A polarization method for flexible ferroelectric nanofilms based on a parallel-plate capacitor model

Abstract

The present invention belongs to the technical field of polarization of flexible ferroelectric nano-films, and specifically relates to a method for polarizing flexible ferroelectric nano-films based on a parallel-plate capacitor model. The present invention includes the preparation and cutting of flexible ferroelectric nano-films; the construction of a polarization device of a parallel-plate capacitor model; the polarization treatment and peeling of flexible ferroelectric nano-films. The present invention uses the inner chamber of an electrospinning instrument as a constant temperature and humidity environment to ensure that the air in the chamber is used as a dielectric material uniformly and constantly; uses the positive and negative high-voltage terminals of the electrospinning instrument as the power supplies for the two electrodes of the polarization device, and controls the high-voltage output through a program; the ferroelectric domains in the ferroelectric film can be flipped only after the external electric field strength reaches a certain level; the high-voltage output of the positive and negative terminals of the electrospinning instrument can generate an electric field with controllable and stable intensity coordination. The present invention can achieve controllable polarization of flexible ferroelectric films, and the operation is safe and convenient.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible ferroelectric nanofilms polarization, and particularly relates to a method for polarizing flexible ferroelectric / semiconductor composite nanofiber films. Background Art

[0002] With the continuous development and progress of information technology, informatization has become an important boost to promote the modernization of industry, agriculture, and national defense. Optical signals are one of the important carriers of informatization. As a conversion bridge between optical signals and electrical signals, photodetectors play an important role in both military and civilian fields such as optical communication, laser guidance, and environmental detection. The action mechanism of photodetection is based on the fact that when the photon energy of the incident light exceeds the semiconductor bandgap, the semiconductor absorbs photons and excites photo-generated electron-hole pairs, thereby generating a photocurrent response under the action of an electric field. Huang Wei, the chief scientist of the Flexible Electronics Frontier Science Center at Northwestern Polytechnical University, believes that flexible electronics technology can break through the intrinsic limitations of classical silicon-based optoelectronics and provide innovative leadership for technological changes such as device design integration and energy revolution in the post-Moore era.

[0003] With the continuous development of technology, more stringent requirements are put forward for the performance of photodetectors such as response speed and detectivity. At present, the large aspect ratio of one-dimensional nanofibers is beneficial to the transport of charges, and good mechanical flexibility will meet the construction of flexible electronic devices.

[0004] Since the discovery of ferroelectric materials, they have received extensive attention from researchers due to their unique hysteresis phenomenon. Ferroelectric materials show great potential in the fields of information storage, energy harvesting, photodetection, etc. Ferroelectric materials are divided into organic ferroelectric materials and inorganic ferroelectric materials according to their structural composition. Compared with semi-crystalline organic ferroelectric polymers, inorganic ferroelectric material crystals usually have higher crystallinity and stronger remanent polarization intensity. Since the Curie temperature of inorganic ferroelectric materials is much higher than that of organic polymers, they exhibit better stability, and thus have higher adaptability in energy harvesting and information storage. Perovskite oxides are typical ferroelectric materials. Due to the tendency of spontaneous formation of low-energy asymmetric center structure distortion inside the crystal, the positive and negative charge centers no longer coincide, that is, the material exhibits spontaneous polarization. Lattice regions with the same spontaneous polarization direction will further form ferroelectric domains. However, usually, the ferroelectric domains in inorganic ferroelectric materials are randomly oriented, and the self-polarization of ferroelectric materials is usually very weak. Usually, an external electric field of a certain intensity needs to be applied to the ferroelectric material. Under the action of the external field, the ferroelectric domains are flipped, the ferroelectric orientation degree is improved, and the remanent polarization intensity is enhanced. In traditional processes, electrodes are adhered to the two surfaces of the ferroelectric material, and by applying an external electric field, the ferroelectric material shows a certain remanent polarization. Kim et al. used magnetron sputtering to prepare gold electrodes for polarization on both sides of the BaTiO 3 nanoparticle film. Ding et al. used aluminum foil to adhere to BaTiO3 On both sides of the nanofiber membrane, this realizes the polarization treatment. However, this polarization design not only destroys the macroscopic structure of the nanofiber membrane, but also is not conducive to the testing of optoelectronic devices.

[0005] Based on this, the present invention proposes to use a parallel plate capacitor model to maximize the protection of the macroscopic structure of the ferroelectric semiconductor fiber thin film from being damaged while introducing a stable and controllable external electric field, so that the polarized ferroelectric semiconductor nanofiber thin film can be directly used for the construction of optoelectronic detector devices after polarization. Summary of the Invention

[0006] The purpose of the present invention is to provide a simple and efficient method for polarizing ferroelectric thin films.

[0007] The flexible ferroelectric nanofilm polarization method provided by the present invention is based on a parallel plate capacitor model, and the specific steps are as follows:

[0008] (1) Preparation and cutting of the flexible ferroelectric nanofilm;

[0009] Specifically, an optoelectronic semiconductor nanofiber thin film integrated with inorganic ferroelectric nanofibers, that is, a ferroelectric / semiconductor composite nanofiber thin film, is prepared by using electrospinning technology;

[0010] According to the design requirements of optoelectronic devices, the ferroelectric / semiconductor composite nanofiber thin film is mechanically cut into a specified shape and size.

[0011] (2) Construction of the polarization device of the parallel plate capacitor model;

[0012] (2.1) According to the design requirements of optoelectronic detection devices, metal thin plates with a size ratio matching that of the ferroelectric / semiconductor composite nanofiber thin film are selected as the electrodes of the parallel plate capacitor polarization device; a non-conductive material is used as the carrier of the metal electrodes to keep the electrodes from deforming; the size of the electrodes matches the size ratio of the ferroelectric / semiconductor composite nanofiber thin film, and the distance between the two electrodes at both ends of the positive and negative poles is: 5 - 30 cm; the two electrodes have equal areas;

[0013] (2.2) The positive high-voltage end and negative high-voltage end of the electrospinning instrument are used as the power supplies for the two electrodes on both sides of the parallel plate capacitor, and direct current is used; the voltage range of the positive high-voltage end is: 8 - 20 KV, and the voltage range of the negative high-voltage end is: 0 - (-5) KV;

[0014] (2.3) Air in an environment with constant temperature and humidity is used as the dielectric material;

[0015] (2.4) In the parallel plate capacitor model polarization device, by adjusting the distance between the two electrodes and the polarization time, the polarization degree of the ferroelectric / semiconductor composite nanofiber thin film and the ferroelectric domain orientation are adjusted; following the physical mathematical relationship, as follows:

[0016]

[0017] Among them, d 0 is the thickness of the ferroelectric nanofiber film, and d is the distance between the two metal plates. is the actual applied voltage value on the nanofiber surface, is the voltage difference between the positive high voltage and the negative high voltage applied to the two metal plates.

[0018] (3) Polarization treatment of the flexible ferroelectric nanofilm;

[0019] The specific process of polarizing the ferroelectric / semiconductor composite nanofiber film prepared in step (1) by using the polarization device of the parallel plate capacitor model constructed in step (2) is as follows:

[0020] (3.1) The polarization device of the parallel plate capacitor model needs to be completely placed in the inner chamber of the electrospinning to ensure the safety of the polarization treatment operation;

[0021] (3.2) The ferroelectric / semiconductor composite nanofiber film is adhered to the middle position of the metal plate at the negative high voltage end so that the fiber film is regulated by a uniform electric field;

[0022] (3.3) Use a dryer to regulate the humidity of the inner chamber of the electrospinning, and the constant range is: 30%-42%; regulate the temperature, and the constant range is: 20°C-30°C;

[0023] (3.4) Regulate the distance between the two metal plates at both ends, and the distance range is: 5-30 cm;

[0024] (3.5) Use the positive high voltage end and the negative high voltage end of the electrospinning instrument as the power supplies for the two side plates of the parallel plate capacitor; the voltage range of the positive high voltage end is: 8-20 KV, and the voltage range of the negative high voltage end is: 0-(-5) KV; slowly regulate the voltage to the required value; adopt the DC power supply mode to remove the edge effect and form a stable and constant electric field between the two metal plates with equal areas;

[0025] (3.6) Control the polarization time to be: 1-48 h.

[0026] (4) Peeling of the flexible ferroelectric nanofilm; after the polarization is completed, the nanofiber film is slowly peeled off from the plate by mechanical peeling to ensure that the macroscopic structure of the fiber film is not damaged to the greatest extent.

[0027] Furthermore:

[0028] In step (1), the ferroelectric / semiconductor composite nanofiber film has types such as SrTiO 3 / MoS 2 , BaTiO 3 / ZnO, etc.;

[0029] In step (1), the specifications of the cut ferroelectric / semiconductor composite nanofiber film are as follows: the aspect ratio of length to width is 1:1 - 5:1.

[0030] In step (2), the metal conductor plate material is copper foil or aluminum foil; the non-conductor carrier is a rigid cardboard, etc.

[0031] In step (3), the materials for adhering the nanofiber film include double-sided tape, etc.

[0032] In the present invention, the ratio range of the length of the ferroelectric semiconductor composite nanofiber film to the metal plate is 1:20 - 1:10; the ratio range of the width is 1:20 - 1:10.

[0033] Beneficial effects

[0034] (1) The present invention proposes to construct a ferroelectric thin film polarization device design using a parallel plate capacitor model. The physical principle of this device is clear, the device design structure is simple, and it is easy to operate.

[0035] (2) The present invention uses the inner chamber of an electrospinning instrument as a constant temperature and humidity environment to ensure that the air in the chamber is used as a dielectric material uniformly and constantly; uses the positive and negative high voltage terminals of the electrospinning instrument as the power sources for the two plates, and the high voltage output is controlled by a program, with safe operation; the ferroelectric domains in the ferroelectric thin film can only be flipped after the external electric field strength reaches a certain intensity; the high voltage output from the positive and negative terminals of the electrospinning instrument can generate an electric field with controllable and stable intensity.

[0036] (3) After the polarization of the nanofiber film is completed, the mechanical peeling method can ensure that the macroscopic physical structure of the flexible fiber film is not damaged, thus facilitating the subsequent design of optoelectronic detection devices. Description of the drawings

[0037] Figure 1 is the cross-sectional scanning electron microscope image (SEM image) of the BaTiO 3 @TiO 2 nanofiber film prepared by electrospinning selected in Example 1.

[0038] Figure 2 is the schematic diagram of the polarization device of the parallel plate capacitor model in Example 1.

[0039] Figure 3 is the schematic diagram of the polarization of the ferroelectric / semiconductor composite nanofiber film based on the parallel plate capacitor model in Example 1.

[0040] Figure 4 is the ferroelectric hysteresis loop of the BaTiO 3 @TiO 2 nanofiber film after polarization under different electric fields.

[0041] Figure 5 is the BaTiO in Example 1 3 @TiO 2 Phase-voltage curve, phase-voltage curve, and piezoresponse force microscopy (PFM) image of the nanofiber film after polarization under different electric fields. Detailed implementation manners

[0042] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0043] The samples used in the embodiments are as follows:

[0044] Flexible barium titanate composite titanium dioxide nanofiber film (BaTiO 3 @TiO 2 NFs) prepared by electrospinning combined with in-situ heat treatment, electrospinning apparatus, aluminum foil (specification: thickness 15 μm, length 1 m, width 30 cm), non-conductive carrier for metal electrodes (cardboard thickness 5 mm), double-sided tape, small dryer, small digital temperature controller with temperature display, hygrometer, caliper, small manual cutter, forceps.

[0045] Example 1, Polarization treatment of BaTiO 3 @TiO 2 nanofiber film

[0046] (1) Select a BaTiO 3 @TiO 2 nanofiber film with a flat surface and uniform thickness. The film thickness is 200 nm, as Figure 1 shown; cut it with a small manual cutter to ensure that the cutting edge of the nanofiber film is neat and flat. The length-width ratio of the BaTiO 3 @TiO 2 nanofilm is 1.25:1 (unit: cm);

[0047] (2) Use a non-conductive material (cardboard) as the carrier for the metal electrode. Cut the cardboard with a small manual cutter to ensure that the cutting edge of the cardboard is neat and flat. The length-width ratio of the cardboard is 1.25:1 (unit: dm); evenly adhere the aluminum foil to the entire surface of the electrode carrier and keep the surface flat. The two electrodes are fixed vertically and completely parallel in the electrospinning chamber; the cut nanofiber film is adhered to the middle of the electrode at the negative pole position;

[0048] (3) Use a small dryer to adjust the humidity in the electrospinning chamber, and use a hygrometer to monitor the humidity in the chamber in real time; use a small digital temperature controller to monitor the temperature in the chamber in real time, so that the electrospinning chamber reaches a relatively constant humidity and temperature state; the temperature is 25°C ± 2°C, and the humidity is 40 ± 2;

[0049] (4) Adjust the distance between the two metal plates to 15 cm;

[0050] (5) Connect the two metal plates to the positive and negative electrodes of the electrospinning respectively. Using the electrospinning operation panel, gradually increase the voltage until it is stable. The negative electrode is (-2) KV, and adjust the positive electrode to 8 KV and 13 KV respectively; the polarization time is 10 h; as Figure 2 shown is the schematic diagram of the device model;

[0051] (6) After polarization is completed, use tweezers to lift one side of the fiber film and slowly peel it off from the metal plate; by adjusting the electric field strength, polarized fiber films with different degrees of polarization are obtained; as Figure 3 shown is the schematic diagram of the ferroelectric domain polarization orientation in the fiber film under different electric field strengths.

[0052] Example 2, BaTiO 3 @TiO 2 Ferroelectricity test of nanofiber film

[0053] (1) Use a magnetron sputtering instrument to symmetrically prepare conductive silver electrode films on both surfaces of the polarized nanofiber film, with an area of 5 mm × 5 mm;

[0054] (2) Use a ferroelectric tester (model: TF2000), frequency 100 Hz, to test the PE curve of the polarized fiber film; as Figure 4 shown, although the remanent polarization intensity of the fiber film is weak, the remanent polarization intensity of the polarized fiber film is higher than that of the initial state fiber film; in addition, the remanent polarization intensity increases with the increase of the applied electric field strength;

[0055] (3) Use a piezoresponse force microscope to test the ferroelectric orientation and amplitude value of the fiber film; as Figure 5As shown, after polarization, the fiber films all exhibit obvious ferroelectric hysteresis loops, and the amplitude curve is in the shape of a typical "butterfly curve"; this indicates that the nanofiber films exhibit ferroelectric properties; there is no obvious change in the "window" of the ferroelectric hysteresis loop, which indicates that the polarization device of the parallel-plate capacitor model does not change the intrinsic ferroelectricity of the nanofibers; the amplitude curve shows that the amplitude value at the (+10V) bias is greater than that at the (-10V) bias, which indicates that the ferroelectric domain orientation in the nanofibers is more inclined downward; the PFM test further confirms this result; in the PFM image, the bright regions represent ferroelectric domain regions with the same orientation and the direction is upward; the dark regions represent ferroelectric domain regions with the same orientation and the direction is downward; as shown, the ferroelectric domain orientation is more inclined downward with the increase of the polarization intensity of the nanofibers.

[0056] In summary, it is shown that the ferroelectric film polarization device constructed by using the parallel-plate capacitor model proposed in the present invention can effectively, safely and conveniently realize the polarization of flexible ferroelectric film fibers.

Claims

1. A polarization method for flexible ferroelectric nanofilm based on a parallel plate capacitor model, Characterized in that, The specific steps are as follows: (1) Preparation and cutting of the flexible ferroelectric nanofilm; Specifically, an optoelectronic semiconductor nanofiber film integrated with inorganic ferroelectric nanofibers, that is, a ferroelectric / semiconductor composite nanofiber film, is prepared by using electrospinning technology; According to the design requirements of optoelectronic devices, the ferroelectric / semiconductor composite nanofiber film is mechanically cut into a specified shape and size; (2) Construction of a polarization device for the parallel plate capacitor model; (2.1) According to the design requirements of optoelectronic detection devices, metal sheets are used as the electrodes of the parallel plate capacitor polarization device, and non-conductive materials are used as the carriers of the metal electrodes; the size of the electrodes is proportionally matched with the size of the ferroelectric / semiconductor composite nanofiber film, and the distance between the two electrodes at both the positive and negative ends is: 5 - 30 cm; the two electrodes have equal areas; (2.2) The positive high-voltage terminal and the negative high-voltage terminal of the electrospinning instrument are used as the power supplies for the two electrodes on both sides of the parallel plate capacitor, and direct current is used; the voltage range of the positive high-voltage terminal is: 8 - 20 KV, and the voltage range of the negative high-voltage terminal is: 0 - (-5) KV; (2.3) Air in an environment with constant temperature and humidity is used as the dielectric material; In the polarization device of the (2.4) parallel plate capacitor model, by adjusting the distance between the two plates and the polarization time, the polarization degree of the ferroelectric / semiconductor composite nanofiber film and the ferroelectric domain orientation are regulated; following the physical mathematical relationship as follows: ; Among them, d 0 is the thickness of the ferroelectric nanofiber film, d is the distance between two metal plates, φ 0 is the actual acting voltage value on the nanofiber surface, and Δφ is the voltage difference between the positive high voltage and the negative high voltage acting on the two metal plates; (3) Polarization treatment of the flexible ferroelectric nanofilm; The ferroelectric / semiconductor composite nanofiber film prepared in step (1) is polarized by using the polarization device of the parallel plate capacitor model constructed in step (2), and the specific process is as follows: (3.1) The polarization device of the parallel plate capacitor model is completely placed in the inner chamber of the electrospinning to ensure the safety of the polarization treatment operation; (3.2) The ferroelectric / semiconductor composite nanofiber film is adhered to the middle position of the metal electrode at the negative high-voltage terminal so that the fiber film is regulated by a uniform electric field; (3.3) A dryer is used to regulate the humidity in the inner chamber of the electrospinning to 30% - 42%; the temperature is regulated to 20°C - 30°C; (3.4) Regulate the distance between the two metal electrodes; (3.5) Regulate the voltage to the required value; adopt the direct current power supply mode to eliminate the edge effect and form a stable and constant electric field between the two metal electrodes with equal areas; (3.6) Control the polarization time to be: 1 - 48 h; (4) Stripping; after polarization is completed, the nanofiber film is slowly stripped from the electrode by mechanical stripping to ensure that the macroscopic structure of the fiber film is not damaged to the greatest extent.

2. The polarization method for flexible ferroelectric nanofilm according to claim 1, Characterized in that, The ferroelectric / semiconductor composite nanofiber film described in step (1) is made of SrTiO 3 / MoS 2 or BaTiO 3 / ZnO.

3. The polarization method for flexible ferroelectric nanofilm according to claim 1, Characterized in that, The aspect ratio of the cut ferroelectric / semiconductor composite nanofiber film in step (1) is: 1:1 - 5:

1.

4. The polarization method for flexible ferroelectric nanofilm according to claim 1, Characterized in that, The metal electrode material in step (2) is copper foil or aluminum foil; the non-conductor carrier is a rigid cardboard.

5. The polarization method for flexible ferroelectric nanofilm according to claim 1, Characterized in that, The material for adhering the nanofiber film in step (3) is double-sided tape.

6. The polarization method for flexible ferroelectric nanofilm according to claim 1, Characterized in that, The ratio of the length of the ferroelectric / semiconductor composite nanofiber film to that of the metal electrode plate: 1:20 - 1:10; the ratio of the width: 1:20 - 1:10.

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