-tellurium composite chiral metasurface comprises multiple periodically arranged silicon-germanium-antimony-tellurium composite chiral nanostructures. Each chiral nanostructure consists of two vertically connected rectangular nanorods in an "L" shape. From bottom to top, the silicon-germanium-antimony-tellurium composite chiral nanostructure is a bilayer chiral nanostructure of germanium-antimony-tellurium and silicon. The operating wavelength of the chiral metasurface can be dynamically adjusted through the germanium-antimony-tellurium phase transition.

2. The tunable narrowband chiral metasurface as described in claim 1, characterized in that, The transverse rectangular nanorods of the silicon-germanium-antimony-tellurium composite chiral nanostructure have a long side of 800–1200 nm and a short side of 400–700 nm.

3. The tunable narrowband chiral metasurface as described in claim 1, characterized in that, The longitudinal rectangular nanorods of the silicon-germanium-antimony-tellurium composite chiral nanostructure have a long side of 700–900 nm and a short side of 400–700 nm.

4. The tunable narrowband chiral metasurface as described in claim 1, characterized in that, The thicknesses of the germanium-antimony-tellurium bilayer structure and the silicon bilayer structure in the silicon-germanium-antimony-tellurium composite chiral nanostructure are 50–100 nm and 500–700 nm from bottom to top, respectively.

5. The tunable narrowband chiral metasurface as described in claim 1, characterized in that, The period of the silicon-germanium-antimony-tellurium composite chiral nanostructure is 1600–2200 nm.

6. The tunable narrowband chiral metasurface as described in claim 1, characterized in that, The substrate is any one of glass, silicon, alumina, or barium fluoride.

7. A method, characterized in that, The method for preparing the tunable narrowband chiral metasurface based on the silicon-germanium-antimony-tellurium composite nanostructure as described in any one of claims 1 to 6 comprises the following steps: First, two thin films, germanium-antimony-tellurium and silicon, are deposited on the substrate from bottom to top using magnetron sputtering technology; Then, an electron beam resist is spin-coated onto the above film, and the electron beam resist is etched into a periodically arranged nanostructure by electron beam etching technology; The thin film not covered by the electron beam resist is then removed by reactive ion beam etching. Finally, after removing the remaining electron beam gel, a periodically arranged silicon-germanium-antimony-tellurium composite nanostructure was obtained.

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