阅读说明：本技术 一种基于热压工艺的柔性多层膜超材料制备及表征方法 (Flexible multilayer film metamaterial preparation and characterization method based on hot pressing process ) 是由 赵国忠 孟田华 于 2020-05-28 设计创作，主要内容包括：一种基于热压工艺的柔性多层膜超材料制备及表征方法。包括针对常规柔性多层膜的热压模具、热压环境、后期淬火方法和太赫兹波谱无损表征手段。该多层膜超材料制备及表征方法,依据COMSOL软件对热压模型热传递的仿真模拟结果所确定的热压温度,通过调控压制温度、淬火时间来实现多层膜超材料的制备,同时辅助高分辨率的真空太赫兹时域光谱无损检测手段对其进行压制性能的表征,相较常规的电子束刻蚀(EBL)、聚焦离子束(FIB)、干涉刻蚀(IL)和纳米压印刻蚀(NIL)技术等多层柔性材料制备技术,此方法具有低成本、高精度、可制备大面积多层膜超材料等特点。(A method for preparing and characterizing a flexible multilayer film metamaterial based on a hot pressing process. The method comprises a hot-pressing die, a hot-pressing environment, a later quenching method and a terahertz spectrum nondestructive characterization means aiming at the conventional flexible multilayer film. According to the method for preparing and characterizing the multilayer film metamaterial, the preparation of the multilayer film metamaterial is realized by regulating and controlling the pressing temperature and the quenching time according to the hot pressing temperature determined by the simulation result of the COMSOL software on the heat transfer of a hot pressing model, and the characterization of the pressing performance of the multilayer film metamaterial is performed by a high-resolution vacuum terahertz time-domain spectroscopy nondestructive testing method.)

1. A flexible multilayer film metamaterial preparation and characterization method based on a hot pressing process is characterized in that a plurality of flexible super-surface single film layers with specific performance are alternately stacked and pressed into a multilayer film metamaterial by utilizing a vacuum hot pressing method, wherein each flexible super-surface single film layer is composed of a single-layer sub-wavelength metal structure layer and a dielectric layer serving as a substrate, and finally, a terahertz time-domain spectroscopy is utilized to evaluate a hot pressing effect and characterize the performance of the flexible multilayer film metamaterial;

the preparation method comprises the following specific steps:

(1) determining the hot pressing temperature according to the melting point value of the dielectric layer material and the simulation result of COMSOL simulation hot pressing model heat transfer, and presetting the heating temperature value of the vacuum drying oven;

(2) after the vacuum drying oven reaches a preset hot-pressing temperature value, accurately stacking a plurality of flexible super-surface single-layer film materials to be hot-pressed in a direction determined by the structural performance of the super-materials, putting the materials into the center of a stainless steel mold, clamping and fixing the materials, putting the materials into the vacuum drying oven, vacuumizing and continuously heating the materials;

(3) after the vacuum drying oven reaches the preset hot pressing temperature again, maintaining for a period of time T;

(4) taking out the die from the vacuum drying oven, and naturally quenching to obtain the hot-pressed flexible multilayer film metamaterial;

(5) and carrying out nondestructive characterization on the prepared multilayer film metamaterial by using a terahertz time-domain spectroscopy system (THz-TDS), and providing a THz detection spectrogram of the multilayer film metamaterial.

2. The method for preparing and characterizing the flexible multilayer film metamaterial based on the hot pressing process as claimed in claim 1, wherein the material of the sub-wavelength metal structure layer is selected from one or two of Au, Ag, Nb, Cu or Al, and the metal super-surface is composed of sub-wavelength structural units in the terahertz band, and the metal has good conductivity; the thickness of the sub-wavelength metal structure layer is 100 nm-250 nm;

the material of the dielectric layer is selected from the following flexible polymer film materials with lower dielectric constant: polyimide (PI), Mylar (Mylar), Parylene-C (Parylene-C), Polyethylene terephthalate (PET), Polyethylene Naphthalate (PEN), magnesium fluoride (MgF)₂) (ii) a Benzocyclobutene (BCB), Polystyrene (PS), Cyclic Olefin Copolymer (COC), polymethyl methacrylate (PMMA); the mediumThe thickness of the layer is 20 to 80 μm.

3. The method for preparing and characterizing a flexible multilayer film metamaterial according to claim 2, wherein the sub-wavelength metal structure layer is made of Au; the thickness of the sub-wavelength metal structure layer is 200 nm; the dielectric layer is made of polyimide; the thickness of the dielectric layer is 50 μm.

4. The hot pressing process-based flexible multilayer film metamaterial preparation and characterization method of claim 1, wherein: and (2) the hot-pressing temperature value in the step (1) is a temperature value which is lower than the melting point value of the medium layer in the multi-layer film metamaterial structure and corresponds to the temperature value just reaching the molten state for 3 min.

5. The hot pressing process-based flexible multilayer film metamaterial preparation and characterization method of claim 1, wherein: the time T maintained in the step (3) is determined by the time when the dielectric layer reaches the preset hot pressing temperature in the simulation result of the COMSOL simulation hot pressing model heat transfer.

6. The hot pressing process-based flexible multilayer film metamaterial preparation and characterization method of claim 1, wherein: and (4) naturally quenching for 10-15 min.

7. The hot pressing process-based flexible multilayer film metamaterial preparation and characterization method of claim 1, wherein: the nondestructive characterization by using the THz-TDS is to test the prepared multilayer film metamaterial by using a vacuum THz-TDS system and provide THz spectrograms at not less than 6 uniformly distributed point positions to characterize the thickness of the multilayer film and the performance of the metamaterial.

Technical Field

The invention relates to an artificial electromagnetic material, in particular to a flexible multilayer film metamaterial preparation and terahertz spectrum nondestructive characterization method based on a hot pressing process.

Background

Metamaterials (metamaterials) refer to artificial composites with artificially designed structures and exhibiting unique electromagnetic properties not found in natural materials. By using the design concept of metamaterials, research on artificial material devices such as perfect lenses (perfect lenses), polarizers, plane filters, electromagnetic wave absorbers, electrically small antennas and the like has been carried out. In recent years, the terahertz (THz) technology has been rapidly developed in terms of THz sources, imaging, security inspection, and the like, and various functional devices such as THz filters, absorbers, sensors, and the like have been designed using a multilayer-structured metamaterial, and a multilayer-film metamaterial is considered as one of the most potential materials for filling "THz voids". In order to realize a high-performance THz functional device and meet the requirements of practical application, flexible multilayer film metamaterials become the focus of attention of people.

Like many branches of material science, the research focus of the terahertz metamaterial is not only theoretical analysis, design and performance detection, but also preparation technology and structure realization of a specific micro-nano structure. In the aspects of theoretical prediction and simulation, no matter how peculiar physical phenomena exist, the theoretical prediction and simulation results can only be really verified when the structure of the physical phenomena can be really realized, and further the real application purpose is realized. In recent years, with the development of nano-processing technology, particularly the appearance of photolithography, femtosecond laser and advanced optical manufacturing technology, the preparation technology of optical metamaterials is rapidly developed. Due to the fact that the structural unit of the metamaterial needs to be controlled in the light wavelength range, namely hundreds of nanometers, compared with a metamaterial structure in a microwave frequency band, the preparation of the optical metamaterial is more challenging. At present, the preparation methods of optical metamaterials mainly include methods such as electron beam Etching (EBL), Focused Ion Beam (FIB), interference etching (IL), nanoimprint etching (NIL), and the like. However, the main disadvantages of EBL are low efficiency, long time and high price. Therefore, the method is not suitable for manufacturing large-area or batch preparation of optical metamaterial structures; although the FIB method is highly time efficient, it is not the first choice for producing high quality optical metamaterials. Because the process is essentially a kind of damage and pollution, high-energy ion beams can be injected into the surface of a sample in the preparation process to cause the composition and the shape of a metamaterial structural unit to be changed, so that the actual detection performance of the metamaterial is different from the predicted result; the IL method still belongs to the photoetching process and is also limited by the diffraction limit of light waves. Furthermore, unlike EBL and standard photolithography techniques which can process patterns of almost any shape, the IL method is very limited in the geometry of the periodic structure; the NIL technique, although successfully applied to the preparation of infrared chiral metamaterial structures at room temperature, is rarely used for the preparation verification of novel metamaterial structures because the template or mold preparation process is quite complicated, and other etching processes, such as electron beam etching, photoetching, focused ion beam etching, reactive ion etching and the like, are often involved. Other methods for preparing the metal-dielectric layer-metal structure optical metamaterial nanostructure include electron beam direct writing, focused ion beam chemical vapor deposition, three-dimensional holographic lithography and the like, but most of the methods are strictly limited by materials and geometric structures.

Disclosure of Invention

The invention aims to solve the problems of multiple preparation process steps, high cost, limited preparation size, air gaps between membrane layers during single-layer super surface accumulation, accurate alignment and the like in the prior art, and provides a method for preparing and characterizing a flexible multilayer membrane metamaterial based on a hot pressing process.

The technical scheme of the invention is as follows:

a flexible multilayer film metamaterial preparation and characterization method based on hot pressing technology is characterized in that a plurality of flexible super-surface single-film layers with specific performance are alternately stacked and pressed into a multilayer film metamaterial by utilizing a vacuum hot pressing method, wherein each flexible super-surface single-film layer is composed of a single-layer sub-wavelength metal structure layer and a dielectric layer serving as a substrate, the outermost layers on two sides are sub-wavelength metal structure layers, and finally, a terahertz time-domain spectrum is utilized to evaluate hot pressing effect and characterize the performance of the flexible multilayer film metamaterial; the preparation and characterization method comprises the following steps:

(1) determining the hot-pressing temperature as the heating temperature value of the preset vacuum drying oven according to the melting point value of the dielectric layer and the simulation result of COMSOL simulation hot-pressing model heat transfer;

(2) after the vacuum drying oven reaches a preset hot-pressing temperature value, accurately stacking a plurality of flexible super-surface single-film layer materials (structure original units) to be hot-pressed in the direction determined by the structural performance of the super-materials, putting the materials into the center of a stainless steel mold, clamping and fixing the materials, putting the stainless steel mold into the vacuum drying oven, vacuumizing and continuously heating the stainless steel mold;

(3) after the vacuum drying oven reaches the preset hot pressing temperature again, maintaining for a period of time T;

(4) after the die is taken out from the vacuum drying oven for natural quenching, the hot-pressed flexible multilayer film metamaterial can be obtained;

(5) and performing nondestructive spectral characterization on the prepared multilayer film metamaterial by using a terahertz time-domain spectroscopy system (THz-TDS), and providing a THz detection spectrogram of the multilayer film metamaterial.

Optionally, the flexible multilayer film metamaterial is formed by alternately stacking and hot-pressing a sub-wavelength metal structure layer, a dielectric layer, a sub-wavelength metal structure layer … …, a dielectric layer and a sub-wavelength metal structure layer.

Optionally, the multi-layer film metamaterial structure is formed by stacking and hot-pressing a structure original unit, namely a super-surface single film layer; the structure original unit is formed by evaporating metal on the single-layer dielectric layer by using a photoetching evaporation method;

preferably, the flexible multilayer film metamaterial is characterized in that the material of the sub-wavelength metal structure layer is selected from one or two of Au, Ag, Nb, Cu or Al, and the metal super-surface is composed of sub-wavelength structure units in a terahertz waveband, and the metal has good conductivity; the thickness of the sub-wavelength metal structure layer is 100 nm-250 nm; the dielectric layer is made of the following flexible polymer film material with a lower dielectric constant: polyimide (PI), Mylar (Mylar), Parylene-C (Parylene-C), Polyethylene terephthalate (PET), Polyethylene Naphthalate (PEN), magnesium fluoride (MgF)₂) (ii) a Benzocyclobutene (BCB), Polystyrene (PS), Cyclic Olefin Copolymer (COC), Polymethyl Methacrylate (PMMA); the thickness of the dielectric layer is 20-80 μm.

Preferably, the hot-pressing temperature value in the step (1) is a temperature value which is lower than the melting point value of the medium layer in the multi-layer film metamaterial structure and corresponds to a temperature value just before the molten state is reached for 3 min.

Preferably, the time T maintained in step (3) is determined by the time for the dielectric layer to reach the preset thermocompression temperature in the simulation result of COMSOL simulation thermocompression model heat transfer.

Preferably, the natural quenching time in the step (4) is 10min to 15 min.

Preferably, the THz-TDS vacuum system is used for detecting the prepared flexible multilayer film metamaterial, and THz transmission spectrograms at no less than 6 uniformly distributed point positions are provided for characterizing the performance of the multilayer film metamaterial.

The invention has the advantages and beneficial effects that:

the preparation of the multilayer film metamaterial structure is carried out in the vacuum heating box, so that the cleanness and the surface flatness of the multilayer film metamaterial structure are ensured, the flexible selection of the dimension of the die provides the possibility of preparing the structure in a large area, and in addition, the representation of the performance of the hot-press molding metamaterial by utilizing the THz-TDS vacuum system can also provide effective reference for the precise regulation and control of the preparation process. Therefore, the invention solves the technical problems of complex preparation process, multiple steps, high cost and limited preparation size of the multilayer metamaterial structure prepared by the prior art, and realizes the technical effect of preparing the high-quality flexible multilayer film metamaterial by the hot pressing process. In addition, the terahertz time-domain spectroscopy system is selected to represent the prepared flexible multilayer film metamaterial, and compared with a conventional scanning electron microscope, an atomic force microscope and the like, the technology not only can accurately represent the surface flatness, but also can obtain the internal flatness of the material; and the method for checking the internal uniformity of the cross section with relatively high destructiveness also embodies the advantages of no damage and no contact.

Drawings

FIG. 1 is a schematic diagram of a flexible multilayer film metamaterial manufacturing environment;

in the figure, 1 vacuum drying oven, 2 mould and sample;

FIG. 2 is an enlarged schematic view of the mold and metamaterial sample placement and fixation position of FIG. 1;

FIG. 3 is a reference graph of the preset temperature and heating time values determined by the substrate material and COMSOL simulation results in examples 1 and 2;

FIG. 4 is an optical microscope photograph of a multilayer film metamaterial structure in example 1;

FIG. 5 is a THz spectrum of a multilayer film metamaterial structure prepared by applying the present invention in example 1;

FIG. 6 is an optical microscope photograph of a multilayer film metamaterial structure in example 2;

FIG. 7 is a THz spectrum of a multilayer film metamaterial structure prepared by applying the method of the invention in example 2.

Detailed Description

In order to make the technical scheme, the achieved purpose and the efficacy of the present invention easily understood, the following will explain in detail the flexible multilayer film metamaterial preparation method based on the hot pressing process with reference to the drawings and the specific embodiments.